Chemistry of deposition of fine particles in catalytic hydrotreaters

• Main Author: Wang, Sanyi
• Format: Dissertation
• Language: English
• Subjects: engineering, chemical
• ISBN: 0612600378; 9780612600379

This thesis, consisting of three related sections, focuses on the role of chemistry in particle deposition under controlled hydrodynamic conditions. (1) Toluene-insoluble (TI) organic matter was deposited along with inorganic solids in hydrotreating reactors. At elevated temperatures, an emulsion of carbon-rich TI fraction in oil was formed, based on the observation of distinct carbon-rich spheres of ca. 2 mum under SEM. This TI fraction wetted the surfaces of non-polar solids such as asphaltene-treated kaolin and carbon black, giving convincing evidence of liquid coke formation at elevated temperatures and suggesting that surface properties have great influence on coke formation behavior. (2) The effect of surface properties of depositing particles, such as kaolin and iron sulfide, on their deposition was studied in packed beds of either glass beads or catalyst pellets in an autoclave at 375--380°C. Kaolin particle size (0.68--5 mum) was less significant than its specific coverage with asphaltenes in determining its deposition. The treatment with asphaltenes had no effect on the deposition of iron sulfide because its catalytic activity likely converted the asphaltenes, giving a clean mineral surface. (3) The role of polar compounds, such as water, ammonia, quinoline, on the deposition of asphaltene-treated kaolin was studied by adding them into the reactor at reaction temperatures. Water enhanced the removal of the adsorbed organic layer from authentic TI solids from Athabasca vacuum residue (525°C+). Representative bases (ammonia and quinoline), on the other hand, showed no effect on deposition of kaolin.
Overall, these studies showed that the deposition behavior of fine particles depended on their surface chemistry at hydrotreating conditions, governing interactions with coke (1), and agglomeration and deposition on collector surfaces (2 & 3). The gradual increase in reaction temperature along the hydrotreater would enhance desorption of asphaltenes. Water would be generated by hydrodeoxygenation of gas oils, which would in turn promote removal of this asphaltene layer. Consequently, the reaction conditions would give the lowest concentration of asphaltenes on the mineral surface in the most active zone of the reactor, which would lead to the highest rate of particle deposition on the catalyst. (Abstract shortened by UMI.)