Pore Size Control Of Nano CaO-based Sorebent And Its CO₂ Sorption Performance

Calcium looping can be applied into not only flue gas decarbonization but also reactive sorption-enhanced reforming(ReSER)of methane for hydrogen production.Nano CaO-based sorbent is still the hot research area in calcium looping.In this thesis,in order to improve the sorption rate,nano CaO-based sorbents with various microstructures are prepared utilizing organic templates,and the influence of pore size on their CO2 sorption performance is investigated.Firstly,a series of nano CaCO3 were prepared using organic templates,such as polyvinyl pyrrolidone,and characterized by Brunauer-Emmett-Teller equation(BET)and Thermogravimetric Analysis(TGA).Results indicate that their special surface areas(SSA)are located in 0.83-10.15 m2/g and average pore diameters vary from 15 m/g to 173 m/g.Enlarging average pore diameter could promotes the thermal decomposition of nano CaCO3 and lowers the final decomposition temperature by 15?.The enlargement of pore diameter from 15 nm to 113 nm can also accelerate carbonation rate,and improve the carbonation conversion from 27.4%to 46.9%.This thesis proposes the concept of pore size distribution proportion for the first time,and investigates the relationship between this proportion and carbonation rate.The results indicates increasing the proportion of pore size in 26-96 nm from 0.38 to 0.91 could accelerate the fastest carbonation rate by 67.1%and the average rate in fast regime by 138.3%.SSA also affects the carbonation behavior.For nano CaCO3 with equal average pore diameter,increasing SSA could significantly improve the carbonation rate and corresponding conversion.There exist certain interactions among average pore diameter,SSA and carbonation conversion.Increasing average pore diameter at various SSA or increasing SSA at various pore diameters is in favor of the improvement of conversion.Therefore,this thesis calculates the partial correlation coefficients among them using statistical approach.The partial correlation coefficient of average pore diameter and conversion is 0.549,while the coefficient of SSA and conversion is 0.795,indicating the effect of SSA is more significant than average pore diameter.Additionally,a series of nano CaO-based sorbents were prepared by template method using alumina sol and nano CaCO3,and characterized by BET and TGA.The SSA of obtained sorbents is in 14.50-48.90 m2/g and their pore diameters vary in 15-55 nm.The kind of templates,content and aluminium source all will affect the SSA and pore size distribution of derived sorbents.Nano CaCO3 has little impact on sorbent's pore size distribution.The enlargement of average pore diameter could accelerate the decomposition rate of CaCO3,but has little effect on the decomposition curve and final decomposition temperature.Average pore diameter has vital influence on cyclic CO2 sorportion performance.At similar SSA,enlarging the diameter form 19 nm to 54 nm markedly accelerates the sorption rate and increases sorption capacity from 2.70 mol-CO2/kg-sorbent to 3.93 mol-CO2/kg-sorbent.It also deduces that pore size distribution proportion is related to CO2 sorption rate.Increasing the proportion of pore size in 47-96 nm could significantly accelerate the fastest carbonation rate and average rate in fast regime by 219.0%and 142.5%,respectively.At similar average pore diameter,increasing SSA could enhance the sorption rate and capacity.There exist certain interactions among average pore diameter,SSA and sorption capacity.At various levels,increasing pore diameter or SSA could both improve the CO2 sorption rate and capacity.The partial correlation coefficient of average pore diameter and sorption capacity is 0.733,while the coefficient of SSA and sorption capacity is 0.709,proving that pore diameter has more significant effect on sorption capacity rather than SSA.