(706a) Sustainable Dmc Production from CO2 and Renewable Ammonia and Methanol

Green Chemistry principles are entering the traditional chemical industry aiming to reduce or avoid the generation of hazardous substances. Dimethyl carbonate (DMC) is a green chemical that it is attracting attention nowadays. Different applications have been proposed for it: as a solvent, due to its appropriate features like low viscosity and good solvency, as a fuel additive, due to the high oxygen content, or as a chemical reagent in methylation, carbonylation and methoxycarbonilation reactions (Pyo et al., 2017). A widely range of processes have been proposed to synthetize DMC (Kongpanna et al., 2015). One of the early process to produce it uses methanol and phosgene as feedstocks. This process has been discarded due to the high toxicity of phosgene. To substitute this path, the oxidative carbonylation of methanol was presented in the eighties. This technology is the most widespread currently. However, the most promising alternatives to produce DMC are focused on the production of it using CO₂ as raw material. The use of CO₂ as a reagent in chemical reaction is one of the more promising alternatives to use the CO₂ from carbon dioxide capture.

In this work, the synthesis of DMC from methanol, ammonia and carbon dioxide has been evaluated. In a first section, the synthesis of urea is carried out using ammonia and carbon dioxide. A stripping process is selected where the inlet carbon dioxide is used as stripping agent. The Vapor-Liquid Equilibrium (VLE) is used to model the performance of the system. The urea reactor is modelled based on an empirical correlation and for the stripper a surrogate model was created taking into account the main variables involved. Then, the urea produced is sent to the DMC synthesis section combining it with methanol. Two reaction steps take place. The first one combines methanol with urea to produce methyl carbamate (MC) and the second one producing DMC from MC and methanol. Experimental results for different pressures and temperatures in the reactors have been considered for the modelling of the reactors. A sequence of distillation columns is set up to separate the different components produced during the DMC synthesis. One of the most important advantages of this method is the possibility of producing a 100% renewable DMC using renewable ammonia (Sánchez & Martín, 2018) and renewable methanol (Martín, 2016). The entire process is modelled with an equation based approach. The optimization is carried out in GAMS and the decision variables are the operating conditions in the different equipment including pressures, temperatures and flow ratios.

The results show that the proposed process can be an efficient and sustainable alternative to produce DMC from renewable sources. The investment cost is about 90 MM€ with a production cost of 550€/t. The feedstocks for the process can be produced from different paths (renewable or non-renewable). Due to this fact, a wide variability in the raw materials cost is presented. Therefore, a sensitivity analysis is carried out to evaluate the influence of the price of the raw materials in the DMC operating cost. A simplified environmental index to evaluate the process is also presented.

References:

Kongpanna, P., Pvarajarn, V., Gani, R., Assabumrungrat, S. (2015). Techno-economic evaluation of different CO₂-based processes for dimethyl carbonate production. Chemical Engineering Research and Design, 93, 496-510.

Martín, M. (2016). Methodology for solar and wind energy chemical storage facilities design under uncertainty: Methanol production from CO₂ and hydrogen. Computers and Chemical Engineering, 92, 43-54.

Pyo, S.H., Park, J.H., Chang, T.S., Hatti-Kaul, R. (2017). Dimethyl carbonate as a green chemical. Current Opinion in Green and Sustainable Chemistry, 5, 61-66.

Sánchez, A.; Martín, M. (2018) Scale up and scale down issues of renewable ammonia plants: Towards modular design. Sustainable Production and Consumption, 16, 176-192.