Various fractions are more important at different times of year . During the summer driving months , the public consumes vast amounts of gasoline , whereas during the winter more fuel oil is consumed. These demands also vary depending upon whether you live in the frigid north , or the humid south . Modern refineries are able to alter the ratios of the different fractions to meet demand , and maximize profit. The Five Pillars of Refining While distillation can separate oil into fractions, chemical reactors are required to create more of the products that are in high demand .
Refineries rely on four major processing steps to alter the ratios of the different fractions.
Each of these methods involves feeding reactants to a reactor where they will be partly converted into products . The unreacted reactants are then separated from the products with a distillation column . The unreacted reactants are recycled for another pass, while the products are further separated and mixed with existing streams. In this way complete conversion of reactants can be obtained, even though not all of the reactants are converted on a given pass through the reactor. The four processing methods , along with distillation , are the pillars of petroleum refining .