Cyclic Reaction Characteristic Of Co-capture CO₂/SO₂and Kinetic Study For Synthetized Anti-sintering Calcium-based Sorbents

It is significant to control and reduce CO2emissions in industrial processes forpreventing global warming and green house effect. Calcium-based sorbents with theircarbonation/calcinations cycles are widely employed as one of most importantapproaches for CO2capture. High efficiency and anti-sintering calcium-based sorbentsare pursed to improve cyclic reaction capacity. So far, most of methods for synthesizingcalcium-based sorbents are complex. A new simple method to produce high capacitysorbents should be found. For new synthesized sorbents, cyclic reaction characteristicfor co-capture CO2/SO₂should be investigated. The separation of rapid and slowreaction step for carbonation process, carbonation kinetics for calcium-based sorbents,calcination kinetics and intrinsic kinetics for carbonation should be further studied. Theabove scientific questions are focused and studied. The results can provide theoreticalsupport for co-capture CO2/SO₂with calcium-based sorbents. The research hasimportant academic value and application prospect.Current situation for CO2capture with calcium-based sorbents were concerned. Asimple wet mixing method for producing new sorbents was used. Effects ofcalcium-precursors, additives on cyclic CO2absorption capacity and stability wereinvestigated. The anti-sintering and high efficiency calcium-based sorbents weresynthesized. The co-capture CO2/SO₂characteristic for synthesized sorbents wasstudied. Effects of SO₂on cyclic CO2capture capacity of calcium-based sorbents wereanalyzed. Carbonation/carbonation kinetics for calcium-based sorbents was investigated.Models of rapid and slow reaction steps in carbonation were discussed. The key kineticparameters were obtained. The intrinsic kinetic for calcium-based sorbents wasspecially investigated. The reaction rate constant and activation energy in differentdriving power were analyzed. The control mechanism of variation reaction order wasdiscussed.The calcium-based sorbents produced from organic precursors such as calciumgluconate, calcium lactate and calcium formate were investigated for cyclic CO2capture.The results show that G-CaO sorbent produced from calcium gluconate exhibits thehighest cyclic absorption and stability. According to experimental study on additiveelements and categories, Mg elements can effectively improve cyclic absorptioncapacity while Al elements can improve cyclic stability. After many cycles tests, G（Ca）-G（Mg）75shows the best cyclic absorption efficiency while G（Ca）-L（Al）75has the highest cyclic stability. The two sorbents are high-efficiency calcium-based sorbents for CO2capture. The reaction characteristic for synthesized sorbents related to specific surface area and pore volume. The absorption reaction can be benefited on higher specific surface area and pore volume.Cyclic characteristic of co-capture CO2/SO2with synthesized calcium-based sorbents were investigated. The micro-structure changes of calcium-based sorbents caused by SO2were observed. The results show that SO2seriously impedes CO2capture by calcium-based sorbents. When number of cycles increase, CO2absorption capacity decreases while cumulative SO2absorption capacity increases. Total calcium utilization ratio first decreases and then increases while calcination decomposition ratio decreases with number of cycles. In co-capture CO2/SO2process, grains reunite becomes seriously with number of cycles, specific surface area decreases rapidly. Bigger pores caused by sintering were emerged. The above are major reasons for rapid decrease of CO2capture capacity. The CO2capture capacity decreases more quickly with higher SO2concentrations while cumulative SO2conversion ratio becomes much higher.In carbonation/calcination cycle kinetics study, Logistic equation was employed to fit conversion ration curve as a function of time at the rapid reaction step. Avrami equation can well describe the conversion ration variation with time. The key kinetic parameters in calcination stage were obtained by a non-isothermal method. According to conversion ration variation with number of cycles, conversion rations of G（Ca）-G（Mg）75and G（Ca）-L（Al）75stabilize after200cycles, with their value0.813and0.735respectively.In the intrinsic kinetics study of carbonation for calcium-based sorbents, the variable reaction order was found. The intrinsic reaction order changed abruptly from first-order to zero-order when the driving force （PCO2-PCO2,eq） exceeded an equilibrium value about lOkPa in this work. The intrinsic reaction rate constants were relative to （PCO2-PCO2,eq）.The activation energies were found to be24.9kJ/mol and21.12kJ/mol for G（Ca）-G（Mg）75and G（Ca）-L（Al）75, respectively. The transition of reaction order suggested a shift of control mechanism. When the order was first, carbonation was controlled by whereas, controlled by when the order was zero. In this thesis work, a series of investigations for calcium-based sorbents was taken systematically, such as preparation of synthesis sorbents and cyclic reactioncharacteristics for CO₂capture and simultaneous CO₂/SO₂capture. Anti-sinteringcalcium-based sorbents were obtained with high reaction capacity. The reactioncharacteristics and pattern for simultaneous CO₂/SO₂capture were also concluded. Thekinetic model and key parameters were achieved for carbonation/calcination cyclicreaction. Besides, the control mechanism of variable order reaction for intrinsic surfacereaction stage was studied. This thesis work could help advancing the further researchfor simultaneous CO₂/SO₂capture and enriching the research findings for CO₂capture,and also gives a theory support for the utilization of calcium-based sorbents whensimultaneously capturing CO₂/SO₂.