Chemical Engineering Answers

By what percentage would the rate of absorption be increased or decreased by increasing

the total pressure from 100 to 200 kN/m2

in absorption of ammonia from a mixture of

ammonia and air containing 10% ammonia by volume, using pure water as solvent. Assume

that all the resistance to mass transfer lies within the gas phase. The diffusivity can be

assumed to be inversely proportion to the absolute pressure.

Ammonia is diffusing through a non-diffusing gas mixture of methane and hydrogen in

volume ratio 2:1 under steady state condition. The total pressure is 1 atm. and the temperature

is 100C. The partial pressure of ammonia at two planes 2 mm apart is 13000 and 6500 N/m2

,

respectively. Calculate the flux of ammonia through the layer. Estimate also the quantity of

ammonia diffusing in kg/ day, if the area of cross section of stagnant gas film is 2 m2

.

NH 3 H 2

D  = 7.0 x 10-5 m

2

/ s at 303 K and 1 atm.

NH 3 CH 4

D  = 2.0 x 10-5 m

2

/ s at 288 K and 1.5 atm. (

If the hydrometer is to be constructed with a cylindrical floating rod. Nine fiduciary marks are to be placed along the rod to indicate densities of 0.98 g/cm3, 1.00 g/cm3, 1.02 g/cm3, 1.04 g/cm3, . . . 1.14 g/cm3. The row of marks is to start 0.200 cm from the top end of the rod and end 1.80 cm from the top end. Determine: (2.2) The required length of the rod; (2.3) The average density? (2.4) Should the marks be equally spaced? Explain your answer.

30,000 kg/h of n- butyl alcohol at 99oC is to be cooled to 40oC using water from 35oC to 46oC. Available for the service, is a 1-2 exchanger 48.9 cm I.D. shell with 204 tubes 19.05 mm O.D., 15.75mm ID, 4.88m long arranged on 2.54 cm square pitch. Vertically cut baffles are spaced 12.7 cm apart. Pressure drops of 0.7 kg/cm2 are allowable for both the tube and the shell sides. Find the dirt factor and test the suitability of the unit. Properties Cp (kcal/kg oC) µ , cp n- butyl alcohol at 69.5oC 0.7 0.91 k kcal/ kg m hr 0.142 Water at 40.5oC 1.0 0.70 0.543

Gaseous A absorbs and reacts with B in liquid according to

A(g) + B(1) R(I). -TA-KCACB

S. No.

k, m² liquid/mol hr H. Pa m' liquid/mol

HX

in a packed bed under conditions where

1

2

10⁰

10.

10⁰

10⁰

ka=0.1 mol/hr-m² of reactor - Pa

f₁ = 0.01 m³ liquid/m³ reactor

DA P=10 m³/hr

3

10

10³

ka = 100 m² liquid/m² reactor hr

a = 100 m²/m³ reactor

st 4

10

1

5

10-2

1

At a point in the reactor where p = 100 Pa and C₁ = 100 mol/m³ liquid

9

108

(a) calculate the rate of reaction in mol/hr-m¹ of reactor.

(b) describe the following characteristics of the kinetics:

location of the major resistance (gas film, liquid film, main body of liquid)

behavior in the liquid film (pseudo first-order reaction, instantaneous. second-order reaction, physical transport) for the following values of reaction rate and Henry's law constant.

A solid catalyzed gaseous reaction has the form A + B ↔ C (6) assuming the operating condition of the catalyst is such that the external and internal diffusion steps have negligible pressure gradients, propose rate equations for the following cases: (a) The adsorption of A on the catalyst is controlling (b) The surface interaction between adsorbed A and adsorbed B is controlling (c) The desorption of C from the surface is controlling

The reduction of CO2 with H2 on Pt catalysts is described by the equation CO2(G) + H2 (ads) → H2O + CO According to which well-known mechanism does this hydrogenation proceed (with explanation)?

The following data was obtained for the adsorption of nitrogen on alumina at 77 K. The vapor pressure of N2 at 77 K is 1 atm. Estimate the surface area (m2/g) by BET method assuming the area occupied by one N2 molecule to be 16.2 x10-20 m2. (6) Pressure, mm Hg 8 30 50 102 130 148 233 258 330 442 480 Volume adsorbed, cm at STP 103 3 116 130 148 159 163 188 198 221 270 294

A mixture of benzene and toluene containing 40 mole % of benzene is to be separated to give a product of 90 mole % benzene at top and a bottom product with not more than 10mole % benzene. Using an average value of 2.4 for relative volatility of benzene relative to toluene, calculate the number of theoretical plates required at total reflux. Also calculate the minimum reflux ratio, if the feed is liquid and is at its boiling point

In a mass transfer apparatus operating at 1 atm. the individual

mass transfer coefficients have the following values

kx = 22 kmol/ m2

. h (Δx = 1)

ky = 1.07 kmol/ m2

. h (Δy = 1)

The equilibrium compositions of the gaseous and liquid phases are

characterized by Henry’s law:

p = 0.08 x 106

x, mm of Hg

(i) Determine the overall mass transfer coefficients Kx and Ky.

(ii) Determine the ratio of diffusional resistances of the liquid and gaseous

phases.