| Control the volatile organic compounds (VOCs) is a hot topic in the environmental protection. Right now, adsorption process use activated carbon as adsorbent is widely adopted to abate volatile organic compounds from exhaust gas. This dissertation studies the theory and experiments of organic vapors treatment by adsorption and Pressure Swing Adsorption (PSA) based on an analysis of the current technology of organic vapor treatment. This dissertation is composed of three parts: study of adsorption capacity of activated carbon, simulant study of dynamic behavior of concentration distribution in the adsorber, experimental study of abatement two components organic exhaust by PSA.The adsorption isotherms of acetone, toluene and dichloromethane on activated carbon C40/4 were measured at 288.15K, 293.15K and 298.15K using an activated carbon bed developed for this purpose. The experimental data have been analyzed theoretically by the Dubinin-Radushkevich theory, based on the theoretical analysis some experienced adsorption isotherm models, which can describe the adsorption isotherm of acetone, toluene and dichloromethane on activated carbon C40/4, were proposed. Excellent agreement was observed between data obtained from experienced models and experimental results. The average relative tolerance is less than 3 %. Capillary condensation appeared when partial pressure of these organic vapors were higher, so the data forecasted by the models were lower than the experimental data.It is significant to forecast some other adsorptive isotherm only use little adsorptive isotherm data. In this research the adsorption isotherms of acetone, toluene and dichloromethane on activated carbon C40/4 were tested at 288.15K, 293.15K and 298.15K. The adsorptive isotherm at 293.15K was predicted by isosteric heat which was calculated by the Clausius-lapeyron formula, use the adsorptive isotherm at 288.15K and 298.15K. Compared the results of mathematical computation and experiments data we have obtained that the adsorptive isotherm predicted by the Clausius-lapeyron formula is consistent with the isotherm tested by experiments. The same result was obtained when we validated the isotherm by some data cited from a literature. It is a new means to gain adsorptive data by use the Clausius-lapeyron formula, it only need two isotherm at different temperature.An experimental and theoretical study was carried out to study the concentration distribution of acetone during the adsorption and purge step on the fixed activated carbon bed. Both adsorption and purge experiments were taken on an activated carbon bed at normal temperature and pressure. Breakthrough and purge curves were measured during the experiments. Mathematical model composes of mass equilibrium, adsorption equilibrium and linear driving force model was established, and it was calculated by courtesy of FORTRAN. Compared the results of mathematical computation and experiments data we have obtained the total mass transfer coefficient of this system. During the adsorption and purge step, the dynamic behavior of concentration distribution on the fixed activated carbon bed and effects on concentration distribution of some parameters such as initial concentration,temperature and gas vacant speed in the bed were explored using the model which have been developed. Results of simulation indicated that, higher the inlet gas concentration and higher the temperature and quicher the gas velocity are, faster the column will be penetrated at the adsorption step. The concentration distribution curve of acetone in the mass transfer zone approximately became a line at some later period of the purge step, and the increase of gas vacant speed in the bed can hardly enhance the desorption of acetone which located in the adsorption center of activated carbon.A small-scale two-column four-step pressure swing adsorption (PSA) processes utilizing activated carbon C40/4 as adsorbent was performed at normal temperature to separate and recover acetone from exhaust gas. Concentration distribution of acetone in the adsorption column was measured when the processes were stable. Mathematical model composes of mass equilibrium, adsorption equilibrium and linear driving force model was established, and it was calculated by courtesy of chemical engineering software ATHENA VIUAL WORKBENCH. As we had expected, the modeling results were in good agreement with the experimental data. The dynamic behavior of concentration distribution in the adsorber and effects on concentration distribution of some parameters such as axial diffusion coefficient,mass transfer coefficient,temperature and gas vacant speed in adsorption column were explored using the model which have been developed. We fined that, the effective diffusion coefficient of adsorption is decided by both molecule dispersion and Knudsen diffusion it is 3.6×10-4s-1of the system we studied in this part; axial diffusion has trivial effects on concentration distribution it often can be ignored in the model which was used to simulate the PSA processes for separating VOCs from exhaust gas; small variety of temperature can bring changes to mass transfer coefficient and adsorption ability of activated carbon but it can hardly alter the shape of the concentration distribution profile, it only can make the profile move to left or right.It is still a new mean to use pressure swing adsorption to dispose organic gas. A binary toluene-xylene mixture was purified by two tower three step pressure swing adsorption used activated carbon CAN-230 as adsorbent. The effects of pressure at vacuum desorption step, relative humidity, the mutual impacts of toluene and xylene and the saturated degree of adsorbent were evaluated. Experimental study showed that the pressure at vacuum desorption step is inadvisable to be more than 0.03MPa when adopt vacuum pressure swing adsorption to dispose the binary toluene-xylene mixture. Results indicated that when relative humidity is less than 50% it has little effects on the efficiency, however, when relative humidity is more than 60% there is intense restraining effect of water vapour on the adsorption of organic gas, the concentration of augment with the increase f humidity. There is competitive adsorption between toluene and xylene, augment of one's concentration at the inlet of adsorption tower can make the concentration of the other in purified gas larger. The saturated degree of activated carbon loaded in the adsorption column can not affect the efficiency of purification, when the PSA process is steady. |
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