DE2718391B1 - Process for the production of methyldichlorophosphine - Google Patents

Description

The method of the invention can furthermore be optional and preferred be characterized in that a) the reaction zone from a There is a preheating zone and a main heating zone and is electrically heated from the outside, whereby on the one hand the exit of the preheating zone with the entrance to the main heating zone as well 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 via a solids separation zone are connected; b) the hot, solids-free reaction gas in a quenching zone working on the principle of the Venturi tube; c) man the reaction gas by quenching into a gas phase and liquefied reaction mixture 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) man which consists essentially of unreacted methane and hydrogen chloride Gas phase of adhering vaporous phosphorus trichloride and methyldichlorophosphine by condensing out with the help of two-stage cooling at temperatures up to to - 55 "C, whereby the condensate is released into the circuit as a quenching liquid acting liquefied reaction mixture recirculates, and the gas phase in a washing zone by sprinkling with water and then with dilute sodium hydroxide solution freed from hydrogen chloride, whereupon the remaining purified methane gas compressed, dried and returned to the reaction zone; e) one continuously any partial flow of the circulated as a quenching liquid liquefied reaction mixture is withdrawn and from it such an amount of a phosphorus trichloride / methyldichlorophosphine mixture distilled off and, mixed with the soluble nonionic surfactant, in the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, as to maintain this cycle is required; that one of the continuous new formation as the distillation bottoms of methyldichlorophosphine deducts the corresponding amount of liquefied reaction mixture and distilled off from the non-volatile impurities in a thin film evaporator; and that from the distillate containing phosphorus trichloride and methyldichlorophosphine pure methyldichlorophosphine wins.

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

In addition, the process for the preparation of methyldichlorophosphine preferred according to the old German patent applications P 26 29 299.9 and P 27 01 389.4 be carried out in such a way that methane and phosphorus trichloride are used in the presence of 2 up to 7 mol% carbon tetrachloride, calculated on phosphorus trichloride, as a starter reacted in a reaction zone, with constant residence times of 0.1 to 0.9 seconds by varying the reaction temperature between 500 and 650 "C den 50 to 80 * carbon tetrachloride converts.

The method of the invention is now exemplified using the in The flow chart shown in the drawing is explained in more detail: Line 1 becomes PCl3 and introduced via line 2 CCI4 in such a proportion that the liquid mixture has a certain CCI4 content between 2 and 7 mol%. Via conduction 3 methane is introduced into the apparatus and finally arrives via the pipe 4 together with the PC13 / CCL mixture in the circulation evaporator 5, where saturation of methane with PCWCCb takes place at a preselectable, elevated temperature In this way, a gas mixture always flows in a desired, constant molar ratio from CH4 PCl3: CCl4 via line 6 into the electrically heated tubular reactor 7. This consists of a preheating zone 7a and a main heating zone 7b. In the preheating zone 7a, the starting mixture is brought to the reaction temperature (501 to 650 "C) while it is kept at a constant reaction temperature in the main heating zone 7b. One Such a division into two is beneficial for compliance with defined residence times. The two parts of the tubular reactor 7 are arranged so that the exit of the preheating zone 7a with the entrance of the main heating zone 7b via an outside of the actual boiler room of the reactor 7 located first solids separation zone 7c is connected. The exit the main heating zone 7b opens - again outside the boiler room - into a second one Solids separation zone 7d This measure prevents the penetration of solids effectively prevented in the subsequent fluid cycle.

The hot, gaseous reaction mixture then escapes from the second Solids separation zone 7d via line 8 into a venturi tube Quench system 9. The quench liquid used in the continuous process liquefied reaction mixture, to which a nonionic soluble therein via line 33 Surfactant was added. The liquefied reaction mixture is released from the bladder Quench column 11 withdrawn via line 12 with the aid of pump 13 and after precooling introduced into the quench system 9 in the circuit in the heat exchanger 14. In the quench system 9 the hot, gaseous reaction mixture is quenched and converted into a gas phase and a liquid phase (liquefied reaction mixture) separated.

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 Hydrogen chloride formed and vaporous components of PCl3 and CH3PC12. Since HCl inhibits the reaction, the methane must be freed from it before it can be recycled.

In order to minimize the production losses during this process it is advisable to keep the vaporous components of PC13 and CH3PC12 beforehand to get out of the gas phase. This is done in the quench column 11 by the Gas phase first in the cooler 11a to -10 "C to + 10" C and then in the cooler t 1 b is cooled to -40 "C to -55" C. The condensate thus obtained is over Line 15 returned to the quench column 11.

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

The gas phase, largely freed from phosphorus compounds, is left behind the cooler 11b is introduced into the scrubbing column 17 from below via the line 16. The gases containing HCI flow through a lower one equipped with packing elements Part of the column exposed to water in countercurrent from above via line IS This removes most of the hydrogen chloride. The fine cleaning the methane takes place in the middle part of the column, which is provided with bubble-cap trays and charged in countercurrent from above via line 19 with dilute sodium hydroxide solution will. The combined wastewater, which contains NaCl and HCI, leaves the ground the washing column 17 via line 35.

The purified methane leaves the scrubbing column 17 via line 20 and combines with the fresh methane fed in via line 3. The entire Methane is compressed by means of pump 21, in which with a desiccant, e.g. B. Silica gel, filled dryer 22 of water to a residual content of at most 25 ppm, preferably only 10 ppm H2O, freed and via line 4 to the circulation evaporator 5 supplied When the continuous process is started, via line 36 air / nitrogen and methane / nitrogen mixtures are discharged.

The liquefied part of the reaction mixture is on the pressure side taken from the pump 13 upstream of the cooler 14 and via line 23 to a circulation evaporator 24 supplied. This circulation evaporator 24 is operated so that each in the sump newly formed methyldichlorophosphine, unreacted PCI3 and all by-products remain, while a mixture of methyldichlorophosphine and PCI3 is distilled off overhead, 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 that are in the quench circuit 9 to 14 would lead to malfunctions, already diverted beforehand.

The bottom product of the circulation evaporator 24 passes through the line 25 in a thin film evaporator 29, where it is converted into a distillate consisting of a PCI3 / methyldichlorophosphine mixture, and a residue is decomposed, which is via line 32 is continuously withdrawn and discarded. The distillate is in the cooler 30 liquefied and removed via line 31. It contains 15 to 25% by weight methyldichlorophosphine 1 to 2% by weight COLI, remainder PCI3. From this purified intermediate can the desired methyldichlorophosphine in pure form in a manner known per se by distillation or win according to the method of US Pat. No. 35 19685.

With the described procedure, with PCI3 sales of 20 Up to 26% methyldichlorophosphine trouble-free for any length of time produce. However, the addition of the nonionic surfactant via line is omitted 33, you can only have a few days with PCI3 sales of 10 to 15% and with sales of 20% only work a few hours without problems.

Example 1 Via line 3, first of all, the air is replaced by nitrogen, then the nitrogen is replaced by methane by leaving the gas cycle via pipe 36 a corresponding amount of gas is discharged. The quench column then becomes the bubble 11 and the associated quench circuit 12, 13, 14, 9 via line 10 with PCI3 filled and by switching on the Pump 13 and the heat exchanger 14 in operation taken. Meanwhile, the preheating zone 7a gradually becomes 501 "C and the main heating zone 7b is electrically heated to 535 "C, while the cooler 118 is heated to -5" C, the cooler 11b can be set to -500C.

100 kg / h of PClk are now transferred via line 1 to 4 kg / h via line 2 CCl4 and via line 4 90 Nm3 / h methane in the circulation evaporator 5 at a constant liquid temperature of 40 "C. That results in consideration the apparatus pressure conditions a molar PCI3 / methane ratio in the reactor from 1: 4.3. The residence time of the starting mixture in the main heating zone 7b of the tubular reactor 7 was 0.4 sec. The methane consumed in the reaction (3.3 Nm3 / h) is continuous added via line 3 to the gaseous discharge of PCI3 and CH3PCl2 if possible To keep it low, the gas phase in the quench column 11 is cooled down to -50 ° C Only then is the methane freed of HCI in a combined NaOH-water scrubber 17. Some of the moisture in the unreacted, recovered methane is carried through Compression 21 removed Before being returned to the circulation evaporator 5, the cleaned Methane in the dryer 22 filled with silica gel to less than 10 ppm water dried Simultaneously with the commissioning of the quench circuit, the liquid phase via line 33 1.5 kg / h of an ethoxylated, unbranched C161C18 fatty alcohol (molar ratio: 7 OC2Hs groups to 1 OH group) metered in this measure will reduce the deposition of solid by-products, especially on the surfaces the heat exchanger 14 and the circulation evaporator 24 prevented another part the by-products that interfere with the process flow are removed from the quench circuit removed by any partial flow of the liquefied via line 23 The reaction mixture is drawn off and introduced into the circulation evaporator 24, all of which are non-volatile By-products that lead to malfunctions remain in the sump, while overhead in the Cooler 25 a solid-free methyldichlorophosphine / PCl3 mixture is obtained, which by means of the pump 26 is returned to the quench circuit via line 27.

After the desired operating values in all parts of the device have been reached, is from the bottom of the circulation evaporator 24 continuously The amount of reaction mixture removed via line 28, which the new formation of Methyldichlorophosphine corresponds to Below the reaction conditions mentioned the conversion of PCI3 to methyldichlorophosphine 20.2 mol- *.

Via line 28, 101.7 kg / h of reaction mixture are as follows Composition taken: 16.9% by weight methyldichlorophosphine, 2.1% by weight 9b Carbon tetrachloride, 1.0 weight * chloroform, 0.2 weight 96 phosphorus oxychloride, 1.5 orbs by weight of non-volatile components from the addition of the ethoxylated Cl6 / C ,,, - fatty alcohol, 0.2 weight-96 unknown components, remainder phosphorus trichloride.

In the thin film evaporator 29 are 1.5 kg / h of 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 attack.

In this device, the production takes place under the stated conditions of methyldichlorophosphine can be operated for any length of time without interference. From here The crude product obtained can be methyldichlorophosphine in a manner known per se to be isolated.

Example 2 In the same device and under the same conditions as in Example 1, to prevent the separation of solid by-products, 1.5 kg of a higher ethoxylated, unbranched C16 / C18 fatty alcohol (molar ratio: 80 OC2H5 groups to 1 OH group) are used.

With a PCl3 conversion to methyldichlorophosphine of 24 mol% could trouble-free continuous operation can be achieved.

Example 3 Analogous to example 1, to prevent the deposition solid by-products 1.4 kg of an ethylene oxide polymer, molecular weight 4000, used.

With a PCI3 conversion to methyldichlorophosphine of 21 mol-Yo trouble-free continuous operation can be achieved.

Example 4 Analogously to example 1, to prevent solid deposits 1.4 kg of an ethylene oxide-propylene oxide copolymer (molar ratio = 38: 62) are used With a PCI3 conversion to methyldichlorophosphine of 26 mol-O / o, they were in continuous operation no disturbances observed.

Example 5 In the continuous production of methyldichlorophosphine in the same device and under the same reaction conditions as in the example 1, the supply of nonionic surfactant via line 33 was turned off. Already The heat exchanger 14 and the circulation evaporator were 2 hours after switching off 24 so documented by solid deposits that the performance of this heat exchanger dropped to about 85% of normal performance. After 10 hours of operation without addition a nonionic surfactant had to be stopped.

Claims (6)

Claims: 1. Process for the production of methyldichlorophosphine by converting methane and phosphorus trichloride at temperatures above 500 "C, characterized in that the hot reaction gas leaving the reaction zone mechanically freed of solids and quenched with liquefied reaction mixture, 0.3 to 5% by weight, preferably 0.5 to 3% by weight, of a nonionic Contains dissolved surfactant. 2. The method according to claim 1, characterized in that the reaction zone consists of a preheating zone and a main heating zone and is electrically heated from the outside 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, each outside the electrically heated reaction zone, each via a solids separation zone are connected. 3. The method according to claim 1 or 2, characterized in that the hot, solids-free reaction gas in a according to the principle of Venturi working quenching zone. 4. The method according to any one of the preceding claims, characterized in, that the reaction gas by quenching in a gas phase and liquefied reaction mixture separates, which is mixed with the soluble nonionic surfactant and as a quenching liquid is pumped back into the quenching zone via a cooling zone. 5. The method according to claim 4, characterized in that the gas phase consisting essentially of unreacted methane and hydrogen chloride of adhering vaporous phosphorus trichloride and methyldichlorophosphine Condensation with the help of two-stage cooling at temperatures down to -55 ° C freed, whereby the condensate is in the circuit of acting as a quenching liquid Recirculates liquefied reaction mixture, and the gas phase in a washing zone by sprinkling with water and then with dilute sodium hydroxide solution of hydrogen chloride freed, whereupon the remaining purified methane gas is compressed, dried and returned to the reaction zone 6. The method according to any one of claims 4 or 5, characterized in that one continuously any partial stream of the Liquefied reaction mixture circulated as a quenching liquid subtracts 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 quench liquid, as to maintain this cycle is required; that one of the continuous new formation as the distillation bottoms of methyldichlorophosphine deducts the corresponding amount of liquefied reaction mixture and distilled off from the non-volatile impurities in a thin film evaporator; and that from the phosphorus trichloride and Distillate containing methyldichlorophosphine pure methyldichlorophosphine wins. The older German patent application P 26 31 608.5 already describes a process for the production of methyldichlorophosphine by converting methane with phosphorus trichloride at temperatures above 500 "C, which is characterized is that the hot reaction gas leaving the reaction zone of solids mechanically freed and in a quench zone with liquefied reaction mixture that 0.3 to 3 o / o by weight of an organic barium compound dissolved as a stabilizer contains, deters. 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 type soluble barium phenolate sulfonate mixtures, but also through nonionic surfactants can prevent just as effectively. The fact that both pure methyldichlorophosphine and freshly distilled methyldichlorophosphine-phosphorus trichloride mixtures are already close to these boiling points, i.e. in the range above 70 "C according to the reaction scheme: Form compounds that preferably deliver solids of salt-like, largely undefined type, shows that you can use conventional means alone, such as. B. not prevent distillations, soiling of the apparatus, ie cannot guarantee their functionality. The resulting disadvantages have already been discussed in detail in patent application P 26 31 608.5 and therefore do not need to be repeated here. They can be avoided if small amounts of a nonionic surfactant are added to the methyldichlorophosphine to be handled or its mixtures. This class of substances includes, for example, ethoxylated unbranched fatty alcohols, higher ethylene oxide polymers and ethylene oxide-propylene oxide polymers. In particular, the invention relates to a method of manufacture of methyldichlorophosphine through the reaction of methane and phosphorus trichloride Temperatures above 5000 C, which is characterized in that the the The hot reaction gas leaving the reaction zone is mechanically freed from solids and quenching with liquefied reaction mixture that is 0.3 to 5 weight-4 / o, preferably 0.5 to 3 o / o by weight of a nonionic surfactant in dissolved form.