Forest Products Laboratory (U.S.)

Harris, Elwin E.

Saeman, Jerome F.

Sherrard, Earl Charles

Undetermined

ScholarsArchive@OSU

IHYDIROGLNATION CF LIGNININ A.QUICUS SOLUTI4 NSMarch, 1940SCHOOL OF FORESTRYOiON STATE COLLEGECORVAUJS . OREGO N_UNITED STATES DEPARTMENT OF AGRICULTUREJOREST• SERVIC EFOREST PRODUCTS LABORATOR YMadison, Wises-wai nIn Cooperation with the University of WisconsinHYDROGENATIONOF LIGNIN INAQUEOUSSOLUTIONS-ByELWIN E. HARRIS, Chemis tJERO E SAEMAN, Research Assistan tandE . C . SHERRARD, Principal Chemis tIn previous publications (1, 2) it was shown tha tlignin reacted with hydrogen in dioxane solution in thePresence of copper chromite catalyst . Recently it was foundthat nil catalyst promoted the hydrogenation of lignin i nWatsr or a* an aqueous alkaline solution or suspension, andthus caused approximately 35 moles of hydrogen for eachequivalent weight of lignin (900 grams) to be taken up .The time required for the reaction was short, and it wouldthus be possible to hydrogenate lignin in continuous hydro-genation equipment .The lignin, obtained from various sources, such a smethanol lignin, Cellosolve lignin, lignin from wood aftertreatment 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 start-ing material and the alkalinity of the aqueous suspensio nmedium .When alkali was used, the reaction was more rapi dthan with water alone ; at the same time, the alkali had th eeffect of protecting the catalyst from various impuritie sthat may have been present in the solution and thereby mad eit possible to hydrogenate samples that were readily obtaine das 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,	1! + • yiMas :, S +ptern_l3dr'-I14-1_5 ; 193,,k' n r~~	,,= "~.	,►	ga	ti I ~and = Engih&ring' Chemistry 32(l)4.14,0-	L'•iii i•a	i' -	ti r.N.219The increased reactivity in alkaline solution may b ethe result of a better contact between the hydrogen and thelignin, 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 cleav-age products . Alkali in higher concentrations was used b yFreudenberg and Wacek to promote cleavage in the ligni nmolecule, but the yields were low because decompositio naccompanied the reaction . When hydrogenolysis and alkalin etreatment are used together, almost quantitative recover yof the products is possible . This is similar to the recoveryobtained when lignin reacted with hydrogen in organic sol-vents (1, 2) .The use of water or alkaline solution for the hydro-genation also_has the advantage that it is not necessary t odry , the samples, as was the case when organic solvents wer eused.Prepargtion of MaterialMethanol lignin w4s prepared in the manner descri .b-edin a pi, eviolAs publication (2) except that it era 's used with=out fu.r•""thee purification after the hydrochloric acid wa swashed out, -The material could be used in the vet past eform, since it was necessary only to determine the-dry lignin .content `of the paste .Soda liquor lignin was obtained from the soda pulp-ing liquor from aspen wood by saturating the liquor wit hcarbon dioxide and filtering to remove the excess salts an dcarbohydrate derivatives . Lignin thus obtained was moresatisfactory if .Used in paste form because it tends to forma hard, horny' mass if allowed to dry without the use o forganic solvents ,. The dry lignin content Was determined o nthe 'paste, and the amount used in the experiment was calcu-lated' .Lignin f.ret'a commercial soda-pulping process wa sequally satis=factory without further Purification . Somesamples contained acid, but the addition of alkali made it 'possible to hydrogenate the material without changing th epr.ocedure i	.Purified-'soda-l,i uor lignin (1) ' was satisfactory bu treacted no more readily and 'took up no more hydrogen tha ndid the materials described above ,A1219	-2-rSulfuric-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 jacketedglass-lined mixer with approximately 3 .6 liters of 70 to 7 2percent sulfuric acid for 4 to 5 hours . A temperature of 15°to l8° C . was maintained by passing cold water through th ejacket of the mixer . , It was then diluted with sufficien twater to reduce the acid concentration to 3 percent andboiled for 4 hours to hydrolyze the carbohydrates and anylignin sulfonates that may have been formed . It was the nfiltered on a stoneware filter jar and washed until free o facid . The product was dried on a tray with a small amountof heat . The yield of the product agreed with that obtainedby analytical methods .Cellosolve lignin was prepared by heating extracte dsawdust with approximately 10 parts of Cellosolve containin g3 percent by weight of hydrogen chloride for 24 hours on asteam bath, then filtering to remove the residue, evaporat-ing under diminished pressure to reduce the volume to aboutone-third, and pouring into water to precipitate the lignin .The residue was washed to remove the acid . This material i srather difficult to dry and was used in paste form for hydro-genation . The yield of dried recovered lignin derivativ ewas approximately 20 percent greater than the actual ligni ncontent of the wood . A lignin determination made on th eresidue showed that 95 percent of the lignin had been removed .The water from which the lignin derivative was precipitate dcontained approximately 0 .1 percent of the total lignin .Hydrogenatio nOne hundred and fifty grams of lignin, calculate dfrom the air-dried or wet material, were suspended in 1liter of water, and varying amounts of sodium hydroxid ewere added, depending on the type of final product desired .A 1 percent alkali solution was used most frequently . T othis was added a suspension of Raney nickel calculated t ocontain approximately 5 grams of the catalyst . The mixtur ewas placed in a 2-liter bomb, and hydrogen under 1,500 t o2,500 pounds pressure per square inch (100 to 175 atmospheres )was introduced. The bomb was then shaken and at the sam etime heated to 225° to 250° C . until hydrogenation had ceased .Hydrogenation was half completed in 1 to 1 .5 hours ; 6 to 1 0hours were required for complete hydrogenation .411	R1219When the bomb was opened, a light yellow resinou slayer was floating on the water layer . The water layer wa sdecanted from the bomb and distilled to recover methano lformed in the process . After the temperature of the dis-tillation had reached 100 0 C ., the remaining liquor wa sacidified . This caused the precipitation of a light yellow ,material which was at first flocculent but later coagulatedinto a sof`, resin .The resinous, water-insoluble material was poure dfrom the bomb after heating on the steam bath to melt theresin . That adhering was removed by dissolving in alcohol .The total resinous material (approximately 100 grams) wassubjected to distillation . The distillation products (a t1 mm . pressure) were divided as follows : Fraction I, below55 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 startingmaterial and were identified as being similar to those ob-tained when methanol lignin was hydrogenated in dioxane i nthe presence of copper chrbmite catalysts .Fraction I consisted chiefly of n-propylcyclohexane .Fraction II was identified as n-propylcyclohexanolby comparison with the known material,Fraction III contained a mixture of two or more com-pounds containing the n-propylcyalohexane nucleus tFraction IV, the residue, consisted of several sub -stances having the general formula (C6H10 or 11 0)x •AcknowledgmentThe lignin from the commercial soda-pulping proces swas 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, . ~„81219	., .1{,..,	r_titi -

Hydrogenation of lignin in aqueous solutions

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Hydrogenation of lignin in aqueous solutions

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