Synthesis And CO₂Adsorption Of Porous Titanium Dioxide Composites

With the growth of world economy, the amount of anthropogenic CO2emissions will continue to increase, which causes serious concern for the global climate change, since CO2is generally accepted as a greenhouse gas with significant contribution to global warming. To mitigate the CO2emissions, carbon capture and sequestration (CCS) is considered one of the most promising solutions. Among all kinds of CO2capture methods, adsorption via solid sorbents has been proposed as an energy-efficient method. However, the success of this technology depends to a great extent on devising sorbents with excellent CO2adsorption performance. In this thesis, we synthesized a series of amine-impreganted porous titanium dioxide composites and their CO2adsorption properties were investigated. The summaries of the results are as follows:1. Synthesis of porous titanium oxides with different surface areas and pore volumes by different alkylamines as templates.Porous titanium dioxides were synthesized by a ligand-assisted templating method using alkylamine as the template and titanium isopropoxide as the precursor. In order to achieve porous titania with different surface area, pore volume, pore size and pore distribution, alkylamines with different lengths of carbon chain were chosen as the templates such as hexylamine, octylamine, dodecylamine and octadecylamine. During the adsorbent synthesis process, the aging process is the key to get structurally stable porous titania materials. In this thesis, two aging methods were explored. The first one is to age the mixture of reactants by gradual raising the heating temperatures from room temperature to140℃and the second one is to treat the mixture by ultrasonic waves for12-24h. Extraction by alcohol washing is used to remove the templates. The effect of the washing time on the porous texture of the as-synthesized titania was also investigated. The results show that a sorbent (C8-Ti) synthesized using an octylamine template has the maximum surface area of1037m2/g and pore volume of0.62cm3/g, respectively, among all the samples. During the synthesis of C8-Ti, the reactant mixture is gradually heated to140℃and each alcohol washing time is one day.2. Preparation and CO2adsorption of titania modified by diethylenetriamineHigh-surface-area titanium oxides (C8-Ti) were modified with different amount of diethylenetriamines (DETA) by a wet impregnation method for CO2adsorption. These new composite sorbents were characterized by powder X-ray diffraction, transmission electron microscope, nitrogen adsorption, Fourier transform infrared spectroscopy and thermogravimetric analysis. CO2capture performances of the adsorbents were tested in a fixed-bed reactor. Experimental results revealed that titania with30wt%DETA loading exhibited a high CO2adsorption capacity of2.30mmol/g under the conditions of similatd flue gas (10.0%(v/v) CO2in N2at75℃, ambient pressure), which is higher than analogue DETA impregnated SBA-15, and all the other DETA-impregnated materials reported in the literature. This high adsorption capacity is possibly due to the synergy between the guest DETA and the porous TiO2supports in the adsorption of CO2. It was also found that at low temperatures, adsorbents with moderate DETA contents are more capable than their highly loaded counterparts possibly due to the increased dispersion of amine sites and the strong and productive interactions between the DETA and surface of Ti oxide. Cyclic CO2adsorption-desorption tests demonstrated that with moderate amine loading, the titania-based sorbent is regenerable and stable.3. Effects of porous texture of the titania supports, type and loading amounts of organic amines on the CO2adsorption performaces of the titania compositesA series of titania composites were synthesized by modifying different pristine titania supports with different kinds and loading amounts of organic amines. CO2adsorption performances of these composites were investigated. The results show that the CO2uptake capacity increases with increasing loading amount of amines. Under the same amine loading level, the composite prepared by amine with smaller size has a higher CO2adsorption capacity. Generally, higher surface area and pore volume of the supports are benificial to the CO2adsorption, while pore size of the support also plays an important role in determining the CO2uptake of the composites. Larger pore size allows the better distribution of amine sites on the pore channel of the support and thus can improve the CO2adsorption capacity of the composites.