On Adsorption And Regeneration Of Biomass-based Adsorbent In Separation Of Tert-butyl Alcohol-water Azeotrope

Anhydrous tert-butyl alcohol (TBA) is an important organic solvent, additive andalkylating agent. However, the raw TBA contains water and forms azeotropic mixture,making ordinary distillation hardly to dehydrate TBA azeotrope. In this work, thefeasibility of biosorptive separation of TBA-water mixture using biomass adsorbentwas investigated. To move forward, this work focused on investigating the optimumadsorption and regeneration conditions of biosorptive separation process, and theadsorption mechanism.Firstly, this paper investigated the feasibility of selective separation of TBA andwater azeotrope using biomass adsorbent, CSA, was investigated by invers gaschromatography. The experimental results showed that CSA can preferentialadsorptive separation of water, and low temperature propitious to the separationprocess.Then, this work turned to the adsorption and regeneration behavior of CSA infixed-bed apparatus through orthogonal design method. The optimal adsorptioncondition was determined through the productivity of TBA under different bed depth,bed temperature and kettle temperature, and the optimal regeneration condition wasobtained through regeneration efficiency of CSA under different air flowrate, airtemperature and regeneration time. Then, the cyclic adsorption/regenerationexperiments were carried out under the best adsorption and regeneration condition.The experimental results demonstrated that the optimum adsorption condition of CSAin fixed-bed separation of TBA-water azeotrope is the kettle temperature of102℃,the bed temperature of84℃and the bed depth of30cm, and the influence degree ofeach factor on the productivity is kettle temperature>bed temperature>beds depth,without interaction between each factors; the optimum regeneration conditions ofCSA in fixed-bed are the air flowrate of60L/h, the air temperature of120℃and theregeneration time of40min, the influence degree of each factor on regenerationefficiency of CSA is air temperature>regeneration time>air flowrate, and the factorsaffect the process in an interaction-independent way. The observations in five cyclicadsorption-regeneration experiments show complete generations with imperceptiblychange in data of regeneration efficiency. Finally, characterizations were done of CSA before and after adsorption, as wellas after regeneration. And the thermodynamic parameters were examined inbiosorptive separation of TBA-water azeotrope to investigate the adsorptionmechanism. The experimental results showed that CSA mainly containing themacropore that play a significant role in water adsorption. CSA was saturated bywater after adsorption, and completely regenerated after the regeneration operation byalmost restoring the natural structure. The adsorption heat of CSA for water wasobtained to be-38.3kJ/mol, and the corresponding value for TBA was-5.46kJ/mol,which further proved the priority of water adsorbed on CSA. The adsorption wastherewith verified to be a physisorption, exothermic process and low temperaturepreference adsorption process. The free energy of adsorption for water and TBAconfirmed the above conclusion, and indicated that the adsorption of water on CSAisspontaneous.