(58d) Conversion of Captured Carbon Dioxide to Value-Added Dimethyl Carbonate Using Reactive Distillation

The present design study focuses on converting captured carbon dioxide (CO2) to high-value dimethyl carbonate (DMC) that can be an intermediate for other carbonate-based products.  The capture and conversion of carbon dioxide (CO2) to chemicals represents a niche opportunity of significance.  However, CO2 recovery schemes may leave trace components such as Oxygen that affect the downstream use of even high purity CO2 product (>99% CO2).  As a consequence, the downstream impacts of CO2 capture from reducing environments are typically much lower cost than capture from combustion environments and should prove more favorable.  The source of the CO2 for this study is from a chilled methanol (Rectisol®) unit following gasification and shift as part of a proposed Petcoke gasification complex that will produce methanol and power (Oil & Gas Journal 6/6/2011). 

The overall chemical pathway of the DMC production is represented by:  CO2 + 2MeOH >> DMC + H2O.  In the first stage 1) captured CO2 and recovered ammonia will be converted to urea and water using a commercial process; 2) the urea is then reacted with methanol to produce methyl carbamate and ammonia in a heat-integrated reactive distillation (HIRD) column with side-reactors and pervaporation (PerVap) membrane separation, 3) this is followed by additional methanol reaction to yield dimethyl carbonate (DMC) and ammonia.  Ammonia is regenerated as an end product and recycled to the process for urea formation, thereby acting as a chemical path carrier.  Application of HIRD with side reactors and PerVap membrane separation significantly enhanced the techno-economic viability of the process.  The proposed HIRD process would replace phosgene based production of DMC.  The numerous and expanding uses for DMC make it an ideal candidate, with favorable economics, for consumption of captured CO2.         

Global consumption of polycarbonate stands at 5 million tons per year, with growth rate of about 7% globally. Lithium ion battery electrolytes use organic carbonates such as DMC and complexes of lithium ions.  DMC is also being evaluated as oxygenated fuel additives. DMC is not corrosive and it will not produce environmentally damaging by-products, it also is a valuable commercial product finding utility as an organic solvent and in the production of other alkyl and aryl carbonates.  If implemented worldwide, this production route has the potential to consume in excess of 5 million metric tons/yr of CO2.

This design study presents an AspenPlus process analysis of an integrated process of HIRD with side reactors and PerVap membrane separation.  The analysis demonstrates a design methodology for rapidly scaling the batch kinetic data to a commercial plant.  The methodology developed in this study is applicable to other chemical manufacturing processes where HIRD with side reactors can be applied.