Download - Methanol Synthesis - Theory and Operation
Theory and Operation of Methanol Synthesis
Gerard B. Hawkins Managing Director, CEO
Introduction
Flowsheets Catalysts Catalyst Deactivation
Methanol Flowsheet
Methanol Flowsheet
Natural Gas
Sulphur Removal Saturator
Reforming
Air Condensate
Compression
BFWDemin Water
CW
CW
SynthesisDistillation
MP Steam
Purge to Fuel
Crude Methanol
ProductMethanol
Fusel Oil
Refining Column Bottoms
HP Steam
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
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.
OHPCOPActivity
dtOHdCH TRE∆−∝
Equilibrium Equilibrium defined by
Which can be rearranged to
Which is far more useful
[ ] [ ][ ] [ ]322
23
..HPCOP
OHPOHCHPKp =
[ ][ ] [ ]322
23 .
][.HPCOPOHPKpOHCHP =
Effect of Temperature on Kp
Effect of Temperature on CH3OH %
Effect of Pressure on CH3OH %
Definition of ATE
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
Effect of Operating Temperature on Equilibrium and Kinetics
Concept of Maximum Rate Line If reaction follows the max rate line then
minimum catalyst volume for maximum production
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
Methanol Synthesis Catalyst History
Over 30 years manufacturing experience
45,000+ m³ of methanol synthesis catalyst made
4,000 m³ of VSG-M101series catalyst currently installed in PRC
Methanol Synthesis Catalyst Properties
Effect Property Activity - Copper surface area Life - Microstructure Strength - Macrostructure Selectivity - Formulation
Methanol Synthesis Catalyst Properties
Typical composition for VSG-M101 • CuO 64 wt% • Al2O3 10 wt% • ZnO 24 wt%
Methanol Synthesis Catalyst Properties
Spherical Pellet • Diameter 5 mm • Height 4 - 5 mm
Bulk density 1,400 - 1,600 kg/m³ Radial crush strength >205N/m
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.
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
Activ
ity
Copper Surface Area
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
Catalyst Deactivation
Either by • Sintering • Poisoning from
Sulfur Chlorides Carbonyls
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
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
How does catalyst deactivate ?
Cu Cu
Cu
Cu
Cu
Cu Cu
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
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
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
Catalyst Deactivation Model
0.175
0.275
0.375
0.475
0.575
0 12 24 36 48
Time Months
Activ
ity
High Temperature Operation
Low Temperature Operation
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
Copper Surface Area’s of Catalyst
0
1 Act
ivity
Comp A Comp A2 Comp B Comp C Comp C2 VSG-M101
1.80
Activity of VSG-M101
Time on line (months) 0 2 4 6 8 10
0.0 0.1
0.2 0.3 0.4
Rel
ativ
e ac
tivity
0.5
VULCAN VSG-M101
VULCAN VSG-M101D
0.6
0.7
0.8
0.9
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
Loop Design
Very similar not matter what type of converter
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
Tube Cooled Converters
Very simple design which integrates catalyst and process gas preheat
Allows for heat recovery into saturator circuit
TCC Design
Steam Raising Many types Recover heat to steam Tracks max rate line closely Each has own Pro’s and Con’s
Linde Variobar
Toyo MRF
Lurgi SRC
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