Chemical Engineering - Industrial Organic Chemistry

Exercise 3 - Text

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INDUSTRIAL ORGANIC CHEMISTRY – EXERCISE 3 Methanol synthesis: design of the methanol separation units The effluent stream from the reactor (F) is sequentially treated to separate th e methanol from the unreacted species . The system consists of two sequential flash units. The first operates at the same pressure of the reactor ( 65 bar ) and at 40 °C . The gas stream (V1) is recycled to the reactor while the liquid stream (L1) is laminated and sent to a second flash drum. The second flash operate s at much lower pressure (5 bar ) and at 40°C . The gas stream leaving is sent to the fuel gas line while the liquid stream goes to the distillation trains . Both flash units are isothermal. It is required to evaluate: 1. The dew temperature of the F stream by considering the following hypothesis on the volumetric behavior of the gas and mixtures: a. Ideal gas and ideal mixture b. Real gas and real mixture 2. Evaluate the extent of vaporization of the first flash by assuming as volumetric behavior real gas and real mixture 3. Evaluate the flow rates and the composition of the streams (L1, V1) leaving Flash 1 4. By assuming as volumetric behavior of the flash ideal gas and ideal mixture , evaluate the extent of vaporization of Flash 2. 5. Evaluate the composition of the streams L2 and V2 6. Evaluate the recover y efficiency of methanol end the effect of different flash temperature on this parameter in the range 20 °C < Tf < 40°C 7. Evaluate the duty to the Flash 2 by neglecting the contribution of the gas dissolved in the liquid streams for the case of Tf = 40°C Operating conditions: Absolute pressure Flash 1 : 65 bar Absolute pressure Flash 2: 5 bar Flash temperature : 40 °C Total inlet flow rate: 5330 kmol/h Composition (mol/mol): CO 0.036 CO 2 0.088 H2 0.51 H2O 0.023 CH 3OH 0.049 N2 0.038 CH 4 0.256 Thermodynamic properties: Henry constant H: CO CO2 H2 CH4 N2 H(bar) @ Tf 2500 16 4 6200 1130 3660 Antoine equation : A B C log 10 ������0(�)= � − � � + � � [������] - ������0(�) [bar] CH 3OH 5.2041 1581.34 -33.50 H2O 6.2096 2354.731 7.559 Enthalpy of formation and specific heats: �������������������[J/mol /K] �������������������[J/mol /K] Δℎ�������������� @ ���������� ,� [kJ/mol ] CO - 29.08 - CO 2 - 38.40 - H2 - 28.76 - H2O 75.55 34.58 39.50 CH 3OH 79.93 47.61 35.14 N2 - 29.07 - CH 4 - 36.33 - The enthalpies of vaporization are given at the normal boiling temperature of the species. Equation of state (RKS) : �3− �2+ (�− �− �2)⋅�− �⋅� = 0 Parameters : �= 0.42748 ⋅������⋅(�������������� ⋅�������) ������������ 2 �= 0.08664 ⋅�������������� ⋅������� ������������ ������= (1+ �⋅(1− √�������))2 �= 0.48 + 1.574 ⋅������ − 0.176 ⋅������2 � = �⋅������ (�������������� ⋅�)2 � = �⋅������ �������������� ⋅� Parameters and mixing rules: �������= �������⋅������ (�������������� ⋅�)2 �������= �������⋅������ �������������� ⋅� �������������� = (∑ ������������⋅√������� ������������ ������ ) 2 �������������� = ∑ ������������⋅������� ������������ ������ �������������� = �������������� ⋅������ (�������������� ⋅�)2 �������������� = �������������� ⋅������ �������������� ⋅� Fugacity coefficients of specie i in mixture with composition xi ln ������̂(�,������,������������)= ������� �������������� ⋅(�− 1)+ �������������� �������������� ⋅( ������� �������������� − 2⋅√ ������� �������������� )⋅������������ (�+ �������������� � )− ������������(�− �������������� )