Thesis of Balssam Hamieh

Thesis defense of Balssam Hamieh  - laboratory UCCS Abstract : Hydrotreating processes (HDT) aim to purify petroleum fractions by reducing their sulfur content and by hydrogenating some of the aromatic compounds present in order to meet the specifications imposed for each type of fuel. These treatments are carried out under hydrogen pressure of the petroleum fraction in the presence of sulfided based catalysts supported on alumina. More and more stringent regulations on the sulphur content in fuels especially gas oils are driving the research for more efficient hydrodesulfurization (HDS) catalysts.
The catalysts usually used in HDS of petroleum fractions are made of molybdenum disulfide nano-sheets promoted by cobalt and deposited on a support which is previously shaped according to the industrial application: extruded, beads.... A catalyst is obtained by impregnation of a solution containing the elements to be deposited (Co, Mo, and P), followed by different treatment steps: drying and calcination. The activation of the catalyst is then obtained after sulfurization between 300 and 400°C of the oxide precursor in the presence of H2/H2S.
Gamma alumina is the most common used industrial support because it has a good mechanical strength, good textural properties (large specific surface...) and it is easily shaped. However the use of other supports has been investigated in order to increase the catalytic performances of these systems. Some studies have shown that silica can be used to obtain catalysts for which the activity per gram of active metals was higher than that observed with the alumina support. Nevertheless alumina supported catalysts are generally preferred HDS due to their better mechanical properties and higher metal content which can be deposit maintaining optimal dispersion. These disadvantages of silica constitute a barrier for the development of catalysts based on silica or other support. The idea of this thesis is to combine the interesting properties of alumina (textural, mechanical) and silica (surface properties) in order to obtain efficient catalysts for HDS of oil crudes.
We have chosen to prepare catalysts based on mixed Al-Si supports obtained either by deposition of Si on industrial gamma alumina or by deposition of Al on mesoporous silica SBA-15 via various methodologies. The objective of the work is to study the impact of the nature of these mixed supports on the dispersion of the oxide and sulfide phases for an application in HDS.
The first part of the thesis consist in optimizing the silica content added on the gamma alumina. CoMoP/Al-Six catalysts have been synthesized with different Si contents according to the number of OH groups located on the alumina (between 0 and 5 Si/nm2) and with a molybdenum content equal to 10% or 14% MoO3.
The second part of the work consist in comparing two types of alumina A and B with different textural properties (pore volume and specific surface) in order to determine the the impact of these parameters on the dispersion of active species. We fixed the silica content at 3 Si/nm2 (the acidity of the initial support is not modified). Four series of catalysts were prepared by varying the MoO3 content (8-16% MoO3): CoMoxP/AlA, CoMoxP/AlB and CoMoxP/AlA-Si3, CoMoxP/AlB-Si3.
In addition, a study of Mo, CoMo supported on Al and Al-Si3 catalysts was carried out for comparison with CoMoP catalysts.
A final study focused on mixed supports obtained by addition of Al in SBA-15 using aluminium butoxide and alumina nitrate as precursors, the MoO3 content used is 14% and 28% MoO3.
The thesis focuses on the characterization of the supports and catalysts at different stages of their preparation by different physicochemical and spectroscopic characterization techniques. An impact of the nature of the support as well as of the Si or Al content on the nature of the oxide phases (in particular CoMoO4, MoO3) and on the rate of sulphurization of the catalysts has been highlighted. Keywords : HYDRODESULFURATION,CATALYST,ALUMINE,SILICA,SULFIDE,OXIDE