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Study of Cationic Impregnation Method on Zeolite Catalyst for Upgrading of Methanol to Gasoline (MTG)Process

Kazemi Zangeneh, Fatemeh | 2020

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 53490 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Ghanbari, Bahram
  7. Abstract:
  8. In the present research, the conversion of methanol to hydrocarbons was studied over a new series of mesoporous low-silica HZSM-5 (Si/Al=11) catalysts impregnated with cations such as Fe, Zn, Mo and Cr. A systematic study on the effect of stepwise modification of the catalysts for the conversion of methanol to gasoline (MTG) was undertaken in a fixed-bed tubular reactor under ambient pressure at 375 °C, feeding with weight hourly space velocity (WHSV) of 2 h−1. The catalysts were prepared in the absence and presence of cationic promoted factors, in both alkaline and neutral aqueous solutions. The final catalysts characterized by using Fourier-transform infrared, X-ray diffraction, X-ray fluorescence, thermogravimetric analysis, pyridine infrared spectroscopy, transmission electron microscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, temperature programmed desorption of ammonia and N2 adsorption/desorption techniques. On the basis of the gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) results, [0.2Fe, 0.3Zn]-alk-HZSM-5 catalyst exhibited the greatest improvement in selectivity for aromatic hydrocarbons, yielded up to >86 wt.% together with highly selectivity for xylenes (44.7 wt.%) and very low content of benzene (0.1 wt.%). Meanwhile, alkaline HZSM-5 catalyst produced aromatic compounds with xylenes selectivity 39.4% and the benzene selectivity (0.0 wt.%). The catalyst lifetime for both HZSM-5 and [0.2Fe, 0.3Zn]-alk-HZSM-5 catalysts were significantly high enough to keep >96% of its activity after 8 h. Furthermore, GC and GC-MS measurements demonstrated a selectivity of up to 86 wt % (65.7 wt % for benzene, toluene, and xylene (BTX)) over 2[Mo]HZ5 and the alkali-treated Mo-HZ5 catalyst (2[Mo]alk-HZ5) afforded 40.3% alkyl aromatics, 0% benzene, and 0% toluene. Also, Cr-1-HZ5 catalyst showed that the aromatics selectivity 82.1%. Furthermore, in order to optimize the required conditions in preparation and modification of ZSM-5 zeolite for maximum production aromatics in MTA process, the statistical Taguchi experimental design method has been employed. In these Taguchi experimental design, reaction temperature, Si/Al ratio, polymetallic impregnation in terms of metal ions contents as well as the presence of alkaline treatment and WHSV were selected as the principal parameters affecting the properties. In addition, to upgrading the zeolite catalyst, the N,N,N',N'-tetramethyl-N,N'-dipropyl-ethylenediammonium diiodide (TMDP) synthesized and used for the ZSM-5 zeolite synthesis as template for the first time. Also, synthesized zeolite selectivity (MFI  MOR) driven by synthesis aging time has been studied. Using TMDP as organic structure-directing agent (OSDA), the zeolite phases obtained at 2 h (MFI 97%), 8 h (MFI 84%, MOR 16%) and 24 h (MFI 43%, MOR 57%) have been characterized by powder X-ray diffraction. Different techniques (FT-IR, 13C MAS NMR, TGA/DTG and HC microanalysis) have been employed to verify the OSDA inside the zeolite. A computational study was performed using a force field theory and confirmed that the conversion of MOR phase to a more stable phase of MFI with increasing the aging time. Furthermore, the extraction of TMDP and recycling of tetrapropylammonium hydroxide (TPAOH) as the most frequently used OSDA in ZSM-5 synthesis, were successfully performed by water from as-synthesized zeolites at atmospheric pressure and room temperature
  9. Keywords:
  10. Zeolite Catalyst HZSM-5 ; Methanol Conversion to Gasoline (MTG)Process ; Cationic Impregnation ; Methanol Conversion ; Metal Cations

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