Cellulase enzymes contribute to the largest portion of operation cost on production of cellulosic ethanol. The industrial cellulases available on the industrial enzyme market from different makers and sources vary significantly in hydrolysis and ethanol, and finally lead to the changes of enzyme cost. Therefore, the selection of the proper industrial cellulase enzymes for commercial-scale production of cellulosic ethanol is crucially important in terms of high performance and cost reduction.In this study, three major cellulase enzyme products available on the Chinese industrial enzyme market were selected and evaluated as the biocatalysts for the biorefining process of lignocellulose biomass into high-titer ethanol. The cellulase enzymes included Cellic CTec 2.0 from Novozymes (Beijing), and LLC 4 from Vland (Qingdao), as well as # 7 from an industrial enzyme maker. The detailed assays on the filter paper activity, the cellobiase activity, and the total protein contents of the enzymes were conducted according to the standard protocols. When the cellulase enzymes were applied to the practical hydrolysis and ethanol-fermentation operation under the conditions of high solids loading and low range of cellulase dosage, the hydrolysis yield shows the significant difference, and the difference was narrowed in the final ethanol yield.The commercially available cellulase enzymes showed different performances in the activities, the cellulose hydrolysis yield, and the ethanol fermentation yields based on the protein dosage per gram of cellulose of corn stover. In general, the industrial cellulase products give satisfactory performance and can be applied for the practical cellulosic ethanol production on commercial scale.
In order to reduce the enzyme cost of lignocellulosic enzymatic hydrolysis, upper critical solution temperature (UCST) additives are used to recover and reuse cellulase by regulating the temperature. A sulfobetaine polymer, PSPE, showed a sensitive UCST response in buffer, and its UCST-performance was optimised by adjusting the molecular weight of the polymer. PSPE-3 (Mw = 355.1 kDa) was added to the cellulase buffer at 50 °C, and PSPE-3 and cellulase were co-precipitated by cooling to the room temperature of 25 °C. PSPE-3 and cellulase co-precipitated mainly through hydrophobic interactions via cooling. Compared with octadecyl sulfobetaine (SB3–18), PSPE-3 had a more sensitive UCST response and stronger cellulase recovery ability. Adding only 40% PSPE-3 (accounting for the mass fraction of cellulase) can save more than 50% cellulase in the enzymatic hydrolysis system of eucalyptus chips pre-treated with dilute acid (Eu-DA). However, for the Eu-DA system, adding 100% SB3–18 can only save about 30% of cellulase. In this work, efficient recycling of cellulase was achieved at room temperature by adding UCST-type PSPE. The process is green without consuming acid and alkali, and this work provides a new idea for reducing the production cost of cellulosic ethanol.
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