A virtuous cycle for thermal treatment of polyvinyl chloride and fermentation of lignocellulosic biomass

In this study, a highly corrosive substance, hydrogen chloride (HCl), obtained through the dechlorination of polyvinyl chloride (PVC), was utilized for acid pretreatment in the production of lignocellulosic bioethanol. The study determined that the optimal concentration of HCl was 5 wt%, resulting in the highest sugar recovery of 85.98% from oak sawdust when treated at 130 °C for 2 h. The production of bioethanol (BE) by Pichia stipitis using the hydrolysates treated with 5% HCl and enzymes, supplemented with N-sources, demonstrated efficient productivity compared to the control group. To achieve a virtuous cycle, two residues from the dechlorination of PVC and saccharification of oak sawdust were pyrolyzed in a carbon dioxide (CO2) environment. The generation of carbon monoxide (CO) was significantly enhanced by the homogeneous reaction between CO2 and volatiles. This homogeneous reaction led to the modification of the compositional matrix in the oil. The generation of low-molecular-weight hydrocarbons in oil was observed under CO2 conditions. To impart high reactivity to CO2, the catalytic pyrolysis of the residues was performed in the presence of Ni/SiO2. Indeed, the CO2 reactivity was catalytically enhanced, which greatly expedited the redox kinetics underlying the chemical reactions of CO2 with volatiles from PVC. The experimental findings provide a great avenue for hybridizing the thermochemical process of PVC and the biological bioethanol production process of lignocellulosic biomass. Such efforts are promising from the perspective of economic viability in the waste-to-energy and biofuel fields.