Chemical Engineering - Industrial Organic Chemistry

Exercise 8 - Text

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aINDUSTRIAL ORGANIC CHEMISTRY – EXERCISE 8 Proof test The production of styrene (St) is carried out by catalytic dehydrogenation of ethylbenzene (EB). A fresh feed (1) consisting of ethylbenzene, benzene (B) and toluene (Tol) is fed to an isothermal flash operating at 3 bar. The liquid stream (2) leaving t he flash is then vaporized in HE -1 and mixed with water steam (5). The resulting stream (6) is fed to the first adiabatic reactor (R -1) where the synthesis of styrene is carried out. The stream leaving the first reactor is heat up in a furnace and fed to t he second reactor (R -2) to increase the ethylbenzene conversion. Hypothesis: • The gas mixture is ideal and consists of ideal gas. The liquid mixture is ideal and the Poynting correction is negligible • The flash (F -1) is designed to recover in the outlet liqu id stream (2) the 85% of ethylbenzene contained in stream (1) • The pressure in each unit is equal to 3 bar and pressure drops are negligible • Both reactors are adiabatic • Benzene and toluene can be considered inert in both reactors • The water steam (5) is preheated to 950 K • The stream (4) leaving HE -1 reaches a temperature of 650 K • The ratio between the molar flowrate of ethylbenzene and water steam fed to R -1 (stream (6)) is 1:10 • The reactor R -1 and R -2 operate under thermodynamic e quilibrium • The overall conversion of ethylbenzene in reactor R -1 and R -2 is 40 % It is required to evaluate: 1. The dew point and bubble point of the inlet stream mixture at the flash operating pressure 2. The flash temperature and the extent of vaporization (������) 3. The molar flowrate of the liquid (2) and vapor (3) streams leaving the flash 4. The molar composition of the liquid stream (2) and vapor (3) leaving the flash 5. The heat supplied to the heat exchanger HE -1 normalized with respect to the flow rate of stream (2) 6. The temperature and molar composition of the stream (7) leaving the first reactor (R -1) 7. The outlet temperature from the second reactor (R -2), the extent of the reaction ( λ2) in R -2 and the heat provided to the second heat exchanger (HE -2) both normal ized with respect to the flow rate of stream (2) Data : Molar fractions : Et B Tol H2O Stream (1) 0.6 0.3 0.1 0 Stream (5) 0 0 0 1 Thermodynamic data (reference state: ideal gas at 1 bar ) Styrene synthesis: ∆������������0(������)=127619 .9−������52134 .02 ⋅������ [J/mol] where T in [K] H0F(298K) [kJ/mol] ������������� [J/mol/k] ���������������� @��������������� ,� [cal/mol] Cp coefficients gas phase a b c d �������,������������(������)=�������+�������⋅������+�������⋅������2+�������⋅������3 [J/mol/K] – gas phase H2 0 - - 27.0 0.009 -1.37e -5 7.61e -9 Et 29.8 184 8580 -20.5 0.600 -3.08e -4 3.52e -8 B 82.9 172 7344 -31.3 0.470 -3.11e -4 8.52e -8 Tol 12.4 157 8025 -24.1 0.520 2.94e -4 6.12e -8 St 147.5 187 10253 71.2 0.050 6.48e -4 -6.99e -7 H2O -242 79 8395 32. 1 0.00 2 1.05 e-5 -3.58 e-9 Antoine equation : A B C log 10������0(������)=�− � �+������ ������ [������] - ������0(������) [bar] Et 4.40536 1695.026 -23.698 B 4.60362 1701.073 20.806 T 4.54436 1738.123 0.394