Bioconversion Of Energy Grass Into Butanol

Energy grasses are a kind of plants that have strong resistance to drought and salinity,which could be grown at marginal land.As a result,energy crops present a cheap,rich and renewable carbon source for butanol fermentation.Bioconversion of lignocellulosic materials generally involves four major unit processes: pretreatment,enzymatic hydrolysis,fermentation and product recovery.At present,the optimal pretreatment of energy crops has not been obtained,which leads to the low efficiency of enzymatic hydrolysis and the failure to meet the demand of fermentation microorganisms,which is the main factor limiting the production of butanol.Secondly,the fermentation product of butanol has feedback inhibitory effect on enzymatic hydrolysis,which further reduces the production efficiency of butanol.In this paper,the effect of sodium chlorite with(SCA)and without acetic acid(SC)pretreatment on chemical composition,enzymatic hydrolysis and butanol fermentation of silvergrass were compared.The results indicated that the SC pretreatment retained more hemicelluloses,and obtained higher glucose yield(70.5%)than that of SCA pretreatment(58.7).By synergistic action of cellulase and xylanase,the glucose yield of SC pretreated(12 h)samples reached to 93.5% with 808.7 mg/g DM total reducing sugars yields.But the ABE(acetone-butanol-ethanol)output is 0.03 g/g glucose from enzymatic hydrolysate of SC pretreated materials,via Clostridium acetobutylicum ATCC824 fermentation,lower than that of control(0.21 g/g),may be related to the pretreatment method of sodium chlorite or silvergrass itself fermentation performance.In order to further study the effect of pretreatment and type raw materials on the fermentation performance of butanol,three energy crops(Hybrid Pennisetum,Spartina alterniflora and silvergrass)were pretreated via different methods and the enzymatic hydrolysis of those pretreated materials was investigated.The results showed that hydrolysis efficiency of different type energy grass pretreated by dilute sulphuric acid have no difference.After pretreatment of sodium hydroxide,the hydrolysis efficiency of the high concentration of three energy crops was low(the glucose concentration of silvergrass,Hybrid Pennisetum and Spartina alterniflora were 17.4,1.8 and 3.8 g/L,respectively).The enzymatic efficiency of alkaline sulfite pretreated spartina alterniflora and silvergrass or sodium chlorite pretreated silvergrass in high concentration of substrates(8%)are high(32 and 39 g/L),their hydrolysates could be used for further butanol fermentation.The performances of butanol fermentation of the hydrolysates from above were investigated.The results indicated that the hydrolysate was used to ferment could shorten the final solvent yield was reduced compared with the control of pure glucose.In addition,the enzyme hydrolysis efficiency of the spartina alterniflora(20.5 g/L)was lower than that of the silvergrass(38.3 g/L),but the ability of solvent fermentation(0.12 g/g glucose)was higher than that of silvergrass(0.06g/g glucose).This may be related to the promotion and inhibition mechanism of fermentation by other components in enzyme hydrolysates,which needs further investigation.This paper also explored the effect of butanol fermentation products on enzyme hydrolysis and the activity of cellulase components in hydrolysis solution,mainly including CBH?,EG ?and ?-G.The results showed that acetone,ethanol and butanol existed singly or in the mixtures,which promoted enzymatic hydrolysis at lower concentrations.When 5g/L of butanol was added,the hydrolysis yield of Avicel and Hybrid Pennisetum increased from 30% and 61.9% to 62.8% and 75.0%;When 20 g/L of acetone and ethanol was added,the hydrolysis yield of Avicel increased to 57.8% and 58.3%;the hydrolysis yield of alkaline pretreated Hybrid Pennisetum increased to 79.2% and 85.6%.The mixture of acetone,butanol,ethanol,acetic acid and butyric acid can also promote the hydrolysis of cellulase,which is mainly dominated by butanol and has no cumulative effect.And butanol has a promoting effect on CBH?,EG ?enzyme activity in hydrolysis solution,and the promoting effect of EG generated ?more prominent,namely when 5g/L of butanol,CBH?,EG? enzyme activity increased from 27.3% and 62.9% to 59.9% to 142.8%;Ethanol and acetone are mainly contributed to the thermal stability of CBH ?,but had little impact on the EG activity?.All products had no effect on the ?-G activity.The result in this work evaluated the feasibility of producing biobutanol from energy grass by fermentation from efficient pretreatment,enzymatic hydrolysis and butanol fermentation capacity,which will provide basic theoretical guidance for the butanol fermentation.At the same time,the influence of the end product of butanol fermentation on enzymatic hydrolysis was studied,which will provide guidance for the SSF.