Alkaline Deacylation of Corn Stover to Reduce Toxicity of Prehydrolyzates and Improve Enzymatic Hydrolysis
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Hydrolysates from dilute acid pretreatment of biomass contain various biomass degradation products which are inhibitory to enzymes and toxic to microorganisms. One of the main inhibitory compounds is acetic acid which is released from the lignin-hemicellulose matrix in the biomass. Acetic acid at the level of 1 g/L inhibits cellulase activity by 10%. In most pretreatment liquors its concentration is in the range of 3-10 g/L and inhibition of cellulase activity by acetic acid at these concentrations is 20-60%. In this study, sodium carbonate was investigated as a deacylation reagent that can selectively remove part of the acetyl components in corn stover and reduce the acetyl concentration in the pretreatment hydrolysate. Sodium carbonate was chosen since it is a mild alkali that can preserve carbohydrates under the deacylation process conditions. It is inexpensive and can easily be recovered through established Kraft recovery process. Sodium carbonateof 5-10 wt% was used over 30-60ºC for deacylation. A dilute-acid pretreatment was then applied under the conditions of 0.5-1% H2SO4 at 60-110ºC in order to assess the effects of deacylation. The two-step process operated under optimized conditions led to reduction of the final acetyl concentration by 50-80%, and minimal loss of hemicellulose at 2-12%. The combined process further improved the glucan and xylan hydrolysis yields of the pretreated corn stover over those of the dilute-acid pretreatment alone.