Biogas is a renewable energy source of methane that can be used directly as fuel for combustion engines, gas turbines, and fuel cells as an energy source after its purification. CO2 being the major contaminant (30–50%), its removal from methane becomes one of the critical steps in upgrading to increase the energy content of the biogas. Commercial techniques such as scrubbing and pressure swing adsorption has major disadvantages like corrosion problems, heavy use of water and decreased efficiencies due to the high temperatures used in the regeneration step. Production of CNG requires high pressures in order to separate CO2 from CH4 and compressor costs can be high. CO2 adsorption using amine based silica is a low pressure process and using this reduces the capital and operating expenses of compressors required for biogas upgrading. Mesoporous silica functionalized with amine groups are have proven to be good adsorbents of CO2 with high selectivity, low energy utilization and low regeneration costs. APTES modified silica has been studied before but never tested for CO2 separation with actual landfill gas. Also, there is an interest in studying EDTA functionalized silica, since they have more amine groups present and are likely to behave as a better adsorbent. In work reported here, amine modified silica using APTES and EDTA were prepared using conventional grafting techniques. Techniques including XRD, N2 physisorption, FTIR, TPO were used for catalyst characterization. We tested a series of APTES modified SBA-15 for adsorption experiments of CO2 at room temperature and 1 atm for a dry 50% CO2 in He feed. Results show that with an increase in APTES loading (from 21 wt % APTES to 50 wt% APTES) the CO2 adsorption capacity increases. The adsorption capacity of 21 wt % APTES to 50 wt% APTES was 0.46 mmol CO2/g and 1.8 mmol CO2/g respectively. The adsorbents were regenerated at 100 oC. The APTES modified SBA-15 sample after two regeneration cycles showed 18% decrease in CO2 adsorption capacity. The future work will include testing the EDTA modified silica with different loadings and finding the minimum loading for each adsorbent to get the maximum adsorption capacity. The best sample will be tested against real landfill gas which contains 30 - 40 % CO2 as the major contaminant in addition to small amounts of impurities like H2S, NH3, O2, N2, H2 and CO. The regeneration for large number of cycles will also be tested.

Cabon dioxide removal from surrogate biogas using amine based silica sorbents

2019 Spring National Meeting

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