Co-production of ethanol and cellulose fiber from Southern Pine: A technical and economic assessment

Hemicellulose can be extracted from loblolly pine by dilute acid hydrolysis, and the remaining wood mass can be delignified to produce cellulose fiber. This paper contains an assessment of the technical and economic feasibility of co-producing ethanol and bleached cellulose fiber from loblolly pine, for a mill producing 1268 ton d−1 of unbleached fiber. Ethanol is produced by extracting between 6% and 18% of the dry wood mass prior to pulping. The extracted wood mass, which contains about 70% carbohydrate (primarily sugars from hemicellulose) is conditioned and fermented to ethanol. Our analysis indicates that ethanol can be produced at a cost between $352 and $771 m−3 ($1.33 and $2.92 per US gallon), depending upon process conditions and selectivity of hemicellulose removal. For comparison, the total production cost for ethanol produced by complete hydrolysis of the carbohydrates in loblolly pine is between $388 m−3 when 75% of wood carbohydrates are recovered for ethanol production, and $314 m−3 when 95% are recovered. Neither biofuel subsidies nor credits for co-products such as acetic acid and for sale or sequestration of CO2 were considered in this study.