Abstract
BackgroundThe inevitable depletion of fossil fuels has resulted in an increasing worldwide interest in exploring alternative and sustainable energy sources. Lignocellulose, which is the most abundant biomass on earth, is widely regarded as a promising raw material to produce fuel ethanol. Pretreatment is an essential step to disrupt the recalcitrance of lignocellulosic matrix for enzymatic saccharification and bioethanol production. This paper established an ATSE (alkaline twin-screw extrusion pretreatment) process using a specially designed twin-screw extruder in the presence of alkaline solution to improve the enzymatic hydrolysis efficiency of corn stover for the production of fermentable sugars.ResultsThe ATSE pretreatment was conducted with a biomass/liquid ratio of 1/2 (w/w) at a temperature of 99°C without heating equipment. The results indicated that ATSE pretreatment is effective in improving the enzymatic digestibility of corn stover. Sodium hydroxide loading is more influential factor affecting both sugar yield and lignin degradation than heat preservation time. After ATSE pretreatment under the proper conditions (NaOH loading of 0.06 g/g biomass during ATSE and 1 hour heat preservation after extrusion), 71% lignin removal was achieved and the conversions of glucan and xylan in the pretreated biomass can reach to 83% and 89% respectively via subsequent enzymatic hydrolysis (cellulase loading of 20 FPU/g-biomass and substrate consistency of 2%). About 78% of the original polysaccharides were converted into fermentable sugars.ConclusionsWith the physicochemical functions in extrusion, the ATSE method can effectively overcome the recalcitrance of lignocellulose for the production of fermentable sugars from corn stover. This process can be considered as a promising pretreatment method due to its relatively low temperature (99°C), high biomass/liquid ratio (1/2) and satisfied total sugar yield (78%), despite further study is needed for process optimization and cost reduction.
Highlights
The inevitable depletion of fossil fuels has resulted in an increasing worldwide interest in exploring alternative and sustainable energy sources
Composition changes of corn stover after Alkaline twin-screw extrusion (ATSE) pretreatment The effects of ATSE pretreatment under different conditions on glucan, xylan and lignin content of the pretreated corn stover are shown in Figure 2, which presents that ATSE pretreatment can drastically change the composition of corn stover
The lignin content of the biomass was significantly reduced after ATSE pretreatments and the lignin reduction increased from 14% to 83% as the pretreatments were intensified, as shown in Figure 2c, but the lignin removal increased slowly with extending heat preservation
Summary
The inevitable depletion of fossil fuels has resulted in an increasing worldwide interest in exploring alternative and sustainable energy sources. With the gradual short supply of petroleum source, it has been a hot research field in exploitation and utilization of lignocellulosic biomass such as the wastes of agriculture and forestry (e.g., corn stalk, rice straw, wheat straw, bagasse, saw dust, etc.) by converting them into liquid fuels or chemicals, as it is of great importance to establish a circular economy mode of sustainable development. The enzymatic conversion of carbohydrates in lignocellulosic biomass to fermentable sugars is difficult as these sugar-based polymers are compactly associated with lignin [1,2]. Some structural factors, such as content of lignin, hemicelluloses, and acetyl group, cellulose crystallinity, degree of polymerization, accessible surface, etc., can impact enzymatic hydrolysis to different extent [3,4,5,6]. Pretreatment is required to disrupt the natural recalcitrance of lignocellulosic biomass for effective enzymatic saccharification
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