Production of furfural and carboxylic acids from waste aqueous hemicellulose solutions from the pulp and paper and cellulosic ethanol industries

Abstract

In this paper we present a new process to produce furfural and co-products of formic and acetic acids from waste aqueous hemicellulose solutions using a continuous two zone biphasic reactor. We estimate this approach uses 67% to 80% less energy than the current industrial processes to produce furfural. An economic analysis indicates that furfural can be produced with this process at 366 US$ per metric ton which is 25% of the selling price of furfural in the U.S. market today. This analysis assumes a plant capacity of 78 kiloton per year of furfural, 12 kiloton per year of formic acid and 44 kiloton per year of acetic acid (processing 160 ton per hour of hemicellulose solutions with a xylose concentration of 10.7 wt%) and is based on the data collected in this paper. Formic acid and acetic acid are probably produced from the acid hydrolysis of formylated and acetylated xylose oligomers, respectively. Furfural is produced in a two-step process consisting of the hydrolysis of xylose oligomers followed by the dehydration of xylose monomers and then extraction of the furfural into an organic solvent. Two types of hemicellulose solutions were used as the feedstock including a hot water extract and a green liquor extract derived from Northeastern hardwood trees. The hemicellulose solution contains mainly xylose oligomers as well as glucose, arabinose, lactic acid, acetic acid, formic acid, and other minor products. We found that the reaction temperature, the space velocity, the volumetric organic to aqueous phase ratio, and the acid concentration have significant effects on the furfural production. Under the optimized condition, a furfural yield of 90% can be achieved in the reactor from the hot water extract containing 10.7 wt% xylose. A conceptual design is performed for the integration of the production of furfural, formic and acetic acids, the liquid–liquid split, and subsequent three-stage distillations. We demonstrate that high purity (>99%) of furfural, formic and acetic acids can be obtained, with a final recovery of more than 97%, 56%, and 88% of the furfural, formic acid and acetic acid, respectively.