Asphalts, distillation products

Large amounts of tar or pitch by-products are produced by industrial processes. The distillation of cmde petroleum (qv) yields a pitch-like residue termed bitumen or asphalt (qv). In the United States, these terms are interchangeable, but in Europe the term asphalt is generally restricted to naturally occurring rock or lake asphalt, whereas the residual product of cmde-od distillation is termed bitumen. Although these are important industrial materials produced in millions of metric tons annually, they are not included herein (see Asphalt Petroleum, products). 

ASTM D 402. 2008. Standard test method for distillation of cutback asphaltic (bituminous) products. West Conshohocken, PA ASTM International. 

Vacuum tower residuum properties can be set in various ways. When distillate production is to be maximized, the amount of gas oil allowed to remain in the bottoms stream must be minimized, and this material, usually 0 to 5 degrees API, is blended into residua fuels. This is called pitch operation. In asphalt operation, some gas oil must be left in the residuum in order to provide the proper degree of plasticity. The gravity of asphalt streams usually falls in the range of 5 to 8 degrees API. Not all crudes can be used to make asphalt since this is a question of whether or not the particular residuum has the proper composition of matter to render it suitable in asphalt applications. This question can only be answered experimentally and is usually contained in a detailed crude assay. Pitch operation can be practiced with any type of crude. 

The products could be classified as a function of various criteria physical properties (in particular, volatility), the way they are created (primary distillation or conversion). Nevertheless, the classification most relevant to this discussion is linked to the end product use LPG, premium gasoline, kerosene and diesel oil, medium and heavy fuels, specialty products like solvents, lubricants, and asphalts. Indeed, the product specifications are generally related to the end use. Traditionally, they have to do with specific properties octane number for premium gasoline, cetane number for diesel oil as well as overall physical properties such as density, distillation curves and viscosity. 

Simple conventional refining is based essentially on atmospheric distillation. The residue from the distillation constitutes heavy fuel, the quantity and qualities of which are mainly determined by the crude feedstock available without many ways to improve it. Manufacture of products like asphalt and lubricant bases requires supplementary operations, in particular separation operations and is possible only with a relatively narrow selection of crudes (crudes for lube oils, crudes for asphalts). The distillates are not normally directly usable processing must be done to improve them, either mild treatment such as hydrodesulfurization of middle distillates at low pressure, or deep treatment usually with partial conversion such as catalytic reforming. The conventional refinery thereby has rather limited flexibility and makes products the quality of which is closely linked to the nature of the crude oil used. 

Asphalt, prepared from petroleum, often resembles native asphalt. When asphalt is produced by distillation, the product is called residual, or straight-mn, asphalt. However, if the asphalt is prepared by solvent extraction of residua or by light hydrocarbon (propane) precipitation, or if it is blown or otherwise treated, the name should be modified accordingly to qualify the product, eg, propane asphalt. 

Cmde oil containing about 30% asphalt can be refined completely in an atmospheric unit to an asphalt product. However, most cmde oil cannot be distilled satisfactorily to an asphalt product at atmospheric pressure because of the presence of substantial proportions of high boiling gas oil fractions. Thus, as a supplement to the atmospheric process, a second fractionating tower (a vacuum tower) is added (Fig. 1). 

Propane Asphalt. As noted above, cmde oils contain different quantities of residuum (Fig. 2) and, hence, asphalt. Asphalt is also a product of the propane deasphalting and fractionation process (5,6,21,22) which involves the precipitation of asphalt from a residuum stock by treatment with propane under controlled conditions. The petroleum charge stock is usually atmospheric-reduced residue from a primary distillation tower. 

Air entrainment and foaming in hydrocarbon liquids can cause operational problems with high-speed machinery in physical-chemical processes such as petroleum production, distillation, cracking, coking, and asphalt processing. 

Over the years, the refinery has produced a range of petroleum products including liquid petroleum gas, gasoline, chemicals, solvents, distillate fuels, gas oils, lubricating oils, greases, asphalt products, and bunker fuels. The primary products of the refinery are currendy gasoline, jet fuel, and diesel. Minor products include coke, sulfur, naphtha, and fuel oil. The refinery processes approximately 200,000 barrels... 

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