金属盐强化乙醇预处理和添加剂联合对杨木酶解的影响

Effects of different metal-salts catalyzed ethanol pretreatment and additives on the enzymatic hydrolysis of poplar

农林废弃物的生化转化是木质纤维类生物质能源化利用的重要手段之一。其中,木质纤维素是生物质能源最重要的形式,通过生化转化将木质纤维素转化为可发酵糖,进而转化为燃料乙醇和化学品,是生物炼制的重要途径之一。该研究以杨木为研究对象,采用不同金属盐强化的乙醇溶液对杨木进行预处理,探究不同金属盐(FeCl_(3)、CrCl_(3)、CuCl_(2)、FeCl_(2)、ZnCl_(2)、MnCl_(2)、MgCl_(2)、CaCl_(2)NaCl和LiCl)强化乙醇预处理对杨木组分和酶解效果的影响,同时在酶解段进行不同种类添加剂(吐温80、茶皂素、牛血清白蛋白和木聚糖酶)的添加,探究不同金属盐强化乙醇预处理和不同添加剂联合对杨木酶解效率的影响,从而得到杨木酶解最优的金属氯化物和添加剂组合。结果表明:金属盐强化乙醇预处理能显著去除半纤维素和木素,破坏杨木原料的致密结构,提升预处理底物中纤维素含量,暴露更多可接触位点,提高酶对纤维素的可及性,其中三价和部分二价金属盐(过渡金属盐)强化乙醇预处理能一定程度地提升酶解效果,获得较高的葡萄糖得率。添加剂的加入可不同程度的提升酶解速度、缩短酶解时间,并提升预处理样品的最终葡萄糖得率,其中在吐温80的作用下,FeCl_(3)强化的乙醇预处理后杨木酶解可获最高葡萄糖得率达93.44%,该研究结果可为农林废弃物利用提供参考。

The biochemical transformation of lignocellulosic biomass is one of the important methods for producing environmentally friendly bioenergy from agricultural and forestry wastes.Among them,lignocellulose is the most important form of biomass energy,and it is one of the important ways of biorefinery to convert lignocellulosic into fermentable sugar by means of biochemical transformation,and further conversion into fuel ethanol and chemicals,which has received extensive attention and research from various countries.In this study,Poplar wood was added to 60%ethanol aqueous solution with a solid-liquid ratio of 1:10(w/v)with 0.025 mol/L of metal salts(FeCl_(3),CrCl_(3),CuCl_(2),FeCl_(2),ZnCl_(2),MnCl_(2),MgCl_(2),CaCl_(2),NaCl and LiCl)at a speed of 300 r/min,and the reaction continued for 10 min at 200℃in a high-pressure reactor.The influence of different metal-salts catalyzed ethanol pretreatment of poplar on the chemical composition,sugar composition,microstructure and enzymatic glucose yield of poplar were studied.Furthermore,the additives(Tween 80,tea saponin,BSA,and xylanase)were added to the enzymatic hydrolysis,the effects of different metal-salts catalyzed ethanol pretreatment and additives on enzymatic hydrolysis of poplar were explored by comparing the glucose yield,resulting in the optimal combination of metalsalt and additive for poplar enzymatic hydrolysis.Through the pretreatment of poplar wood with different metal salts catalyzed ethanol pretreatment,it was found that the degradation of hemicellulose and lignin by trivalent and divalent metal salts was obvious.Through XRD,the crystallinity(CrI)of poplar raw material was 64.14%,and its CrI increased to 78.63%,78.65%,78.92%,77.26%,75.79%and 70.33%after pretreatment with FeCl_(3),CrCl_(3),FeCl_(2),MgCl_(2),NaCl and LiCl-catalyzed ethanol.This is because the relative crystallinity of crystalline cellulose in pretreated poplar is increased due to the removal of amorphous hemicellulose and lignin during the ethanol pretreatment process catalyzed by metal salts.It has been found that all metal salt-catalyzed ethanol pretreatment has the effect of promoting enzymatic hydrolysis efficiency.Among them,the trivalent metal salt is better than the trivalent metal salt and the monovalent metal salt as a whole.Through XRD and SEM,it could be seen that the dense structure formed by poplar fiber was destroyed,and the increase of cellulose content led to an increase in its relative crystallinity and exposed more accessible sites,thereby improving its enzymatic hydrolysis efficiency.By analyzing the effects of the addition of four additives on the yield and growth rate of enzymatic hydrolysis of poplar in the pretreatment of metal salt-catalyzed ethanol,it was found that the addition of additive could increase the enzymatic hydrolysis speed,shorten the enzymatic hydrolysis time and increase the enzymatic hydrolysis efficiency.Among them,Tween 80 has the widest application range and better effect on poplar pretreated with metal salt catalyzed ethanol.The addition of Tween 80 to the enzymatic hydrolysis of poplar after pretreatment with FeCl_(3)-catalyzed ethanol yielded the highest glucose yield of 93.44%.