HU185023B - Process for producing alkyl-thiol-esters of chloro-formic acid from gas mixtures containing phosgene and/or alkyl-mercaptanes - Google Patents

Abstract

The present invention relates to a process for recovering phosgene and / or alkyl mercaptan from a gas mixture containing phosgene and / or C 1 -C 8 alkyl mercaptan and to preparing alkyl thiol esters of chloroacetic acid in such a way that the gas mixture is filled in one or two steps in a circulating column reactor at -20 ° C and At a temperature of +70 ° C, the pressure is absorbed by a liquid chloroformate alkylthiol ester at a pressure of 0.8 to 15 [deg.] C. in a current or counter current, and the solution containing phosgene and / or alkyl mercaptan is used in a circulating reactor to produce the alkyl thiol ester of chloroacetic acid. -1-

Description

The present invention relates to the recovery and use of phosgene and / or alkylmercaptan in gas mixtures.

In the last decade, thio-carbamate-type herbicides have been widely used in chemical pesticides, the reaction of which is carried out by reaction of secondary amines with alkylthiol esters of chloropotassium acid.

The alkyl thiol esters of chloroformate are therefore of particular importance and the processes for their preparation are the subject of several patents.

These processes are essentially S-acylation reactions using phosgene, which produces by-product hydrogen chloride gas, which almost always contains unreacted phosgene and alkyl mercaptan, as well as inert gases (nitrogen, carbon monoxide, chlorine).

A process for the preparation of alkyl thiol esters of chloroformic acid is disclosed in U.S. Patent Nos. 3,093,537 and 3,165,544 by reaction of alkyl mercaptan with phosgene in the presence of an activated carbon catalyst. The reaction is carried out with a significant excess of phosgene, sometimes in excess of 20%, but the yield of alkyl · mercaptan is only 70-75% and the crude thiol ester content is about 90% with a significant amount of disulphide impurities, which is distilled before further use. needs cleaning.

According to DOS No. 2,652,959, the disulfide content can be reduced and the alkyl mercaptan conversion rate improved by the reaction of phosgene and alkyl mercaptan in two series-connected tank reactors using an activated carbon catalyst in a liquid phase, when the phosgene dissolved in alkyl mercaptan is introduced into the first reactor and the reaction mixture leaving the reactor leaving the reactor at a temperature between 0-50 ° C and the reactor leaving the reactor at 50-65 ° C is cooled to 18-25 ° C. is introduced into a second tank reactor, from which the crude reaction mixture leaving after 50-90 minutes is fed to a heated column, and the crude chloroformate alkyl thiol ester is purified by distillation to give the chloroformate alkyl thiol ester containing up to 2% of disulfide impurities alkyl-mer also has a conversion rate of about 90%. However, this process also uses a significant excess of phosgene (1.62 moles of phosgene per mole of alkyl mercaptan in the two steps).

Similarly, DOS process 2,721,683 aims to improve the conversion of alkyl mercaptan by using two reactors to which a gas separation column is coupled, whereby an inert gas (primarily nintrogen gas) is blown out of the crude reaction mixture and is recycled to the first reactor into which alkyl mercaptan is fed directly to the activated carbon catalyst in a direct current stream, whereby alkyl mercaptan is in excess.

From the first reactor, the reaction mixture containing the alkyl thioester of chloroformate and alkyl mercaptan is fed to the second reactor, and the same feed is added in excess of phosgene to unreacted alkyl mercaptan.

From the system, gases (hydrogen chloride gas, inert gas) leave the system at the top of the first reactor. There is no doubt that the phosgene content of the effluent mixture is lower than that of the other processes, but that the content of silicone mercaptan is increased precisely because alkyl mercaptan is used in excess in the first reactor.

Thus, the recovery and reuse of phosgene and / or alkylmercaptans from tail gas in processes for the preparation of chloroformate alkyl thiol esters is both important and desirable both from the point of view of economics of the processes and from the environmental point of view.

In our research, we have found that phosgene is surprisingly well soluble in chloroformic acid alkyl thiol esters. It has been found that the saturation concentration of phosgene at 26 ° C in various alkyl thiol esters of chloroformate is as follows:

chloroformic acid alkyl thiolester phosgene saturation concentration,% ethyl chloroformate thiolester 46.5 chloroformate propyl thiolester 38.3 chloroformate octyl thiolester 25.2

Our research results confirmed that phosgene can be absorbed from the gas mixture of carbon monoxide, nitrogen, chlorine gas and hydrochloric acid from different composition gases and the resulting solution can be recycled to the thiol ester reactor. However, alkyl mercaptans can also be recovered with alkyl thiol esters and similarly returned to the thiol ester-forming reactor.

Based on these findings, the present invention relates, on the one hand, to the extraction of phosgene from phosgene-containing gases in an appropriate apparatus by absorption with chlorothionic acid alkylthiolester and, on the other hand, to the use of the phosgene solution thus formed for the preparation of chloroformic acid alkylthiolesters.

The invention also relates to the recovery and use of mercaptan from mercaptan-containing gases by the method described above.

In other words, the present invention relates to a process for the preparation of an alkyl thiol ester of chloroformate which, in a suitable apparatus, enables the recovery and use of phosgene and / or mercaptan from gaseous phosgene and / or mercaptan for the preparation of alkyl thiol esters of chloroformate.

The process according to the invention is preferably carried out on the equipment shown in Figure 1.

To the thiol ester-forming reactor 1, which is known to be filled with activated carbon catalyst, the phosgene-containing gas mixture is introduced via line 2 and the

Pipeline 3 recovers alkyl mercaptan, Pipes 5 and 6 recycle crude reaction product, and Pipes 18 and 6 recycle phosgene and / or mercaptan absorbed into the chloroformate alkyl ester.

A mixture of gaseous hydrochloric acid, phosgene and alkyl mercaptan leaving the thiolester reactor 1 through line 13, together with the gas mixture leaving line 8 through the charge separator 8, and line 15 with gas from other locations in the system. .wire using all. is transferred to an absorption column.

It exits from the ester-forming reactor 1 via line 4

The main mass of the reaction mixture is passed through line 7 to the separator system 8, from which, after separation, the liquid chlorothionic acid alkylthiol ester a9. leaving the line. The main weight of this is recovered from the system via line 12, while the required amount is recovered through line 10. is added to an absorption column in which the phosgene and / or alkyl mercaptan in the gas mixture is absorbed, and the resulting solution is returned to the ester-forming reactor 1 via lines 18 and 6.

Divide the chloroformic acid alkylthiol ester leaving the separator 8 through line 9 into the product taken from the system and line 10 all the way down. depends on the carbon number of the chloroformate alkyl thiol ester produced and depends on the phosgene and / or alkyl mercaptan content of the gas mixture.

All. In the absorption column, a temperature range of -20 +70 C and a pressure range of 0.8 to 15 att can be used for the recovery mode. It is advantageous to operate the column between wetting and total flooding.

From column 11, the phosgene and / or alkyl mercaptan-depleted pure hydrochloric acid gas (which may also contain an inert gas) exits line 17 and can be absorbed with water, using appropriate equipment, to prepare a technical solution of hydrochloric acid.

As stated above, our process is extremely economical because phosgene and / or alkylmercaptan is recovered from the gas mixture by recycle to the chloroformic acid alkylthiol ester reactor, while hydrochloric acid gas can be prepared for industrial use.

It also means that our process eliminates pollutants from the production system.

The process of the present invention is illustrated by the following examples, which are not limited to the claims. In the examples, the continuous apparatus shown in Figure 1 was used, with the amounts of material entering and exiting each device in the quantities added and withdrawn per hour.

Example 1

53 kg of ethyl mercaptan and 27.5 Nm ^{3 of} phosgene gas containing 20% by volume of carbon monoxide are fed into the activated carbon packed reactor 1 via line ³ .

The crude reaction mixture leaving the ester-forming reactor 1 via line 4 is fed back to the top of the reactor via piping 5 and 6 with 150 kg of crude reaction mixture. From reactor 1, conduit 13 to gas 25.5 Nm ³ containing 20% by volume of carbon monoxide, hydrochloric acid, 3 kg of ethyl mercaptan, 10 kg of phosgene and 20 kg of ethyl thiol ester of chloroformate to the absorption tower 11 led by line 16.

All. 60 ° C and 10 att pressure in the absorption tower.

270 kg of the crude product leaving Reactor 1 is fed through line 7 to the desorber system 8 where 20 kg of phosgene and 2 kg of ethyl mercaptan are separated and also fed through lines 14 and 16. into the absorption column.

124 kg of the chloroformate ethyl thiol ester leaving the desorber separator system 9 through line 9 are removed from line 12 as a finished product and from line 10 150 kg at the top of the absorption column 11. column, in which phosgene and ethyl mercaptan are absorbed from the gases, and the resulting solution of 179 kg of ethyl thiol ester of chloroformate is recycled through lines 18 and 6 to the ester-forming reactor 1.

Yield: 96.5% for ethyl mercaptan and 95% for phosgene Yield: 124 kg ethyl ethyl thiol ester of chloroformate.

Example 2

The procedure described in Example 1 was followed except that 67 kg of n-propyl mercaptan was added to line 3 into the ester-forming reactor 1 and 135 kg of 97% active n-propyl thiolester of chloroformate in the system. we take it. In the absorption tower 11, a temperature of 30 ° C and a pressure of 5 att are used.

Yield: 97% for n-propyl mercaptan and 94% for phosgene Yield: 135 kg of n-propyl thiolester of formic acid.

Example 3

The procedure is the same as in Example 1 except that 150 kg of n-octyl mercaptan is added to the ester-forming reactor 1 via line 3 and 208 kg of chloroformic acid octyl ester is removed from the system via line 12. The temperature in the 11th absorption tower is -20 ° C and the pressure is 0.8 att.

Yield: 97% for n-octyl mercaptan and 95% for phosgene

Yield: 208 kg of octyl thiol ester of chloroformate.

Example 4

The same procedure as in Example 1 was followed, except that 27.5 Nm ^{3 of} phosgene gas, containing 20% CO, was added via line 2 and line 15. In the 11th absorption tower the temperature is 20 -25 ° C and the pressure is 1 att.

The yield is the same as in Example 1.

Example 5

The same procedure as in Example 1 was followed except that line 15 was fed with 27.5 Nm ^{3 of} 10% carbon monoxide and 20% nitrogen, supplemented with 2.75 Nm ^{3 of} pure phosgene gas added at 2 .

The yield is the same as in Example 1.

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Example 6

The same procedure as in Example 1 is followed except that line 13 is closed and the reaction mixture leaving reactor 1 on lines 4 and 7 is fed to a desorber filled with activated carbon 8. The inert gas in the reaction mixture facilitates the removal of phosgene and mercaptan from the crude chloroformate ethyl thiol ester. At position 12, ethyl ethyl thiol ester of chloroformate was obtained in 99% purity.

I

Yield: 97.0% for ethyl mercaptan and 96% for phosgene. /

Example 7

The procedure described in Example 1 was followed with the exception that 55 kg of ethyl mercaptan was added at the 3 rd place, and at 15 the place was supplemented with a 5 Nm ³ gas mixture containing 3 kg of ethyl mercaptan (ethyl mercaptan, H ₂ S). with ethylene, diethyl sulfide, nitrogen).

The yield is the same as in Example 1.

Example 8

Example 1 was performed with the difference that the 27.5 Nm ³ phosgene-containing gas added to reactor 1 contained 20% CO and 0.1% chlorine.

Example 9

A 20.4 Nm ³ gas mixture from reactor 1 and desorber system 8 in the scheme of Figure 1, containing 3 kg of ethyl mercaptan and 10 kg of phosgene in addition to hydrochloric acid gas, is introduced into absorption tower 11, from which it is counter-current -5. Phosgene and mercaptan were recovered at 150C by adding 150 kg of CO 2 and returned to reactor 1 supplemented with 22 Nm ^{3 of} phosgene and 53 kg of ethyl mercaptan per hour.

The reactor was pressurized to 0.5 att.

The reaction mixture leaving at 50-60 ° C is desulfurized with phosgene and mercaptan on the 8th desorber system.

Of this, 124 kg is withdrawn per hour as a finished product and 150 kg is discharged. is added to an absorption tower. Yield: 124 kg TWO

Yield: 95.6% for ethyl mercaptan and 95% for phosgene.

Example 10

Example 9 except that 10 Nm ^{3 of} nitrogen was introduced into the desorber system 8, so that 30.4 Nm ^{3 of} gas mixture entering the 11 absorption tower, in addition to hydrochloric acid, contained 10 kg of phosgene, 3 kg of ethyl mercaptan and 10 Nm Also contains ³ N ₂ .

Claims (5)

A process for recovering phosgene and / or alkyl mercaptan from gas mixtures containing phosgene and / or C 1-8 alkyl 2q mercaptan, characterized in that the gases containing phosgene and / or alkyl mercaptan are prepared in one or two steps. in a packed circulation column reactor at either -20 ° C and 25 ° C + 70 ° C, with a liquid chloroformic acid alkylthiol ester, at a pressure of 0.8-15 att, in countercurrent or countercurrent reaction with the absorbed phosgene and alkyl mercaptan. 2. A process according to claim 1, wherein the phosgene and / or ethyl mercaptan is absorbed from the gases with ethyl thiolester of formic acid. 3. A process according to claim 1 wherein the gases are phosgene 35 and / or propyl mercaptan is absorbed with chloroformic acid propyl thiolester. 4. The process of claim 1 wherein the gaseous phosgene and / or octyl mercaptan is absorbed with chloroformate octyl thiol ester. 5. Process according to claims 1 to 3, characterized in that the gases contain carbon monoxide and / or nitrogen and / or chlorine gas and / or hydrochloric acid.