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1、CHEMISTRY OF PETROCHEMICALPROCESSESProf. Dr. Hasan FaragHydrocarbon IntermediatesvNatural gas and crude oils are the main sources for hydrocarbon intermediates or secondary raw materials for the production of petrochemicals.vFrom natural gas, ethane and LPG are recovered for use as intermediates in
2、the production of olefins and diolefins. Important chemicals such as methanol and ammonia are also based on methane via synthesis gas. vOn the other hand, refinery gases from different crude oil processing schemes are important sources for olefins and LPG. Crude oil distillates and residues are prec
3、ursors for olefins and aromatics via cracking and reforming processes.Paraffinic hydrocarbonsvParaffinic 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.vParaffin
4、s are relatively inactive compared to olefins, diolefins, and aromatics. vFew chemicals could be obtained from the direct reaction of paraffins with other reagents. However, these compounds are the precursors for olefins through cracking processes. vThe C6C9 paraffins and cycloparaffins are especial
5、ly important for the production of aromatics through reforming.Methane (cH4)vAs 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 condition
6、s. vFor 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.Ethane (CH3-CH3)vEthane is an important paraffinic hydrocarbon
7、 intermediate for the production of olefins, especially ethylene.vEthanes relation with petrochemicals is mainly through its cracking to ethylene.Propane (CH3CH2CH3)vPropane is a more reactive paraffin than ethane and methane. This is due to the presence of two secondary hydrogens that could be easi
8、ly substituted.vChemicals directly based on propane are few, although as mentioned, propane and LPG are important feedstocks for the production of olefins.Butanes (C4H10)vDehydrogenation of isobutane produces isobutene, which is a reactant for the synthesis of methyl tertiary butyl ether (MTBE). vTh
9、is compound is currently in high demand for preparing unleaded gasoline due to its high octane rating and clean burning properties.Olefinic hydrocarbonsvThe most important olefins used for the production of petrochemicals are ethylene, propylene, the butylenes, and isoprene. vThese olefins are usual
10、ly coproduced with ethylene by steam cracking ethane, LPG, liquid petroleum fractions, and residues. Olefins are characterized by their higher reactivities compared to paraffinic hydrocarbons. vThey can easily react with inexpensive reagents such as water, oxygen, hydrochloric acid, and chlorine to
11、form valuable chemicals. Olefins can even add to themselves to produce important polymers such as polyethylene and polypropylene.vEthylene is the most important olefin for producing petrochemicals, and therefore, many sources have been sought for its production.Ethylene (CH2=CH2)vEthylene (ethene),
12、the first member of the alkenes, is a colorless gas with a sweet odor. It is slightly soluble in water and alcohol. It is a highly active compound that reacts easily by addition to many chemical reagents. vFor example, ethylene with water forms ethyl alcohol. Addition of chlorine to ethylene produce
13、s ethylene dichloride (1,2-dichloroethane), which is cracked to vinyl chloride. Vinyl chloride is an important plastic precursor.v Ethylene is also an active alkylating agent. Alkylation of benzene with ethylene produces ethyl benzene, which is dehydrogenated to styrene.vStyrene is a monomer used in
14、 the manufacture of many commercial polymers and copolymers. Ethylene can be polymerized to different grades of polyethylenes or copolymerized with other olefins.vCatalytic oxidation of ethylene produces ethylene oxide, which is hydrolyzed to ethylene glycol. Ethylene glycol is a monomer for the pro
15、duction of synthetic fibers.vThe main source for ethylene is the steam cracking of hydrocarbons (Chapter 3). vTable 2-2 shows the world ethylene production by source until the year 2000.4 U.S. productionPropylene (CH3CH=CH2)Propylene can be polymerized alone or copolymerized with other monomers such
16、 as ethylene. Many important chemicals are based on propylene such as isopropanol, allyl alcohol, glycerol, and acrylonitrile.Butylenes (C4H8)There are four butene isomers: Three unbranched, “normal butenes (n-butenes) and A branched isobutene (2-methylpropene). The three nbutenes are 1-butene and c
17、is- and trans- 2-butene. The following shows the four butylene isomers:The dienesvDienes are aliphatic compounds having two double bonds. When the double bonds are separated by only one single bond, the compound is a conjugated diene (conjugated diolefin).v Nonconjugated diolefins have the double bo
18、nds separated (isolated) by more than one single bond. vThis latter class is of little industrial importance.v Each double bond in the compound behaves independently and reacts as if the other is not present.vAn important difference between conjugated and nonconjugated dienes is that the former comp
19、ounds can react with reagents such as chlorine, yielding 1,2- and 1,4-addition products.Butadiene (CH2=CH-CH=CH2)vButadiene is by far the most important monomer for synthetic rubber production. vIt can be polymerized to polybutadiene or copolymerized with styrene to styrene-butadiene rubber (SBR). B
20、utadiene is an important intermediate for the synthesis of many chemicals such as hexamethylenediamine and adipic acid. Both are monomers for producing nylon. vChloroprene is another butadiene derivative for the synthesis of neoprene rubber.vThe unique role of butadiene among other conjugated diolef
21、ins lies in its high reactivity as well as its low cost.vButadiene is obtained mainly as a coproduct with other light olefins from steam cracking units for ethylene production. vOther sources of butadiene are the catalytic dehydrogenation of butanes and butenes, and dehydration of 1,4-butanediol.vIs
22、oprene (2-methyl-1,3-butadiene) is a colorless liquid, soluble in alcohol but not in water. Its boiling temperature is 34.1C. Isoprene is the second important conjugated diene for synthetic rubber production. The main source for isoprene is the dehydrogenation of C5 olefins (tertiary amylenes) obtai
23、ned by the extraction of a C5 fraction from catalytic cracking units. It can also be produced through several synthetic routes using reactive chemicals such as isobutene, formaldehyde, and propene.vThe main use of isoprene is the production of polyisoprene. It is also a comonomer with isobutene for
24、butyl rubber production.Aromatic hydrocarbonsvBenzene, toluene, xylenes (BTX), and ethylbenzene are the aromatic hydrocarbons with a widespread use as petrochemicals. vThey are important precursors for many commercial chemicals and polymers such as phenol, trinitrotoluene (TNT), nylons, and plastics
25、. vAromatic compounds are characterized by having a stable ring structure due to the overlap of the -orbitals (resonance).vAccordingly, they do not easily add to reagents such as halogens and acids as do alkenes.vAromatic hydrocarbons are susceptible, however, to electrophilic substitution reactions
26、 in presence of a catalyst.vAromatic hydrocarbons are generally nonpolar. They are not soluble in water, but they dissolve in organic solvents such as hexane, diethyl ether, and carbon tetrachloride.Extraction ofaromaticsvBenzene, toluene, xylenes (BTX), and ethylbenzene are obtained mainly from the
27、 catalytic reforming of heavy naphtha. The product reformate is rich in C6, C7, and C8 aromatics, which could be extracted by a suitable solvent such as sulfolane or ethylene glycol.vThese solvents are characterized by a high affinity for aromatics, good thermal stability, and rapid phase separation
28、. The Tetra extraction process by Union Carbide (Figure 2-2) uses tetraethylene glycol as a solvent.vThe feed (reformate), which contains a mixture of aromatics, paraffins, and naphthenes, after heat exchange with hot raffinate, is countercurrentIy contacted with an aqueous tetraethylene lycol solut
29、ion in the extraction column. vThe hot, rich solvent containing BTX aromatics is cooled and introduced into the top of a stripper column. The aromatics extract is then purified by extractive distillation and recovered from the solvent by steam stripping. vExtractive distillation has been reviewed by
30、 Gentry and Kumar. The raffinate (constituted mainly of paraffins, isoparaffins and cycloparaffins) is washed with water to recover traces of solvent and then sent to storage. vThe solvent is recycled to the extraction tower. The extract, which is composed of BTX and ethylbenzene, is then fractionat
31、ed. Benzene and toluene are recovered separately, and ethylbenzene and xylenes are obtained as a mixture (C8 aromatics).vDue 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
32、ethylbenzene from the xylene mixture.vBecause p-xylene is the most valuable isomer for producing synthetic fibers, it is usually recovered from the xylene mixture.v Fractional crystallization used to be the method for separating the isomers, but the yield was only 60%. Currently, industry uses conti
33、nuous liquid-phase adsorption separation processes. vThe overall yield of p-xylene is increased by incorporating an isomerization unit to isomerize o- and m-xylenesto p-xylene.vAn overall yield of 90% p-xylene could be achieved. Figure 2-3 is a flow diagram of the Mobil isomerization process. In thi
34、s process, partial conversion of ethylbenzene to benzene also occurs. The catalyst used is shape selective and contains ZSM-5 zeolite.BenzenevBenzene (C6H6) is the simplest aromatic hydrocarbon and by far the most widely used one. vBefore 1940, the main source of benzene and substituted benzene was
35、coal tar. Currently, it is mainly obtained from catalytic reforming. Other sources are pyrolysis gasolines and coal liquids.vAromatic hydrocarbons, like paraffin hydrocarbons, react by substitution, but by a different reaction mechanism and under milder conditions.vAromatic compounds react by additi
36、on only under severe conditions. vFor 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:vBenzene is an important chemica
37、l intermediate and is the precursor for many commercial chemicals and polymers such as phenol, styrene for poly-styrenics, and caprolactom for nylon 6.EthylbenzenevEthylbenzene (C6H5CH2CH3) is one of the C8 aromatic constituents in reformates and pyrolysis gasolines. vIt can be obtained by intensive
38、 fractionation of the aromatic extract, but only a small quantity of the demanded ethylbenzene is produced by this route.v Most ethylbenzene is obtained by the alkylation of benzene with ethylene.Methylbenzenes (Toluene and Xylenes)vMethylbenzenes occur in small quantities in naphtha and higher boil
39、ing fractions of petroleum. vThose presently of commercial importance are toluene, o-xylene, p-xylene, and to a much lesser extent m-xylene.vThe primary sources of toluene and xylenes are reformates from catalytic reforming units, gasoline from catcracking, and pyrolysis gasoline from steam reformin
40、g of naphtha and gas oils. As mentioned earlier, solvent extraction is used to separate these aromatics from the reformate mixture.vOnly a small amount of the total toluene and xylenes available from these sources is separated and used to produce petrochemicals.Liquid petroleum fractions and residue
41、sNaphtha:vNaphtha from atmospheric distillation is characterized by an absence of olefinic compounds. Its main constituents are straight and branchedchain paraffins, cycloparaffins (naphthenes), and aromatics, and the ratios of these components are mainly a function of the crude origin.vNaphthas obt
42、ained from cracking units generally contain variable amounts of olefins, higher ratios of aromatics, and branched paraffins.vDue 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 produc
43、ed by hydrocracking units.vIn refining operations, however, it is customary to blend one type of naphtha with another to obtain a required product or feedstock.vSelecting the naphtha type can be an important processing procedure.vFor example, a paraffinic-base naphtha is a better feedstock for steam
44、 cracking units because paraffins are cracked at relatively lower temperatures than cycloparaffins. vAlternately, a naphtha rich in cycloparaffins would be a better feedstock to catalytic reforming units because cycloparaffins are easily dehydrogenated to aromatic compounds.vReformates are the main
45、source for extracting C6-C8 aromatics used for petrochemicals. Chapter 10 discusses aromatics-based chemicals.vNaphtha is also a major feedstock to steam cracking units for the production of olefins. vThis route to olefins is especially important in places such as Europe, where ethane is not readily
46、 available as a feedstock because most gas reservoirs produce non-associated gas with a low ethane content.vNaphtha could also serve as a feedstock for steam reforming units forthe production of synthesis gas for methanol. KerosinevKerosines with a high normal-paraffin content are suitable feedstock
47、s for extracting C12-C14 n-paraffins, which are used for producing biodegradable detergents. Currently, kerosine is mainly used to produce jet fuels,PRODUCTION OF OLEFINSvThe most important olefins and diolefins used to manufacture petrochemicals are ethylene, propylene, butylenes, and butadiene. Bu
48、tadiene, a conjugated diolefin, is normally coproduced with C2C4 olefins from different cracking processes.v Separation of these olefins from catalytic and thermal cracking gas streams could be achieved using physical and chemical separation methods.v However, the petrochemical demand for olefins is
49、 much greater than the amounts these operations produce. Most olefins and butadienes are produced by steam cracking hydrocarbons.STEAM CRACKING OF HYDROCARBONS(Production of Olefins)Steam Cracking ProcessvA typical ethane cracker has several identical pyrolysis furnaces in which fresh ethane feed an
50、d recycled ethane are cracked with steam as a diluent.v Figure 3-12 is a block diagram for ethylene from ethane. The outlet temperature is usually in the 800C range. The furnace effluent is quenched in a heat exchanger and further cooled by direct contact in a water quench tower where steam is conde
51、nsed and recycled to the pyrolysis furnace.v After the cracked gas is treated to remove acid gases, hydrogen and methane are separated from the pyrolysis products in the demethanizer.vThe effluent is then treated to remove acetylene, and ethylene is separated from ethane and heavier in the ethylene
52、fractionator. vThe bottom fraction is separated in the deethanizer into ethane and C3+ fraction. Ethane is then recycled to the pyrolysis furnace.Process Variables:The important process variables are reactor temperature, residence time, and steam/hydrocarbon ratio. Feed characteristics are also cons
53、idered, since they influence the process severity.1.Temperature:Steam cracking reactions are highly endothermic. Increasing temperature favors the formation of olefins, high molecular weight olefins, and aromatics. Optimum temperatures are usually selected to maximize olefin production and minimize
54、formation of carbon deposits.2. Residence Time:vIn steam cracking processes, olefins are formed as primary products. Aromatics and higher hydrocarbon compounds result from secondary reactions of the formed olefins. Accordingly, short residence times are required for high olefin yield. vWhen ethane a
55、nd light hydrocarbon gases are used as feeds, shorter residence times are used to maximize olefin production and minimize BTX and liquid yields; residence times ofv0.51.2 sec are typical. vCracking liquid feedstocks for the dual purpose of producing olefins plus BTX aromatics requires relatively lon
56、ger residence times than for ethane. vHowever, residence time is a compromise between the reaction temperature and other variables.3. Steam/Hydrocarbon Ratio:vA higher steam/hydrocarbon ratio favors olefin formation. Steam reduces the partial pressure of the hydrocarbon mixture and increases the yie
57、ld of olefins.v Heavier hydrocarbon feeds require more steam than gaseous feeds to additionally reduce coke deposition in the furnace tubes.vLiquid feeds such as gas oils and petroleum residues have complexpolynuclear aromatic compounds, which are coke precursors. Steam to hydrocarbon weight ratios
58、range between 0.21 for ethane and approximately 11.2 for liquid feeds.4. Feedstocks:vFeeds to steam cracking units vary appreciably, from light hydrocarbon gases to petroleum residues. Due to the difference in the cracking rates of the various hydrocarbons, the reactor temperature and residence time
59、 vary.v As mentioned before, long chain hydrocarbons crack more easily than shorter chain compounds and require lower cracking temperatures.vFor example, it was found that the temperature and residence time that gave 60% conversion for ethane yielded 90% conversion for propane.vFeedstock composition
60、 also determines operation parameters. The rates of cracking hydrocarbons differ according to structurevParaffinic hydrocarbons are easier to crack than cycloparaffins, and aromatics tend to pass through unaffected. vIsoparaffins such as isobutane and isopentane give high yields of propylene. This i
61、s expected, because cracking at a tertiary carbon is easier.Cracking Liquid FeedsvLiquid feedstocks for olefin production are light naphtha, full range naphtha, reformer raffinate, atmospheric gas oil, vacuum gas oil, residues, and crude oils. The ratio of olefins produced from steam cracking of the
62、se feeds depends mainly on the feed type and, to a lesser extent, on the operation variables.v For example, steam cracking light naphtha produces about twice the amount of ethylene obtained from steam cracking vacuum gas oil under nearly similar conditions.v Liquid feeds are usually cracked with low
63、er residence times and higher steam dilution ratios than those used for gas feedstocks. vThe reaction section of the plant is essentially the same as with gas feeds, but the design of the convection and the quenching sections are different. This is necessitated by the greater variety and quantity of
64、 coproducts. vAn additional pyrolysis furnace for cracking coproduct ethane and propane and an effluent quench exchanger are required for liquid feeds. Also, a propylene separation tower and a methyl acetylene removal unit are incorporated in the process.v Figure 3-14 is a flow diagram for cracking
65、naphtha or gas oil for ethylene production. As with gas feeds, maximum olefin yields are obtained at lower hydrocarbon partial pressures, pressure drops, and residence times. These variables may be adjusted to obtain higher BTX at the expense of higher olefin yield.vOne advantage of using liquid fee
66、ds over gas feedstocks for olefin production is the wider spectrum of coproducts. For example, steam cracking naphtha produces, in addition to olefins and diolefins, pyrolysis gasoline rich in BTX. vTable 3-16 shows products from steam cracking naphtha at low and at high severities.vIt should be not
67、ed that operation at a higher severity increased ethylene product and by-product methane and decreased propylene and butenes.Production of diolefinsvThe most important industrial diolefinic hydrocarbons are butadiene and isoprene.Butadiene (CH2 = CH-CH = CH2)vButadiene is the raw material for the mo
68、st widely used synthetic rubber, a copolymer of butadiene and styrene (SBR).v In addition to its utility in the synthetic rubber and plastic industries (over 90% of butadiene produced), many chemicals could also be synthesized from butadiene.vIn some parts of the world, as in Russia, fermented alcoh
69、ol can serve as a cheap source for butadiene. vThe reaction occurs in the vapor phase under normal or reduced pressures over a zinc oxide/alumina or magnesia catalyst promoted with chromium or cobalt.v Acetaldehyde has been suggested as an intermediate: two moles of acetaldehyde condense and form cr
70、otonaldehyde, which reacts with ethyl alcohol to give butadiene and acetaldehyde.vIsoprene (2-methyl 1,3-butadiene) is the second most important conjugated diolefin after butadiene. Most isoprene production is used for the manufacture of cis-polyisoprene, which has a similar structure to natural rub
71、ber. It is also used as a copolymer in butyl rubber formulations.Dehydrogenation of Tertiary Amylenes (Shell Process)vt-Amylenes (2-methyl-1-butene and 2-methyl-2-butene) are produced in small amounts with olefins from steam cracking units. vThe amylenes are extracted from a C5 fraction with aqueous
72、 sulfuric acid. vDehydrogenation of t-amylenes over a dehydrogenation catalyst produces isoprene. The overall conversion and recovery of t-amylenes is approximately 70%. vThe C5 olefin mixture can also be produced by the reaction of ethylene and propene using an acid catalyst.From Acetylene and Acet
73、one:vA three-step process developed by Snamprogetti is based on the reaction of acetylene and acetone in liquid ammonia in the presence of an alkali metal hydroxide.v The product, methylbutynol, is then hydrogenated to methylbutenol followed by dehydration at 250300C over an acidic heterogeneous cat
74、alyst.Carbon blackvCarbon 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.vCarbon black consists of elemental c
75、arbon 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.vCarbon black is produced by the partial combustion or the thermal decomposition of natural gas
76、 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.vThese feeds produce blacks with a carbon content of approximately 92 wt%. vCoke produced
77、 from delayed and fluid coking units with low sulfur and ash contents has been investigated as a possible substitute for carbon black.v Three processes are currently used for the manufacture of carbon blacks. These are the channel, the furnace, and the thermal processes.The furnace black processvThi
78、s is a more advanced partial combustion process. The feed is firstvpreheated and then combusted in the reactor with a limited amount of air.vThe hot gases containing carbon particles from the reactor are quenched with a water spray and then further cooled by heat exchange with the air used for the p
79、artial combustion. vThe type of black produced depends on the feed type and the furnace temperature. The average particle diameter of the blacks from the oil furnace process ranges between 200500 , while it ranges between 400700 from the gas furnace process. Figure 4-4 shows the oil furnace black pr
80、ocessSynthesis gasvSynthesis 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.vDuring World War II, the Germans obtained synthesis gas by gasifying co
81、al. vThe mixture was used for producing a liquid hydrocarbon mixture in the gasoline range using Fischer-Tropsch technology. vAlthough 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 (
82、SASOL, II, and III).vThere 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.v It can also be obtained by gasifying coal to a medium Btu gas (medium Btu gas c
83、onsists of variable amounts of CO, CO2, and H2 and is used principally as a fuel gas).v Figure 4-5 shows the different sources of synthesis gas.Naphthenic acidsvNaphthenic acids are a mixture of cyclo-paraffins with alkyl side chains ending with a carboxylic group. The low-molecular-weight naphtheni
84、c acids (812 carbons) are compounds having either a cyclopentane or a cyclohexane ring with a carboxyalkyl side chain.v These compounds are normally found in middle distillates such as kerosine and gas oil. High boiling napthenic acids from the lube oils are monocarboxylic acids, (Cl4-Cl9) with an a
85、verage of 2.6 rings. Naphthenic acids constitute about 50 wt% of the total acidic compounds in crude oils. vNaphthenic-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 a
86、cids from middle distillates occurs by extraction with 710% caustic solution.vThe formed sodium salts, which are soluble in the lower aqueous layer, are separated from the hydrocarbon layer and treated with a mineral acid to spring out the acids. vThe free acids are then dried and distilled.vUsing s
87、trong caustic solutions for the extraction may create separation problems because naphthenic acid salts are emulsifying agents.Uses of naphthenic acids and its saltsvFree naphthenic acids are corrosive and are mainly used as their salts and esters. vThe sodium salts are emulsifying agents for prepar
88、ing agricultural insecticides, additives for cutting oils, and emulsion breakers in the oil industry.vOther metal salts of naphthenic acids have many varied uses. For example, calcium naphthenate is a lubricating oil additive, and zinc naphthenate is an antioxidant.v Lead, zinc, and barium naphthena
89、tes are wetting agents used as dispersion agents for paints. Some oil soluble metal naphthenates, such as those of zinc, cobalt, and lead, are used asdriers in oil-based paints. vAmong the diversified uses of naphthenates is the use of aluminum naphthenates as gelling agents for gasoline flame throw
90、ers (napalm).v Manganese naphthenates are well-known oxidation catalysts.Cresylic acidvCresylic acid is a commercial mixture of phenolic compounds including phenol, cresols, and xylenols. This mixture varies widely according to its source.Uses of Cresylic AcidvCresylic acid is mainly used as degreas
91、ing agent and as a disinfectant of a stabilized emulsion in a soap solution.vCresols are used as flotation agents and as wire enamel solvents. vTricresyl phosphates are produced from a mixture of cresols and phosphorous oxychloride. vThe esters are plasticizers for vinyl chloride polymers. vThey are
92、 also gasoline additives for reducing carbon deposits in the combustion chamber.Chemicals Based on MethaneChloromethanesUses of Chloromethanes:vThe major use of methyl chloride is to produce silicon polymers.vOther uses include the synthesis of tetramethyl lead as a gasoline octane booster, a methyl
93、ating agent in methyl cellulose production, a solvent, and a refrigerant.vMethylene chloride has a wide variety of markets.v 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.vChloroform is mainly us
94、ed to produce chlorodifluoromethane (Fluorocarbon 22) by the reaction with hydrogen fluoride:SYNTHESIS GAS (STEAM REFORMING OF NATURAL GAS)vFor the production of methanol, this mixture could be used directly with no further treatment except adjusting the H2/(CO + CO2) ratio to approximately 2:1.vFor
95、 producing hydrogen for ammonia synthesis, however, further treatment steps are needed. First, the required amount of nitrogen for ammonia must be obtained from atmospheric air.vThis is done by partially oxidizing unreacted methane in the exit gas mixture from the first reactor in another reactor (s
96、econdary reforming).vThe main reaction occurring in the secondary reformer is the partial oxidation of methane with a limited amount of air. The product is a mixture of hydrogen, carbon dioxide, carbon monoxide, plus nitrogen, which does not react under these conditions.v The reaction is represented
97、 as follows:vThe second step after secondary reforming is removing carbon monoxide, which poisons the catalyst used for ammonia synthesis. vThis is done in three further steps, shift conversion, carbon dioxide removal, and methanation of the remaining CO and CO2.Chemicals based on synthesis gasvThe
98、two major chemicals based on synthesis gas are ammonia and methanol. vEach 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).v Each of these chemicals is also a precur
99、sor of more chemicals. vMethanol, the second major product from synthesis gas, is a unique compound of high chemical reactivity as well as good fuel properties. vIt is a building block for many reactive compounds such as formaldehyde, acetic acid, and methylamine.v It also offers an alternative way
100、to produce hydrocarbons in the gasoline range (Mobil to gasoline MTG process). vIt may prove to be a competitive source for producing light olefins in the future. Hydrocarbons from methanol (methanol to gasoline MTG process)vfuture because of the multisources of synthesis gas. vWhen oil and gas are
101、depleted, coal and other fossil energy sources could be converted to synthesis gas, then to methanol, from which hydrocarbon fuels and chemicals could be obtained.v During the early seventies, oil prices escalated (as a result of 1973 Arab-Israeli War), and much research was directed toward alternat
102、ive energy sources.v In 1975, a Mobil research group discovered that methanol could be converted to hydrocarbons in the gasoline range with a special type of zeolite (ZSM-5) catalyst.Ethylene glycolDEHYDROGENATION OF PROPANE (propene production)vThe process could also be used to dehydrogenate butane
103、, isobutane, or mixed LPG feeds.v It is a single-stage system operating at a temperature range of 540680C and 520 absolute pressures. Conversions in the range of 5565% are attainable, and selectivities may reach up to 95%.vFigure 6-2 shows the Lummus-Crest Catofin dehydrogenation process.Nitropropan
104、es are good solvents for vinyl and epoxy resins. They are also used to manufacture rocket propellants. Nitromethane is a fuel additive for racing cars.Aromatics ProductionvLiquefied petroleum gas (LPG), a mixture of propane and butanes, is catalytically reacted to produce an aromatic-rich product. T
105、he 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.vThese compounds then dehydrocyclize to BTX aromatics. The following reaction sequence illustrates the formation of benzene from 2 propane molec
106、ules:vAlthough olefins are intermediates in this reaction, the final product contains a very low olefin concentration. The overall reaction is endothermic due to the predominance of dehydrogenation and cracking.v Methane and ethane are by-products from the cracking reaction. vTable 6-1 shows the pro
107、duct yields obtained from the Cyclar process developed jointly by British Petroleum and UOP.10 A simplified flow scheme for the Cyclar process is shown in Figure 6-6.Chemicals from high molecular weight n-paraffinsvHigh molecular weight n-paraffins are obtained from different petroleum fractions thr
108、ough physical separation processes. Those in the range of C8-C14 are usually recovered from kerosines having a high ratio of these compounds. vVapor phase adsorption using molecular sieve 5A is used to achieve the separation. The n-paraffins are then desorbed by the action of ammonia. vContinuous op
109、eration is possible by using two adsorption sieve columns, one bed on stream while the other bed is being desorbed. n- Paraffins could also be separated by forming an adduct with urea. For a paraffinic hydrocarbon to form an adduct under ambient temperature and atmospheric pressure, the compound mus
110、t contain a long unbranched chain of at least six carbon atoms.Oxidation of paraffins (fatty Acids and Fatty Alcohols)vThe catalytic oxidation of long-chain paraffins (Cl8-C30) over manganese salts produces a mixture of fatty acids with different chain lengths. vTemperature and pressure ranges of 10
111、5120C and 1560 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. vThe main source for fatty acids for soap manufacture, however, is the hydrolysis of fats and oils (a nonpetroleum source).SULFONATION OF n-PARAFFINS(Sec
112、ondary Alkane Sulfonates SAS)The reaction is catalyzed by ultraviolet light with a wave-length between 3,3003,600. The sulfonates are nearly 100% biodegradable, soft and stable in hard water, and have good washing properties.Fermentation using n-Paraffins (Single Cell Protein SCP)vThe term single ce
113、ll protein is used to represent a group of microbial cells such as algae and yeast that have high protein content.v The production of these cells is not generally considered a synthetic process but microbial farming via fermentation in which n-paraffins serve as the substrate. vSubstantial research
114、efforts were invested in the past two decades to grow algae, fungi, and yeast on different substrates such as n-paraffins, methane, methanol, and even carbon dioxide.v The product SCP is constituted mainly of protein and variable amounts of lipids, carbohydrates, vitamins, and minerals.vSome of the
115、constituents of SCP limit its usefulness for use as food for human beings but can be used for animal feed.v A commercial process using methanol as the substrate was developed by ICI. The product Pruteen is an energy-rich material containing over 70% proteinChemicals Based on EthylenevEthylene reacts
116、 by addition to many inexpensive reagents such as water, chlorine, hydrogen chloride, and oxygen to produce valuable chemicals. vIt can be initiated by free radicals or by coordination catalysts to produce polyethylene, the largest-volume thermoplastic polymer.v It can also be copolymerized with oth
117、er olefins producing polymers with improved properties. vFor example, when ethylene is polymerized with propylene, a thermoplastic elastomer is obtained. Figure 7-1 illustrates the most important chemicals based on ethylene.Ethylene Glycol (CH2OHCH2OH)vEthylene glycol (EG) is colorless syrupy liquid
118、, and is very soluble in water. vThe boiling and the freezing points of ethylene glycol are 197.2 and 13.2C, respectively.vCurrent world production of ethylene glycol is approximately 15 billion pounds. vMost of that is used for producing polyethylene terephthalate (PET) resins (for fiber, film, bot
119、tles), antifreeze, and other products.vApproximately 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 acidEthanolaminesvA mix
120、ture of mono-, di-, and triethanolamines is obtained by the reaction between ethylene oxide (EO) and aqueous ammonia. vThe reaction conditions are approximately 3040C and atmospheric pressure:Ethanolamines are important absorbents of acid gases in natural gastreatment processes. Another major use of
121、 ethanolamines is the production of surfactants.Chlorination of ethylenevThe direct addition of chlorine to ethylene produces ethylene dichloride (1,2-dichloroethane). vEthylene dichloride is the main precursor for vinyl chloride, which is an important monomer for polyvinyl chloride plastics and res
122、ins.Vinyl Chloride (CH2=CHCl)vVinyl chloride is a reactive gas soluble in alcohol but slightly soluble in water. It is the most important vinyl monomer in the polymer industry. vVinyl chloride monomer (VCM) was originally produced by the reaction of hydrochloric acid and acetylene in the presence of
123、 HgCl2 catalyst. The reaction is straightforward and proceeds with high conversion (96% on acetylene):vHowever, ethylene as a cheap raw material has replaced acetylene for obtaining vinyl chloride. vThe production of vinyl chloride via ethylene is a three-step process. The first step is the direct c
124、hlorination of ethylene to produce ethylene dichloride. Either a liquid- or a vapor-phase process is used:vThe exothermic reaction occurs at approximately 4 atmospheres and 4050C in the presence of FeCl3, CuCl2 or SbCl3 catalysts. Ethylene bromide may also be used as a catalyst. The second step is t
125、he dehydrochlorination of ethylene dichloride (EDC) to vinyl chloride and HCl. The pyrolysis reaction occurs at approximately 500C and 25 atmospheres in the presence of pumice on charcoal:Chemicals Based on PropylenevPropylene, “the crown prince of petrochemicals, is second to ethylene as the larges
126、t-volume hydrocarbon intermediate for the production of chemicals.vAs an olefin, propylene is a reactive compound that can react with many common reagents used with ethylene such as water, chlorine, and oxygen. vHowever, structural differences between these two olefins result in different reactiviti
127、es toward these reagents.vThe 1997 U.S. propylene demand ws 31 billion pounds and most of it was used to produce polypropylene polymers and copolymers (about 46%). vOther large volume uses are acrylonitrile for synthetic fibers (Ca 13%), propylene oxide (Ca 10%), cumene (Ca 8%) and oxo alcohols (Ca 7%).Uses of Acrylonitrile:1.Acrylonitrile is mainly used to produce acrylic fibers, resins, and elastomers.2.Copolymers of acrylonitrile with butadiene and styrene are the ABS resins and those with styrene are the styrene-acrylonitrile resins SAN that are important plastics.
