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 Porosity Liquid sulfur can fill up the pores of the catalyst when operating below sulfur dew point Prevention/Remedy:  Operate around 15 o C above sulfur dew point Sulfur condensation in smallest pores – Unavoidable

Reduced accessibility of surface area Porosity Soot formation  Prevention: proper operation line burner. Ammonium Salts  Prevention: ensure thermal stage temperature of > 1250 0 c for optimal ammonia destruction Coating by CarSul  Prevention: ensure hydrocarbon destruction in thermal stage

Reduced accessibility of surface area Porosity Cracking of BTX in catalyst pores  Prevention: thermal stage temperature of > 1050 o C for hydrocarbon destruction

Poisoning by sulfation Purity • Formed rapidly if the catalyst comes in contact with oxygen – H 2 S/SO 2 ratio below 2 – Presence of unreacted oxygen after direct fired reheaters • More stable at lower temperature – Therefore most common in the second and third Claus reactor  Remedy: rejuvenation procedure

Titania surface is far more resistant to sulfation Purity Temperature programmed reduction of a sulfated titania and alumina catalyst with H 2 S H 2 S 1 The hydrolysis of Carbonyl Sulfide, Carbon Disulfide and Hydrogen Cyanide on Titania Catlayst. H.M. Huisman .1994

Loss in surface area by ageing Surface Area 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

Ageing of Titania catalyst Surface Area 150 125 Specific Surface Area / m2.g-1 100 75 50 25 0 0 20 40 60 80 100 120 140 Severe Ageing Time (h) Pure TiO2 Diluted TiO2

Limited Activity decline by ageing Pure TiO 2 Diluted TiO 2 CS 2 hydrolysis activity after hydrothermal aging, CS 2 hydrolysis activity after hydrothermal aging, SV = 1832 h -1 SV = 1832 h -1 100 100 80 80 CS 2 conversion / % CS 2 conversion / % 60 60 40 40 20 20 0 0 270 280 290 300 310 320 330 270 280 290 300 310 320 330 T-inlet / dgC T-inlet / dgC Fresh Mild ageing 16h severe ageing 132h severe sgeing ES-Al2O3 Fresh Lower SA but higher activity!

Purity and Poisoning Observed difference in activity not explained by surface area or porosity. 0.07 0.06 Fresh Pure Diluted Incremental Pore Volume TiO 2 TiO 2 0.05 Surface area (m 2 /g) 149 123 (mL/g) 0.04 Strength (N/mm) 35 37 0.03 Pore volume (mL/g) 0.42 0.32 TiO 2 (wt%) >99 86 0.02 Ca(SO 4 ) (wt%) 0 12 0.01 Density (kg/m 3 ) 823 1009 0 2 4 8 16 32 64 128 256 Mean Pore Diameter (nm) Pure Titania Diluted Titania Surface area and strength at the expense of purity and activity

Poisoning by (earth) alkali Purity CS2 conversion vs purity Activity at 300 C, GHSV = 1800/h, after Mild ageing 100 120 CaO content 98 100 NaO2 content 96 94 CS2 conversion (%) CS2 conversion (%) 80 92 90 60 88 40 86 84 20 82 80 0 0 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 Alkali content (XRF)/wt% (Earth)alkali impurities have detrimental effect on catalyst activity

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

Main reactions I • SO 2 and S hydrogenation (CoMo) • COS and CS 2 hydrolysis (support) • CO conversion (CoMo) – CO + H 2 O → CO 2 + H 2 Water gas shift, H 2 production – CO + H 2 S → COS + H 2 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 100 95 Low T. 90 Titania based COS conversion (%) 85 Low T. 80 Alumina based 75 70 Hight T. 65 Alumina Hight T. based 60 Alumina type 1 based 55 type 2 50 200 220 240 260 280 300 320 Inlet Temperature (dgC)

Titania based catalyst shows higher activity after low temperature I n I n- u pre-sulfiding conditions sit u 100 95 Low T. 90 Titania based COS conversion (%) 85 80 75 70 65 Low T. Alumina 60 based 55 50 200 210 220 230 240 250 260 Inlet Temperature (dgC)

Titania based catalyst shows a higher resistance to oxygen slip and easier resulfiding 290 °C 230 °C 100 230 °C ex O2 80 230 °C + O2 60 230 °C ex O2 COS conversion % 40 20 0 230 °C + O2 -20 -40 TiO2 based commercial catalyst -60 Leading Al2O3 based catalyst -80 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 Time (hh:mm:ss) 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 Commercial LT-TGTU catalyst activity fresh vs. after 2 years testing GHSV =1500/h , COS conversion (%) 100.0 230 °C 260 °C 90.0 80.0 70.0 Conversion (%) 60.0 50.0 40.0 30.0 20.0 10.0 0.0 TiO2- TiO2- Al2O3- Al2O3- TiO2- TiO2- Al2O3- Al2O3- based, based 2 based, based, 2 based, based 2 based, based, 2 SOR years SOR years SOR years SOR years

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

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BACKUP SLI DES

Dilution effect on performance? Pure TiO 2 catalyst Diluted TiO 2 catalyst 1000 L 1000 L kg/m 3 kg/m 3 850 1000 >99% TiO 2 86% TiO 2 >842 kg Pure TiO 2 860 kg Pure TiO 2 120 kg CaSO 4 120 kg additional material in reactor does not contribute anything to performance 28

Raw data activity measurement 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 1832 h -1 916 h -1 100 COS and CS2 conversion / % 90 80 (320°C) (300°C) (280°C) (320°C) (300°C) (280°C) 70 60 50 40 COS 30 CS2 20 0 10 20 30 40 50 60 70 80 90 Time on stream / hrs 29

Main reactions I • Hydrogenation and shift reactions catalyzed by metal sulfides • Claus and hydrolysis reactions catalyzed by support • SO 2 and S conversion – 2 H 2 S + SO 2 ↔ 3/n S n + 2H 2 O Claus reaction – SO 2 + 3H 2 ↔ H 2 S + 2H 2 O SO 2 hydrogenation – 3/n S n + H 2 ↔ H 2 S Sulfur hydrogenation • CO conversion – CO + H 2 O ↔ CO 2 + H 2 Water gas shift, H 2 production – CO + H 2 S ↔ COS + H 2 COS production in sour gas shift – CO + S ↔ COS COS production from sulfur 31-03-2015

Main reactions I I • Hydrolysis (support) – COS + H 2 O ↔ CO 2 + H 2 S COS removal – CS 2 + 2H 2 O ↔ CO 2 + H 2 S CS 2 removal • CS 2 hydrogenation – CS 2 + 3H 2 ↔ CH 3 SH Mercaptan production • CH 3 SH conversion – CH 3 SH + H 2 ↔ CH 4 + H 2 S Mercaptan removal – CH 3 SH + 3/nS n ↔ CS 2 + 2H 2 S Mercaptan removal – CH 3 SH + SO 2 ↔ CS 2 + 2H 2 O Mercaptan removal 31-03-2015

HT vs. LT • High temperature – (in)direct fired reheaters – consumption of natural gas – Conventional tail-gas catalyst – HT-sulfiding of catalyst; Co x Mo y O z + H 2 + H 2 S  CoMoS x + H 2 O • Low temperature – Steam reheaters, T in, max. = 240 o C – Special catalyst – In-situ or ex-situ presulfiding 31-03-2015

Test conditions, evaluation High Temperature (HT) pre-sulfiding • Heat up the catalyst to 375 °C • in 1 mol% H 2 S, 4 mol% H 2 , N 2 balance, • at a space velocity (GHSV) of 650 Nm 3 /m 3 /h. • Keep the catalyst at 375 °C for 16 hours. • Cool to test temperature and switch to test gas. 31-03-2015