DE2300844C3 - Process for the recovery of 1,2-dichloroethane from a gas stream - Google Patents

Description

The invention relates to the extraction method shown in the preceding claim of dichloroethane from a gas stream.

The invention relates in particular to the isolation of dichloroethane from an oxychlorination gas stream of ethylene according to the following equation:

C ₂ H <+ 2 HCl + V ₂ O ₂ - C ₂ H ₄ Cl ₂ + H ₂ O,

where, for economic reasons, air is used as the source of oxygen.

Because air is usually used in excess and carbon dioxide is also formed by side reactions is, the proportion of dichloroethane and water in the reaction gas is less than 50%. This brings Difficulties in obtaining the dichloroethane with it.

The main part of the dichloroethane is separated from the gas stream by cooling. A considerable one However, the amount remains in the inert gas. It is necessary to remove the residual dichloroethane with the help of a obtain suitable absorbent from the gas stream. Subsequent to the absorption it must Dichloroethane can be recovered from the absorbent by distillation.

The following conditions must be placed on a suitable absorbent:

1. good solubility of dichloroate hand vapors,

2. no reaction with dichloroethane,

3. sufficiently low vapor pressure,

4. the absorbent must not form an azeotropic mixture with dichloroethane,

5. good thermal stability,

6. good corrosion resistance.

Because of its low cost, kerosene is often used as an absorbent in practice. Kerosene however, contain components whose boiling points overlap the boiling range of dichloroethane. About that in addition, the absorption capacity of kerosene for dichloroethane is unsatisfactory.

In DE-OS 17 93 199 are for the same purpose _A |. Em a _Siedebereich_ of 130-190 ⁰ C as an absorbent door ~ DicHIorä "tHäh described kylbenzple_ w ith Such aromatic compounds are, for example, under the protected name Solvessö 150th

expelled.

Surprisingly, it has now been found that the polyalkylene glycol ether is the initially in claim mentioned formula meet the requirements placed on an absorbent and beyond essentially have better absorption capacity for dichloroethane than kerosene or aromatic mixtures. The greater absorption capacity of the liquids according to the invention for dichloroethane offers in practice Operation a number of advantages. The inert gases released into the environment contain a substantial amount less dichloroethane. With the same absorption performance, smaller amounts of the absorbent are used from, which results in a downsizing of the system and cost savings. the In contrast to the liquids of the prior art, liquids according to the invention tend less for cracking, resulting in longer running times of the filter, the circulation evaporator and the absorption column guaranteed.

example 1

Diethylene glycol dimethyl ether
(MoL weight 134, bp 160 ° C)

The absorption capacity for ethylene chloride was determined by means of a faxing test arrangement on diethylene glycol dimethyl ether checked:

A nitrogen stream of 20 l / h. As a result, the gas stream is loaded with approx. 8% by volume of dichloroethane. This gas flow will now passed through a washing tower equipped with a glass frit, the one with the liquid to be tested is filled. The content of the bottle is 100 ml, the filling height is 20 cm. The absorption is at 10 ° C carried out After passing through the washing tower, the gas flow is monitored by means of a gas chromatograph unabsorbed dichloroethane analyzed. The measurements are carried out at 1 hour intervals. In the attached diagram, the percentage absorption of the original dichloroethane is plotted against the Time applied. For comparison, the absorption media currently used in practice are kerosene and Solvessö 150 (see above). The diagram clearly shows that diethylene glycol dimethyl ether has a much better absorption capacity for dichloroethane than those mentioned Comparison substances.

In a subsequent distillation of a mixture of dichloroethane and diethylene glycol dimethyl ether im The ratio of 1: 1 showed that the two substances do not form an azeotrope. The removal of dichloroethane from the absorption medium therefore presents no difficulties.

Example 2

Polyethylene glycol diethyl ether
(Mol.wt. Approx. 200, bp 174 ° C)

Example 3

Methyl tetraethylene glycol tert-butyl ether
(MoL-Gew. 272, Kp 28O ⁰ C)

.Example .4

Polyethylene glycol
(Mol.wt. 400, b.p. over 280 ° C)

23 OO

Example 5

Polyethylene glycol monoether (molar weight approx. 140, bp 203 ⁰ C)

Example 6

Polyethylene glycol monobutyl ether (molar weight approx. 210, bp 265-350 ⁰ C)

Example 7

Triethylene glycol monomethyl ether (MoL weight approx. 164, bp 240-260 ° C)

10

Example 8

Diethylene glycol monobutyl ether
(MoL weight 162, bp 230 ° C)

The absorption capacity of the examples 2 to 8 named substances for Diehloräthan was tested according to Example 1. The results are the to be taken from the attached diagram (curves 2 to 8).

None of the products given in Examples 2 to 8 forms an azeotrope with dichloroethane. That Distilling off the dichloroethane from the compounds mentioned therefore presents no difficulty.

1 sheet of drawings

Claims (1)

Claim: Process for the production of 1,2-dichloroethane from a gas stream by means of absorption in liquid organic compounds and subsequent distillative Separation of the 1,2-dichloroethane from the absorbent, characterized in that that the absorbent is polyalkylene glycol ether the general formula Ri- (OCH ₂ CH ₂ ) ,, - OR »
in the Ri is hydrogen or a straight-chain or branched-chain alkyl radical with 1 to 4 carbon atoms and π is an integer from 2 to 10, used