Operating Economics: II. Refined Products
O il, which is now becoming the world's most widely used fuel, is hardly ever burned raw. All crude oil is a mixture of a long series of hydro-carbon compounds, but the nature of the mixture varies considerably between crudes from different oilfields and types of sedimentary strata. Here we are concerned with the chemistry of petroleum only in terms of the range of products that can be processed from these crudes; broadly, they can be ranked in three main families, paraffinic, asphaltic, and mixed base crudes. Paraffin based crudes, when refined, will give a high yield of gasoline and a fairly high yield of kerosene, a residue from which lubricating oils can be made, and solid paraffin waxes as a by-product. Asphaltic based crudes give a low yield of the lighter products, and a large yield of the black oils, with a semi-solid residue that is marketed as bitumen. Mixed base crudes come in between the other two. The first crude oils commercially refined, from the Pennsylvania fields in the eighteen-sixties, were paraffinic crudes rich in light products (which suited the early demand for lamp oil, though the gasoline yield was a nuisance). Venezuelan, Mexican and Californian crudes are asphaltic with a particularly high yield of fuel oil. Most of the crudes produced in the Middle East and in the main basins of the United States are of mixed base, with yields of products between the two extremes.
The main range of liquid petroleum products, again, can be ranked in terms of end-use. There are a range of light products, primarily the gasolines, but including diesel oil, from which energy is best obtained by explosive combustion; these are mainly used in road and air transport. Then come a range of diverse general fuels, from paraffin to heavy fuel oil, from which one obtains energy mainly by simple burning -- though paraffin is used in aircraft jet engines and attempts have long been made to run gas turbines on heavy fuel oil. Certain gases, in particular butane and propane, are separated as by-products of refining