Corn cob dry

Changes in chemical composition

During storage, Dunning et al. (1948) quoted that on a 24 months outside storage,

cellulose and hemicellulose were the ones that mostly decreased. In depth of 0.6m, it decreased

from 38.6 to 30% cellulose and Pentosan from 33.9 to 24.7%. However, these components did

not change when cobs were air dried and stored inside. Pentosan content decreased more than

cellulose content during storage, Smith et al., (1985) showing the highest loss of 21% from wet

layer samples of large piles after 18 months storage, while cellulose decrease were 11% lower

than control. Decrease in cellulose and pentosan content resulted in higher proportion of lignin

(mostly) and ashes, hence resulted in an increase of heat of combustion (on a dry base).

These carbohydrates were particularly reduced in the wet layers where weathering and

microbes could have greater chances to grow. Important considerations must be taken in regards

to quantity and quality during outside storage when moisture contents are above 20% (Smith et

al. 1985). The combined effects of mass loss and composition change resulted in losses of 43%

of the available Pentosan (main component of the hemicelluloses fraction) while cellulose had

11% less than the control in the wet layers after 18 months of storage. The interior layer of cobs

was dried below 12% before stored, not being significantly deteriorated. All studies point out the

importance of moisture associated with deterioration, whether is weathering the cause of water

gain or high initial moisture content. If the material is being stored for chemical production or to
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be fermented, where it is specifically interested in these carbohydrates, outside storage for long

periods of time might not be the best solution. On the other hand, if the material is to be burned

or pyrolyzed might not be such a detrimental problem besides the loss of material and energy.

Certainly, gains of moisture will consume greater fraction of the heat released thus having less

energy available as a whole. Nevertheless, the gross heat of combustion increases with

deterioration of cobs, on a dry basis, due to increased proportion of lignin that has less oxygen

content and more energy density for thermochemical processes than the carbohydrates. Outside

storage for farm scale piles (Smith et al., 1985) resulted in losses of up to 33% of the available

energy in high material moisture due to dry matter loss and water gains within the pile. In

contrast, the energy loss was reduced to about 20% for the interior of the pile when it was dried

with ambient air.