low temperature catalytic oxidation of h2s over · pdf filefuel(vehicles(( heat( electricity...

Low temperature catalytic oxidation of H2S

over V2O5/CeO2 Catalysts

DIIN- Department of Industrial Engineering University of Salerno

Vincenzo Palma*, Daniela Barba , Paolo Ciambelli

*[email protected]

December 11-13, 2013

European Fuel Cell Technology & Applications

Biogas INTRODUCTION

Renewable Energy Source Agricultural

Waste Biomass

Sewage Sludge

Industrial Waste Utilization

Fuel Vehicles Heat Electricity Fuel Cell

Molten Carbonate Fuel Cells (MCFC)

CO2 + ½ O2 + 2e-‐ →CO32-‐ Catode

H2 + CO3

2-‐ →H2O + CO2 + 2e-‐ Anode

q  Can lead to the poisoning of the anode and electrolite q  Can deactivate of sites for the oxidation

INTRODUCTION

Poisoning problem of the cells by H2S

(sulphur content allowed <1 ppm)

Clean-‐up Biogas : Purification Processes

Dry Processes

Chemical Absorption in aqueous solutions

Physical Solvent Membrane Separation

Biological Desulfurization

INTRODUCTION

Clean-‐up Biogas : Oxidation Processes

Ø  Catalytic Oxidation: Claus Process

Ø  Selective Catalytic Oxidation at Low Temperature:

T=950-‐1250°C

T=170-‐350°C

T=150-‐250°C

𝟐𝐇↓𝟐 𝐒 + 𝐒𝐎𝟐= 𝟑⁄𝐧 𝐒𝐧+ 𝟐𝐇↓𝟐 𝐎

𝐇↓𝟐 𝐒 + 𝟑⁄𝟐 𝐎𝟐= 𝐒𝐎↓𝟐 + 𝐇↓𝟐 𝐎

𝟏⁄𝐧 𝐒↓𝐧  + 𝐎𝟐= 𝐒𝐎↓𝟐  Temperature and catalyst influence the reaction

mechanism and the process selectivity

Innovative process for H2S abatement

INTRODUCTION

Catalysts Formulation (2.55%-‐20% v2o5)

Temperature (150-‐250°C)

Contact Time (4-‐80 ms)

Aim of the work Ø Previous works.. Among the others V/Ce seems to be most promising

Ø  IN THIS WORK IMPROVE THE PROCESS SELECTIVITY TO SULFUR

V2O5/CeO2 Catalysts

2.55%

8%

20% 10%

5%

Wet Impregnation of the support with NH4VO3 aqueous solution

Drying @120°C overnight

Calcination @400°C for 3h, dT/dt =10°C/min

EXPERIMENTAL Preparation Method

Characterization Tecniques

X-RAY

Diffraction

Raman Spectroscopy

Specific Surface

Area

Catalysts Characterization

(*) B.E.T. Method, Pretreatment in He @T=150 C for 1h

DECREASE OF THE SPECIFIC AREA UPON V2O5 ADDITION

Sample Fresh Catalyst SSA, m2/g

CeO2 80

2,55% V2O5/CeO2 75

5% V2O5/CeO2 57

8% V2O5/CeO2 39

10% V2O5/CeO2 32

20% V2O5/CeO2 17

Catalysts Characterization

CeO2

EXPERIMENTAL

CeO2

V=O

V2O5

Polyvanadate

Laboratory Apparatus Plant

Feed Section

Analysis Section

Reaction Section

Analysis Section Mass Spectrometer

FT-‐IR

O2

Atmospheric Pressure

Temperature : 150-‐250°C

H2S Concentration: 200 ppm

O2/H2S (mol:mol) : 0.5

Total Flow Rate : 600 Ncm3/min

GHSV : 180,000 h-‐1 (τ : 20 ms)

Laboratory Apparatus Plant

OPERATING CONDITIONS:

Catalytic Activity Tests

H2S

O2

SO2

T=150°C, 60 min

H2O

sig

nal,

-

H2O

Catalytic Activity Tests RESULTS

High Activity at any temperature

H2S conversion >90% @T≥200°C


T, °C CeO2 V2O5

150 1 4

200 3 14

244 6 19


H2S conversion (~100%)

for the 20%V2o5/Ceo2

Minimization of So2 selectivity (~1%) for the 20%V2o5/Ceo2


Decrease of H2S conversion

With the temperature

Increase of SO2 selectivity

With the temperature

SSA Fresh Catalyst = 17 m2/g


Increase of the surface area

Oxidation of sulphur deposited on the catalyst

surface H2S --> S --> SO2

T=150°C

Contact Time, ms 4 10 20 40 80

xH2S, % 50 88 94 96 98

SO2, ppm 0 2 4 13 14

Y SO2,% 0 0,5 1 2,7 3

T=150°C

Increase of SO2 concentration

Conclusion X-‐Ray Diffraction & Raman Spectroscopy

Ø Good dispersion of V2O5 for all the catalysts Ø Low content of crystalline vanadium on the 20%V2O5/CeO2

Influence of the vanadium loading

Ø Improvement of the catalytic activity to the increase of V2O5 Ø Highest H2S conversion (~100%) and lowest SO2 selectivity (1%) @150°C for the 20%V2O5/CeO2 catalyst

Influence of the Contact Time

Ø Effect on the specific area and the SO2 selectivity

FUTURE WORKS

Effect of Temperature (<150°C) with the Contact Time

Influence of the vanadium loading (>20%)

Identification of sulphur species

Low temperature catalytic oxidation of H2S over V2O5/CeO2 Catalysts

Vincenzo Palma*, Daniela Barba , Paolo Ciambelli

*[email protected]

DIIN- Department of Industrial Engineering University of Salerno

Piero Lunghi Conference, December 11-13, 2013

0

20

40

60

80

100

0 2 4 6 8 10 12

Gas Velocity, cm/s

H2S

Con

vers

ion,

%

External Diffusion

External and Internal Mass Transfer resistance

T=250°C, H2S=200 ppm, O2/H2S=0.5

Internal Mass Transfer resistance was observed for size particles > 180 μm

Flow Rate: 200, 300, 400, 800 Ncm3/min

0102030405060708090100

H2S

co

nve

rsio

n,

%

38-180 180-355 355-710

Size Particles, micrometer

Size Particles, µm : • 38-180 • 180-355 • 355-710

Flow Rate, Ncm3/min VGAS, cm/s XH2S, %

200 2.6 56

300 4 64

400 5.3 67

800 10.6 67

External Mass Transfer resistance was observed for linear gas velocity < 5 cm/s

t = 2ms

Ø  Pressure: 1 atm 2 atm 3 atm

Ø  H2S Concentration = 200 ppm

Complex Equilibrium : S8 ↔4 S2

3 S8↔4 S6 S6↔3 S2

H2S + O2→ aSO2+ bS2+ cS6+dS8 + eH2O+ fH2

Temperature,°C

H 2S Co

nversion

, % H2S conversion

Higher at P=1 atm

H2S conversion Higher

At P=3 atm

370°C

Ø  O2/H2S = 0.5

Thermodynamic Study

Thermodynamic Study


Ø  O2/H2S = 0.5 Ø  H2S Concentration = 200 ppm


Temperature,°C

SO2 selecKv

ity, %

T<200°C Low SO2 Selectivity

200°C

Complex Equilibrium : S8 ↔4 S2

3 S8↔4 S6 S6↔3 S2

Thermodynamic Study


Ø  O2/H2S = 0.5 Ø  H2S Concentration = 200 ppm


Temperature,°C

S 2 se

lecKvity, %

0

20

40

60

80

100

120

0 200 400 600 800 1000

Temperatura, °C

Sele

ttivi

tà S

2, %

Increase of S2 Selectivity

T> 200°C

Increase of S8 Selectivity

0

20

40

60

80

100

120

0 200 400 600 800 1000

Temperatura, °C

Sele

ttivi

tà S

8, %

Temperature,°C

S 8 se

lecKvity, %

T< 200°C

Adsorption Test of H2S T = 160°C, H2S = 800 ppm

0

100

200

300

400

500

600

700

800

0 10 20 30 40 50 60 70Time, min

H2S

Con

cent

rati

on, p

pm

0

1E-11

2E-11

3E-11

4E-11

5E-11

6E-11

7E-11

H2O

sig

nal m

/z=

18, t

orr

H2S

H2O

H2S adsorbs and reduces the catalyst producing H2O

OHSH ofg 211)(2 +↔+ θθ

Reaction between H2S adsorbed and O2 of the phase active

After the O2 activation via adsorption, the reoxidation of the previously reduced

vanadium to the oxidized vanadium occurs No SO2 , SO3 , H2O formation detected

Kinetics Mechanism Study 1/1

Goodness of fit experimental data to the power law model

T = 200°C, 600 ppm H2S

Langmuir-Hinshelwood Mechanism

Design Equation for a Plug Flow Reactor (PFR)

( ) CATSHSH dWrdF ⋅−=− 22

Kinetic Expression

ooSH Kr 21)(2

θθ ⋅⋅=−

tot

CAT

SHO

inOSHSH

inSH

SHO

inOSHSH

inSH

inSH

SH QdW

)R

X.(PK)X(PK

)R

X(PK)X(PK

CKdX ⋅

⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢

⎣

⎡

⎥⎦

⎤⎢⎣

⎡−⋅+−⋅⋅+

−⋅⋅⋅−⋅⋅⋅= 2

2111

211

222222

222222

2

2

=

2222

22

1 OOSHSH

SHSH

PKPKPK

⋅+⋅+

⋅o1θ

o2θ

2222

22

1 OOSHSH

OO

PKPKPK

⋅+⋅+

⋅=

RDS

Goodness of fit experimental data to the power law model

Kinetics Mechanism Study 2/1

T = 200°C 600 ppm H2S

0

5

10

15

20

25

30

35

0,000012 0,000022 0,000032 0,000042

W/QTOT, (g min/Ncm3)

H2S

Con

vers

ion

, %

20 ppm O2

40 ppm O2

60 ppm O2

100 ppm O2 Experimental Data

Calculation Model

tot

CAT

SHO

inOSHSH

inSH

SHO

inOSHSH

inSH

inSH

SH QdW

)R

X.(PK)X(PK

)R

X(PK)X(PK

CKdX ⋅

⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢

⎣

⎡

⎥⎦

⎤⎢⎣

⎡−⋅+−⋅⋅+

−⋅⋅⋅−⋅⋅⋅= 2

2111

211

222222

222222

2

2

Good fitting of the experimental data

with the L-H model

Effect of the CH4

0

10

20

30

40

50

60

0

50

100

150

200

250

0 20 40 60 80 100 120

CH

4 Con

cent

ratio

n , v

ol%

H2S

Con

cent

ratio

n, p

pm

Time, min

H2S

CH4

x H2S = 96% CH4 FEED = 30%

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