US2192202A

US2192202A - Pulping process

Info

Publication number: US2192202A
Application number: US107144A
Authority: US
Inventors: Floyd C Peterson; Louis E Wise
Original assignee: Individual
Current assignee: Individual
Priority date: 1936-10-23
Filing date: 1936-10-23
Publication date: 1940-03-05
Anticipated expiration: 1957-03-05

Description

Patented Mar. 5, 1940 UNITED STATES PULPING PROCESS Floyd 0. Peterson, Midland, Mich., and Louis E. Wise, Winter Park, Fla.

No Drawing. Application October 23, 1936, Serial No. 107,144

14 Claims.

This invention concerns the pulping of lignocellulosic materials, and particularly relates to a process for the production of alpha-cellulose and other valuable products from ligno-cellulosic materials.

Of the various methods for the digestion of cellulosic materials, the soda, sulphate, and sulphite processes are the best known and most widely used. Of these, the soda and the sulphate processes are alkaline cooks, the soda cook being used primarily in digesting deciduous woods such as aspen, birch, white maple, basswood, etc., While the sulphate process is well adapted for. digestion of highly resinous coniferous woods.

In. the soda process the sodium hydroxide is drastic in its action on the ligno-cellulosic struc-- ture and yields a purified cellulosic fiber which is weak and possesses in general inferior chemical properties. The mixture of sodium hydroxide and sodium sulphide in the sulphate process has a milder action on cellulosic fibers but produces a pulp which contains a considerable amount of lignin and other contaminating products. Both of these processes produce a pulp having a comparatively high bleach consumption and not of a sufliciently high grade for use as chemical cellulose in making derivatives thereof.

The sulphite process is an acid cook and pro duces a higher grade pulp than the above alkaline digestions. The application thereof, however, is limited to the digestion of the less resinous woods, such as spruce, fir, and hemlock, and since it exerts but slight action on the res- 35 inous constituents of wood and allows a high percentage of the same to pass through into the pulp, thereby creating a problem of resin removal in the, later stages of fabrication.

Each of the above processes yields a waste 40 liquor from which residual pulping agent and valuable by-products such as lignin are difiicult of recovery and which are not well adapted to further manufacture. At present such materials are either thrown away or used in the prepara- 5 tion of fertilizers, spreading or dispersing agents,

for the preparation of cellulosic derivatives such as ethers and esters. Other objects will be apparent from the following detailed description of certain preferred embodiments of our invention.

We have now-found that ligno-cellulosic material can be pulped by digesting the same with a pulping fluid comprising a major proportion of an alkylol-amine. The ligno-cellulosic material, in a suitable state of division, is saturated with, and suspended in, the digesting fluid and thereafter cooked for a period of time, and at temperatures and pressures varying with the type of material being pulped, the amount of alkylolamine present in proportion to the cellulosic raw material being treated, and the degree of digestion desired. When the cellulosic material is sufiiciently cooked, the waste liquor is recovered therefrom and the residual pulpy fiber washed, screened, and further purified by bleaching according to any of the known methods. The strength of this pulp, as shown by the beater test (Technical Association Pulp and Paper Industry ofiicial standard method No. T200M), is as high or higher than the strength of pulps otherwise obtained, and other properties such as viscosity are improved, indicating that the mild action of the organic pulping agent causes less degradation and decomposition of the cellulosic portion of the treated raw material than is caused by other pulping agents ordinarily used. The recovered treating liquor may be (1) reutilized in the pulping of additional ligno-cellulosic material without purification, (2) fractionally distilled to remove therefrom unreacted alkylolamines in a substantially pure state and to recover valuable ligneous residues, or (3) treated with an excess of alcohol, cyclic ether, hydroxyether, or dilute acid, thereby precipitating out the ligenous bodies, which may be separated, as by filtration. The lignin bodies obtainable from the above-recovered waste, or black, liquors are valuable raw materials for the preparation of various well known lignin type plastics.

While our process is particularly adapted to utilize the alkylol-amines in substantially pure form, we have found that the crude commercial mixtures of the above, such as are obtained by the reaction of the olefine oxides and ammonia, or by the reaction of the chloroh'ydrins and ammonia, may be advantageously employed as pulping agents. The presence in the treating liquor of water or other inert solvent forthe active pulping agent is not prejudicial to the satisfac-' tory performance of the pulping action. Other pulping agents such as sodium hydroxide, so-

dium sulphide, etc., may be used in combination with the alkylol-amines, but are not necessary for the carrying out of the reaction. We generally employ a treating liquor containing between approximately 70 per cent to 100 per cent by weight of alkylol-amine, in most instances an alkylol-amine concentration of to per cent of the digesting fluid being preferred. The amount of such alkylol-amine composition preferably used by us in a pulping run is inversely proportional to the concentration of the alkylolamine therein. We frequently use 4 to 5 pounds of alkylol-amine per pound of treated material in order to cover or suspend the ligno-cellulosic material therein completely. Only a small proportion of the treating fluid is, however, usedup in such case, and the recovered liquor may be reutilized a number of times, i. e. until no free alkylol-amine remains therein, to give a satisfactory pulping action. No upper limit on the .amount of alkylol-amine which may be present has been determined, since the waste liquors of one run, as pointed out above, may be repeatedly recycled in the process.

In applying our process to the preparation of a high grade cellulose pulp, the wood, preferably in the form of oven-dried chips, is introduced into a suitable pressure cooking vessel and the treating liquor added thereto. The cooking vessel is then sealed and-the contents gradually heated to, and maintained at, the desired digestion temperature, generally between room temperature and 200 C.,

under the vapor pressure of the reactants at such temperature, until the desired degree of digestion is obtained. We generally prefer a digestion temperature of 100 to 180 0., although at temperatures as low as 25 C. appreciable pulping action has been observed. The wood is usually completely pulped in from 4 to 20 hours, although the time of reaction varies with the amount'and concentration of alkylol-amine present in the treating liquor, the type of wood being pulped, and the temperature at which cooking is carried out. When the wood is properly cooked, the charge is blown or otherwise removed from the reactor into a suitable draining or filtering device, 9. 5., a wash pit, wherein the waste liquor is removed from the solid product. The resulting fibrous pulp is washed free of digestive liquors, screened, and may thereafter be bleached if desired. Prior to the bleaching step, the crude pulp maybe washed with a dilute aqueous inorganic acid, e. g. 5 per cent hydrochloric acid, which step insures amore complete and eificient bleaching action than is obtained if the bleaching step be carried, out without such wash. The pulp is then ready for further manufacture into any desired cellulosic product, such as ethyl-cellulose, cellulose acetate, or regenerated cellulose. If the primary waste liquor is to be used for further digestion it should be diluted as little as possible with wash liquors.

The following examples are illustrative of vari- Ous ways in which we have applied the principle of our'invention, but are not to be construed as limiting the same. 1

Example 1 3 pounds of dried poplar chips and 15 pounds of substantially pure monoethanol-amine were charged into a pressure cooker equipped with suitable means for repeatedly circulating the treating liquor through and over the mass of chips. The temperature of the reaction mixture was gradually raised to 180 C. and maintained 5 hours.

thereat under a pressure of 30 pounds gauge for 5- hours, after which the charge was blown into bodies, and had a beater strength of 114 in' terms of points/100 pounds ream.

The recovered treating liquor, comprising the major portion of the, monoethanol-amine in unreacted form, contained approximately 3.0 per cent by weight of the Wood constituents dissolved therein, and was adapted to be used as a pulping agent in later runs.

Example 2 3 pounds of dried spruce chips were digested, as described in Example 1, with 15 pounds of monoethanol-amine. The duration of the cook was 5 hours and the maximum temperature 180 C. 1.89 pounds ofdry unbleached pulp was recovered therefrom, having an alpha-cellulose content of 84.28 and containing only 0.9 per cent of lignin.

Example 3 3 pounds of dried spruce chips, 12 pounds of monoethanol-amine and 3 pounds of water were charged into a pressure cooking vessel and reacted together at a temperature of 175 C. and under a pressure of 95 pounds gauge for approximately The waste treating liquor was separated from the solid products of reaction as described above and the crude pulp washed to remove residual digestive fiuids. The finely divided product was then screened and dried, yielding 2 pounds of unbleached fibrous material having an alpha-cellulose content of 88.69 per cent.

Example 4 3 pounds of dried poplar chips were digested, as described in Example 1, with a treating solution consisting of 14.4 pounds of 1.3-diamino-2-hydroxypropane and 3.6 pounds of water at a temperature of 162 C., a pressure of pounds gauge, and for a period of approximately 5 hours. 2.28 pounds of dry unbleached pulp was recovered therefrom, having an alpha-cellulose content of 89.53 per cent by weight and containing only 0.07

per cent by weight of lignin bodies. Screenings from the above cook amounted to 0.57 per cent based upon the unscreened pulp.

Example 5 2.08 pounds of dried poplar chips, 8.3 pounds of monoethanol-amine, 2.08 pounds of water, 0.105 pounds of sodium hydroxide, and 0.035 pounds of sodium sulphide were charged into a pressure cooking vessel and reacted together at a temperature of 180 C. and under a pressure of pounds The resultant crude reaction Example 6 2 grams of 60-80 mesh poplar sawdust was refluxed for 5 hours at 180 C. with 200 grams of The suspended solids were then separated from the liquor by filtration, washed successively with hot triethanol-amine, hot water, alcohol, and ether, and dried,yield ing 1.511 grams of dry unbleached pulp high in alphacellulose and low in lignin.

Example 7 0.939 pounds of dried poplar chips, 6.58 pounds of a high boiling still residue obtained in the fractional distillation of the crude reaction product of glycerol dichlorohydrin (alpha) and a mmonia, and 1.65 pounds of water were charged into a pressure cooker and reacted together at a temperature of C. and under a pressure of 110 poundsgauge for 5 hours. The resultant crude reaction mixture was worked up substantially as described in Example 1, resulting in the isolation of 0.43 pounds of dry unbleached pulp high in alpha-cellulose and low in lignin content.

If desired, the digestion process may be interrupted prior to the complete delignification of the treated material as described in the foregoing examples. The resulting semi-refined cellulosic bodies have been found to be useful in the preparation of manufactured articles such as ropes, mats, etc., where the presence of a certain amount of lignin in the finished product isnot objectionable.

While the above examples describe only the treatment of poplar and spruce, our process is equally useful in the pulping of other deciduous and coniferous woods such as birch, white maple, basswood, fir, pine, etc. It is also adapted to produce cellulose from such cellulose-containing raw materials as corn stalks, cotton linters,

wheat straw, and other agricultural waste products.

In a similar manner cellulose may be prepared by the digestion of ligno-cellulosic materials with other alkylol-aminecompounds, solutions of the same in inert solvents such as water, and mixtures and/or combinations of the same and I known pulping agents. Among the alkylolamine compounds which may be so employed are diethanol-amine, monopropanol-amine, dipropanol-amine, tripropanol-amine, monobutanolamine, tributanol-amine, ,pentanol-amines, 1.2- diamino 3 hydroxy-propane, 1.2-dihydroxy-3- amino-propane, the crude reaction products of ethylene chlorohydriin and/or glycerol dichlorohydrin and ammonia, mixtures of the above, etc.

The term alkylol-amine as employed herein. and in the appended claims is understood to include not only the simple alkylol-amines, such as ethanol-amine, etc., but also amino-alkylolamines, such as diamino-hydroxypropane, etc.

alkylol-amine mixtures without the separation therefrom of their constituents, (5) it produces a pulp having a high alpha-cellulose content, (6) the pulp so produced has unusually desirable characteristics as a starting material'for the preparation of cellulosic derivatives such as ethers, esters, etc., and ('7) the mild action of i the pulping agent causes less degradation and decomposition of the cellulose in the treated raw material than results in processes ordinarily used,

- and thereforeresults in a high yield of desired product relatively'free from cellulose decomposition products such as sugars, etc., which would tend to reduce its value for chemical use.

Other modes of applying the principle of our invention may be employed instead of those explained, change being made as regards the methods herein disclosed, provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be employed.

We therefore particularly point out and distinctly claim as our invention:

1. In a process for pulping raw ligno-cellulosic materials, the step which consists in digesting the same with. a treating liquor comprising at least '70 per cent by weight of an alkylol-amine as an active pulping agent.

2.In a process for pulping raw ligno-cellulosic materials, the steps which consist in digesting the same with a. treating liquor comprising at least 70 per cent by weight of an alkylol-amine as an activepulpingagent and thereafter recovering the digestive liquors from the solid products of reaction and reutilizing such recovered liquors in the digestion of additional cellulosic raw material. I

3. In a process for pulping raw ligno-cellullosic materials, the steps which consist in digesting the same with a treating liquor comprising at least 70 per cent by weight of an alkylol-amine as an active pulping agent, separating the crude pulp therefrom, screening the same, washing the screened pulp with dilute inorganic acid, and thereafter bleaching the washed pulp.

.4. In a process for pulping raw ligno-cellulosic materials, the step which consists in digesting the same with a treating liquor comprising at least '70. per cent by weight of an ethanol-amine as anactive pulping agent.

'5. In a process for pulping raw ligno-cellulosic materials, the steps which consist in digesting the same with a treating liquor comprising at least 70 per cent by weight of an ethanol-amine as an active pulping agent at temperatures not in excess of C. under the vapor pressure of the reaction at such temperature.

6. In a process for pulping raw ligno-cellulosic materials, the step which consists in digesting the same with a treating liquor comprising at least 70 per cent by weight of monoethanol-famine as an active pulping agent. if

'7. In a process for pulping raw ligno-cellulosic materials, thesteps which consist in digesting the same with a treating liquor comprising at least 70 per cent by weight of monoethanol-amine as an active pulping agent and thereafter recovering the digestive liquors from the solid products of reaction and reutilizing such recovered liq; uors in the digestion of additional cellulosic raw material.

8. In a process for pulping raw ligno-cellulosic materials, the stepswhich consist in digesting the same with a treating liquor comprising at least 70 per cent by weight of monoethanol-amine as an active pulping agent at temperatures not in excess of 180 C. under the vapor pressure of the reaction at such temperature.

9.'In a process for pulping raw ligno-cellulosic materials, the steps which consist in digesting the samewith a treating liquor comprising at least 70 per cent by weight of monoethanol-amine as I an active pulping agent, separating the crude pulp therefrom, screening the same, washing the screened pulp with dilute inorganic acid, and thereafter bleaching the washed pulp.

10. In a process for pulping raw ligno-cellulosic materials, the step which consists in digesting the same with a treating liquor comprising at least "70 per cent by Weight of the product resulting from the reaction of ammonia with a compound selected from the class consisting of the olefine oxides and the halohydrins as an active pulping agent.

11. In a process for pulping raw ligno-cellulosic materials, the steps which consist in digesting the same with a treating liquor comprising at least 70 per cent by weight of 1.3-diamino-2-hydroxypropane as an active pulping agent at temperatures not in excess of 180 C. under the vapor pressure of the reaction at such temperature.

12. In a process for removing lignin bodies from raw ligno-cellulosic materials, the step which consists in digesting the same with a treating liquor comprising at least 70 per cent by weight of monoethanol-amine as an active pulping agent.

13. In a process for removing lignin bodies from raw ligno-cellulosic materials, the step which consists in digesting the same with a treating liquor comprising at least 70 per cent by weight of triethanol-amine as an active pulping agent.

14. In a process for removing lignin bodies from raw ligno-cellulosic materials, the step which consists in digesting the same with a treating liquor comprising at least 70 per cent by weight of 1.3-diamino-Z-hydroxy-propane as an active pulping agent. FLOYD C. PETERSON.

LOUIS E. WISE.