Chemical Engineering - Industrial Organic Chemistry

Exercise 5 - Text

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INDUSTRIAL ORGANIC CHEMISTRY – EXERCISE 5 Methanol synthesis: simplified ICI layout A simplified layout of an ICI process for the methanol production consists of two adiabatic reactors in series with intermediate quench. The fresh feed (1) is split in two streams: the first (2) is sent to the first adiabatic reactor (R -1) where the conve rsion of CO and H 2 to CH 3OH occurs. The stream (4) leaving the reactor is mixed with the remaining feed (3) and with a make -up stream (9) consisting of pure CO 2 (at 453 K) to obtain a temperature of stream (5) equal to 520 K and sent to the second reactor (R -2). The stream (6) leaving the reactor is isoenthalpically laminated and sent to an isothermal methanol condenser (F -1). By assuming: • The gas mixture is ide al and consists of real gas . As a first approximation, a ������������������������������� = ������������������������������ ������������22 ������������������ = 0.7 and �������������������� = ������������������2������������2 ������������2������������������������ = 1.2 can be assumed for the evaluation of the ������������ of the methanol synthesis and of the WGS, respectively . The liquid m ixture is ideal and the Poynting correction is negligible • The pressure in each reactor is equal to 70 bar and pressure drops are negligible , while the separator works at 10 bar. • The reactor R -1 is designed to work with a conversion of CO equal to the 90% of the equilibrium one at the adiabatic temperature . • The molar fraction of CO 2 in stream (5) is equal to 0.1 5 • The reactor R -2 is designed to achieve thermodynamic equilibrium at the temperature of 570 K. • The methanol condenser (F -1) is designed to obtain a recovery efficiency of methanol equal to 70 % in stream (8) • As a first approximation, supercritical components can be assumed as not dissolved in the liquid. It is required to evaluate: 1. The temperature and the composition (molar fractions) of the stream leaving reactor R -1 2. The ratio between the streams (2) and (3) and the ratio between the molar flowrate of CO 2 and stream (2). 3. The composition (molar fractions) of the stream (6) leaving reactor R -2, the heat exchanged in the reactor and the overall conversion of CO 4. The extent of vaporization , the flash temperature and t he molar composition of the liquid and vapor stream leaving the flash 5. The state of the feed to the flash (6) before the lamination valve and the heat removed per mole of stream (6) in the methanol condenser (F -1) Data : Molar fractions and temperature: CH4 H2 CO CO 2 T [K] Stream (1) 0.05 0.75 0.20 0 453 Stream (9) 0 0 0 1 453 Thermodynamic data (reference state: ideal gas at 1 atm) Methanol synthesis : ∆�������0(������)=−22828 +56 .02 ⋅������ [cal/mol] where T in [K] Water gas shift reaction: ∆�������,��������0 (������)=−8514 +7.71 ⋅������ [cal/mol] where T in [K] H0F(298K) [cal/mol] ������������� [cal /mol/k] ���������������� @��������������� ,� [cal/mol] Cp coefficients gas phase a b x 10 3 c x 10 6 d x 10 9 �������,������������(������)=�������+�������⋅������+�������⋅������2+�������⋅������3 [cal/mol/K] – gas phase H2 0 6.483 2.215 -3.298 1.826 CO -26420 7.373 -3.070 6.662 -3.037 CO 2 -94050 4.728 17.54 -13.38 4.097 CH 4 -17890 4.598 12.450 2.860 -2.709 H2O -57800 19.09 8395 7.701 0.4595 2.521 -0.859 CH 3OH -48080 18.05 9436 5.062 16.94 6.179 -6.811 Antoine equation : A B C log 10������0(������)=�− � �+������ ������ [������] - ������0(������) [bar] H2O 6.2096 2354.731 7.559 CH 3OH 5.2041 1581.34 -33.50