Sulfiding of Sour Shift Catalyst

Sulfiding of Sour Shift Catalyst

VULCAN Series VIG SGS-201/202/203

Gerard B. Hawkins Managing Director

Introduction to Sour Shift Catalysts VIG SGS-201/202/203

Feedstock's from the gasification of coal or heavy oil contain high levels of sulfur.

Conventional iron-chrome catalysts are not suitable

“Sour” or “Dirty” shift catalysts were developed.

These catalysts achieve maximum activity in the sulfided state.

Require treatment with Sulfur prior to start-up.

Can only be used in streams that contain sufficient sulfur to maintain them in this state

Introduction to VULCAN Catalysts Sulfiding VIG SGS-201/202/203

Sulfur can be supplied from the process gas stream or a separate sulfiding agent.

Sulfiding agents are typically H2S, COS, or CS2

Sulfiding agent to be added at 60kg of Sulfur per tonne of catalyst at a uniform rate over 24-36hrs.

The process is typically carried out at 200-300oC

Initial heating carried out in dry inert gas

The end of sulfurization is determined by a high increase of H2S outlet of the reactor.


CoO + H2S ↔ CoS + H2O ∆H = -13.5kJ/mol

MoO3 + 2H2S + H2 ↔ MoS2 + 3H2O ∆H = -

48.3kJ/mol

CS2 + 4H2 ↔ CH4 + 2H2S ∆H = -242.6kJ/mol COS + H2O ↔ CO2 + H2S ∆H = -35.3kJ/mol


CO + H2O ↔ CO2 + H2 ∆H = -41.2kJ/mol

CO + 3H2 ↔ CH4 + H2O ∆H = -

215.7kJ/mol • The shift reaction starts when process gas is introduced at temperatures around 200oC.

• Methanation occurs at higher temperatures and pressures.


The aim is to add sufficient sulfur to fully activate the catalyst without generating excessive heat.

The control of temperature is essential!

The sulfiding is usually carried out using the main process stream itself.

However, it is possible to use a separate recycle system.


Probability of methanation reaction is high,. Especially at higher pressures.

Reactor should be nitrogen purged and heated to 220oC at a rate of 50oC/hr, at a pressure of 10bar

Wet gas is added to the nitrogen, 25% Wet gas:75% Nitrogen.

After 15-30 minutes a temperature rise is observed due to the starting of the shift reaction

(1) Using process gas


Once conditions are stable the wet gas rate can be increased by a factor of 2 and the nitrogen rate decreased proportionally to maintain the linear gas velocity.

At this point additional sulfur compounds can be added to speed up the sulfiding process

Sulfur concentration exit the bed should be carefully monitored throughout.


The reactor should be purged free of oxygen and heated to about 220oC in a stream of inert carrier gas containing 10% hydrogen.

The temperature rise due to the sulfiding process must be limited to 20oC.

Sulfur is added at 50% of the required rate to begin with until the condition settle then the rate can be increased.

Significant break through of sulfur at the exit of the last bed indicates sulfiding is close to completion.

(2) Using a recycle loop


At this stage the temperature should be increased at a rate of 15oC/h to 280-300oC.

In multi-bed systems it may be necessary to increase Bed 1 inlet temperature to above 300oC

Temperatures above 350oC should be avoided.

VULCAN Catalysts Sulfiding Experience

– Ammonia plant East Asia

– The plant is being adapted to accept a coal slurry feedstock via a single gasification unit.

– New shift train comprising 3 reactors using the more active sulphur tolerant shift catalyst.

– Two beds of VULCAN Catalysts followed by two beds of a local competitors catalyst.

Introduction


SHE Site safety systems were none existent Limited use of PPE No safety induction House keeping was poor by any standards There was no evidence of a permit to work

system


– The Reactors were heated in a recirculating stream of nitrogen to 220oC over a period of 22hours.

– The procedure stated that the reactors should be heated to 120oC and held at that temperature for 4 hours.

– Process gas from the POX unit (H2:CO ratio 1:1) was introduced to produce 10% H2 at the outlet of the Nitrogen blower.

The Sulfiding Process – Take 1


– Beginning with a targeted rate of 60kg/h, CS2 was added to the recirculating gas.

– A purge from the recycle loop was used to keep the CH4 content to <20% of the N2 content.

– Water generated from the sulfiding process was periodically drained from the knockout drum

It quickly became apparent that:

•The CO content of the loop was low •The H2S at the inlet of bed 1 was high •The H2 content was quickly decreasing


The client then communicated that the CS2 flow meter was faulty and the laboratory analysis was unreliable.

Further analysis indicated low CO, high CO2 and a very low H2 content.

Conditions were proving to be particularly unstable and the laboratory analysis look increasingly unreliable.

The sulfiding was abandoned after convincing the customer to sulfide using make-up gas instead of process gas!


– Recycle loop purge to reduce the CO2 and H2S levels in the loop.

– A make-up gas stream (75% H2) was introduced to maintain a H2 content of >10%.

– A new CS2 flow meter was also installed which also turned out to be faulty.

– Once conditions were stable, bed 1 temperature was increased to 240oC and CS2 addition increase to around 90kg/hr.

– Temperature continued to be increased until Bed 2 temperature reached 280oC.

The Sulfiding Process – Take 2


– The sulfiding was completed over 33hours.

– The total CS2 consumed was 5.4Te, the catalyst required 2600kg CS2.

– Upon completion the client was advised to purge the loop, lower the bed temperatures to approx. 60oC and store under positive N2 pressure.

– The client was also advised that a process stream which does not contain Sulfur should not be passed over the catalyst.


The sulfiding was believed to be successful based upon consumption of CS2, the control of bed temperatures, the control of the H2 content and the duration.

The client was concerned about how future catalyst sulfiding would be carried out as the MUG used would not be available.

Two options were discussed: the use of bottled H2 and using process gas without recycling.

Technology

Sulfiding of Sour Shift Catalyst