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Investigation of Fischer-Tropsch reaction for synthesis of hydrocarbons and alcohols

Iqbal, Sarwat 2009. Investigation of Fischer-Tropsch reaction for synthesis of hydrocarbons and alcohols. PhD Thesis, Cardiff University.

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Abstract

Fischer Tropsch (FT) technology as a source of alternate fuels is unique. The FT products are of excellent quality and their environmental properties are valuable in increasing drive towards cleaner fuels. There was surge of interest in FT in the thirties and fifties (during the Second World War) and now again in last couple of years. Fischer Tropsch technology has a disadvantage of broad product spectrum. There is strong requirement of improvement in the optimization of reaction in order to get a maximum yield of high value commercial products, mainly high value molecular weight products, alcohols and short chain hydrocarbons. Most of the investigations reported in this thesis have dealt with study and possible modifications in the preparation and reaction conditions of previously studied CoMnOx catalyst. Co-precipitation method for preparation of this catalyst has been studied in detail. Precipitation by variable pH has been found to be better than constant pH. pH, ageing time of precipitates and temperature of precipitation mixture are very important parameters which affect the selectivity pattern of products. This selectivity pattern was found to be further influenced by reaction temperature and pressure during CO hydrogenation reaction. An improvement in the selectivities for CO hydrogenation reaction has been developed using a modified co-precipitated Co/Mn oxide catalyst. This modification was achieved by using two different metal promoters, i.e., Potassium and ruthenium. Addition of these promoters has influenced the catalytic properties in a variety of ways as was observed from characterization and reaction results. Addition of small quantity of potassium (0.15%), and ruthenium (0.1%) promoters shifted the product spectrum to long chain hydrocarbons along with decrease in methane selectivity. Further improvements in catalytic activity and selectivity were made by addition of two different types of activated carbons (wood and peat shell) into Co/Mn catalyst. Co and Mn impregnated on wood peat carbon were found to be highly selective for high molecular weight hydrocarbons along with low selectivity of CO<sub>2</sub> compared with pure CoMnOx catalyst. An increase in concentration of metals with these carbons showed an increase in selectivity of CO<sub> 2</sub>. One particular catalyst system of iron and manganese was studied with peat and wood carbons and was found to be highly selective for CO<sub> 2</sub> formation. Alcohols, an important product of FT reaction are a good substitute to motor fuel which can enhance the octane number and can reduce the environmental pollution. Cobalt molybdenum sulphide is a patented catalyst system for alcohols synthesis. Present study has investigated the influence of transition metal promoters on selectivity pattern of this catalyst. Ti, Ni and Zr metals have been used as promoters. Addition of Ni and Ti into C0M0S2 have shown good catalytic activity but the major product was CO<sub>2</sub>. Zr addition has shown less CO<sub>2</sub> and more hydrocarbons. Pure C0M0S2 catalyst was found to be better for synthesis of higher alcohols.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
ISBN: 9781303214998
Funders: SABIC
Date of First Compliant Deposit: 30 March 2016
Last Modified: 05 Jun 2017 04:16
URI: http://orca.cf.ac.uk/id/eprint/54875

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