HK1068903B - Method for the production of aliphatic oligocarbonate diols - Google Patents

Description

Method for preparing aliphatic oligocarbonate diol

The invention relates to a novel method for producing aliphatic oligocarbonate diols by transesterification of aliphatic diols with dimethyl carbonate (DMC) at elevated pressure. The process of the present invention makes it possible to industrially produce aliphatic oligocarbonate diols in large scale starting from readily available DMC as starting material in high space-time yields (STY).

Aliphatic oligocarbonate diols are important precursor products in the production of, for example, plastics, paints and adhesives. They are reacted with, for example, isocyanates, epoxides, (cyclo) esters, acids or anhydrides. Aliphatic oligocarbonate diols can in principle be prepared by reacting aliphatic diols with phosgene (e.g.DE-A1595446), bischloroformates (e.g.DE-A857948), diaryl carbonates (e.g.DE-A1915908), cyclic carbonates (e.g.DE-A2523352: ethylene carbonate) or dialkyl carbonates (e.g.DE-A2555805).

Among the carbonate starting materials used, diphenyl carbonate (DPC), which is a diaryl carbonate, is of particular importance, since aliphatic oligocarbonate diols of particularly high quality can be prepared from DPC (e.g.U.S. Pat. No. 3, 3544524,EP-A292772). DPC reacts quantitatively with aliphatic OH functions relative to all other carbonate starting materials, so that after removal of the phenol formed, all terminal hydroxyl groups of the oligocarbonate diol are available for reaction, for example with isocyanate groups. In addition, the process requires only a very low concentration of soluble catalyst, so that this small amount of catalyst can also remain in the product.

However, the DPC-based production process has the following disadvantages:

only about 13 wt% of the total amount of DPC remains in the oligocarbonate as CO groups; the remainder was distilled off in the form of phenol. While a considerable proportion of dialkyl carbonate remains in the oligocarbonate, depending on the relevant alkyl radical. Thus, about 31% by weight of dimethyl carbonate (DMC) remains in the oligocarbonate as CO groups, since the molecular weight of the distilled methanol is rather lower than that of phenol.

Since the high-boiling phenol (normal boiling point 182 ℃) has to be separated off from the reaction mixture, only diols having a boiling point well above 182 ℃ remain to be used in the reaction, in order to prevent undesired losses of diols by distillation.

Since they are easy to produce dialkyl carbonates, in particular dimethyl carbonate (DMC), they are referred to as starter materials because of their greater availability. DMC can be obtained, for example, by direct synthesis from MeOH and CO (e.g.EP-A0534454, DE-A19510909).

A large number of documents (e.g.US-A2210817, US-A2787632, EP-A364052) relate to the reaction of dialkyl carbonates with aliphatic diols:

in the prior art, an aliphatic diol is placed in a reaction vessel together with a catalyst and a dialkyl carbonate (e.g., diethyl carbonate, diallyl carbonate, dibutyl carbonate), and the resulting alcohol (e.g., ethanol, butanol, allyl alcohol) is distilled off from the reaction vessel via a distillation column. In this column, the dialkyl carbonate with the higher boiling point is separated from the alcohol with the lower boiling point and recycled back to the reaction mixture.

Although dimethyl carbonate (DMC) is readily available, its use in the production of aliphatic oligocarbonate diols has only recently been known (e.g.U.S. Pat. No. 4, 5171830, EP-A798327, EP-A798328, DE-A19829593).

EP-A0798328 describes the reaction of the relevant diol component with DMC with distillation of the azeotrope at atmospheric pressure. Subsequently, deblocking was effected by vacuum distillation, in which the availability of the terminal hydroxyl groups reached approximately 98% under very vigorous vacuum conditions (1 torr, about 1.3mbar) (EP-A0798328: Table 1).

EF-A798327 describes a related two-step reaction process in which, firstly, a diol is reacted with excess DMC to form an oligocarbonate whose terminal hydroxyl groups are present as methyl ester-based end groups and are completely inaccessible, with distillation of the azeotrope at atmospheric pressure. After removal of the catalyst and distillation of the excess DMC under vacuum (65 torr, 86mbar), in a second step, oligocarbonate diols are obtained by adding further amounts of diol and a solvent, such as toluene, as entrainer for the methanol formed. The residual solvent must then be distilled off under vacuum (50 torr, 67 mbar). The disadvantage of this process is the high operating costs for carrying out the process due to the use of solvents, the need for repeated distillations, and the high consumption of DMC.

DE-A19829593 discloses the reaction of a diol with DMC, with the methanol formed being distilled off at atmospheric pressure. The process does not take into account the complex problems of azeotropes, except for the fact that the term "azeotrope" is mentioned once in the table headed "table of the process of the invention". The fact that DMC was used in excess can be calculated from the examples, which was also distilled off azeotropically. About 27.8% by weight of the DMC used was lost.

According to U.S. Pat. No. 3, 5171830, a diol is first heated together with DMC, and the volatile constituents are then distilled off (azeotropically). After subjecting the product to vacuum distillation under vigorous vacuum conditions (1 torr, 1.3mbar), treatment in chloroform (take-up), precipitation with methanol and drying, the oligocarbonate diol was obtained in a theoretical yield of 55 wt% (this patent, example 6). The present invention does not address the availability of terminal hydroxyl groups and the azeotrope problem in detail. Although the fifth column, lines 24-26 of US-a 5171830 mentions that the process can be carried out under vacuum, atmospheric pressure and elevated pressure, i.e. essentially under any pressure regime, the pressure conditions particularly preferred for use cannot be determined. It is only one step of removing the volatile components mentioned using reduced pressure.

Thus, in the above-mentioned hitherto known documents, there has not been described a process which is easy to industrially produce in which DMC is reacted with an aliphatic diol to produce an oligocarbonate diol in a high space-time yield and whose terminal hydroxyl groups have a high availability.

It is therefore an object of the present invention to provide a simple, productive process which can be used simultaneously also for large-scale industrial production, which enables oligocarbonate diols to be prepared in high space-time yields by transesterification of aliphatic diols with dimethyl carbonate by simple means, optionally using a catalyst in an amount which is sufficiently low that the catalyst remains in the product after the reaction has been completed, the product having a high degree of deblocking of the terminal hydroxyl groups.

We have now found that a process in which aliphatic oligocarbonate diols are formed by reacting aliphatic diols with dimethyl carbonate at elevated pressure, optionally with the addition of catalysts, which increases the reaction rate, leads to high space-time yields. To complete the reaction and to deblock (make available) the terminal hydroxyl groups, the last methanol residue and traces of dimethyl carbonate are removed from the product under reduced pressure, optionally with the introduction of an inert gas.

The invention accordingly relates to a process for the production of aliphatic oligocarbonate diols, characterized in that an aliphatic diol is reacted with dimethyl carbonate under elevated pressure and optionally with the addition of a catalyst to accelerate the reaction rate, and that unreacted methanol and dimethyl carbonate are subsequently removed from the product under reduced pressure, optionally with the introduction of an inert gas, in order to complete the reaction and to deblock the terminal hydroxyl groups (make them available).

The process of the invention is carried out at elevated pressure, preferably at a pressure of from 1.5 to 100bar, most preferably at a pressure of from 3 to 16bar, the reaction temperature depending on the pressure used being in the range of from 100 ℃ to 300 ℃ and preferably from 160 ℃ to 240 ℃.

When the catalyst concentration is constant, the elevated pressure leads to a better conversion of the DMC, shortens the reaction time and has a positive effect on the space-time yield.

The reaction can be completed and the terminal hydroxyl groups unblocked (made available) by finally removing the last residual methanol and traces of dimethyl carbonate under reduced pressure. In a preferred embodiment, the inert gas (e.g., N) is introduced under a low vacuum of only about 150mbar₂) Into the oligocarbonate diol to affect the completion of the reaction and the de-capping (making available) of the terminal hydroxyl groups. The inert gas bubbles are saturated with methanol or DMC so that methanol is almost completely removed from the reaction batch. The methanol is removed by stripping with inert gas, the equilibrium is shifted further in favour of the product formation and the transesterification reaction is completed, so that the end groups become available. The quality of the obtained oligocarbonate diol can be improved to the level of DPC-based oligocarbonate diol, and the availability of the terminal hydroxyl groups is improved to more than 98%, preferably 99.0-99.95%, most preferably 99.5-99.9%.

The gas bubbles can be obtained by introducing inert gases, such as nitrogen, noble gases, such as argon, methane, ethane, propane, butane, dimethyl ether, dry natural gas or dry hydrogen, into the reaction vessel, wherein a gas stream which partly comprises methanol and dimethyl carbonate and is freed from the oligocarbonate formed can be recycled to the oligocarbonate to saturate it. Nitrogen is preferably used. Due to the severe coloration of the product, air can be used to prepare the final product without any requirements in terms of color.

The gas bubbles can also be obtained by introducing inert low-boiling liquids, such as pentane, cyclopentane, hexane, cyclohexane, petroleum ether, diethyl ether or methyl tert-butyl ether, etc., wherein these substances can be introduced in liquid or gaseous form, and the gas stream which partly contains methanol and dimethyl carbonate and is freed from the oligocarbonate formed can be recycled to the oligocarbonate to saturate it.

The gas bubble-forming substances can be introduced into the oligocarbonate via simple submerged lines, preferably via annular nozzles or gasification stirring devices. The availability of the resulting terminal hydroxyl groups depends on the duration of deblocking, the number, size and distribution of gas bubbles: as the duration of the deblocking is extended, the degree of utilization is also higher with better distribution of the gas bubbles (such as better distribution, larger phase boundaries, caused by a greater number of smaller gas bubbles when the latter are introduced via the gasification stirring apparatus). For example, by introduction via a gasification stirring device, the degree of utilization can reach about 99% after 1 hour and about 99.8% after 5 to 10 hours when using nitrogen (for example, 8 container volumes per hour at 150 mbar).

The selective introduction of inert gas bubbles into the reaction mixture promotes deblocking, which is carried out at 160 ℃ to 250 ℃, preferably 200 ℃ to 240 ℃, at an operating pressure in the range from 1 to 1000mbar, preferably 30 to 400mbar, more preferably 70 to 200 mbar.

During the preparation of the oligocarbonate diols, the DMC was distilled off. The amount of DMC distilled off from the reaction batch was determined by measuring the DMC content in the distillate. These lost DMC must be replenished to make the terminal hydroxyl groups available before stripping off methanol with inert gas under vacuum. In this way, the mixture of DMC and methanol is reformed again. The lost DMC was replaced again and part of it was distilled off again. The amount of DMC distilled off per replenishment becomes smaller and the expected stoichiometric value can be approached.

This expensive process can be simplified by incorporating a unique supplemental step. The amount of DMC distilled off from the previous batch by a unique make-up step is known. It is therefore possible to make up for the loss of DMC completely in a single step at a later time.

In this way, the total amount of DMC required is added directly in the initial step, this total amount being predetermined by the stoichiometric value of the desired product amount and the amount of DMC distilled off as the reaction proceeds.

There is also a small loss of DMC during the distillation of methanol and the deblocking of the terminal hydroxyl groups at the end of the reaction when inert gas bubbles are introduced. This amount of loss should also be taken into account in the addition of DMC. Based on experience, the amount of DMC necessary can be determined from the previous batch.

In a preferred variant of the process, DMC is added in excess, calculated at the beginning of the reaction, so that, after the azeotrope has been distilled off and deblocked, a product is formed which contains all the functionalities of the terminal hydroxyl groups but also has an excessively high degree of polymerization. Then, in order to correct the degree of polymerization, a certain amount of a diol component is further added to conduct a simple transesterification reaction again. The correction can be derived first from mass balance, i.e.by determining the amount of DMC in the total distillate and then comparing it with the total amount added, or on the basis of measurable properties of products with too high a degree of polymerization (e.g.OH number, viscosity, average molecular weight, etc.). It is not necessary to re-cap after the rectification is performed, since all of the terminal hydroxyl groups are freely available before rectification and the addition of the diol component does not lead to re-capping.

For products containing very little DMC, after vaporization with an inert gas to effect de-capping, DMC addition to correct can lead to re-capping.

According to the invention, the diol and optionally the catalyst are placed in a reaction vessel, the reaction vessel is heated, the pressure is increased and DMC is subsequently metered in.

Thus, the process of the invention comprises the following process steps:

-feeding the diol component, and optionally the catalyst, to a vessel.

-heating, increasing the pressure.

Addition and reaction of DMC. The amount of DMC has been calculated so that after all the steps (DMC addition and uncapping) have been removed by distillation, the amount of DMC is still precisely the necessary amount, if not a slight excess of DMC which remains in the reaction solution after the reaction. The metering of DMC can be carried out according to the following two methods:

a) the entire amount of DMC was metered in rapidly in one step. Thus, the STY is optimized. A DMC-methanol mixture (e.g., azeotrope) containing a relatively high DMC content, which is considerably less than the mixture obtained under zero pressure conditions, is distilled off.

b) DMC was metered in two portions. DMC was first slowly metered in, so that the DMC-methanol mixture of lower DMC content was distilled off. DMC was not metered rapidly until later, indicated at the very point, i.e., when the DMC content in the distillate increased substantially, even though it increased at the same rate that DMC was added slowly, to form a distillate with a high DMC content (e.g., a DMC-methanol azeotrope).

Method b) enables better utilization of DMC, but lower STY.

-deblocking: by extracting the final residue of methanol and DMC under reduced pressure,optionally by generation of gas bubbles (e.g. addition of an inert gas such as N)₂) So that the terminal hydroxyl group can be utilized.

-correcting: the stoichiometry is corrected, if necessary, by further addition of the diol component and a renewed simple transesterification reaction.

Of course, the process of the present invention may also be carried out with the addition of an excess of diol. If this method is used, it is then necessary to rectify the DMC. This also results in repeated decapping steps.

In another example of the invention, up to 100%, preferably up to 70%, more preferably up to 50%, and most preferably up to 30% of the DMC is added to the reaction vessel at the beginning of the reaction, along with the diol and optionally the catalyst. The reaction vessel was then closed, heated, and pressurized. 100% of the distillate is first recycled back to the reaction vessel (recycle). Sampling from the distillate stream enabled determination of DMC content. Depending on the optimization objective (DMC yield or STY), the reflux rate can be 100% used before the DMC content in the distillate is minimized or before the time for the distillation process to be reversed (DMC/methanol mixture distilled off) is fixed. The residual DMC is then metered in and deblocked, if necessary, by correcting the stoichiometry by further addition of the diol component and restarting a simple transesterification reaction.

The process of the invention uses aliphatic diols containing 3 to 20 carbon atoms in the chain, such as: 1, 7-heptanediol, 1, 8-octanediol, 1, 6-hexanediol, 1, 5-pentanediol, 1, 4-butanediol, 1, 3-propanediol, 2-methyl-1, 3-propanediol, 3-methyl-1, 5-pentanediol, 2-methylpentanediol, 2, 2, 4-trimethyl-1, 6-hexanediol, 3,3, 5-trimethyl-1, 6-hexanediol, 2,3, 5-trimethyl-1, 6-hexanediol, cyclohexanedimethanol, and the like or mixtures of different diols.

Addition products of diols with lactones (ester diols) can also be utilized, such as caprolactone, valerolactone, and the like, as can mixtures of diols with lactones, without the diols having to be transesterified with lactones initially.

In addition, addition products of diols and dicarboxylic acids can also be used, such as: adipic acid, glutaric acid, succinic acid, malonic acid, etc., or dicarboxylic acid esters and mixtures of diols with dicarboxylic acids or with dicarboxylic acid esters, it not being necessary for the diols to be transesterified initially with dicarboxylic acids.

Polyether polyols such as polyethylene glycol, polypropylene glycol and polytetramethylene glycol, polyether polyols obtained by copolymerization of ethylene oxide with 1, 2-propylene oxide, or poly-1, 4-butanediol obtained by ring-opening polymerization of Tetrahydrofuran (THF) can also be used.

Mixtures of different diols, lactones and dicarboxylic acids can be employed.

1, 6-hexanediol, 1, 5-pentanediol and/or a mixture of 1, 6-hexanediol and caprolactone is preferably used in the process of the present invention.

In the preparation of oligocarbonate diols, epsilon-caprolactone is preferably prepared in situ from the starting materials without prior reaction.

In principle, all known soluble catalysts for transesterification can be used selectively as catalysts in the present invention (homogeneous catalysts), heterogeneous transesterification catalysts can also be used. The process of the invention is preferably carried out in the presence of a catalyst.

Hydroxides, oxides, metal alcoholates, carbonates and organometallic compounds of metals of the main groups I, II, III, IV and of the subgroups II, IV of the periodic Table of the elements, and organometallic compounds of rare earth elements, in particular of Ti, Zr, Pb, Sn and Sb, are particularly suitable for use in the process according to the invention.

Suitable examples include: LiOH, Li₂CO₃，K₂CO₃，KOH，NaOH，KOMe，NaOMe，MeOMgOAc，CaO，BaO，KOt-Bu，TiCl₄Titanium tetraalkoxide or terephthalate, zirconium tetraalkoxide, octanoic acidTin, dibutyltin dilaurate, dibutyltin oxide, tin oxalate, lead stearate, antimony trioxide, zirconium tetraisopropoxide, and the like.

Aromatic nitrogen-containing heterocyclic compounds can also be used in the process of the invention, such as those of the formula R₁R₂R₃Tertiary amines of N, in which R_1-3Represents C₁-C₃₀Hydroxyalkyl of (C)₄-C₁₀Aryl or C of₁-C₃₀Especially trimethylamine, triethylamine, tributylamine, N-dimethylcyclohexylamine, N-dimethyl-ethanolamine, 1, 8-diaza-bicyclo- (5.4.0) undec-7-ene, 1, 4-diazabicyclo- (2.2.2) octane, 1, 2-bis (N, N-dimethyl-amino) -ethane, 1, 3-bis (N-dimethyl-amino) propane and pyridine.

Sodium and potassium alcoholates with hydroxides (NaOH, KOH, KOMe, NaOMe), titanium, tin or zirconium alcoholates (e.g. Ti (OPr))₄) And organotin compounds are preferably used, with preference being given to using titanium, tin and zirconium tetraalkoxides together with diols carrying an ester function or with mixtures of diols and lactones.

In the process of the invention, the homogeneous catalyst may be used in a concentration (expressed by weight percentage of metal relative to the aliphatic diol used) of at most 1000ppm (0.1%), preferably from 1ppm to 500ppm (0.05%), most preferably from 5ppm to 100ppm (0.01%). When the reaction is complete, the catalyst can remain in the product or be separated, neutralized or masked from the product. Preferably the catalyst remains in the product.

The molecular weight of the oligocarbonate diols produced by the process of the present invention can be adjusted by the molar ratio of diol to DMC in the range of from 1.01 to 2.0, preferably from 1.02 to 1.8, most preferably from 1.05 to 1.6. Of course, the above ratios illustrate the stoichiometry of the product, i.e., the effective ratio of glycol to DMC after the DMC-methanol mixture is distilled off. Due to the azeotropic distillation of DMC, the amount of DMC used in each case is correspondingly greater. The calculated molecular weight range of the oligocarbonate diol prepared by the process of the present invention, for example, when 1, 6-hexanediol is used as the diol component, is 260-15000g/mol, preferably 300-7300g/mol, most preferably 350-3000 g/mol. If higher or lower molecular weight diols are used, the molecular weight of the oligocarbonate diols obtained by the process of the invention will be correspondingly higher or lower.

The process method of the invention can produce the compound with the structural formula of HO-R¹-[-O-CO-O-R¹-]_n-OH-oligocarbonate diols having a carbon number of 7 to 1300, preferably 9 to 600, most preferably 11 to 300, wherein R¹Represents an alkyl group containing from 3 to 50 carbon atoms (from the corresponding aliphatic diol), preferably from 4 to 40, most preferably from 4 to 20.

The diols can furthermore contain ester, ether, amide and/or nitrile functions. Diols or diols containing an ester function are preferred, for example products obtained from caprolactone and 1, 6-hexanediol. If two or more diol components are used (e.g. mixtures of different diols or mixtures of diols with lactones), two adjacent R's in one molecule¹The groups must be different from each other (randomly distributed).

The process of the invention enables high-quality oligocarbonate diols to be prepared from DMC in high space-time yields and with low degree of end capping of the terminal hydroxyl groups.

The oligocarbonate diols produced by the process of the present invention can be used, for example, by reaction with isocyanates for the production of plastic polymers, fibers, coatings, lacquers and adhesives, or for the production of epoxides, (cyclo) esters, acids or anhydrides. They can also be used as binder carriers, binder carrier components and/or as reactive diluents in polyurethane coatings. They are also suitable as constituents of moisture-hardening coatings or as binder carriers or binder carrier components for solvent-containing or aqueous polyurethane coatings. They can also be used as building blocks for the synthesis of polyurethane prepolymers containing free NCO groups or in polyurethane dispersions.

The oligocarbonate diols prepared by the process of the present invention can also be used in the production of synthetic thermoplastic materials, such as aliphatic and/or aromatic polycarbonates, thermoplastic polyurethanes, and the like.

Examples

Examples 1 to 6 according to the invention are some examples of syntheses of oligocarbonate diols having an OH number of from 53 to 58mg KOH/g, a residual methanol content of < 10ppm, which are prepared by an elevated pressure process. The comparative example illustrates the synthesis under non-pressure conditions.

Example 1

2316kg of 1, 6-hexanediol, 2237kg of epsilon-caprolactone and 0.54kg of titanium tetraisopropoxide were placed in a reaction vessel equipped with a cross-arm stirrer. Nitrogen was passed through and the pressure was increased to 5.2bar (absolute). The reaction batch was then heated to 205 ℃ for 3 hours. The pressure was kept constant at 5.2bar by a pressure control system. After the desired temperature had been reached, 800kg of dimethyl carbonate were introduced via a submerged pipe (about 200kg/h) over a period of 4 hours. At the same time, the distillate containing about 11% DMC was distilled into a receiver. After this time, the temperature was lowered to 195 ℃ and a further 1200kg of dimethyl carbonate (approx. 100kg/h) were metered in over a period of 12 hours. After 400kg of 1200kg had been metered in, the DMC content in the distillate was about 15%, after 800kg had been metered in, the DMC content in the distillate was about 24%, at the end of the DMC addition, about 29%. After a further reaction time of 4 hours, the temperature was raised to 200 ℃ and the pressure was reduced from 5.2bar to 100mbar in a period of 7 hours. 10Nm³Is introduced via an immersion feed pipe. The residual methanol was removed. After 4 hours, the OH number was 42.5mg KOH/g and the viscosity was 25, 464 mPa.s. 80kg of 1, 6-hexanediol were added. After a further reaction time of 9 hours, the OH number was 50.0mg KOH/g and the viscosity was 20,748 mPas. 50kg of 1, 6-hexanediol were further added. After further reaction for 5 hours, the OH number was 57.9mgKOH/g, and the viscosity was 14, 513 mPa.s. The residual methanol content was < 10 ppm. The total reaction time was about 48 hours.

Example 2

2316kg of 1, 6-hexanediol, 2237kg of ε -caprolactone, 0.54kg of titanium tetraisopropoxide and 1000g of dimethyl carbonate were placed in a reaction vessel equipped with a cross-arm stirrer. Nitrogen was passed through and the pressure was increased to 5.2bar (absolute). The reaction batch was then heated for 2 hours to 180 ℃. The pressure was kept constant at 5.2bar by a pressure control system. A slight reflux is generated and the refluxed liquid is returned to the reactor. 1 hour after the temperature reached 180 ℃, the dimethyl carbonate content of the reflux was about 17%, and after a further 5 hours, it dropped to about 12.5%.

The apparatus used for the conversion was such that the distillate entered a receiver and the reaction batch was heated to 194 ℃. Methanol with a DMC content of about 12% was distilled off. The distillation was completed in about 4 hours.

1000kg of dimethyl carbonate were added at a rate of 250kg/h via a submerged pipe, and a methanol/DMC azeotrope with a DMC content of about 20 to 25% was distilled off. The reaction batch was then heated to 200 ℃ over a period of 1 hour. After further stirring for 2 hours, the pressure was reduced to 200mbar over a period of 7 hours. Then, 8Nm3 of nitrogen was introduced via the submerged feed pipe and the residual methanol was removed. After 6 hours, the OH number was 43.2mg KOH/g and the viscosity was 23,371 mpa.s. 74kg of 1, 6-hexanediol were then added. After a further 6 hours, the OH number was 48.8mg KOH/g and the viscosity was 20,001 mPa.s. The residual methanol content was 20 ppm. 55kg of 1, 6-hexanediol were further added. After further reaction for 6 hours, the OH number was 56.5mgKOH/g, and the viscosity was 15,500 mPa.s. The residual methanol content was < 10 ppm. The total reaction time was about 45 hours.

Example 3

A200 l stirred vessel with paddle mixer was equipped with a 2.5m long packed distillation column (11 cm outside diameter, packed with pall), a condenser and a 100 l receiving vessel. The distillate received in the receiving vessel can be recycled back to the reactor via a bottom pump (bottompump) and base flange (basal flare).

62,353kg of hexanediol (adipol), 60,226kg of ε -caprolactone, 12g of titanium tetraisopropoxide and 23.5kg of DMC were placed in the reactor. After evacuating the reactor twice to a pressure of 300mbar and subsequently inerting the reactor atmosphere with nitrogen, the reaction batch was heated to 80 ℃ over a period of 1 hour and homogenized. The pressure in the reactor was kept constant by a pressure control system, with nitrogen being introduced under pressure to give a pressure of 5.2 bar. The reaction batch was heated to 194 ℃ over a period of 2 hours, and the temperature was held constant for 2 hours.

33.49kg of DMC were further metered into the stirred vessel over a period of 2 hours at 194 ℃. After the addition of the DMC, the reaction batch was heated to 196 ℃ for more than 30 minutes, and the temperature was maintained for 5 hours. The reaction batch was subsequently heated for more than 30 minutes to 200 ℃ and all of the DMC/methanol mixture (31kg, DMC content 25.7%) was distilled off over a period of 2 hours. The pressure was then reduced to 100mbar over a period of 1 hour, nitrogen being passed through the reaction batch. When nitrogen was passed through the reaction batch at 200 ℃ and 100mbar, after 7 hours of vacuum distillation the OH number was 60.3mg KOH/g and the viscosity was 8,667 mPas (23 ℃), after 2 hours of further reaction the OH number was 55.8 and the viscosity was 13,099 mPas, after 7 hours of further reaction the OH number was 53.7 and the viscosity was 15,794 mPas.

The reaction time was 40 hours and the DMC content in the distillate was 25.7%.

Example 4

9,267kg of 1, 6-hexanediol, 0.13g of tetraisopropyl titanate, were placed in a 20 l autoclave equipped with a cross-arm stirrer, a distillation column, a downstream condenser and a receiving vessel. After evacuating the reactor twice and subsequently inerting the reactor atmosphere with nitrogen, the pressure in the reactor and in the surrounding components (distillation column, condenser, receiving vessel) was adjusted to 5.2bar with nitrogen. The reaction batch was heated to 197 ℃ and 9.63kg of DMC were metered into the reactor over a period of 6 hours. After the metering phase, the batch was heated to 200 ℃ and distilled at this temperature for 2 hours. 6.17kg of distillate with a DMC content of 25.1% were obtained. The pressure was reduced to 100mbar and nitrogen was passed through the reaction batch. After 9 hours, the OH number had reached 159mg KOH/g. The pressure was again set to 5.2bar and 1kg of DMC were metered in over a period of 1 hour. After the metered addition, the batch was stirred for 2 hours and then the pressure was reduced to 100mbar, the reaction batch being distilled as nitrogen passed through the batch. After a further vacuum distillation at 100mbar and 200 ℃ for 18 hours, an OH number of 65.5mgKOH/g was reached. The pressure was then increased to 5.2bar, 96g of DMC were metered in, the reaction batch was stirred for 2 hours, then the pressure was reduced and a vacuum was applied to 100mbar, which distilled off as nitrogen passed through the reaction batch. After 19 hours, the final product had an OH number of 56.0mg KOH/g and a viscosity of 1,699mPa.s (75 ℃ C.).

Example 5

A reactor: a20 liter Hagemann reactor equipped with a cross arm stirrer, a distillation column, a downstream condenser, and a receiving vessel. Dimethyl carbonate was metered directly into the reactor via a diaphragm pump (non-submerged).

6.68kg of 1, 6-hexanediol (0.057kmol), 6.45kg of ε -caprolactone (0.057kmol) and 1g of tetraisopropyl titanate were placed in a reactor. After evacuating the reactor twice to a pressure of 300mbar and subsequently inerting the reactor atmosphere with nitrogen, the reaction batch was first heated to 80 ℃ over a period of 1 hour and then to 194 ℃ over a period of 1 hour.

At 194 ℃ 6.14kg of dimethyl carbonate (0.068kmol) were metered in over a period of about 5 hours. After the metering-in was complete, the reaction batch was held at 196 ℃ for 4 hours and then warmed to 200 ℃. After holding at 200 ℃ for 2 hours, the pressure in the reactor was reduced to atmospheric pressure and the omitted distillate (2.9kg) was removed from the receiver. After all the distillate had been removed, the pressure was reduced to 100mbar and nitrogen was passed through the reaction batch. After 6 hours, its OH number was 29.8mg KOH/g and viscosity was 42,135 mPas. To achieve the desired OH number range of 53-58mg KOH/g, 0.413kg of 1, 6-hexanediol was subsequently added, and the reaction batch was held at 200 ℃ for a further 6 hours at a pressure of 100mbar while passing through nitrogen. The OH number of the polyurethane resin reaches 45.8mg KOH/g, and the viscosity of the polyurethane resin is 21,725mPa. 0.150kg of hexanediol was further added. After 8 hours of continued reaction, the viscosity reached 18,330mpa.s and the OH number reached 56.8 mgKOH/g.

The total reaction time was about 36 hours.

Example 6

9270kg of 1, 6-hexanediol, 8950kg of ε -caprolactone were placed in a reactor at 100 ℃ which was stirred by a cross-arm stirrer and was equipped with a distillation column, a complete condenser. 1.5kg of titanium tetraisopropoxide was added. The vessel pressure was then increased to 5.2bar (abs.) by passing nitrogen and thereafter heating the reaction batch to 200 ℃. 7300kg of dimethyl carbonate were added uniformly over a period of 15 hours. Methanol having a dimethyl carbonate content of 15 to 19% by weight is formed and is distilled off at the same time. The temperature was then reduced to 180 ℃ over a period of 3 hours and the pressure was reduced to atmospheric pressure. Thereafter, the vacuum was increased to 60mbar (absolute pressure) over a period of 12 hours. 2Nm³Is introduced into the reaction mixture via a submerged feed pipe, the vacuum being increased to 20mbar in order to remove residual methanol. The reaction batch was stirred further at 180 ℃ for 24 hours to reduce the non-hydroxyl end groups (especially methyl carbonate groups) to less than 5 mol% of the total. The hydroxyl number and viscosity were measured and corrected if necessary. The reactor was then aerated and the batch was cooled to 100 ℃ and then filtered. 20,000kg of a clean, colorless resin were obtained which did not crystallize at room temperature, had an OH number of 56 at 23 ℃ and a viscosity of 15,000 mPa.s.

Comparative example

Preparation of the product of example 5 under non-pressure conditions

A reactor: a20 liter Hagemann reactor equipped with a cross arm stirrer, a distillation column, a downstream condenser, and a receiving vessel. Dimethyl carbonate was metered directly into the reactor via a diaphragm pump (non-submerged).

6.68kg of 1, 6-hexanediol (0.057kmol), 6.45kg of ε -caprolactone (0.057kmol) and 1g of tetraisopropyl titanate were placed in a reactor. After evacuating the reactor twice to a pressure of 300mbar and subsequently inerting the reactor atmosphere with nitrogen, the reaction batch was first heated to 80 ℃ over a period of more than 1 hour and then further heated to 140 ℃ over a period of more than 1 hour. At 140 ℃ 6.14kg of dimethyl carbonate (0.068kmol) are metered in so that the temperature at the top of the distillation column does not exceed 67 ℃. The time for metering was about 24 hours and the temperature at the bottom of the distillation column was 140 ℃ and 182 ℃. After the metering-in was complete, the temperature was raised to 200 ℃ over a period of about 1 hr. 4 hours after reaching 200 ℃ the OH number was determined to be 85.7mg KOH/g. The reaction batch was cooled to 140 ℃ and rectified with 0.357kg pure dimethyl carbonate, while the column top temperature was limited to 65 ℃. The time of metering in was about 3.5 hours. Subsequently, the batch was heated again to 200 ℃ over a period of 2 hours. Thereafter, stirring was carried out at 200 ℃ under normal pressure for 3 hours and then at 100mbar for 5 hours. Thereafter, the OH number was 31.3mg KOH/g, and the viscosity was 33,320 mPas. To achieve the desired OH number, 0.395kg of hexanediol was subsequently added. After the reaction had continued at 200 ℃ under normal pressure for about 3 hours and then at 100mbar for 7 hours, the OH number was 52.5mg KOH/g and the viscosity was 15,737 mPa.s.

The total reaction time was about 36 hours.

The longer the reaction time, the higher the catalyst requirements and the greater the loss of DMC compared to example 5.

Claims (27)

1. A process for producing aliphatic oligocarbonate diols, characterized in that an aliphatic diol is reacted with dimethyl carbonate, optionally in the presence of a catalyst, at a pressure of 1.5 to 100bar, and subsequently, in order to complete the reaction and to deblock the terminal hydroxyl groups, the methanol and dimethyl carbonate formed are removed under reduced pressure, optionally with the introduction of an inert gas.

2. The process as claimed in claim 1, wherein the diol used and the catalyst optionally present are initially introduced into a reaction vessel, the reaction vessel is heated, the pressure is increased and subsequently the dimethyl carbonate is metered in.

3. The process as claimed in claim 2, characterized in that dimethyl carbonate is initially metered slowly into the reactor until the rate at which dimethyl carbonate is metered is increased to such an extent that the corresponding dimethyl carbonate/methanol azeotrope is distilled off.

4. The process as claimed in claim 1, wherein the dimethyl carbonate is metered in rapidly in one portion.

5. The process according to claim 1, characterized in that up to 100% of the required amount of dimethyl carbonate is added together with the diol and optionally the catalyst; the reactor is heated; raising the pressure; 100% of the distillate is recycled to the reactor until the dimethyl carbonate content in the distillate reaches a constant or defined value; subsequently, the dimethyl carbonate/methanol mixture is distilled off and the remaining dimethyl carbonate is metered in.

6. The process as claimed in claim 1, wherein the reaction of dimethyl carbonate with the aliphatic diol is carried out at a pressure in the range from 1.5 to 100bar and a temperature in the range from 100 ℃ to 300 ℃.

7. The process as claimed in claim 1, wherein, for the completion of the reaction and the deblocking of the terminal hydroxyl groups, the final residual methanol and traces of dimethyl carbonate are removed from the product under reduced pressure, optionally with the introduction of inert gas, wherein the deblocking is carried out at a temperature in the range from 160 ℃ to 250 ℃ and a pressure in the range from 1 to 1000mbar, and after the completion of the reaction, the deblocking of the terminal hydroxyl groups is effected by pumping off the final residual methanol, and the transesterification is effected by introducing inert gas bubbles into the reaction mixture.

8. The process as claimed in claim 7, wherein the deblocking of the terminal hydroxyl groups is effected after the reaction has been completed by introducing an inert gas into the reactor and generating gas bubbles therein.

9. The process of claim 8 wherein the inert gas is nitrogen, noble gases, methane, ethane, propane, butane, dimethyl ether, dry natural gas, or dry hydrogen.

10. The process according to claim 7, wherein the terminal hydroxyl groups are made available after the reaction is completed by introducing a low-boiling inert liquid into the reactor and generating gas bubbles in the reactor, wherein the above-mentioned substances can be introduced in liquid or gaseous state.

11. The process according to claim 10, wherein the low boiling inert liquid is pentane, cyclopentane, hexane, cyclohexane, petroleum ether, diethyl ether or methyl tertiary butyl ether.

12. A process according to claim 1, wherein the gas stream comprising methanol and dimethyl carbonate which is freed from the oligocarbonate diol is partly recycled back to the oligocarbonate diol and is again saturated.

13. The process as claimed in claim 1, wherein the total amount of dimethyl carbonate required is also taken into account directly, this amount being determined by the stoichiometry of the desired product and the total amount of dimethyl carbonate distilled off as the reaction proceeds

14. A process according to claim 1, characterized in that at the start of the reaction, a calculated excess of dimethyl carbonate is added, so that after the azeotrope has been distilled off and deblocked, a product is formed which has the full functionality of the terminal hydroxyl groups but also an excessively high degree of polymerization, and the defined stoichiometry of the oligocarbonate diol is subsequently obtained by adding the corresponding amount of diol component and restarting the transesterification reaction.

15. The process according to claim 1, characterized in that the aliphatic diol is an aliphatic diol having 3 to 20 carbon atoms in the chain, or a mixture of different diols.

16. The process according to claim 1, characterized in that the aliphatic diol is an addition product of a diol and a lactone, or a mixture of a diol and a lactone.

17. The method of claim 16, wherein the lactone is caprolactone or valerolactone.

18. The process according to claim 1, characterized in that the aliphatic diol is a condensation product of a diol with a dicarboxylic acid or with a dicarboxylic ester, or a mixture of a diol with a dicarboxylic acid or with a dicarboxylic ester.

19. The process according to claim 18, wherein the dicarboxylic acid is adipic acid, glutaric acid, succinic acid or malonic acid.

20. The process according to claim 1, characterized in that the aliphatic diol is a polyether polyol.

21. The method according to claim 20, wherein the polyol is polyethylene glycol, polypropylene glycol or polybutylene glycol.

22. The process according to claim 1, characterized in that the aliphatic diol is 1, 6-hexanediol, 1, 5-pentanediol or a mixture of 1, 6-hexanediol and caprolactone.

23. The process according to claim 16, 18 or 22, characterized in that the ester is prepared in situ from the starting materials during the preparation of the oligocarbonate diol.

24. The process as claimed in claim 1, wherein the molar ratio of aliphatic oligocarbonate diol/dimethyl carbonate in the product is in the range from 1.01 to 2.0.

25. The process according to claim 1, characterized in that the catalyst is a soluble catalyst known for transesterification reactions.

26. The process as claimed in claim 25, wherein the soluble catalyst is used in a concentration of at most 0.1% by weight.

27. The process of claim 1, wherein the catalyst is a heterogeneous transesterification catalyst.