CA2163480C - Nanofiltration of concentrated aqueous salt solutions - Google Patents
Nanofiltration of concentrated aqueous salt solutionsInfo
- Publication number
- CA2163480C CA2163480C CA002163480A CA2163480A CA2163480C CA 2163480 C CA2163480 C CA 2163480C CA 002163480 A CA002163480 A CA 002163480A CA 2163480 A CA2163480 A CA 2163480A CA 2163480 C CA2163480 C CA 2163480C
- Authority
- CA
- Canada
- Prior art keywords
- liquor
- concentration
- feed
- compound
- permeate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 238000001728 nano-filtration Methods 0.000 title claims abstract description 43
- 239000012266 salt solution Substances 0.000 title description 4
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims abstract description 135
- 239000011780 sodium chloride Substances 0.000 claims abstract description 67
- 239000012528 membrane Substances 0.000 claims abstract description 62
- 238000000034 method Methods 0.000 claims abstract description 62
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 53
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 claims abstract description 44
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 claims abstract description 40
- 229910052938 sodium sulfate Inorganic materials 0.000 claims abstract description 40
- 235000011152 sodium sulphate Nutrition 0.000 claims abstract description 40
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 27
- BZSXEZOLBIJVQK-UHFFFAOYSA-N 2-methylsulfonylbenzoic acid Chemical compound CS(=O)(=O)C1=CC=CC=C1C(O)=O BZSXEZOLBIJVQK-UHFFFAOYSA-N 0.000 claims abstract description 17
- -1 dichromate ions Chemical class 0.000 claims abstract description 15
- 230000000694 effects Effects 0.000 claims abstract description 6
- 239000012466 permeate Substances 0.000 claims description 46
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims description 32
- 150000001875 compounds Chemical class 0.000 claims description 28
- 150000001450 anions Chemical class 0.000 claims description 12
- 238000001556 precipitation Methods 0.000 claims description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 5
- TZCXTZWJZNENPQ-UHFFFAOYSA-L barium sulfate Chemical compound [Ba+2].[O-]S([O-])(=O)=O TZCXTZWJZNENPQ-UHFFFAOYSA-L 0.000 claims description 4
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 claims description 4
- 238000001914 filtration Methods 0.000 claims description 4
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 3
- 229910052804 chromium Inorganic materials 0.000 claims description 3
- 239000011651 chromium Substances 0.000 claims description 3
- 238000001704 evaporation Methods 0.000 claims description 2
- 230000008020 evaporation Effects 0.000 claims description 2
- 229940043430 calcium compound Drugs 0.000 claims 1
- 150000001674 calcium compounds Chemical class 0.000 claims 1
- 239000012267 brine Substances 0.000 abstract description 43
- XTEGARKTQYYJKE-UHFFFAOYSA-M Chlorate Chemical compound [O-]Cl(=O)=O XTEGARKTQYYJKE-UHFFFAOYSA-M 0.000 abstract description 24
- 239000000243 solution Substances 0.000 abstract description 21
- 150000002500 ions Chemical class 0.000 abstract description 15
- 150000003839 salts Chemical class 0.000 abstract description 10
- HFFLGKNGCAIQMO-UHFFFAOYSA-N trichloroacetaldehyde Chemical compound ClC(Cl)(Cl)C=O HFFLGKNGCAIQMO-UHFFFAOYSA-N 0.000 abstract description 4
- JHWIEAWILPSRMU-UHFFFAOYSA-N 2-methyl-3-pyrimidin-4-ylpropanoic acid Chemical compound OC(=O)C(C)CC1=CC=NC=N1 JHWIEAWILPSRMU-UHFFFAOYSA-N 0.000 abstract 1
- 241001397173 Kali <angiosperm> Species 0.000 abstract 1
- 239000007832 Na2SO4 Substances 0.000 description 27
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 21
- 239000000203 mixture Substances 0.000 description 11
- 239000012527 feed solution Substances 0.000 description 10
- 238000004519 manufacturing process Methods 0.000 description 9
- 239000002253 acid Substances 0.000 description 8
- 239000000047 product Substances 0.000 description 8
- 238000000926 separation method Methods 0.000 description 8
- 241000894007 species Species 0.000 description 8
- 238000001223 reverse osmosis Methods 0.000 description 7
- 235000011121 sodium hydroxide Nutrition 0.000 description 7
- 230000003204 osmotic effect Effects 0.000 description 6
- 238000011084 recovery Methods 0.000 description 6
- 239000011734 sodium Substances 0.000 description 6
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 5
- 150000007513 acids Chemical class 0.000 description 5
- 239000012141 concentrate Substances 0.000 description 5
- 239000012452 mother liquor Substances 0.000 description 5
- 229910052708 sodium Inorganic materials 0.000 description 5
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 4
- 101000995114 Doryteuthis pealeii 70 kDa neurofilament protein Proteins 0.000 description 4
- 230000002378 acidificating effect Effects 0.000 description 4
- 239000000460 chlorine Substances 0.000 description 4
- 230000004907 flux Effects 0.000 description 4
- 239000012535 impurity Substances 0.000 description 4
- 239000002002 slurry Substances 0.000 description 4
- 238000000108 ultra-filtration Methods 0.000 description 4
- BHPQYMZQTOCNFJ-UHFFFAOYSA-N Calcium cation Chemical compound [Ca+2] BHPQYMZQTOCNFJ-UHFFFAOYSA-N 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 3
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 3
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 3
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 3
- 229910001424 calcium ion Inorganic materials 0.000 description 3
- 229910052801 chlorine Inorganic materials 0.000 description 3
- ZCDOYSPFYFSLEW-UHFFFAOYSA-N chromate(2-) Chemical compound [O-][Cr]([O-])(=O)=O ZCDOYSPFYFSLEW-UHFFFAOYSA-N 0.000 description 3
- 229910052681 coesite Inorganic materials 0.000 description 3
- 229910052906 cristobalite Inorganic materials 0.000 description 3
- 238000005868 electrolysis reaction Methods 0.000 description 3
- 239000003792 electrolyte Substances 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 239000011148 porous material Substances 0.000 description 3
- 239000011347 resin Substances 0.000 description 3
- 229920005989 resin Polymers 0.000 description 3
- 235000012239 silicon dioxide Nutrition 0.000 description 3
- KIEOKOFEPABQKJ-UHFFFAOYSA-N sodium dichromate Chemical compound [Na+].[Na+].[O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O KIEOKOFEPABQKJ-UHFFFAOYSA-N 0.000 description 3
- 238000001179 sorption measurement Methods 0.000 description 3
- 229910052682 stishovite Inorganic materials 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 229910052905 tridymite Inorganic materials 0.000 description 3
- 229910052726 zirconium Inorganic materials 0.000 description 3
- 229910021578 Iron(III) chloride Inorganic materials 0.000 description 2
- TWRXJAOTZQYOKJ-UHFFFAOYSA-L Magnesium chloride Chemical compound [Mg+2].[Cl-].[Cl-] TWRXJAOTZQYOKJ-UHFFFAOYSA-L 0.000 description 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 230000002411 adverse Effects 0.000 description 2
- 239000003513 alkali Substances 0.000 description 2
- 125000000129 anionic group Chemical group 0.000 description 2
- 239000002585 base Substances 0.000 description 2
- 238000010923 batch production Methods 0.000 description 2
- 238000003843 chloralkali process Methods 0.000 description 2
- JOPOVCBBYLSVDA-UHFFFAOYSA-N chromium(6+) Chemical compound [Cr+6] JOPOVCBBYLSVDA-UHFFFAOYSA-N 0.000 description 2
- 239000002131 composite material Substances 0.000 description 2
- 230000003750 conditioning effect Effects 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- VDQVEACBQKUUSU-UHFFFAOYSA-M disodium;sulfanide Chemical compound [Na+].[Na+].[SH-] VDQVEACBQKUUSU-UHFFFAOYSA-M 0.000 description 2
- 238000005194 fractionation Methods 0.000 description 2
- 238000005342 ion exchange Methods 0.000 description 2
- RBTARNINKXHZNM-UHFFFAOYSA-K iron trichloride Chemical compound Cl[Fe](Cl)Cl RBTARNINKXHZNM-UHFFFAOYSA-K 0.000 description 2
- 239000002655 kraft paper Substances 0.000 description 2
- 229910017604 nitric acid Inorganic materials 0.000 description 2
- 150000002894 organic compounds Chemical class 0.000 description 2
- 230000036961 partial effect Effects 0.000 description 2
- 238000010926 purge Methods 0.000 description 2
- 229940083608 sodium hydroxide Drugs 0.000 description 2
- VWDWKYIASSYTQR-UHFFFAOYSA-N sodium nitrate Chemical compound [Na+].[O-][N+]([O-])=O VWDWKYIASSYTQR-UHFFFAOYSA-N 0.000 description 2
- 229910052979 sodium sulfide Inorganic materials 0.000 description 2
- 235000011149 sulphuric acid Nutrition 0.000 description 2
- NWUYHJFMYQTDRP-UHFFFAOYSA-N 1,2-bis(ethenyl)benzene;1-ethenyl-2-ethylbenzene;styrene Chemical compound C=CC1=CC=CC=C1.CCC1=CC=CC=C1C=C.C=CC1=CC=CC=C1C=C NWUYHJFMYQTDRP-UHFFFAOYSA-N 0.000 description 1
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- 241000861718 Chloris <Aves> Species 0.000 description 1
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 1
- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 description 1
- WQZGKKKJIJFFOK-GASJEMHNSA-N Glucose Natural products OC[C@H]1OC(O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-GASJEMHNSA-N 0.000 description 1
- 101001126084 Homo sapiens Piwi-like protein 2 Proteins 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- JLVVSXFLKOJNIY-UHFFFAOYSA-N Magnesium ion Chemical compound [Mg+2] JLVVSXFLKOJNIY-UHFFFAOYSA-N 0.000 description 1
- 101100400378 Mus musculus Marveld2 gene Proteins 0.000 description 1
- 102100029365 Piwi-like protein 2 Human genes 0.000 description 1
- 239000004952 Polyamide Substances 0.000 description 1
- 229910020489 SiO3 Inorganic materials 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- GYMWQLRSSDFGEQ-ADRAWKNSSA-N [(3e,8r,9s,10r,13s,14s,17r)-13-ethyl-17-ethynyl-3-hydroxyimino-1,2,6,7,8,9,10,11,12,14,15,16-dodecahydrocyclopenta[a]phenanthren-17-yl] acetate;(8r,9s,13s,14s,17r)-17-ethynyl-13-methyl-7,8,9,11,12,14,15,16-octahydro-6h-cyclopenta[a]phenanthrene-3,17-diol Chemical compound OC1=CC=C2[C@H]3CC[C@](C)([C@](CC4)(O)C#C)[C@@H]4[C@@H]3CCC2=C1.O/N=C/1CC[C@@H]2[C@H]3CC[C@](CC)([C@](CC4)(OC(C)=O)C#C)[C@@H]4[C@@H]3CCC2=C\1 GYMWQLRSSDFGEQ-ADRAWKNSSA-N 0.000 description 1
- 239000006096 absorbing agent Substances 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000005273 aeration Methods 0.000 description 1
- 229910001508 alkali metal halide Inorganic materials 0.000 description 1
- 150000008045 alkali metal halides Chemical class 0.000 description 1
- 239000004760 aramid Substances 0.000 description 1
- 229920003235 aromatic polyamide Polymers 0.000 description 1
- WDIHJSXYQDMJHN-UHFFFAOYSA-L barium chloride Chemical compound [Cl-].[Cl-].[Ba+2] WDIHJSXYQDMJHN-UHFFFAOYSA-L 0.000 description 1
- 229910001626 barium chloride Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 239000011575 calcium Substances 0.000 description 1
- 239000001110 calcium chloride Substances 0.000 description 1
- 229910001628 calcium chloride Inorganic materials 0.000 description 1
- GYZGFUUDAQXRBT-UHFFFAOYSA-J calcium;disodium;disulfate Chemical compound [Na+].[Na+].[Ca+2].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O GYZGFUUDAQXRBT-UHFFFAOYSA-J 0.000 description 1
- 239000003729 cation exchange resin Substances 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- UNJPQTDTZAKTFK-UHFFFAOYSA-K cerium(iii) hydroxide Chemical compound [OH-].[OH-].[OH-].[Ce+3] UNJPQTDTZAKTFK-UHFFFAOYSA-K 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 150000001805 chlorine compounds Chemical class 0.000 description 1
- OSVXSBDYLRYLIG-UHFFFAOYSA-N chlorine dioxide Inorganic materials O=Cl=O OSVXSBDYLRYLIG-UHFFFAOYSA-N 0.000 description 1
- 235000019398 chlorine dioxide Nutrition 0.000 description 1
- 229910001902 chlorine oxide Inorganic materials 0.000 description 1
- QBWCMBCROVPCKQ-UHFFFAOYSA-N chlorous acid Chemical compound OCl=O QBWCMBCROVPCKQ-UHFFFAOYSA-N 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 239000000805 composite resin Substances 0.000 description 1
- 238000010924 continuous production Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- SOCTUWSJJQCPFX-UHFFFAOYSA-N dichromate(2-) Chemical compound [O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O SOCTUWSJJQCPFX-UHFFFAOYSA-N 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 229940093476 ethylene glycol Drugs 0.000 description 1
- 239000003337 fertilizer Substances 0.000 description 1
- 239000008103 glucose Substances 0.000 description 1
- 229910001385 heavy metal Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 239000004615 ingredient Substances 0.000 description 1
- 239000003014 ion exchange membrane Substances 0.000 description 1
- FLTRNWIFKITPIO-UHFFFAOYSA-N iron;trihydrate Chemical compound O.O.O.[Fe] FLTRNWIFKITPIO-UHFFFAOYSA-N 0.000 description 1
- 229910001629 magnesium chloride Inorganic materials 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000005374 membrane filtration Methods 0.000 description 1
- 229910000000 metal hydroxide Inorganic materials 0.000 description 1
- 150000004692 metal hydroxides Chemical class 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000006396 nitration reaction Methods 0.000 description 1
- 150000002891 organic anions Chemical class 0.000 description 1
- ISWSIDIOOBJBQZ-UHFFFAOYSA-N phenol group Chemical group C1(=CC=CC=C1)O ISWSIDIOOBJBQZ-UHFFFAOYSA-N 0.000 description 1
- 235000011007 phosphoric acid Nutrition 0.000 description 1
- 229920002647 polyamide Polymers 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000012716 precipitator Substances 0.000 description 1
- 230000002028 premature Effects 0.000 description 1
- 230000002829 reductive effect Effects 0.000 description 1
- 239000013535 sea water Substances 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- WBHQBSYUUJJSRZ-UHFFFAOYSA-M sodium bisulfate Chemical compound [Na+].OS([O-])(=O)=O WBHQBSYUUJJSRZ-UHFFFAOYSA-M 0.000 description 1
- 229910000342 sodium bisulfate Inorganic materials 0.000 description 1
- 235000017550 sodium carbonate Nutrition 0.000 description 1
- 229910000029 sodium carbonate Inorganic materials 0.000 description 1
- 235000010344 sodium nitrate Nutrition 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000003784 tall oil Substances 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- 239000002351 wastewater Substances 0.000 description 1
- 239000003643 water by type Substances 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
- B01D61/027—Nanofiltration
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
- B01D61/025—Reverse osmosis; Hyperfiltration
- B01D61/026—Reverse osmosis; Hyperfiltration comprising multiple reverse osmosis steps
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D3/00—Halides of sodium, potassium or alkali metals in general
- C01D3/14—Purification
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2317/00—Membrane module arrangements within a plant or an apparatus
- B01D2317/02—Elements in series
- B01D2317/022—Reject series
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
Abstract
A nanofiltration process using a conventional nanofiltration membrane module under a positive applied pressure is used to selectively change the concentration of one solute, such as sodium chloride or sodium chlorate providing monovalent ions, from another solute such as sodium sulfate or sodium dichromate providing multivalent ions in high salt aqueous concentrations. The process is particularly useful in favourably lowering the concentration of silica and dichromate ions in chloral kali and chlorate brine containing solutions and favourably raising the sodium sulphate level relative to sodium chloride in chloraldhali liquor. The relatively high salt concentration, surprisingly, effects little or no monovalent, particularly, Cl rejection.
Description
- ~163480 NANOFILTRATION OF CONCENTRATED
AQUEOUS SALT SOLUTIONS
FIELD OF THE INVENTION
This invention relates to a process for red~lcin~ the concentration of undesirable compounds, particularly, solutes, in aqueous solutions by nanofiltration using a filtration membrane. More particularly, it relates to the substantial removal of sulfate, dichromate and silica divalent anions from brine solutions, optionally,0 cont~inin~ chlorate.
BACKGROUND TO THE INVENTION
Pressure driven membrane separation processes are known wherein organic molecules or inorganic ionic solutes in aqueous solutions are concentrated or separated to various degrees by the application of a positive osmotic pressure to one side of a filtration membrane. Examples of such pressures are reverse osmosis (RO), ultrafiltration (UF) and nanofiltration (NF). These pressure driven membrane processes employ a cross-flow mode of operation wherein only a portion of a feed solution (F) is coll~te~ as a permeate solution (P) and the rest is collected as a pass solution (C).
In this speçifi~tion and claims, the exit process stream from the nanofiltration module, which stream has not passed through the membrane is referred to as the "pass stream".
This stream is often referred to by practitioners in the membrane filtration art as the "conce~ ~" stream.
In the case of separation of two solutes A and B, say, NaCl and Na2SO4, the efficiency of the separation process is identified by the following parameters:
[A]p- [A]p % Rejection = x 100% (same relationship for solute B) [A]~
`- ~1634~0 % Recovery = x 100%
Fp Fp Permeate Flux = [litres/min/m2]
Membrane Area wherein [A]p is solute A concentration in feed solution;
[A]p is solute A concentration in permeate solution;
Fp is permeate solution flow; and Fl7 is feed solution flow When a se~aldtion of solute A from solute B is required, a high % Rejection of solute A and a low Rejection of solute B, or vice versa, high % Recovery and high Permeate Flux is desired.
Nanofiltration membranes are structurally very similar to reverse osmosis membranes in that chemi~lly they, typically, are cros~link~d aromatic polyamides, which are cast as a thin "skin layer", on top of a micn~polous polymer sheet support to form a composite membrane structure. The separation properties of the membrane are controlled by the pore size and çl~tric~l charge of the "skin layer". Such amembrane structure is usually referred to as a thin film composite (TFC). However, unlike RO membranes the NF membranes are char~cteri7çd in having a larger pore size in its "skin layer" and a net negative ~lçctri~l charge inside the individual pores. This negative charge is lcsponsible for rejection of anionic species, according to the anion surface charge density. Accordingly, divalent anions, such as SO4=, are more strongly rejected than monovalent ones such as Cl-. Commercial NF membranes are availablefrom known suppliers of RO and other pleSSul~ driven membranes. Examples include:
Desal-5 membrane (De~lin~tion Systems, Escondido, CA), NF70, NF50, NF40 and NF40HF .. e.. bl~ncs (FilmTec Corp., Minneapolis, MN), SU 600 membrane (Toray,Japan), and NTR 7450 and NTR 7250 membranes (Nitto Electric, Japan). The NF
membranes are typically packaged as membrane moclllles. A so-called "spiral wound"
module is most popular, but other membrane module configurations such as tubularmembranes enclose~ in a shell or plate-and-frame type are also known.
Nanofiltration is characterized by a fractionation capacity for organic - 2163~80 solutes with a molec~ r "cut-off" range of about 300 g/mol; and a fractionation capacity for multivalent vs. monovalent ions, which is especially pronounced foranions.
Nanofiltration membranes have been reported to show no or little rejection of low molecular weight organic molecules, such as, methanol, ethanol and ethyleneglycol, but a ~ignifi-~nt rejection of higher molecular weight organic species, such as glucose. Among inorganic ionic solutes, low to me~ m rejection has been reported for simple 1:1 electrolytes, such as NaCl or NaNO3 and high rejection of other electrolytes where multivalent ionic species are involved, such as Na2SO4, MgCl2 and FeCl3. Such a characteristic differentiates NF from RO which rejects all ionic species, and from ultrafiltration (UF), which does not reject ionic species and only rejects organic compounds with molecular weights typically in excess of 1,000 g/mol.
Sodium chloride (Cl-) finite % Rejections have been published in the following publications, namely:
(a) Desal-5 Membrane Product Application Note, publication of De~lin~tion Systems, Inc (Escondido, CA), April 1991, wherein the Figure on page E-19.3 shows NaCl rejection in the 55 to 85~ range;
(b) NF70 Membrane, Product Specific~ion~ publication of Filmtec Corp.
(lUinne~rolis, MN), cites Rejection of 60%; and (c) "Membrane Handbook", ed. by W.S.W. Ho and K.K. Sirkar, Van Norstrand Reinhold, New York 1992 at Table 23.2. "Characteristics of Selected Nanofiltration Membranes", cites NaCl % Rejection of: 80%
for NF70 membrane (Filmtec), 45% for NF40 membrane (Filmtec), 50% for NTF-7250 membrane (Nitto), 47% for Desal-5 membrane (DesAlin~tion Systems), and 55% for SU200HF membrane (Toray).
During the NF process, a minimum l~lCS:iUlC equal to the osmotic pressure difference between the feed/pass liquor on one side and the permeate liquor on the other side of the membrane must be applied since osmotic pressure is a function of the ionic strengths of the two streams. In the case of separation of a multivalent solute, such as Na2SO4, from a monovalent one, such as NaCl, the osmotic pressure difference is moderated by the low NaCl rejection. Usually, a pressure in excess of the osmotic prcs~ difference is employed to achieve practical permeate flux. In view - ~63180 of lower NaCl rejection, NF has been used successfully for removal of sulfate and the hardness cations, Ca2+ and Mg2+ from brackish waters and even seawater, without the necessity to excessively pre~ n7e the feed stream. The reported typical pressure range for NF is 80 to 300 psi, although membrane elem~nt~ are de~ipn~d to withstand pressures of up to 1,000 psi.
Reported uses of NF include the aforesaid water softening, removal of dissolved multivalent ions such as Ra2+, reduction of silica as a part of feedwater conditioning for a subsequent RO step or removal of medium of medium molecular weight organic compounds. It has also been demonstrated that high rejection of ionic species could be obtained by proper conditioning of the stream i.e. by ch~nging its pH.
Thus, effective removal (rejection) of call,onate anion could be achieved by adjusting the pH of the feed solution to about 12, to ensure that carbonate would predominantly exist as CO3=, which anion is more strongly rejected by the NF membrane than theHCO3 = ionic form.
Dissolved or suspended silica in brine feed for chloralkali processes, especially the so-called membrane chloraL~ali process, presents a problem in that the silica forms scale on the surface or in the interior of the ion exchange membrane separator. This causes the cell voltage and, hence, power consumption to increase.
In general, in the membrane chloralkali process, the concentration of silica in the feed brine should not exceed 10 ppm, although even a lower level may be needed if some other cont~ in~nt~, such as A13+, are present, since these cont~min~nt~ enhance the scaling capacity of silica.
In other types of chloralkali and in sodium chlorate manufacturing processes, silica, if present in the feed brine also leads to insoluble deposits on the anode which also leads to increased cell voltage and a premature wear of the anode coating. Ln general, however, in these processes, somewhat higher levels of silica, e.g.
30 ppm or more could still be tolerated.
Silica is recognized as a difficult cont~",in~llt to remove from water and/or brine. In chloraL~ali practice, it is usually removed by the addition of MgCI2 or FeCl3 to brine, followed by pH adj~lstment to precipitate the respective metal hydroxide in a form of a floc. This freshly formed floc is an effective absorber for dissolved silica, which may then be separated from brine by e.g. filtration. One - ~163480~ 5 method combining aeration of brine, to convert Fe(II) present therein to Fe(III), which then forms Fe(OH)3 floc is described in U.S. Pat. No. 4,405,463.
Use of strongly basic anion eYrh~n~e membranes for silica removal from feedwater has been reported. However, the liteldtulG also recognizes that, in case there S is a substantial background of other salts, the selectivity of the IX resin towards silica is greatly re lnçed.
Product literature from FilmTec Corp., Minneapolis, MN describes removal of silica from feedwater with a NF70 nanofiltration membrane, as part of a ," . . .e.nt for a subsequent RO step. A red~ction of silica concçntration in r~e~lw~er from 400 ppm to 50-60 ppm has been mentioned. The lite.dLule is silent, however, on use of NF metho~s for silica removal from higher concent~tion salt solutions such as chloralkali brine.
Sodium chlorate is generally preGpaled by the electrolysis of sodium chloride wherein the sodium chloride is electrolyzed to produce chlorine, sodiumhydroxide and hydrogen. The chlorine and sodium hydroxide are immer~i~tely reacted to form sodium hyporhlorite, which is then converted to chlorate and chloride under controlled con~litil~ns of pH and t~ G,dture.
In a related ch~mi~l process, chl- rine and caustic soda are p~G~al~ in an electrolytic cell, which contains a membrane to prevent chlorine and caustic soda reacting and the sep~A~d çh.omic~l~ are removed.
The sodium chloride salt used to p~e~alG the brine for electrolysis to sodium chlorate generally contains impurities which, depe-n-ling on the nature of the illlpulily and pr~duction techniques employed, can give rise to plant operational problems f~mili~r to those skilled in the art. The means of controlling these impurities are varied and inclu~le, purging them out of the system into ~lt~ tive processes or to the drain, precipitation by conversion to insoln~Qle salts, cryst~1li7~tion or ion e~c-h~n~e tre~tment The control of anionic impurities pr~.ll~ more complex problems than that of c~tionic impurities.
Sulfate ion is a common ingredient in commercial salt. When such salt is used directly, or in the form of a brine solution, and specific steps are not taken to remove the sulfate, the sulfate enters the electrolytic system. Sulfate ion ,n~it~l~;n~ its identity under the con~lition~ in the electrolytic system and thus ~1~31~ 6 , accumulates and progressively increases in concentration in the system unless removed in some manner. In chlorate plants producing a liquor product, the sulfate ion will leave with the product liquor. In plants producing only crystalline chlorate, the sulfate remains in the mother liquor after the cryst~lli7~tion of the chlorate, and is recycled to S the cells. Over time, the concentration of sulfate ion will increase and adversely affect electrolysis and cause operational problems due to localized precipitation in the electrolytic cells. Within the chloralkali circuit the sodium sulfate will concentrate and adversely effect the membrane, which divides the anolyte (brine) from the catholyte (caustic soda).
It is in~ustri~lly desirable that sodium sulfate levels in concentrated brine, e.g., 300 g/l NaCl be reduced to at least 20 g/l in chlorate production and 10 g/l in chloraLkali production.
U.S. Pat. No. 4,702,805, Burkell and Warren, issued Oct. 27, 1987, describes an improved method for the control of sulfate in an electrolyte stream in a crystalline chloMte plant, whereby the sulfate is crysPlli7~d out. In the production of crystalline sodium chlorate according to U.S. Pat. No. 4,702,805, sodium chloMte is cryst~lli7e~ from a sodium chlorate rich liquor and the crystals are removed to provide a mother liquor comprising principally sodium chlorate and sodium chloride, together with other components int~,lu-ling sulfate and dichromate ions. A portion of the mother liquor is cooled to a t~mpe~lule to effect cryst~lli7~tion of a portion of the sulfate as sodium sulfate in admixture with sodium chlorate. The cryst~lli7eA admixture is removed and the res~lltin~ spent mother liquor is recycled to the electrolytic process.
It has been found subsequently, that the cry.ct~lli7~1 admixture of sulfate and chloMte obtained from typical commercial liquors according to the process of U.S.
Pat. No. 4,702,805 may be discoloured yellow owing to the unexpected occlusion of a chromium component in the crystals. The discolouration cannot be removed by washing the sepaMted ~lmixt~lre with liquors in which the cryst~lli7ed sulfate and chloMte are insoluble. It will be appreciated that the presence of chromium in such a sulfate product is detrimental in subsequent utili7~tion of this product and, thus, this reple~nts a limit~tion to the process as taught in U.S. Pat. No. 4,702,805.
U.S. Pat. No. 4,636,376 - Maloney and Carbaugh, issued January 13, 1987, discloses removing sulfate from aqueous chromate-conlaining sodium chloMte 2163~83 liquor without simultaneous removal of ~ignifir~nt quantities of chromate. The chromate and sulfate-co~ ining chlorate liquor having a pH in the range of about 2.0 to about 6.0 is treated with a calcium-cont~ining m~tPri~l at a temperature of between about 40C and 95C, for between 2 and 24 hours to form a sulfate-containing ~ ,ci~i~te. The precipil~te is predo",in~,lly glauberite, Na2Ca(SO4)2. However, the addition of calcium cations requires the additional expense and effort of the treatment and removal of all excess ~1cium ions. It is known that calcium ions may form anunwanted deposit on the cathodes which increases the el~ctri(~l resi~Pnce of the cells and adds to ope~ling costs. It is, typically, n~es~ry to remove calcium ions by means of ion eYch~nge resins.
U.S. Pat. No. 5,093,089 - Alford and Mok, issued March 3, 1992 describes an improved version of the selective cryst~lli7~tiQn process of aforesaid U.S.
Pat. No. 4,702,805, wherein process conditions are selected to provide precipitation of sulfate subst~nti~lly free of chlol-liul-- cont~,..ill~-t Typically, organic anion eYch~nge resins have a low selectivity for sulfate anions in the presence of a large excess of chloride ions. United States Pat. No.
304,415,677 describes a sulfate ion absorption method, but which method has disadv~nt~ges.
The method consists of removing sulfate ions from brine by a macropor~us ion eYch~nge resin composite having polymeric zirconium hydrous oxide contained in a vessel. This method is not economical because the efficiency is low and a large amount of expensive cation exchange resin is required for carrying polymeric zirconium hydrous oxide. Further, the polymeric Lir~oniunl hydrous oxide adsorbing sulfate ions comes into contact with acidic brine cont~inin~ sulfate ions, re~lltin~ in loss of polymeric ~,ilCOlliUIIl hydrous oxide due to acid-induce~ dissolution. Soluble zirconyl ions precipilates as hydroxide in the lower portion of the vessel to clog flow paths.
United States Pat. No. 4,556,463 - Minz and Vajna issued December 3, 1984, describes a process to decrease sulfate concentr~tion levels in brine solutions using an organic ion e~ch~nge m~t~ l with brine streams under carefully controlled dilutive conditions.
~163~80 ~_ 8 U.S. Pat. No. 5,071,563 - Shiga et al, issued December 10, 1991, describes the selective adsorption of sulfate anions from brine solutions using zirconium hydrous oxide slurry under acidic conditions. The ion exchange compound may be regenerated by ~ ..,ellt with allcali.
S J~r~nese Patent Kokai No. 04321514-A, published November 11, 1992 to K~nt~L~ Co,~-dlion describes the selective adsorption of sulfate anions from brine solutions using cerium hydroxide slurry under acidic conditions. The ion eYçh~nge compound may be regenerated by tre~tment with alkali.
J~p~nese Patent Kokai No. 04338110-A - K~ne~ Corporation, published November 25, 1992 describes the selective adsorption of sulfate anions from brine solutions using titanium hydrous oxide slurry under acidic conditions. The ion exchange compound may be regenerated by tre~tmçnt with alkali.
J~p~nese Patent Kokai No. 04334553-A - K~n.o~, published November 11, 1992 describes the removal of sulfate ions from brine using ion-adsorbing cakes in a slurry.
There still rem~in~, however, a need for an improved, cost-effective, practical method for the removal of sulfate, silica and chromium (VI) ions from alkali metal halide solutions, particularly, from sodium chloride solutions used in theelectrolytic production of sodium chlorate and chlorine/caustic soda.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process of ch~nging the ratio of the concentr~tion of two or more compounds in an aqueous liquor so as to obtain subst~n~ y complete or partial removal of one compound from the another in the liquor.
It is a further object of the invention to provide a process of reduçing the concentration of sodium sulfate in a brine liquor or a brine/chlorate liquor.
Accordingly, in its broadest aspect the invention provides in a nanofiltration process for filttqring an aqueous liquor comprising feeding a feed liquor to a nanofiltration membrane module under a positive pressure to provide a pass liquor ~163~80 g and a permeate liquor for selectively ch~ngin~e the concentration of a first compound relative to the concentration of a second compound in said aqueous liquor wherein said first compound has a first feed concentration and said second compound has a second feed concentration, said process comprising feeding said aqueous liquor to said S nanofiltration membrane module, collecting said pass liquor wherein said first compound is at a first pass concentration and said second compound is at a second pass concentration, and collecting said permeate liquor wherein said first compound has a first permeate concentration and said second compound is at a second permeate concentration, the improvement comprising said first compound having a first concentration of greater than 50 g/l.
Thus, surprisingly I have found that nanofiltration membrane processes can be used to bençfici~lly reduce the concentration of multivalent ions, such as S04=, CrO4= or Cr207= and dissolved silica in concenl,ated solutions of sodium chloride, such as brine, and concentrated sodium chlorate process liquors where the main colllpollents are sodium chlorate and sodium chlori~le.
I have most surprisingly found, notwithshn-ling the t~ching.s that commercially available nanofiltration membranes have a monocharged anion rejection property, e.g. a Cl- ion rejection in the range 20-50%, that such membranes when used with concentrated salt solutions exhibit no Cl- ion rejection. This unexpected absence of chloride rejection by the nanofiltration membrane has a significant practicalimportance in minimi7ing the osmotic pres~ e across the membrane and hence the energy required for press.~. ;7ing the feed to achieve a given permeate flow. Further, in surprising contrast, the rejection of multivalent ions such as S04=, CrO4= or Cr2O7=
and also silica remains high.
Accordingly, such unexpected ion membrane selectivity at relatively high salt concentrations offers attractive applications such as, for example, in the treatment of chloraL~ali brine liquors having sodium sulfate levels unacceptable in recycle systems. As illustrated in an application of sulfate removal from brine, because there is no buildup in concentration of sodium chloride in the pass liquor stream over its origin~l level in the feed stream, it is possible to increase the content of sodium sulfate in the pass liquor to a higher level than would have been possible if the NaCl level of the pass liquor had increased. Accordingly, it is now possible to realize a desirable lo- ~16318~
-high % Recovery, and, in the case of chloralkali brine, to minimi7P the volume of brine purge, and/or the size of a reactor and the amount of chemicals for an, optional, subsequent sulfate pr~cipilation step.
Accordingly, in a further aspect the invention provides a process as hereinabove defined wherein said first solute is sodium chloride and said second solute is sodium sulfate.
Preferably, the sodium chloride is at a co~centration of greater than 50 g/l, more preferably greater than 100 g/l and yet more preferably in the range 150-350 g/l, and wherein the sodium sulfate conc~ntration is greater than 0.25 g/l, preferably 5-40 g/1.
In a further aspect, the invention provides a process for the selective removal of sulfate anion from sodium chloride liquors as hereinabove defined further comprising sodium chlorate, as obtained in the manufacture of sodium chlorate.
In yet further aspects, the invention provides processes as hereinabove defined wherein the concentrated sodium chloride liquors comprise silica as a cont~min~nt or have un~cceptable levels of CrO4- or Cr2O7S.
In still yet further aspects of the invention there is provided beneficial nanofiltration processes for reducine the concentration of multivalent species and/or organic solutes with a molecular weight of 200 or more from matrices of concentrated solutions of acids, bases, salts, ~ u~s of acids and salts and I~ ules of bases and salts which concentration is at least 50 g/l as total dissolved solids or acids. Some of such applications of indlls~ ignifi~nce are listed as follows.
- Removal of multivalent metals from brine. Also from acids such as H2SO4, HNO3, HCl, HF or mLlctures thereof such as galvanic wastewater, metal clç~ning, metal etching and the like.
- Separation of NaCl from Na2SO4 and Na2CO3 in a dissolved precipitator catch from a recovery boiler in a Kraft pulp mill. Removal of chlorides is required to reduce the corrosivity of recovered process chemical streams within a Kraft mill which is subst~nti~lly closed, i.e. effl~lent free.
- Pllrific~tion of fertilizer grade of orthophosphoric acid from heavy metals to make it suitable for t~-hni~l application, i.e. upgrading to technical grade acid.
- Recovery of H2SO4 and HNO3 from spent nitration acid. Here the nitrated 11- ~16348 :) organic byproducts remain in the pass liquor strearn, while purer and desired acids are collected as a permeate.
- Separation of phenolic salts from a product rinse water during production of nitrobPn7Pnes, nitrotol~lenP-s, nitroxylenses and other nitroorganic compounds.
- Segregation of sodium sesq~ ulf~te solution, Na3H(SO4)2 into Na2SO4 in the pass liquor stream and NaHSO4 in the permeate. The latter could be used within a pulp mill as an acid, e.g. for generation of ClO2 or in an acidulation step to produce a tall oil.
- Fraction~tion of White Liquor into a Na2S-rich pass liquor and a NaOH-rich permeate fraction.
It will be readily understood that the present invention may be practised in systems involving aqueous solutions cont~ining more than two solutes providedselectivity characteri~tics as between the individual solutes are a~prop~iate and suitable for desired selective separations or concentrations.
The processes of the invention as hereinabove defined may further comprise further tre~tm~nt of the pass liquor or the permeate liquor. For example, the pass liquor of the above chloralkali brine - sodium sulfate liquor may be, for e~mI)le, either treated with calcium chloride or barium chloride to effect precipitation of calcium sulfate or barium sulfate, or to effect fractional cryst~lli7~tion by cooling directly or after partial evaporation of water.
The process is of particular value with spent de~-~lorin~ted brine as feed liquor. It is also of value using a chlorate liquor cont~ining unwanted amounts of sulfate and/or chromate or dicl~ol-,ate. Such chlorate liquor may be obtained ascryst~lli7Pr mother liquor or from other sources in a sodium chlorate manufacturing plant circuit, inclu~in the brine feed.
In the case of the removal of unwanted materials such as silica anions which are capable of being present as monovalent sperieS~ it is highly desirable that the pH of the liquor be adjusted, where ap~r~,iate, to m~ximi~e the concentration of the di- or higher valent anions of that species. For exarnple, aqueous silica species should be converted to SiO3= and other divalent anions rather than HSiO3- or other monovalent anions. Similarly, SO4= anion concentration should be optimized over HSO4-.
The processes of the invention are applicable as either simple stage batch - 12- ~ 1634~
processes with optional recycle of either pass liquor or permeate liquor to the nanofiltration me,l,bl~e module, or as part of a multi-stage, multi-module system.
The processes of the invention as hereinabove defined may be operated at any suitable and desired ~"~ re selected from 0C to the boiling point of thefeed liquor; and positive ples~ules applied to the feed side, generally selected from 50-1200 psi.
BRIEF DESCRIPIION OF THE DRAWINGS
In order that the invention may be better understood, prere led embodim~-nt~ will now be described by way of example only with reference to the acco".pallying drawing wlle.Gin Fig 1 re~,lesenls a di~r~mm~tic flow sheet of a single stage membrane nanofiltration system of use in a process according to the invention.
DETAILED DESCRIPrION OF
PREFERRED EMBODIMENTS OF THE INVENTION
Fi~ l shows generaUy as 10, a single stage membrane nanofiltr~tion system for the s~ ~ation of, for example, solute A from solute B in an aqueous liquor.
System 10 comp ,ses a feed solution holding tank 12 connected to a nanofiltration membrane module 14 by a feed conduit 16 though a high pressure pump 18 (Model I-2401, CID Pumps Inc.) Module 14 comprises a single spiral wound type nanofiltration module conl;~;ning Desal-5, DL2540 polyamide membrane 20 having
AQUEOUS SALT SOLUTIONS
FIELD OF THE INVENTION
This invention relates to a process for red~lcin~ the concentration of undesirable compounds, particularly, solutes, in aqueous solutions by nanofiltration using a filtration membrane. More particularly, it relates to the substantial removal of sulfate, dichromate and silica divalent anions from brine solutions, optionally,0 cont~inin~ chlorate.
BACKGROUND TO THE INVENTION
Pressure driven membrane separation processes are known wherein organic molecules or inorganic ionic solutes in aqueous solutions are concentrated or separated to various degrees by the application of a positive osmotic pressure to one side of a filtration membrane. Examples of such pressures are reverse osmosis (RO), ultrafiltration (UF) and nanofiltration (NF). These pressure driven membrane processes employ a cross-flow mode of operation wherein only a portion of a feed solution (F) is coll~te~ as a permeate solution (P) and the rest is collected as a pass solution (C).
In this speçifi~tion and claims, the exit process stream from the nanofiltration module, which stream has not passed through the membrane is referred to as the "pass stream".
This stream is often referred to by practitioners in the membrane filtration art as the "conce~ ~" stream.
In the case of separation of two solutes A and B, say, NaCl and Na2SO4, the efficiency of the separation process is identified by the following parameters:
[A]p- [A]p % Rejection = x 100% (same relationship for solute B) [A]~
`- ~1634~0 % Recovery = x 100%
Fp Fp Permeate Flux = [litres/min/m2]
Membrane Area wherein [A]p is solute A concentration in feed solution;
[A]p is solute A concentration in permeate solution;
Fp is permeate solution flow; and Fl7 is feed solution flow When a se~aldtion of solute A from solute B is required, a high % Rejection of solute A and a low Rejection of solute B, or vice versa, high % Recovery and high Permeate Flux is desired.
Nanofiltration membranes are structurally very similar to reverse osmosis membranes in that chemi~lly they, typically, are cros~link~d aromatic polyamides, which are cast as a thin "skin layer", on top of a micn~polous polymer sheet support to form a composite membrane structure. The separation properties of the membrane are controlled by the pore size and çl~tric~l charge of the "skin layer". Such amembrane structure is usually referred to as a thin film composite (TFC). However, unlike RO membranes the NF membranes are char~cteri7çd in having a larger pore size in its "skin layer" and a net negative ~lçctri~l charge inside the individual pores. This negative charge is lcsponsible for rejection of anionic species, according to the anion surface charge density. Accordingly, divalent anions, such as SO4=, are more strongly rejected than monovalent ones such as Cl-. Commercial NF membranes are availablefrom known suppliers of RO and other pleSSul~ driven membranes. Examples include:
Desal-5 membrane (De~lin~tion Systems, Escondido, CA), NF70, NF50, NF40 and NF40HF .. e.. bl~ncs (FilmTec Corp., Minneapolis, MN), SU 600 membrane (Toray,Japan), and NTR 7450 and NTR 7250 membranes (Nitto Electric, Japan). The NF
membranes are typically packaged as membrane moclllles. A so-called "spiral wound"
module is most popular, but other membrane module configurations such as tubularmembranes enclose~ in a shell or plate-and-frame type are also known.
Nanofiltration is characterized by a fractionation capacity for organic - 2163~80 solutes with a molec~ r "cut-off" range of about 300 g/mol; and a fractionation capacity for multivalent vs. monovalent ions, which is especially pronounced foranions.
Nanofiltration membranes have been reported to show no or little rejection of low molecular weight organic molecules, such as, methanol, ethanol and ethyleneglycol, but a ~ignifi-~nt rejection of higher molecular weight organic species, such as glucose. Among inorganic ionic solutes, low to me~ m rejection has been reported for simple 1:1 electrolytes, such as NaCl or NaNO3 and high rejection of other electrolytes where multivalent ionic species are involved, such as Na2SO4, MgCl2 and FeCl3. Such a characteristic differentiates NF from RO which rejects all ionic species, and from ultrafiltration (UF), which does not reject ionic species and only rejects organic compounds with molecular weights typically in excess of 1,000 g/mol.
Sodium chloride (Cl-) finite % Rejections have been published in the following publications, namely:
(a) Desal-5 Membrane Product Application Note, publication of De~lin~tion Systems, Inc (Escondido, CA), April 1991, wherein the Figure on page E-19.3 shows NaCl rejection in the 55 to 85~ range;
(b) NF70 Membrane, Product Specific~ion~ publication of Filmtec Corp.
(lUinne~rolis, MN), cites Rejection of 60%; and (c) "Membrane Handbook", ed. by W.S.W. Ho and K.K. Sirkar, Van Norstrand Reinhold, New York 1992 at Table 23.2. "Characteristics of Selected Nanofiltration Membranes", cites NaCl % Rejection of: 80%
for NF70 membrane (Filmtec), 45% for NF40 membrane (Filmtec), 50% for NTF-7250 membrane (Nitto), 47% for Desal-5 membrane (DesAlin~tion Systems), and 55% for SU200HF membrane (Toray).
During the NF process, a minimum l~lCS:iUlC equal to the osmotic pressure difference between the feed/pass liquor on one side and the permeate liquor on the other side of the membrane must be applied since osmotic pressure is a function of the ionic strengths of the two streams. In the case of separation of a multivalent solute, such as Na2SO4, from a monovalent one, such as NaCl, the osmotic pressure difference is moderated by the low NaCl rejection. Usually, a pressure in excess of the osmotic prcs~ difference is employed to achieve practical permeate flux. In view - ~63180 of lower NaCl rejection, NF has been used successfully for removal of sulfate and the hardness cations, Ca2+ and Mg2+ from brackish waters and even seawater, without the necessity to excessively pre~ n7e the feed stream. The reported typical pressure range for NF is 80 to 300 psi, although membrane elem~nt~ are de~ipn~d to withstand pressures of up to 1,000 psi.
Reported uses of NF include the aforesaid water softening, removal of dissolved multivalent ions such as Ra2+, reduction of silica as a part of feedwater conditioning for a subsequent RO step or removal of medium of medium molecular weight organic compounds. It has also been demonstrated that high rejection of ionic species could be obtained by proper conditioning of the stream i.e. by ch~nging its pH.
Thus, effective removal (rejection) of call,onate anion could be achieved by adjusting the pH of the feed solution to about 12, to ensure that carbonate would predominantly exist as CO3=, which anion is more strongly rejected by the NF membrane than theHCO3 = ionic form.
Dissolved or suspended silica in brine feed for chloralkali processes, especially the so-called membrane chloraL~ali process, presents a problem in that the silica forms scale on the surface or in the interior of the ion exchange membrane separator. This causes the cell voltage and, hence, power consumption to increase.
In general, in the membrane chloralkali process, the concentration of silica in the feed brine should not exceed 10 ppm, although even a lower level may be needed if some other cont~ in~nt~, such as A13+, are present, since these cont~min~nt~ enhance the scaling capacity of silica.
In other types of chloralkali and in sodium chlorate manufacturing processes, silica, if present in the feed brine also leads to insoluble deposits on the anode which also leads to increased cell voltage and a premature wear of the anode coating. Ln general, however, in these processes, somewhat higher levels of silica, e.g.
30 ppm or more could still be tolerated.
Silica is recognized as a difficult cont~",in~llt to remove from water and/or brine. In chloraL~ali practice, it is usually removed by the addition of MgCI2 or FeCl3 to brine, followed by pH adj~lstment to precipitate the respective metal hydroxide in a form of a floc. This freshly formed floc is an effective absorber for dissolved silica, which may then be separated from brine by e.g. filtration. One - ~163480~ 5 method combining aeration of brine, to convert Fe(II) present therein to Fe(III), which then forms Fe(OH)3 floc is described in U.S. Pat. No. 4,405,463.
Use of strongly basic anion eYrh~n~e membranes for silica removal from feedwater has been reported. However, the liteldtulG also recognizes that, in case there S is a substantial background of other salts, the selectivity of the IX resin towards silica is greatly re lnçed.
Product literature from FilmTec Corp., Minneapolis, MN describes removal of silica from feedwater with a NF70 nanofiltration membrane, as part of a ," . . .e.nt for a subsequent RO step. A red~ction of silica concçntration in r~e~lw~er from 400 ppm to 50-60 ppm has been mentioned. The lite.dLule is silent, however, on use of NF metho~s for silica removal from higher concent~tion salt solutions such as chloralkali brine.
Sodium chlorate is generally preGpaled by the electrolysis of sodium chloride wherein the sodium chloride is electrolyzed to produce chlorine, sodiumhydroxide and hydrogen. The chlorine and sodium hydroxide are immer~i~tely reacted to form sodium hyporhlorite, which is then converted to chlorate and chloride under controlled con~litil~ns of pH and t~ G,dture.
In a related ch~mi~l process, chl- rine and caustic soda are p~G~al~ in an electrolytic cell, which contains a membrane to prevent chlorine and caustic soda reacting and the sep~A~d çh.omic~l~ are removed.
The sodium chloride salt used to p~e~alG the brine for electrolysis to sodium chlorate generally contains impurities which, depe-n-ling on the nature of the illlpulily and pr~duction techniques employed, can give rise to plant operational problems f~mili~r to those skilled in the art. The means of controlling these impurities are varied and inclu~le, purging them out of the system into ~lt~ tive processes or to the drain, precipitation by conversion to insoln~Qle salts, cryst~1li7~tion or ion e~c-h~n~e tre~tment The control of anionic impurities pr~.ll~ more complex problems than that of c~tionic impurities.
Sulfate ion is a common ingredient in commercial salt. When such salt is used directly, or in the form of a brine solution, and specific steps are not taken to remove the sulfate, the sulfate enters the electrolytic system. Sulfate ion ,n~it~l~;n~ its identity under the con~lition~ in the electrolytic system and thus ~1~31~ 6 , accumulates and progressively increases in concentration in the system unless removed in some manner. In chlorate plants producing a liquor product, the sulfate ion will leave with the product liquor. In plants producing only crystalline chlorate, the sulfate remains in the mother liquor after the cryst~lli7~tion of the chlorate, and is recycled to S the cells. Over time, the concentration of sulfate ion will increase and adversely affect electrolysis and cause operational problems due to localized precipitation in the electrolytic cells. Within the chloralkali circuit the sodium sulfate will concentrate and adversely effect the membrane, which divides the anolyte (brine) from the catholyte (caustic soda).
It is in~ustri~lly desirable that sodium sulfate levels in concentrated brine, e.g., 300 g/l NaCl be reduced to at least 20 g/l in chlorate production and 10 g/l in chloraLkali production.
U.S. Pat. No. 4,702,805, Burkell and Warren, issued Oct. 27, 1987, describes an improved method for the control of sulfate in an electrolyte stream in a crystalline chloMte plant, whereby the sulfate is crysPlli7~d out. In the production of crystalline sodium chlorate according to U.S. Pat. No. 4,702,805, sodium chloMte is cryst~lli7e~ from a sodium chlorate rich liquor and the crystals are removed to provide a mother liquor comprising principally sodium chlorate and sodium chloride, together with other components int~,lu-ling sulfate and dichromate ions. A portion of the mother liquor is cooled to a t~mpe~lule to effect cryst~lli7~tion of a portion of the sulfate as sodium sulfate in admixture with sodium chlorate. The cryst~lli7eA admixture is removed and the res~lltin~ spent mother liquor is recycled to the electrolytic process.
It has been found subsequently, that the cry.ct~lli7~1 admixture of sulfate and chloMte obtained from typical commercial liquors according to the process of U.S.
Pat. No. 4,702,805 may be discoloured yellow owing to the unexpected occlusion of a chromium component in the crystals. The discolouration cannot be removed by washing the sepaMted ~lmixt~lre with liquors in which the cryst~lli7ed sulfate and chloMte are insoluble. It will be appreciated that the presence of chromium in such a sulfate product is detrimental in subsequent utili7~tion of this product and, thus, this reple~nts a limit~tion to the process as taught in U.S. Pat. No. 4,702,805.
U.S. Pat. No. 4,636,376 - Maloney and Carbaugh, issued January 13, 1987, discloses removing sulfate from aqueous chromate-conlaining sodium chloMte 2163~83 liquor without simultaneous removal of ~ignifir~nt quantities of chromate. The chromate and sulfate-co~ ining chlorate liquor having a pH in the range of about 2.0 to about 6.0 is treated with a calcium-cont~ining m~tPri~l at a temperature of between about 40C and 95C, for between 2 and 24 hours to form a sulfate-containing ~ ,ci~i~te. The precipil~te is predo",in~,lly glauberite, Na2Ca(SO4)2. However, the addition of calcium cations requires the additional expense and effort of the treatment and removal of all excess ~1cium ions. It is known that calcium ions may form anunwanted deposit on the cathodes which increases the el~ctri(~l resi~Pnce of the cells and adds to ope~ling costs. It is, typically, n~es~ry to remove calcium ions by means of ion eYch~nge resins.
U.S. Pat. No. 5,093,089 - Alford and Mok, issued March 3, 1992 describes an improved version of the selective cryst~lli7~tiQn process of aforesaid U.S.
Pat. No. 4,702,805, wherein process conditions are selected to provide precipitation of sulfate subst~nti~lly free of chlol-liul-- cont~,..ill~-t Typically, organic anion eYch~nge resins have a low selectivity for sulfate anions in the presence of a large excess of chloride ions. United States Pat. No.
304,415,677 describes a sulfate ion absorption method, but which method has disadv~nt~ges.
The method consists of removing sulfate ions from brine by a macropor~us ion eYch~nge resin composite having polymeric zirconium hydrous oxide contained in a vessel. This method is not economical because the efficiency is low and a large amount of expensive cation exchange resin is required for carrying polymeric zirconium hydrous oxide. Further, the polymeric Lir~oniunl hydrous oxide adsorbing sulfate ions comes into contact with acidic brine cont~inin~ sulfate ions, re~lltin~ in loss of polymeric ~,ilCOlliUIIl hydrous oxide due to acid-induce~ dissolution. Soluble zirconyl ions precipilates as hydroxide in the lower portion of the vessel to clog flow paths.
United States Pat. No. 4,556,463 - Minz and Vajna issued December 3, 1984, describes a process to decrease sulfate concentr~tion levels in brine solutions using an organic ion e~ch~nge m~t~ l with brine streams under carefully controlled dilutive conditions.
~163~80 ~_ 8 U.S. Pat. No. 5,071,563 - Shiga et al, issued December 10, 1991, describes the selective adsorption of sulfate anions from brine solutions using zirconium hydrous oxide slurry under acidic conditions. The ion exchange compound may be regenerated by ~ ..,ellt with allcali.
S J~r~nese Patent Kokai No. 04321514-A, published November 11, 1992 to K~nt~L~ Co,~-dlion describes the selective adsorption of sulfate anions from brine solutions using cerium hydroxide slurry under acidic conditions. The ion eYçh~nge compound may be regenerated by tre~tment with alkali.
J~p~nese Patent Kokai No. 04338110-A - K~ne~ Corporation, published November 25, 1992 describes the selective adsorption of sulfate anions from brine solutions using titanium hydrous oxide slurry under acidic conditions. The ion exchange compound may be regenerated by tre~tmçnt with alkali.
J~p~nese Patent Kokai No. 04334553-A - K~n.o~, published November 11, 1992 describes the removal of sulfate ions from brine using ion-adsorbing cakes in a slurry.
There still rem~in~, however, a need for an improved, cost-effective, practical method for the removal of sulfate, silica and chromium (VI) ions from alkali metal halide solutions, particularly, from sodium chloride solutions used in theelectrolytic production of sodium chlorate and chlorine/caustic soda.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process of ch~nging the ratio of the concentr~tion of two or more compounds in an aqueous liquor so as to obtain subst~n~ y complete or partial removal of one compound from the another in the liquor.
It is a further object of the invention to provide a process of reduçing the concentration of sodium sulfate in a brine liquor or a brine/chlorate liquor.
Accordingly, in its broadest aspect the invention provides in a nanofiltration process for filttqring an aqueous liquor comprising feeding a feed liquor to a nanofiltration membrane module under a positive pressure to provide a pass liquor ~163~80 g and a permeate liquor for selectively ch~ngin~e the concentration of a first compound relative to the concentration of a second compound in said aqueous liquor wherein said first compound has a first feed concentration and said second compound has a second feed concentration, said process comprising feeding said aqueous liquor to said S nanofiltration membrane module, collecting said pass liquor wherein said first compound is at a first pass concentration and said second compound is at a second pass concentration, and collecting said permeate liquor wherein said first compound has a first permeate concentration and said second compound is at a second permeate concentration, the improvement comprising said first compound having a first concentration of greater than 50 g/l.
Thus, surprisingly I have found that nanofiltration membrane processes can be used to bençfici~lly reduce the concentration of multivalent ions, such as S04=, CrO4= or Cr207= and dissolved silica in concenl,ated solutions of sodium chloride, such as brine, and concentrated sodium chlorate process liquors where the main colllpollents are sodium chlorate and sodium chlori~le.
I have most surprisingly found, notwithshn-ling the t~ching.s that commercially available nanofiltration membranes have a monocharged anion rejection property, e.g. a Cl- ion rejection in the range 20-50%, that such membranes when used with concentrated salt solutions exhibit no Cl- ion rejection. This unexpected absence of chloride rejection by the nanofiltration membrane has a significant practicalimportance in minimi7ing the osmotic pres~ e across the membrane and hence the energy required for press.~. ;7ing the feed to achieve a given permeate flow. Further, in surprising contrast, the rejection of multivalent ions such as S04=, CrO4= or Cr2O7=
and also silica remains high.
Accordingly, such unexpected ion membrane selectivity at relatively high salt concentrations offers attractive applications such as, for example, in the treatment of chloraL~ali brine liquors having sodium sulfate levels unacceptable in recycle systems. As illustrated in an application of sulfate removal from brine, because there is no buildup in concentration of sodium chloride in the pass liquor stream over its origin~l level in the feed stream, it is possible to increase the content of sodium sulfate in the pass liquor to a higher level than would have been possible if the NaCl level of the pass liquor had increased. Accordingly, it is now possible to realize a desirable lo- ~16318~
-high % Recovery, and, in the case of chloralkali brine, to minimi7P the volume of brine purge, and/or the size of a reactor and the amount of chemicals for an, optional, subsequent sulfate pr~cipilation step.
Accordingly, in a further aspect the invention provides a process as hereinabove defined wherein said first solute is sodium chloride and said second solute is sodium sulfate.
Preferably, the sodium chloride is at a co~centration of greater than 50 g/l, more preferably greater than 100 g/l and yet more preferably in the range 150-350 g/l, and wherein the sodium sulfate conc~ntration is greater than 0.25 g/l, preferably 5-40 g/1.
In a further aspect, the invention provides a process for the selective removal of sulfate anion from sodium chloride liquors as hereinabove defined further comprising sodium chlorate, as obtained in the manufacture of sodium chlorate.
In yet further aspects, the invention provides processes as hereinabove defined wherein the concentrated sodium chloride liquors comprise silica as a cont~min~nt or have un~cceptable levels of CrO4- or Cr2O7S.
In still yet further aspects of the invention there is provided beneficial nanofiltration processes for reducine the concentration of multivalent species and/or organic solutes with a molecular weight of 200 or more from matrices of concentrated solutions of acids, bases, salts, ~ u~s of acids and salts and I~ ules of bases and salts which concentration is at least 50 g/l as total dissolved solids or acids. Some of such applications of indlls~ ignifi~nce are listed as follows.
- Removal of multivalent metals from brine. Also from acids such as H2SO4, HNO3, HCl, HF or mLlctures thereof such as galvanic wastewater, metal clç~ning, metal etching and the like.
- Separation of NaCl from Na2SO4 and Na2CO3 in a dissolved precipitator catch from a recovery boiler in a Kraft pulp mill. Removal of chlorides is required to reduce the corrosivity of recovered process chemical streams within a Kraft mill which is subst~nti~lly closed, i.e. effl~lent free.
- Pllrific~tion of fertilizer grade of orthophosphoric acid from heavy metals to make it suitable for t~-hni~l application, i.e. upgrading to technical grade acid.
- Recovery of H2SO4 and HNO3 from spent nitration acid. Here the nitrated 11- ~16348 :) organic byproducts remain in the pass liquor strearn, while purer and desired acids are collected as a permeate.
- Separation of phenolic salts from a product rinse water during production of nitrobPn7Pnes, nitrotol~lenP-s, nitroxylenses and other nitroorganic compounds.
- Segregation of sodium sesq~ ulf~te solution, Na3H(SO4)2 into Na2SO4 in the pass liquor stream and NaHSO4 in the permeate. The latter could be used within a pulp mill as an acid, e.g. for generation of ClO2 or in an acidulation step to produce a tall oil.
- Fraction~tion of White Liquor into a Na2S-rich pass liquor and a NaOH-rich permeate fraction.
It will be readily understood that the present invention may be practised in systems involving aqueous solutions cont~ining more than two solutes providedselectivity characteri~tics as between the individual solutes are a~prop~iate and suitable for desired selective separations or concentrations.
The processes of the invention as hereinabove defined may further comprise further tre~tm~nt of the pass liquor or the permeate liquor. For example, the pass liquor of the above chloralkali brine - sodium sulfate liquor may be, for e~mI)le, either treated with calcium chloride or barium chloride to effect precipitation of calcium sulfate or barium sulfate, or to effect fractional cryst~lli7~tion by cooling directly or after partial evaporation of water.
The process is of particular value with spent de~-~lorin~ted brine as feed liquor. It is also of value using a chlorate liquor cont~ining unwanted amounts of sulfate and/or chromate or dicl~ol-,ate. Such chlorate liquor may be obtained ascryst~lli7Pr mother liquor or from other sources in a sodium chlorate manufacturing plant circuit, inclu~in the brine feed.
In the case of the removal of unwanted materials such as silica anions which are capable of being present as monovalent sperieS~ it is highly desirable that the pH of the liquor be adjusted, where ap~r~,iate, to m~ximi~e the concentration of the di- or higher valent anions of that species. For exarnple, aqueous silica species should be converted to SiO3= and other divalent anions rather than HSiO3- or other monovalent anions. Similarly, SO4= anion concentration should be optimized over HSO4-.
The processes of the invention are applicable as either simple stage batch - 12- ~ 1634~
processes with optional recycle of either pass liquor or permeate liquor to the nanofiltration me,l,bl~e module, or as part of a multi-stage, multi-module system.
The processes of the invention as hereinabove defined may be operated at any suitable and desired ~"~ re selected from 0C to the boiling point of thefeed liquor; and positive ples~ules applied to the feed side, generally selected from 50-1200 psi.
BRIEF DESCRIPIION OF THE DRAWINGS
In order that the invention may be better understood, prere led embodim~-nt~ will now be described by way of example only with reference to the acco".pallying drawing wlle.Gin Fig 1 re~,lesenls a di~r~mm~tic flow sheet of a single stage membrane nanofiltration system of use in a process according to the invention.
DETAILED DESCRIPrION OF
PREFERRED EMBODIMENTS OF THE INVENTION
Fi~ l shows generaUy as 10, a single stage membrane nanofiltr~tion system for the s~ ~ation of, for example, solute A from solute B in an aqueous liquor.
System 10 comp ,ses a feed solution holding tank 12 connected to a nanofiltration membrane module 14 by a feed conduit 16 though a high pressure pump 18 (Model I-2401, CID Pumps Inc.) Module 14 comprises a single spiral wound type nanofiltration module conl;~;ning Desal-5, DL2540 polyamide membrane 20 having
2.5m2 of active membrane area. Exiting module 14 is a pass liquor conduit 22 having a pressure control valve 24 and a permeate liquor conduit 26.
System 10 has a pass liquor recycle conduit 28 controlled by a valve 30, which, optionaUy, is used when recycle of the feed/pass liquor to tank 12 is desired.
In operation, aqueous feed liquor col.~ining solute A and solute B at feed concentrations Ap and BF~ r~ s~eclively, are passed to module 14 under a high pre~u~
of 400 + psi, feed solution pr~s~ul~ PF~ by pump 18, at a feed solution flow rate of FF.
21634~0 Exiting through conduit 22 is pass liquor at a flow rate Fc cont~ining solutes A and B at pass liquor concentrations of Ac and Bc, respectively. Exiting through conduit 26 is permeate liquor at a flow rate of Fp cont~ining solutes A and B
at permeate liquor concentrations of Ap and Bp, l- spec~i~ely.
S The process depicted in Fig 1 r~sel ts a single stage or batch-type process, wherein the pass liquor or the permeate liquor may be of sufficient and desired quality for use in a subsequent process or discharge. However, each of the pass and permeate streams, optionally, individually, may be sent through a nanofiltrationmembrane process again, in one or more cycles, in either a batch or continuous processes. In industrial processes of use in the practise of the invention, the pass stream from the first stage may be sent to the second stage to increase the overall % Recovery. Altern~tively, the NF process may be con~lcted in a batch mode with the pass liquor recycled back to the feed tank. Accordingly, in consequence, the feed composition will vary with time as will the Membrane Flux and possibly the %
Rejection.
The following Examples illustrate specific compounds used in the process as desçribe~l by Fig 1.
Example 1 A batch of 80 litres of brine solution con ~ining 196.0 grams/litre NaCl and 9.45 grams/litre Na2SO4 at a temperature of 50C was added to tank 12. High ~s~ll~ pump 18 was turned on and the pres~ on the feed side was adjusted to 400 + 5 psi and kept constant during the run. Both permeate and pass liquor streams were collected into s~dle tanks over a period of 11.5 minutes. Both the permeate and the pass liquor flow rates were approxim~t~ly co~-~t~nt during the run at about 2.0 lpm and
System 10 has a pass liquor recycle conduit 28 controlled by a valve 30, which, optionaUy, is used when recycle of the feed/pass liquor to tank 12 is desired.
In operation, aqueous feed liquor col.~ining solute A and solute B at feed concentrations Ap and BF~ r~ s~eclively, are passed to module 14 under a high pre~u~
of 400 + psi, feed solution pr~s~ul~ PF~ by pump 18, at a feed solution flow rate of FF.
21634~0 Exiting through conduit 22 is pass liquor at a flow rate Fc cont~ining solutes A and B at pass liquor concentrations of Ac and Bc, respectively. Exiting through conduit 26 is permeate liquor at a flow rate of Fp cont~ining solutes A and B
at permeate liquor concentrations of Ap and Bp, l- spec~i~ely.
S The process depicted in Fig 1 r~sel ts a single stage or batch-type process, wherein the pass liquor or the permeate liquor may be of sufficient and desired quality for use in a subsequent process or discharge. However, each of the pass and permeate streams, optionally, individually, may be sent through a nanofiltrationmembrane process again, in one or more cycles, in either a batch or continuous processes. In industrial processes of use in the practise of the invention, the pass stream from the first stage may be sent to the second stage to increase the overall % Recovery. Altern~tively, the NF process may be con~lcted in a batch mode with the pass liquor recycled back to the feed tank. Accordingly, in consequence, the feed composition will vary with time as will the Membrane Flux and possibly the %
Rejection.
The following Examples illustrate specific compounds used in the process as desçribe~l by Fig 1.
Example 1 A batch of 80 litres of brine solution con ~ining 196.0 grams/litre NaCl and 9.45 grams/litre Na2SO4 at a temperature of 50C was added to tank 12. High ~s~ll~ pump 18 was turned on and the pres~ on the feed side was adjusted to 400 + 5 psi and kept constant during the run. Both permeate and pass liquor streams were collected into s~dle tanks over a period of 11.5 minutes. Both the permeate and the pass liquor flow rates were approxim~t~ly co~-~t~nt during the run at about 2.0 lpm and
3.3 lpm, respectively. Following the run, 251 of permeate with a composition of 190.1 gpl NaCl and 0.25 gpl Na2SO, and 34 1 of concentrate with a composition of190.7 gpl NaCl and 15.3 gpl Na2SO4 were collected while 201 of the feed brine remained in the feed tank. Calculated NF membrane % Rejections are: 97.3 % for Na2S O4 and 3.0 ~o for NaCl.
The approximate mass b~l~nces are shown as follows wherein the 215~80 volumes of liquor are within +2 litres.
Concentration VolumeAmountConcentration Feed Liauor la/l) (1) (Ka) Ratio*
NaCl 196 60 11.76 20.7 Na2SO4 9.45 60 0.57 Pass Liouor NaCl 190.7 34 6.48 12.4 0 Na2S04 15.3 34 0.52 Permeate Liquor NaCl 190.1 25 4.75 760 Na2SO4 0.25 25 0.06 * NaCl: Na2S04 Example 2 A simi_ar process was carried out under the same conditions as for Example 1, wherein the volume of feed brine was 76 litres containing 195.9 gpl NaCl and 18.0 gpl Na2SO4.
After 10 minutes of operation with a feed pass pressure maintained at 400 + 5 psi, 18 1 of permeate and 38 1 of concentrate were collected while 19 1 of the feed brine remained in the feed tank. The composition of the permeate was 194.7 gpl NaCl and 0.37 gpl Na2SO4. The composition of concentrate was 192.0 gpl NaCl and 26.3 gpl Na2SO4.
Calculated NF membrane % Rejections are: 97.9% for Na2SO4 and 0.6% for NaCl.
Concentration VolumeAmountConcentration Feed Liquor (~/1) (1) (K~) Ratio*
NaCl 195.9 57 11.17 10.9 Na2S04 18.0 57 1.03 Pa~ Liquor NaCl 192 38 7.30 7.3 Na2SO4 26.3 38 1.00 Permeate Liquor NaCl 194.7 18 3.50 526 Na2S04 0.37 18 0.06 * NaCl: Na2S04 Example 3 In this example a recycle batch mode of operation was carried out wherein the pass stream was recycled back to the brine feed tank. A starting volume of feed brine was 76 1 having a composition of 197.5 gpl NaCl and 16.7 gpl 216348~
Na2SO4- The flow rate of permeate was kept constant at 1.3 lpm. The resulting feed pass pressure was initially at 295 psi and at the end of the process at 315 psi. After 45.5 minutes 50 l of permeate were collected while the volume in the brine feed tank decreased to 25 l. The composition of permeate was 200.4 gpl NaCl and 0.38 gpl Na2S04. The composition of brine solution remaining in the feed tank was 188.4 gpl NaCl and 44.8 gpl Na2S04. The calculated NF
membrane % Rejections were 97.7% for Na2SO4 and -1.5% for NaCl.
Concentration Volume Amount Concentration Feed Liquor(q/l) (1~(Xq) Ratio*
NaCl 197.5 7615.01 11.83 Na2SO4 16.7 761.27 Pas~ Liquor NaCl 188.4 254.71 4.21 Na2SO~ 44.8 251.12 Permeate Liquor NaCl 200.4 5010.02 526 Na2SO4 0.38 500.02 * NaCl: Na2S0~
Example 4 A recycle batch process similar to that of Example 3 was carried out with a liquor further containing silica and having a pH of 10.7. The initial volume of brine feed solution was 75 l and had a composition of 246.9 gpl NaCl, 30.0 gpl Na2SO4 and 9.1 ppm sio2. The feed pass liquor pressure was kept constant at 320 + 5 psi. After 64 minutes 50 l of permeate was collected while the volume of solution in the feed tank decreased to 24 l. The composition of permeate was 257.5 gpl NaCl, 0.85 gpl Na2SO4 and 5.5 ppm SiO2.
The composition of brine solution remaining in the feed tank was 240.5 gpl NaCl, 79.8 gpl Na2SO4 and 15.1 ppm Sio2. The calculated Nf membrane ~ Rejections were 97.2% for Na2S04, -
The approximate mass b~l~nces are shown as follows wherein the 215~80 volumes of liquor are within +2 litres.
Concentration VolumeAmountConcentration Feed Liauor la/l) (1) (Ka) Ratio*
NaCl 196 60 11.76 20.7 Na2SO4 9.45 60 0.57 Pass Liouor NaCl 190.7 34 6.48 12.4 0 Na2S04 15.3 34 0.52 Permeate Liquor NaCl 190.1 25 4.75 760 Na2SO4 0.25 25 0.06 * NaCl: Na2S04 Example 2 A simi_ar process was carried out under the same conditions as for Example 1, wherein the volume of feed brine was 76 litres containing 195.9 gpl NaCl and 18.0 gpl Na2SO4.
After 10 minutes of operation with a feed pass pressure maintained at 400 + 5 psi, 18 1 of permeate and 38 1 of concentrate were collected while 19 1 of the feed brine remained in the feed tank. The composition of the permeate was 194.7 gpl NaCl and 0.37 gpl Na2SO4. The composition of concentrate was 192.0 gpl NaCl and 26.3 gpl Na2SO4.
Calculated NF membrane % Rejections are: 97.9% for Na2SO4 and 0.6% for NaCl.
Concentration VolumeAmountConcentration Feed Liquor (~/1) (1) (K~) Ratio*
NaCl 195.9 57 11.17 10.9 Na2S04 18.0 57 1.03 Pa~ Liquor NaCl 192 38 7.30 7.3 Na2SO4 26.3 38 1.00 Permeate Liquor NaCl 194.7 18 3.50 526 Na2S04 0.37 18 0.06 * NaCl: Na2S04 Example 3 In this example a recycle batch mode of operation was carried out wherein the pass stream was recycled back to the brine feed tank. A starting volume of feed brine was 76 1 having a composition of 197.5 gpl NaCl and 16.7 gpl 216348~
Na2SO4- The flow rate of permeate was kept constant at 1.3 lpm. The resulting feed pass pressure was initially at 295 psi and at the end of the process at 315 psi. After 45.5 minutes 50 l of permeate were collected while the volume in the brine feed tank decreased to 25 l. The composition of permeate was 200.4 gpl NaCl and 0.38 gpl Na2S04. The composition of brine solution remaining in the feed tank was 188.4 gpl NaCl and 44.8 gpl Na2S04. The calculated NF
membrane % Rejections were 97.7% for Na2SO4 and -1.5% for NaCl.
Concentration Volume Amount Concentration Feed Liquor(q/l) (1~(Xq) Ratio*
NaCl 197.5 7615.01 11.83 Na2SO4 16.7 761.27 Pas~ Liquor NaCl 188.4 254.71 4.21 Na2SO~ 44.8 251.12 Permeate Liquor NaCl 200.4 5010.02 526 Na2SO4 0.38 500.02 * NaCl: Na2S0~
Example 4 A recycle batch process similar to that of Example 3 was carried out with a liquor further containing silica and having a pH of 10.7. The initial volume of brine feed solution was 75 l and had a composition of 246.9 gpl NaCl, 30.0 gpl Na2SO4 and 9.1 ppm sio2. The feed pass liquor pressure was kept constant at 320 + 5 psi. After 64 minutes 50 l of permeate was collected while the volume of solution in the feed tank decreased to 24 l. The composition of permeate was 257.5 gpl NaCl, 0.85 gpl Na2SO4 and 5.5 ppm SiO2.
The composition of brine solution remaining in the feed tank was 240.5 gpl NaCl, 79.8 gpl Na2SO4 and 15.1 ppm Sio2. The calculated Nf membrane ~ Rejections were 97.2% for Na2S04, -
4.3% for NaCl and 39.6~ for sio2.
Concentration Volume Amount Concentration Feed Liquor(q/l) (1)(Rq) Ratio*
NaCl 246.9 7518.52 8.23 Na2SO4 30.0 752.25 SiO29.1 (ppm) 75 6.8 x 10-4 parts _ -16-~1~3~8~
Pa~ Li~uor NaCl 240.5 245.77 3.01 Na2SO4 79.8 241.92 SiO2 lS.l (ppm) 243.62 x 104 parts Permeate Liquor NaCl 257.5 5012.88 303 Na2SO4 0.85 500.04 SiO2 5.5 (ppm) 502.75 x 104 partq * NaCl: Na2SO4 Exampl~ 5 This example illustrates the simultaneous reduction lS in sulfate and chromium (VI) concentration in a sodium chlorate feed liquor solution.
A bath of 75 l of chlorate liquor feed solution containing 395 gpl NaCl03, 101.1 gpl NaCl, 20.8 gpl Na2S04,
Concentration Volume Amount Concentration Feed Liquor(q/l) (1)(Rq) Ratio*
NaCl 246.9 7518.52 8.23 Na2SO4 30.0 752.25 SiO29.1 (ppm) 75 6.8 x 10-4 parts _ -16-~1~3~8~
Pa~ Li~uor NaCl 240.5 245.77 3.01 Na2SO4 79.8 241.92 SiO2 lS.l (ppm) 243.62 x 104 parts Permeate Liquor NaCl 257.5 5012.88 303 Na2SO4 0.85 500.04 SiO2 5.5 (ppm) 502.75 x 104 partq * NaCl: Na2SO4 Exampl~ 5 This example illustrates the simultaneous reduction lS in sulfate and chromium (VI) concentration in a sodium chlorate feed liquor solution.
A bath of 75 l of chlorate liquor feed solution containing 395 gpl NaCl03, 101.1 gpl NaCl, 20.8 gpl Na2S04,
5.1 gpl Na2Cr3O7 at a pH of 7 and a temperature of 45C was added to tank 12. The high pressure on the feed side was adjusted to 505+10 psi and kept constant during the run.
Both permeate and pass liquor streams were collected into separate tanks over a period of 91 minutes. In total, 20 l of permeate liquor and 10 l of pass liquor were collected, while about 44 l of feed solution remained in tank 12 at the end of the run. The calculated average permeate liquor and concentrate liquor flows were 0.22 lpm and 0.11 lpm, respectively. Subsequent chemical analysis revealed that the permeate liquor had 398 gpl NaCl03, 101.5 gpl NaCl, 4.1 gpl Na2S04 and 2.0 gpl Na2Cr207, while the pass stream had 380 gpl NaCl03, 96 gpl NaCl, 48.8 gpl Na2S04 and 9.5 gpl Na2Cr207.
Calculated NF membrane % Rejections were: ~0.4% for NaCl, -0.7% for NaCl03, 80.3% for Na2S04 and 60.8% for Na2Cr207.
Concentration Volume Amount Concentration Feed Liouor(q~l) (1) IK~) Ratio NaClO3 395.0 31 12.24 4.86*
NaCl 101.1 31 3.13 19.0**
Na2SO4 20.8 31 0.64 77.5***
Na2Cr2O7 5.1 31 0.16 19.8****
Paq~ Liquor NaClO3 380.0 10 3.8 1.96*
NaCl 96.0 10 0.96 7.78**
Na2SO4 48.8 lO 0.49 40.0***
Na2Cr207 9.5 lO 0.09 10.0****
- 17- ~163 1~0 Permeate Liauor NaCl03 398 . 0 20 7 . 96 24 . 8*
NaCl 101. 5 20 2 . 03 97 . 0**
Na2SO4 4.1 20 0.08199.0***
Na2Cr2O7 2.0 20 0.0451.0****
wherein: -* NaCl: Na2SO~
* * NaClO3: Na2S0~
0 ` * * * NaClO3: Na*r2O7 * * * * NaCl: Na2Cr2O7 Although this disclosure has described and illustrated certain preferred embodiments of the invention, it is to be understood that the invention is not restricted to those particular embodiments which are functional or mechanical equivalence of the specific embodiments and features that have been described and illustrated.
Both permeate and pass liquor streams were collected into separate tanks over a period of 91 minutes. In total, 20 l of permeate liquor and 10 l of pass liquor were collected, while about 44 l of feed solution remained in tank 12 at the end of the run. The calculated average permeate liquor and concentrate liquor flows were 0.22 lpm and 0.11 lpm, respectively. Subsequent chemical analysis revealed that the permeate liquor had 398 gpl NaCl03, 101.5 gpl NaCl, 4.1 gpl Na2S04 and 2.0 gpl Na2Cr207, while the pass stream had 380 gpl NaCl03, 96 gpl NaCl, 48.8 gpl Na2S04 and 9.5 gpl Na2Cr207.
Calculated NF membrane % Rejections were: ~0.4% for NaCl, -0.7% for NaCl03, 80.3% for Na2S04 and 60.8% for Na2Cr207.
Concentration Volume Amount Concentration Feed Liouor(q~l) (1) IK~) Ratio NaClO3 395.0 31 12.24 4.86*
NaCl 101.1 31 3.13 19.0**
Na2SO4 20.8 31 0.64 77.5***
Na2Cr2O7 5.1 31 0.16 19.8****
Paq~ Liquor NaClO3 380.0 10 3.8 1.96*
NaCl 96.0 10 0.96 7.78**
Na2SO4 48.8 lO 0.49 40.0***
Na2Cr207 9.5 lO 0.09 10.0****
- 17- ~163 1~0 Permeate Liauor NaCl03 398 . 0 20 7 . 96 24 . 8*
NaCl 101. 5 20 2 . 03 97 . 0**
Na2SO4 4.1 20 0.08199.0***
Na2Cr2O7 2.0 20 0.0451.0****
wherein: -* NaCl: Na2SO~
* * NaClO3: Na2S0~
0 ` * * * NaClO3: Na*r2O7 * * * * NaCl: Na2Cr2O7 Although this disclosure has described and illustrated certain preferred embodiments of the invention, it is to be understood that the invention is not restricted to those particular embodiments which are functional or mechanical equivalence of the specific embodiments and features that have been described and illustrated.
Claims (12)
1. In a nanofiltration process for filtering an aqueous liquor comprising feeding a feed liquor to a nanofiltration membrane module under a positive applied pressure to provide a pass liquor and a permeate liquor for selectively changing the concentration of a first compound relative to the concentration of a second compound in said aqueous liquor wherein said first compound has a first feed concentration and said second compound has a second feed concentration, said process comprising feeding said aqueous liquor to said nanofiltration membrane module, collecting said pass liquor wherein said first compound is at a first pass concentration and said second compound is at a second pass concentration, and collecting said permeate liquor wherein said first compound has a first permeate concentration and said second compound is at a second permeate concentration, the improvement comprising said first compound having a first concentration of greater than 50 g/l.
2. A process as defined in claim 1 wherein said first compound is sodium chloride and said second compound is sodium sulfate.
3. A process as defined in claim 2 wherein said feed liquor further comprises sodium chlorate.
4. A process as defined in claim 2 wherein said first feed concentration of said sodium chloride is greater than 100 g/l.
5. A process as defined in claim 4 wherein said first feed concentration of said sodium chloride is selected from the range 150-350 g/l.
6. A process as defined in claim 1 wherein said feed liquor further comprises silica.
7. A process as defined in claim 3 wherein said first feed liquor further contains a divalent anion of chromium.
8. A process as defined in claim 1 wherein said pass liquor or said permeate liquor is recycled back to said nanofiltration membrane module.
9. A process as defined in claim 1 further comprising treatment of said pass liquor to effect precipitation of sulfate ion as calcium sulfate, barium sulfate or sodium sulfate by addition of a calcium compound; or by water removal by evaporation.
10. A process as defined in claim 1 wherein said feed liquor is spent dechlorinated brine.
11. A process as defined in claim 3 wherein said feed liquor comprises sodium chlorate plant liquor.
12. A process as defined in claim 6 further comprising adjustment of the pH to provide substantially divalent silica anion.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US08/422,935 US5587083A (en) | 1995-04-17 | 1995-04-17 | Nanofiltration of concentrated aqueous salt solutions |
US08/422,935 | 1995-04-17 |
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CA2163480A1 CA2163480A1 (en) | 1996-10-18 |
CA2163480C true CA2163480C (en) | 1999-11-16 |
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CA002163480A Expired - Lifetime CA2163480C (en) | 1995-04-17 | 1995-11-22 | Nanofiltration of concentrated aqueous salt solutions |
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US (2) | US5587083A (en) |
EP (1) | EP0821615B2 (en) |
JP (1) | JP3256545B2 (en) |
KR (1) | KR100385465B1 (en) |
CN (1) | CN1111081C (en) |
AU (1) | AU691415B2 (en) |
BR (1) | BR9608054A (en) |
CA (1) | CA2163480C (en) |
DE (1) | DE69614516T3 (en) |
NZ (1) | NZ304801A (en) |
TW (1) | TW343157B (en) |
WO (1) | WO1996033005A1 (en) |
ZA (1) | ZA962807B (en) |
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US5858240A (en) | 1999-01-12 |
DE69614516T2 (en) | 2002-05-08 |
JPH11504564A (en) | 1999-04-27 |
CN1180322A (en) | 1998-04-29 |
KR19990007852A (en) | 1999-01-25 |
WO1996033005A1 (en) | 1996-10-24 |
NZ304801A (en) | 1998-12-23 |
EP0821615B1 (en) | 2001-08-16 |
DE69614516T3 (en) | 2006-11-30 |
AU691415B2 (en) | 1998-05-14 |
US5587083A (en) | 1996-12-24 |
BR9608054A (en) | 1999-11-30 |
EP0821615A1 (en) | 1998-02-04 |
CA2163480A1 (en) | 1996-10-18 |
JP3256545B2 (en) | 2002-02-12 |
CN1111081C (en) | 2003-06-11 |
ZA962807B (en) | 1996-10-11 |
AU5267096A (en) | 1996-11-07 |
DE69614516D1 (en) | 2001-09-20 |
EP0821615B2 (en) | 2006-04-26 |
TW343157B (en) | 1998-10-21 |
KR100385465B1 (en) | 2003-08-19 |
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