DE2718391C2 - Process for the production of methyldichlorophosphine - Google Patents

Description

Cl

2CH, - P

- > PCl ₃ + CIP

CH ₃

CH,

CI

CHj-P

CH ₃

CH,

Cl

CI

PCi ₃ + P (CH ₃ I ₃

Forming compounds which preferably deliver solids of a salt-like, largely undefined type, shows that one with conventional means alone, such as. B. Do not prevent distillations or contamination of the apparatus, d. H. thus cannot guarantee their functionality. The resulting disadvantages were already discussed in detail in the patent application P 26 31 608.5 and therefore do not need here to be repeated. They are avoidable if you have to handle the methyldichlorophosphine or mixed with small amounts of a nonionic surfactant. Belong to this class of substances for example ethoxylated unbranched fatty alcohols, higher ethylene oxide polymers as well as ethylene oxide Propylene oxide polymers.

In detail, the invention relates to a process for the production of methyldichloiphosphine by reaction of methane and phosphorus trichloride at temperatures above 500 ° C, which is characterized is that the hot reaction gas leaving the reaction zone is mechanically freed from solids And quenched with liquefied reaction mixture, the 0.3 up to 5% by weight, preferably 0.5 to 3% by weight ( contains a non-organic surfactant dissolved

The method of the invention can further optionally and preferably be characterized in that

a) the reaction zone consists of a preheating zone and a main heating zone and electrically from the outside is heated, on the one hand the exit of the preheating zone with the entrance to the main heating zone and on the other hand the exit of the main heating zone with the entrance to the quenching zone, respectively outside the electrically heated reaction zone, each connected via a solids separation zone are;

b) the hot, solids-free reaction gas in a venturi tube principle working quenching zone quenching;

c) the reaction gas is converted into a gas phase and liquefied reaction mixture by quenching separates, which is mixed with the soluble nonionic surfactant and as a quenching liquid pumped back into the quenching zone via a cooling zone;

d) the gas phase consisting essentially of unreacted methane and hydrogen chloride of adhering vaporous phosphorus trichloride and methyldichlorophosphine by condensation freed with the help of a two-stage cooling at temperatures up to - 55 ° C, whereby one the condensate in the circuit of the liquefied reaction mixture acting as a quenching liquid recirculates, and the gas phase in a washing zone by sprinkling with water and then freed from hydrogen chloride with dilute sodium hydroxide solution, whereupon the remaining purified methane gas, compressed, dried and returned to the reaction zone;

e) one continuously any partial stream of the liquefied reaction mixtures pumped around as a quenching liquid withdraws and from it such an amount of a phosphorus trichloride / methyldichlorophosphine mixture distilled off and, mixed with the soluble nonionic surfactant, in the circuit of the quenching liquid returns as necessary to maintain this cycle; that one as a distillation sump an amount corresponding to the continuous formation of new methyldichlorophosphine The liquefied reaction mixture is drawn off and stored in a thin-film evaporator from the non-volatile Impurities distilled off; and that one of the phosphorus trichloride and methyldichlorophosphine containing distillate wins pure methyldichlorophosphine.

The nonionic surfactant used can be an ethoxylated unbranched fatty alcohol with 6 to 30 C atoms, in particular an ethylene oxide polymer or an ethylene oxide-propylene oxide polymer.

In addition, the process for the preparation of methyldichlorophosphine according to the earlier German patent applications P 26 29 299.9 and P 27 01 389.4 can preferably be carried out in such a way that methane and phosphorus trichloride are used in the presence of 2 to 7 mol% carbon tetrachloride, calculated on phosphorus Irichloi ' id, as a starter in a reaction zone, converting the carbon tetrachloride by up to 80% ^{by varying the reaction temperature between 500 and 650 ° C. with constant dwell times of 0.1 to 0.9 seconds}

The method of the invention is now exemplified with reference to that shown in the drawing Flow sheets explained in more detail:

_{PCl 3} is introduced _{via line 1 and CCl 4} via line 2 in such a proportion that the liquid mixture has a certain CCU content between 2 and 7 mol%. Methane is introduced into the apparatus via line 3 and finally arrives via the line 4 together with the PCls / CCU mixture in the circulation evaporator 5, where the methane is saturated with PCWCCU at a preselectable, elevated temperature

In this way, a gas mixture always flows in a desired, constant _{molar ratio of CH 4} : PCl ₃ : CCl ₄ via line 6 into the electrically heated tubular reactor 7. This consists of a preheating zone and a main heating zone 7a Tb. In the preheating zone 7a, the starting mixture to the reaction temperature is brought (501 to 65O ⁰ C), while it is held in the main heating Tb at a constant reaction temperature. Such a division in two is beneficial for compliance with defined dwell times. The two parts of the reactor 7 are arranged in such a way that the outlet of the pre-heating zone 7a is connected to the inlet of the main heating zone 76 via a first solids separation zone Tc located outside the actual heating space of the reactor 7. The outlet of the main heating zone Tb opens - again outside of the boiler room - into a second solid matter separation zone Td This measure effectively prevents solid matter from entering the downstream liquid cycle

The hot, gaseous reaction mixture then passes from the second solids separation zone Td via line 8 into a quench system 9 designed in the manner of a Venturi tube. The quenching liquid used in the continuous process is liquefied reaction mixture to which a nonionic surfactant soluble in it was added via line 33. The liquefied reaction mixture is withdrawn from the bubble of the quench column 11 via line 12 with the aid of the pump 13 and, after precooling in the heat exchanger 14, is introduced into the quench system 9 in the circuit. liquefied reaction mixture) separately. Both phases pass via line 34 into the quench column 11. The gas phase consists essentially of unconverted methane, which according to the reaction equation

CCI ₄
CH ₄ + - PCI * CH ₁ PCI ₂

HCl

Hydrogen chloride formed and vaporous portions ie: 5 of PCl ₃ and CH ₃ PCl ₂ . Since HCl inhibits the reaction, the methane must be freed from it before it can be recycled.

In order to keep the production losses as low as possible during this process, it is expedient to remove the vaporous proportions of PCl ₃ and CH ₃ PCl ₂ from the gas phase beforehand. This is done in the quench column 11 by the gas phase in the first cooler 11a - is cooled and 1O ⁰ C to + 1O ⁰ C anschlieDend in cooler 116 to -4o ⁰ C to -55 ° C. The condensate obtained in this way is returned via line 15 to the quench column 117iir.

The quench column 11 can pass once through line 10 when the continuous process is started be charged with pure PCI3 as the initial quench liquid.

The phosphorus compounds largely freed gas phase is behind the radiator lib introduced via line i6 from below into the washing column 17th The HCl-containing gases flow through a lower part of the column which is equipped with random packings and which is exposed to water in countercurrent from above via line 18. This removes most of the hydrogen chloride. The methane is finely cleaned in the middle part of the column, which is provided with a bell bottom and is charged with dilute sodium hydroxide solution via line 19 in counter flow from ι ο above. The combined wastewater, which contains NaCl and HCl, leaves the bottom of the washing tub 17 via line 35.

The purified methane leaves the scrubbing column 17 via line 20 and combines with that via line

3 supplied fresh methane. All the methane is compressed by means of pump 21, in which with a Desiccants, e.g. B. silica gel, filled dryer 22 of water to a residual content of at most 25 ppm, preferably only 10 ppm H2O, exempted and on line

4 fed to the circulation evaporator 5. When the continuous process is started, over Line 36 air / nitrogen and methane / nitrogen mixtures are discharged.

The liquefied part of the reaction mixture is on the pressure side of the pump 13 upstream of the cooler 14 taken and fed via line 23 to a: circulation evaporator 24. This circulation evaporator 24 is operated so that the newly formed methyldichlorophosphine in the sump, unreacted PCI3 and all by-products remain, while a mixture of Methyidichlorphosphan and overhead PCI3 is distilled off, condensed in the cooler 25 and by means of pump 26 via line 27 into the quench column 11 is returned. In this way, some of the by-products in the quench circuit 9 to 14 are increased Disruptions would result, already diverted beforehand.

The bottom product of the circulation evaporator 24 reaches a thin-film evaporator via the line 28 29, where it turns into a distillate consisting of a PClj / methyldichlorophosphine mixture, and a Residue is decomposed, which is continuously drawn off via line 32 and discarded. The distillate will Liquefied in the cooler 30 and removed via line 31. It contains 15 to 25% by weight Methyldichlorophosphine 1 to 2% by weight CCU, remainder PCI3. This can be done from this purified precursor desired methyldichlorophosphine in pure form in a manner known per se by distillation or according to the so Process of US-PS 35 19 685 win.

With the process described, methyldichlorophosphine can be produced without problems for any length of time with PCb conversions of 20 to 26%. If, however, the addition of the nonionic surfactant via line 33 is _{omitted, then with PCI 3} conversions of 10 to 15% it is only possible to work trouble-free for a few days and with conversions of 20% for only a few hours.

example 1

Via line 3, first the air is replaced by nitrogen, then the nitrogen by methane, by subsequently discharging a corresponding amount of gas from the gas circuit via line 36 the bubble of the quench column 11 and the associated quench circuit 12, 13, 14, 9 via the Line 10 filled with PCI3 and switched on

eo

65 pump 13 and the heat exchanger 14 put into operation. Meanwhile, the Vorheizzöne 7a is electrically heated gradually to 501 ⁰ C and the main heating zone Tb to 535 ° C, while the condenser 11a is set to -5 ° C, the cooler Wb to -50 ° C.

100 kg / h PCIj 1 are now introduced _{via line 1,} via line 2, 4 kg / h of CCl ₄ and via line 4, 90 NmVh methane into the circulation evaporator 5 at a constant liquid temperature of 40.degree Pressure ratios a molar PCl / methane ratio in the reactor of 1: 4.3. The residence time of the starting mixture in the main heating zone 7b of the pipe reactor 7 was 0.4 seconds. The methane consumed in the reaction (3.3 Nm ³ / h ) is added continuously via line 3. in order to maintain the vaporous effluent from PCU and CH3PCI2 low as possible, the gas phase is cooled in the quenching column 11 to -50 ⁰ C. Only then is the methane in a combined NaOH-water wash 17 of Part of the moisture in the unconverted, recovered methane is removed by compression 21 he dried as 10 ppm water

Simultaneously with the commissioning of the quench circuit, the liquid phase is transferred through the line 33 1.5 kg / h of an ethoxylated, unbranched C15 / C18 fatty alcohol (Moiveratio: 7 CX -Hv groups to 1 OH group) the deposition of solid by-products, especially on the surfaces of the heat exchanger 14 and the Circulation evaporator 24 prevents another part of the by-products that disrupt the process flow removed from the quench circuit by any partial flow of the liquefied via line 23 The reaction mixture is withdrawn and introduced into the circulation evaporator 24, with all non-volatile by-products, which lead to disturbances, remain in the sump, while overhead in the cooler 25 a solids-free " Methyldichlorphosphine / PCh mixture is obtained by means of the pump 26 is returned to the quench circuit via line 27.

After the desired operating values have been achieved in all parts of the device, is from the bottom of the circulation evaporator 24 continuously via line 28 the amount of reaction mixture taken, which corresponds to the formation of methyld'chlorphosphine. Under the reaction conditions mentioned, the conversion of PCI3 to methyldichlorophosphine is 20.2 mole percent.

101.7 kg / h of reaction mixture are passed through line 28 taken from the following composition:

163% by weight methyldichlorophosphine, 2.1% by weight carbon tetrachloride, 1.0% by weight chloroform,
0.2% by weight of phosphorus oxychloride, 1.5% by weight of non-volatile components from the addition of the ethoxylated Cie / Cie fatty alcohol,

0.2% by weight of unknown components, remainder phosphorus trichloride

In the thin film evaporator 29 are 1.5 kg / h non-volatile impurities via line 32 as

Sump removed, while behind the cooler 30 100.2 kg / h of crude product with a content of 17 % By weight of methyldichlorophosphine are incurred.

In this device, the production of methyldichlorophosphine can be operated for any length of time under the stated conditions. The methyldichlorophosphane can be isolated in a conventional manner from the hierbi ¹ · obtained crude product.

Example 2

In the same apparatus and under the same conditions as in Example 1 were IUEF prevent the deposition of solid by-products 1.5 kilograms of a higher äthoxylierteri, unbranched CVCie-Fettalköhols (molar ratio: 80 OC ₂ H ₅ groups to 1 OH group) is used.

Β ·.: Ί a PCb conversion to methyldichlorophosphine of 24 mol%, trouble-free continuous operation could be achieved.

10

15th

20th

Example 3

As in Example 1, 1.4 kg of an ethylene oxide polymer, molecular weight 4,000, were used to prevent the deposition of solid by-products. 2Ϊ

With a conversion of PCb to methyldichlorophosphine of 21 Mof-% a trouble-free continuous operation could be realized.

Example 4

Analogously to Example 1, 1.4 kg of an ethylene oxide-propylene oxide copolymer were added to prevent solid deposits (Molar ratio = 38: 62) used.

With a conversion of PCb to methyldichlorophosphine out of 26 MoM / o no disturbances were observed in continuous operation.

Example 5

In the continuous production of methyldichlorophosphine in the same device And among the The same reaction conditions as in Example 1 were used to supply hj.Ghtionisshem surfactant via the line 33 shut down Already 2 hours after shut down, the heat exchanger 14 and the circulation evaporator were 24 so documented by solid deposits that the performance of this heat exchanger to about 85% of the Normal performance dropped. After 10 hours of operation without adding a nonionic surfactant, the had to Operation can be stopped.

1 sheet of drawings

Claims (6)

Claims: methyldichlorophosphine-containing distillate pure methyldichlorophosphine wins 30 35 1. Process for the production of methyldichlorophosphine by reacting methane and Phosphorus trichloride at temperatures above 500 ° C, characterized in that im an the hot reaction gas leaving the reaction zone is mechanically freed from solids and with liquefied reaction mixture quenched 0.3 to 5% by weight, preferably 0.5 to 3% by weight, contains a nonionic surfactant dissolved 2. The method according to claim 1, characterized in that the reaction _{zone consists of a preheating i D} zone and a main heating zone and is electrically heated from the outside, on the one hand the output of the preheating zone with the input to the main heating zone and on the other hand the output of the main heating zone with the input are connected to the quenching zone, each outside the electrically heated reaction zone, via a solids separation zone. 3. The method according to claim 1 or 2, characterized in that the hot, solids The released reaction gas is quenched in a quenching zone that works on the principle of the Venturi tube 4. The method according to any one of the preceding claims, characterized in that ₀ is emic separating the reaction by quenching in a gas phase and liquefied Reaktioni "which is added with the soluble nonionic surfactant and as Abschreckf! ^R -ssigkeit circulated via a cooling zone again pumped back into the quenching zone 5. The method according to claim 4, characterized in that one consists essentially of Cl - P unreacted methane and hydrogen chloride existing gas phase of adhering vapor Phosphorus trichloride and methyldichlorophosphine by condensing out with the help of a two-stage cooling at temperatures down to - 55 ° C freed with the condensate in the Recirculation of the liquefied reaction mixture functioning as a quenching liquid, and the gas phase in a washing zone by sprinkling with water and then with diluted Sodium hydroxide solution freed from hydrogen chloride, whereupon the remaining purified methane gas compressed, dried and returned to the reaction zone. 6. The method according to any one of claims 4 or 5, characterized in that any partial stream of the liquefied reaction mixture pumped around in the circuit as a quenching liquid is continuously withdrawn and such an amount of a phosphorus trichloride / methyldichlorophosphine mixture is distilled off and mixed with the soluble nonionic surfactant in recycle the quench fluid as necessary to maintain that cycle; that an amount of liquefied reaction mixture corresponding to the continuous formation of new methyldichlorophosphine is withdrawn as the distillation bottom and the non-volatile impurities are distilled off in a thin-film evaporator; and that one from the phosphorus trichloride and The older German patent application P? fi 31 6083 already describes a process for the preparation of methyldichlorophosphine by reacting methane with phosphorus trichloride at temperatures above 500 ⁰ C ₁ which is characterized in that the hot reaction gas leaving the reaction zone from Solids are mechanically freed and quenched in a quenching zone with a liquefied reaction mixture which contains 03 to 3% by weight of an organic barium compound dissolved as a stabilizer It has now been found that soiling of important parts of the apparatus, such as. B. the heat exchanger, not only by adding ionic surfactants of the soluble barium phenolate sulfonate mixture type, but can also be effectively prevented by using nonionic surfactants. The fact that both pure methyldichlorophosphine and freshly distilled methyldichlorophosphine-phosphorus trichloride mixtures already in the vicinity of these boiling points, i.e. in the range above 70 ° C after Reaction scheme: