US2783146A - Semi-hydrotropic chemical lignocellulose pulping process - Google Patents

Description

United States Patent C SEMI-HYDROTROPIC CHEMICAL LIGNOCELLU- LOSE PULPING PROCESS Application January 7, 1955, Serial No. 480,400

14 Claims. (Cl. 92-9) This invention relates to a process for making cellulosic pulps and the product therefrom. More particularly, it relates to a process for cooking lignin containing cellu losic material, without appreciable loss in weight of the lignin content of the material due to solvent action, to render said material suitable for rapid disintegration into its fibrous components.

Most chemical processes for treating ligno-cellulosic material to obtain the cellulose fibers therefrom, require a cooking with a chemical solution at an elevated temperature to induce a solvent action upon the lignin. The dissolving of the lignin frees the cellulose fibers but since lignin constitutes about 20 to 30 percent of the ligno-. cellulosic material, it is apparent that a considerable portion of the wood is not available in this type of chemical pulp.

It is an objective of this invention to provide a process for pulping lignocellulose material which will yield a high percent of pulp, for example 90 percent of the original material being pulp.

It is another objective of this invention to provide a process requiring little equipment cost and which may be carried out in open tanks. v

It is a further objective of this invention to provide a continuous process for pulping cellulosic rawmaterials, It is another objective to provide a chemical pulp having substantiallyall the original lignin and having a high opacity.

It is another objective .to provide a chemical paper pulp having a high absorbency value and which is resistant to becoming brittle due to light and which does not 'discolo'r appreciably due to ultra-violet light.

It is another objective of this invention to provide a paper pulp making process wherein the cooking solution maybe used a plurality of times and with successively increasing efiectiveness.

It is yet another objective of this invention to provide a chemical paper pulp having substantially natural lignin and in an amount substantially that present in the raw lignocellulose material to obtain said pulp.

These and other objectives of this invention will betion taken in conjunction with a flow sheetdiagram showing the continuous pulping of lignocellulose material by the inventive process.

According to thisinvention, a chemical paper pulp is produced which contains substantially all the lignin origi-- originally present in the lignocellulose material are dissolved by this inventive process. As a result, a high yield of chemical pulp, for example 90 percent of the weight of the original lignocellulose is obtainable by the process of this invention. The commonly used sulfite or sulfate processes gives a pulp yield of only about 50 percent of the original weight of the lignocellulose material.

Substantially any lignocellulose material may be pulped by this process, for example, the various woody plants, such as poplar, maple, etc. the various grasses such as kunai and wheat'straw, also bamboo, kenaf and the like type of lignocellulose may be pulped by this process, as well as the bagasse obtained from the sugar cane industry. The pulp obtained by the process of this invention is a chemical pulp. It contains about /2 the pentosan content of the original lignocellulose just as is the case for chemi cal pulps. Yet it possesses many of the desirable qualities of groundwood, which contains substantially 100 percent of 'the pentosans, without possessing the undesirable groundwood properties such as turning yellow or brow on exposure to ultra-violet light.

The pulp obtained in this invention is a novel product and inventive as such, since it possesses a fibrous texture and strength characteristics similar to that of the commonly available chemical sulfite and sulfate pulps, yet it also possesses the high opacity of groundwood pulps.

Chemical pulps for example, bleached sulfate pulp, ex-

- trary, a sheet or paper made from chemical pulp produced by this process compares very well to the tear test and burst test properties of paper made from sulfite or sulfate pulp.

In short, the high lignin pulp of this invention is a' chemical pulp exhibiting qualities comparable to substantially'ligniu-fr ee sulfite or fulfate chemical pulp. Thus, while the percentage of chemical constituents of this pulp approximates groundwood pulp, the desirable physical properties of this new pulp approximates that of the commonly available unbleached chemical sulfite or sulfate pulps. The chemical pulp of this invention is distinguished in that it contains the naturally occurring lignin in substantially its natural chemical condition and in substantially the percentage amount occurring in the lignocellulose raw material used.

- In U. S. Patent No. 2,308,564 a process employing a concentrated (25 to 40 percent) solution of hydrotropic salts was employed to dissolve out substantially all of the lignin present in the lignocellulose raw material being treated.

come apparent upon reading the following descriptive dis: closure of several illustrative embodiments of this inven- The chemical pulp process of this present invention is different in kind since substantially no lignin is dissolved. In this present process a weak hydrotropic solution is used. Such a weak solution contains only about 1 to about 5 percent of a hydrotropic salt solution, and by the term hydrotropic salts as used herein, the term is intended to include the hydrotropic acids which may be pentosan content originally present, whereas the prior art hydrotropic process is based upon the removal of lignin.

In other words, in the instant hydrotropic process the cellulose fibers are liberated by removing or weakening the cementing or bonding action due to pentosans whereas in-the prior art hydrotropic' process the fibers are Patented Feb. 26, 1957;

shown in the drawing, as for example, two refiners in series'may be used in place of the single refiner 26. Also Where bamboo, kenaf, bagasse and some woods are pulped the product from the refiner 26, being cream colored, it is useable as such without bleaching.

This invention will be better understood by reference to the following illustrative examples, which show the broad latitude of the scope of this invention.

Example I One part by weight of bagasse was heated with twelve parts by weight of a 1 percent aqueous solution of sodium Xylenesulfonate for two hours at 95 C. The pulp was removed from the cooking solution, then washed with water, refined and bleached using three treatments of dilute hypochlorite solution with intermediate washings with water. The resulting product was refined and made into paper. This paper compared with paper made from 100 percent commercially produced spruce groundwood pulp, a high opacity pulp. The paper made from 100 percent spruce groundwood pulp-showed an opacity of only 92 percent whereas the paper made from 100 percent bagasse pulp made by the hydrotropic process of this invention showed an opacity figure 4 percent higher or 96 percent. Standard newsprint of 80 percent groundwood and 20 percent spruce sulphite shows an opacity of about 90 percent and whole bagasse bleached kraft chemical pulp shows an opacity of about 79 percent.

Analysis of the bagasse pulp showed a lignin content of 17 percent and a pentosan content of 21 percent. The original bagasse composition was 19 percent lignin and 27 percent pentosans. Therefore, there was 2 percent removal of lignin and 6 percent removal of pentosans. The used solvent had a pH of about 4 and was the color of very weak tea.

Example II Bamboo chips (Phyllostachy bambusoides) were heated with ten times its weight of a 2 percent aqueous solution of sodium xylenesulfonate which had been previously used for the same purpose and which had a pH of about 4. The heating was in an open kettle for three hours at 95 to 100 C. The residual chips were washed with water and refined but not bleached, since the resulting bamboo pulp was light in color and sufliciently opaque to be used in newsprint in place of groundwood. The residual light colored cooking liquor had a pH of 4 and with a slight strengthening back to 2 percent with additional hydrotropic salt it was ready for reuse. Analysis of the pulp showed that the bamboo pulp had substantially the same lignin content as the bamboo chips but only about of the original pentosan content. The yield of pulp was 87 percent of the bamboo chips taken.

Example III One part by weight of the woody residue left from the stalks of kenaf after removal of the fibrous bark was heated at 95 C. for three hours with ten parts by weight of a 1 percent aqueous sodium xylenesulfonate solution to which suflicient Xylenesulfonic acid had been added to bring the solution to a pH of 3. The resulting pulp, after washing and refining but with no bleaching, was almost white and possessed a high opacity.

Example 1V One part of weight of chips of aspen poplar (Populus tremuloides) were heated for 4 hours at 100 C. with 7 parts by weight of a 2 percent sodium cymenesulfonate solution made acid to a pH of 4 by addition of a small amount of cymenesulfonic acid. After washing and refining, the pulp was a light tan color which could easily be bleached to a light cream color by use of a hypochlorite or a peroxide solution. The resulting pulp was of excellent quality. It was obtained in high yield and it had a lignin content of 22 percent and only 14 percent pentosans.

yellow birch (Betula lutea) were poured into a tank con taining ten parts by weight of a 2 percent solution of sodium xylenesulfonate of pH 6 held at 98 C. A stainless steel weight was then placed upon the chips to keep them submerged in the tank. In twenty minutes the pH of thesolvent had changed to 4.5 and in an hour to 4.0.

Heating was continued for a total period of three hours at 97 to 100 C. The liquid was then removed, the chips'roughly washed with cold water, and then refined by passage at successively closer settings, three times through a small Sutherland disk refiner. The resulting pulp Was screened on a 12 cut screen and the fines rescreened on an 8 cut commercial type screen. Only a small proportion of screenings were obtained. The pulp through the 8 cut screen was bleached at a pH of 9 with about 8 percent of chlorine in the form of hypochlorite solution. The resulting birch pulp on analysis showed a lignin content within 1 percent of the percentage of lignin present in the untreated chips but the percentage of pentosans in the pulp had been reduced by some 8 percent compared to the amount in the original birch chips. The yield pulp was 88 percent and the color of the pulp was a cream white. The pulp possessed high opacity. In general it was not as strong or as permanent a type of pulp as that made by the sulphite process but it was of better color and quality than would have been obtained from yellow birch by the groundwood process.

Having read the disclosure hereinabove it is apparent that a generic invention has been made in that the lignocellulose pulp process of this invention pulps lignocellulose by the selective removal of pentosans without any substantial removal of lignin, whereas the lignocellulose pulping processes prior to this invention eifected the pulping process by substantially the complete removal of lignin.

It is also apparent that those skilled in the art, having now been introduced to this invention, will readily perceive various possible changes, but all these changes being within the skill of the art are deemed to be within the scope of this invention and covered by the claims herein.

It is further apparent that this process produces a novel pulp, in large part suggestive of the chemical pulps as to pentosan content, color and strength characteristics, but also the novel pulp is suggestive of groundwood in that it is highly opaque and has good absorbency.

In the following claims by a dilute solution is meant one having a concentration of about one to about five percent of the hydrotropic salt in water and by cooking is meant a process similar to that of preparing food by boiling food in water in an open vessel or a pressure cooker.

I claim:

1. The process for producing a lignocellulose pulp from pentosan containing lignocellulose material said pulp having substantially the lignin content of the lignocellulose material comprising cooking said starting material with a dilute 1 to 5 percent aqueous solution of a hydrotropic compound selected from the group consisting of benzoic acid, salicylic acid, xylenesulfonic acid, cymenesulfonic acid, phenolsulfonic acid, toluenesulfonic acid and their alkali metal salts until a substantial amount of the pentosans is removed.

2. The process of claim 1 wherein the temperature of cooking is about 100 C. and wherein from A to /h of the pentosans are removed.

3. The process of claim 1 wherein the temperature of cooking is substantially the boiling point of the aqueous hydrotropic solution.

4. The process of claim 1 wherein the cooking is done in an open vessel at atmospheric pressure.

5. The process of claim 1 wherein the cooking is done 7 in a closed vessel at a temperature and pressure above that of normal atmospheric conditions.

6. The process of claim wherein the time of cooking is about one hour.

7. The processof claim 1 wherein the cooking is done under reflux condenser conditions whereby the cooking vapors are condensed.

8. The process for producing a lignocellulose pulp from pentosan containing lignocellulose material said pulp having substantially the lignin content of the lignocellulose material comprising cooking said starting material with a dilute l to 5 percent aqueous solution of a hydrotropic compound selected from the group consisting of benzoic acid, salicylic acid, xylenesulfonic acid, cymenesulfonic acid, phenolsulfonic acid, toluenesulfonic acid and their alkali metal salts at from 95 C. to 100 C. until from /3 to /z of the original pentosan content is removed.

9. The process of claim 8 wherein the time of cooking is a plurality of hours.

10. The process of claim 8 wherein the hydrotropic compound is sodium xylenesulfonate.

11. The process of claim 10 wherein the lignocellulose material is bagasse.

12. The process of claim 10 wherein the lignocellulose material is wood.

13. The process of claim 8 wherein the cooking of the lignocellulose material is done by moving said material continuously through said aqueous cooking solution until /3 to /2 of the pentosan content of the lignocellulose material is removed, and thereafter removing the so 9 cooked'inate'rial continuously from said cooking solution. 14. The process of claim 13 wherein the cooking is done in ariopen vessel and wherein dilute aqueous cooking solution is added continuously to said vessel to make up for solution losses due to removal of cooked material from said vessel.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Hydrotropic Solutions as Solvents of Lignin, by Pelipetz, Columbia Univ., New York, pp. 10, 14, 15, 18, 19, 24, 25, and (1937). Copy in Div. 67.

Aronovsky et al.: Industrial and Engineering Chemistry, November 1936, pp. 1270-1276.

Casey: Pulp. and Paper, published by Interscience Publishers, New York, 1952, volume I, p. 205.

Claims (1)

1. THE PROCESS FOR PRODUCING A LIGNOCELLULOSE PULP FROM PENTOSAN CONTAINING LIGNOCELLULOSE MATERIAL SAID PULP HAVING SUBSTANTIALLY THE LIGNIUM CONTENT OF THE LIGNOCELLULOSE MATERIAL COMPRISING COOKING SAID STARTING MATERIAL WITH A DILUTE 1 TO 5 PERCENT AQUEOUS SOLUTION OF A HYDROTROPIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF BENZOIC ACID, SALICYLIC ACID, XYLENESULFONIC ACID, CYMENESULFONIC ACID, PHENOLSULFONIC ACID, TOLUENESULFONIC ACID AND THEIR ALKALI METAL SALTS UNTIL A SUBSTANTIAL AMOUNT OF THE PENTOSANS IS REMOVED.

Images