Development and evaluation of a process to produce Dimethyl Carbonate

Energy transition is the new driver for companies to reach the net-zero goals and Shell aims to become a net-zero supplier by 2050. In the meantime, electric vehicles (EVs) powered by batteries offer a promising alternative to hydrocarbon. Shell has recognized the increasing demand for EVs as an opportunity to join the market for the battery production. Batteries are comprised by electrolytes, which consist of metal salts and a blend of carbonate solvents. The right mixture of the carbonate solvents can have an impact on the performance of individual battery cells. Shell has technology to produce alkyl carbonates such as Ethylene Carbonate (EC), Diethyl Carbonate (DEC) and Ethyl Methyl Carbonate (EMC) with some preliminary work for a process to produce Dimethyl carbonate (DMC). The aim of this project is the development and evaluation of a process to produce DMC, as part of the suite of carbonate products. The focus of this project was to come up with a preliminary design for the DMC recovery and purification section.
A literature review was carried out to gather information on processes to separate DMC from methanol (MeOH), existing Shell knowledge and existing patents around DMC technology. Potential Extractive Distillation (ED) solvents were identified and narrowed down to solvent 1 (S1), solvent 2 (S2) and solvent 3 (S3) as the top three candidates. In parallel, an extensive archive review was carried out on Shell’s existing DMC process development work. The patent review covered competitors’ technologies, which were compared with Shell’s technology. Following the review, experiments for an alternative catalyst and the results showed that this is not very promising. Extraction solvent selection experiments were carried out internally but the first tests with S1 were inconclusive thus the approach was discontinued and a third-party company was approached to complete the analysis.
Extractive distillation was selected as the DMC recovery process and two cases were developed using AspenPlus simulation package. Two cases for S1 and S2 as the extractive distillation solvents were built. The models consist of one extractive distillation column for the separation of the DMC /MeOH azeotrope and a DMC/solvent separation column. Sensitivity studies were carried out to come up with the optimum design for each solvent. The two cases were then compared in terms of solvent to feed ratios, overall DMC recoveries and energy consumption leading to S2 as a more promising candidate. As for the technoeconomic evaluation, this was covered qualitatively; the required amount of S1 versus S2, as an ED solvent, is four times higher. The S1 case operates with an overall bigger number of stages than the S2 case. Therefore, S1 case is estimated to have a higher Capital Expenditure (CAPEX) compared to S2. Finally, the two cases require different utilities for the condensers of the DMC/Solvent separation columns, making the S1 case more costly.
A preliminary check was made on the third solvent candidate, S3, where the results showed that it was effective at separating the DMC/MeOH azeotrope. Due to time constraints this was not investigated further, the recommendation is to build a design case with S3 as an ED solvent.
To conclude, the S2 case requires a lower solvent amount, lower steam consumption and higher DMC recovery making S2 a more promising ED solvent for the DMC/MeOH separation.