DE2554454A1 - Sepg hydrogen sulphide from carbon dioxide - by dissolving in aq soln contg bicarbonate ion - Google Patents

Abstract

H2S is preferentially removed from a gas mixt. of H2S by treating the gas mixt. with an aq. soln. contg. a sufficient concn. of HCO3- ion to establish an equilibrium imbalance preventing substantial dissolution of CO2 and pref. also contg. inert salts. The HCO3 ion reduces the solubility of CO2 the soln. and maintains the pH fairly constant. The soln. does not require monitoring.

Description

Process for the separation of hydrogen sulfide

from a gas stream The invention relates to the separation of hydrogen sulfide from gas streams that contain other gases, in particular carbon dioxide, in addition to H2S.

Gas or exhaust gas flows are encountered in many technical processes, which contain H2S and C02 as well as possibly other gases. Since you at least have the H2S percentage such gas or exhaust gas flows due to its toxicity and its foul odor cannot be released into the atmosphere, there are already numerous processes for the separation of H2S from gas or exhaust gas flows by absorption has become known.

Some of these known methods use mono- and / or for absorption Diethanolamine. Other known methods use alkali carbonates and alkali arsenates or a mixture of tetrahydrothiophone-11 dioxide and alkanolamines. It is further known to separate H2S and C02 by absorption in alkaline aqueous solutions, there the solubility of both gases in aqueous solutions with increasing pH increases.

Absorption methods of the above type are described, for example, in the journals "The Oil and Gas Journal", August 1967, page 131 or June 1968, 90 and Chemical Engineering ", May 1972, p. 66.

However, these known methods are disadvantageous in that the The absorbents used are consumed and either constantly supplemented or need to be regenerated.

In some of the known methods, the pH of the absorption solution must also be determined constantly monitored and kept constant. In many of these known processes it is difficult to remove the dissolved hydrogen sulfide from the absorption solution, in order to recycle it. A disadvantage of the known method that a Using alkaline aqueous absorption solution lies in the fact that they contain both H2S as well as C02 from a gas or exhaust gas stream. In many cases, however, it would be sufficient and beneficial to absorb the H2S alone, as C02 is harmlessly released into the atmosphere could be fired. A "selective" absorption of H25 was known with these However, this method has not yet been practicable.

U.S. Patent 3,576,738 and filed November 17, 1971 USA patent applications Serial No. 199,777, 199,779 and 199,780 are already procedures for the catalytic oxidation of H2S dissolved in aqueous absorbents, however, these processes are not aimed at separating H2S from gas or gas. Exhaust gas flow.

The method of the invention was therefore based on the object described To remedy disadvantages of the known method or at least to mitigate and a To create a process with which from a gas stream, which contains H2S and C02, of one aqueous solution quickly and almost exclusively separated 1125 and in the absorption solution can optionally be catalytically oxidized to elemental sulfur.

The invention relates to a process for separating off hydrogen sulfide from a gas stream which, in addition to hydrogen sulfide, carbon dioxide and possibly other Contains gases, by absorption in an alkaline aqueous salt solution, which thereby is characterized in that the gas stream with a solution containing hydrogen carbonate ions in a concentration at which almost exclusively hydrogen sulfide is absorbed is, contains, is treated.

The invention also relates to a preferred embodiment this method, which is characterized in that the aqueous absorption solution a salt of a catalytically active transition metal and one for essentially complete oxidation of the absorbed hydrogen sulfide to sulfur is sufficient Amount of oxygen is added.

The method of the invention thus provides for a 1125 and in particular C02 or similar gas mixture containing gases which are soluble in water with an acidic reaction to treat with an aqueous solution containing hydrogen carbonates and 1125 to be absorbed in it and separated from the gas flow, the C02 being predominantly remains in this treated gas stream. The absorption solution should in particular Contains alkali hydrogen carbonate (s) (bicarbonates). The aqueous absorption solution also contains dissolved inert salts. This absorption solution is said to be at the preferred embodiment of the method of the invention additionally salts one contain catalytically active transition metal and an oxidizing agent.

In the method of the invention, the concentration of the hydrogen or bicarbonate ions in the absorption solution should be so high that the solution equilibrium of H2S and COS in an aqueous medium is disturbed and dissolution of CO2 is largely excluded. As taught in US Pat. No. 1,918,133, the reaction is in equilibrium on the right, as C02 is a slightly stronger acid than H2S. As has been found, however, the equilibrium of this reaction can be shifted to the left if a high concentration of bicarbonate ions at atmospheric pressure is ensured in the aqueous solution. The shift in the reaction equilibrium to the left is increased if NaHS is removed from the equilibrium, for example by oxidation to elemental sulfur. The oxidation of the bound H2S to sulfur takes place very quickly, so that the absorption solution can separate and dissolve a further 1125 from the gas stream at the same time or immediately thereafter. A preferred embodiment of the invention provides to add an oxidizing agent, in particular oxygen, and a salt of a transition metal which catalyzes the oxidation to the bicarbonate-containing absorption solution and to carry out absorption and oxidation simultaneously and in a single container. However, it is also possible to transfer the absorption solution with the 1125 bound in it to another container and only carry out the oxidation there.

The absorption of the process according to the invention can be particularly Use advantageous where a gas or exhaust gas stream contains 1125 and C02 and you only must separate the H2S, but can leave the C02 in the gas stream.

The advantages of the method of the invention are particularly evident if the concentration of C02 in the gas stream to be cleaned is greater than that of 1125 is, as in the known processes, the alkaline aqueous absorption solutions use, which absorbs C02 depending on its concentration in the gas flow and the pH of the solution up to a value at which no more H2S is absorbed is reduced, which requires the addition of fresh base to the absorption solution. The method of the invention avoids major fluctuations in the pH of the absorption solution by the presence of hydrogen carbonate ions in the solution, as explained below will.

When C02 is dissolved in water, the following equilibrium is established: If the solution now contains an excess of bicarbonate ions, the equilibrium solubility of carbonic acid (H2CO3) is reduced, consequently the solubility of CO2 is also reduced and the pH of the solution is kept constant.

The solubility of 1125 in water obeys the following equilibrium: The equilibrium solubility of 1125 decreases as the pH of the solution decreases.

Because now the presence of bicarbonate ions keeps the pH high and prevents dissolution of CO 2, it is preferentially absorbed 1125 by the solution, i. In percentage terms, more 112S than C02 is dissolved.

In the absorption stage of the process according to the invention, a 1125 and C02 containing gas mixture with one rich in hydrogen or bicarbonate brought into contact with aqueous solution. This can be done in any conventional gas / liquid contacting device or washer. So the gas mixture can with the sprayed aqueous solution washed or treated in a packed or trickle column. One can the gas mixture also through a vessel containing the bicarbonate solution (bubble column) let pearls. However, any other known washing method can also be used will.

The necessary content of bicarbonate ions can be found in the aqueous absorption solution secure in the usual way. In the simplest case, this is done by adding water-soluble substances Bicarbonates, such as ammonium, sodium, potassium, magnesium or calcium bicarbonate or the bicarbonates of transition metals. Sodium and potassium bicarbonates are preferred because they are very easily soluble and extremely stable and because they do not form any mineral deposits on the walls of the washer.

When any of the above bicarbonate salts are dissolved in the washing solution the bicarbonate ions are available immediately afterwards, so that the solution from the beginning of the washing treatment on the described selectivity for the dissolution of 1125 has.

The method of the invention can, however, also be carried out in such a way that the bicarbonate ions are only generated in the absorption solution ("in situ"). For example, soluble carbonates can be added to the aqueous solution and these carbonates can be converted into bicarbonates with C02 according to the following equation: The resulting bicarbonate wash solution will then also selectively absorb 112S.

The conversion of the carbonates can be achieved by pretreating the solution made with pure C02. However, since the conversion to bicarbonate takes place very quickly, you can also use the gas mixture to be cleaned itself as a C02 source and the Save pretreatment with pure C02.

Another way to make the bicarbonate wash solution, consists in the fact that pure C02 or the gas stream containing C02 to be cleaned even to an aqueous solution of acidic phosphates, such as the water-soluble ammonium, Alkali or alkaline earth phosphates, can act.

For example, two- and three-base NH4-, Na-, K-, Ca-, Mg- and 3a-orthophosphate.

If such phosphates are added to the aqueous solution, C02 is first absorbed by the solution and converted into bicarbonate according to the following equations: The bicarbonates formed then prevent the further dissolution of C02.

The process of the invention can be carried out with aqueous washing or absorption solutions perform the except for bicarbonates in the concentration explained below contain other inert, i.e. neutrally reacting, salts. These additional Salts, however, must not change the pH value of the solution significantly; so are E.g. carbonates are only permitted in traces.

The concentration of bicarbonate ions must be in the absorption solutions supplying salts be so large that they shift the solution equilibrium and prevent significant amounts of C02 from dissolving. The higher the concentration of Bicarbonate ions are in the solution, the easier it 1125 takes up. The highest Concentration of bicarbonate ions in the solution is determined by practical considerations determined, approximately the desired concentration of bound 1125 in the absorption solution or the most appropriate rate of circulation of the solution through the scrubber. Absorption solutions, containing 0.01-0.25 mol / l bicarbonate salts are preferred, but can Solutions with a higher bicarbonate concentration can also be used.

The method of the invention can be at room temperature and perform satisfactorily at atmospheric pressure; tougher working conditions are generally not necessary.

The catalytic oxidation of bound H2S Once H2S has been removed the absorption solution is added, it can be in the preferred embodiment oxidize the invention with dissolved oxygen to elemental sulfur. As already mentioned, absorption and oxidation of H2S can be in one and the same, with the container filled with the aqueous bicarbonate solution take place at the same time.

It is, however, possible to separate absorption and oxidation of the 1125 in two Carry out containers. In any case, the oxidation of the bound HZS in an aqueous solution in which a catalytically active transition metal salt and oxygen is dissolved.

A soluble salt is used as a catalyst for this oxidation reaction a transition metal such as nickel, cobalt, manganese, copper or iron is preferred.

The concentration of this catalyst in the solution should be so great that that the oxidation proceeds sufficiently quickly.

A ratio of 1 part by weight of catalyst to 2000 parts by weight of the Bound hydrogen sulfide to be oxidized can already suffice. Up the catalyst concentration is limited only by its solubility. In practice, proportions of far more than 1 part by weight of catalyst per 20 wt. -Parts of bound H2S did not significantly improve the catalytic activity result. It is therefore preferred to use 1 part by weight of catalyst per 50-200 parts by weight bound 1125 to use.

The aqueous solution used in the oxidation stage must at least contain as much dissolved oxygen as required for complete conversion of the bound H2S in S is required stoichiometrically. An O2 excess can contribute to completeness oxidation may be necessary. The oxygen can be used in any convenient manner in the aqueous solution Ways to be dissolved, for example by blowing into the solution or by spraying the Dissolution in oxygen or air and similar measures. Also the oxidation in the preferred embodiment of the invention can be at room temperature and normal pressure be carried out satisfactorily, stricter conditions are possible but im generally not required.

The contact time between the gas stream to be cleaned and the absorption solution must be sufficient to adjust the solution equilibrium, so that a maximum of 1125 is absorbed.

If the mixture is well mixed, im to establish the equilibrium generally rarely more than 20 seconds, often only Is or less necessary. the required contact time mainly depends on the bubble size and the mixing effectiveness. The better the mixing, the shorter the contact time be.

The method of the invention is illustrated by the following examples further explained.

Example 1 This example illustrates the ability of a non-ventilated aqueous bicarbonate solution, 1125 to be selectively separated from a mixture of 1125 and C02.

An aqueous solution was passed through a contact device (bubble column) unpulept from top to bottom. In this device, a 96.33% C02 and 3.67% 1125 existing gas mixture is blown in countercurrent to the aqueous solution.

Two test runs were made. In the first (comparative) attempt the aqueous solution did not contain bicarbonate. In the 2nd experiment, the aqueous Solution a bicarbonate. In both experiments the contact time between gas was and Liquid about 3 s.

The following result was obtained: Experiment composition of the gas mixture No before treatment after treatment % H2S% CO2% H2S% CO2 1 3.67 96.33 1.8 98.2 2 3.67 96.33 0.76 99.24 As this comparison shows, an aqueous solution containing bicarbonate preferably takes up 1125.

Example 2 A contacting device that consists of a The vertically arranged glass tube was topped with an aqueous solution charged, which was withdrawn from the bottom of the device.

In countercurrent to this aqueous solution was in the device at the bottom a gas mixture consisting of 95.5% CO2 and 4.5% 1125 is introduced.

5 test runs were made. In the 1st experiment, the aqueous Solution aerated with oxygen only. In the 2nd and 3rd

The experiment contained the aqueous solution 02 and NaHCO3. In the 4th attempt The aqueous solution contained 02 and NiCl2 catalyst as well as Na11CO3. The contact time between gas and liquid was approx. 2 s in all experiments were obtained: Ver H2S content in the gas mixture,% washing solution such as before treatment after treatment contained: No.

1 4.5 2.92 O2 2 4.5 2.05 02 + NaHCO 3 4.5 2.02 o; + NaHCO 3 4 4.5 1.70 02 + NiCl2 5 4.5 0.27 02 + NiCl2 + NaHCO3 The ability of the scrubbing solution, the gas mixture To withdraw 1125, evidently increased steadily from experiment 1 to experiment 5.

Example 3 The preferred embodiment of the invention became longer lasting Tests checked in a pilot plant in natural gas field trials. In these field trials a bicarbonate was used to absorb 1125 from the acidic gas mixture containing CO2 containing aqueous solution used. This solution was made by dissolving soda in fresh water and blowing in C02 (which originated from the acidic gas mixture) in made the soda solution until all the soda was converted to NaHCO3. That in this Bicarbonate solution was absorbed by the addition of a nickel salt and aeration oxidized to sulfur.

The pilot plant used consisted of a converted tubular furnace (heater treater) that had the heating tube and manifold removed, and had one Diameter of 2.4 m and a height of 8.5 m. In this container, the one with the bicarbonate solution was charged, the acidic gas mixture was that from the regeneration of an amine plant originated, introduced through a pipe that was approximately 2.5 cm (1 inch) in diameter and was perforated with 8 holes of approx. 8 mm. Through another 1 "pipe, which was perforated with 13 holes of approx. 8 mm, was blown over a Aperture flow meter, air introduced into the absorption container. The discharge velocities of acidic gas mixture and air were adjusted by valves and pressure regulators.

From the absorption tank the solution flowed into a settling tank, which had a diameter of 3 m and a height of 4.6 m. From the sedimentation tank the clarified solution could be drawn off at the bottom and at different heights and in pumped back into the absorption canister. The settling mud was drained from time to time.

A catalyst solution consisting of nickel chloride became the feed pump for the absorption container added immediately.

The course of the experiment was as follows: About 40 m3 fresh water, 227 kg Soda and 0.45 kg NiCl2. 6 1120 were entered into the pilot plant. The catalyst solution for the metering or feed pump was made by dissolving 0.03 kg of nickel chloride hexahydrate produced per m3 of fresh water. The circulation pump was started and the Overflow valves set so that there is a level for the absorption solution of 5.6 m. Then acidic gas mixture, air and catalyst solution were in the Absorption container let in.

Laboratory tests showed that the sulfur produced and consumed The catalyst did not need to be removed from the solution more than once a day, therefore an attempt was made to adjust the circulation pump for the solution so that the daily circulation speed the volume of the absorption container (from 25.4 m3) at a stand height of 5.6 m. The circulation pump wanted to be so lower Circulation speed does not work. So totaled in all carried out before May 19th Try the circulation rate 2.0-2.6 mS / h; after May 19, the circulation pump operated for only 30 minutes per day and solution from the absorption container during the pumping time drained through a bottom valve.

The solution in the absorption vessel was sampled once or twice a day taken and their PH value as well as their content of free C02 and bicarbonate (according to "Analysis of Oil Field Water", API-RP 45, 2nd edition, methods 3.5 and 2.2). Furthermore, the H25 content in the acidic gas mixture used was determined (according to the von Tutweiler) and in the cleaned residual or exhaust gas (with a gas detector) or measured twice a day.

The acidic gas mixture was analyzed three times and contained 0.041 (4.1 Vol .-%), 0.046 (4.6 Vol.-5 ') and 0.042 (4.2 Vol. -5') m3 112S per m3 gas mixture. The pH of the absorption solution ranged between 6.4 and 7.7 and took with it increasing bicarbonate concentration. The concentration of free CO2 in the solution ranged between 0.156 and 0.360 kg / m3 or 156-360 mg / l. With regard to the For measured values in the tests, reference is made to Tables I and II.

The subsequent calculations and discussions of the test results is based on an H2S content of the acidic gas mixture used of 4.3 vol. -5 ', which results as the mean value from the 3 measurements mentioned.

The purified exhaust gas escaping from the absorption vessel was a mixture of desulphurized C02 and air. When calculating the percentage Separation of 112S from the acidic gas mixture used based on the H2S concentrations in the cleaned exhaust gas and in the gas mixture used, the dilution of the Exhaust gas with air taken into account.

The values given in Tables I and II were calculated using the following equation: % separated H2S = 100 - ppm H2S in the exhaust gas / 4.3 x 10-2 x x (feed mixture + air throughput) / feed mixture throughput As laboratory tests have shown, the primary product of the H25 oxidation is sulfur, but thiosulphate and H ions are formed in the following secondary reaction: The H ions neutralize bicarbonate ions according to: The concentration of bicarbonate ions in the solution was maintained by adding soda, which was quickly converted to bicarbonate.

Soda consumption fluctuated with the hourly tests between 0 and 0.072 kg / m3 solution. The latter value was only obtained in the 1st test preserved and probably explained by the hardness of the fresh water used, which may have led to the precipitation of magnesium and calcium carbonates.

Tests Nos. 1-13 (Table I), carried out from May 2-8, show that 96 - 98 f of the hydrogen sulfide contained in the feed gas mixture is separated were if (1) the throughput ratio of air to feed gas mixture was one, (2) the treatment speed of the feed gas mixture 76 m3 / h and (3) the standing height the solution was 5.6 m. A reduction in the air: feed gas mixture throughput ratio from 3 to 1 increased the percentage of 1125 separated.

Tests Nos. 13-18 show that at a throughput ratio of Air to feed gas of about 1 and a feed gas treatment rate from 70 - 75 m3 / h the percentage of the separated H2S with the level of the solution decreases. Tests conducted May 15-18 teach that the percentage of the separated 1125 decreases only slightly with the level of the solution, provided the air throughput per cross-sectional area of the solution with 12-14 m3 / h m2 and the throughput of feed gas per room part of the solution remained constant at 1.7 - 1.9 m3 / h.m3.

As Table II shows, there is air to feed gas at a throughput ratio of about 1 the percentage of 1125 cut back little when the throughputs can be increased (Table II gives averaged flow rates of air from several tests and feed gas mixture).

Table I Test results of the pilot plant test date clock air flow rate Kataly Stand Temp. H2S in Bicar- Abge-Nr. time through- operator- high solution Exhaust gas bonat separator gas supply d. Lo- ° C ppm concentrated m3 / h m3 / h kg / day solution tra- H2S m tion% mg / l 1 2.5. 22h00 130.8 45.9 0.454 5.64 26.7 400 4,050 96 2 3.5. 7h30 130.8 45.9 0.454 5.64 25.0 1,100 3,470 90 3 3.5. 20h00 126 67.8 0.454 5.64 28.9 800 4,310 95 4 4.5. 8h30 126 67.8 0.907 5.64 26.7 3,650 5 4.5. 7:30 p.m. 115.8 75 0.59 5.64 32.2 500 3,100 97 6 5.5. 8h30 91.8 76.2 0.68 5.64 31.1 2,700 2,220 86 7 5.5. 18h30 93.6 76.2 0.59 5.64 32.2 500 5,310 97 8 6.5. 8h30 93.6 75 0.59 5.64 28.9 1,100 4,050 94 9 6.5. 18h30 93.6 76.2 0.907 5.64 31.1 400 3,630 98 10 7.5. 7:30 am 88.2 76.2 0.907 5.64 28.3 900 3,260 96 11 7.5. 17h00 69.6 76.2 0.907 5.64 32.8 500 2,900 98 12 8.5. 8h30 71.4 75 0.68 5.64 32.2 400 2,410 98 13 8.5. 18h30 67.8 71.4 0.907 4.42 33.9 850 2,210 96 14 9.5. 9h30 67.8 71.4 0.907 4.42 32.8 7,000 2,930 68 15 9.5. 15h30 66 69.6 0.907 3.20 36.7 9,000 2,660 59 16 10.5. 9h00 66 69.6 0.907 3.20 32.8 14,000 2,340 37 17 10.5. 14h15 67.8 71.4 0.907 4.42 32.8 5,000 2,300 77 18 11.5. 5h15 67.8 71.4 0.907 4.42 33.9 7,500 1,870 66 19 15.5. 8h00 44.2 52.7 1.50 5.64 25.6 150 6,700 99.4 20 15.5. 7:30 pm 52.7 52.7 0.907 5.64 23.9 85 6,750 99.6 Tabel I test results of the pilot plant test date clock air throughput catalyzer stand Temp.d. H2S in Bicar- Abge-Nr. time through- use- height solution exhaust gas bonat separating set gas supply of solution ° C ppm concentration m³ / h m³ / h kg / day sung H2S m tion % mg / l 21 16.5. 7h30 54.4 44.2 1.59 5.64 22.8 45 6,690 99.8 22 17.5. 1.30 p.m. 51 40.8 0.23 4.42 27.8 250 6,420 98.7 23 17.5. 7pm 51 42.5 0.45 4.42 30.0 230 6,150 98.8 24 18.5. 8h00 61.2 28.8 0.45 3.20 27.8 500 5,860 96.5 25 18.5. 20h00 34 35.7 0.45 5.64 37.8 120 5,730 99.5 26 19.5. 8h00 30.6 30.6 0.45 5.64 32.2 100 5,920 99.5 27 19.5. 7:30 pm 52.7 52.7 0.45 5.64 37.8 100 5,310 98.8 28 20.5. 7h00 57.8 52.7 0.45 5.64 35.0 230 5,130 98.9 29 20.5. 18h45 54.4 52.7 0.18 5.64 38.9 260 4,830 98.8 30 21.5. 6h10 47.6 52.7 0.36 5.64 33.9 500 4,470 97.8 31 21.5. 18h30 69.6 63 0.36 4.72 40.6 300 4,030 98.5 32 22.5. 18h20 49.3 45.9 0.23 5.49 - 20 4,770 99.9 33 23.5. 18h10 51 51 0.32 5.49 - 160 7,120 99.3 34 24.5. 20h35 51 51 0.32 5.49 - 3 6,520 99.9 35 25.5. 19h35 51 51 0.36 5.49 - 14 5,880 99.9 36 26.5. 17h30 51 51 0.36 5.49 - 68 5,520 99.8 37 27.5. 17h15 51 51 0.36 5.49 - 120 4,790 99.4 38 28.5. 17h15 51 51 0.36 5.49 - 110 3,970 99.5 Table II Separation of 112S as Function of the feed gas throughput Number Avg. Mean through- cut the throughput rate of use H2S,% tests air, gas, m3 / h m3 / h 2 71 76 98 14 51 51 99.4 2 32 34 99.5

Claims (5)

P a t e n t a n 5 p r i c h e 1) Process for the separation of hydrogen sulfide from a gas stream, the network hydrogen sulfide carbon dioxide and possibly others Contains gases, by absorption in an alkaline aqueous salt solution, d a d u r c h e k e n n n n e t that the gas flow with a solution containing hydrogen carbonate -Ions in a concentration at which almost exclusively hydrogen sulfide is absorbed, contains, is treated. 2) Method according to claim 1 d a d u r c h g e k e n n z e i c h n e t that the solution is alkali hydrogen carbonate in a concentration of v, C11 - 0.25 Contains moles / liter. 3) Method according to claim 1 or 2, characterized in that the Gas stream is treated with a solution that can be obtained by dissolving alkali hydrogen carbonate or by reacting carbon dioxide with aqueous solutions of an alkali carbonate or acidic alkali metal phosphate. 4) Method according to one of claims 1 - 3, characterized in that that the aqueous absorption solution contains a salt of a catalytically active transition metal and one for essentially full oxidation of the absorbed hydrogen sulfide A sufficient amount of oxygen is added to the sulfur. 5) Method according to claim 4 d a d u r c h g e k e n n z e i c h n e t that the aqueous absorption solution 1 part by weight of transition metal salt, in particular Nickel chloride, each containing 50-200 parts by weight of absorbed hydrogen sulfide.