Loading...

Enhanced Performance of Modified Pd/AL2O3 Catalysts by Triphenyl phosphine Ligand in Acetylene Selective Hydrogenation

Jafari Najafi, Niloofar | 2018

702 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50766 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Khorasheh, Farhad; Takht Ravanchi, Maryam
  7. Abstract:
  8. Ethylene is considered as one of the key materials in the petrochemical industry and has a particular importance. Polymerized ethylene produces polyethylene, which is widely used in plastics and pipe-manufacturing industries. Ethylene is mainly produced by the processes of catalytic cracking or thermal cracking of heavier hydrocarbon compounds. In these processes, acetylene is produced as a by-product, which deactivates the Ziegler-Nata catalysts in the polymerization unit of ethylene. Therefore, there should be some considerations to reduce acetylene to its minimum value -around zero. For this purpose, the fixed bed catalytic reactor is used to hydrogenate acetylene to ethylene. Various catalysts have been investigated in this process, among which Pd/Al2O3 has shown better performance in terms of high activity in the conversion of acetylene and high selectivity in ethylene production. Also in industry, alloyed palladium silver catalyst on alumina support is used. In this study, four samples of Pd / Al2O3 catalyst containing 0.03% wt of palladium, by wet impregnation and with different molar ratios of ligand to palladium, including 0.0 , 0.02 , 0.1 and 2.5, were synthesized. In order to compare the methods of synthesis of the catalyst, samples containing the ligand with expressed ratios were also prepared by reverse colloidal impregnation method. The reaction catalytic test of the synthesized catalysts in the acetylene selective hydrogenation process is carried out in a fixed cylinder bed reactor of 2 cm long and 1.45 cm in diameter, under pressure of 10 bar, temperature of 60 ° C, and GHSV of 4000 h-1, for approximately 24 hours. Generally, in all experiments, the catalyst performance is evaluated by determining the acetylene conversion and ethylene selectivity versus the production of ethylene and the results are compared. The feed into the reactor contains 96% molar of ethylene and the remainder includes hydrogen and acetylene gas with molar ratios equal to 1.5, 3 and 6. Finally, the G-58C industrial catalyst was used as reference sample and its performance were compared with the results obtained from the best synthesized catalyst sample. Also CO-TPD and FTIR specification tests on fresh catalysts and FTIR tests were performed on catalysts used in the test. The test results comparison showed the superiority of the catalyst performance with 2.5 molar ratio of triphenyl phosphine ligand to palladium. The 99% acetylene conversion for the Pd/Al2O3 sample without ligand reached to 99.77% conversion for the PPh3(2.5)-Pd/Al2O3 sample and the ethylene waste also raised from 3.13% in the Pd/Al2O3 sample to 59 / 0 +% ethylene production in PPh3(2.5)-Pd/Al2O3 sample. The results of the analysis of CO-TPD also confirmed the superiority of this catalyst by reducing the number of sites with high coordination number. Comparison of the results obtained from traditional impregnation method and reverse colloidal impregnation showed the superiority of traditional impregnation method. Also, by examining the inlet molar ratio of hydrogen to acetylene, it was observed that in lower proportions, lower by-products would be produced but the conversion of acetylene was also decreased
  9. Keywords:
  10. Ligands ; Triphenylphosphine ; Selective Hydrogenation ; Acetylene Hydrogenation ; Lead/Aluminum Oxide Catalyst

 Digital Object List

 Bookmark

No TOC