catalysis and catalysts - manufacture solid catalysts by reactor fixed-bed catalysts –relatively...
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Catalysis and Catalysts - Manufacture
Solid Catalysts by ReactorSolid Catalysts by Reactor
Fixed-bed catalysts– relatively large particles (several mm)– mechanical strength important (fines formation)
Moving-bed catalysts– idem fixed-bed– spherical particles (to flow smoothly)
Slurry-reactor catalysts– powders (25 m)– attrition resistance important– usually high density important (for easy settling)
Fluidised-bed and entrained-flow reactor catalysts– powders (20 - 200 m); well-controlled size distribution– attrition residence important
Structured catalytic reactors, e.g. monoliths
Catalysis and Catalysts - Manufacture
Shapes of Industrial CatalystsShapes of Industrial Catalysts
Surface-volume ratio a’Mechanical strengthPressure dropPore-diffusion resistanceManufacture methods; costs
Irregular granule Sphere Pellet Extrudedcylindrical
TrilobeRing Minilith Wagon wheel
Monolithceramic
Monolithmetallic
Foam
Catalysis and Catalysts - Manufacture
Comparison of Catalyst ShapesComparison of Catalyst Shapes
HydrodesulphurisationMethanationImpregnated noble-metal
Ammonia synthesisSilver cat. For formaldehyde
Carbon monoxide shiftHydrogenation
Hydrodesulphurisation
Steam reformingEthylene oxide production
Exhaust gas cleaning
Ammonia oxidationOther high-T processes
Low manufacturing costsRelatively high pressure dropLarge diffusion length
Not commonLow-surface-area catalysts
Regular shape; Most commonGood mechanical strength
Low pressure drop; Poor strength
High strength; Low pressure dropSmall diffusion length
Low pressure drop; Insensitive to dust; Small diffusion length
Low-surface-area catalysts
Spheres
Granules
Pellets
Extrudates
Rings
Monoliths
Gauzes
Catalysis and Catalysts - Manufacture
Pt GauzePt Gauze
Reactor with gauze SEM images
New
Used
Catalysis and Catalysts - Manufacture
MonolithsMonoliths
Catalysis and Catalysts - Manufacture
Specific Surface Area for NiSpecific Surface Area for Ni
Crystalline Size, d (nm)
Spe
cific
Sur
face
Are
a, S
A (
m2/g
)
Catalysis and Catalysts - Manufacture
Examples of Catalyst ManufactureExamples of Catalyst Manufacture
Mo salt Fe salt
Precipitation gelling
Drying
Grinding
Hydrothermic treatment Ripening
Drying
Pelleting
Calcining
Fe-moylbdate
Silicate Acid
Formation clear sol
Gelling
Water wash
Drying
SiO2
Melting
Cooling
Crushing
Screening
Leaching (pH ~ 14)
Raney Nickel
Ni-Al alloy
Catalysis and Catalysts - Manufacture
Catalyst PreparationCatalyst Preparation
Bulk catalysts Supported catalysts
– Supports• Silica• Alumina• Zeolites• Activated Carbon
– Attachment of active phase• Co-precipitation• Impregnation• Deposition-precipitation• Chemical vapour deposition (CVD)• Sol-gel method
Catalysis and Catalysts - Manufacture
Raney NickelRaney Nickel
Mixing
Melting
Cooling
Crushing
Screening
Exposure to NaOH
solution (pH ca. 14
Porous Ni
High activity
High settling rate
Regeneration difficult
Unsatisfactory reproducibility
Pyrophoric
Catalysis and Catalysts - Manufacture
Ammonia Synthesis CatalystFusion Route
Ammonia Synthesis CatalystFusion Route
electric furnace
casting table
crushing
iron-oreH2, diluted O2
reductionpassivation
stabilized catalyst
undersized particles
screen
Catalysis and Catalysts - Manufacture
Catalyst SupportsCatalyst Supports
Function
– carrier active phase
– stabilizes active phase
– access to active sites
Important properties
– stability at reaction conditions
– stability at regeneration conditions
– texture (surface area, pore structure)
– active phase support interaction
– inert/reactive
– heat capacity
– thermal conductivity
– shape,size
– mechanical strength
– cost
Catalysis and Catalysts - Manufacture
Catalysts Supports and ApplicationsCatalysts Supports and Applications
Alumina Hydrogenation, dehydrogenation, hydrotreating, hydrocracking,
FCC, reforming, isomerisation, car exhaust treatment,
methanol synthesis, low-temperature CO shift, steam reforming,
methanation, selective oxidation, alkene methathesis
Silica Polymerisation, hydrogenation, oxidation, hydrodemetallisation
Silica-alumina Ammoxidation, dehydrogenation
Zeolites FCC, hydrocracking, isomerisation, cyclisation, dewaxing,
methanol-to-gasoline process, light alkanes-to-aromatics,
organic synthesis
Catalysis and Catalysts - Manufacture
Catalysts Supports and ApplicationsCatalysts Supports and Applications
Diatomceous earth SO2 oxidation, hydrogenation
Clays Hydrogenation, condensation
Cordierite monoliths Car exhaust, after-burning
Activated carbons Oxychlorination, hydrogenation (fine chemicals)
Titania Selective oxidation, SCR
Magnesium aluminate Steam reforming, methanation, methanol synthesis
Catalysis and Catalysts - Manufacture
Production of Silica (Porous SiO2)Production of Silica (Porous SiO2)
Start from solution Na-silicate
Polymerisation
Gelation
Washing, Drying
H+
Catalysis and Catalysts - Manufacture
Production of Silica (Porous SiO2)Production of Silica (Porous SiO2)
S i
O -
O -
O -
-O S i
O -
O -
-O O S i O S i
O -
O -
O -
O -
O - S i
O -
O -
-O O S i
O -
O -
O -
S iO 44 - S i3O 10
8 - S i2O 76 -
Silicate anions
Si
O-
-O OSi
O-
O-
O O
Si OSi O-
O-O-
-O
Si4O128-
Four-ring
Formation of silanol groups
-O-Si-O- + H+ -O-Si-OH
Generation of Si-O-Si bonds
-O-Si-OH + -O-Si-O- -O-Si-O-Si-O + OH-
Formation of ring structures
Catalysis and Catalysts - Manufacture
Formation of Silica ParticleFormation of Silica Particle
Si
OH
OH
OHHO
Si
OH
OHHO
O
SiHO OH
OH
Si
O O
OHOH Si
O O
OH OHSi
O O
OH OHSi
O O
OHOH
OH
OO
Si
OH
+ H2O
1 2 followingpolymerization
monomer dimer particle of silica polycondensate
Catalysis and Catalysts - Manufacture
Formation of Gels: Sol-Gel MethodFormation of Gels: Sol-Gel Method
Solution of micelles (Hydro) gel
Colloidal solution Gel
pH ?? Surface charge depends on pH pH < 4 -Si-OH2+
pH > 9 -SiO -
Porous structures can be formed at pH 6 - 7
-Si-OH + -O-Si-OH -Si-O-Si- + OH-
Catalysis and Catalysts - Manufacture
Silica Production ProcessSilica Production Process
Silicate Acid
Mixing
Drying
MillingClassification
Washing
Packaging
Mixing
Washing
Drying
Milling
Classifi-cation
Packaging
Silicate Acid
Catalysis and Catalysts - Manufacture
DryingDrying
Critical step• capillary forces cause compression• pores collapse, porosity reduced
Can this be prevented?• exchange water for less polar fluid (e.g., alcohol)• dry under supercritical conditions
After drying • at low Temperature : hydrophilic• at high temperature: concentration of silanol groups low
hydrophobic
Si-O O Si O Si O Si O-
OH OH OH OH
OOOO
Catalysis and Catalysts - Manufacture
Fumed Silica’sFumed Silica’s
SiCl4 + 4 H2 + O2 SiO2 + 4 HCl
Pyrogenic silica
To HCl absorption
Cyclone
Deacidification
Burner
Cooler
Vaporiser
Mixer
Hydrogen
Oxygen (air)
Silicon tetrachloride
Catalysis and Catalysts - Manufacture
Production of Alumina (Porous Al2O3)Production of Alumina (Porous Al2O3)
low pH, soluble
solution of Al2(SO4)3
base
precipitate
high pH, soluble
solution of Al(OH)3
acid
precipitate
Al is amphoteric
Catalysis and Catalysts - Manufacture
Precipitation Regions of Aluminium CompoundsPrecipitation Regions of Aluminium Compounds
pH
solubility
2 4 6 8 10 12
Region ofprecipitation
Al3+ AlO2-
14
Am
orp
ho
us
pre
cip
itate
Po
orly
cry
sta
llise
d
pse
ud
o b
oe
hm
ite
Cry
sta
llize
d b
aye
rite
p
lus
am
orp
ho
us
ma
teria
l
Cry
sta
llise
d
hyd
rarg
illite
Al-oxide amphoteric Soluble at low and high pH
Several precipitates,
dependent on conditions
Catalysis and Catalysts - Manufacture
Formation of Different AluminasFormation of Different AluminasAl-sulphate solution
Al2O3.3 SO3
pH < 2+
Base
at 3 < pH < 6precipitation of
microcrystalline boehmite gelAlO(OH)
Amorphous Al2O3
Na-aluminate solutionNa2O.Al2O3
pH > 12+
Acid
at 8 < pH < 11precipitation of
bayerite gelAl(OH)3
at 6 < pH < 8precipitation of
crystalline boehmite gelAlO(OH)
ageing at pH 8 and 353 K ageing at high pH
-Al2O3 -Al2O3
spinel structure: cubic close packing
Heating at about 1170 - 1270 K
-Al2O3 -Al2O3
-Al2O3
corund structure: hexagonal close packing
gibbsite gelAl(OH)3
-Al2O3
-Al2O3
Heating above 1370 K
Heating above 770 K
Catalysis and Catalysts - Manufacture
Dehydration of Alumina upon HeatingDehydration of Alumina upon Heating
Al O Al O Al
O O O
O
O O O
O
H H
H
O
H H
H
O
H H
H
H H H
Al O Al O Al
O O O
O
O O O
Al O Al O Al
O O O
O
O-+ +
Chemically bonded H2O
Catalysis and Catalysts - Manufacture
Applications of AluminaApplications of Alumina
Catalysis and Catalysts - Manufacture
Pore Volume DistributionsPore Volume Distributions
0.00
0.02
0.04
0.06
0.08
0.10
1 10 100 1000d pore (nm)
dV/dd
(m
l/g/
nm)
0.000
0.002
0.004
0.006
0.008
0.010
1 10 100 1000d pore (nm)
dV/dd
(m
l/g/
nm)
0.0
0.1
0.2
0.3
0.4
0.5
1 10 100 1000d pore (nm)
dV/dd
(m
l/g/
nm)
0
2
4
6
8
10
0.0 0.5 1.0 1.5 2.0d pore (nm)
dV/dd
(m
l/g/
nm)
Wide-pore Silia -Alumina
-Alumina ZSM-5
Catalysis and Catalysts - Manufacture
Early Zeolite Synthesis MethodEarly Zeolite Synthesis Method
Alumina Alkali Hydroxide Silica
Gel
Zeolite
373 K
Catalysis and Catalysts - Manufacture
Industrial Production of Na Aluminosilicate ZeoliteIndustrial Production of Na Aluminosilicate Zeolite
NaOH Al-source
vapour
H2O Si-source
slurry
Crystallisation
freshwater
Product todrying andcrushing
Belt conveyer
slurry
vapour
concentrated mother liquor
Mixing vessels
Catalysis and Catalysts - Manufacture
Zeolite ApplicationsZeolite Applications
Catalysts 14% AdsorbentsDesiccants
Natural 11%zeolites
Detergents 67%
8%
Catalysis and Catalysts - Manufacture
Kinetic Diameters of Molecules Compared with Zeolite Pore SizeKinetic Diameters of Molecules
Compared with Zeolite Pore Size
0
0.2
0.4
0.6
0.8
1
Kin
eti
c d
iam
ete
r [n
m]
Zeolite-X, Y
ZSM-5
Zeolite-4A
Kin
etic
dia
met
er (
nm)
Catalysis and Catalysts - Manufacture
Preparation of H-Zeolite from Na-ZeolitePreparation of H-Zeolite from Na-Zeolite
NH4+
- NH3> 570 K
Catalysis and Catalysts - Manufacture
Ion-Exchange of Zeolite Y for Na RemovalIon-Exchange of Zeolite Y for Na Removal
1st Exchange
Filtration & washing
Heating
2nd Exchange
Filtration & washing
Final drying
NaY sieve
NH4+ or
RE3+ solution
NH4+ or
RE3+ solution
Na+ solution
Na+ solution
Catalysis and Catalysts - Manufacture
Zeolites Classified by their Si/Al RatioZeolites Classified by their Si/Al Ratio
Catalysis and Catalysts - Manufacture
Solid-State Reactions in Y Zeolite During SteamingSolid-State Reactions in Y Zeolite During Steaming
Al
O
O
O
O
Si
Si
Si
Si Si OH
OH
Si
OH
Si
HO Si + Al(OH)3
Si OO SiSi
Si
O
Si
O
Non-framework species
Si(OH)4
H2O
H2O
From other parts of the lattice (creating meso-pores)
Catalysis and Catalysts - Manufacture
Trends in Catalytic Cracking Catalyst PerformanceTrends in Catalytic Cracking Catalyst Performance
50 60 70 80
10
9
8
7
6
5
4
Conversion (vol%)
Cok
e yi
eld
(wt%
on
FF
)
Low a
lumina
am
orph
ous c
ats
High a
lumina
am
orph
ous c
ats
Zeolite ca
talysts
Zeolites +
riser c
racking
Coke selective zeolites (R
E-H-Y)
Highly coke selective cats (USY)
(1946)
(1955)(1964)
(1968-72)
(1980’s)
Catalysis and Catalysts - Manufacture
Activated CarbonsActivated Carbons
Positive– stable at all pH, T– high adsorption capacity– wide variety textural properties– "soft" ligand– not much erosion pumps, etc– inert
Negative
– chemical reactivity (O2,.)
– mechanically weak– fines
Catalysis and Catalysts - Manufacture
Activated CarbonActivated Carbon
Carbonaceous material peat, coal, biomass, sugar,polymers
High TPyrolysis
Porous material
H2OPartial gasification
Additional porosity Activated carbon
Catalysis and Catalysts - Manufacture
Structure of Activated Carbon from WoodStructure of Activated Carbon from Wood
Catalysis and Catalysts - Manufacture
Functional GroupsFunctional Groups
O-
O
OO O O
O
O
O
OH
O
+ H2O, OH-
+ H2O, OH-
OOH
O
O
+ OH-
+ OH-
+ H-
+ H-
+ H- + H-+ H-
+ OH-, H-
Catalysis and Catalysts - Manufacture
Reactions with Carbon-supported Catalysts
Reactions with Carbon-supported Catalysts
Catalysis and Catalysts - Manufacture
Carbon-based Monolith SupportCarbon-based Monolith Support
a. b.monolithicstructure
carbon
Carbon-coated monolith Integral-type carbon support
Catalysis and Catalysts - Manufacture
(Co)Precipitation(Co)Precipitation
Solution solution
supersaturated solution
nucleation
growth
Coprecipitation mixed oxides
homogeneous orheterogeneous
Parameters – nature salts
– cA,cB,...
– T , pH– ripening time– nucleation promotors– .......
Catalysis and Catalysts - Manufacture
Production of Catalysts by PrecipitationProduction of Catalysts by Precipitation
Precipitation and ageing
Mixed metal nitrates tank
Sodium carbonate tank
Mixed oxides and
carbonates
Filter
Drier and calciner
Mill
Weighing machines
Pelleting machine
Powder mixing bin
Catalyst pellets
Catalysis and Catalysts - Manufacture
CoprecipitationCoprecipitation
Positive– components well
mixed on an atomic scale
– high loading possible– at high loadings
relatively high dispersion
– high thermostability
Negative– difficult scale-up– at low loadings
relatively low dispersion
Catalysis and Catalysts - Manufacture
Structure of Coprecipitate in Synthesis of Cu-Zn/Al2O3
Structure of Coprecipitate in Synthesis of Cu-Zn/Al2O3
brucitelayer
interlayer
brucitelayer
interlayer
brucitelayer
interlayer
brucitelayer
c0
= metal ions (Cu2+, Zn2+, Al3+)
= hydroxyl ions
= interlayer compounds (CO32-, H2O)
Catalysis and Catalysts - Manufacture
Catalysts Prepared by CoprecipitationCatalysts Prepared by Coprecipitation
Catalysis and Catalysts - Manufacture
ImpregnationImpregnation
Wetting of support with solution precursor– "Wet" Excess solution– "Dry" Amount of solution=Pore Volume
Drying– Critical, tendency towards "egg-shell" catalyst
Calcination– Critical
• bursting support• interaction compounds• sintering
Catalysis and Catalysts - Manufacture
Catalyst Preparation by ImpregnationCatalyst Preparation by Impregnation
Wet impregnation
Dry impregnation
Bucket conveyor
Drip chute
Bucket
Drive wheel
Bucket filter
Tipper
To drying
Impregnating solution
Impregnating basin
Impregnating solution
Spray header
Support to be impregnated
Rotating drum
a.
b.
Catalysis and Catalysts - Manufacture
Relation between PZC and Surface ChargeRelation between PZC and Surface Charge
H H+
Si O Si O Si
O- O- O-
Si O Si O Si
O O OH+ H HH+
Si O Si O Si
O O OH H H
Lower pH Higher pHpH = PZC
pH
Surface Charge
Species
Adsorption
pH increase
pH < PZC
positive
MOH2+
anions
pH = PZC
neutral
MOH
pH > PZC
negative
MO-
cations PZC
Alumina 8 - 9
Silica ~ 3
10% Alumina/Silica ~ 5
Catalysis and Catalysts - Manufacture
Adsorption from [Pt(NH3)4]2+ solutionAdsorption from [Pt(NH3)4]2+ solution
Silica gel
-Alumina
0.3
0.2
0.1
06 7 8 9 10
pH
Adsorbed [Pt(NH3)4]2+ (mmol/g)
Catalysis and Catalysts - Manufacture
Active-Phase DistributionsActive-Phase Distributions
Uniform Egg-shell Egg-white Egg-Yolk
a b c d
Active phase Support
Catalysis and Catalysts - Manufacture
Processes during ImpregnationProcesses during Impregnation
Solution flow into pores
adsorption
adsorption
diffusion
evaporation
Adsorption/desorption + diffusion
Drying
Catalysis and Catalysts - Manufacture
Impregnation of -Alumina with PtImpregnation of -Alumina with Pt
4-
Al
OH+ PtCl62-2
Pt ClCl
Cl Cl
O O
Al Al
+ 2 HCl
Active phase Support
Impregnation time increases
Catalysis and Catalysts - Manufacture
Impregnation of -Alumina with PtInfluence of Coadsorbing Ions
Impregnation of -Alumina with PtInfluence of Coadsorbing Ions
a b c
Increasing citric acid concentration
Pt/Al2O3 Al2O3
Catalysis and Catalysts - Manufacture
Impregnation of Monoliths with NiInfluence of Drying Method
Impregnation of Monoliths with NiInfluence of Drying Method
a. b. c. d. e.
Conventional drying
Forced-flow drying
Microwave drying
Freeze drying 1 h 24 h
Catalysis and Catalysts - Manufacture
Homogeneous Deposition PrecipitationHomogeneous Deposition Precipitation
Applicable in precipitation upon increasing pH
– example: Ni2+ Ni(OH)2
Upon heating (370 K) urea in water decomposes slowly:
CO(NH2)2 + 3 H2O CO2 + 2 NH4+ + 2 OH-
pH increases slowly throughout particle– homogeneous loading
Catalysis and Catalysts - Manufacture
Homogeneous Deposition PrecipitationHomogeneous Deposition Precipitation
2 g/L NaOH
SiO2 2 g / 2 LNi(NO3)2.6H2O 0.5 g / 2 L
Peristaltic Pump (Gilson Minipuls)Injection Speed 50 mL/h pH Electrode
Time
pH
Catalysis and Catalysts - Manufacture
Chemical Vapour DepositionChemical Vapour Deposition
Catalysis and Catalysts - Manufacture
Oil-Drop CoagulationOil-Drop Coagulation
Organic phase
Aqueous phase
Oil overflow to recirculation
Oil
Water
Distributor coneSol
Product to ripening, washing, and drying