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Petroleum Refining refining processes: ethylene, propylene, the butylenes, benzene, toluene, xylene,...

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  • Chapter 7

    Petroleum Refining Processes

    1. INTRODUCTION

    Before beginning our study of pure organic chemicals, we need to obtainsome background into the chemistry of petroleum, since it is from thissource that nearly all the major organic chemicals are derived. Table 7.1lists the seven important organic chemicals, all of which are obtained bypetroleum refining processes: ethylene, propylene, the butylenes, benzene,toluene, xylene, and methane. From these are made all 31 highest volumeorganic chemicals (some have more than one source and are listed twice). Itseems appropriate that we study petroleum and its major refining processesin detail before discussing these chemicals.

    Petroleum refining is not a part of our usual definition of the chemicalindustry, which includes Chemical Manufacturing (NAICS 325). However,the chemical process industries include those sectors of manufacturing asshown in Fig. 7.1: Paper Manufacturing (NAICS 322), Petroleum and CoalProducts Manufacturing (324), Chemical Manufacturing (325), Plastics andRubber Products Manufacturing (326), and Nonmetallic Mineral ProductManufacturing (327). All of these are important to the chemical industry.Petroleum refining is the largest part of Petroleum and Coal ProductsManufacturing. It provides the raw materials for a large portion of thechemical industry and employs many chemists. NAICS 324 was down to$125 billion of shipments in 1986 after a record $224 billion in 1981. Theslump was due mainly to decreased prices rather than production. In 1998 itstill had not bounced back and was at $137 billion. It has suffered comparedto Chemical Manufacturing, which has grown faster than the other classes.

  • By far the major product of this industry is the gasoline fraction frompetroleum. Fig. 7.2 demonstrates this, since U.S. shipments of gasoline weredown in 1986 as well. Gasoline in Fig. 7.2 follows a curve similar toPetroleum and Coal Products Manufacturing in Fig. 7.1. Other productssuch as jet fuel, kerosene, and fuel oils contribute substantially less to thetotal value of petroleum.

    The olefinsethylene, propylene, and the butylenesare derived fromnatural gas and petroleum. Methane is the major constituent in natural gas.The aromaticsbenzene, toluene, and the xylenesare derived frompetroleum. About 90% by weight of the organic chemicals in the worldcomes from natural gas and petroleum. But actually only 3% of this crudeoil and 6% of refinery output in the U.S. is processed into chemicals, withthe rest going as various fuels. Although we are a small user of thepetroleum industry, this 3-6% going to petrochemical feedstock is importantto us!

    The petrochemical industry had its birth in the early 190Os. In 1913propylene, a by-product of cracking, was introduced. In 1920 isopropylalcohol was made from petroleum. In 1923 the first derivatives of ethylenewere commercialized: ethylene chlorohydrin, ethylene glycol, anddichloroethane. By the 1940s petrochemicals were fully developed in the

    Table 7.1 Highest Volume Organic Chemicals Listed by Source

    Ethylene

    Ethylene dichlorideVinyl chlorideEthylbenzeneStyreneAcetic acidVinyl acetateEthylene oxideEthylene glycol

    Propylene

    AcrylonitrilePropylene oxideCumeneAcetonePhenolBisphenol Att-Butyraldehyde

    C4 Fraction

    ButadieneAcetic acidVinyl acetateIsobutyleneMethyl /-butyl ether

    Methane

    MethanolFormaldehydeDimethyl terephthalateMethyl /-butyl etherAcetic acidVinyl acetatew-ButyraldehydeUrea

    Benzene

    EthylbenzeneStyreneCumeneAcetonePhenolBisphenol ACyclohexaneAdipic acidNitrobenzene

    Toluene

    Benzene

    Xylene

    p-XyleneTerephthalic acidDimethyl terephthalate

  • ChemicalsPetroleum and CoalPaperPlastics and RubberNonmetallic Mineral

    Bill

    ion

    s of

    Do

    llars

    Year

    Figure 7.1 U.S. Shipments in the Chemical Process Industries. (Source: Annual Survey ofManufactures)

    GasolineLight Fuel OilsJet FuelHeavy Fuel OilsKerosene

    Bill

    ion

    s o

    f D

    olla

    rs

    Year

    Figure 7.2 U.S. Shipments of petroleum products. (Source: Annual Survey of Manufacturesand Chemical Economics Handbook)

  • Table 7.2 World Reserves and Production

    Area Known World Reserves, % Oil Production, %Middle East 66 31United States 2 10North America other than U.S. 5 7Africa 7 11Western Europe 2 10Asia-Pacific 4 11South and Central America 8 9Eastern Europe 6 HSource: Chemical Economics Handbook

    U.S. and the 1950s and '60s saw rapid production increases. The oil crisis of1973 caused huge increases in prices. The 1980s were characterized bymuch slower growth rates than the '5Os and '60s, and we still did notrebound completely in the 1990s.

    Oil is the largest segment of our energy raw materials use, being 40%,while coal use accounts for 27%, gas 21%, and hydroelectric/nuclear 12%.Table 7.2 summarizes the known world reserves of oil and the production byregion. We immediately see that most countries, including the U.S., outsidethe Middle East region import oil in large amounts for their production and

    Apparent ConsumptionDomestic ProductionImports

    Bill

    ion

    s o

    f B

    arre

    ls

    Year

    Figure 7.3 U.S. supply/demand for crude petroleum. (Source: Chemical EconomicsHandbook)

  • use. Two thirds of the known reserves in the world are in the Middle East.Fig. 7.3 demonstrates the growing dependence of the U.S. on imports.While our domestic production has not grown since the 1950s, imports havegrown dramatically from 0.3 billion barrels of oil in 1955 to 3.0 billionbarrels in 1997. We have increased our percentage of imports fromapproximately 13% in 1970 to 55% in 2000. A barrel (bbl) of crude oil is 42gallons and 1 ton of crude oil is approximately 7.3 bbl. More meaningfulfigures of our tremendous use of oil can be quoted in terms of bbl used perday. We use approximately 18 million bbl/day of oil in this country.Worldwide production is about 56 million bbl/day. With only knownreserves, this level of worldwide production could remain constant for only43 years.

    The reserves of coal are much greater than those for oil, and coaltechnology could be resurrected if necessary and if the industry and publicwant to pay the price for this development.

    Finally we look at the price of oil. Fig. 7.4 shows the average U.S.,domestic wholesale price for a barrel of oil. Note the very low prices in theearly 1970s, the large increases in the late 1970s after the oil embargo, andthe gradual levelling and final drop of prices in the late 1980s, with 1990sprices being fairly constant. The highest price of oil thus far has been $32 in1981, an average for a whole year, but a brief period at $40 /bbl in late 1990,immediately after Iraq entered Kuwait, did occur. In parts of 2000 the pricewas back up to $34/bbl. An uncertain future lies ahead.

    Dol

    lars

    /Bar

    rel

    Year

    Figure 7.4 U.S. prices of crude oil. (Source: Chemical Economics Handbook)

  • Table 7.3 Fractions of Petroleum

    Approximate bp (0C)350C

    >350C

    NameGases

    Light naphtha(mainly C5-C6)

    Heavy naphtha(mainly C7-C9)

    Kerosene

    Gas oil

    Lubricating oil

    Heavy fuel oil

    Asphalt

    UsesCH4, C2H6, C3H8, C4H10 similar to naturalgas and useful for fuel and chemicals.C4-C10 aliphatic and cycloaliphaticcompounds. May contain some aromatics.Useful for both fuel and chemicals.C4-C10 aliphatic and cycloaliphaticcompounds. May contain some aromatics.Useful for both fuel and chemicals.Contains C9-C16 compounds useful for jet,tractor, and heating fuel.Contains C15-C25 compounds useful fordiesel and heating fuel. Catalyticallycracked to naphtha and steam-cracked toolefins.Used for lubrication. May be catalyticallycracked to lighter fractions.Boiler fuel. May be catalytically cracked tolighter fractions.Paving, coating, and structural uses.

    Source: Wittcoff& Reuben

    2. DISTILLATION

    Several thousand compounds are present in petroleum. Few areseparated as pure substances. Many of the uses of petroleum can be servedby certain fractions from the distillation of crude oil. Typical distillationfractions and their uses are given in Table 7.3 and a distillation unit is shownin Fig. 7.5. The complexity of the molecules, molecular weight, and carbonnumber increase with the boiling point. The higher boiling fractions areusually distilled in vacuo at lower temperature than their atmospheric boilingpoints to avoid excessive decomposition to tars.

    Each fraction of distilled petroleum still contains a complex mixture ofchemicals but they can be somewhat categorized. A certain sample ofstraight-run gasoline (light naphtha) might contain nearly 30 aliphatic,noncyclic hydrocarbons, nearly 20 cycloaliphatic hydrocarbons (mainlycyclopentanes and cyclohexanes) sometimes called naphthenes, and 20aromatic compounds.

  • Figure 7.5 Large petroleum distillation columns like this one in the foreground canprocess over 400,000 barrels of crude oil per day into nearly 210,000-230,000 barrels ofgasoline. That is enough to fill 678,000 13-gallon automobile tanks or 441,000 20-gallonautomobile tanks. (Courtesy of BP Amoco, Texas City, TX)

    Although petroleum basically consists of hydrocarbons, there are smalleramounts of other types of materials. For example, carboxylic acids occur tothe extent of about 0.1-3%. These can be isolated quite easily by baseextraction and the mixture is known as naphthenic acid, which can be used

    naphthenic acid

    as its metal salt for paint drying, catalysts, lube additives, woodpreservatives, and tire adhesion promoters. Approximately 20 million Ib are

  • used each year. A smaller amount of cyclohexyl derivatives are included inthe mixture as well.

    A small

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