钾钠盐类对钙基CO2吸附剂循环碳酸化的影响

钙基CO2吸附剂如石灰石在循环煅烧/碳酸化过程中随着循环次数的增加碳酸化转化率迅速衰减，这对CO2的捕捉极为不利。该文在常压煅烧/碳酸化反应器系统上研究KCl、K2CO3、NaCl和Na2CO3作为添加剂对CaCO3循环碳酸化特性的影响。结果表明，在初始循环时，钾钠盐类的添加造成CaCO3碳酸化转化率的明显衰减，但随着循环次数的增加，添加剂使CaCO3转化率下降缓慢，反而高于原CaCO3转化率。钾盐较钠盐对CaCO3循环捕捉CO2能力有更好的促进作用，钾/钠氯化物比钾/钠碳酸盐效果更好。在CaCO3中添加质量比为0.5%~0.6%的KCl，碳酸化温度在680~700℃时，吸附剂能取得最高的循环碳酸化转化率，经20次循环反应后转化率可达0.44，而在相同条件下原CaCO3转化率仅为0.21。KCl对CaCO3碳酸化的影响包括两方面。一方面，KCl虽然在初始循环时使CaCO3煅烧后的比表面积和比孔容减小，但在长期的循环中能够使它们保持稳定；另一方面，KCl能增加反应中碳酸化产物层的缺陷浓度，有可能增大未反应Ca离子通过产物层的扩散率。因此添加了KCl的CaCO3能够在长期煅烧/碳酸化循环中保持良好的碳酸化性能。

Effect of Potassium and Sodium Salts on Cyclic Carbonation of Calcium-based CO2 Sorbent

It is unfavorable to CO2 capture that the carbonation conversion of calcium-based CO2 sorbent decays sharply as the number of cycles increases during the calcination/carbonation process. The effects of KCl, K2CO3, NaCl and Na2CO3 as the additive on cyclic carbonation characteristics of CaCO3 were investigated in the atmospheric calcination/carbonation reactor system. The result shows that CaCO3 doped with potassium or sodium salts exhibits a substantial decrease in carbonation conversion at initial couple of cycles; however, it displays a slow decay in conversion with number of cycles. The carbonation conversion of CaCO3 doped with the additive is higher than that of original CaCO3 after several cycles. Potassium salt has better effect than sodium salt on improving CO2 cyclic capture capacity of CaCO3, similarly, potassium or sodium chloride shows better effect than potassium or sodium carbonate. CaCO3 doped with 0.5%~0.6% of KCl shows the highest cyclic conversion at carbonation temperature of 680~700 ℃, and it achieves a conversion of 0.44 after 20 cycles, while original CaCO3 reaches a conversion of 0.21 at the same reaction conditions. The effect of KCl as the additive on carbonation of CaCO3 includes two aspects. On the one hand, although KCl decreases specific surface area and pore volume of calcined CaCO3 at initial cycles, it can maintain specific surface area and pore volume during multiple cycles; on the other hand, KCl increases the void defect concentration in CaCO3 product layer and then the diffusivity of unreacted Ca ion is maybe increased in product layer. Therefore, CaCO3 doped with KCl can maintain better carbonation performance during the long-term calcination/ carbonation cycles.