Catalysis12

In the name of Allah the most Gracious and MercifulKnowledge of Ammonia Catalysts

By: Nasir Hussain

Pak Arab Fertilizers Multan

13-12-12

Training outline Introduction to catalysis Principal characteristics of a catalyst Ammonia plant catalysts Poisoning of catalysts Replacement/Reduction of catalysts Catalysts catastrophes

Introduction Catalysis is the change in rate of a chemical reaction due to the

participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations. Catalysts that speed the reaction are called positive catalysts. Substances that slow a catalyst's effect in a chemical reaction are called inhibitors. Substances that increase the activity of catalysts are called promoters, and substances that deactivate catalysts are called catalytic poisons.

Introduction cont.….

Catalyst is a substance that increases the rate of the reaction at which a chemical system approaches equilibrium , without being substantially consumed in the process.

Catalyst affects only the rate of the reaction, i.e. Kinetics. It changes neither the thermodynamics of the reaction nor the equilibrium composition.

Introduction cont.…. Activation Energy can be defined as the minimum energy required to start a

chemical reaction. The activation energy of a reaction is usually denoted by Ea, and given in units of kilojoules per mole. The Activation Energy (Ea.) determines how fast a reaction occurs, the higher Activation barrier, the slower the reaction rate. The lower the Activation barrier, the faster the reaction

Activation EnergyCatalyst lowers the activation energy for both forward and reverse reactions.

Activation Energy

This means , the catalyst changes the reaction path by lowering its activation energy and consequently the catalyst increases the rate of reaction

Principal Characteristics The efficiency of the catalyst depends upon three components

Good mechanical strength

Activity

Selectivity

Life

low pressure drop

· high tolerance for contaminants

Activity It is the extent to which the catalyst influence the rate of change of a

reaction as measured by the disappearance of the reactants i.e. conversion

It is often expressed as a rate per unit volume. The activity per unit volume is of practical importance because process economics can depend critically upon the cost of packed reactor space. The bulk density of a catalyst must always be as small as possible , consistent with other requirements.

Selectivity The selectivity of a catalyst is the ability to promote a particular reaction

whilst minimizing the production of unwanted compounds. Very often a catalyst can be made more specific for a particular reaction whilst the activity can be diminished by poisoning with some other metal.

Life of a catalyst The life of a catalyst is the period during which it produces the required

product at the required degree of activity and selectivity. The life of a catalyst is usually ended because of loss of mechanical strength or because of unacceptable changes in activity and selectivity.

Hydrogenation Hydrogenation is the conversion of organic Sulphur compound into

inorganic Sulphur compound.

For example

RSH + H2 = RH + H2S Exothermic

R2S + 2H2 = 2RH + H2S

Hydrotreator 107-D Catalyst CoMo

Catalyst Type ICI 41-6T

Form Cylinders

Size Dia 3.2 mm Length 10mm

CoO 3.3 %

MoO 14 %

Alumina Balance

Bulk Density 700 kg/m3 or 0.9 kg/lit

Volume 2 Beds each of 6.35 m3

Loaded Jan 2008

2.0 H2S Removal

H2S is removed by ZnO bed according to following reaction

ZnO + H2S = ZnS + H2O

There are Two vessels for H2S removal

101-D & 102-D

Desulphrisers 101/102-D101-D

Catalyst Type Mixture of Catalysts (ZnO)

Volume 22.5 m3 (NCT 305 +10.5 Mixture)

Loaded on 2010

Bulk density 1.1 kg/lit

Shape Pellets

Service Life 2 years

102-D

Catalyst Type Mixture of Catalysts (ZnO)

Volume 22.5 m3 (NCT 305 +10.5 Mixture)

Loaded on 2010/2008

Bulk density 1.1 kg/lit

Shape Pellets

Primary Reformer 101-B Catalyst Type R-67-7H/R-67-R7H (Topsøe)

Volume 15.5 m3

Loaded on 2004

Shape Pellets

Catalyst Size 11*16 & 13*20 mm

Carrier of catalyst Magnesium Aluminate

NiO 16 ~ 18 wt. %

Carrier Balance

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Primary reformer catalyst Performance of reforming catalysts is periodically evaluated by considering

following parameters and operating conditions are duly adjusted :

Approach to equilibrium

Methane slip

Pressure drop

Tube skin temperature

101-B catalyst

Primary Reformer 101-B (cont.)

Secondary Reforming Air is introduced in secondary reformer.

The combustion of a part of H2 & CH4 takes place at top portion.

Heat of combustion is utilized for further reforming.

CH4 + H2O = CO +2 H2

CH4 + O2 = CO + 3H2

2H2 + O2 = 2 H2O - 242 kJ / mole

The gases leaves the secondary reformer at 996 OC.

Secondary Reformer 103-D

Catalyst Type ICI 54-4

NiO 10.5 %

Catalyst Volume 33.5 m3

Loaded on 1993

HTSC The purpose of HTS converter is to oxidize CO to CO2.

Reaction

CO + H2O = CO2 + H2 - 41.1 KJ / mole

The CO slippage from HTS should be less than 3.0 %.

The principle operating variables are steam to gas ratio & temperature.

Increasing steam results in an increase to CO conversion.

Under

severe condition magnetite can be reduced to FeO or even metallic iron. Such change of phases and over

reduction causes crystallite changes in the catalyst that lead to physical degradation, weakening and

fracture of pellets, and increase in pressure drop. Metallic iron promotes side reaction such as Fisher

Tropsh reaction. Such reactions can affect adversely the performance of down stream catalysts.

HTSC 110-D Catalyst Type C-12-4 (SUD CHEMIE)

Catalyst Volume 53 m3

Loaded on 2006


Size Dia 9 * 5 ~ 7 mm

Shape Tablet

Fe2O3 88 %

Cr2O3 09 %

CuO 2.6 %

Catalyst is supplied in the form of Fe2O3 Hematite

Catalyst is reduced to active Fe3O4 Magnetite

LTSC 104-D Catalyst Type LK-821-2 & LSK-2


Loaded on 2012


Size 4.5*3.4 mm & 4.5*4.5 mm

Shape Tablets

CuO

ZnO

Al2O3

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LTSC by product CO2+H20 CH3OH+H20

Methanol increase with

• High temperature

• High inlet CO levels

• Low S:C ratio

Methanator The Methanation reactions are:

CO2 + 4 H2 = CH4 + 2 H2O -165 KJ/Kg mole

CO + 3 H2 = CH4 + 1 H2O -206 KJ /kg mole

74 oC rise in temp for 1 % CO

60 oC Rise in temp for 1 % CO2

Methanator 106-D

Catalyst Type ICI 11-3


Loaded on 1993


Size 5.4*3.6 mm

Shape Cylindrical Pellets

Bulk Density 1.23 kg/lit

NiO 35 % wt.

MgO 4 % wt.

Support Balance

Ammonia Converters 105-D A/B Catalyst Type KM1R & KM1 (Haldor Topsøe)

Catalyst Volume 2 Beds 9.3 m3 & 23.4 m3

Loaded on 2011

Size 1.3*3.0 mm

Shape Irregular

Fe

FeO

Fe oxides

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Promotors Ammonia synthesis catalyst is based on metallic iron promoted with

alkali (potash) and various metal oxides such as those of aluminum, calcium or magnesium. The main component of the catalyst is magnetite (Fe3O4). Various promoters in catalyst plays main role in catalyst activity.

Such promoters are classified as structural or electronic depending on their accepted mode of action. Production and preservation of porous structure during reduction of ammonia synthesis catalyst is main role of

structural promoters such as alumina, magnesia and chromium. Alkali metal such as calcium, potassium ,rubidium etc. are essential components of catalyst to attain high activity, are called electronic promoter.

Promoters Chromium promoted Iron catalyst is of HTSC.

Poisons for Ammonia CatalystsCatalysts Poisons

LTSC S power full poison( trapped by the catalyst as CU2S and ZNS)Cl, reacts with Cu and Zn to from chlorides.CuCl provides the mechanism for loss of activity by sintering. Water, excess water can damage the catalysts du to thermal shock

101B S, can affect the catalyst by chemisorption on its surface.C

105-D Main poisons to synthesis catalyst are oxygenated compounds such as water, CO, CO2.(reversible)chloride and sulphur affect the catalyst irreversibly.

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Poisons for Ammonia Catalysts106-D S, Catacarb solution blocks pores of Ni

catalyst by evaporating K2CO3Arsenic

107-D Carbon, this cab be avoided by operating at low temperatures.

Heating rate of 107-D p-29 op. m

Thanks

Catalysis12

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