Chemical Engineering - Industrial Organic Chemistry

Exercise 7 - Text

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-INDUSTRIAL ORGANIC CHEMISTRY – EXERCISE 7 Proof test Methanol is produced according to the layout reported on the left. The fresh feed (1) is split into two stream (2) and (7). Stream (2) is fed to the first reactor (R -1). The stream leaving the reactor (3) is sent to the methanol separator (F -1). The gas stream leaving the separator (4) is then mixed with stream (7) and fed to the second reactor (R -2). By assuming: • Both the methanol synthesis reaction and the WGS reaction occur in reactors R -1 and R -2 • The volumetric behavior of the gas mixture in the react ors R -1 e R -2 is of ideal mixture of real gas. In this view, a value of ������������������������������� = ������������������������������ ������������22 ������������������ = 0.9 e �������������������� = ������������������2������������2 ������������2������������������������ = 1.05 can be assumed for the evaluation of the ������������ for the methanol synthesis and for the WGS. • The pressure in each unit is equal to 100 bar and pressure drops are negligible • Reactor R -1 achieve s thermodynamic equilibrium • The 90% of the CO reacted in reactor R -1 produces methanol • In the separator, thermodynamic equilibrium is achieved • In the separator, the gas mixture is ideal and consists of ideal gas. The liquid mixture is ideal and the Poynting correction is negligible. As a first approximation, the Henry’s constant can be considered constant with temperature. The enthalpy of the gas species dissolve d in the liquid can be assumed as negligible • The separator is designed to recover in the liquid stream (6) the 60% of the methanol contained in stream (3) • The reactor R -2 is adiabatic • The conversion of CO in the second reactor is equal to 4 8 %, whereas the overall yield of methanol with respect to CO 2 is 70 % It is required to evaluate: 1. The temperature and the composition (molar fractions) of the stream leaving reactor R -1 2. The heat removed per mole of stream (2) in the reactor R -1 and the sta te of the feed sent to the separator 3. The extent of vaporization and the separator (F -1) temperature 4. The molar composition of the liquid and vapor stream leaving the flash 5. The composition (molar fractions) of the stream (5) leaving reactor R -2 and the rat io between stream (7) and stream (2) 6. The heat removed in the flash per unit of feed (2) and the overall conversion of CO in the plant Data : Molar fractions and temperature: CH4 H2 CO CO 2 H2O T [K] Stream (1) 0.11 0.62 0.12 0.10 0.05 453 Thermodynamic data (reference state: ideal gas at 1 bar) 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 Henry’s Law : CO CO2 H2 CH4 H(bar) 2500 164 6200 1130