Abstract
Dynamic thermogravimetric analysis is applied to investigate the thermal devolatilization of dry distiller’s grain with solubles (DDGS), the major by-product of bioethanol plants. Compared with lignocellulosic biomass, the DDGS devolatilization occurs over a much wider temperature range and with slower rates. This reveals complex dynamics attributable to a peculiar chemical composition comprising, in addition to lignocellulose, proteins, starch and other minor components. The evolution of lumped volatile product classes is well described by a five-step reaction mechanism. The numerical solution of the ordinary differential equations together with a minimization of the objective function leads to activation energies invariant with the heating rate. The estimated values of 89, 120, 158, 102 and 113 kJ/mol are, on average, higher than those obtained under oxidative environments but still lower than those typically estimated for wood.
Highlights
The dry distiller’s grains with solubles (DDGS), the major by-product of the grainbased bioethanol industry, is a protein- and lignin-rich biomass [1]
Though a semi-global mechanism capable of capturing the different stages of the conversion process has been proposed [2] for the combustion of DDGS and the resulting char, given the influence of oxygen on the decomposition pathways [21,22,23], it cannot be applied under pyrolysis conditions
The kinetic analysis, carried out using experimental data produced at various heating rates, indicates that the process is well described by five global reactions with activation energies that are lower than those typically estimated for lignocellulosic fuels
Summary
The dry distiller’s grains with solubles (DDGS), the major by-product of the grainbased bioethanol industry, is a protein- and lignin-rich biomass [1]. Especially in bio-chemical [7,11] and thermo-chemical [2,3,5,12,13,14] conversion The latter processes can be profitably applied to convert DDGS to renewable bioenergy, biofuels and biomaterials. Pyrolysis is a more versatile technology that may be able to effectively convert this protein- and lignin-rich biomass into energy-dense biofuels, namely bio-oil and biochar, with the potential concomitant production of value-added chemicals. Though a semi-global mechanism capable of capturing the different stages of the conversion process has been proposed [2] for the combustion of DDGS and the resulting char, given the influence of oxygen on the decomposition pathways [21,22,23], it cannot be applied under pyrolysis conditions. The influences of the air (versus nitrogen) on the devolatilization kinetics are addressed by means of a comparison with results already available for the former [2]
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