The production of polypropylene pellets at Merseyside Works began with propylene, a refined gas received in tank cars. Propylene was purchased from four refineries in England that produced it in the course of refining crude oil into gasoline. In the first stage of the production process, polymerization, the propylene gas was combined with a diluents (or solvent) in a large pressure vessel. In a catalytic reaction, the polypropylene precipitated to the bottom of the tank and was then concentrated in a centrifuge.