Modification of wheat straw in a high‐shear mixer

Abstract

Wheat straw (Ws)was treated in a pilot-scale continuous mixer to disrupt the lignin-hemicellulose-cellulose (LHC) complex. An efficient and practical method was desired to remove lignin and hemicellulose (pentosans)rapidly and efficiently from the lignocellulose complex and to make the cellulose accessible to enzymatic hydrolysis. Milled WS in the presence of various chemicals in aqueous solutions was extruded from the mixer under several processing conditions. Chemicals used were sodium hydroxide (NaOH) sodium sulfide (Na(2)S), anthraquinone (AQ), anthrahydroquinone (AHQ), hexamethylenediamine (HMDA), hexamethylenetetramine (HMTA) hydrogen peroxide (H(2)O(2)), and ferrous ammonium sulfate (FAS), which were used alone and in selected combinations. Concomitantly, WS was treated in laboratory batches using similar reaction conditions, except for mixing and shearing. In extrusion treatments of WS at 20% concentration at 97 degrees C for 5.5 min with NaOH (15.7%, dry WS basis), NaOH (15.7%) + AHQ (0.3%), and NaOH (12.7%) + Na(2)S (5.0%), 64-72% of the WS lignin and 36-43% of the pentosans were removed from aqueously washed extrudates (residues). This compares with 46-56% and 23-27%, respectively, for batch treatments. AHQ and Na(2)S enhanced delignification. Cellulase treatment of the residues, which contained about 99%of the WS cellulose, converted 90-92%of the cellulose to glucose compared with 61-69%for the batch pretreatments. Treatments of WS with amines and H(2)O(2) (alone or combined with NaOH)were less effective for LHC disruption. In all instances the relatively high-shear extrusion treatments were superior to the laboratory-batch treatments.