IHYDIROGLNATION CF LIGNI N IN A.QUICUS SOLUTI4 N S

Transcription

1 IHYDIROGLNATION CF LIGNI N IN A.QUICUS SOLUTI4 N S March, 1940 SCHOOL OF FORESTRY OiON STATE COLLEGE CORVAUJS. OREGO N _UNITED STATES DEPARTMENT OF AGRICULTURE JOREST SERVIC E FOREST PRODUCTS LABORATOR Y Madison, Wises-wai n In Cooperation with the University of Wisconsin

2 HYDROGENATIONOF LIGNIN INAQUEOUSSOLUTIONS- By ELWIN E. HARRIS, Chemis t JERO E SAEMAN, Research Assistan t and E. C. SHERRARD, Principal Chemis t In previous publications (1, 2) it was shown tha t lignin reacted with hydrogen in dioxane solution in th e Presence of copper chromite catalyst. Recently it was foun d that nil catalyst promoted the hydrogenation of lignin i n Watsr or a* an aqueous alkaline solution or suspension, an d thus caused approximately 35 moles of hydrogen for eac h equivalent weight of lignin (900 grams) to be taken up. The time required for the reaction was short, and it woul d thus be possible to hydrogenate lignin in continuous hydrogenation equipment. The lignin, obtained from various sources, such a s methanol lignin, Cellosolve lignin, lignin from wood afte r treatment with sulfuric acid, and lignin from pulping liquor, was converted into a mixture of practically colorless products. These products were varied somewhat, depending on the starting material and the alkalinity of the aqueous suspensio n medium. When alkali was used, the reaction was more rapi d than with water alone ; at the same time, the alkali had th e effect of protecting the catalyst from various impuritie s that may have been present in the solution and thereby mad e it possible to hydrogenate samples that were readily obtaine d as by-products from pulping processes without purification. -Presented before the Division of Cellulose Chemiltxv at t] 98th Meeting of the American Chemical So,iety on, Mas :, S + ptern_l3dr'-i14-1_5 ; 193,,k' n r~~,,= "~., ga and = Engih&ring ' Chemistry 32(l)4.14,0- L' iii i a i' - * 1! + yi ti I ~ ti r. N.219

3 The increased reactivity in alkaline solution may b e the result of a better contact between the hydrogen and th e lignin, since an alkaline solution is a solvent for lignin ; or it maybe the result of a cleavage of the molecule pro - moted 1y alkali followed by the hydrogenation of the cleavage products. Alkali in higher concentrations was used b y Freudenberg and Wacek to promote cleavage in the ligni n molecule, but the yields were low because decompositio n accompanied the reaction. When hydrogenolysis and alkalin e treatment are used together, almost quantitative recover y of the products is possible. This is similar to the recover y obtained when lignin reacted with hydrogen in organic solvents (1, 2). The use of water or alkaline solution for the hydrogenation also_has the advantage that it is not necessary t o dry, the samples, as was the case when organic solvents wer e used. Prepargtion of Materia l Methanol lignin w4s prepared in the manner descri.b-ed in a pi, eviolas publication (2) except that it er a 's used with = out fu.r ""thee purification after the hydrochloric acid wa s washed out, -The material could be used in the vet past e form, since it was necessary only to determine the-dry lignin. content `of the paste. r Soda liquor lignin was obtained from the soda pulping liquor from aspen wood by saturating the liquor wit h carbon dioxide and filtering to remove the excess salts an d carbohydrate derivatives. Lignin thus obtained was mor e satisfactory if.used in paste form because it tends to for m a hard, horny' mass if allowed to dry without the use o f organic solvents,. The dry lignin content Was determined o n the 'paste, and the amount used in the experiment was calculated'. Lignin f.ret'a commercial soda-pulping process wa s equally satis=factory without further Purification. Som e samples contained acid, but the addition of alkali made it possible to hydrogenate the material without changing th e pr.ocedure i. ' Purified-'soda-l,i uor lignin (1) ' was satisfactory bu t reacted no more readily and 'took up no more hydrogen tha n did the materials described above, A

4 Sulfuric-acid-processlignin was prepared as follows : Thirty-six hundred grams of air-dried, extracted sawdust, ground to pass a 14-0-mesh screen, were mixed in a jackete d glass-lined mixer with approximately 3.6 liters of 70 to 7 2 percent sulfuric acid for 4 to 5 hours. A temperature of 15 to l8 C. was maintained by passing cold water through th e jacket of the mixer., It was then diluted with sufficien t water to reduce the acid concentration to 3 percent an d boiled for 4 hours to hydrolyze the carbohydrates and any lignin sulfonates that may have been formed. It was the n filtered on a stoneware filter jar and washed until free o f acid. The product was dried on a tray with a small amoun t of heat. The yield of the product agreed with that obtaine d by analytical methods. Cellosolve lignin was prepared by heating extracte d sawdust with approximately 10 parts of Cellosolve containin g 3 percent by weight of hydrogen chloride for 24 hours on a steam bath, then filtering to remove the residue, evaporating under diminished pressure to reduce the volume to abou t one-third, and pouring into water to precipitate the lignin. The residue was washed to remove the acid. This material i s rather difficult to dry and was used in paste form for hydrogenation. The yield of dried recovered lignin derivativ e was approximately 20 percent greater than the actual ligni n content of the wood. A lignin determination made on th e residue showed that 95 percent of the lignin had been removed. The water from which the lignin derivative was precipitate d contained approximately 0.1 percent of the total lignin. Hydrogenatio n One hundred and fifty grams of lignin, calculate d from the air-dried or wet material, were suspended in 1 liter of water, and varying amounts of sodium hydroxid e were added, depending on the type of final product desired. A 1 percent alkali solution was used most frequently. T o this was added a suspension of Raney nickel calculated t o contain approximately 5 grams of the catalyst. The mixtur e was placed in a 2-liter bomb, and hydrogen under 1,500 t o 2,500 pounds pressure per square inch (100 to 175 atmospheres ) was introduced. The bomb was then shaken and at the sam e time heated to 225 to 250 C. until hydrogenation had ceased. Hydrogenation was half completed in 1 to 1.5 hours ; 6 to 1 0 hours were required for complete hydrogenation. 411 R1219

5 When the bomb was opened, a light yellow resinou s layer was floating on the water layer. The water layer wa s decanted from the bomb and distilled to recover methano l formed in the process. After the temperature of the distillation had reached C., the remaining liquor wa s acidified. This caused the precipitation of a light yellow, material which was at first flocculent but later coagulate d into a sof`, resin. The resinous, water-insoluble material was poure d from the bomb after heating on the steam bath to melt th e resin. That adhering was removed by dissolving in alcohol. The total resinous material (approximately 100 grams) wa s subjected to distillation. The distillation products (a t 1 mm. pressure) were divided as follows : Fraction I, belo w 55 0 C ; fraction II, 55 to 90 ; fraction III, 90 to 170 ; fraction IV, above 170 C. The amounts of each fraction varied with the startin g material and were identified as being similar to those obtained when methanol lignin was hydrogenated in dioxane i n the presence of copper chrbmite catalysts. Fraction I consisted chiefly of n-propylcyclohexane. Fraction II was identified as n-propylcyclohexano l by comparison with the known material, Fraction III contained a mixture of two or more compounds containing the n-propylcyalohexane nucleus t Fraction IV, the residue, consisted of several sub - stances having the general formula (C6H10 or 11 0) x Acknowledgmen t The lignin from the commercial soda-pulping proces s was supplied by the courtesy of the Mead Corporation. Literature Cited (1) Harris, E. E., and Adkins, H., Paper Trade J. 107 :58 (1938). (2) Harris, E. E. D'Ianni, J. and Adkins, H., Jour. Amer. Chem. Soo, 60 :1467 (1938). J,. ~ ,.1{,.., r _titi -