Modelling and technoeconomic assessment for industrial production of dimethyl carbonate from CO2 and methanol

Abstract

With the world straining under the combined weight of rising global temperatures and rapid growth of energy demand, the replacement of fossil fuels with alternative green sources of energy have become crucial. Dimethyl carbonate (DMC), a synthetic fuel, can be synthesised by carbonylation of methanol on CeO2 catalyst. The reaction, being severely equilibrium limited, is carried out in the presence of 2­cyanopyridine to absorb the water formed as by­product to shift the reaction forward. The process is scaled up to produce 100 kt/a of DMC at above 99.5% purity and simulated on Aspen Plus. The reaction, modelled with Langmuir Hinshelwood mechanism, takes place in a fixed bed multitubular reactor, operated at 393 K and 3 MPa. Since DMC and methanol forms an azeotrope at atmospheric pressure, high pressure distillation is performed to obtain the final product. 2­-cyanopyridine is regenerated in a reactive distillation setup in the presence of a solvent at vacuum pressure. Heat and utility integration was performed for the process with heat pumps, district heating and electrical evaporator chosen to provide the cooling and heating duty required. A techno­economic analysis carried out for a base year 2019 for Germany yielded a net production cost of 1.12 € per kg of DMC, which is comparable to the market price of conventionally produced DMC. The utility integration and economic assessment was performed using the German Aerospace Center's in­house software, Techno-­Economic Process Evaluation Tool (TEPET). More than 50% of the net production cost was constituted by the raw material and utility expenses. A process design alternative was developed and simulated to understand the interplay of various factors such as the operating pressure of distillation columns and heating utilities on each other as well as the capital and operating expenses. A part of the purification scheme was simulated at 2.5 MPa as opposed to atmospheric pressure in the alternative design leading to a reduction in capital of almost 50% while the net production costs increased by 5.4% largely due to a rise in the heating demand.