CHEMICAL PROCESS TECHNOLOGY
Module name: Process Chemistry III
Module code: CPI3011
Name of student: Mosiya Anggalo Bonolo
Lecturer:Dr M Phiri
Title of assignment:Assignment 2
Date of submission:24 April 2018
A catalyst speeds up the reaction by decreasing the activation energy by providing an alternative reaction pathway that has a lower activation energy. Catalyst brings molecules together, thereby increasing the number and nature of collisions. The catalyst reacts with one of the reactants creating an intermediate compound that reacts with the other reactant to form the desired product.
Figure 1: Energy profile diagram.
Three features of a catalyst needed in petroleum refining are:
Catalyst activity basically tells how fast a reaction can proceed in the presence of a catalyst. It is thus related to the rate of reaction. Activity depends upon the adsorption of reactants on the surface of the catalyst. It is desirable to choose a catalyst with high and stable activity, this will mean that it has more active sites and large surface are and thus the number off collisions increases and thus the reaction.
This measures the fraction at which raw materials are converted to desired product in the presence of other undesirable reactions. It is thus related to the porous nature of the catalysts. Porosity is used to control certain molecules to active sites.
The life-time of a catalyst is determined by stability. This will tell how resistant a catalyst is to chemical, thermal, biological and mechanical degradation.
Small catalyst Particles Large catalyst particle
Type of reactor Fixed bed reactor Fixed bed reactor
Chemical reaction involved Copper as a catalyst
Carbon monoxide reacting with hydrogen to produce methanol
CO + 3H2 ? CH3OH Vanadium(V) oxide or platinum as catalyst
Oxidation of sulphur(IV) oxide to sulphur(VI) in the contact process for the manufacture of H2SO4, 2SO2(g) + O2(g) 2SO3(g)
Evaluate the performance Has large surface area which means an increase in collision and thus fast reaction rate. It is inactive and thus results in the reaction rate to be slower.
Problems associated with each size If temperature is not properly monitored sintering can occur. Shorter life and lower activity and will deactivate fast.
3.1. Catalyst degradation is loss of catalyst activity due to mechanical, chemical and mechanical processes. It is the change in selectivity, undesirable side reactions rate increase, pores get blocked, active sites are covered and the catalyst structure changes. Degradation can be caused by poisoning, sintering and fouling.
Catalyst deactivation can be minimized by tailoring catalyst properties and process operations, are presented, as well as reactor configurations suitable for the regeneration of deactivated catalysts. This basically means by ensuring that process is operated within its limits.
3.2. Sintering is the loss of catalyst active surface due to crystallite growth of either the support material or the active phase. It happens under high temperatures. When sintering occur the physical characteristics of the catalyst will change by melting or the active metals will vaporize. High temperatures cause the passageways or openings in the catalyst to fuse together, which basically means that the pores of the catalyst will close.
Figure 2: Sintering illustration.
Sintering can be prevented by minimizing and controlling the temperature of reaction, by lowering reaction temperature. Thermal stabilizers can be used and by avoiding water and other substances that facilitate metal migration.
Sintering is a permanent condition and thus cannot be reversed. The only recovery is to replace the catalyst.
3.3. A chemical reaction takes place because of the collisions between the reactants. To collide with one another, they must come close and intermix. The intermixing of reactants cannot take place easily if they are in solid state. This is due to restriction in their molecular motion. However, in liquid state as well as in gaseous state the intermixing is possible, and chances of their collision become larger. Thus, the reaction will be faster if the reactants are mixed in liquid phase or solution phase. Hence a solvent is needed to change the phase of the reactants and thus result in the increase of the reaction rate
This can be illustrated with the help of following reaction between lead nitrate and potassium iodide.
131445071120Pb (NO3)2 + 2KI PbI2 + 2KNO3
(i) In one of the experiment, solid Pb(NO3)2 is mixed with solid KI in a dish with the help of spatula.
(ii) In another experiment, aqueous solution of Pb(NO3)2 is mixed with aqueous solution of KI in a beaker.
It will be observed that rate of formation of Pbl2 is much faster in the second experiment because the reactants are now a solution and thus in a liquid phase which resulted in more collisions.N2(g) + 3H2(g) 2NH3(g)
-13(?H2?t)= 12 ?NH3?t-130.045= 12 ?NH3?t -130.045×2= ?NH3?t?NH3?t= -0.03 mol/LsTherefore, the rate of formation of ammonia gas is equal to -0.03 mol/Ls.