Gaseificação do endocarpo do coco da baía usando água supercrítica e nanocatalisador à base de níquel

Abstract

The utilisation of residual solid biomass for energy generation and intermediate compounds has sparked industry interest due to societal and governmental pressures regarding global climate issues. In Brazil, coconut husk, especially the endocarp, is an abundant residual biomass with significant potential for energy utilization. Among various thermochemical conversion routes for biomass, Supercritical Water Gasification (SCWG) stands out, converting biomass into synthesis gas with higher H2 concentration and low tar and coal content. This technology is relatively understudied in the literature. To enhance SCWG efficiency, an alternative is the impregnation of biomass with nanocatalysts. This thesis investigated a nanostructured nickelbased catalyst impregnated into coconut endocarp for its gasification using supercritical water (T > 375°C and P > 22.1 MPa) as a reactive medium. The Box-Behnken experimental design, following the Response Surface Methodology (RSM), was chosen for planning the SCWG tests on coconut husks. The effects of the following variables on the efficiency and yield of the gasification process were evaluated: temperature (400, 450, and 500°C), residence time (20, 40, and 60 minutes), and biomass concentration (20, 25, and 30%). Additionally, the characteristics of gas, liquid, and solid products were also analysed. The impact of the presence and concentration of the catalyst on the efficiency and yield of supercritical water gasification of biomass was particularly assessed. From the characterization of biomass impregnated with nickel salt solutions at concentrations of 1 Molar (1M) and 2 Molar (2M), it was observed that nickel was present at 1.6 and 5.6 wt%, with particle sizes of 7.2 and 13.5 nm. Through the application of RSM, it was observed that temperature had the greatest effect on the composition of the gas product. The higher nickel concentration in the 2M sample resulted in higher H2 content (15.2 mol%), process efficiencies, and the transition of nickel ions to the form of nanoparticles (Ni(0)). Additionally, the chemical composition of the liquid product demonstrated the significant ability of nickel to promote lignin decomposition into phenol, facilitating the hydrogenation reaction of phenol and subsequent gas production. This thesis generated a new knowledge in the promising field of the SCWG process by impregnating a nickel nanocatalyst into coconut biomass, aiming to increase the efficiency of its conversion into synthesis gas, with a focus on obtaining a higher concentration of renewable hydrogen.