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Separation of Xylene Isomers

Khademi, Mahmoud | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40996 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Molaei Dehkordi, Asghar
  7. Abstract:
  8. Xylene isomers have similar boiling points and, therefore, their separation by conventional distillation is not practical. The industrial separation of these isomers is generally performed by adsorption or crystallization processes, which are very energy consuming. In this work, the various methods of the separation of these isomers have been reviewed and the equilibrium adsorption of these components in liquid phase using two commercial types of zeolite including Z-700 and Na-BETA as adsorbent at 15, 25, and 35 oC and an initial concentration range of up to 50 wt% as well as in single and binary solutions was investigated. It was found that Z-700 adsorbent has no selectivity for the binary solutions consisting of paraxylene and orthoxylene at 25 oC but in the case of Na-BETA adsorbent in the range of initial concentrations and temperatures, paraxylene was the more strongly adsorbed component followed by ethylbenzene, metaxylene, and orthoxylene, that means this adsorbent is selective for paraxylene. The single paraxylene, metaxylene, orthoxylene, and ethylbenzene adsorption isotherms on Na-BETA adsorbent were obtained by chromatographic method and were fitted with Langmuir equation. A good agreement was obtained between the experimental data and the Langmuir model predictions. The saturation adsorption capacity of the Na-BETA adsorbent was determined to be 143 mg/g for paraxylene, 105 mg/g for ethylbenzene, 83 mg/g for metaxylene, and 68 mg/g for orthoxylene at 25 oC. Moreover, the heat of adsorption was determined to be 12.0 kJ/mol for paraxylene, 11.4 kJ/mol for ethylbenzene, 9.6 kJ/mol for metaxylene, and 8.3 kJ/mol for orthoxylene. The separation of xylene isomers using Na-BETA zeolite was tested in binary solutions. Furthermore, the values of selectivity factor for paraxylene/orthoxylene and paraxylene/ethylbenzene were about 4 and 2, respectively.

  9. Keywords:
  10. Separation ; Adsorption ; Selectivity ; Isotherm ; Xylene Isomers ; Zeolite BETA

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