Low-cost natural carbon dioxide sorbents available in the Czech Republic

Abstract

The article deals with the issue of carbon dioxide adsorption on mineral samples, two of which are rich in montmorillonite and one in kaolinite. The last comparative sample is clinoptilolite, which is widely used as a sorbent in agriculture, water treatment, etc. The theoretical part summarizes several current researches on the use of bentonites as adsorbents, both in their raw form and after various chemical treatments. The study presented here does not suggest any modification procedure, but tests untreated samples and samples subjected to calcinations at temperatures of 250-750 ° C. The calcination of units of grams was carried out by means of a carousel TGA, which made it possible to record curves of mass changes and to obtain a sufficient amount of calcinates for further analyses at the same time. From the point of view of achieving the highest specific surface area and the total pore volume, the optimal calcination temperature for the phyllosilicate samples ranged from 250 to 450 °C. Natural zeolite, on the other hand, showed a deterioration of both of these parameters at any temperature exceeding 150 °C. The same temperature dependence was found in the case of adsorption capacities determined by an automatic analyser Autosorb IQ using pure CO2. Measurements on this instrument also confirmed that selected inexpensive natural materials provide comparable adsorption capacities as the commercially available 13X molecular sieve used as a reference sample. Based on the performed analyses, the initial conditions of sample preparation for the upcoming measurement of adsorption properties on a larger apparatus operating in the PSA/TSA mode were determined. The primary aim of the tests using the selfdesigned high-pressure adsorption unit will be to determine the adsorption capacities that will take into account the temperature and pressure conditions in a real postcombustion carbon dioxide capture system. Unlike the automatic analyser described above, it will be possible to quantify the influence of important factors such as: flue gas humidity, the presence of other permanent gases (especially SO2) and last but not least various CO2 partial pressures and absolute pressure during adsorption and desorption. The experiments will verify the extent to which the presence of noncondensing moisture in the gaseous mixture is problematic. In the case of phyllosilicates, it is not just the parallel adsorption of H2O that affects the adsorption capacity available for CO2 capture. It will be empirically determined to what extent the swelling of the sorbent occurs in the wet gas, changing the gas flow through the layer and especially the pressure loss. The results of measurements on high-pressure apparatus will be the basis for the design and construction of a larger pilot scale unit.