Optimization and Heat Exchanger Network Design of Diethyl Carbonate Two-step Synthesis Process from CO₂ and Propylene Oxide

CO₂ has been deemed crucial as an alternative carbon source recently due to its low price and the urge to utilize it as a way to reduce its amount in the atmosphere. Diethyl carbonate (DEC) is a potential candidate for CO₂ conversion because it can serve as good fuel additive or solvent for lithium batteries. However, CO₂ conversion reaction often suffers from low conversion rate because of its very stable chemical activity. Not only catalyst development is essential, but the research from a process systems engineering (PSE) perspective is also necessary when considering the practical implementation in the future. In the previous work from our group (Chen & Chien, 2018), three processes of DEC synthesis from CO₂ and propylene oxide (PO) were proposed and compared. The results showed that the two-step process performed relatively better in CO₂ emission amount. The two step process includes PO reacting with CO₂ to produce propylene carbonate (PC) and PC reacting with ethanol to produce DEC. Nevertheless, after environmental evaluation throughout the two-step process, the positive net CO₂ emission amount indicated that it still couldn't be a strategy for CO₂ emission mitigation. In this study, the root cause of the high energy consumption of the process was reviewed, and it was found that the large excess ratio of the second step reaction led to massive energy consumption in the separation stage. Consequently, process optimization has been executed by sequential iterative procedure. Heat exchanger network according to pinch analysis along with thermally coupled configuration has been developed for the two-step DEC synthesis process, and the results showed that the new design can save at least 75% CO₂ emission amount for the process. The purpose of this work is to investigate the potentiality of the system to be a CO₂ emission reduction route.