Hydrogen and methane are often considered as principle fuels of the future. Hydrogen is the most environmentally friendly fuel because its burning does not pollute the environment. Methane is next to hydrogen as CH4 emits less CO2 upon burning than other hydrocarbon-based fuels.
Some technological applications require a high purity of fuels. For example, fuel cells require hydrogen feed to contain less than 10 ppm CO in order to avoid catalysts poisoning. Removal of N2 from natural gas is essential to achieve efficient utilization of CH4 (e.g., to meet the requirements of pipes).
Adsorption-based technologies for purification of gases have attracted increased interest because of their energy efficiency. These technologies have the potential to achieve high selectivity in gas separation processes that need to be further developed and optimized.
In this presentation CuI-ZSM-5 will be considered as an adsorbent material for obtaining high quality H2 and CH4 gases free from impurities like CO and N2. Cu-ZSM-5 samples are prepared by conventional aqueous and solid state ion exchange (SSIE) of H-ZSM-5 with CuII and CuI ions, respectively. In the former case, CuII ions need to be reduced to CuI state, while in the latter CuI ions are directly inserted in the zeolite matrix by using a CuCl salt. In this study, the reduction of CuII in Cu-ZSM-5 material is achieved by CO, as followed by temperature-programmed reduction (CO-TPR). The adsorption properties of the samples are further characterized by in situ FTIR spectroscopy, pulse adsorption and temperature-programmed desorption of CO (CO-TPD). We find in this work, that CO strongly binds to CuI sites forming CuI-CO complexes; these complexes can be destructed at high temperature. Studying 15N2 adsorption, we observed formation of CuI-15N2 complexes and most of the CuI sites are occupied at low pressure; N2 is removed after prolonged evacuation at room temperature (RT). The effects of water vapor and O2 on the adsorption of CO and N2 are also studied by FTIR. In the presence of O2, the CuI state is stable up to 100oC. Addition of H2O vapor to the system with pre-adsorbed CO leads to formation of CuI(CO)(H2O)x complexes, which can be back converted to CuI-CO species upon outgassing at RT. N2 adsorption is hardly affected by H2O at low levels of humidity. The adsorption of H2 and CH4 is much weaker and practically take place only at low temperature. Finally, the potential of materials for gas adsorption/separation processes is verified by pulse technique and TPD. Under flow conditions, CO can effectively be captured at RT, while N2 is caught at water freezing temperature. Using the SSIE method, materials with almost completely exchanged protons are achieved. Thus, high number of Cu+ sites active for CO and N2 adsorption is obtained, while acid OH groups active for adsorption of both N2 and CH4 are eliminated.