CN102875418A - Method for preparing isocyanate by means of atomizing type gas-liquid two-phase phosgenation - Google Patents

Abstract

The invention belongs to the technical field of chemical product preparation, and relates to a method for preparing isocyanate by spray-type gas-liquid two-phase phosgenation. Firstly, liquid-phase amine and high-temperature gas-phase phosgene are passed into a mixer to mix and react to obtain a mixture. Heating to a superheating temperature of 5-50°C; then quenching the mixture with an inert solvent and then entering a spray reactor to generate isocyanate. The reactor can quickly disperse liquid amine or its mixture solution into droplets with a particle size of 0.01-3mm Droplets, the nozzle of the reactor is a Venturi or Lafal structure, and the liquid phase amine enters from the nozzle or from the side annulus of the nozzle; finally, the generated isocyanate is removed from phosgene, HCl and solvent respectively The product isocyanate is obtained through rectification and purification; the process steps are scientific and reasonable, the principle is reliable, the equipment and devices used are simple in structure, low in cost, safe and reliable in operation, high in production efficiency and friendly in production environment.

Description

A method for preparing isocyanate by spray-type gas-liquid two-phase phosgenation

Technical field:

The invention belongs to the technical field of chemical product preparation, and relates to a method for preparing isocyanate, in particular to a method for preparing isocyanate by spray-type gas-liquid two-phase phosgenation.

Background technique:

At present, the industrial production of isocyanate is obtained by reacting amine with excess phosgene in the presence of an inert solvent, that is, phosgenation reaction; phosgenation can be divided into liquid-phase phosgenation and gas-phase phosgenation. The so-called liquid phase method and gas phase method are classified according to the phase state of the amine material before entering the reactor. The process of TDA in the supercooled liquid state of the reactor is called the liquid phase phosgene method, and the process of entering the reactor in the gas state is called the gas phase. Phosgenation. Liquid phase phosgenation is currently the most common isocyanate production process, but the liquid phase phosgenation production method has two disadvantages: one is the use of highly toxic phosgene, especially the large excess of phosgene in the production process, which makes The safety of the process is reduced, and there are potential safety hazards; the second is the existence of excess solvent and phosgene, which makes the energy consumption of the whole process very high, which increases the product cost and pollutes the environment, which is not conducive to energy saving and emission reduction; in order to solve The disadvantage of high energy consumption in the liquid phase method, people only proposed the gas phase phosgenation method, the material residence time of the gas phase reaction is shorter, which can increase the output per unit time, obtain a greater space-time yield, thereby reducing investment costs; EPA593334 patent A process is disclosed for the preparation of aromatic diisocyanates in the gas phase by reacting diamines with phosgene in a tubular reactor which has no dynamic components and whose walls taper along the longitudinal axis; the reactor in this process has no Moving parts can reduce the leakage of phosgene; EPA699657 patent discloses a method for preparing aromatic isocyanate in the gas phase. The reaction of appropriate diamine and phosgene is completed in two parts. The first part accounts for 20% of the total reaction volume. -80% mixed system, the second part is a reaction system close to plug flow accounting for 80-20% of the total reaction volume; EP289840 patent discloses the preparation of diisocyanates by phosgenation in the gas phase. Phosgenation is carried out in a cylindrical chamber without dynamic components, the reaction temperature is 200-600 ° C, and the reaction conditions are turbulent; CN101205197A patent discloses a method for preparing isocyanate in the gas phase. Under the conditions above the boiling point of the primary amine, it is carried out under the condition that the average contact time is 0.05-0.15 seconds; CN200610110937.X patent discloses a method for phosgenation of amine in the gas phase, in which the amine is passed through a A specific type of heat exchanger is used to vaporize amines; the EPA928785 patent discloses the use of microarchitecture mixers in the phosgenation of amines in the gas phase. The microstructure mixer can strengthen the mixing reaction of amine and phosgene, but this microstructure mixer may block the mixer even if a very small solid; CN101429138A patent discloses a method for preparing isocyanate, which method comprises primary amine, light The gas and the inert gas are preheated to a temperature 5-100°C higher than the boiling point of the primary amine, and then the preheated primary amine and the inert gas are mixed to obtain a primary amine mixed gas, and the primary amine mixed gas and phosgene are mixed in the mixer Mix and carry out preliminary reaction to obtain preliminary reaction mixture, which enters the tubular reactor for further reaction; gas-phase phosgenation has its own disadvantages: first, the large-scale vaporization process of amine consumes a lot of energy and also causes amine Second, because the gas phase reaction speed is very fast and the temperature is very high, coke residue is often generated during the reaction process, which reduces the reaction yield and may block the equipment; the third is the high temperature gas phase reactant after the reaction Rapid condensation into a liquid phase is required, requiring the addition of an inert solvent and consuming refrigeration.

Invention content:

The purpose of the present invention is to overcome the deficiencies in the prior art, and seek to design and provide a process for preparing isocyanates by spray-type gas-liquid two-phase phosgenation. The heat released by the amine is used to vaporize a considerable amount of amine. Match the heat of reaction of the amine with the heat of vaporization. Use the heat of reaction to vaporize the amine and then perform a gas phase reaction, which can save the heat consumed by vaporizing the amine in the gas phase phosgenation method. , reduce the temperature in the reactor, which is beneficial to reduce the formation of solids, avoid clogging the reactor, save quenching cooling capacity, reduce the amount of inert solvent used for quenching, and achieve energy saving and emission reduction. Side reactions such as decomposition occur during the gasification process, which increases the yield of isocyanate products.

In order to achieve the above object, the specific process of the present invention is to first pass the liquid phase amine and high-temperature gas phase phosgene into the mixer and mix and react to obtain a mixture. Before the liquid phase amine and phosgene are mixed, they are heated by electric heating or steam heating to The superheated temperature is 5-50°C. The amine solution in the superheated state is conducive to the subsequent gasification; the liquid phase amine and phosgene are mixed without adding an inert solvent or adding an inert solvent. The added inert solvent includes toluene, xylene, and isophthalic acid. Diethyl ester, chlorobenzene and dichlorobenzene, the weight ratio of liquid phase amine to inert solvent is 1:1~10; then the mixture from the mixer is quenched with an inert solvent and enters the spray reactor for further reaction to form Isocyanate, the reactor with spray structure can quickly disperse liquid amine or its mixture solution into droplets with a droplet size of 0.01-3mm. The nozzle of the spray reactor is Venturi or Lafal structure, and the liquid phase amine Enter from the nozzle or enter from the side annulus of the nozzle, or use other sprayers that can reach the distribution range of the spray droplet size; finally, the generated isocyanate is removed from phosgene, HCl and solvent, and then purified by rectification The product isocyanate is obtained.

The phosgene involved in the present invention is heated to 200-600°C to be vaporized into a gas, then added to the mixer, and heated by electric heating, steam heating or heat conduction oil; the pressure when the liquid-phase amine and phosgene are mixed and reacted is 0-10 bar; the involved liquid The molar ratio of the amino group of the phase amine to phosgene is 1:1-10, and the molar ratio of the amino group of the liquid phase amine to the inert solvent is 1:0-6.

The liquid phase amine involved in the present invention is mixed with phosgene and the quenching temperature of the high-temperature gas after the initial reaction is higher than the decomposition temperature of the acid chloride. The inert solvent for quenching includes toluene, xylene, diethyl isophthalate, chlorobenzene and Dichlorobenzene; the raw material liquid-phase amines are dichlorodiphenylmethane (MDA), toluenediamine (TDA), hexamethylenediamine (HDA) and isophoronediamine (IPDA).

Compared with the prior art, the present invention has scientific and reasonable process steps, reliable principle, simple structure of equipment and devices used, low cost, safe and reliable operation, high production efficiency and friendly production environment.

Description of drawings:

Fig. 1 is a schematic diagram of the process flow structure of the present invention for preparing isocyanates.

Detailed ways:

The present invention will be further described below by way of examples and in conjunction with the schematic diagram of the process flow.

In this embodiment, the raw material liquid phase amine A is heated to the superheated temperature after passing through the first heat exchanger 4, and the inert solvent C is heated to the same temperature as that of the liquid phase amine A after passing through the first heat exchanger 4 through the second heat exchanger 5. Temperature, the two streams are mixed and enter the nozzle of mixer 1, the gasified raw material phosgene B is heated to a temperature of 200-600°C by heat mixer 6, and then enters mixer 1 from the side, and is mixed in mixer 1 The amines are mixed and reacted initially. The reacted mixture from the mixer 1 enters the reactor 2 for further reaction. The crude isocyanate from the reactor 2 first enters the distillation tower 3 to remove HCl and phosgene, and then the liquid phase Substances enter subsequent rectification and purification to obtain pure isocyanate products.

Example 1:

In this example, the solution of toluene diamine (TDA) and chlorobenzene heated to 320°C with a molar ratio of 1:2 enters mixer 1 from the nozzle of the mixer, and the high-temperature phosgene gas heated to 380°C flows from the ejection flow of the mixer The strand enters the mixer 1, the molar ratio of phosgene and TDA entering the mixer 1 is 4:1, the pressure of the mixer 1 is 1 bar, in the mixer 1, TDA and amine are mixed and undergo a preliminary reaction, and come out of the mixer 1 After the gas enters the reactor 2 and contacts with chlorobenzene, it is quenched to 150°C and continues to react in the reactor 2 to form isocyanate. The pressure of the reactor 2 is 1 bar. After degassing, rectification and purification are carried out to obtain toluene diisocyanate (TDI).

Example 2:

In this example, the toluene diamine (TDA) liquid heated to 320°C with a molar ratio of 1:2 enters the mixer 1 from the nozzle of the jet stream mixer of the mixer, and the high-temperature phosgene gas heated to 380°C flows from the mixer The nozzle enters the mixer 1, the molar ratio of phosgene and TDA entering the mixer 1 is 4:1, the pressure of the mixer 1 is 1bar, in the mixer 1, TDA and amine are mixed and carry out preliminary reaction, from the mixer 1 The gas that comes out enters the reactor 2 and is quenched to 150°C after being contacted with chlorobenzene, and continues to react in the reactor 2 to form isocyanate. The pressure of the reactor 2 is 1 bar. After waiting for the gas, carry out rectification and purification to obtain toluene diisocyanate (TDI).

Example 3:

In this example, the hexamethylenediamine (HDA) and chlorobenzene solution heated to 230°C with a molar ratio of 1:1.5 enters the mixer 1 from the nozzle of the mixer, and the high-temperature phosgene gas heated to 360°C is introduced from the outlet of the mixer 1. The jet stream enters the mixer, and the molar ratio of phosgene and HDA entering the mixer 1 is 4:1, and the pressure of the mixer 1 is 1.5 bar. In the mixer 1, HDA and amine are mixed and undergo a preliminary reaction. From the mixer 1 The gas that comes out enters the reactor 2 and is quenched to 120 ° C after being contacted with chlorobenzene, and continues to react in the reactor 2 to form isocyanate. Gas and other gases, and then rectified and purified to obtain hexamethylene diisocyanate (HDI).

Claims (3)

1. A method for preparing isocyanates by spray-type gas-liquid two-phase phosgenation is characterized in that liquid-phase amine and high-temperature gas-phase phosgene are passed into a mixer to mix and react to obtain a mixture, and before liquid-phase amine and phosgene are mixed, Use electric heating or steam heating to heat to a superheated temperature of 5-50°C. The overheated amine solution is conducive to subsequent gasification; do not add an inert solvent or add an inert solvent before mixing the liquid-phase amine and phosgene, and the added inert solvent includes Toluene, xylene, diethyl isophthalate, chlorobenzene and dichlorobenzene, the weight ratio of liquid phase amine to inert solvent is 1:1~10; then the mixture coming out of the mixer is quenched with an inert solvent After entering the spray reactor for further reaction to generate isocyanate, the reactor with spray structure can quickly disperse the liquid amine or its mixture solution into droplets with a droplet size of 0.01-3mm. The nozzle of the spray reactor is Venturi or Lafalian structure, the liquid phase amine enters from the nozzle or from the side annulus of the nozzle; finally, the generated isocyanate is removed from phosgene, HCl and solvent, and then purified by rectification to obtain the product isocyanate. 2. The method for preparing isocyanate by spray-type gas-liquid two-phase phosgenation according to claim 1, characterized in that the phosgene is heated to 200-600°C to be vaporized into a gas and then added to the mixer, using electric heating, steam heating or heat conduction The oil is heated; the pressure when the liquid phase amine and phosgene are mixed and reacted is 0 to 10 bar; the molar ratio of the amino group of the liquid phase amine to phosgene is 1:1 to 10, and the molar ratio of the amino group of the liquid phase amine to the inert solvent is 1: 0~6. 3. the method for preparing isocyanate by spray type gas-liquid two-phase phosgenation according to claim 1 is characterized in that the high-temperature gas quenching temperature after the preliminary reaction after liquid phase amine mixes with phosgene is higher than the decomposition temperature of acid chloride, Inert solvents for quenching include toluene, xylene, diethyl isophthalate, chlorobenzene, and dichlorobenzene; starting liquid-phase amines are dichlorodiphenylmethane, toluenediamine, hexamethylenediamine, and isophorone diamine.

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