The project object1ve was to develop a two layer fixed-bed catalyst systemsuitable for high conversion hydrocracking of heavy oil feedstocks. Heavy oi1feedstocks contain a large fraction of pitch material (components boiling above525 °C) which are difficult to convert to lower boiling fractions. Conversionof 90-100 wt % of the pitch material while maintaining reasonable catalyst lifewas a primary goal of the work. Typical hydrotreating catalysts quicklydeactivate when they are used in high-pitch conversion hydrocracking processes.Catalyst mixtures have been used with some success in lower conversion(<50 wt %pitch conversion) processes. The plan was to experiment withlow cost upstream stabilizing catalysts to stabilize the converted materialprior to the hydrotreating catalyst, and significantly extend the catalyst'suseful life.
Two heavy oil feedstocks were tested, Lloydminster atmospheric resid and Athabasca bitumen. A typical cobalt-molybdenum (Co-Mo) commercial hydrotreatingcatalyst was used in the downstream layer. A variety of stabilizing catalystswas prepared for the upstream layer. The purpose of the stabilizing catalystwas to stabilize the demetallized and thermally- cracked conversion products(rendering them less reactive through the addition of hydrogen) making themless likely to form coke on the hydrotreating catalyst.
Deactivation characteristics of the Co-Mo catalyst were established with eachfeedstock by performing extended continuous experiments. The highest conversionconditions were established with an extended run using the stabilizing catalystalone.
Two-layer experiments were performed with both feedstocks. A series of runs wasperformed where the reactor temperature profile was man1pulated to achieve nearcomplete conversion in the stabilizing layer, therefore reducing coke formationin the downstream layer. The stabilizing catalyst proved ineffective inextending catalyst life. Coke formation hindered unit operation preventingcomplete pitch conversion and causing rapid catalyst deactivation.
The project investigated means for improving the suitability of the fixedcatalyst bed hydrocracking process for high-conversion heavy oil and bitumenupgrading. Conversion of the pitch fraction (material boiling higher than 525°C) into lower boiling components with typical hydrocrack1ng catalysts isdifficult to achieve because coke formation causes rapid catalyst deactivation.At high-pitch conversion conditions (>SO wt %) the typical fixedcatalyst bed hydrocracking process is not economical because of catalystreplacement costs.
The concept advanced in this project was to use a two-layer catalyst bed withthe upstream layer to i e stabiljzing bed and the downstream layer to betypical hydrotreating catalyst. Several process licensors have experimentedwith the use of guard bed reactors, mixtures of different pore size catalysts.and are applying these with some degree of success in commercial operation. Therole of the stabilizing catalyst will be to stabilize conversion products(through the addition of hydrogen) so that coke formation is minimized. It isgenerally accepted that pitch conversion is a result of thermal hydrocracking.Furthermore, the research work performed at Canada Centre for Mineral and Energy Technology (CANMET) and in Venezuela clearly indicates that cheapadditives can be used for demetalization.
