Note: Descriptions are shown in the official language in which they were submitted.
~ 1 337905
Title: CATALYTIC REMOVAL OF SULPHUR-CONTAINING
COMPOUNDS FROM FLUID STREAMS BY DECOMPOSITION
Field of Invention
The desirability of identifying an effective
05 means for removing sulphur compounds from fluid streams
will be readily appreciated. This invention comprises a
novel method and catalyst for effecting such removal and
the subsequent treatment of such sulphur compounds to
produce elemental sulphur. More particularly this
invention is applicable to the removal of hydrogen
sulphide and other sulphur compounds from sour natural
gas, and other fluid streams, and the conversion of the
sulphur therein to elemental sulphur.
Background of the Invention
Sulphur compounds are often considered to be
undesirable compounds in gas mixtures and other fluid
streams. The most common example of this is that of
natural gas containing hydrogen sulphide. Natural gas
may also contain as undesirable sulphur compounds,
quantities of carbonyl sulphide, carbon disulphide, mono
and dialkyl sulphides, alkyl-type disulphides and
thiophenes.
1 3379~5
-- 2
The removal of such sulphur-containing compounds
from gas streams has been addressed by a number of
methods in the past. These methods generally rely on
direct reactions with the sulphur compounds, or proceed
05 to first separate the sulphur compounds from the gas
stream by an absorption stage. In the latter case, the
sulphur and other constituent elements of the absorbed
compounds must then be extracted, if the absorptive
medium is to be regenerated. A particularly desirable
regenerative process would be one which produces
elemental sulphur from the same reaction bed.
Various systems have been explored with the view
of removing hydrogen sulphide from gas streams and
producing elemental sulphur. The Claus process, as
currently applied, is a complex multi-stage system
involving the absorption of the hydrogen sulphide in an
amine absorbent, flashing of H2S from the amine,
followed by the burning of part of the hydrogen sulphide
to sulfur dioxide, and subsequently reacting the hydrogen
sulphide with the sulfur dioxide to produce sulphur as
the final product as elemental sulphur.
It would be obviously desirable to provide a
method for removal of hydrogen sulphide and other sulphur
containing compounds from a fluid stream at ambient
temperatures followed by the subsequent conversion at
moderate temperatures of the sulphur compounds into
elemental sulphur and other decomposition products.
X '
_ ~ 3 ~ ~ 3 37 ~ 05
Objects of the Invention
It is therefore an object of the invention to
remove sulphur compounds from a fluid stream and recover
elemental sulphur therefrom. It is further an object to
05 do so in the same reaction bed.
It is also an object of the invention to provide
a means which will allow removal and decomposition of
hydrogen sulphide from a gas stream, and the separation
of the sulphur so produced, at a modestly elevated
temperature (circa 250C - 600C).
A further object of the invention is to remove
sulphur dioxide, nitrogen peroxide and carbon dioxide,
separately or collectively from a gas stream, and then to
convert the sulphur dioxide to sulphur, convert the
nitrogen perioxide to nitric oxide, and separately
release the carbon dioxide, nitric oxide and sulphur so
produced.
These and other objects of the invention will
become apparent from the description of the invention and
claims thereto which follow.
Summary of the Invention
This invention comprises a specially prepared
bed for absorbing hydrogen sulphide from a fluid stream
and subsequently decomposing it into elemental sulphur.
~X
~ - 4 - 1 3 37 ~ S
This same bed may be used to absorb nitrogen peroxide and
carbon dioxide from a gas stream for subsequent separate
recovery.
A suitable bed for treating hydrogen sulphide or
05 sulphur dioxide comprises a microporous support adapted
to accommodate or absorb hydrogen sulphide or sulphur
dioxide therein, which support contains an alkali metal
sulphide or selenide together with a sulphide or
sulphides, (or selenide/s) of metals showing polyvalent
and/or amphoteric character deposited therein, and is
thereby capable of providing "reactive oxygen", e.g.
having peroxide-like characteristics after exposure to a
source of oxygen.
The use of "and/or" in the above discussion, and
throughout this disclosure, is to be taken in its non-
exclusory sense. Thus, a mixture of both amphoteric and
polyvalent compounds may be used in place of either
alone, and a metal which is both amphoteric and
polyvalent is intended to be included by this expression.
The reference to "reactive oxygen" is intended to
refer to oxygen in an elevated energy state whereby the
oxygen is available to react with the non-sulphur
component of the compounds being treated so as to release
sulphur.
Amphoteric metals are those metals which show a
capacity to react both with acids and bases.
A bed so prepared, according to this invention is
X also adapted to remove and decompose carbonyl sulphide,
~- - 5 - 1 3 37 ~ 0 5
carbon disulphide, mono and dialkyl sulphides, alkyl-type
disulphides, and thiophenes from a gas or liquid stream
by contacting such a stream with the aforesaid bed.
This same bed is capable of absorbing oxygen-
05 containing compounds to provide reactive oxygen.Suitable compounds for this effect are sulphur dioxide
and nitrogen peroxide.
Examples of amphoteric or polyvalent metal
sulphides or selenides suitable for use in this invention
include, amongst others, sulphides or selenides of metals
from the group consisting of zinc, manganese, iron,
copper, cobalt, aluminum, vanadium, molybdenum, tin and
nickel as well as mixtures thereof. Examples of alkali
metals suitable for use in this invention include
lithium, potassium, sodium, cesium and rubidium, as well
as mixtures thereof.
One method of preparing the bed is by:
(a) preparing in aqueous solution a mixture of an
alkali metal salt and a polyvalent and/or
amphoteric metal salt;
(b) impregnating a support with the mixture described
in (a) above;
(c) drying the support after it has been so
impregnated;
25 (d) sulphiding (or seleniding) the impregnated
support at ambient or higher temperatures by
exposing it to a gas stream containing a reactive
sulphur (or selenide) compound such as hydrogen
- 6 - ~ 337 q 05
sulphide, carbonyl sulphide or carbon disulphide,
or their selenide equivalents which has the
effect of converting the metal and alkali salts
to sulphides or selenides;
05 (e) heating the impregnated support at an elevated
temperature to drive off excess sulphur, or
selenium so as to thereby form the bed in its
pre-oxygenated form; and then,
(f) exposing the bed to a source of oxygen whereby
reactive oxygen becomes available within the bed
and thereby create the bed in its oxygen-activated form.
This invention further comprises the production
of elemental sulphur by the method of exposing a gas
stream containing hydrogen sulphide to the oxygenated bed
and then regenerating the bed. The bed is regenerated by
first applying heat at a predetermined elevated
temperature or temperatures (such as in the range of
250C to 600C) in the presence of a substantially non-
reactive sweep gas. This will drive off water and
elemental sulphur thus purging the bed of these
substances. The regeneration process is then completed
by exposure of such bed to an unreactive sweep gas
containing an amount of oxygen as described abovd.
Optionally, oxygen may also be provided during the
initial purging step either as an alternative to
subsequent treatment with an oxygen source, or in
addition.
X
- - 7 - ~ 33 7 9 05
The amount of oxygen accompanying the sweep gas
in the final step may range from a stoichiometric amount
necessary to oxidize the sulphur compound to be treated
and release elemental sulphur, up to a concentration of
05 about 25~, although this is not necessarily limiting in
all cases. In certain cases excess oxygen must be
avoided to prevent damage to the bed.
This invention further comprises the method by
which sulphur dioxide and nitrogen peroxide are first
removed from a gas stream by permitting these
compositions to be absorbed within a bed comprised of a
microporous support which contains an alkali metal
sulphide or selenide, and a sulphide or selenide of
metals showing polyvalent and/or amphoteric character.
The bed, so impregnated, is then exposed to a stream of
hydrogen sulphide whereby the absorbed sulphur dioxide
and hydrogen sulphide are converted to water and
elemental sulphur and the nitrogen peroxide is converted
to nitric oxide. These products are then purged from the
bed by heating the bed in the presence of a sweep gas,
thus returning the bed to a condition whereby it is ready
to repeat the cycle.
These and further features of the invention and
its various aspects will be apparent from the description
of the examples and test results set forth in the
following.
;~'
1 337~05
-- 8 --
Summary of the Figures
Figure 1 is a graph showing the effect of
05 temperature on the rate of desorption of hydrogen
sulphide from a series of sample catalytic beds which
have been saturated with hydrogen sulphide.
Characterization of the Catalyst within the Bed
The active catalyst within the bed that provides
reactive oxygen is believed to be characterized by a
chemical having as its constituents a complex containing
the combination of an amphoteric and/or polyvalent metal
(hereinafter referred to as the "metal"), an alkali
metal, (hereinafter referred to as the "alkali"), sulphur
or selenium and the capacity to retain an active oxygen-
containing moiety that contains an available reactive
oxygen group. This complex should preferably be formed
within a microporous support having a relatively high
surface area and a microporosity adapted to receive the
sulphur or oxide compound to be decomposed.
Alumina is considered a preferred support because
of its high surface area. Also, it is believed that
alkali metal incorporated into the support to form the
active complex will react with alumina to form an alkali
aluminate and facilitate bonding of the active complex to
the carrier. Alumina may thereby provide an etchable
substrate upon which active sites may be more readily
formed.
X
- 9 - 1 337905
The process of solvent extraction using methylene
chloride, when applied to an activated catalyst
containing manganese and potassium sulphides on alumina
(Alcoa #S-100), showed the following extracted
05 constituents:
free manganous sulphide - 51% (by weight)
free potassium sulphide - 18%
other constituents including
potassium aluminate and - 31%
potassium hydroxide
An attempt to utilize methanol on the same catalyst
produced inconclusive results as the constituents were
apparently modified by the methanol as a solvent (perhaps
by hydrolysis of the manganous sulphide) as was indicated
by a change in colour of the solution from green to brown
shortly after extraction.
It has been found that the catalyst is capable of
decomposing a small portion of absorbed hydrogen sulphide
without the addition of oxygen during the decomposition
heating phase. The activity of the catalyst under such
conditions, however, declines rapidly. It is believed
that the catalyst is intrinsically capable of supplying
small amounts of oxygen, but that this capacity is
rapidly depleted. This belief is supported by the
observation that exposure of the catalyst to a reducing
atmosphere causes catalytic decompositional activity to
drop to virtually zero.
- lo - 1 337 9 0 5
The provision of oxygen to the catalytic bed,
either while decomposition is occurring or upon
regeneration of the catalytic bed has been found
necessary to preserve or restore the activity of the
05 catalyst. Thus while oxygen may be consumed in the
decomposition cycle, it is readily restorable by exposure
of the catalyst thereafter to a source of oxygen in
either molecular or compound form.
Preparation of the Catalytic Bed - Method 1
Catalytic beds were prepared by two alternate
methods. The first method commenced by dissolving a
predetermined amount of the alkali sulphide (sodium or
potassium) in water sufficient to form the ultimate
desired loading on the support and optionally boiling the
solution. To this solution a molar equivalent amount of
an amphoteric and/or polyvalent metal sulphide was added
and the solution was boiled again until the volume was
reduced to a point short of saturation. Then the support
(generally in the form of Alcoa alumina spheres, #S-loO)
which had been dried by being heated to 250C for 4
hours was added to the hot solution and mixed until all
the solution was absorbed into the support. The
partially prepared catalytic bed was then dried (using a
nitrogen gas flow at 400C) and cooled. The catalytic
bed was then sulphided by exposure to a stream of 10%
hydrogen sulphide in nitrogen or methane at ambient
conditions until hydrogen sulphide was detected in the
- - 11 - 1 33 790~
effluent and for at least one hour thereafter. It was
then purged of excess sulphur by heating in a nitrogen
gas flow at 400-500C for a period of 0.5 to 1.0 hours to
drive off free sulphur.
05 The partially prepared catalytic bed can also be
sulphided by exposure first to a stream of 10% hydrogen
sulphide in nitrogen or methane at 400-500C for 4 hours
and then to a stream of nitrogen or methane at 400-500C
to remove any excess sulphur. Some tests were run in
which the conditioning gas was a 50/50 mixture of
hydrogen sulphide and hydrogen and the active metal in
the catalyst was manganese. This change in the nature of
the conditioning gas considerably reduced its activity
for the sample catalyst so prepared.
Preparation of the Catalyst - Method 2
A second method of preparing the catalytic bed
was as follows. A sulphate, chloride or nitrate of a
polyvalent and/or amphoteric metal was dissolved in an
aqueous solution. The mixture was then heated to ensure
rapid dissolution. (This, as above, is considered an
optional step.)
The solution was then impregnated on a previously
dried alumina support (Alcoa S-100 {Trade Mark~, 1/4 in.
spheres) and the impregnated support dried.
A molar equivalent or greater amount of an alkali
metal sulphide was then prepared in an aqueous solution
and impregnated on the support. Again, heating was
X
- - 12- 1 337 9 05
optionally employed to effect rapid dissolution.
The impregnated support was then heated to a
temperature of 125C for a period of 2 hours in order to
fix the active ingredients within the support. This was
05 followed by a washing of the impregnated support with
water until all available alkali sulphate, chloride or
nitrate had been flushed from the support. The
impregnated support was then dried at 125C.
It is believed that at this stage most of the
sulphate, chloride or nitrate originally impregnated has
become converted to a sulphide of the amphoteric and/or
polyvalent metal. The available sulphate, chloride or
nitrate salts of the alkali metal were washed out of the
support because they were not believed to contribute to
the activity of the catalyst and were thought to reduce
the availability of active sites within the support. The
catalyst could be prepared without this step and still be
capable of producing some decomposition of hydrogen
sulphide. However, it is believed that the catalyst
would generally show reduced activity without this step.
A stoichiometric amount of the alkali metal
sulphide was then prepared in an aqueous solution and
impregnated on the carrier a second time. The
impregnated support was finally dried at 125C, and
sulphided and purged of excess sulphur as described in
Method 1.
X
- - 13 - I 337905
Preparation of the Catalytic Bed - Further Alternate
Methods
The above process has been carried-out with a
variety of amphoteric and/or polyvalent metals in the
05 form of sulphates, chlorides or nitrates and, it is
believed, may be carried-out with any soluble salts of
such metals including zinc, iron, vanadium, copper,
nickel, molybdenum, aluminum and manganese. It is
believed that an active catalyst would be produced when
these methods are carried out with all amphoteric and/or
polyvalent metals. It is further believed that these
methods would be effective in producing an active
catalyst whether sulphide or selenide salts of all
amphoteric and/or polyvalent metals are used. Where less
soluble compounds are employed, it may be appropriate to
employ a basic aqueous solution in order to facilitate
dissolution. A sufficiently basic solution can be
created by adding alkali hydroxide to the solution of the
amphoteric and/or polyvalent metal salt and boiling this
mixture.
Method 2 described above has been followed using
either sodium or potassium as the alkali element. It is
believed that lithium, rubidium or cesium sulphides may
also be substituted for the elements sodium or potassium,
and still form an active catalyst using either methods.
It is further believed that selenium may be
substituted for the sulphur in the alkali sulphide and
still produce an active catalyst.
1 337905
- 14 -
Based on sample tests, a satisfactory standard of
performance for the catalyst in terms of both absorptive
and decomposing capacity can be obtained with an
approximate l:l molar ratio between the metal and alkali
05 components, and a similar l:l molar ratio where an alkali
hydroxide is additionally employed.
Absorptive capacity for hydrogen sulphide is
maximized for various metal sulphides at different levels
of impregnation of the support. For example, this occurs
between the 0.5% to 2.5% loading (by weight) range for a
catalyst incorporating a zinc sulphide/sodium sulphide
mixture deposited by Method l on the Alcoa carrier (S-100
spheres).
Preparation of the Catalytic Bed - Activation with Oxygen
The bed may be activated in conjunction with the
sulphiding steps by exposing it at ambient or higher temp-
eratures to an unreactive gas containing hydrogen sulphide,
followed by heat treatment in an unreactive sweep gas at a
temperature of 250C - 700C containing an amount of oxygen
as referenced below. Alternately, after treatment with the
sweep gas at elevated temperatures the bed may be exposed
to oxygen at temperatures down to ambient conditions.
"Unreactive" is used here and throughout in the
sense of a gas that does not substantially react in this
system.
It is most desirable that the activating gas
streams not contain appreciable amounts of compounds or
,~
- 15 - I 33~ 90~
elements, such as hydrogen, which will have a major
reductive effect on the activity of the catalyst. It is
also important that the catalyst be exposed by the
conclusion of the conditioning process to sufficient
05 oxygen to ensure that reactive oxygen will be available
within the catalyst to render it activated.
Sweetening, Decomposition, Purging and Reactivation
Procedures
The procedure followed to verify and quantify the
production of sulphur from hydrogen sulphide was as
follows.
A sample of a catalytic bed that had been purged
of free sulphur and hydrogen sulphide by regenerating it
at 400C under an unreactive sweep gas (nitrogen or
methane) and then activated by exposure to oxygen was
weighed while placed in a reaction tube. A measured
volume of unreactive gas containing a known percentage of
hydrogen sulphide was then passed over the catalyst bed
at a specific temperature, usually ambient, to remove the
hydrogen sulphide from the gas stream. This was
designated as the "sweetening" cycle. The length of
exposure was either that required to produce an
indication of hydrogen sulphide "breakthrough" at the
exit end (as measured by the blackening of standardized
lead acetate paper, or other standard methods), or some
lesser period of time. A run to breakthrough was said to
have saturated the bed. A run carried to a point short
of saturation was designated as a "partial run".
1 337~05
- 16 -
The catalytic bed in its tube was then weighed to
determine either the saturation loading of the bed, or
the partial loading of the bed, in terms of its
absorption of hydrogen sulphide.
05 Throughout all experiments, the catalytic beds
utilizing molecular sieves or alumina supports showed a
capacity in the foregoing sweetening phase of maintaining
the hydrogen sulphide level in the out-flowing stream
below the measurable threshold vis, 1 part per million
prior to breakthrough.
The catalytic bed in its reaction tube was then
put through the purging phase by exposing the bed to an
unreactive sweep gas (nitrogen or methane) at a specific
temperature above the vapourization point for elemental
sulphur for a period of time. The bad may then be
reactivated by exposing it to a source of oxygen. This
may be done, for example, by utilizing a sweep gas
containing oxygen at levels of 0.01 to 25%. Oxygen may
also be supplied in the form of sulphur dioxide or
nitrogen perioxide.
It has been found that with certain metals, such
as manganese, that the catalytic bed deteriorates if ex-
posed to excessive levels of oxygen, e.g. over 10%. This
may, it is believed, be due to the formation of a sulphate.
The catalyst in such a case was restored to activity on
re-exposure to hydrogen sulphide. However, it is believed
that the concentration of oxygen should preferably be
limited in order to avoid such deleterious effects.
~r~
- 17 - 1337~05
The sweep gas exiting the catalytic bed was
caused to pass through a portion of the reaction tube
that was maintained at room temperature. During this
process, when carried out with the bed at temperatures
oS over about 250C - 300C, sulphur consistently condensed
on the inside walls of a cooler, exit portion of the
reaction tube in a condensation zone. Sample tests with
glasswool placed downstream of such deposits indicated
that further sulphur could not be collected by
condensation from the cooled exiting gas stream beyond
the condensation zone.
A further procedure followed in some experiments
was to collect the exiting sweep gas during regeneration
step and then determine its hydrogen sulphide
concentration by gas chromotography. As further
discussed below, little or no hydrogen sulphide was
detected in the regeneration phase when the catalyst bed
was only partially loaded with hydrogen sulphide, well
below the saturation level for the bed. For higher
loadings and approaching saturation, much more hydrogen
sulphide was detected in the regeneration stage of
treatment.
After sulphur ceased to be forming further within
the cooler portion of the reaction tube, the tube and bed
were reweighed. Comparisons of this weight with the
weight of the tube following sweetening showed that
virtually all of the sulphur remained in the system, up
1 337905
- 18 -
to this point. Then heat was applied to the outside
portion of the reaction tube where sulphur had deposited
and the sweep gas flow was maintained. This procedure
was continued until all of the sulphur in the reaction
05 tube had been vapourized and carried out of the tube.
The reaction tube and bed were then reweighed.
The catalyst bed, for purposes of experimental
certainty, was then put through a super-purging phase by
performing the previous procedure at 400-500C for 1-2
hours. This step was shown through tests at higher
temperatures to be capable of completely purging the
catalyst bed of remaining traces of free sulphur and
residual hydrogen sulphide.
The inclusion of amounts of oxygen in the sweep
gas during the super-purging phase was not found to be
essential if it had been previously present as part of
the earlier treatment. Apparently, if sufficient oxygen
is available during the normal purging phase, then the
catalyst is reactivated. However, no deleterious effects
occurred where oxygen was present on the super-purging
phase as well. If insufficient oxygen was present during
the purging or super-purging phases, then oxygen should
be supplied to the bed as a further step, which may be
carried out at room temperature.
The exposure of alumina to sulphur dioxide would
normally be expected to result in the production of
aluminum sulphite. If oxygen is present, as well, then
aluminum sulphate will form. Where, however, alumina has
X
1 337905
-- 19 --
been treated by the deposition therein of the combination
of sulphide or selenide salts of amphoteric or polyvalent
metals combined with sulphite or selenide salts of alkali
metals, the tendency of the alumina to form aluminum
05 sulphite or sulphate is believed to be significantly
reduced.
It has been found that when sulphur dioxide used
as the source for oxygen, it is relatively tenaciously
contained within alumina-type supports. This enables an
activated bed to be prepared in one location, and then
transported to another. Similarly where the bed is only
partially saturated with hydrogen sulphide in the
sweetening cycle, the bed material is readily
transportable.
These features will allow the establishment of
centralized regeneration facilities for a number of
sweetening units placed in the field.
From the foregoing procedures calculations were
made to determine the extent to which the hydrogen
sulphide was converted to sulphur. The quantity of
hydrogen sulphide absorbed in the catalyst bed was
calculated based both on the gas flow rate, and on the
gain in weight of the bed and tube during the sweetening
phase. The quantity of sulphur produced was obtained
from the heat-vaporization procedure. The actual
quantity of hydrogen sulphide decomposed was also
determined by the difference between the volume of
hydrogen sulphide absorbed by the catalyst, and the
X
1 331~05
_ - 20 -
volume of hydrogen sulphide collected by a gas bag during
the regeneration. Of these methods, the mass of sulphur
vaporized off the interior of the reaction tube was taken
as the more reliable measure of the minimum decomposition
05 that had occurred.
Absorption of Sulphur Dioxide
The procedure of utilizing the bed first to absorb
hydrogen sulphide followed by reactivation with sulphur
dioxide may be reversed or shifted in order. Thus, where
it is desired to remove sulphur dioxide from a gas stream
the bed is first purged of sulphur dioxide by exposure to
hydrogen sulphide, then purged of sulphur by heating in
the presence of a sweep gas. So prepared, the bed will
then readily absorb sulphur dioxide to the limit of
saturation. Once the bed has been saturated with sulphur
dioxide, it may be again exposed to hydrogen sulphide.
Desorption Runs - Effects of Physical AbsorPtion
From the results of the tests performed, it was
determined that hydrogen sulphide was believed to be both
physically and chemically absorbed within alumina based
catalysts. Tests on a blank alumina support, containing
no active ingredients, indicated that virtually all
absorbed hydrogen sulphide could be driven out of such a
support by heating it to 350 C under a sweep gas for a
period of time of 90 minutes. Supports that had been
impregnated with ingredients to form the catalyst showed
1 3~79~5
- 21 -
a tendency not to have released as much hydrogen sulphide
at that temperature as did the blank support.
Figure l shows this effect in which a blank Alcoa
(S-lO0) alumina support is compared with catalysts
05 prepared by Method 1 with Zinc and Potassium sulphide;
Zinc, Copper and Potassium sulphides, and Copper and
Potassium sulphides all on the same type of S-lO0
support. All beds were loaded to saturation and then
treated in the sweetening phase for 90 minutes at various
temperatures. Figure l shows the percentage of the
hydrogen sulphide evolved, as a function of temperature
after heating for 90 minutes at various temperatures.
Table 1 summarizes the data depicted in Figure l
and adds the accumulated percent decomposition obtained
both after the 90 minute heating at a constant
temperature and after the final regeneration at 400C.
These percentages are based in both cases on conversion
of sulphur, being the mass of sulphur vaporized divided
by the mass of sulphur available in the quantity of
hydrogen sulphide originally absorbed.
1 3 3 7 9 !13 5
- 22 -
Table 1
Effect of Heating at Various Temperature on
Hydrogen Sulphide Desorption and Decomposition
for Saturated Catalyst/Beds
05 Catalyst/Bed HeOting Temp % Desorption % Sulphur Conversion
( C) H S After Total after
After Heating Heating Regeneration
Blank
Crushed Alcoa
Support #S-10018C 35 -- --
100 73 --
150 82 -- --
200 83 -- --
250 93 -- --
300 93 -- --
325 94 __ __
350 loo --
Zinc -
Sodium 18 42 -- 1.6
Sulphides 100 70 -- 7.8
150 80 -- 10.3
200 83 -- 17.2
250 90 1.6 10.2
300 87 3.3 10.2
350 88 7.0 7.5
400 93 6.1 6.1
Zinc
Copper - 18 n/a -- 2.6
Sodium 68 -- 14.7
Sulphides 200 79 -- 9.8
300 81 3.2 10.8
350 94 5.3 6.3
400 96 3.2 3.2
Copper-
Sodium 18 42.1 -- 8.2
Sulphides 350 95.7 1.1 1.5
(Heating Time: 90 minutes)
- 23 -
1 337905
Partial Runs
The foregoing data on saturated catalyst beds
give a clear indication that decomposition is occurring
by the showing of elemental sulphur that is produced.
05 However, the decomposition effect is being masked by the
large proportion of hydrogen sulphide that is being
physically absorbed, and then being desorbed without
decomposing. The masking effect of physically absorbed
hydrogen sulphide can be largely eliminated by exposing
the catalyst to hydrogen sulphide streams for periods of
time less than that necessary to saturate the bed. These
are called "partial runs". In such partial runs, the
amount of hydrogen sulphide evolved on regeneration was
substantially reduced. Correspondingly, higher
percentage figures for the amount of available sulphur in
the hydrogen sulphide converted to elemental sulphur were
obtained.
The catalyst, when used in association with
microporous supports such as alumina or zeolite, rapidly
absorbs hydrogen sulphide. It may be that the rapidity
with which the hydrogen sulphide is absorbed permits the
catalytic bed, at suitable flow rates, to saturate
progressively when exposed to a sour gas stream. If the
sweetening phase is terminated with only a portion of the
bed exposed (and saturated) with hydrogen sulphide, then,
as heat is applied to the bed in the presence of a sweep
gas absorbed hydrogen sulphide that may be desorbed is
swept into a region of the bed containing unexposed
- 24 - 1 3 37 ~ 0 5
catalyst. Consequently, a bed that is partially loaded
to saturation along only a portion of its length would be
capable, in the separation phase, it is believed, of
exposing virtually all of the hydrogen sulphide to
05 chemical-absorption leading to decomposition.
Thus, on whatever basis, it has been found that
with appropriately chosen partial loadings, it is
possible to obtain virtually 100~ dissociation.
Tested Catalyst Variants
The dissociative capacity of different catalyst
formulations were tested and some of the results obtained
were as set out in Tables 2 and 3.
TABLE 2
CATALYST LOADING % SULPHUR CO~v~
15 (including method (gms/100 gms (cumuOative, at
of preparation) and as a % 400 C)
of saturation)
Zn-K-lC-l 0.6(20%) >90%
Zn-K-2W-1 0.7(23%) >80%
Cu-K-lW-2 1.4(100%) >70%
Mn-K-lC-l 0.6(20%) >90%
Catalyst designation code:
Zn - K - lC
main amphoteric alkali carrier: method of
25 or polyvalent metal 1 - Alcoa preparation
metal 2 - ICI 1 - method 1
c - crushed 2 - method 2 using
w - whole a sulphate.)
X~
1 33790~
- 25 -
The data in Table 2 provides quantitative figures on the
extent of decomposition of hydrogen sulphide obtained,
stated in terms of the percent conversion to sulphur.
Table 3 lists combinations of further ingredients
05 all found to produce nonquantified but definite amounts
of elemental sulphur upon the consecutive exposure of the
catalytic bed to a 10% hydrogen sulphide/90% nitrogen gas
stream at ambient temperature 18C), followed by
regeneration of the catalyst at temperatures ranging from
350-400C as previously described. All runs were carried
out using as a support the Alcoa alumina carrier No. S-
100. All of the samples listed in Table 3 were prepared
from sulphides in accordance with the procedure of Method 1.
The column entitled "Absorptive Capacity"
indicates the percentage ratio of mass of sulphur
absorbed to the mass of catalyst, at the point where the
catalyst bed ceased to fully absorb further hydrogen
sulphide (as tested by the darkening of lead acetate
paper at the exit).
;\/
i,~
- 26 - 1 337 9 5
TABLE 3
Metal AlkaliElemental Absorptive Capacity
Metal Sulphur (% sulphur loaded
Detected per mass of catalyst)
05 Zinc Sodium Yes 2.4
Zinc Potassium Yes 1.4
Iron Sodium Yes 2.4
Vanadium Sodium Yes 2.3
Copper (I) Sodium Yes 2.9
10 Copper (II) Sodium Yes 2.0
Copper (II) 2 SodiumYes 2.4
Copper (II) Potassium Yes 2.2
Nickel Sodium Yes 2.9
Molybdenum Sodium Yes 2.3
15 Aluminum Sodium Yes 2.7
Manganese Sodium Yes 2.8
Manganese Potassium Yes 2.3
Cobalt Sodium Yes n/a
Tested Catalyst Variants - Mixed CatalYsts
A number of combined catalysts incorporating two
or three amphoteric and/or polyvalent metals have been
tested. Table 4 sets out the absorptive capacity at room
temperature for all such catalysts based on the alumina
support, Alcoa No. S-100. In all cases the catalyst was
prepared by Method 1 using a sulphide of the metal as the
initial salt. All components were incorporated into the
support in equal molar ratios.
_ - 27 - 1 33 7 ~ 05
TABLE 4
Metal Components Alkali Component Absorptive Capacity
(gms sulphur equivalent
from H2S in 100 gms
05 catalyst)
Iron & Zinc Sodium Sulphide 2.3
Iron, Copper & Sodium sulphide and
Zinc Sodium hydroxide 2.2
Manganese & Zinc Sodium sulphide and
Sodium hydroxide 2.0
Manganese & Zinc Sodium sulphide 2.3
Manganese & Nickel Potassium sulphide 1.5
Manganese &
Molybdenum Potassium sulphide 1.7
15 Iron & Zinc Potassium sulphide 1.2
In all of the cases listed in Table 4, sulphur
was observed to be evolved when the catalysts were
regenerated at a temperature of 400C.
Supports
The principal support used in testing has been
alumina in the form of Alcoa 1/4 or 3/4 inch spheres (#S-
100). Other supports tested for absorptive capacity
include alumina in the form of Norton 5/16" rings
(#6573), Norton spheres (#6576); CIL Prox-Svers non-
uniform spheres, Davison Chemical molecular sieves (type
13x, 4-8 mesh beads), silica and char. The Alcoa support
was chosen as the preferred carrier due to its high
absorptive capacity, which was due, in turn, to its large
surface area (325m /gm).
~ - 28 - 1 33 7 9 0 5
The Alcoa support referenced is essentially
alumina that is reported as being in the gamma and
amorphous form. It is not believed that the type of
crystalline form in which the alumina may be found is of
05 significance to the dissociative capacity of the
catalyst.
Activity has been found where there is aluminum
present in the support. The presence of aluminum in the
support is relevant in that alumina will invariably be
formed. When preparing the catalyst, the alkali metal
will attack the alumina and form alkali aluminate and
species containing available reactive oxygen. Thus the
aluminum-containing supports inherently are capable of
providing active centres necessary to support the
activity of the catalyst. Such supports also provide an
etchable base upon which actively catalytic sites are
thought to be more likely to form.
Supports were tested for decomposition activity
when aluminum was not present. A distinct but non-
quantified showing of production of elemental sulphuroccurred on repeated cycles of exposure of an oxygen
activated catalyst formed on a silica support, to a
continuous stream of 10~ hydrogen sulphide. This was
based upon manganese and sodium as the active metal and
alkali respectively. Due to the reduced surface area of
this latter carrier, only trace amounts of sulphur were
produced, and no quantitative measurements of
1 337~05
- 29 -
decomposition were made. However, this test demonstrated
that it is not essential that the support upon which the
catalyst is based contain aluminum.
The capacity of the support to fully absorb
05 hydrogen sulphide and/or other sulphur compounds is an
important feature when it is desired to remove all
significant traces of such compounds from a gas stream.
This characteristic is believed to be dominated by the
support itself. When the production of sulphur is the
primary objective, the efficiency of absorption by the
carrier is less critical. In such cases supports may be
used that do not effect 100% absorption of hydrogen
sulphide prior to saturation.
Recyclability of the Catalyst
The prepared catalysts were run through at least
4 cycles of absorption and regeneration before quantified
tests were carried out on them. These initial cycles
were found appropriate to stabilize the catalyst and
obtain relatively consistent results in subsequent tests.
Generally, the activity of the catalyst in terms of its
decomposing capacity increased following these
preliminary recyclings. The presence of oxygen at least
in small amounts during or after the purging phase of the
process was found to be essential to restore the activity
of the catalyst. It is believed that the catalyst
oxidizes the non-sulphur components of the absorbed
X
1 337qo5
- 30 -
compounds using internally available oxygen. In the case
of hydrogen sulphide, this results in the release of
water. Oxygen is then required to replenish the oxygen
so consumed.
05 No significant decline or loss of activity in
dissociative capacity of the catalyst has been found
despite a number of consecutive absorption and
regeneration cycles so long as replacement oxygen is
available. The absorptive capacity of the catalyst has
been shown to remain relatively unchanged through at
least 30-40 cycles of absorption and regeneration.
Effects of Carbon Dioxide, Water and Heavy Hydrocarbons
and Decomposition on Hydrogen Sulphide Absorption
When carbon dioxide is present in the gas stream
it does not substantially affect the capacity of the
catalytic bed to absorb hydrogen sulphide, but is itself
absorbed. The presence of absorbed carbon dioxide within
the bed does not significantly affect the decomposition
of hydrogen sulphide.
When water is present in or exposed to the
catalytic bed as a vapour component in a gas stream, the
performance of the alumina-supported catalyst in terms of
absorptive capacity is somewhat enhanced. Water has not
been found, however, to have a significant effect on
the decomposing capacity of the catalyst.
When used to remove hydrogen sulphide from gas
streams containing high boiling point hydrocarbons,
X
1 337905
- 31 -
contamination of the catalyst can occur. Prior scrubbing
of the gas stream has been found necessary to reduce the
effects of this problem.
Pressure Effects on Absorptive Capacity for
05 Hydrogen Sulphide
The absorptive capacity of the catalyst (in terms
of the ratio of the mass of hydrogen sulphide removed in
the absorption stage to the mass of the catalyst) is
relatively insensitive to the concentration of hydrogen
sulphide in the gas stream for concentrations of hydrogen
sulphide up to 10%. It rises, however, approximately
linearly with total pressure, up to at least 500 psig.
At modest flow rates, the rate of removal of
hydrogen sulphide by absorption in the case of alumina
carriers is relatively high, up to the point where the
catalyst bed has been nearly totally saturated with
hydrogen sulphide at ambient temperature and pressure.
Some tests were done with a 3 minute residence
time. Other tests were done with a 0.7 minute residence
time. In both cases Alcoa alumina carriers impregnated
with the necessary ingredients to form the catalyst were
capable, before saturation, of removing virtually 100~ of
the hydrogen sulphide from the gas stream. The level of
hydrogen sulphide prior to breakthrough was below the
threshold of measurability, in both cases being below 1
ppm.
- - 32 - 1 337qO~
Throughout the laboratory tests, nitrogen or
methane containing small amounts of oxygen was used in
most cases to reactivate the catalyst after the sulphur
was driven-off using oxygen-free nitrogen or methane as
05 the sweep gas. In some tests effected using a source of
sour natural gas, the hydrogen sulphide absorptive
capacity of sample catalytic beds (based on the Alcoa
carrier) was similar to that obtained with the nitrogen
as the background gas. While quantitative measurements
of decomposing capacity were not made in these latter
tests, visual examination of the catalyst bed after
exposure to sour natural gas and before regeneration
showed clear deposits of yellow sulphur. From this it is
concluded that the substitution of natural gas for
nitrogen or pure methane as the background gas and as the
sweep gas does not significantly decrease the absorptive
or dissociative capacity of the catalyst.
Decomposition of Other Sulphur Compounds
While tests have been carried out mainly on
hydrogen sulphide as the decomposed sulphide, it is
believed that the catalyst will be active in decomposing
carbonyl sulphide, carbon disulphide, mono and dialkyl
sulphides, alkyl-type disulphides and thiophene. It
would also be suitable for removing all of the foregoing
from a mixture of more complex natural gas components in
gaseous or liquid phase, such as from butane or propane.
7~
33 ~ 337905
Absorption of Oxygen Compounds
Tests based on the activation of a 2Na S/ZnS form
of calatyst deposited in S-100 Alcoa spheres (at 1%
loading, by weight) show a capacity for such a bed to
05 absorb up to 6% by weight of sulphur dioxide, 9.1% by
weight of nitrogen per oxide and 6% of carbon dioxide,
simultaneously. The gas stream used for this test
contained 10-12% of C02; 4-6% of 2; 1000-2000 ppm of S02
and 100-400 ppm of NO2. These ratios are typical for a
flue gas. The absorption capacities for each of these
components do not appear to be substantially cross-
related.
When a combination bed of oxygen-activated
catalyst, con-taining all three of the above components
was treated with hydrogen sulphide, the oxides of sulphur
and nitrogen reacted with the hydrogen sulphide to
produce sulphur and water. Then, on heating, the bed was
purged of sulphur, nitric oxide and carbon dioxide.
Conclusion
The foregoing disclosure has identified various
features of the invention. These and further aspects of
the invention, in its most general and more specific
senses, are now described and defined in the claims which
follow.
