Modem Petroleum Processing

A modem petroleum refinery is a complex system of chemical and physical operations. The cmde oil is first separated by distillahon into fractions such as gasoline, kerosene, and fuel oil. Some of the distillate fractions are converted to more valuable products by cracking, polymerization, or reforming. The products are treated to remove undesirable components, such as sulfur, and then blended to meet the final product specifications. A detailed analysis of the entire petroleum production process, including emissions and controls, is obviously well beyond the scope of this text. 

The fatty oil industry has not yet made the same progress in the chemical processing of its products as is the case in the petroleum industry. After the initial success attained in the development of the fat-hardening technique, this industry has remained stationary for many years. However, the chemical modification of fatty oils is of vital importance and the development of modem processes in the fatty oil industry will depend to a large extent on the basic knowledge of its raw materials and the fundamental study of possible chemical transformations. 

The alcohol ether sulfates (AES) represent approximately 9% of industrialized surfactant consumption. Because of their perceived mildness, they are used primarily in personal care products. They have a strong position in terms of raw materials since they can be made from either petroleum or renewable (i.e., agriculturally derived) raw materials. One possible disadvantage of AES surfactants is the possible presence of dioxane derivatives as a byproduct of the ethoxylation process. Although modem processes have been shown to effectively eliminate the presence of such contaminants, emotional factors and lack of good information must always be considered, especially where consumer products are concerned. 

There are many other processes used in refineries not mentioned here. The list above is intended only to emphasize the wide diversity of processing which is common to petroleum refining and to introduce in a very general way some of the more important of these processes. Also it must be emphasized that only fundamental principles of refinery operations have been discussed and modem manufacmring techniques vary widely from company to company. 

Distillation may be defined as the separation of the constituents of a liquid mixture by partial vaporization of the mixture, followed by separate recovery of the vapor and liquid residue. Since crude petroleum is the most complex mixture of liquids found in nature, it is not surprising that distillation is one of the most important processes in modem petroleum refining. 

Sulphuric acid is the largest volume chemical in the world with an annual production of about 180 mill, t/year which is used primarily for phosphate fertilizers, petroleum alkylation, copper ore leaching and in smaller quantities for a number of other purposes (pulp and paper, other acids, aluminium, titanium dioxide, plastics, synthetic fibres, dyestuffs, sulphonation etc.). The major sulphur sources for sulphuric acid production are sulphur recovered from hydrocarbon processing in the refineries and from desulphurisation of natural gas, SO2 from metallurgical smelter operations, spent alkylation acid, and to a minor extent mined elemental sulphur and pyrites. A simplified flow sheet of a modem double-absorption plant for sulphuric acid production from sulphur is shown in Fig. 1. 

A modem petroleum refinery in the United States processes between 100,000 and 500,000 barrels/day of crude oil. The incoming cmde is first desalted and then passed through an atmospheric pressure distillation column that separates it into fractions, as shown in Figure 2-12. 

Figure 1731. Fluidized bed reactor processes for the conversion of petroleum fractions, (a) Exxon Model IV fluid catalytic cracking (FCC) unit sketch and operating parameters. (Hetsroni, Handbook of Multiphase Systems, McGraw-Hill, New York, 1982). (b) A modem FCC unit utilizing active zeolite catalysts the reaction occurs primarily in the riser which can be as high as 45 m. (c) Fluidized bed hydroformer in which straight chain molecules are converted into branched ones in the presence of hydrogen at a pressure of 1500 atm. The process has been largely superseded by fixed bed units employing precious metal catalysts (Hetsroni, loc. cit.). (d) A fluidized bed coking process units have been built with capacities of 400-12,000 tons/day.

Hydrocracking is probably the most versatile of modem petroleum processes. This versatility has been achieved by the development of specific families of catalysts, of processing schemes designed to allow these catalysts to function efficiently, and of optimum refining relationships between hydrocracking and other refining processes. 

As refineries have evolved, distillation has remained the prime means by which petroleum is refined (Speight, 1999). Indeed, the distillation section of a modem refinery is the most flexible unit in the refinery since conditions can be adjusted to process a wide range of refinery feedstocks from the lighter cmde oils to the heavier, more viscous cmde oils. However, the maximum permissible temperature (in the vaporizing furnace or heater) to which the feedstock can be subjected is 350°C (660°F). The rate of thermal decomposition increases markedly above this temperature if decomposition occurs within a distillation unit, it can lead to coke deposition in the heater pipes or in the tower itself with the resulting failure of the unit. 

Modem refineries use a combination of heat, catalyst and hydrogen to convert the petroleum constituents into these products. Conversion processes include coking, catalytic cracking, and hydrocracking (Chapter 7) to convert the higher molecular weight constituents into lower molecular weight products and reduce the heteroatom content to create environmentally acceptable products. 

Chemical reactors are unquestionably the most vital parts of many chemical, biochemical, polymer, and petroleum processes because they transform raw materials into valuable chemicals. A vast variety of useful and essential products are generated via reactions that convert reactants into products. Much of modem society is based on the safe, economic, and consistent operation of chemical reactors. 

Cranmore, R.E., and Stanton, E. 2000. In Modem Petroleum Technology. Volume 1 Upstream. R.A. Dawe (Editor). John Wiley Sons, New York. Chapter 9. Crawford, D.B., Durr, C.A., Finneran, J.A., and Turner, W. 1993. Chemicals from natural gas. In Chemical Processing Handbook. J.J. McKetta (Editor). Marcel Dekker, New York. Page 2. 

The catalytic reforming process is, together with catalytic cracking, one of the most important processes in modem refinery schemes. It is used to convert low octane n-alkanes and cycloalkanes with 5 to 10 carbon atoms contained in the petroleum naphtha into high-octane isoalkanes and aromatics gasoline components and hydrogen. Typically, reformer reactors operate at temperatures of 425-525 °C and hydrogen pressures of 0.5-3.0 MPa. 

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