Chemical Engineering Answers

Methanol (M) is to be separated from water (W) by atmospheric distillation. The feed contains 22 kg/hr methanol and 25 kg/hr water. The distillate contains 90 mol% methanol and the bottom product contains 5 mol% of methanol. The feed is saturated.

(a) Calculate the molar flow rates of methanol and water in the bottom and distillate product stream.

(b) Determine the minimum number of stages and minimum reflux for the problem. If the equilibrium data is given as;

x 0.032 0.0523 0.075 0.154 0.225 0.349 0.813 0.918 1

y 0.19 0.2494 0.352 0.516 0.593 0.703 0.918 0.953 1

Methanol (M) is to be separated from water (W) by atmospheric distillation. The feed contains 22 kg/hr methanol and 25 kg/hr water. The distillate contains 90 mol% methanol and the bottom product contains 5 mol% of methanol. The feed is saturated. Calculate the molar flow rates of methanol and water in the bottom and distillate product stream.

200 kg/min of feed are fed to a continuous distillation column. The stream contains

70 kg /min NaOH and the difference is water. The distillate flows out of the column at

90 kg /min and contains 4 kg /min NaOH. Determine the bottom stream mass flow

rate and the composition of all streams. Draw and label the flowchart.

A packed counter-current water cooling tower is used to cool

1.356 kg/s.m2

of water from 43.3 °C to 26.7 ºC. The air enters from the bottom

of the tower at 23.9 ºC with a wet bulb temperature of 21.1 ºC. The whole of the

resistance to heat and mass transfer can be considered as being within the gas

phase and the product of the mass transfer coefficient and the transfer surface

per unit volume of column (KG.a) may be taken as 1.207×10-7

kmol/s.m3

.Pa.

The tower operates at atmospheric pressure. Calculate the minimum air flowrate

and the necessary height of the tower when 1.5 times of minimum is used as

actual air flowrate.

Data: Latent heat of water at 0 ºC = 2501 kJ/ kg

Heat capacity of dry air = 1.005 kJ/ kg. ºC

Heat capacity of water vapour = 1.88 kJ/ kg. ºC

Density of air = 1.198 kg/ m3

Enthalpy of saturated air-water vapour data are as follows:

Hyi, kJ/kg dry air 84 97.2 112.1 128.9 148.2 172.1 197.2

Temperature, ºC 26.7 29.4 32.2 35 37.8 40.6 43.3

A 30-plate bubble cap column is to be used to remove n-pentane

from oil by means of pure steam stripping. The inlet oil contains 6% n-pentane

by volume and it is desired to reduce the n-pentane to 0.1% by volume. Assume

isothermal operation and an overall plate efficiency of 30%. Find out the ratio

of actual to minimum steam consumption. The equilibrium relation for the

system is y=3x.

A can of pumpkin puree 8.73cm diameter by 11.43cm in height is being heated in a steam retort in which the steam pressure is 100 kPa above atmospheric pressure. The pumpkin has a thermal conductivity of 0.83Jm's "C", a specific heat of 3770Jkg and a density of 1090kgm³. The temperature in the can prior to retorting was 20°C. Plot out the temperature at the centre of the can as a function of time until this temperature reaches 115°C. Assume is very high

A barite composed of 100% BaSO4 is fused with carbon in the form of coke containing 6% ash (which is infusible). The composition of the fusion mass is

BaSO4 11.1%

BaS 72.8

C 13.9

Ash 2.2

_____

100%

Reaction:

BaSO4 + 4C → BaS + 4CO

Find the excess reactant, the percentage of the excess reactant, and the degree of completion of the reaction. 

A tank of volume 0.00354 m³ contains 0.00292 kg of saturated water vapour at 0.143 MPa. A line is attached to the tank in which water vapour flows at 0.7 MPa and 200 °C. Steam from this line enters the tank until the pressure in the tank is 0.7 MPa.

                             i)     Why can this process be analysed as uniform flow?

[2 marks]

ii) State THREE assumptions, other than uniform flow, that must be made when analysing this process.

[3 marks]

ii)              Use the mass balance to write an expression for the final mass of steam, m₂, in the tank.

[2 marks]

iii)            Write an expression for the energy balance for the system based on the assumptions made in part (ii) and calculate the mass of steam that enters the tank. The properties of steam under these conditions are:

h_in = 2845.3 kJkg^-1 u₁ = 2517.6 kJkg^-1 and u₂ = 2749.9 kJkg^-

1

[5 marks] v) Predict and explain what would happen to the temperature of the steam in the tank during this process.

[3 marks] 

Variation of the rate constant with temperature for the reaction

2N2O5 2N2O4+O2

is given in the following table.

Determine graphically, the activation energy for the reaction and frequency factor. (BL-3)

What is the physical significance of NTU?