Effects of chemical preconditioning on organic acid production from woody biomass.

INTRODUCTION

Recovering hemicellulose from woody biomass prior to acid hydrolysis/dehydration (AHDH) processing can improve the yield and economics of levulinic acid (LA) production, but the effects of chemical preconditioning on subsequent LA yields and process economics remain to be characterized for softwood feedstocks.

METHODS

A pilot-scale chemical preconditioning system (CPS), operated with and without dilute sulfuric acid (0.25 wt%) and steam, was used to recover hemicellulose from raw white pine wood chips (39.5% glucan, 16.6% total hemicellulose [3.8% xylan, 10.1% mannan, 1.9% galactan, 0.7% arabinan], and 44.6% acid-insoluble lignin, oven-dry basis) prior to processing in a bench-scale AHDH reactor. Preconditioning was evaluated across a range of temperatures, residence times, biomass species, moisture contents, and particle sizes (1 mm to ∼18 mm) to determine effects on LA yield. A techno-economic analysis was also performed to estimate the minimum selling price of the resulting mixed sugar stream.

RESULTS

CPS effectively removed hemicellulose from wood chips, achieving complete xylan removal at 200 °C. Preconditioning at 170 °C for 30 minutes with 0.25 wt% H2SO4 increased LA yield from 0.21 mol/mol glucan (untreated) to 0.52-0.53 mol/mol glucan, a 2.5-fold improvement. CPS temperature, residence time, and biomass species influenced LA yields, whereas moisture content and particle size did not have a significant effect. The techno-economic analysis estimated a minimum selling price of $0.42/kg for a mixed sugar stream at ∼100 g/L concentration.

DISCUSSION: The LA yields achieved through mild chemical preconditioning (0.52-0.53 mol/mol glucan) were comparable to those obtained using more severe dilute acid (0.64 mol/mol) and SPORL (0.60 mol/mol) pretreatments, suggesting that CPS offers a less severe, potentially lower-cost alternative for enhancing LA production. The estimated minimum selling price of $0.42/kg falls within the $0.30-$0.60/kg range typical of commercial mixed C5/C6 fermentation feedstocks, indicating that CPS-based hemicellulose recovery is economically competitive and could be integrated into softwood-based AHDH processing without the need for more severe pretreatment conditions.