KR830000018B1 - Production method of phosgene - Google Patents

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Description

Production method of phosgene

The present invention relates to a method for producing phosgene, which is obtained by exothermic reaction of chlorine with carbon monoxide in the presence of an activated carbon catalyst. More specifically, the present invention is directed to the reaction of chlorine with carbon monoxide, which has an improvement in that both raw materials of chlorine and carbon monoxide are effectively used and the amount of unreacted raw materials, especially carbon monoxide, which is discarded as waste is reduced. It relates to a method for producing phosgene.

Basic methods for producing phosgene by exothermic reaction of chlorine and carbon monoxide in the presence of a carbon catalyst are known in the art. According to the known method for producing phosgene, a gaseous mixture of chlorine and carbon monoxide is introduced into a reactor containing a catalyst of activated carbon, and the chlorine and carbon monoxide are then reacted as indicated by the equation To form.

In most commercial adaptations, two reactors are used in series. In the primary reactor, more of the reactant is converted to phosgene. This process is then transferred to a process by a secondary reactor, where the remaining unreacted portion is further reacted so that the reactant is substantially completely converted to phosgene.

It is generally desirable to convert as much of the amount of chlorine as possible into the reactor into phosgene and to reduce the amount of residual chlorine in the reaction product. This is generally achieved by maintaining a stoichiometric excess of carbon dioxide in the reactor to react chlorine almost completely.

The phosgene is recovered from the product gas by cooling the gas to the chiller, where the gas is cooled sufficiently to condense the phosgene contained therein. This condensed phosgene is then recovered as a liquid product (usually under pressure).

Uncondensed product gases, chlorine, hydrogen chloride and other by-products containing unreacted carbon monoxide (i.e. excess carbon monoxide supplied to the reactor without passing through the reactor) do not pass through the adsorber with a small amount of phosgene. In the adsorption system, hydrogen chloride and phosgene are neutralized by dilute alkaline solution.

The product gas excluding hydrogen chloride and phosgene adsorbed in the adsorber is discharged from the adsorber and sent to an incinerator for combustion.

This basic method is very effective for chlorine conversion, but not as effective for carbon monoxide. This is because excess carbon monoxide supplied to the reactor for the first time is not reacted but is sintered through the reactor. This means waste of this raw material. As a result, the net amount of carbon monoxide consumed by this method is actually greater than the amount actually required for the phosgene formation reaction.

Therefore, there is a need for a method for producing phosgene by reacting chlorine with carbon monoxide, which does not require a substantial net excess of raw materials.

It is an object of the present invention to provide a process for producing phosgene from chlorine and carbon monoxide, in which the excess of carbon monoxide consumed beyond the stoichiometric requirements is substantially reduced.

It is another object of the present invention to provide a process for producing phosgene from chlorine and carbon monoxide in which the amount of carbon monoxide discarded as waste product is substantially reduced.

The objects are, according to the present invention, by reacting chlorine with carbon monoxide in the presence of excess carbon monoxide, recovering at least a portion of excess carbon monoxide from the reaction product, and recycling it to the reactor with chlorine and a new carbon monoxide input. Is achieved.

According to the present invention, combustion and carbon monoxide are reacted in a reaction zone to produce a product consisting of unreacted phosgene light-reacted carbon, which substantially separates all phosgene from the unreacted carbon and at least not reacts. A method for producing phosgene is provided by improving the raw material yield of the process by reducing a portion of the carbon monoxide which has not been recycled to the reaction zone and reducing the amount of carbon monoxide that is discarded as the waste flow amount.

In preparing phosgene by the process of the present invention, a gas mixture of chlorine and carbon monoxide is fed to a first reactor containing an activated carbon catalyst. The first reactor (hereinafter referred to as primary reactor) is followed by the second reactor (hereinafter referred to as final reactor). The reaction between chlorine and carbon monoxide is essentially complete in the primary reactor, and the final reactor is used to remove the residual amount of unreacted chlorine remaining in the product from the primary reactor. The effluent gas from the reactor (ie the final product from the input passing through the primary and final reactors) should generally contain an amount of unreacted chlorine of about 200 ppm or less. To achieve this, it is generally necessary to maintain an excess of carbon monoxide in the reactor of about 5 to 20 mole percent, preferably about 11 to 15 mole percent.

The new carbon monoxide used to prepare the feed gas mixture will usually come from a local power plant and contain hydrogen, methane and nitrogen. This carbon monoxide is supplied under a gauge pressure of about 5.0 to 10.0 kg / cm 2.

The chlorine used to make the feed mixture is vaporized by heating in a vaporizer to vaporize at a gauge pressure of about 5 to 10.0 kg / cm 2 before mixing with carbon monoxide, usually supplied in liquid form.

Chlorine and carbon monoxide are mixed together in an appropriate amount by any kind of technique known in the gas mixing art. In a more preferred method, these two gases pass together through a pipe section with a static mixer designed to uniformly mix the two gases.

As another alternative, they may pass through a pipe equipped with a Venturi mixing jet or mixing orifice. The final feed mixture is generally sent to the reactor at a temperature of about 40 ° C. to 90 ° C. and a gauge pressure of about 5.0 to 10.0 kg / cm 2.

This feed mixture is supplemented by adding recycled carbon monoxide recovered from the final product, as described below in accordance with the practice of the present invention.

This recycled carbon monoxide may be added to either side of the feed animal prior to mixing by the use of a non-lubricated compressor, or may be added directly to the mixing device as a third individual feed fluid. More importantly, the kinetic energy of the incoming chlorine or new carbon monoxide may be used via venturi jets to pump recycled carbon monoxide to process inlet pressure.

The ratio of total carbon monoxide to chlorine in the feed gas mixture is adjusted to provide a stoichiometric excess of carbon monoxide in the feed to the primary reactor. In this way, the amount of new carbon monoxide used to prepare the feed gas mixture will depend on the specific excess of carbon monoxide required in the reaction zone and the amount of recycled carbon monoxide supplied to the mixture.

Excess carbon monoxide in the reaction zone can vary from at least about 2% to at least about 30% of the stoichiometric requirement for reacting with chlorine. However, in general, excess of 2% or more can hardly be profitable, and any increased conversions made by this excess will sometimes be overburdened by the increased costs involved in maintaining this high excess. Therefore, it is more desirable to maintain an excess of about 10 to 25% stoichiometric carbon monoxide in the reaction zone.

As mentioned earlier, the reaction between chlorine and carbon monoxide is very exothermic. Due to the exothermic nature of the reaction, the reaction mass can be at a high temperature above 500 ° C. Such high temperatures can cause some difficulties. This is because phosgene once formed tends to dissociate at high temperatures. Therefore, the reaction product should be cooled as soon as possible after the formation of phosgene. Rapid cooling of the reaction product to minimize dissociation of phosgene can be achieved by using a shell-and-tube-type reactor or a jacketed tank type reactor. More preferably it is carried out in itself.

This "shell-and-tube-type" reactor is very similar to a shell-and-tube heat exchanger. This type of reactor is more preferably used for the first order reaction. In a shell-and-tube-type reactor, an activated carbon catalyst is contained in the tube, which is surrounded by coolant that circulates through the shell. Circulating water cools the tubes as well as the product gases contained therein. The temperature of the cooling water is controlled by external means depending on the temperature desired for the product exiting the reactor. The reactor may also be cooled by boiling water (ie, using thermocypin-thermosphon) to produce a useful gas.

Shell-and-tube-type reactors may be used for other final reactors, but are generally unnecessary for use. This is because the amount of heat released in the final reactor is substantially less than the amount of heat released in the primary reactor and the large cooling capacity of the shell-and-tube reactor is not required. Therefore, it is better to use conventional water or water or low pressure steam-jackted tank-type reactors for availability. This type of reactor consists of a fixed bed of activated carbon catalyst in a tank with a cooling jacket. The coolant circulates through the jacket in the same way as it circulates around the tube in the shell-and-tube reactor to control the internal temperature.

In cooling the reaction product in the reactor, care should be taken to ensure that the phosgene does not condense too early. If phosgene begins to condense in the cooling section of the reactor, the flow through the reactor will be limited by the condensate and cause difficulty in working. This is generally avoided because the cooling water is kept at a temperature below the appropriate temperature of the reaction product (typically 40 to 60 ° C depending on the pressure).

The gauge pressure of the gas in the reactor is from about 5.0 kg / cm 2 to about 10 kg / cm 2 depending on various factors such as feed gas pressure, production rate, reactor size, and the like. In addition, since the product gas contains hydrogen chloride and chlorine, it is corrosive. The reactor must therefore be designed to operate at high pressures and the process side of the reactor should be dried with corrosion resistant materials such as monel and stainless steel.

Under appropriate operating conditions, the final reaction product (gas) after passing through the primary and final reactors may contain, in addition to carbon monoxide not reacted with phosgene (ie, generally less than about 10% by weight) of nitrogen, hydrogen chloride and traces ( That is, it will generally contain up to about 1% by weight of oxygen) and carbon tetrachloride and up to 100 ppm chlorine.

This final reaction will cause the phosgene contained in the product to condense it and contain it as a liquid product as a collection.

This final reaction product gas is introduced into the condenser at a temperature of about 50 ° C. to 70 ° C. and a gauge pressure of about 1.5 kg / cm 2 to about 4.5 kg / cm 2, where they essentially condense all of the phosgene into the product of the liquid. Cool down to a temperature that can be collected. In this system, the gas is first cooled as practically as possible using water cooling equipment and then further cooled using refrigeration cooling equipment. It is generally practical to cool the product gas to a temperature of about 30 ° C. to 40 ° C. using standard water cooled shell-and-tubeneat exchange, depending on the temperature of the cooling water available. .

When cooled under this temperature and a gauge pressure of about 1.5 kg / cm 2 to 4.25 kg / cm 2, approximately 50 to 80% of phosgene can condense and collect from the product gas. After being cooled as practically as possible using a chilled water exchanger, the product gases are introduced into a refrigerated chilled heat exchanger, where they are cooled to a temperature of about -20 ° C to -30 ° C and the remaining phosgene is condensed and recovered.

In essence, all phosgene is removed and the main component remaining in the uncondensed product gas is carbon monoxide. This carbon monoxide remaining in the product gas has conventionally been considered a waste product and has thus been disposed of so far.

According to the invention the carbon monoxide remaining in the product gas is recovered and recycled to the reactor where it becomes part of the feedstock. By recovering these valuable raw materials, which have been regarded as fluids of waste so far, the present invention not only reduces the amount of carbon monoxide consumed in the production of phosgene, but also reduces the waste disposal requirements associated with the phosgene production process. . This benefit is brought in accordance with the present invention while still maintaining the same reactor conditions essentially as the prior art method for carbon monoxide.

According to the present invention, most carbon monoxide-rich gases can be recycled to the reactor. The amount recycled depends on the cost of the new carbon monoxide, the disposal cost of the carbon monoxide waste gas, and the amount and nature of the pollutants present in the carbon monoxide-rich gas.

Carbon monoxide can be recycled back to the reactor using the power provided by any kind of technology. In this way, for example, after passing a liquid knockout pot or entertainment separator, it may be supplied to a mechanical compressor which increases the gas pressure sufficient to return it to the reactor, or it may be supplied with a jet compressor ( That is, by using an ejector, it can be introduced into any of the new feed flows, where the new feed flow serves as a pumping fluid.

In some cases, the product gas contains some oxygen contaminants that would have an adverse effect on the activated carbon catalyst if present in large quantities (ie at least about 2% by weight) in the recycle. For example, a measurable amount of combustion of an activated carbon catalyst may occur if coral content in excess of about 1.5 mole percent (based on carbon monoxide) is allowed in the reactor. The oxygen content in the primary reactor feed gas should be controlled to at least about 0.25 mole percent (based on carbon monoxide) in order to achieve the long life of the solvent.

In order to limit the accumulation of these contaminants in the recirculated gas stream, the recirculating gas (ie product gas after phosgene has been removed) must be cleaned before recirculation. Removal rates of about 10 to 35% of the product gas that can be recycled have been established as incentives in most cases to moderate the catalyst life of the activated carbon. Therefore, the amount of carbon monoxide recycled is usually in the range of about 65 to 90% of the carbon monoxide contained in the product gas from the reactor.

The purge gas can be disposed of properly by neutralizing and removing hydrogen chloride and phosgene by scrubbing it with a dilutecaustic solution and then igniting the residue.

Caustic scribing can be accomplished by passing gas through an absorption tower through which dilute caustic solution (ie, about 3 to 5% sodium hydroxide, NaOH) is circulated. The unadsorbed gas is then exhausted from the adsorption tower into an incinerator. Of course, the total amount of gas to be sintered will be substantially less than if all carbon monoxide had to be sintered as in the prior art. Therefore, in addition to reducing the residual amount of raw materials required to produce phosgene, the present invention also substantially reduces waste disposal loading, equipment and other requirements related to affirmation.

In order that the present invention may be more fully understood, the following examples are replaced by the drawings. It should not be construed as a limitation to the present invention, except in the specific specification contained in this embodiment and as long as they appear in the appended claims.

EXAMPLE

Liquid chlorine is discharged to the commercial phosgene plant and the primary reactor inlet at a rate of 100 pounds per hour (45.36 Kg, mols) at a temperature of approximately 23 ° C and a pressure of approximately 90 PSIG (6.3 kg / cm 2). It is vaporized and supplied to the intake nozzle of a pump. The dichlorine vapor flow contains 99.6 mole percent chlorine. At a temperature of -10 to -30 °, the recycled carbon monoxide flow is fed to the inlet of the jet pump at a rate of 16.25 pound moles (7.37 Kg, mols) per hour.

The new carbon monoxide flow, consisting of 99.5 percent carbon monoxide, 0.12 mole percent methane and 0.05 mole percent oxygen (remaining nitrogen), yields a rate of 1044 pounds moles (47.35 Kg, mols) per hour at a temperature of 30 ° C. It is also supplied to the inlet of the car reactor.

These three feed streams (chlorine, fresh carbon monoxide and recycled carbon monoxide) are mixed together by a mixing orifice in the suction line of the primary reactor. The mixed gas passes through a reactor consisting of a shell and a tube-type reactor, which is equipped with a tube containing an activated carbon catalyst (with a surface area of 1100 m 2) and surrounded by circulating coolant in the shell. Are stacked. The idealized carbon and chlorine gas react to form phosgene as they pass through the tube containing the catalyst in the reactor. It is absorbed by the water in the shell of the thermosensitive reactor generated by the exothermic reaction, the temperature of which is concluded above the dew point to maintain the temperature of the product gas exiting the reactor.

In the primary reactor, about 99% of chlorine is converted to phosgene.

The product flow from the primary reactor passes through the jacketed tank-type final reactor. The reactor is filled with the same type of activated carbon catalyst as used in the primary reactor tube and is enclosed by coolant that circulates through the entire jacket. Most of the remaining 1% of the initially introduced chlorine is converted to phosgene as it passes through the catalyst bed of the final reactor.

The product from the final reactor passes through a water cooled shell and tube heat exchanger at a temperature of 50 to 70 ° C. where it is cooled to a temperature of 30 to 40 ° C. to cause partial condensation of the phosgene.

The cooled and partially condensed product flows from the water-cooled heat exchanger to a surge tank whereby the fraction of liquid in the unit is collected and the gas fraction is a refrigerated shell and tube. Sent to the heat exchanger. In a refrigerated heat exchanger the product is further cooled to a temperature of -25 ° whereby essentially all residual phosgene condenses. This flow then passes through the knockout tank where the liquid and gas portions are separated. This liquid portion is sent back from the no-out tank to the thunder tank where it is mixed with the liquid collected by the water cooling method and the gas portion is partly sent to the waste disposal device and partly recycled to the primary reactor.

The combined phosgene accumulated in the surge tank and the phosgene sent from the knockout tank amounted to 99.5 pounds per mole (44.9 Kg, mols) per hour, approximately 99.66 mole percent phosgene, 0.02 mole percent carbon tetrachloride, and trace traces of hydrogen chloride. Consists of chlorine.

The portion of the gas sent out from the knockout tank (under a pressure of about 58 PSIG (4.1 kg / cm 2)) is 71.3 mole percent carbon monoxide, 15.6 mole percent nitrogen, 1.2 mole percent oxygen, 8.9 mole percent hydrogen chloride, 3.4 mole percent phosgene And 0.2 mole percene of carbon tetrachloride. This flow amounts to 21.6 pounds of mol (9.8 Kg, mols) per hour. 16.25 pounds of mol (7.4 Kg, mols) per hour in the total flow are recycled to the primary reactor and 5.35 pounds of mol (2.4KG, mols) per hour are sent to the waste treatment unit.

Purge tank The waste treatment device, which flows out, consists of a caustic scrubbing system followed by an incinerator. Hydrogen chloride and phosgene contained in the purge flow are neutralized and adsorbed by 3% caustic solution circulating in the scrubber, and then the residual purge gas flow is burned in the incinerator.

The recycle gas flow is supplied to the inlet of the Venturi jet pump as described above.

The phosgene yield is calculated to be 99.3% of chlorine input and 96% of carbon monoxide input.

Thus, the present invention achieves a high raw material efficiency for both raw materials without requiring substantial net excess of carbon monoxide, and improves substantially on the amount of carbon monoxide that is discarded as waste products compared to the prior art methods. You will find that it provides a way to make pot and gen from chlorine and carbon monoxide.

Therefore, as will be apparent from the foregoing description, the above-mentioned objects will be effectively obtained, and any change in the method may be made without departing from the present invention, and therefore all matters contained in the above description are illustrative. It should not be interpreted in a restrictive sense.

Claims (1)

In the process for producing phosgene, which is made by reacting chlorine with carbon monoxide in the presence of an activated carbon catalyst, a gas mixture composed of phosgene and unreacted carbon monoxide by reacting chlorine with substantially pure carbon monoxide in a reaction zone. And substantially all of the phosgene is separated from the unreacted carbon monoxide by passing the gas mixture through a fractionation zone, whereby a major portion of the unreacted carbon monoxide is directly added to the reaction zone. By recycling to a process, the production of phosgene, characterized in that the raw material yield of the process is increased and the amount of carbon monoxide discarded as waste is reduced.