| Fuel ethanol is regarded as the optimal fuel substituting for and economizing gasoline at abroad. As a kind of biomass sources, fuel ethanol is hopeful that it will partly replace fossil fuel decreasing increasingly. Adding Fuel ethanol to gasoline not only substitutes partly for gasoline, but also substitutes for MTBE .As a result, the demand for fuel ethanol will be very great. However, the cost of produce of fuel ethanol is a pivotal factor which will decide whether ethanol gasoline is used widely or not.Producing anhydrous ethanol attracts many researchers. Using biomass adsorbent to separate water from ethanol is a way of producing anhydrous ethanol with low cost.In this experiment the object of study is a kind of adsorbent exploited by center of biochemical engineering of Zhengzhou University, and the adsorption characteristic of the adsorbent for gaseous phase selective adsorption for anhydrous ethanol was investigated via a fixed-bed adsorber so as to provide theoretical foundation for design and product of adsorption project. The relation between superficial velocity and bed pressure drop , and the relation between bed depth and bed pressure drop were studied. The impact of superficial velocity, bed depth, vapor temperature and bed pressure on the time of breakthrough and the amount of adsorption. The method of fixed-bed breakthrough curves has been applied to develop the dynamic adsorption model and attained the outer mass transfer coefficient and internal mass transfer coefficient. In this experiment, wafting with anhydrous ethanol vapor in vacuum , the desorption and the adsorption were investigated. The vapor of ethanol-water where ethanol concentration was 93.44%(mass) was used as the medium of this experiment .The range of bed depth was from 1.35 —2.35 meters. The range of superficial velocity was 0.064~0.294 m/s. The range of internal pressure was 1~ 1.4atm. The range of temperature in the feed was 78.3 ~ 94 °C .The ethanolconcentration in the outlet was determined by gas chromatography .Through analysis of experimental results of different cases, Conclusions deserved in this paper are:The pressure drop of per meter's adsorber is very little and grows with increasing of the gas superficial velocity. They meet the relation of two orders function. The higher the bed depth is, the greater the pressure drop of per meter's adsorber is. And the difference is decreasing with the increasing of the superficial velocity. The vapor temperature in the feed has little impact on the adsorption capacity of water. Gas superficial velocity has great influence on the adsorption. The breakthrough time and the amount of adsorption will be decreased if the gas superficial velocity increases. Gas superficial velocity has little impact on the ethanol concentration of outlet before the breakthrough time, but has great impact on it after the breakthrough point. Bed depth has great impact on the adsorption capacity of water, and the higher the bed depth is, the longer the breakthrough time is. The breakthrough time can be calculated from equation supplied by Bohart-Adams. The higher the bed depth is, the more the amount of adsorption is. Bed pressure has some effect on adsorption. Increasing bed pressure benefits the adsorption, but it has little effect on adsorption when it increases to certain value. A product of ethanol purity of 99.4% (mass) could be obtained after wafting with anhydrous ethanol vapor in vacuum, but the discrepancy was not large between the wastage of anhydrous ethanol used in desorption and the obtained anhydrous ethanol in adsorption. The internal mass transfer coefficient is almost a certain value which has nothing to do with the gas superficial velocity and the bed depth. The external mass transfer coefficient and the total mass transfer coefficient increase with increasing of the gas superficial velocity, but have nothing to do with the bed depth. The internal mass transfer coefficient and the external mass transfer coefficient affect together the total mass transfer coefficient. |
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