CATALYST DEACTIVATION AND REGENERATION
SONAM V. SANCHETIM. Tech. Green Technology
14GRT201529/11/2014
Catalyst:
“A catalyst is a substance that changes the rate of chemical reaction without
itself appearing in the products.”
Helps to attain equilibrium by reducing PE barrier in the reaction path.
Provides an alternate route for reactant molecule to become products with
a lower activation energy and different transition state.
Enters the reaction cycle and regenerated back without getting consumed.
Ideally remains unchanged after the completion of reaction.
But does it remain unchanged practically?
INTRODUCTION
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INTRODUCTIONWhat is catalyst deactivation?Loss in catalytic activity due to chemical, mechanical or thermal processes.Heterogeneous catalysts are more prone to deactivation.
Mechanism Type Brief definition/descriptionPoisoning Chemical Strong chemisorption of species on catalytic sites, thereby
blocking sites for catalytic reaction.Fouling, Coking Mechanical
or Chemical
Physical deposition of species (carbonaceous material) from fluid phase onto the catalytic surface and in catalyst pores.
Sintering(Thermal degradation)
Thermal Thermally induced loss of catalytic surface area, support area, and active phase–support reactions.
Chemical reactions; AndPhase transformations
Chemical Chemical Reaction of fluid, support, or promoter with catalytic phase to produce inactive phase.Reaction of gas with catalyst phase to produce volatile compound.
Attrition/Crushing Mechanical Loss of catalytic material due to abrasion, Loss of internal surface area due to mechanical-induced crushing of catalyst
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DEACTIVATION MECHANISMS
Not only blocks the active sites, but also induce changes in the electronic or
geometric structure of the surface.
Poisons mainly include Groups VA and VIA elements (N, P, As, Sb, O, S, Se, Te) Group VIIA elements (F, Cl, Br, I ) Toxic heavy metals and ions (Pb, Hg, Bi, Sn, Zn, Cd, Cu, Fe) Molecules, which adsorb with multiple bonds(CO, NO, HCN, benzene)
Types: Selective Anti-selective Non-Selective
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POISONING
Reversible Non- reversible
•Bartholomew C.H., “Mechanisms of Catalyst Deactivation”, Appl. Catal. A: General, 212, 17-60 (2001).
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Reaction Catalyst Poisons
Catalytic Cracking Silica-alumina, Zeolites Organic bases, hydrocarbons heavy metals
Hydrogenation , dehydrogenation
Nickel, Platinum, Palladium
Compounds of S, P, As, Zn, Hg, halides, Pb,
NH3, C2H2
Steam reforming of methane, naphtha
Nickel H2S, As
Ammonia synthesis Iron or Ruthenium O2, H2O, CO, S, C2H2, H2O
Fischer–Tropsch synthesis
Cobalt or Iron H2S, COS, As, NH3, metal carbonyls
Hydrocracking Noble metals on zeolites NH3, S, Se, Te, P
Industrial examples of catalyst deactivation due to poisoning
Example: Sulphur as poison in methane synthesis using Ni/γ-Al2O3 Catalyst
• Legras B., Ordomsky V.V., Dujardin C., Virginie M., Khodakov A.Y., “Impact and Detailed Action of Sulfur in Syngas on Methane Synthesis on Ni/γ-Al2O3 Catalyst”, ACS Catal., 4, 2785−2791 (2014).
Advantages of poisoning
Pt-containing naphtha reforming catalysts are often pre-sulfided to minimize
unwanted cracking reactions.
S and P are added to Ni catalysts to improve isomerisation selectivity in the
fats and oils hydrogenation industry.
V2O5 is added to Pt to suppress SO2 oxidation to SO3 in diesel emissions
control catalysts.
S and Cu added to Ni catalyst in steam reforming to minimize coking.
For selective hydrogenation from alkynes to alkenes, Lindlar catalyst
(Pt/CaCO3) is partially poisoned with Pb and quinoline.
6• Bartholomew C. H., Farrauto R. J., “Fundamentals of Industrial Catalytic Processes” Second edition, John Wiley & Sons, Inc., pp 269-323,(2006).
Physical deposition of species from the fluid phase onto the catalyst surface is
fouling
Fouling of catalyst due to carbon deposition is coking. coke may contains
soot, produced in gas phase (non-catalytic carbon),
ordered or disordered carbon, produced on an inert surface (surface carbon),
ordered or disordered carbon, produced on surface which catalyses formation
of carbon (catalytic carbon),
condensed high molecular weight aromatic compounds which may be liquid or
solid (tar).
Coking can be studied under two headings:
Coke formation on supported metal catalysts
Coke formation on metal oxide and sulphide catalysts 7
DEACTIVATION MECHANISMS FOULING/COKING
Formation of coke on supported metal catalysts Chemically by chemisorption or carbide formation Physically due to blocking of surface sites, metal crystalline encapsulation ,
plugging of pores and destruction of catalyst pallets
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Cα Adsorbed, atomic (surface carbide); Cβ Polymeric, amorphous films or filaments
Cv Vermicular filaments, fibers, and/or whiskers ; Cγ Nickel carbide (bulk)
Cc Graphitic (crystalline) platelets or films
Formation, transformation and
gasification of carbon on metal surface
Formation of coke on oxides and sulfides Carbonaceous materials (coke precursor) , feed for cracking reaction lead to
formation of coke Catalyzed by acidic sites. Dehydrogenation and cyclization reactions of carbocation intermediates
formed on acid sites lead to aromatics which react further to higher molecular weight polynuclear aromatics and condense as coke.
Because of the high stability of the polynuclear carbocations, they can continue to grow on the surface for a relatively longer time before a termination reaction occurs through the back donation of a proton.
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Polymerization of Olefins
Cyclization of Olefins
Formation of polynuclear aromatics
Zeolite Coking: Shape-selective processes Formation and retention of heavy aromatic clusters in pores and pore
intersections Acid-site poisoning and pore blockage participate in the zeolite deactivation
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Four possible modes of deactivation by
carbonaceous deposits in HZSM5
(1) reversible adsorption on acid sites
(2)irreversible adsorption on sites with
partial blocking of pore intersections
(3) partial steric blocking of pores,
(4)extensive steric blocking of pores
by exterior deposits.
• Guisnet M., Magnoux P., Martin D., in: Bartholomew C.H.,Fuentes G.A. (Eds.), “Catalyst Deactivation”, Stud. Surf.Sci. Catal., Vol. 111, Elsevier, Amsterdam, p. 1, (1997).
Support Sintering
Driving force is to lower the surface energy and the transport of material
Coalescence of particles, particle growth and elimination of the pores.
Reaction atmosphere also promotes sintering.eg. Water vapour
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DEACTIVATION MECHANISMS SINTERING
γ-Alumina to δ-alumina to α-phase via θ-phase
A model representing surface dehydroxylation from contact region of two adjacent particles of alumina.
• Neyestanaki A.K., Klingstedt F., Salmi T., Murzin D.Y., “Deactivation of postcombustion catalysts, a review”, Fuel, 83, 395–408 (2004).
Metal sintering
Temperature: Sintering rates are exponentially dependent on T.
Atmosphere: Decreases for supported Pt in the following order: NO, O2, H2, N2
Support: Thermal stability of supports Al2O3 > SiO2 > carbon for given metal
Pore Size: Sintering rates higher in case of non-porous materials
Additives: C, O, CaO, BaO, CeO2 decrease atom mobility
Promoters: Pb, Bi, Cl, F, or S; oxides of Ba, Ca, or Sr are trapping agents that
decrease sintering rates.
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Reactions of gas/vapour with solid to produce volatile compounds Direct volatilization temperatures for metal vaporization exceed 1000°C metal loss via formation of volatile metal compounds can occur at moderate
temperatures (even room temperature)
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DEACTIVATION MECHANISMS CHEMICAL TRANSFORMATIONS & PHASE TRANSITIONS
Gaseous environment Compound type Example of compound
CO, NO Carbonyls , nitrosyl carbonyls Ni(CO)4, Fe(CO)5, (0-300oC)
O2 Oxides RuO3(25oC), PbO (>850oC), PtO2 (>700oC)
H2S Sulphides MoS2 (>550◦C)
Halogens Halides PdBr2, PtCl4, PtF6
Reactions of gas/vapour with solid to produce inactive phases Chemical modifications are closely related to poisoning But the loss of activity is due to the formation of a new phase altogether.
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Catalytic Process Gas-vapour composition Catalysts Inactive phases formed
Automobile emission
control N2,O2,HCS,CO NO Pt-Rh / Al2O3 RhAl2O4
Ammonia synthesis
and regenerationH2,N2,O2,H2O Fe/K/Al2O3 FeO
Catalytic cracking HCs,H2,H2O La-Y zeolite H2O induced Al migration
from zeolite causing zeolite
destruction
Fischer –Tropsch CO, H2O, H2, HCs Co/SiO2 CoO.SiO2 and collapse of
SiO2 , by product water
Steam reforming and
regeneration in H2O
CH4,CO,CO2,H2, H2O Ni/Al2O3 Ni2Al2O4
Catalytic process Catalytic Solid Deactivating Chemical reaction
Ammonia Synthesis Fe/K/Al2O3 Formation of KAlO2 on catalytic surface
Catalytic cumbustion PdO/Al2O3,PdO/ZrO3 PdOPd at temp.>800oC
Fischer –Tropsch Fe/K,Fe/K/CuO Transformation of active carbides to inactive
carbides
Benzene to maleic
anhydrideV2O5-MoO3 Decreased selectivity due to loss in MoO3 and
formation of inactive vanadium compounds.
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Solid-state reactions
Crushing of granular, pellet or monolithic catalyst forms due to a load.
Attrition, the size reduction and/or breakup of catalyst granules or pellets to
produce fines, especially in fluid or slurry beds.
Erosion of catalyst particles or monolith coatings at high fluid velocities. collisions of particles with each other or with reactor walls,
shear forces created by turbulent eddies or collapsing bubbles (cavitations) at
high fluid velocities
gravitational stress at the bottom of a large catalyst bed.
Thermal stresses occur as catalyst particles are heated and/or cooled rapidly
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DEACTIVATION MECHANISMS MECHANICAL DEGRADATION
Surface area ; Pore volume ; Pore size distribution
The deactivation of Cu/ZnO/Al2O3 catalyst used in a methanol synthesis because of
sintering. After reaction overall surface area of a catalyst and a metal area of Cu decreases
Gas mixture (Oxygen diluted in Helium) is used to perform analysis
Dynamic TPO with on-line mass spectrometry is used to monitor oxygen consumption and which confirms percent coking occurred in a catalyst
Important technique to measure coking
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CHARACTERIZATION BET Surface area
Catalyst Fresh Cu/ZnO/Al2O3 Spent Cu/ZnO/Al2O3
BET surface area (m2/g) 96.0 41.5
Cu surface area (m2/g) 25.4 11.1
TPO( Temperature programmed oxidation)
• Sun J.T., Metcalfe I.S., and Sahibzada M., “Deactivation of Cu/ZnO/Al2O3 Methanol Synthesis Catalyst by Sintering", Ind. Eng. Chem. Res., 38, 3868-3872 (1999).
Give information of external morphology (texture), surface topography.
Provide information on the structure, texture, shape and size of the sample.
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SEM (Scanning Electron Microscopy)
SEM images of de-NOx catalyst V2O5-WO3/TiO2 before and after deactivation
TEM (Transmission Electron Microscopy)
TEM images of fresh and deactivated Co-alumia catalyst in Fischer-Tropsch synthesis
• Sahib A.M., Moodleya D.J., Ciobica I.M., Haumana M.M., Sigwebela B.H., Weststrate C.J., Niemantsverdriet J.W., Loosdrecht J., “Fundamental understanding of deactivation and regeneration of cobalt Fischer–Tropsch synthesis catalysts”, Catal. Today, 154, 271 (2010).
Identify the elemental composition of materials EDX spectra of V2O5-WO3/TiO2 catalyst a: fresh catalyst b: deactivated catalyst
EDX is used as attachment with SEM and TEM so that to give elemental composition along with surface analysis.
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EDX (Energy Dispersive X-ray analysis)
• Yu Y., He C., Chen J., Meng X., “Deactivation mechanism of de-NOx catalyst (V2O5-WO3/TiO2) used in coal fired power plant”, J. Fuel Chem. Technol., 40, 11, 1359−1365 (2012).
Investigation of the bulk phase composition, degree of crystallinity, unit cell parameters, new crystalline phases of solid catalysts samples
Determine mass loss or gain due to decomposition, oxidation, or loss of volatiles
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XRD (X-ray Diffraction)
X-ray diffraction patterns of catalyst V2O5-WO3/TiO2 (De-NOx catalyst)a: fresh catalyst, b: deactivated catalyst
TGA (Thermogravimetric analysis)
Thermogravimetry analysis of De-NOx
catalystsa: fresh catalyst, b: deactivated catalyst
• Yu Y., He C., Chen J., Meng X., “Deactivation mechanism of de-NOx catalyst (V2O5-WO3/TiO2) used in coal fired power plant”, J. Fuel Chem. Technol., 40, 11, 1359−1365 (2012).
FCC catalyst consists of a mixture of an inert matrix (kaolin), an active matrix (alumina), a binder (silica or silica–alumina) and a HY zeolite.
Reversible deactivation in FCC
Coking Charge properties Operating conditions Zeolite acidity Zeolite porous structure
Oxygen poisoning Oxygenated molecules present in feedstock
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DEACTIVATION CASE STUDY Fluidized catalytic cracking (FCC)
• Cerqueira H.S., Caeiro G., Costa L., Ramôa Ribeiro F., “Deactivation of FCC catalysts”, J. Mol. Catal. A: Chemical, 292 ,1 (2008).
Nitrogen Poisoning Impurities in feed like alkyl derivatives of pyridine, quinoline, isoquinoline,
acridine and phenanthridine. Prevented by hydrotreatment, adsorption, liquid/liquid extraction,
neutralization, use of nitrogen-resistant FCC catalysts.
Sulphur Poisoning Non hydrotreated feeds like alkylated thiophenes, benzothiophenes and
dibenzothiophenes
Sulphur contained coke on oxidation in regenerator produces toxic SOx
22• Cerqueira H.S., Caeiro G., Costa L., Ramôa Ribeiro F., “Deactivation of FCC catalysts”, J. Mol. Catal. A: Chemical, 292 ,1 (2008).
Irreversible deactivation in FCCHydrothermal dealumination During reaction and regeneration temperatures 700-800oC in presence of steam
Metal Poisoning Most common are V, Ni, Na and Fe Trace elements such as Fe, Zn, Pb, Cu, Cd, Cr, Co, As, Sb, Te, Hg, Au or Ag Deposition of these metal porphyrins and increase coking V and Na damage alumina in presence of steam at high temperature.
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a. Dehydroxylation
b. Al-segregation
• Cerqueira H.S., Caeiro G., Costa L., Ramôa Ribeiro F., “Deactivation of FCC catalysts”, J. Mol. Catal. A: Chemical, 292 ,1 (2008).
Poisoning Purification of feed (desulfurization followed by ZnO guard bed) Additives, which selectively adsorb poison Reaction conditions, which lower adsorption strength
Coking Avoid coke precursors
Add gasifying agents (e.g. H2, H2O)
Incorporate catalyst additives to increase rate of gasification (eg. In steam
reforming. MgO, K2O, U3O8, promote the gasification of carbon by facilitating
H2O adsorption.
Decrease acidity of oxide or sulfide Use shape selective molecular sieves Control on temperature
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PREVENTION
Sintering Lower reaction temperature Use of thermal stabilizers (e.g. addition of Ba , Zn ,La ,Mn as
promoters that improves thermal stability of alumina); (Ru, Rh to Ni as thermal stabilizer)
Avoid water and other substances that facilitate metal migration.
Mechanical degradation Increasing strength by advanced preparation methods Adding binders to improve strength and toughness Coating aggregates with a porous but very strong material such as
ZrO2
Chemical or thermal tempering of agglomerates to introduce compressive stresses, which increase strength and attrition resistance
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Some frequently used regeneration techniques include (regeneration of sulfur-poisoned Ni, Cu, Pt, and Mo) treatment with
O2 at low oxygen partial pressure
Steam at 700-800oC
80% removal of surface sulfur from Mg- and Ca-promoted Ni steam reforming
catalysts occurs at 700°C in steam.26
REGENERATION Regeneration of poisoned catalysts
•Hashemnjad S.M, Parvari M., “Deactivation and Regeneration of Nickel-Based Catalysts for Steam-Methane Reforming”, Chin. J. Catal., 32, 273 (2011).
Gasification with O2, H2O, CO2, and H2
• C + O2 CO2
• C + H2O CO + H2
• C + CO2 2CO
• C + 2H2 CH4
Promoters can be added to increase rate of gasification (eg.K or Mg in Ni for steam reforming)
Washing with chlorobenzenes or liquefied propanes
Other foulants can also be removed by such as shaking or abrasion.
Metal-catalyzed coke removal with H2 or H2O can occur at a temperature as
low as 400°C
But more graphitic or less reactive carbons or coke species in H2 or H2O may
require temperatures as high as 700-900°C 27
Regeneration of coked catalysts
• Trimm D.L., “The regeneration or disposal of deactivated heterogeneous catalysts”, Appl. Catal. A: General, 212, 153–160 (2001).
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Redispersion of sintered catalysts
High-temperature treatment oxychlorination
Sintering is very hard to reverse
Redispersion of alumina-supported platinum is also possible in a chlorine-free
oxygen atmosphere if chlorine is present on the catalyst
A mechanism for platinum redispersion by oxygen and chlorine
• Bartholomew C. H., Farrauto R. J., “Fundamentals of Industrial Catalytic Processes” Second edition, John Wiley & Sons, Inc., pp 269-323,(2006).
20 wt % Co on alumina promoted with 0.5 wt % Pt prepared by slurry phase impregnation
Deactivation Poisoning by means of sulphur and nitrogen containing compound Impact of nitrogen containing compounds can be reversed with a mild hydrogen
treatment. Inactive phase formation with reaction with Oxygen i.e. cobalt oxide formation Cobalt aluminate or silicate formation accelerated by water (does not significantly
influence) Sintering contribute 30% loss in activity Coking due to dissociation of CO Coking is important deactivation mechanism in F-T Synthesis due to both bulk
cobalt carbide and polymeric carbon 29
CASE STUDY OF CATALYST DEACTIVATION AND REGENERATION
Fischer-Tropsch synthesis catalyst: Supported Co catalyst
Regeneration procedure:• The spent catalyst was solvent washed with heptane at 100 o C to remove excess
wax.
• The catalyst sample was subsequently subjected to a calcinations (i.e. oxidation)
step in a fluidized bed calcination unit, using an air/N2 mixture and the following
heating program: 2 ◦C/min to 300oC, 6–8 h hold at 300 o C.
• The oxygen concentration was gradually increased from 3 to 21% O2/N2 to control
the exotherm.
• The oxidized catalyst sample was subsequently subjected to a reduction in pure hydrogen in a fluidised bed unit using the following heating program: 1 oC/min to 425 o C, 15 h hold at 425 ◦C. The reduced catalyst was off loaded into wax.
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1 • Dewaxing
2 • Oxidation
3 • Reduction• Sahib A.M., Moodleya D.J., Ciobica I.M., Haumana M.M., Sigwebela B.H., Weststrate C.J., Niemantsverdriet J.W., Loosdrecht J., “Fundamental understanding of deactivation and regeneration of cobalt Fischer–Tropsch synthesis catalysts”, Catal. Today, 154, 271 (2010).
Regeneration results
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TPO analyses of a 56-day-old spent catalyst following hydrogenation at 350 ◦C as compared to the same sample following regeneration
Comparison between TEM images of fresh, deactivated and regenerated cobalt catalyst.
The oxidative regeneration procedure is able to reverse the major deactivation mechanism, i.e. sintering, carbon deposition and surface reconstruction.
• Moodley D.J., Loosdrecht J., Saib A.M., Overett M.J., Datye A.K., Niemantsverdriet J.W., “Carbon deposition as a deactivation mechanism of cobalt-based Fischer–Tropsch synthesis catalysts under realistic conditions”, Appl. Catal. A:Gen, 354, 102(2009).
In addition of having high catalyst activity, selectivity; catalyst deactivation and
ease of regeneration is very important topic for industrial catalyst development.
The regeneration of deactivated heterogeneous catalysts depends on chemical,
economic and environmental factors.
Regeneration of precious metals is always necessary.
Disposal of catalysts containing non-noble heavy metals (e.g. Cr, Pb, or Sn) is
environmentally problematic and should be regenerated.
Generally poisoned, coked, fouled catalysts are regenerated by washing,
abrasion and careful oxidation.
In case of sintering; best way is to add promoters and additives to prevent
sintering
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CONCLUSION
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THANK YOU….
