CA2015223A1 - Process for the preparation of polyisocyanates - Google Patents
Process for the preparation of polyisocyanatesInfo
- Publication number
- CA2015223A1 CA2015223A1 CA 2015223 CA2015223A CA2015223A1 CA 2015223 A1 CA2015223 A1 CA 2015223A1 CA 2015223 CA2015223 CA 2015223 CA 2015223 A CA2015223 A CA 2015223A CA 2015223 A1 CA2015223 A1 CA 2015223A1
- Authority
- CA
- Canada
- Prior art keywords
- polyisocyanate
- decomposition
- solvent
- carbamic acid
- carbon atoms
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C263/00—Preparation of derivatives of isocyanic acid
- C07C263/04—Preparation of derivatives of isocyanic acid from or via carbamates or carbamoyl halides
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C263/00—Preparation of derivatives of isocyanic acid
- C07C263/18—Separation; Purification; Stabilisation; Use of additives
- C07C263/20—Separation; Purification
Abstract
Mo3360 LeA 26,273 A PROCESS FOR THE PREPARATION OF POLYISOCYANATES
ABSTRACT OF THE DISCLOSURE
The present invention relates to a process for the preparation of a polyisocyanate comprising (a) thermally decomposing a solution of an N-substituted carbamic acid ester corresponding to said polyisocyanate at temperatures above 150°C in a solvent or solvent mixture serving as a decomposition medium and with provision for continually removing by distillation the alcohol produced by the thermal decomposition of said carbamic acid ester, wherein said solvent or solvent mixture (i) is capable of dissolving the carbamic acid ester, (ii) is stable at the decomposition temperature and chemically inert towards the carbamic acid esters and the polyisocyanate formed during the decomposition reaction, and (iii) has at least one miscibility gap with the extracting agent used according to extraction step (b);
(b) extracting the polyisocyanate from the decomposition medium with an extracting agent that is at least partly immiscible with the decomposition medium and is a solvent for the polyisocyanate, and optionally distilling the resultant solution of the polyisocyanate in the extracting agent; and (c) recycling the portion of the decomposition medium remaining after the polyisocyanate is extracted.
Le A 26 273
ABSTRACT OF THE DISCLOSURE
The present invention relates to a process for the preparation of a polyisocyanate comprising (a) thermally decomposing a solution of an N-substituted carbamic acid ester corresponding to said polyisocyanate at temperatures above 150°C in a solvent or solvent mixture serving as a decomposition medium and with provision for continually removing by distillation the alcohol produced by the thermal decomposition of said carbamic acid ester, wherein said solvent or solvent mixture (i) is capable of dissolving the carbamic acid ester, (ii) is stable at the decomposition temperature and chemically inert towards the carbamic acid esters and the polyisocyanate formed during the decomposition reaction, and (iii) has at least one miscibility gap with the extracting agent used according to extraction step (b);
(b) extracting the polyisocyanate from the decomposition medium with an extracting agent that is at least partly immiscible with the decomposition medium and is a solvent for the polyisocyanate, and optionally distilling the resultant solution of the polyisocyanate in the extracting agent; and (c) recycling the portion of the decomposition medium remaining after the polyisocyanate is extracted.
Le A 26 273
Description
20~223 Mo3360 LeA 26,273 A PROCESS FOR THE PREPARATION OF POLYISOCYANATES
BACKGROUND OF THE INVENTION
This invention relates to a novel process for the preparation of organic polyisocyanates by thermal decomposition of the corresponding carbamic acid esters upon which the polyisocyanates are based.
It has long been known that N-substituted urethanes can be thermally decomposed in the gaseous or the liquid phase into isocyanates and alcohol. Fsr example, A.W. Hofmann, Ber.
o Dtsch. Chem. Ges., 3, 653 (1870); and H. Schiff, Ber. Dtsch Chem. Ges., 3, 649 (1870).
U.S. Patent 2,409,712 discloses a process in which recombination of the products obtained from the solvent-free decomposition of carbamic acid esters can be prevented by introducing the products into a cyclohexane-water mixture.
This process, however, provides only moderate isocyanate yields because of the partial hydrolysis of the resulting isocyanate at the phase interface.
The processes according to U.S Patents 3,962,302 and 3,919,278, for example, take place in the presence of inert high boiling solvents. In these processes, the two products of decomposition, that is, the alcohol and the isocyanate, are together continuously distilled from the decomposition medium and separated by fractional condensation. The disadvantages of these processes lie in the considerable technical expenditure required for the separation of the alcohol and isocyanate vapors and the moderate yields obtained. Readily volatile isocyanates are difficult to remove from the decomposition medium by distillation because of the high dilution and consequent low partial vapor pressure. Less volatile isocyanates, such as polyisocyanates of the diphenylmethane series, cannot be produced by these processes.
Le A 26 273 2~ 5223 In the process according to U.S. Patent 3,919,279, German Offenlegungsschrift 2,635,490 or German Offenlegungs-schrift 2,942,543, homogeneous or heterogeneous catalysts are used for increasing the volume/~ime yields. According to 5 European Application 61,013, secondary isocyanate reactions are suppressed by the addition of stabilizing additives, but such additives cannot reduce the difficulties encountered in the required distillation of the isocyanates.
The object of the present invention is to provide a o new process for the preparat;on of organic polyisocyanates by ther~al decomposition of the carbamic acid esters corresponding to the desired polyisocyanates, whereby the polyisocyanates obtained would be prevented from recombining with the alcohol formed and would be carefully isolated from the decomposition 15 medium. Such a process would be particularly suitable for the preparation of difficultly volatile polyisocyanates. This object has been accomplished by the process of the invention described below.
SUMMARY OF THE INVENTION
The present invention relates to a process for the preparation of a polyisocyanate comprising (a) thermally decomposing a solution of an N-substituted carbamic acid ester corresponding to said polyisocyanate at temperatures above about 150-C in a solvent or solvent mixture serving as a decomposition medium and with provision for continually removing by distillation the alcohol produced by the thermal decomposition of said carbamic acid ester, where~n said solvent or solvent mixture (i) is capable of dissolving the carbamic acid ester, (ii) is stable at the decomposition temperature and chemically inert towards the carbamic acid esters and the polyisocyanate formed during the decomposition reaction, and (iii) has at least one miscibility gap with an extracting agent used according to extraction step (b~;
Le A 25 273 2~223 (b) extracting the polyisocyanate from the decomposition medium (optionally after concentrating said polyisocyanate by fractional distillation) with an extracting agent, wherein said extracting agent is at least partly immiscible with the decomposition medium and is a solvent for the polyisocyanate, and optionally distilling the resultant solution of the polyisocyanate in the extracting agent, thereby yielding the polyisocyanate in substantially purified form; and o (c) recycling the portion of the decomposition medium remaining after the polyisocyanate is extracted in extraction step (b) (preferably by addition to the decomposition step (a)).
DETAILED DESCRIPTION OF THE LNYENTION
The carbamic acid esters used in the process according to the invention are compounds or mixtures of compounds corresponding to the formula Rl(NHCOOR2)n wherein Rl is an aliphatic hydrocarbon containing about 4 to about 18 carbon atoms and optionally containing inert substituents, a cycloaliphatic hydrocarbon group containing about 6 to about 25 carbon atoms and optionally containing inert substituents, an araliphatic hydrocarbon group containing 7 to about 25 carbon atoms and optionally containing inert substituents, or an aromatic hydrocarbon group containing 6 to about 30 carbon atoms and optionally containing inert substituents, 30 R is an alkyl group containing 1 to about 18 carbon atoms, a cycloalkyl group containing 5 to about 15 carbon atoms, an aralkyl group containing 7 to about 10 carbon atoms, or an aryl group containing 6 to about 10 carbon atoms; and n is an integer of from 2 to about 5, Le A 26 273 201~223 with the proviso that the corresponding alcohols R2-OH, wherein R2 has the meaning indicated above, have boil;ng points at atmospheric pressure at least lO-C lower than the boiling point of the solYent used as the decomposition medium and the boiling point of the corresponding polyisocyanate Rl(NCO)n, wherein has the meaning indicated above.
The preferred carbamic acid esters of the above formula used for the process according to the invention are those wherein o Rl is preferably an aliphatic hydrocarbon group containing 4 to 12 (more preferably 6 to 10) carbon atoms, a cycloaliphatic hydrocarbon group containing 6 to 15 carbon atoms, a xylylene group, or an aromatic hydrocarbon group containing a total of 7 to 30 carbon atoms and optionally carrying methyl substituents and/or methylene bridges;
R is preferably an alkyl group having 1 to 6 (preferably 1 to 4) carbon atoms, a cyclohexyl group, or a phenyl group;
and n is from 2 to 5.
Examples of suitable carbamic acid esters include l-(butoxycarbonylamino)-3,3,5-trimethyl-5-(butoxycarbonylamino-methyl)cyclohexane, l-methyl-2,4-bis(ethoxycarbonylamino)-benzene, l-methyl-2,6-bis(ethoxycarbonylamino)benzene, 1,10-bis(methoxycarbonylamino)decane, 1,12-bis(butoxycarbonylamino)-dodecane, 1,12-bis(methoxycarbonylamino)dodecane, 1,12-bis-(phenoxycarbonylamino)dodecane, 1,18-bis(butoxycarbonylamino)-octadecane, 1,18-bis(benzoyloxycarbonylamino)octadecane, 1,3-bis[(ethoxycarbonylamino)methyl]benzene, 1,3-bis(methoxy-carbonylamino)benzene, 1,3-bisl(methoxycarbonylamino)methyl]-benzene, 1,3,6-tr~s(methoxycarbonylamino)hexane, 1,3,6-tris-(phenoxycarbonylamino)hexane, 1,4-bis(2,4-dimethylphenoxy)-carbonylamino]butane, 1,4-bis(ethoxycarbonylamino)butane, 1,4-bis(ethoxycarbonylamino)cyclohexane, 1,5-bis~ethoxy-carbonylamino1naphthalene, 1,6-bis(ethoxycarbonylamino)hexane, 1,6-bis(methoxycarbonylamino~hexane, 1,6-bis~methoxymethyl Le A 26 ~73 201~223 carbonylamino)hexane, 1,8-bis(ethoxy-carbonylamino)octane, 1,8-bis(phenoxycarbonylamino)-4-(phenoxycarbonylaminomethyl)-octane, 1,8-bis(propoxycarbonyl-amino)octane, 2,2'-bis(4-propoxycarbonylaminophenyl)propane, 2,2'-bis(methoxycarbonyl-5 amino)diethyl ether, 2,4'-bis(ethoxy-carbonylamino)diphenyl-methane, 2,4-bis(methoxycarbonylamino)-cyclohexane, 4,4'-bis-(ethoxycarbonylamino)dicyclohexylmethane, 4,4'-bis(ethoxy-carbonylamino)diphenylmethane, 2,2-bis[(4-methoxycarbonyl-amino)cyclohexyl]propane, 4,4'-bis(methoxy-carbonylamino)-biphenyl, 2,2 bis[(4-butoxycarbonylamino)cyclohexyl]propane, 4,4'-bis(phenoxycarbonylamino)dicyclohexyl-methane, and 4,4'-bis(phenoxycarbonylamino)diphenylmethane. Also suitable are mixtures of the above exemplified 2,4'- and 4,4'-bis(alkoxy-carbonylamino)diphenylmethanes with corresponding higher 15 nuclear homologues in which more than two alkoxycarbonylamino-substituted benzene rings are joined together by methylene bridges. Such "carbamate mixtures of the diphenylmethane series" may be obtained, for example, by acid catalyzed condensation of mono-alkoxycarbonylamino-substituted benzenes 20 Wi th formaldehyde.
Suitable solvents for use as the reaction media for carrying out the decomposition of the invention are polar solvents that have a boiling point above 150-C (preferably above 200C) under the decomposition conditions of the process or that cannot be distilled at all without decomposing and, in addition to these properties, must also satisfy the following requirements. Suitable solvents must dissolve both the carbamic acid ester starting materials and the isocyanate reaction prDducts under the conditions of the extraction method described below, must be substantially stable to heat under the decomposition conditions, must be chemically inert towards the carbamic acid esters used ~n the process and the isocyanates formed in the process, and must have at least one miscibility gap with the extracting agent used in the extraction step of 35 the process of the invention.
Le A 26 273 2 ~ 2 3 Examples of solvents which conform to these criteria and are suitable as the reaction medium for the process of the invention include aliphatic sulfones, such as diethyl sulfone, dipropyl sulfone, dibutyl sulfone, and ethyl propyl sulfone;
cyclic sulfones, such as sulfolane, 2-methylsulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane; araliphatic sulfones, such as methyl phenyl sulfone and ethyl phenyl sulfone; aromatic sulfones, such as diphenyl sulfone and 4-methylphenyl phenyl sulfone; aromatic nitro compounds, such as nitrobenzene, 2-nitrotoluene, 3-nitrotoluene, and 4-chloronitrobenzene; and mixtures of such compounds.
Preferred solvents include sulfolane, 3-methyl sulfolane, and nitrobenzene, particularly sulfolane.
Suitable extracting agents include, in particular, aliphatic and cycloaliphatic hydrocarbons and aliphatic ethers having a boiling point or boiling range of from about 30 to about 200C (preferably from 30 to 150C) at 1013 mbar.
Examples of suitable extracting agents include hexanet isooctane, petroleum hydrocarbon fractions conforming to the above definitions, cyclohexane, methylcyclohexane, and aliphatic ethers containing at least 4 (preferably 4 to 12) carbon atoms, such as diethyl ether, isomeric butyl ethers, tert-butyl methyl ether, and heptyl methyl ether. Aromatic hydrocarbons such as benzene, toluene, and xylene are also suitable but less preferred. The aliphatic and cycloaliphatic hydrocarbons exemplified above are particularly preferred extracting agents. Any mixtures of the extracting agents exemplified above may, of course, also be used.
The process according to the invention may be carried out according to several variations. Generally, a solution containing 1 to 99X by weight (preferably S to 90% by weight and most preferably 15 to 75% by weight) of the carbamic acid ester in a solvent or solvent mixture of the type described above serving as reaction medium is heated to temperatures from 150 to 350-C (preferably from 150 to 280- C), optionally in the Le A 26 273 _ . .
2~5223 presence of up to 10 mole% (preferably up to 1 mole%) of a catalyst, in a suitable reaction vessel at a pressure of from about 0.001 to about 5 bar. The alcohol vapors that result from decomposition are distilled off, optionally using a 5 dephlegmator. To ensure that the alcohol decomposition product will be rapidly and effectively removed from the decomposition reactor, it may be advisable to pass through the reaction mixture an inert gas or an inert liquid that is low boiling under normal conditions and is easily separated from the o alcohol.
The decomposition reaction may be carried out continuously, batchwise, or intermittently in known apparatus known. If the reaction mixture is a solution of up to 30% by weight of the carbamic acid ester in a solvent of the type 15 described above, the decomposition reaction is preferably carried out continuously in a cascade of tanks designed to provide a sufficient dwell time of the solution fed into the tanks to ensure substantial decomposition of the carba~ic acid ester. The reaction time may vary from a few minutes to 20 several hours, depending on the reactivity of the carbamic acid ester to be decomposed and on the reaction temperature employed.
The conditions are preferably chosen that at least 10% (prefer2bly more than 50%) of the theoretical amount of 25 starting materials undergo conversion within reaction times of from about 30 minutes to about 5 hours. Because of the luw concentrations used in the react~on mixture, the formation of polymeric by-products is to a large extent avoided.
It has been found that if thP solutions have a carbamic acid concentration above 3CX by weight, it is advantageous to carry out the decomposition reaction by passing the solution in a thin layer along the internal wall of a heated tube. The dwell time of the solution in the reaction tube is kept very short in order to suppress side reactions.
The alcohol released in the decomposition reaction is removed ~O~L~J~23 ~verhead as gaseous product, whereas the isocyanate-containing reaction mixture is discharged as sump product. If the tube reactors are placed vertically, the reaction mixture introduced into them may be distributed over the internal walls of the s tubes without the aid of special apparatus, if the reaction mixture is applied uniformly over the wall of the tube by means of a suitable device, for example, a nozzle. Distribution of the reaction mixture may, however, also be achieved with the aid of a mechanical stirrer or s;milar devices. If the tube reactors are not placed vertically, it is generally necessary to use a mechanical stirrer or some other suitable device.
As previously indicated, suitable decomposition catalysts, such as those described, for example, in German Offenlegungsschrift 2,635,490 and U.S. Patent 3,919,279, may be added to the reaction mixture to accelerate the decomposition reactions.
The thermal decomposition step of the process of the invention may be carried out at elevated or reduced pressure in the range of from about 0.001 to about 5 bar but is preferably carried out at reduced pressures in the range of from 0.005 to 0.5 bar to ensure rapid removal of the alcohol from the reaction mixture.
The decomposition reaction ~hould be carried out at fiuch temperatureC and pre~ ures, within the ranges indicat~d aboYe, that the alcohol~ g3nerated will be the only componenL l~aving tho rsaction mixture in a gaseou-for~. This r~qUiremQnt ~ay ba ensured not only by suit~ble c~oice of the decomposition ~mperature but ecpoci~lly al~o by cu;table choice of the dephlegmator ~mparatur0~
When c~rrying out th~ process of ~h~ in~ention, it is i~port~nt for bo~h ~h~ csrb~mic acid ~cters b3ing deco~poced ond tha icocyan~tes bsing formed to be in ~olution under the condition~ u~ed for extraction that follow6 the decomposition rea~tion.
The cruds solution obt~in~d from the thermal decomposition of carb~mic ~cid e6~rfi, which con~ist Le A 26 273 2~1 ~i223 predominantly of the polyisocyanate products but also of residues of carbamic acid esters that have not decomposed or have only partly decomposed, are cooled to a temperature below the decomposition temperature and extracted in the second stage 5 of the process. If desired, the crude solution may~ of course, be concentrated by fractional distillation before carrying out the extraction.
For carrying out the extraction of the invention, the isocyanate-containing crude solution is vigorously mixed with o an extracting agent, as exemplified above, that is liquid at room temperature. This extracting agent is used in about 0.1 to about 25 (preferably 0.5 to 5) times the quantity by weight of the crude solution to be extracted. The crude solution is generally mixed with the extracting agent within a temperature range of from about -20C to about 150~C ~preferably from 10C
to 100-C). This procedure generally results in the spontaneous formation of a diphasic mixture of two liquid phases which, after phase deposition, can be separated into a upper phase and a lower phase. The formation of a diphasic system may in special cases be promoted by cooling the mixture of the crude solution and the extracting agent. Thus, for example, mixing can be carried out at about 70C to 100-C and the resultant mixture may then be cooled to a lower temperature, for example, in the range of from 10-C to 40C.
The upper phase of the diphasic system generally constitutes the main phase and the lower phase the secondary phase, although the ratio by volume depends to a large extent on the quantity of extracting agent used. In the process of the invention, phase separation may be carried out by known 30 methods, for example, by discharging the lower phase, by decanting, by siphoning, or by other suitable methods of phase separation. Part of the polyisocyanate that is to be recovered in pure form is then present in the upper main phase. Other components of the upper phase include part of the solvent used 35 as decomposition medium and the major proportion of the Le A 26 273 203. ~23 -lo-extracting agent used. ~he lower phase consists mainly of the solvent used as decomposition medium, the unreacted or only partially reacted carbamic acid esters, the by-products of the decomposition reaction, and that part of the polyisocyanate product that has not been transferred into the upper phase. To obtain this part of the polyisocyanate in pure form, the lower phase may be subjected to one or more additional extractions carried out in the manner described.
In a preferred embodiment of the process of the o invention, mixing the crude solution with the extracting agent and subsequent phase separation ~that is, extraction of the crude solution) are carried out continuously using conventional continuously operating counterflow extraction apparatus.
~he extraction gives rise to one or more upper S extraction phases containing the polyisocyanate and a generally homogeneous second phase mainly containing unreacted or only incompletely reacted carbamic acid ester. Multiple upper extracts can optionally be combined. The lower phase may be reused as solvent for the decomposition reaction. It has been found that when the lower phase is reused, it is advantageous to discharge a proportion of the phase and replace it with fresh solvent to avoid accumulation of the by-products present in the lower phase.
~o obtain the polyisocyanates in the pure form, the upper extraction phases are wsrked up by distillation, the extracting agent generally constituting the first fraction to be removed by distillation. Separation of the polyisocyanates from residual solvent used as the decomposition medium may also be carried out by distillation, during which the polyisocyanate or the solvent used as the decomposition medium forms the distillation residue. It is generally preferred to use decomposition solvents having a clearly different boiling point from that of the polyisocyanate product so that the two can easily be separated. ~hen the upper extraction phases are worked up by distillation, the polyisocyanate generally Le A 26 273 _ constitutes the distillation residue. Workup by distillation can also be carried out continuously using known distillation apparatus. If desired, polyiso~yanates obtained as distillation residue can be subjected to a further, fine distillation, but even without such fine distillation the lo polyisocyanates obtained as distillation residues can sometimes have a purity of greater than 90% by weight.
It is a particular advantage of the process of the invention that the polyisocyanates obtained from the decomposition reaction are isolated not by a distillation associated with unnecessary exposure to heat but by extraction under mild conditions of any reaction by-products. As a result, the known secondary reactions of isocyanates, which can in some cases be catalyzed by the by-products of the decomposition reaction and by the carbamic acid esters used in the process, are to a large extent suppressed. Thus, a subst~ntially higher proportion of the polyisocyanate formed in the decomposition reaction remains undecomposed and may be isolated in pure form.
The following examples further illustrate details for the proceçs of this invention. The invention, which is set forth in the foregoing disclosure, is not to be limited either in spirit or scope by these examples. Those skilled in the art will readily understand that known variations of the conditions of the following procedures can be used. Unless otherwise noted, all temperatures are degrees Celsius and all percentages are molar percentages.
Le A 26 273 2~ 5223 The first cycle yields are ba6ed on ~he actual yields obtained in the Examplee. The rontinuou6 pro-cess yields refer to the to~al amount of diisocyana~e obtalned by (1) recovering addi~ional diisocyanate from the first cycle and t2) converting unreacted and par-tially reacte~ carbamic acid ester ~o produ~ in subse-quent decompo ition steps. Thi~ y;eld i5 calculated ~s the limiting value o~ a ~eometric row and is given by:
l-(s1-Y1)/lOO
where y = con~inuous process yield (%) Y1 = first cycle yield (%) ~1 = sum of total amount of dii~ocy~nate and unreacted and par~ially reac~ed carbamic e 6 ters (%) EXAMPLES
Procedure ~A).
The selected solvent is heated to a temperature about Z~ C below ~he de~ired decomposition tempersture in a fla6k equipped with a glass-cover6d blade ~tirrer, a thermomster, a nitrogen inlet opening below the liquid ~urf~cel and a dephlegmator ti.e., a ro~s flow cooling device). The carb~mic acid e~t~r to be decomposed (and, if us~d, cataly6t~ and/or ctabilizerc) are ~dded and the entire content6 of the ~lac~ are heat~d with vigorous ~tirring under a con~tant stream of nitrog0n to the required decompositlon temperature. A redused Le A 26 273 201522~
pressure is regulated to proviae vlgorous reflux in the dephlegmator. The temperature of the dephlegmator should be maintained between the boiling points of the solvent used and the alcohol to be removed. The decomposition gases are condensed or partially condensed at the upper end of the dephlegmator with a water-cooled Liebig condenser and collected in a receiver that is optionally cooled with cooling mixture (e.g., dry ice-acetone).
The extent of conversion obtain~d by the decomposition reaction is determined by removing small samples of the reaction solution with a syringe inserted through a septum and the isocyanate content of the samples is determined by titration (i.e., by reaction with dibutyl amine and back titration of the excess amine with hydrochloric acidj.
When the desired extent of decomposition has been reached, the decomposition reaction is stopped by cooling the reaction solution to a temperature suitable for extraction and by then extracting the solution as described below.
Procedure (B):
~he decomposition reactor for this procedure is a cylindrical thin-layer evaporator (effective length 3~0 mm and diameter 35 mm3 equipped with a metal propeller stirrer whose movable blades extend to the wall of the thin-layer evaporator.
A heatable addition funne1 at the head of the thin-layer evaporator is used for introducing the carbamic acid ester to be decomposed. Reaction products which cannot be evaporated are discharged through a closable tap dt the bottom of the thin-layer evaporator, whereas components of the reaction mixture which can be evaporated are removed through a heated transverse flow condensor placed at the head of the thin-layer evaporator and having a condensation coil with discharge outlet at the upper end. Evacuation of the decomposition apparatus is ~e A 26 2?3 2 ~ 3 carried out using a rotary disk pump with a cooling trap behind the condensation coil.
The isocyanate-containing mixture obtained during the decomposition reaction is warmed to a temperature suitable for extraction, optionally after the addition of further solvent, and extracted by the method described below.
Extraction:
The mixture i5 extracted in a heatable flask which has a discharge device at the bottom and is equipped with a glass-covered blade stirrer, a thermometer, and a reflux condensor. This extraction is carried out by adding the extracting agent and mixing the two components vigorously for 30 minutes. After the mixture has been allowed to stand for 10 minutes, the resulting two phases are separated. In some examples, the lower phase is subjected to one or more further extractions with fresh extracting agent. The upper phases are combined and then tested for their composition by means of high performance liquid chromatography ("HPLC"), as are the lower phases left over after extraction.
The abbreviation suffixes used below ha~e the following meanings: "Dl" denotes polyisocyanates free from urethane, in particular diisocyanatei ~IU" denotes partially decomposed product containing urethane and isocyanate groups, in particular isocyanatourethane; and ~U" denotes unchanged starting material, in particular diurethane.
Example 1 Using Procedure (A), a solution of 151 9 of 1,5-bis(ethoxycarbonylamino)naphthalene (nNDUn) and 2.60 9 of dibutyltin dilaurate in 1346 9 of sulfolane is thermolized at 200-C for 300 minutes. The reaction mixture, which has an isocyanate value of 2.26% by weight (80.7X of theoretical), is cooled to 70-C and extracted four times each with 4700 9 portions of cyclohexane. According to HPLC analysis, the collected extracts contain 58.9 9 of 1,5-diisocyanato-naphthalene (~NDIa~ and 23.9 g of 1-ethoxycarbonylamino-Le A 26 273 20~.5~23 5-isocyanatanaphthalene ("NIU"). me ~'DU content is belaw the limit of detection. After extraction, the sulfolane phase contains 15.6 9 of NIU and 2.4 9 of NDU. The NDI content is below the limit of detection. The isolable yields of 1,5-di-5 isocyanatonaphthalene calculated from these figures are 56.0%after a first cycle and 80.6% for a continuous process.
Example ?
Using Procedure tB), a solution of 225 9 of 2,4-bis-(ethoxycarbonylamino)toluene (nTDU"), 0.55 9 of dibutyltin dilaurate, and 2.2 9 of stearic acid chloride in 75 9 of sulfolane and 30 9 of chlorobenzene is introduced over a period of 6.5 hours (dripping rate of 50 g/h) from the addition funnel which is thermostatically controlled at 100-C into the thin-layer evaporator which is heated to 290-C. The pressure in the 15 apparatus is 200 mbar during the decomposition reaction. A
yield of 261 9 of sump product is obtained. According to HPLC, this sump product contains 70.7 9 of TDU, 99.2 9 of the corresponding ethoxycarbonylaminoisocyanatotoluene (~TIU") isomeric mixture, and 24.7 9 of 2,4-diisocyanatotoluene 20 ("TDI"). The sump is extracted at 50-C four times each with 260 9 portions of isooctane. After the last extraction, the sulfolane phase contains 65.7 9 of TDU, 85.7 g of TIU, and 4.7 g of TDI. The combined extracts contain a total of 2.0 g of TDU, 15.8 9 of TIU, and 19.4 9 of TDI. The isolable yields of 2,4-diisocyanatotoluene salculated from these figures are 13.3%
after a first cycle and more than 98% for a continuous process.
ExamDle 3 Using Procedure IA), a solution of 85.6 g of a mixture of 4,4'-bis(ethoxycarbonylamino)diphenylmethane homologs (npolymeric MDU") having a total MDU content of 73.5%
by weight and 0.26 g of dibutyl tin dilaurate in 1414 9 of sulfolane is thermolyzed at 250'C for 70 minutes. The reaction mixture9 which has an isocyanate value of 0.97% by weight ~94.4% of theoretical), is cooled to 20-C and extracted four times each with 1740 g portions of a mixture of tert-butyl Le A 26 2?3 201~23 methyl ether and isooctane (1:1). According to HPLC analysis, the combined extracts contain 28.7 9 of a mixture of 4,4'-di-isocyanatodlphenylmethane homologs ("polymeric MDI"), 1.0 g of a mixture of the corresponding ethoxycarbonylaminoisocyanato-5 diphenylmethane homologs ("polymeric MIU"), and 0.9 g ofpolymeric MDU. The sulfolane phase conta;ns 12.5 g of polymeric MDI, 3.0 9 of polymeric MIU, and 0.7 9 of polymeric MDU after extraction. The isolable yields of the mixture of 4,4'-diisocyanatodiphenylmethane homologs calculated from these o figures are 61.9% after a first cycle and 98.3% for a continuous process.
ExamPle 4 Using Procedure (B), a solution of 140 g of 4,4'-bis-(ethoxycarbonylamino)diphenylmethane ("MDU") and 0.35 g of dibutyltin dilaurate in 140 9 of sulfolane and 28 g of chlorobenzene is introduced over a period of 6.25 hours (dripping rate of 50 g/h) from the addition funnel which is thermostatically controlled at 125-C into the thin-layer evaporator which is heated to 260-C. The pressure in the 20 apparatus during the decomposition reaction is 150 mbar. A
yield of 261 g of sump product is obtained. According to HPLC, this sump product contains 51.7 9 of MDU, 38.6 9 of the corresponding ethoxycarbonylaminoisocyanatodiphenylmethane ("MIU"), and 28.4 9 of 4,4'-diisocyanatodiphenylmethane 25 ("MDI"). The sump product is extractcd four times each with 260 9 portions of cyclooctane at 80-C. After the last extraction~ the sulfolane phase contains 49.3 9 of MDU, 26.8 g of MIU, and 5.5 9 of MDI. The combined extracts contain a total of 2.8 9 of MDU, 10.8 9 of MIU, and 25.4 9 of MDI. The 30 isolable yields of 4,4'-diisocyanatodiphenylmethane calculated from these figures are 24.8% after a first cycle and ~4.7% for a continuous process~
Le A 26 273 __~ _ _ 2~ 23 ExamPle 5 Using Procedure (A~, a solution of 75 g of 1-(ethoxy-carbonylamino)-3,3,5-trimethyl-5-(ethoxycarbonylaminomethyl~-cyclohexane ("IPDU") and 0.26 9 of dibutyltin dilaurate in 1425 9 of sulfolane is thermolyzed at 250-C for 60 minutes. The reaction mixture, which has an isocyanate value of 1.13% by weight (84.9% of theoretical), is cooled to 20DC and extracted four times each with 860 g portions of cyclohexane. Accord;ng to HPLC analysis, the combined extrac~s contain 34.8 9 of 1-isocyanato-3,3,5-trimethyl-5-(isocyanatomethyl)cyclohexane ~"IPDI"), and 2.0 9 of the corresponding (ethoxycarbonylamino)-(isocyanatomethyl)-3,3~5-trimethylcyclohexane ("IPIU") ;someric mixture. (The carbamic acid ester IPDU9 which has remained unchanged in the decomposition reaction, is not detected in the HPLC analysis.) After the extraction, the sulfolane phase contains 7.0 g of IPDI and 5.5 g of IPIU. The isolable yields of 1-isocyanato-3,3,5-trimethyl-5-(isocyanatomethyl~cyclohexane calculated from these figures are 66.0% after a first cycle and more than 88% for a continuous process.
Example 6 Using Procedure (B), a solution of 112 9 of TDU, 0.27 g of dibutyltin dilaurate, and 1.1 9 of stearic acid chloride in 37 9 of sulfolane and 15 9 of chlorobenzene is introduced over a period of 9 hours (dripping rate of 18 g/h) from the addition funnel which is thermostatically controlled at 100C
into the thin-layer evaporator which is heated to 290-C. The pressure in the apparatus during the decomposition reaction is 200 mbar. A yield of 123 9 of sump product is obtained.
According to HPLC, this sump product contains 16.0 9 of TDU, 34.5 9 of the corresponding TIU isomeric mixture, and 30.7 9 of TDI. The sump is extracted four times each time with 125 S
psrtions of cyclooctane at 20-C. After the last extraction, the sulfolane phase contains 15.1 9 of TDU, 28.4 9 of TIU, and 5.9 g of TDI. The comhined extracts contain a total of 0.6 9 of TDU, 5.5 9 of TIU, and 25.0 9 of TDI. The isolable yields Le A 26 2?3 2~1~223 of 2,4-diisocyanatotoluene calculated from these figures are 34.2% after a first cycle and 82.8% for a continuous process.
Le A 26 273 ~ . .
BACKGROUND OF THE INVENTION
This invention relates to a novel process for the preparation of organic polyisocyanates by thermal decomposition of the corresponding carbamic acid esters upon which the polyisocyanates are based.
It has long been known that N-substituted urethanes can be thermally decomposed in the gaseous or the liquid phase into isocyanates and alcohol. Fsr example, A.W. Hofmann, Ber.
o Dtsch. Chem. Ges., 3, 653 (1870); and H. Schiff, Ber. Dtsch Chem. Ges., 3, 649 (1870).
U.S. Patent 2,409,712 discloses a process in which recombination of the products obtained from the solvent-free decomposition of carbamic acid esters can be prevented by introducing the products into a cyclohexane-water mixture.
This process, however, provides only moderate isocyanate yields because of the partial hydrolysis of the resulting isocyanate at the phase interface.
The processes according to U.S Patents 3,962,302 and 3,919,278, for example, take place in the presence of inert high boiling solvents. In these processes, the two products of decomposition, that is, the alcohol and the isocyanate, are together continuously distilled from the decomposition medium and separated by fractional condensation. The disadvantages of these processes lie in the considerable technical expenditure required for the separation of the alcohol and isocyanate vapors and the moderate yields obtained. Readily volatile isocyanates are difficult to remove from the decomposition medium by distillation because of the high dilution and consequent low partial vapor pressure. Less volatile isocyanates, such as polyisocyanates of the diphenylmethane series, cannot be produced by these processes.
Le A 26 273 2~ 5223 In the process according to U.S. Patent 3,919,279, German Offenlegungsschrift 2,635,490 or German Offenlegungs-schrift 2,942,543, homogeneous or heterogeneous catalysts are used for increasing the volume/~ime yields. According to 5 European Application 61,013, secondary isocyanate reactions are suppressed by the addition of stabilizing additives, but such additives cannot reduce the difficulties encountered in the required distillation of the isocyanates.
The object of the present invention is to provide a o new process for the preparat;on of organic polyisocyanates by ther~al decomposition of the carbamic acid esters corresponding to the desired polyisocyanates, whereby the polyisocyanates obtained would be prevented from recombining with the alcohol formed and would be carefully isolated from the decomposition 15 medium. Such a process would be particularly suitable for the preparation of difficultly volatile polyisocyanates. This object has been accomplished by the process of the invention described below.
SUMMARY OF THE INVENTION
The present invention relates to a process for the preparation of a polyisocyanate comprising (a) thermally decomposing a solution of an N-substituted carbamic acid ester corresponding to said polyisocyanate at temperatures above about 150-C in a solvent or solvent mixture serving as a decomposition medium and with provision for continually removing by distillation the alcohol produced by the thermal decomposition of said carbamic acid ester, where~n said solvent or solvent mixture (i) is capable of dissolving the carbamic acid ester, (ii) is stable at the decomposition temperature and chemically inert towards the carbamic acid esters and the polyisocyanate formed during the decomposition reaction, and (iii) has at least one miscibility gap with an extracting agent used according to extraction step (b~;
Le A 25 273 2~223 (b) extracting the polyisocyanate from the decomposition medium (optionally after concentrating said polyisocyanate by fractional distillation) with an extracting agent, wherein said extracting agent is at least partly immiscible with the decomposition medium and is a solvent for the polyisocyanate, and optionally distilling the resultant solution of the polyisocyanate in the extracting agent, thereby yielding the polyisocyanate in substantially purified form; and o (c) recycling the portion of the decomposition medium remaining after the polyisocyanate is extracted in extraction step (b) (preferably by addition to the decomposition step (a)).
DETAILED DESCRIPTION OF THE LNYENTION
The carbamic acid esters used in the process according to the invention are compounds or mixtures of compounds corresponding to the formula Rl(NHCOOR2)n wherein Rl is an aliphatic hydrocarbon containing about 4 to about 18 carbon atoms and optionally containing inert substituents, a cycloaliphatic hydrocarbon group containing about 6 to about 25 carbon atoms and optionally containing inert substituents, an araliphatic hydrocarbon group containing 7 to about 25 carbon atoms and optionally containing inert substituents, or an aromatic hydrocarbon group containing 6 to about 30 carbon atoms and optionally containing inert substituents, 30 R is an alkyl group containing 1 to about 18 carbon atoms, a cycloalkyl group containing 5 to about 15 carbon atoms, an aralkyl group containing 7 to about 10 carbon atoms, or an aryl group containing 6 to about 10 carbon atoms; and n is an integer of from 2 to about 5, Le A 26 273 201~223 with the proviso that the corresponding alcohols R2-OH, wherein R2 has the meaning indicated above, have boil;ng points at atmospheric pressure at least lO-C lower than the boiling point of the solYent used as the decomposition medium and the boiling point of the corresponding polyisocyanate Rl(NCO)n, wherein has the meaning indicated above.
The preferred carbamic acid esters of the above formula used for the process according to the invention are those wherein o Rl is preferably an aliphatic hydrocarbon group containing 4 to 12 (more preferably 6 to 10) carbon atoms, a cycloaliphatic hydrocarbon group containing 6 to 15 carbon atoms, a xylylene group, or an aromatic hydrocarbon group containing a total of 7 to 30 carbon atoms and optionally carrying methyl substituents and/or methylene bridges;
R is preferably an alkyl group having 1 to 6 (preferably 1 to 4) carbon atoms, a cyclohexyl group, or a phenyl group;
and n is from 2 to 5.
Examples of suitable carbamic acid esters include l-(butoxycarbonylamino)-3,3,5-trimethyl-5-(butoxycarbonylamino-methyl)cyclohexane, l-methyl-2,4-bis(ethoxycarbonylamino)-benzene, l-methyl-2,6-bis(ethoxycarbonylamino)benzene, 1,10-bis(methoxycarbonylamino)decane, 1,12-bis(butoxycarbonylamino)-dodecane, 1,12-bis(methoxycarbonylamino)dodecane, 1,12-bis-(phenoxycarbonylamino)dodecane, 1,18-bis(butoxycarbonylamino)-octadecane, 1,18-bis(benzoyloxycarbonylamino)octadecane, 1,3-bis[(ethoxycarbonylamino)methyl]benzene, 1,3-bis(methoxy-carbonylamino)benzene, 1,3-bisl(methoxycarbonylamino)methyl]-benzene, 1,3,6-tr~s(methoxycarbonylamino)hexane, 1,3,6-tris-(phenoxycarbonylamino)hexane, 1,4-bis(2,4-dimethylphenoxy)-carbonylamino]butane, 1,4-bis(ethoxycarbonylamino)butane, 1,4-bis(ethoxycarbonylamino)cyclohexane, 1,5-bis~ethoxy-carbonylamino1naphthalene, 1,6-bis(ethoxycarbonylamino)hexane, 1,6-bis(methoxycarbonylamino~hexane, 1,6-bis~methoxymethyl Le A 26 ~73 201~223 carbonylamino)hexane, 1,8-bis(ethoxy-carbonylamino)octane, 1,8-bis(phenoxycarbonylamino)-4-(phenoxycarbonylaminomethyl)-octane, 1,8-bis(propoxycarbonyl-amino)octane, 2,2'-bis(4-propoxycarbonylaminophenyl)propane, 2,2'-bis(methoxycarbonyl-5 amino)diethyl ether, 2,4'-bis(ethoxy-carbonylamino)diphenyl-methane, 2,4-bis(methoxycarbonylamino)-cyclohexane, 4,4'-bis-(ethoxycarbonylamino)dicyclohexylmethane, 4,4'-bis(ethoxy-carbonylamino)diphenylmethane, 2,2-bis[(4-methoxycarbonyl-amino)cyclohexyl]propane, 4,4'-bis(methoxy-carbonylamino)-biphenyl, 2,2 bis[(4-butoxycarbonylamino)cyclohexyl]propane, 4,4'-bis(phenoxycarbonylamino)dicyclohexyl-methane, and 4,4'-bis(phenoxycarbonylamino)diphenylmethane. Also suitable are mixtures of the above exemplified 2,4'- and 4,4'-bis(alkoxy-carbonylamino)diphenylmethanes with corresponding higher 15 nuclear homologues in which more than two alkoxycarbonylamino-substituted benzene rings are joined together by methylene bridges. Such "carbamate mixtures of the diphenylmethane series" may be obtained, for example, by acid catalyzed condensation of mono-alkoxycarbonylamino-substituted benzenes 20 Wi th formaldehyde.
Suitable solvents for use as the reaction media for carrying out the decomposition of the invention are polar solvents that have a boiling point above 150-C (preferably above 200C) under the decomposition conditions of the process or that cannot be distilled at all without decomposing and, in addition to these properties, must also satisfy the following requirements. Suitable solvents must dissolve both the carbamic acid ester starting materials and the isocyanate reaction prDducts under the conditions of the extraction method described below, must be substantially stable to heat under the decomposition conditions, must be chemically inert towards the carbamic acid esters used ~n the process and the isocyanates formed in the process, and must have at least one miscibility gap with the extracting agent used in the extraction step of 35 the process of the invention.
Le A 26 273 2 ~ 2 3 Examples of solvents which conform to these criteria and are suitable as the reaction medium for the process of the invention include aliphatic sulfones, such as diethyl sulfone, dipropyl sulfone, dibutyl sulfone, and ethyl propyl sulfone;
cyclic sulfones, such as sulfolane, 2-methylsulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane; araliphatic sulfones, such as methyl phenyl sulfone and ethyl phenyl sulfone; aromatic sulfones, such as diphenyl sulfone and 4-methylphenyl phenyl sulfone; aromatic nitro compounds, such as nitrobenzene, 2-nitrotoluene, 3-nitrotoluene, and 4-chloronitrobenzene; and mixtures of such compounds.
Preferred solvents include sulfolane, 3-methyl sulfolane, and nitrobenzene, particularly sulfolane.
Suitable extracting agents include, in particular, aliphatic and cycloaliphatic hydrocarbons and aliphatic ethers having a boiling point or boiling range of from about 30 to about 200C (preferably from 30 to 150C) at 1013 mbar.
Examples of suitable extracting agents include hexanet isooctane, petroleum hydrocarbon fractions conforming to the above definitions, cyclohexane, methylcyclohexane, and aliphatic ethers containing at least 4 (preferably 4 to 12) carbon atoms, such as diethyl ether, isomeric butyl ethers, tert-butyl methyl ether, and heptyl methyl ether. Aromatic hydrocarbons such as benzene, toluene, and xylene are also suitable but less preferred. The aliphatic and cycloaliphatic hydrocarbons exemplified above are particularly preferred extracting agents. Any mixtures of the extracting agents exemplified above may, of course, also be used.
The process according to the invention may be carried out according to several variations. Generally, a solution containing 1 to 99X by weight (preferably S to 90% by weight and most preferably 15 to 75% by weight) of the carbamic acid ester in a solvent or solvent mixture of the type described above serving as reaction medium is heated to temperatures from 150 to 350-C (preferably from 150 to 280- C), optionally in the Le A 26 273 _ . .
2~5223 presence of up to 10 mole% (preferably up to 1 mole%) of a catalyst, in a suitable reaction vessel at a pressure of from about 0.001 to about 5 bar. The alcohol vapors that result from decomposition are distilled off, optionally using a 5 dephlegmator. To ensure that the alcohol decomposition product will be rapidly and effectively removed from the decomposition reactor, it may be advisable to pass through the reaction mixture an inert gas or an inert liquid that is low boiling under normal conditions and is easily separated from the o alcohol.
The decomposition reaction may be carried out continuously, batchwise, or intermittently in known apparatus known. If the reaction mixture is a solution of up to 30% by weight of the carbamic acid ester in a solvent of the type 15 described above, the decomposition reaction is preferably carried out continuously in a cascade of tanks designed to provide a sufficient dwell time of the solution fed into the tanks to ensure substantial decomposition of the carba~ic acid ester. The reaction time may vary from a few minutes to 20 several hours, depending on the reactivity of the carbamic acid ester to be decomposed and on the reaction temperature employed.
The conditions are preferably chosen that at least 10% (prefer2bly more than 50%) of the theoretical amount of 25 starting materials undergo conversion within reaction times of from about 30 minutes to about 5 hours. Because of the luw concentrations used in the react~on mixture, the formation of polymeric by-products is to a large extent avoided.
It has been found that if thP solutions have a carbamic acid concentration above 3CX by weight, it is advantageous to carry out the decomposition reaction by passing the solution in a thin layer along the internal wall of a heated tube. The dwell time of the solution in the reaction tube is kept very short in order to suppress side reactions.
The alcohol released in the decomposition reaction is removed ~O~L~J~23 ~verhead as gaseous product, whereas the isocyanate-containing reaction mixture is discharged as sump product. If the tube reactors are placed vertically, the reaction mixture introduced into them may be distributed over the internal walls of the s tubes without the aid of special apparatus, if the reaction mixture is applied uniformly over the wall of the tube by means of a suitable device, for example, a nozzle. Distribution of the reaction mixture may, however, also be achieved with the aid of a mechanical stirrer or s;milar devices. If the tube reactors are not placed vertically, it is generally necessary to use a mechanical stirrer or some other suitable device.
As previously indicated, suitable decomposition catalysts, such as those described, for example, in German Offenlegungsschrift 2,635,490 and U.S. Patent 3,919,279, may be added to the reaction mixture to accelerate the decomposition reactions.
The thermal decomposition step of the process of the invention may be carried out at elevated or reduced pressure in the range of from about 0.001 to about 5 bar but is preferably carried out at reduced pressures in the range of from 0.005 to 0.5 bar to ensure rapid removal of the alcohol from the reaction mixture.
The decomposition reaction ~hould be carried out at fiuch temperatureC and pre~ ures, within the ranges indicat~d aboYe, that the alcohol~ g3nerated will be the only componenL l~aving tho rsaction mixture in a gaseou-for~. This r~qUiremQnt ~ay ba ensured not only by suit~ble c~oice of the decomposition ~mperature but ecpoci~lly al~o by cu;table choice of the dephlegmator ~mparatur0~
When c~rrying out th~ process of ~h~ in~ention, it is i~port~nt for bo~h ~h~ csrb~mic acid ~cters b3ing deco~poced ond tha icocyan~tes bsing formed to be in ~olution under the condition~ u~ed for extraction that follow6 the decomposition rea~tion.
The cruds solution obt~in~d from the thermal decomposition of carb~mic ~cid e6~rfi, which con~ist Le A 26 273 2~1 ~i223 predominantly of the polyisocyanate products but also of residues of carbamic acid esters that have not decomposed or have only partly decomposed, are cooled to a temperature below the decomposition temperature and extracted in the second stage 5 of the process. If desired, the crude solution may~ of course, be concentrated by fractional distillation before carrying out the extraction.
For carrying out the extraction of the invention, the isocyanate-containing crude solution is vigorously mixed with o an extracting agent, as exemplified above, that is liquid at room temperature. This extracting agent is used in about 0.1 to about 25 (preferably 0.5 to 5) times the quantity by weight of the crude solution to be extracted. The crude solution is generally mixed with the extracting agent within a temperature range of from about -20C to about 150~C ~preferably from 10C
to 100-C). This procedure generally results in the spontaneous formation of a diphasic mixture of two liquid phases which, after phase deposition, can be separated into a upper phase and a lower phase. The formation of a diphasic system may in special cases be promoted by cooling the mixture of the crude solution and the extracting agent. Thus, for example, mixing can be carried out at about 70C to 100-C and the resultant mixture may then be cooled to a lower temperature, for example, in the range of from 10-C to 40C.
The upper phase of the diphasic system generally constitutes the main phase and the lower phase the secondary phase, although the ratio by volume depends to a large extent on the quantity of extracting agent used. In the process of the invention, phase separation may be carried out by known 30 methods, for example, by discharging the lower phase, by decanting, by siphoning, or by other suitable methods of phase separation. Part of the polyisocyanate that is to be recovered in pure form is then present in the upper main phase. Other components of the upper phase include part of the solvent used 35 as decomposition medium and the major proportion of the Le A 26 273 203. ~23 -lo-extracting agent used. ~he lower phase consists mainly of the solvent used as decomposition medium, the unreacted or only partially reacted carbamic acid esters, the by-products of the decomposition reaction, and that part of the polyisocyanate product that has not been transferred into the upper phase. To obtain this part of the polyisocyanate in pure form, the lower phase may be subjected to one or more additional extractions carried out in the manner described.
In a preferred embodiment of the process of the o invention, mixing the crude solution with the extracting agent and subsequent phase separation ~that is, extraction of the crude solution) are carried out continuously using conventional continuously operating counterflow extraction apparatus.
~he extraction gives rise to one or more upper S extraction phases containing the polyisocyanate and a generally homogeneous second phase mainly containing unreacted or only incompletely reacted carbamic acid ester. Multiple upper extracts can optionally be combined. The lower phase may be reused as solvent for the decomposition reaction. It has been found that when the lower phase is reused, it is advantageous to discharge a proportion of the phase and replace it with fresh solvent to avoid accumulation of the by-products present in the lower phase.
~o obtain the polyisocyanates in the pure form, the upper extraction phases are wsrked up by distillation, the extracting agent generally constituting the first fraction to be removed by distillation. Separation of the polyisocyanates from residual solvent used as the decomposition medium may also be carried out by distillation, during which the polyisocyanate or the solvent used as the decomposition medium forms the distillation residue. It is generally preferred to use decomposition solvents having a clearly different boiling point from that of the polyisocyanate product so that the two can easily be separated. ~hen the upper extraction phases are worked up by distillation, the polyisocyanate generally Le A 26 273 _ constitutes the distillation residue. Workup by distillation can also be carried out continuously using known distillation apparatus. If desired, polyiso~yanates obtained as distillation residue can be subjected to a further, fine distillation, but even without such fine distillation the lo polyisocyanates obtained as distillation residues can sometimes have a purity of greater than 90% by weight.
It is a particular advantage of the process of the invention that the polyisocyanates obtained from the decomposition reaction are isolated not by a distillation associated with unnecessary exposure to heat but by extraction under mild conditions of any reaction by-products. As a result, the known secondary reactions of isocyanates, which can in some cases be catalyzed by the by-products of the decomposition reaction and by the carbamic acid esters used in the process, are to a large extent suppressed. Thus, a subst~ntially higher proportion of the polyisocyanate formed in the decomposition reaction remains undecomposed and may be isolated in pure form.
The following examples further illustrate details for the proceçs of this invention. The invention, which is set forth in the foregoing disclosure, is not to be limited either in spirit or scope by these examples. Those skilled in the art will readily understand that known variations of the conditions of the following procedures can be used. Unless otherwise noted, all temperatures are degrees Celsius and all percentages are molar percentages.
Le A 26 273 2~ 5223 The first cycle yields are ba6ed on ~he actual yields obtained in the Examplee. The rontinuou6 pro-cess yields refer to the to~al amount of diisocyana~e obtalned by (1) recovering addi~ional diisocyanate from the first cycle and t2) converting unreacted and par-tially reacte~ carbamic acid ester ~o produ~ in subse-quent decompo ition steps. Thi~ y;eld i5 calculated ~s the limiting value o~ a ~eometric row and is given by:
l-(s1-Y1)/lOO
where y = con~inuous process yield (%) Y1 = first cycle yield (%) ~1 = sum of total amount of dii~ocy~nate and unreacted and par~ially reac~ed carbamic e 6 ters (%) EXAMPLES
Procedure ~A).
The selected solvent is heated to a temperature about Z~ C below ~he de~ired decomposition tempersture in a fla6k equipped with a glass-cover6d blade ~tirrer, a thermomster, a nitrogen inlet opening below the liquid ~urf~cel and a dephlegmator ti.e., a ro~s flow cooling device). The carb~mic acid e~t~r to be decomposed (and, if us~d, cataly6t~ and/or ctabilizerc) are ~dded and the entire content6 of the ~lac~ are heat~d with vigorous ~tirring under a con~tant stream of nitrog0n to the required decompositlon temperature. A redused Le A 26 273 201522~
pressure is regulated to proviae vlgorous reflux in the dephlegmator. The temperature of the dephlegmator should be maintained between the boiling points of the solvent used and the alcohol to be removed. The decomposition gases are condensed or partially condensed at the upper end of the dephlegmator with a water-cooled Liebig condenser and collected in a receiver that is optionally cooled with cooling mixture (e.g., dry ice-acetone).
The extent of conversion obtain~d by the decomposition reaction is determined by removing small samples of the reaction solution with a syringe inserted through a septum and the isocyanate content of the samples is determined by titration (i.e., by reaction with dibutyl amine and back titration of the excess amine with hydrochloric acidj.
When the desired extent of decomposition has been reached, the decomposition reaction is stopped by cooling the reaction solution to a temperature suitable for extraction and by then extracting the solution as described below.
Procedure (B):
~he decomposition reactor for this procedure is a cylindrical thin-layer evaporator (effective length 3~0 mm and diameter 35 mm3 equipped with a metal propeller stirrer whose movable blades extend to the wall of the thin-layer evaporator.
A heatable addition funne1 at the head of the thin-layer evaporator is used for introducing the carbamic acid ester to be decomposed. Reaction products which cannot be evaporated are discharged through a closable tap dt the bottom of the thin-layer evaporator, whereas components of the reaction mixture which can be evaporated are removed through a heated transverse flow condensor placed at the head of the thin-layer evaporator and having a condensation coil with discharge outlet at the upper end. Evacuation of the decomposition apparatus is ~e A 26 2?3 2 ~ 3 carried out using a rotary disk pump with a cooling trap behind the condensation coil.
The isocyanate-containing mixture obtained during the decomposition reaction is warmed to a temperature suitable for extraction, optionally after the addition of further solvent, and extracted by the method described below.
Extraction:
The mixture i5 extracted in a heatable flask which has a discharge device at the bottom and is equipped with a glass-covered blade stirrer, a thermometer, and a reflux condensor. This extraction is carried out by adding the extracting agent and mixing the two components vigorously for 30 minutes. After the mixture has been allowed to stand for 10 minutes, the resulting two phases are separated. In some examples, the lower phase is subjected to one or more further extractions with fresh extracting agent. The upper phases are combined and then tested for their composition by means of high performance liquid chromatography ("HPLC"), as are the lower phases left over after extraction.
The abbreviation suffixes used below ha~e the following meanings: "Dl" denotes polyisocyanates free from urethane, in particular diisocyanatei ~IU" denotes partially decomposed product containing urethane and isocyanate groups, in particular isocyanatourethane; and ~U" denotes unchanged starting material, in particular diurethane.
Example 1 Using Procedure (A), a solution of 151 9 of 1,5-bis(ethoxycarbonylamino)naphthalene (nNDUn) and 2.60 9 of dibutyltin dilaurate in 1346 9 of sulfolane is thermolized at 200-C for 300 minutes. The reaction mixture, which has an isocyanate value of 2.26% by weight (80.7X of theoretical), is cooled to 70-C and extracted four times each with 4700 9 portions of cyclohexane. According to HPLC analysis, the collected extracts contain 58.9 9 of 1,5-diisocyanato-naphthalene (~NDIa~ and 23.9 g of 1-ethoxycarbonylamino-Le A 26 273 20~.5~23 5-isocyanatanaphthalene ("NIU"). me ~'DU content is belaw the limit of detection. After extraction, the sulfolane phase contains 15.6 9 of NIU and 2.4 9 of NDU. The NDI content is below the limit of detection. The isolable yields of 1,5-di-5 isocyanatonaphthalene calculated from these figures are 56.0%after a first cycle and 80.6% for a continuous process.
Example ?
Using Procedure tB), a solution of 225 9 of 2,4-bis-(ethoxycarbonylamino)toluene (nTDU"), 0.55 9 of dibutyltin dilaurate, and 2.2 9 of stearic acid chloride in 75 9 of sulfolane and 30 9 of chlorobenzene is introduced over a period of 6.5 hours (dripping rate of 50 g/h) from the addition funnel which is thermostatically controlled at 100-C into the thin-layer evaporator which is heated to 290-C. The pressure in the 15 apparatus is 200 mbar during the decomposition reaction. A
yield of 261 9 of sump product is obtained. According to HPLC, this sump product contains 70.7 9 of TDU, 99.2 9 of the corresponding ethoxycarbonylaminoisocyanatotoluene (~TIU") isomeric mixture, and 24.7 9 of 2,4-diisocyanatotoluene 20 ("TDI"). The sump is extracted at 50-C four times each with 260 9 portions of isooctane. After the last extraction, the sulfolane phase contains 65.7 9 of TDU, 85.7 g of TIU, and 4.7 g of TDI. The combined extracts contain a total of 2.0 g of TDU, 15.8 9 of TIU, and 19.4 9 of TDI. The isolable yields of 2,4-diisocyanatotoluene salculated from these figures are 13.3%
after a first cycle and more than 98% for a continuous process.
ExamDle 3 Using Procedure IA), a solution of 85.6 g of a mixture of 4,4'-bis(ethoxycarbonylamino)diphenylmethane homologs (npolymeric MDU") having a total MDU content of 73.5%
by weight and 0.26 g of dibutyl tin dilaurate in 1414 9 of sulfolane is thermolyzed at 250'C for 70 minutes. The reaction mixture9 which has an isocyanate value of 0.97% by weight ~94.4% of theoretical), is cooled to 20-C and extracted four times each with 1740 g portions of a mixture of tert-butyl Le A 26 2?3 201~23 methyl ether and isooctane (1:1). According to HPLC analysis, the combined extracts contain 28.7 9 of a mixture of 4,4'-di-isocyanatodlphenylmethane homologs ("polymeric MDI"), 1.0 g of a mixture of the corresponding ethoxycarbonylaminoisocyanato-5 diphenylmethane homologs ("polymeric MIU"), and 0.9 g ofpolymeric MDU. The sulfolane phase conta;ns 12.5 g of polymeric MDI, 3.0 9 of polymeric MIU, and 0.7 9 of polymeric MDU after extraction. The isolable yields of the mixture of 4,4'-diisocyanatodiphenylmethane homologs calculated from these o figures are 61.9% after a first cycle and 98.3% for a continuous process.
ExamPle 4 Using Procedure (B), a solution of 140 g of 4,4'-bis-(ethoxycarbonylamino)diphenylmethane ("MDU") and 0.35 g of dibutyltin dilaurate in 140 9 of sulfolane and 28 g of chlorobenzene is introduced over a period of 6.25 hours (dripping rate of 50 g/h) from the addition funnel which is thermostatically controlled at 125-C into the thin-layer evaporator which is heated to 260-C. The pressure in the 20 apparatus during the decomposition reaction is 150 mbar. A
yield of 261 g of sump product is obtained. According to HPLC, this sump product contains 51.7 9 of MDU, 38.6 9 of the corresponding ethoxycarbonylaminoisocyanatodiphenylmethane ("MIU"), and 28.4 9 of 4,4'-diisocyanatodiphenylmethane 25 ("MDI"). The sump product is extractcd four times each with 260 9 portions of cyclooctane at 80-C. After the last extraction~ the sulfolane phase contains 49.3 9 of MDU, 26.8 g of MIU, and 5.5 9 of MDI. The combined extracts contain a total of 2.8 9 of MDU, 10.8 9 of MIU, and 25.4 9 of MDI. The 30 isolable yields of 4,4'-diisocyanatodiphenylmethane calculated from these figures are 24.8% after a first cycle and ~4.7% for a continuous process~
Le A 26 273 __~ _ _ 2~ 23 ExamPle 5 Using Procedure (A~, a solution of 75 g of 1-(ethoxy-carbonylamino)-3,3,5-trimethyl-5-(ethoxycarbonylaminomethyl~-cyclohexane ("IPDU") and 0.26 9 of dibutyltin dilaurate in 1425 9 of sulfolane is thermolyzed at 250-C for 60 minutes. The reaction mixture, which has an isocyanate value of 1.13% by weight (84.9% of theoretical), is cooled to 20DC and extracted four times each with 860 g portions of cyclohexane. Accord;ng to HPLC analysis, the combined extrac~s contain 34.8 9 of 1-isocyanato-3,3,5-trimethyl-5-(isocyanatomethyl)cyclohexane ~"IPDI"), and 2.0 9 of the corresponding (ethoxycarbonylamino)-(isocyanatomethyl)-3,3~5-trimethylcyclohexane ("IPIU") ;someric mixture. (The carbamic acid ester IPDU9 which has remained unchanged in the decomposition reaction, is not detected in the HPLC analysis.) After the extraction, the sulfolane phase contains 7.0 g of IPDI and 5.5 g of IPIU. The isolable yields of 1-isocyanato-3,3,5-trimethyl-5-(isocyanatomethyl~cyclohexane calculated from these figures are 66.0% after a first cycle and more than 88% for a continuous process.
Example 6 Using Procedure (B), a solution of 112 9 of TDU, 0.27 g of dibutyltin dilaurate, and 1.1 9 of stearic acid chloride in 37 9 of sulfolane and 15 9 of chlorobenzene is introduced over a period of 9 hours (dripping rate of 18 g/h) from the addition funnel which is thermostatically controlled at 100C
into the thin-layer evaporator which is heated to 290-C. The pressure in the apparatus during the decomposition reaction is 200 mbar. A yield of 123 9 of sump product is obtained.
According to HPLC, this sump product contains 16.0 9 of TDU, 34.5 9 of the corresponding TIU isomeric mixture, and 30.7 9 of TDI. The sump is extracted four times each time with 125 S
psrtions of cyclooctane at 20-C. After the last extraction, the sulfolane phase contains 15.1 9 of TDU, 28.4 9 of TIU, and 5.9 g of TDI. The comhined extracts contain a total of 0.6 9 of TDU, 5.5 9 of TIU, and 25.0 9 of TDI. The isolable yields Le A 26 2?3 2~1~223 of 2,4-diisocyanatotoluene calculated from these figures are 34.2% after a first cycle and 82.8% for a continuous process.
Le A 26 273 ~ . .
Claims (10)
1. A process for the preparation of polyisocyanate comprising (a) thermally decomposing a solution of an N-substituted carbamic acid ester corresponding to said polyisocyanate at temperatures above 150°C in a solvent or solvent mixture serving as a decomposition medium and with provision for continually removing by distillation the alcohol produced by the thermal decomposition of said carbamic acid ester, wherein said solvent or solvent mixture (i) is capable of dissolving the carbamic acid ester, (ii) is stable at the decomposition temperature and chemically inert towards the carbamic acid esters and the polyisocyanate formed during the decomposition reaction, and (iii) has at least one miscibility gap with an extracting agent used according to extraction step (b);
(b) extracting the polyisocyanate from the decomposition medium with an extracting agent, wherein said extracting agent is at least partly immiscible with the decomposition medium and is a solvent for the polyisocyanate, and optionally distilling the resultant solution of the polyisocyanate in the extracting agent, thereby yielding the polyisocyanate in substantially purified form; and (c) recycling the portion of the decomposition medium remaining after the polyisocyanate is extracted in the extraction step (b).
(b) extracting the polyisocyanate from the decomposition medium with an extracting agent, wherein said extracting agent is at least partly immiscible with the decomposition medium and is a solvent for the polyisocyanate, and optionally distilling the resultant solution of the polyisocyanate in the extracting agent, thereby yielding the polyisocyanate in substantially purified form; and (c) recycling the portion of the decomposition medium remaining after the polyisocyanate is extracted in the extraction step (b).
2. A process according to Claim 1 wherein the polyisocyanate formed during the decomposition reaction of step (a) is concentrated by fractional distillation before being extracted in step (b).
3. A process according to Claim 1 wherein the portion of the decomposition medium remaining after the extraction step (b) is recycled by addition to the decomposition step (a).
Le A 26 273
Le A 26 273
4. A process according to Claim 1 wherein the solvent or solvent mixture serving as a decomposition medium is a polar solvent that has a boiling point above 150°C under the decomposition conditions of step (a) or a polar solvent that cannot be distilled without decomposing or a mixture thereof.
5. A process according to Claim 1 wherein the solvent or solvent mixture serving as a decomposition medium is sulfolane or 3-methylsulfolane.
6. A process according to Claim 1 wherein the extracting agent is one or more solvents having a boiling point or boiling range of from 30 to 200°C at 1013 mbar selected from the group consisting of aliphatic, cycloaliphatic, and araliphatic hydrocarbons, and aliphatic ethers.
7. A process according to Claim 1 wherein the extracting agent is isooctane, cyclohexane, toluene, and/or tert-butyl methyl ether.
8. A process according to Claim 1 for the preparation of a polyisocyanate comprising (a) thermally decomposing a solution of an N-substituted carbamic acid ester corresponding to said polyisocyanate at temperatures above 150°C in sulfolane or 3-methyl-sulfolane serving as a decomposition medium and with provision for continually removing by distillation the alcohol produced by the thermal decomposition of said carbamic acid ester;
(b) extracting the polyisocyanate from the decomposition medium with isooctane, cyclohexane, toluene, and/or tert-butyl methyl ether as extracting agent, and optionally distilling the resultant solution of the polyisocyanate in the extracting agent, thereby yielding the polyisocyanate in substantially purified form; and (c) recycling the portion of the decomposition medium remaining after the polyisocyanate is extracted in the extraction step (b).
Le A 26 273
(b) extracting the polyisocyanate from the decomposition medium with isooctane, cyclohexane, toluene, and/or tert-butyl methyl ether as extracting agent, and optionally distilling the resultant solution of the polyisocyanate in the extracting agent, thereby yielding the polyisocyanate in substantially purified form; and (c) recycling the portion of the decomposition medium remaining after the polyisocyanate is extracted in the extraction step (b).
Le A 26 273
9. A process according to Claim 1 wherein the N-substituted carbamic acid ester is a compound corresponding to the formula R1(NHCOOR2)n wherein R1 is an aliphatic hydrocarbon containing 4 to 18 carbon atoms and optionally containing inert substituents, a cycloaliphatic hydrocarbon group containing 6 to 25 carbon atoms and optionally containing inert substituents, an araliphatic hydrocarbon group containing 7 to 25 carbon atoms and optionally containing inert substituents, or an aromatic hydrocarbon group containing 6 to 30 carbon atoms and optionally containing inert substituents;
R2 is an alkyl group containing 1 to 18 carbon atoms, a cycloalkyl group containing 5 to 15 carbon atoms, an aralkyl group containing 7 to 10 carbon atoms, or an aryl group containing 6 to 10 carbon atoms; and n is an integer of from 2 to about 5, with the proviso that the corresponding alcohol R2-OH, wherein R2 has the meaning indicated above, has a boiling point at atmospheric pressure at least 10°C lower than the boiling point of the solvent used as the decomposition medium and the boiling point of the corresponding polyisocyanate R1(NCO)n, wherein R1 has the meaning indicated above.
R2 is an alkyl group containing 1 to 18 carbon atoms, a cycloalkyl group containing 5 to 15 carbon atoms, an aralkyl group containing 7 to 10 carbon atoms, or an aryl group containing 6 to 10 carbon atoms; and n is an integer of from 2 to about 5, with the proviso that the corresponding alcohol R2-OH, wherein R2 has the meaning indicated above, has a boiling point at atmospheric pressure at least 10°C lower than the boiling point of the solvent used as the decomposition medium and the boiling point of the corresponding polyisocyanate R1(NCO)n, wherein R1 has the meaning indicated above.
10. A process according to Claim 9 wherein the N-substituted carbamic acid ester is a compound corresponding to the formula R1(NHCOOR2)n wherein R1 is an aliphatic hydrocarbon group containing 4 to 12 carbon atoms, a cycloaliphatic hydrocarbon group Le A 26 273 containing 6 to 15 carbon atoms, a xylylene group, or an aromatic hydrocarbon group containing a total of 7 to 30 carbon atoms and optionally carrying methyl substituents and/or methylene bridges;
R2 is an alkyl group having 1 to 6 carbon atoms, a cyclohexyl group, or a phenyl group; and n is from 2 to 5.
Le A 26 273
R2 is an alkyl group having 1 to 6 carbon atoms, a cyclohexyl group, or a phenyl group; and n is from 2 to 5.
Le A 26 273
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3915183.2 | 1989-05-10 | ||
| DE19893915183 DE3915183A1 (en) | 1989-05-10 | 1989-05-10 | METHOD FOR PRODUCING POLYISOCYANATES |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2015223A1 true CA2015223A1 (en) | 1990-11-10 |
Family
ID=6380341
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2015223 Abandoned CA2015223A1 (en) | 1989-05-10 | 1990-04-24 | Process for the preparation of polyisocyanates |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0396976A3 (en) |
| JP (1) | JPH02295958A (en) |
| BR (1) | BR9002163A (en) |
| CA (1) | CA2015223A1 (en) |
| DE (1) | DE3915183A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5502244A (en) * | 1994-03-18 | 1996-03-26 | Mitsubishi Gas Chemical Company, Inc. | Process for producing isocyanates |
| US9056819B2 (en) | 2007-03-30 | 2015-06-16 | Asahi Kasei Chemicals Corporation | Isocyanate production process using composition containing carbamic acid ester and aromatic hydroxy compound, and composition for transfer and storage of carbamic acid ester |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IT1244476B (en) * | 1990-12-21 | 1994-07-15 | Enichem Sintesi | CONTINUOUS PROCEDURE FOR THE PREPARATION OF ISOCIAMATI |
| DE10209095A1 (en) * | 2002-03-01 | 2003-09-11 | Basf Ag | Process for the preparation of isocyanates |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3919280A (en) * | 1974-07-05 | 1975-11-11 | Atlantic Richfield Co | Recovery of solvents employed in the production of isocyanates from esters of carbamic acids |
| DE3108990A1 (en) * | 1981-03-10 | 1982-09-23 | Bayer Ag, 5090 Leverkusen | METHOD FOR PRODUCING POLYISOCYANATES |
| DE3430022A1 (en) * | 1984-08-16 | 1986-02-27 | Bayer Ag, 5090 Leverkusen | METHOD FOR OBTAINING PURE DIISOCYANATES |
-
1989
- 1989-05-10 DE DE19893915183 patent/DE3915183A1/en not_active Withdrawn
-
1990
- 1990-04-24 CA CA 2015223 patent/CA2015223A1/en not_active Abandoned
- 1990-04-27 EP EP19900108012 patent/EP0396976A3/en not_active Withdrawn
- 1990-05-08 JP JP11703090A patent/JPH02295958A/en active Pending
- 1990-05-09 BR BR9002163A patent/BR9002163A/en not_active Application Discontinuation
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5502244A (en) * | 1994-03-18 | 1996-03-26 | Mitsubishi Gas Chemical Company, Inc. | Process for producing isocyanates |
| US9056819B2 (en) | 2007-03-30 | 2015-06-16 | Asahi Kasei Chemicals Corporation | Isocyanate production process using composition containing carbamic acid ester and aromatic hydroxy compound, and composition for transfer and storage of carbamic acid ester |
| US9637445B2 (en) | 2007-03-30 | 2017-05-02 | Asahi Kasei Chemicals Corporation | Isocyanate production process using composition containing carbamic acid ester and aromatic hydroxy compound, and composition for transfer and storage of carbamic acid ester |
Also Published As
| Publication number | Publication date |
|---|---|
| BR9002163A (en) | 1991-08-13 |
| EP0396976A2 (en) | 1990-11-14 |
| DE3915183A1 (en) | 1990-11-15 |
| JPH02295958A (en) | 1990-12-06 |
| EP0396976A3 (en) | 1992-01-15 |
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