DE2740585A1 - Di:fluoro-chloroethane continuous prodn. - by photochlorination of di:fluoroethane in liquid phase, minimising by=product formation - Google Patents

Abstract

In the continuous prodn. of 1,1-difluoro-1-chloroethane (I) from 1, 1-difluoroethane (II) and Cl2 in the liquid phase by the action of high energy light, a (II) content of is not 10 wt.% is maintained in the liquid phase by addn. of (II). The content of (I) in the liq. phase is maintained at 40-80 wt.%. Chlorination is carried out at 0.5-5 bar and -30 degrees C to +50 degrees C. The liq. phase contains 1 wt.% F2ClC-CHCl2 and F2ClC-CH2Cl. The liq. phase is discharged continuously from the photoreactor and distilled fractionally, the fraction, i.e. mixt. of (I) and (II), with a b.pt. -25 degrees C at normal pressure, being recycled to the photoreactor. The formation of by-prods. and esp. of HF is minimised.

Description

The present application relates to continuous manufacturing

of 1,1-difluoro-1 1,1-difluoro-1-chloroethane by photochlorination of 1.1 The fluoroethane in the liquid phase. The starting product for this process - 1,1-Difluoroethane - is accessible from vinyl chloride or acetylene as well as hydrofluoric acid.

The representation of 1,1-difluoro-1-chloroethane by radical photochlorination in the liquid phase according to the scheme: F2HC-CH3 + Cl2 -> ClF2C-CH3 + HCl is on known (DT-PS 100 2303). In doing so, however, the by-products almost always occur F2ClC-CH2Cl, F2ClC-CHCl2 and F2ClC-CCl3. Both with continuous and if the process is carried out discontinuously, the proportion of these is highly chlorinated By-products relatively high (approx. 5 - 10 t). This is especially true when high Sales are targeted.

"Highly chlorinated by-products" here generally include compounds to understand the ethane series, which have more than one chlorine atom in the molecule. In addition In addition to the three compounds listed above, this also includes those compounds in where one or two fluorine atoms of 1,1-difluoro-1-chloroethane are replaced by chlorine such as Cl2FC-CH3 and C13C-CH3.

If there are such low-fluorine compounds in the photochlorination reactor have formed, it means the simultaneous emergence of a corresponding one Amount of hydrofluoric acid in the liquid phase. This will extend the life of the photochloric drug lamp greatly shortened.

The above-mentioned higher chlorinated fluorine-containing by-products will be generally separated off by distillation, but are practically worthless.

The object was therefore to provide a process for the production of 1,1-Difluoro-1-chloroethane develop in which only small amounts of by-products in particular, only very small amounts of hydrofluoric acid are obtained.

There has now been a process for the continuous production of l, l-difluoro-l-chloroethane from 1,1-difluoroethane and chlorine through the action of high-energy light in liquid Phase found, which is characterized in that by adding 1,1-difluoroethane a content of at least 10% by weight 1,1-difluoroethane in the liquid phase holds. Content determinations can easily be carried out by gas chromatography.

The concentration of 1,1-difluoro-1-chloroethane in the liquid phase should preferably be 40 to 80, in particular 45 to 55%.

The process works best at temperatures from -30 ° C to +50 C and pressures between 0.5 and 5 bar.

For better discharge of impurities, it is advisable to in the stationary phase of the photochlorination reactor a low, approximately constant Maintain proportion of by-products of the formula F2ClC-CH2Cl and F2ClC-CHC12. This can easily be done by stripping off the stationary phase, distillation and recycling the lower chlorinated proportions. The content of the said higher chlorinated By-products should be a maximum of 1%. Contents of 0.01 are preferred up to 0.05%. Of course, lower contents are also possible, but must then too large amounts of the stationary phase are continuously distilled and recycled will. At a stationary concentration of 55% l, l-difluoro-l-chloroethane becomes obtained a yield of 98 to 99.5% of this product.

A particularly favorable device for carrying out the process is described below with reference to the figure.

Description of the apparatus About a filter (1) covered with aluminum oxide is filled, chlorine is fed through line (2) into the central part of a photoreactor (3) Introduced in gaseous form. The photoreactor is about 2/3 at the beginning of the reaction filled with liquid 1,1-difluoroethane and contains a UV lamp (5).

By feeding the chlorine into the middle part of the reactor the aim is to ensure that most of the chlorine is rapidly in the range of the UV lamp (5) reacts and only a little chlorine reaches the lower part of the reactor. That brought in Chlorine creates sufficient turbulence in the upper to middle part of the reactor. An additional stirring is therefore unnecessary.

The 1,1-difluoroethane added during the reaction works best metered into the reactor in liquid form. This is done via line (6), the possibly also contain a filter (7).

At least a partial stream of 1,1-difluoroethane should be below the inlet point for chlorine must be entered so that it reaches the lower part of the reactor Chlorine is captured. In this way, other parts of the apparatus (for example on a bottom of the fractionating column, which is mainly liquid l, l-difluoro-l-chloroethane contains) another reaction with chlorine to form more highly chlorinated impurities effectively prevented.

In principle, chlorine and difluoroethane must be introduced in equimolar amounts will. In the starting phase, however, difluoroethane is only specified; then in introduced chlorine into the reactor until the desired ratio of difluoroethane / difluorochloroethane is set in the reactor. Then chlorine and difluoroethane in equimolar Quantities continued to be metered in. After reaching the steady operating state flows the liquid content (4) of the reactor (3) via a throttle valve (8) into the evaporation vessel (9). Here, the reaction mixture is excepted by a heater (not shown) non-volatile impurities (e.g. ferric chloride and polymer components) evaporates. These can be discharged through valve (10). The vaporized reaction mixture passes through line (21) into the bubble (11), which is below the fractionating column (12) is attached. The supply line (21) consists partially of quartz glass to the presence to be able to better monitor chlorine. Kick, for example If there are still chlorine residues, a lamp on this supply line can be used the radical formation of 1,1-difluoro-1-chloroethane with consumption of the chlorine restarted.

The bladder (11) does not require any heating, as the material to be distilled is in it passes in gaseous form from (9). In this bubble, however, the more chlorinated ones collect Impurities. They can be drained via a valve (not shown). Liquid contents of the bladder must not escape from (11) into the evaporator (9). In the cooled fractionation column (12), the reaction mixture is the desired 1,1-difluoro-1-chloroethane is withdrawn via line (13) and valve (23). The unreacted starting substance (Difluoroethane) arrives in gaseous form via the top (14) of the column via line (15) into a descending cooler (16). 1,1-Difluoroethane condenses in this cooler and runs in liquid form into the reactor (3) below. To the extent that in the difluorochloroethane formed is drawn off from the column (12) via line (13) is, the corresponding proportion of difluoroethane is reintroduced into the reactor (3). This stationary equilibrium can easily be established.

* separated.

It can be advantageous to use lines (17) and (18) in the Valves (19) and (20) are installed, also pure starting product (via line 17) or a mixture of starting product with 1,1-difluoro-1-chloroethane (via line 18) to be returned to the reactor in liquid form. Line (18) is advantageous connected to that bottom of the fractionating column (I, the liquid phase of which has a ratio Having difluoroethane / difluorochloroethane, which has about the composition desired for (4) is equivalent to. In this way you can create the desired one with little expenditure of energy Maintain the proportion of the starting product in the liquid phase of the photoreactor (3).

The hydrogen chloride released during the reaction is via a Cooler (22), which retains entrained and volatile components, derived. The hydrogen chloride can then be worked up to commercial hydrochloric acid will.

The temperatures at which the photochlorination is carried out judge according to the pressure under which the procedure is carried out.

In general, one will be between the boiling points of difluoroethane and chlorine work. At normal pressure, the temperature in the reaction vessel must be approximately between -220 C and -34 ° C. The return flow cooler (22) through which the chlorine water escapes, must be operated at temperatures of -34 to -50 "C in order to effectively hold back chlorine to be able to.

The method according to the invention is illustrated by the examples below explained in more detail: Example 1 In the apparatus described (reactor volume approx. 1.5 1) approx. 13.5 mol of 1,1-difluoroethane were poured in and then slowly Initiated chlorine (total 11.9 mol). During the introduction of chlorine were 10.5 mol of 1,1-difluoroethane were gradually added. The valves 19, 20 and 23 remain closed during the attempt.

The temperature of the liquid phase was set to -25 "C at the beginning and later rose to -19 to -220 C. The temperatures measured in the gas space were initially at -25 ° C and later at -21 ° C. The reflux condenser for the hydrogen chloride (22) was kept at -440C. A lab immersion lamp served as the radiation source (5) with cooling tube (UV quartz lamp TQ 150 from Quarzlampen GmbH, Hanau). During the For chlorination, the rate of addition of the reactants was 1.5 to 1.6 mol / h. The experiment was terminated after 8 hours. The liquid phase of the reaction vessel contained 11.1 moles of difluorochloroethane and 11.3 moles of unreacted difluoroethane. The proportion of highly chlorinated components was below 0.1%.

Example 2 Example 1 was repeated, except that the amount of chlorine was increased to 19.6 moles. The duration of the experiment was 10.5 hours.

18.8 mol of difluorochloroethane and 3 mol of unreacted were obtained Difluoroethane. The proportion of highly chlorinated compounds was approx. 0.1%.

Comparative Example Example 1 was repeated, except that the amount of chlorine was increased to a total of 24.8 moles. The experiment was terminated after 15.5 hours. The product withdrawn from the reactor (3) had the following composition: 68.3 % Difluorochloroethane (corresponding to 15.3 mol), 27.2% highly chlorinated components and approx.

4.5% unreacted starting product. The highly chlorinated compounds consisted of about 66 t of ClF2CCH2Cl, ClF2C-CHCl2 and ClF2C-CCl3. So much for the rest was identifiable, it consisted of compounds with a maximum of 1 fluorine atom in the Molecule contained.

Claims (6)

Process for the production of 1,1-difltior-1-chloroethane PATENT CLAIMS: '1.7 Process for the continuous production of 1,1-difluoro-1-chloroethane from 1,1-Difluoroethane and chlorine due to the action of high-energy light in liquid Phase, characterized by d = e, that by adding 1,1-difluoroethane in the liquid phase a content of at least 10 wt. of this compound upright holds. 2. The method according to claim 1, characterized in that in the liquid phase has a content of 40-80% by weight of 1,1-difluoro-1-chloroethane holds. 3. The method according to claim 1, characterized in that the Performs chlorination in a range from 0.5 to 5 bar and -30 ° C to +50 C. 4. The method according to claim 1, characterized in that in the content of the compounds of the formula F2ClC-CHCi2 and F2ClC-CH2Cl in the liquid phase holds less than 1 wt .-%. 5. The method according to claim 1, characterized in that the the liquid phase is continuously withdrawn from the photoreactor and fractionally distilled, where proportions with a boiling point (at normal pressure) of below -250 C in the Photoreactor are returned. 6. The method according to claim 5, characterized in that a liquid Recirculated mixture of 1,1-difluoroethane and 1,1-difluoro-1-chloroethane in the photoreactor will.