Kwon HBCU Monolith R

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					Conversion of Hydrogen Sulfide in Coal Gases to
Liquid Elemental Sulfur with Monolithic Catalysts


       Kyung C. Kwon, Claudell Burnell, and Laneddye Carter

                  Chemical Engineering Department
                       Tuskegee University



                                Robie Lewis

 U.S. Department of Energy National Energy Technology Laboratory,
                  Morgantown, WV 26507 -0880



       2006 DOE/NETL HBCU/OMI Contractors Review Conference, June 8, 2006
      Outline

Introduction
Motivation
Objectives
Experimental Setup
Results and Discussion
Summary
IGCC (Integrated Gasification Combined Cycle)
                      Motivation
Conversion of coal into clean raw syngas by coal gasification
is the primary step in advanced coal utilization processes

Increased removal of hydrogen sulfide (H2S) and reduced
formation of carbonyl sulfide (COS) from raw syngas and
elemental sulfur recovery are necessary.

Conventional amine-based processes for sulfur removal and
recovery are equipment intensive and expensive, requiring
upstream COS hydrolysis reactor, amine scrubber, amine
regenerator, Claus plant and tail-gas treatment plant.

Tuskegee University (TU) is developing the Single-Step Sulfur
Recovery Process (SSRP) using Claus catalysts in monolithic
form instead of conventional Claus catalysts in fine pellet
form.
                       Objectives
To study kinetics of direct oxidation of H2S to elemental sulfur
and formation of COS over selective catalysts in the presence
of SO2, moisture, CO, CO2, and hydrogen, using a monolithic
catalyst-loaded reactor.

To investigate effects of concentrations of H2S, SO2, and
moisture, as well as pressure, space time, catalyst age, and
temperature on conversion of H2S into elemental sulfur and
formation of COS.

To formulate catalysts for the Single-Step Sulfur Recovery
Process (SSRP) and regenerate elemental sulfur poisoned
catalyst.

To develop kinetic rate equations and model the direct
oxidation process with experimental data.
         Monolithic Catalyst Support




Cell Shape                                  square
Cells/inch2 (CPSI)                          400
Wall Thickness, cm                          0.02
Flat Area/Cell/Length, cm2/cell/cm-length   0.345
Chemical Composition, (2MgO-2AL2O3-SIO2)    Cordierite
             Monolithic Catalyst

       Top View                     Side View




Diameter, cm              2
Length, cm                15
Number of Square Cells    200
Flat Surface Area, cm2    1,040
Wash Coat                 γ-Al2O3
Schematic Diagram of the Monolithic Catalyst Reactor Assembly.

                                                              Pressure
                                                              Indicator
   N2 Mass
   Flow Meter

                                                                                 Vent




                                               Honeycomb
                                               Catalyst Bed
  H2S /CO/CO2/H2/
                                                               Water     Pressure       Gas
  N2 Mass Flow                                                                                          Computer
                                                               Condenser Regulator      Chromatograph
  Meter




                    Heat      Heat           Honeycomb
                    Exchanger Exchanger      Reactor

    Water Pump                                                                1/16-inch Tubing
                                                                              1/4-inch Tubing
                                      Oven
                                                                              Filter

                                                                              Check Valve
   SO2 / N2 Mass
   Flow Meter
Monolithic Catalyst Reactor Assembly
The monolithic catalyst loaded reactor assembly consists
of one high pressure liquid pump for water, three mass
flow meters for gases, three filters and check valves for
gases, two preheaters, one monolithic catalyst reactor,
one oven, one water condenser, and one pressure
regulator protected by a filter.

The monolithic catalyst reactor is fabricated with a γ-
alumina-wash-coated 400-CPSI monolithic catalyst and a
2.2-cm-ID x 15-cm-long stainless steel HPLC column.

A heat exchanger is made of 20-ft-long 1/16-inch Teflon
tubing.

Most surfaces in contact with process gas mixtures are
Teflon.
Experimental Setup
    Mass Flow Meters
mass flow meter, water pump, rotameter, gas bag, and pressure indicator


                                      Rotameter, Gas Bag, and Pressure Indicator




       Water Pump
Reactor, Condenser, and Heaters

Reactor and Condenser   Reactor and Heat Exchangers in the oven
         Experimental Procedures
The reactor, loaded with a γ-alumina wash-coated
monolithic catalyst, is placed inside the oven to be
heated to a desired temperature.

Nitrogen is introduced into the catalyst-loaded
reactor during testing leakage of the fittings for the
reactor and preheating the reactor.

When the temperature of the reactor is raised to the
desired temperature, a gaseous reaction mixture
was introduced into the reactor, by switching
nitrogen with the reaction mixture.

Conversion of H2S into elemental sulfur and
formation of COS are analyzed with a gas
chromatograph and a computer.
    Typical Experimental Conditions
Volume of the monolithic catalyst bed, cm3:                   47
Temperature, oC:                                              120 -150
Reaction Pressure, psia:                                      118 -205
Space Time under the reaction conditions, s:                  90 - 560
Gas Feed Rate, cc/min at room temperature and 1 atm (SCCM):   30 -180
Concentration of H2S, ppmv:                                   3,600 - 4,000
Concentration of SO2, ppmv:                                   1,800 - 2,000
Carbon monoxide, vol %:                                       36 - 41
Hydrogen, vol %:                                              23 - 27
Carbon dioxide, vol %:                                        10 - 12
Moisture, vol %:                                              0 - 10
Nitrogen, vol %:                                              Remainder
  Stoichiometric Reaction Formula
                         Catalyst

   2H2S (g) +SO2 (g) <=>3S (λ) + 2H2O (g)
                 Le Chatelier’s Principal
Conversion of H2S increases with increased total pressure,
and increased concentrations of both H2S and SO2.
Conversion of H2S decreases with increased moisture and
increased temperature, since the reaction is exothermic
Conversion of H2S is not affected by amounts of liquid
elemental sulfur, since volume of liquid elemental sulfur is
negligible in comparison with volume of water vapor
produced.
        Properties of Liquid Elemental Sulfur

Melting point of solid elemental sulfur, oC                          110 - 119
Boiling point of solid elemental sulfur, oC                          445
Density of elemental solid sulfur at 20 oC, g/cm3                    1.92 - 2.07
Density of elemental liquid sulfur at 125 oC, g/cm3                  1.7988
Surface tension at 120 oC, dyne/cm                                    60.83
Apparent viscosity of liquid elemental sulfur at 120 oC, poise        0.011 - 0.035

   Liquid elemental sulfur is non-Newtonian fluid.
   Viscosity of liquid elemental sulfur decreases with temperature up to 157oC,
   and then rapidly increases with temperature.
             Experimental Difficulties

Poor reproducibility of experimental data, since both
SO2 and H2S are very reactive in addition of peculiar
behavior of liquid elemental sulfur.

Plugging problems, since viscous non-Newtonian
liquid sulfur as well as solid sulfur are produced out of
gaseous H2S and SO2.

Leakage of reaction gas mixtures through Teflon
fittings due to irreversible thermal deformations of
Teflon fittings and tubing under the reaction
conditions.

Frequent upset of the gas chromatograph
                              Figure 7. Effects of catalyst age on conversion of H2S to elemental
                              sulfur and formation of COS with a 120 SCCM feed stream
                              containing 3,600-ppm H2S, 1,800-ppm SO2 as an oxidant, and 10-
                              v% moisture at 140oC, 119 -124 psia, and 139 – 143 s space time.

                               1
                                                                              conversion of H2S
                                                                                                     200
                                                                                                                                                         Removal of H2S decreases and
                              0.9
                                                                              formation of COS
                                                                                                                                                         formation of COS increases with
                              0.8                                                                                                                        increased catalyst age
                                                                                                     150
                              0.7




                                                                                                           C o n c e n t ra t io n s o f C O S , p p m
                                                                                                                                                         Poor diffusion of the reaction
C o n v e rs io n o f H 2 S




                              0.6
                                                                                                                                                         products such as liquid sulfur
                              0.5                                                                    100
                                                                                                                                                         and H2O vapor from the
                              0.4                                                                                                                        monolithic catalyst internal
                              0.3                                                                                                                        surface to the external
                              0.2
                                                                                                     50
                                                                                                                                                         monolithic catalyst surface
                              0.1
                                                                                                                                                         through the monolithic catalyst
                                                                                                                                                         pores.
                               0                                                                     0
                                    0   500   1000        1500         2000        2500           3000                                                   Deposition of some liquid
                                                     Catalyst Age, s                                                                                     element sulfur on the internal
                                                                                                                                                         and external monolithic catalyst
                                                                                                                                                         surface
                                            Figure 8. Effects of catalyst age on formation of COS with a 120 SCCM
                                            feed stream containing 3600-ppm H2S, 1800-ppm SO2 as an oxidant, and
                                            10-v% moisture at 140oC, 119 - 124 psia, and 139 – 143 s space time

                                           100
                                                     blank product mixture
                                                     reaction product mixture                                             Formation of COS increases with
                                            80
                                                     feed mixture from cylinders                                          catalyst age
C o n ce n tra tio n s o f C O S , p p m




                                            60
                                                                                                                          Formation of COS is higher in the
                                                                                                                          absence of catalyst than in the
                                                                                                                          presence of catalyst
                                            40



                                                                                                                          COS is formed by both thermal
                                            20
                                                                                                                          reaction and catalytic reaction.

                                             0
                                                 0       500         1000          1500          2000   2500   3000   Thermal Reaction:    H2S + CO → COS + H2
                                                                               Catalyst Age, s
                                                                                                                      Catalytic Reaction: 2H2S + SO2 + 3CO → 3COS + 2H2O
                             Figure 9. Effects of conversion of H2S to elemental sulfur on
                             formation of COS with a 120 SCCM feed stream containing 3,600-
                             ppm H2S, 1,800-ppm SO2 as an oxidant, and 10-v% moisture at
                             140oC, 119 -124 psia, 139 – 143 s space time, and 230 – 2670 s
                             catalyst age.


                        90
                                                                            Formation of COS
                        80                                                  decreases with
                        70
                                                                            increased conversion of
Formation of COS, ppm




                        60

                        50                                                  H2S.
                        40



                                                                            COS is formed by
                        30

                        20

                        10                                                  combining H2S with CO
                                                                            in addition to S with CO
                         0
                             0.5    0.6          0.7           0.8   0.9
                                          Conversion of H 2S



                                                                           CO + H2S → COS + H2
                                                                           S + CO → COS
                        Figure 2. Effects of space time on conversion of H2S to elemental sulfur
                        and formation of COS with a 30 - 180 SCCM feed stream containing
                        3600-ppm H2S, 1800-ppm SO2 as an oxidant, and 10-v% moisture at
                        140oC, 118 - 123 psia, and 90 -560 s space time.


                              0.9                                                     250

                              0.8        conversion of H2S                                                                            Removal of H2S and
                              0.7                                                     200
                                                                                                                                      formation of COS




                                                                                            C o n c e n tra tio n o f C O S , p p m
                              0.6
                                                                                                                                      increase with increased
C o n v e rs io n o f H 2 S




                                                                                      150
                              0.5

                              0.4
                                                                                      100
                                                                                                                                      space time.
                              0.3

                              0.2
                                                                                      50
                              0.1

                              0.0                                                     0
                                    0   100       200        300        400   500   600


                                                        Space Time, s
                                                      Figure 3. Effects of space time on formation of COS with a 30 -
                                                      180 SCCM feed stream containing 3,600-ppm H2S, 1,800-ppm SO2
                                                      as an oxidant, and 10-v% moisture at 140oC, 118 - 123 psia, and
                                                      90 -560 s space time.


                                            250                                                                         Formation of COS
                                                        reaction product mixture
                                                        blank mixture product
                                                                                                                        increases with space
                                            200         feed mixture from cylinders
                                                                                                                        time in the presence
C o n c e n tra tio n s o f C O S , p p m




                                            150
                                                                                                                        and in the absence of
                                                                                                                        catalyst.
                                            100




                                             50
                                                                                                                        Formation of COS is
                                                                                                                        higher in the presence
                                              0
                                                  0         100           200             300         400   500   600
                                                                                                                        of catalyst than in the
                                                                                      Space Time, s                     absence of catalyst.
                                    Figure 4. Effects of conversion of H2S on formation of COS with a
                                    30 - 180 SCCM feed stream containing 3,600-ppm H2S, 1,800-ppm
                                    SO2 as an oxidant, and 10-v% moisture at 140oC, 118 - 123 psia,
                                    and 90 – 560 s space time.


                        230                                                               Formation of COS
                        190
                                                                                          increases with
Formation of COS, ppm




                        150
                                                                                          conversion of H2S.
                        110


                         70
                                                                                          COS is mostly formed by
                         30
                                                                                          combining elemental
                        -10
                              0.3      0.4   0.5         0.6           0.7   0.8   0.9    sulfur with CO.
                                                   Conversion of H2S
                                                                                         2H2S + SO2 + 3CO ↔ 3COS + 2H2O
                                  Figure 6. Effects of moisture on conversion of H2S to elemental
                                  sulfur and formation of COS with a 108 – 120 SCCM feed stream
                                  containing 3,600 - 4,000 ppm H2S, 1800 - 2,000 ppm SO2, and 0 -
                                  10-v% moisture at 140oC and 118 - 123 psia.

                        1.0                                                                           140                                 Removal of H2S decreases with
                                                              conversion of H2S
                        0.9
                                                              formation of COS from reaction run      120
                                                                                                                                          increased moisture.
                        0.8                                   formation of COS from blank run
                                                                                                      100                                 2H2S + SO2 ↔ 3S + 2H2O




                                                                                                            F orm ation of C O S, ppm
                        0.7
C onv ers ion of H 2S




                        0.6
                                                                                                      80
                        0.5

                        0.4
                                                                                                      60                                  Formation of COS decreases with
                        0.3                                                                           40                                  increased moisture.
                        0.2

                        0.1
                                                                                                      20                                2H2S + SO2 + 3CO ↔ 3COS + 2H2O
                        0.0                                                                            0
                          -2.00    0.00   2.00         4.00        6.00          8.00   10.00      12.00
                                                 Concentration of Moisture, v%
                                       Figure 10. Effects of catalyst regeneration on conversion of H2S
                                       for conversion to elemental sulfur with a feed stream containing
                                       3600-ppm H2S, 1800-ppm SO2 and 10-v% moisture at 121- 122
                                       psia . Catalyst is regenerated with 140oC N2 overnight


                              1
                                                                                                              Catalyst poisoned with
                             0.8                                                                              elemental sulfur
C o n v e rs io n o f H2 S




                             0.6
                                                                                                              Catalyst can be
                             0.4                                                                              regenerated by removing
                             0.2
                                                                not regenerated                               liquid elemental sulfur from
                                                                 regenerated with N2 at 140oC
                                                                overnight
                                                                                                              catalyst with N2 at 140oC
                              0
                                   0   500   1000   1500     2000    2500    3000    3500       4000   4500
                                                           Catalyst Age, S
                                                             Figure 5. Effects of temperature on conversion of H2S to elemental
                                                             sulfur and formation of COS with a feed stream containing 3,600-
                                                             ppm H2S, 1,800-ppm SO2 and 10-v% moisture at 121- 123 psia and
                                                             136 - 142 s space time, using regenerated catalysts.
                                                       0.9   .                                                                                                 80




                                                                                                                                                                                                 Removal of H2S
                                                       0.8

                                                       0.7
                                                                                                                                                               60




                                                                                                                                                                     Concentration of COS, ppm
                                                                                                                                                                                                 decreases with
                                                       0.6            conversion of H2S
                                  Conversion of H S
                                                 2




                                                                      COS in feed stream
                                                       0.5            COS formation, catalytic
                                                                                                                                                               40


                                                                                                                                                                                                 increased reaction
                                                                      COS formation, thermal
                                                       0.4

                                                       0.3



                                                                                                                                                                                                 temperature.
                                                                                                                                                               20
                                                       0.2

                                                       0.1

                                                       0.0                                                                                                      0



                                                                                                                                                                                                 Formation of COS
                                                          115         120         125           130          135         140         145         150         155
                                                                                                      Temperature, o C




                                                                                                                                                                                                 increases with reaction
                                  0.006



                                  0.005


                                                                                                                                                                                                 temperature.
Vapor Pressure of Sulfur , psia




                                  0.004



                                  0.003



                                  0.002                                                                                                                                                          COS is mainly formed by
                                  0.001
                                                                                                                                                                                                 reacting CO with vapor
                                                      0
                                                       110      115         120           125          130
                                                                                                  Temperature, oC
                                                                                                                   135         140         145         150     155                               sulfur.
                                         Figure 10. Effects of conversion of H2S on formation of COS with a
                                         120-SCCM feed stream containing 3,600-ppm H2S, 1,800-ppm SO2
                                         and 10-v% moisture at 121- 123 psia and 120 - 150oC, using
                                         regenerated catalysts.


                                    60                                                        Formation of COS
                                    50
                                               150oC
                                               140oC
                                                                                              increases steeply with
                                               130oC
                                               120oC
                                                                                              conversion of H2S over
                                    40
                                                                                              the temperature range of
F o r m a tio n o f C O S , p p m




                                    30                                                        140 – 150oC.
                                    20
                                                                                              Formation of COS
                                    10
                                                                                              increases slightly with
                                    0
                                         0.6       0.65   0.7             0.75   0.8   0.85
                                                                                              conversion of H2S over
                                                           Conversion of H2S                  the temperature range of
                                                                                              120 – 130oC
                             Figure 12. Effects of pressure on conversion of H2S and formation of
                             COS with a 120-SCCM feed stream containing 3,600-ppm H2S, 1,800-
                             ppm SO2 and 10-v% moisture at 121- 208 psia and 140oC, using a
                             regenerated catalyst.

                                                                                                                      Conversion of
                                                                                                                      H2S and
                     1                                                                 100


                                conversion of H2S                                      90
                    0.9         formation of COS
                                                                                       80
                                                                                                                      formation of
                    0.8
                                                                                       70
                                                                                                                      COS decrease
                                                                                                                      slightly with




                                                                                             Formation of COS, ppmv
                                                                                       60
Conversion of H2S




                                                                                                                      pressure
                    0.7

                                                                                       50

                    0.6
                                                                                       40


                    0.5                                                                30


                                                                                       20
                    0.4
                                                                                       10


                    0.3                                                                0
                       110             130          150           170      190   210
                                                          Pressure, psia
                                        Figure 12. Effects of conversion of H2S on formation of COS with a 120-
                                        SCCM feed stream containing 3,600-ppm H2S, 1,800-ppm SO2 and 10-
                                        v% moisture at 121- 208 psia and 140oC, using a regenerated catalyst.

                             60                                                             Formation of COS
                                           121 psia
                                           208 psia
                                                                                            increases with
                             50
                                                                                            conversion of H2S
Form ation of CO S , ppm v




                             40



                             30



                             20



                             10



                             0
                                  0.6                 0.7                       0.8   0.9
                                                            Conversion of H2S
                                   Summary
Removal of H2S increase with increased space time. Formation of COS increases
with space time in the presence and in the absence of catalyst. Formation of COS
increases with conversion of H2S. Formation of COS is higher in the presence of
catalyst than in the absence of catalyst. COS in the presence of catalyst may be mostly
formed by combining elemental sulfur with CO. COS in the absence of catalyst may be
mostly formed by combining hydrogen sulfide with CO.
Removal of H2S and formation of COS decreases with increased moisture. decreases with
increased moisture.                     .
Removal of H2S decreases and formation of COS increases with increased catalyst
age. Poor diffusion of the reaction products such as liquid sulfur and H2O vapor
through the monolithic catalyst pores and deposition of liquid element sulfur on the
internal monolithic catalyst surface may reduce catalytic activities. Formation of COS
is lower in the presence of catalyst than in the absence of catalyst. COS is formed
by both thermal reaction and catalytic reaction. Formation of COS decreases with
increased conversion of H2S. COS is formed by combining H2S with CO in addition to S
with CO.
Catalyst can be regenerated by removing liquid elemental sulfur from catalyst with N2.
Removal of H2S decreases and formation of COS increases with increased reaction
temperature. COS is mainly formed by reacting CO with vapor sulfur.
Removal of H2S and formation of COS is affected slightly by pressure
                Acknowledgements

U. S. Department of Energy National Energy Technology
Laboratory supports this research project through the
contract number DE-FG26-04NT42129.