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Catalyst deactivation and regeneration

For enhancing the rate of chemical reaction use of catalyst is mandatory. Study of catalyst activity after use is described in the slides

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Catalyst deactivation and regeneration

  1. 1. SONAM V. SANCHETI M. Tech. Green Technology 14GRT2015 29/11/2014
  2. 2. 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 2
  3. 3. INTRODUCTION What 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/description Poisoning 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; And Phase 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 3
  4. 4. 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 4  POISONING  Reversible  Non- reversible •Bartholomew C.H., “Mechanisms of Catalyst Deactivation”, Appl. Catal. A: General, 212, 17-60 (2001).
  5. 5. 5 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).
  6. 6. 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).
  7. 7. 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
  8. 8. 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 8 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
  9. 9. 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. 9 Polymerization of Olefins Cyclization of Olefins Formation of polynuclear aromatics
  10. 10. 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 10 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).
  11. 11. 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 11 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).
  12. 12. 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. 12
  13. 13. 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) 13 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
  14. 14. 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. 14 Catalytic Process Gas-vapour composition Catalysts Inactive phases formed Automobile emission control N2,O2,HCS,CO NO Pt-Rh / Al2O3 RhAl2O4 Ammonia synthesis and regeneration H2,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
  15. 15. Catalytic process Catalytic Solid Deactivating Chemical reaction Ammonia Synthesis Fe/K/Al2O3 Formation of KAlO2 on catalytic surface Catalytic cumbustion PdO/Al2O3,PdO/ZrO3 PdOPd at temp.>800oC Fischer –Tropsch Fe/K,Fe/K/CuO Transformation of active carbides to inactive carbides Benzene to maleic anhydride V2O5-MoO3 Decreased selectivity due to loss in MoO3 and formation of inactive vanadium compounds. 15 Solid-state reactions
  16. 16. 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 16 DEACTIVATION MECHANISMS  MECHANICAL DEGRADATION
  17. 17. 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 17 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).
  18. 18. Give information of external morphology (texture), surface topography. Provide information on the structure, texture, shape and size of the sample. 18  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).
  19. 19. 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. 19  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).
  20. 20. 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 20 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 catalysts a: 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
  21. 21. 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 21 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).
  22. 22. 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).
  23. 23. Irreversible deactivation in FCC Hydrothermal 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. 23 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).
  24. 24. 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 24 PREVENTION
  25. 25. 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 25
  26. 26. 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).
  27. 27. 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).
  28. 28. 28  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).
  29. 29. 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
  30. 30. 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. 30 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).
  31. 31. Regeneration results 31 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).
  32. 32. 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 32 CONCLUSION
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