Chemical Constituents of Cottonseed Hulls A Partial Separation by Nonchemical Methods MANNING A. SJIITH AND C. B. PURVES JIassachusetts Institute of Technology, Cambridge, &lass. concentrates of either pentosan or “lignin” arc potentially available to industry, although largescale uses for them have yet to be discovered. The possibility that some other species of plant material, particularly other types of hulls, would respond to the new analytical technique was not investigated. The detailed results on cottonseed hulls were in agreement w-ith the hypothesis that the pentosan and the “lignin” were present as separate chemical complexes, both of w-hich included uronic anhydride. Klason “lignin” prepared from the hulls contained no methoxyl groups and differed sharply, in this respect at least, from wood lignins.
Crushed cottonseed hulls, extracted in alcoholbenzene, were ground for a suitable time in a ball mill and the less fibrous portion was separated by sieves and by sedimentation from water into coarse and fine fractions. These were analyzed by standard methods for pentosan, uronic anhydride, and “lignin” (no assumptions were made concerning the chemical nature of the hull constituent responsible for the analytical data). The original hulls contained pentosan, uronic anhydride, and “lignin” to the extent of 27, 6.5, and 25 per cent; the corresponding figures were approximately 3, 9, and 50 per cent for the finest fraction and 40, 6, and 24 per cent, for coarser ones. Thus, unusually rich
A
the small amount of carbon dioxide evolved from hexosesT(19). A sample weight of about 2 grams in 100 cc. of 12 per cent hydrochloric acid was heated in a bath kept at 135” for 5 hours in all cases. Whenever possible, the customary estimation for pentosan ( I ) was corrected for uronic anhydrides by means of a relationship derived from artificial mixtures of xylose and glucuronic acid (euxanthic acid) (6). The validity of this proceeding was doubtful, but no more appropriate correction was found. Cross and Bevan cellulose was prepared generally as described by Doree (6), chlorine being passed for a few minutes through an aqueous suspension of the finely divided hulls to minimize local heating. Three chlorinations, alternated with hot sodium sulfite extractions, left a white powder containing 0.4 to 3.5 per cent of “lignin”. An attempted isolation of holocellulose (14) from finely ground hulls gave a product containing 17 per cent of “lignin” after four chlorinations and extractions with alcohol-pyridine at room temperature. Still less success was obtained with unground samples.
MAJOR difficulty in studying the chemistry of plant
tissue is caused by the sensitiveness of the components t,o chemical change during isolation, usually by extraction of the plant material with acid or alkaline solutions or by hydroxylic organic solvents. Lignin, for example, has never been separated in substantial amount in a native condition and the question as to whether i t exists as a chemical individual in the plant or is combined with other constituents is still undecided. While studying the hull of the cottonseed, routine estimations led to the conclusion t h a t the dust from the hulls differed markedly in composition from coarser fragments. This foreshadowed a new method of separation which could be conducted without the possibility of chemical change, although the efficiency would probably vary with the botanical structure and chemical composition of the various species of plants. The present study describes the nature and extent of such nonchemical separations of cottonseed hull constituents. Published work on these hulls has been restricted to analytical data (IO), attempts to find economic uses for them ( I I ) , and detailed investigations of hemicellulose fractions (3, 4). The hulls, which had not been treated in any way with chemicals, consisted of oily, hard, cup-shaped brown fragments covered with short fiber. They were exhaustively extracted with hot alcohol-benzene and dried in the air. A qualitative test for nitrogen was negative.
TABLEI. hlILLIsc CONDITIONS AND COMPOSITION OF HULL FRACTIONS Fiber Milling Yield Hour8 % 12 0 6
11
6
12
2
31
Yield
>60 60-100
38 16
>60 60-100 60 60-100
43 9 29 49 0
