CO2 Utilization through Dry Reforming of Methane Process

Dry Reforming of Methane (DRM) is one of the CO2 utilization processes in which CO2 reacts with methane to produce syngas (a mixture of CO and H2). The DRM process faces 3 major challenges. Firstly, the highly endothermic nature of DRM (ΔH°298 K = 247 kJ/mol) is much higher than that of the conventional Steam Methane Reforming (SMR) which produces a higher quality syngas (higher H2/CO ratio). Secondly, due to low O/C and H/C ratios in the reaction mixture, catalyst deactivation due to coke formation is a major concern for the DRM process. Thirdly, the syngas ratio (H2/CO ratio) obtained from DRM is ≤ 1. This low syngas ratio is only suited for the production of few chemicals and cannot be extended to Fischer-Tropsch process or petrochemicals like methanol. Despite these obstacles, DRM has received a considerable amount of interest by both academia and industry. Using an Optimization approach, this study aims to better understand the CO2 balance of a process incorporating DRM and compare the performance with existing conventional processes. The objective is to ascertain the regions of operation where DRM helps reduce overall CO2 emissions of syngas production. In the first step of the study, all required data pertaining to CO2 emissions related to existing process was collected from various sources. Emission data for oxidant production (steam, oxygen) and upstream emissions for natural gas were taken GREET® software. In the next step, reformer modeling was performed in LINGO® software. A previously developed Gibbs Free Energy Minimization model [1] has been modified to include fugacity coefficients so that equilibrium calculations can be done at 20 bar pressure. Existing processes considered in the study were Steam Methane Reforming (SMR), Partial Oxidation of Methane (POx) and Auto-Thermal Reformer (ATR). These processes mainly differ in the oxidant/methane ratios and steam-to-carbon ratios used. These constraints have been set to simulate industrial reformer conditions. In the cases which involve DRM, 3 cases were used – stand-alone DRM, DRM+SMR in parallel and DRM+POx in parallel. Though CO2 utilization is the main objective of this study, it is essential to note that an objective function only involving CO2 minimization might result in lower syngas production which is undesirable as it directly reduces plant throughput. Hence, an epsilon method approach was used to iteratively reduce the overall CO2 emissions while maximizing overall syngas production. This method was repeated for each syngas ratio for each reformer case. Results indicate that stand-alone DRM helps achieve a near zero carbon footprint but only at syngas ratio close to 1. Combining equally sized DRM with SMR and POx units does not appreciably reduce overall CO2 emissions. The operating costs of reforming networks involving DRM are highly sensitive to the CO2 purification cost. This assessment shows that incorporating a DRM unit directly into any generic syngas production infrastructure does not have an appreciable reduction in CO2 emissions. Nevertheless, there could still be certain special scenarios where DRM helps in achieving the CO2 reduction objective. To investigate this further, case studies have been used to study the CO2 balance for different processing plants utilizing syngas of different H2/CO ratios. Preliminary findings show that in certain specific regions of operation, DRM assisted reforming helps in overall CO2 reduction objective. The operating cost comparison of these options will be the major criterion which will decide the future of these processing options incorporating DRM. REFERENCES [1] M. M. B. Noureldin, N. O. Elbashir, and M. M. El-Halwagi, “Optimization and selection of reforming approaches for syngas generation from natural/shale gas,” Ind. Eng. Chem. Res., vol. 53, no. 5, pp. 1841–1855, 2014. ACKNOWLEDGMENTS This work was supported by Qatar National Research Fund (QNRF), member of Qatar Foundation (NPRP X – 100 – 2 – 024). The statements made herein are solely the responsibility of the authors. The authors would like to appreciate the continuous support of our industrial partner, Total.