US 4,036,942 AGrant
Process for the Removal of Hydrogen Sulfide and Mercaptans From Liquid and Gaseous Streams
Issue Date:1977-07-19
•16 Claims
•2 Drawing Sheets
Abstract
A process is provided for removing hydrogen sulfide and alkyl mercaptans from fluid streams by reaction with oxygen in the presence of a metal amino acid chelate in aqueous solution containing an amine, converting hydrogen sulfide to sulfur and alkyl mercaptans to dialkyl disulfides, and separating these from the aqueous metal chelate solution. A process is also provided for removing hydrogen sulfide and alkyl mercaptans from fluid streams in which the gaseous or liquid stream is dispersed in aqueous metal chelate solution in a fine dispersion short of foam formation and passed through a reaction zone at a high flow velocity, where hydrogen sulfide is catalytically oxidized to sulfur, and alkyl mercaptans to dialkyl disulfides, and then into a relatively wide quiescent zone where the dispersion breaks, the gases are separated, and the metal chelate solution recovered.
Metadata
Assignee
- Rhodia, Inc.
Inventors
- Jacques Pierre Sibeud
- Charles David Ruff
Application Information
Application Number:US 3254828
Filing Date:1973-01-22
Priority Date:1971-07-28
Art Unit:113
Classifications
IPC:
B01D 5334
Field of Search:
423208210226-229;573;245;24320763
Patent Drawings (2 sheets)
Description
Preferred embodiments of apparatus for carrying out the process of the invention are shown in the drawings, in which:
FIG. 1 represents one form of reaction system adapted for continuous operation in accordance with the invention in which the gases and catalyst are introduced at the bottom of the contactor, the gases intimately dispersed into the liquid catalyst phase, and the resulting dispersion passed through a relatively short reaction zone and then into a relatively wide gas separation zone, where the dispersion breaks, the gases escape and are vented, and the catalyst phase is recycled after separation of sulfur and dialkyl disulfides.
FIG. 2 represents another form of reaction system adapted for continuous or semicontinuous operation in which the gases are dispersed in the liquid phase, the dispersion passed through a relatively narrow annular reaction zone, and then to a gas separation zone, the gases separated and vented, and the catalyst returned to the bottom of the reaction zone via a downcomer tube running through the center of the zone. The catalyst solution is taken from the bottom of the apparatus, passed through a sulfur/disulfide separating system, and then returned to the reaction zone.
FIG. 3 shows a more conventional sieve tray column adapted for continuous operation, and useful in the chelateamine catalytic process of the invention, in which the reaction zone is in the form of an elongated narrow tube, with sieve trays, and the gas separation chamber is omitted.
The apparatus shown in FIG. 1 comprises a tubular stainless steel contactor, represented here as defining a relatively short reaction chamber or zone 1, 10 feet in diameter and 3 feet long, and a cylindrical coaxial stainless steel separator, defining a separation chamber 2, 30 feet in diameter and 3 feet high, directly above and connected to the reaction chamber 1. An appropriate gas distribution system 3 is provided at the bottom of the contactor, such as several gas turbomixers with spargers to adequately disperse the gaseous mixture into the liquid catalyst solution. One or more sieve trays 4 are disposed in the contactor, if necessary, in order to ensure proper distribution of flow of the dispersion through the contactor. A gas feed inlet is provided, leading into the gas distribution system 3, and a liquid catalyst line 13 leads to the reaction chamber 1 above the gas distribution system 3.
The diameter of the separator chamber 2 can, for example, be from about 1.2 to about 10 times, preferably about 1.2 to about 3 times, greater than the diameter of the reaction chamber 1.
The separation chamber 2 is provided at its upper part with a screen or baffle 5 in order to capture any liquid entrained with the exiting gases, which escape through the outlet 6 above. The annular recess 7 extending circumferentially about the separation chamber is connected to line 8 by means of which liquid catalyst solution containing suspended sulfur and dialkyl disulfides is withdrawn from the chamber. The vent 9 serves to discharge gases which might be entrained by the liquid.
Line 8 leads to an appropriate conventional system for separating the solid suspended sulfur. That shown in the drawing by way of example includes centrifugal separator 10 and a liquid-liquid phase separator 11 for the separation of the dialkyl disulfide liquid from the aqueous catalyst phase. Storage tanks 12 and other equipment are also provided but these can be omitted. The line 13 leads thence to the reaction chamber 1.
In operation, the gas containing oxygen (air), hydrogen sulfide and alkyl mercaptans is continuously fed via the gas feed inlet line to the bottom of the contactor into the gas distribution system 3, while the liquid catalyst solution is fed in via line 13 and mixed therewith to form an intimate dispersion short of foam formation in the reaction chamber 1. A continuing feed of gases and liquid into the gas distribution system 3 and of dispersion thence into the reaction chamber 1 leads to an upward flow of reaction solution through the reaction zone to the separator chamber 2, the transit time through the reaction zone to the separator chamber constituting the reaction time. This may be very brief, of the order of 0.1 second, to several seconds or more, as desired or necessary for the gases being treated.
The gas-catalyst dispersion enters the separation chamber 2 where, due to the greatly increased diameter, and relatively slow flow rate, or relatively quiescent condition, the dispersion breaks and the gas separates, and is vented through the outlet 6. Such gas is substantially free from hydrogen sulfide and mercaptans. The catalyst solution, containing suspended sulfur and dialkyl disulfides, overflows into the annular recess 7 of the separator chamber 2, and is withdrawn through the outlet line 8. The sulfur is separated in the centrifuge 10, and the dialkyl disulfides in the phase separator 11. The catalyst solution, which does not require regeneration, is then recirculated to the reaction chamber 1 via line 13.
The apparatus shown in FIG. 2 has a similar construction, but the system for separation and recirculation of aqueous catalyst solution is different. In this case, the tubular reaction chamber 14 is glass-walled, 4 inches in internal diameter, and is annular; the annulus is 11/4 inches wide, surrounding a 11/2 -inch diameter stainless steel central downcomer or tube 15, 43/4 feet long, which extends from a point corresponding to the dispersion level in the separator chamber 16 to the bottom of the reaction chamber 14. Thence, line 21 leads from ports 20 to a tank 22 and a filter 23. A return line 24 for liquid catalyst solution leads to the reaction chamber 14.
The cylindrical glass separation chamber is 12 inches in diameter and 10 inches high but the height is not critical.
In this case, the gas feed inlet 17 at the bottom of the reaction chamber 14 terminates in a sieve tray or turbomixer 18, which is capable of forming an intimate dispersion of the entering gases in the liquid catalyst phase entering the annular reaction chamber 14 via line 24.
In operation, the dispersion passes upwardly through the reaction chamber 14, and enters the separator chamber 16, where the gas separates, and is vented via outlet 19. The liquid catalyst solution containing sulfur and any dialkyl disulfides overflows into downcomer 15, and passes downwardly through the downcomer 15 to the bottom of the annular reaction chamber 14. There it is led out via port 20 and line 21 to a tank 22, followed by filter 23, where the sulfur is separated. If dialkyl disulfides are present, a liquid-liquid separator is added for their removal. The liquid catalyst solution is returned to the reaction chamber through the catalyst feed line 24.
The sieve tray column shown in FIG. 3 comprises an elongated glass tubular reactor 25, 4 inches in diameter and 22 feet long, in pilot plant dimensions, with a gas inlet line 26 at the bottom, for entry of oxygen (air) and the gas stream containing hydrogen sulfide and alkyl mercaptans, and a liquid catalyst inlet line 27 and gas outlet 28 at the top. The tower has seventy polypropylene sieve plates 29 for redistribution of gas in the liquid in the tower.
In operation, the liquid catalyst solution passes countercurrently downwardly in a turbulent flow against the upward gas flow through the tubular reactor, capturing the hydrogen sulfide and alkyl mercaptans therefrom in the course of this transit. The gas, now freed from hydrogen sulfide and alkyl mercaptans, escapes through the outlet 28, and passes to a mist separator 30, where any entrained liquid catalyst is removed and recycled. The main body of catalyst solution containing sulfur and dialkyl disulfides is separated through the outlet port 31 at the bottom of the reactor, and is passed to a filter 32, where the sulfur is separated, and then to a liquid-liquid separator 33, where the dialkyl disulfides are separated, and recycled via line 34. The reactor of FIG. 3 can also be used in the form of a packed column, replacing the sieve trays with, for instance, Berl saddles or 1/2 inch polypropylene Pall rings.
The following Examples in the opinion of the inventors represent preferred embodiments of the invention.
Example 1
Gas containing from 2,000 to 10,000 ppm of hydrogen sulfide mixed with nitrogen and oxygen (as air) was run through an elongated narrow glass column or pilot plant contactor tower similar to that shown in FIG. 3, countercurrently at 10 cfm against a highly turbulent downward flow of 5 l/min of aqueous iron chelate catalyst solution. The catalyst solution had the following composition:
In these experiments, the contact reaction time was varied from 0.36 second to 25 seconds, and the concentration of catalyst containing ferric iron ranged from 0.1 to 50% by weight of the solution, as shown in Table I.
The two-inch diameter glass column of Group I, Runs a) to i), was packed with Berl saddles. The four-inch diameter glass tower of Group II, runs j) to m), was 22 feet long, and was fitted with 70 polypropylene sieve plates. Both gave good emulsification of gas in the catalyst solution.
The results obtained are given in Table I.
It is apparent from the above results that the hydrogen sulfide can be virtually quantitatively removed from the gas stream, at concentrations as low as 2,000 ppm and as high as 100,000 ppm, and at catalyst concentrations as low as 0.1% and as high as 50%, at catalyst contact times of from 0.36 to 25 seconds.
For comparison purposes, a number of control runs were carried out, without dispersion of the gas stream in the catalyst solution. In these experiments, the catalyst solution was allowed to remain static, and held in a closed flask with the sample of the gas held over the solution.
It is apparent that under static conditions when contact time is sufficiently long, the hydrogen sulfide can be quantitatively removed, but of course in these circumstances the time is far too long for practical use when large volumes of gas have to be treated. It is quite surprising that increasing the state of subdivision of the gas in the liquid catalyst solution greatly increases the reaction rate, to the point where the reaction is quantitative in as short a time as 0.36 second, as the above results show. Under static conditions at least 60 minutes' contact time is required, and the time increases rapidly as the catalyst concentration is reduced to as low as 0.3%.
Example 2
Using the pilot plant contactor and separator shown in FIG. 2, a number of runs were carried out to determine the effectiveness of removal of hydrogen sulfide from gas containing hydrogen sulfide, nitrogen and oxygen (as air), and carbon dioxide. Two different types of aqueous ferric chelate catalyst solution were used, having the compositions:
Using catalyst A, the system was operated at room termperature, the temperature ranging from 20.degree. to 27.6.degree. C. from the start to the conclusion of the run, which was continuous for 5 hours. The gas contained 1% hydrogen sulfide (10,000 ppm), and was well dispersed in the catalyst solution. The pH of the catalyst was 7.9 at the start of the reaction, and 7.8 at the conclusion of the reaction. At the start of the test, 1,300 ppm hydrogen sulfide was present in the effluent, but this rose to from 2,400 to 2,800 ppm at the conclusion of the test. The gas was fed through the system at a rate of 10 cubic feet per minute, and the catalyst solution was fed through at a rate of 5 liters per minute. The flow was highly turbulent.
Using catalyst B and the same highly turbulent conditions, at a gas feed rate of 10 cubic feet per minute, a liquid catalyst feed rate of 5 liters per minute, a temperature ranging from 22.degree. C., to 26.5.degree. C., and a feed gas containing 1% hydrogen sulfide (10,000 ppm), the percentage of hydrogen sulfide in the effluent was less than 2 ppm. The pH of the catalyst remained at 9.6 throughout the approximately 5 hours of operation.
It is apparent that the monoethanolamine present in catalyst B materially increased the effectiveness of the catalyst to remove hydrogen sulfide.
Example 3
Using the pilot plant contactor shown in FIG. 3, gas containing approximately 0.1% hydrogen sulfide (1,000 ppm), was treated with the catalyst systems A and B of Example 2.
Using catalyst A, the reaction was carried out at room temperature. The hydrogen sulfide content of the feed ranged from 1,200 to 1,700 ppm. The pH of the catalyst was maintained at approximately 7.5 . This required several additions of 10% sodium hydroxide solution. The feed gas was run through the reactor at a rate of 4 cubic feet per minute, and the catalyst solution at a rate of 0.5 to 0.8 gallon per minute. The flow was highly turbulent.
Under these conditions, the H.sub.2 S content in ppm of the gaseous effluent ranged from 300 ppm at the beginning of the process to 500 ppm at the conclusion of the test.
Using catalyst B and the same process conditions, the pH of the catalyst system was maintained at about 7.3 throughout the test and without any addition of further alkali, while the hydrogen sulfide concentration in the gaseous effluent ranged from 100 to 135 ppm at the beginning of the test to 25 to 60 ppm at the conclusion of the test. Thus, the amine considerably enhanced the efficiency of removal of hydrogen sulfide. EXAMPLE 4
Using the pilot plant shown in FIG. 3, waste gases containing hydrogen sulfide in concentrations from 1,000 to 15,000 ppm in gases containing up to 95.5% carbon dioxide were treated with a catalyst solution having the composition of catalyst B of Example 2. The catalyst concentration was 5%. The flow rate of gases was 4 cfm and the flow rate of catalyst solution was 1 gpm. The flow was very turbulent.
The results show that nearly complete oxidation of the hydrogen sulfide can be achieved even in a stream containing virtually all carbon dioxide. Moreover, at the end of a 5-hour continuous run, the pH of the catalyst solution had not changed materially.
Example 5
A synthetic gas stream having the composition 400 ppm H.sub.2 S, 300 ppm SO.sub.2, 5% oxygen, 12% CO.sub.2, 83% nitrogen, was treated in the pilot plant of FIG. 3 with a catalyst having the composition of catalyst B of Example 2. During the run, the pH of the catalyst solution was kept above 7 by the addition of stoichiometric amounts of caustic soda. The flow rate of gases was 4 cfm and the flow rate of catalyst solution was 1.0 gpm. The flow was very turbulent. A 95% removal of the hydrogen sulfide was obtained, showing that the catalyst is active in the presence of sodium sulfite.
Example 6
An aqueous catalyst solution comprising a ferric ion chelate was prepared by dissolving 93 lbs. ferric sulfate (21.8% Fe) in 464 lbs. water. To the solution was added with agitation 373 lbs. trisodium salt of N-hydroxyethyl ethylene diamine triacetic acid as a 41% aqueous solution. To the clear solution was added 70 lbs. monoethanolamine, with stirring so as to obtain 1,000 lbs. of clear orange-brown catalyst concentrate solution, pH 10.2. For use as a catalyst solution, this concentrate was diluted with various amounts of water. The concentrate contained 2.0% Fe, a 10% solution at 0.2% Fe.
H.sub.2 S was removed from a gas stream by passing it countercurrently to the liquid catalyst stream in apparatus similar to FIG. 3, under the following conditions:
Column: 22 ft. high, 4 inches internal diameter, packed with 1/2 inch Pall rings. Sampling cocks at six levels.
Catalyst Solution: 40 liters 10% solution at 0.2% Fe.
H.sub.2 s stream: 1500 ppm H.sub.2 S in air (by volume).
Duration of Test: 17 hours. Oxidation-Reduction Cycles: 38
pH Catalyst Solution: 7.7 to 7.2. Temperature: 20.degree.-28.degree. C.
Rate of Gas Stream: 4 cfm.
Pressure Drop through Column: 32 inches water.
Rate of Catalyst Solution Flow: 0.9 gal./min.
The following results were obtained:
The efficiency of H.sub.2 S removal was limited only by the fact that at higher flow rates foaming occurred, which interfered with the operation; prolonged operation caused deposit of sulfur on the packing, with resulting clogging of the column.
Example 7
Using the same catalyst solution as in Example 6 in the sieve tray column described in FIG. 3, under the following conditions:
Column: 22 ft. high, 4 in. internal diameter, containing 70 sieve plates.
Catalyst Solution: 40 liters 10% solution at 0.2% Fe.
H.sub.2 s stream: 1500 to 20,000 ppm in air.
Duration of Test: 23 hours. Oxidation-Reduction Cycles: 16
pH Catalyst Solution: 8.0 to 7.5. Temperature: 20.degree.-30.degree. C.
Rate of Gas Stream: 4 cfm.
Pressure Drop through Column: 32 inches water.
Rate of Catalyst Solution Flow: 0.6 gal./min.
The H.sub.2 S concentration in air was subsequently raised to higher levels, as shown below, to determine the limit of complete removal. The following results were obtained for various concentrations of H.sub.2 S in air:
The sieve tray column is more efficient than the packed column, since with 4 seconds residence time it removes 94.7% of a 1500 ppm H.sub.2 S stream, compared to 60% for the packed column. In this column also, higher rates of flow caused foaming.
Example 8
In the presence of large amounts of CO.sub.2 in a gas stream, the removal of H.sub.2 S is less efficient. However, in the sieve tray column of Example 7, good results were obtained in removing H.sub.2 S from almost pure CO.sub.2 gas, under the following conditions:
Catalyst Solution: 40 liters 9.2% solution at 0.2% Fe.
Duration of Test: 23 hours. Oxidation-Reduction Cycles: 16
H.sub.2 s stream: 2.5% H.sub.2 S, 5% oxygen, 92.5% CO.sub.2.
pH Catalyst Solution: 8.0 to 6.5. Temperature: 20.degree.-30.degree. C.
Rate of Gas Stream: 4 cfm.
Pressure Drop through Column: 32 inches water.
Rate of Catalyst Solution Flow: 0.6 gal./min.
The following results were obtained:
Excellent removal of H.sub.2 S was obtained.
Example 9
Using the contactor of FIG. 2, under the following conditions, hydrogen sulfide was removed from a gas stream containing equal amounts of H.sub.2 S and CO.sub.2 :
Contactor Dimensions: Column: 40 in. high, 4 in. internal diameter, containing 1 perforated plates; catalyst solution occupies 32 in. of tubular reaction chamber.
Separator Chamber: 12 in. internal diameter and 16 in. high.
Catalyst Solution: 40 liters 50% solution at 2% Fe (prepared from catalyst concentrate of Example 6)
H.sub.2 s stream: 1% H.sub.2 S, 1% CO.sub.2, 20% Oxygen, 78% Nitrogen.
Duration of Test: 62 hours. Oxidation-Reduction Cycles: 80
pH Catalyst Solution: 9.5 to 8.7 Temperature: 22.degree.-26.degree. C.
Rate of Gas Stream: 10 cfm.
Pressure Drop through Column: 24 in. water.
Rate of Catalyst Solution Flow: 1.2 gal./min.
The following results were obtained:
By changing the catalyst solution above to 40 liters 87% solution at 1.75% Fe, during a 20-hour run, the H.sub.2 S removal was further improved:
A comparison of the results in Examples 7 and 9 demonstrates that the contactor is much more efficient than the sieve tray column. It achieves 99.9% H.sub.2 S removal in 0.35 second residence time, compared to about 10 seconds for the sieve tray column, a favorable factor of about 30:1.
In order to obtain an equivalent H.sub.2 S removal in the absence of a contactor to increase the liquid-gas interface, the residence time is 3600 seconds. The factor in favor of the contactor is about 10,000:1. This is shown by the following experiment, carried out under nonmixing, i.e., stationary, conditions:
A 5-liter glass flask was filled with air containing 2000 ppm H.sub.2 S. 50 ml of a 10% catalyst solution prepared as in Example 6 was added, and the flask closed. The flask was occasionally shaken, and the H.sub.2 S content of the gas phase determined. Only after 60 hours had the H.sub.2 S concentration decreased to 20 ppm, corresponding to an H.sub.2 S removal of 99%. Residence Time: 3600 seconds.
Claims
Having regard to the foregoing disclosure the following is claimed as the inventive and patentable embodiments thereof:
1. A cyclic continuous process for the removal of hydrogen sulfide contained in gaseous streams, and the substantially quantitative catalytic conversion thereof to elemental sulfur, while inhibiting the buildup in the system of water-soluble by-products such as sulfates, which comprises contacting the gaseous stream with free oxygen gas and an aqueous solution of a water-soluble polyvalent metal chelate catalyst retaining the metal in soluble form in the aqueous solution, an inorganic alkali in an amount to adjust the pH to within the range from about 6.8 to about 10, and a strongly alkaline free organic amine in an amount within the range from about 0.1% to about 50% sufficient to inhibit water-soluble by-product formation, thereby concurrently forming sulfur and causing polyvalent metal catalyst oxidation and regeneration reactions in the oxidation-reduction metal chelate reaction system to proceed concurrently, while lessening buildup of water-soluble by-products in the catalyst solution; separating the sulfur from the aqueous metal chelate solution; and recycling the regenerated aqueous polyvalent metal chelate catalyst solution thereby recovered to contact another portion of the gaseous stream.
2. A process in accordance with claim 1, in which the metal amino acid chelate catalyst is formed from a chelating amino acid of the formula ##STR2## in which from two to four of the groups X are selected from the group consisting of acetic acid and propionic acid groups and any remaining groups are selected from the group consisting of hydrogen and CN, and in which R is selected from the group consisting of alkylene having at least two carbon atoms, cyclohexylene in which the nitrogen atoms attached to the ring are in the 1,2-positions, and phenylene in which the nitrogen atoms attached to the ring are in the 1,2-positions, and a member selected from the group consisting of chlorine and methyl being substituted for hydrogen in at least one of the 3- and 6-positions in the cyclohexylene or phenylene ring.
3. A process in accordance with claim 2, in which the amino acid is ethylene diamine tetraacetic acid.
4. A process in accordance with claim 2, in which the amino acid is N-hydroxyethyl ethylene diamine triacetic acid.
5. A process in accordance with claim 1, in which the sulfur is separated as a solid.
6. A process in accordance with claim 1, in which the sulfur is liquefied, and sulfur is separated by liquid-liquid phase separation.
7. A process in accordance with claim 1, in which the polyvalent metal is selected from the group consisting of iron, cobalt and nickel.
8. A process in accordance with claim 6, in which the polyvalent metal is iron.
9. A cyclic continuous process for the removal of hydrogen sulfide contained in gaseous streams, and the substantially quantitative catalytic conversion thereof to elemental sulfur, while inhibiting the buildup in the system of water-soluble by-products such as sulfates, which comprises contacting the gaseous stream with free oxygen gas and an aqueous solution of a water-soluble polyvalent metal chelate catalyst retaining the metal in soluble form in the aqueous solution and a strongly alkaline free organic amine in an amount within the range from about 5% to about 50% sufficient to adjust the pH to within the range from about 6.8 to about 10 and to inhibit water-soluble by-product formation, thereby concurrently forming sulfur and causing polyvalent metal catalyst oxidation and regeneration reactions in the oxidation-reduction metal chelate reaction system to proceed concurrently, while lessening buildup of water-soluble by-products in the catalyst solution; separating the sulfur from the aqueous metal chelate solution; and recycling the regenerated aqueous polyvalent metal chelate catalyst solution thereby recovered to contact another portion of the gaseous stream.
10. A process in accordance with claim 9, in which the metal amino acid chelate catalyst is formed from a chelating amino acid of the formula ##STR3## in which from two to four of the groups X are selected from the group consisting of acetic acid and propionic acid groups and any remaining groups are selected from the group consisting of hydrogen and CN, and in which R is selected from the group consisting of alkylene having at least two carbon atoms, cyclohexylene in which the nitrogen atoms attached to the ring are in the 1,2-positions, and phenylene in which the nitrogen atoms attached to the ring are in the 1,2-positions, and a member selected from the group consisting of chlorine and methyl being substituted for hydrogen in at least one of the 3- and 6-positions in the cyclohexylene or phenylene ring.
11. A process in accordance with claim 10 in which the amino acid is ethylene diamine tetraacetic acid.
12. A process in accordance with claim 10 in which the amino acid is N-hydroxyethyl ethylene diamine triacetic acid.
13. A process in accordance with claim 9 in which the sulfur is separated as a solid.
14. A process in accordance with claim 9 in which the sulfur is liquefied, and sulfur is separated by liquid-liquid phase separation.
15. A process in accordance with claim 9, in which the polyvalent metal is selected from the group consisting of iron, cobalt and nickel.
16. A process in accordance with claim 15, in which the polyvalent metal is iron.
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