Preparation Of Calcium Based High-Temperature CO₂Adsorbent And Adsorption Performance

Excessive emissions of greenhouse gases from the industrial processes are widely considered one of the main causes of global climate change. Carbon dioxide isan important greenhouse gas, andcarbon emission reduction is significant to prevent devastating damage with the climate system. High-temperature CO2adsorption technology is a cost-effective way to reduce CO2emissions directly from flue gases in power plants and from hydrogen preparation process by methane-steam reforming et al. Calcium based sorbent is a promising high-temperature CO2adsorbent material, since it has the advantages of lower preparation cost and higher CO2adsorption capacity. However, the rapid deactivation of calcium based sorbent due to sintering will reduce the CO2capture ability and lose the stability of sorbent during the multicyclic adsorption-desorption processes. This thesis will focus on the preparation of novel calcium based sorbents to improve the multicyclic adsorption/desorption stability and CO2capture ability at high temperature.Calcium oxide sorbents are prepared by directly calcining some raw materials, including oyster shell, scallop shell, limestone. precipitated calcium carbonate, calcium acetate monohydrate, calcium citrate tetrahydrate. and calcium d-gluconate monohydrate. The CO2capture performance and anti-sintering behavior of the prepared CaO materials are investigated. The deactivated lime sorbents are reactivated through hydration, and the effects of hydration reactivation on CO2capture performance, morphologies and microstructure of lime sorbents are studied. The practicability of the prepared CaO materials in calcium looping CO2capture is evaluated through comparing the CO2capture performance and the preparation cost of sorbents.Binary CaO-Al2O3and CaO-MgO sorbents. ternary CaO-Al2O3-MgO sorbent, are prepared through the liquid mixing reaction and following a four-step calcination method, where the precipitated calcium carbonate. aluminum nitrate, magnesium nitrate, and citric acid are used as raw materials. Effects of dopants (Al2O3and MgO) on the cyclic CO2capture performance of the prepared calcium-based sorbents are studied, and the anti-sintering mechanisms of three kinds of calcium based materials are analyzed and discussed. The results show that Al2O3doping can improve the cyclic CO2adsorption/desorption stability due to the formation of the inert supporting Ca3Al2O6framework, MgO doping can promote CaO carbonation reaction rate. By analysis of the microstructure of binary CaO-Al2O3material after many cycles, it is found that CaO grains are loaded on the inert supporting Ca3Al2O6framework. and grow and move on the Ca3Al2O6framework. thereby avoiding the sintering of material in a large range. Ternary CaO-Al2O3-MgO sorbent is composed of CaO. Ca3Al2O6and MgO. CO2capture ability and stability can be regulated by changing the mass ratio of Ca3Al2O6to MgO. For the ternary sorbent with high stability but low CO2capture ability due to low CaO content, the CO2capture ability can he improved by increasing the content of MgO without deteration of stability.Long-term CO2adsorption/desorption cyclic tests are performed using CaO-Al2O3CaO-MgO, CaO-Al2O3-MgO and CaO sorbents, and the CO2capture abilities and CO2capture efficiencies in calcium looping process are estimated. The results show that, both CaO-Al2O3and CaO-Al2O3-MgO sorbents can effectively reduce the make-up flow of fresh sorbent, when compared with calcium oxide sorbent prepared by precipitated calcium carbonate. The prepared CaO-Al2O3and CaO-Al2O3-MgO materials in this thesis should have good industrial application prospect in the high-temperature CO2adsorption field.