Abstract
Biorefineries need cost-efficient pretreatment processes that overcome the recalcitrance of plant biomass, while providing feasible valorization routes for lignin. Here we assessed aqueous ammonia for the separation of lignin from hydrothermally pretreated wheat straw prior to enzymatic saccharification. A combined severity parameter was used to determine the effects of ammonia concentration, treatment time and temperature on compositional and physicochemical changes [utilizing elemental analysis, cationic dye adsorption, FTIR spectroscopy, size-exclusion chromatography (SEC), and 31P nuclear magnetic resonance (NMR) spectroscopy] as well as enzymatic hydrolysability of straw. Pretreatment at the highest severity (20% NH3, 160°C) led to the maximum hydrolysability of 71% in a 24 h reaction time at an enzyme dosage of 15 FPU/g of pretreated straw. In contrast, hydrolysabilities remained low regardless of the severity when a low cellulase dosage was used, indicating competitive adsorption of cellulases on nitrogen-containing lignin. In turn, our results showed efficient adsorption of cationic, anionic and uncharged organic dyes on nitrogen-containing lignin, which opens new opportunities in practical water remediation applications.
Highlights
The hierarchical and recalcitrant structure of renewable plant biomass hampers its enzymatic hydrolysis for the production of biofuels (Himmel et al, 2007; Chundawat et al, 2011a,b)
The pre-treatment process was scaled up to allow for production of N-lignin for dye adsorption tests. It is well-known that efficient saccharification of the pre-treated biomass requires opening up the recalcitrant lignocellulose structure by the removal or modification of lignin
The effects of ammonia concentration, treatment time and temperature on ammonolysis of technical lignins have been studied in a series of detailed investigations (Capanema et al, 2001, 2002, 2006)
Summary
The hierarchical and recalcitrant structure of renewable plant biomass hampers its enzymatic hydrolysis for the production of biofuels (Himmel et al, 2007; Chundawat et al, 2011a,b). Organosolv and alkaline pre-treatments dissolve lignin and allow for its isolation in a Aqueous Ammonia Process Lignin Adsorbent relatively pure form (Hage et al, 2009; Mousavioun and Doherty, 2010). This is important since besides its detrimental effects on enzyme activity, lignin is a potential raw material for aromatic chemicals (Zakzeski et al, 2010) and biobased polymers (Laurichesse and Avérous, 2014), with substantial effect on the profitability of cellulosic ethanol plants (Ragauskas et al, 2014)
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