Hydrolysis of anhydrosugars derived from pyrolysis of lignocellulosic biomass for integration in a biorefinery

Abstract

The pyrolysis of iron sulfate pretreated lignocellulosic biomass can produce high yields of anhydrosugars with levoglucosan being the most prominent carbohydrate-derived product. In principle, these anhydrosugars can be acid hydrolyzed to fermentable sugars suitable for the production of ethanol fuel. However, currently reported methods for hydrolyzing pyrolytic anhydrosugars fall short in addressing the challenges of integrating the process into a pyrolysis biorefinery. Furthermore, the hydrolysis of anhydrosugars produced from pyrolysis of biomass pretreated with iron sulfate has not been previously explored. Among the important process variables are acid concentration and hydrolysis temperature. Increasing the concentration of acid, although promoting hydrolysis, upon neutralization produces soluble salts that can inhibit subsequent fermentation of the sugar. Processing at temperatures above the boiling point of water also enhances hydrolysis rates but requires the use of expensive corrosion-proof pressure vessels. In this work, we have developed a milder process suitable for hydrolyzing anhydrosugars at temperatures as low as 95–115 °C using only 50–150 mM sulfuric acid concentrations. We have applied this process to anhydrosugars produced from the autothermal pyrolysis of lignocellulosic biomass. Using only 150 mM sulfuric acid at 115 °C a high concentration of glucose (154 g L⁻¹), suitable for downstream separation and fermentation, was achieved within 3 h of reaction time. Overall, 100 wt% of levoglucosan in bio-oil was converted to glucose.