For the low pressure ammonia synthesis (approx 1 MPa,573-623 K),40-80 kPa of ammonia produced must be separated.For this purpose,the absorption behavior of five kinds of alkaline earth metal halides (MgCl_2,CaCl_2,CaBr_2,SrCl_2,and SrBr_2) and their hydrated forms were studied under 0 to 80 kPa of ammonia at 298 to 473 K.Although the equilibrium data of the ammine complex formation of these materials are known,the absorption started at higher pressure than the equilibrium data,due to the presence of enough chemical potential DELTAmu for ammonia absorption.Initial absorption (to low numbers of coordinated ammonia) was slow and depended on the sample specific surface area.The successive absorption (beyond 1 or 2 of ammonia coordination) occurs easily and reversibly.The "quasi" absorption and desorption isotherms studied here were useful for the design of ammonia separation materials.MgCl(OH),CaCl_2,and CaBr_2 were found to be practical for TSA (Temperature Swing Absorption) material working between 298 and 473 K at 40 kPa.Especially,the ammonia separation capacity of MgCl(OH) (26.1 mmol g~(-1)) was 5.5 times as high as that of Na exchanged Y-zeolite.
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