液氨和过氧化氢预处理对稻草酶解效果的影响机制

Mechanism on effect of liquid ammonia and hydrogen peroxide pretreatment on rice straw enzymatic hydrolysis

稻草是一种重要的木质纤维素资源,可以作为纤维素乙醇转化的原料。该试验通过高温过氧化氢(高温HP)、低温过氧化氢(低温HP)和液氨预处理(liquid ammonia treatment,LAT)3种预处理方式来克服生物质原料的酶解顽抗性,促进稻草酶解转化为可发酵单糖。对预处理后的稻草进行酶解试验,利用高效液相色谱法(high performance liquid chromatography,HPLC)定量测定了酶解液中的单糖含量,通过酶解转化率和单糖产量对预处理效果进行了分析比较。试验结果表明高温HP、低温HP和LAT 3种预处理方式均有效提升酶解率,其中LAT预处理的酶解促进作用效果最佳,高温HP预处理次之。稻草在120℃、预处理时间为60 min、30%H2O2水溶液与原料质量比为0.75∶1的高温HP预处理下,在纤维素酶添加量为15U/g时葡聚糖和木聚糖的酶解率分别为61.55%和47.82%,每千克干基稻草原料经144h酶解可生产单糖334.5 g。稻草在90℃、含水率60%、驻留时间为5 min、液氨与原料比例为1∶1的LAT预处理下,在纤维素酶添加量为15 U/g时,葡聚糖和木聚糖的72 h酶解率分别为88.62%和79.29%,每千克干基稻草原料经144 h酶解可生产单糖554.1 g,是未处理原料的2.9倍,总糖回收率达到90%。综上所述,LAT预处理稻草的酶解率显著高于其他单一预处理方法,该研究结果可为稻草制取燃料乙醇提供基础数据。

Biomass is a promising,eco-friendly,and renewable source for generating energy,fuels,and bio-chemicals that could partially replace fossil fuels to reduce the pressure of environmental pollution problems.Rice straw is one of the most important lignocellulosic biomass in China,which is a potential feedstock to produce bio-ethanol by enzyme hydrolysis method.The production process of bio-ethanol is composed of three stages,namely pretreatment,enzymatic hydrolysis,and fermentation.The pretreatment process is important step to overcome biomass recalcitrance,and improve the performance of enzymatic hydrolysis.In this study,three types of pretreated method,namely high-temperature hydrogen peroxide pretreatment(HTHP),low-temperature hydrogen peroxide pretreatment(LTHP),and liquid ammonia pretreatment(LAT),were used to overcome biomass recalcitrance and improve the performance of enzymatic hydrolysis.Then,a caparison of the performance of enzymatic hydrolysis and the yield of monosaccharides were carried out by using three pretreatment methods.The contents of monosaccharide(glucose,xylose,and arabinose)of the enzymatic hydrolysate were quantitative determined by high performance liquid chromatography(HPLC).Results showed that three pretreatment methods were effective to enhance the performance of enzymatic hydrolysis,and ordered as LAT>HTHP>LTHP.Based on the chemical component analysis before and after pretreatment,the content of glucan decreased from 35.54%of control sample to 33.76%of HTHP pretreatment,35.12%of LTHP pretreatment,and 35.86%of LAT pretreatment.The content of xylan decreased from 19.06%of control sample to 14.69%of HTHP pretreatment,17.53%of LTHP pretreatment,while increase to 19.07%of LAT pretreatment.The optimal pretreatment conditions of HTHP were 120℃,mass ratio of 0.75:1(w/w)between 30%H2O2 solution and biomass ratio,and 60 minutes’residence time.The conversion rates of glucan and xylan were 61.55%and 47.82%,respectively,after 72 hours enzymatic hydrolysis at 1%glucan loading using 15 FPU/(g of glucan)of cellulase.The sugar yield was 334.5 g per kg of rice straw(dry basis)after 144 hours enzymatic hydrolysis.The effect of H2O2 addition on the enzymatic hydrolysis effect was significant,and the excessive addition amount(more than 1.0:1)led to a rapid decrease in the enzymatic hydrolysis rate.The optimal pretreatment conditions of LAT were 90℃,mass ratio of 1:1(w/w)between liquid ammonia and biomass ratio,60%moisture content(drybasis)and 5 minutes’residence time.The conversion rates of glucan and xylan were 88.62%and 79.29%,respectively,after 72 hours enzymatic hydrolysis at 1%glucan loading using 15 FPU/(g of glucan)of cellulase.The sugar yield was 554.1 g per kg of dry rice straw after 144 hours enzymatic hydrolysis,which is 2.9-fold of producing from untreated straw.The total sugar recovery rate was almost 90%.In conclusion,the performance of LAT pretreatment was more effective than other two pretreatment methods(HTHP and LTHP).This study would be useful to supply scientific and basic data for industrial application of rice straw.