MXPA99002063A - Selective removal and recovery of sulfur dioxide from effluent gases using organic phosphorous solvents - Google Patents

Abstract

A process for the selective removal and recovery of sulfur dioxide from effluent gases is disclosed. The sulfur dioxide is recovered in a sulfur dioxide absorption/desorption cycle which utilizes a liquid solvent to selectively absorb sulfur dioxide from the effluent gas. The liquid solvent comprises an organic phosphorous compound selected from phosphate triesters, phosphonate diesters, phosphinate monoesters and mixtures thereof. Preferably, the liquid solvent comprises phosphonate diesters of formula (I) wherein R1, R2 and R3 are independently aryl or C1 to C8 alkyl. The organic phosphonate diesters are substantially water immiscible, the solubility of water in the organic phosphonate diester being less than about 10 weight percent at 25°C, and have a vapor pressure less than about 1 Pa at 50°C. In accordance with a preferred embodiment, the liquid solvent comprises dibutyl butyl phosphonate. The absorbed sulfur dioxide is subsequently stripped to regenerate the organic phosphorous solvent and produce a gas enriched in sulfur dioxide content. The sulfur dioxide-enriched gas may be used as part of the feed gas to a contact sulfuric acid plant or a Claus plant for the preparation of elemental sulfur or be cooled to condense sulfur dioxide in the form of a liquid product. The present invention is particularly useful in producing a sulfur dioxide-enriched gas from gases relatively weak in sulfur dioxide content.

Description

REMOVAL AND SELECTIVE RECOVERY OF SULFUR DIOXIDE FROM EFFLUENT GASES USING ORGANIC PHOSPHORO SOLVENTS BACKGROUND OF THE INVENTION This invention relates to the selective removal and recovery of sulfur dioxide from effluent gases. More particularly, the present invention relates to the recovery of sulfur dioxide from effluent gases in a sulfur dioxide absorption / desorption process using a liquid solvent that includes certain organic phosphorus compounds to selectively absorb sulfur dioxide from the sulfur dioxide. effluent gas. The absorbed sulfur dioxide is subsequently removed to regenerate the solvent and produce a gas enriched in sulfur dioxide content. The gas enriched with sulfur dioxide can be used as part of the feed gas for a contact sulfuric acid plant or a Claus plant for the preparation of elemental sulfur or be cooled to condense the sulfur dioxide in the form of a liquid product. The present invention is particularly useful in producing a gas enriched with sulfur dioxide from relatively weak effluent gases in sulfur dioxide content. Gaseous effluents containing sulfur dioxide are produced by a variety of operations, including calcination or smelting of sulphide metal ores and concentrates and combustion of sulfur-containing fuels (e.g., combustion gases). Sulfur dioxide in these effluent gases can be combined with oxygen and fed to a contact sulfuric acid plant and recovered as sulfuric acid and / or oil. However, these gas streams often have a relatively low concentration of sulfur dioxide and a high concentration of water vapor. When the concentration of the sulfur dioxide in the gas fed to a sulfuric acid plant is less than about 4 to 5% by volume, the problems may increase with respect to the water balance and the energy balance in the acid plant. More particularly, the material balance of a conventional sulfuric acid plant requires that the molar ratio of H 2 O / SO 2 in the sulfur dioxide-containing gas stream fed to the plant is not higher than the molar ratio of H 2 O / SO 3 in the acid of the product. If the acid concentration of the desired product is 98.5% or higher, this ratio can not be more than about 1.08 in the gas stream containing sulfur dioxide fed to the plant. As it is generated, effluent gases from metallurgical processes and combustible gases from the combustion of sulfur fuels often have a water vapor content much higher than 1.1 which can not be sufficiently reduced by cooling the gas without significant costs of capital and energy. In addition, if the gas strength of the sulfur dioxide of the source gas is less than about 4 to 5% by volume, it can not be sufficient for the autothermal operation of the catalytic converter. That is, the heat of the conversion of the sulfur dioxide to sulfur trioxide can not be large enough to heat the incoming gases to the operating temperature of the catalyst and, as a consequence, the heat must be supplied from some external source. This in turn increases both operating costs and capital requirements for the installation of sulfuric acid. One way to increase the strength of sulfur dioxide from gaseous effluents is by selectively absorbing the sulfur dioxide in a suitable solvent and subsequently removing the absorbed sulfur dioxide to produce regenerated solvent and a gas enriched in sulfur dioxide content. A variety of aqueous and organic solvents have been used in the sulfur dioxide absorption / desorption processes. For example, aqueous solutions of alkali metals (for example, sulfite / sodium bisulfite solution), amines, (eg, alkanolamines, tetrahydroxyethylalkylenediamines, etc.) and amine salts have been used as regenerable sorbent absorbers of sulfur dioxide. The organic solvents used in the sulfur dioxide absorption / desorption processes include dimethylaniline and tetraethylene glycol dimethyl ether. However, conventional solvents are impeded by one or more defects with respect to the desirable characteristics in an absorbent used in a sulfur dioxide absorption / desorption cycle. Many of the solvents currently employed have a relatively low sulfur dioxide absorption capacity, especially at the partial sulfur dioxide pressures typically found in weak sulfur dioxide-containing effluents (eg, from about 0.1 to about 100% sulfur dioxide). 5 kPa). Often, conventional solvents absorb substantial amounts of water vapor from the effluent containing sulfur dioxide which results in a significant reduction in the absorption capacity of the sulfur dioxide of the solvent. As a result, the molar flow rates of conventional solvents necessary to satisfy the desired sulfur dioxide absorption efficiency are increased. In addition, the absorption of large amounts of water vapor in the solvent can lead to excessive corrosion of the process equipment used in the sulfur dioxide absorption / desorption process. In addition, some conventional solvents are susceptible to excessive degradation, such as hydrolysis, when the solvent is exposed to high temperatures in acidic environments and / or suffer from high volatility, leading to large solvent losses. In this way, there continues to be a need for effective sulfur dioxide absorption procedures and solvents for selective removal and recovery of sulfur dioxide from effluent gases.

BRIEF DESCRIPTION OF THE INVENTION Among the various objects of the present invention, therefore, may be noted the provision of an improved process for selectively removing and recovering sulfur dioxide from a gas source containing sulfur dioxide; the disposition of said procedure can be implemented with capital and relatively low operating costs; the arrangement of said process using the sulfur dioxide absorption solvent has a relatively low vapor pressure and an improved sulfur dioxide absorption capacity, especially at relatively low sulfur dioxide partial pressures; the arrangement of said process using a sulfur dioxide absorbing solvent that can substantially be submerged with water and have a reduced tendency to corrode the process equipment and the arrangement of a process that can be used in conjunction with a contact sulfuric acid plant to produce concentrated sulfuric acid from sulfur dioxide source streams having a relatively low sulfur dioxide gas force and a molar ratio of H2O / SO2 greater than the molar ratio of H2O / SO3 in the acid stream of the product. Therefore, briefly, the present invention is directed to a process for selectively moving and recovering sulfur dioxide from a gas source containing sulfur dioxide. The method includes having contact with a feed gas stream to process that includes the gas source with a liquid solvent for selective absorption of sulfur dioxide in a sulfur dioxide absorber. Sulfur dioxide is hereby transferred from the feed gas stream of the process to the solvent to produce an exhaust gas, from which the sulfur dioxide has been substantially removed and a solvent rich in sulfur dioxide. According to one embodiment of the present invention, the liquid solvent includes at least one organic phosphonate diester immiscible with water of formula R30-P-R; L 0R2 where R, R2 and R3 are independently aryl or C] _ to C3 alkyl. The organic phosphonate diester has a vapor pressure of less than about 1 Pa at 25 ° C and the solubility of the water in the organic phosphonate diester is less than about 10 weight percent at 25 ° C. The absorbed sulfur dioxide is subsequently removed from the solvent rich in a sulfur dioxide separator to produce a lean solvent and a stripping gas enriched with sulfur dioxide, so that the ratio of the concentration of sulfur dioxide in the sulfur dioxide gas drag to the concentration of sulfur dioxide in the gas source is greater than about 1.1. The lean solvent is subsequently recycled to the sulfur dioxide absorber for further selective absorption of sulfur dioxide from the gas source. According to another embodiment of the present invention, the liquid solvent includes an organic phosphorous compound selected from phosphate triesters, phosphonate diesters, phosphinate monoesters and mixtures thereof, substituents attached to the phosphorous atom and the organic radicals of the functionality of the ester are independently aryl or C 1 to Cg alkyl • Absorbed sulfur dioxide is subsequently removed from the solvent rich in a sulfur dioxide separator by contacting the rich solvent with a non-condensable gas and oxygen-containing entrainer in the sulfur dioxide separator to produce the entrained gas enriched with sulfur dioxide and in lean solvent which is recycled to the sulfur dioxide absorber. The present invention is further directed to a process for producing sulfuric acid from a gas source containing sulfur dioxide. The method includes having contact with a process feed gas stream that includes the gas source with a liquid solvent including dibutyl butyl phosphonate for selective absorption of sulfur dioxide in a sulfur dioxide absorber. Sulfur dioxide is hereby transferred to the feed gas stream of the process to the phosphonate solvent to produce an exhaust gas, from which the sulfur dioxide has been substantially removed, and a solvent rich in sulfur dioxide. Subsequently, the sulfur dioxide is removed from the solvent rich in a sulfur dioxide separator to produce a stripping gas enriched with sulfur dioxide and a lean solvent to recycle the sulfur dioxide absorber for greater selective absorption of sulfur dioxide. of the process feed gas. A feed gas stream of the oxygen-containing converter, which includes the stripping gas, is introduced into a catalytic converter for oxidation of the sulfur dioxide to sulfur trioxide to produce a conversion gas including sulfur trioxide. Subsequently, the conversion gas comes into contact with sulfuric acid for the absorption of sulfur trioxide thereof in a sulfur trioxide absorber to produce sulfuric acid and / or oil and a decreased gas stream of the sulfur trioxide absorber, which leaves the trioxide absorber of sulfur trioxide. The source of gas containing sulfur dioxide fed to the sulfur dioxide absorber includes the gas stream diminished from the sulfur trioxide absorber, whereby the sulfur dioxide is recovered from the gas decreased for a final conversion to sulfuric acid and / or oil. Other objects and characteristics will be evident in part and the rest will be described later.

BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 and 2 are graphical representations of the absorption of sulfur dioxide by dibutyl butyl phosphonate at 25 ° C and 100 ° C, respectively, showing the grams of sulfur dioxide absorbed per liter of dibutyl butyl phosphonate at partial pressures variants of sulfur dioxide. Figure 3 is a schematic flow diagram illustrating one embodiment of the method of the invention.

DESCRIPTION OF THE PREFERRED MODALITIES In the process of the present invention, a gas source containing sulfur dioxide is subjected to an absorption / desorption cycle of sulfur dioxide to remove and recover sulfur dioxide in the form of gas enriched with sulfur dioxide (e.g. , a gas that has an increase in the content of sulfur dioxide with respect to the gas source). The absorption / desorption process of the sulfur dioxide of the present invention is characterized by contacting the gas source containing sulfur dioxide with a liquid solvent, which includes certain organic phosphorus compounds in a sulfur dioxide absorber. The organic phosphorous solvent selectively absorbs sulfur dioxide from the gas source, by which means the sulfur dioxide is transferred from the gas source to the solvent and produces an exhaust gas, from which the sulfur dioxide has been substantially removed, and a solvent rich in sulfur dioxide. The enriched solvent leaving the absorber is removed from the sulfur dioxide in a sulfur dioxide separator to produce a stripping gas enriched with sulfur dioxide and a lean solvent. Preferably, the enriched solvent leaving the absorber is removed from the sulfur dioxide by contacting the rich solvent with a non-condensable entraining gas containing oxygen (eg, air) in the sulfur dioxide separator. The lean solvent is subsequently recycled to the sulfur dioxide absorber for further selective absorption of the sulfur dioxide from the gas source. In general, the liquid solvent used in the practice of the present invention includes certain organic phosphorus compounds, more specifically, phosphate triesters, phosphonate diesters, phosphinate monoesters, and mixtures thereof. Preferably, the substituents attached to the phosphorous atom, as well as the organic radicals of the ester functionality, are independently aryl or C 1 to Cg alkyl. Examples of phosphate triesters include: tributyl phosphate, tripentyl phosphate, trihexyl phosphate, and triphenyl phosphate. Examples of phosphinate monoesters include: d-4-butyl butyl phosphinate, pentylpentyl phosphinate, dihexyl hexyl phosphinate and diphenyl phenyl phosphinate. According to a preferred embodiment of the present invention, the liquid solvent includes at least one organic phosphonate diester immiscible with water of formula O II R O-P-R-, I 0R2 where R, R, and R3 are independently aryl or alkyl of C] _ a Cg, R, R, and R are selected so that the organic phosphonate diester has a vapor pressure less than about 1 Pa at 25 ° C and The solubility of the water in the organic phosphonate diester is less than about 10% by weight at 25 ° C. A solvent that includes at least one organic phosphonate diester as defined above is more preferred in the practice of the present invention, since said solvent possesses a combination of characteristics that is particularly useful in a sulfur dioxide absorption / desorption process. , including: increased solubility of sulfur dioxide, especially at low partial pressures of sulfur dioxide in the gas source; high heating of solution that reduces the amount of energy required to remove the sulfur dioxide from the enriched solvent; low melting points so the solvent will remain as a liquid during a large scale of the temperature of the procedure; low viscosity that allows the size of both thermal and absorption / removal equipment to be reduced; low vapor pressure that reduces solvent losses; decrease in the tendency to react with water and undergo hydrolysis; and being substantially immiscible with water (eg, non-hydroscopic), whereby the solubility of water in the solvent decreases. The fact that organic phosphonate diesters are substantially immiscible with water is particularly advantageous in the practice of the present invention. This feature provides a solvent that does not absorb excessive amounts of water from the gas source that contains sulfur dioxide. The absorption of large amounts of water in the solvent is detrimental, since a higher water content in the solvent tends to decrease the solubility of sulfur dioxide, requires more energy and a main outlet to evaporate and condense the water absorbed to separate it of lean solvent and can lead to excessive corrosion of the process equipment. Examples of organic phosphonate diesters suitable for use in the practice of the present invention include dibutyl butyl phosphonate, dipentylpentyl phosphonate, dihexylhexyl phosphonate and phenyl diphenyl phosphonate. Preferably, the organic phosphonate is a dialkylalkyl phosphonate and R1, R2, and R3 are independently Ci to Cg alkyl. More preferably, to simplify the preparation and reduce the manufacturing costs of the phosphonate solvent, R, R, and RJ are identical and each contains more than three carbon atoms. In accordance with an especially preferred embodiment of the present invention, the liquid solvent includes dibutylbutyl phosphonate. Dibutylbutyl phosphonate is a neutral diester of phosphonic acid and is a clear, colorless liquid with a relatively low viscosity and a mild odor. Dibutyl butyl phosphonate has a molecular weight of 250.3 and a vapor pressure of about 0.1 Pa at 25 ° C. The solubility of water in dibutylbutyl phosphonate is about 5.5% by weight at 25 ° C. Figures 1 and 2 are graphical representations of the absorption of sulfur dioxide by dibutylbutyl phosphonate at 25 ° C and at 100 ° C, respectively, grams of sulfur dioxide absorbed per liter of dibutylbutyl phosphonate are shown at varying partial pressures of sulfur dioxide. Figure 3 is a schematic flow chart illustrating one embodiment of the process of the present invention for selectively removing and recovering sulfur dioxide from a gas source containing sulfur dioxide. A stream of process feed gas 10 includes the gas source containing sulfur dioxide, which is introduced into a sulfur dioxide absorber 11, where it comes in contact with an organic phosphorous solvent as described above. The source of gas containing sulfur dioxide can be derived from a variety of sources including combustible gas, generated in the combustion of sulphurous fuels, gaseous effluents from metal calcination operations, the incinerator of a Claus plant or the trioxide absorber. of sulfur or a contact sulfuric acid plant. In addition to sulfur dioxide, the gas source typically contains carbon dioxide, water vapor, oxygen, nitrogen and other inert components. As described above, the present invention is particularly suitable for the recovery of sulfur dioxide from relatively weak effluents in sulfur dioxide content. Thus, in accordance with a preferred embodiment of the present invention, the gas source contains from about 0.1 to about 5 volume% of sulfur dioxide. Typically, the gas source is at an elevated temperature and may contain impurities of entrainment particles. In said examples, as shown in Figure 3, the process feed gas stream may be conditioned prior to entering the absorber 11 by cleaning the gas to remove the particles and cooling the gas to maintain the desired temperature in the absorber . By depending on the composition temperature of the gas source containing sulfur dioxide, the feed gas stream of process 10 can be suitably conditioned by a variety of conventional practices well known to those skilled in the art. For example, the feed gas stream from the process can first pass through a thermal waste boiler, where the gas is cooled by generating high pressure current before sequentially passing through a humidification tower and one or more indirect heat exchangers, where the gas is cooled more, for example, with the water of the cooling tower and an electrostatic precipitator, where residual particles are removed from the cooled gas. Alternatively, the feed gas stream of the process can be conditioned by passing the gas through one or more inverted jet gas scrubbers of the type sold by Monsanto Enviro-Chem Systems, Inc., Saint Louis, Missouri 63178-4547 under the trade name "DYNAAVE". After conditioning, the feed gas stream of process 10 is introduced into the absorber 11, which is typically saturated with steam water at a temperature of about 10 ° C to about 50 ° C. However, it should be understood that in the practice of the present invention, the stream of process feed gas 10 introduced into the absorber 11 can be substantially anhydrous, for example, when the gas source is the effluent of the sulfur trioxide absorber of a contact sulfuric acid plant. The sulfur dioxide absorber 11 includes a vertical tower 12 containing means for promoting mass transfer between the gas and liquid phases which can include a bed of random packings 13 as supports or rings. Preferably, in order to maximize the sulfur dioxide transfer, the feed gas stream of process 10 comes into countercurrent contact with the lean solvent in the absorber 11. As shown in FIG. 3, the gas stream Process feed 10 is introduced through an inlet near the bottom of the tower 12 and a stream of lean liquid solvent 14 is introduced through a liquid inlet near the top of the tower and distributed over the 13. A solvent stream rich in sulfur dioxide 16 is ejected from a liquid outlet near the bottom of the tower 12 and an exhaust gas stream 18 substantially free of sulfur dioxide is removed from an outlet close to the outlet. the top of the tower. Although a conventional randomly packed tower can be used as an absorber 11, those skilled in the art will appreciate that other configurations can be used properly. For example, the tower 12 may contain a structured package or include a platform tower, in any of which the process streams will preferably flow countercurrently. The condensation of water vapor from the gas source containing sulfur dioxide in the absorber 11 can lead to the formation of a separate water phase, which can increase the corrosion rate of the metal process equipment and complicate the subsequent removal of the Sulfur dioxide absorbed in the subsecond 4th step of solvent regeneration. In this way, to avoid the condensation of. water vapor, the temperature of organic phosphorous solvent introduced into the absorber is preferably higher than the dew point temperature of the feed gas stream of procedure 10. The ratio of the mass flow rate (L / G) of the stream of the lean solvent 14 and the feed gas stream of process 10 necessary to achieve substantial transfer of sulfur dioxide from the gas source to the organic phosphorous solvent in the absorber 12 can be determined by conventional design practice. Preferably, the sulfur dioxide absorber is designed and operated, whereby the content of the sulfur dioxide in the exhaust gas stream 18 leaving the absorber is less than about 500 ppmv, more preferably less than 200 ppmv. This amount of sulfur dioxide indicator together with carbon dioxide, oxygen, nitrogen and other inert components and most of the water vapor contained in the process gas feed stream are removed from the system as part of the gas stream of exhaust discharged from the upper part of the absorber. If it is necessary to achieve satisfactory emission standards, the exhaust gas stream 18 can pass through a mist eliminator 19 for the recovery of the entrainment liquid before it is discharged through a chimney. The solvent rich in sulfur dioxide is transferred to a sulfur dioxide separator where, the sulfur dioxide is removed from the rich solvent, producing a lean solvent and a stripping gas enriched with sulfur dioxide having an increase in the concentration of sulfur dioxide in relation to the gas source fed to the absorber. The use of the highly effective organic phosphorous solvents described here allows the concentration of sulfur dioxide in the gas enriched with sulfur dioxide leaving the separator to be significantly higher than the concentration of sulfur dioxide in the gas source fed into the system . For example, for gas sources containing from about 0.1 to about 5 volume% sulfur dioxide, the process of the present invention can be operated, so that the ratio of the concentration of sulfur dioxide in the gas that it leaves the separator at the concentration of the sulfur dioxide in the gas source is greater than about 1.1, at least about 2, at least about 5, at least about 10 or even higher, depending on the concentration of the sulfur dioxide of the gas source and the concentration of the desired sulfur dioxide in the enriched gas. When the enriched stripping gas is fed to a contact sulfuric acid plant, the ratio of the concentration of the sulfur dioxide in the stripping gas to the concentration of the sulfur dioxide in the gas source is preferably at least 1, approximately . Various methods for removing the sulfur dioxide absorbed from the rich solvent can be employed. In the embodiment illustrated in Figure 3, the sulfur dioxide is removed by contacting the rich solvent with a non-condensable entrainment gas containing oxygen in the separator 20, whereby the sulfur dioxide is transferred from the rich solvent to the gas of drag to produce the entrained gas enriched with sulfur dioxide and the lean regenerated solvent. Preferably, the non-condensable oxygen entraining gas introduced into the separator 20 includes air. In fact, one of the advantages provided by the solvents include organic phosphorus compounds used in the present invention, especially solvents including phosphonate diesters, is its inherent flame retarding its capacity and resistance to oxidation. Thus, in spite of some organic solvents used in the conventional absorption / desorption cycles of sulfuric acid (for example, tetraethylene glycol dimethyl ether), the organic solvents used in the present invention can be easily removed from the sulfur dioxide using a gas separator that contains oxygen as air with minimal risk of solvent degradation or explosion. The separator 20 includes a vertical tower 21 containing means for promoting mass transfer between the gas and liquid phases. Like the absorber 11, the separator 20 is shown in Figure 3 as configured in the form of a packed tower containing it. a conventional random packing bed 22. Preferably, in order to maximize the transfer of sulfur dioxide, the rich solvent comes into countercurrent contact with the separating gas in the separator 20. In this way, as shown in FIG. 3, a noncondensable entrained gas stream which contains oxygen 23 is introduced through an inlet near the bottom of the tower 21 and a stream of rich solvent 16 is introduced through a liquid inlet above the packing bed 22 and distributed over the packaging material. The lean solvent stream 14 is ejected from a liquid outlet near the bottom of the tower 21 and a stream of entrain gas enriched with sulfur dioxide 26 is removed from the outlet near the top of the tower. The lean solvent stream 14 is removed from the bottom of the separator 20 and recycled to the liquid inlet near the top of the sulfur dioxide absorber 11 and serves as the solvent for a greater absorption of the sulfur dioxide from the stream Process Feeding Gas 10. Although a conventional packed tower may be employed, those skilled in the art will appreciate that the separator, such as the absorber, may have other suitable configurations, including a tower containing a structured package or a platform tower. The ratio of the mass flow index (L / G) of the rich sunlight stream 16 and the entrained gas stream containing non-condensable oxygen 23, necessary to achieve a substantial transfer of sulfur dioxide from the rich solvent to the drag gas stream enriched to 26 in the separator 20, can be determined by a conventional design practice. Preferably, essentially all (eg, at least about 90%) of the sulfur dioxide contained in the rich solvent, more preferably, at least about 95%, is transferred to the stripping gas. The entraining gas stream 26 leaving the top of the separator 20 passes to an upper condenser 28 and a portion of the water vapor contained in the entrained gas condenses by heat transfer to the cooled water. This condensate and trawl residue enriched with sulfur dioxide are subsequently transferred to a liquid / gaseous phase separator 30. A stream of entrained gas enriched with sulfur dioxide and cooled 31 leaves the separator 30 and a liquid stream 32. , which includes the condensate, is refluxed and introduced into the upper section of the separator 20 over a second bed of packing material 33. The solvent that can be vaporized in the separator can also be condensed in the upper condenser and form part of the condensate that refluxes again to the separator. However, to avoid the formation of two liquid phases in the separator 30, it is preferred to operate the condenser 28 whereby the reflux condenser to the separator 20 consists essentially of condensed water vapor from the entrainment gas. Although the embodiment illustrated in Figure 3, the rich solvent comes into contact with a entrained gas containing non-condensable oxygen in the separator 20 to recover the sulfur dioxide absorbed in the rich solvent, other removal configurations may be used. For example, current distillation, for example when the rich solvent comes into contact with a live stream introduced into the lower part of the trailing column, can be used in place of the entrained gas containing non-condensable oxygen. Regardless of how the sulfur dioxide separation / solvent regeneration step is conducted, the sulfur dioxide is preferably separated from the solvent under non-reduced conditions. In addition, the energy requirements of the sulfur dioxide absorption / desorption process of the present invention are moderate. To increase the absorption of sulfur dioxide in the solvent, the absorber 11 is preferably operated at an average temperature of about 10 ° C around 50 ° C, more preferably from about 30 ° C around 40 ° C. To promote the desorption of sulfur dioxide and avoid thermal degradation of the solvent, preferably the separator 20 is operated at an average temperature of about 80 ° C to about 120 ° C, more preferably about 90 ° C around 110 ° C. The preferred operating pressure in the absorber 11 is approximately 50 about 150 kPa total. The pressure increases the amount of sulfur dioxide, which the solvent can absorb, but the absorption can be carried out at a relatively low ratio so that equipment costs are reduced. When an entrainment with air is employed, the preferred operating pressure in the separator 20 is about 20 about 150 kPa total. The temperature control within the absorber 11 and the separator 20 can be achieved by controlling the temperature of several streams of processes fed to these apparatuses. Preferably, the temperature of the separator 20 is maintained within the desired range by controlling only the temperature of the rich stream 16, even when the air is introduced at ambient temperature as entrained gas containing non-condensable oxygen. Referring again to Figure 3, the solvent stream rich in sulfur dioxide 16 leaving the absorber 11 at a temperature of about 10 ° C to about 50 ° C passes through a solvent heat exchanger 34, where it is preheated by an indirect heat transfer of the deficient solvent stream 14 being recirculated from the separator 20 to the sulfur dioxide absorber. If further heating is required to achieve the desired temperature in the separator, the preheated rich solvent leaving the exchanger 34 can pass through the solvent heater 36 and be further heated by indirect heat exchange with steam. The lean solvent stream 14, leaving the separator 20 at a temperature of about 80 ° C to about 120 ° C, is cooled in the exchanger 34 by heat transfer to the rich solvent stream 16 leaving the absorber itself. it requires further cooling to maintain the desired temperature in the absorber, the lean solvent leaving the exchanger 34 can pass through the solvent cooler 38 and cool further by indirect heat exchange with water from the chiller tower. The use of the solvent exchanger 34 reduces the energy demands of the solvent heater 36 and reduces the chilled water required in the solvent cooler 38. During the course of commercial operation, inorganic salts and strong acids can accumulate in the circulating solvent between the absorber 11 and the separator 20. When this occurs, a purge stream 39, as illustrated in Figure 3, can be removed periodically or continuously from the stream of the deficient solvent 14 between the separator and the absorber to a purification vessel of the solvent 40. An aqueous wash stream 41, such as water or mildly alkaline aqueous solution - (eg, sodium bicarbonate solution) is also introduced into the purification vessel and comes into contact with the purge stream. The resulting two-phase mixture can subsequently be decanted to separate the aqueous phase containing the contaminants from the inorganic salts of the organic phase including regenerated deficient solvent having a reduced concentration of contaminants, a waste stream 42 that includes the waste water is discharged from the purification vessel, even though a liquid stream 43, which includes the purified organic phase, is returned to the stream of the deficient solvent 14 which enters the absorber 11. The amount of the deficient solvent treated in this way must be sufficient to maintain the concentration of the contaminant in the circulating solvent at a level low enough to provide low corrosion rates of the process equipment and that does not materially include the absorption efficiency of the sulfur dioxide. It should be understood that the washing of the deficient solvent can be carried out batchwise or continuously. If the poor solvent is washed continuously, a liquid-liquid phase separator suitable as a centrifugal switch can be used to separate the aqueous waste and the purified organic phases. The gas stream from the cooled sulfur dioxide enriched separator leaving the separator 30 can be used to prepare elemental sulfur by the Claus process or it can be further cooled to condense the sulfur dioxide in the form of a liquid product. For example, the gas source containing sulfur dioxide may include the gaseous effluent from the incinerator of a Claus plant and the gas stream from the separator enriched with sulfur dioxide 31 may be recycled to the Claus incinerator inlet. Alternatively, as shown in the embodiment illustrated in Figure 3, the gas from the separator can be fed to a contact sulfuric acid plant 44, whereby the sulfur dioxide contained in the gas from the separator is finally recovered as concentrated sulfuric acid and / u oil. The process of the present invention is particularly useful for altering the composition of a relatively weak gas source in sulfur dioxide (e.g., about 0.1 to about 5% by volume) and having a higher molar ratio of H2O / SO2. that the molar ratio of H2O / SO3 in the desired acid product to provide a gas enriched with sulfur dioxide, having a composition suitable for a final conversion to concentrated sulfuric acid and / or oil in a contact sulfuric acid plant. In the plant 44, the entrainment gas is introduced into a catalytic converter as part of a supply gas stream of the oxygen-containing converter. In the converter, the feed gas mixture passes over a suitable catalyst (eg, vanadium or cesium vanadium) for the oxidation of sulfur dioxide to sulfur trioxide, thereby producing a conversion gas that includes sulfur trioxide . Subsequently, the conversion gas comes into contact with the sulfuric acid in a sulfur trioxide absorber to absorb sulfur trioxide from the conversion gas and produce a product stream 46 which includes concentrated sulfuric acid and / or oil and a gas stream. final 48 which includes a reduced gas of the sulfur trioxide absorber. The force of the sulfur dioxide in the entrainment gas stream 31 leaving the separator 20 is preferably sufficient to provide a gas force of at least about 8% by volume in the feed gas stream of the converter produced by mixing the traction gas with air or other gas containing oxygen. When the sulfur dioxide content of the feed gas of the converter is 8% by volume or higher, the ratio of inert components to sulfur dioxide is sufficiently low that the heat transfer from the conversion gas to the feed gas of the converter is sufficient, without needing any external heat source to bring the converter feed gas to a high enough temperature to initiate a self-supporting conversion reaction in the catalytic converter. In a beneficent way, when the entrainment of the rich solvent air is used, the air used for entrainment can provide all or part of the oxygen required in the feed gas of the converter. If all the oxygen is supplied by the air used to entrain the rich solvent, the separated gas enriched with sulfur dioxide must have a sulfur dioxide gas strength of at least about 8% by volume, preferably from about 10 to about 15% in volume. If the separator gas is mixed with additional air or oxygen when preparing the converter feed gas, a proportionally higher sulfur dioxide gas force is required in the separator gas. For example, the sulfur dioxide-enriched gas separator gas having a gas strength of 20 to 95% by volume can be mixed with air to produce a converter feed gas containing the desired concentration of sulfur dioxide. Despite the force of the feed gas stream of process 10 entering the absorber 11, the separator gas enriched with sulfur dioxide can be produced having a substantial content of sulfur dioxide, more than adequate to provide the autothermal operation of the contact acid unit and control of water balance. At any point that is supplied, the air or oxygen is mixed with the sulfur dioxide removed from the rich solvent to provide a converter feed gas containing at least about 0.07 moles of oxygen, preferably about 0.9 to about 1.2 moles of oxygen , per mole of sulfur dioxide. The feed gas of the converter including the entrained gas can be dried by contacting the gas with the concentrated sulfuric acid in a drying tower before introducing the gas into the converter. Alternatively, when the air is used to entrain the sulfur dioxide from the rich solvent, the feed gas of the converter including the resultant stripping gas does not need to be dried before being introduced into the converter. To control sulfur dioxide emissions, high capacity sulfuric acid 4o plants are commonly operated using the. dual absorption. The sulfur dioxide is converted to sulfur trioxide in a catalytic converter containing a plurality of catalyst beds, each containing a vanadium or cesium vanadium catalyst. Typically, the converter contains four beds. In a double absorption plant, the partially converted gas stream leaving the second or third bed passes through an intermediate absorber (eg, interpass absorber) to remove the sulfur trioxide in the acid form of the product. The gas leaving the intermediate absorber returns to the next bed of the converter. Since the conversion of sulfur dioxide to sulfur trioxide is an equilibrium reaction, the removal of sulfur trioxide in the interphase absorber helps to drive forward reaction in the last or last beds of the converter to achieve high conversions, and therefore control the emissions of sulfur dioxide in the flue gas leaving the final sulfur trioxide absorber. The supply of an intermediate absorber contributes substantially to the capital and operating cost of a double absorption plant. However, even with double absorption, the catalytic converter must adapt to the size moderately to ensure high conversions and consequently low sulfur dioxide emissions. Emission standards usually require at least 99.7 percent dioxide <Sulfur entering the converter to recover in the form of sulfuric acid, for example, no more than 0.3 percent of the incoming sulfur dioxide leaves the system in the final gas of the sulfur trioxide absorber. According to one embodiment of the present invention, the feed gas stream of the process 10 fed to the absorber 11 includes all or part of the final gas stream 48 leaving the sulfur trioxide absorber of the contact sulfuric acid plant . That is, the method of the present invention illustrated in Figure 3 can be operated, whereby at least a portion of the reduced gas leaving the absorber of the sulfur trioxide is recirculated as part of the gas source containing introduced sulfur dioxide. in the absorber 11. The sulfur dioxide not converted to the final gas leaving the sulfur trioxide absorber is therefore recaptured in the rich solvent leaving the absorber 11, is separated from the solvent rich in the separator 20 and returned to the the contact sulfuric acid plant as part of the stripping gas enriched with sulfur dioxide for a final recovery as acid product. Inert components and oxygen, excess content in the sulfur trioxide conversion gas, are recirculated in the final gas stream 48 and purged from the process in an exhaust gas stream 18, which exits the absorber 11. As a consequence of this purge, the total final gas stream can be recirculated, so that no flue gas is released to the ambient environment at the outlet of the sulfur trioxide absorber. This is, when recirculating. all the final gas stream 48 to the absorber 11, the sulfur dioxide emissions from the contact sulfuric acid plant 44 can be essentially eliminated. In this way, even when the non-condensable gases separated from the process gas in the absorbers of sulfur trioxide and sulfur dioxide must be purged to the atmosphere, the emissions are confined to a single source, thus facilitating both monitoring and control. control of sulfur dioxide emissions. By recirculating all of the final gas stream 48 to the absorber 11, 99.7% or more of the sulfur dioxide in the feed gas stream of the process 10 fed to the sulfur dioxide absorber, it can be recovered as the product acid, even though the efficiency of the conversion in the sulfuric acid plant 44 is relatively low. In this way, the recirculation of the total final gas stream 48 allows the acid plant to be operated with a single absorber, completely eliminating the interpase absorption step that has become a standard throughout most of the industry. of sulfuric acid as a means to control sulfur dioxide emissions. Furthermore, even with a single absorption instead of a double absorption, the converter can be designated by a conversion efficiency of less than 98%, preferably less than 96%, for example, by the use of only three, or preferably only two, catalyst beds. 4 The operation is viable even at a conversion efficiency no greater than approximately 9.0%. The total recirculation of the final gas stream of the sulfur trioxide absorber allows the sulfur dioxide in the final gas to be recovered in the absorption circuit of the sulfur dioxide and recirculated to the converter. By using the solvents including organic phosphorus compounds described herein that essentially provide for the quantitative removal of sulfur dioxide from the gas in the absorber 11, the converter can be operated at conversions as low as 95% or lower, while maintaining the final recovery of 99.7 percent sulfur dioxide from the gas source in the form of sulfuric acid product. In a beneficial manner, the method of the invention can be implemented by using a single absorption system and / or by using only two or three catalyst beds in the converter, as mentioned earlier. Alternatively, an existing contact acid plant, operating for example by using a relatively weak source of sulfur dioxide gas, can be modified to operate at levels higher than the design yield without exceeding the emission limit. Those skilled in the art will further recognize that, depending on the efficiency of the converter, the emission standards can be brought together by recirculating less than all of the reduced sulfur trioxide gas to the sulfur dioxide scavenger 4e. Depending on this parameter and prevailing local emission standards, target emissions can be met by recirculating 90 percent, 75 percent or even 50 percent of the last gas stream 48, with some resulting savings in energy costs for compressing gas. However, it is ordinarily preferred that substantially all of the last gas stream 48 be recirculated from the contact sulfuric acid plant to the sulfur dioxide absorber 11. The present invention is illustrated by the following example, which is only for the purposes of the illustration and not with respect to limiting the scope of the invention or in the form that can be practiced.

EXAMPLE By using a computer model, the performance of a sulfur dioxide absorption / desorption process according to the present invention was ensured (see Figure 3). The model was based on the use of a boiler furnace gas as the gas source containing sulfur dioxide, dibutyl butyl phosphonate (DBBP) as an absorption solvent and the removal of air from the rich solvent. The start of flow, temperature and composition of the relevant gas streams are summarized in Table 1 and the flow index of temperature and composition of the relevant liquid streams are summarized in Table 2. In Table 1, Gl designates the gas of incoming combustion, G2 designates the flue gas stream after the gas is cooled and cleaned, which is introduced into the sulfur dioxide absorber, G3 designates the exhaust gas stream of the sulfur dioxide absorber, G4 designates the enriched gas stream leaving the sulfur dioxide separator, G5 designates the enriched and cooled entrained gas stream leaving the separator of the G6 entrainment phases designates the entrainment air stream.

TABLE 1 In Table 2, Ll designates the deficient solvent stream introduced into the sulfur dioxide absorber and L2 designates the rich solvent stream introduced into the sulfur dioxide separator. The temperature of the deficient solvent stream leaving the sulfur dioxide separator was 86 ° C. The temperature of the rich solvent stream leaving the sulfur dioxide absorber was 39 ° C. 4 TABLE 2 4

Claims (9)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for selectively removing and recovering sulfur dioxide from a source of sulfur dioxide-containing gas consisting of: contacting a feed gas stream of the process including said gas source with a liquid solvent for the selective absorption of sulfur dioxide in a sulfur dioxide absorber, thus transferring the sulfur dioxide from said feed gas stream from the process to said solvent and producing an exhaust gas, from which the sulfur dioxide has been substantially removed and a solvent rich in sulfur dioxide, said liquid solvent includes at least one organic phosphonate diester substantially immiscible with formula water where R, R and R3 are independently aryl or C ^ a alkyl Cg, said organic phosphonate diester 4r having a vapor pressure less than about 1 Pa at 25 ° C, the solubility of the water in said organic phosphonate diester is less than about 10 weight percent at 25 ° C; Removing the sulfur dioxide separates the sulfur dioxide from said rich solvent in a sulfur dioxide separator to produce a deficient solvent and a stripping gas enriched with sulfur dioxide, the ratio of the concentration of the sulfur dioxide in said sulfur dioxide to the sulfur dioxide. The sulfur dioxide concentration in said gas source is greater than 1.1 and recirculate said deficient solvent to said sulfur dioxide absorber for a greater selective absorption of sulfur dioxide from said gas source.

2. A process according to claim 1, further characterized in that said at least one organic phosphonate diester is an alkyldialkyl phosphonate and R, R and R are independently C 1 to Cg alkyls.

3. - A method according to claim 2, further characterized in that R1, R and R are identical and each contains more than 3 carbon atoms.

4. - A method according to claim 3, further characterized in that said liquid solvent includes dibutylbutyl phosphonate.

5. - A method according to claim 1, further characterized in that said source of gas contains about 0.1 about 5 volume% of sulfur dioxide.

6. - A method according to claim 5, further characterized in that the ratio of the concentration of the sulfur dioxide in said entrain gas enriched with sulfur dioxide to the concentration of sulfur dioxide in said gas source is at least 5. 5. - A method according to claim 6, further characterized in that said entrain gas enriched with sulfur dioxide contains at least about 8 volume% sulfur dioxide. 8. - A method according to claim 5, further characterized in that said source of gas containing sulfur dioxide includes combustion gas from the combustion of a sulfurous fuel or a gaseous effluent from a metal calcination operation, the incinerator of a Claus plant or sulfur trioxide absorber from a sulfuric acid plant. 9. - A method according to claim 1, further characterized in that the temperature in said sulfur dioxide absorber is maintained at a temperature of about 10 ° C to about 50 ° C. 10. A method according to claim 9, further characterized in that the process gas feed stream further includes water vapor at the temperature of said liquid solvent coming into contact with the feed gas stream. The process in said sulfur dioxide absorber is greater than the dew point of said process gas stream. 11. A method according to claim 1, further characterized in that the sulfur dioxide is removed by contacting said rich solvent with a stripping gas containing non-condensable oxygen in said sulfur dioxide separator, the sulfur dioxide is so sulfurized from said rich solvent to said stripping gas. to produce said stripping gas enriched with sulfur dioxide and said deficient solvent. 12. - A method according to claim 11, further characterized in that said entrain gas containing non-condensable oxygen includes air. 13. - A method according to claim 12, further characterized in that the temperature in said sulfur dioxide separator is maintained at a temperature of about 80 ° C around 120 ° C. 14. - A method according to claim 1, further characterized in that said entrain gas enriched with sulfur dioxide is introduced into a catalytic converter for oxidation of sulfur dioxide to sulfur trioxide as part of the feed gas stream of the sulfur dioxide. oxygen-containing converter, by which it produces a conversion gas that includes sulfur trioxide, said 4-fold gas comes into contact with sulfuric acid in a sulfur trioxide absorber for absorption of sulfur trioxide thereof to produce sulfuric acid or oil and a reduced gas stream of the sulfur trioxide absorber exiting said sulfur trioxide absorber. 15. - A method according to claim 14, further characterized in that said source of sulfur dioxide-containing gas includes said reduced gas stream of sulfur trioxide absorber, whereby the sulfur dioxide is recovered from said reduced gas for the final conversion to sulfuric acid or oil. 16. A process according to claim 15, further characterized in that the sulfur dioxide in said entrain gas enriched with sulfur dioxide is converted to sulfuric acid in a contact sulfuric acid process that includes a single absorber of sulfur trioxide . 1

7. A method according to claim 15, further characterized in that said catalytic converter includes less than four catalyst beds. 1

8. A method according to claim 1, further characterized in that said liquid solvent includes dibutylbutyl phosphonate, the method further includes: introducing a supply gas stream of the oxygen-containing converter including said entrain gas in a catalytic converter for oxidation of 4 sulfur dioxide to sulfur trioxide, thus producing a conversion gas that includes sulfur trioxide• and contacting said conversion gas with sulfuric acid for absorption of sulfur trioxide thereof in a sulfur trioxide absorber to produce sulfuric acid or oil and a reduced gas stream from the sulfur trioxide absorber, which exits from the sulfur trioxide absorber. said sulfur trioxide absorber, said gas source containing sulfur dioxide includes said reduced gas stream the sulfur trioxide absorber, whereby the sulfur dioxide is recovered from said reduced gas for a final conversion to sulfuric acid or oil. 1

9. A method for selectively removing and recovering sulfur dioxide from a sulfur dioxide-containing gas source that includes: contacting a feed gas stream from the process including said gas source with a liquid solvent for absorption selective sulfur dioxide in a sulfur dioxide absorber, thus transferring the sulfur dioxide from said process gas feed stream to said solvent and producing an exhaust gas, from which the sulfur dioxide has been substantially removed and a solvent rich in sulfur dioxide, said liquid solvent including an organic phosphorous compound selected from phosphate triesters, phosphonate diesters, phosphinate monoesters and mixtures thereof, the substituents attached to the phosphorous atom and the organic radicals of the ester functionality are 4 independently aryl or alkyl C] _ to Cg; separating the sulfur dioxide from said rich solvent in a sulfur dioxide separator by contacting said rich solvent with an entraining gas containing oxygen in said sulfur dioxide separator, the sulfur dioxide is transferred from said rich solvent to said solvent. drag gas to produce a deficient solvent and a stripping gas enriched with sulfur dioxide and recirculate said deficient solvent to said sulfur dioxide absorber for a greater selective absorption of sulfur dioxide from said gas source. 20. A method according to claim 19, further characterized in that said entrained gas containing non-condensable oxygen includes air. 21. A process according to claim 1, further characterized in that said entrain gas enriched with sulfur dioxide is fed to a Claus plant for the preparation of sulfur elementa. 22. - A method according to claim 21, further characterized in that said Claus plant includes an incinerator, said source of gas containing sulfur dioxide that includes gaseous effluent from said incinerator of the Claus plant, whereby the dioxide Sulfur is recovered from said effluent from the Claus plant incinerator for the final conversion to elemental sulfur. 23. A process according to claim 1, further characterized in that the sulfur dioxide is separated 4a from said rich solvent under non-reductive conditions. 24. - A method according to claim 23, further characterized in that at least about 90% of sulfur dioxide absorbed in said rich solvent introduced into said separator is transferred to said entrain gas enriched with sulfur dioxide. 25. A method according to claim 18, further characterized in that the sulfur dioxide is separated from said rich solvent under non-reductive conditions. 26. A method according to claim 25, further characterized in that at least about 90% of the sulfur dioxide absorbed in said rich solvent introduced in said separator is transferred to said entrain gas enriched with sulfur dioxide. 27. A method for selectively removing and recovering sulfur dioxide from a sulfur dioxide-containing gas source that includes: contacting a feed gas stream of the process including said gas and water vapor source with a solvent liquid for the selective absorption of sulfur dioxide in a sulfur dioxide absorber, thus transferring the sulfur dioxide from said stream of process feed gas to said solvent and producing an exhaust gas, from which the sulfur dioxide has been substantially removed and a solvent rich in sulfur dioxide, the temperature of said solvent rich that came into contact with said process gas feed stream in said absorber is higher than the dew point of said process gas feed stream, said liquid solvent includes at least one organic phosphonate diester substantially immiscible with water of formula where R, R ^ and R are independently aryl or alkyl of C] _ to Cg, said organic phosphonate diester having a vapor pressure less than about 1 Pa at 25 ° C, the solubility of water in said phosphonate diester organic is less than about 10% by weight at 25 ° C; separating sulfur dioxide from said solvent rich in a sulfur dioxide separator to produce a deficient solvent and a stripping gas enriched with sulfur dioxide and recirculating said deficient solvent to said sulfur dioxide absorber for a greater selective absorption of carbon dioxide. sulfur of said gas source. 28. A method for selectively removing and recovering sulfur dioxide from a source of sulfur dioxide-containing gas including: contacting a stream of process feed gas including said source of gas with a liquid solvent for absorption Selectively sulfur dioxide in a sulfur dioxide absorber, thereby transferring the sulfur dioxide from said process gas feed stream to said solvent and producing an exhaust gas, of which the sulfur dioxide has been substantially removed, and a solvent rich in sulfur dioxide, said liquid solvent includes at least one organic phosphonate diester substantially immiscible with water of formula io 3 where R, R and R are independently alkyl or C] _ to Cg, said organic phosphonate diester having a vapor pressure of less than 1 Pa at 25 ° C, the solubility of water in said phosphonate diester organic is less than about 10 weight percent at 25 ° C; separating sulfur dioxide from said rich solvent in a sulfur dioxide separator to produce a deficient solvent and a stripping gas enriched with sulfur dioxide; treating said deficient solvent to remove contaminants upon contacting an amount of said deficient solvent with an aqueous wash to produce a two phase liquid mixture including an aqueous phase containing contaminants removed from said deficient solvent and an organic phase including a solvent deficient having a concentration of reduced contaminants and separating said organic phase and said aqueous phase and recirculating said organic phase including solvent deficient for said sulfur dioxide absorber for a greater selective absorption of sulfur dioxide from said gas source. 29. A method according to claim 28, further characterized in that said aqueous wash is selected from the group consisting of water of an aqueous alkaline solution. 30. A method according to claim 28, further characterized in that the treatment of said solvent deficient to remove contaminants is conducted in a group form. 31.- A method according to claim 28, further characterized in that the treatment of said solvent deficient to remove contaminants is conducted continuously. 32. - A method according to claim 31, further characterized in that said organic phase is separated from said aqueous phase by using a centrifugal switch. 33.- A method according to claim 1, further characterized in that the process limiting gas stream also includes steam. 34. - A method according to claim 1, further characterized in that the operating pressure in said sulfur dioxide absorber is about 50 about 150 kPa total. 35. A method according to claim 12, further characterized in that the operating pressure in said sulfur dioxide separator is about 20 about 150 kPa total. SUMMARY OF THE INVENTION A procedure for the removal and selective recovery of sulfur dioxide from effluent gases is described; Sulfur dioxide is recovered in a cycle of absorption / desorption of sulfur dioxide, which uses a liquid solvent to selectively absorb sulfur dioxide from the effluent gas; the liquid solvent includes an organic phosphorus compound selected from phosphate triesters, phosphonate diesters, phosphinate monoesters and mixtures thereof; preferably, the liquid solvent includes phosphonate diesters of the formula (I) wherein R, R and R ° are independently aryl or alkyl of Ci to Cg; the organic phosphonate diesters are substantially immiscible with water, the solubility of the water in organic phosphonate diester is less than about 10. % at 25 ° C and has a vapor pressure less than 1 Pa at 50 ° C; according to a preferred embodiment, the liquid solvent includes dibutylbutyl phosphonate; the absorbed sulfur dioxide is subsequently removed to regenerate the organic phosphorus solvent and produce a gas enriched in sulfur dioxide content; the gas enriched with sulfur dioxide can be used as part of the feed gas for a sulfur:: or contact plant or a Claus plant for the preparation of elemental sulfur or it can be cooled to condense sulfur dioxide in the form of a liquid product; The present invention is particularly useful for producing a gas enriched with sulfur dioxide from gases relatively weak in sulfur dioxide content. DC / cgm * xal * xma * mmr P99 / 182F i -