Preparation And Performance Study Of High Selective Hygroscopic Adsorbent

With the improvement of people's need for indoor air quality, air conditioning has been widely used to adjust indoor temperature and air quality. However, energy consumption in air conditioning is very high. Fresh air total heat recovery is an efficient method to reduce energy consumption. Among them, the rotary wheel total heat exchanger is widely recommended. Hygroscopic adsorbents are key for rotary wheel total heat exchanger to control indoor air quality. Compared with the conventional adsorbents, the hygroscopic adsorbents for rotary wheel total heat exchanger should have high selectivity as well as high moisture adsorption capacity and adsorption rate. That is to say that they should adsorb more water vapor and less VOCs such as toluene and acetaldehyde. The existing adsorbents hardly have either high moisture adsorption capacity or high selectivity, limiting their application in air conditioning system. In this paper, silica gel was modified by chemical graft and impregnation to prepare organic-silica gel composite adsorbents with high selectivity. Adsorption performances for water vapor, toluene and acetaldehyde were studied. Selectivity of water vapor to toluene and acetaldehyde were further investigated. Thermal resistance was also measured by recycling experiment. In addition, selective mechanism was explored by temperature programmed desorption technology.The results show that the organic-silica gel composite adsorbents have comparative water vapor adsoption capacity to siliga gel. They adsorb much less VOCs such as toluene and acetaldehyde than silica gel. And their adsorption capcity for VOCs depends on the chemical property and microstructure of organic molecule or polymer on the surface of silica gel. Hydroxy group and crosslinked polymer are favorable to decrease adsorption for VOCs. C-MA, B-PVA and B-PVA-MA adsorb least toluene and acetaldehyde. As relative humidity increases, selectivity of organic-silica gel composite adsorbents for water vapor to toluene, water vapor to acetaldehyde increases more significantly than siliga gel. Therefore, the organic-silica gel composite adsorbents show excellent selectivity for moisture to VOCs and large adsorption capacity for water vapor, especially in the case of high humidity. Among them, C-MA and B-PVA-MA have perfect selectivity and moisture adsorption performance. Recycling experiment indicates that the prepared adsorbents have good thermal resistance. In addition, the TPD results confirm that the organic-silica gel composite adsorbents show high selectivity for moisture to VOCs because of the different interaction between the surface of adsorbants and the adsorbate such as moisture and VOCs, known as the thermodynamic equilibrilium effect.