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Abstract
BackgroundUltrafine grinding is an environmentally friendly pretreatment that can alter the degree of polymerization, the porosity and the specific surface area of lignocellulosic biomass and can, thus, enhance cellulose hydrolysis. Enzyme adsorption onto the substrate is a prerequisite for the enzymatic hydrolysis process. Therefore, it is necessary to investigate the enzyme adsorption properties of corn stover pretreated by ultrafine grinding.ResultsThe ultrafine grinding pretreatment was executed on corn stover. The results showed that ultrafine grinding pretreatment can significantly decrease particle size [from 218.50 μm of sieve-based grinding corn stover (SGCS) to 17.45 μm of ultrafine grinding corn stover (UGCS)] and increase the specific surface area (SSA), pore volume (PV) and surface composition (SSA: from 1.71 m2/g of SGCS to 2.63 m2/g of UGCS, PV: from 0.009 cm3/g of SGCS to 0.024 m3/g of UGCS, cellulose surface area: from 168.69 m2/g of SGCS to 290.76 m2/g of UGCS, lignin surface area: from 91.46 m2/g of SGCS to 106.70 m2/g of UGCS). The structure and surface composition changes induced by ultrafine grinding increase the enzyme adsorption capacity from 2.83 mg/g substrate of SGCS to 5.61 mg/g substrate of UGCS. A film–pore–surface diffusion model was developed to simultaneously predict the enzyme adsorption kinetics of both the SGCS and UGCS. Satisfactory predictions could be made with the model based on high R2 and low RMSE values (R2 = 0.95 and RMSE = 0.16 mg/g for the UGCS, R2 = 0.93 and RMSE = 0.09 mg/g for the SGCS). The model was further employed to analyze the rate-limiting steps in the enzyme adsorption process. Although both the external-film and internal-pore mass transfer are important for enzyme adsorption on the SGCS and UGCS, the UGCS has a lower internal-pore resistance compared to the SGCS.ConclusionsUltrafine grinding pretreatment can enhance the enzyme adsorption onto corn stover by altering structure and surface composition. The film–pore–surface diffusion model successfully captures features on enzyme adsorption on ultrafine grinding pretreated corn stover. These findings identify wherein the probable rate-limiting factors for the enzyme adsorption reside and could, therefore, provide a basis for enhanced cellulose hydrolysis processes.
Highlights
Ultrafine grinding is an environmentally friendly pretreatment that can alter the degree of polymerization, the porosity and the specific surface area of lignocellulosic biomass and can, enhance cellulose hydrolysis
Compared with the lignin surface area of the sieve-based grinding corn stover (SGCS) (91.46 m2/g), that of the ultrafine grinding corn stover (UGCS) (106.7 m2/g) moderately increased. These results indicated that the substrate pretreated by ultrafine grinding can induce more exposure of the surface composition, which will be favorable to enzyme adsorption
The results showed that the ultrafine grinding pretreatment can significantly decrease the particle size and increase the specific surface area (SSA), pore volume (PV) and surface composition (SSA: from 1.71 m2/g of SGCS to 2.63 m2/g of UGCS, PV: from 0.009 cm3/g of SGCS to 0.024 m3/g of UGCS, cellulose surface area: from 168.69 m2/g of SGCS to 290.76 m2/g of UGCS, lignin surface area: from 91.46 m2/g of SGCS to 106.70 m2/g of UGCS)
Summary
Ultrafine grinding is an environmentally friendly pretreatment that can alter the degree of polymerization, the porosity and the specific surface area of lignocellulosic biomass and can, enhance cellulose hydrolysis. It is necessary to investigate the enzyme adsorption properties of corn stover pretreated by ultrafine grinding. Lignocellulosic biomass, such as crop residues, is the only renewable and sustainable resource that can be. To overcome biomass recalcitrance and improve cellulose accessibility, many chemical pretreatment methods (acid [4], alkali [5], ammonia fiber explosion [2] and so on [6]) were employed. Mechanical comminution is an environmentally friendly pretreatment that can alter the degree of polymerization, crystallinity degree, porosity and specific surface area of lignocellulosic biomass and, enhance cellulose hydrolysis [7]. Most previous studies on the mechanical comminution pretreatment of lignocellulosic biomass were usually carried out by chipping (10–30 mm), grinding and milling (0.2–2 mm) [7,8,9]
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