HK1065998B - A process for quenching a gaseous reaction mixture during the gas phase phosgenation of diamines - Google Patents

Description

Quenching method of gas reaction mixture in diamine gas phase phosgenation process

Technical Field

The invention provides a process for quenching a gaseous reaction mixture during the gas-phase phosgenation of diamines to give diisocyanates, wherein the gaseous mixture contains at least diisocyanate, phosgene and hydrogen chloride. Quenching is achieved by injecting a quenching liquid into the gas mixture.

Background

The preparation of diisocyanates by reaction of diamines with phosgene in the gas phase is described, for example, in EP 0289840. The diisocyanates formed in cylindrical reaction chambers, such as tubular reactors, are thermally unstable at reaction temperatures of 300 ℃ and 500 ℃. It is therefore desirable to cool the reaction gas rapidly to below 150 ℃ after the phosgenation reaction in order to avoid thermal decomposition of the diisocyanates or further reaction to form undesirable side reaction products. To this end, in EP0289840, a gas mixture comprising diisocyanate, phosgene and hydrogen chloride is continuously discharged from the reaction chamber and passed into an inert solvent, for example dichlorobenzene. A disadvantage of this method is that the flow rate of the gas mixture through the solvent bath must be relatively slow, since too fast a flow rate will carry away the solvent and the compounds dissolved therein. In a subsequent step, the liquid compounds have to be separated from the gas. Another disadvantage is that: due to the low flow rate and the short heat exchange time, a large solvent vessel must be used to achieve the cooling effect.

Furthermore, methods are known which use heat exchangers and/or expand the gas to vacuum to cool the reaction gas. The disadvantages of the heat exchanger are: due to the poor heat transfer, a large exchange surface and thus a large heat exchanger are required for effective cooling. In addition, solids deposition occurs on the relatively cool surfaces of the heat exchanger due to side reactions such as decomposition or polymerization of the gas mixture on the heat exchanger surfaces. The heat transfer is further impaired by these deposits and leads to longer residence times and thus to a further increase in by-products. This is followed by an undesirable shutdown of the entire plant due to the purge cooling step.

Disclosure of Invention

The present invention reduces or eliminates the disadvantages inherent in the prior art, as mentioned above, by rapidly cooling the gaseous reaction mixture to a temperature at which the associated reaction product is thermally stable during the phosgenation of diamines in the gas phase to produce diisocyanates. While suppressing the formation of undesirable by-products.

Drawings

The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which:

FIG. 1 shows a cross-sectional view of a quenching zone of a first embodiment; and

FIG. 2 illustrates a cross-sectional view of the quenching zone of a second embodiment.

Detailed Description

The present invention will now be described for purposes of illustration and not limitation. Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities, percentages, and so forth, in the specification are to be understood as being modified in all instances by the term "about".

The invention provides a process for quenching a gaseous reaction mixture during the gas-phase phosgenation of diamines to give diisocyanates, wherein the gaseous reaction mixture contains at least diisocyanate, phosgene and hydrogen chloride, and a quenching liquid is injected into the gaseous reaction mixture as it flows continuously out of a cylindrical reaction zone and into a downstream cylindrical quenching zone, wherein the quenching liquid is injected by means of at least two spray nozzles (spray nozzles) arranged at equal distances along the circumference of the quenching zone at the inlet of the quenching zone.

In addition to phosgene, hydrogen chloride and the main product diisocyanate, the gaseous reaction mixture may also contain further by-product isocyanates, nitrogen and/or organic solvents.

Examples of diisocyanates produced by the gas phase phosgenation of diamines include, but are not limited to: 1, 6-Hexamethylene Diisocyanate (HDI), isophorone diisocyanate (IPDI), Naphthylene Diisocyanate (NDI), Toluene Diisocyanate (TDI), diphenylmethane diisocyanate, and dicyclohexylmethane diisocyanate (HMDI).

One advantage of the method according to the invention is that: when the gas mixture comprising diisocyanate, hydrogen chloride and excess phosgene leaves the reactor, it is rapidly cooled from 300 ℃ to 400 ℃ up to 150 ℃ by spraying it with a suitable quenching liquid. The contact time during cooling is shortened to 0.2-3 seconds.

The liquid spray is carried out at the exit of the reaction zone or at the entrance of the quenching zone using conventional nozzles or openings, such as slots or holes. If there are only two nozzles, they are preferably arranged diametrically opposite one another. The nozzles are preferably individual nozzles (nozzles). More preferably, however, spray heads (nozzle heads) are used which have at least two separate nozzles, wherein nozzles of a single material are preferably used.

Another advantage of the method of the invention is that: the quenching liquid is sprayed into the gas stream in such a way that the hot reaction gases do not come into contact with the relatively cold surfaces of the quenching zone or nozzles and their lances. Only after the gas mixture has cooled to the stable temperature range of the particular diisocyanate does it come into contact with the relatively cold walls of the quenching zone or other components.

The nozzles are preferably arranged independently of one another in such a way that the angle between the flow direction of each quench liquid and the flow direction of the gas mixture is preferably between 0 and 50 deg., more preferably between 20 and 35 deg.. The flow direction of the gas mixture is substantially along the axial direction of the cylindrical reaction zone or quenching zone. If the tubular reactor is in an upright position, the gas flows from top to bottom through the reaction zone and the downstream quenching zone. Also, the flow direction of the quenching liquid is along the axial direction of the nozzle. The cone angles of the nozzles are preferably 20 ° to 90 °, more preferably 30 ° to 60 °, independently of one another. In one embodiment, all nozzles arranged in one plane have the same angle of flow and the same cone angle as the flow of the gas mixture.

Suitable quenching liquids are organic solvents or mixtures of different organic solvents which do not react with the diisocyanate formed. The solvent is furthermore selected according to the solubility of phosgene. Suitable solvents are, for example, toluene, chlorotoluene, xylene and chloronaphthalene. Monochlorobenzene and o-dichlorobenzene are particularly suitable. It is also possible to use solutions of the diisocyanates formed in one of these organic solvents. In this case, the solvent proportion is preferably 40 to 90% by volume. Preferably the quench temperature is 100 ℃ and 170 ℃. In one embodiment, the quenching liquid is an organic solvent, a mixture of different organic solvents, or a solution of a diisocyanate in an organic solvent.

The quenching zone downstream of the cylindrical reaction zone is also cylindrical. The diameter of the quenching zone can be selected to be substantially the same as or greater than the diameter of the reaction zone. The reaction zone is preferably a tubular reactor without baffles.

Further advantages of the method according to the invention are: the reaction gas can be cooled rapidly after the start of the reaction, preferably within 0.2 to 3 seconds, since the gas stream flowing out of the reactor does not have to be slowed down and/or flowed into a vessel, but directly through the atomized quench liquid stream. In addition, the quenching zone is designed in such a way and the nozzles are installed in such a way that the hot gas mixture does not come into contact with any relatively cold surfaces in the quenching zone. To achieve this, for example, the diameter of the cylindrical quenching zone can be larger than the diameter of the reaction zone.

In another embodiment of the process of the present invention, quenching the reaction gas may be carried out in several steps, preferably two steps. In this case, each quenching step includes at least two nozzles arranged equidistantly along the periphery of the quenching zone. The same quenching liquid can be used in the different quenching steps. However, it is more preferred to use different quenching liquids in the two-step quenching process. The first step uses an organic solvent, preferably monochlorobenzene or ortho-dichlorobenzene. The second step uses a solution of the diisocyanate formed in the organic solvent used in the first step. The volume ratio of the solvent is preferably 40 to 90%.

In the following description, the method according to the invention is explained in more detail with reference to the drawings.

FIG. 1 shows the gas mixture flowing through a cylindrical reaction zone 1 from top to bottom along the dotted line 9. Upon leaving reaction zone 1, the gas mixture flows through an identical cylindrical quenching zone 5. In the quenching zone 5 there are two spray heads 3, each having two separate nozzles 4, which are arranged diametrically opposite to each other. The quenching liquid is delivered to the spray head 3 through the conduit 2. The preferred arrangement of the nozzles 4 and the spray heads 3 is such that the angle between the flow direction of the quenching liquid (indicated by the dashed line 8) and the gas flow 9 is 0 to 50, more preferably 20 to 35, so that the hot gas mixture does not come into contact with the colder nozzles and spray heads. In the quenching zone 5, the reaction gas is cooled by evaporating the atomized liquid. The remaining liquid and cooled reaction gas enter a liquid collector 6, which is located below the quenching zone and which can serve both as a pump tank and as a means for separating gas and liquid.

The embodiment of the quenching zone shown in FIG. 2 is in principle identical to the embodiment shown in FIG. 1. Identical or similar parts have therefore the same reference numerals as in fig. 1. The embodiment shown in fig. 2 differs from the embodiment shown in fig. 1 in that the diameter of the quenching zone 5 is larger than the diameter of the tubular reactor 1.

Examples

A gas mixture comprising isophorone diisocyanate, hydrogen chloride and excess phosgene was flowed at 400 ℃ and a pressure of 1000 ℃ and 1800mbar at 6700kg/h from a vertically disposed tubular reactor having a diameter of 260mm and at a velocity of 18m/s into a downstream quenching zone having a diameter of 510 mm. The tube section from the reactor to the quenching zone widens at 75 ° from the vertical. Within the widening zone, four separate nozzles are mounted at equal distances along the periphery. At 130 × 10³kg/h of a monochlorobenzene solution of isophorone diisocyanate at a temperature of 120 ℃ with a volume ratio of 20: 80 was sprayed. The angle between the flow direction of the quenching liquid and the flow direction of the gas mixture was 35 °. The nozzle cone angle was 30 °. The reaction gas was cooled in the quenching zone. Evaporation solutionThe condensable components in solution and the monochlorobenzene required for cooling. The liquid/gas mixture enters a separator. After 0.8-1.3 seconds of contact, the temperature of the concentrated isophorone diisocyanate solution collected in the separator was 140 ℃. The temperature of the gas exiting the separator was 145 ℃.

Although the present invention has been described in detail in the foregoing with reference to the illustrated embodiments, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims (10)

1. In a process for quenching a gaseous reaction mixture during the production of a diisocyanate compound by the gas phase phosgenation of a diamine, wherein the gaseous mixture contains at least diisocyanate, phosgene and hydrogen chloride, the improvement which comprises injecting a quenching liquid into the gaseous mixture as it flows continuously from a cylindrical reaction zone and into a downstream cylindrical quenching zone using at least two nozzles arranged equidistantly around the circumference of the quenching zone at the entrance to the quenching zone, wherein the temperature of the quenching liquid is 100-.

2. The process of claim 1, wherein the nozzles are independently arranged such that the angle between the flow direction of each quenching liquid and the flow direction of the gas mixture is from 0 ° to 50 °.

3. A method according to claim 1, wherein the cone angle of the nozzle is independently 20 ° -90 °.

4. The method of claim 1, wherein the nozzle comprises a showerhead having at least two separate nozzles.

5. The process of claim 1 wherein the quenching liquid is an organic solvent, a mixture of different organic solvents, or a solution of a diisocyanate in an organic solvent.

6. The method of claim 1, wherein the quenching process comprises two or more steps.

7. The method of claim 6, wherein different quenching liquids are used in the quenching step.

8. A method according to claim 2, wherein the angle is 20 ° -35 °.

9. A method according to claim 3, wherein the angle is between 30 ° and 60 °.

10. The method of claim 1, wherein the quenching liquid is selected from the group consisting of monochlorobenzene and ortho-dichlorobenzene.