Research On Amine-loaded Porous Materials As Adsorbents For CO₂ Capture

The greenhouse effect has aggravated due to increasing emissions of greenhouse gases from the widespread use of fossil fuels such as coal, petroleum and natural gas, which leads to global warming and has negative impacts on the ecological environment of the earth. CO2 is considered to be the significant greenhouse gas because of its huge emissions. CO2 capture, sequestration and storage have been considered as the key means of mitigating the greenhouse effect, global warming and ecological deterioration. Therefore, researches on CO2 capture, sequestration and storage are of great importance. Adsorption has appeared as one of the promising methods for CO2 capture and sequestration with its low energy consumption, cost-effectiveness, relatively simple technological process, non-corrosive to the equipments and extensive applicability over a relatively wide range of temperatures and pressures. Development of new and high-efficient solid adsorbents is crucial to enhance competitiveness of this process.In this research, novel CO2 adsorbents were developed using bamboo charcoal, silica aerogel and activated carbon aerogel as carrier impregnated with amine (polyethylene polyamine(PEPA), polyethyleneimine(PEI) or tetraethylenepentarnine(TEPA)). The adsorbents were characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FITR), N2 adsorption/desorption and thermogravimetric analysis (TGA). The contents are as follows:(1) The effects of amine loadings, temperature and moisture on the CO2 adsorption performance of bamboo charcoal were investigated. The highest adsorption capacity of PEPA-loaded bamboo charcoal is 0.58 mmol/g-sorbent under the conditions of 23.1wt.% PEPA loadings,50℃ and 0.04% CO2. At 28.6wt.% of PEI loading in BC-PEI, CO2 reaches the highest adsorption capacity of 0.81mmol/g-sorbent under the conditions of 50℃ and 0.04% CO2. The CO2 adsorption capacities on amino polymers-modified bamboo charcoal increase in the presence of water vapor.(2) The silica aerogel and its composite aerogels were prepared by sol-gel method, hydrophobic modification and ambient pressure drying and then modified by amine. The effects of adsorbent materials (silica aerogel, its composite aerogels and commercial silica aerogel), preparation conditions (hydrophobic modifier, PEI loadings), adsorption conditions (temperature, pressure) on the CO2 capture performance of the amine-loaded silica aerogel and its composite aerogels were evaluated. The results show that the CO2 adsorption performance of the silica aerogel modified by trimethylchlorosilane and PEI is better than that of commercial hydrophobic silica aerogel modified by PEI. The saturated adsorption capacity of the silica aerogel modified by trimethylchlorosilane and PEI is 2.67mmol/g-adsorbent under the conditions of 25℃,5% molar fraction CO2,0.3Mpa adsorption pressure and 50wt.% PEI loadings. The increased adsorption pressure improves the CO2 adsorption capacity of the adsorbents.(3) The activated carbon aerogels were prepared by sol-gel method, ambient pressure drying and KOH activation. The effects of the mass ratio of KOH to carbon aerogel, type of amine, amine loadings, addition of polyethylene glycol or surfactants and adsorption temperature on the CO2 capture performance of amine-loaded activated carbon aerogel as well as the regeneration capability were examined. The adsorption capacity of amine-loaded activated carbon aerogel first experiences an upward trend with the increasing temperature then declines. The optimum adsorption temperature and amine loadings were 75℃ and 55wt.% respectively when the carbon aerogel was activated by KOH at the mass ratio of 1 and impregnated with PEI. In these optimum conditions, the PEI-loaded adsorbent reaches the highest adsorption capacity and amine utilization efficiency. The CO2 adsorption capacity of TEPA-loaded activated carbon aerogel is higher than that of PEI-loaded activated carbon aerogel. However, the low thermal stability of TEPA-loaded activated carbon aerogel makes it difficult to regenerate for cyclic use. In comparison, the PEI-loaded activated carbon aerogel has relatively stable regeneration capability. The CO2 adsorption capacity reaches 2.06mmol/g-adsorbent under the conditons of 75℃,5% CO2 molar fraction,0.3Mpa adsorption pressure and 55wt.% PEI loadings. Addition of polyethylene glycol facilitates the formation of carbamate type zwitterions and further enhances the CO2 adsorption capacity.