CA1337905C - Catalytic removal of sulphur-containing compounds from fluid streams by decomposition - Google Patents
Catalytic removal of sulphur-containing compounds from fluid streams by decompositionInfo
- Publication number
- CA1337905C CA1337905C CA 614855 CA614855A CA1337905C CA 1337905 C CA1337905 C CA 1337905C CA 614855 CA614855 CA 614855 CA 614855 A CA614855 A CA 614855A CA 1337905 C CA1337905 C CA 1337905C
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- Prior art keywords
- sulphide
- support
- sulphur
- salts
- sulfur
- Prior art date
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/8603—Removing sulfur compounds
- B01D53/8612—Hydrogen sulfide
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/02—Sulfur, selenium or tellurium; Compounds thereof
- B01J27/04—Sulfides
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/02—Sulfur, selenium or tellurium; Compounds thereof
- B01J27/057—Selenium or tellurium; Compounds thereof
- B01J27/0576—Tellurium; Compounds thereof
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/02—Preparation of sulfur; Purification
- C01B17/04—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides
- C01B17/0404—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides by processes comprising a dry catalytic conversion of hydrogen sulfide-containing gases, e.g. the Claus process
- C01B17/0426—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides by processes comprising a dry catalytic conversion of hydrogen sulfide-containing gases, e.g. the Claus process characterised by the catalytic conversion
- C01B17/0434—Catalyst compositions
Abstract
This invention provides a catalyst and method for removing sulphur compounds from a fluid stream and decomposing such compounds to produce sulphur. Sour natural gas can be sweetened effectivey by this invention, and sulfur can be prepared thereby. The invention employs a catalyst containing an alkali metal sulfide and sulfides(s) or selenide(s) of metal(s) showing polyvalent and/or amphoteric character, e.g. Zn, etc. The catalyst is generally impregnated on a microporous type support (e.g., alumina) and is capable of providing reactive oxygen. Its activity is sustained by exposure to small amounts of oxygen either while decomposing the sulphur compound, or thereafter.
Description
~ 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 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.
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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 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
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
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.
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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.
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 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.
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- 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 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
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 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 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 -- --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) 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.
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~
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).
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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 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 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 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
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.
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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.
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 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.
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~ - 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 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
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
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.
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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.
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 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.
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- 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 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
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 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 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 -- --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) 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.
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~
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,~
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 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 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 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
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.
Claims (27)
1. In a catalytic composition deposited on a catalytic support suitable for use for treating a fluid composition having a compound with a sulfur component and at least one non-sulfur component, the improvement wherein said composition comprises a mixture of at least two salts, the first of said salts comprising a sulphide or selenide of at least one metal selected from the group of amphoteric or polyvalent metals, or mixtures thereof, the second of said salts being a sulphide or selenide of an alkali metal, and there being present at least one component capable of providing or generating reactive oxygen whereby said reactive oxygen is reactable with said non-sulfur component of the said compound to form sulphur.
2. A catalytic composition as in Claim 1, wherein said support is selected from the group of supports comprised by alumina, zeolites, molecular sieves, silica and char.
3. A catalytic composition as in claim 1, wherein said support is adapted to absorb alkyl or hydrogen sulphides.
4. A catalytic composition as in claim 1, wherein one of said salts is a sulfide.
5. A catalytic composition as in claim 1, wherein both of said salts are sulphides.
6. A catalytic composition as in claim 1, wherein said metal is selected from the group consisting of zinc, manganese, iron, copper, cobalt, aluminum, vanadium, molybdenum, tin and nickel, and mixtures thereof.
7. A catalytic composition as in claim 1, wherein one of said salts is a selenide.
8. A catalytic composition as in claim 1, wherein both of said salts are selenides.
9. A catalytic composition as in claim 1, 4 or 5, wherein the alkali metal is selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, and mixtures thereof.
10. A catalytic composition as in claim 6, 7 or 8, wherein the alkali metal is selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, and mixtures thereof.
11. A catalytic composition as in claim 6 , wherein said alkali metal salt is a sulfide, the alkali metal is selected from the group consisting of sodium and potassium, said support is micro-porous alumina, and said composition is capable of absorbing hydrogen sulphide from an otherwise chemically non-reactive gas, said catalytic composition being capable of decomposing hydrogen sulphide into precipitated sulphur.
12. A catalytic composition as in claim 1, 6, or 11 which is prepared by the method of dissolving a mixture of a sulphide of the amphoteric or polyvalent metal, or a mixture thereof in an aqueous solution together with a sulphide or selenide salt of the alkali metal, impregnating the resulting solution so formed onto a catalytic alumina support, drying the support, conditioning said catalytic composition by exposing it to a gaseous stream containing a reactive sulphur compound to convert said mixture to include sulphides of said metals, and heating said catalytic composition to drive off excess sulphur.
13. A method of decomposing reactable sulphur-containing compounds from a gas stream containing such compounds to produce elemental sulphur including contacting said gas with a catalyst composition deposited on a catalytic supporting comprising a mixture of at least two salts, the first of said salts comprising a sulphide or selenide of at least one metal selected from the group of amphoteric or polyvalent metals, or mixtures thereof, the second of said salts being a sulphide or selenide of an alkali metal, and there being present, immobilized in the catalyst, at least one component capable of providing or generating reactive oxygen whereby said reactive oxygen reacts with said non-sulfur component of the said compound to form sulphur followed by the step of regenerating said catalyst by heating it in the presence of an unreactive sweep gas containing a minor amount of oxygen to drive-off elemental sulphur and recondition the catalyst.
14. A method as in claim 13 wherein said support is selected from the group of supports comprised by alumina, zeolites, molecular sieves, silica and char.
15. A method as in claim 13 wherein said support is adapted to absorb alkyl or hydrogen sulphide.
16. A method as in claim 13 wherein one of the salts is a sulphide.
17. A method as in claim 13 wherein both of said salts are sulphides.
18. A method as in claim 13 wherein said amphoteric or polyvalent metal is selected from the group consisting of zinc, manganese, iron, copper, cobalt, aluminum, vanadium, molybdenum, tin and nickel, and mixtures thereof.
19. A method as in claim 16, 17 or 18 wherein the alkali metal is selected from the group consisting of lithium, potassium, sodium, cesium and rubidium.
20. In a catalytic composition deposited on a catalytic support suitable for use for treating a sulfur-containing composition having at least one sulfur compound containing a reactable non-sulfur component, the improvement wherein said composition is a composition obtained by the method of treating said support with a mixture of at least two salts, one of said salts comprising at least one sulphide or selenide of at least one metal selected from the group of amphoteric or polyvalent metals, or mixtures thereof, the other of said salts being at least one sulphide or selenide of an alkali metal, drying said support once so treated, then conditioning said composition by exposure of said support to a stream of hydrogen-sulphide, then removing excess sulphur by heating said support in the presence of a sweep gas, and exposing said support to an amount of oxygen in order to conclude the conditioning, there being present reactive oxygen whereby said reactive oxygen reacts with said non-sulfur component of said sulfur-containing compound to form sulfur.
21. A method of sweetening a sour natural gas stream comprising providing a stream of a sour natural gas, containing at least one sulfur compound having a reactable non-sulfur component and exposing said stream to an active catalytic composition deposited on a catalytic support wherein said composition contains a mixture of at least two salts, one of said salts comprising at least one sulphide or selenide of at least one metal selected from the group of amphoteric or polyvalent metals, or mixtures thereof, the other of said salts being at least one sulphide or selenide of an alkali metal, there being present reactive oxygen whereby said reactive oxygen reacts with a non-sulfur component of a sulfur-containing compound to form sulfur.
22. A method of sweetening a sour natural gas stream comprising providing a stream of a sour natural gas, containing at least one reactable sulfur compound having a non-sulfur component and exposing said stream to an active catalytic composition deposited on a catalytic support wherein said composition is obtained by treating said support with a mixture of at least two salts, one of said salts comprising at least one sulphide or selenide of at least one metal selected from the group of amphoteric or polyvalent metals, or mixtures thereof, the other of said salts being at least one sulphide or selenide of an alkali metal drying said support once so treated, then conditioning said composition by exposure of said support to a stream of hydrogen-sulphide, then removing excess sulphur by heating said support in the presence of a sweep gas, and exposing said support to an amount of oxygen in order to conclude the conditioning, thereby being present reactive oxygen whereby said reactive oxygen reacts with a non-sulfur component of a sulfur-containing compound to form sulfur.
23. A method of producing sulphur from a composition containing a sulfur compound having a reactable non-sulfur component comprising providing a source of a composition containing a sulfur compound having reactable a non-sulfur component, exposing said source to an active catalytic composition deposited on a catalytic support wherein said composition contains a mixture of at least two salts, one of said salts comprising at least one sulphide or selenide of at least one metal selected from the group of amphoteric or polyvalent metals, or mixtures thereof, the other of said salts being at least one sulphide or selenide of an alkali metal, there being present reactive oxygen whereby said reactive oxygen reacts with the reactable non-sulfur component of said sulfur-containing compound to form sulfur, and recovering the resulting sulfur produced thereby.
24. A method of producing sulphur from a composition containing a sulfur compound having a reactable non-sulfur component comprising providing a source of a composition containing a sulfur compound having a reactable non-sulfur component, exposing said source to an active catalytic composition deposited on a catalytic support wherein said composition is obtained by treating said support with a mixture of at least two salts, one of said salts comprising at least one sulphide or selenide of at least one metal selected from the group of amphoteric or polyvalent metals, or mixtures thereof, the other of said salts being at least one sulphide or selenide of an alkai metal, drying said support once so treated, then conditioning said composition by exposure of said support to a stream of hydrogen-sulphide, then removing excess sulphur by heating said support in the presence of a sweep gas and, exposing said support to an amount of oxygen in order to conclude the conditioning, there being present reactive oxygen within the catalytic composition whereby said reactive oxygen reacts with a non-sulfur component of a sulfur-containing compound to form sulfur, and recovering the resulting sulphur produced thereby.
25. A method, as defined in claim 23 or 24, wherein said source comprises a gaseous source and said reactable non-sulphur component is selected from the group consisting of carbonyl sulphide, carbon disulphide, mono and dialkyl sulphides, alkyl-type disulphides and thiophenes.
26. A method as defined in claim 23 or 24, wherein said source comprises a sour natural gas.
27. A method as defined in claims 23 or 24 wherein said source comprises a liquid source and said reactable non-sulphur component is selected from the group consisting of carbonyl sulphide, carbon disulphide, mono and dialkyl sulphides, alkyl-type disulphides and thiophenes.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 614855 CA1337905C (en) | 1989-09-29 | 1989-09-29 | Catalytic removal of sulphur-containing compounds from fluid streams by decomposition |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 614855 CA1337905C (en) | 1989-09-29 | 1989-09-29 | Catalytic removal of sulphur-containing compounds from fluid streams by decomposition |
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| Publication Number | Publication Date |
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| CA1337905C true CA1337905C (en) | 1996-01-09 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2013180763A1 (en) * | 2012-01-18 | 2013-12-05 | Intramicron, Inc. | Catalysts for oxidative sulfur removal and methods of making and using thereof |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2013180763A1 (en) * | 2012-01-18 | 2013-12-05 | Intramicron, Inc. | Catalysts for oxidative sulfur removal and methods of making and using thereof |
| US10159962B2 (en) | 2012-01-18 | 2018-12-25 | Intramicron, Inc. | Catalysts for oxidative sulfur removal and methods of making and using thereof |
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