CN117321027A

CN117321027A - Process for preparing easily polymerizable compound

Info

Publication number: CN117321027A
Application number: CN202280035856.5A
Authority: CN
Inventors: S·科里尔; D·波洛尔; B·劳克斯; C·毛尔
Original assignee: Roma Chemical Co ltd
Current assignee: Roma Chemical Co ltd
Priority date: 2021-05-19
Filing date: 2022-05-04
Publication date: 2023-12-29
Also published as: EP4341238A1; WO2022243038A1; TW202311221A

Abstract

The invention relates to a method for producing easily polymerizable, in particular hydroxy-functional compounds, in particular (meth) acrylic esters, using at least one suitable reactor, an intermediate vessel in which the crude solution formed in the reactor is stored in the middle and is then fed to a suitable distillation purification device, from which the easily polymerizable compound is obtained again in a form meeting the specifications.

Description

Process for preparing easily polymerizable compound

Technical Field

Background

Monomers such as styrene or (meth) acrylates have a tendency to undergo undesired side reactions during preparation and storage, even discoloration and premature polymerization. In order to prevent this, inhibitors are used during the preparation and subsequent storage and/or further processing to stabilize them and in particular to achieve short residence times during the preparation process. The preparation process generally consists here of a reaction process and a purification process. Long storage times between the reaction process and the purification process promote unwanted side reactions in this case.

JP 2008143814 describes a reaction process for obtaining easily polymerizable alkylene oxide derivatives. The purification process is not further explained in this document.

JP 2008127302 describes a process for obtaining easily polymerizable alkylene oxide derivatives. In this case, a batch reactor is used, and the crude solution obtained after the end of the reaction is transferred to a separate distillation apparatus and distilled therein batchwise.

A preferred method for purifying hydroxyalkyl (meth) acrylates is described in particular in EP 1 090904. According to this document, the reaction mixture comprising hydroxyalkyl (meth) acrylate can be purified particularly effectively by distillation in combination with a thin film evaporator.

EP 1 125 919 describes a stabilised hydroxyalkyl (meth) acrylate which contains a concentration of from 0.0001 to 2% by weight of a hydroxyalkyl saturated carboxylate and a concentration of from 0.001 to 0.5% by weight of a phenolic compound, in each case based on the hydroxyalkyl (meth) acrylate, wherein the mixing ratio of hydroxyalkyl saturated carboxylate to phenolic compound is in the range from 0.1 to 100 by weight, and wherein the hydroxyalkyl saturated carboxylate is at least one component selected from the group consisting of hydroxyethyl acetate, hydroxyethyl propionate, hydroxyethyl isobutyrate, hydroxypropyl acetate, hydroxypropyl propionate and hydroxypropyl isobutyrate. This successfully prevents or delays unwanted polymerization, for example during storage.

EP 2 857 382 describes a process for preparing hydroxyalkyl (meth) acrylates comprising the step of reacting (meth) acrylic acid with alkylene oxide in the presence of a catalyst, wherein the water content in the overall reaction mixture is adjusted to not more than 0.05% by weight. This successfully achieves limiting the formation of the by-product diethylene glycol formed during the reaction to a minimum. If more than 0.05% by weight of diethylene glycol is present, the hydroxyalkyl (meth) acrylate is unstable and may start to polymerize undesirably during storage. The disadvantage of this method is that only raw materials with a very low water content can be used, or that the water content in these raw materials must be reduced in advance in an expensive and inconvenient manner.

Known processes and apparatus for preparing readily polymerizable compounds bring about acceptable yields and quality of the desired product. However, there is still a further need to improve the economics of these processes. In particular, this involves increasing the time of productive use of the split device of the preparation process without reducing this time due to process-related downtime.

Disclosure of Invention

Technical problem

In view of the prior art, the technical problem addressed by the present invention is to provide a process for preparing easily polymerizable compounds, in which the apparatus of the reaction process and the purification process is used in an efficient manner and at the same time undesired side reactions during storage between the reaction process and the purification process can be avoided.

In particular, the technical problem addressed by the present invention is generally to provide a process for the preparation and isolation of readily polymerizable (meth) acrylate compounds, in particular particularly readily polymerizable hydroxy-functional (meth) acrylates, in which the reaction section is carried out in batch or semi-batch mode and, in contrast, the purification can be carried out continuously or semi-continuously.

A further technical problem is thus derived to provide isolated readily polymerizable (meth) acrylate compounds with consistently high monomer quality and to prevent the fluctuations that are normally produced by batch or semi-batch modes.

Other technical problems not explicitly mentioned may result from the following description of the invention, the claims, the embodiments, or the overall association of the invention.

Solution scheme

These technical problems are solved by providing a novel process for preparing easily polymerizable compounds, in particular (meth) acrylates. The novel process starts from (meth) acrylic acid which is reacted with an epoxide-functional compound. The method has at least the following method steps:

a) (meth) acrylic acid is reacted with an epoxy functional compound in the presence of a catalyst in a reactor, wherein the gas phase and the liquid phase in the reactor are continuously mixed with each other.

b) At reaction time t ₁ Thereafter, the content of the epoxy-functional compound in the gas phase and the liquid phase is reduced by removing the gas phase from the reactor. According to the invention, the reaction time t is when the (meth) acrylic acid concentration in the liquid phase is less than 1.0% by weight, preferably less than 0.5% by weight, particularly preferably less than 0.1% by weight ₁ And (5) ending.

c) At reaction time t ₁ Thereafter, the (meth) acrylate-containing mixture present in the reactor as a liquid phase is subsequently removed and this liquid phase is transferred to an intermediate vessel.

d) Average residence time t of the mixture in the intermediate vessel ₂ The mixture is then transferred from the intermediate vessel to a distillation column I.

e) In this distillation column I, the mixture is separated into a (meth) acrylate-containing fraction, which is obtained at the top of the column and subsequently condensed, and a bottom fraction containing catalyst and high-boiling by-products.

f) Optionally, the bottom fraction from process step e) is then also separated in a separation device II into a further (meth) acrylate-containing fraction and a high-boiling fraction.

The easy-to-polymerize compounds were successfully prepared simply and efficiently in an unforeseen manner by this novel process. Furthermore, the process provides a very constant product quality. Side reactions and discoloration are surprisingly effectively avoided with the process according to the invention.

The process according to the invention is particularly suitable for preparing hydroxyalkyl (meth) acrylates. The expression hydroxyalkyl (meth) acrylate in this case includes hydroxyalkyl methacrylates, hydroxyalkyl acrylates and mixtures thereof. This applies correspondingly to the expression "(meth) acrylic acid", which includes methacrylic acid and acrylic acid or mixtures thereof.

Hydroxyalkyl (meth) acrylates are well known in the art as esters of (meth) acrylic acid, the alcohol residue of which has at least one hydroxyl group. For example, preferred hydroxyalkyl (meth) acrylates include 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl methacrylate, especially 2-hydroxypropyl methacrylate and 3-hydroxypropyl methacrylate, and/or hydroxypropyl acrylate, especially 2-hydroxypropyl acrylate and 3-hydroxypropyl acrylate.

The epoxy functional compound is preferably alkylene oxide (Oxiran), particularly preferably ethylene oxide or propylene oxide. Correspondingly, the (meth) acrylic acid esters are preferably hydroxyalkyl-substituted (meth) acrylic acid esters, particularly preferably 2-hydroxyethyl methacrylate or hydroxypropyl methacrylate. The hydroxypropyl methacrylate may in turn be 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate or an isomer mixture thereof.

The molar ratio of the total (meth) acrylic acid used to the total epoxy-functional compound used may advantageously be in the range from 2:1 to 1:2, particularly preferably in the range from 1.1:1 to 0.9:1.

The interfering by-products mentioned may be, for example, diethylene glycol (meth) acrylate or ethylene glycol di (meth) acrylate as a particularly attractive by-product. Ethylene glycol di (meth) acrylate is particularly interesting here because it is a cross-linking agent that can seriously impair the properties of the final product by cross-linking, especially in the desired polymerization process.

In process step a), preference is given to first mixing with the catalyst and optionally with auxiliaries, such as stabilizersMethacrylic acid was initially added. After reaching a temperature T ₁ After a reaction initiation temperature in the range, the addition of the epoxy-functional compound is started, for example by homogeneous metering. Reaction time t according to the invention ₁ Starting from the start of the addition. Theoretically, this addition can be carried out as a homogeneously metered addition or as an addition of individual batches up to t ₁ And (5) ending. However, this addition is generally t ₁ The end is already done before the end. However, other methods are alternatively conceivable in which methacrylic acid and/or catalyst are subsequently added. Variations are also possible in which all the starting materials are initially added and the reaction is started by increasing the temperature. In the latter case, t ₁ Starting at a time at which a first exotherm can be recorded.

The catalyst used is preferably a metal-containing compound. Alternatively, for example, two or more metal-containing compounds may also be used. Preferred catalysts are disclosed in particular in EP 12 312 04.

It is further preferred that the reaction in process step a) is at a temperature T of between 40 and 120 ℃, preferably between 50 and 100 ℃, particularly preferably between 60 and 80 DEG C ₁ The following is performed. Temperature T ₁ In this case not the temperature which is constantly present, but at t ₁ A temperature window during which the reaction is carried out. T (T) ₁ Of course, this can vary within this range, in particular due to metering, exothermic nature of the reaction and evaporation processes within the reactor. Nor is it excluded that the temperature is raised here to a very short time, i.e. less than 5 minutes, slightly above 100 ℃. However, a reaction scheme that avoids this is preferred.

The reaction of (meth) acrylic acid with epoxide may be carried out continuously, or batchwise or semi-batchwise. Batch or semi-batch modes of operation have been commercially established because they are easy to implement on equipment and the reaction can be carried out until the desired endpoint. The process for preparing hydroxyalkyl (meth) acrylates can be carried out in bulk, i.e. without the use of further solvents. Inert solvents may also be used if desired. The degree of conversion based on (meth) acrylic acid is preferably at least 99 mol%, particularly preferably at least 99.5 mol%. The degree of conversion can be adjusted in particular by the duration of the reaction and the reaction temperature.

Reaction time t in batch or semi-batch mode according to the invention ₁ Typically between 2 and 10 hours, preferably between 4 and 8 hours. The pressure used for the preparation of the hydroxyalkyl (meth) acrylate is preferably in the range from 0.5 to 25 bar, particularly preferably in the range from 1 to 3 bar, where these data are in each case absolute pressure.

For mixing of the gas and liquid phases, an ejector mixing nozzle is particularly suitable. The preferred type of construction and geometry of the ejector-mixing nozzle is desirably configured so that a relatively high suction ratio can be achieved. The suction ratio (SVH) is defined as svh=v1 [ m ³ /h]/V2[m ³ /h]Wherein

V1=volumetric flow of the suction gas from the reactor;

v2=volumetric flow of drive medium

The ejector-mixing nozzle typically has a supply of gas and a supply of liquid streams. Furthermore, the gas supply of the injector-mixing nozzle is connected to the gas space of the reactor via a gas line, which is connected to at least one reactant feed line, so that gas can be sucked out of the reactor via the gas supply of the injector-mixing nozzle by the liquid stream. It may be advantageous in particular to provide a throttle valve in the gas line connecting the gas space of the reactor to the injector-mixing nozzle. In particular, the gas flow in the gas line can thereby be regulated independently of the liquid flow being circulated to the ejector-mixing nozzle. Preferably, the reactor may have an agitator in addition to the ejector-mixing nozzle, which may be arranged in the reactor, for example.

These ejector-mixing nozzles are only one particularly preferred example of an apparatus for mixing a gas phase and a liquid phase. Further examples of such devices are known to those skilled in the art. For example, a particular stirrer geometry alone may bring about such mixing. It is also obviously possible to withdraw the gas phase and to reinject it, for example, at the bottom of the reactor, where particularly small bubbles should preferably be ensured.

In a particular variant of the process according to the invention, there is more than one reactor, wherein all of these reactors are in this case arranged in parallel with one another. This means that the reaction can be carried out in one or more reactors, which are all connected via one or more lines to an intermediate vessel, and the respective liquid phases are emptied into said intermediate vessel.

The reaction of (meth) acrylic acid with epoxide may be carried out in the presence of polymerization inhibitors, which in many cases may already be used in the reactor. The polymerization inhibitors preferably used include, in particular, phenolic compounds such as hydroquinone, hydroquinone ethers, for example hydroquinone monomethyl ether, tert-butylhydroquinone, 2, 6-di-tert-butylhydroquinone, 2, 5-di-tert-butylhydroquinone, 2, 4-dimethyl-6-tert-butylphenol or di-tert-butylcatechol; para-phenylenediamines, such as N, N ' -diphenyl-para-phenylenediamine, N ' -di-2-naphthyl-para-phenylenediamine, N ' -di-p-tolyl-para-phenylenediamine, N-1, 3-dimethylbutyl-N ' -phenyl-para-phenylenediamine, and N-1, 4-dimethylpentyl-N ' -phenyl-para-phenylenediamine; amines such as thiodiphenylamine and phenothiazine; copper dialkyldithiocarbamates, such as copper dimethyldithiocarbamate, copper diethyldithiocarbamate and copper dibutyldithiocarbamate; nitroso compounds such as nitrosodiphenylamine, isopentyl nitrite, N-nitrosocyclohexylhydroxylamine, N-nitroso-N-phenyl-N-hydroxylamine and salts thereof; and an N-oxyl compound, wherein the N-oxyl compound is a compound, for example 2, 4-tetramethylazetidine 1-oxy, 2-dimethyl-4, 4-dipropylazetidine 1-oxy 2, 5-tetramethyl-pyrrolidine-1-oxy, 2, 5-tetramethyl-3-oxo-pyrrolidine-1-oxy, 2, 6-tetramethyl-piperidine-1-oxy 2, 5-tetramethyl-pyrrolidin-1-oxy, 2, 5-tetramethyl-3-oxo-pyrrolidin-1-oxy 2, 6-tetramethylpiperidine 1-oxyl; methylene blue, nigrosine BA, 1, 4-benzoquinone, sterically hindered phenols, such as 2, 4-dimethyl-6-tert-butylphenol and/or tocopherol compounds, preferably alpha-tocopherol.

The polymerization inhibitors may be used alone or in the form of a mixture and are generally commercially available. For further details, reference is made to the general technical literature, in particular-Lexikon Chemie; edit J.Falbe, M.Regitz; stuttgart, new York; 10 th edition (1996); the keyword "Antioxidantien" (antioxidants) and references cited therein.

The surprising advantage can be achieved in particular by preference for reaction mixtures which contain from 1 to 5000ppm, particularly preferably from 5 to 1000ppm, very particularly preferably from 10 to 200ppm, of polymerization inhibitor.

With respect to process step b), it should be noted that the point in time at which the (meth) acrylic acid concentration in the liquid phase is less than 1.0% by weight can be initially determined, for example by sampling, pH measurement or refractive index measurement or other optical methods. If more experience is available with the reaction mechanism, the point in time can be determined externally during the reaction by a person skilled in the art, ideally without sampling, simply based on temperature distribution and/or other readily measurable process parameters. Preferably, process step b) is carried out at a temperature T of from 60 to 100 DEG C ₂ I.e. at a temperature similar to the actual reaction temperature, and, due to the exothermic nature of the reaction, is absolutely possible even higher than the internal temperature of the reactor during the start of the reaction.

Furthermore, it has proven to be advantageous to achieve a reduction in the content of epoxy-functional compounds in process step b) with a concomitant reduction in pressure. In this case, the epoxide-functional compound dissolved in the liquid phase is additionally degassed and removed from the reactor with the gas phase.

With regard to the method step c), in particular with regard to the design and operation of the intermediate vessel, it has proven to be particularly advantageous for the pressure p in the reactor to be ₁ Greater than the pressure p in the intermediate container ₂ . It is also preferred that the internal temperature T in the intermediate container ₃ Below T ₂ Which is the temperature inside the reactor during the removal of the gas phase, i.e. process step b).

The intermediate container may also optionally be equipped with cooling and/or heating elements, which are mounted internally or externally, preferably externally.

According to the invention, the ratio of the internal volume of the intermediate vessel to the working volume of the reactor is preferably between 1:1 and 20:1, preferably between 1.5:1 and 10:1, very particularly preferably between 1:2 and 5:1. In the case of a variant with a plurality of reactors connected in parallel to one another, these data relate to the ratio of the internal volume of the intermediate vessel to the sum of the working volumes of all the reactors. Working volume is understood here to be the maximum filling volume of the respective reactor. This successfully keeps the residence time between the reaction process and the purification process short and thus avoids undesired side reactions.

According to a particular design, the liquid phase present in each case can be treated with a gas after the reaction process in the reaction apparatus or intermediate storage vessel and before the purification process, i.e. between process steps b) and c), during process step c) and/or during process step d). For this purpose, air or nitrogen can be guided through the liquid phase. By this arrangement it is possible to separate and remove gaseous or volatile components from the liquid phase present here before subjecting the liquid phase present here to further purification, preferably distillation.

With respect to process step d), it is preferred that the residence time t ₂ Less than 200 hours, particularly preferably less than 100 hours, particularly preferably less than 50 hours. With respect to process step d), it is preferred that the residence time t ₂ With reaction time t ₁ The ratio of (2) is less than 25, preferably less than 12, particularly preferably less than 6.

In this case, the intermediate vessel is connected to the one or more distillation columns I via one or more lines.

Although not necessary and therefore less preferred according to the invention, it is contemplated that more than one intermediate vessel may be used, also arranged in parallel with each other. Independently of this, it is also possible to use a plurality (more than one) of distillation columns I arranged parallel to one another.

For process step e) it is preferred that at least one substream of the catalyst-comprising bottom fraction from the distillation column I is recycled continuously or discontinuously to the reactor. The design of the invention is preferably directed to the use of a column with internals acting as separation technology, which for example constitute or correspond to a separation stage.

With respect to the distillation column I used in process step e), it is possible in particular to achieve surprising advantages by means of a specific optional design of such a distillation column I, for example with low separation efficiency. Due to this design, the yield and energy efficiency of the device can be improved in particular. Accordingly, the distillation column I used has not more than 4, particularly preferably not more than 3, separation stages. According to a particular aspect, a column with preferably at least two separation stages is used.

In the present invention, the number of separation stages refers to the number of trays in a tray column or the number of theoretical separation stages in the case of a column containing structured packing or a column containing random packing.

The feeding of the crude solution into the distillation column I can be carried out above or below the internals described above, it also being possible, depending on the nature of these internals, for the crude solution to be introduced into the region of the internals. Particular advantages are achieved especially when the crude solution is fed to the distillation column I above the internals. The term "above the internals" means that the high boilers of the introduced composition pass through the internals before being taken out of the distillation column I. This may particularly achieve advantages in terms of yield and purity. Furthermore, the method can be performed particularly efficiently.

The distillation column I of the present invention can be operated with or without column reflux, wherein particularly high purities can surprisingly be achieved by embodiments in which column reflux is not present. These advantages can be preferably achieved by feeding the composition of the invention into the distillation column I above any internals that may be present.

According to a particular aspect of the invention, the distillation column I is preferably operated at a pressure of not more than 2Pa ^0.5 Is operated under a gas loading factor of (2). The gas loading factor of the second evaporator is preferably 0.8 to 1.8Pa ^0.5 Within a range of (2). The gas loading factor (F factor) is calculated from the square root of the gas velocity multiplied by the gas density based on the air cross section of the pipe used to guide the removal gas.

Preferably, the distillation is carried out at temperatures of from 40 to 130 ℃, particularly preferably from 60 to 110 ℃, very particularly preferably from 80 to 95 ℃, where these data are based on the bottom temperature and may vary depending on the end product produced. The pressure at which the distillation is carried out may preferably be in the range from 0.1 to 20 mbar absolute, particularly preferably from 0.5 to 10 mbar absolute, very particularly preferably from 1 to 5 mbar absolute, where these data are based on the column top pressure.

In order to avoid undesired polymerization of the polymerizable compound to be purified, a polymerization inhibitor is optionally added to the process, as described above. Polymerization inhibitors that may be preferably used include those described above or mixtures of two or more of these stabilizers. In addition to or less preferably as an alternative to metering into the reactor, it is also possible to meter into the intermediate vessel or the distillation column I. In the case of metering the inhibitors into the distillation column I, this is preferably carried out at the top. The high boilers, such as the added inhibitors, can be removed from the bottom by conventional means, for example by means of thin-film evaporators or devices for similar tasks, which recycle the vaporizable substances into the rectification column and remove the non-vaporizable high boilers.

With respect to the optional process step f), the separation device II is preferably a second distillation column, a thin film evaporator or a short path evaporator. It is particularly preferred here to recycle the (meth) acrylate-containing fraction obtained from this separation device II into the intermediate vessel or into the distillation column I, in particular to recycle at least one substream from the top fraction of the separation device II into the intermediate vessel and/or into the distillation column I.

If the optional process step f) is carried out, it is particularly advantageous to continuously or discontinuously recycle at least one substream of the catalyst-comprising bottom fraction from the separation apparatus II into the reactor. This can also be carried out as described above with the corresponding substream from the bottom fraction of the distillation column I.

In this process step f), it is therefore optional but preferred, in order to increase the yield, to convert a portion of the composition obtained from the bottom of the distillation column I into the gas phase using at least one evaporator, for example a thin film evaporator or a circulation evaporator. Accordingly, preferred apparatus for carrying out the process for purifying hydroxyalkyl (meth) acrylate include a thin film evaporator and/or a circulation evaporator.

Examples of the components which can be used in process steps e) and f) which can be used are found in particular in EP 1 090904.

When carrying out the process according to the invention according to the present description, it is often observed that the freshly used catalyst in the reactor comprises anions which differ, at least to some extent, from the catalyst present in the bottom fraction of the distillation column I and/or the separation device II, even if no preferred embodiment is used. In particular, the catalyst present in the bottom fraction of the distillation column I and/or the separation device II is present here wholly or partly as metal (meth) acrylate.

A particularly preferred design of the process according to the invention is characterized in that process steps a) to c) are carried out semi-continuously, so that after the reactor has been emptied in process step c), the reactor can be operated at a time t ₃ The inner direct refill is used to directly carry out the method step a). In this case t ₃ Should preferably be greater than t ₁ Short. In this particularly preferred case, the process steps d) to f) can then be carried out continuously.

Such a scheme may thus be of the form: after the end of the reaction, the liquid phase is transferred from the reactor to the intermediate vessel, and then a new batch or half-batch can be carried out in the reactor only after a short time without downtime. At the same time, the crude solution is supplied from an intermediate vessel to a purification process consisting of one or more distillation purification systems. Desirably, the work-up of the products in process steps d) and e) or up to f) is carried out continuously.

In such a continuously carried out aftertreatment in method steps d) to e) or f), the efficiency of the method according to the invention results from the process output of such a purification process. Downtime due to excessively low crude solution yields must be avoided. Furthermore, the crude solution yield is not allowed to be greater than the process output of the purification process, as otherwise the crude solution would accumulate in the intermediate vessel. This can be counteracted more flexibly by preferably using a plurality of reactors which are operated in parallel, in particular staggered in time.

It is therefore preferred that the process output of the purification process in tons of crude solution per hour is at least as great as the production output of the reaction process in tons of liquid phase withdrawn per hour. The production output of the reaction process is in this case the average value over time of the sum of the production outputs of the individual reactors.

In addition to the process of the invention, the apparatus for carrying out the process is also a component of the invention. The apparatus has at least one reactor, an intermediate vessel and at least one distillation column I.

The device is characterized in that

(I) The reactor and the intermediate vessel are connected to each other by a pipeline,

(II) the ratio of the internal volume of the intermediate vessel to the internal volume of the reactor is between 1 and 20, wherein the intermediate vessel is designed such that the distillation column I can be operated continuously without interruption and the process steps a) to c) can be carried out semi-continuously without interruption between process steps c) and a), and

(III) optionally a pressure regulating valve is present in the line between the reactor I and the intermediate vessel I.

The device preferably additionally comprises the following aspects:

(IV) the intermediate vessel and the distillation column I are connected together by a pipeline,

(V) the distillation column I is designed such that at t ₁ The volume of the feed stream entering the distillation column I during this is at least as large as the volume of the liquid phase in the reactor during process step a),

(VI) optionally a pressure regulating valve is present in the line between the intermediate vessel and the distillation column I.

Particularly preferably, such a device also has a plurality of reactors arranged in parallel with one another. These reactors are all connected here to an intermediate vessel or optionally to a plurality of intermediate vessels arranged in parallel with one another. Very particularly preferably, however, the intermediate vessel or vessels are directly connected to only one distillation column I.

List of reference numerals

One preferred apparatus for preparing the readily polymerizable compound is illustrated based on FIG. 1: FIG. 1 is a schematic diagram of an apparatus suitable for preparing a readily polymerizable compound and having reaction equipment, which is not intended to be limiting.

Raw material 1 and raw material 2 each enter reactor a via feed lines 1 and 2, where the reaction process is carried out in a batch or semi-batch process. Auxiliaries such as catalysts and/or stabilizers can be fed to the reaction apparatus via a further feed line 3. After the end of the reaction process the crude solution is transferred via line 4 to intermediate vessel B. From this intermediate vessel B, the crude solution is continuously transferred via line 5 to distillation purification apparatus C. The readily polymerizable compound is obtained in a form conforming to the specifications from distillation purification apparatus C via line 6. The high boiling residue is removed from the distillation purification unit via line 7. Optionally, the high-boiling residue can be recycled in whole or in part to the reaction apparatus a via line 8.

A particularly preferred apparatus for preparing the readily polymerizable compounds is additionally illustrated by way of example in fig. 2: FIG. 2 is a schematic diagram of an apparatus suitable for preparing a readily polymerizable compound and having two reactors, which is not intended to be limiting.

Raw material 1 and raw material 2 enter reactors A1 and A2 via feed lines 11 and 21, respectively, and 12 and 22, where the reaction process is carried out in a batch or semi-batch process. Auxiliaries such as catalysts and/or stabilizers can be fed into the respective reactor via further feed lines 13 and 23. After the end of the reaction process the crude solution is transferred via lines 14 and 24 to intermediate vessel B. From this intermediate vessel B, the crude solution is continuously transferred via line 5 to distillation purification apparatus C. The readily polymerizable compound is obtained in a form conforming to specifications from the distillation purification plant via line 6. The high boiling residue is removed from the distillation purification unit via line 7. Optionally, the high boiling residue may be recycled in whole or in part to reactors A1 and/or A2 via lines 18 and 28.

1 raw material 1 feed line

2 feed line for raw material 2

3 feed lines for auxiliaries (e.g. stabilizers, catalysts)

A reactor

4 crude solution line from reactor A to intermediate vessel B

B intermediate container B

5 crude solution line from intermediate vessel B to distillation purification apparatus C

C distillation purification equipment C

6 line for withdrawing a desired product, in the form of a polymerisable compound=an acceptable specification

7 high boiling residue take-off line

8 optionally, a line for recycling the high-boiling stream

Additional items related to fig. 2:

11. 21 feed line of raw material 1 into two different reactors A1 or A2

12. 22 feed line of raw material 2 into two different reactors A1 or A2

13. 23 auxiliary (e.g. stabilizer, catalyst) into the feed line of two different reactors A1 or A2

A1, A2 parallel-operated reactors A1 or A2

4. Crude solution line from reactor to intermediate vessel B

18. 28 optionally a line for recycling the high-boiling stream

Detailed Description

Examples

The following is intended to illustrate the invention by way of examples and comparative examples, which are not intended to be limiting.

Example 1

Methacrylic acid is reacted with ethylene oxide in the apparatus according to fig. 1. For this, 5300 kg (61.6 kmol) of methacrylic acid are added via feed line 1 to a working volume of 8m ³ 12 kg (52.4 mol) of chromium acetate as catalyst and 2.5 kg (20.1 mol) of hydroquinone monomethyl ether (HQME) as stabilizer were added thereto via feed line 3, and the mixture was heated to a temperature of 70 ℃. The mixture was then started to circulate and pump through the external circuit, where it was regulated for about 70m ³ The circulating volume flow per h and the mixture is metered into the reactor again at the top via an ejector-mixing nozzle. However, the method is that2720 kg (61.7 kmol) of ethylene oxide was then added via feed line 2. The amount metered in is chosen such that the reaction temperature does not exceed 70 ℃. The amount metered in was adjusted to approximately 900kg/h (20.4 kmol/h). The time from the charging of methacrylic acid to the end of the ethylene oxide metering was 3 hours.

After the addition of the predetermined amount, the reaction mixture was further guided through an external circuit as described above at a temperature of 70 ℃. In this case, after a further 3 hours, samples were taken from the reactor contents per hour and analyzed for residual methacrylic acid content by means of acid-base titration. The first sample had a residual methacrylic acid content of 0.63 wt%, the second sample after 7 hours had a residual methacrylic acid content of 0.18 wt%, and the third sample after 8 hours had a residual methacrylic acid content of 0.05 wt%. This process step thus ends after 5 hours.

The reaction mixture was thereafter cooled to 60 ℃. The pressure was then slowly released over several minutes via a needle valve mounted on the reaction equipment cover. The exhaust gas is here led via a line to a gas scrubbing device.

The resulting 8 tons of crude solution are then discharged via line 4 to a volume of 10m ³ In the intermediate container B of (a). This process lasted 15 minutes. Thereafter, a new reaction of methacrylic acid with ethylene oxide is carried out directly in reactor A as described above.

The resulting crude solution was analyzed, wherein the proportion of 2-hydroxyethyl methacrylate was about 95.4 wt.%. This was determined by means of GC-FID (gas chromatography combined with flame ionization detector). Diethylene glycol methacrylate constitutes the greatest proportion of by-products, with a proportion of about 3.60% by weight. A particularly notable byproduct is ethylene glycol dimethacrylate, in a proportion of approximately 0.11% by weight. Other by-products are listed in table 1.

The crude solution is then fed from an intermediate storage vessel to a continuously operated distillation purification unit C. The distillation purification equipment consists of a distillation tower, a top condenser and a thin film evaporator. The crude solution is transferred via line 5 at a metering flow of 970kg/h into a distillation column which is in this case equipped with internals which in the case of separation technology correspond approximately to the separation stage. The composition is fed over the inner member. The overhead product is cooled in the overhead condenser and withdrawn from the plant via line 6. The bottom product contains mainly the high-boiling minor components and the catalyst, which is now substantially present as chromium methacrylate.

Immediately after the purification of the crude solution of the first batch had ended, the distillative purification of the second batch which had been pumped circularly into the intermediate vessel was carried out without interruption. This procedure was continued until 10 batches were prepared and purified. Thus 80 tons of crude solution were purified after 90.75 hours.

After purification, 2-hydroxyethyl methacrylate was obtained with a purity of 98.8% by weight, which contained approximately 50ppm of hydroquinone monomethyl ether. Other by-products are listed in table 1. The color number of the resulting 2-hydroxyethyl methacrylate was measured by the method given in DE 10 131 479. The color value is less than 5.

The storage stability of the composition was measured by measuring the color value. The storage properties were thus determined at 30℃over 6 months. To this end, 25 g of the composition was filled into a 30 ml flask (brown, wide neck). Stored in a circulating air oven at 30 ℃. Color values were measured after 6 months. This is much less than 5.

Comparative example 1

Example 1 was essentially repeated, wherein after 8 hours the crude solution after the end of the reaction was transferred directly to a distillation purification plant at a metering rate of 1000 kg/h.

The resulting crude solution was analyzed as shown in example 1, with a 2-hydroxyethyl methacrylate ratio of about 95.4 wt.%. Diethylene glycol methacrylate is formed at a rate of about 3.60% by weight and ethylene glycol dimethacrylate is formed at a rate of about 0.12% by weight. Other by-products are listed in table 1.

The next batch is started after purification of one batch is completed. Thus 80 tons of crude solution were purified after 160 hours. The cyclic operation of the distillation purification plant may result in about 5% yield loss during start-up and shut-down procedures, as compared to the continuous mode of operation as performed in example 1.

After purification, 2-hydroxyethyl methacrylate was obtained with a purity of 98.8% by weight, which contained approximately 50ppm of hydroquinone monomethyl ether. Other by-products are listed in table 1. The color number of the resulting 2-hydroxyethyl methacrylate measured as shown in example 1 was less than 5.

The color value determined by the method as shown in example 1 was 6 after 6 months.

Example 2

Example 1 was essentially repeated, wherein all 10 batches were first transferred to a tank after the reaction and then purified by distillation by feeding from the tank. Residence time t ₂ In this case greater than 200 hours based on the last batch.

The crude solution obtained from the tank was analyzed before distillation purification, wherein the proportion of 2-hydroxyethyl methacrylate, as determined by GC-FID (gas chromatography combined with flame ionization detector), was about 95.0 wt.%. Diethylene glycol methacrylate constitutes the greatest proportion of by-products, with a proportion of about 3.95% by weight. A particularly notable by-product is ethylene glycol dimethacrylate, in a proportion of approximately 0.16% by weight. Other by-products are listed in table 1.

After purification, 2-hydroxyethyl methacrylate was obtained with a purity of 98.2% by weight, which contained approximately 50ppm of hydroquinone monomethyl ether. The color number of the resulting 2-hydroxyethyl methacrylate was measured by the method given in DE 10 131 479. This is less than 5.

The storage stability of the composition was measured by measuring the color value. The storage properties were thus determined at 30℃over 6 months. To this end, 25 g of the composition was filled into a 30 ml flask (brown, wide neck). Stored in a circulating air oven at 30 ℃. Color values were measured after 6 months. The color value is 8.

Although the results of example 2 show good colour stabilization compared to example 1, this is due to the extended residence time t of more than 200 hours ₂ This is not ideal but rather results in a poor color value when the finished product is stored for a longer period of time. This embodiment of the invention is therefore not preferred over the embodiment in example 1.

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Claims

1. A process for the preparation of (meth) acrylic esters, starting from (meth) acrylic acid and an epoxy-functional compound, with the following process steps:

a) Reacting (meth) acrylic acid with an epoxy-functional compound in the presence of a catalyst in a reactor, wherein a gas phase and a liquid phase in the reactor are continuously mixed with each other,

b) At reaction time t ₁ Thereafter, when the concentration of (meth) acrylic acid in the liquid phase is less than 1.0% by weight, the content of the epoxy-functional compound in the gas phase and the liquid phase is reduced by removing the gas phase from the reactor,

c) Then take out at reaction time t ₁ The (meth) acrylate-containing mixture which is then present in the reactor as a liquid phase and this liquid phase is transferred to an intermediate vessel,

d) Average residence time t of the mixture in the intermediate vessel ₂ Thereafter, the mixture is transferred from the intermediate vessel to a distillation column I,

e) Separating the mixture into a (meth) acrylate-containing fraction which passes through the top of the distillation column I and subsequently condenses this fraction, and a bottom fraction containing catalyst and high-boiling by-products, and

f) Optionally, the bottom fraction from process step e) is separated in a separation device II into a further (meth) acrylate-containing fraction and a high boiling fraction.

2. Process according to claim 1, characterized in that the epoxy-functional compound is an alkylene oxide, preferably ethylene oxide or propylene oxide, and the (meth) acrylate is a hydroxyalkyl-substituted (meth) acrylate, preferably 2-hydroxyethyl methacrylate or hydroxypropyl methacrylate.

3. The process according to claim 1 or 2, characterized in that the catalyst is one or more metal-containing catalystsAnd the reaction in process step a) is at a temperature T of between 50 and 100 DEG C ₁ The following is performed.

4. A process according to at least one of claims 1 to 3, characterized in that at least one substream of the catalyst-comprising bottom fraction from the distillation column I and/or the separation device II is recycled continuously or discontinuously to the reactor.

5. The process according to claim 1 to 4, characterized in that the separation device II is a second distillation column, a thin film evaporator or a short path evaporator and the (meth) acrylate-containing fraction obtained from such a separation device II is recycled to the intermediate vessel and/or the distillation column I.

6. A process as claimed in claim 1 to 5, wherein the pressure p in the reactor I is ₁ Greater than the pressure p in the intermediate container ₂ 。

7. The process according to claim 1 to 6, characterized in that process step b) is carried out at a temperature T of 60 to 100 DEG C ₂ Down-going and internal temperature T in the intermediate vessel ₃ Below T ₂ 。

8. The process according to claim 1 to 7, characterized in that at a reaction time t ₁ The (meth) acrylic acid concentration in the liquid phase of the reactor is then less than 0.5% by weight, preferably less than 0.1% by weight.

9. Process according to at least one of claims 1 to 8, characterized in that the reduction of the content of epoxy-functional compounds in process step b) is effected by pressure reduction.

10. The method according to at least one of claims 1 to 9, characterized in that the ratio of the internal volume of the intermediate vessel to the internal volume of the reactor is between 1:1 and 20:1.

11. The process according to at least one of claims 1 to 10, characterized in that the residence time t ₂ Less than 200 hours, preferably less than 100 hours, particularly preferably less than 50 hours.

12. The process according to at least one of claims 1 to 11, characterized in that the residence time t ₂ With reaction time t ₁ The ratio of (2) is less than 25, preferably less than 6.

13. Process according to at least one of claims 1 to 12, characterized in that at least one substream from the overhead fraction of the separation device II is recycled to the intermediate vessel and/or to the distillation column I.

14. Process according to at least one of claims 1 to 13, characterized in that the freshly used catalyst in the reactor comprises at least to some extent anions different from the catalyst present in the bottom fraction of the distillation column I and/or the separation device II and that the catalyst present in the bottom fraction of the distillation column I and/or the separation device II is wholly or partly present as metal (meth) acrylate.

15. The process according to at least one of claims 1 to 14, characterized in that process steps a) to c) are carried out semi-continuously, so that after the reactor has been emptied in process step c), the reactor is operated at a time t ₃ Direct refilling and carrying out method step a), wherein t ₃ Ratio t ₁ Short and the process steps d) to f) are carried out continuously.

16. Device for carrying out the process according to at least one of claims 1 to 15, having a reactor, an intermediate vessel and at least one distillation column I, characterized in that

(I) The reactor and the intermediate vessel are connected to each other by means of a line,

(II) the ratio of the internal volume of the intermediate vessel to the internal volume of the reactor is between 1 and 20, wherein the intermediate vessel is designed such that the distillation column I can be operated continuously without interruption and the process steps a) to c) can be operated semi-continuously without interruption between process steps c) and a), and

17. The apparatus of claim 16, wherein

(IV) the intermediate vessel and the distillation column I are connected to each other by a line,

(V) design of distillation column I such that at t ₁ The volume of the feed stream which is fed into the distillation column I during this time is at least as large as the volume of the liquid phase in the reactor during process step a), and

18. The plant according to claim 16 or 17, characterized in that the plant has a plurality of reactors arranged in parallel with each other and all connected to intermediate vessels or optionally to a plurality of intermediate vessels arranged in parallel with each other, and that the intermediate vessel or vessels are directly connected to only one distillation column I.