Turton_AppB_Part1.qxd 5/11/12 Appendix B 12:21 AM Page 67 Information for the Preliminary Design of Fifteen Chemical Processes 67 The reaction takes place on an amorphous alumina catalyst treated with 10.2% silica. There are no significant side reactions at less than 400°C. At greater than 250°C the rate equation is given by Bondiera and Naccache [2] as: − rmethanol 5 k0 exp 3 RT 4p − E0 methanol (B.1.2) where k0 = 1.21 3 106 kmol/(m3cat.h.kPa), E0 = 80.48 kJ/mol, and pmethanol = partial pressure of methanol (kPa). Significant catalyst deactivation occurs at temperatures greater than 400°C, and the reactor should be designed so that this temperature is not exceeded anywhere in the reactor. The design given in Figure B.1.1 uses a single packed bed of catalyst, which operates adiabatically. The temperature exotherm occurring in the reactor of 118°C is probably on the high side and gives an exit temperature of 368°C. However, the single-pass conversion is quite high (80%), and the low reactant concentration at the exit of the reactor tends to limit the possibility of a runaway. In practice the catalyst bed might be split into two sections, with an intercooler between the two beds. This has an overall effect of increasing the volume (and cost) of the reactor and should be investigated if catalyst damage is expected at temperatures lower than 400°C. In-reactor cooling (shell-and-tube design) and cold quenching by splitting the feed and feeding at different points in the reactor could also be investigated as viable alternative reactor configurations. B.1.3 Simulation (CHEMCAD) Hints The DME-water binary system exhibits two liquid phases when the DME concentration is in the 34% to 93% range [2]. However, upon addition of 7% or more alcohol, the mixture becomes completely miscible over the complete range of DME concentration. In order to ensure that this nonideal behavior is simulated correctly, it is recommended that binary vapor-liquid equilibrium (VLE) data for the three pairs of components be used in order to regress binary interaction parameters (BIPs) for a UNIQUAC/UNIFAC thermodynamics model. If VLE data for the binary pairs are not used, then UNIFAC can be used to estimate BIPs, but these should be used only as preliminary estimates. As with all nonideal systems, there is no substitute for designing separation equipment using data regressed from actual (experimental) VLE. B.1.4 References 1. 2. B.2 “DuPont Talks about Its DME Propellant,” Aerosol Age, May and June 1982. Bondiera, J., and C. Naccache, “Kinetics of Methanol Dehydration in Dealuminated H-Mordenite: Model with Acid and Basic Active Centres,” Applied Catalysis 69 (1991): 139–148. ETHYLBENZENE PRODUCTION, UNIT 300 The majority of ethylbenzene (EB) processes produce EB for internal consumption within a coupled process that produces styrene monomer. The facility described here produces 80,000 tonne/y of 99.8 mol% ethylbenzene that is totally consumed by an on-site styrene Turton_AppB_Part1.qxd 68 5/11/12 12:21 AM Page 68 Appendix B Information for the Preliminary Design of Fifteen Chemical Processes facility. As with most EB/styrene facilities, there is significant heat integration between the two plants. In order to decouple the operation of the two plants, the energy integration is achieved by the generation and consumption of steam within the two processes. The EB reaction is exothermic, so steam is produced, and the styrene reaction is endothermic, so energy is transferred in the form of steam. B.2.1 Process Description [1, 2] The PFD for the EB process is shown in Figure B.2.1. A refinery cut of benzene is fed from storage to an on-site process vessel (V-301), where it is mixed with the recycled benzene. From V-301, it is pumped to a reaction pressure of approximately 2000 kPa (20 atm) and sent to a fired heater (H-301) to bring it to reaction temperature (approximately 400°C). The preheated benzene is mixed with feed ethylene just prior to entering the first stage of a reactor system consisting of three adiabatic packed-bed reactors (R-301 to R-303), with interstage feed addition and cooling. Reaction occurs in the gas phase and is exothermic. The hot, partially converted reactor effluent leaves the first packed bed, is mixed with more feed ethylene, and is fed to E-301, where the stream is cooled to 380°C prior to passing to the second reactor (R-302), where further reaction takes place. High-pressure steam is produced in E-301, and this steam is subsequently used in the styrene unit. The effluent stream from R-302 is similarly mixed with feed ethylene and is cooled in E-302 (with generation of high-pressure steam) prior to entering the third and final packed-bed reactor, R-303. The effluent stream leaving the reactor contains products, by-products, unreacted benzene, and small amounts of unreacted ethylene and other noncondensable gases. The reactor effluent is cooled in two waste-heat boilers (E-303 and E-304), in which highpressure and low-pressure steam, respectively, is generated. This steam is also consumed in the styrene unit. The two-phase mixture leaving E-304 is sent to a trim cooler (E-305), where the stream is cooled to 80°C, and then to a two-phase separator (V-302), where the light gases are separated and, because of the high ethylene conversion, are sent overhead as fuel gas to be consumed in the fired heater. The condensed liquid is then sent to the benzene tower, T-301, where the unreacted benzene is separated as the overhead product and returned to the front end of the process. The bottoms product from the first column is sent to T-302, where product EB (at 99.8 mol% and containing less than 2 ppm diethylbenzene [DEB]) is taken as the top product and is sent directly to the styrene unit. The bottoms product from T-302 contains all the DEB and trace amounts of higher ethylbenzenes. This stream is mixed with recycle benzene and passes through the fired heater (H-301) prior to being sent to a fourth packed-bed reactor (R-304), in which the excess benzene is reacted with the DEB to produce EB and unreacted benzene. The effluent from this reactor is mixed with the liquid stream entering the waste-heat boiler (E-303). Stream summary tables, utility summary tables, and major equipment specifications are shown in Tables B.2.1–B.2.3. B.2.2 Reaction Kinetics The production of EB takes place via the direct addition reaction between ethylene and benzene: C6H6 + C2H4 → C6H5C2H5 benzene ethylene ethylbenzene (B.2.1) Turton_AppB_Part1.qxd 5/11/12 Appendix B 12:21 AM Page 69 69 Information for the Preliminary Design of Fifteen Chemical Processes The reaction between EB and ethylene to produce DEB also takes place: C6H5C2H5 + C2H4 → C6H4(C2H5)2 ethylbenzene ethylene (B.2.2) diethylbenzene Additional reactions between DEB and ethylene yielding triethylbenzene (and higher) are also possible. However, in order to minimize these additional reactions, the molar ratio of benzene to ethylene is kept high, at approximately 8:1. The production of DEB is undesirable, and its value as a side product is low. In addition, even small amounts of DEB in EB cause significant processing problems in the downstream styrene process. Therefore, the maximum amount of DEB in EB is specified as 2 ppm. In order to maximize the production of the desired EB, the DEB is separated and returned to a separate reactor in which excess benzene is added to produce EB via the following equilibrium reaction: C6H4(C2H5)2 + C6H6 A 2C6H5C2H5 diethylbenzene benzene (B.2.3) ethylbenzene The incoming benzene contains a small amount of toluene impurity. The toluene reacts with ethylene to form ethyl benzene and propylene: C6H5CH3 + 2C2H4 → C6H5C2H5 + C3H6 toluene ethylbenzene (B.2.4) propylene The reaction kinetics derived for a new catalyst are given as a b c e –ri = ko,i e–Ei/RTCethylene CEB Ctoluene C dbenzeneCDEB (B.2.5) where i is the reaction number above (B.2.i), and the following relationships pertain: i 1 2 3 4 Ei kcal/kmol 22,500 22,500 25,000 20,000 ko,i a b c d e 1.00 × 106 6.00 × 105 7.80 × 106 3.80 × 108 1 1 0 2 0 1 0 0 0 0 0 1 1 0 1 0 0 0 1 0 The units of ri are kmol/s/m3-reactor, the units of Ci are kmol/m3-gas, and the units of ko,i vary depending upon the form of the equation. 70 kPa °C Ethylene 2 FIC 22 FIC P-301 A/B 3 V-301 23 H-301 P-305 A/B H-301 2000 4 500 R-301 6 400 R-304 Transalkylation Reactor bfw R-304 10 bfw 13 E-302 hps 110 170 bfw lps 280 bfw hps cw 80 E-306 Benzene Reboiler V-302 E-303 E-304 E-305 17 V-302 T-301 L/V Benzene Separator To wer R-303 14 12 380 E-305 Reactor Effluent Cooler 11 R-302 9 E-301 hps 8 380 E-304 LP Steam Boiler 16 2000 E-306 lps 15 V-303 Benzene Reflux Drum T- 301 E-307 Benzene Condenser LIC E-308 LIC V-304 20 LIC E-309 P-303 A/B FIC cw P-305 A/B Benzene Recycle Pumps P-303 A/B EB Reflux Pumps 19 Ethylbenzene Fuel Gas P-304 A/B DEB Recycle Pumps E-308 E-309 V-304 EB EB EB Reboiler Condenser Reflux Drum P-304 A/B hps T- 302 18 LIC E-307 V-303 cw T-302 EB To wer P-302 A/B FIC 110 P-302 A/B Benzene Reflux Pumps Figure B.2.1 Unit 300: Ethylbenzene Process Flow Diagram 5 7 E-303 HP Steam Boiler 12:21 AM LIC 1 21 H-301 R-301/2/3 E-301/2 Feed Ethylbenzene Reactor Heater Reactors Intercoolers 5/11/12 Benzene P-301 A/B Benzene Feed Pumps V-301 Benzene Feed Drum Turton_AppB_Part1.qxd Page 70 Turton_AppB_Part1.qxd 5/11/12 Appendix B 12:21 AM Page 71 71 Information for the Preliminary Design of Fifteen Chemical Processes Table B.2.1 Stream Table for Unit 300 Stream Number 1 2 3 Temperature (°C) 25.0 25.0 110.0 0.0 Pressure (kPa) Vapor mole fraction Total kg/h Total kmol/h 4 5 6 58.5 25.0 25.0 383.3 2000.0 110.0 2000.0 2000.0 1985.0 1.0 0.0 1.0 1.0 1.0 7761.3 2819.5 17,952.2 845.9 986.8 18,797.9 99.0 100.0 229.2 30.0 35.0 259.2 27.90 32.55 Component Flowrates (kmol/h) Ethylene 0.00 Ethane 0.00 7.00 0.00 2.10 2.45 2.10 Propylene 0.00 0.00 0.00 0.00 0.00 0.00 Benzene 97.00 0.00 226.51 0.00 0.00 226.51 Toluene 2.00 0.00 2.00 0.00 0.00 2.00 Ethylbenzene 0.00 0.00 0.70 0.00 0.00 0.70 1,4-Diethylbenzene 0.00 0.00 0.00 0.00 0.00 0.00 Stream Number Temperature (°C) Pressure (kPa) Vapor mole fraction Total kg/h Total kmol/h 7 93.00 8 0.00 9 10 11 27.90 12 444.1 380.0 453.4 25.0 380.0 449.2 1970.0 1960.0 1945.0 2000.0 1935.0 1920.0 1.0 1.0 1.0 1.0 1.0 1.0 18,797.9 19,784.7 19,784.7 986.8 20,771.5 20,771.5 234.0 269.0 236.4 35.0 271.4 238.7 Component Flowrates (kmol/h) Ethylene 0.85 33.40 0.62 32.55 33.17 0.54 Ethane 2.10 4.55 4.55 2.45 7.00 7.00 Propylene 1.83 1.81 2.00 0.00 2.00 2.00 Benzene 203.91 203.91 174.96 0.00 174.96 148.34 Toluene 0.19 0.19 24.28 24.28 49.95 0.00 49.95 70.57 0.87 0.87 4.29 0.00 4.29 10.30 Ethylbenzene 1,4-Diethylbenzene 0.0026 0.00 0.0026 0.00 (continued) Turton_AppB_Part1.qxd 5/11/12 12:21 AM 72 Page 72 Appendix B Information for the Preliminary Design of Fifteen Chemical Processes Table B.2.1 Stream Table for Unit 300 (Continued) Stream Number 13 Temperature (°C) Pressure (kPa) 15 16 17 18 497.9 458.1 73.6 73.6 81.4 145.4 1988.0 1920.0 110.0 110.0 105.0 120.0 1.0 1.0 1.0 0.0 0.0 0.0 4616.5 25,387.9 1042.0 24,345.9 13,321.5 11,024.5 51.3 290.0 18.6 271.4 170.2 101.1 Vapor mole fraction Total kg/h 14 Total kmol/h Component Flowrates (kmol/h) Ethylene 0.00 0.54 0.54 0.00 0.00 Ethane 0.00 7.00 7.00 0.00 0.00 0.00 Propylene 0.00 2.00 2.00 0.00 0.00 0.00 Benzene 29.50 177.85 8.38 169.46 169.23 0.17 Toluene 0.00 0.00 0.00 0.00 0.00 0.00 21.69 92.25 0.71 91.54 0.92 90.63 10.37 0.013 10.35 0.00 10.35 Ethylbenzene 1,4-Diethylbenzene 0.071 Stream Number 19 20 21 22 Temperature (°C) 139.0 191.1 82.6 82.6 121.4 Pressure (kPa) 110.0 140.0 2000.0 2000.0 2000.0 0.0 0.0 0.0 0.0 0.0 1485.9 10,190.9 3130.6 4616.5 40.0 51.3 Vapor mole fraction Total kg/h 9538.6 Total kmol/h 89.9 11.3 130.2 0.00 23 Component Flowrates (kmol/h) Ethylene 0.00 Ethane 0.00 0.00 0.00 0.00 0.00 Propylene 0.00 0.00 0.00 0.00 0.00 Benzene 0.17 0.00 129.51 39.78 39.78 Toluene Ethylbenzene 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 89.72 0.91 0.70 0.22 1.12 10.35 0.00 0.00 10.35 1,4-Diethylbenzene 0.0001 Table B.2.2 Utility Summary Table for Unit 300 Stream Name Flowrate (kg/h) Stream Name Flowrate (kg/h) * bfw to E-301 bfw to E-302 bfw to E-303 bfw to E-304 cw to E-305 851 1121 4341 5424 118,300 lps to E-306 cw to tE-307 hps to E-308* cw to E-309 3124 125,900 4362 174,100 Throttled and desuperheated at exchanger Turton_AppB_Part1.qxd 5/11/12 Appendix B 12:21 AM Page 73 73 Information for the Preliminary Design of Fifteen Chemical Processes Table B.2.3 Major Equipment Summary for Unit 300 Heat Exchangers E-301 A = 62.6 m2 1-2 exchanger, floating head, stainless steel Process stream in tubes Q = 1967 MJ/h Maximum pressure rating of 2200 kPa E-306 A = 57.8 m2 1-2 exchanger, fixed head, carbon steel Process stream in shell Q = 9109 MJ/h Maximum pressure rating of 200 kPa E-302 A = 80.1 m2 1-2 exchanger, floating head, stainless steel Process stream in tubes Q = 2592 MJ/h Maximum pressure rating of 2200 kPa E-307 A = 54.6 m2 1-2 exchanger, floating head, carbon steel Process stream in shell Q = 7276 MJ/h Maximum pressure rating of 200 kPa E-303 A = 546 m2 1-2 exchanger, floating head, stainless steel Process stream in tubes Q = 10,080 MJ/h Maximum pressure rating of 2200 kPa E-308 A = 22.6 m2 1-2 exchanger, fixed head, carbon steel Process stream in shell Q = 5281 MJ/h Maximum pressure rating of 200 kPa E-304 A = 1567 m2 1-2 exchanger, fixed head, carbon steel Process stream in tubes Q = 12,367 MJ/h Maximum pressure rating of 2200 kPa E-309 A = 17.5 m2 1-2 exchanger, floating head, carbon steel Process stream in shell Q = 5262 MJ/h Maximum pressure rating of 200 kPa E-305 A = 348 m2 1-2 exchanger, floating head, carbon steel Process stream in shell Q = 4943 MJ/h Maximum pressure rating of 2200 kPa Fired Heater H-301 Required heat load = 22,376 MJ/h Design (maximum) heat load = 35,000 MJ/h Tubes = Stainless steel 75% thermal efficiency Maximum pressure rating of 2200 kPa (continued) Turton_AppB_Part1.qxd 5/11/12 74 12:21 AM Page 74 Appendix B Table B.2.3 Information for the Preliminary Design of Fifteen Chemical Processes Major Equipment Summary for Unit 300 (Continued) Pumps P-301 A/B Positive displacement/electric drive Carbon steel Actual power = 15 kW Efficiency 75% P-304 A/B Centrifugal/electric drive Carbon steel Actual power = 1.4 kW Efficiency 80% P-302 A/B Centrifugal/electric drive Carbon steel Actual power = 1 kW Efficiency 75% P-305 A/B Positive displacement/electric drive Carbon steel Actual power = 2.7 kW Efficiency 75% P-303 A/B Centrifugal/electric drive Carbon steel Actual power = 1 kW Efficiency 75% Reactors R-301 316 stainless steel packed bed, ZSM-5 molecular sieve catalyst V = 20 m3 11 m long, 1.72 m diameter Maximum pressure rating of 2200 kPa Maximum allowable catalyst temperature = 500°C R-303 316 stainless steel packed bed, ZSM-5 molecular sieve catalyst V = 30 m3 12 m long, 1.97 m diameter Maximum pressure rating of 2200 kPa Maximum allowable catalyst temperature = 500°C R-302 316 stainless steel packed bed, ZSM-5 molecular sieve catalyst V = 25 m3 12 m long, 1.85 m diameter Maximum pressure rating of 2200 kPa Maximum allowable catalyst temperature = 500°C R-304 316 stainless steel packed bed, ZSM-5 molecular sieve catalyst V = 1.67 m3 5 m long, 0.95 m diameter Maximum pressure rating of 2200 kPa Maximum allowable catalyst temperature 5 525°C Towers T-301 Carbon steel 45 SS sieve trays plus reboiler and total condenser 42% efficient trays Feed on tray 19 Additional feed ports on trays 14 and 24 Reflux ratio = 0.3874 24-in tray spacing Column height = 27.45 m Diameter = 1.7 m Maximum pressure rating of 300 kPa T-302 Carbon steel 76 SS sieve trays plus reboiler and total condenser 45% efficient trays Feed on tray 56 Additional feed ports on trays 50 and 62 Reflux ratio = 0.6608 15-in tray spacing Column height = 28.96 m Diameter = 1.5 m Maximum pressure rating of 300 kPa Turton_AppB_Part1.qxd 5/11/12 Appendix B 12:21 AM Page 75 Information for the Preliminary Design of Fifteen Chemical Processes Table B.2.3 75 Major Equipment Summary for Unit 300 (Continued) Vessels V-301 Carbon steel Horizontal L/D = 5 V = 7 m3 Maximum operating pressure = 250 kPa V-303 Carbon steel Horizontal L/D = 3 V = 7.7 m3 Maximum operating pressure = 300 kPa V-302 Carbon steel with SS demister Vertical L/D = 3 V = 10 m3 Maximum operating pressure = 250 kPa V-304 Carbon steel Horizontal L/D = 3 V = 6.2 m3 Maximum operating pressure = 300 kPa B.2.3 Simulation (CHEMCAD) Hints A CHEMCAD simulation is the basis for the design. The thermodynamics models used were K-val = UNIFAC and Enthalpy = Latent Heat. It should be noted that in the simulation a component separator was placed after the high-pressure flash drum (V-302) in order to remove noncondensables from Stream 16 prior to entering T-301. This is done in order to avoid problems in simulating this tower. In practice, the noncondensables would be removed from the overhead reflux drum, V-303, after entering T-301. As a first approach, both towers were simulated as Shortcut columns in the main simulation, but subsequently each was simulated separately using the rigorous TOWER module. Once the rigorous TOWER simulations were completed, they were substituted back into the main flowsheet and the simulation was run again to converge. A similar approach is recommended. The rigorous TOWER module provides accurate design and simulation data and should be used to assess column operation, but using the shortcut simulations in the initial trials speeds up overall conversion of the flowsheet. B.2.4 References 1. 2. B.3 William J. Cannella, “Xylenes and Ethylbenzene,” Kirk-Othmer Encyclopedia of Chemical Technology, online version (New York: John Wiley and Sons, 2006). “Ethylbenzene,” Encyclopedia of Chemical Processing and Design, Vol. 20, ed. J. J. McKetta (New York: Marcel Dekker, 1984), 77–88. STYRENE PRODUCTION, UNIT 400 Styrene is the monomer used to make polystyrene, which has a multitude of uses, the most common of which are in packaging and insulated Styrofoam beverage cups. Styrene is produced by the dehydrogenation of ethylbenzene. Ethylbenzene is formed by reacting ethylene and benzene. There is very little ethylbenzene sold commercially, because most ethylbenzene manufacturers convert it directly into styrene.