CATALYST POISONS

CATALYST AND POISON

CATALYST: A substance which does not take part in a

reaction, but influences the rate of desirable reactions.

Eg., Nickel-Molybdenum

POISON:A Substance, either in the reactant stream or that

produced by the reaction, which lowers the activity of the

catalyst.

Eg., Carbon, Steam, Sodium etc.

CATALYST

A Catalyst accelerates reaction by providing alternate paths to products.

The activation energy of each catalytic step is less than that for the non catalytic reaction.

In the reaction cycle, active centers of catalyst first combine with at least one reactant and then are reproduced with the

appearance of product.

The freed center then recombines with reactant to produce another cycle and so on.

Comparatively small quantities of catalytic centers are required to produce large amounts of product.

Equilibrium conversion is not altered by a catalyst.

A catalyst can radically alter selectivity.

CATALYSTS USED IN REFINERY

Silica-Alumina in Fluidized Catalytic Cracking Unit (FCC)

Nickel-Molybdenum in Diesel Hydrodesulphurization Unit

(DHDS) and Naphtha Hydro treating Unit (NHT).

Platinum in Continuous Catalytic Regeneration Unit

(CCR).

Titanium and Alumina in Sulphur Recovery Unit (SRU).

POISON

A substance that appreciably diminishes the catalytic

reaction rate is called a Poison.

A poison can be either in the reactant stream or produced

by the reaction.

A Poison lowers the activity of the catalyst.

Poisoning can be due to chemisorption or due to physical

deposition active sites of catalyst.

Eg., Nitrogen compounds are chemisorbed on FCC

Catalyst and Coke causes deactivation by deposition.

POISONS FOR CATALYSTS USED

IN REFINERY PROCESSES

PLANT CATALYST POISON

FCCU Silica-Alumina Nickel,Vanadium,Sodium,

Nitrogen,Coke

DHDS Nickel-Molybdenum Metals,Silica,Coke

NHT Nickel-Molybdenum

Metals,Silica,Coke

CCR Platinum Metals,Silica,Sulphur.

SRU Activated Alumina

and Titanium dioxide

Steam, Carbon

TYPES OF POISONS

Deposited Poisons: Carbon deposition on catalysts

used in Refinery Processes.

Eg., Carbon (Coke) deposition on FCC Catalyst.

This type of Poison can be removed by regeneration of

the catalyst.

Regeneration can be accomplished by burning carbon to

CO and CO2 with air and/or steam.

TYPES OF POISONS

Chemisorbed Poisons: Compounds of Sulphur and

other materials are chemisorbed on Nickel, Copper and

Platinum Catalysts.

The poison covers the active sites of the catalyst, which would

otherwise adsorb reactant molecules.

The activity of catalyst will be regained when the poison is

removed from the reactants.

If the adsorbed material is tightly held by the active sites of

catalyst, the poisoning is permanent.

TYPES OF POISONS

Selectivity Poisons: Some materials in the reactants

will adsorb on the surface of the catalyst and then catalyze

other undesirable reactions.

Eg., Small amounts of Nickel and Vanadium in FCC feed will

get deposited on the catalyst and act as dehydrogenation

catalysts.

This results in increased yields of Hydrogen and coke and

lower the yield of Gasoline.

This type of poisons cause permanent loss of catalyst activity.

TYPES OF POISONS

Stability Poisons: Water vapor present in SO2-Air

mixture supplied to a Platinum-Alumina Catalyst, will

decrease the oxidation activity of the catalyst.

This type of poisoning is due to the effect of water on the

structure of Alumina carrier.

Temperature has a pronounced effect on stability poisoning.

Sintering and localized melting may occur as the temperature

is increased ,which changes the catalyst structure.

TYPES OF POISONS

Diffusion Poisons: Blocking the pores of catalyst

prevents the diffusion of reactants into the inner surface.

Entrained solids in the reactants or fluids which can react

with the catalyst to form a solid residue can cause this

type of poisoning.

Eg., Carbon deposition on FCC Catalyst

FCC REACTOR-REGENERATOR SECTION

FEED

FCC

FCC is a secondary processing unit.

Cracks Heavy Vacuum Gas Oil to more valuable products.

Uses Si-Al catalyst in the form of fine powder(70 microns).

Catalyst is continuously circulated in the unit @30-40

MT/min.

Residence time of feed in Riser is 1.5-2 sec.

COMPONENTS OF FCC CATALYST

ZEOLITE-Primary Catalytic Component for selective

cracking.

MATRIX-Forms the continuum that holds together the

Zeolite crystals.

FILLER-A clay incorporated into the catalyst to dilute its

activity.

BINDER-Serves as a glue to hold the Zeolite,Matrix and

Filler together.

FCC CATALYST COMPONENTS

ZEOLITE STRUCTURE

ACTIVE SITES OF ZEOLITE

TYPES OF POISONS OF FCC CATALYST

Poisons which damage FCC Catalyst can be divided into

the following categories.

Poisons which damage or weaken the catalyst structure.

Eg., Sodium

Poisons which block acid sites.

Eg., Coke, Nitrogen

Poisons which catalyze undesirable reactions.

Eg., Nickel, Vanadium

STRUCTURAL CHANGES IN THE CATALYST

Structural changes can occur in both Zeolite and matrix.

Changes take place when catalyst is exposed to high

temperatures(>750degC) and water. This is called

hydrothermal deactivation.

Two stage Regeneration eliminates this problem, as

most of the water is removed in the first stage

Regenerator, where the temperature is < 700 degC.

The presence of contaminants like Sodium, Vanadium

aggravates the harmful effect on the stability of Zeolite.

DEACTIVATION DUE TO COKE

Coke formed during cracking blocks the active sites and pores of the catalyst.

Coke formed in FCC can have the following origins:

Catalytic Coke: Coke produced from cracking reactions that occur at the active sites of Zeolite and matrix.

Contaminant Coke: Coke produced by heavy metals (Cu, Ni, V, Fe) deposited on the catalyst.

Occluded Coke: Coke resulting from the carry over of hydrocarbons in the catalyst pores.

Feed Residue Coke: Coke contributed by carbon residue in the feed.

CATALYST POISONS

NITROGEN

SODIUM

NICKEL

VANADIUM

NITROGEN

Organic Nitrogen compounds in FCC feed are the source of Nitrogen.

The source and Sp. Gravity range of Crude influence the amount of Nitrogen in FCC feed.

Basic Nitrogen is 25-30% of total Nitrogen in feed.

Basic nitrogen reacts with the active acidic sites of FCC Catalyst.

It results in temporary loss of catalyst activity.

Nitrogen which blocks the active sites is burnt in Regenerator.

Burning of Nitrogen in Regenerator restores the activity of catalyst.

NITROGEN

Approx.300 ppm increase in Basic Nitrogen results in

loss of 1 vol% conversion.

Nitrogen content in FCC feed can be reduced by

A) Selecting crudes with low Nitrogen content

B) Hydro treating FCC feed

C) Increasing the Zeolite content and active Matrix of FCC

Catalyst.

FCC Feed Nitrogen is monitored regularly.

SODIUM

Sodium causes permanent deactivation of catalyst by neutralizing its acid sites.

Sodium is used in the manufacture of FCC Catalyst.

Other sources of Sodium are

A) Inadequate Desalter operation in CDU.

B) Addition of Caustic downstream of Desalter.

C) Processing of refinery slop.

D) Purchased FCC feed

E) Use of Steam that contains sodium.

The adverse effects of Sodium are the same regardless of its origin.

SODIUM

Sodium is detrimental to Zeolite stability and its activity.

It decreases the hydrothermal stability of catalyst.

It forms an eutectic with Catalyst, which fuses at Regenerator conditions .

Increase in Sodium content reduces the RON of FCC Gasoline.

Sodium causes a permanent loss in Catalyst activity.

Sodium in FCC feed is monitored regularly.

Sodium in E cat (Na2O) is monitored to know the sodium contamination due to Catalyst.

NICKEL

Nickel is a permanent Poison for FCC Catalyst

Deactivates mild acid sites of Matrix and the stronger sites on the

zeolite exterior surface.

Promotes dehydrogenation reactions.

Results in High yields of hydrogen and Coke.

Nickel is present in heavier FCC feed.

The detrimental effects of Nickel can be reduced by

A) Increasing the metal tolerance of FCC Catalyst.

B) Using Nickel Passivator

C) Using flushing catalyst with low metals.

VANADIUM

Vanadium is a permanent poison for FCC Catalyst.

It is present in heavier FCC feed.

It gets deposited on Catalyst during Cracking.

It results in loss of Surface Area and activity.

Vanadium on Catalyst promotes dehydrogenation reactions.

This results in high yields of Hydrogen and coke.

The detrimental effects of Vanadium can be reduced by:

A) Using Catalyst with high Vanadium tolerance.

B) Using Vanadium Passivator.

C) Using flushing Catalyst with low metals.

FCC E CATALYST METALS

Date C Cu Ni V Ca K Mg P Sb

Taken wt% ppm ppm ppm ppm ppm wt% wt% ppm

30-Jul-09 0.02 25 2014 5826 688 714 0.10 0.04 289

23-Jul-09 0.01 25 2065 6015 649 670 0.09 0.04 288

20-Jul-09 0.02 25 1963 5893 645 673 0.09 0.05 231

16-Jul-09 0.00 25 1922 6004 658 670 0.10 0.04 189

13-Jul-09 0.01 25 1775 5705 633 655 0.10 0.04 164

9-Jul-09 0.06 25 1750 5597 618 649 0.10 0.04 260

6-Jul-09 0.01 25 1819 5758 639 641 0.10 0.04 139

3-Jul-09 0.03 25 1811 5740 665 662 0.08 0.05 303

3-Jul-09 0.03 25 1821 5657 658 629 0.09 0.04 251

26-Jun-09 0.05 25 1752 5745 642 602 0.08 0.05 221

21-Jun-09 0.08 25 2030 5818 699 612 0.38 0.09 151

19-Jun-09 0.02 25 1990 6295 613 606 0.11 0.05 280

NICKEL & VANADIUM IN FCC E CATALYST

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