Syed Shatir Asghrar Syed-Hassan

The turquoise hydrogen production route via methane (natural gas) pyrolysis by molten media catalysts is driven by its eco‐friendly credentials as it circumvents carbon dioxide emissions. In this article, the performance of numerous molten metals and salts towards hydrogen selectivity, methane conversion, and solid carbon quality, is analysed. With aims to provide guidance in the catalyst selection, formulation, and configuration in the bubble column reactor, we present: (i) the fundamental understanding in chemically formulating the molten metal catalyst system for optimal catalytic activity performance, and (ii) the approach in selecting eutectic molten salts for achieving high carbon product purity based on their relevant physical properties. We also review the effects of feed gas to inert ratio, temperature, gas hourly space velocity, and pressure on the pyrolysis performance, providing important insight into operating the reactor under optimal conditions. Finally, the challenges and feasibility of this technology are discussed.

Rapid urbanisation and population growth have led to a surge in sewage sludge (SS) generation, posing environmental challenges due to its complex composition, particularly heavy metal content. This study investigates heavy metal analysis, thermal decomposition behaviour, and slow pyrolysis of SS to address these concerns. SS samples were collected from a sewage treatment plant and analysed for heavy metals using ICP-OES. Thermogravimetric analysis (TGA) clarified thermal decomposition behaviour, while slow pyrolysis experiments at varying temperatures provided insights into product yields. Results revealed significant concentrations of heavy metals and other elements in SS, with pyrolysis temperatures between 450°C and 600°C ensuring complete conversion of volatile matter. Slow pyrolysis predominantly yielded biochar, indicating limited suitability for bio-oil production. Additionally, pyrolysis enriched biochar with heavy metals while decreasing cobalt concentration, highlighting complex mechanisms in heavy metal redistribution. This research contributes to understanding heavy metal behaviour and thermal conversion dynamics in sewage sludge, informing sustainable waste management strategies for mitigating environmental impacts.

Hydrothermal carbonization (HTC) is an attractive, green technology for the management of sewage sludge. In this study, low-value secondary sewage sludge was subjected to an HTC treatment in a 1 L batch hydrothermal reactor and transformed into a high-energy-density hydrochar under varying HTC conditions (temperature of 150–300 °C, carbonization time of 30–150 min and a solid loading of 10–30%). The resulting hydrochar fuel characteristics were analyzed for ultimate and proximate analyses, functional group composition and energetic parameters. It was found that the hydrochar yield decreased with the increasing HTC temperature and reaction time, primarily due to the loss of organic volatile matter and functional groups. Under the optimum conditions of 150 °C, 30 min of carbonization time and 30% solid loading, 80.56% of the hydrochar was recovered, providing a maximum energy yield of 90.32% and a high heating value of 18.49 MJ/kg. Compared to the raw sewage sludge (H/C ratio of 2.67 and O/C ratio of 0.51), the hydrochar also had lower H/C and O/C atomic ratios of 1.42 and 0.18, respectively. The results suggest that significant dehydration and decarboxylation during the HTC treatment of sewage sludge have resulted in the formation of carbonaceous hydrochar with energetic properties close to the sub-bituminous coals.

The conversion of abundantly available and renewable biomass, e.g. oil palm waste, into combustible gas mixture provides good opportunities for reducing the greenhouse gas effect and the reliance on fossil fuel in energy sector. The use of catalyst in the reforming/cracking of tarry materials, e.g. biomass-derived bio-oil or tar in the gasification outlet gas, helps to achieve the required gas quality for various energy and power generation applications. Catalyst deactivation which leads to shortened catalyst lifetime, however, limits the application of many commercial catalysts in the production of clean producer gas from biomass, especially for a large-scale system, contributing to the increase in operating expenditure and creating waste management issue arising from the disposal of spent catalyst. It is therefore important to develop an environmentally-friendly low-cost catalyst that can efficiently convert biomass tarry materials into clean burnable gas for practical application. This paper reports some of our recent studies on the development and testing of tar cracking/reforming catalyst for the production of low-tar, highly burnable gas from oil palm biomass. Iron-loaded activated carbon was prepared using a stepwise impregnation method that allows high loading of iron without severe deterioration on catalyst dispersion and porosity of the catalyst support. The catalyst was tested in the lab-scale bio-oil reforming as well as in the pilot-scale biomass gasification. Results indicate that this low-cost practical catalyst can reduce tar content in the producer gas with performance comparable to other commercial catalysts.