Benzoic acid and its salts have been found useful as ingredients of a number of industrial products, among which

are adhesive, rubber latex, and soap.

Benzoic acid is being produced by the vapor phase oxidation of toluene in a continuous flow reactor, fitted with a fixed bed of the catalyst. The toluene is fed to a vertical-tube vaporizer, which uses superheated steam. Air for oxidation is passed inside the tubes of a horizontal-tube preheater, where it is heated from 20 C to 90 C by hot oil flowing outside the tubes counter-currently to the air flow. Both hot air and the toluene vapors are mixed before introducing into the fixed-bed reactor. The reaction is only 85% complete and therefore the vapors coming out from the reactor are passed to a cooler condenser where non-condensable gases are disposed. The liquids exit from the condenser are phase-separated in a gravity settler.

The following information is available:

The feed rate of toluene to the vaporizer is 200 kg/hr.

Excess air used for oxidation is 50%.

Percent recovery of product and unreacted toluene is 100%.

Overall heat transfer coefficient in the air preheater is 6 W/m2.K.

Tubes used in the preheater are 50 mm in diameter and 2 m long.

Hot oil is fed to the air preheater at 250 C and leaves at 195 C.

Air composition: N2 (79 mole %) and O2 (21 mole %); its molecular weight is 29; its specific heat is 1.1

kJ/kgK.

- Atomic weights: (C=12;H=1;O=16). Required A. Draw a qualitative flow sheet showing the main and auxiliary units of the operation and identify all the streams of the process. B. Determine the utilitics required for the benzoic acid plant. C. Calculation: i. Perform a complete mass balance around the reactor and calculate the composition of the inlet and the outlet stream. ii. The rate of production of benzoic acid and recycle rate of untreated toluene (in kg/hr.). iii. The number of tubes required in the air preheater