斜发沸石和丝光沸石的吸水性能

用离子交换、酸和碱处理斜发沸石来提高它的吸水能力没有取得明显效果。测得的斜发沸石、丝光沸石吸附水的等温线具有非线性特征,但25℃的等温线在水蒸气分压高于2400Pa 时,斜发沸石、丝光沸石和有粘合剂的合成分子筛的吸水量随着分压的升高而增加。这是由于样品中含有粘土矿物产生水蒸气的毛细凝聚作用而引起的。根据沸石的吸附热和水的蒸发热,用沸石作为吸附剂和水作为工质能建立一个高效的沸石太阳能利用体系。

WATER-SORPTION CAPACITY OF CLINOPTILOLITE AND MORDENITE

Water-sorption capacity of natural clinoptilolite and mordenite were lower than that of synthetic molecular sieves, such as A-type, X-type, and Y-type zeolites. An attempt of improving water-sorption capacity was made for the clinoptilolite by cation-exchange method to transform the exchangeable cations into hydrogen, sodium, potassium, ammonium, and calcium and by treatment with solutions of sodium hydroxide and hydrochloric acid. But the water-sorption capacities of the clinoptilolite before and after treatment were 11.54 and 9.62-11.75 wt% respectively. So, as compared with original speciment, no obvious improvement instead a little deterioration for some specimens was observed. Adsorption isotherms for water vapor on clinoptilolite, mordenite, and synthetic 5A-type and 13X-type molecular sieves were determined. They exhibited obvious non-linear characteristics with the exception for the isotherms for the clinoptilolite, mordenite, and 13X-type molecular sieve with binder at 25℃. For these isotherms the water-sorption capacities of the zeolites were increased when the partial pressure of water vapor went higher than 15 mm Hg at 25℃. The reason for this Was thought to be the capillary condensation of water vapor in pores of the clay minerals presented in these zeolite specimens which occurred under lower temperature and higher partial pressure of water vapor. The fact that no similar behaviour was observed for 13X-type molecular sieves without binder was enough to prove the conclusion mentioned above. The differences in adsorbed water of the zeolites between 100℃ and 50℃, 100℃ and 25℃ were 4 wt% and 5 wt% to 6 wt% respectively by calculation based on the adsorption isotherms. From the results of isosteric heats measured it was concluded that the adsorption and desption of the zeolite for water vapor were essentially a physical process and the adsorbent and adsorbate would be inert to each other, that is, the zeolite and water vapor in the zeolite-water vapor system are chemically stable which is important for the absorption system.The maximun theoretical efficiency for cooling with a zeolite can be roughly examined by the heat of water vaporization (9.7 Kcal/mole) divided by the heat of water-sorption on the zeolite (12-19 Kcal/mole for natural zeolites). So natural zeolite have maximun theoretical efficiency of about 50-80%. It is thus clear that the heat of adsorption of zeolites is of critical importance for solar energy application.