Sustainable production of hydrogen, pyridine and biodiesel from waste-to-chemicals valorization plant: Energy, exergy and CO2-cycle analysis

This study deals with the simulation of waste-to-chemicals plant for the conversion of municipal solid waste to hydrogen, biodiesel and pyridine. The study analyses a Waste to Chemical plant, in order to evaluate the future scenarios of the integrated management of municipal waste from a technical and economic point of view and compare them, both in terms of material flows and related costs. In a first phase, the characteristics of the simulation model created with the help of the Aspen Plus software are analysed. Subsequently, with the help of a calculation model, the operating costs, emissions and energy and exergy efficiency are evaluated for the two identified scenarios. Starting from about 3000 t/h of waste, as a main result, about 8.4 t/h of pyridine and 300 t/h of biodiesel are produced and about 7.94 t/h of H2 as a by-product. The main purpose of the design cycle is to reduce the amount of waste to landfill, valorising it and limiting CO2 emitted in the atmosphere at the same time. Two system configurations are considered to maximize the reuse of all waste streams. In particular, the comparison was made between two scenarios: in the first the stream separated by extraction is considered a waste for the plant, while in the second scenario, this stream is sent to a fermentation section to obtain an excess bioethanol stream, which represents another product with high added value. The treatment of the stream separated from the extraction in the second scenario allows to obtain an additional stream of bioethanol in addition to the target products. A complete energy, exergy, environmental and economic analysis of the simulated plant have been carried out. The work shown that in the second case the waste exergy is dramatically reduced, leading to a raise of exergy efficiency from 30.2% up to 84.9%. While, from the environmental point of view both scenarios have low CO2 emissions, 0.52 kgCO2/kg products and 0.87 kgCO2/kg products respectively.