US3007917A

US3007917A - Production of oxycellulose material

Info

Publication number: US3007917A
Application number: US420751A
Authority: US
Inventors: Pauling Harry
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-04-02
Filing date: 1954-04-02
Publication date: 1961-11-07
Anticipated expiration: 1978-11-07

Description

rates tet 3, ll@7,9l7 Patented Nov. 7, 1 961 3,007,917 PRODUCTION OF OXYCELLULOSE MATERIAL Harry Pauling, Reichertshofen, Upper Bavaria, Germany,

assignor, by mesne assignments, to Leon Simon, Washington, DC.

No Drawing. Filed Apr. 2, 1954, Ser. No. 420,751 Claims priority, application Germany Apr. 2, 1953 9 (Ilairns. (Cl. ee-212 The present invention relates to a novel process for the preparation of oxycellulose and to a novel form of oxycellulose so prepared having acidic properties and retaining substantially all of the original strength and other characteristics of the cellulose from which it is formed.

It has been previously known that when cellulose is treated for oxidation with nitrogen dioxide or nitrogen tetroxide a material soluble in dilute alkali and known as oxycellulose may be so prepared. In accordance with United States Patent No. 2,232,990 to Yackel et al. it has been proposed to treat cellulose with gaseous nitrogen dioxide in a reaction vessel at relatively low tempertures so as to prepare an oxidized cellulose which was soluble in 2% sodium hydroxide solution and having a C equivalent of at least 13%. In accordance with the methods hereinbefore known, as for example as set forth in the Yackel et a1. patent and in other publications, it has not been possible to prepare oxycelluloses from paper or similar material without considerable damage to the paper or to the properties of the material during the course of the oxidation process. It was therefore believed that only comparatively small quantities could be processed in a batch process, since when using larger quantities of material as would be required for large scale technical applications, the elimination of the reaction heat and maintenance of other reaction conditions caused difliculty.

It is known that the principal cause of the difi'iculties is occasioned by the formation of nitric acid which is unavoidable under the conditions of the reaction, since the reaction water liberated from the cellulose during the oxidation forms nitric acid in accordance with the following equation:

Obviously, according to the above reaction, the higher the nitrogen dioxide content of the oxidizing gases the stronger the nitric acid that is formed, so that up to 70% of monohydrate may thus be produced. This reaction of the nitrogen dioxide and nitrogen tetroxide with the water content of the material takes place immediately upon initiation of the oxidation treatment so that in the usual treatment with nitrogen dioxide and nitrogen tetroxide, at the usual temperature of about 20 C., an acid with a concentration of about 60 to 70% of nitric acid is formed on and in the oxidized cellulose. It has been previously proposed to avoid this difliculty by drying the material prior to treatingthe same with nitrogen dioxide or nitrogen tetroxide, however, it is impossible to vigorously dry paper in this manner since the vigorous or high-temperature drying causes damage to the paper.

In accordance with the present invention, the surprising discovery has been made that the various difficulties set forth previously can be avoided by treating a cellulose material such as paper in stages wherein the first stage the nitrogen dioxide is substantially diluted with an inert gas such as air or superheated steam at a relatively low temperature. In this Way it is possible to utilize the heat of formation of the nitric acid which is especially strong at the beginning of the oxidation process for evaporating this nitric acid into the gas current and avoid to a considerable extent the impregnation of the material with the formed nitric acid. It has further been discovered that with the use of diluting gas or the like higher temperatures, i.e. of from 45 to 60 C. may be used.

ii In accordance with the present invention it has been found to be especially desirable to treat the cellulose material in the initial stage with an oxidizing gas comprising nitrogen dioxide or nitrogen tetroxide in an amount by volume of from 2 to approximately 6.5% of the diluting gas as for example air, and to thereafter treat the cellulose material for a further period with slightly more concentrated gas as for example a gas containing about 10.5% of nitrogen dioxide and the balance a diluting inert gas, and finally to treat the cellulose material in the last stage with a more concentrated oxidizing gas as for example a gas having a volume of approximately 38.5% of nitrogen dioxide until the desired carboxyl content, for example up to 12%, has been produced.

As a result of the stagewise oxidation of the cellulose material it is possible to produce in the beginning of the process a relatively dilute nitric acid, i.e. nitric acids, of a maximum concentration of from 25 to 30%, and to evaporate the nitric acid as it is formed by the heat of reaction. Although it is important to prevent accumulation of nitric acid, especially if it is highly concentrated on the cellulose material, nitric acid of such low concentration may be considered harmless inasmuch as the physical properties of the cellulose material are not impaired thereby.

lt has been further discovered in accordance with the present invention that under the conditions of'relatively low nitrogen dioxide concentration, paper material and cotton may be treated at temperatures of from 45 to 60 C. without any damage to the physical properties thereof. it has been possible to treat in accordance with the process of the present invention cellulose material of comparatively thick cross section since it is possible to oxidize the entire mass with great uniformity and prevent cornification or other damage to the cellulose material. It is within the broad purview of the present invention to either utilize an inert gas or in the al ernative to utilize a gas under reduced pressure, i.e. the pressure involved during the process being such that it is equivalent to the partial pressure of the nitrogen dioxide when using a diluting gas. It is also within the scope of the present invention to utilize a combination of reduced pressure and diluting gas so long as the partial pressure of the nitrogen dioxide is equivalent to that produced in accordance with a process involving, as previously set forth, an initial limited volume of nitrogen dioxide to diluting gas followed by, as previously set forth, successively increasing stages of greater nitrogen dioxide concentration. In either type of procedure the fact remains that the nitric acid is removed almost quantitatively from the oxidized material especially in the initial stages of the reaction.

As previously pointed out the inert gas may be super heated steam, however, the super heated steam should be of such temperature and pressure that the fibers of the material being oxidized will not suffer damage. Preferably, a moderately super heated steam at a temperature of 50 to C. and at a reduced pressure corresponding to this temperatures is utilized. The advantage of utiiizing super heated steam of this type is that the residual nitric acid retained by the oxidized cellulose establishes an equilibrium with the super heated steam according to the composition of the steam and nitrogen dioxide and nitric acid evaporates from the liquid adhering to the oxycellulose into the super heated steam without changing the moisture content of the material undergoing oxidation. It is within the scope of the present invention to recirculate the super heated steam after rectifying the same to remove the weak nitric acid and thereafter super heating the steam again to the required degree of dryness. If a portion of the steam is condensed during this rectification it is then replaced by fresh steam and the nitric acid recovered during the rectification can be reused in the process. Although nitric acid from any suitable source may be utilized for the process of the present invention, it is especially desirable to reuse the nitric acid and nitrogen dioxide by submitting them in a convenient manner to thermic cleavage into nitroge oxide, oxygen and steam. The product of the present process is especially suitable for commercial purposes in the form of paper, fibers, flakes or wool and it is especially suitable for removing alkaline values from gas vapors and liquids. It is, for instance, suitable for absorbing quantitatively the ammonia from a gas mixture containing ammonia and hydrogen sulfide without removing any of the hydrogen sulfide. The material may also be utilized for purification or alkali removal from various types of gases such as coke gases or synthetically produced gases. Since the material produced in accordance with the present process is especially strong and retains all of the original strength of the cellulose material from which it is formed, it is possible to wash a gas with acid in order to free it of alkaline ingredients and to remove the alkali from this wash water by the use of the oxidized material of the present invention. The material can also be utilized as filter bodies or filter paper, and in connection with its use as a filter it is especially desirable for the use as filters in cigarettes or other tobacco products. Due to the extremely low de gree of cornification and saccharification of the cellulose material prepared in accordance with the present invention, it makes an especially desirable filter for the removal of nicotine and tar. The material forms for example with the nicotine of the tobacco smoke a water insoluble salt so that the nicotine can be removed from the tobacco smoke without doing harm to the tobacco flavor. Experiments have indicated that nicotine removal of more than 70% and considerable tar removal can be carried out with the material of the present invention without using any greater amount of filtering surface than those customarily used for cigarette filters. The oxycellulose produced in accordance with the present invention has been found soluble in dilute alkali, as for example 2% sodium hydroxide, at a rather low carboxyl value for example carboxyl values of 6.5%. It can therefore be utilized with great facility for the preparation of alkaline solutions of cellulose, as for example for the preparation of transparent cellulose films, or for the preparation of artificial filaments by the viscose or other processes. The material, in view of its high strength, is also of special value for pharmaceutical and medicinal purposes since this material can be used as a substitute for cat gut or for wound tampons since its high alkaline solubility renders it capable of being readily dissolved in the alkaline body fluids.

The following specific examples serve to illustrate but are not intended to limit the present invention.

Example I One layer of creped cellulose paper and one layer of plain cellulose Wool in commercial sizes were superposed and wound up to form a roll. This material was treated during 40 minutes at a temperature of about 45 C. with nitrogen dioxide-air mixture at a concentration of 6.5% per volume N in a conveniently shaped reaction vessel. Thereafter the nitrogen dioxide concentration was increased to 10.5% per volume and treatment was continued for 20 minutes. Thereafter, the nitrogen dioxide concentration was increased to 38.5% per volume and the oxidation was carried out in the course of four hours. At this time the desired carboxyl content of had been reached.

The material was dried with air and subsequently washed with distilled water for quantitative removal of nitric acid. This material could be processed without difficulty into cigarette filters using standard machinery.

4 Example 11 The same material as in Example I was submitted to the same pre-treatment, but was treated with a nitrogen dioxide-air mixture at a concentration of 38.5 per volume of N0 for three hours only. The material had a carboxyl content of 6.5% and was soluble in 2% sodium hydroxide.

Example III Pre-purified coke gas which still contained small quantities of hydrogen sulfide and ammonia was passed through a glass tube filled with the oxidized cotton wool of the present invention. Outcoming gas was completely free of ammonia.

Example IV The gas water which is obtained in the technical wash of coke gas and which apart from ammonia contained also hydrogen sulfide and carbon dioxide was passed through a filter cylinder consisting of oxidized cellulose paper and oxidized cellulose wool prepared according to Example I. The filtrate was free of ammonia.

Example V (a) Oxidized cotton prepared according to Example I was processed into cigarette filters of usual size and the nicotine absorption from the tobacco smoke was analyzed. The degree of absorption was 70.6%.

(b) Oxidized cotton wool and oxidized paper of Example I were processed into cigarette filters of usual size and the nicotine absorption of the tobacco smoke was analyzed. The degree of absorption was 71.5

Example V1 04527 grams of oxidized cotton wool prepared according to Example I were pressed into a small glass tube and 54 cc. of an aqueous nicotine solution containing 25.4 mg. of nicotine was allowed to pass through the tube in the course of 9% minutes without using vacuum. The cotton wool removed the nicotine quantitatively. The filtrate was free of nicotine.

Iclaim:

1. A process for the preparation of oxycellulose which comprises treating cellulose with a mixture of nitrogen dioxide and diluting gas selected from the group consisting of superheated steam and air in a plurality of stages of increasing nitrogen dioxide concentration, the concentration of the nitrogen dioxide during the first stage of treatment being between approximately 2% by volume and 6.5 by volume.

2. A process for the preparation of oxycellulose which comprises treating cellulose with a mixture of nitrogen dioxide and diluting gas selected from the group consisting of superheated steam and air in a plurality of stages of increasing nitrogen dioxide concentration and at a temperature below about 60 C., the concentration of the nitrogen dioxide during the first stage of treatment being between approximately 2% by volume and 6.5 by volume.

3. The process of claim 1 wherein, at least in part, in place of the diluting gas reduced pressures are utilized.

4. The process of claim 2 wherein, at least in part in place of the diluting gas reduced pressures are utilized.

5. A process for the preparation of oxycellulose which comprises treating cellulose with a mixture of nitrog n dioxide and diluting gas selected from the group consisting of superheated steam and air in a plurality of stages of increasing nitrogen dioxide concentration, the concentration of the nitrogen dioxide during the first stage of treatment being between approximately 2% by volume and 6.5% by volume, and thereafter removing nitric acid from the material by treating the same with diluting gas.

6. The process of claim 5 wherein the diluting gas used for removing the nitric acid is superheated steam at a reduced pressure.

6 7. The process of claim 1 wherein the cellulose maof treatment is between about 45 C. and 60 C. and terial is paper. the cellulose material is paper.

8. The process of claim 1 wherein the temperature of References Cited in the fil of this patent treatment is between about 45 C. and 60 C.

UNITED STATES PATENTS 9. The process of claim 1 wherein the temperature 5 2,232,990 Yackel et a1. Feb. 25, 1941

Claims

1. A PROCESS FOR THE PREPARATION OF OXYCELLULOSE WHICH COMPRISES TREATING CELLULOSE WITH A MIXTURE OF NITROGEN DIOXIDE AND DILUTING GAS SELECTED FROM THE GROUP CONSISTING OF SUPERHEATED STEAM AND AIR IN A PLURALITY OF STAGES OF INCREASING NITROGEN DIOXIDE CONCENTRATION, THE CONCENTRATION OF THE NITROGEN DIOXIDE DURING THE FIRST STAGE OF TREATMENT BEING BETWEEN APPROXIMATELY 2% BY VOLUME AND 6.5% BY VOLUME.