Question

A liquid stream containing mixture of 67.0 mole% benzene (C6H6) and the balance toluene (C7H8) is fed into an evaporator at 90˚C. Due to the reduced pressure in the evaporator, a portion of the mixture evaporates to form vapor. The liquid product contains 34.5 mole% toluene and the balance benzene. The vapor product emerges at a rate of 35.0 mol/s containing 71.4 mole% benzene and the balance toluene. Both liquid and vapor product streams are in equilibrium at 55˚C. Neglect the effects of pressure changes on enthalpies. Taking [benzene (l, 90˚C), toluene (l, 90˚C)] as reference for enthalpy calculations, prepare and fill in the inlet-outlet enthalpy table and calculate the required heat input rate in kilowatts.

Answer 1

To answer the question, an inlet-outlet enthalpy table is needed for the process involving the separation of benzene and toluene in an evaporator. This requires the data of enthalpies of vaporization and heat capacities along with the streams' compositions and vapor rate.

Step-by-step explanation:

Inlet-Outlet Enthalpy Table for Benzene-Toluene Evaporator

To calculate the required heat input rate, we need to construct an inlet-outlet enthalpy table for the evaporator process where a mixture of benzene and toluene is separated. The enthalpies of the inlet and outlet streams must be estimated based on the given data: the composition of the streams, the rate of the vapor product, and that the streams are in equilibrium at 55°C. It is also important to note that the enthalpy of vaporization for benzene at its normal boiling point (80.1 °C) is 30.8 kJ/mol, as this will be used in estimating the enthalpies of vaporization for the process taking place at 90°C.

Since we are asked to neglect the effects of pressure changes on enthalpies, the calculations would involve determining the mole fractions of the components in the liquid and vapor streams, using these to calculate the enthalpies of the components, and then applying energy balance equations to determine the heat input rate.

The specifics of the table and the calculation of the heat input rate would require additional data such as the enthalpy of vaporization for toluene and the heat capacities of the liquid and vapor phases of benzene and toluene. However, without this detailed information, we cannot complete the calculation here.