DESIGNING AN ENERGY-EFFICIENT GREEN METHANOL PRODUCTION PROCESS USING A SOLAR-REDOX CYCLE AND CAPTURED CO2 FROM THE CEMENT INDUSTRY

Abstract

Future chemical industry is predicted to rely heavily on methanol as a crucial commodity, both as a wide-use precursor, but as fuel and hydrogen carrier. Methanol is typically synthesized using syngas, which is primarily derived from fossil fuels. However, the solar-redox cycle is a promising thermochemical process that can serve as a renewable alternative route for syngas production. This process uses CO2 and water as feedstocks, and if the CO2 is captured from unavoidable point source industries, the final methanol produced using syngas from the redox cycle can be termed as blue-methanol. However, the renewable-energy based methanol production route requires access to high-temperature (up to 1500 °C) for the redox cycle, which can only be achieved in a solar-abundant region using a solar tower. The dependency on solar energy makes the production process intermittent and jeopardizes the continuous production of methanol. To counter the challenges of intermittency of solar energy, this study aims to design an encompassing energy-efficient process chain linking CO2 capture to methanol production. The CO2 capture unit is designed in ASPEN Plus to treat flue gases from the cement industry and uses the novel CESAR1 solvent, and deliver the capture gas to the solar redox cycle. The high temperature redox cycle produces syngas, which is further synthesized via the traditional route to methanol synthesis. While both the solar-redox cycle and methanol synthesis are exothermic, associated units like distillation columns and amine regeneration require thermal energy input. Process integration, specifically pinch analysis, is applied for the recuperation of waste heat from the products of the redox cycle to maximize energy efficiency. The system is dimensioned for a conservative production of 10 kTon/y of methanol, and excess CO2 removed from cement flue gases can be disposed of via established CCS(Carbon Capture and Storage) methods.