Preparation of levoglucosan by pyrolysis of cellulose and its citric acid fermentation

Levoglucosan (LG), 1,6-anhydro-β- -glucopyranose, was produced by pyrolysis of cellulose. A response surface method was used to optimize the reaction parameters: X1, temperature; X2, time required for heating cellulose from room temperature to the designed pyrolysis temperature; and X3, vacuum, and a Box–Behnken design was employed for this purpose. The optimal temperature and time were found to be 388°C and 26.2 min by fixing the vacuum at 1 mm Hg. The levoglucosan prepared was fermented to citric acid by Aspergillus niger CBX-209, which was a mutant derived by γ-ray mutagenesis of the parent strain CBX-2. The mutant could produce increasing citric acid with increasing LG purity and had a citric acid yield of 87.5% when using purified levoglucosan as the sole carbon source in a 5 day fermentation period.