(507g) Design of Reactive Separation Process for CO2 Sequestration From Exhaust Gases of Process Plants

Methanol production by catalytic reduction of carbon dioxide is an option for carbon sequestration to reduce the carbon footprint of power plants and other process industries. Pre- and post-combustion capture of carbon dioxide has been a big area of research. For example, in coal fired thermal power plants, gasification of coal is used for pre-combustion capture carbon dioxide. Chemical absorption processes using mixtures of amines are well established for post-combustion capture. Of various technologies for CO₂ sequestration, reduction with hydrogen to produce methanol is of interest to us.

Hydrogen is mostly produced from the natural gas. Electrolysis of water, though an energy intensive alternative, is also used for production of hydrogen. Hydrogen so obtained can be used for catalytic hydrogenation for CO₂ sequestration. The catalytic hydrogenation of CO₂ over promoted Cu-ZnO catalysts under pressurized conditions produces mainly CH₃OH, CO and H₂O [1, 2]. At higher temperature, a small amount of CH₃OCH₃ (as well as some methane) may also be produced. Therefore, main reactions are shown in the following equations: (a) CO₂ + 3H₂ ↔ CH₃OH + H₂O and (b) CO₂ + H₂ ↔ CO + H₂O. Increase in selectivity could also be due to decrease in CO yield through the reaction of CO with hydrogen to produce methanol (c) CO + 2H₂ ↔ CH₃OH.

This work will highlight a range of different reactive separation processes for catalytic synthesis of methanol for sequestering carbon dioxide. The key objective is to design and optimize a viable option for catalytic conversion of CO₂ to methanol on Cu/ZnO based catalyst. The traditional design or optimization method is to increase the productivity of methanol. However, the objective here is to meeting the environmental regulation of CO₂ emission by sequestration. Different approaches by which we can enhance the conversion of CO₂ will be studied. Some of them include, (1) manipulating the temperature / pressure profiles in order to drive the reaction for methanol synthesis depriving other reactions [1], and (2) removal of methanol as soon as it is formed while maintaining the conditions favorable for methanol synthesis.

Keywords: CO₂ Sequestration, Thermodynamic analysis, Reactive separation, Kinetic analysis

References

[1] H. Arakawa, J.-L. Dubois, and K. Sayama, Selective conversion of CO₂ to methanol by catalytic hydrogenation over promoted copper catalyst, Energy Convers. Mgmt, 33 (5-8), 1992, 521-528.

[2] K. Takeshi, H. Itaru, M. Hirotaka, M. Kozo, U. Kenji, W. Taiki, and S. Masahiro, Kinetic study of methanol synthesis from carbon dioxide and hydrogen, Applied Organometal. Chem., 15, 2001, 121-126