Chemical composition of petroleum
Chemical composition of petroleum
Petroleum is not a uniform material. In fact, its chemical and physical (fractional) composition can vary not only with the location and age of the oil field but also with the depth of the individual well. Indeed, two adjacent wells may produce petroleum with markedly different characteristics.
-petroleum is a complexmixture of hydrocarbons with small amounts of organic compounds containing sulfur, oxygen, and nitrogen, as well as compounds containing metallic constituents, particularly vanadium, nickel, iron, and copper.
-The hydrocarbon content may be as high as 97% w/w, for example in the lighter paraffinic crude oil.
-or as low as 50% w/w in heavy crude oil and bitumen.
-Note:Bitumen is a mixture of organicliquids that are highly viscous, black, sticky, entirely soluble in carbon disulfide, and composed primarily of highly condensed polycyclic aromatic hydrocarbons.
-With few exceptions, the proportions of the elements (carbon, hydrogen, nitrogen, oxygen, sulfur, and metals) in petroleum (whatever and wherever the source) vary over fairly narrowlimits
Hydrogen, 10.0% to 14.0%
Nitrogen, 0.1% to 2.0%
Oxygen, 0.05% to 1.5%
Sulfur , 0.05% to 6.0%
Metals (Ni and V), <1000 ppm
(2) nitrogen compounds;
(3) oxygen compounds;
(4) sulfur compounds;
(5) metallic constituents.
(1)Saturated constituents include normal alkanes, branched alkanes, and cycloalkanes (paraffins, iso-paraffins, and naphthenes, in petroleum terms),
(2) alkene constituents (olefins) are rare
(3) monoaromatic constituents range from benzene to multiple fused ring analogs (naphthalene, phenanthrene, etc.),
(4) thiol constituents contain sulfur as do thioethers and thiophene forms,
(5) nitrogen-containing and oxygen-containing constituents
(1) Nonhydrocarbon compounds
But there is more to the composition of petroleum than the hydrocarbon content. The inclusion of organic compounds ofsulfur, nitrogen, and oxygen.
-The presence of traces of nonhydrocarbon compounds can impart objectionable characteristics to finished products:
1-leading to discoloration.
2-lack of stability during storage.
(2) HYDROCARBON CONSTITUENTS
-the hydrocarbon components of petroleum are composed of paraffinic, naphthenic, and aromatic groups, Olefin groups are rare in crude oils , and acetylenic hydrocarbons are very rare indeed.
-It is therefore convenient to divide the hydrocarbon components of petroleum into the following three classes:
1. Paraffins , which are saturated hydrocarbons with straight or branched chains, but without any ring structure
2. Naphthenes , which are saturated hydrocarbons containing one or more rings, each of which may have one or more paraffinic side chains (more correctly known as alicyclic hydrocarbons )
3. Aromatics, which are hydrocarbons containing one or more aromatic nuclei, such as benzene, naphthalene, and phenanthrene ring systems, which may be linked up with (substituted) naphthene rings or paraffinic side chains
Note: The relationship between the various hydrocarbon constituents of crude oils is one of hydrogen addition or hydrogen loss
-The proportion of paraffins in crude oil varies with the type of crude, but within anyone crude oil, the proportion of paraffinic hydrocarbons decreases with increasing molecular weight and there is an increase in aromaticityand the relative proportion of heteroatoms (nitrogen, oxygen, and sulfur).
a. Normal paraffin
b. iso-paraffins (branched)
a. Normal paraffin
-( n-paraffins, straight-chain paraffins) occur in varying proportions in most crude oils . In fact , n-paraffins may make up to 20% to 50% of paraffinic petroleum by weight in the gas oil fraction.
-However, naphthenic or asphaltic crude oils sometimes contain only very small amounts of normal paraffins .
b. iso-paraffins (branched)
-The 2- and 3-methyl derivatives are the most abundant, and the 4-methyl derivative is present in small amounts
-the slightly branched paraffinspredominate over the highly branched materials.
2-Cycloparaffin Hydrocarbons (Naphthenes)
-cyclohexanederivatives, cyclopentanederivatives, and decahydronaphthalene (decalin) derivatives are largely represented in oil fractions.
-Petroleum also contains polycyclicnaphthenes, such as Terpenes.
-Naphthene rings may be built up of a varying number of carbon atoms three-, four-, five-, six-, seven-, and eight-carbon atoms. It is now generally believed that crude oil fractions contain chiefly five and six-carbon rings.
-Thermodynamic studies show that naphthene rings with five and six carbon atoms are the most stable.
-Several series of cycloparaffins, usually containing five- or six-membered rings or their combinations, occur as polycyclic structures.
-The contentofcycloparaffinsin petroleum varies up to 60% of the total hydrocarbons.
-The principal structural variation of naphthenes is the number of rings present in the molecule.
-The mono- and bicyclicnaphthenesare generally the major types of cycloparaffins in the lower boiling fractions of petroleum.
-with boiling point or molecular weight increased by the presence of alkyl chains.
- the naphthene ring systems carry alkyl chains that are generally shorter than the alkyl substituents carried by aromatic systems.
-the majority of these aromatics containparaffinic chains, naphthene rings , and aromatic rings side by side.
-There is a general increase in the proportion of aromatic hydrocarbons with increasing molecular weight.
-Aromatic hydrocarbons without the accompanying naphthene rings or alkyl-substituted derivatives seem to be present in appreciable amounts only in the lower petroleum fractions.
- Aromatics without naphthenerings appear to be relatively rare in the heavier fractions of petroleum.
- In the higher molecular weight fractions, the rings are usually condensed together(components with two aromatic rings are presumed to be naphthalene derivatives and those with three aromatic rings may be phenanthrene derivatives.)
-in the higher boiling point petroleum fractions, many Polycyclic structures occur in naphthenoaromatic systems.
-it has been generally assumed that as the boiling point of a petroleum fraction increases, so does the number of condensed rings in a polycyclic aromatic system.
-dienes , acetylenes.
-The presence of olefins in petroleum has been under dispute for many years.
-olefins are present in crude oil in only a few special cases.
-spectroscopic and chemical methods showed that the crude oils , as well as all distillate fractions, contained up to 3% w/w olefins.
-Crude oils contain appreciable amounts of organic nonhydrocarbon constituents, mainly sulfur-, nitrogen-, and oxygen-containingcompounds and, in smaller amounts, organometallic compounds in solution and inorganic salts in colloidal suspension.
-Although their concentration in certain fractions may be quite small, their influence is important.
1-the decomposition of inorganic salts suspended in the crude can cause serious breakdowns in refinery operations.
2-the thermal decomposition of deposited inorganic chlorides with evolution of free hydrochloric acid can give rise to serious corrosion problems in the distillation equipment .
3-The presence of organic acid componentscan also promote metallic corrosion.
4- poisoning of the catalyst can be caused by deposition of traces of metals (vanadium and nickel ).
5-The presence of traces of nonhydrocarbons may impart objectionable characteristics in finished products, such as discoloration, lack of stability on storage.
-there are many varieties of sulfur compounds as shown below.
-In general, the higher the density of the crude oil the higher the sulfur
-the total sulfur in the crude oil can vary from 0.04% w/w for light crude oilto about 5.0% for heavy crude oiland tar sand bitumen.
-The presence of sulfur compounds in finished petroleum products often produces harmful effects.
-For example, in gasoline, sulfur compounds are believed to promote corrosion of engine parts, especially under winter conditions, when water containing sulfur dioxide from the combustion.
- Free sulfur is also corrosive, as are sulfides, disulfides, and thiophenes,
-gasoline with a sulfur content between 0.2% and 0.5% has been used without obvious harmful effect.
-In diesel fuels, sulfur compounds increase wear and can contribute to the formation of engine deposits.
b. Oxygen Compounds
-Oxygen in organic compounds can occur in a variety of forms (R–OH , Ar–OH, R–O–R ,R–CO2H, AR–CO2H, R–CO2R, ArCO2R, R–CO–Ras well as the cyclic furan derivatives).
-The total oxygen content of crude oil is usually less than 2% w/w.
-when the oxygen content is phenomenally high it may be that the oil has suffered prolonged exposure to the atmosphere.
-the nonvolatile residua may have oxygen contents up to 8% w/w.
- Oxygen compounds in crude oil: In addition to the carboxylic acids and phenolic compounds, the presence of ketones, esters, ethers , and anhydrides has been claimed for a variety of crude oils .
c. Nitrogen Compounds
-Nitrogen in petroleum may be classified arbitrarily as basic andnonbasic.
1- The basic nitrogen compound (as shown below) which are composed mainly of pyridine homologsand occur throughout the boiling ranges, have a decided tendency to exist in the higher boiling fractions and residua.
2-The nonbasicnitrogen compounds, which are usually of the pyrrole, indole, and carbazoletypes, also occur in the higher boiling fractions and residua.
-In general, the nitrogen content of crude oil is low and generally falls within the range 0.1% to 0.9%.
-In refinery operations , Nitrogen compounds can be responsible for the poisoning of cracking catalysts.
-Metallic constituents are found in every crude oil Cause particular problems because they poison catalysts used for sulfur and nitrogen removalas well as other processes such as catalytic cracking.
-The trace metals Ni and V are generally orders of magnitude higher than other metals in Petroleum except when contaminated with coproduced brine salts (Na, Mg, Ca, and Cl) or corrosion products gathered in transportation (Fe).
-Even minute amounts of Fe, Cu, and particularly Ni and V in the charging stocks for catalytic cracking affect the activity of the catalyst and result in increased gas and coke formation and reduced yields of gasoline.
-Two groups of elements appear in significant concentrations in the original crude oil associated with well-defined types of compounds.
1-Zinc, titanium, calcium, and magnesium appear in the form of organometallic soaps.
2-However, V, Cu, Ni , and part of the Fe found in crude oils seem to be in a different class and are present as oil soluble compounds, they are capable of complexing with pyrrole pigment compounds.
-Distillation concentrates the metallic constituents in the residues although some can appear in the higher boiling distillates , but the latter may be due in part to entrainment.
-The majority of the V, Ni, Fe, an d Cu in residual stocks may be precipitated along with the asphaltenes by hydrocarbon solvents. Thus , removal of the asphaltenes with n-pentane reduces the vanadium content of the oil by up to 95% with substantial reductions in the amounts of iron and nickel.
-it is a method by which the constituents of petroleum can be separated and identified.
-Distillation is a means of separating chemical compounds (usually liquids) through differences in theirvapor pressures.
-In the mixture, the components evaporate, such that the vapor has a composition determined by the chemical properties of the mixture.
-Distillation of a given component is possible, if the vapor has a higher proportion of the given component than the mixture.
-This is caused by the given component having a higher vapor pressure and a lower boiling point than the other components.
it is theoretically impossible to completely separate and purify the individual components of petroleum when the possible number of isomers are considered for the individual carbon numbers that occur within the paraffin family.
-However, petroleum can be separated into a variety of fractions on the basis of the boiling points of the petroleum constituents.
-Such fractions are primarily identified by their respective boiling ranges and, to a lesser extent , by chemical composition.
-However, it is often obvious that as the boiling ranges increase, the nature of the constituents remains closely similar and it is the carbon number of the substituents that caused the increase in boiling point.
GASES AND NAPHTHA
-Gases: Methane is the main hydrocarbon component of petroleumgases with lesser amounts of ethane, propane, butane, isobutane, and some C4 hydrocarbons. Other gases, such as hydrogen, carbon dioxide, hydrogen sulfide, and carbonyl sulfide, are also present.
-Naphtha :Saturated constituents , with lesser amounts of mono- and di-aromatics dominate the naphtha fraction.
-Whereas naphtha covers the boiling range of gasoline, most of the raw petroleum naphtha molecules have low octane number.
-However, most raw naphtha is processed further and combined with other process naphtha and additives to formulate commercial gasoline.
1-Within the saturated constituents in petroleum gases and naphtha, every possible paraffin frommethane (CH4) to n-decane (n-C10H22).
2-In addition to aliphatic molecules, the saturated constituents consist of cycloalkanes (naphthenes) with predominantlyfive- or six-carbon rings. Methyl derivatives of cyclopentane and cyclohexane, which are commonly found at higher levels than the parent unsubstituted structures may be present.
-Fused ring dicycloalkanessuch as cis-decahydronaphthalene (cis-decalin) and trans-decahydronaphthalene (trans-decalin) and hexahydroindan are also common.
3-The numerous aromatic constituents in petroleum naphthabegin with benzene, but its C1 to C3 alkylated derivatives are also present.
-Benzene derivatives having fused cycloparaffinrings (naphtheno-aromatics), such as indane and tetralin.
-Naphthalene is included in this fraction, while the 1- and 2-methyl naphthalenes and higher homologs of fused two-ring aromatics appear in the mid-distillate fraction.
4-Sulfur-containing compounds are the only heteroatom compoundsto be found in this Fraction.
-Usually, the total amount of the sulfur in this fraction accounts for less than 1% of the total sulfur in the crude oil.
-In naphtha from high-sulfur (sour) petroleum, 50% to 70% ofthe sulfur may be in the form of mercaptans (thiols).
-In naphtha from low-sulfur (sweet) crude oil, the sulfur is distributed between sulfides (thioethers) and thiophenes.
-Saturated species are the major componentin the mid-distillate fraction of petroleum.
-but aromatics, which now include simple compounds with up to three aromatic rings, and heterocyclic compounds are present and represent a larger portion of the total.
-Kerosene, jet fuel, and diesel fuel are all derived from raw middle distillate, which can also be obtained from cracked and hydroprocessed refinery streams.
1-Within the saturated constituents, the concentration of n-paraffins decreases regularly from C11 to C20.
2- Mono- and di-cycloparaffinswith five or six carbons per ring constitute the bulk of the naphthenes in the middle distillate boiling range, decreasing in concentration as the carbon number increases.
-the alkylatednaphthenesmay have a single long side chain as well as one or more methyl or ethyl groups.
-substituted three-ring naphtheneshave been detected.
3-The most abundant aromatics in the mid-distillate boiling fractions are di- and tri-methyl naphthalenes.
-Other one- and two-ring aromatics are undoubtedly present in small quantities as either naphtheno or alkyl homologs in the C11–C20 range.
-the mid-distillate contains some fluorene derivatives and phenanthrene derivative.
-this appears to continue through the higher boiling fractions of petroleum.
4-The five-membered heterocyclic constituents in the mid-distillate range are primarily the thiacyclane derivatives, benzothiophene derivatives, and dibenzothiophene derivatives.
-Alkylthiophenes are also present.
-As with the naphtha fractions, these sulfur species account for a minimal fraction of the total sulfur in the crude.
-Although only trace amounts (usually ppm levels) of nitrogen are found in the middle distillate fractions.
-Pyrrole derivatives and indole derivatives account for about two-thirds of the nitrogen, whereas the remainder is found in the basic alkylated pyridine and alkylatedquinolinecompounds.
Vacuum Gas Oil (VGO).
-The saturate constituents contribute less to the vacuum gas oil (VGO) than the aromatic Constituents.
-Vacuum gas oil is occasionally used as a heating oil, but most commonly it is processed by catalytic cracking to produce naphtha or extraction to yield lubricating oil.
1-The bulk of the saturated constituentsin vacuum gas oil consist of iso-paraffins and especially naphthene species although isoprenoid compounds, such as squalane (C30) and lycopane (C40), have been detected.
2-Generally, the naphthene constituents account for approximately two-thirds or 60% of the saturate constituents, but the overall range of variation is from <20% to >80%.
-the naphthenes contain from one to more than six fused rings accompaniedby alkyl substitution.
3-The aromatics in vacuum gas oil may contain one to six fused aromatic rings that may bear additional naphthene rings and alkyl substituentsin keeping with their boiling range. about 50% of the aromaticsare Mono and di-aromatics in petroleum vacuum gas oil samples.
4- Heterocyclic constituents are significant contributors to the vacuum gas oil fraction.
-In terms of sulfur compounds, thiophene and thiacyclane sulfur predominate over sulfide sulfur.
-Some molecules even contain more than one sulfur atom.
-thiophene forms of sulfur , The benzothiophenes and dibenzothiophenes are the prevalent.
-In the vacuum gas oil range, the nitrogen-containing compounds include higher molecular weight pyridines, quinolines, benzoquinoline derivatives, amides, indoles, carbazole, and molecules with two nitrogen atoms (diaza compounds).
-Oxygen levels in the vacuum gas oil parallel the nitrogen content. Thus, the most commonly identified oxygen compounds are the carboxylic acids and phenols, collectively called naphthenic acids
VACUUM RESIDUA (1050 F)
-This fraction, the vacuum bottoms is the most complex of petroleum.
-Vacuum residua contain the majority of the heteroatomsoriginally inthe petroleum.
-molecular weight of the constituents range, as near as can be determined subject to method of dependence, up to several thousand.
-Separation of vacuum residua by group type becomes difficult and confused because of the multisubstitution of aromatic and naphthenic species.
-The insoluble fraction, the pentane- or heptane-asphaltenes, may be as much as 50% by weight of a vacuum residuum.
-the levels of nitrogen and oxygen may begin to approach theconcentrationof sulfur.
-The nickel and vanadium that are concentrated into the vacuum residuum appear to occur in two forms: (1) porphyrins and (2) nonporphyrins.
- petrochemicals are chemicals derived frompetroleum and natural gas.
- petrochemicals is any of a large group of chemicals manufactured from petroleum and natural gas as distinct from fuels and other products.
- The definition has been broadened to include the whole range of organic chemicals (fig).
- Petrochemicals are generally considered chemical compounds derived from petroleum either by direct manufacture or indirect manufacture as by-products from the variety of processes that are used during the refining of petroleum.
- The refinery gas (or the process gas) stream and the products of naphtha cracking are the source of a variety of petrochemicals.
- Gasoline, kerosene, fuel oil, lubricating oil, wax, asphalt , and the like are excluded from the definition of petrochemicals, as they are not, in the true sense, chemical compounds but are in fact intimate mixtures of hydrocarbons.
2- On the other hand, they may be present , if at all, in trace amounts and are synthesizedduring the refining operations.
-Example, unsaturated (olefin) hydrocarbons, which are not usually present in crude oil , are nearly always manufactured as intermediates during the various refining sequences.
1- Primary petrochemicals include: olefins (ethylene, propylene, and butadiene), aromatics (benzene, toluene , and xylenes ), and methanol (fig).
2- Petrochemical intermediates are generally produced by chemical conversion of primary petrochemicals to form more complicated derivativeproducts.
-Petrochemical derivative products can be made in a variety of ways: directly from primary petrochemicals
a) through intermediate products that still contain only carbon and hydrogen; and , through intermediates that incorporate chlorine, nitrogen or oxygen in the finished derivative.
b) In some cases, they are finished products; in others, more steps are needed to arrive at the desired composition.
- ethylene, the most important of the petrochemical building blocks.
- Ethylene is polymerized to produce polyethylene or, in combination with propylene, to produce copolymers that are used extensively in food -packaging wraps, plastic household goods, or buildingmaterials.
- Petrochemical products include such items as plastics , soaps and detergents, solvents, drugs, fertilizers, pesticides , explosives, synthetic fibers and rubbers, paints , epoxy resins . and flooring and insulating materials. Petrochemicals are found in products as diverse as aspirin, luggage , boats, automobiles, aircraft, polyesterclothes, and recording discs and tapes.
Types of petrochemicals
-there are four general types of petrochemicals: (1) aliphatic compounds, (2) aromatic compounds, (3) inorganic compounds, and (4) synthesis gas (carbon monoxide and hydrogen) .
(1)- Synthesis gas is used to make ammonia (NH3) and methanol (methyl alcohol, CH3OH). Ammonia is used primarily to form ammonium nitrate (NH4NO3), a source of fertilizer. Much of the methanol produced is used in making formaldehyde (HCHO). The rest is used to make polyester fibers, plastics, and siliconerubber.
(2)-An aliphatic petrochemical compound is an organic compound that has an open chain of carbon atoms , be it normal (straight), for example, n-pentane (CH3CH2CH2CH2CH3) or branched, for example, iso -pentane [2-methylbutane, CH3CH2CH(CH 3)C H3], or unsaturated. The unsaturated compounds, olefins, include important starting materials such as ethylene (CH2CH 2), propylene (CH 3CHCH2), butene-1 (CH3CH2CH2CH2), iso–butene(2-methylpropene [C H3(CH3)CCH 2] ) and butadiene (CH2CHCHCH2).
- Ethylene is the hydrocarbon feedstock used in greatest volume in the petrochemical industry.
-Propylene is also an important source of petrochemicals and is used in making such products as acrylics, rubbing alcohol, epoxy glue, and carpets.
-Butadiene is used in making synthetic rubber, carpet fibers, paper coatings, and plastic pipes.
(3)- An aromatic petrochemical is also an organic chemical compound but one that contains, or is derived from, the basic benzene ring system.
-A highly significant proportion of these basic petrochemicals is converted into plastics,synthetic rubbers, and synthetic fibers. Together these materials are known as polymers, because their molecules are high-molecular-weight compounds made up of repeated structural units that have combined chemically. The major products are polyethylene, polyvinyl chloride, and polystyrene, all derived from ethylene, and polypropylene, derived from monomer propylene. Major raw materials for synthetic rubbers include butadiene, ethylene, benzene, and propylene.
-Among synthetic fibers the polyesters, which are a combination of ethylene glycol and terephthalic acid (made from xylene), are the most widely used. They account for about one-half of all synthetic fibers. The second major synthetic fiber is nylon, its most important raw material being benzene. Acrylic fibers, in which the major raw material is the propylene derivative acrylonitrile, make up most of the remainder of the synthetic fibers.
CHEMICALS FROM PARAFFINS
-chlorine can be introduced into the molecules of all the hydrocarbon types present in petroleum has resulted in the commercial production of a number of widely used compounds.
-With saturated hydrocarbons, the reactions are predominantly substitution of hydrogen by chloride and are strongly exothermic, difficult to control, and inclined to become explosively violent:
-Methane yields four compounds upon chlorination in the presence of heat or light:
These compounds, known as chloromethane or methyl chloride, dichloromethane or methylene chloride, trichloromethane or chloroform, and tetrachloromethane or carbon tetrachloride, are used as solvents or in the production of chlorinated materials.
-Other examples of the chlorination reaction include the formation of ethyl chloride by the chlorination of ethane:
-Reaction with acetic acid produces the corresponding amyl acetates, which find wide use as solvents.
-Hydrocarbons that are usually gaseous (including normal and iso-pentane) react smoothly in the vapor phase with nitric acid to give a mixture of nitro-compounds.
-Ethane, for example, yields nitromethane and nitroethane,
-Propane yields nitromethane, nitroethane, 1-nitropropane, and 2-nitropropane:
The nitro-derivatives of the lower paraffins are colorless and noncorrosive and are used as solvents or as starting materials in a variety of syntheses.
-Methane undergoes two useful reactions at 90 C in the presence of iron oxide (Fe3O4) as a catalyst:
-The carbon dioxide produced then reacts with methane at 900 C in the presence of a nickel catalyst:
-Methanol is the second major product produced frommethane.
-Most of the methanol is then oxidized by oxygen from air to formaldehyde,
-Formaldehyde is used to produce synthetic resins.
-The major nonpetrochemicaluse of methane is in the production of hydrogen for use in the Haber synthesis of ammonia. Ammonia synthesis requires nitrogen, obtained from air and hydrogen.
-When propane and butane are oxidized in the vapor phase a wide variety of products is obtained ketones, ethylene oxide, esters, formals, acetals, and others.
-Cyclohexane is oxidized. Cyclohexanol derivatives are the initial products, but prolonged oxidation produces adipic acid.
-The preparation of carboxylic acids from petroleum, particularly from paraffin wax
-ex: Iso-butane has been added to butenes to give a mixture of highly branched octanes(e.g., heptanes) by a process called alkylation.
-The first step in the process is the formation of a carbocation by combination of an olefin with an acid proton:
-The second step is the addition of the carbocation to a second molecule of olefin to form a dimercarbocation.
-The extensive branching of the saturated hydrocarbon results in high octane. In practice, mixed butenes are employed (iso-butylene, 1 butene, and 2-butene), and the product is a mixture of isomeric octanes that has an octane number of 92 to 94.
-paraffin hydrocarbons are known to undergothermolysis when treated under high-temperature, low-pressure vapor-phase conditions.
-Cracking is the major process for generating ethylene and the other olefins that are the reactive building blocks of the petrochemical industry.
-Cracking reactions involve the cleavage of carbon–carbon bonds with the resulting redistribution of hydrogen to produce smaller molecules.
-Thus , cracking of petroleum or petroleum fractions is a process by which larger molecules are converted into smaller, lower boiling molecules.
-In addition, cracking generates two molecules from one, with one of the product molecules saturated (paraffin) and the other unsaturated (olefin).
-At the high temperatures of refinery crackers cracking is favored.
-Unfortunately, in the cracking process certain products interact with one another to produce products of increased molecular weight over that in the original feedstock.
-Thus , some products are taken off from the cracker as useful light products (olefins, gasoline, and others ), but other products include heavier oil and coke.
CHEMICALS FROM OLEFINS
-These unsaturated materials enter into polymers: rubbers, and with other reagents react to form a wide variety of useful compounds, including alcohols, epoxides, amines, and halides.
-Olefins present in gaseous products of catalytic cracking processes.
-Cracking paraffin hydrocarbons and heavy oils also produces olefins.
-For example, cracking ethane, propane, butane, and other feedstock such as gas oil, naphtha, and residua produces ethylene.
-Propylene is produced from thermal and catalytic cracking of naphtha and gas oils, as well as propane and butane.
-Ethylene manufacture via the steam cracking process is in widespread practice throughout the world.
-Propylene andbutyleneare largely derived from catalytic cracking units and from cracking a naphtha or light gas oil fraction to produce a full range of olefin products.
-all propene or propylene is made from propane, which is obtained from natural gasor from refinery gases:
-The uses :
*propene include gasoline,.
*polypropylene made detergents.
-butenes or butylenes:
-Butadiene can be recovered fromrefinery streams as butenes, or as butanes; the latter two on appropriate heated catalysts dehydrogenate to give 1,3-butadiene:
-An alternative source of butadiene is ethanol, which on appropriate catalytic treatment also gives the compound di-olefin:
-Olefins containing more than four carbon atoms are in little demand as petrochemicals and thus are generally used as fuel. The single exception to this is 2-methyl-1,3-butadiene or isoprene, which has a significant use in the synthetic rubber industry.
-It is more difficult to make larger than 1,3-butadiene. Some are available in refinery streams, but more is manufactured from refinery stream 2-butene by reaction with formaldehyde:
-Ethylene, produced from ethane by cracking, is oxidized in the presence of a silver catalyst to ethylene oxide:
-The vast majority of the ethylene oxide produced is hydrolyzed at 100 C to ethylene glycol:
-Approximately 70% of the ethylene glycol produced is used as automotive antifreeze and much of the rest is used in the synthesis of polyesters.
- ethylene glycol(Hydroxylation) another way:
c. The hydrolysis of ethylene chlorohydrin.
-Propylene glycol is alsomade by the hydrolysis of its chlorohydrinor oxide.
-Glycerin can be derived from propylene by high-temperature chlorination to produce alkyl chloride, followed by hydrolysis to allyl alcohol and then conversion with aqueous chloride to glycerol chlorohydrin, a product that can be easily hydrolyzed to glycerol (glycerin).
-Glycerin has found many uses over the years; important among these are as solvent, emollient, sweetener, in cosmetics, and as a precursor to nitroglycerin and otherexplosives.
-at ordinary temperatures, chlorine reacts with olefins by addition. Thus, ethylene is chlorinated to 1,2-dichloroethane (dichloroethane) or to ethylene dichloride:
-There are some minor uses for ethylene dichloride, but about 90% of it is cracked to vinyl chloride, the monomer of polyvinyl chloride (PVC):
-At slightly higher temperatures, olefins and chlorine react by substitution of a hydrogen atom by a chlorine atom. Thus, in the chlorination of propylene, a rise of 50 C changes the product from propylene dichloride [CH3CH(Cl)CH2Cl] to allyl chloride (CH2CHCH2Cl).
-ethylene–propylene and ethylene–butene mixtures, can be treated to give high-molecular-weight copolymers of good elasticity.
-Polyethylene has excellent electrical insulating properties; its chemical resistance, toughness, machinability, light weight, and high strength make it suitable for many other uses.
-Lower molecular weight polymers, such as the dimers, trimers, and tetramers, are used as such in motor gasoline.
-Propylenetrimer (dimethylheptenes) and tetramer (trimethylnonenes) are applied in the alkylation of aromatic hydrocarbons for the production of alkylarylsulfonatedetergents
CHEMICALS FROM AROMATICS
-benzene is used to make styrene (C6H5CHCH2), the basic ingredient of polystyrene for plastics, as well as paints, epoxy resins, glues, and other adhesives.
-The process for the manufacture of styrene proceeds through ethylbenzene, which is produced by reaction of benzene and ethylene at 95 C in the presence of a catalyst:
-In the presence of a catalyst and superheated steam ethylbenzenedehydrogenatesto styrene:
-Toluene is usually added to the gasoline pool or used as a solvent, but it can be dealkylated to benzene by catalytic treatment with hydrogen:
-Similar processes are used for dealkylation of methyl-substituted naphthalene.
-Toluene is also used to makesolvents, gasoline additives, and explosives.
-Toluene is usually in demand as a source of trinitrotoluene (TNT) but has fewer chemical uses than benzene.
-Aromatics are more resistant to oxidation than the paraffin hydrocarbons, and higher temperatures are necessary.
-Ortho-xylene is oxidized by nitric acid to phthalic anhydride, m-xylene to iso-phthalic acid, and p-xylene with nitric acid to terephthalic acid.
-From these oxidation reactions, these acid products are used in the manufacture of fibers, plastics, and plasticizers.
CHEMICALS FROM ACETYLENE
-Acetylene is the only petrochemical produced in significant quantity that contains a triple bond, and is a major intermediate species.
-It can be made by hydrolysis of calcium carbide produced in the electric furnace from calcium oxide (CaO) and carbon:
-An alternative method of manufacturing acetylene is by cracking methane:
-Acetylene is used as a special fuel gas (oxyacetylene torches) and as a chemical raw material.
CHEMICALS FROM NATURAL GAS
-Natural gas can be used as a source of hydrocarbons (e.g., ethane and propane) that have higher molecular weight than methane and are important chemical intermediates.
-methane (natural gas) should be regarded as some of the building blocks of the petrochemical industry.
-the chiefsources of large-scale hydrogen (used mainly for ammonia manufacture) were the cracking of methane (or natural gas) and the reaction between methane and steam. In the latter, at 900 C to 1000 C conversion into carbon monoxide and hydrogen results in:
-If this mixture is treated further with steam at 500 C over catalyst, the carbon monoxide present is converted into carbon dioxide and more hydrogen is produced:
-The reduction of carbon monoxide by hydrogen is the basis of several syntheses, including the manufacture of methanol and higher alcohols.
-The major products are olefins and paraffins, together with some oxygen-containing organic compounds in the product mix that may be varied by changing the catalyst or the temperature, pressure, and carbon monoxide–hydrogen ratio.
-Iso-paraffin formation is more extensive over zinc oxide (ZnO) or thoria (ThO2) at 400 C to 500 C and at higher pressure.
-Paraffin waxes are formed over ruthenium catalysts at relatively low temperatures (170 C to 200 C) high pressures ,and with a carbon monoxide–hydrogen ratio.
-The more highly branched product made over the iron catalyst is an important factor in a choice for the manufacture of automotive fuels.
-The small amount of aromatic hydrocarbons found in the product benzene, toluene, ethylbenzene, xylene, n-propylandiso-propylbenzene, methylethylbenzenes, and trimethylbenzenes have been identified; naphthalene derivatives and anthracene derivatives are also present.
-an inorganic petrochemical is one that does not contain carbon atoms; typical examples are sulfur (S), ammonium sulfate [(NH4)2SO4)], ammonium nitrate (NH4NO3), and nitric acid (HNO3).
-Of the inorganic petrochemicals , ammonia is by far the most common. Ammonia is produced by the direct reaction of hydrogen with nitrogen, with air being the source of nitrogen:
-Ammonia production requires hydrogen from a hydrocarbon source.
-The ammonia is used predominantly for the production of ammonium nitrate (NH4NO3) as well as other ammonium salts and urea (H2HCONH2), which are major constituents of fertilizers.
-Carbon black (also classed as an inorganic petrochemical) is made predominantly by the partial combustion of carbonaceous (organic) material in a limited supply of air.
-The carbonaceous sources vary from methane to aromatic petroleum oils to coal tar by-products.
-Carbon black is used primarily for the production of synthetic rubber.
-Sulfur, another inorganic petrochemical, is obtained by the oxidation of hydrogen sulfide:
-Hydrogen sulfide is a constituent of natural gas and also of the majority of refinery gas Streams.
-A large majority of the sulfur is converted to sulfuric acid for the manufacturer of fertilizers and other chemicals.
-Other uses for sulfur include the production of carbon disulfide, refined sulfur, and pulp and paper industry chemicals.
-Synthesis gas is a mixture of carbon monoxide (CO) and hydrogen (H2) that is the beginning of a wide range of chemicals.
-The thermal cracking of petroleum or fractions thereof was an important method for producinggas.
-Synthesis gas can be produced from heavy oil by partially oxidizing the oil:
Another production metods:
-A second group of refining operations that contribute to gas production are the catalytic cracking processes, such as fluid-bed catalytic cracking, and other variants, in which heavy gas oils are converted into gas, naphtha, fuel oil, and coke.
-The catalysts will promote steam-reforming reactions that lead to a product gas containing more hydrogen and carbon monoxide and fewer unsaturated hydrocarbon products than the gas product from a noncatalytic process.
-The catalyst also influences the reactions rates in the thermal cracking reactions, which can lead to higher gas yields and lower tar and carbon yields.
-Almost all petroleum fractions can be converted into gaseous fuels, although conversion processes for the heavier fractions require more elaborate technology to achieve the necessary purity and uniformity of the manufactured gas stream.