Petroleum Fractions and Residues

Liquid Petroleum fractions are light naphtha, heavy naphtha, kerosine and gas oil. The bottom product from distillation units is the residue. These 

Naphtha is a generic term normally used in the petroleum refining industry for the overhead liquid fraction obtained from atmospheric distillation units. The approximate boiling range of light straight-run naphtha (LSR) is 35-90°C, while it is about 80-200°C for heavy straight-run naphtha (HSR).  

Naphtha is also obtained from other refinery processing units such as catalytic cracking, hydrocracking, and coking units. The composition of naphtha, which varies appreciably, depends mainly on the cmde type and whether it is obtained from atmospheric distillation or other processing units. 

Naphtha from atmospheric distillation is characterized by an absence of olefinic compounds. Its main constituents are straight and branched-chain paraffins, cycloparaffms (naphthenes), and aromatics, and the ratios of these components are mainly a function of the crude origin. 

Naphthas obtained from cracking units generally contain variable amounts of olefins, higher ratios of aromatics, and branched paraffins. Due to presence of unsaturated compounds, they are less stable than straight-mn naphthas. On the other hand, the absence of olefins increases the stability of naphthas produced by hydrocracking units. In refining operations, however, it is customary to blend one type of naphtha with another to obtain a required product or feedstock. 

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Natural gas and crude oils are the main sources for hydrocarbon intermediates or secondary raw materials for the production of petrochemicals. From natural gas, ethane and LPG are recovered for use as intermediates in the production of olefins and diolefms. Important chemicals such as methanol and ammonia are also based on methane via synthesis gas. On the other hand, refinery gases from different crude oil processing schemes are important sources for olefins and LPG. Crude oil distillates and residues are precursors for olefins and aromatics via cracking and reforming processes. This chapter reviews the properties of the different hydrocarbon intermediates—paraffins, olefins, diolefms, and aromatics. Petroleum fractions and residues as mixtures of different hydrocarbon classes and hydrocarbon derivatives are discussed separately at the end of the chapter. 

The most important olefins used for the production of petrochemicals are ethylene, propylene, the butylenes, and isoprene. These olefins are usually coproduced with ethylene by steam cracking ethane, LPG, liquid petroleum fractions, and residues. Olefins are characterized by their higher reactivities compared to paraffinic hydrocarbons. They can easily react with inexpensive reagents such as water, oxygen, hydrochloric acid, and chlorine to form valuable chemicals. Olefins can even add to themselves to produce important polymers such as polyethylene and polypropylene. Ethylene is the most important olefin for producing petrochemicals, and therefore, many sources have been sought for its production. The following discusses briefly, the properties of these olefmic intermediates. 

Reduce harmful impurities in petroleum fractions and residues to control pollution and to avoid poisoning certain processing catalysts. For example, hydrotreatment of naphtha feeds to catalytic reformers is essential because sulfur and nitrogen impurities poison the catalyst. 

The main route for producing light olefins, especially ethylene, is the steam cracking of hydrocarbons. The feedstocks for steam cracking units range from light paraffinic hydrocarbon gases to various petroleum fractions and residues. The properties of these feedstocks are discussed in Chapter 2. 

Gasmaco [Gas Machinery Company] A process for making a substitute natural gas from petroleum fractions and residues by thermal cracking. Developed from the Hall (2) process in the 1940s by the American Gas Association. See also Petrogas. 

Bouquet, M. and A. Bailleul (1986), Routine method for quantitative carbon 13 NMR spectra editing and providing structural patterns. Application to every kind of petroleum fraction including residues and asphaltenes . Fuel, Vol. 65, p. 1240. 

Solvent extraction may also be used to reduce asphaltenes and metals from heavy fractions and residues before using them in catalytic cracking. The organic solvent separates the resids into demetallized oil with lower metal and asphaltene content than the feed, and asphalt with high metal content. Figure 3-2 shows the IFP deasphalting process and Table 3-2 shows the analysis of feed before and after solvent treatment. Solvent extraction is used extensively in the petroleum refining industry. Each process uses its selective solvent, but, the basic principle is the same as above. 

RCC [Reduced crude oil conversion] A process for converting reduced crude oil (a petroleum fraction), and other petroleum residues, into high-octane gasoline and other lighter fuels. Based on the FCC process, but adapted to accommodate higher levels of metal contaminants which can harm the catalyst. Developed by Ashland Oil Company and UOP and... 

Analytical separation and spectroscopic techniques normally used for petroleum crudes and residues were modified and used to characterize coal liquids, tar sands bitumens, and shale oils. These techniques include solvent extraction, adsorption, ion-exchange, and metal complexing chromatography to provide discrete fractions. The fractions are characterized by various physical and spectroscopic methods such as GLC, MS, NMR, etc. The methods are relatively fast, require only a few grams of sample, provide compound type fractions for detailed characterization, and provide comparative compositional profiles for natural and synthetic fuels. Additional analytical methods are needed in some areas. 

Experience has shown that to obtain meaningful results in analyzing petroleum crudes and residues, it is necessary to separate a sample into a certain number of well-defined fractions and to analyze these fractions in detail. Conclusions as to the composition of the original sample are then made by combining the results of the analyses on each fraction in a manner consistent with the steps performed to obtain them. This same approach is used for the synthetic liquid fuels, and this paper reports our results obtained on such materials. 

Separation Into Fractions. The separation procedure, developed for petroleum crudes and residues (40) is illustrated in Figure 1. This procedure is applicable to samples having a boiling point higher than 470° F. 

Data reporting (i.e., the statement of the results of the proximate analysis test methods) usually includes (in some countries but not in all countries) descriptions of the color of the ash and of the coke button. As an interesting comparison, the test for determining the carbon residue (Conradson), the coke-forming propensity of petroleum fractions and petroleum products (ASTM D-189 ASTM D-2416), advocates the use of more than one crucible. A porcelain crucible is used to contain the sample, and this is contained within two outer iron crucibles. This corresponds to the thermal decomposition of the sample in a limited supply of air (oxygen) and the measurement of the carbonaceous residue left at the termination of the test. 

Chemical composition of waste plastic cracking products depends on shares of the individual polymers (PE, PP, PS) in the feed and process parameters. This fact decides the technological application of the final products. Important products of the cracking process, both petroleum fractions and waste plastics, are coke residues. Coke residue yield increases considerably, up to 10 wt%, in cracking of municipal and industrial waste plastics since they contain various inorganic impurities and additives. It can be applied as solid fuel, like brown coal. In the fluid cracking the solid residue is continuously removed from the process by combustion in a regenerator section. 

Diethyl ether, diisopropyl ether, tetrahydrofuran, and dioxan, as well as the hydrocarbons decalin and tetralin and even petroleum fractions and xylene, usually contain peroxides. Owing to their involatility, peroxides become enriched in distillation residues and have often given rise to very severe explosions.13 To avoid accidents when working with these solvents it is essential to test for the presence of peroxides and, if they are present, to take steps to remove them. Then, to suppress formation of further peroxides in these solvents, they must be stored in dark flasks and access of atmospheric oxygen must be very rigidly excluded. 

Jenkins (16) has isolated cyclic monocarboxylic and fatty acids as well as aliphatic esters from petroleum distillates and residues of several crudes. Seifert and Howells (17), through an elaborate extraction and separation scheme, have recovered phenols and carboxylic acids with molecular weights of 300 to 400 from the Midway-Sunset crude. The acidic extracts have been shown to give ultra low (< 10 dyne/cm) interfacial tensions when contacted with an alkali aqueous phase. Phenolic components isolated from the crude were found to diminish the interfacial activity of the acidic fraction. 

Properties. The properties of naphtha, gas od, and H-od products from an H-coal operation are given in Table 7. These analyses are for Hquids produced from the syncmde operating mode. Whereas these Hquids are very low in sulfur compared with typical petroleum fractions, they are high in oxygen and nitrogen levels. No residual od products (bp > 540° C) are formed. 

Feeds to hydrotreatment units vary widely they could he any petroleum fraction, from naphtha to crude residues. The process is relatively simple choosing the desulfurization process depends largely on the feed type, the level of impurities present, and the extent of treatment needed to suit the market requirement. Table 3-12 shows the feed and product properties from a hydro treatment unit. ... 

Water hydrolyzes diethyl phosphorochloridate [chloro-diethoxyphosphorus(V) oxide] readily but does not affect the diene. Alternatively, the reaction mixture can be processed by fractionation. Evaporation of the petroleum ether and fractionation of the residue through a 25-cm. x 2.2-cm. column of glass helices yields 170 g. (98.5%) of diethyl phosphorochloridate, b.p. 34-36°/0.2 mm., d 1.4210-1.4250 (the refractive index indicates that it contains 5-10% of the title compound), and 240-255 g. (90-96%) of l,2,3,4,5-pentachloro-5-ethylcyclo-pentadiene, b.p. 51-53°/0.2 mm., 1.5398. 

Figure 5.1 Key aspects of the SPMD sampling and residue analysis process. Often class fractionation is required following SEC when extracts contain complex mixtures of chemicals. Reprinted with permission from the American Petroleum Institute (Huckins et al., 2002).

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