Abstract
Mechanical pre-treatment (disc refining) of wheat straw, at both atmospheric and elevated pressure, is shown to be an efficient process to access fermentable monosaccharides, with the potential to integrate within the infrastructure of existing first-generation bioethanol plants. The mild, enzymatic degradation of this sustainable lignocellulosic biomass affords ca. 0.10–0.13 g/g (dry weight) of d-glucose quantifiable voltammetrically in real time, over a two hundred-fold range in experimental laboratory scales (25 mL to 5.0L), with pressure disc refining of the wheat straw enabling almost twice the amount of d-glucose to be generated during the hydrolysis stage than experiments using atmospheric refining (0.06–0.09 g/g dry weight). Fermentation of the resulting hydrolysate affords 0.08–0.10 g/g (dry weight) of ethanol over similar scales, with ethanol productivity at ca. 37 mg/(L h). These results demonstrate that minimal cellulose decomposition occurs during pressure refining of wheat straw, in contrast to hemicellulose, and suggest that the development of green, mechanochemical processes for the scalable and cost-effective manufacture of second-generation bioethanol requires improved cellulose decomposition.
Highlights
Ethanol is an important bulk chemical [1,2], used as a fuel/fuel additive, industrial solvent and disinfectant, cf., disinfectants for Covid19
More over, wheat straw is a by-product from wheat, and as such, is an economically elastic commodity – its supply moves with the changing demand for the primary food source based on local demographic need [5]: over the last 60 years in the United Kingdom, the production of wheat has tripled [6,7], with yields ranging between 3.9 and 8.5 tonnes/ ha; the derived straw yield is typically between 2 and 5 tonnes/ha [8,9,10], so that 0.24–1.3 tonnes of straw are produced per tonne of wheat
Compared with atmospherically refined (AR) wheat straw, whilst there is no significant change in the cellulose content as a result of pressurised refining (PR), the hemicellulose content decreases with increasing pressure used in the thermo-mechanical process; in contrast, the non-fibrous content increases with refining pressure
Summary
Ethanol is an important bulk chemical [1,2], used as a fuel/fuel additive, industrial solvent and disinfectant, cf., disinfectants for Covid19. Compared with atmospherically refined (AR) wheat straw, whilst there is no significant change in the cellulose content as a result of pressurised refining (PR), the hemicellulose content decreases with increasing pressure used in the thermo-mechanical process; in contrast, the non-fibrous content increases with refining pressure. Advanta geously, this approach enables a real-time measurement of D-glucose, Table 1 Experimental parameters used for the thermo-mechanical refining of wheat straw used in this work, together with compositional analysis of the fibres.
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