(681e) The Design of Sustainable Carbon Dioxide Capture and Conversion Processes Considering Various Locations, Products and Routes

Due to climate change and growing concerns about global warming, methods of mitigating carbon dioxide emissions are important. The three most common approaches to mitigating emissions and reducing the concentration in the atmosphere are: improving the efficiency of processes, carbon dioxide capture and storage (CCS), and carbon dioxide capture and utilization (CCU). It is questionable, however, if they alone can satisfy the requirements; therefore, they need to be developed concurrently to provide an overall sustainable solution. Carbon dioxide utilization, which takes the captured carbon dioxide and reuses it, can provide an economic offset to the costs of capture and other new technologies in the formation of commercial products. Therefore, the sustainable design of carbon dioxide capture and utilization, especially conversion, technologies is important. To ensure this, a computer-aided, systematic framework for the synthesis-design of carbon dioxide utilization processes, inclusive of carbon dioxide capture, has been developed. This framework uses three stages, (i) process synthesis, (ii) process design and (iii) innovation, for the design of sustainable processes. In this work, the framework is implemented so that various scenarios - varying locations, prices or objective function – could be investigated. The results provide insight into what processes and products should be produced via carbon dioxide conversion and how much of emissions can be mitigated in this way.

In the first stage, a superstructure of 23 steps containing over 150 intervals is optimized to find the optimal route, amongst over 30 feasible routes, to take captured carbon dioxide to a product. To aid the optimization, the developed database contains over 20 reactions, and the production of over 10 products and byproducts (methanol, dimethyl ether, ethanol, methane, dimethyl carbonate, ethylene carbonate, ethylene glycol, propylene carbonate, propylene glycol, acetic acid and succinic acid) via over 30 feasible processing routes. Optimizations for seven different scenarios are performed, in terms of prices, demands, locations and objective, to determine the impact that carbon dioxide capture and conversion can have. The seven scenarios include, (i) optimization for a fixed amount of captured CO₂ considering operating costs and capital costs (covers 2 scenarios), (ii) optimization under price uncertainty with respect to products (1 scenario), (iii) optimization with price variability for utilities, chemicals and products, to reflect sensitivity and location variability (covers 2 scenarios), (iv) optimization with variable conversion (1 scenario), and (v) optimization considering a fixed demand of the products to determine the amount of CO₂ utilized for different paths (1 scenario). The results show that if the prices of certain products changed, such as if the price of dimethyl carbonate were doubled or the price of succinic acid were decreased by half, what to produce and how to produce it is greatly influenced. Changing the parameters – such as prices of utilities and materials or demands and availability of carbon dioxide sources - according to uncertainty and location, changes the optimal processing route. Considering seven scenarios, the optimal routes are found to produce succinic acid, dimethyl carbonate and methanol, amongst other value-added products.

After the optimal processing paths are found for the scenarios, they are simulated and analyzed in the second stage. A simulation library containing over 30 different capture and conversion processes to various products has been developed, including the optimal routes determined in the scenarios. In Stage 3, the production of dimethyl carbonate via different carbon dioxide utilization routes and the production of succinic acid are selected for further improvement as they are among the highest rated processes. For these cases, the targeted sustainability indicators can be improved; in the case of dimethyl carbonate production via ethylene carbonate, for example, the net carbon dioxide emissions (considering also energy production), operating costs and capital costs can be reduced by more than 10%. For already innovative processes, this is not always necessary. However, for processes which already exist or are not already carbon dioxide reducing, this can be used to find more sustainable processes.

This presentation will highlight the framework and the corresponding models, methods and tools, especially the database and simulation library. In addition, the application of this framework will be highlighted through a case study, which will encompass superstructure optimization of a large network of capture and utilization processes for all seven scenarios. The detailed design and analysis will be shown for the results of these scenarios. Finally, some conclusions about the role of capture and utilization as a bridge between current and future technology will be discussed.