CO2 adsorption at intermediate and low temperature by geopolymer-hydrotalcite composites

Geopolymer-hydrotalcites composites have been prepared and compared to explore their use in the field of CO2 adsorption for a wide range of working temperatures and relative applications. Two commercial hydrotalcites, with different Mg:Al ratio, were tested as fillers for a geopolymer matrix up to the maximum of 37 wt%. A high compressive strength (25–27 MPa) was retained in composites at 500 C, which is the temperature of hydrotalcites transformation into amorphous mixed solid oxides able to adsorb CO2. Composites were characterized in term of working capacity by testing the CO2 adsorption at low (35 C) and intermediate (200 C) temperature, with cycles of adsorption/desorption and regeneration at 500 C. At 35 C, CO2 physisorption capacity was between 0.079 and 0.154 mmol g1, while at 200 C, the total CO2 capacity value was between 0.114 and 0.141 mmol g1. 1. Introduction In recent years, the sequestration of CO2 downstream of industrial processes has been the subject of in-depth investigations [1]. The adsorption of CO2 is also of great importance for the direct use of biogas [2] where the methane must be purified before being introduced into the distribution network, as a renewable alternative to natural gas. The choice of the separation technology depends on the impact of the industrial process, on the efficiency of the adsorbent and on economic factors. Physical adsorption is a less-energy-intensive separation technology resulting an economic alternative in comparison to others [3]. In most cases, the solid adsorbents are in the form of monoliths or granules to facilitate handling and storage [4]. The adsorbent material must have high resistance to abrasion and withstand rapid changes in temperature and/or pressure, as the methods of regenerating the adsorbent with the release of CO2 require fluctuations in pressure and/or temperature [5,6]. The key parameter for assessing the validity of an adsorbent is the specific adsorption capacity of CO2 (moles of CO2 per kg of material), which depends on