Chemical Engineering - Industrial Organic Chemistry

Exercise 4 - Text

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INDUSTRIAL ORGANIC CHEMISTRY – EXERCISE 4 Methanol synthesis: design of recycle Methanol is produced in a multi -stage adiabatic reactor where the following reactions take place: CO + 2H 2 → CH 3OH CO 2 + H 2 → CO + H 2O A make -up flowrate of CO 2 (FM) is added to the fresh feed (F 0), to guarantee the modulus ������ = ������2−������������2 ������������2+������������ = 3 in the stream entering in the reactor (FF) . The effluent stream (FA) is fed to the methanol separator. The gas stream leaving the separator is recycled to the reactor after being purged. The liquid stream (P) is sent to the distillation trains. The separator works with recovery efficiencies ( ������������= ������������/�������������) equal to 0.88, 0.95 and 0.0 095 for methanol, water and carbon dioxide, respectively. Methane, hydrogen, carbon monoxide and nitrogen can be assumed to be present only in the G stream. The CO conversion and the carbon yield to methanol per passage inside the reactor are equal to 0. 42 and to 0.30 , respectively . By defining the recycle fraction as ������= ������/�, evaluate: a) The recycle fraction required to achieve an overall conversion of CO equal to 98% b) The flowrate and the composition of all the stream in the process c) The recycle ratio ( ������ = ������/�) d) The overall methanol conversion , the concentration of the inert in the recycle stream and the rec ycle ratio as a function of ������ e) The temperature of the stream R and FA1 after the first heat exchanger (HE – 1) f) The heat duty to HE – 2 to obtain that stream FF entering in the reactor is at 245 °C DATA : The feed stream F 0 consists of: Species CO CO 2 H2 CH 4 CH 3OH H2O N2 F0 [kmol/h] 148.57 75.42 696.72 24.79 0.00 1.77 3.17 Temperature : Stream/Unit F FM FF FA FA2 Separator T [°C] 550 550 245 264 110 40 Heat capacity: Specie a b c d CO 29.556 -6.5807e -3 2.0130e -5 -1.2227e -8 CO2 27.437 4.2315e -2 -1.9555e -5 3.9968e -9 H2 25.399 2.0178e -2 -3.8549e -5 3.1880e -8 CH4 34.942 -3.9957e -2 1.9184e -4 -1.5303e -7 CH3OH 40.046 -3.8287e -2 -2.4529e -4 -2.1679e -7 H2O 33.933 -8.4186e -3 2.9906e -5 -1.7825e -8 N2 29.342 -3.5395e -3 1.0076e -5 -4.3116e -9 ������������������(������)= �������+ �������⋅������+ �������⋅������2+ �������⋅������3 [J/mol/K ] T [K]