Thermomechanical and Thermo-mechano-chemical Pretreatment of Wheat Straw using a Twin-screw Extruder

Abstract

Different thermo-mechanical extrusion pretreatments were evaluated as alternatives to traditional biomass pretreatments for lignocellulosic ethanol production. Wheat straw, a commonly available agricultural co-product, was chosen as the substrate model for the study. Five thermo-mechanical pretreatments were evaluated: one purely thermo-mechanical (TM) using just water, and the rest thermo-mechano-chemical (TMC), thus using acid, alkaline, oxidant in alkaline medium, and organic solvent. The parietal constituents, hemicelluloses, cellulose, and lignin were quantified to enable the amounts extracted by the pretreatment to be estimated. The digestibility of cellulose was evaluated by quantifying the hydrolysability with an enzyme cocktail. Water thermomechanical treatment gave strong straw defibration; however the digestibility only attained 35%, whereas ground wheat straw was already 22%. This improvement is insufficient to prepare material for direct enzymatic hydrolysis; thus a combination of the thermo-mechanical and chemical treatment is required. All chemical treatments produced greater improvements in cellulose digestibility. For the acidic treatments, hydrolysability was between 42 and 50%, and reached 89% with alkaline pretreatment.

Keywords

• Wheat straw
• Twin-screw extruder
• Pretreatment
• Enzymatic hydrolysis
• Bio-ethanol
• Alkaline
• Acid
• Glycerol
• Hydrogen peroxide