METHOD AND SYSTEM FOR INTRODUCING CATALYST PRECURSOR INTO HEAVY OIL USING PARALLEL MIXER LINES AND BYPASS LINE

System and method for mixing a catalyst precursor into heavy oil include parallel mixing lines configured to receive and mix a diluted precursor mixture (catalyst precursor premixed with a hydrocarbon diluent) with heavy oil to form a conditioned feedstock. One of the mixing lines can be periodically taken offline (e.g., for maintenance) while one or more remaining mixing lines continue to form conditioned feedstock. A bypass line maintains substantially continuous flow volume of heavy oil when one of the mixing lines is taken offline. Valves and flow meters can be used to regulate flow through the mixing lines and bypass line. The system permits virtually unlimited scaleup of the mixing process while permitting periodic maintenance of the system without taking it completely offline. Mixing a catalyst precursor into heavy oil forms colloidal-sized catalyst particles in situ having high catalytic activity that promote beneficial upgrading reactions when hydroprocessing heavy oil.