A study of colloidal hydrocracking catalysts prepared in reverse micelles

• Main Author: Hall, Andrew Graham
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/4506

Slurry phase reactors employing dispersed metal sulfide catalysts offer the potential of high conversion with minimal coke yield for the hydrocracking of heavy oil. Currently, the dispersed catalysts are prepared by the addition of organometallic compounds to the heavy oil feed, but this synthesis technique offers little control over the size of the catalyst particles. Colloidal suspensions of a wide range of metals and metal compounds in hydrocarbons can be prepared from water-soluble metal salts dissolved within the water pools of a microemulsion. This synthesis technique allows for the simple control of particle size, a factor which together with their narrow size distribution makes these colloids potentially attractive as dispersed heavy oil hydrocracking catalysts. The synthesis of reduced metal and metal sulfide colloids in the water pools of the water/polyoxyethylene-4-laurylether/hexane microemulsion was investigated in the present study. The sizes of the reverse micelles were determined by dynamic light scattering (DLS), while the reduced Ni, Co and Fe colloids and the Ni, Co and Fe sulfide colloids were characterized by DLS, transmission electron spectroscopy (TEM), energy dispersive x-ray spectrometry (EDX) and xray photoelectron spectroscopy (XPS). The catalytic activity of the metal sulfide catalysts was also determined using the hydrocracking of diphelylmethane as a model reaction. The water:surfactant ratio (ψ) and metal ion concentration were found to be the key factors affecting the size of the reverse micelles in the water/PE4LE/hexane system. Monodisperse Co and Fe colloids with sizes ranging from 10-23 nm were prepared in the microemulsion system by the addition of N₂Fl₄, and the size of the metal colloids was found to be directly related to ψ. Ni, Co and Fe sulfide colloids were prepared in reverse micelles using 5% H₂S in H₂, and XPS analysis identified MS and CoS₂ on the surface of these colloids. The metal sulfides proved difficult to characterize due to their extreme sensitivity to atmospheric oxygen. The Fe sulfide colloids oxidized readily, and could not be identified using XPS. The NiS and CoS₂ colloids had average sizes of 67 and 71 nm respectively (as determined by TEM), and were more polydisperse than the reduced metal colloids prepared in the same system. The metal sulfide catalysts prepared in the water/polyoxyethylene-4-laurylether/hexane microemulsion were found to he less active for the hydrocracking of diphenylmethane than a dispersed catalyst prepared from the decomposition of Co naphthenate. The crystallite size was similar for both catalyst preparations (20-30 nm), suggesting that diffusion limitations may have controlled the rate of reaction in the case of the aggregated metal sulfide catalyst prepared in the microemulsion.