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


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


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


Pt Gauze

Reactor with gauze SEM images

New

Used


Monoliths


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


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


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


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


Ammonia Synthesis CatalystFusion Route

electric furnace

casting table

crushing

iron-oreH2, diluted O2

reductionpassivation

stabilized catalyst

undersized particles

screen


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


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


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


Production of Silica (Porous SiO2)

Start from solution Na-silicate

Polymerisation

Gelation

Washing, Drying

H+


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


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


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-


Silica Production Process

Silicate Acid

Mixing

Drying

MillingClassification

Washing

Packaging

Mixing

Washing

Drying

Milling

Classifi-cation

Packaging

Silicate Acid


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


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


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


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


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


bayerite gelAl(OH)3


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


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


Applications of Alumina

Alumina Application

-alumina hydrotreating

hydrocracking

methanation

reforming

hydrogenation

-alumina isomerisation

-alumina car exhaust

-alumina steam reforming

ethylene oxidation


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


Early Zeolite Synthesis Method

Alumina Alkali Hydroxide Silica

Gel

Zeolite

373 K


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


Zeolite Applications

Catalysts 14% AdsorbentsDesiccants

Natural 11%zeolites

Detergents 67%

8%


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)


Preparation of H-Zeolite from Na-Zeolite

NH4+

- NH3> 570 K


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


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.


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)


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)


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


Activated Carbon

Carbonaceous material peat, coal, biomass, sugar,polymers

High TPyrolysis

Porous material

H2OPartial gasification

Additional porosity Activated carbon


Structure of Activated Carbon from Wood


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-


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


Carbon-based Monolith Support

a. b.monolithicstructure

carbon

Carbon-coated monolith Integral-type carbon support


(Co)Precipitation

Solution solution

supersaturated solution

nucleation

growth

Coprecipitation mixed oxides

homogeneous orheterogeneous

Parameters – nature salts– cA,cB,...

– T , pH– ripening time– nucleation promotors– .......


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


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


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)


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


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


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.


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


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)


Active-Phase Distributions

Uniform Egg-shell Egg-white Egg-Yolk

a b c d

Active phase Support


Processes during Impregnation

Solution flow into pores

adsorption

adsorption

diffusion

evaporation

Adsorption/desorption + diffusion

Drying


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


Impregnation of -Alumina with PtInfluence of Coadsorbing Ions

a b c

Increasing citric acid concentration

Pt/Al2O3 Al2O3


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


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


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


Chemical Vapour Deposition


Oil-Drop Coagulation

Organic phase

Aqueous phase

Oil overflow to recirculation

Oil

Water

Distributor coneSol

Product to ripening, washing, and drying

catcat03 - good info on support production

Documents

homogeneous

specific surface

ta ly

al um

2o3 al

active phase

ho si

activated