A Novel Method to Prepare Silica Based Carbon Dioxide Capture Sorbent

by Di Wu

Institution: University of Akron
Department: Chemical Engineering
Degree: MS
Year: 2008
Keywords: Chemical Engineering; TEPA; 10oC/min; rate of 10oC/min; 150cc/min; Silica68B; CO2; rate of 150cc/min
Record ID: 1834128
Full text PDF: http://rave.ohiolink.edu/etdc/view?acc_num=akron1215095709


An innovative preparation method is developed to highly improve the carbon dioxide capture capacity of the silica sorbents. In the previously used sorbent treatment method, free hydroxyl groups of silica available for further reaction are obtained by silica dehydration at high temperature. This new approach, however, grafts tetraethylenepentamine (TEPA) onto silica surface directly via incipient wetness impregnation (IWI) of TEPA/ethanol solutions at room temperature. The CO2 adsorption/desorption performance of the catalysts is studied by Diffused Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and Mass Spectrometer (MS) spectroscopy both qualitatively and quantitatively. The concentration of TEPA/ethanol solutions influences the deposit process of pentamine molecules onto silica particles by controlling the concentration differential of TEPA between the bulk solution and the surface layer. Samples treated with more concentrated solutions had higher maximum carbon dioxide adsorption values, calculated from the calibrated CO2 desorption peak area of MS spectra. The loading amount of solution also affects the mass transfer rate and equilibrium of TEPA. After the concentration is equilibrated between the bulk and the surface, the system lost the concentration gradient between bulk solution and silica surfaces, excessive pentamine solution removes the grafted pentamine molecules, and makes the carbon dioxide capture capacity curve drop from the peak point. The 0.03g silica treated by 2%, 10% and 20% TEPA/EtOH solution got the CO2 adsorption capacity of 1545.03, 4590.28 and 7674.99 µmol/g-sorbent, respectively. Two pretreatment methods of silica sorbents, ethanol pretreatment and carbon dioxide pretreatment, are used to further enhance the adsorption performance. In the former pretreatment, ethanol solvent is injected before each injection of TEPA solution, and in the latter, TEPA solution is injected in the atmosphere of a carbon dioxide gas. The principles behind these pretreatments underlie mass and momentum transfer processes. After the injection of TEPA/ethanol solution, the TEPA layer on silica surface becomes more and more concentrated with the solvent evaporation. Pores and channels are likely to be blocked by the high viscous TEPA on silica surfaces. Sufficient solvent molecules in the ethanol pretreatment help more than keep the concentration gradient between the bulk and surface and maintain a driving force to deposit the TEPA onto silica surfaces, an appropriate viscosity assists TEPA molecules diffuse deeper. 0.03g silica at the loading of 200 µl, 20% TEPA/EtOH solution, the maximum CO2 adsorption capacity is 8362.36 µmol/g-sorbent with Ethanol pretreatment approach. The grafted pentamine molecules on silica surface can form inter-molecular H-bonds, which consume the functional amine groups and reduce the surface area available for CO2 capture. Carbon dioxide was used to protect these free NH groups in the carbon dioxide pretreatment. DRIFTS and MS spectroscopy analysis shows either way gives…