Question

6) Mass balance and reactor design You have been hired as a high priced consultant to assess the performance of a reactor designed to treat a toxic chemical C to a "safe" level. You are given the following information: Q = 300 m²/d V = 2000 m Influent concentration (Ci) = 500 mg/L Required removal rate = 95% Degradation occurs according to the reaction rate equation r= -dC/dt = kС, where k= 3/d a. What order is this reaction? (2 points) b. What is the predicted effluent C? Is the required removal rate met? (8 points) To get full credit, you must write the mass balance equation (A = 1 - 0 + R) for this system.

Answer 1

a. The order of above reaction is First order.

as r= dc/dt = kC

That means dC/dt $\alpha$ C

Ie rate of reaction proportional to first power of concentration.

b) Writing mass balance reaction;

A = I - O + R

V dC/dt = Q Co - Q Ce + VdC/dt (reaction)

For steady state condition;

0 = 300 * 500 - 300 Ce + 2000 * - K Ce

0 = 300*500- 300Ce + 2000* ( -3Ce)

Ce = 23.81 mg/L ( predicted effluent)

Required removal rate is 95 %

Required effluent concentration = 500*(100-95) /100 = 25 mg/L

Predicted effluent concentration is less than required removal rate and hence reactor design is fine