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Chapter 8: Catalyst Materials and Properties

Awareness of catalysts and catalyst supports

Awareness of key properties of supports

Knowledge of the preparation and characterisation of zeolites

Knowledge of the use of zeolites in refinery operations

Chapter Summary

Introduction to common supports and zeolites. The reader should obtaina good understanding of various zeolites and the importance of selectivity. Also some common uses in the oil and gas industry will becovered.

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Common Supports and Catalysts

Activated Alumina

Most common, varied acidity and SA

HSA = Gibbsite and boehmite prepn. by ppn. at varied pHs

CarbonPrepared from natural sources by pyrolysis in inert gas,

such as CO2 and/or steam:Active carbon (T = 800 1500 oC in active environment) Graphitic (T up to 3000 oC in inert environment)

Used in organic hydrogenations in fine chemical industry

Zeolites crown jewels of catalysis

Crystalline aluminosilicates with pores of molecular dimensions

Shape Selective Cracking Catalysts

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What are Zeolites ?

Characteristics

Crystalline aluminosilicates

3D frameworks built up from SiO44- and AlO4

5- tetrahedra

Channels and cages of molecular size (defined by structure)

Cation exchange properties

Stability to heat and radiation

25% of Periodic table can be incorporated into structure

Surface area typically 400-500 m2 g-1

Large internal surface area (> 90%)

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Faujasite or Zeolite Y

(12 T atoms = 0.74 nm)

ZSM-5 (10 T atoms = 0.55 x 0.51nm)

Mordenite(12 T = 0.7 x 0.65 nm & 8 T =0.57 x 0.26 nm)

Linde A (8 T atoms = 0.41 nm)

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Breck DW., Zeolite Molecular sieves, J Wiley & Sons, NY (1974)

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ZSM-5

(10 T atoms = 0.55 x 0.51nm)

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Reactant Shape

Selectivity

n-BuOH dehydrated

using zeolite A

but not i-BuOH

Product Shape

Selectivity

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Zeolites in Catalysis

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Zeolites application in refinery context

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Energy for process is balanced. The highly endothermic reaction is balancedby the highly exothermic coke burn-off.

Flue GasStack

FractionatingColumn

Reactor

Regenerator

FCCU

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Note 1: changed productdistribution with increasedparaffins and aromaticswhen using HY

Note 2: changed productdistribution reduced the no.of barrels required to beprocessed/day

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Zeolites in a refinery (FCC)

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ZSM-5

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Deactivation / coking

Rapid due to coke deposition

Slower due to metals in feed deposition and sintering

More rapid due to pore blockage

Coke Deposition Initial soft coke deposited (lower T)

H rich

Cycloparaffins, naphthenes, aromatics

Dehydrogenation follows hard coke deposited (higher T and longerreaction times)

H deficient

polyaromatics

Coke deposition modifies pore size distribution Decreased diffusion

Decreased activity

Coke deposition is reversed by oxidative regeneration

Coke formation heavily influenced by architecture of zeolite catalyst

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Awareness of catalystsand catalyst supports

Learning Outcomes

Knowledge of the preparationand characterisation of

zeolites

Awareness of key properties

of supports

Knowledge of the use of

zeolites in refinery operations

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