HU181418B - Method for isolateing vapours for gas mixture - Google Patents

Abstract

Gas mixtures (1) containing the vapours of volatile compounds, e.g. industrial solvents and volatile oils, are contacted with an aqueous solution of cyclodextrins and/or cyclodextrin derivatives, preferably in an absorber (2), the volatile compounds forming inclusion complexes with the cyclodextrins. The cyclodextrin inclusion complex obtained may if desired be separated, e.g. in settling tank (5) from the aqueous solution phase. It is then subjected (8) to thermal dissociation and the volatile compound released is isolated from the vapour phase, preferably by condensation (12). The mother liquor (14) left behind after separating the cyclodextrin inclusion complex and the solution (9) obtained from the thermal dissociation, containing cyclodextrin as the main component, are combined, and, if the process is carried out in an absorber, the combined solution is recycled (16) into that absorber. Water can be added to the combined solution, to ensure that the gas mixtures which are passed through the absorber are saturated with water. <IMAGE>

Description

The present invention relates to a process for removing vapors of a small amount of water-insoluble organic solvents in an inert carrier gas, preferably air, by washing the gas phase with a soluble liquid phase and heating the liquid phase with an absorbent, water-insoluble organic solvent. and recovering the solvent vapors formed by condensation.

According to the invention, the inert gas, preferably air, containing solvent vapors is washed with an aqueous solution containing β-cyclodextrin, methylated β-cyclodextrin or a water-soluble β-dclodextrin polymer and optionally a surfactant. The absorbed solvent is removed from the wash liquid by boiling, the solvent vapors are condensed in a manner known per se, and the de-solvent wash is cooled back to the washing step after cooling.

In the case of technologies processing large quantities of volatile compounds and their vapors (for example, solvent distillation, regeneration, tank exchange), volatile compound vapors are virtually unavoidable. This could reduce the amount of volatile compounds released into the environment for 20 years, either with intensively cooled condensers or with activated carbon adsorbers. The efficiency of cooling was determined by the quantity, temperature and, in extreme cases, the quality (hardness) of the cooling water available. 25 Because of its very high equipment and energy requirements, artificial cooling is rarely used. For example, in the case of solvent regeneration under vacuum, the use of water-cooled condensers, despite the presence of large amounts of solvent vapor in the vacuum pump exhaust pipe. This is partly an economically damaging loss of solvent, but even more damaging to the environment. From the vapor phase, said volatile compounds can be recovered by adsorption only by the use of activated carbon. Since the solid phase must be distributed over a large surface area so as not to cause high resistance to the flowing gas or vapor phase, the equipment must be large. Regeneration of activated carbon is a separate problem and can only be achieved in batch operation.

It can be seen from the foregoing that up to now no process has been available which has been able to efficiently recover volatile compound vapors in gas mixtures at low operating costs.

Cyclodextrins are known to form inclusion complexes with many organic materials. For example, U.S. Patent No. 3,541,077. U.S. Pat. No. 4,123,115 discloses the liquid phase complex of α-cyclodextrin with cyclohexane. Here, the organic compound to be encapsulated in the aqueous solution of cyclodextrin, or a water-miscible organic solvent solution thereof, and the excellent inclusion complex are separated.

The Bull. Chem. Soc. Japan, 52 (10), 2808-2814. (1979) report the thermodynamics of alcohol adducts of cyclodextrins.

A J. A. C. S., 100 (3), 916-919. (1978) provides an energetic description of α-cyclodextrin and benzene and β-iodaniline complexes.

No. 7,596,530. a process for separating p-alkyl-toluene from isomeric mixtures from Japanese Kokai is known. The separation is carried out with α-cyclodextrin.

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In a substantially similar embodiment, the separation of p-dimethylbenzene from isomeric mixtures is disclosed in U.S. Pat. No. 75,151,827. Japanese Kokai.

The CA 83,69,530 d reference paper discloses a crystalline complex of α-cyclodextrin with methanol. From the above articles dealing with the inclusion complexes of cyclodextrins, it can be stated that in each case the components of the inclusion complexes are in liquid phase. In each case, the process was prepared by mixing the aqueous or aqueous alcoholic solution of cyclodextrin with the organic compound to be complexed or with a solution thereof (usually alkanols) in a water-miscible solvent. This was necessary because, as is known, complexation is a reversible process which requires the concentration (activity) of the components involved in the reaction to be as high as possible. Since most of the organic compounds to be incorporated in the complex are insoluble in water, an auxiliary solvent has been used to achieve the required higher concentration.

Based on the above, it was not expected that solvent vapors could be effectively removed from dilute gas mixtures containing only very poorly soluble water vapors with an aqueous solution.

Surprisingly, it has been found that vapors of water-insoluble organic solvents which are present in a small amount in the inert carrier gas, preferably air, can be removed and recovered if the inert gas, preferably air, contains from 0.01 to 1.0 g / l of solvent vapor. Washed with an aqueous wash containing from 1 to 30% by weight of β-cyclodextrin, dimethyl-β-cyclodextrin or a water-soluble β-cyclodextrin polymer and optionally 0.1 to 2% by weight of a surfactant at a temperature of from 10 to 30 ° C. After washing, the solvent vapor from the hot washer fluid is condensed in a manner known per se and recycled to the wash step after cooling the solvent free from the solvent to 10-30 ° C.

The process of the present invention can remove vapors of aliphatic and aromatic hydrocarbon, halogenated hydrocarbon and alkyl ether solvents from the inert carrier gas.

The inert carrier gas can be any gas that does not react with water or the components of the aqueous wash liquid. Mostly, the inert carrier gas is air, but it can be any other gas that is inert to the washing step.

The active component of the aqueous washing liquid used in the present invention is β-cyclodextrin or a β-cyclodextrin derivative. These derivatives are known per se. For example, dimethyl-β-cyclodextrin is disclosed in Carbohydrate Research, 76, 59-66. (1979) and water soluble cyclodextrin polymerizates are disclosed in U.S. Pat. British Patent Specification No. 4,684,198.

The washing step of the process of the present invention can be carried out in any scrubber using a washing liquid. The essential requirement is that the device be capable of contacting the gas stream to be cleaned over a large area with the washing liquid and that any crystalline precipitation does not impede its operation. The absorbed solvent can be easily recovered from the scrubbing liquid from the scrubber by "boiling". Preferably, the washing liquid leaving the scrubber is fed to a boiling reactor, for example by means of a slurry pump, preferably through a heat exchanger. Here, by heating the liquid phase to 90-100 ° C, the absorbed solvent can be boiled from the wash liquid. The solvent vapors leaving the condensate are condensed in a refrigerator and the solvent-free washing liquid is returned to the scrubber, preferably through a heat exchanger and a condenser. With the above assembly, the purification of the gas stream and the regeneration of the solvent can be made continuous.

The process of the present invention achieves significant solvent savings in the recovery of solvent vapors previously used in solvent-intensive industries (such as the chemical industry, the dry-cleaning industry, the paint industry) and previously removed by air. In addition to its economic benefits, it also has the advantage of reducing pollutant pollution.

Further details of the present invention are illustrated by the following non-limiting examples.

Example 1

A gas purification apparatus is constructed as shown in Figure 1. The gas to be purified, air in this example, is introduced into the scrubber 2 through the pipe 1 at a rate of 500 liters / hour. Its benzene content is 0.26g / liter. The gas washer is a 120 cm high, 10-lattice column in which the grids ensure an even distribution of the introduced gas. The scrubber is filled with 8 liters of an aqueous solution containing 5% by weight of β-cyclodextrin and 0.5% by weight of cetyltrimethylammonium bromide. Cooling water is passed through the cooling pipe coil 15 of the scrubber to ensure that the scrubber charge is not warmed to room temperature. Purified gas leaves the scrubber through the pipe 20. The washing liquid 6 is fed by the slurry pump 6 at a rate of 20 liters / hour via the line 7 to the heat exchanger 8. The upper part of the heat exchanger 8 is designed as a boiler space, where the steam introduced into the tube snake 21 is heated to 90-100 ° C. At this temperature, the cured benzene is removed in the form of steam. The benzene vapor passes through conduit 11 to condenser 12, where it condenses and recovers the recovered benzene in collector 13. From the boiler space, the washing liquid is returned to the scrubber 2 via the heat exchanger 8 through the pipe 9.

The following results were obtained with the apparatus: Benzene content of inlet air: 0.26 g / liter. Purified air benzene content: 0.05 g / liter. Decrease in benzene content: 80%.

Regenerated benzene in 13 collectors: 75 g / h.

Regenerated benzene as a percentage of benzene entering the plant: 57%.

Similar results are obtained when the benzene content of the inlet air ranges from 0.03 to 0.35 g / l, or when the benzene is polychlorinated hydrolyzed with epichlorohydrin instead of the solvent to be removed and β-cyclodextrin instead of toluene, hexane, chloroform, carbon tetrachloride, trichlorethylene, dichloromethane, diisopropyl ether. used.

Example 2

The procedure described in Example 1 was followed except that 20% by weight of dimethyl-h-cyclodextrin solution was used as the washing liquid. The results are shown in the following table. The inert gas is nitrogen.

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solvent name and concentration a reduction in solvent content regenerated solvent in the inlet gas in the exhaust gas isopropyl ether 0.5 g / l 0.05 g / l 90% 65% benzene 0.5 g / l 0.15 g / l 70% 60% carbon tetrachloride 0.5 g / l 0.1 g / l 80% 65% trichlorethylene 0.5 g / l 0.1 g / l 80% 65% dichloromethane 0.5 g / l 0.1 g / l 80% 65%

Example 3

Example 1 was repeated except that 10% water-soluble β-cyclodextrin solution was used as the washing liquid. The inert gas is air, the solvent vapor to be bound is carbon tetrachloride. Intake air flow rate 5001 / h, Intake air carbon tetrachloride content: 0.47 g / liter. Exhaust air carbon tetrachloride content: 0.16 g / liter. Decrease in carbon tetrachloride content: 66%. The amount of recovered carbon tetrachloride in the 13 collectors: 107 g / h (47%).

Claims (4)

A process for removing vapors of water-insoluble organic solvents present in an inert carrier gas, preferably air, in an amount of 0.01 to 1.0 g / l, followed by heating and recovering the organic solvent from the wash liquid by condensing the solvent vapors formed. characterized in that the inert gas containing vapors of ali5 woody and aromatic hydrocarbon, halogenated hydrocarbon or alkyl ether solvents has a temperature of 10 to 30 ° C, 1 to 30% by weight of β-cyclodextrin, dimethyl 2-cyclodextrin or water-soluble β-cyclodextrin, and optionally After washing, the resulting washing liquid is heated to 90-100 ° C after isolation, the solvent vapors leaving the hot washing liquid are condensed in a manner known per se and freed from the solvent. the liquid is recycled to 10-30 ° C and returned to the washing step. 2. The process of claim 1, wherein the washing liquid is 5% by weight of β-cildodextile. 20 rins and an aqueous solution containing 0.5% cetyltrimethylammonium bromide as surfactant. 3. The process of claim 1 wherein the washing fluid is 20% by weight dimethyl-β. An aqueous solution of 25-cyclodextrin was used. 4. The process of claim 1, wherein the washing liquid is an aqueous solution containing 10% by weight of a β-cyclodextrin polymer.