Problem 2.5.6

Monochlorobenzene (MCB) is burned with 10 percent excess air in an incinerator at 1200 degrees centigrade. If MCB feed rate is one pound mole per hour, how much chlorine will be present in the flue gas. Equilibrium constant is given as 0.033 for the following reaction:

2 moles of Hydrochloric acid react with 0.5 moles of oxygen producing one mole of water and one mole of chlorine.

Second reaction: One mole of MCB reacts with 7 moles of oxygen to produce 6 moles of carbon dioxide, 2 moles of water and one mole of hydrochloric acid.

Solution:

What is the oxygen requirement?

Oxygen requirement is 1.1 times 7 or 7.7 moles.

How much nitrogen is fed under this situation? 3.764 times 7.7 or 28.983 moles

Nitrogen remains the same, 28.983 moles of nitrogen will be leaving with the outgoing gases.

How much carbon dioxide is being produced? 6 times 1 or 6 moles

If X moles of chlorine are being produced, then

Hydrochloric acid gas: 1 minus 2 X

Amount of water produced: 2 plus X

Amount of oxygen 0.1 times 7 – 0.5 times X or 0.7 minus 0.5 times X

Total moles: 38.683 minus 0.5 X

Partial pressure of water: (2 plus X)/(38.683 minus 0.5X)*P_T

Partial pressure of chlorine: X/(38.683 minus 0.5X)*P_T

Partial pressure of hydrochloric acid: (1 minus 2 X)/(38.683 minus 0.5X)*P_T

Partial pressure of oxygen: (0.7 minus 0.5 X)/(38.683 minus 0.5X)*P_T

K_P is equal to p_H2O p_Cl2 /(p_HCl² p_O2^0.5 )

K_P is equal to 0.033

Solving for X, amount of chlorine produced is 2.195 times 10^-3 moles.

Total number of moles of product gas: 38.682 moles

Mole fraction of chlorine: 5.67 times 10^-5 or 56.7 ppm