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Mo- Modified HZSM -5 Zeolite for the Dehydrooligomerisation and Aromatisation of Methane in the Absence of Oxygen

Sinnathambi, Chandra Mohan (2005) Mo- Modified HZSM -5 Zeolite for the Dehydrooligomerisation and Aromatisation of Methane in the Absence of Oxygen. PhD thesis, Universiti Teknologi Petronas.

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Abstract

Methane dehydrogenation aromatisation (MDA) has been highly pursued since 1993 as a route of converting methane to aromatics. It is believed to proceed via a by bi-functional catalyst namely Mo modified HZSM where by methane is activated by the Mo carbide by dehydrogenation process and the intermediate species are oligomerised and dehydrocyclised over the acid site of the HZSM-5 zeolite. The aim of this study is to optimise catalytic activity with high yield and selectivity to aromatics and low coke yield and selectivity. This will include basic principles behind catalyst design, activation and stabilisation. The MDA analysis was carried out on a quartz micro reactor operating at 1 atm. and 700°C using an on-line GC and a list of catalyst characterisation equipments to explain the findings. The optimum catalytic activities were investigated using methane on Mo modified HZSM5 (Si/Al =41). Mo wt% loadings used were 3, 5 and 10 prepared by wet impregnation of ammonium heptamolybdate on HZSM- 5. The preliminary micro reactor test showed that a GHSV of 1500 h-1 was the optimum flow rate for the process. Based on investigation on the hcp ~-Mo2C and fcc a-MoC 1-x , Mo loading of 10wt% is found to be the optimum catalytic loading for MDA for both. Re-dispersion of the Mo03 species over the catalyst surface and into the channels of the zeolite or pore is governed by calcination. Based on this study for the hcp ~-Mo2C catalyst 600°C was the optimum calcination temperature while for the a-MoC 1-x it was 500°C. Activation of the Mo03 species results in the formation of hcp ~-Mo2C and fcc a-MoC1.x. the active Mo carbide phase which is responsible for methane activation and follow different route of preparation. It was found the hcp ~-Mo2C catalyst has higher catalytic activity than the fcc aMoC1. x counterpart. This higher catalytic activity for the hcp ~-Mo2C is attributed by the higher coke deposition as compared fcc a-MoC1_x which has lower coke yield and selectivity but higher aromatic yield and selectivity at lower calcinations temperature. Catalytic activity and stability was found to be improved by co-dosing with CO onto both the hcp ~-Mo2C and MoC1-x catalysts. CO dosing was found to prevent coke build up during MDA reactions. From this investigation, it was found CO dosing is more significant towards higher Mo loading of 10wt% rather than for the lower loading of 3wt%. The most suitable CO for the !Owt% a-MoC 1-x was 4 v/v%, while for 10 wt % hcp ~-Mo2C it is 12 v/v%

Item Type: Thesis (PhD)
Academic Subject : Academic Department - Chemical Engineering - Material Development
Subject: T Technology > TP Chemical technology
Divisions: Engineering > Chemical
Depositing User: Users 2053 not found.
Date Deposited: 30 Sep 2013 16:55
Last Modified: 25 Jan 2017 09:46
URI: http://utpedia.utp.edu.my/id/eprint/8041

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