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Catalyst Selectivity Synthesis gas applications

CH 3 OH. CH 4. Ni. Cu. H 2 / CO. Cu + Co. Fe, Co. C n H 2n+1 OH (n = 1 - 6). C n H 2n+2 C n H 2n. Catalyst Selectivity Synthesis gas applications. b. 1.0 0.8 0.6 0.4 0.2 0.0. Methanol Yield (g cm -3 h -1 ). r (rel). p GHSV T. = 70 bar = 35000 h -1 = 515 K.

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Catalyst Selectivity Synthesis gas applications

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  1. CH3OH CH4 Ni Cu H2 / CO Cu + Co Fe, Co CnH2n+1OH (n = 1 - 6) CnH2n+2 CnH2n Catalyst SelectivitySynthesis gas applications Catalysis and Catalysts - Activity, Selectivity and Stability

  2. b 1.0 0.8 0.6 0.4 0.2 0.0 Methanol Yield (gcm-3h-1) r (rel) pGHSV T = 70 bar = 35000 h-1 = 515 K CO + 2 H2 CH3OH 0 500 1000 Time (h) 0 3 6 9 12 15 Time (h) Examples of Catalyst Deactivation c FCC Methanol Synthesis a HDS S-344 (660 K) 5 k1.85 (gcm-3h-1%S-0.85) S-324 (655 K) 0 0 1000 1800 Catalysis and Catalysts - Activity, Selectivity and Stability Time (h)

  3. d C12H26 C12H24 + H2 2 30 pH pHC LHSV T = 1.35 bar = 0.10 bar = 1 h-1 = 745 K Catalyst Pt (0.2%) / Al2O3 20 Conversion (% olefins/initial paraffins) + 0.17% W + 0.17% Re + 0.04% Ru 10 + 0.04% Ir Pt only 0 100 200 Time (h) Catalytic Reforming (Gasoline Production) Deactivation due to coke deposition Alloying quite successful Catalysis and Catalysts - Activity, Selectivity and Stability

  4. -1 0 1 2 3 4 5 6 7 8 10 10 10 10 10 10 10 10 10 10 Hydrocracking HDS Catalytic reforming FCC EO C dehydrogenation MA 3 Formaldehyde Aldehydes Hydrogenations Acetylene Oxychlorination Fat hardening NH oxidation 3 SCR Time / seconds TWC -1 0 1 2 3 4 5 6 7 8 10 10 10 10 10 10 10 10 10 10 1 hour 1 day 1 year Time-Scale of Deactivation Most bulk processes 0.1-10 year Batch processes hrs-days Catalysis and Catalysts - Activity, Selectivity and Stability

  5. Deactivation of catalystsirreversible loss of activity • Types of deactivation: • Poisoning: strong chemisorption of impurity in feed (Inhibition: competitive adsorption, reversible) • Fouling: secondary reactions of reactants or products, • ‘coke’ formation • Thermal degradation: sintering (loss of surface area), evaporation • Mechanical damage • Corrosion/leaching Fouling or ‘self-poisoning’ often cause of deactivation Catalysis and Catalysts - Activity, Selectivity and Stability

  6. Types of Deactivation Catalysis and Catalysts - Activity, Selectivity and Stability

  7. What are poisons? Examples High M.W. product producer Strong chemisorber Surface active metal or ion Sintering accelerator • Bases • H2S on Ni • NH3 on Si-Al • ‘Toxic compounds’ • (free electron pair) • Cu on Ni • Ni on Pt • Pb or Ca on Co3O4 • Pb on Fe3O4 • Fe on Cu • Fe on Si-Al • from pipes • acetylenes • dienes • H2O (Al2O3) • Cl2 (Cu) from feed or product Catalysis and Catalysts - Activity, Selectivity and Stability

  8. I II III activity Amount of poisoning Catalytic activity coke metals Time-on-Stream Typical Stability Profiles in Hydrotreating • Initially high rate of deactivation • mainly due to coke deposition • Subsequently coke in equilibrium • metal deposition continues Catalysis and Catalysts - Activity, Selectivity and Stability

  9. Influence of Pore Size on Vanadium DepositionHydrotreating of Heavy Feedstock Catalysis and Catalysts - Activity, Selectivity and Stability

  10. Carbon Formation on Supported Metal Catalyst Catalysis and Catalysts - Activity, Selectivity and Stability

  11. Carbon Filaments due to CH4 Decompostion 873 K, Ni/CaO catalyst Catalysis and Catalysts - Activity, Selectivity and Stability

  12. SBET (m2/g) Tcalc (K) Sintering of Alumina upon Heating Sintering Reduction of surface area Catalysis and Catalysts - Activity, Selectivity and Stability

  13. particles migrate coalesce migrating metastable stable Sintering of Supported Catalysts monomer dispersion 2-D cluster 3-D particle vapour surface interparticle transport • Dependent on: • carrier properties • temperature • composition of bulk fluid • …. Predictable? Catalysis and Catalysts - Activity, Selectivity and Stability

  14. THüttig and TTamman Sintering is related to melting THüttig : defects become mobile Ttamman: bulk atoms become mobile Tmelting THüttig Ttamman Al2O3 2318 695 1159 Cu 1356 407 678 CuO 1599 480 800 CuCl2 893 268 447 Catalysis and Catalysts - Activity, Selectivity and Stability

  15. Deactivation due to Mechanical Damage • during transport, storage, packing, use • loading in barrels, unloading, packing of reactor • in reactor: weight of column of particles • attrition in moving systems (fluid beds, moving beds) • during start-up, shut-down • temperature variations (thermal shocks) • chemical transformations • sulphiding, reduction • regeneration: high T, steam Catalysis and Catalysts - Activity, Selectivity and Stability

  16. Corrosion / Leaching - Examples • Alumina • dissolves at pH > 12 and pH < 3, so close to these pH-values corrosion and leaching • use carbon instead at very low or very high pH • Sulphiding of oxides in the presence of H2S • Liquid-phase catalysis • in heterogenisation of homogeneous catalysts activity was due to the leached compounds rather than the solid phase • in solid-catalysed fat hydrogenation traces of the Ni catalyst appear in the product; with Palladium this is not the case Catalysis and Catalysts - Activity, Selectivity and Stability

  17. conversion or kobs process time Influence of Deactivation on Reaction Rate initial level ‘constant’ ‘variable variable • blocking of pores • loss of surface area • loss of active sites Fouling Sintering Catalysis and Catalysts - Activity, Selectivity and Stability Poisoning

  18. Deactivation - depends on? Catalysis and Catalysts - Activity, Selectivity and Stability

  19. Stability too low; What to do? • Understand the cause of deactivation • Take logical measures • at catalyst level • sound reactor and process design • good engineering practice Catalysis and Catalysts - Activity, Selectivity and Stability

  20. Catalyst Level • improvement of active phase or support • e.g. use titania instead of alumina in SCR • optimisation of texture • use wide-pore catalyst in HDM to prevent pore blocking • profiling of active phase • e.g. egg-yolk profile will protect active sites against poisoning and fouling if these are diffusion-limited and the reaction is not • reduce sintering by structural promoters or stabilisers • make catalyst more attrition resistant • encapsulation of active material in porous silica shell increases attrition resistance without influencing activity Catalysis and Catalysts - Activity, Selectivity and Stability

  21. Tailored Reactor and Process Design Relation between time-scale of deactivation and reactor type Time scale Typical reactor/process type years fixed-bed reactor; no regeneration months fixed-bed reactor; regeneration while reactor is off-line weeks fixed-bed reactors in swing mode, moving-bed reactor minutes - days fluidised-bed reactor, slurry reactor; continuous regeneration seconds entrained-flow reactor with continuous regeneration Catalysis and Catalysts - Activity, Selectivity and Stability

  22. Different Engineering Solutions allowing for Regeneration Propane dehydrogenation - deactivation by coke formation Catalysis and Catalysts - Activity, Selectivity and Stability

  23. Good Engineering Practice • Feed purification for removal of poisons • upstream reactor • poison trap inside reactor on top of catalyst (if flow is downward) • overdesign of reactor if catalyst itself is poison trap • Optimisation of reaction conditions • use of excess steam in steam reforming decreases coke deposition • catalyst deactivation in selective hydrogenation of CCl2F2 strongly increases above 500 K  operate below 510 K • Optimisation of conditions as function of time-on-stream • compensate for activity loss by increasing T with time Catalysis and Catalysts - Activity, Selectivity and Stability

  24. Examples Catalysis and Catalysts - Activity, Selectivity and Stability

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