USRE20217E - Production of pulp - Google Patents

Description

Dec. 29, 1936. T. L. DUNBAR Re. 20,217

PRODUCTION OF PULP Original Filed April 16, 1932 ATTORN Y Reissued Dec. 29, 1936 UNITED STATES PATENT OFFICE PRODUCTION OF PULP Thomas Leonidas Dunbar, Watertown, N. Y assig-nor to Chemipulp Process, Incorporated, Water-town, N. Y., a corporation of New York 19 Claims.

This invention relates to the production of pulp, and in. particular to the production of a super-quality sulphite pulp for use in the manufacture of paper.

- It is an object of my invention to provide a process capable of producing a sulphite pulp from which may be made sulphite paper of unusually high strength. a

A further object is to provide a process for the production of ,sulphite pulp capable of giving a higher yield of pulp than is obtainable by processes now in use.

' Further, it is my object to produce a highcellulose pulp from which may be made a paper similar to kraft in strength, but more pliable than krai't.

A further object is the provision of a flexible process capable of variation of producing pulp with varying characteristics as may be. desired.

A still further object is the provision of a sulphite process by the use of which a saving of acid is effected.

The higher strength of kraft pulp is due primarily to residual'lignin which is not removed by the kraft process. While my improved process removes the greater part of this residual lignin and pentosans, in doing so it leaves a cellulose of unusually high strength, thereby imparting highly desirable characteristics to the finished prod- Briefiy, in the practice of my improved process the digester is first filled with raw material and bisulphite liquor in accordance with the disclosure of my United States Patents Nos. 1,646,084 and 35 1,669,234 and Dunbar et a1. U. 8. Patent No. 1,699,056. A working pressure and temperature sufllcient to release extractives from the raw .material is then built up and the digester is closed in for a soaking period suitable to the wood con- 40 ditions as hereinafter pointed out. The-bisulphite liquor is then drained from the digester and may be conducted to the acid settling tank or to other parts of the acid system where partially prepared liquor is contacted with liquors from the 45 digester. The raw material is then subjected to a bisulphite cook in accordance with principles hereinafter set forth. At the termination of this cook, the material is subjected to a further treatment with precipitated alkaline water.

5 The accompanying drawing is a diagrammatic view of apparatus-suitable for the practice of my improved process.

In the drawing, I is a milk of lime acid tower. This is shown by way of example only, as the 5s applicability of my invention is not limited to the milk of lime system, but is equally applicable to the limestone tower system. 2 is a line leading from the tower l to the settling tank 3. From the settling tank, the line 4 leads to the pump 5, which forces the liquor into the acid storage 5 tank 1 through the line 6. The pump 0 forces the liquor from the storage tank 1 through the line 9 to the eductor i0, where it is contacted with relief fluids from the digesters i5. Although four digesters are shown, any number may be used.

- The drop or condenser leg 'leads from the eductor I0 through the exchange heater 23 to the bottom of the accumulator l I. i2 is a pump for forcing the bisulphite liquor into any one of the digesters as required, by means of line Hand 15 the valved branch filling lines ll. 2| is an exchange heater interposed in the line IS. a

I6 is a valved branch leading from the top of each digester for venting relief gases and fluids through the header IT to the eductor VI 0, while 22 20 is a valved side relief branch for conducting liquors from the digester to the header ii. The valved branch line 25 leads from the top of the digester to the header 21, which header discharges into the acid storage tank I. 26 is a valved 25 branch of! from the line 25, venting to the atmosphere. The operation of; these vent lines has been fully described in my copending application Ser. No. 446,046, new Patent 1,859,384 dated May 24, 1932.

Liquor may be drained from the digesters through the strainer l8, the line 20 having therein the valve i9, and the header 2| leading back to the settling tank I.

In the practice of my improved process, I may proceed as follows: 1 l

The digester having been charged with chips,

the valve in the branch 28 is opened and the digester is filled with hot preconditioned bisulphite liquor, heated to a temperature of 10 C. or more, 40 from the accumulator II by means of the pump i2, line It and valved branch I 4, in accordance with the disclosure of my copending application, Ser. No. 446,046. when the digester has been filled, the valve in the branch 261s closed and a pressure of approximately pounds is applied to the contents of the digester by running the pump l2 until this has been accomplished. The valve in the line II is thenclosed and the pump l2 shut down, and the chips are subjected to a 50 soaking or penetration period under pressure,

' with all the valves of the digester lines closed.

The duration of this soaking period, as well as v the temperature, will vary with the kind and quality of .the raw material. and with its initial moisture content, this soaking period being prefersbly continued until the extractives (by which I mean the so-called water-solubles") are reloasedfromthematerialandalltherawmaterial- I ispiacedin aconstantstate asregardsmoisture content. The bisulphitc liquor penetrates the chills. to scene extimt, leaving a deposit of acid 10 addition, this initial penetration may partially thesucceedingstageoftheprocess.

At the termination of this w: a period, the

bisulphite liquor is drained out of the digester.

16 through 20 and is returned inthebisulphitellquordrainedbacktothesettlirutsnkareneutralisedbyanexcessofalkaline bsseintherswliquon' After the soaking period has been completed andthellquorhasbeendrainedirom thedigester, the digesteris again filled with hot bisulphite liquor, steam is admitted tothe digester,

through line (not shown) and the cooking 'is carried on'intheusualmanneruntil alargepart ntent of the wood is removed. 'lh'is stage of my improved process diil'ers, however,fromtheacidcookaspracticedinthepresent single-stale process. In the single-stage procms, the extractives, resinous matter and lignln are substantially dissolved out by acid. This produces, particularly toward the end of the cook, chemical which have aideteriorating elect on thefibres. Inmy improved processthe fonnationofthese compoundsistoalarge extent prevented.duetothefactthatupontheirappearanceinquantities which would injurethe cellulose,thecookisstopped,allorapartof the thematerialisthentreatedinathirdstagewith lime (or other suitable alkaline) water. The

. Ihavefoundthatitissometimesdesirable,in

ordertopmducespecialgradesofpulp,torepeatthecoohorsecondstageofmyprocess. In thhcssaapsrtonlyofthiscookisaccomplished with each separate charge of bisulphite liquor 79 and consequently there is a progressive increase in the maflmum temperature for each recooking. For example. I have found that in the production of a sulphlte pulp with the strength characteristicsctahighgradekraftpulnthecook' "ihelfmaybecarriedominthreestageathe maximum temperature during the first being 110' 0., during the second approximately 120 C. and

during the third approximately 132 C.

After the completion of the cook, the valve I.

is again openedand all or part of the digester I liquor is drained back to the settling, tank for reuse. the solutestherein being neutralized by the addition of an alkaline liquor. The digester is then filled up (as, for example, by means of the connection 32) with precipitated lime water, and

coils.

After this last cooking with precipitated lime water, the pulp may be blown into a blow pit or other suitable draining medium in the usual manner, viz., normally the blow oi! valve (not shown) at the bottom of the digester is opened and. the as I contents of the digester are forced out by the pressure existing therein. In some cases it is possible to carry out the alkaline cook in the blow pit or elsewhere, after the stock has left the digester. The liquor that drains oil from the 8 blow pit is conducted to settling or clarifying tanks for reuse.

The precipitated lime water has a mildly alkaline reaction and neutralizes any ligno sulphonic acids which may remain in contact with the cel- 35 lulose fibres after the acid cook. This action produces a much stronger and more pliable pulp than that produced by the single stage acid cook process and gives the pulp many characteristics of krait'pulp which'is produced by the alkaline 40 process.

The strength and folding of the pulp may be varied by varying the point in the digestion process at which the precipitated lime (or other alkaline) water is applied. For

example, if a pulp is desired having strength characteristics nearly the same as ordinary sulphite pulp, the seco'ndstsge, or bisulpbite cook,

of my process is continued longer and at a higher temperature. If a pulp of much greater strength is desired, this cook is stopped and the acid removed from the digester as soon as deteriorating compounds appearandthelimewatercookis continued for a comparatively longer time.

Theterms lime water" and "precipitated lime to wa ,"areusedinthisspecificstionandinthe appended claims to refer to a liquor which may or may notcontain considerable ma nesium in addition to the calcium present.

The applicability of my process is not limited .0 to the spruce, hemlockahd fir ordinarily used for the production of sulphite pulp.

By my process I am able to produce a novel. sulphite pulp having an unusually high mullen,

tear and fold test, but much more pliable than 06 a kraft pull).

nor with fresh liquor for reuse, digesting the II fibrom material under heat and presure in bisulphite liquor until the lignin is substantially removed therefrom, withdrawing bisulphiteliqnor from the material and mingling it with fresh liquor for reuse, and cooking the fibrous material in alkaline liquoruntil the incrustants of the cellulose are substantially removed.

2. A process for the production of pulp which comprises soaking fibrous material in heated bisulphite liquor under pressure until the extractives are substantially removed therefrom and the material is of uniform moisture content, withdrawing the bisulphite. liquor and mingling it with 'fresh liquor or reuse, digesting the fibrous material in bisulphite liquor under heat and pressure until deteriorating compounds appear and thereupon draining liquor from the material and cooking the material in-alkaline liquor. I

3. A process for theproduction of pulp which comprises soaking fibrous material in bisulphite liquor until the extractives are removed therefrom and the liquor has penetrated the chips, draining oil the bisulphite liquor and mingling it with fresh liquor for reuse, digesting the fibrous material in bisulphite liquor imder heat and pressure to remove lignin therefrom, draining oiI- liquor from the material, and finally cooking the material in precipitated lime water.

4., A process for theproduction of sulphite pulp which comprises soaking fibrous material in bi sulphite liquor, draining off the liquor, digesting I said material under heat and pressure in additional bisulphite liquor, and finally cooking said material in alkaline liquor.

5. A process for the production of sulphite pulp which comprises first soaking wood chips in' bisulphite liquor under pressure, then cooking the chips in bisulphite. liquor under pressure at a temperature above 100 C., and finally cooking in precipitated lime water.

6. In the production of sulphite pulp, charging a digester with fibrous material, filling the charged digester with bisulphite liquor from an accumulator and soaking the fibrous material in the digester under heat and pressure untfl the extractives' are substantially put into solution, withdrawing liquor from the digester and returning it to the accumulator, refilling the digester with bisulphite liquor from the accumulator and digesting the fibrous material in the digester under heat and pressure to remove lignin therefrom, withdrawing liquor from the digester, adding. alkaline liquor to the digester and cook-- ing the fibrous material in such alkaline liquor.

7. In the productionoi sulphite pulp, charging a digester with fibrous material, filling the charged digester with bisulphite liquor and soaking the fibrous material therein under pressure, withdrawing liquor from the digester, refilling the digester with bisulphite liquor and digesting the fibrousmaterial therein under heat and pressure, again withdrawing liquor from thedigester, admitting precipitated lime water thereto and cookingthematerial therein.

8. In a process for the production of pul soaking fibrous material in bisulphite quor under heat and pressure until are substantially removed therefrom andtheliquorhas penetratedthechips,dralnlngliquorfl'omthe fibrous material, then subiectingthe fibrous materialtoaseriesoi'digestionpmcessesinbisulphite liquor imderheatandpressuraandfinally cookingthefibrousmaterialinalkalineliquor.

9. Inaprocessfottheprodutitlmofpulmsoab. ing fibrous material'mbuulphiteliquor under heat and pressure until the extractives are substantially removed therefrom, then subjecting the fibrous material to a series of digestion processesunder pressure and at successively higher temperatures, and finally cooking the fibrous material in alkaline liquor. I

10. In a process for the production of pulp, charging a digester with fibrous material and soaking said material therein in bisulphite liquor under heat and pressure to remove extractives therefrom, withdrawing liquor from the digester, refilling the digester with bisulphite liquor and digesting the fibrous material therein under heat and pressure to remove lignin therefrom, dis? charging the fibrous material from the digester and thereafter cooking thefibrous material'in alkaline liquor. V

ii. A process for the production of sulphite pulp which comprises first soaking fibrous material in bisulphite liquor under heat and pressure until extractives are substantially removed therefrom and the material is of uniform moisture content, then digesting the fibrous material in bisulphite liquor under heat and pressure until the formation of ligno sulphonlc acid reaches a point deleterious to the material, and finally cooking the fibrous material in alkaline liquor until the incrustants of the cellulose are substantially removed therefrom.

12. Sulphite pulp obtained by soaking fibrous material in heated bisulphite liquor under pressure until'the extractives are substantially put into solution and the bisulphite has penetrated the fibrous material, withdrawing said liquor, cooking the material in fresh bisulphite liquor under heat and pressure, withdrawing said liquor, and cooking the material in alkaline liquor.

13. A process for the production of pulp which comprises charging a digester with fibrous ma- Y terial, introducing hot acid liquor to the "digester while venting air therefrom, sealing the digester and forcing in additional quantities of the hot liquor to establish a high hydrostatic pressure on the liquor; maintaining the hot high pressure liquid in contact with the material until such liquid has substantially completely penetrated 'the material, then draining the liquor from the sealed digester; introducing another batch of hot digestion liquor to the digester and raising the mass to reaction temperatures.

14. A process for the production of pulp which comprises charging a digester'with fibrous material, establishing a body of hot liquor in a separatefeceptac'le, introducing the hot liquor from the receptacle into the digester while venting air from the digester, sealing the digester and forcing in additional quantities of the hot liquor to establish a .high hydrostatic pressure on the liquor; maintaining the hot high' pressure liquor incontact'with the material until the liquor has penetrated the material, then draining the liquor from the bottom portion of the digester. while maintaining the upper portion of the digester sealed, mixing such drained liquor with fresh liquor for reuse; admitting further quantities of hot liquor from the receptacle intwthe digester and raising the mass to reaction temperatures.

15. A process for the production of pulp which comprises soaking fibrousmaterial in' heated bisulphite liquor under a pressure of the order of fifty pounds, maintaining the liquor in contact with the material until it has substantially completely penetrated the material, then draining the liquor from the material, while preventing access of air to the material, subsequently contacting 15 the soaked material with additional quantities of hot liquor and raising the liquor to reaction temperatures.

16. A method of treating fibrous material which comprises introducing a mass of the material to a digester, forcing a quantity of hot digestion liquor into the digester while displacing air from the upper part of the digester, sealing the upper part of the digester and forcing in additional quantities of the hot liquor until a high hydrostatic pressure is established on the liquor; maintaining the hot high pressure liquor in contact with the material for a period of time sumciently long to effect saturation of the material, and to extract certain of the constituents of the material, then withdrawing the liquor from the bottom of the digester while maintaining the top SeaIed admitting fresh hot digestion liquor into the bottom of the digester and then raising the mass to reaction temperatures.

17. In the digestion of fibrous material, charging a digester with fibrous material, then admitting a hot digesting liquor while expelling air from the digester, sealing the digester after the expulsion of the air and admitting additional quantities of the liquor to establish a high hydrostatic pressure on the liquor; maintaining the fibrous material in contact with the liquor until it is saturated thereby; then draining the excess liquor from the digester and admitting fresh hot liquor, and cooldng the fibrous material in such fresh liquor.

18. In the digestion of fibrous material, charging a digester with fibrous material, admitting hot acid liquor to the digester while expelling air therefrom, forcing in a sufficient volume of the liquor to establish a hydrostatic pressure of the order of fifty pounds, maintaining the liquor in contact with the material until the extractives are solubilized and the material is permeated with the liquor; then draining the excess liquor from the digester and admitting fresh hot liquor and digesting the material in such fresh liquor at elevated temperature and pressure.

19. In the digestion of fibrous material, charging a digester with fibrous material, admitting hot acid liquor, to the bottom of the digester while displacing air from the top of the digester; sealing the top of the digesterafter the expulsion of air and forcing in additional quantities of the hot liquor to establish a hydrostaticpressure of the order of fifty pounds on the liquor; maintaining the hot high pressure liquor in contact with the fibrous material until such material is saturated; then draining the liquor from the bottom of the digester while maintaining the top sealed and after such drainage introducing fresh hot acid liquor to the digester and cooking the material under cooking temperature and pressure.

THOMAS LEONIDAS DUNBAR. 3

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