Preparation And CO₂ Adsorption Capacity Of CaO-based Sorbent Via PSS-assisted Fast Precipitation

Environmental change and climate disasters caused by excessive emissions of carbon dioxide as main anthropogenic greenhouse gases pose a serious threat to the survival and long-term development of mankind. The effective technology, the capture, storage and utilization of carbon dioxide, experiences rapid development in recent years. Aiming at the emissions situation of high concentration and high-temperature carbon dioxide in the process of coal gas technology, CaO-based sorbent has recently drawn increasing attention due to wide availability, low cost, high initial capacity and fast kinetics. In this thesis, the emphasis was put on the preparation and CO₂ adsorption capacity of CaO-based sorbents via sodium poly-?styrene sulfonate??PSS?-assisted fast precipitation.PSS was added during the precipitation process of CaCO3. Due to the three dimensional structure of PSS and the strong dispersion effect of sulfonic acid group, the porous sphere CaCO3 was obtained and its BET surface area enlarged to 110.5m2/g. The obtained porous structure facilitated CO₂ to diffuse and react with inner CaO. The adsorption process was mostly occurred in rapid phase and the initial capacity was enhanced to 74.2%.Furthermore, in order to gain sorbents with high anti-sintering property, proper amount of Mg2+ precursor solution was added during the fast precipitation process. CaO-based sorbent maintained the porous spherical structure with the addition of Mg2+. SEM-EDS results indicated the uniform distribution of Ca and Mg in the sorbent. MgO with high melting point distributed evenly among CaO particles, inhibiting the serious sintering during the adsorption/desorption process. As a result, the carbonation capacity was 59.0% and almost stable in the process of 18 carbonation and calcination cycles, presenting excellent capacity and stability.On the other hand, CaCO3 precipitation modified by PSS was further treated by hydro-thermal process. The samples presented cotton-shaped and the average pore size enlarged over 20 nm, which facilitated the reaction between CO₂ and the inner CaO sorbent. As a result, the residual capacity was enhanced and the carbonation capacity of sorbent pretreated at 100 oC for 4h was 50.4% after 18 carbonation and calcination cycles. The capacity increased by almost 20% compared with sorbent without treatment, proving that hydro-thermal treatment could enhance the long-term stability of pure CaO sorbent.