Cell wall disruption in low temperature NaOH/urea solution and its potential application in lignocellulose pretreatment

Abstract

Pretreatments of wheat straw by NaOH/urea solvent at low temperature were investigated. To understand the cell wall disruption during this low temperature process, and its impacts on enzymatic hydrolysis, morphology, cellulose crystal structure, and chemical properties were investigated by using the following instruments: optical microscopy, confocal laser scanning microscopy, Fourier transform infrared spectra, and X-ray diffraction. The results implied that the deconstruction of plant cell wall at low temperature was attributed to disruption of the hydrogen bonds in cellulose and solubilization of hemicellulose and lignin. Meanwhile, the pretreatment approach resulted in almost full recovery of cellulose, approximately 60 % of lignin and 70 % of xylan removal, respectively. It’s interesting to note that cellulose I crystal structure in the substrate pretreated at a solid loading of 10 % was partially changed to cellulose II structure, while wheat straw pretreated at a higher solid loading of 20 %, retained the cellulose I structure. Almost complete saccharification (>95 %) of cellulose in pretreated substrates was achieved at a relatively low cellulase loading of 10 FPU/g substrates within 48 h. The loss of xylan in pretreated substrate had a negative effect on the total sugar recovery.