| Summary: |
As a result of stricter environmental regulations worldwide, alternatives to coal fired power plants for production of electricity and hydrogen are needed. In this sense, integrated coal gasification combined cycle (IGCC) plants have been regarded as one of the most promising technologies for energy production of the future, eliminating nearly all air pollutants and potentially greenhouse gas emissions [1]. The water-gas shift (WGS, CO + H2O = H2 + CO2) is a reversible and exothermic reaction used to increase the hydrogen contents of the syngas generated on such plants. Typically, further H2 clean-up units are needed (e.g., PSA or cryogenic distillation) to increase the final H2/CO ratio for applications such as ammonia or methanol production. For stationary fuel cells, high-purity hydrogen streams are required.
Generally speaking, the CO conversion in the WGS reaction can be enhanced by selectively removing one or both products (H2 and/or CO2) from the reaction zone. This can be attained in a membrane reactor (MR) where the membrane separation process is coupled with the catalytic reaction in a single unit. However, improvements at the catalytic level are also crucial. In recent years, gold-based and platinum-based catalysts have gained much attention to overcome the limitations of the samples typically used to conduct such reaction. Actually, Au- and Pt-based catalysts are described to undergo a lower inhibition effect by the reaction products when compared with the traditional samples . However, due to the low particle size of such catalysts, the packed-bed reactor configuration is not suitable for industrial applications. Therefore, the deposition of such catalysts onto monolith structures should be an important progress. With this improvement, significant advantages for conducting the WGS reaction are expected, namely operating at much higher space velocities than with particulate catalysts, lowering the pressure drops, reducing the amount of catalyst requi  |
Summary
As a result of stricter environmental regulations worldwide, alternatives to coal fired power plants for production of electricity and hydrogen are needed. In this sense, integrated coal gasification combined cycle (IGCC) plants have been regarded as one of the most promising technologies for energy production of the future, eliminating nearly all air pollutants and potentially greenhouse gas emissions [1]. The water-gas shift (WGS, CO + H2O = H2 + CO2) is a reversible and exothermic reaction used to increase the hydrogen contents of the syngas generated on such plants. Typically, further H2 clean-up units are needed (e.g., PSA or cryogenic distillation) to increase the final H2/CO ratio for applications such as ammonia or methanol production. For stationary fuel cells, high-purity hydrogen streams are required.
Generally speaking, the CO conversion in the WGS reaction can be enhanced by selectively removing one or both products (H2 and/or CO2) from the reaction zone. This can be attained in a membrane reactor (MR) where the membrane separation process is coupled with the catalytic reaction in a single unit. However, improvements at the catalytic level are also crucial. In recent years, gold-based and platinum-based catalysts have gained much attention to overcome the limitations of the samples typically used to conduct such reaction. Actually, Au- and Pt-based catalysts are described to undergo a lower inhibition effect by the reaction products when compared with the traditional samples . However, due to the low particle size of such catalysts, the packed-bed reactor configuration is not suitable for industrial applications. Therefore, the deposition of such catalysts onto monolith structures should be an important progress. With this improvement, significant advantages for conducting the WGS reaction are expected, namely operating at much higher space velocities than with particulate catalysts, lowering the pressure drops, reducing the amount of catalyst required (mass transfer resistances are decreased) and achieving faster responses to transients [3]. In this project, we propose the innovative approach of using monolith structures to support the catalyst combined with MRs.
The application of the MR for the WGS reaction has been reported widely. It can be found in the literature that, by using different types of membranes, high CO conversions, beyond the thermodynamic equilibrium ones or close to 100%, can be attained [e.g., 4]. Despite its price, Pd and its alloys are the materials mainly envisaged in this application due to the unique ability to permeate only H2. However, the main difficulty preventing the application of these types of materials is the preparation of thin (highly permeable), defect free (highly selective), sulfur resistant, and durable membranes in a large scale.
In this project thin Pd-based membranes will be synthesized by both diffusion welding and electroless plating techniques. The performance of the proposed approach can still be improved by combining the MR concept with the sorption-enhanced of CO2 for its selective removal (removing so both products from the reaction zone). In addition, this would allow decreasing the required Pd membrane area, often limitative due to its price. The concept of in situ capture of CO2 at high temperatures using a selective adsorbent is another intensive research area, where improvements on the adsorptive material are required. Hydrotalcite materials have been regarded as cost-effective adsorbents for CO2 separation and capture at high temperature. In addition to their low price, these natural clays show enhanced CO2 adsorption capacity and slow rate of deactivation in presence of water vapor when impregnated with alkaline metals like K, Cs or Sr. |