Reference no: EM132555305
Question 1 - PFR energy balance with multiple reactions
Allyl chloride is to be produced in a 25-ft long 2-in ID tube operating as a PFR. The feed is a 4:1 molar ratio of propylene to chlorine and it enters at a feed rate of 0.85 lbmol/hr, 2 atm of pressure, and 392oF. The reactor pressure may be assumed constant.
Cl2 + C3H6 →k_1 C3H5Cl +HCI
Cl2 + C3H6 →k_2 C3H6Cl2
The rate constants have units of lbmol/(hr ft3 atm2) and are
k1 = 2.06 x 105exp (-27200/(RT))
k2 = 11.7 x exp -6860/RT
in which T is in oR and R is in Btu/(lbmoloR). The rate expressions are
r1 = k1PC_3H_6PCl_2
r2 = k2PC_3H_6PCl_2
The thermodynamic data for this reaction are listed in Table 1. The partial molar heat capacities are expressed in units of cal/mol K and can be calculated using
Cpj = Aj + BjT + CjT2 + DjT3
Two modes of operation have been considered for this PFR, adiabatic and constant wall temperature. A constant wall temperature of 392oF can be realized by boiling ethylene glycol on the outer surface of the reactor wall. The inside heat-transfer coefficient is 5 Btu/hr ft2oF for a feed rate of 0.85 lbmol/hr and 2 atm total pressure.
(a) Compute the molar flow rates of Cl2, C3H5Cl and C3H6Cl2, and the reactor temperature as a function of reactor length for adiabatic operation. Plot these dependent variables versus reactor length.
(b) Compute the molar flow rates of Cl2, C3H5Cl and C3H6Cl2, and the reactor temperature as a function of reactor length for constant wall temperature operation. Plot these dependent variables versus reactor length. What do you notice when you compare the extent of product formation and reactor temperature for both cases? Why do you think this happens?
(c) Now compare the exact solutions developed above to the approximate solution where the component heat capacities and the heat of reaction are evaluated at the inlet temperature and assumed constant. Plot the molar flow rates of C3H5Cl and C3H6Cl2 for the exact and approximate solutions on different graphs, one for adiabatic and one for non-adiabatic operation. Prepare similar plots for the temperature. Comment on the errors this approximation introduces.
Question 2 - Ethane cracker
Ethane cracking in presented in terms of a drastically simplified molecular model containing 7 reactions. This reaction scheme and the corresponding kinetic model was derived from the radical scheme developed by Sundaram and Froment [1977]. Table 1 gives the kinetic parameters of these reactions. Table 2 is the matrix of stoichiometric coefficients.
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Attachment:- Assignment file - PFR energy balance.rar