Sustainable hydrogen and syngas production from waste valorization of biodiesel synthesis by-product: Green chemistry approach

Abstract

Currently, global concerns about greenhouse gas emissions, climate changes, and over-consumption of fossil fuels have drawn human attention to the use of environmentally friendly biofuels and renewable energy sources such as biodiesel. Though biodiesel can serve as an alternative source to fossil diesel fuel, it is quite comparatively expensive to produce. This challenge can be nullified by converting glycerol, a main by-product during biodiesel synthesis, into valuable products such as hydrogen. Catalytic steam reforming of bio-glycerol is one of the potential technologies to address this requirement, which is the main subject of this research. However, this process suffers from energy supply and environmental issues due to CO2 emissions. In an attempt to resolve this problem, an energy self-sufficient approach has been developed to provide the required energy in an eco-friendly way through the combustion of a part of the produced hydrogen. Among the impacts of this novel procedure on environmental and energy resources management, the following can be mentioned: eliminating dependence on hydrocarbon energy resources; non-greenhouse gas emissions; hydrogen production as renewable energy; and syngas production suitable for methanol and GTL synthesis processes. After sensitivity analysis and optimization of thermal efficiency, the highest hydrogen recovery (≅70%) and H2:CO≅2 can be achieved at acceptable glycerol conversion (≅81%) and the lowest level of hydrogen consumption (which is 1/5 of the total produced hydrogen). Furthermore, comparing this process with other conventional hydrogen production technologies showed that it was competitive with other ones in terms of thermal efficiency (≅50%), making it highly promising for commercialization.