Xylosaccharides purification from eucalyptus residues for the production of lactic acid.

Abstract

In this work, phosphoric acid pretreatment of eucalyptus residues was performed to recover the hemicellulosic fraction (mainly xylose) for further conversion to lactic acid by fermentation with Bacillus coagulans DSM 2314. Optimal pretreatment conditions were determined using a central composite design, aiming to achieve the highest recovery and concentration of xylose in the pretreatment liquor while minimizing the amount of phosphoric acid used. Under the best conditions (160ºC, 0.6% H3PO4, 40 min), the composition of the liquor was (in g/L): 24.8 xylosaccharides (20.3 as xylose), 2.1 glucosaccharides, 7.8 acetic acid, 0.7 furfural, and 2.1 acid soluble lignin (ASL). Pretreatment liquor was purified using adsorptive (Amberlite® XAD-4) or anionics (Dowex®66 and Dowex®-Marathon®11) resins. The resin to liquor ratio was analyzed to maximize xylose concentration in the eluate while retaining lignin, furfural and acetic acid in the resins. Under the best condition (Amberlite® XAD-4 and 3:1 resin:eluate ratio), furfural was completely removed and 90% of ASL was eliminated, with a retention of around 20% of the xylosaccharides. The lactic acid production yield increased from 28% (without purification) to 71% after resin treatment. Subsequently, the pretreated liquor was concentrated in a vacuum oven at 60°C, and the concentrated liquor was also purified with resins at the previous selected conditions. In the eluted from the concentrated liquor, 100% of furfural, 80% of ASL and 45% of acetic acid were removed, with a loss of 25% of the xylosaccharides. The fermentation of this eluate yielded a global lactic acid production of 72%.