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temperature in vacuo over sulfuric acid. This portion had
TABLE I. COMPOSITIOS OF SLUDGE FROM FRESH UNPRESERVED a bad odor when removed, indicating bacterial or enzymic
LATEX
Moisture in wet sludge 83.5 % D r y sludge in undiluted latex 0.11 D r y sludge in latex total solids 0.27 1. Acetone ext. of dry sludge 29.5% 2. Rubber content of dry sludge0 36.0 3. Nz i,n extd. residue. based on original dry sludge 3 . 4 4 4. Ns In ext., based on original dry sludge 0.63 5. Protein equivalent t o No. 3 (% N , X 6 . 2 5 ) 21.5 6. Ash in extd. residue, based on original dry sludge 1.5 7. Ash in ext., based on original dry sludge 2.5
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Total 91.0 a Obtained b y extracting the acetone-extracted sludge with carbon tetrachloride.
which was removable a t this centrifuging speed had been removed. This sludge was immediately suspended in distilled water, the suspension centrifuged, and the process repeated in order to wash out any latex remaining in the sludge. Inasmuch as the diluted latex had a density of about 0.98, it mas possible that a portion of the sludge could have remained in the wash water if it had had a density slightly below 1.00. To prove this, the washings were treated with one per cent of a proprietary emulsifying agent, sold under the name of Emulphor 0, and then made up to contain 20 per cent by volume of ethyl alcohol. The density of such a solution is near that of the latex, and the Emulphor 0 has been found by experiment to prevent coagulation of the small amount of latex rubber in the washings when alcohol is added, but not to prevent sedimentation of such sludge. This mixture 17-as recentrifuged, but only a trace of sludge was obtained; thus the major portion of this fresh latex sludge has a density greater than that of distilled water, since it sediments out almost entirely if a water suspension is centrifuged. A portion of the wet sludge was dried 8 hours in an oven a t 100” C. to constant weight. The dry material was slightly elastic but very “short”, and resembled highly compounded rubber. Each granule was covered by an oily film, and the surface of the dish in which it was dried was oily. The material was found to be sufficiently rubbery so that it would cohere if milled with the rolls set not too close together. Another portion was evaporated nearly to dryness a t room
action. A third portion was treated while wet with three separate quantities of redistilled acetone, filtered, and dried in vacuo over sulfuric acid. The acetone washings were dried on the steam bath, and the acid number of the residue was obtained. From ash, nitrogen, acetone-extract, and carbon tetrachloride-extract analyses of the first and last portions described above, the composition of this sludge appears to be as shown in Table I. The 9 per cent unaccounted for represents error in the analyses, possible error in the use of the factor of 6.28 for calculating the protein content from the nitrogen content, water lost by dehydration of inorganic bodies during ashing, and possibly a small amount of an unidentified substance. Of the acetone extract, 20.6 per cent was present in the acetone washings of the original l\-et sludge. This was quite oily and had an acid value of 71.25, equivalent to a free acid content, calculated as stearic, of 36.13 per cent. The remaining 8.9 per cent was removed slowly by acetone extraction in a Soxhlet type of extractor and had an acid value of 4.8. This latter portion of the extract was a yellow, waxy semisolid resembling the Hevea lipin described by Rhodes and Bishop (4).It should be noted that Hevea lipin prepared in this laboratory was found t o have an acid value of 2.3, whereas Rhodes and Bishop reported a value of 14. The fresh u-et sludge is rapidly dispersible in dilute ammonia or other alkalies to yield a permanent suspension from which only traces of sediment can be removed by even longcontinued and exhaustive centrifugation. The residue after acetone and carbon tetrachloride extraction is only slightly dispersible in dilute ammonia solution, but is sufficiently so to give a strong biuret test for protein.
Literature Cited (1) Bruce, Trop. Agr., 59, 267 (1922). (2) Harpen, van, Arch. Rubbercultuur, 21, 63 (1937). (3) Hauser, “Latex” (tr. by Kelly), p. 101, New York, Chemical Catalog Co., 1930. (4) Rhodes and Bishop, Rubber Research Inst. Malaya Quart. J., 2, 125 (1930).
Hydrogenation of Lignin in Aqueous Solutions ELWIN E. HARRIS, JEROME SAEMAN, AK’D E. C. SHERRARD Forest Products Laboratory, Madison, Wis.
I
N PREVIOUS publications ( I , 2 ) it was shown that
lignin reacted with hydrogen in dioxane solution in the presence of copper chromite catalyst. Recently it was found that nickel catalyst promoted the hydrogenation of lignin in water or in an aqueous alkaline solution or suspension, and thus caused approximately 35 moles of hydrogen for each equivalent weight of lignin (900 grams) to be taken up. The time required for the reaction was short, and it would thus be possible to hydrogenate lignin in continuous hydrogenation equipment.
The lignin, obtained from various sources, such as methanol lignin, Cellosolve lignin, lignin from wood after 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 suspension medium. When alkali was used, the reaction was more rapid than with water alone; a t the same time, the alkali had the effect of protecting the catalyst from various impurities that may
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INDUSTRIAL AND ENGINEERING CHEMISTRY
have been present in the solution and thereby made it possible to hydrogenate samples that were readily obtained as byproducts from pulping processes without purification. The increased reactivity in alkaline solution may be the result of a better contact between the hydrogen and the lignin, since an alkaline solution is a solvent for lignin; or it may be the result of a cleavage of the molecule promoted by alkali followed by the hydrogenation of the cleavage products. Alkali in higher concentrations was used by Freudenberg and Wacek to promote cleavage in the lignin molecule, but the yields were lorn because decomposition accompanied the reaction, When hydrogenolysis and alkaline treatment are used together, almost quantitative recovery of the products is possible. This is similar to the recovery 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 were used.
Lignin reacted with hydrogen in aqueous solution i n the presence of Raney nickel to give colorless cleavage products comprising methanol, propylcyclohexane, hydroxy derivatives of propylcyclohexane, alkali-soluble resins, and an alkali-insoluble resin.
Preparation of Material METHAKOL LIGNINwas prepared in the manner described in a previous publication ( 2 ) except that it was used without further purification after the hydrochloric acid was washed out, The material could be used in the wet paste form, since it was necessary only t o determine the dry lignin content of the paste. SODALIQUORLIGNINwas obtained from the soda pulping liquor from aspen wood by saturating the liquor with carbon dioxide and filtering to remove the excess salts and carbohydrate derivatives. Lignin thus obtained was more satisfactory if used in paste form because it tends to form a hard, horny mass if allowed to dry without the use of organic solvents. The dry lignin content was determined on the paste, and the amount used in the experiment was calculated. Lignin from a commercial soda-pulping process mas equally satisfactory without further purification. Some samples contained acid, but the addition of alkali made it possible to hydrogenate the material without changing the procedure. Purified soda-liquor lignin ( I ) was satisfactory but reacted no more readily and took up no more hydrogen than did the materials described above. SULFURIC-ACID-PROCESS LIGNINwas prepared as follows: Thirty-six hundred grams of air-dried, extracted sawdust, ground t o pass a 40-mesh screen, were mixed in a jacketed glass-lined mixer with approximately 3.6 liters of 70 to 72 per cent sulfuric acid for 4 to 5 hours. A temperature of 15" to 18" C. was maintained by passing cold water through the jacket of the mixer. It was then diluted with sufficient water t o reduce the acid concentration to 3 per cent and boiled for 4 hours t o hydrolyze the carbohydrates and any lignin sulfonates that may have been formed. It was then filtered on a stoneware filter jar and washed until free of acid. The product was dried on a tray with a small amount of heat. The yield of the product agrees with that obtained by analytical methods.
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CELLOSOLVE LIGK~N was prepared by heating extracted sawdust with approximately 10 parts of Cellosolve containing 3 per cent 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 about one third, and pouring into water to precipitate the lignin. The residue was washed to remove the acid. This material is rather difficult t o dry and was used in paste form for hydrogenation. The yield of dried recovered lignin derivative was approximately 20 per cent greater than the actual lignin content of the wood. A lignin determination made on the residue showed that 95 per cent of the lignin had been removed. The water from which the lignin derivative was precipitated contained approximately 0.1 per cent of the total lignin. Hydrogenation One hundred and fifty grams of lignin, calculated from the air-dried or wet material, were suspended in 1 liter of water, and varying amounts of sodium hydroxide nere added, depending on the type of final product desired. A l per cent alkali solution mas used most frequently. To this was added a suspension of Raney nickel calculated to contain approximately 5 grams of the catalyst. The mixture was placed in a 2-liter bomb, and hydrogen under 1500 t o 2500 pounds pressure per square inch (100 to 175 atmospheres) was introduced. The bomb was then shaken and a t the same time heated to 225-250" C. until hydrogenation had ceased. Hydrogenation was half completed in 1 to 1.5 hours; 6 to 10 hours were required for complete hydrogenation. Separation and Identification of Products When the bomb was opened, a light yellow resinous layer was floating on the water layer. The water layer was decanted from the bomb and distilled to recover methanol formed in the process. After the temperature of the distillation had reached 100" c., the remaining liquor was acidified. This caused the precipitation of a light yellow material which was a t first flocculent but later coagulated into a soft resin. The resinous. m-ater-insoluble material was poured from the bomb after heating on the steam bath to melt the resin. That adhering was removed by dissolving in alcohol. The total resinous material (approximately 100 grams) v-as subjected t o distillation. The distillation products (at 1 mm. pressure) were divided as follow: Fraction I, below 55" C.; fraction 11, 55" to 90"; fraction 111, 90" t o 170"; fraction IV, above 170" C. The amounts of each fraction varied with the starting material and were identified as being similar to those obtained when methanol lignin was hydrogenated in dioxane in the presence of copper chromite catalysts. Fraction I consisted chiefly of n-propylcyclohexane, Fraction I1 was identified as n-propylcyclohexanol by comparison with the known material. Fraction 111contained a mixture of two or more compounds containing the n-propylcyclohexane nucleus. Fraction IV, the residue, consisted of several substances having the general formula (CeH10 or llO)z. Acknowledgment The lignin from the commercial soda-pulping process mas 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., J . Am. Chem. Soc., 60, 1467 (1938). PREEENTBD before the Division of Cellulose Chemistry a t t h e 98th Meeting of the American Chemical Society, Boston, hlass.
