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Petrochemical & Petroleum Refining Technology CHAPTER 5 : PETROCHEMICALS  PETROCHEMICALS Petrochemicals are chemicals made from crude oil and natural gas. Crude oil and natural gas are made up of hydrocarbon molecules, which are comprised of one or more carbon atoms, to which hydrogen atoms...

Petrochemical & Petroleum Refining Technology CHAPTER 5 : PETROCHEMICALS  PETROCHEMICALS Petrochemicals are chemicals made from crude oil and natural gas. Crude oil and natural gas are made up of hydrocarbon molecules, which are comprised of one or more carbon atoms, to which hydrogen atoms are attached.  Overall Overview Up Stream: Oil & Gas fields Offshore production platforms Mid Stream: Transportation & Storage Pipeline transmission (Gas & Oil) LNG Down Stream: Upstream Petrochemicals Oil Refinery Petrochemical plants Intermediate Petrochemicals Fertilisers Downstream Petrochemicals  PETROCHEMICALS Currently, oil and gas are the main sources: 1. Least expensive 2. Most readily available 3. Can be processed most easily into primary petrochemicals.  PETROCHEMICALS Petrochemicals have had a dramatic impact on our food, clothing, shelter and leisure. Some synthetics, tailored for particular uses, actually perform better than products made by nature because of their unique properties.  PETROCHEMICALS Raw Materials or Feedstocks The usual feedstocks are natural gas, natural gas liquids (NGL), naphtha, gas oil and refinery gases. These products come from crude oil and natural gas. Crude oil is processed into naphtha, gas oil and refinery gas streams. NGLs (ethane, propane, butane) are separated from natural gas.  Feed Stock The starting material used for the production of petrochemicals is called feed stock. There are two common feed stocks for the manufacture of petrochemicals; these are : 1. Natural gas 2. Naphtha and reformed naphtha Natural gas occurs in nature in association with petroleum. The major hydrocarbon component of natural gas is methane. Naphtha is a fraction obtained during refining of petroleum The choice for the use of natural gas or naphtha as feed stock by a particular country or industry depends upon the availability of a particular feed stock or the availability of technology for the manufacture of petrochemicals. Petrochemical feedstock sources. Petrochemical raw materials  Intermediates and Derivatives The petrochemicals obtained from primary petrochemicals by chemical reaction are called (secondary) intermediate petrochemicals. Petrochemicals are also referred to as first generation petrochemicals and second generation petrochemicals; first generation petrochemicals are converted to second generation petrochemicals. These intermediate petrochemicals may be put to some use or these may be further processed to get derivatives of petrochemicals by a chemical reaction or a series of reactions to get products for other end uses.  Intermediates and Derivatives Petrochemical intermediates are generally produced by chemical conversion of primary petrochemicals to form more complicated derivative products Petrochemical derivative products can be made in a variety of ways: 1. Directly from primary petrochemicals 2. Through intermediate products which still contain only carbon and hydrogen 3. Through intermediates which incorporate chlorine, nitrogen or oxygen in the finished derivative.  Intermediates and Derivatives In some cases, they are finished products; in others, more steps are needed to arrive at the desired composition Of all the process used, one of the most important is polymerization. It is used in the production of plastics, fibers and synthetic rubber, the main finished petrochemical derivatives. Intermediates and Derivatives Some typical petrochemical intermediates are: vinyl acetate for paint, paper and textile coatings vinyl chloride for polyvinyl chloride (PVC) resin manufacture ethylene glycol for polyester textile fibres styrene which is important in rubber and plastic manufacturing Relationship between petroleum, feedstock, primary petrochemicals, secondary (intermediate) petrochemicals and useful end products. Petrochemical products  Petrochemical Industries BASF Dow Chemical ExxonMobil Chemical DuPont Sumitomo Chemical Behn Meyer Titan Chemicals  Petrochemicals Industry in Malaysia Shell Exxon Mobil Dow Chemical Conoco Phillips Kaneka Polyplastics Toray BP BASF (Badische Anilin- und Soda-Fabrik (English: Baden Aniline and Soda Factory) Idemitsu Titan Eastman Chemicals Petrochemicals Production in Malaysia Olefins Polyolefins Aromatics Acetic acid Styrene monomer Ethylene oxides Polystyrene Glycols Ethylbenzene Vinyl chloride Oxo-alcohol PVC Exthoxylates Acrylic acids Phtalic anhydride Petrochemical industry were divided into 3 groups as follows:  Hydrocarbon Intermediates 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 diolefins. 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. Paraffinic hydrocarbons Paraffinic hydrocarbons used for producing petrochemicals range from the simplest hydrocarbon, methane, to heavier hydrocarbon gases and liquid mixtures present in crude oil fractions and residues. Paraffins are relatively inactive compared to olefins, diolefins, and aromatics. Few chemicals could be obtained from the direct reaction of paraffins with other reagents. However, these compounds are the precursors for olefins through cracking processes. The C6–C9 paraffins and cycloparaffins are especially important for the production of aromatics through reforming.  Down Stream Petrochemicals The petrochemicals obtained from a given feedstock by a series of reactions are called down stream petrochemicals. Down stream means that a particular petrochemical comes at a later stage in the sequence of chemicals produced. For example in the following reaction. CH4 → CH3Cl → CH3OH Methyl alcohol is referred to as a down stream petrochemical  Methane (CH ) 4 As a chemical compound, methane is not very reactive. It does not react with acids or bases under normal conditions. It reacts, however, with a limited number of reagents such as oxygen and chlorine under specific conditions. For example, it is partially oxidized with a limited amount of oxygen to a carbon monoxide-hydrogen mixture at high temperatures in presence of a catalyst. The mixture (synthesis gas) is an important building block for many chemicals. Chemicals Based on Methane  Petrochemicals from Methane Methane is the major hydrocarbon component of natural gas. Methane is also obtained in large quantities as a by product of petroleum refining. The major petrochemicals produced from methane are: 1. Chlorinated products 2. Carbon black 4. Hydrogen 5. Methyl alcohol 1. Chlorinated products of methane Methane is chlorinated to get methyl chloride (CH3CI), methylene chloride (CH2CI2), chloroform (CHCI3) and carbon tetrachloride (CCI4). Most of the chlorinated products of methane are used as a solvent. CH4  CI2 CH3CI  CH2CI2  CHCI3  CCI4 Chloromethanes  Uses of Chloromethanes: The major use of methyl chloride is to produce silicon polymers. Other uses include the synthesis of tetramethyl lead as a gasoline octane booster, a methylating agent in methyl cellulose production, a solvent, and a refrigerant. Methylene chloride has a wide variety of markets.  One major use is a paint remover. It is also used as a degreasing solvent, a blowing agent for polyurethane foams, and a solvent for cellulose acetate. Chloroform is mainly used to produce chlorodifluoromethane (Fluorocarbon 22) by the reaction with hydrogen fluoride: 2. Carbon black Methane is converted into carbon black (a form of carbon) by pyrolysis (cracking) and hydrogen is obtained as a by product. Carbon black is used as a black pigment in manufacture of black printing ink and in rubber tyre industry.  C  2H2 CH4 heated 3. Hydrogen Hydrogen obtained by pyrolysis of methane is used for the manufacture of ammonia gas. Ammonia is used as a raw material for manufacture of urea (a fertilizer), ammonium nitrate and several other products. 4. Methyl alcohol Methane is converted into methanol (methyl alcohol, CH3OH) by catalytic oxidation. catalyst CH4 + O2  CH3OH (methanol) Methyl alcohol (methanol is further oxidized to get formaldehyde. Formaldehyde is an important raw material for number of useful products, for example phenol-formaldehyde resins (bakelite). Methyl alcohol is an important industrial solvent. CH3OH  HCHO (formaldehyde) Questions 1. Give 2 examples of raw materials and 2 examples of primary petrochemicals. 2. Give 3 examples of derivatives for methane. 3. Provide 1 example of reaction to produce methyl alcohol and the usage of methyl alcohol.  Ethane (CH3-CH3) Ethane is an important paraffinic hydrocarbon intermediate for the production of olefins, especially ethylene. Ethane's relation with petrochemicals is mainly through its cracking to ethylene.  Propane (CH CH CH ) 3 2 3 Propane is a more reactive paraffin than ethane and methane. This is due to the presence of two secondary hydrogens that could be easily substituted. Chemicals directly based on propane are few, although as mentioned, propane and LPG are important feedstocks for the production of olefins.  Butanes (C H ) 4 10 Dehydrogenation of isobutane produces isobutene, which is a reactant for the synthesis of methyl tertiary butyl ether (MTBE). This compound is currently in high demand for preparing unleaded gasoline due to its high octane rating and clean burning properties.  Oxidation of paraffins (fatty Acids and Fatty Alcohols) The catalytic oxidation of long-chain paraffins (Cl8-C30) over manganese salts produces a mixture of fatty acids with different chain lengths. Temperature and pressure ranges of 105–120°C and 15–60 atmospheres are used. About 60 wt% yield of fatty acids in the range of Cl2-Cl4 is obtained. These acids are used for making soaps. The main source for fatty acids for soap manufacture, however, is the hydrolysis of fats and oils (a nonpetroleum source).  SULFONATION OF n-PARAFFINS (Secondary Alkane Sulfonates SAS) The reaction is catalyzed by ultraviolet light with a wave-length between 3,300–3,600Å.  The sulfonates are nearly 100% biodegradable, soft and stable in hard water, and have good washing properties.  Olefinic hydrocarbons The most important olefins used for the production of petrochemicals are ethylene, propylene, the butylenes, and isoproprene. 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.  Ethylene (CH =CH ) 2 2 Ethylene (ethene), the first member of the alkenes, is a colorless gas with a sweet odor Slightly soluble in water and alcohol Highly active compound that reacts easily by addition to many chemical reagents. For example, ethylene with water forms ethyl alcohol. Chemicals Based on Ethylene Ethylene reacts by addition to many inexpensive reagents such as water, chlorine, hydrogen chloride, and oxygen to produce valuable chemicals. It can be initiated by free radicals or by coordination catalysts to produce polyethylene, the largest-volume thermoplastic polymer.  It can also be copolymerized with other olefins producing polymers with improved properties. For example, when ethylene is polymerized with propylene, a thermoplastic elastomer is obtained.  Petrochemicals from Ethylene Ethylene is obtained by pyrolysis of natural gas or from naphtha by cracking. Ethylene is an unsaturated hydrocarbon and has a carbon-carbon double bond. Therefore, ethylene is very reactive and can be converted to a variety of petrochemicals and useful end products. The major petrochemicals produced from ethylene are : 1. Ethyl alcohol 2. Ethylene oxide 3. Ethylene glycol 4. Dichloroethane 5. Vinyl chloride 6. Polyethylene 7. Ethyl benzene 1. Ethyl Alcohol Ethyl alcohol (ethanol) is made by hydration of ethylene. Ethyl alcohol is used as a solvent and a raw material for the manufacture of acetic acid, ethyl acetate and a large number of other useful products. 2. Ethylene Oxide and Industry Ethylene is oxidized to ethylene oxide with air or oxygen in the presence of a catalyst. It is a raw material for the manufacture of ethylene glycol, which is a starting material for the manufacture of polyester. 3. Ethylene Glycol Ethylene glycol ( 1,2-dihydroxyethane) is manufactured by starting with ethylene. There are several methods by which ethylene is converted to ethylene glycol. Glycol is used as an anti freeze in automobiles. Ethylene glycol is an important starting material for the manufacture of polyester. 4. Dichloroethane Dichloroethane (1,2-dichloroethane) is made from ethylene by the reaction of chlorine. It is used as a starting material for several other raw materials like ethylene glycol, vinyl chloride, etc.  Chlorination of ethylene The direct addition of chlorine to ethylene produces ethylene dichloride (1,2-dichloroethane). Ethylene dichloride is the main precursor for vinyl chloride, which is an important monomer for polyvinyl chloride plastics and resins. Catalytic oxidation of ethylene produces ethylene oxide, which is hydrolyzed to ethylene glycol. Ethylene glycol is a monomer for the production of synthetic fibers. The main source for ethylene is the steam cracking of hydrocarbons (Chapter 2).  Ethylene Glycol (CH2OHCH2OH) Ethylene glycol (EG) is colorless syrupy liquid, and is very soluble in water. The boiling and the freezing points of ethylene glycol are 197.2° and –13.2°C, respectively. Current world production of ethylene glycol is approximately 15 billion pounds. Most of that is used for producing polyethylene terephthalate (PET) resins (for fiber, film, bottles), antifreeze, and other products. Approximately 50% of the world EG was consumed in the manufacture of polyester fibers and another 25% went into the antifreeze. The main route for producing ethylene glycol is the hydration of ethylene oxide in presence of dilute sulfuric acid an important plastic material polystyrene. Addition of chlorine to ethylene produces 1,2-dichloroethane, which is cracked to vinyl chloride. Vinyl chloride is an important plastic precursor. Heat Ethylene is also an active alkylating agent. Alkylation of benzene with ethylene produces ethyl benzene, which is dehydrogenated to styrene. dehydrogenated  Vinyl Chloride (CH2=CHCl) Vinyl chloride is a reactive gas soluble in alcohol but slightly soluble in water. It is the most important vinyl monomer in the polymer industry. Vinyl chloride monomer (VCM) was originally produced by the reaction of hydrochloric acid and acetylene in the presence of HgCl2 catalyst. The reaction is straightforward and proceeds with high conversion (96% on acetylene):  Ethanolamines A mixture of mono-, di-, and triethanolamines is obtained by the reaction between ethylene oxide (EO) and aqueous ammonia. The reaction conditions are approximately 30–40°C and atmospheric pressure: Ethanolamines are important absorbents of acid gases in natural gas treatment processes. Another major use of ethanolamines is the production of surfactants.  Chemicals Based on Propylene Propylene, “the crown prince of petrochemicals,” is second to ethylene as the largest-volume hydrocarbon intermediate for the production of chemicals. As an olefin, propylene is a reactive compound that can react with many common reagents used with ethylene such as water, chlorine, and oxygen. However, structural differences between these two olefins result in different reactivities toward these reagents.  Butadiene Butadiene is by far the most important monomer for synthetic rubber production. Itcan be polymerized to polybutadiene or copolymerized with styrene to styrene-butadiene rubber (SBR). Butadiene is an important intermediate for the synthesis of many chemicals such as hexamethylenediamine and adipic acid. Both are monomers for producing nylon. The unique role of butadiene among other conjugated diolefins lies in its high reactivity as well as its low cost. Butadiene is obtained mainly as a co-product with other light olefins from steam cracking units for ethylene production. Other sources of butadiene are the catalytic dehydrogenation of butanes and butenes, and dehydration of 1,4-butanediol.  Aromatic hydrocarbons Benzene, toluene, xylenes (BTX), and ethylbenzene are the aromatic hydrocarbons with a widespread use as petrochemicals. They are important precursors for many commercial chemicals and polymers such as phenol, trinitrotoluene (TNT), nylons, and plastics. Aromatic compounds are characterized by having a stable ring structure due to the overlap of the π-orbitals (resonance). Accordingly, they do not easily add to reagents such as halogens and acids as do alkenes. Aromatic hydrocarbons are susceptible, however, to electrophilic substitution reactions in presence of a catalyst. Aromatic hydrocarbons are generally nonpolar. They are not soluble in water, but they dissolve in organic solvents such as hexane, diethyl ether, and carbon tetrachloride.  Benzene Benzene (C6H6) is the simplest aromatic hydrocarbon and by far the most widely used one. Before 1940, the main source of benzene and substituted benzene was coal tar. Currently, it is mainly obtained from catalytic reforming. Other sources are pyrolysis gasolines and coal liquids. Aromatic hydrocarbons, like paraffin hydrocarbons, react by substitution, but by a different reaction mechanism and under milder conditions. Aromatic compounds react by addition only under severe conditions. For example, electrophilic substitution of benzene using nitric acid produces nitrobenzene under normal conditions, while the addition of hydrogen to benzene occurs in presence of catalyst only under high pressure to give cyclohexane:  Aromatics Production Liquefied petroleum gas (LPG), a mixture of propane and butanes, is catalytically reacted to produce an aromatic-rich product. The first step is assumed to be the dehydrogenation of propane and butane to the corresponding olefins followed by oligomerization to C6, C7, and C8 olefins. These compounds then dehydrocyclize to BTX aromatics. The following reaction sequence illustrates the formation of benzene from 2 propane molecules: Benzene is an important chemical intermediate and is the precursor for many commercial chemicals and polymers such as phenol, styrene for poly-styrenics, and caprolactom for nylon 6. Styrene Due to the narrow range of the boiling points of C8 aromatics (Table 2-4), separation by fractional distillation is difficult. A superfractionation technique is used to segregate ethylbenzene from the xylene mixture. Because p-xylene is the most valuable isomer for producing synthetic fibers, it is usually recovered from the xylene mixture.  Fractional crystallization used to be the method for separating the isomers, but the yield was only 60%. Currently, industry uses continuous liquid-phase adsorption separation processes. The overall yield of p-xylene is increased by incorporating an isomerization unit to isomerize o- and m-xylenes to p-xylene.  Ethylbenzene Ethylbenzene (C6H5CH2CH3) is one of the C8 aromatic constituents in reformates and pyrolysis gasolines. It can be obtained by intensive fractionation of the aromatic extract, but only a small quantity of the demanded ethylbenzene is produced by this route.  Most ethylbenzene is obtained by the alkylation of benzene with ethylene.  Methylbenzenes (Toluene) Methylbenzenes occur in small quantities in naphtha and higher boiling fractions of petroleum. Those presently of commercial importance are toluene, o-xylene, p- xylene, and to a much lesser extent m-xylene. The primary sources of toluene and xylenes are reformates from catalytic reforming units, gasoline from catalytic cracking, and pyrolysis gasoline from steam reforming of naphtha and gas oils. As mentioned earlier, solvent extraction is used to separate these aromatics from the reformate mixture. Only a small amount of the total toluene and xylenes available from these sources is separated and used to produce petrochemicals.  Liquid petroleum fractions and residues Naphtha Naphtha from atmospheric distillation is characterized by an absence of olefinic compounds. Its main constituents are straight and branched chain paraffins, cycloparaffins (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-run 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. Selecting the naphtha type can be an important processing procedure. For example, a paraffinic-base naphtha is a better feedstock for steam cracking units because paraffins are cracked at relatively lower temperatures than cycloparaffins. Alternately, a naphtha rich in cycloparaffins would be a better feedstock to catalytic reforming units because cycloparaffins are easily dehydrogenated to aromatic compounds. Naphtha could also serve as a feedstock for steam reforming units for the production of synthesis gas for methanol. Naphtha is also a major feedstock to steam cracking units for the production of olefins.  Kerosene Kerosenes with a high normal-paraffin content are suitable feedstocks for extracting C12-C14 n-paraffins, which are used for producing biodegradable detergents. Currently, kerosene is mainly used to produce jet fuels,  Carbon black Carbon black is an extremely fine powder of great commercial importance, especially for the synthetic rubber industry. The addition of carbon black to tires lengthens its life extensively by increasing the abrasion and oil resistance of rubber. Carbon black consists of elemental carbon with variable amounts of volatile matter and ash. There are several types of carbon blacks, and their characteristics depend on the particle size, which is mainly a function of the production method. Carbon black is produced by the partial combustion or the thermal decomposition of natural gas or petroleum distillates and residues. Petroleum products rich in aromatics such as tars produced from catalytic and thermal cracking units are more suitable feedstocks due to their high carbon/hydrogen ratios. These feeds produce blacks with a carbon content of approximately 92 wt%. Coke produced from delayed and fluid coking units with low sulfur and ash contents has been investigated as a possible substitute for carbon black.  Synthesis gas Synthesis gas generally refers to a mixture of carbon monoxide and hydrogen. The ratio of hydrogen to carbon monoxide varies according to the type of feed, the method of production, and the end use of the gas. During World War II, the Germans obtained synthesis gas by gasifying coal. The mixture was used for producing a liquid hydrocarbon mixture in the gasoline range using Fischer-Tropsch technology. Although this route was abandoned after the war due to the high production cost of these hydrocarbons, it is currently being used in South Africa, where coal is inexpensive There are different sources for obtaining synthesis gas. It can be produced by steam reforming or partial oxidation of any hydrocarbon ranging from natural gas (methane) to heavy petroleum residues.  It can also be obtained by gasifying coal to a medium Btu gas (medium Btu gas consists of variable amounts of CO, CO2, and H2 and is used principally as a fuel gas).  Figure 4-5 shows the different sources of synthesis gas.  Chemicals based on synthesis gas The two major chemicals based on synthesis gas are ammonia and methanol. Each compound is a precursor for many other chemicals. From ammonia, urea, nitric acid, hydrazine, acrylonitrile, methylamines and many other minor chemicals are produced (see Figure 5-1).  Each of these chemicals is also a precursor of more chemicals. Methanol, the second major product from synthesis gas, is a unique compound of high chemical reactivity as well as good fuel properties. It is a building block for many reactive compounds such as formaldehyde, acetic acid, and methylamine.  It also offers an alternative way to produce hydrocarbons in the gasoline range (Mobil to gasoline MTG process). It may prove to be a competitive source for producing light olefins in the future.  Naphthenic acids Naphthenic acids are a mixture of cyclo-paraffins with alkyl side chains ending with a carboxylic group. The low-molecular-weight naphthenic acids (8–12 carbons) are compounds having either a cyclopentane or a cyclohexane ring with a carboxyalkyl side chain.  These compounds are normally found in middle distillates such as kerosene and gas oil. High boiling napthenic acids from the lube oils are monocarboxylic acids, (Cl4-Cl9) with an average of 2.6 rings. Naphthenic acids constitute about 50 wt% of the total acidic compounds in crude oils. Naphthenic-based crudes contain a higher percentage of naphthenic acids. Consequently, it is more economical to isolate these acids from naphthenic- based crudes. The production of naphthenic acids from middle distillates occurs by extraction with 7–10% caustic solution. The formed sodium salts, which are soluble in the lower aqueous layer, are separated from the hydrocarbon layer and treated with a mineral acid (Ex: sulphuric acid, boric acid) to spring out the acids. The free acids are then dried and distilled. Using strong caustic solutions for the extraction may create separation problems because naphthenic acid salts are emulsifying agents.  Uses of naphthenic acids and its salts Free naphthenic acids are corrosive and are mainly used as their salts and esters. The sodium salts are emulsifying agents for preparing agricultural insecticides, additives for cutting oils, and emulsion breakers in the oil industry. Other metal salts of naphthenic acids have many varied uses. For example, calcium naphthenate is a lubricating oil additive, and zinc naphthenate is an antioxidant.  Lead, zinc, and barium naphthenates are wetting agents used as dispersion agents for paints. Some oil soluble metal naphthenates, such as those of zinc, cobalt, and lead, are used as driers in oil-based paints. Manganese naphthenates are well-known oxidation catalysts.  Cresylic acid Cresylic acid is a commercial mixture of phenolic compounds including phenol, cresols, and xylenols. This mixture varies widely according to its source. Phenol Xylenol  Uses of Cresylic Acid Cresylic acid is mainly used as degreasing agent and as a disinfectant of a stabilized emulsion in a soap solution. Cresols are used as flotation agents and as wire enamel solvents. Tricresyl phosphates are produced from a mixture of cresols and phosphorous oxychloride. They are also gasoline additives for reducing carbon deposits in the combustion chamber.