2-17: Deacylation as a method to improve enzymatic hydrolysis of dilute-acid pretreated corn stover

Hydrolysates from dilute acid pretreatment of biomass contain various biomass degradation products which are inhibitory to enzymes and toxic to microorganisms. Acetic acid has been identified as one of the strongest inhibitors which at the level of 1 g/L inhibits cellulase activity by 10%.  Dilute-acid (DA) hydrolysates of corn stover contain 3-15 g/L acetic acid that inhibits the cellulase activity by 20-60%. Reduction of acetic acid in the hydrolysate can therefore improve the yields significantly in the hydrolysis of DA treated biomass. In this study, acetic acid was selectively removed from the biomass using Na₂CO₃ under mild reaction conditions prior to DA pretreatment. Sodium carbonate was chosen as the deacylation reagent since it is a mild alkali that can preserve carbohydrates under the deacylation conditions. It is inexpensive and can easily be recovered through established Kraft recovery process. Sodium carbonate of 1-7 wt% was used at room temperature for 3-12 h followed by regular dilute acid pretreatment 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 reduced the acetyl concentration in the DA pretreatment liquor by 75%, while it minimized the loss of hemicellulose to about4%. The two-step process improved the glucan and xylan hydrolysis yields of the pretreated corn stover significantly above those of the one-step conventional DA pretreatment.