The effects of different calcination temperatures, load capacities and load methods on the monolayer dispersion of CaCl2 onto silica gel were studied by XRD. It was indicated that calcination temperature of 500℃ is enough for the monolayer dispersion of CaCl2 onto silica gel and the monolayer dispersion threshold is the lower than 0.4g/g. The method of impregnation in aqueous solution is the more suitable than the method of dry mixture for thermal dispersion of CaCl2 onto silica gel. At the same time , it is proved by XRD and FT-IR that the skeleton structure of silica gel will be kept at the lower calcination temperature such as 500℃ but changed obviously when the sample is calcined at 600℃.
The calcium chloride used for adsorption separation of ammonia is promising for its large adsorptive capacity and lower desorption temperature,but difficult to develop because of the liable expansion,lump and chip in the adsorption/desorption process.Composite adsorbents made by monolayer dis-persion of calcium chloride onto carriers with high surface areas exhibit better adsorptive capacity and stability.Several models were developed to confirm the maximum monolayer dispersion capacity of calcium chloride onto the carriers(the distribution threshold value),and the closely packed monolayer dispersion model was considered the most suitable for this study.The distribution threshold values given by this model were 0.60 g CaCl2/(g 10X-zeolite) and 0.38 g CaCl2/(g SiO2).When the divalent salt was dispersed onto the carriers,however,anions were separated into two types,causing that the en-tropy of the system tended to increase and the system was not stable.To minimize the entropy,a new model was put forward as the modified closely packed monolayer dispersion model.Based on this model,the distribution threshold values are 0.52 g CaCl2/(g 10X-zeolite) and 0.33 g CaCl2/(g SiO2),re-spectively.The distribution threshold values were also gained experimentally by XRD quantitative phase analysis:0.61 g CaCl2/(g 10X-zeolite) and 0.31 g CaCl2/(g SiO2).Comparison between experi-mental values of distribution threshold with theoretical ones based on two different model showed that the closely packed monolayer dispersion model fits the monolayer dispersion of calcium chloride onto micro-pore carrier - 10X-zeolite,and the modified closely packed monolayer dispersion model is more suitable for the bigger aperture carrier - macro-pore silica gel.
TANG YouCheng1,2,LI Bin1,YANG JingChang1,CHU Wei1 & LUO ShiZhong1 1 School of Chemical-Engineering,Sichuan University,Chengdu 610065,China
