Catalyst Reduction Introduction Requirements - Use of Hydrogen - Use of Cracked Ammonia - Inert Carrier Poisons Procedures

1. Gerard B. Hawkins
Managing Director, CEO

2.  The reduction is highly exothermic and
temperatures must be controlled carefully during
this period to avoid damaging the catalyst.
 Reduction is carried out using hydrogen or
hydrogen/carbon monoxide mixtures in an inert
carrier gas such as nitrogen or natural gas.
 The inert gas must be free of catalyst poisons.
 The hydrogen plus carbon monoxide in the
circulating gas should be adjusted to control the
reactor temperatures, but will typically be in the
range of 1.5-2.5% at the inlet to the converter.

3.  During the reduction, approx' 15Nm3 of CO2 is evolved
from 1 ton of methanol synthesis catalyst. This must be
purged from the loop to keep the pressure constant.
 Water is also released from the hydrated salts in the
catalyst as well as from the reduction of the copper oxide
by hydrogen. The total quantity of water produced amounts
to approx' 15% of the weight of catalyst installed.
 Less water is produced if the reduction gas contains CO.
 Once the catalyst has been reduced it can be brought on
line immediately.
 Alternatively, it can be put on standby and commissioned
at a later date.

4.  An on line hydrogen analyzer
 A flow meter that shows the rate of hydrogen or synthesis
gas addition.
 Provision to analyse for CO2 content every hour, if possible
by an on-line analyzer.
 Converter temperatures, cold shot flows, heater
temperatures etc., should be within the control room.
 A start up heater specified to be able to handle the
maximum load under reduction conditions as well as any
duties in normal operation.
 Circulator - this must be specified, or at least checked out
with the machine vendor, for reduction gas flow,
temperature, pressure and composition in addition to the
normal circulating gas.

5.  Hydrogen for reduction is normally obtained
from synthesis gas by starting up the reformer.
 The theoretical quantity of hydrogen required
for the reduction of VSG-M101is 145 - 160
Nm3/ton (4900 - 5400 SCF/ton) of catalyst
installed.
 If synthesis containing CO and/or CO2 is used
as a source of hydrogen, this will increase the
need to purge from the loop and there may be
an increased loss of hydrogen due to this extra
purging.

6.  If cracked ammonia is used as the source of
hydrogen, the quantity required for reduction is
unchanged. The extra N2 accumulating in the
loop will have to be purged out and will carry CO2
with it. This will reduce the amount of N2 required
from other sources. The maximum concentration
of NH3 in the circulating gas must not exceed 10
ppm and so ammonia cracking conditions must
be selected to achieve this. An NH3 content of
200 ppm in the cracked gas is normally sufficient
and can be easily achieved.

7.  Reduction is carried out in an inert gas such as nitrogen
or natural gas. The inert gas must not contain
excessively high levels of catalyst poisons, and a
specification for inert gas is:
 Oxygen <1000 ppm v/v
 CO < 1.0% v/v
 H2 < 1.0% v/v
 S < 1.0 ppm v/v
 NH3 < 10 ppm v/v
 Unsaturated Hydrocarbons traces only
 Other poisons e.g. chlorides absent

8.  Purge the synthesis loop with inert gas to less than 1% v/v
oxygen and then increase the pressure to the appropriate
level. For plants designed to operate at 1450 psig, the
reduction pressure should be approx' 100 - 115 psig.
 For the ICI lozenge design, circulate the inert gas through
the converter ensuring that the cold shot valves are closed.
The circulation rate should be sufficient to give a minimum
space velocity of 300-600 Hr-1. The upper limit of the
circulation rate will be fixed by pressure drop through the
system and the characteristics of the circulator. The
advantage of increasing the circulation rate is that a more
rapid and more even reduction is obtained.

9.  In tube cooled converters, gas should be sent directly to the
top of the bed, with no flow up the tubes since this would
lead to uneven reduction, as the catalyst close to the tubes
would be below the reduction 'strike' temperature.
 Heat the converter to 130°C inlet at a rate not exceeding
50°C/hr
 Introduce about 1 % of H2 or (H2 + CO) as a single shot, to
check the calibration of the hydrogen analysers and to
calibrate the reduction gas flow meter.
 Increase the inlet converter temperature to 180°C at a rate
of approx' 20°C/hr. Reduction will commence between 150
and 160°C.

10.  With an inlet temperature of 180°C, introduce reduction
gas initially to maintain a H2 + CO concentration inlet the
converter between 1.0 and 1.5 %.Once the temperatures
have stabilized, this can be increased to between 1.5 and
2.5 %. If the reduction proceeds too slowly the inlet
temperature may be increased to 200°C. The best inlet
temperature is that which gives peak catalyst temperatures
of about 230°C and a H2 concentration at the outlet <0.1
%.
 During the reduction maintain a constant pressure by
purging or making up with extra inert gas as required.
 Ensure that water produced during reduction is drained
from the catchpot. It can be useful to measure the quantity
as an aid to determining when complete reduction has
occured.

11.  If, despite precautions, peak temperatures exceed 240°C,
stop the hydrogen addition. Do not open the cold shot
valves, as this will merely cause overheating to occur
elsewhere in the converter.
 When there is no further sign of reaction (no temperature
point reading higher than the one above it and no
difference in the inlet and exit hydrogen analysis) raise the
inlet temperature to 240°C or as near as possible. If there
is still no sign of reaction, raise the H2 content to 10 - 20 %.
The increase must be stopped immediately if there are
signs of further temperature rise. Holding the catalyst under
high concentrations of H2 and at high temperature is called
'soak'. this period should last for 4 to 6 hours.

12.  Reduction is now complete. The whole process,
excluding the time taken to heat the catalyst to
reduction temperatures (say 150°C) will take
about 24 - 36 hours.

13.  Reduce the converter inlet temperature to 210 -
220°C and wait for all catalyst bed temperatures
to stabilise at this temperature. All converter
temperatures must be between 210 and 220°C.
 Start introducing synthesis gas, which will cause
the pressure to rise. The rate of increase of
pressure should be about 10% of design
operating pressure per hour. This constraint is
imposed by the equipment in the synthesis loop
and not by the catalyst, and is only an estimate.
Different pressurisation rates may be acceptable.

14.  The introduction of synthesis gas will cause
the converter temperatures to rise as the
methanol reaction commences. The partial
pressure of methanol vapour will increase,
but at first this vapor will not condense and
an equilibrium concentration of methanol
will be established. Consequently, the
temperature rise will only persist as long as
synthesis gas is being introduced. Aim to
keep the inlet converter temperature at 210
- 215°C.

15.  When the pressure reaches 145 - 175 psig, the exact
value will depend on the temperature of the cooling water
and the water content of the first methanol made,
methanol will start to condense. This will allow a larger
continuous rate to be fed in for the same rate of pressure
rise. At this stage a temperature rise will consistently
appear across the catalyst.
 When methanol first condenses, commission the cold shot
to the second bed with the control point inlet that bed set
at 210 - 215°C. Commission the cold shot to the
subsequent bed once the temperature at the exit of the
bed is steady. The control point should be 210 - 215°C at
each bed inlet.

16.  In tubular converters as methanol starts to form, the
flow up the tubes should be gradually increased as
the peak bed temperature rises. For steam raising
converters the steam pressure should be set to give
a cooling temperature of about 215°C. This will be
approximately 300 psig. As methanol is formed the
steam pressure can be raised to its flowsheet value.
 As methanol starts to form in sufficient quantity,
commission the level controllers of the separator and
the letdown vessel.
 Commission the purge of flash gas from the letdown
vessel.

17.  When the concentrations of nitrogen and
methane reach flowsheet values, commission
the purge from the synthesis loop. It is usual
anyway to have a small purge from the time that
methanol first starts to condense.
 Maintain the bed inlet temperature at 210 -
215°C by commissioning the interchanger
bypass and admitting cold gas to the converter
inlet gas stream, or by making suitable
adjustments to the heat recovery system.
 When the reaction is autothermal the start up
heater can be shut down.

18.  If the start up cannot follow soon after reduction,
sweep out the loop with an inert gas until the H2
concentration is less than 1% and cool down the
converter. When the catalyst is subsequently
started up, the following procedure is used.

19.  Pressurise the loop with inert gas to 7 - 8
barg. Establish circulation with a space
velocity of at least 300-600 hr -1.
 Heat the reactor inlet temperature to 200°C
with the loop start up heater. Allow all
reactor temperatures to reach a minimum of
180°C.
 Introduce Synthesis gas to the loop and
allow the pressure to rise.

20.  As reactions start the reactor temperatures
will rise and methanol will begin to condense
in the catchpot, (when the pressure reaches
about 10 - 12 barg).
• As the inlet temperatures of the lower beds begin
to rise commission the shot flows to these beds
controlling the inlet temperatures at around 210 -
215 °C
• When sufficient heat generation is taking place the
loop start up heater can be decommissioned.

21.  After shutdowns of a short duration the catalyst
may be hot enough to allow the reactor to be
started without additional heating.
◦ Bring the circulator up to normal speed as
quickly as possible consistent with the vendor's
instructions.
 When the reactor temperatures are above 210
°C bring the circulator up to normal speed.
 Begin to introduce fresh synthesis gas.
 As temperatures begin to rise commission shot
flows as appropriate.

22.  In a start up situation reaction heat for heating
of the reactor inlet gas is not available.
• Steam from the reforming section is used via the
loop start up heater
• Gas is redirected through the start up heater via
valve in the HL interchanger inlet and HIC007.
• Minimum stop valve to prevent isolation of HL interchanger

23.  As reaction occurs reactor exit gas
temperature rises
◦ Heat will be picked up in HL interchanger
• As exit temperature continues to rise HL
interchanger valve can be adjusted to allow more
gas to flow through HL interchanger
• When temperature exit HL interchanger is high
enough to sustain reaction gas flow through start
up heater can be stopped

24. E1113E1112
E1110
V1107
Shot Gas
Converter Inlet
Gas
180 °C
0
0
0
0
Shot Flows
kNm3/hr
From C1102
210 °C
E1111
Loop start Up
Heater
100 bar
steam
TIC
060
HIC 007
240 °C
ShutOpen
180 °C
210
190
230 100
220
210
240 150
25 %
50 %

25.  Stop the synthesis gas
• Continue to circulate the loop gas over the
catalyst to react all the carbon oxides
• When the temperature starts to fall commission
the start up heater and maintain the catalyst
temperature above 200 °C
• Maintain these conditions until synthesis gas is
available again

26.  Carry out the short period shutdown
procedure
• Reduce the circulator to minimum speed and
reduce loop pressure. Allow the catalyst to cool
at a rate of around 50°C/hr
• While the circulator is running purge the loop with
N2 until the H2 content is below 1 %.

27.  While shutdown the loop should be kept
under an inert atmosphere to prevent the
catalyst contacting oxygen

28.  In the event of a trip the loop pressure should
be reduced by 10 %
– This prevents the catalyst overheating due to continuing
reaction of residual carbon oxides
• The purge can then be isolated and loop can be
left to depressurise slowly until ready to start up
again.
– If the trip will last more than 24 hours then the loop
should be shutdown in accordance with the prolonged
shutdown procedure

29.  This procedure has been developed due to the development
of the ICI ARC converter. The new ARC converter has
individual catalyst beds which make it very difficult to
discharge the catalyst from the converter.
◦ To compensate for this GBHE has developed an in-situ oxidation process
that will completely oxidize the catalyst while it is still inside the reactor.
This eliminates both the need for any specialist procedures for catalyst
removal as well as the need to double handle the material after its
discharge.
◦ The oxidized catalyst is suitable for immediate loading into drums or other
suitable containers for shipping off-site.

30.  The process has been carried out several times around the world.
 The procedure takes approx' 24 to 36 hours.
 A significant feature of the oxidation procedure is that the catalyst
is not completely oxidized after just one pass of the exotherm front
through the catalyst bed. It is only 90% oxidised, although the
exact extent of oxidation is a function of the temperature at which it
takes place.
 The catalyst can never be completely oxidised, operators need to
be aware that the catalyst still has the capability to absorb O2 from
the atmosphere, so appropriate precautions must be taken during
entry into a vessel containing oxidised catalyst.

31.  At completion of production, cool the converter to about
150°C
 Letdown the synthesis loop pressure. Purge the synthesis
loop with N2 according to the standard plant procedure.
Hydrogen concentration in the loop must be reduced to
below 2 mol.% before any oxygen is introduced. The loop
H2 analyser may need recalibrating to a range of 1 - 10 %

32.  Maintain the loop with inert N2 at just above atmospheric
pressure to prevent ingress of air.
◦ Ensure that all lines around the synthesis loop not associated with the
oxidation procedure are closed to eliminate the unwanted flow of fluids
in or out of the loop. The level of isolation required are double block
and bleed, slip plating or physical blinding.
◦ Any methanol left in the catchpot/separator should be completely
drained from the vessel before isolation.
◦ If air is to be supplied to the converter via an external air compressor,
an indication of flow will be needed, either at the air compressor or via
a plant gauge that has been recalibrated for the purpose.

33.  Connect up an oxygen analyser upstream and
downstream of the converter. This can be done with one
analyser and a field switch. Lag time must be minimised in
obtaining samples.
 Establish loop circulation with N2. Pressure up to about
100 - 150 psig.
 Commission start up heater to maintain the catalyst bed at
150°C. This temperature should be maintained inlet the
converter for the first stage of the oxidation.
 Check H2 concentration in the loop. H2 concentration
should be monitored continuously throughout the
procedure.

34.  If H2 concentration is below 2 mol.% (NB H2 absorbed will be
released from the catalyst, so purging may be required to
reduce H2 below 2 mol.%), connect air supply and admit air
to a concentration of 0.5 mol.% O2 at the inlet to the
converter. Check that no O2 slip is being seen exit the
converter.
◦ The exotherm associated with the reaction is equivalent to about 100-
120°C per mol.% of O2 inlet the converter. A temperature rise will be seen
after only a few minutes, which will go progressively down the converter -
similar to that seen during catalyst reduction.
◦ Monitor temperature rises, O2 and H2 analysis and air rate regularly and
that they are giving consistent information. Do not increase the oxygen
concentration until inconsistencies have been satisfactorily resolved.

35.  Once air addition has started, the loop will either require
periodic purging, or a continuous small purge, to maintain
the pressure at about 100 - 150 psig.
 Continue at these conditions until the exotherm is
monitored exit the final catalyst bed.
 Increase air addition rate in step-wise intervals, 0.5%
increments over say 30 to 60 minutes, towards a
maximum of 1.5 mol.%, while not exceeding a maximum
average temperature at any level of 250°C and any
individual temperature exceeding 275°C.

36.  As the oxidation proceeds, the reaction front moves down
the catalyst beds. As the reaction front passes, the
temperature will fall at each level. When the temperature
exit the final bed begins to fall the reaction has almost
proceeded to completion. Isolate the air. Raise the
converter inlet to 200°C and maintain at this temperature.
Repeat from 'If H2 concentration is below 2 mol.%........'
 When the final bed exit temperature falls after the second
air cycle, the oxygen level exit the converter should be
observed, for oxygen slipping from the converter. Maintain
O2 at its current level by reducing the air flowrate in step-
wise amounts, then isolate.

37.  Recalibrate O2 analyser to read say 2 mol.% to 20 mol.% range.
Slowly add O2 to the loop to raise the concentration to 10 mol.% at
200°C. This should be done in increments of 2 mol.% allowing time
at each stage to check that conditions are stable. Maintain inlet
temperature at 200°C and loop pressure 100-150 psig. Ensure that
the average peak temperature at any level does not exceed 250°C,
and any single thermocouple does not exceed 275°C. Maintain O2
level at 9-10 mol.% by batchwise addition of air, until there is no
longer movement on the thermocouples. Isolate and shut down the
air compressor.
 The converter needs to be cooled down prior to catalyst discharge.
This should be done, as much as possible, with O2 level maintained
at 10 mol.%. Allow converter to cool at up to 50°C/hr.

38. Fully reduced Cu crystallite
First exposure to oxygen.
Outer layers start to oxidize.
As oxidation continues, oxygen
penetrates throughout.
Later, the oxide layer at the
surface virtually stops any
further oxygen diffusion.

39. Raising the temperature speeds
up the solid diffusion process
and so oxidation resumes...
only to stop again when the thickness of
the oxide layer has increased and halts
any further oxygen diffusion.
Complete Oxidation Can Never Occur

40.  Cool catalyst as much as possible, at least to less than
50°C, preferably to less than 40°C.
 The above procedure should result in a converter full of
oxidised catalyst. However, COMPLETE oxidation CANNOT
be guaranteed, and the charge of catalyst may still be highly
active. Appropriate precautions should be taken during
vessel entry and catalyst discharge.
 In the event of any unusual conditions, high exotherm, high
H2 levels etc., the air supply should be isolated immediately.

41. Process Information Disclaimer
Information contained in this publication or as
otherwise supplied to Users is believed to be
accurate and correct at time of going to press, and is
given in good faith, but it is for the User to satisfy
itself of the suitability of the Product for its own
particular purpose. GBHE gives no warranty as to
the fitness of the Product for any particular purpose
and any implied warranty or condition (statutory or
otherwise) is excluded except to the extent that
exclusion is prevented by law. GBHE accepts no
liability for loss or damage resulting from reliance
on this information. Freedom under Patent,
Copyright and Designs cannot be assumed.