title: Tetralin hydrogenation over supported monometallic and bimetallic catalysts systems
Creators: name: Alasseel, Ahmed Kadhem
Publisher: name: University of Glasgow
Year: 2019
Subjects: subject: Hydrogenation, tetralin, decalin, naphthalene, nickel catalyst, cobalt catalyst.

description: Hydrogenation of multi ring aromatics has become an essential part of the oil and gas industry to upgrade transportation fuel and to reduce their negative impact on the environment. Not enough attention has been paid to minimise these products especially their derivatives. Thus, tetralin was selected in this project as a representative model for partially hydrogenated polyaromatic product hydrogenation in the middle distillate fraction. In this study, an investigation was carried out to examine the feasibility of using monometallic and bimetallic catalytic systems in this process. Several nickel and cobalt catalysts were synthesised utilising different techniques (i.e. incipient wetness impregnation, precipitation deposition, and highly dispersed catalyst techniques) and materials in order to vary the properties of the prepared catalysts. The characteristic properties of the fresh and spent catalysts were determined employing AAS, BET, TGA/MS, XRD, Raman, hydrogen chemisorption, and XPS. In terms of catalytic testing, the activity of the prepared catalysts was evaluated in a continuous down flow fixed bed reactor at fixed space velocities (i.e. WHSV=5 h-1 and LHSV= 3 h-1) and different temperatures (180-280 °C), pressures (5-15 barg), and hydrogen to hydrocarbon ratio (4.3-10.5) for 7 - 80 hours. The pre-reaction characterisation results revealed some differences between the properties of the synthesised catalysts especially metal dispersion and mean particle diameter. The variation in the properties of these catalysts was reflected on their catalytic activities and selectivities. The catalyst testing results suggested that higher activities and trans-decalin selectivity were attained over catalysts with higher dispersion and smaller mean particle size. It was also found that high dispersion, small metal particle size, and small pore size of the support contributed to reducing the deactivation rate. However, the effect of small particle size differed when the type of the support and the population and distribution of metal over the surface of the catalyst were altered in which cis-decalin selectivity was enhanced. Similarly, the type of the metal was another factor that has influenced performance of the prepared catalysts where nickel catalysts exhibited higher activity and better deactivation resistance than cobalt catalysts. Varying metal type resulted in different physical and chemical characteristic properties of the synthesised catalyst and hence their performance was altered. Therefore, it was concluded from this study that several elements may contributed in determining the activity and selectivity of tetralin hydrogenation reaction. The reactivity of the synthesised catalysts was greatly influenced by reaction parameters. The outcome of the reaction conditions optimisation indicated that the high conversion achieved was due to the difference in the reaction temperature compared to literature studies where lower temperature was favoured for hydrogenation reactions. This was supported by a thermodynamic study which suggested that increasing the temperature by 100 °C (i.e 227-327 °C) can shift the reaction from hydrogenation to dehydrogenation. In terms of selectivity, the obtained experimental decalin isomer ratio was far below theoretical thermodynamic values. The findings of this study also revealed that high hydrogen pressure and hydrogen to hydrocarbon ratio enhanced the conversion and drove the reaction to favour trans-decalin selectivity except in some individual cases. However, further increase in hydrogen pressure resulted in faster deactivation rate owing to higher carbon laydown. Based on the optimisation and long runs results it was demonstrated that 100 % conversion (rate of 0.032 mol/g cat/h) and a reduced deactivation rate was attained using the HDC-OH catalyst at 210 °C, 10.5 H2/HC ratio, and 5 -10 barg of hydrogen pressure.