Tutorial 2

REACTION ENGINEERING II (CHE505)

QUESTION 1 (JUN 2016) a) Multiphase reactor is usually preferable in industry application rather than single reactor due to the certain limitations of single reactor. Discuss the three (3) advantages of multiphase reactor in industry. (6 marks) b) A liquid 2-pentanol with the density of 0.812 g/cm3 and MW of 88.1 g/moles contains organic contaminant A which must be removed by hydrogenation in a BCR by the reaction of A + H2 B. The column is installed with an impeller and it is operated at 25 °C. The gas bubbles contains 12 moles% H2 which constantly rise at 10 cm/s velocity. The liquid flow rate is 15 L/s. The mass transfer of H2 is sufficiently fast and remains in equilibrium in liquid phase. List all the necessary assumptions and determine the volume necessary (in m3) to attain 95% conversion at a pressure of 1 atm. Given the Henry’s Law constant of H2 is 3 x 105atm and kl is 2 x 102liter/moles.s. (14 marks) QUESTION 2 (DEC 2015) a) In general, a chemical reactor needs to be able to carry out at least three functions. Multiphase reactor is another type of very important equipment in dealing with the heterogeneous system. Justify the usage of multiphase reactor and give one example of multiphase reactor type. (5 marks) b) A falling film reactor with the diameter of 10 mm is used to remove an organic contaminant A (MW of A =120 g/mol) from and aqueous solution of concentration 10 ppm by weight at 25 °C by air oxidation. The liquid flows at an average velocity of 10 cm/sec and forms a film 1 mm thick on the wall, while the air at 1 atm flows at an average velocity of 2 cm/sec. The reaction in the liquid phase has the stoichiometry A + 2O2 product with a rate rl = klCAlCO2l. Assume the density of water is 1 g/cm3. Given R = R = 82.06 cm3.atm/mol.K. i. Determine the compositions when the reaction has gone to completion. (11 marks) ii. Calculate the number of tubes in parallel required to process 150 L/min of water. (2 marks) QUESTION 3 (JUNE 2015) a) For a reaction in a falling film reactor of A (g) + B (l)  C (g) + D (l), with the aid of simple sketch, derive the residence times equations for both gas and liquid phases. Perform the mass balance equations for both gas and liquid phases with the assumption that there is no gas phase reaction where rl = klCAlCBl. (9 marks) b) A liquid 2-pentanol with the density of 0.812 g/cm3 and MW of 88.1 g/moles contains organic contaminant A which must be removed by hydrogenation in a BCR by the reaction of A + H2 B. The column is installed with an impeller and it is operated at 25 °C. The gas bubbles contains 10 moles% H2 which constantly rise at 12 cm/s velocity. The liquid flow rate is 5 L/s. The mass transfer of H2 is sufficiently fast and remains in equilibrium in liquid phase. List all the necessary assumptions and determine the volume necessary (in m3) to attain 95% conversion at a pressure of 1 atm. Given the Henry’s Law constant of H2 is 3 x 105atm and kl is 2 x 102liter/moles.s. (11 marks)

REACTION ENGINEERING II (CHE505)

QUESTION 4 (DEC 2014) FFR is generally used in processes where it is essential to have large interfacial contact area and also, where temperature is required to be maintained below certain limits, for example, in the manufacture of cosmetics. In the particular reactor, a liquid phase reaction will be carried out by the following reaction: A + 2O2 Products An aqueous solution that contains 15 ppm organic contaminant A with MW of 120 g/mol will be removed by the reaction with oxygen with air. The solution flows at an average velocity of 12 cm/s and forms a liquid film of 2 mm thickness on the wall of reactor. The fluids flow in a counter current direction at 27 °C and a pressure of 1 atm. Diameter of the reactor is 3 cm and air flows at an average velocity of 2 cm/s. a) Calculate the oxygen concentration and organic contaminant in the liquid and gas phases by assuming all contaminants are consumed in the reaction. (6 marks) b) If mass transfer limits the reaction and there is no reaction in gas phase, determine the length of the reactor when conversion is 96%. (14 marks) Additional information: Diffusivity of oxygen: 0.2 cm2/s Rate constant (k) = 102 L/mol.s Henry’s Law constant, H = 1 x 105atm R = 82.06 cm3.atm/mol.K For laminar flow, Sherwood No = 8/3 *

If the reaction process is limited by the reaction in liquid phase, Given the rate of reaction is r = kCACO2

QUESTION 5 CPE 624 (DEC 2013) c) By using appropriate diagram and equation, discuss the effect of fluid velocities and boundary layer thickness on the diffusion of single liquid reactant, A, from the bulk fluid to the surface of non-porous catalyst. State your assumption and examine the limiting cases of reaction. (10 marks) d) A 15 ppm organic contaminant (MW= 120 g/mol) in aqueous solution is being oxidized by air at 1 atm in a FFR. The reaction has the stoichiometry of A + 2O2 P and the diffusion of oxygen through liquid is infinite. The rate of reaction is r = kCACO2. The organic concentration is reduced to 5 ppm at 25 C in a 4 cm diameter and 12 m height of reactor with the volumetric flow rate of liquid is 30 cm3/s. Determine the thickness of film forms on the reactor wall and states your assumption. (12 marks) Additional information: Rate constant, k = 102 L/mol.s Henry’s Law constant = 1 x 105 atm Diffusivity of oxygen = 0.2 cm2/s Water density = 1 g/cm3

REACTION ENGINEERING II (CHE505)

QUESTION 6 CPE 624 (JUN 2012) a) Identify the four different configuration for two phases flow of multiphase reaction. (4 marks) b) An organic solvent (density = 0.78 g/cm3; MW = 84 g/mol) contains contaminant A that must be removed by hydrogenation in bubble column reactor by the reaction A + H2 --> B. The column which is 10 cm in diameter and 2 m high, is operated at 25 C. The bubbles rise at constant velocity of 10 cm/s. The liquid flow rate is 20 cm3/s. The reactor contents are stirred rapidly and the reaction occur homogeneously in the liquid with rate, r = kCACH2 (moles/cm3.s) where the concentration of H2 in the liquid solution is 2.5x10-3 moles/cm3 and k = 5 cm3/moles.s, Determine the reaction conversion if the process is limited by the reaction in the liquid phase.