Abstract
Biogas is a renewable fuel source of methane (CH4), and its utilization as a natural gas substitute or transport fuel has received much interest. However, apart from CH4, biogas also contains carbon dioxide (CO2) which is noncombustible, thus reducing the biogas heating value. Therefore, upgrading biogas by removing CO2 is needed for most biogas applications. In this study, an amine-functionalized adsorbent for CO2 capture from biogas was developed. Mesoporous MgO was synthesized and functionalized with different tetraethylenepentamine (TEPA) loadings by wet impregnation technique. The prepared adsorbents (MgO-TEPA) were characterized by X-ray diffraction (XRD) and N2 adsorption-desorption. The CO2 adsorption performance of the prepared MgO-TEPA was tested using simulated biogas as feed gas stream. The results show that the CO2 adsorption capacities of the adsorbents increase with increasing TEPA loading. The optimum TEPA loading is 40 wt.%, which gives the highest CO2 adsorption capacity of 4.98 mmol/g. A further increase in TEPA loading to 50 wt.% significantly reduces the CO2 adsorption capacity. Furthermore, the stability and regenerability of the adsorbent with 40% TEPA loading (MgO-TEPA-40) were studied by performing ten adsorption-desorption cycles under simulated biogas and real biogas conditions. After ten adsorption-desorption cycles, MgO-TEPA-40 shows slight decreases of only 5.42 and 5.75% of CO2 adsorption capacity for the simulated biogas and biogas, respectively. The results demonstrate that MgO-TEPA-40 possesses good stability and regenerability which are important for the potential application of this amine-based adsorbent.
Highlights
Due to rising fossil fuel prices, greenhouse gas emissions from fossil fuel combustion, and high energy demands, sustainable and renewable energy sources are needed [1, 2]
It has been reported that diffraction intensities are relative to the degrees of pore filling [43]. erefore, the incorporation of amine into the pore channels of the support possibly causes the loss of intensity [28]. is indicates that TEPA is loaded into the pore of the magnesium oxide (MgO) support, which is similar to that observed in MCM-41 loaded with polyethylenimine (PEI) [38]
The CO2 adsorption capacity decreases from 4.98 to 4.71 mmol/g, which is a decrease of only 5.42%. e CO2 adsorption capacity for the biogas exhibits the same trend, decreasing from 4.87 to 4.59 mmol/g after ten cycles, meaning the capacity loss of only 5.75%. ese capacity drops are lower than those of some amine-based adsorbents reported in the literature [49, 65]. e loss of adsorption capacity during the adsorption-desorption cycles could be due to the volatilization of the impregnated TEPA [51, 66]
Summary
Due to rising fossil fuel prices, greenhouse gas emissions from fossil fuel combustion, and high energy demands, sustainable and renewable energy sources are needed [1, 2]. To remove acid gases such as CO2 and H2S from gas streams, several technologies have been developed, including physical absorption, chemical absorption, adsorption, membrane separation, and cryogenic separation [8]. Erefore, modification or functionalization of the solid adsorbents by introducing amines into their porous structure for CO2 adsorption has attracted great interest [22]. Ese adsorbents have the potential to reduce the energy consumption compared to the large amount of energy required to heat bulk water for the regeneration of absorbent in the aqueous amine absorbent process and have high CO2 adsorption capacity and the ability to reduce the corrosion of equipment caused by high concentrated aqueous amine absorbent [10, 23]. Multiple adsorption-desorption cyclic stability of the adsorbents was tested by using simulated biogas and biogas as feed gas streams
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