METHOD AND SYSTEM FOR MIXING CATALYST PRECURSOR INTO HEAVY OIL USING A HIGH BOILING HYDROCARBON DILUENT

System and method for mixing a catalyst precursor into heavy oil using a high boiling hydrocarbon diluent to form a diluted precursor mixture, which is mixed with the heavy oil feedstock to form a conditioned feedstock, which is subsequently heated to decompose the precursor and form dispersed metal sulfide catalyst particles in situ. Because the high boiling hydrocarbon diluent is typically at a temperature above the decomposition temperature of the catalyst precursor, it is first feed through a cooler to reduce its temperature to avoid premature decomposition of the catalyst precursor. The high boiling hydrocarbon diluent may include a portion of the heavy oil feedstock, a portion of the conditioned feedstock, a vacuum tower bottoms product, or other high boiling hydrocarbon material having a boiling point higher than 524° C. A portion of the diluent may optionally include a medium boiling hydrocarbon material having a boiling point less than 524° C.