Method of producing polyisocyanates

FIELD: chemistry.

SUBSTANCE: invention relates to the method of producing polyisocyanate, which involves (a) formation of polyisocyanate in a reaction system through reaction of polyamine, on which polyisocyanate is based, in a solution of inert solvent with phosgene, optionally in a solution of inert solvent; (b) separation of solvent from polyisocyanate, formed at stage (a) by evaporation or fractional distillation; (c) bringing the separated solvent to temperature between 10°C and 150°C and subsequent processing of the separated solvent with isocyanate trimerisation catalyst for trimerisation of isocyanate impurities in the separated solvent; (d) transferring the processed solvent from stage (c) to the reaction system at stage (a).

EFFECT: repeated use of solvent in the process, free from trace amounts of isocyanate and with low level of impurities.

10 cl, 1 dwg

This invention relates to a method for production of organic polyisocyanates in the presence of solvents, in which the solvent is re-used.

Organic polyisocyanates produced in large industrial scale postironium the corresponding primary amines in the presence of inert organic solvents, such as chlorobenzene or ortho-dichlorobenzene.

In the production of industrially important polyisocyanates, especially when receiving hexamethylene diisocyanates, tollen diisocyanates or polyisocyanates of the diphenyl methane series by postironium corresponding di - and polyamines, invariably formed trace amounts of by-products containing isocyanate groups (for example, 6-chloro-exisitent in the production of hexamethylene diisocyanate, tolyl isocyanate in the production tollen diisocyanates and phenyl isocyanate in the production of polyisocyanates biphenyl methane series when vosganian aniline/formaldehyde condensation products). Such unwanted isocyanate compounds seriously degrade the quality of the final products required (polyisocyanates). Thus, an attempt was made to remove these impurities from polyisocyanates by distillation together with the solvent after reaction vosganian and, subsequently, to release Rast is oritel from these impurities, using an improved distillation column. The solvent can then be reused. This cleaning solvent by distillation requires significant energy consumption and costs for the equipment, and the particular difficulties arise when the compounds have a boiling point close to the boiling point of the used solvent.

U.S. patent 4405527 describes a method of producing polyisocyanates in the presence of solvents, in which the solvent is freed from traces of compounds containing isocyanate groups, before reuse. The solvent is treated with compounds containing reactive towards isocyanate hydrogen atoms such as alcohols or amines, in order to turn volatile isocyanates in the reaction products containing urethane or urea groups. The treated solvent is then separated from these reaction products through distillation. Even if these reaction products (which have a much higher boiling point than trace isocyanates) are much more easily separated through distillation, removing these by-products requires a distillation of the entire quantity of solvent required to prepare the solution polyamine. This leads to high energy consumption due to the fact that it requires a large amount of solvent.

If urea or urethane, formed in the way described the data in U.S. patent 4405527, do not remove by distillation, they will enter into the process of vosganian when reusing solvent and will be easily subjected to numerous further reactions with phosgene and with the newly formed isocyanates. The total yield of MDI, the output separated diisocyanate product, if it was formed, and the quality of the polyisocyanates thus reduced. Also formed urethane and urea can during the subsequent formation of polyurethane, using polyisocyanate final product to regenerate phenylisocyanate during thermal decomposition.

In U.S. patent 4745216 solvent, which should be exempt from the trace amounts of isocyanate and should be reused, processed certain polymers and then separated from these polymers mechanically (for example, by decantation or filtration). Used polymers represented a cross-linked polymers, which were insoluble in the solvent and containing at least one functional group selected from primary alcoholic hydroxyl groups, secondary alcoholic hydroxyl groups, primary amino groups and secondary amino groups. It also creates a waste stream.

Thus, the purpose of the present invention is to provide a new method for removing trace amounts of the isocyanate and the solvent, remaining after production of polyisocyanates, in which the solvent is free from trace amounts of isocyanate and/or with low levels of impurities can be obtained without careful distillation of the solvent, recovered and re-used in traditional industrial processes for the production of polyisocyanates.

It was unexpectedly discovered that this problem of the isocyanate in the solvent, which should be reused, can be removed by treatment of the solvent, which must be freed from traces of isocyanate catalysts for the trimerization of isocyanates.

Monoisocyanates low molecular weight becomes, thus, stable trimers with high molecular weight. Mixed trimers can also be formed by the reaction of various products containing isocyanate group.

Upon receipt of the polyisocyanates diphenylmethane series the presence of trimers does not exert any harmful effects on the quality of the polyisocyanates obtained according to the method, and therefore they should not be removed from the solvent before reuse. In other variants of implementation (for example, when receiving tollen diisocyanates) prefer to delete the flow of trimers of the solvent prior to its re-use; this waste stream of trimers t is aetsa safer to handle, what a waste stream of monoisocyanates, which are much more volatile than trimers.

The method of the present invention has the additional advantage that polyamine used as starting substances in the reaction of vosganian may contain a higher proportion of by-products, which would lead to the formation of, respectively, a higher proportion of compounds containing the isocyanate group, which must be removed, which could be valid in the known processes. As a result, the cost of energy and the cost of equipment required for the preparation of the original polyamine, fall considerably in the method of the present invention.

The method of the present invention can be applied in the manufacture of any type of organic MDI. Particular preference is given to such aromatic polyisocyanates, as difenilmetana diisocyanate in the form of its 2,4'-, 2,2'- and 4,4'-isomers and mixtures thereof, mixtures difenilmetana diisocyanates (MDI) and oligomers known in this area as crude or polymeric MDI (polymethylene Polyphenylene the polyisocyanates)having isocyanate functionality of more than 2, toluene diisocyanate in the form of its 2,4 - and 2,6-isomers and mixtures thereof, 1,5-naphthalene diisocyanate and 1,4-diisocyanates. Other suitable organic polyisocyanates which may be the ü mentioned, include aliphatic diisocyanates, as isophorone diisocyanate, 1,6-diisocyanatohexane and 4,4'-diisocyanatohexane.

It is more preferable to use the method of the present invention in the production of polyisocyanates diphenylmethane series.

In this case, the impurities of low molecular weight, containing isocyanate groups, are mainly, but not exclusively, phenylisocyanate, cyclohexyl isocyanate and o - or p-chloromethyl phenylisocyanate.

The present invention relates to a method for the production of polyisocyanates by the reaction of polyamines from which we can get the polyisocyanates, preferably, as solutions in an inert solvent with phosgene, optionally as a solution in an inert solvent, single-stage or multistage reaction vosganian or any varieties known in this field, in the form of portions, in a continuous or properities mode, at atmospheric or elevated pressures. After completion of the reaction vosganian the reaction mixture is distilled. The solvent is then treated to remove trace quantities of isocyanate and used again for the preparation of amine solution and/or solution of phosgene.

In this way can be processed all the number of the regenerated solvent, but it is also possible to handle that is are part of the solvent, used to prepare the amine solution by this method.

Separate embodiments of the present invention include:

(i) gradual distillation of the reaction mixture, which conducted vosganian, in order to receive a stream of solvent, highly enriched in impurities isocyanate, which is subsequently treated to remove its trace amounts;

(ii) further partial processing of the solvent removed from the reaction mixture, which conducted vosganian, or by further distillation, or any other known method to obtain a stream of solvent, highly enriched in impurities isocyanate, which is subsequently treated to remove trace quantities of isocyanate;

(iii) a solvent recovery, which has been treated to remove impurities isocyanate in another appropriate part of the plant for the production of isocyanates, for example, in the reactor vosganian or vessel for distillation of the solvent;

(iv) partial trimerization of impurities isocyanate in the flow of solvent to the extent that very low levels of impurities can be valid for the re-use of solvent;

(v) adding diisocyanate to a predefined level, such as, but not limited to mixtures 4,4'-, 2,4'- and 2,2'- MDI isomers, the mixture which should be trimeresurus, to obtain compounds which have the structure of trimers composed of mixtures of impurities of isocyanates and diisocyanates, and, thus, detrimentally isocyanate groups capable of further reaction, for example, when a polyurethane material of the polyisocyanate product that contains trimeresurus material;

(vi) effect any or all of the above methods or a part of the action either periodic or continuous, or properities mode at atmospheric or increased pressure.

It should be understood that the above embodiments of the described only for purposes of illustration, and that a combination of these or similar variations not specifically described, are also included in the present invention.

The principle used in the present invention for influencing the solvent, especially suitable for multi-stage method of producing polyisocyanates, consists of the following individual steps:

(a) reaction (i) solutions polyamine(s)underlying the MDI(s), in an inert solvent and (ii) with phosgene, optionally in a solution of inert solvent by single-stage or multistage reaction vosganian;

(b) separating the excess phosgene and the hydrogen chloride formed from the liquid d is klonoa mixture, obtained at stage (a);

(c) separating the solvent together with a highly volatile compounds containing isocyanate groups, from the solution obtained in stage (b), evaporation and extraction process as residue after evaporation, which is optionally subjected to an additional process of distillation;

(d) recovering the solvent containing isocyanate compound(I) by condensation of the vapors obtained in stage (C), and reuse of part of the condensate to prepare a solution of amine (i) and optionally other part of the condensate for preparation of a solution of phosgene (ii).

The reaction vosganian carried out by any known method, using the solutions polyamine in an inert solvent, and phosgene, optionally as a solution in an inert solvent. In the method of the present invention, the reaction vosganian can be carried out either in one stage or in several stages. For example, vosganian may be a suspension of chlorides karbinovykh acids at low temperatures and then transforming these suspensions in solutions of polyisocyanates at elevated temperatures (cold/hot vosganian"). Particularly suitable source polyamines are technically such an important polyamine as hexamethylenediamine were; 2,4 - and/or 2,6-diaminotoluene; 2,4'-, 2,2'- and 4'-diaminodiphenyl methane and their mixtures with higher homologues (known as "polianinova mixture diphenylmethane series"), which can be obtained in a known manner aniline-formaldehyde condensation; 1,5-diaminonaphthalene; 1-amino-3,3,5-trimethyl-5-aminomethyl-cyclohexane (isophorone diamine); Tris-(isocyanatophenyl)-methane and perhydroanthracene diaminodiphenylmethane and their mixtures with higher homologues.

In the method of the present invention such source amines, such as those mentioned above as examples may be used in the form of 3-50% (wt.), preferably 5-40% (wt.), solutions in inert solvents. The phosgene required for the reaction vosganian, usually used in the form of 10-60% (wt.), preferably 25-50% (wt.), solutions in an inert solvent or without optional solvent.

Suitable inert solvents for both amine and phosgene known to specialists in this field. Examples of solvents are chlorinated aryl - or alkylaryl-hydrocarbons, such as monochlorobenzene (MRV), o-dichlorobenzene, trichlorobenzene and the corresponding toluene, xylan, connection methylbenzol and naphthalene, as well as many other well-known experts in this field, such as toluene, xylene, nitrobenzene, ketones and esters. Specific examples of appropriate solvents are mono - and dichlorobenzene.

After vosganian was carried out by methods known in this field, the excess of f is Shana and the resulting hydrogen chloride is removed by known methods, such as purging with an inert gas or partial distillation. Product vosganian, existing in the form of a solution, then share or simply by evaporation or fractional distillation of a gas phase containing the solvent, along with volatile compounds with isocyanate groups and a liquid phase consisting mainly of crude MDI. The resulting liquid phase may, optionally, be subjected to distillation in a known manner, if you want to get pure polyisocyanate. This separation of the crude MDI and volatile compounds is usually carried out at a temperature of from 80 to 220°C., preferably from 120 to 190°C.) at a pressure of from 10 to 4000 mbar, preferably from 100 to 3000 mbar).

Pairs containing solvent together with volatile compounds with isocyanate groups, are condensed to form a condensate solvent containing volatile isocyanates, in particular monoisocyanates. The number of isocyanate compounds present in the condensate (calculated as NCO with a molecular mass of 42), can be from 50 to 5000 ppm, in particular from 100 to 1500 ppm (by weight).

The resulting condensate solvent is then treated with a catalyst for the trimerization of isocyanate to convert any trace amounts of isocyanate products.

Anyone with the unity, which catalyzes the reaction of the trimerization of isocyanates may be used as trimerization catalyst, such as tertiary amines, triazine and trimerization catalysts based on metal salts. Examples of suitable trimerization catalysts based on metal salts are alkali metal salts of organic carboxylic acids. Preferred alkali metals are potassium and sodium. While the preferred carboxylic acids are acetic acid and 2-ethylhexanoate acid.

Especially preferred trimerization catalysts are 1,3,5-Tris(3-(dimethylamino)propyl)hexahydro-s-triazine (commercially available as Polycat 41 from Air Products) or Tris(dimethylaminomethyl)phenol (commercially available as DABCO TRM-30 from Air Products).

Another preferred group of catalysts is the so-called "reactive amines containing more reactive to the isocyanate group (HE, NH or NH₂for reaction with the isocyanate. Suitable examples include N,N-dimethylaminoethyl-N'-methyl ethanolamine (commercially available as DABCO T from Air Products). Such catalysts can be used as such for the trimerization or, optionally, after a preliminary reaction with isocyanatomethyl connection.

One or more solvent is for catalyst can also be used.

Processing of condensate above the trimerization catalyst is usually conducted in the temperature range from 10°C to 150°C, preferably from 25°C to 150°C, more preferably from 30°to 60°C.

Preferred are catalysts based on tertiary amines, can be inactivated by formation of salts with, for example, chloride of the remaining hydrogen chloride or other traces of impurities with movable chlorine atoms. Thus, to achieve close to the quantitative removal of compounds containing isocyanate groups, the trimerization catalyst must be used, at least in molar excess relative to the total number inactiveusers components, which can easily be determined experimentally by a person skilled in the art. The development of the trimerization can be monitored by controlling the amount of released heat. Excess trimerization catalyst can be inactivated either by adding additional quantities of hydrogen chloride, or by reaction with hydrogen chloride present in the reaction mixture in which the reaction takes place vosganian.

In one of the embodiments the solvent is then re-used for the preparation of a fresh portion of the solution of amine and/or phosgene. In contrast to the known methods used in this area is, however, subsequent purification by distillation for the removal of compounds containing isocyanate groups, and/or separation of the resulting reaction products from their by-products is not necessary in the process of the present invention.

However, you can certainly remove the resulting trimer of solvent before reuse. In this case, this can be done by fractional distillation.

When the solvent is processed, it can be used again for the preparation of a solution of amine (i) and/or a solution of phosgene (ii). As a result, when the solvent containing volatile isocyanate compounds, is treated according to the method of the present invention, the receive polyisocyanates with sharply reduced content of volatile isocyanate component.

Particularly preferred embodiments of the present invention, including MDI, will be described here in connection with the block diagram shown in the drawing.

The reaction mixture obtained at the end of the sequence vosganian, first cleanse in 3 stages. First remove the excess phosgene and hydrogen chloride. Then remove the MRV solvent containing trace amounts of phenylisocyanate (PI) (100 to 200 ppm); the solvent is recovered at this stage, is recycled back into the reaction sequence untreated. the ri last cleaning MRV solvent, enriched PI and other trace quantities of impurities of the isocyanate is separated from the crude MDI; crude MDI sequentially separated by distillation in the polymer and bifunctional faction.

Enriched MRV fraction is fed continuously to the column for concentrating PI. When the PI concentration at the bottom of the column reaches the value of approximately 10-30% PI in the MRV (preferably 15-25%), which is determined by the boiling temperature of the mixture at atmospheric pressure, usually from 140 to 160°C. (preferably 140 to 155°C), the liquid is transferred into a vessel for the trimerization either continuously or in portions. One or more portions of the concentrated liquid can be transferred on demand. After cooling liquid add Polycat 41 in a small molar excess relative to the deactivating components (usually 4 liters of Polycat 41 800 liters of fluid). Temperature before addition of the catalyst is usually from 10 to 100°C., preferably from 20 to 40°C). For the trimerization after adding the catalyst monitor, controlling the release of heat which raises the temperature up to 35-70°C., typically up to 50°C. After 2-12 hours liquid consisting of MRV, different trimers and some unreacted isocyanates, are transferred back to the reaction system is not necessarily within a short period of time (for example, men who e than one hour), but preferably in the course of a few hours (usually 6-12 hours).

The polyisocyanates obtained in the present process, have a very low level isocyanatomethyl impurities.

For example, upon receipt of the polyisocyanates diphenylmethane series, obtained MDI isomers and polymeric MDI containing very low levels of phenylisocyanate, typically below 50 ppm or even below 10 ppm.

1. Method for the production of MDI, including
(a) formation of MDI in the reaction system by response polyamine, based on the polyisocyanate, in a solution of inert solvent with phosgene, optionally in a solution of inert solvent;
(b) separating the solvent from the MDI formed in stage (a) by evaporation or fractional distillation;
(c) bringing the separated solvent to a temperature in the range from 10 to 150°C and subsequent treatment of the separated solvent catalyst for the trimerization of isocyanates for the trimerization of impurities isocyanate in the separated solvent;
(d) transferring the treated solvent from step (C) into the reaction system at stage (a).

2. The method of claim 1, wherein the solvent is monochlorobenzene or o-dichlorobenzene.

3. The method according to any one of claims 1 and 2, in which the catalyst for the trimerization of isocyanates are 1,3,5-Tris(3-(dimethylamino)PR who drank)hexahydro-s-triazine or Tris(dimethylaminomethyl)phenol.

4. The method according to any one of claims 1 and 2, in which stage (C) is carried out at a temperature of from 10 to 150°C.

5. The method according to any one of claims 1 and 2, where the polyisocyanate is an aromatic polyisocyanate.

6. The method according to any one of claims 1 and 2, where the polyisocyanate is diphenylmethane series.

7. The method according to any one of claims 1, 2 or 6, in which the solvent obtained in stage (C), re-used for solution polyamine to vosganian and/or a solution of phosgene and/or returned to any other suitable part of the line for the production of MDI.

8. The method according to any one of claims 1, 2 or 6, where between stages (a) and (b) from the reaction mixture to separate any excess phosgene and hydrogen chloride formed during the reaction stage (a).

9. The method of claim 8 in which the solvent is recovered from the reaction mixture in stage (b) by evaporation, and the polyisocyanate product is extracted from the residue after evaporation, the solvent is removed by condensation of the vapors.

10. The method according to claim 9, in which at least part of the extracted solvent is subjected to a brief distillation of obtaining solvent, especially enriched in impurities isocyanates, before adding a catalyst for the trimerization of isocyanates to stage (C).