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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