Petroleum refining is an important use for palladium and the other platinum group metals as catalysts for a number of different refining processes. Johnson Matthey includes this use within their catchall category “other uses”.
Distillation is the first step in the process, and alone can separate the heavy crude into its primary fractions of gasoline, jet fuel, diesel, heating oil, and fuel oil. Because the natural ratio of these fractions does not match the demands for the various fuels, additional steps are required to reform some of the products into products that are in demand. This is particularly true for high demand automobile gasoline.
These additional processes are as follows:
• Catalytic Reforming
• Catalytic Cracking
Catalytic Reforming produces high octane gasoline for today’s automobiles. Gasoline and naphtha feedstocks are heated to 500 degrees Celsius and flow through a series of fixed-bed catalytic reactors. Because the reactions absorb heat additional heaters are installed between reactors to keep the reactants at the proper temperature. The catalysts are palladium or other platinum group metal on an alumina base. While catalysts are never consumed in chemical reactions, they can be fouled, making them less effective over time. The series of reactors used in Catalytic Reforming are therefore designed to allow the catalyst can be regenerated.
Alkylation is another process for producing high octane gasoline. The reaction requires an acid catalyst of sulfuric acid or hydrofluoric acid at low temperatures (1-40 degrees Celsius) and low pressures (1-10 atmospheres). Neither palladium nor other platinum group metals are typically involved in this process.
Catalytic Cracking takes long molecules and breaks them into much smaller molecules and in so doing, converts heavy distillate to compounds with lower boiling points (e.g., naphthas), which are fractionated. Cracking is typically conducted in a fluidized bed reactor with a regenerator to continuously reactivate the catalyst. Cracking catalysts are typically zeolites comprised of alumina and silica. Platinum group metals are typically not involved.
Hydroprocessing includes both hydrocracking and hydrotreating techniques. Hydrotreating involves the addition of hydrogen atoms to molecules without actually breaking the molecule into smaller pieces and improves the quality of various products (e.g., by removing sulfur, nitrogen, oxygen, metals, and waxes and by converting olefins to saturated compounds). Palladium, among a number of other catalysts, can be used. Hydrocracking breaks longer molecules into smaller ones. Hydrocracking is a more severe operation than hydrotreating, using higher temperature and longer contact time, resulting in significant reduction in feed molecular size. Typically, Hydrocracking reactors contain fixed, multiple catalyst beds. The catalyst pellets are shaped similarly to Hydrotreating catalysts, the active metals impregnated in the silica-alumina catalyst base are typically palladium, platinum, or nickel, depending on the catalyst licensor.