Conversion of a hemi-cellulose rich pre-pulping extract into long chain alcohols is of great interest to the developing forest product biorefinery. Pulp production requires, in most part, only the cellulose, leaving much of the hemi-cellulose available for extraction from the wood chips with subsequent conversion into petroleum compatible alcohols using the MixAlco™ process. The hemi-cellulose can be extracted without interference to current pulp yield. The by-products produced from the hemi-cellulose stream could assist in alleviating the problems facing the liquid fuel supply and could boost the revenue of the pulp mill.
The process first subjects the extract to a mixed-culture acidogenic fermentation to convert the hemi-celluloses into carboxylate salts. Three chemical pathways to upgrade the carboxylate salts were investigated. The first path uses thermal deoxygenation to decompose the salts into ketones which are then hydrogenated into alcohols. The second path converts the salts to esters and which are then subjected to hydrogenolysis to generate alcohols. The third path converts the carboxylate salts into carboxylic acids, which are then removed from water via liquid-liquid extraction. The acids and then esterified and hydrogenolyzed into alcohols. The three pathways were modeled using ASPENPlus™ to ascertain the material balance and energy requirements. Sizing and energy demands from ASPENPlus™ were input into CAPCost to determine the bare module and operating expenses. The output from these two programs was compared to determine which pathway would be most economically viable based on: alcohol yield, alcohol energy density, and operating and capital costs.
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