The following reactions were found to occur while trying to make a desired produ

Question

The following reactions were found to occur while trying to make a desired product B A rightarrow B r_1 = k_1 C_A^2 k_1 = .05 exp(- 10000/T) A rightarrow X r_2 = k_2 C_A k_2 = 50 exp (- 20000/T) A + X rightarrow Y r_3 = k_3C_AC_X ki_3 = 100 exp (-5000/T) In the expressions above, T is in K, k_1 and k_3 are given in L mol^-1s^-1, and fa is given in s^-1. Species X and Y are both undesirable pollutants. a) Write down an expression for the instantaneous selectivity of B with respect to the two foul pollutants X and Y? Simplify the expression to contain only C_A and T as variables. b) How would you carry out this reaction to maximize the formation of B? Specify the type of reactor and indicate if the operating temperature should be low or high, kept constant or if it should follow a given profile (increasing/decreasing). [Only a qualitative reasoning is required]

Explanation / Answer

rB =-rA1

rx = -rA2 +rA3

ry = -rA3

Selectivity of B with respect to x and y

SBXY = rB rx +ry = -rA1 -rA2 = k1A k2A CA = 0.01 exp[10,000 /T] CA

b) In order to maximize the formation of B, SBXY should be maximized.

- High CA , use PFR

- Low Temperature

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