Hydolysis of multi substrate biomass using para-toluenesulphonic acid for bioethanol production: A promising option over the sulfuric acid treatment

Highlights: • Multi substrate feedstock approach has been used for bioethanol production. • PTSA was used as a catalyst for the hydrolysis of multi substrate. • Hydrolysis with PTSA and H₂SO₄ gave 96 and 78% TRS, respectively. • Fermentation of PTSA and H₂SO₄ hydrolysate gave 17 and 13 g/L ethanol, respectively. • PTSA surpassed the conventional method of treatment both in TRS and ethanol yield. The municipal and agricultural wastes are promising source of ligniocellulosic biomasses (LBs) for bioethanol production. However, the pretreatment-hydrolysis (P–H) of LB is the most difficult process in bioethanol production due to high crystallinity of LB compositional structures. In this study, p-toluenesulphonic acid (PTSA) was investigated for P–H of multi-substrate (MS) sample of LBs. Five alternative MS samples were prepared from 10 single LBs. Based on the total reducing sugar yield, one of the MS was selected for optimization experiment. The factors affecting P–H (acid concentration, time and temperature) were optimized to compare catalytic activity of PTSA and H₂SO₄. Under the optimized conditions, maximum total reducing sugar (TRS) yield of 95.89 and 78.26% was obtained using PTSA and H₂SO₄, respectively. Mass production of hydrolysate was carried out using both catalysts at a substrate load of 50 g.L⁻¹ and fermented at an optimum yeast load of 10% (v/v). The ethanol yield from the hydrolysates of PTSA treatment was 16.89 g L⁻¹ (74.5%) and from H₂SO₄ was 13.17 g L⁻¹ (70.9%) at 48 & 56 h fermentation time, respectively. The PTSA surpassed the conventional method of treatment (H₂SO₄) both in TRS and ethanol yield. The efficiency of PTSA can be noticed in that one third of the acid concentration required in sulfuric acid treatment was used in PTSA to obtain 96% of TRS at lower temperature. This study revealed the potential of aqueous PTSA for the hydrolysis of a mixture of feedstocks which is much more complex and challenging than treating a single substrate.