DE2053104A1 - Process for the removal and / or recovery of sulfur dioxide from a mixture of moist or dry gases - Google Patents

Description

Process for the removal and / or recovery of sulfur dioxide from a mixture of moist or dry gases

The invention relates to a method for removing and / or recovering sulfur dioxide from a sulfur dioxide-containing one Mixture of gases by selective absorption of sulfur dioxide in an N-alkyl-lactam as solvent.

The removal of sulfur dioxide from breath gases and angular gases has always been a major problem, but it has become this problem in recent years because of public discussions about air pollution even more acute. Due to the increasing use of sulfur-rich materials, the Air in ever increasing proportions with the combustion products of sulfur, i. H. has been contaminated with sulfur dioxide. It exists an acute need for methods to better remove sulfur dioxide contaminants from flue gases and others

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Piermühlen \ SOG-containing gases such as flue gases in power generation plants, patent \, smelters, sulfur factories, etc sulfuric acid factories ..

In addition to improving the air, there is also great interest in the extraction of sulfur dioxide from the combustion gases of sulfur or high-sulfur fuels. The sulfur dioxide can be oxidized again, e.g. B. to sulfur trioxide for sulfuric acid production, and it is also possible, in particular in the extraction of sulfur dioxide from the ftattch gases sulfur-rich fuels, the sulfur dioxide mil; Hydrogen sulfide convert to sulfur. Besides' also has the industrial Use of the sulfur dioxide obtained for the production of other valuable products is of great importance.

It has now been found that sulfur dioxide from mixtures of Wet or dry gases can be selectively removed by using a liquid N-alkyl-lactam or a cybloalkyl-lactam as selective solvent in countercurrent contact with the mixtures is brought out of wet or dry gases and the gases are separated will. The preferred N-altylaotam is a lower N-alkylpyrrolidone, such as B. N-methylpyrrolidone.

The N-alkyl lactam used in the process of the invention is preferably an N-alkyl- (or N-Cyoloalkyl-, e.g. -Cyclohexyl-), pyrrolidone or piperidone. The alkyl group should generally contain from about 1 to about 16 carbon atoms, where lower alkyl (including N-cycloalkyl) groups from 1 to 6 carbon atoms are preferred.

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Suitable solvents include; N-ethylpyrrolidone, N-propylpyrrolidone, N-isopropylpyrrolidone, N-t-butylpyrrolidone, N-n-butylpyrrolidone, N-rj-hexylpyrrolidone, N-cyclohexyipyrrolidone, N-n-octylpyrrolidone, N-isoactylpyrrolidone, N-n-decylpyrrolidone, N-undecylpyrrolidori, N-dodecylpyrrolidone, If-tetradecylpyrrolidone, N-hexadecylpyrrolidone, N-methylpiperidone, N-ethylpiperidone, N-Propylpiperidon, N_Isopropylpiperidon, N-t-Butylpiperidon, N-n-butylpiperidone, N-n-hexylpiperidone, N-n-octylpiperidone, N-isooctylpiperidone, N-n-decylpiperidone, N-undecylpiperidone, N-dodecylpiperidone, N-tetradecylpiperidone and N-hexadecylpiperidone.

The N-alkyllactams used in the process according to the invention, including the N-alkylpyrrolidones and piperidones, are "lactams of the gamma and delta amino acids derived from butyric acid, valeric acid and caprylic acid. They are neutral and act as physically dissolving absorbents. As has now been recognized, such N- Alkyl lactams are effective solvents for sulfur dioxide from a mixture of moist and dry gases, which are formed, for example, during the combustion of sulfur-rich fuels or during the production of sulfur itself of the present invention is to DAIB such lactams are water soluble. This feature allows the application of the invention to damp gases and reduced loss of solvent. in addition, it allows Λ tolerating Destimmter amounts of water in the system without affecting the effectiveness of the solvent.

So z. Yy. one in the combustion of sulfur-rich fuels the resulting flue gas, in addition to the sulfur dioxide formed by the combustion of the sulfur, also carbon dioxide, air, Contain nitrogen, water vapor and other different gaseous components. A typical, sulfur dioxide-containing one Gas mixture can according to the invention using a JM-alkyllactam as a selective solvent for the Scliwefeldi-

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oxide treated. The inventive method is of particular importance for various industries in which high sulfur fuels must be used. It can therefore be used to those with the use of high sulfur feeds or high sulfur incineration Fuels in power plants and other industrial plants to eliminate air pollution related.

The process according to the invention is generally carried out by bringing an ascending stream of flue gases containing sulfur dioxide into contact with a descending stream of the N-alkyl lactam or with an aqueous solution of the N-alkyl lactam which contains up to 25 % by weight of water. Any conventional type of absorption tower which allows countercurrent contact of gas and liquid can be used for this purpose. So is z. B. possible, the ascending gas stream with the descending N_Alkyllactam, z. B. N-alkylpyrrolidone, in a conventional bubble cap tower, dust tower, packed tower or in any other suitable column which allows countercurrent contact of gas and liquid.

This enables contact between the gas and liquid streams the selective removal of sulfur dioxide because the descending stream of N-alkyl or Oycloalkyllactam or N-alkyl or cycloalkyl lactam / water solution essentially that all sulfur dioxide is absorbed in the gas stream, with the result that a gas largely freed of sulfur dioxide is the Absorption tower (preferably via a water wash for extraction of all the methylpyrrolidone from the scrubbed gases) leaves, while a liquid stream rich in sulfur dioxide from N-alkyl- or -cycloalkyllactam the bottom of the absorption column or another countercurrent contact system.

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The liquid stream of N-alkyl- or -cycloalkyllaetam containing dissolved SO ₂ and water can then be freed by stripping SOp and some or all of the water, the solvent being recovered for recycling and reuse in the absorption. The recovered SO ₉ can then be used, e.g. B. for production

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of sulfur trioxide and sulfuric acid or for the production of sulfur by reaction with hydrogen sulfide. Stripping the dissolved SO ₂ from the liquid selective solvent can conveniently be done in a stripping column or distillation column operated at higher temperatures and / or lower pressures than are used for the absorption of the SO ₂ in the solvent. Thus, ä that the sulfur dioxide gas is readily removed and recovered, and the solvent can then be reused for the absorption of sulfur dioxide from flue gas further or other gas mixtures can be reached.

The absorption tower used to absorb the sulfur dioxide in the downflowing solvent is best operated at ambient temperatures or slightly above ambient temperatures. The selected N ~ alkyl- or -cycloalkyllactam or their aqueous solutions, which contain up to 25 # water, have a high absorption capacity with respect to the selective absorption of the sulfur dioxide, and therefore it is possible ^ the tower or the respective plant at low to drive economical ™ borne temperatures. Therefore, the tower or the system is preferably operated to 50 ⁰ C at a temperature of about 40 to about 60 ⁰ O, in particular at about 40 microns. The pressure applied is not critical. However, it is preferred to run the system at atmospheric pressure or slightly elevated pressure, ie. at 1 to 1.5 atmospheric pressure in order to achieve a good flow through the tower with the gas.

Albeit the use of anhydrous solvent in the process method according to the invention the best results in the development

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removal of sulfur dioxide from the gas mixture, the solvent can contain significant amounts of water and nevertheless an excellent dissolving power for sulfur dioxide own. In fact, it is often desirable that the solvent chosen contain some water because the presence is less Amounts of water stripping off the dissolved sulfur dioxide wont ease out of the solvent. Some water is generally included in the solvent because it is absorbed from the gases in the absorption tunnel, so that it it is seldom possible to achieve completely anhydrous conditions. The N-alkyl- or -cyoloalkyllactam can be up to about 25 wt. Contain water, and a water content of 15 to 20 weight percent is preferred for most purposes.

The sulfur dioxide released from the selected solvent in the stripping column is preferably deposited at the top of the column withdrawn and introduced into a laundry tower, in which the sulfur dioxide gas is washed with water. The laundry of the Sulfur dioxide gas allows further removal of any entrained solvent, leaving more solvent for the Reuse is recovered. The sulfur dioxide obtained after washing can be used for further use in any Way to be compressed. As already mentioned, the sulfur dioxide obtained in the process according to the invention becomes used with advantage in the extraction of sulfur and sulfuric acid.

example 1

Rauchgas'aus a power plant with a capacity of 250 Ö00 KW, which burns sulphurous fatty coal, was at a rate of 0.75 x 10 ⁶ water / h or 0.9 x 10 ⁶ kg / h and a temperature of about 150 ⁰ C introduced through suitable lines and a fan into a cooler, in which it is washed or cooled by spraying water at the head of the cooler and

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was washed. A fly ash sludge was poured from the bottom of the cooler, which contained traces of N-methylpyrrolidone and SOg, withdrawn from the system through another line. The cooled and washed exhaust gases were at the top of the cooler through a appropriate line withdrawn at a temperature of 43 0.

The composition of the exhaust gases introduced into the radiator was roughly as follows:

SO ₂ = 0.2? 6

GO ₂ = 11.6 $

Og = 6.6 $> Ä

N ₂ = 79.0 96

H ₂ O = 3.0 96

The composition of the gases withdrawn from the cooler was roughly as follows:

SOg = 0.19 96

CO ₂ = 10.92 96

O ₂ = 6.14 #

73.30 96

H ₂ O 9.15 96

ΪΤ-methylpyrrolidone = 0.35 $>

The cooled exhaust gases were introduced into the bottom of a column, which consisted of a lower absorber section and an upper scrubber section. The SOg-rich gas rose through the absorber section in countercurrent to a falling stream of IJ-friethylpyrrolidone, which in the upper part of the absorber

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About section was introduced through a suitable pipe with a temperature _x door of 35 ° C and a speed of 1.13 x 10 kg / h.

From the top of the absorber section, the scrubbed gases, which contained about 0.02 # SO ₂ , passed into the scrubber or trickle section, where they rose in countercurrent to a falling stream of wash water, which at the top of this section through a suitable conduit a temperature of about 35 C and a rate of 70 300 kg / h was introduced. This wash water was used to recover or remove most of the N-methylpyrrolidone that was entrained with the gas entering the Wäscherfe section. The scrubbed gases were drawn off at the head of the scrubber or trickle section and vented to the atmosphere through suitable ducts, where they were dispersed. A more than 10-fold decrease in SOp content was achieved in the gases vented from the system. Only about 363 kg / h SOp was vented compared to about 3,900 kg / h SOp contained in the gases introduced into the system. A small amount of N-methylpyrrolidone, about 72.6 kg, was lost.

The wash water, which contained most of the N-methylpyrrolidone entrained with the washed gases introduced into this section, was withdrawn from the bottom of this section W. If desired, some of the withdrawn water can be returned to the head of the scrubber or trickle section.

_{A solution of SO 2} in aqueous N-methylpyrrolidone was withdrawn from the bottom of the absorber section through a suitable line at a temperature of about 43.degree. This solution was passed through a heat exchanger and introduced into a distillation column, where it was cooled by indirect heat exchange with steam of 31.6 atm in a coil at the bottom of the

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Distillation column was heated further so that the SO ₂ and water were stripped from the solution or distilled off and drawn off at the top of the distillation column. Some of the water was condensed in a partial condenser and returned to a distillation column through a reflux column via a suitable line.

From the bottom of the distillation column, N-methylpyrrolidone was withdrawn at a temperature of about 177 ° G through a suitable line, passing through a heat exchanger in which it underwent an indirect heat exchange with the solution of SO ₂ and N-methylpyrrolidone in a parallel line. Exchanger reached the N-methylpyrrolidone, etc. from the training through a suitable conduit to a heat exchanger in which it was cooled by indirect heat exchange with cooling water further to a temperature of about 35, whereupon it was introduced into the top of the absorber section.

The SO ₂ and water from the partial cooler used for the recycle passed through a suitable line to a compressor where it was compressed to a pressure of about 7 atmospheres, after which it was introduced into a sulfur dioxide distillation column. Live steam was introduced into the bottom of the distillation columns at a pressure of about 8.1 atmospheres and a rate of about _{15,900 kg / h in order to distill off the SO 2} from the water. The freed from UEO ₂ water / withdrawn at the bottom of the distillation column at a temperature of about 163 ⁰ O, and a rate of about 70,000 kg h.

SO ₂ was drawn off at the top of the distillation column at a temperature of about 43 and condensed in a condenser. Part of the condensed SO ₂ was returned to the top of the distillation column for reflux, and the core of the S0 _? was deducted for storage.

This method convincingly proves that N-alkyl lactams and lower N-alkylpyrrolidones in particular highly effective, selective Solvents for sulfur dioxide are.

Example 2

In a further experiment, exhaust gases were introduced into an absorber without prior cooling. The absorption of sulfur dioxide from a flue gas, which contained sulfur dioxide, air, carbon dioxide, nitrogen and water vapor, was brought about by means of OT methylpyrrolidone. Various attempts have been carried out, the input temperature of the gases from 518 to 663 ° C varied and the average temperature of the absorber from 24 to 32 ⁰ C was varied.

The absorber used in these experiments was a column with an internal diameter of 10 cm and a 38 cm high packing of 6.4 mm Contained strong glass fiascnig rings; the calculated number theoretical soils was 4. The solvent rich in sulfur dioxide was placed on a stripping column consisting of a column mounted on the head of a reboiler 5 cm inside diameter, which consisted a 38 cm high pack of 6.4 mm thick rings below the feed inlet and had a stainless steel mesh above this inlet. In this column, excess water, Sulfur dioxide and a small amount of carbon dioxide and inert gases are stripped into a reflux condenser, which is a A very small amount of reflux vapor was removed before the excess reflux was added to a small fractionation tower became. The solvent used in these experiments was N-methylpyrrolidone, the water in amounts of about 10 to contained about 35 wt. #.

The table below gives the results of these tests, with the percentage amount in the last column ^; of absorbed sulfur dioxide appears. ,; -.

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Temperatures in

Mono- exhaust gas laßgas

absorber

Amount of gas lit./min.

H ₉ O Circu- Mol # Mole Mole Κ _ςη L im ^c lierte S0 _? in the liquid vapor / ^OU 2 VK solution solu. / h EiSlaß- hh = Y / X medium gas LV

Absorbed SO ₂

621 117 32.2 56.6 15.7 23.1 524 105.5 26.7 48.7 35.00 30.8 538 113 23.9 64.8 20.0 24.9 ¹⁶⁶⁰ 112 28.3 36.0 18.0 20.3 I 632 112 28.3 36.0 18.0 14.3 593 126 29.4 56.6 ' 10.5 20.4

23.1 0.052 0.337 0.317 1.0 1.06 85.0

0.097 0.802 0.272 3.6 0.82 70.0

0.097 0.477 0.363 1.7 0.77 84.0

0.109 0.370 0.201 1.0 1.84 92.3

0.109 0.262 0.201 1.0 1.3 89.6

0.098 0.298 0.317 053 1.77 80.0

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As the table shows, a very effective absorption of sulfur dioxide from the exhaust gases could be achieved in all tests according to the present invention. However, when the water content in the H-methylpyrrolidone was greater than about 25 % , a slightly lower percentage absorption was observed. In order to achieve optimal results with the most convenient test procedure and the greatest selectivity of the solvent for sulfur dioxide, the moisture or water content of the solvent should best be kept between about 15 and about 20% by weight.

The above experiments show that with the use according to the invention of N-alkyllactams or -cycloalkyllactarns for removal sulfur dioxide from gas mixtures largely eliminates the problem of air pollution from industrial exhaust gases can be.

Example 5

The procedure of Example 1 was repeated, using instead of N-methylpyrrolidone essentially equivalent amounts of the following N-alkyl lactams were used ι N-ethylpyrrolidone, N-tert-butylpyrrolidone, N-isooctylpyrrolidone and N-isopropylpiperidone. The results were equally good.

Here, too, the great benefit of the invention for maintaining the air became evident.

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Claims (9)

Patent claims Process for the purification of a sulfur dioxide containing Mixture of moist or dry gases by selective absorption of the sulfur dioxide, characterized in that this (Jeraisoh with an N-Alky! lactam or Cycloalkyllaotam as a liquid solvent in countercurrent con. is brought tact, the absorbed sulfur dioxide from the liquid solvent is separated, and that of sulfur dioxide largely freed mixture of dry and moist gases is separated. 2. The method according to claim \ _f, characterized in that a lower N-alkylpyrrolidone is used as the solvent. 3. The method according to claim 2, characterized in that N-methylpyrrolidone is used as the solvent. 4 * Method according to Claim 1, characterized in that as Solvent an N-alkyl lactam is used, which 'up to Contains 25 wt. <£ water. j 5. The method according to claim 4, characterized in that the solvent contains about 15 to about 20 wt. '^ Water * 6. The method naoh claim 1, characterized in that the gas mixture in countercurrent at about 40 to about 60 C with the Solvent brought into contact and then the absorbed Sulfur dioxide is stripped from the solvent, 109819/13 (6 by being heated to about 100 "to about 20O ⁰ C. 7. The method according to claim 1 or 6, characterized in that the mixture of nasBen or dry gases is cooled, before ea is brought into contact with the liquid solvent will. 8. The method according to claim 1 or 6, characterized in that that from the mixture of wet or dry gases the Asohe is removed before the mixture with the liquid solvent is brought into contact. 9. The method according to claim 1 or 6, characterized in that that the solvent is recycled for reuse as an absorbent. For GAF Corporation New York, N.Y., V. ^ t.A, Lawyer