CN113105365A

CN113105365A - Process for preparing isocyanate by adopting phosgenation reaction

Info

Publication number: CN113105365A
Application number: CN202110415391.3A
Authority: CN
Inventors: 徐西之; 巩绪干
Original assignee: Xinyi Yongcheng Chemical Industrial Co ltd
Current assignee: Xinyi Yongcheng Chemical Industrial Co ltd
Priority date: 2021-04-18
Filing date: 2021-04-18
Publication date: 2021-07-13

Abstract

The invention relates to the field of preparation methods of isocyanate, in particular to a process for preparing isocyanate by adopting phosgenation reaction, which comprises the following steps: mixing and stirring bis (trichloromethyl) carbonate and a solvent in a preparation kettle to obtain trichloromethyl chloroformate; dropwise adding hydrochloric acid into the amine solution, heating, and condensing to remove water; mixing an amine solution and trichloromethyl chloroformate with a reactor to obtain crude isocyanate; introducing inert gas into the reactor, discharging hydrogen chloride generated by the reaction from the reactor to a tail gas collecting box, and treating the gas in the tail gas collecting box; and purifying the crude isocyanate by a distillation tower to obtain an isocyanate product. The preparation process adopted by the invention is more environment-friendly and safer and can bring higher economic benefit.

Description

Process for preparing isocyanate by adopting phosgenation reaction

Technical Field

The invention relates to the field of preparation methods of isocyanate, in particular to a process for preparing isocyanate by adopting phosgenation reaction.

Background

The isocyanate is used as an important chemical intermediate, is widely applied to the fields of polyurethane, coating, dye, heat insulation material and medicine, and has wide market prospect. The phosgenation reaction technology is the most important method for preparing isocyanate at present, and only a very small amount of isocyanate is produced by adopting a non-phosgenation method in an industrial production device. The phosgenation reaction generally refers to a reaction in which phosgene is involved as a reactant. For organic isocyanates, the specific reaction process can be divided into two stages: in the first stage, organic amine reacts with phosgene to produce acyl chloride and hydrogen chloride, the hydrogen chloride released by the reaction is possibly combined with the amine group of a reactant to form amine salt, and the reaction process releases heat violently, which is called as cold reaction; in the second stage, the acyl chloride is decomposed to generate isocyanate and hydrogen chloride, the amine salt is further reacted with phosgene to generate isocyanate and hydrogen chloride, and the reaction is an endothermic reaction which is also called a thermal reaction. The current literature on isocyanate phosgenation reaction kinetics measurement is not reported due to technical blockade and confidentiality, but the unified consensus is that the cold reaction speed is very high, the hot reaction speed is slow, and the side reaction speed is between the two. For the entire phosgenation process, the reactions for producing acid chlorides and hydrochlorides are the key step of the entire phosgenation reaction process. In general, it is desirable to produce more acid chloride with as little hydrochloride salt as possible because acid chloride is more readily decomposed into the product isocyanate and hydrogen chloride as a byproduct, and the hydrochloride salt reacts much more slowly with phosgene to form the desired isocyanate product. Therefore, the control of the cold reaction is the key core of the whole phosgenation reaction process, and the published phosgenation reaction literature is mainly presented in the patent, and more than 90% of the cold reaction process is aimed at.

The phosgenation reaction technology is the most main technology for producing organic isocyanate in an industrial scale at present, and has the advantages of mature technology, high reaction yield and the like, but because the reaction process involves a highly toxic substance phosgene and a byproduct hydrogen chloride, the method has the hidden dangers of safety, environmental protection and the like. The process for preparing isocyanates using phosgene has been under debate and research into the use of non-phosgene methods instead of phosgene methods has been receiving attention. However, the non-phosgenation isocyanate preparation technology has the short time and is difficult to compete with the phosgenation method in both economic benefit and technical maturity, so that the technology has important practical significance in further research and potential development of the phosgenation isocyanate production technology.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a process for preparing isocyanate by adopting a phosgenation reaction, and the preparation process adopted by the invention is more environment-friendly and safer and can bring higher economic benefit.

The purpose of the invention is realized by the following technical scheme:

a process for preparing isocyanate by adopting phosgenation reaction comprises the following process steps:

step one, mixing and stirring bis (trichloromethyl) carbonate and a solvent in a preparation kettle to obtain trichloromethyl chloroformate;

step two, dripping hydrochloric acid into the amine solution, starting to heat the solution when the PH value of the amine solution is less than 2, and simultaneously separating water in the amine solution through a reflux condenser until no water beads are formed in a water separator;

step three, at least one part of the amine solution after the water removal in the step two and the trichloromethyl chloroformate obtained in the step one are heated and gasified into a gas phase state respectively;

step four, putting the gas-phase amine solution and the liquid-phase amine solution obtained in the step three into a reactor filled with gas-phase trichloromethyl chloroformate for mixing and reacting for 5 hours to obtain crude isocyanate;

introducing inert gas into the reactor, discharging hydrogen chloride generated by the reaction from the reactor to a tail gas collecting box, and treating the gas in the tail gas collecting box;

and step six, purifying the crude isocyanate through a distillation tower to obtain an isocyanate product.

Further, the solvent is a toluene solution or a dichloroethane solution.

Further, the amine is a monoamine or a diamine.

Further, the amine is one or more of 1, 6-diaminohexane, 1, 5-diaminopentane, 1, 3-bis (aminomethyl) cyclohexane.

And further, the tail gas in the fifth step is treated by adopting a cathode oxidation method and a hydrogen chloride catalytic oxidation method to prepare chlorine from the tail gas.

Further, the temperature of the gaseous trichloromethyl chloroformate added in the fourth step is 250-450 DEG C

Wherein phosgene trichloromethyl chloroformate is first mixed with an amine and then converted to isocyanate in a reactor. To prepare the isocyanate, the trichloromethyl chloroformate and the amine are preferably first fed into a mixing zone where the amine and trichloromethyl chloroformate are mixed to form the reaction mixture. Subsequently, the reaction mixture is fed to a reactor where it is converted to isocyanate. The conversion of amine and phosgene in the reactor is preferably carried out in the gas phase. For this purpose, the absolute pressure in the reactor is preferably in the range from 0.3 to 3bar, more preferably in the range from 0.8 to 3.0 bar. The temperature is preferably in the range of 250-550 ℃, especially in the range of 300-500 ℃. In order to be able to carry out the reaction in the gas phase, it is also preferred to add the amine and phosgene in gaseous form. For this purpose, the temperature of the amine is preferably in the range of 200 ℃ and 400 ℃. The absolute pressure of the amine added is preferably in the range from 0.05 to 3 bar. The temperature of the trichloromethyl chloroformate to be fed is preferably in the range of 250 ℃ to 450 ℃. For this purpose, the trichloromethyl chloroformate is generally heated before addition by methods known to those skilled in the art. To heat the trichloromethyl chloroformate and the amine and vaporize the amine, for example, direct or indirect heating using electrical heating or combustion fuel may be used. The fuel used is typically a fuel gas, such as natural gas. But it is also possible to use steam heating, for example, since lowering the pressure lowers the boiling point of the amine. The pressure of the steam is here selected according to the boiling point of the amine. Suitable vapor pressures of the steam are, for example, in the range from 40 to 100 bar. This results in a temperature of the steam in the range of 250 ℃ to 311 ℃. However, it is also possible to use steam with a temperature above 311 ℃ to vaporize the amine. Generally, the amine must be heated to the reaction temperature in multiple stages. Generally, for this purpose, the amine is first preheated, then vaporized and then superheated. Generally, the vaporization process requires the longest residence time, resulting in decomposition of the amine. In order to minimize this, it is advantageous to carry out the evaporation at a lower temperature, for example by reducing the pressure. In order to superheat the vaporized amine to the reaction temperature after vaporization, heating with steam is usually insufficient. For superheating, direct or indirect heating is usually carried out using electrical heating or combustion of fuel. Phosgene is generally vaporized at a relatively low temperature, as opposed to vaporization of amines. Thus, phosgene can generally be vaporized with steam. However, the necessary superheating process to heat the phosgene to the reaction temperature is usually only possible with direct or indirect heating with electrical heating or combustion of fuel. Reactors for the phosgenation of amines to produce isocyanates are known to those skilled in the art. The reactor usually used is a tubular reactor. In the reactor, the amine is reacted with phosgene to give the corresponding isocyanate and hydrogen chloride. Phosgene is usually added in excess, so that the reaction gases formed in the reactor, as well as the isocyanate and hydrogen chloride formed, contain phosgene. Instead of using a tubular reactor, a substantially cuboidal reaction chamber, for example a plate reactor, may also be used. Any desired different cross-section of the reactor is possible. The amines that may be used to prepare the isocyanates are monoamines, diamines, triamines or higher functionality amines. Preference is given to using monoamines or diamines. Depending on the amine used, the corresponding monoisocyanates, diisocyanates, triisocyanates or higher-functional isocyanates can be prepared. Preferably, the monoisocyanates or diisocyanates are prepared according to the process of the present invention. The amines and isocyanates may be aliphatic, cycloaliphatic or aromatic. The amine is preferably aliphatic or cycloaliphatic, more preferably aliphatic. Cycloaliphatic isocyanates are isocyanates which contain at least one cycloaliphatic ring system. Aliphatic isocyanates are isocyanates which have exclusively isocyanate groups bonded to straight-chain or branched chains. Aromatic isocyanates are isocyanates which have at least one isocyanate group bonded to at least one aromatic ring system. The term "aliphatic (cyclo) isocyanate" is used hereinafter to denote cycloaliphatic and/or aliphatic isocyanates. Examples of aromatic monoisocyanates and diisocyanates are preferably those having 6 to 20 carbon atoms, for example phenyl isocyanate, monomeric 2, 4 '-and/or 4, 4' -methylene-bis (phenyl isocyanate) (MDI), 2, 4-and/or 2, 6-Tolylene Diisocyanate (TDI) and 1, 5-or 1, 8-Naphthyl Diisocyanate (NDI). Examples of (cyclo) aliphatic diisocyanates are aliphatic diisocyanates such as 1, 4-tetramethylene diisocyanate, 1, 6-hexamethylene diisocyanate (1, 6-diisocyanatohexane), 1, 8-octamethylene diisocyanate, 1, 10-decamethylene diisocyanate, 1, 12-dodecamethylene diisocyanate, 1, 14-tetradecamethylene diisocyanate, 1, 5-diisocyanatopentane, neopentane diisocyanate, 2-methyl-1, 5-diisocyanatopentane, derivatives of lysine diisocyanate, tetramethylxylylene diisocyanate (TMXDI), trimethylhexane diisocyanate or tetramethylhexane diisocyanate, and 3 (or 4), 8 (or 9) -bis (isocyanatomethyl) tricyclo- [5.2.1.02.6] decane isomer mixtures, and alicyclic diisocyanates such as 1, 4-, 1, 3-or 1, 2-diisocyanatocyclohexane, 4 '-or 2, 4' -bis (isocyanatocyclohexyl) methane, 1-isocyanato-3, 3, 5-trimethyl-5- (isocyanatomethyl) cyclohexane (isophorone diisocyanate), 1, 3-or 1, 4-bis (isocyanatomethyl) cyclohexane, 2, 4-or 2, 6-diisocyanato-1-methylcyclohexane. Preferred (cyclo) aliphatic diisocyanates are 1, 6-diisocyanatohexane, 1-isocyanato-3, 3, 5-trimethyl-5- (isocyanatomethyl) cyclohexane and 4, 4' -bis (isocyanatocyclohexyl) methane. Particular preference is given to 1, 6-diisocyanatohexane, 1, 5-diisocyanatopentane, 1-isocyanato-3, 3, 5-trimethyl-5- (isocyanatomethyl) cyclohexane and 4, 4' -bis (isocyanatocyclohexyl) methane. The amines used in the process of the invention for the reaction to prepare the corresponding isocyanates are those as follows: wherein the amine, the corresponding intermediate and the corresponding isocyanate are present in gaseous form under the reaction conditions selected. Preference is given to using amines which decompose to an extent of at most 2 mol%, more preferably to an extent of at most 1 mol%, most preferably to an extent of at most 0.5 mol% during the reaction under the reaction conditions. Particularly suitable amines here are, in particular, diamines based on aliphatic or cycloaliphatic hydrocarbons having from 2 to 18 carbon atoms. Examples thereof are 1, 6-diaminohexane, 1, 5-diaminopentane, 1, 3-bis (aminomethyl) cyclohexane, 1-amino-3, 3, 5-trimethyl-5-aminomethylcyclohexane (IPDA) and 4, 4-diaminodicyclohexylmethane. Preference is given to using 1, 6-diaminohexane (HDA). Aromatic amines that can be converted to the gaseous state without significant decomposition can also be used in the process of the present invention. Examples of preferred aromatic amines are Toluenediamine (TDA), in the form of 2, 4 or 2, 6 isomers or mixtures thereof, for example in the form of a mixture of 80: 20 to 65: 35(mol/mol), diaminobenzene, 2, 6-xylidine, Naphthyldiamine (NDA) and 2, 4 '-or 4, 4' -methylene (diphenyldiamine) (MDA) or isomer mixtures thereof. Among these amines, diamines are preferably used, particularly preferably 2, 4-and/or 2, 6-TDA or 2, 4 '-and/or 4, 4' -MDA. For the preparation of monoisocyanates, it is likewise possible to use aliphatic, cycloaliphatic or aromatic amines, in particular monoamines. One preferred aromatic monoamine is especially aniline. In the gas-phase phosgenation, it is desirable for the compounds present in the reaction process, i.e. the reactants (amine and phosgene), the intermediates (in particular the mono-and dicarbamoyl chlorides formed as intermediates), the end products (diisocyanates) and any inert compounds metered in, to remain in the gas phase under the reaction conditions. If these or other components are deposited from the vapor phase, for example on the reactor walls or other apparatus components, these deposits can adversely alter the heat transfer or flow-through of the affected components. This is particularly the case when amine hydrochlorides are produced, which are formed from free amino groups and hydrogen chloride, since the amine hydrochlorides formed are very prone to deposition and their revaporization is very difficult. To avoid the formation of by-products, it is preferred to supply an excess of phosgene. In order to supply only the amine in the proportion required for the reaction, the amine may be mixed with an inert gas. The proportion of inert gas in the amine can be used to adjust the amount of amine fed to a feed inlet for amine and phosgene of a given shape. Inert media which can be added are gases which are present in gaseous form in the reaction chamber and do not react with the compounds produced during the reaction. Inert media which can be used are, for example, nitrogen, inert gases such as helium or argon, aromatics such as chlorobenzene, o-dichlorobenzene, trichlorobenzene, toluene, xylene, chloronaphthalene, decalin, carbon dioxide or carbon monoxide. However, preference is given to using nitrogen and/or chlorobenzene as inert medium. Alternatively, to avoid too much excess phosgene, an inert medium may also be added to the phosgene. In general, the amount of inert medium added is such that the gas volume ratio of inert medium to amine or to phosgene is from less than 0.0001 to 30, preferably from less than 0.01 to 15, more preferably from less than 0.1 to 5. To reduce or avoid the formation of undesired by-products and also to suppress the decomposition of the isocyanate formed, the reaction gas is cooled in a quench immediately after the reaction.

The invention has the beneficial effects that:

(1) since hydrogen chloride is present in the product during the preparation of isocyanates. The presence of hydrogen chloride in the product is also an indirect consequence of the use of phosgene as a reactant, since only the C and O atoms of phosgene enter the isocyanate target product, while the other two Cl atoms enter the hydrogen chloride by-product. The presence of hydrogen chloride as by-product brings about two disadvantages: firstly, from the atom economy of the reaction, the utilization rate of the effective atoms in the phosgene is only 28.5 percent, which is not cost-effective, and the economic value of the hydrogen chloride as a byproduct is extremely low; and secondly, due to the existence of the byproduct hydrogen chloride, the requirement of the whole process device on the water content in equipment materials and process materials is extremely high, and the hydrogen chloride forms hydrochloric acid once meeting water, so that the corrosion on metal materials is extremely high.

(2) The invention divides the amine solution into gas state and liquid state to be mixed with the gas phase trichloromethyl chloroformate, because the mass transfer phase rate between gases is far higher than that between gases and liquid, the gas phase amine reacts with the gas phase trichloromethyl chloroformate to release heat, the temperature of the system is raised by the released heat, the liquid amine is heated and gasified, and continuously reacts with the gas phase trichloromethyl chloroformate until the amine reaction is finished, thereby saving the energy consumption of the system, simultaneously controlling the reaction condition and the gas-liquid state to control the reaction process, solving the problems that although the reaction rate is high in the gas phase reaction, the reaction temperature is easy to be too high, the side reaction generates coke residue, the reactor is blocked, and the reaction rate is reduced.

Detailed Description

The technical solution of the present invention is further described in detail with reference to the following specific examples, but the scope of the present invention is not limited to the following.

Example 1

step one, mixing and stirring bis (trichloromethyl) carbonate and a toluene solution or a dichloroethane solution in a preparation kettle to obtain trichloromethyl chloroformate;

step two, dripping hydrochloric acid into the 1, 6-diaminohexane solution, starting to heat the solution when the PH of the amine solution is less than 2, and simultaneously separating water in the amine solution through a reflux condenser until no water beads are formed in a water separator;

step three, shunting 20% of the amine solution subjected to water removal in the step two and heating the trichloromethyl chloroformate obtained in the step one in a gasification furnace respectively to be in a gas phase state;

step four, putting the gas-phase amine solution and the liquid-phase amine solution obtained in the step three into a reactor filled with gas-phase trichloromethyl chloroformate at the temperature of 250 ℃ for mixing and reacting for 5 hours, wherein the absolute pressure in the reactor is 0.3bar, so as to obtain crude isocyanate;

introducing inert gas into the reactor, discharging hydrogen chloride generated by the reaction from the reactor into a tail gas collecting box, and treating the gas in the tail gas collecting box, namely preparing the tail gas into chlorine by adopting a cathode oxidation method and a hydrogen chloride catalytic oxidation method;

In this example, the maximum temperature occurring in the reactor during the reaction of the gas-phase and liquid-phase amine solutions with gaseous trichloromethyl chloroformate was 310 ℃, and no by-products such as coke residue occurred in the reactor.

Example 2

step two, dripping hydrochloric acid into the 1, 5-diaminopentane solution, starting to heat the solution when the PH of the amine solution is less than 2, and simultaneously separating water in the amine solution through a reflux condenser until no water beads are formed in a water separator;

step three, shunting 50% of the amine solution subjected to water removal in the step two and heating the trichloromethyl chloroformate obtained in the step one in a gasification furnace respectively to be in a gas phase state;

step four, putting the gas-phase amine solution and the liquid-phase amine solution obtained in the step three into a reactor filled with gas-phase trichloromethyl chloroformate at the temperature of 350 ℃ for mixing and reacting for 5 hours, wherein the absolute pressure in the reactor is 0.25bar, so as to obtain crude isocyanate;

In this example, the maximum temperature occurring in the reactor during the reaction of the gas and liquid phase amine solutions with gaseous trichloromethyl chloroformate was 360 ℃ and no by-products such as coke residue occurred in the reactor.

Example 3

step two, dripping hydrochloric acid into the 1, 3-bis (aminomethyl) cyclohexane solution, starting to heat the solution when the PH of the amine solution is less than 2, and simultaneously separating water in the amine solution through a reflux condenser until no water beads are formed in a water separator;

step three, shunting 80% of the amine solution subjected to water removal in the step two and heating the trichloromethyl chloroformate obtained in the step one in a gasification furnace respectively to be in a gas phase state;

step four, putting the gas-phase amine solution and the liquid-phase amine solution obtained in the step three into a reactor filled with gas-phase trichloromethyl chloroformate at the temperature of 450 ℃ together for mixing reaction for 5 hours, wherein the absolute pressure in the reactor is 0.2bar, so as to obtain crude isocyanate;

In this example, the maximum temperature occurring in the reactor during the reaction of the gas-phase and liquid-phase amine solutions with gaseous trichloromethyl chloroformate was 500 ℃, and no by-products such as coke residue occurred in the reactor.

Comparative example

step three, mixing the amine solution subjected to water removal in the step two and trichloromethyl chloroformate at the temperature of 450 ℃ in a reactor for reaction for 5 hours, wherein the absolute pressure in the reactor is 3bar, so as to obtain crude isocyanate;

and step five, purifying the crude isocyanate through a distillation tower to obtain an isocyanate product.

In the present comparative example, the maximum temperature occurring in the reactor during the reaction of the liquid-phase amine solution with the liquid-phase trichloromethyl chloroformate was 880 ℃, and a large amount of by-products such as coke breeze occurred in the reactor.

Through the observation and analysis of the experiments of the above examples and comparative examples, it can be seen that the reaction of partial gas phase of the amine solution with gaseous trichloromethyl chloroformate can effectively avoid the excessive reaction heat release, thereby avoiding the blockage of the reaction vessel caused by the generation of by-products, and meanwhile, the collection and treatment of the reaction tail gas in the invention improve the recovery rate of the tail gas and reduce the damage of the tail gas to the environment.

The foregoing is illustrative of the preferred embodiments of this invention, and it is to be understood that the invention is not limited to the precise form disclosed herein and that various other combinations, modifications, and environments may be resorted to, falling within the scope of the concept as disclosed herein, either as described above or as apparent to those skilled in the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A process for preparing isocyanate by adopting phosgenation reaction is characterized by comprising the following process steps:

2. The process for preparing isocyanates by phosgenation according to claim 1, wherein the solvent is a toluene solution or a dichloroethane solution.

3. The process for preparing isocyanates by phosgenation according to claim 1, wherein the amine is a monoamine or a diamine.

4. A process for the preparation of isocyanates by phosgenation according to claim 1 or 3, wherein the amine is one or more of 1, 6-diaminohexane, 1, 5-diaminopentane, 1, 3-bis (aminomethyl) cyclohexane.

5. The process for preparing isocyanate by phosgenation reaction as claimed in claim 1, wherein the tail gas from step five is treated by cathodic oxidation and catalytic oxidation of hydrogen chloride to produce chlorine.

6. The process for preparing isocyanates by phosgenation according to claim 1, wherein the absolute pressure in the four reactors of step 4 is from 0.3 to 3 bar.

7. The process for preparing isocyanate by phosgenation as claimed in claim 1, wherein the temperature of the gaseous trichloromethyl chloroformate added in the fourth step is 250-450 ℃.