Intensification of Hemp Hurds Hydrolysis by Combined Steam-Explosion toward Vacuum and Alkali or Dilute-Acid Spraying Pretreatment

Hemp hurds is an interesting source for ethanol production; this abundant raw material has high cellulose content. In this study, hemp hurds were pretreated with a thermomechanical process developed in our laboratory to increase the enzymatic hydrolysis extent of potentially fermentable sugars. This process involves subjecting the lignocellulosic biomass for a short time to saturated steam pressure, followed by a flash decompression tovacuum at 50 mbar. Increasing of the heat induced by the saturated steam result in intensive vapour formation in the capillary porous structure of the plant material and the subsequent release of the pressure to vacuum allows fixing the structure.This study aims to investigate the efficiency of acid (H2SO4) or alkali (NaOH) impregnation of hemp hurds prior to thermomechanical pretreatment in which moderate temperatures (133 to 165 °C), corresponding to pressures ranging from 0.3 to 0.7 MPa were used, contributing to reduce sugar loss, energy consumption and formation of inhibitors for both enzymes and fermenting microorganisms. The results showed that the acid and alkali solutions at the concentration used does not affect hydrolysis yield while parameters as processing temperature or processing time had a strong effect.