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University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Introductionto Catalysis
David W. Agar
Short Course
26thJune – 4thJuly 2003
Chemical Engineering Department
IISc Bangalore
University of Dortmund
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
University of DortmundFor those who were distracted from the engineering woodsby the chemical trees, a brief summary of yesterday‘s talk:
1. Transition metal – ligand complexes
and now back to more familiar engineering territory..
Hydroformylation – homogeneous catalysis for useful intermediates(RCH=CH2→RCH2CH2CHO)
2. Complex catalyst composition: - Co→Rh metallic active centre- Triphenylphosphine ligands- Triphenylphosphinesulfonate ligands
5. Two-phase catalysis – extraction of water soluble catalyst
3. Well-defined cyclic mechanism (Heck-Breslow)
4. Mild conditions (100°C, 10 bar), high selectivities (95% n-Aldehydes)
6. Reaction engineering: immobilisation, enhanced mass transfer
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
University of Dortmund
Course schedule:
26.06.03 Principles of catalysis
27.06.03 Ammonia synthesis catalysis
30.06.03 Automotive exhaust catalysis
01.07.03 Hydroformylation catalysis
02.07.03 Catalytic partial oxidation of propene
03.06.03 Catalysis in polymerisation
04.06.03 Enzymatic glucose isomerisation
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Propene production
[1992 mio.t]
USA 10.3Western Europe 9.7Japan 4.5Germany 2.0GUS 1.3
world capacity 40
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Propene production and consumption [1984]
(1) acetone, acrolein, acrylic acid, allyl chloride, carbon disulfide, chlorinated solvents, cresols, dichloropentadiene, epichlorhydrin, ethylene-propylene rubber, 4-methyl 1-pentene, oxalic acid, polymethyl methacrylate, paramins...
(2) Steam cracking and catalytic cracking. In 1986 the worldwide production capacity of propylene was 28.3·106 t/a with the following distribution:
geographic areas Western Europe United States Japan WorldUses (% product)
acrylonitrile 17 18 20 18cumene 9 9 5 9isopropanol 6 6 3 5oxo alcohols 13 8 10 11polypropylene 34 35 47 36propylene oxide 10 11 6 9oligomers 7 1 4micellaneous(1) 6 8 8Total 100 100 100 100
Sources (% product)steam cracking 86 53 89 75catalytic caracking 14 47 11 25Total 100 100 100 100
Production (106 t/a) 7.2 7.0 3.0 22.5Capacity (106 t/a)(2) 8.7 9.9 3.0 28.5Consumption (106 t/a) 7.1 6.8 2.9 21.5
11
United States 9.7 Western Europe 8.2 Middle East 0.2Canada 0.7 Eastern Europe 3.3 Japan 3.0Latin America 1.3 Africa 0.1 Asia and Far East 1.8
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
polymerisation47%+NH3/O2
12%
+CO/H2
10%+O2
10%
+benzene7%
+H2O4%
+O2
+Cl2
polypropylene
acrylonitrile
butanal
propylene oxide
cumene
isopropanol
acrylic acid
allyl chloride
isohexenedimerisation
propene
polyacrylonitrileacrylamideadiponitrile
acetone
polyacrylic acid,acrylatesepichlorhydrin
isoprene
phenolacetone
propylenglycololigomer
n-butanol2-ethylhexanol
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Catalytic partial oxidation of propenesubstrates catalysts products
propene +oxygen
acrolein
acrylicacid
acetone
propyleneoxide
acetic acid
1,5-hexa-diene
benzene
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Acrolein derivatives
acrolein
allyl alcohol+H2 (cat.)
acrylic acid+O2 (cat.)
methionine3 stages
pyridine+NH3
CHO
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Acrylic acid derivatives
acrylic acid
acrylates (n-Bu,Et,Me,2-EH)+alcohol
polyacrylic acidpolymeris.
copolymers+ alkenesacrylamide
salts+NH3,
NaOH
COOH
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Acrylic acid production
Acrylic acid derivativesPolyacrylic acid &saltsn-Butylacrylate
Ethylacrylate
Methyl & 2-Ethylhexylacrylatesspecialty acrylates
miscellaneous
Worldwide production: 1.2 (2.0) Mio.tpa
End uses [%]: USA Europe Japan
Surface coatings 42 35 34Textiles 23 18 16Acrylic fibres 6 7 14Adhesives 5 15 20Others* 24 25 16*superabsorber, detergents, water treatment, dispersants
Regional production of acrylic acid & acrylates (1982)
USA
Europe
JapanOther
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Life cycles of acrylic acid syntheses
propene oxidation
new processesReppe process
Cyanohydrin acrylonitrile & propiolactoneprocess
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Historical acrylic acid synthesesReppe process
• low efficiency of acetylene manufacture• toxic & polluting nature of Ni carbonyls
2
140 ,200
2 2 2 2 .bar C
NiBr CuBrC H CO H O CH CHCOOH
°
−+ + → =
2 4H SOaq.soln.
2 2 2 2 255-60°C 175°C
4 4
.
CH CH HCN HOCH CH CN CH CHCOOH
O NH HSO
− + → → =
+
Cyanohydrin process
• toxicity of HCN & ethene cyanohydrin• waste salt by-product
Ketene process
• toxicity of β-propiolactone• multistep synthesis
2 2 4
3 2 2 2750
2
.
H O H SOHCHO
CCH COOH CH C O CH C O CH CHCOOH
CH O
− +
°→ = = → − = → =
−
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Production of acrylic acid from acetylene
(BASF process -Reppe synthesis)
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Acrylic acid synthesis via propene oxidation
3 2 2 2 2
3 2 2 2 2
2 2 2
3 . 594.92
. 340.8
1. . 254.12
R
R
R
CH CH CH O CH CHCOOH H O H kJ
CH CH CH O CH CHCHO H O H kJ
CH CHCHO O CH CHCOOH H kJ
= + → = + ∆ = −
= + → = + ∆ = −
= + → = ∆ = −
Net Reaction:
Two step process:
• limited yield of single step process (50-60%)
• rapid deactivation of single step catalyst (TeO2)
• 1st step: Bi/Mo-Oxide - 300-400°C - >85% yield
• 2nd step: Mo/V-Oxide – 250-350°C - >96% yield
• gas composition: 10% propene, 50% air, 40% steam
• pressure 1.3-2 bar - residence time: 1-3 s.
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Acrolein
Degussa process
mixed aldol-condensation (obsolete)
CH3CHO + HCHO CH2=CHCHO + H2ONa-silicates/SiO2
300-320°C
Direct oxidation of propene
mechanism: via allyl-radicals
catalyst: bismuth molybdate
phosphorus molybdate
selectivity: ~80% (by-products: acrylic acid, acetic acid, acetaldehyde)
CH2=CHCH3 + O2 CH2=CHCHO + H2O ∆RH = -368 kJ/molCat.
350-450°C
+Fe-, Co-, Ti- oxides
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Development of acrolein catalyst
>77310-330Bi, Mo, Fe, P, Ni, Co, W, Si, K1970
60-70330-350Bi, Mo, Fe, P, Ni, Co1964
50-60350-400Bi, Mo, Fe1959
30-40450-500Bi, Mo1957
Acroleinyield [%]
Reactiontemp.[°C]
Catalystcomposition
Year
• catalyst lifetime: 3 years
• transition metals lower operating temperature
• Fe, Co, Ni regulate gas-lattice oxygen exchange
• P & K maintain selectivity
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Catalyic partial oxidation of propene
propene
acrolein
Propene oxidation on bismuth molybdates
hydrogenabstraction allyl radical
adsorption
Desorption
reoxid-ation
(high pO2)eqm.oxid.step
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Acrylic acid catalystproduction
Precipitation
Drying
Activation
activephase
microporosity
Mechanicalproperties of the catalyst pellet
Thermalproperties
porestructure
porestructure
active phase
catalystproperties
Precipitation
Drying
Calcination
Grinding
Adding of formu-lation excipients
Precompression
Shaping
Drying
Sieving
Activation/ Annealing
solution A solution B solution C(NH4)6Mo7O24·4H2OH3PO4
Ni(NO3)2 · 6H2OFe(NO3)2 · 6H2OSiO2
Bi(NO3)3 · 5H2O
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Development of acrolein oxidation catalyst
• catalyst lifetime: >7 years
• by-products: CO2, acetic acid, furfural, oligomers
• two stage structured temperature profile
Catalyst composition Reaction Acrolein Acrylic acid(O-free) temp.[°C] conversion [%] yield [%]
Mo12V1.9Al1.0Cu2.2 (Al-sponge) 300 100 97.5Mo12V3W1.2 (SiO2) 240 98.0 87.0Mo12V3W1.2Mn3 255 99.0 93.0Mo12V2W2Fe3 230 99.0 91.0Mo12V3W1.2Cu1Sb6 272 99.0 91.0Mo12V4.6Cu2.2W2.4Cr0.6 (Al2O3) 220 100 98.0Mo12V2(Li2SO4)2 300 99.8 92.4Mo12V4.8Cu2.2W2.4Sr0.5 (Al2O3) 255 100 97.5Mo12V2.4Cu0.24 (SiC) 290 99.5 94.8Mo12V3W1.2Ce3 288 100 96.1Mo12V4.7W1.1Cu6.3 360 99.0 96.0
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Acrylic acid synthesis via propene oxidation
Two-stageprocess
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Recuperative Heat ExchangeMulti-tubular reactor for partial oxidation reactions
Acrylic acid synthesis h salt bath = 2000 W/m2 • Kh gas = 150 ~ 200 W/m2 • K
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Temperature (& Concentration) profiles inreactors may be manipulated using:
B. Recuperationspatial segregation between reactionmedium & material/heat-sink/sourcee.g. multitubular reactor
T
z
A. Convectionaddition or withdrawal of sidestreams
e.g. cold-shot reactor
T
z
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
... or, less frequently:
C. Regenerationchronological segregation betweenreaction medium & material/heat -sink/sourcee.g. reverse flow reactor
T
z
D. Reactiondirect coupling of main reactionwith thermally/materially compatible supplementary reactione.g. oxydehydrogenation
T
z
C → DA → B
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
What are Hot-spots?Unwanted temperature maxima arising in tubular reactorswith exothermic reactions due to heat transfer limitations
Heat exchange area (A)~ 100 m²/m³Heat transfer coefficient (h)~ 100 W/m²K
Hot-spot adversely effects:- conversion- selectivity- safety- catalyst lifetime- choice of reactor materials
≤ 30K
≤ 100K
25 mm
≤ 25 000 tubes
Reactor feed
Coolant
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Characteristic dimensions of heterogeneouslycatalysed gas phase reactions in tubular reactors
• Chemical activity (Nanostructure)internal surface area ~ 100m²/g⇒ pore diameter ~ 10 nm
• Pore diffusion (Microstructure)Weisz-Modulus < 0,3 ⇒ ‘pellet diameter’ ~ 1mm
• Heat transport (Macrostructure)∆T < 50K ⇒ ‘tube diameter’ ~ 1cm
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Mechanisms of heat transfer in a fixed-bed
1a
1b2a,b
3a
3b
Heatflow
Fluid flow
1a
1b
2a
2b
3a 3b
1
2
3
Heat transfer in fixed-bed reactors
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Classification of the continuum modelsfor steady-state fixed bed reactors
sw
gw
err
eax
h,h,,D,:Parameterdispersion radialHT2:HT3
,:Parameterdispersion radial PH1:PH3
0
ldimensiona two
,,:Parametergradients internal HT1:HT2
,:Parameterboundary phase the at gradients reactor,flow plug Ideal:HT1
,:Parameterdispersion axial PH1:PH2
:Parameterreactorflow plug Ideal:PH1
0
ldimensiona one
ousheterogene shomogeneoupseudo
λλλ
+λ
+
≠∂∂
λ
+
λ+
=∂∂
≠≠==−
esr
grgrw
eg
g
ax
sgsgsgsg
D,h,,,kD,h
Dh,kU,
hkU,
DU,
U
TT;ccTT;cc
r
r
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Mean conversions & axial temperature profilein multitubular partial oxidation reactor
z (m)
x Am
xB
m
x Cm
xAm
xBm
xCm
T'm
T'm
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Multitubular partialoxidation reactor
Radial temperature profiles at various bed depths
T’=T
-To
Rr
Hot-spot scale-upproblems:
• catalyst activation
• thermoelement dis-tortions
• coolant side non-uni-formities
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t CUniversity of Dortmund - Chemical Engineering Department - Institute for Reaction Engineering
How can hot-spots be eliminated?Improved co-ordination between the rates
of heat generation & heat removal in reactor
Cooling
Reaction
Hydrodynamics
Microreactor
Benchmark:Multitubular
reactor
Debottlenecking Strategies:
- diminish catalyst activity• catalyst dilution
- enlarge heat exchange surface (A)• Linde-reactor
- raise heat transfer coefficient (h)• Fluidised bed
- increase both A & h• Microreactor• Millireactor
Fluidised bed
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Improved co-ordination of reaction &cooling using a fluidised bed reactor
Increased heat transfer coefficients due to efficient convective-regenerative particle transport mechanism
+ excellent isothermal behaviour (h~600 W/m²K)
+ higher degree of catalyst utilisation
+ facile catalyst regeneration
– very mechanically resilient catalyst needed
– limited hydrodynamic loading range
– undesirable backmixing
– scale-up?e.g. Ammonoxidation of propene to
acrylonitrile (Sohio process)
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Limitations of catalytic activity
• the chemical processes occurring at the active sites impose an upperlimit on reaction rate (~1µmol/g.cat.s*) and heat generation (~500kW/m³*)
• for chemically limited kinetics, a specific heat exchange surface of ~1,000 m²/m³ is usually adequate to ensure rapid heat removal.
⇒ Microreactors offer excessiveheat exchange surface
⇒ reactor dimensions of 1-5mm,i.e. ‘Millireactors’
* for typical industrial synthesis reactions W.Gerhardt, DECHEMA-GVC, Wernigerode, 06.04.00
0,01
0,1
1
10
100
0,001 0,01 0,1 1 10 100 1000
k [1/s]
d [m
m]
Da =2NTU =100Nu = 3,7a =10-5 m²/s
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Developments
• extension to similar reaction systems e.g. methacrylic acid
• use of propane instead of propene
• operation in rich & even ‚ex‘- composition regionExplosion limits: 2.0 LEL-11.1(15.3) UEL % C3H6
• use of microreactors to improve heat removal
• cut losses due to unwanted polymerisation
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Methyl MethacrylatePreviously
Propylene
Cumene
Acetone
Cyanhydrine
Methacryl Amide
Methyl Methacrylate
Benzene
Hydrocyanic Acid
Sulfuric Acid
Methanol
Now
Ethylene
Propionaldehyde
Methacrolein
Methacrylic Acid
Methyl Methacrylate
CO/H2
Formaldehyde
Air
Methanol
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
Acrylate via acrylic acid esterification
Yield: 95% based on acrylic acid
University of Dortmund – Chemical Engineering Department – Chair for Reaction Engineering
University of Dortmund
I t C
University of DortmundCourse schedule:
26.06.03 Principles of catalysis
27.06.03 Ammonia synthesis catalysis
30.06.03 Automotive exhaust catalysis
01.07.03 Hydroformylation catalysis
02.07.03 Catalytic partial oxidation of propene
03.06.03 Catalysis in polymerisation
04.06.03 Enzymatic glucose isomerisation
Disposable cats?