Font Size: a A A

Meapo-5 (me = Fe, Co, Mn) Molecular Sieve Preparation, Characterization And Catalytic Cyclohexane Oxidation

Posted on:2011-02-23Degree:MasterType:Thesis
Country:ChinaCandidate:Z Q YanFull Text:PDF
GTID:2191360308476522Subject:Chemical processes
Abstract/Summary:PDF Full Text Request
The catalytic oxidation of cyclohexane to cyclohexanone and cyclohexanol (KA oils) is an important industrial process. At present, the conversion of cyclohexane, the selectivity to KA oils and the mass ratio of cyclohexanone to cyclohexanol are low. Moreover, the waste pollution and energy consumption in the current process are serious. Therefore, the catalytic oxidation of cyclohexane has been widely studied at home and abroad. The key issue to solve the problems is to develop efficient catalysts. The heteroatoms substituted aluminophosphate sieves(MeAPO-5) have been a promising multi-functional catalysts because of their special channel structure, good adsorption and thermal stability, the acid sites and the redox active sites. In this paper, various MeAPO-5 molecular sieves were hydrothermally synthesized. The effect of various factors during the preparation of the catalysts on the catalytic performance was investigated, and the structure of the catalysts was characterized by various spectroscopy methods.The effect of the aluminium source, the metal content, the templating agent content, the crystallization temperature and time as well as the calcination temperature on the structure of the MeAPO-5 molecular sieves was investigated. The optimum preparation conditions are as follows: boehmite as aluminium source, triethylamine as template and phosphate as phosphorus source with the molar ratio:χMe:(1.05-χ)Al2O3:1.05P2O5:1.0Et3N:100H2O(χ=0.025,0.05,0.075,0.1); and the crystallization temperature and time, the calcination temperature and time are 180°C, 48 h, 550°C and 6 h, respectively.The crystal structure, morphology and as the chemical state of Fe, Co and Mn in the framework of molecular sieves were characterized by X-ray diffraction(XRD), Fourier transform infrared ray(FT-IR), Hydrogen temperature programmed reduction(H2-TPR), thermal analysis(TG), Nitrogen adsorption-desorption, Ultraviolet-visible diffuse reflectance(UV-Vis) and Scanning electron microscope(SEM). The results show that the molecular sieves have the crystal structure of AlPO-5; the pore size is located between 0.6~1.2 nm; Fe, Co and Mn atoms enter the framework of molecular sieves; Co and Mn exist as the tetrahedral Co2+ or Mn2+, which could be partially oxidized to Co3+ or Mn3+ to form redox centers after calcination. The effect of the reaction temperature, the oxygen pressure, the catalyst loading, the initiator, the pore volume and the metal content on the catalytic performance for cyclohexane oxidation was investigated. The results indicate that FeAPO-5 and CoAPO-5 molecular sieves are more suitable for cyclohexane oxidation when coMPared to MnAPO-5 which shows deep oxidation and low selectivity to KA oils. For the FeAPO-5 catalyst, under the reaction conditions of tert-butyl hydroperoxide as initiator, the catalyst loading of 0.1 g, the oxygen pressure of 1.5 MPa, the ratio of Fe/Et3N of 0.075 and the reaction temperature of 130°C, the cyclohexane conversion, the selectivity to KA oils and the mass ratio of cyclohexanone to cyclohexanol are 7.93%, 93% and 2.87, respectively, which is significantly better than the current industrial values of the cyclohexane conversion of 4~5% and the selectivity to KA oils of 80%. The catalytic stability of the FeAPO-5 catalyst decreases after regeneration by calcining at 550°C.
Keywords/Search Tags:MeAPO-5 molecular sieves, Synthesis, Characterization, Cyclohexane oxidation, KA oil
PDF Full Text Request
Related items