Structural and Thermal Characterization of Wheat Straw Pretreated with Aqueous Ammonia Soaking

Abstract

Production of renewable fuels and chemicals from lignocellulosic feedstocks requires an efficient pretreatment technology to allow ready access of polysaccharides for cellulolytic enzymes during saccharification. The effect of pretreatment on wheat straw through a low-temperature and low-pressure soaking aqueous ammonia (SAA) process was investigated in this study using Fourier transform infrared (FTIR), pyrolysis-gas chromatography/mass spectroscopy (Py-GC/MS), solid and liquid state nuclear magnetic resonance (NMR), and thermogravimetry/differential thermogravimetry (TG/DTG) to demonstrate the changes in lignin, hemicellulose, and cellulose structure. After treatment of 60 mesh wheat straw particles for 60 h with 28-30% ammonium hydroxide (1:10 solid/liquid) at 50 °C, sugar recovery increased from 14% (untreated) to 67% (SAA treated). The FTIR study revealed a substantial decrease in absorbance of lignin peaks. Solid and liquid state NMR showed minimal lignin structural changes with significant compositional changes. Activation energy of control and pretreated wheat straw was calculated according to the Friedman and ASTM methods and found to be decreased for SAA-treated wheat straw, from 259 to 223 kJ/mol. The SAA treatment was shown to remove significant amounts of lignin without strongly affecting lignin functional groups or structure.

Comparison of the Delignifiability and Hydrolysability of Wheat Straw and Corn Stover in Aqueous Ammonia Pretreatment

“…3). These adsorptions may be generated by cleavage of the acetyl group, and the ester linkage between the lignin and hemicelluloses may be broken after the aqueous ammonia pretreatment (Gao et al 2012). According to previous research (Kim et al 2003), the lignin characteristic peaks are at 1218 cm −1 , 1268 cm −1 (C-O of the guaiacyl ring), 1315 cm −1 (C-O of syringyl ring), and 1502 to 1600 cm −1 (aromatic skeletal vibration).…”

“…Aqueous ammonia has been widely used for the pretreatment of lignocelluloses and is recyclable due to its volatility. As previous studies have reported, ammonia pretreatment allows the retention of most of the cellulose and hemicellulose components while removing a portion of lignin and altering its structure (Kim et al 2003;Li et al 2010;Rémond et al 2010;Gao et al 2012). An aqueous ammonia pretreatment can delignify lignocellulose by disrupting the C-O-C bonds in lignin as well as the ester bonds in the LCC (Hsu et al 2010;Alvira et al 2010;Balat 2011;Nguyen et al 2010).…”

“…Generally, lower temperatures and pressures are used in alkali pretreatment compared to acid pretreatment. Sodium hydroxide, ammonia, and lime are suitable alkaline agents for pretreatment, among which ammonia has been studied by many researchers (Gupta and Lee 2010;Nguyen et al 2010;Rollin et al 2010;Li and Kim 2011;McIntosh and Vancov 2011;Gao et al 2012). Aqueous ammonia has been widely used for the pretreatment of lignocelluloses and is recyclable due to its volatility.…”

Biomass Pyrolysis of Helianthus annuus Stems: Qualitative and Quantitative Study Based on Py-GC/MS

“…The DTG curve had two peaks. The first peak was the pyrolysis of hemicellulose and cellulose, and the second peak pyrolysis may be that of lignin (Gao et al 2012). This phase pyrolyzed Helianthus annuus stems into numerous small and large molecules of gas condensable volatiles, resulting in a significant weight loss.…”

Two-Stage Flow-Through Pretreatment of Helianthus tuberosus Residue for Enzymatic Production of Fermentable Sugar by Alkaline and Acidic Solutions

“…Aqueous ammonia pretreatment can remove 60% of lignin from cellulosic biomass while achieving 70% enzymatic digestibility. In addition, ammonia can selectively react with lignin, ester, and especially ether bonds, causing the selective removal of lignin in biomass (Gao et al 2012;Jurado et al 2013;Wanga et al 2016). Ammonia pretreatment material is a suitable substrate for enzymatic hydrolysis and ethanol production.…”