chapter 8-catalyst materials and properties_2013_lecture(1)
TRANSCRIPT
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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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