New High-Temperature Shift CatalystsSolve the Fischer-Tropsch Problem

New high-temperature shift catalysts eliminate the by-product for-mation when operating at very low steam to carbon ratios.

Jack H. Carstensen and John B. HansenHaldor Topsçfe A/S, Copenhagen, Denmark

andPeter S. Pedersen

Haldor Topsçie, Inc., Houston, TX

IntroductionIn recent years, the ammonia industry has

focused more and more on problems

encountered in the high and low tempera-

ture shift converters due to lowering of

the steam to carbon ratio.

Operating ExperienceWhile the savings by lowering the steam to

carbon ratio in the primary reformer are

obvious, a number of drawbacks have

been experienced in the high and low

temperature shift converters:

1 ) By-product formation in the HTS

2) Pressure drop build-up in the HTS

3) Reversible poisoning of low tempera-

ture shift catalyst

4) Higher CO equilibrium concentrations

exit HTS and LTS

Re1):Already in 1980, laboratory work carried

out by Haldor Tops0e A/S [1] had proved

that lowering of the steam to carbon ratio

to below approximately 3.5 caused a

transformation of some of the iron oxide

in a classical HTS catalyst into a Fischer-

Tropsch (and shift) active carbide phase

according to:

5 F63O4 + 32 CO < = > 3 F65C2 + 26 CÜ2

The carbide phase will catalyze the

formation of hydrocarbons and oxyge-

nates, which causes a hydrogen loss and

some deactivation of the LTS catalyst and

thereby production loss.

139

Example: One large 1000 TPD ammoniaplant experienced a production loss of 6TPD when the steam to carbon ratio wasdecreased from 3.5 to 3.1, and this onlyincludes hydrogen consumption related tothe Fischer-Tropsch reactions, not produc-tion loss related to increased purging [2].

Figure 1 illustrates how the decreasedsteam to carbon ratio influenced theproduction loss in this plant, and it isevident that for instance lowering thesteam to carbon ratio to 2.8 or belowwould most likely become uneconomicaldue to the production loss if a classicalHTS catalyst was applied.

In Figure 1 is also shown the relationbetween steam to carbon ratio and(Kp/Ke) V32 ratio for this specific plant.The value of (Kp/Ke)V32 is a measure ofthe thermodynamical affinity for theformation of the Fischer-Tropsch activeiron-carbide phase [1]. If (Kp/Ke)1/32 isbelow 1 there is affinity for Fischer-Tropsch synthesis and the lower it is themore Fischer-Tropsch by-products areformed. For a given steam to carbon ratioplants operating with excess air to thesecondary reformer and/or with additionof steam to the secondary reformer orthe HTS will operate at a less critical(Kp/Ke) 1/32 value inlet HTS than plants

without these features. Also the secondaryreformer exit temperature, the hightemperature shift operating temperatureand the operating pressure will affect the(Kp/Ke) V32 value for a given steam to

carbon ratio.

Figure 1

Production Loss versus S/C ratioin a 1000 t/d Ammonia Plant

18

16

14-

12

10-

8

6

4

2

0

Production loss, t/dIncludes only hydrogen loss related directly to the Fnol production loss related to increased purging

V

0.5 0.6 0.7 0.8 0.9 1.0-*• (Kp/Ke)1'32

-r-* S/C ratio2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8

The given relation between (Kp/Ke) "» and S/C rato is based upon Hie operating conditionsprevailing in this pfant and cannot be used directly for other plants

Re 2):Some plants where the steam to carbonratio has been lowered have experiencedproblems with unexplained weakening ofthe HTS catalyst and pressure drop build-up. This is most likely caused by phasetransformations in the HTS catalyst whenthe steam to carbon ratio is changed.

Re 3):Oxygenates formed in the HTS along withthe hydrocarbons cause a deactivation ofthe LTS catalyst [2]. Even though theeffect is of a completely reversible nature,the LTS catalyst volume necessary toobtain a certain CO conversion is increasedas long as one wants to operate at lowersteam to carbon ratio.

Re 4):The less favourable equilibrium conditionsencountered in the shift section when thesteam to carbon ratio is lowered result ina significant production loss unless ahighly active LTS catalyst is used incombination with a low inlet temperature.

140

The first solution suggested by Haldor

Tops0e A/S for operation at low steam to

carbon ratio was to replace the HTS

catalyst with a copper based iron free

medium temperature shift catalyst denomi-

nated LK-811 [3]. This catalyst was

commercialized in 1984 and has given

excellent service, especially in hydrogen

plants operating at low steam to carbon

ratio. The maximum operating temperature

of LK-811 is, however, limited to about

350°C (662°F) and this makes it difficult

to use this catalyst in existing plants

being modified for operation at low steamto carbon ratio.

Haldor Tops0e A/S has, therefore searched

for other solutions and can now, based on

extensive laboratory research, offer, two

fundamentally different catalysts for

avoiding the by-product formation in the

HTS at low steam to carbon ratio.

1) Modified Classical HTS Catalyst.One way of relieving the by-product

formation problem has proven to be the

use of a classical, iron-based HTS catalyst

promoted with a small content of Cu.

Hereby, the Fischer-Tropsch by-product

formation is almost eliminated. Besides

preventing formation of by-products, the

addition -of Cu gives the modified HTS

catalyst a higher activity for the shift

reaction. Tops0e's modified HTS catalyst is

designated SK-201.

Experimental laboratory data.

The properties of this modified high

temperature shift catalyst have in our

laboratories been studied in parallel with

Tops0e's classical iron/chromium-based

catalyst designated SK-12.

The feed gas used in all the experiments

contained 15 % CO, 10 % CÛ2, 3 % argon

and hydrogen as balance. The steam to dry

gas ratio was varied by means of peristaltic

pumps, introducing water to the gas. The

pressure in all the experiments was 22 bar

g(319psig).

In one set of experiments, the activity

and stability of the SK-12 and SK-201

were investigated. The results are given in

Figure 2, where the activity as function of

time is shown. The activity is expressed as

a correction factor to the preexponential

term using the kinetic expression described

in [4].

Figure 2

Activity of HTS catalysts

2.0

1.5

1.0

0.5

Activity

Modified Fe-catalyst(SK-201)

Classical catalyst(SK-12)

0 100 200 300 400 500 600 700 800 900 10001100Hours on stream

141

It can be seen that the stability of the

two catalyst types is comparable. The

activity of the modified catalyst SK-201 is,

however, approximately 50 % higher than

that of the classical catalyst SK-12.

The tendency to produce Fischer-Tropsch

by-products over the classical high tempe-

rature shift catalyst SK-12 was checked by

varying the steam to dry gas ratio and the

temperature. In Figure 3, the tendency to

produce Fischer-Tropsch by-products is

expressed by the methane formed over thecatalyst as function of time and operating

conditions. Methane is, of course, not the

only by-product. Higher alkanes, olefines,

acids, aldehydes, ketones, and alcohols are

produced as well in amounts roughly

proportional to the methane formation.

The experiment started at a temperatureof 380°C (716°F) and with a (Kp/Ke)1/32

ratio around 1.1 (corresponding to a steam

to carbon ratio of about 3.9 in a normal

ammonia plant) in order to stabilize the

catalyst. After approximately 100 hours the(Kp/Ke)1/32 ratio was lowered to 0.6

(corresponding to a steam to carbon ratio

of about 2.6 ). After a certain induction

period, the production of methane started

and stabilized around 500 ppm. The Fischer-

Tropsch by-product formation is not only

governed by thermodynamics but also by

kinetics; this is demonstrated by the factthat the methane formation rate increased

to give a stable value of 2500 ppm when

the temperature was raised from 380°C

(716°F)to4000C(752°F).

3000

2500

2000

1500

1000

500

Figure 3

Methane Formation over Classicalppm CH4

HTS Catalyst

S/C = 3.8—I

0 100 200 300 400 500 600 700 800 900 1000 1100Hours on stream

The results from a similar experiment with

SK-201 are shown in Figure 4. Please note

the changed scale on the vertical axis

(reduced by a factor 10). As no hydrocar-

bon formation could be detected even after200 hours at (Kp/Ke)1/32

raf,o of 0.6, the

(Kp/Ke)1/32 ratio was further reduced to

0.25 (corresponding to a steam to carbon

ratio of about 1.6) in order to increase the

severity of the selectivity test.

300

250

200

150

100

50

0

Figure 4

Methane Formation over Modifiedppm CH4

HTS CatalystSIC * 2.6—| S/C . 16—|

0 200 400 600 800 1000 1200 1400 1600 1800Hours on stream

142

The methane exit the reactor stabilizedaround 70 ppm at 380°C (716T). At a

temperature of 400°C (752T), the value

levelled off at 230 ppm. Interestingly, a

methane production of 50 ppm pertained

when the temperature was lowered to380°C (716T) and a (Kp/Ke)1/32 ratio of

0.6 (corresponding to a steam to carbon

ratio of about 2.6) was re-established,

indicating that the catalyst has a "memory",

i.e. if it once has been carburized, it will

have a greater propensity to produce

hydrocarbons etc. This is important as an

industrial high temperature shift catalyst

charge often is subjected to variations in

steam to carbon ratio or temperature

level. This memory effect is also borne out

by the last operating period where the

(Kp/Ke)V32 ratio was again lowered to 0.25

(corresponding to a steam to carbon ratio

of about 1.6) at 380°C (7t6°F).

Here, the methane stabilized around 150

ppm, more than double of that in first

period at the same conditions.

The amount of oxygenate by-products

produced by the two catalyst types is

shown in Table 1. It should be remembered

that these are the real culprits when

discussing a deactivating effect on the low

temperature shift catalyst [2]. The data

are from a period with 400°C (752°F) anda (Kp/Ke)1/32 ratio of 0.6 (corresponding

to a steam to carbon ratio of about 2.6).

Table 1

Wtppmin condensas

Catalyst

SK-12SK-201

Ethanol

4711

Propano! Acetone Methytethylkstom

2 41 8• 2

Methanol was found in the condensate

from both catalysts corresponding to the

equilibrium value (approx. 100 wt ppm.)

Conclusion on Modified HTS Catalyst.

SK-201.

From the above described experiments, it

can be concluded that the problems

associated with Fischer-Tropsch by-product

formation in iron-based high temperature

shift catalyst at low steam to carbon

ratios can be almost eliminated at least

for some time by using the modified

catalyst SK-201. However, if the operatingconditions become very severe or opera-

tional upsets are frequent, a more radical

solution is needed, namely:

2) Iron-free HTS Catalyst.Haldor Tops0e A/S has also searched for a

more radical solution to the problems

with by-product formation, namely to

replace the classical high temperature

shift catalyst with an iron free catalyst

capable of operating at these conditions.

With the introduction of a new Cu-based

catalyst designated, KK-142 this goal has

now been achieved.

143

Experimental laboratory data.The activity, stability, selectivity, andreaction kinetics for KK-142 have beenexamined in both pilot and bench-scalereactors.

Activity and stability:One experiment was done in a reactorsystem divided into 10 different beds inseries. The size of the unit ensures closeto adiabatic operating conditions.

Activities found from experiments atvarious steam to carbon ratios in this unitare shown in Figure 5. The inlet temperat-ure was varied from 340°C (644°F) to380°C (716°F) and the outlet temperaturefrom 390°C (734°F) to 410°C (770°F). Thefeed gas contained 15 vol.% CO, .12.5 %CÜ2, and hydrogen as balance. Operating

pressure was maintained at 28 bar g (406

psig).

Figure 5

Activity of Iron-free and of ClassicalHTS Catalysts

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

Activity

Iron free HTS Catalyst(KK-142)

ClassicalHTS Catalyst(SK-12)

200 400 600 800 1000Hours on stream

1200 1400

The activity is calculated from a kineticexpression developed for KK-142. Thiswill be further explained below. It isnoteworthy that although the activitydeclines rather fast in the beginning com-pared to classical or modified high temper-ature shift catalysts, it stabilizes after500 hours at a level considerably abovethat of the iron-based catalyst. A mathe-matical deactivation model has been develo-ped based on these data and is included inFigure 5. Based on predictions by thismodel, it is found that at poison-freeconditions the activity would even stayabove that of SK-201 for periods of morethan 4 years.

Mechanical stability:It is a well-known fact that classical iron-based high temperature shift catalysts losea considerable part of their strengthduring reduction. Up to 80-90 % loss isnot uncommon, especially when operatingin the Fischer-Tropsch region. Actually,increasing pressure drop due to catalystdisintegration is a frequent motivationbehind a change-out of high temperatureshift charges. KK-142 on the contrary isexceptional as the catalyst keeps itsstrength after reduction and operation.

The crushing strength of new KK-142 isapprox. 300 kg/cm2 (4300 psi) which isabout the same as for classical HTS catalyst

as new.

KK-142 has in pilot plant operation for

more than 5000 hours proved to retain itsmechanical properties, i.e. no loss ofstrength.

144

It should be emphasized that most of thetime during the pilot experiment, the

KK-142 has been operated well within the

Fischer-Tropsch region and that the

catalyst has even been exposed to condi-

tions corresponding to a steam to carbonratio of 1.85 ((Kp/Ke)1/32 ratj0 of

0.35).

Activated KK-142 withstands exposure to

boiling water and also withstands start-up

in condensing steam without any effect on

the mechanical properties.

The stable mechanical integrity of KK-142

allows the use of alternative shapes of

this catalyst, such as rings or 7-hole

cylinders, which would result in a signi-

ficantly lower and a stable pressure drop

across the high temperature shift reactor.

Selectivity:

KK-142 has been tested at the most

demanding conditions, which can be

envisaged for a modern natural gas based

ammonia plant. As an example, a feed gas

of 19 vol.% CO, 10.5 % CO2, and 70.5 %

H2 has been used with temperatures up to435°C (815°F). The water addition to thefeed gas corresponded to a (Kp/Ke)V32 of

0.5 (corresponding to a steam to carbon

ratio of about 2.3). No by-products whatso-

ever could be determined in the exit gas

except for methanol, which, as with

classical iron-based catalysts, is present in

the exit gas in an amount corresponding

to the chemical equilibrium. In other

experiments, this very high selectivity has

been confirmed at conditions correspondingto a (Kp/Ke)1/32 of 0.35 (corresponding

to a steam to carbon ratio of about 1.85).

It has also been established that no

ammonia formation takes place in the

presence of nitrogen. On the other hand,

unlike copper-based low temperature shift

catalysts the activity of KK-142 is not

affected by the presence of ammonia in

the feed gas [2]. In the above mentioned

pilot experiment, 0.15 wt.% NHs was added

to the water introduced to the feed gas

without any noticeable effect on catalyst

activity. This can probably be ascribed to

the different operating temperature levels

for low temperature shift catalysts and

KK-142.

Poison resistance:

While KK-142 is very superior to iron-

based high temperature shift catalyst as

far as to activity, mechanical integrity,

and selectivity it has, however, one

drawback: It is sensitive to sulphur

poisoning. Protection of the catalyst by a

top-layer of zinc oxide is impossible at

the operating temperature level of classical

high temperature shift catalysts, as the

equilibrium

ZnO + H2S < = > ZnS + H2O

is displaced to the left at high tempera-

tures.

In order to be able to predict reliably the

effect of sulphur poisoning, a long-term

pilot experiment was carried out at

conditions similar to those of an ammonia

plant operating at a steam to carbon ratio

of 2.3. 10 ppb of H2S, which is typical or

slightly higher than normal for a modern

ammonia plant, was introduced to the dry

feed gas, and the activity followed as a

145

function of time for 3100 operating hours.The space velocity was 20,000 vol./vol./hor much higher than for the industry

where the space velocity typically is 2500vol./vol./h, so the catalyst did not convertthe gas to chemical equilibrium. This made

possible a reliable determination of the

catalyst activity.

After the experiment, the catalyst from

each bed was analyzed for the sulphur

content. The result is given in Figure 6.

Figure 6.

Sulphur Content of KK-142 after Pilot Testwt ppm S on Catalyst

800

700

600

500

400

300

200

100

4 5Bed number

When evaluating the slope of the curve,

the very high space velocity should beborne in mind as this will stretch out the

poisoning front. In an industrial charge,

the poisoning front would be confined to

the upmost part of the reactor.

The catalyst from bed No. 1 was also farfrom saturated with sulphur. A microprobe

analysis for sulphur along diameters ofcatalyst pellets demonstrated that thesulphur was confined to a sharp shell in

the outmost part of the pellets. This

analysis also established that the saturationsulphur coverage of KK-142 is comparable

to low temperature shift catalysts.

Samples of the catalyst from beds No. 1

and No. 7 were transferred to microreactors

and the activity determined. The resultsappear from Figure 7. It is seen that even

the catalyst from bed No. 1 with 720 ppmsulphur still had a resonable activity.

Figure 7.

Activity of KK-142 after PoisoningExperiment

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

Activity

7. bed - 200 wt ppm S on Catalyst

1. bed - 720 ppm wt ppm S on Catalyst

0 50 100 150 200 250 300 350 400 450Hours on stream

146

Kinetics:

The reaction kinetics of KK-142 have been

studied in both micro- and pilot-scale. The

dependency of pressure and the molar

fractions of carbon monoxide and water

found for the classical high temperature

shift catalysts describe the behaviour of

KK-142 fairly well. The temperature

dependency on the rate of reaction, or theactivation energy, is, however, much lower

for KK-142. In fact, the activation energy

is only approximately 1/5 of that of

classical high temperature shift catalystSK-12. This means that the conversion

rate is only slightly affected by the

operating temperature.

This is an interesting characteristic

because, combined with the high thermo-

stability of KK-142, this feature allows for

the use of brand new reactor concepts in

new ammonia plants. One could for

instance, envisage KK-142 operating in a

boiling water reactor, producing high

pressure steam. If classical, low temperature

or medium temperature shift catalysts was

used, the only way of recovering the heat

of the shift reaction would be as low

pressure steam or the like because the

reaction would have to be carried out at a

much lower steam temperature in a boiling

water reactor.

Start-up of KK-142.

Due to the nature of the KK-142 (copper-

based) it must be reduced in a similar

manner as for an LTS catalyst before it

can be put on stream. This will in most

existing plants require some modification.

Conclusion on Iron-free HTS Catalyst.

KK-142.

Longterm laboratory tests have proved that

KK-142 can operate at the most demanding

conditions which can be envisaged for a

modern natural gas based ammonia plant

without forming Fischer-Tropsh by-products

and its unique mechanical stability will

ensure a low pressure drop throughout its

life, at any operating conditions.

Effect on LTS Catalyst

With a new type of HTS catalyst installed,

it is, of course, equally important how the

downstream LTS catalyst is affected. As

already discussed, the oxygenates formed

over a classical HTS catalyst at low steam

to carbon ratios reduce the activity of the

LTS catalyst whereby the CO leakage and

also the lifetime are adversely affected. By

applying a HTS catalyst type, which

prevents the formation of by-products, this

problem is eliminated and the full activityof the LTS catalyst can be utilized.

When a copper-promoted HTS catalyst

(SK-201) is used in the HTS, compounds

which are poisonous to the LTS catalyst,

such as sulphur and chlorine will migrate

through the HTS and end up poisoning the

LTS catalyst just like it is the case when

using a classical HTS catalyst.

When KK-142 is used in the HTS, the

situation is quite different. Due to

KK-142's nature (Cu-based), LTS catalyst

poisons will be retained by the KK-142 and

147

slowly poison this catalyst. KK-142 thereby

acts as a guard for the LTS catalyst.

Consequently, the consumption of LTS

catalyst becomes negligible, and only

deactivation due to sintering of the LTS

catalyst needs to be taken into considera-

tion when predicting the LTS life andperformance.

One could say that the use of KK-142 in

the HTS transfers the catalyst consumption

from the LTS reactor to the HTS reactor.

In case KK-142 is used in the HTS, you

could thus expect shorter HTS catalyst

lifetimes and much longer LTS catalyst

lifetimes. This is best illustrated by the

following calculation examples where the

overall shift performance (HTS and LTS as

a whole) at different steam to carbon

ratios is discussed.

As basis, we have chosen a steam to

carbon ratio of 3.1, which will be a typical

goal for revamps, and, as an extreme, we

have made the same calculations for a

steam to carbon ratio of 2.5.

The calculations have been carried out

based on the extensive industrial feedback

on activity and lifetime from the industry

for HTS catalyst SK-12 and LTS catalyst

LK-821 and on long-term laboratory

experiments (ageing, poisoning, etc.) for

the new HTS catalysts SK-201 and KK-142.

The catalyst volumes, types, and inlet

conditions are shown in Table 2. We have

considered 3 cases for each steam to

carbon ratio:

Case 1 : Classical HTS catalyst SK-12

Super-active LTS catalyst LK-821

Case 2: Cu-promoted HTS catalyst SK-201

Super-active LTS catalyst LK-821

Case 3: Cu-based iron- and chromium-free

catalyst KK-142

Super-active LTS catalyst LK-821

The CO leakage from the HTS and theLTS has been calculated over an 8-year-

period and shown for steam to carbon

ratio of 3.1 in Figure 8 and for a steam to

carbon ratio of 2.5 in Figure 9.

The economics in terms of production

gains and catalyst consumption have been

evaluated in Table 3.

From Table 3, it is seen that, compared to

a modified HTS catalyst, the use of a

classical HTS catalyst would cause a

certain production loss even at a steam to

carbon ratio of 3.1, and the use of a

classical HTS catalyst at a steam to carbon

ratio of 2.5 would surely be prohibitive. It

is further noted that especially at a steam

to carbon ratio of 2.5, the consumption of

the iron-free HTS catalyst KK-142 is more

than compensated for by the savings in

LTS catalyst consumption.

148

Table 2 Figure 9

HTS and LTS CatalystPerformance Predictions for

1150 STPD NH3 Plant atS/C = 3.1 and S/C = 2.5

HTS and LTS performance at S/C = 2.5

1. Catalyst Volume :HTS: 1947cu.lt (SSW*)

LTS: 2075 caft (59m3)

2. Catalyst Typos:

Case 1 : HTS : SK-12

Case 2: HTS:SK-201

Case3: HTS:KK-142

3. HTS Inlet Conditions:

Dry gas (low, MSCFH, (Nm3/h)

Dry gas composition, mole %

H2

N2

COC02

AT

CH4

S/DG ratio

Inlet pressure, psig (kg/cm2g)

Inlet temperature, 'FfC)

4. LTS Inlet Conditions:

LTS : LK-821

LTS : LK-821

LTS : LK-821

S/C - 3.1

4875

(131000)

56.15

22.62

13.24

7.39

0.27

0.33

0.52

460(32)

644-716

(340-380)

S/C - 2.5

4875

(131000)

55.73

22.66

14.42

6.41

0.27

0.51

0.41

460(32)

644-716

(340-380)

Gas composition: Equal to HTS exit conditions.

Inlet pressure, psig (kg/cm j)

Inlet temperature, T (°C)440 (31)

392-428

(200-220)

440 (31)

374-428

(190-220)

dry%COex« HTS

4.2

4.0-

3.8-

3.6-

3.4-

<*y%COeût LTS

Age. years

6 Age, years

8 Age, years

Figure 8 Table 3

HTS and LTS performance at S/C = 3.1

8 Age, years

Benefits from usingAlternative HTS Catalysts atS/C = 3.1 and S/C = 2.5 seen

over an 8-year-per!od

S/C = 3.1

Case 1 Case 2 Case 3

SK-12/LK-821 SK-201/LK-821 KK-142/LK-82

Production gain due tono by-product formation. ST* o

(STPD) O

Production gain due tolower CO leakage, ST* 0

(STPD) 0

Catalyst consumption,charges-HTS 1*'charges - LTS 2

19000(7)

5500(2)

1 1/3

19000(7)

6500(2 1/2)

21/2

S/C = 2.5 .

Case 1 Case 2 Case 3

SK-12/LK-821 SK-201/LK-821 KK-142/LK-821

Production gain due tono by-product formation, ST*

(STPD)

Production gain due tolower CO leakage, ST*

(STPD)

Catalyst consumption,charges - HTScharges - LTS

33000(12 1/2)

28000(10 1/2)

39000(14 2/3)

30000(11 1/4)

21/2

8 Age, years

* If no purge recovery for hydrogen takes place, the gain is approximately50 % higher.

** Provided that the catalyst survives pressure drop-wise.

149

It should be emphasized that the above

examples solely serve to illustrate how the

high and low temperature shift catalyst

performance is affected by decreasing thesteam to carbon ratio. Depending upon the

lay-out of the individual plant, other

factors may be equally important when

evaluating the economics of a lower steam

to carbon ratio.

Conclusion

In the 1988 AlChE paper "Low Tempera-

ture Shift Catalyst Performance at Low

Steam Dry Gas Ratio", Haldor Tops0e A/S

discussed and quantified the problems and

economic drawbacks encountered when

operating the classical iron/chromium-basedhigh temperature shift catalyst at low

steam to carbon ratios.

We have in this year's paper presented

two solutions to the problems:

1) The first and more simple solution is

to modify the classical high tempera-

ture shift catalyst by a moderate

copper promotion. Tops0e's modified

catalyst SK-201, significantly reduces

the amounts of by-products formed

and in addition gives a much higher

catalyst activity for the shift reaction.

2) The second and more radical solution,

is the use of Tops0e's iron- and

chromium-free high temperature shift

catalyst KK-142, which completely

eliminates the Fischer-Tropsch

synthesis. Besides having a very high

activity for the shift reaction,

KK-142 is in possession of a remark-

ably high crushing strength, which is

unchanged even after long-time

exposure to conditions of low steam

to carbon ratio or exposure to

condensate.

The copper-based KK-142 opens the

possibilities for a completely new

shift technology as this catalyst can

be operated at normal HTS operating

temperatures as well as at lower

temperatures, thus maximizing both

heat recovery and carbon monoxide

conversion.

References:

[1] "Catalysts and Processes for the

Water Gas Shift Reaction", presented

at Communiçacao ao Colóquio Nacional

de Catalise Industrial, Lisboa, 1981

by P E H0jlund-Nielsen and J B0gild-

Hansen

[2] "Low Temperature Shift Catalyst

Performance at Low Steam to Dry

Gas Ratio", presented at the Ame-

rican Institute of Chemical Engineers

Ammonia Safety Meeting, Denver 1988

150

by John B0gild-Hansen, JackCarstensen and Peter S. Pedersen.

H. by the American Institute of ChemicalEngineers.

[3] "Revamp of Ammonia Plants", byAnders Nielsen, John B0gild-Hansen, Jens Houken and Erik AndreasGam in a reprint from the July 1982issue of "Plant/Operations Progress"

[4] "An Investigation on the Kinetics ofthe Conversion of Carbon Monoxidewith Water Vapour over Iron-OxideBased Catalyst"by H Bohlbro, Gjellerup 1969

DISCUSSIONT.L. HUURDEMAN, DSM Fertilizers: What are thevolumes of this new high-temperature shift catalyst? Canthe old vessels still be used when one changes from iron-based to copper-based catalysts?

PEDERSEN: Yes. As shown in our performanceexample, exactly the same volumes were assumed asare presently installed in the plants, as well as the samevessels and the same operating conditions.

JOHN BENNETT, Cheuron: You mentioned thepoisoning effect of sulfur. What effect do chlorides havewith your copper-based catalyst and copper-promotedcatalyst?

PEDERSEN: The chlorides will not poison the copper-promoted iron chromium catalyst, but they will poisonthe copper-based catalyst just as a low-temperature shiftcatalyst would become poisoned.

KEITH WILSON, Columbia Nitrosen: Some of usoperate plants with somewhat relaxed reformingconditions from the secondary reformer: that is CO andCÛ2 concentrations are somewhat different from thoseused in conventional plants. Your parameters seemedto represent steam to carbon ratio. Did you also look

to how CO or CÛ2 might impact the performance ofthese different catalysts?

PEDERSEN: Yes, in the presentation I did not mentionCO and COz. It is discussed in the paper in the formof a certain calculated KP/KE ratio. It is the actualthermodynamic value for which the CO/COz ratio andother parameters like temperature and pressure areconsidered when looking at this thermodynamic ratio.

KNUT BJORGO: Concerning the copper-basedcatalyst, do you have any information on methanolformation over this?

PEDERSEN: Yes, the copper-based catalyst will makemethanol in the same amount as a classic iron chromium-based high-temperature shift catalyst, which converts toequilibrium at the exit conditions. At normal high-temperature shift conditions, one cannot really makemuch methanol because of the low methanol equilibriumconcentration at the high-temperature level. So, lookingat what you can have in the process condensate, that'swhere plant operators usually measure methanol. Onecan only have, say, in the range from 30 to 150 partsper million of methanol from the high-temperature shift.

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