catcat03 - good info on support production

Catalysis and Catalysts - Manufacture

Solid 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 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 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 Gauze

Reactor with gauze SEM images

New

Used

Catalysis and Catalysts - Manufacture

Monoliths

Catalysis and Catalysts - Manufacture

Specific Surface Area for Ni

Crystalline Size, d (nm)

Spe

cific

Sur

face

Are

a, S

A (

m2/g

)

0

100

200

300

400

500

600

700

0 10 20 30 40 50

Catalysis and Catalysts - Manufacture

Examples 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 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 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

electric furnace

casting table

crushing

iron-oreH2, diluted O2

reductionpassivation

stabilized catalyst

undersized particles

screen

Catalysis and Catalysts - Manufacture

Catalyst 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 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 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)

Start from solution Na-silicate

Polymerisation

Gelation

Washing, Drying

H+

Catalysis and Catalysts - Manufacture

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 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 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 Process

Silicate Acid

Mixing

Drying

MillingClassification

Washing

Packaging

Mixing

Washing

Drying

Milling

Classifi-cation

Packaging

Silicate Acid

Catalysis and Catalysts - Manufacture

Drying

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’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)

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 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 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 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 Alumina

Alumina Application

-alumina hydrotreating

hydrocracking

methanation

reforming

hydrogenation

-alumina isomerisation

-alumina car exhaust

-alumina steam reforming

ethylene oxidation

Catalysis and Catalysts - Manufacture

Pore 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 Method

Alumina Alkali Hydroxide Silica

Gel

Zeolite

373 K

Catalysis and Catalysts - Manufacture

Industrial 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 Applications

Catalysts 14% AdsorbentsDesiccants

Natural 11%zeolites

Detergents 67%

8%

Catalysis and Catalysts - Manufacture

Kinetic 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-Zeolite

NH4+

- NH3> 570 K

Catalysis and Catalysts - Manufacture

Ion-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 Ratio

Si/Al Ratio Zeolite Properties

Low (1-1.5) A, X Relatively low stability of frameworkLow stability in acidsHigh stability in basesHigh concentration of acid groupswith moderate acid strengthHydrophilic

Intermediate (2-5) ErioniteChabaziteClinoptiloliteMordeniteY

High (~10 to ) ZSM-5a Relatively high stability of frameworkErionitea High stability in acidsMordenitea Low stability in basesYa Low concentration of acid groups

with high acid strengthHydrophobic

a

By dealumination.

Catalysis and Catalysts - Manufacture

Solid-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 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 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 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 Wood

Catalysis and Catalysts - Manufacture

Functional 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

Reaction Active Phase

Hydrogenations Pt, Pd, Ni

Acetylene + HCl to vinyl chloride HgCl2

Acetylene + HAc to vinyl acetate Zn(OCOCH3)2

Catalysis and Catalysts - Manufacture

Carbon-based Monolith Support

a. b.monolithicstructure

carbon

Carbon-coated monolith Integral-type carbon support

Catalysis and Catalysts - Manufacture

(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 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

Coprecipitation

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

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 Coprecipitation

Reaction Catalytic elements

Catalysts

Hydrogenation Ni/Al

Steam reforming Ni/Al, Ni/Mg/Al

Methanol synthesis Cu/Zn/Al, Zn/Cr, Cu/Zn/Mg/Al

Higher Alcohol Synthesis Cu/Co/Zn/Al, Cu/Co/Zn/Cr

Fischer-Tropsch Co/Cr, Fe/Al

Supports for catalysts

Basic support Mg/Al

Catalysis and Catalysts - Manufacture

Impregnation

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 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 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+ 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 Distributions

Uniform Egg-shell Egg-white Egg-Yolk

a b c d

Active phase Support

Catalysis and Catalysts - Manufacture

Processes during Impregnation

Solution flow into pores

adsorption

adsorption

diffusion

evaporation

Adsorption/desorption + diffusion

Drying

Catalysis and Catalysts - Manufacture

Impregnation 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

a b c

Increasing citric acid concentration

Pt/Al2O3 Al2O3

Catalysis and Catalysts - Manufacture

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 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 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 Deposition

Catalysis and Catalysts - Manufacture

Oil-Drop Coagulation

Organic phase

Aqueous phase

Oil overflow to recirculation

Oil

Water

Distributor coneSol

Product to ripening, washing, and drying