Date of Award

1998

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Wayne E. Marshall

Second Advisor

Ramu M. Rao

Abstract

Representative samples of soft, low density, group 1 (rice straw, rice hulls, sugarcane bagasse) and hard, high density, group 2 agricultural by-products (pecan shells) were converted into granular activated carbons (GACs). Prior to pyrolysis, group 1 by-products were mixed with four binders, sugarcane molasses, sugar beet molasses, corn syrup and coal tar. GACs were produced from group 1 and 2 materials by physical activation (carbon dioxide, steam) or from group 2 materials by chemical activation (phosphoric acid). Carbons were evaluated for their physical (hardness, bulk density), chemical (ash, pH), surface (total surface area, pore size distribution, surface oxides) and adsorption properties (molasses color removal, sugar decolorization). Principal component and cluster analyses were used to compare agricultural by-product-based GACs to two commercial reference carbons. The results show that the type of by-product, binder and activation method determine the properties of activated carbons, with surface properties being the most influential on the decolorizing capacity of GACs. Combination of sugarcane or sugar beet molasses with group 1 materials, for instance, was unsatisfactory because it yielded GACs that were brittle and possessed low surface area, low bulk density, high pH and excessive ash content. The use of coal tar yielded GACs with good physical, chemical and surface properties, but with very limited surface area and, thus poor adsorption efficiency. Regardless of the binder, sugarcane bagasse showed a better potential than rice straw or rice hulls as precursor of GACs with the desirable properties of a sugar decolorizing carbon. Pecan shells produced GACs that were closest to the reference carbons. Steam and phosphoric acid activation showed promise in producing GACs with characteristics similar to the commercial carbons. Steam activation of pecan shells produced the best carbon among the agricultural by-product-based GACs and produced GAC with high surface area, good pore size distribution and weakly charged surface, which are good characteristics for sugar decolorizers. This study demonstrated that agricultural by-products can be used to produce GACs that are as effective as the commercial carbons in removing sugar colorants, offering a potential low cost alternative to the existing coal-based commercial carbons used in the sugar refining industry.

ISBN

9780599213371

Pages

116

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