Common Causes of Catalyst Deactivation Differences of using Alumina - - PowerPoint PPT Presentation

Common Causes of Catalyst Deactivation

Differences of using Alumina versus Titania as Claus Catalyst and Tail Gas Catalyst carrier

Mark van Hoeke, MSc, Dr. Bart Hereijgers Euro Support B.V., Amersfoort, The Netherlands

Outline

• Common Causes of Catalyst Deactivation
• Advantages of using Pure Titania as Tail Gas Catalyst

Carrier

Euro Support Catalyst test-unit 4 identical stainless steel reactors used in parallel or in series

COMMON CAUSES OF CATALYST DEACTI VATI ON

Definition of a catalyst

“A substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change”

The performance of an Alumina catalyst predominantly depends on available surface area

Unfortunately catalytic activity will decrease over time due to various reasons

The main mechanisms of catalytic deactivation are through:

• 1. Porosity

blocking access to active sites

• 2. Purity

deactivation of active sites

• 3. Surface Area

decrease in number of active sites

Reduced accessibility of surface area

Liquid sulfur can fill up the pores

• f the catalyst when operating

below sulfur dew point Prevention/Remedy:

 Operate around 15oC above

sulfur dew point Sulfur condensation in smallest pores

– Unavoidable

Porosity

Reduced accessibility of surface area

Soot formation

 Prevention: proper operation line

burner. Ammonium Salts

 Prevention: ensure thermal stage

temperature of > 12500c for

• ptimal ammonia destruction

Coating by CarSul

 Prevention: ensure hydrocarbon

destruction in thermal stage

Porosity

Reduced accessibility of surface area

Cracking of BTX in catalyst pores

 Prevention: thermal stage

temperature of > 1050oC for hydrocarbon destruction

Porosity

Poisoning by sulfation

• Formed rapidly if the catalyst

comes in contact with oxygen

– H2S/SO2 ratio below 2 – Presence of unreacted

• xygen after direct fired

reheaters

• More stable at lower

temperature

– Therefore most common in

the second and third Claus reactor

 Remedy: rejuvenation procedure

Purity

Titania surface is far more resistant to sulfation

Temperature programmed reduction of a sulfated titania and alumina catalyst with H2S

1 The hydrolysis of Carbonyl Sulfide, Carbon Disulfide and Hydrogen Cyanide on

Titania Catlayst. H.M. Huisman .1994

H2S Purity

Loss in surface area by ageing

Hydrothermal aging

• Presence of steam in

combination with higher temperatures and pressure results in loss of surface area Thermal aging

• Sintering of pores due to

excessive temperature results in loss of surface area

Surface Area

Ageing of Titania catalyst

25 50 75 100 125 150 20 40 60 80 100 120 140 Specific Surface Area / m2.g-1 Severe Ageing Time (h) Pure TiO2 Diluted TiO2

Surface Area

Limited Activity decline by ageing

20 40 60 80 100 270 280 290 300 310 320 330

CS2 conversion / % T-inlet / dgC

Pure TiO2

CS2 hydrolysis activity after hydrothermal aging, SV = 1832 h-1 Fresh Mild ageing 16h severe ageing 132h severe sgeing ES-Al2O3 Fresh

20 40 60 80 100 270 280 290 300 310 320 330

CS2 conversion / % T-inlet / dgC

Diluted TiO2

CS2 hydrolysis activity after hydrothermal aging, SV = 1832 h-1

Lower SA but higher activity!

Purity and Poisoning Observed difference in activity not explained by surface area or porosity. Surface area and strength at the expense of purity and activity

Fresh Pure TiO2 Diluted TiO2

Surface area (m2/g) 149 123 Strength (N/mm) 35 37 Pore volume (mL/g) 0.42 0.32 TiO2 (wt%) >99 86 Ca(SO4) (wt%) 12 Density (kg/m3) 823 1009

0.01 0.02 0.03 0.04 0.05 0.06 0.07 2 4 8 16 32 64 128 256

Incremental Pore Volume (mL/g) Mean Pore Diameter (nm) Pure Titania Diluted Titania

Poisoning by (earth) alkali

20 40 60 80 100 120 80 82 84 86 88 90 92 94 96 98 100 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 CS2 conversion (%) CS2 conversion (%) Alkali content (XRF)/wt%

CS2 conversion vs purity Activity at 300 C, GHSV = 1800/h, after Mild ageing

CaO content NaO2 content

(Earth)alkali impurities have detrimental effect on catalyst activity Purity

ADVANTAGES OF USI NG PURE TI TANI A AS TAI L GAS CATALYST CARRI ER

Main reactions I

• SO2 and S hydrogenation (CoMo)
• COS and CS2 hydrolysis (support)
• CO conversion (CoMo)

– CO + H2O → CO2 + H2

Water gas shift, H2 production

– CO + H2S → COS + H2

COS production in sour gas shift

– CO + S → COS

COS production from sulfur

Titania based catalyst shows higher activity at lower temperatures than commercial leading Low Temperature Alumina based catalyst

50 55 60 65 70 75 80 85 90 95 100 200 220 240 260 280 300 320

COS conversion (%) Inlet Temperature (dgC)

Low T. Titania based Low T. Alumina based Hight T. Alumina based type 1 Hight T. Alumina based type 2

Titania based catalyst shows higher activity after low temperature I n

I n- sit u u pre-sulfiding conditions

50 55 60 65 70 75 80 85 90 95 100 200 210 220 230 240 250 260

COS conversion (%) Inlet Temperature (dgC)

Low T. Titania based Low T. Alumina based

Titania based catalyst shows a higher resistance to oxygen slip and easier resulfiding

• 80
• 60
• 40
• 20

20 40 60 80 100 0:00:00 24:00:00 48:00:00 72:00:00 96:00:00 120:00:00 144:00:00 168:00:00 192:00:00

COS conversion %

Time (hh:mm:ss)

TiO2 based commercial catalyst Leading Al2O3 based catalyst 290 °C 230 °C 230 °C + O2 230 °C ex O2 230 °C ex O2 230 °C + O2 Test at Tin = 230 °C Feed (%wet/%dry): H2S (1/1.28), SO2(0.5/0.64), COS and CS2 (0.025/0.032), H2 (1.5/1.92), CO (1.1/1.41), CO2

(16.7/21.4), H2O (22/), GHSV 1500 h-1. O2 (0.3/0.43 or 0).

Deactivation of Tailgas catalyst

0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0 TiO2- based, SOR TiO2- based 2 years Al2O3- based, SOR Al2O3- based, 2 years TiO2- based, SOR TiO2- based 2 years Al2O3- based, SOR Al2O3- based, 2 years

Conversion (%)

Commercial LT-TGTU catalyst activity fresh vs. after 2 years testing GHSV =1500/h, COS conversion (%)

230 °C 260 °C

Conclusions

• Activity of Titania catalysts depends on more than just

surface area

• Added Calcium Sulfate to enhance strength of Titania

Catalyst has a negative impact on the catalytic activity

• Titania based Tail Gas Treating catalyst provides superior

performance and operational benefits over Alumina based Tail Gas Treating catalyst

THANK YOU

BACKUP SLI DES

Dilution effect on performance?

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Pure TiO2 catalyst 1000 L Diluted TiO2 catalyst 1000 L 850 kg/m3 1000 kg/m3 >99% TiO2 86% TiO2 >842 kg Pure TiO2 860 kg Pure TiO2 120 kg CaSO4 120 kg additional material in reactor does not contribute anything to performance

Raw data activity measurement

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20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90

COS and CS2 conversion / % Time on stream / hrs

CS2/COS hydrolysis. Pure Titania Catalyst, after SEVERE ageing. 4-R-1 Feed gas (set points in mol% wet/mol% dry basis): H2S (8/10.67); SO2 (4.5/6); COS (0.5/0.67); CS2 (0.5/0.67); O2 (0.02/0.0267); H2O (25/-); N2 balance

COS CS2

(320°C) (300°C) (280°C) (300°C) (320°C) (280°C) 1832 h-1 916 h-1

Main reactions I

• Hydrogenation and shift reactions catalyzed by metal sulfides
• Claus and hydrolysis reactions catalyzed by support
• SO2 and S conversion

– 2 H2S + SO2 ↔ 3/n Sn + 2H2O

Claus reaction

– SO2 + 3H2 ↔ H2S + 2H2O

SO2 hydrogenation

– 3/n Sn + H2 ↔ H2S

Sulfur hydrogenation

• CO conversion

– CO + H2O ↔ CO2 + H2

Water gas shift, H2 production

– CO + H2S ↔ COS + H2

COS production in sour gas shift

– CO + S ↔ COS

COS production from sulfur

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Main reactions I I

• Hydrolysis (support)

– COS + H2O ↔ CO2 + H2S

COS removal

– CS2 + 2H2O ↔ CO2 + H2S

CS2 removal

• CS2 hydrogenation

– CS2 + 3H2 ↔ CH3SH

Mercaptan production

• CH3SH conversion

– CH3SH + H2 ↔ CH4 + H2S

Mercaptan removal

– CH3SH + 3/nSn ↔ CS2 + 2H2S

Mercaptan removal

– CH3SH + SO2 ↔ CS2 + 2H2O

Mercaptan removal

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HT vs. LT

• High temperature

– (in)direct fired reheaters – consumption of natural gas – Conventional tail-gas catalyst – HT-sulfiding of catalyst; CoxMoyOz + H2 + H2S  CoMoSx + H2O

• Low temperature

– Steam reheaters, Tin, max. = 240 oC – Special catalyst – In-situ or ex-situ presulfiding

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Test conditions, evaluation

High Temperature (HT) pre-sulfiding

• Heat up the catalyst to 375 °C
• in 1 mol% H2S, 4 mol% H2, N2 balance,
• at a space velocity (GHSV) of 650 Nm3/m3/h.
• Keep the catalyst at 375 °C for 16 hours.
• Cool to test temperature and switch to test gas.

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I n I n-sit u u pre-sulfiding conditions for a Low Temperature TGT catalyst

• Heat up the catalyst to 130 °C
• Feed Gas Composition:

1.5 mol% H2S, 6.0 mol% H2 6.7 mol% H2O, N2 balance, GHSV = 450 Nm3/m3/h.

• Tin, max = 240 °C,

in plant additional ΔT from exothermal sulfiding reaction gives Tbed = 300 °C

• Test sequence: 220 – 230 – 235 – 220 – 200 – 215 – 220 – 230 – 240 °C

50 100 150 200 250 300 350 4 8 12 16 20 24 Inlet Temperature (dg) Time (h)

+ΔT = 300oC, ‘exotherm’

Test conditions, evaluation

Performance evaluation

• Start at 290 °C inlet temperature in test gas.
• Feed gas (N2 balance):

1 mol% H2S, 0.5 mol% SO2, 0.025 mol% COS, 0.025 mol% CS2, 1.5 mol% H2, 1.1 mol% CO, 22 mol% H2O, 16.7 mol% CO2, GHSV = 1500 Nm3/m3/h.

• Analyze dry feed gas and dry, sulfur free product gas.
• Temperature sequence: 290 – 260 – 230 – 200 – 220 – 215 °C.

31-03-2015

• Low hydrogenation activity (CoMoSx):

– CO shift reaction efficiency decreases – COS emmision increases through COS formation from CO.

• Low hydrolysis activity (support):

– CS2 hydrogenation competes with hydrolysis; – Formation of CH3SH increases – When catalytic activity is extremely low, CH3SH formation drops

to zero as well!

Assessing Catalyst Quality

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• CO conversions (CoMoSx)

– CO + H2O → CO2 + H2 Water gas shift (DECREASES) – CO + H2S → COS + H2

Sour gas shift (INCREASES)

– CO + S → COS

COS production from S (INCREASES) Upon deactivation COS emissions will increase due to the reactions above. The COS that is formed in the lower layer of the bed cannot be hydrolysed anymore by the carrier.

• CS2 hydrolysis-hydrogenation competition

– CS2 + 2H2O → CO2 + H2S CS2 Hydrolysis (DECREASES) – CS2 + 3H2 → CH3SH

Mercaptan production (INCREASES) Upon deactivation CS2 hydrogenation starts competing with the hydrolysis. This means mercaptans are formed that will contribute to emissions. When catalytic activity is extremely low, also CS2 hydrogenation activity drops to zero.

Assessing Catalyst Deactivation

Back up slide

TI TANI A AS CLAUS CATALYST P

. D. Clark, N. I. Dowling and M. Huang, 2015

• Ti3+ cations under Claus process conditions -> Proton donor

(Bronsted Acid) -> promotes the adsorption/activation of SO2 and, hence, increases its Claus reaction rate.

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