Gasification of algal residue for synthesis gas production

Abstract

It is highly imperative to recover energy from not only the lipid fraction of microalgae but also the residual biomass after lipid-extraction to augment energy potential and to facilitate the sustainability of algal-based bioenergy. Herein, we present the production of syngas from microalgae residual biomass (Chlorella vulgaris), upon its extraction as by-product from biodiesel production system, in a lab-scale fixed bed reactor (FBR). The influences of two gasification parameters such as temperature (700, 800 and 900 °C) and catalysts type (Y2O3, Ni and eggshell derived CaO) have been studies in terms of CnHm/CO/H2 gas yield and composition, carbon conversion efficiency (CCE%), lower heating value (LHV) of syngas under 5% O2 and 95% Ar gasification environment. From the results, 800 °C was found to be an optimum temperature producing highest H2 yield (4.53 mmol g−1 biomass with purity of 34.62 vol%) and highest generation peak intensity of 0.14 mmol min−1 g−1, whereas highest LHV (8.92 MJ N m−3), total gas yield (73.54 wt%) and CCE (49.54%) were obtained at 900 °C. Addition of catalysts further improved H2 yield and its volume fraction, total gas yield and CCE%. The Ni catalyst was found to be the most effective catalyst in terms of the maximum H2 yield (8.22 mmol g−1 biomass with purity of 56.12 vol%), highest total gas yield of 80.21 wt%, and CCE of 49.06% owing to its relatively high catalytic activity for promoting water-gas shift, as well as tar and char reforming reactions. The average LHV of syngas was obtained to be 9 MJ N m−3. Furthermore, the considerable decrease in tar and char contents from 20.12 wt% and 21.77 wt% (without catalyst at 700 °C) to 9.32 wt% and 10.47 wt% (with Ni catalyst) was recorded.