Corn cobs, acid hydrolyzate

Relatively pure xylan isolated from the holocellulose of aspen (Populus) wood is said to contain 85% of xylose residues.78 One of the characteristic properties of xylan is its ease of hydrolysis. Because it hydrolyzes much more readily than cellulose, mild acid treatment may be employed to bring about preferential hydrolysis of xylan from plant material. Xylose is ordinarily prepared in the laboratory by direct sulfuric acid hydrolysis of the native xylan in ground corn cobs.74 Hydrolysis in hydrochloric acid proceeds rapidly, but decomposition to furfural also occurs to some extent.76 A commercial method for the production of D-xylose from cottonseed hulls76 and straw77 and from corn cobs17 78 has been described. 

Iowa. Modem industrial prepns start with agricultural residues such as oat hulls, corn cobs, rice hulls, bran, etc, which have a relatively high pentosan content (Ref 10). In these processes pentosans are hydrolyzed to pentoses by acid digestion, and these split out water internally to form forfurals ... 

Coarsely ground corn cobs or crude xylan can be used as starting materials. The xylan in either source is hydrolyzed with 7% (v/v) sulfuric acid by refluxing for 2.5 h. The mixture is filtered through cloth on a Buchner funnel with as much liquid as possible obtained by suction. The residue is washed with an equal volume of water by suspension as thin slurry and then filtered. A few drops of 1-octanol are added to the combined filtrates that are neutralized with barium carbonate. The solids (primarily barium sulfate) in the mixture are filtered and the residue washed by suspension in water and filtered. If corn cobs are used as the starting material. 

Cao et al. [60-62] examined a fractionation option that used corn cob and aspen woodchip as the substrates. In this biomass fractionation scheme (Fig. 6), the majority of lignin, alkaline extractives, and acetate were solubilized and separated from cellulose and hemicellulose fractions by alkaline treatment. Hemicellulose was then hydrolyzed to its sugar constituents with dilute acid (0.3 M HCl). Hemicellulose carbohydrates were then fermented to ethanol by a xylose-fermenting yeast strain (Fig. 7). The cellulose fraction, after separation from lignin and hemicellulose, was used as the substrate in the SSF process for ethanol production using a thermotolerant yeast strain as the biocatalyst (Fig. 8). 

Sulfuric acid, and combinations of sulfuric acid and nitric acids, were used in attempts to hydrolyze pine needles, corn cobs, water hyacinth and rice hulls for subsequent in-situ phenolic resin generation. Under the conditions investigated, results were not very encouraging since good, water resistant panels were not obtained (Table 7). 

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