(331c) Superstructure-Based Optimization of Carbon Dioxide Conversion and Utilization Via Syngas Intermediate

CO₂ is one of the primary components in greenhouse gas (GHG) emissions due to human activities [1]. Global levels of CO₂ emissions have been steadily increasing over the decades reaching an unprecedented high of 45 Gt in 2017. An effective way to mitigate the rising GHG emissions is to convert the CO₂ present in feedstocks such as flue gas, natural gas and biogas to syngas [2]. In chemical industries, syngas is prevalently used as an intermediate for manufacturing several value-added products including methanol, dimethyl ether, olefins and gasoline [3,4]. Most of the previous optimization studies on CO₂ conversion and utilization have focused on producing specific fuels or chemicals, thereby resulting in sub-optimal process flowsheet routes. This creates a need for developing a comprehensive superstructure encompassing viable alternatives to obtain optimal CO₂ utilization and process costs [5].

In this work, we postulate a superstructure consisting of multiple layers to form process intermediates and products. To achieve a desired conversion, each layer is comprised of necessary reaction, separation and product upgradation steps along with heating and compression steps which produce auxiliary emissions. The first layer of the superstructure consists of seven process alternatives (dry reforming, partial oxidation, steam methane reforming, auto-thermal reforming and their hybrid combinations) for syngas formation starting from flue gas, natural gas and biogas. The second layer forms intermediates (e.g., methanol, dimethyl ether, heavy olefins) which can further be processed to produce hydrogen-based fuels and chemicals in subsequent layers. The overall superstructure is then used to identify an optimal CO₂ conversion and utilization route in GAMS environment with two separate objectives – maximization of net CO₂ utilization and minimization of total annualized cost. Specifically, we obtain a maximum net CO₂ utilization of 57% for feedstock conversion to syngas with consideration of the auxiliary emissions. The presentation would also cover further conversion of syngas to subsequent value-added products.

References

[1] M. M. F. Hasan, F. Boukouvala, E. L. First, and C. A. Floudas, “Nationwide, regional, and statewide CO2 capture, utilization, and sequestration supply chain network optimization,” Ind. Eng. Chem. Res., vol. 53, no. 18, pp. 7489–7506, 2014.

[2] S. S. Iyer, I. Bajaj, P. Balasubramanian, and M. M. F. Hasan, “Integrated Carbon Capture and Conversion To Produce Syngas: Novel Process Design, Intensification, and Optimization,” Ind. Eng. Chem. Res., vol. 56, no. 30, pp. 8622–8648, 2017.

[3] K. Roh, R. Frauzem, T. B. H. Nguyen, R. Gani, and J. H. Lee, “A methodology for the sustainable design and implementation strategy of CO2 utilization processes,” Comput. Chem. Eng., vol. 91, pp. 407–421, 2016.

[4] Z. Yuan, M. R. Eden, and R. Gani, “Toward the development and deployment of large-scale carbon dioxide capture and conversion processes,” Ind. Eng. Chem. Res., vol. 55, no. 12, pp. 3383–3419, 2015.

[5] P. Balasubramanian, I. Bajaj, and M. M. F. Hasan, “Simulation and optimization of reforming reactors for carbon dioxide utilization using both rigorous and reduced models,” J. CO2 Util., vol. 23, pp. 80–104, 2018.