StyreneS Guy B. Woodle UOP LLC, Des Plaines, Illinois, U.S.A. INTRODUCTION Styrene is one of the most important aromatic monomers used for the manufacture of plastics. Small-scale commercial production of styrene began in the 1930s. Demand for styrene-based plastics has grown significantly, and in 2003 the worldwide annual production capacity was approximately 24.5 million metric tons.[1] About 65% of styrene is used to produce polystyrene. Polystyrene is used in the manufacture of many commonly used products such as toys, household and kitchen appliances, plastic drinking cups, housings for computers and electronics, foam packaging, and insulation. Polystyrene finds such widespread use because it is relatively inexpensive to produce and is easy to polymerize and copolymerize, resulting in plastics with a broad range of characteristics. In addition to polystyrene, styrene is used to produce acrylonitrile–butadiene– styrene polymer, styrene–acrylonitrile polymer, and styrene–butadiene synthetic rubber (SBR). The development of styrene technologies was mainly driven by demand for cheap synthetic rubber during and immediately after World War II. Between 5% and 10% of total styrene produced becomes a component of synthetic rubbers, which are copolymers of styrene and butadiene (SBR). Styrene copolymers containing acrylonitrile are specialty materials that are used for specific applications. Demand for styrene for the period 2004–2009 is estimated to grow at a rate of approximately 4% per year.[1] its unsaturated side chain and aromatic ring. For example, styrene can be oxidized to form benzoic acid, benzaldehyde, styrene oxide, and other oxygenated compounds. Styrene oxide is used in the production of various cosmetics, perfumes, agricultural and biological chemicals. REACTION KINETICS AND THERMODYNAMICS Essentially all commercially produced styrene uses ethylbenzene (EB) as a feedstock. Between 85% and 90% of worldwide styrene production is based on EB dehydrogenation. The remaining 10–15% of styrene is obtained as a coproduct in a process to produce propylene oxide. Ethylbenzene Dehydrogenation Ethylbenzene is catalytically dehydrogenated in the presence of steam according to the equation: CH3 CH2 + H2 PHYSICAL AND CHEMICAL PROPERTIES Styrene is a colorless aromatic liquid. It is only very slightly soluble in water, but infinitely soluble in alcohol and ether. Additional properties are listed in Table 1. Styrene is chemically reactive with the most important reaction being its polymerization to form polystyrene. Styrene can also copolymerize with other monomers, such as butadiene and acrylonitrile, to produce a variety of industrially important copolymers. In addition to polymerization, styrene can undergo other types of reactions due to the chemical nature of Encyclopedia of Chemical Processing DOI: 10.1081/E-ECHP-120007970 Copyright # 2006 by Taylor & Francis. All rights reserved. The reaction is highly endothermic and conversion is limited in extent by equilibrium. The reaction equilibrium constant is defined as: Keq ¼ ðPsty à Ph2Þ=Peb where Psty is the partial pressure of styrene, Ph2 is the partial pressure of hydrogen; and Peb is the partial pressure of ethylbenzene. High temperature, steam dilution, and low system pressure produce an equilibrium more favorable to styrene. For endothermic vapor-phase reactions, the equilibrium constant increases with temperature and 2859 In addition to losing valuable EB feed by dealkylation. Ed. allowing greater EB conversions to be obtained with the same inlet temperature.. Consequently.5 100 82. and water–gas shift side reactions should be avoided.[3] .0 5 18. (From Perry. C Critical temperature.) can be determined equation:[2] according to the following The key dealkylation reactions can be described by the following equations: CH3 ln Keq ¼ 16:12 À ð15. styrene. 901 pp...903 À30. steam reforming.1 1 À7.628 145. 350=TÞ where Keq is the equilibrium constant in atmospheres and T is the temperature in K. Ethylene and Its Industrial Derivatives.2 373 46.8 10 44.0 200 101. Eds. steam supplies heat to the reacting mixture. steam is believed to suppress the deposition of carbonaceous material on the catalyst. Perry’s Chemical Engineers Handbook. The reaction feed mixture undergoes certain other reactions that are not equilibrium limited under typical operating conditions. D. The net hydrogen formation gives an unfavorable shift in equilibrium. Most important among these are the dealkylation reactions that result in the formation of benzene and ethylene or toluene and methane.. Steam dilution provides the same effect as a reduction in total pressure. Therefore. S. if possible. mm Hg at T C a 104. Green. Other reactions produce small amountsof a-methylstyrene and other high boiling components.H. 6th Ed. the catalyst will become fouled and its activity will decline to unacceptable levels.W. C Boiling point. First.2 Density is at 20 C referred to water at 4 C. while the presence of carbon dioxide has a negative effect on dehydrogenation catalyst activity. atm Vapor pressure. Another method to create a positive shift in equilibrium is the use of steam dilution to reduce the partial pressures of EB.0 20 30. R. Second.3 400 122. + H 2C CH2 CH3 CH3 + H2 + CH4 Both methane and ethylene undergo steam reforming reactions according to the following equations: CH4 þ H2 O ! CO þ 3H2 C2 H4 þ 2H2 O ! 2CO þ 4H2 The water–gas shift reaction also occurs and is generally near equilibrium at the reaction temperature: CO þ H2 O $ CO2 þ H2 The combination of dealkylation. The actual quantity of steam varies with the type of catalyst used..A. McGraw-Hill: New York. Third. and hydrogen.5 760 145. If the carbonaceous material is allowed to accumulate. C Critical pressure.2860 Styrene Table 1 Physical properties of styrene Molecular weight Specific gravitya Melting point. a minimum amount of steam appears to keep the catalyst in the required oxidation state for high activity. 3-60 and Miller. the resultant net formation of carbon dioxide and hydrogen by this combination of reactions inhibits the primary dehydrogenation reaction. 1984. Steam dilution has several other important benefits.152 0. the drop in temperature for a given EB conversion is lower. Lower pressure results in greater EB conversion without an accompanying significant decrease in styrene selectivity. a higher total pressure will shift the reaction equilibrium to the left and reduce EB conversion. The equilibrium constant has the dimension of pressure since two moles of products are formed for each mole of EB converted.6 40 59.8 60 69.. molybdenum oxide. the rate of benzene formation increases significantly relative to the rate of styrene formation. Potassium has been shown to provide other benefits. The critical operating and design parameters for EB dehydrogenation are discussed in the following paragraphs. The key side reactions are largely independent of reaction pressure. which prolongs catalyst life. which form benzene and toluene by-products. Small catalyst particles. The most widely used catalysts are composed of iron oxide. Compensation for aging catalyst is achieved by adjusting other operating parameters. to gain the advantage of increased surface area without incurring the penalty of increased pressure drop and reaction pressure. and various metal oxide promoters. such as ribbed extrudates. S . the equilibrium constant is less favorable at lower temperature. In particular. the EB conversion reaches equilibrium before the outlet of the catalyst bed. in a normal design. However. To address this. As a result. about 80% of the temperature drop occurs in approximately the first third of the catalyst bed. and maintaining the catalyst’s active surface in a desirable state. Reaction pressure is established during the plant design at the lowest practical level. potassium carbonate. Too little catalyst will prevent a close approach to equilibrium. Properties such as catalyst size and shape also impact performance. Catalyst type and properties Ethylbenzene dehydrogenation is generally catalyzed by a potassium-promoted iron oxide catalyst. a high inlet catalyst temperature is required. which has the effect of decreasing the effective active catalyst quantity for reaction. there is less methane and ethylene present in the effluent of a reactor than would be expected from the benzene and toluene formation. Carbon monoxide is generally about 10 mol% of the total carbon oxides. and catalyst stability can be optimized by selecting the best catalyst or a combination of catalysts for a particular application. catalyst developers have used specialized shapes. However. the reaction mixture temperature decreases as the reaction proceeds. then distillation costs associated with recovery and recycle of the unconverted EB can become significant. Catalysts typically lose activity with time onstream. Modern commercial reactors operate below atmospheric pressure. and vanadium oxide. Both companies offer a wide range of catalysts to suit individual processing needs. Reaction temperature is generally adjusted by changing either the steam temperature or the steam-to-oil ratio. cerium oxide. the reaction temperature. Reaction temperature Because the dehydrogenation reaction is endothermic. With too much catalyst. Dow and BASF manufacture proprietary catalysts. as temperature is increased. while the side reactions continue leading to loss of selectivity. it reduces the formation of carbonaceous deposits on the catalyst surface. Catalyst quantity The amount of catalyst relative to EB feed is an important parameter for optimum reactor performance. smaller sized catalyst will increase reaction rates by providing more available catalyst surface area than larger sized catalyst. however. The reaction rate slows because of the closer approach to equilibrium and the decrease in kinetic reaction rate with the decreasing temperature. Increasing the steam-to-oil ratio has the net effect of improving the EB conversion and styrene yield.Styrene 2861 Typically. If EB conversion is low. Furthermore. This means there is an effective upper limit to the inlet temperature if high styrene selectivity is a required criterion. operating at lower pressures also provides higher styrene yield. Examples of metal oxide promoters include chromium oxide. high temperature also increases the rates of nonselective thermal reactions and dealkylation reactions. The optimum catalyst quantity is achieved by balancing the EB conversion level and the styrene yield. Pressures as low as 300 mm Hg or lower are common. Lower pressure favors higher equilibrium conversion to styrene. Ethylbenzene conversion. Therefore. Steam dilution or steam-to-oil ratio The main functions of steam dilution are to act as a diluent to reduce the hydrocarbon partial pressures. styrene selectivity. hence.[4] The potassium component substantially increases catalyst activity relative to an unpromoted iron oxide catalyst. In particular. providing heat for the endothermic dehydrogenation reaction. catalyst activity. Reaction pressure Ethylbenzene dehydrogenation results in a significant increase in the volume of reactants due to the reaction stoichiometry. The Sud-Chemie Group and Criterion Catalysts are the major catalyst developers and manufacturers for the styrene industry. which have been mainly for use in their own respective technologies. have a disadvantage in that they result in greater pressure drop through a reactor and higher overall reaction pressures. costs associated with generating and superheating the dilution steam also increase and eventually offset the reaction advantages. In theory. in particular. which in turn can be dehydrated to a more desirable coproduct. The design and operation of a propylene oxide= styrene process plant is complicated and includes numerous pieces of equipment. Reactor design and catalyst bed configuration are key factors for controlling thermal reactions. but become a considerable factor affecting overall yield when temperatures rise above 655 C. The dehydrated reaction mixture is typically stripped of light components and rerun in a styrene column to remove heavy by-products. As a result. the hydroperoxide is essentially converted to the corresponding alcohol.[5] During the epoxidation reaction. The EB primary steam is combined with the major part of the dilution steam immediately prior to entering the dehydrogenation catalyst bed. such as anthracene and=or pyrene. The method involves superheating EB vapor. the total combined feed mixture reaches the desired catalyst inlet temperature. to a temperature below approximately 580 C.2862 Styrene Propylene Oxide with Styrene Co-production In the late 1960s. The EB is vaporized with a certain amount of steam—commonly called primary steam—to suppress coking.[6] Although higher conversions are attractive from an EB recovery and recycle standpoint. the total investment cost for a commercial-scale plant is about four times that of an EB dehydrogenation plant to produce the same quantity of styrene product. COMMERCIAL PRODUCTION Reactor Design One important aspect of modern day EB dehydrogenation reactor design is managing the operating conditions to minimize thermal reactions. The main steam is superheated to a temperature such that. Styrene is coproduced in the form of this process that uses EB hydroperoxide as the epoxidizing agent. a method was discovered to produce propylene oxide by the epoxidation of propylene using organic hydroperoxides as the epoxidizing agent. The oxidation is carried out in the liquid phase with a target EB conversion of approximately 13%. The major portion of the dilution steam is generally referred to as main steam. along with a portion of the dilution steam. 1 Propylene oxide–styrene process chemistry. In the last step. Fig. when it is mixed with the EB and the primary steam. The first step is oxidation of EB to form EB hydroperoxide. as well as coke. The second step is epoxidation of propylene to form propylene oxide product and 1-phenylethanol. 1. One technique to reduce thermal reactions is to delay heating the EB to the reaction inlet temperature until the last possible moment before being exposed to the catalyst. the 1-phenylethanol is dehydrated to styrene and water. Thermal reactions do not occur at a significant level below about 600 C. . The chemistry of this process can be broken down into three main reactions as shown in Fig. there is a significant disadvantage because the EB hydroperoxide selectivity declines sharply. resulting in a purified styrene product. The major by-product from the thermal reaction of EB to styrene is benzene with significant subsequent conversions to a complex mixture of higher aromatics. and a dehydrogenated mixture. The process condensate is stripped of organics and either recycled for use within the styrene plant or exported. Modern day commercial reactors are highly engineered. Since that time. If the singlestage reactor effluent is reheated. The hydrogen rich off-gas stream is recovered through an off-gas compressor for use as a fuel gas. This radial outflow geometry requires a much lower inlet volume to obtain proper distribution of the feed vapor through the catalyst bed than either an axial flow or a radial inflow reactor configuration. 2 Lummus=UOP classic SM process. more than 50 projects have been licensed with more than 40 plants in commercial operation as of 2004. benzene. and steam dilution is limited to 40–50% per pass conversion of EB. however. and toluene. This process of reheating and adding catalyst stages can be repeated as frequently as economically feasible. A single-stage reactor with practical limits of temperature. is fed to the distillation section of the plant. A typical Lummus=UOP Classic SM process flow diagram is shown in Fig. . However.Styrene 2863 Commercial adiabatic reactors are typically of radial flow construction with the flow path moving from in to out. Fig. 2. styrene product. To minimize thermal reactions. The radial flow reactor design also provides the advantage of low pressure drop since the flow path through the catalyst is much shorter relative to an axial flow reactor. but there are key differences in the details. Fresh and recycled EB are combined with steam and fed to the dehydrogenation reaction section of the plant. process condensate. which later became the Lummus= UOP technology. The dehydrogenated mixture. pressure. S Commercial Adiabatic Dehydrogenation Processes Most commercial styrene plants are based on either the Lummus=UOP technology or the Fina=Badger technology. With each additional reaction stage. Designers use specialized computational fluid dynamics programs to study flow characteristics throughout a reactor. too small a diameter will produce a high pressure drop through the centerpipe. When the reheated reaction mixture is fed to a second stage of catalyst. the reaction mixture moves away from equilibrium allowing for higher EB conversion. Lummus/UOP Classic SMTM Process The first commercial plant based on the Lummus= Monsanto technology. then total EB conversions of 60–75% per pass can be achieved. potentially causing flow maldistribution and causing the feed vapor to enter the catalyst bed with a velocity that can result in erosion and attrition of catalyst particles. consisting mainly of unconverted EB. To obtain high EB conversions. typically two or three reactors are used in series with some type of reheating between the reactors to raise the temperature of the reaction mixture. was commissioned in 1972. These technologies are generally similar. generally with a corresponding decrease in styrene selectivity. The reactor effluent is condensed and separated into off-gas. a progressively smaller incremental EB conversion is achieved. Dow Chemical is a major styrene producer and uses its own technology. the reactor centerpipe diameter should be as small as possible to minimize residence time at the highest temperature throughout the reactor. The equipment is designed to minimize pressure drop from the dehydrogenation reactors inlet to the off-gas compressor. which is then fed to the dehydrogenation reactors. The main equipment in the dehydrogenation reaction section of a Lummus=UOP Classic SM plant includes a steam superheater. two dehydrogenation reactors. The distillation section of a Lummus=UOP Classic SM plant consists of four distillation columns. The first column in the sequence splits the EB and the lighter components from styrene. Lummus/UOP Smart SMTM Process The Lummus=UOP Smart SM process is based on an oxidative reheat technology invented by UOP.[7] Polymerization inhibitors are injected into the splitter to restrict polymer formation. A unique feature of the Lummus=UOP Classic SM process is the noncompressive azeotropic heat recovery option. in particular into the bottom section of the column. The cooled steam exiting the interchanger is reheated in the steam superheater prior to being fed to the first stage dehydrogenator. and an off-gas compressor (Fig. Superheated main steam is mixed with the EB and the primary steam immediately before entering the first stage dehydrogenator.2864 Styrene Fig. The main steam is superheated and used to reheat the reaction mixture for the second stage dehydrogenator.[8] In this option. The EB=SM splitter bottoms’ stream is fed to the SM column where the styrene is purified by removal of any heavy residual tars. Oftentimes.[9] Although this technology can be used in the design of . The process steam from the reactor effluent stream is condensed and separated by gravity from the liquid hydrocarbon components. such as Sulzer Mellapak Plus packing. in particular. the benzene recovered in this scheme is recycled as feed to the upstream EB plant. The EB=styrene monomer (EB=SM) splitter is operated under vacuum and uses structured packing. 3). The superheated steam can range from 700 C to as high as approximately 850 C to achieve the desired inlet temperature for the first stage dehydrogenator. a series of waste heat exchangers. This energy savings potential makes the azeotropic heat recovery option economically attractive. in regions with moderate to high steam costs. The condensation of the splitter overhead vapor produces approximately 500 kcal=kg styrene. Tertiary-butyl catechol (TBC) is injected into the overhead of the SM column. Subsequent stages are used to generate steam at different pressures. to minimize temperature and polymer formation. and the column is operated under vacuum to minimize polymer formation. 3 Lummus=UOP classic SM process dehydrogenation section. The condensate is stripped of hydrocarbons and revaporized for use as process steam. Benzene and toluene by-products in the recovery column overhead stream are separated in a benzene=toluene splitter. the EB=SM splitter overhead vapor is used to boil an EB–water azeotrope mixture. Hydrogen and light hydrocarbons removed from the condensed reactor effluent are compressed and used as fuel gas in the steam superheater. which are directed for use elsewhere in the styrene plant or larger EB–styrene complex. The reactor is designed to provide a uniform reaction mixture while minimizing residence time in the centerpipe to avoid thermal reactions. The reaction mixture is reheated in a specially designed interchanger located inside the second stage dehydrogenator vessel shell. The first stage of waste heat recovery is used to superheat the EB and the primary steam. The reactor effluent is cooled in a series of three waste heat exchangers before final cooling and condensing. The overhead product from the EB=SM splitter is fed to an EB recovery column. Typically intermediate pressure steam and low pressure steam are generated. The EB recovery column net bottoms’ stream is recycled to the dehydrogenation section. it is most commonly used in a revamp of an existing plant to increase styrene production by as much as 60% with minimal capital investment cost. Recycled and fresh EB Fig. . 4. The most recent design uses a flow diagram as shown in Fig. The Mitsubishi Chemical plant was designed with a dehydrogenation section containing two combination oxidation–dehydrogenation reactors as shown in Fig. In the first zone. 5 Fina=Badger styrene process. Fina/Badger Styrene Process The Fina=Badger styrene process has evolved through many generations. The oxygen is diluted in steam and the oxygen=steam mixture is well mixed to ensure the reaction mixture remains outside the flammability envelope at all times. another benefit of this technology is it shifts the reaction equilibrium in a favorable direction by removing the hydrogen byproduct. a grassroots plant. In addition to providing the full reheating requirement. The temperature rise in the oxidation zone is proportional to the amount of oxygen reacted across the catalyst bed. which is directly fed into the second zone where the standard EB dehydrogenation reaction occurs. The Lummus=UOP Smart SM technology uses a specially designed reactor that contains two concentric catalyst zones. This shift in equilibrium allows for higher EB conversion without a corresponding decrease in styrene yield.Styrene 2865 S Fig. A cross-sectional view of the concentric oxidation and dehydrogenation catalyst beds is also shown in Fig. 4 Lummus=UOP smart SM process dehydrogenation section. hydrogen is selectively oxidized across a noble metalcontaining catalyst. Japan. 5. 4. The direct combustion of hydrogen reheats the reaction mixture. The Lummus=UOP Smart SM technology was first commercialized in 1995 at Mitsubishi Chemical in Kashima. The benzene and toluene mixture is typically sent to an integrated EB plant where it is further fractionated. 6 Fina=Badger styrene process dehydrogenation section. the majority of which is hydrogen. which consists of three distillation columns. prior to being fed to the primary dehydrogenation reactor. This is accomplished by heating the reaction mixture more directly through a combustion and convective heat transfer process. to develop a reheating technology called Flameless Distributed Combustion (FDC) for application in EB dehydrogenation. Tertiary-butyl catechol is injected into the overhead of the finishing column to prevent polymerization. The reactor effluent is condensed and separated into vent gas. steam transfer lines. and a series of feed=effluent exchangers (Fig. 6). High pressure steam is also generated by the recovery of heat from the reactor effluent stream.2866 Styrene Fig. Recent EB recovery columns use high efficiency packing to obtain minimum pressure drop through the column. This allows the column bottoms’ temperature to be maintained below 100 C. The main types of equipment in the dehydrogenation section of the plant are the steam superheater. Flameless Distributed Combustion technology enables specific constraints in the conventional dehydrogenation system to be overcome. A low steam-tooil ratio is desirable because of the substantial energy savings associated with superheating less steam. a practical lower steam-to-oil ratio limit exists due to the metallurgy of the steam superheater. Flameless Distributed Combustion allows for operation at molar steam-to-oil ratios less than 7 : 1 without a costly metallurgy upgrade. and hydrocarbon.[10] Flameless Distributed Combustion technology is patented by Shell Oil Company and was originally used as a heat injector for enhanced recovery of hydrocarbons from subterranean formations. the benzene by-product is ultimately consumed in the EB unit and the toluene becomes a by-product stream from the EB plant. in particular designing for low steam-to-oil ratios. The reactor effluent is cooled in a series of three heat exchangers that heat the EB and steam feed to the reactors and generate steam. condensate. The EB recovery column bottoms’ stream is fed to a finishing column where the styrene is purified by the removal of any heavy residue. In 1997. The condensate is stripped and used as feed water for steam generation. The vent gas. are mixed with steam and fed to the primary and the secondary dehydrogenation reactors. is used as fuel gas. Fina=Badger joined with Shell Technology Ventures. and interstage reheater. The Fina=Badger distillation section consists of three distillation columns. . The first column in the sequence splits the benzene and toluene byproducts from the unconverted EB and styrene product. In this case. The hydrocarbon portion of the reactor effluent is fed to the distillation section of the plant. The EB recycle column separates the unconverted EB for recycle to the dehydrogenation reactors. a subsidiary of Shell Oil Company. However. The major portion of steam is superheated and used to reheat the reaction mixture for the secondary dehydrogenation reactor. This is an important aspect of the design as styrene polymerization becomes significant at temperatures higher than approximately 100 C. Tertiary-butyl catechol is widely used to prevent styrene polymerization during storage. The dehydrogenation reactors are designed to provide low pressure drop and uniform flow distribution. As the cooled steam exits the reheater it is superheated again in the steam superheater. the primary and secondary dehydrogenation reactors. All the columns are designed to operate under vacuum to minimize temperature and polymer formation. 2 357.Styrene 2867 Flameless Distributed Combustion technology.[12] Tertiary-butyl catechol is added occasionally during storage to maintain the concentration in the desired range. The utilities cost includes fuel.8 (15. and chemical costs required to Table 2 Styrene economics for conventional EB dehydrogenation process UNIT Produce Styrene Raw materials Ethylene Benzene By-product credits Toluene Light ends Net feedstock costs Utilities Fixed cost Total cost of production Basis: North America. The second step is oxidative dehydrogenation of the 4-vinylcyclohexene to produce styrene.0401 Price $/UNIT 751 629 453 378 289 Cost $/MT 751. maintaining the styrene at the lowest practical temperature is critical to preserving product quality.2912 0.0 35 644. cooling water. 2003 Quantity UNIT/MT 1. hence it does not obtain the benefit of a favorable shift in equilibrium. utilities. One area that has been examined involves a two-step process to convert butadiene to styrene. which allows for storage times of around 10 weeks. Although both vapor-phase and liquid-phase processes have been studied. Even a 5 C increase in the storage temperature to 25 C can reduce the storage time to less than 4 weeks. The industry standard styrene storage inhibitor is TBC and is typically used at concentrations between 10 ppm and 15 ppm.6) 514. Other Processes Propylene oxide/styrene process Aside from EB dehydrogenation. styrene polymerization is prevented by maintaining low temperature and using an appropriate polymerization inhibitor.0000 0. it appears that liquid-phase reactions are preferred because they achieve higher butadiene conversion levels.2 95. Special handling and storage procedures are required to maintain the styrene product quality and to avoid a potentially dangerous situation involving uncontrolled polymerization. The reaction is exothermic and can be catalyzed by either a copper-containing zeolite catalyst or an iron dinitrosyl chloride catalyst complex.0 183. This technology was developed as an alternative to the chlorohydrin method for producing propylene oxide. the only other commercial-scale production of styrene is through a propylene oxide=styrene process that produces roughly 15% of worldwide styrene.7898 0. unlike the Lummus=UOP Smart SM technology. Styrene storage facilities are generally maintained at temperatures below about 20 C. TBC requires dissolved oxygen to be present in concentrations roughly equal to the TBC concentration. During storage. S ECONOMICS The cost of styrene production can be broken down into three main components: raw materials. does not directly combust hydrogen from the reaction mixture.0401 0. To be effective. steam. This situation has motivated a lot of research toward using alternative. Dow has led the research effort in this area and has identified catalyst formulations that provide more than 90% conversion of 4-vinylcyclohexene with approximately 92% selectivity to styrene.1) (11. catalyst.2 MT MT MT MT MT .[11] Storage Preventing polymerization is the key to successful styrene storage. there is little room for significant additional reduction in production costs. and the fixed cost associated with the plant. Styrene from Butadiene Because the conventional EB dehydrogenation technologies are relatively mature. The first step of the process involves the cyclodimerization of butadiene to 4-vinylcyclohexene. lower cost feedstocks for styrene production. electricity. In addition to adding TBC inhibitor. hence.0400 Price $/UNIT 751 629 453 465 43 289 1227 257 Cost $/MT 751.6 10.2 371. which account for approximately 80% of the total cost of production.9 (28. 2003 Quantity UNIT/MT 1. the economics of styrene production are highly dependent on benzene price.8194 0.4500 0.0 197.1000 0.1) (10.0 95 312. The major cost components for styrene production using conventional adiabatic dehydrogenation process are listed in Table 2.0000 0. The benzene cost is the largest cost component.6 65.9) (552. The major cost of production is for the ethylene and benzene raw materials. 7 Distribution of styrene production cost components.3) 152.6 MT MT MT MT MT MT MT MT . operate the plant.3541 0.2529 0. The raw materials cost has two components—one dictated by the stoichiometry and the other caused by Table 3 Styrene economics for propylene oxide-styrene process UNIT Product Styrene Raw materials Ethylene Benzene Propylene Oxygen By-product credits Light ends Propylene oxide Tars Net feedstock costs Utilities Fixed cost Total cost of production Basis: North America.2868 Styrene Fig.3135 0.2 164. Chem Systems.[13] The result of the shift of focus from variable to fixed costs is that plants are being designed for larger capacities. In many cases. 2001. Forni. 3. 179–188. H. If the unalterable stoichiometric raw material consumption is removed from the cost of production. December 9. Kollar. 1995. 2004. The chemical processing technologies that have been developed are sophisticated.nsf=(WebContentByDocID)=0AF6F53F1881D0AA8626CD90082 E36A?OpenDocument. 65–79. while ever-increasing complexity and more stringent regulations have greatly increased the fixed costs. US Patent 4. T. 1991. S REFERENCES 1. 9. styrene.136. CONCLUSIONS Since the first commercial-scale production in the 1930s. June 22– 25. For example in 2003. 2004 World Petrochemical Conference. 281–285. the raw materials’ cost is only about 15% of the incremental cost of production and the utilities and fixed costs become dominant. F.635. Most people come in contact with numerous styrene-based products throughout the course of a normal day. Kinetics of catalytic dehydrogenation of ethylbenzene to styrene. 2001. 12. ABB Lummus Global. 1998. AIChE Spring National Meeting.sterlingchemicals. Catal. March 6. Enhancements in EB=SM technology. Houston: TX.. there is a profound impact on the styrene market supply=demand balance. Dev. 4. 67. Matsui. P. New York. L. is a growing influence on the overall styrene market economics. T. Sodesawa. 11. S. Appl.. T. the total cost of styrene production can be approximately 50% of conventional EB dehydrogenation technology. producing styrene to meet the demand at low cost.. V. When viewed from the perspective that styrene is the primary product and propylene oxide is a by-product. efforts are aimed at further improvements in existing technologies and identification of new technologies for styrene production opportunities. Research and development . Prague. Demand for styrene is expected to continue growing at a rate comparable to the gross domestic product growth rate. Although propylene oxide=styrene plants are built to produce propylene oxide. 2. 26. April 22–26. Chemical Marketing Associates. the only other commercial process for production of styrene. Welch. Czech Republic. 4 (3). Catal. 1965. 7. Dehydrogenation of Dehydrogenatable Hydrocarbons. such as larger plant capacities and globalization of the styrene market. Imai. Advanced styrene dehydrogenation with flameless distributed combustion. Ind Eng Chem Process Des. com=SCI=WEBSITE=scihome. Lidback. 2003. Appl. EB-SM splitter energy recovery options. Other recent trends. New York. The propylene oxide=styrene process. 1986. Hirano. Technical Bulletin on Safe Handling & Storage of Styrene Monomer http:==www.: Houston: TX. The drive to reduce fixed costs has led to numerous revamps of existing plants to substantially increase capacity. Dehydrogenation Process for Production of Styrene from Ethylbenzene Comprising Low Temperature Heat Recovery and Modification of the Ethylbenzene–Styrene Feed therewith. Roles of potassium in potassium-promoted iron oxide catalyst for dehydrogenation of ethylbenzene. AIChE Spring National Meeting. 93S3. 1986. Chem Systems PERP Report. 13. typical new styrene plants in the Asia Pacific Region produced an average of 350 KMTA styrene per year. Epoxidation Process. have also resulted in higher fixed costs. nearly double the capacity of typical plants started up just 5 years earlier. March 23–25. US Patent 3. 7. Styrene—This is Not a Drill. November 7. S. the trend appears to be reversing and propylene oxide=styrene processes are accounting for less of newly installed capacity. J. Mullen. More recently. Styrene Conference. the resultant distribution of cost components appears very different. A. Propylene Oxide 97=98–7. 6. Tarrytown. and UOP LLC. Inc. 2003. In AIChE 2003 Spring Meeting Proceedings. In AIChE 2003 Spring Meeting Proceedings. In Styrene Conference General Session. April 22–26. Nozaki. has become an integral part of life. 1967. Sud-Chemie AG. Houston: TX. Styrene from Butadiene. as shown in Fig.435. Influence of carbon dioxide addition upon decay of activity of a potassium-promoted iron oxide catalyst for dehydrogenation of ethylbenzene. From this perspective. 1984.628. Ram.351. US Patent 4.Styrene 2869 yield losses occurring as a result of the process technology. 5. mainly through its derivatives. 8.607. Carra. Recent catalyst and process design improvements have reduced the variable costs of styrene production. Approximately 33% of the styrene capacity added between 1998 and 2003 was produced using propylene oxide=styrene technology. Sardina. Tarrytown. capacity expansions on the order of 50% are being implemented. the economics of this process appear encouraging (Table 3). J. Depending on the credit value assigned to the propylene oxide coproduct. 10.