(558g) Design and Intensification of Integrated Carbon Capture and Conversion to Chemicals

To address the rising CO₂ levels in the atmosphere, research efforts are directed towards making widespread deployment of carbon capture, utilization and sequestration (CCUS) cost-effective. CO₂ utilization can be implemented to produce as much as 2 Gt/yr. of fuels and 200 Mt/yr. of chemicals.¹ Utilization of CO₂ to deliver high-value products such as fuels and chemicals is an attractive and promising option. Existing standalone capture and utilization technologies perform energy-intensive CO₂ capture from dilute streams such as flue gas and then convert the captured CO₂ to syngas which is again energy-intensive. To intensify the capture and utilization steps to reduce energy inputs and hence costs, we design and optimize modular and multi-functional processes for direct utilization of CO₂ from flue gas to value-added fuels and chemicals.

We propose one such intensified process exploiting an integrated adsorption-purge-reaction system², which operates cyclically involving CO₂ adsorption from flue gas in the first step, followed by purging due to methane rich feed in the second step. The desorption of CO₂ from the column is achieved by a concentration driving force difference brought about by introduction of a second feed with a composition very different from that of flue gas. The N₂ separated from the column is vented out, while the CH₄/CO₂ purge mixture becomes the feed for dry reforming of CO_2­ in the subsequent reactor section. A variety of methane rich feeds such as natural gas, fuel gas, unused methane, biogas etc. can be used by the process. The novel aspect of the process is the elimination of pressure and temperature swings employed in every cycle in conventional standalone CO₂ capture and integrating it with reactor feed pre-mixing which results in reduction in the overall cost of CO₂ capture and utilization. The process is integrated with existing CO₂ capture and utilization technologies.

The entire process is simulated using high-fidelity non-linear algebraic partial differential equation (NAPDE) model to identify the key decision variables, process metrics and the interactions between the adsorption and reaction sections. While it is important to operate the process such that it meets constraints pertaining to greenhouse gas emissions and product quality, it is only possible to obtain the values of these constraints after performing computationally intensive simulations. This poses a challenge in identifying the feasible and optimal operating conditions of the process. A data-driven constrained grey-box optimization framework is employed to obtain feasible operating conditions and to proceed towards the optimal objective desired. Applying the optimization framework, we are able to achieve a maximum of 99.67% net overall CO₂ utilization while accounting for auxiliary CO₂ emissions at costs ranging from $110-$130 per ton of syngas. About 14.6% of the total CO₂ input to the process is captured with low cost “directly” from flue gas while still maintaining 91% overall CO₂ utilization. The rest of the CO₂ input is sourced from existing capture plants integrated with the developed process.

Using the above design, intensification and optimization framework, we also develop a novel cyclic process for the direct utilization of CO₂ to methanol. This process again uses a two-step process and exploits synergies between CO₂ capture, CH₄/CO₂ mixing, syngas production and syngas conversion to methanol. In this presentation, we will further elucidate the techno-economic feasibility of the methanol process.

References:

(1) Quadrelli, E. A.; Centi, G.; Duplan, J.-L.; Perathoner, S. Carbon Dioxide Recycling: Emerging Large-Scale Technologies with Industrial Potential. ChemSusChem 2011, 4 (9), 1194–1215.

(2) Iyer, S. S.; Bajaj, I.; Balasubramanian, P.; Hasan, M. M. F. Modular Process Intensification of Carbon Capture and Conversion to Syngas. Submitted.