A topping refinery is a part of the process of converting crude oil into lighter and more valuable products. A refinery separates various fractions from crude oil and transforms them into more useful products. The "topping" process aims to separate heavier hydrocarbon molecules to obtain lighter and more valuable products. In this process, heavier hydrocarbon fractions, such as diesel or heavy fuels, are converted into lighter products, such as gasoline or jet fuel. This process serves as a starting point for further processing of crude oil and is commonly used as a primary separation process in refineries.