[ C O N T R I B U T I O N FROM T H E
DEPARTMENT O F CHEMISTRY,
THE U N I V E R S I T Y O F T E X A S ]
CATALYTIC HYDROGESATIOS OF COTTOX HULL FIBER HENRY R. HENZE, BRUCE B. ALLEW,
AND
B. WOODROW WYATT2
Received August 26, 1941
In view of the fact that cellulose has been made the subject of a very large amount of research, it may be surprising to some to learn that such investigation has devoted very little attention to study of reduction of cotton, and even less to the effect of molecular hydrogen in the presence of catalysts. Most of the earlier experiments involving the reduction of cellulose have been associated either with attempted production of liquid fuels by hydrogenation or with the destructive distillation of wood or cotton cellulose in the presence of hydrogen in attempts to obtain improved yields of methanol. Although in most cases molecular hydrogen has been the reducing agent, a certain amount of research has been accomplished using other substances. Thus, in connection with the hydrogenation of coal to oils, Fischer and Schrader (l),in 1921, heated cellulose with sodium formate and water a t 400" in an autoclave for three hours and obtained, in 12.9% yield, XA etber extract which was a mobile, brown oil with an ethereal odor. I n 1922, Willstatter and Kalb (2) reduced cellulose with hydriodic acid and red phosphorus a t 250'; the yields of the products formed were : ether-insoluble residue, 9% ; liquid hydrocarbons, 8%; solid hydrocarbons, 1 2 7 . Waterman and Kortlandt (3) attempted to reduce cellulose, in a liquid dispersing medium of melted paraffin wax, with a mixture of steam and carbon monoxide a t a tempeyature of 423" and a maximum prcssure of 115.9 atmospheres. There was substantial carbonization oi the cotton fiber, but no evidence of any hydrogellation. Berl and Biebesheimer (4) treated cotton with 1 N sodium hydroxide soliltion at 310-330" and 180-200 atmospheres and hydrogenated the material thus obtained with ferrum reductuin and iodine a t 420-460O. The reduction product was a liquid resembling petroleum physicallp, and contained aliphatic, olefinic, naphthenic, and aromatic hydrocarbons, the distribution of which in the various fractions was similar to that in natural petroleum. In 1913, Bergius (5) hydrogenated a coal-like residue obtained by the thermal decomposition of cellulose and produced a small amount of liquid resembling crude petroleum. The work of Eergius led Bomen and associates (6) to a study of the action of molecular hydrogen on cellulose. These workers found that cotton yarn did not undergo any appreciable reduction when heated with hydrogen a t 440" and under pressures of the order of 120-130 atmospheres. 1
Cotton Research Fouqdation Post-doctorate Fellow 1938-1939. Cotton Research Foundation Fellow 1938-1940. 48
HYDROGENATION OF COTTON HULL FIBER
49
Under similar conditions of pressure and temperature, after the cellulose had been impregnated with nickel salts, practically the whole of the material was converted to liquid and gas when hydrogenated, “the percentage weight of hydrogen adsorbed by the ash-free cellulose being 4.00 and 2.99” in two experiments. The liquid product consisted of an opaque, viscous tar containing carboxylic acids, phenols, and neutral oil, the material as a whole resembling the crude tar products obtained by the hydrogenation of coal. Vanadium oxide and ferric vanadate were found to have only a slight catalytic effect. After noting that the dry distillation of cellulose was not influenced appreciably by hydrogen in the absence of catalysts even under pressures up to 300 atmospheres, Fierz-Darid ( 7 ) , and Fierz-David and Hannig (8) attempted to prepare a liquid fuel by treating cotton cellulose with nickel hydroxide and distilling at 450-470” under hydrogen pressure of 150-220 atmospheres. The distillate was a yellow liquid, dzo 1.017, containing aldehydes, ketones, phenols, alkplfurans, a cyclic glycol, and fatty acids. Copper was found to have much less effect than nickel, and iron almost no effect. Fierz-David suggested that the practically complete volatilization of the cellulose was not due to hydrogenation but that the hydrogen merely acted as an inert gas improving the mechanism of the precess. Frolich, Spalding, and Bacon (9), in an effort to determine the applicability of Fierz-David’s suggestion, found that 86% of sulfite-pulp cellulose was converted to volatile products and 14% to coke in the presence of nitrogen and nickel at 400-500” and under a pressure of 200 atmospheres. The use of hydrogen in the presence of nickel brought about almost complete conversion of the sulfite-pulp cellulose to liquids and gases. Waterman and Perquin (10) have confirmed previous observations that cellulose is not hydrogenated to oils in the absence of a catalyst. Boomer, Argue, and Edwards (11) subjected absorbent cotton to the action of hydrogen at 350” and 185-275 atmospheres pressure in a tetralin suspension medium without any catalyst, the tetralin apparently acting as a hydrogen carrier in fulfilling the function of a catalyst. A high conversion of the cotton to liquids and gases was reported, acidic material and a light oil having an aldehyde-like odor being present in the liquid portion. il patent (12), issued in 1927, claims the conversion of cellulose in aqueous suspension to dihydroxypropane and glycerol by the action of hydrogen at 250-260” and 70-110 atmospheres in the presence of a nickel catalyst. Dihydroxypropane was the chief product using a copper catalyst and also with a copper-cobalt catalyst, but in the latter instance “isosorbid” appeared in the products. Similar experiments are claimed in which dimethylcellulose and diethylcellulose on hydrogenation gave dimethoxytrihydroxyhexane and diethoxytrihgdroxyhexane, respectively. The expenses of this investigation of the high-temperature-high-pressure catalytic hydrogenation-hydrogenolysis of cotton hull fiber were shared by the Cotton Research Foundation of Memphis, Tennessee, as administered through the Mellon Institute of Industrial Research and by the University of Texas.
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HENZE, ALLEN, AND WYATT
We are particularly indebted to Dr. L. W. Bass and Dean A. P. Brogan for this support. EXPERIMENTAL
Two hydrogenation units were used in this investigation. Both were purchased from the American Instrument Company (Washington, D. C.) and consist of hydrogenation bombs, constructed of chrome vanadium steel, electrically heated, the jacket being controlled by micromax indicating controllers (Leeds and Northrup). One bomb has a capacity of 310 cc., the other 4535 cc. I n use, either bomb was filled half full, and hydrogen was introduced at 23-25' to a pressure of 2500 lbs./sq. in. and heated to 250". Usually, 150 cc. of 4 1 5 % aqueous sodium hydroxide solution was used in the smaller bomb and the pressure developed a t 250" was about 4850 lbs./sq. in., whereas in the larger bomb, 2300 cc. of 7% aqueous sodium hydroxide solution was used and, at 250" the pressure rose to about 5425 lbs./sq. in. I n preparing the Raney (13) nickel catalyst according to the procedure described by Covert and Adkins (14), the nickel was washed by decantation until the wash water was neutral to litmus and then stored under water in glass-stoppered bottles. Orientation experiments were carried out on cotton batting suspended in 4% sodium hydroxide solution to show that very little or no drop in pressure occurred when the fiber was heated for four hours at 225' in the presence of Raney nickel catalyst and hydrogen a t 4175 lbs./sq. in. Upon cooling and opening the bomb, the cotton fiber appeared little changed except for slight embrittlement. However, when cotton batting or cotton hull fiber received preliminary digestion with alkali solutions under 75-85 lbs./sq. in. steam pressure and was transferred to the hydrogenation unit and exposed at 250" to hydrogen at 4800-5400 lbs./sq. in., a definite and extensive pressure drop was observed. I n such experiments, upon cooling and opening the bomb, the cotton fiber had disappeared completely and a colorless, homogeneous solution was obtained. Further exploratory experiments substantiated (15) that the solubility of cellulose in hot alkaline solutions increases with increasing concentration of alkali, and served to indicate the maximum concentration of alkali a t which substantial hydrogenation took place in the presence of Raney nickel. Hydrogenation proceeded to a much greater extent in the presence of 7% alkali than with 10% or 15% alkali. Since the various preliminary experiments indicated also that variations in the treatment of the cellulose previous to hydrogenation occasioned considerable differences in the products formed, such as the amount of acids volatile with water and amount of alcohol-soluble material, definite conditions under which this study was to be made were established. 9typical experiment involved removal from cotton hull fiber of proteins, fats, waxes, and portions of hull by extraction with 0.5% caustic solution followed by a dilute acid wash and drying a t 110". B fairly constant loss of 16% of weight was noted during the preliminary treatment of the fiber. Twenty grams of such material was suspended in a solution of 10 g. of sodium hydroxide in 150 cc. of water. This mixture was digested two hours in an iron autoclave under 80-90 lbs./sq. in. steam pressure. After cooling to room temperature, the material was transferred t o the small hydrogenation unit and hydrogenated in the presence of 8-10 g. of Raney nickel at 250". I n eleven hydrogenations, the pressure-drops varied from 860 lbs./sq. in. to 980 lbs./sq. in., with an average of 920 lbs./sq. in. The resulting colorless solutiou was filtered from the catalyst into an amount of 1:3 sulfuric acid solution equivalent to the sodium hydroxide employed in hydrogenation. Some effervescence was noted; therefore, in another experiment, the amount of carbon dioxide present was determined, and found to represent 0.05 mole per 100 g. of purified hull fiber. The neutral solution was extracted with three 50-cc. portions of ether. The ether extracts from eleven such hydrogenations were combined and dried over anhydrous sodium
51
HYDROGENATION OF COTTON HULL FIBER
sulfate. Removal of the ether under 2Q mm. pressure left a residue of 37.6 g. of liquid material which waa quite acidic. This liquid was fractionally distilled: FBACTION
I
B.P. RANGE
up to 150" (754 mm.) 76-96' (33 mm.) 75-105" (5 mm.) 110-114' (5 mm.) 114-146' ( 3 . 5 mm.)
0.9734 0.9825 1.0746 1.0819
1.4118 1.4358 1.4442 1.4499
18.3 2.0 2.0 2.7 2.6
Neutralization and saponification data were obtained on fraction 4: free acid, 84.2%; ester, 15.8%; neutral equivalent, 137.1. Anal. Calc'd for a mixture of 84.2% of CsHlzOs and 15.8% of CeHloOz: C, 55.88; H, 9.10; MR (mixture of hydroxycaproic acid and lactone in molar ratio of 84.2:15.8), 32.40. Found: C, 55.1; H, 8.99; MI(, 31.97. Fraction 1 was subjected to further fractionation in an unsuccessful attempt to separate the acidic components for characterization by formation of solid derivatives. Qualitative tests, using the method of Dyer (16), suggested the presence of acetic acid and either propionic acid or one of the butyric acids in these sub-fractions. No evidence of the presence of formic acid was obtained. After being extracted with ether, the reaction solution was concentrated under diminished pressure. The combined aqueous distillates from the eleven hydrogenations contained 0.270 equivalent of acids volatile with water and not extracted with ether. Evaporation to obtain the dry salts yielded an amount of material indicating the average equivalent weight of the acids to be 88.3. Each of the eleven residues was boiled with absolute methanol to extract the organic material present. After removal of alcohol from the combined extracts, 83.5 g. of a viscous, brown syrup remained. This material could not be crystallized. It was leached with absolute ether and placed in a vacuum desiccator for seventy-two hours, then warmed a t 100" under a pressure of 0.001 mm. for thirty hours. The residual material was of a lanolinlike consistency. With ferric chloride-amyl alcohol, there was produced a yellow-brown solution identical in color with that produced by known lactic acid. Neutralization and saponification data indicated the presence of 38.43% free acid and 61.577, ester or lactone. Anal. Calc'd for mixture (38.43% of CsHloO4 and 61.57% of CLHBOB) : C, 49.05; H , 7.17. Found: 48.51; H, 6.78. The semi-solid mixture was acetylated, the excess acid chloride was decomposed by reaction with ethanol, the mixture was ether-extracted and distilled under 0.01 mm. pressure. A fraction boiling a t 95-120" was collected; diO 1.1376; n?,' 1.4458; apparent mol. wt. 85.1. Distillation of the saponification solution yielded material in which ethyl alcohol was definitely present. The analytical and other data are indicative of the presence of the ethyl ester of the diacetylated derivative of a dihydroxyvaleric acid; C4H~0z(CH&0)2COOC2H5. Anal. Calc'd for C11HlsOe: C, 53.65; H , 7.37; mol. wt., 246.27; MR, 57.96. Found: C, 54.23; H , 7.30;mol. wt., 255.3 (3 X 85.1); ME,57.72. B typical experiment of hydrogenation and hydrogenolysis using the larger unit: One hundred grams of purified hull fiber was suspended in a solution of 50 g. of sodium hydroxide in 700 cc. of water. The mixture was digested two hours in an autoclave under 8C-90 lbs./sq. in. steam pressure. The materials resulting from three such experiments were combined and placed in the large hydrogenation bomb and hydrogenated in the presence of 100 g. of Raney nickel. Seventy-two minutes after heating was begun, the maximum pressure of 5600 lbs./sq. in. a t 250" was recorded. Reaction began within five to ten minutes after this temperature and pressure were reached and, the temperature remaining constant, the
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HENZE, ALLEN, AND WYATT
pressure decreased rapidly during the first three hours t o 4350 lbs./sq. in.; no further decrease in pressure was noted after continued heating for an additional two hours. The p Z 3 O was 955 lbs./sq. in., and d p was calculated to be 195 lbs./sq. in.; thus the apparent moles of hydrogen used equalled 4.80. Gas samples were collected and the residual gases after hydrogenation were found to contain 42.87, gaseous hydrocarbon (most likely, methane). Since there were 7.73 moles of gas remaining in the bomb after hydrogenation, 3.31 moles of hydrocarbon were formed. The actual number of moles of hydrogen used, therefore, was 8.11. Titration of the filtered, alkaline reaction solution, which was clear and colorless immediately after filtering but bccame yellow upon standing exposed to the air, indicated that 2.39 moles of the alkali present was bound by acidic products of the hydrogenation. An amount of sulfuric acid equivalent to that of the alkali used initially was added, the solution was extracted with four 150-cc. portions of ether, thus extracting all suspended waterinsoluble material and color. Aftzr drying over sodium sulfate, the ether extract was disti1lt.d at 50-70" (20 mm.). The distillate, veighing 43.9 g . , was acidic. Whzn fractiocatcd, it yielded: Fraction 1, (15.9 g . ) b.p. range 40-73" (33-35 mm.); Fraction 2, (20 g . ) b.p. range 59-103" (5-7 rnm.); an appreciable residue could not be distilled under 4-5 mm. pressure. Fraction 2 was redistilled: Portion 1, b.p. 93-94" (5 mm.); n z 1.4440; d i 0 1.0938; neutralization and saponification data indicated 78.8y0 acid and 21.2'3, ester or lactone. Anal. Found: C, 52.57; H, 8.30. Portion 2, b.p. 94-95" (5 mm.); n: 1.4436; d i 0 1.1117; 81% acid; 19% ester or lactone. The aqueous distillate, obtained n hen the ether-extracted hydrogenation solution was evaporated, was found to be acidic and required 262 cc. of 1 N sodium hydroxide solution for neutralization to phenolphthalein. The s i l t which prscipitated (41.3 g.) when the neutrnlized solution was concentrated, gave a positive test for acetate. The mixed inorganic and organic material, which remained upon complete evaporation, was extracted n-ith four 500-cc. portions of hot nbsolute ethanol. When the alcohol v a s removed under rcduccd pressure, there remained a viscous, light brown syrilp; from the hydrogenation of 300 g. of hull fiber 126.6 g. of this syrup was obtained. A portion, 42 g., of this syrupy materinl wzs acetylated, filtered from a small amount of insoluble, gummy solid, diluted with absolute ethanol, saturated with hydrogen chloride, and heated for two hours, dilutcd m-ith absolute ether, and filtered from a small amount of ether-insoluble gum. ilfter removal of ether, 34.6 g. of liquid remained and was fractionated. A fraction, weighing about 11 g., was t a k m boiling between 74-80" (38-39 mm.); ngo 1.4140; dzo 1.0264. The fraction was saponified (mol. wt. 118.3), and distilled. I n the distillate, ethyl alcohol was positively identified. The residue in the flask, upon heating with concentrated sulfuric acid, yielded acetaldehyde. Anal. Calc'd for C5H1003:Mol. wt. 118.13; C, 50.88; H, 8.54. Found: Mol. wt. 118.3; C, 51.49; H, 8.65. The identification of ethyl lactate establishes the production of lactic acid in the products of the hydrogenation-hydrogenolysis of cotton hull fiber. DISCCSSIO?? OF RESULTS
The solubility of cellulose in hot alkaline solutions increases with increasing concentration of alkali (15) and the preliminary experiments of this investigation served to indicate the maximum concentration of alkali at which substantial hydrogenation took place in the presence of Raney nickel. Hydrogenation proceeded to a much greater degree in the presence of 7y0alkali than in either 10% or 1501, alkali. Since these experiments indicated also that variation in the treatment of cellulose previous to hydrogenation occasioned considerable differences in the products formed, such as acids volatile with water and amount of
HYDROGENATION OF COTTON HULL FIBER
53
alcohol-soluble material, definite conditions under which this study was to be made were established. High-pressure-high-temperature hydrogenation, termed destructive hydrogenation or hydrogenolysjs, involves two principal reactions : thermal decomposition and hydrogenation (11). From the fact that essentially no hydrogenation was found to take place until a temperature of 250" was reached, it appears probable that thermal decomposition of the cellulose a t this temperature is followed by stabilization of the unsaturated fragments by hydrogenation. Indications that hydroxy acids were among the products from cotton cellulose necessitated attempts to hydrogenate some of the more common hydroxy acids in alkaline solution. From this study (17) it was found that "at temperatures below 250" and hydrogen pressures not exceeding 330 atmospheres, alpha- and gamma-hydroxy acids are not affected, whereas beta-hydroxy acids are converted into the corresponding unsubstituted acids. . . . Of particular importance was the conversion, in alkaline solution a t 250" and under a hydrogen pressure of 330 atmospheres, of formic acid into methane and carbon dioxide". From a consideration of these results, the dihydroxyvaleric acid and corresponding lactone found in the products from hull fiber may be given the following probable formulations : HO CHzCH2CH2CHOHC0 OH a , 6-Dihydroxyvaleric acid
-0 1 I CH2CHzCH2CHOHCO a-Hydroxy-6-valerolactone
The following reasoning was employed in arriving at the formulations pictured: the pyranose ring was accepted as being present in the structural unit of cellulose, namely, cellobiose. Hydrogenolysis of the CH2OH- grouping, which must necessarily be attached to the pyranose ring, might well result in the production of methace. (The very small amount of carbon dioxide in the residual gases of the hydrogenation obviates the possibility that the methane arose as the result of the hydrogenation of an intermediately-formed formic acid molecule.) The five carbon residue remaining after such cleavage would then possess the carbon chain represented in the formulas presented. Cleavage at the ether linkage between the units would give rise to the -COOgrouping, producing a or the corresponding delta-lactone. The replacement tetrahydroxyvaleric acid of the beta- and gamma-hydroxyl groups by hydrogen is made probable by the faci that the former is in itself unstable under hydrogenation conditions, while the latter would bear a 1 , 3 structural relationship to the alpha-hydroxyl group (the presence of which in the product was demonstrated). Connor and Adkins (18) have shown that hydroxyl groups in 1 . 3 relationship to each other are unstable towards hydrogenation, and one is almost invariably replaced by hydrogen. or else there is hydrogenolysis of carbon-to-carbon bonds. Since the hydrosycaproic acid found in the products of hydrogenation was in equilibrium with a lactone form, the hydroy-i group in this acid must be in either the gamma or delta position. I k j ti.??Pamn::: position, a - pointed out, is
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HENZE, ALLEN, AND WYATT
improbable after hydrogenation, hence the acid is formulated as being the 6-hydroxycaproic. Lactic acid was found to be stable in alkaline solution towards hydrogenation (17); it thus was to be expected as a product from hydrogenation of cotton in alkaline solution, and especially so in view of the fact that Heuser (19) has found that cellulose is converted largely into lactic acid when heated with strong alkali under high pressure and a t high temperature. The claim made in a patent (12), that cellulose in aqueous suspension and in the presence of a nickel catalyst is converted into dihydroxypropane and glycerol by action of hydrogen a t 250-260" and 70-110 atmospheres, caused us to search for such materials in the products of our experiments. No evidence of these materials was to be found. In fact, in other experiments (20), it has been possible to show that when glycerol is heated with Raney nickel in the presence of alkali, hydrogen is evolved in the region 150-BO", and above this temperature continues to be evolved along with carbon dioxide. Hence, our failure to find glycerol among the products of hydrogenation-hydrogenolysis of cotton hull fiber is wholly explainable, in fact, is to be anticipated. SUMMARY
1. Cotton cellulose in an aqueous medium containing 7% of sodium hydroxide has been converted to semi-solid, liquid, and gaseous products by the action of hydrogen at 250" and under pressures of 325-380 atmospheres in the presence of Raney nickel. 2. From three hundred grams of cotton hull fiber, there was formed by the action of 8.11 moles of hydrogen: 3.31 moles of gaseous hydrocarbon (chiefly methane) ;0.15 mole of carbon dioxide; and 2.39 moles of acidic material. 3. The acidic material has been found to contain: lower fatty acids, including acetic and possibly propionic and one of the butyrics or both; lactic acid; gammaor delta-hydroxycaproic acid and the corresponding lactone; and a dihydroxyvaleric acid and the corresponding lactone, with one hydroxyl of the acid in the alpha-position and the other probably in the delta-position. 4. Under the conditions employed in this investigation, cotton cellulose does not undergo hydrogenation at 225". 5. A larger hydrogen pressure drop was observed when 7% aqueous solution of sodium hydroxide was used as the suspension medium than when 10% or 15% solutions of this alkali were used. AUSTIN, TEX.
REFERENCES (1) FISCHER AND SCHRADER, Brennstoff-Chem.,2, 161 (1921).
(2) (3) (4) (5) (6)
WILLSTATTERAND KALB,Ber., 66, 2637 (1922). WATERMAN AND KORTLANDT, Rec. trav. chim., 43, 691 (1924). BERLAND BIEBESHEIMER, Ann., 604, 38 (1933). BERGIUS, J . SOC. Chem. Ind., 32, 462 (1913). BOWEN,SHATWELL, AND NASH, J.SOC.Chem. Ind., 44,507T (1925).
HYDROGENATION OF COTTON HULL FIBER
55
(7) FIERZ-DAVID, Chemistry & Industry, 44,942 (1925); Chem. Abstr., 20, 103 (1926). (8) FIERZ-DAVID AND HANNIG, Helv. Chim. Acta, 8, 900 (1925). (9) FROHLICH, SPALDING, AND BACON, Znd. Eng. Chem., 20, 36 (1928). (10) WATERMAN AND PERQUIN, Rec. trav. chim., 46, 638 (1926). ARGUE,AND EDWARDS, Can. J. Research, 13B, 337 (1935). (11) BOOMER, (12) German Patent 541,362; FrdE., 17, 2572 (1932). (13) Raney, U. S. Patent, 1,628,190. (14) COVERT AND ADKINS,J. Am. Chem. Soe., 64, 4116 (1932). (15) TAUSS, Dinglers Polytech. J., 276,411 (1890); HEUSER,WEST,AND ESSELEN,“Textbook of Cellulose Chemistry,” McGraw-Hill Book Company, New York, 1924, p. 26. (16) DYER,J. BioE. Chem., 28, 445 (1917). (17) ALLEN,WYATT,AND HENZE,J . Am. Chem. SOC.,61, 843 (1939). (18) CONNOR AND ADKINS,J. Am. Chem. SOC., 64, 4678 (1932). (19) HEUSER,Paper Trade J.,89T,271 (1929); GILMAN,“Organic Chemistry,” John Wiley and Sons, Inc., New York, 1938,Vol. 11,p. 1540. (20) Henae and Isbell, Unpublished data.
