Hydrogen production from supercritical water gasification of lignosulfonate over CuO-ZnO: Sulfur transport and catalyst regeneration

Abstract

In this study, sodium lignosulfonate was gasified in supercritical water over CuO-ZnO, and the gasification performance and sulfur transport and fate were investigated experimentally. The products and catalysts were characterized with GC-MS, IC, FTIR, XRD and XPS. It was found that the presence of CuO-ZnO improved the gasification efficiency, and the H2 yield peaked at 9.35 mol/kg with 1.5 g CuO-ZnO. The sulfur element was mainly distributed as H2S and CH3SH in the gas product owing to the reducing reaction atmosphere and SO42- in the liquid product. The presence of CuO-ZnO facilitated the conversion of sulfur from H2S and CH3SH in the gas product to SO42- in the liquid product. And the CuO component was converted into Cu2S, which fixed some sulfur in the solid residues. Three regenerating methods were tested for the sulfur-poisoned CuO-ZnO, and calcination showed superiorities over SCW and SubCW treatment. The calcination eliminated the sulfur and carbon deposited on the catalyst, and also converted Cu2S into CuO by oxidation. The calcined catalyst showed relatively high catalytic activity as the fresh catalyst. With further optimization, CuO-ZnO can be a promising catalyst for SCWG of sulfur-containing organic wastes.