With the objective of obtaining the most complete recovery of carbohydrate content from agricultural wastes, a process has been studied which involves three stages: (1) water-soluble sugar extraction; (2) pentose preparation by mild hydrolysis; and (3) hydrolysis under more drastic conditions of residual lignocellulose. In this paper we report on the mild hydrolysis of pentosans from corn cobs in pre-pilot columns. This was done using a process which involved impregnation with sulfuric acid, heating to hydrolyse the wet acidic waste, and watery pentose extraction. The influence of acid concentration and heating time at 100??C on the hydrolysis as well as on sugar degradation and yields has been studied. The optimum conditions of the process were 9% sulfuric acid and 3 hours heating. Under these conditions, 89% of the total pentosans (t.p.) were hydrolyzed (28% of the raw dry material, r.d.m.); 33% t.p. (9% r.d.m.) were degraded, and 67% t.p. (20% r.d.m.) were recovered in the broths. The broths obtained were purified with ion-exchange resins and good yields of xylose were obtained by crystallization. Conditions for the direct reduction of the deionized xylose broths to xylitol, as well as yields and the technical properties of the products, were also studied. ?? 1990.
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