RU2110472C1 - Method and installation for scrubbing gases to remove hydrogen sulfide - Google Patents

Abstract

FIELD: gas treatment. SUBSTANCE: method includes absorption of hydrogen sulfide, oxidation of the latter into elementary sulfur using liquid-phase redox system, electrochemical regeneration of the system in electrolyzer to form catholyte and anolyte, and separation of elementary sulfur. Absorption is carried out with catholyte, pH 10-12, as solvent-absorbent, hydrogen sulfide oxidation is effected by introducing anolyte into solution obtained, and electrochemically regenerated is anolyte-catholyte mixture after separation of sulfur. Installation contains: scrubber with its inlets connected to crude gas line and solvent-absorbent source; sulfur separator constructed in the form of filter press; filtrate collector; electrolyzer with cell set including two electrodes and diaphragm separating cells into cathode and anode chambers; and mixer disposed between scrubber and filter press. Cathode chamber is connected with scrubber, anode chamber with mixer, filtrate collector with the two cell chambers, and cathode chamber with crude gas line to release hydrogen gas. Installation is designed for application in chemical-recovery, oil and gas production, and processing industries. EFFECT: enhanced gas scrubbing efficiency. 3 cl, 2 dwg

Description

 The invention relates to the field of purification of sulfur-containing gases from hydrogen sulfide and can be used to increase the efficiency of capture of hydrogen sulfide, sulfur utilization in the coke, oil and processing industries.

Образовавшаяся суспензия направляется в отстойник, где происходит отделение твердой фазы от маточного раствора. Поглотительный раствор поступает на регенерацию и электролизер, где происходит суммарная реакция:

Регенерированный раствор поступает обратно в скруббер, а газообразный водород подается в газовую магистраль.There is a method of electrolytic cleaning of gases from hydrogen sulfide [1], according to which a gas containing hydrogen sulfide enters the scrubber, interacts with the absorption solution in it, which is a product of the anode process of regeneration of the absorption solution in the electrolyzer, with the following reaction:

The resulting suspension is sent to the sump, where there is a separation of the solid phase from the mother liquor. The absorption solution enters the regeneration and electrolyzer, where the total reaction occurs:

The regenerated solution is fed back to the scrubber, and gaseous hydrogen is fed into the gas line.

 Although this method allows you to extract up to 80% sulfur, it is quite energy intensive. In addition, the absorption solution must often be changed.

 A device for implementing this method comprises a scrubber for absorbing hydrogen sulfide, connected to a sump, the outlet of which is connected to a filter press. The outlet of the filter press is connected to the scrubber, and the outlet (gas) is connected to the purified gas line.

 The disadvantage of this device is the lack in the cell separating the anode and cathode space of the partition, which leads to increased energy intensity of the method, because due to convective and diffusion transport, the products of anodic oxidation and cathodic reduction can react on the opposite electrode.

Closest to the invention is a method for the separation of hydrogen sulfide from gases and non-aqueous liquids [2], according to which a gas containing hydrogen enters the scrubber (Fig. 1), which is also fed from the anolyte collector an oxidizer-rich solution in a scrubber at pH 0- 1 the absorption of hydrogen sulfide by anolyte
H ₂ S + J ₂ _ → S + 2H ⁺ + 2J ^-
The scavenger solution from the scrubber enters the sulfur separator (the structure is not disclosed), from which the liquid phase is returned to the anolyte collector, and the solid phase in the form of sulfur (the so-called “acid”, which differs from elemental sulfur in physical and chemical properties) is sent for further processing in order to separate from the residues of the anolyte by interaction with organic solvents (xylene or toluene) at T = 95 - 105 ^o C followed by cooling and the allocation of elemental sulfur.

 The second output of the anolyte collector is connected to the input of the anode chamber of the electrolyzer, the output of which is connected to the second input of the anolyte collector. The cathode chamber of the electrolyzer is closed to a catholyte collector. Hydrogen gas released in the catholyte is removed from the cathode chamber. The cell contains a cation exchange membrane that separates the inner cavity of the cell into a cathode and anode chamber. The composition of the membrane is not known, the anode is made of graphite, and the cathode is made of platinum titanium.

 The degree of sulfur recovery by the prototype method depends on the concentration of the oxidizing agent in the anolyte, as a result of which strict coordination of the anolyte and gas flows is necessary.

 The disadvantage of the prototype solution should be recognized in the field of the method is insufficient completeness of removal of hydrogen sulfide (85% according to the experimental verification of the authors), and in the field of the device is the excessive complexity of the design.

 The authors have developed the following method of purification of gases from hydrogen sulfide.

 A gas containing hydrogen sulfide is treated with catholyte at a pH of 10-12, then the catholyte with absorbed hydrogen sulfide enters the mixer unit, in which the anolyte absorbed hydrogen sulfide is oxidized to elemental sulfur. A suspension of elemental sulfur in a mixture of catholyte and anolyte enters the filter press. The sulfur precipitate is washed with warm water and sent to the apparatus for melting sulfur, and the filtrate and wash water through the collector are sent back to the process to recharge the cell. After regeneration in the electrolyzer, a solution of catholyte and anolyte is used in the process, and the released hydrogen gas is sent to the purified gas line.

 To implement the above method, the authors developed the device shown in FIG. 2.

 The device contains a scrubber, the output of which is connected to the mixer. Anolyte is fed into the mixer. The output of the mixer is connected to the filter press, from where the filtrate through the intermediate tank enters the regeneration in the cell. Sulfur sediment is supplied for further processing. The catholyte from the cathode chamber of the electrolyzer enters the scrubber. The cell contains an anode, a cathode, and a diaphragm separating the anode and cathode spaces.

 The authors experimentally selected materials: for the cathode - steel, for the anode - graphite, while other materials can be used, but with slightly worse results.

 The authors do not know methods and devices for wet purification of gases from hydrogen sulfide, characterized by the same set of essential features as the present invention. Therefore, the authors believe that the present invention meets the criteria of the invention of "novelty."

 The authors are also not aware of methods and devices for the wet purification of gases from hydrogen sulfide, in which the authors introduced the features in the characterizing part of the claims, would be used for the same purpose as in the present invention. Therefore, the authors believe that the present invention meets the eligibility criterion of "technical level". Since the proposed invention is disclosed in the application materials with sufficiency for reproduction by a potential user, all the operations of the method and the device units are individually known and collectively provide the desired effect and can be implemented without additional invention by the potential user, the claimed invention meets the eligibility criteria "industrial applicability" .

 Now it is necessary to prove the materiality of the features introduced by the authors in the distinctive part of the claims.

 The absorption of hydrogen sulfide by catholyte leads to the almost complete (99%) recovery of hydrogen sulfide, provided that the pH at the inlet to the scrubber is 10 - 12, and at the outlet from the scrubber no lower than 9, which allows the use of catholyte as an absorber according to the experimental data of the authors. The deposition of hydrogen sulfide in the mixer allows you to select almost completely (99%) elemental sulfur.

 Connections of nodes introduced by the authors in the distinctive part of the second paragraph of the claims, allows to increase the service life of absorbing and oxidizing solutions and thereby increase the degree of purification.

 The authors note that the anode and cathode in the electrolyzer can be made of various materials, like the membrane, however, according to the experimental data of the authors, the graphite anode and steel cathode lead to some improvement in the results.

 The method is implemented as follows.

 Hydrogen sulfide-containing gas is fed into a scrubber irrigated with an absorption solution with a pH of 10 - 12. Absorption of hydrogen sulfide occurs in accordance with the reactions.

NH ₄ OH + H ₂ - NH ₄ HS + H ₂ O
KOH + H ₂ S = KHS + H ₂ O
The purified gas is removed from the upper part of the scrubber, and the spent absorption solution at pH ≥ 9 enters the mixer, where an anolyte oxidizer is also fed. The oxidation process in the mixer occurs according to the reactions:
KHS + 2K ₃ [Fe (CN) ₆ ] = K ₄ [Fe (CN) ₆ ] + K ₃ H [Fe (CN) ₆ ] + S ⁰
NH ₄ HS + 2K ₃ [Fe (CN) ₆ ] = K ₃ NH ₄ [Fe (CN) ₆ ] + K ₃ H [Fe (CN) ₆ ] + S ⁰
In an alkaline environment, acid salts turn into medium:
K ₃ H [Fe (CN) ₆ ] + KOH = K ₄ [Fe (CN) ₆ ] + H ₂ O
K ₃ H [Fe (CN) ₆ ] + NH ₄ OH = K ₃ NH ₄ [Fe (CN) ₆ ] + H ₂ O
The resulting solution with a suspension of elemental sulfur is fed to the filter press. Sulfur is filtered off, washed and fed for further processing. The filtrate through the filtrate collector is fed into the electrolyzer for regeneration. In the anolyte, hexacyanoferrate (II) - the ion is oxidized to the hexacyanoferrate (III) ion with the formation of a red blood salt, which is fed to the mixer. Hydrogen gas is released at the cathode. The proceeding reactions are described by the following summary equations:
2K ₄ [Fe (CN) ₆ ] + 2H ₂ O = 2K ₃ [Fe (CN) ₆ ] + 2KOH + H ₂
2K ₃ NH ₄ [Fe (CN) ₆ ] + 2H ₂ O = 2K ₃ [Fe (CN) ₆ ] + 2NH ₄ OH + H ₂
When hydrogen is released in catholyte, an alkaline absorption solution is formed, which is fed into the scrubber, and hydrogen gas is sent to the purified gas line.

The current efficiency of electrolysis products is close to 100%. The types of diaphragms are not specified in the application materials, they are selected from the position of ensuring the lowest voltage drop on the cell with satisfactory braking, undesirable transfer processes between the catholyte and anolyte. The anode current density is 1 A / dm ² , while the anode potential is 0.75 V, the cathode potential is 0.32 V, and the total cell voltage is not higher than 2.5 V.

The sulfur recovery rate is 99%, the working solution resource is not less than 100,000 m ^{3 of} gas per 1 m ^{3 of} working solution, at an energy cost of not more than 4 kW • h / kg. The device consists of a scrubber, to the first input of which the line of the gas to be cleaned is connected, to the second entrance - the line of catholyte. The scrubber is a hollow steel apparatus of cylindrical sectional plate type, equipped with nozzles for supplying the solution and the gas to be cleaned. The first output of the scrubber is connected to the purified gas line, the second output is designed to output catholyte with absorbed hydrogen sulfide and is connected to the first input of the mixer. The mixer is a continuous reactor equipped with nozzles for supplying reagents and a stirrer. Anolyte trunk is connected to the second input of the carrier. From the mixer, the suspension is fed to a filter press, from where sulfur is used for further processing, to the filtrate - to the electrolyzer for registration. The cell contains a set of cells consisting of an anode chamber with an anode, a cathode chamber and a separating diaphragm. The cathode chamber is connected to the scrubber by a catholyte line, and a hydrogen gas line to the gas line to be purified. The anode chamber is connected to the mixer by the anolyte line.

Bibliography
1. Aronov S.G. Sulfur. Extraction from industrial and waste gases. Kharkov - Moscow: Metallurgizdat, 1940.

 2. US patent N 4526774, CL. C 01 B 17/05, 1985.

Claims (3)

 1. The method of wet cleaning of gases from hydrogen sulfide, including the absorption of hydrogen sulfide by a scavenger, the oxidation of hydrogen sulfide to elemental sulfur using a liquid phase redox system, electrochemical regeneration of the system in an electrolytic cell to produce catholyte and anolyte, separating elemental sulfur, characterized in that the absorption is carried out using catholyte as a solution-absorber at pH 10 - 12, the oxidation of hydrogen sulfide to elemental sulfur is carried out with the introduction of ano lithium, and a mixture of anolyte and catholyte is subjected to electrochemical regeneration after separation of sulfur.  2. Installation for wet cleaning of gases from hydrogen sulfide, containing a scrubber, the inlets of which are connected to the line of the gas to be cleaned and the source of the absorbing solution, a sulfur separator, a filtrate collector and an electrolyzer with a set of cells including two electrodes and a diaphragm that separates the cells into the cathode and anode chamber, characterized in that it further comprises a mixer, the sulfur separator is made in the form of a filter press, the mixer being located between the scrubber and the filter press, the cathode chamber is connected to the scrubber, the anode the second chamber is with a mixer, the filtrate collector is connected to both chambers of the cells of the electrolyzer, and the cathode chamber is connected to the line of the gas to be purified for the release of gaseous hydrogen.  3. Installation according to claim 2, characterized in that the cathode is made of steel.

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