1.Theory and Operation of Methanol Synthesis Gerard B. Hawkins Managing Director, CEO
2. Introduction Flowsheets Catalysts Catalyst Deactivation 3. Methanol Flowsheet 4. Methanol Flowsheet Natural Gas Sulphur Removal Saturator Reforming Air Condensate Compression BFW Demin Water CW CW Synthesis Distillation MP Steam Purge to Fuel Crude Methanol Product Methanol Fusel Oil Refining Column Bottoms HP Steam 5. Methanol Synthesis Reactions Purpose of synthesis loop is to convert H2, CO and CO2 to methanol CO + 2H2 CH3OH H = - 90.64 kJ/kmol CO + H2O CO2 + H2 H = - 41.17 kJ/kmol Both reactions are revisible and exothermic Combine to give CO2 + 3H2 CH3OH + H2O H = - 49.74 kJ/kmol 6. Methanol Synthesis Reactions Methanol is produced from CO2 Proven by use of radioactive C14 CO is shifted to CO2 and then to methanol Rate of reaction is given by 5.0 2 2]./[3 ][ ][ .exp. OHP COP Activity dt OHdCH TRE 7. Equilibrium Equilibrium defined by Which can be rearranged to Which is far more useful [ ] [ ] [ ] [ ]3 22 23 . . HPCOP OHPOHCHP Kp = [ ] [ ] [ ]3 22 2 3 . ][. HPCOP OHPKp OHCHP = 8. Effect of Temperature on Kp 9. Effect of Temperature on CH3OH % 10. Effect of Pressure on CH3OH % 11. Definition of ATE 12. Effect of Operating Parameters on Equilibrium and Kinetics For good conversion need following conditions Parameter Equilibrium Kinetics Temperature Low High Pressure High High Catalyst Activity High High So there is a conflict for temperature 13. Effect of Operating Temperature on Equilibrium and Kinetics 14. Concept of Maximum Rate Line If reaction follows the max rate line then minimum catalyst volume for maximum production 15. Methanol Synthesis Catalyst VSG-M101 Available as VSG-M101 Synthesis of methanol from mixtures of CO, CO2 and H2 Copper on a ZnO-Al2O3 support Proprietary metal oxides are added to prevent sintering and improve dispersion of copper crystallites 16. Methanol Synthesis Catalyst History Over 30 years manufacturing experience 45,000+ m of methanol synthesis catalyst made 4,000 m of VSG-M101series catalyst currently installed in PRC 17. Methanol Synthesis Catalyst Properties Effect Property Activity - Copper surface area Life - Microstructure Strength - Macrostructure Selectivity - Formulation 18. Methanol Synthesis Catalyst Properties Typical composition for VSG-M101 CuO 64 wt% Al2O3 10 wt% ZnO 24 wt% 19. Methanol Synthesis Catalyst Properties Spherical Pellet Diameter 5 mm Height 4 - 5 mm Bulk density 1,400 - 1,600 kg/m Radial crush strength >205N/m 20. Methanol Synthesis Catalyst Poisons Poison Sulfur Chlorine Iron Elemental Carbon Metals e.g. V, K, Na Nickel Ammonia HCN Oxygen Ethene Ethyne Particulates Effect & Limit Activity, 0.20% mass Activity, 0.02% mass 0.15% mass Absent Selectivity, Absent Selectivity, 0.04% mass TMA, 10 ppmv Amines, Absent Activity, 1000 ppm 20 ppmv 5 ppmv Absent ppmv figures refer to MUG composition. % mass figures refer to accumulation on catalyst. 21. Relationship of Copper Surface Area and Activity 0 10 20 30 40 0 0.2 0.4 0.6 0.8 1 1.2 Copper Surface Area m2/gram Activity Copper Surface Area 22. VSG-M101Properties As noted before, Catalyst deactivation is caused by thermal sintering Copper crystallites grow - the surface area falls It also improves the catalyst's ability to maintain the separation of crystallites with time This prevents sintering and so activity is more stable 23. Catalyst Deactivation Either by Sintering Poisoning from Sulfur Chlorides Carbonyls 24. Thermal Sintering Historically always believed to be due to thermal sintering But also reactant and carbonyl poisoning Thermal sintering of copper catalysts is unavoidable Rate is critically dependent on temperature Therefore the hotter the catalyst the faster the rate of deactivation Operation at low temperatures reduces activity loss due to sintering Rate of sintering slows as the catalyst ages 25. What Causes Thermal Sintering ? Hence activity rules reflected this by defining activities by temperature bands Also defined activities by converter type This does include a temperature effect Also effect of gas mal distribution For example cold cores in Quench Lozenge converters 26. How does catalyst deactivate ? CuCu Cu Cu Cu CuCu Cu Cu Cu Cu Cu Cu Thermal sintering Cu molecules migrate and join other Cu particles to make bigger particles but with a smaller surface area 27. Sulfur Poisoning Sulfur is a powerful poison for Cu/Zn catalysts The ZnO component provides a sink for sulfur by formation of ZnS An effective catalyst requires an intimate mixture of Cu and ZnO and a high free ZnO surface area 28. Chloride Poisoning Chloride reacts with copper to form CuCl (mp = 430oC) CuCl provides a mechanism for loss of activity by sintering Catalyst requires well dispersed and stabilized copper to minimize the effects of chloride poisoning 29. Catalyst Deactivation Model 0.175 0.275 0.375 0.475 0.575 0 12 24 36 48 Time Months Activity High Temperature Operation Low Temperature Operation 30. What Causes Deactivation ? Now looking at the effect of Iron and Nickel Carbonyls Seen some high levels 5,000 ppm on discharged catalyst samples Looking at the most effective guard beds Could be worth 10 % extra on activity Consider the above to be confidential 31. Copper Surface Areas of Catalyst 0 1 Activity Comp A Comp A2 Comp B Comp C Comp C2 VSG-M101 1.80 32. Activity of VSG-M101 Time on line (months) 0 2 4 6 8 10 0.0 0.1 0.2 0.3 0.4 Relativeactivity 0.5 VULCAN VSG-M101 VULCAN VSG-M101D 0.6 0.7 0.8 0.9 33. Converter Types Many different converter types Tube Cooled Quench Lozenge; ARC and CMD Steam raising Aim is the same Keep process gas cool Contain the catalyst Maximize reaction rate 34. Loop Design Very similar not matter what type of converter 35. Quench Type Converters Original very simple mechanical design not the most efficient Replaced with slightly more complex design which is more efficient (better mixing) ARC Converter Quench Converter 36. Tube Cooled Converters Very simple design which integrates catalyst and process gas preheat Allows for heat recovery into saturator circuit TCC Design 37. Steam Raising Many types Recover heat to steam Tracks max rate line closely Each has own Pros and Cons Linde Variobar Toyo MRF Lurgi SRC 38. 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