| Cresol, as an important chemical intermediates, has three isomers:paracresol, metacresol and orthocresol. The cresol mixture of the three isomers is usually obtained through the separation from coal. O-cresol has an adequate difference in the boiling point from the other isotherms and can be separated and purified by the conventional distillation method. However, the boing point of p-cresol and m-cresol is too close to make the separation easily. The methods for the separation of p-cresol and m-cresol are divided into two categories:chemical methods and physical method. The alkylation method is one of the commonly used chemical methods. The most-often used physical methods include separation by adsorption process, urea complexation, crystallization, and so no. The separation by adsorption process was used in this article.Separation by adsorption process has been a widely-used method in industries. Zeolites with unique regular microporous channel structure show good performance in size-selective separation when used as adsorbents. Nevertheless, the subnanosized micropore channel hinders the diffusion of the adsorbate molecules into zeolites, resulting in the low effectiveness of zeolite when zeolites was used as the adsorbents in the separation of cresol isotherms by adsorption process. In this thesis, we investigate the case of ZSM-5 as the cresol adsorbent. Hierarchical ZSM-5 zeolites have been synthesized with the aid of 3-glycidoxypropyltrimethoxysilane (GPTMS). The synthesized hierarchical ZSM-5 zeolites show good performance in the selective adsorption of m-/p-cresol due to the enhanced mass transfer properties. Additionally, the adsorption of para selectivity has been further improved through the modification by ion exchange on the synthesized hierarchical zeolites. The thesis mainly consists of two parts as follows:1) Hierarchical ZSM-5 have been synthesized in the presence of (3-oxiranylmethoxy-propyl) trimethoxysilane (GPTMS) through the hydrothermal synthesis method. The liquid adsorption of cresol isothems on the syntheized hierarchical ZSM-5 were investigated. Compared to the ZSM-5 synthesized in the absence of GPTMS, the hierarchical ZSM-5 show greatly enhanced adsorption rate for cresol without sacrificing the para selectivity, benefiting from the introduction of mesopores. The effect of Si/Al ratio on the cresol adsorption on the hierarchial ZSM-5 has been investigated in the case of the optimized GPTMS dosage, indicating that the para selectivity is greatly improved with increasing the Si/Al ratio.2) The sample of ZSM-5 syntheized with the GPTMS dosage of 0.1 and the Si/Al ratio of 400 has been modified by the ion exchange with H+ Li+ K+. Both the adsorption rate and amount of p-cresol on the ion-exchanged zeolites changes little and the time required for adsorption equilibrium remains the same as that on the parent zeolites. Whereas, the adsorption behavior of m-cresol changes greatly. Both the adsorption rate and the equlibrium amount adsorbed significantly increase when the sample was ion-exchanged with smaller ion radius of H+ and Li+. On the other hand, the equlibrium amount adsorbed of m-cresol greatly decreases when the K+ exchanged ZSM-5 sample was used, resulting in the significant improvement of the para selectivity. Different Si/Al ratio ZSM-5 has been modified by the ion exchanged with K+. Found that low silica alumina ratio KZSM-5 para selectivity increased significantly... |
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