HK1090632B - Method for continuously producing alkylamino (meth)acrylamides - Google Patents

Description

Method for the continuous production of alkylamino (meth) acrylamides

Technical Field

The invention relates to a more continuous process for preparing alkylamino (meth) acrylamides (C) by continuous ammonolysis of methyl (meth) acrylate (A) with an amine (B) with liberation of methanol (D), for example according to the following reaction equation:

wherein:

R¹hydrogen or methyl

R²Is a linear, branched or cyclic alkyl group; aryl which may also be substituted with one or more alkyl groups; the linear, cyclic or branched alkyl group may have a chain length of 2 to 12 carbon atoms, such as ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, isooctyl, nonyl, decyl, undecyl, and optionally may be represented by-NR³R⁴OR-OR⁵Mono-or polysubstituted, where R is³Or R⁴May be hydrogen, and further:

-R³、R⁴or R⁵Which may be the same or different, and is an alkyl group having 1 to 12 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, isooctyl, nonyl, decyl, undecyl or hydrogen.

-R²Can also be

[(R⁶-0)_n]-R⁷

Wherein:

-R⁶can be C₁-C₄Alkyl, which may also be branched, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl or tert-butyl.

Alkyl amido (meth) acrylates

m：1-4

R⁷And may be methyl or ethyl.

Useful amines include the following compounds:

dimethylaminoethylamine, diethylaminoethylamine, dipropylaminoethylamine, diisopropylaminoethylamine, dibutylaminoethylamine, diisobutylaminoethylamine, dimethylaminopropylamine, diethylaminopropylamine, dipropylaminopropylamine, diisopropylaminopropylamine, dibutylaminopropylamine, diisobutylaminopropylamine, dimethylaminobutylamine, diethylaminobutylamine, dipropylaminobutylamine, diisopropylaminobutylamine, dibutylaminobutylamine, methylamine, cyclohexylamine, dimethylaminohexylamine, diethylaminohexylamine.

In addition to dimethylaminopropylamine, particular preference is given to dimethylaminoethylamine, dimethylaminobutylamine, dimethylaminopentylamine and dimethylaminohexylamine.

Prior Art

Many discontinuously carried out transesterification processes (batch transesterification processes) in combination with different catalysts are described in the literature.

The search for more economical processes has led to the discovery of continuous transesterification processes, in which reactants are fed continuously and products are withdrawn continuously. The continuous transesterification method has the following advantages over the batch transesterification method: the process can be automated more easily and can be operated with reduced personnel requirements, the product quality is better reproducible and is less fluctuating, the plant capacity is increased because the sequential operations (charging, reaction, low-boiling compound separation, product separation, emptying) of the individual preparation steps are eliminated. The process has a higher space-time yield than batch processes.

Continuous transesterification processes are known.

EP 0960877(Elf Atochem s.a.) describes a continuous process for preparing methacrylic esters of dialkyl amino alcohols. The dialkylaminoalcohol is typically reacted with methyl (meth) acrylate and the dialkylaminoalkyl (meth) acrylate is obtained by:

the mixture of the starting materials methyl (meth) acrylate and dialkylaminoalcohol is continuously fed, together with a tetraalkyl titanate, such as tetrabutyl titanate, tetraethyl titanate or tetrakis (2-ethylhexyl) titanate, as transesterification catalyst, and at least one polymerization inhibitor, such as phenothiazine, tert-butylcatechol, hydroquinone monomethyl ether or hydroquinone, to a stirred reactor, in which the conversion to dialkylaminoate (meth) acrylate is carried out at a temperature of 90 to 120 ℃ while the methyl (meth) acrylate/methanol azeotrope is continuously removed. The crude reaction mixture (crude ester) is fed to a first distillation column, in which at the top of the distillation column a stream essentially free of catalyst is removed under reduced pressure and at the bottom of the distillation column the catalyst and a small amount of dialkylaminoalkyl (meth) acrylate are removed. The top stream of the first distillation column is then fed to a second distillation column, in which at the top a low-boiling product stream with a small amount of dialkylaminoalkyl (meth) acrylate is removed under reduced pressure, and at the bottom a stream consisting essentially of dialkylaminoalkyl (meth) acrylate and one or more polymerization inhibitors is removed and fed to a third distillation column. In a third distillation column, rectification is carried out under reduced pressure, wherein at the top the desired pure dialkylaminoalkyl (meth) acrylate is removed and at the bottom essentially the polymerization inhibitor or inhibitors are removed. The bottom stream of the first distillation column is further purified by means of a thin-film evaporator and returned to the reactor as the top stream from the second distillation column.

This process eliminates the dehydration of the alcohol prior to use, which may lead to increased deactivation of the tetraalkyl titanate used by hydrolysis to form undesirable solid deposits. Furthermore, this method has the disadvantages that: the catalyst is thermally stressed at a relatively high temperature at the bottom in the first distillation column. This may easily lead to decomposition of the catalyst. In this process, both the unconverted reactants and the products are subjected to a total of two top distillations. This requires a very high energy consumption and a total of 4 rectification columns, some of which must have very large dimensions. Thus, the process is associated with very high capital and operating costs.

EP 0968995(Mitsubishi Gas Chemical Comp.) describes a continuous process for preparing alkyl (meth) acrylates using a reaction column. Here, the transesterification is carried out directly in a distillation column (i.e.the reactor for removing the methyl (meth) acrylate/methanol azeotrope and the distillation column form one apparatus) to which the starting materials ((methyl (meth) acrylate and alcohol) are continuously fed. The necessary catalyst, here again preferably a titanium compound, is located in the distillation column. In the case of homogeneous catalysts, the catalyst is metered continuously into the distillation column. However, the use of a homogeneous catalyst in a distillation column results in an increased catalyst requirement due to the flushing effect by liquid reflux in the distillation column and, when a solid precipitate of the catalyst occurs, in fouling of the column internal structure. In the case of heterogeneous catalysts, the catalyst is located in a reaction column. However, the placement of the catalyst in the distillation column is disadvantageous, since an increased pressure drop ensues in the distillation column and, in addition, the distillation column has to be operated with very high expenditure for periodic cleaning. Furthermore, heterogeneous catalysts may deactivate, for example, as a result of undesired polymerization reactions.

DE 4027843(GmbH) describes a continuous process for preparing N-substituted (meth) acrylamides by transesterification of alkyl esters of (meth) acrylic acid with aliphatic and aromatic amines. The reaction temperature is > 150 ℃ and the pressure is approximately 160 bar. Operated without catalyst.

Disclosure of Invention

Object of the Invention

It is an object of the present invention to provide a continuous process for the ammonolysis of methyl (meth) acrylate using amines having a higher boiling point relative to methanol, which avoids the disadvantages of the two processes described above. The (meth) acrylate or alkyl (meth) acrylate refers hereinafter to esters and derivatives of acrylic acid and esters and derivatives of methacrylic acid, such as methyl methacrylate or ethyl methacrylate. Furthermore, the products intended to be provided by the novel process are of better quality than those sold hitherto. The better quality means a lower content of crosslinker or a lower content of addition products of amines onto the double bonds of the starting ester or onto the double bonds of the product ester. A possible crosslinker formed is an alkylmethacrylamide. Furthermore, the novel process should produce amino (meth) acrylates at the lowest possible cost and expense and with a more energetically favorable (i.e. cost-favorable) yield. The personnel expenditure required for operating the plant should be reduced.

This object and other objects which are not explicitly detailed but can be easily deduced or derived from the introductory discussion of the prior art are all achieved by the method of the present invention. Advantageous modifications of the process according to the invention are also protected in the present invention.

The invention relates to a continuously operated method for producing alkylamino (meth) acrylamides of general formula (C),

in the formula, R₁Is H or CH₃A group, and R₂Is a linear, branched or cyclic alkyl or aryl group having 2 to 12 carbon atoms, by reacting a compound of the general formula (B) with a compound of the general formula (A) in the presence of a transesterification catalyst and in the presence of at least one polymerization inhibitor in an apparatus for continuous reaction,

R₂NH₂ (B)

in the formula, R₂Has the above-mentioned definition, and can be used for making various foods,

in the formula, R₁Is H or CH₃A group, and R³Is a methyl group or an ethyl group,

the method is characterized in that: the reactants are fed continuously into a suitable reaction apparatus (1) and the alcohol formed in the reaction is removed continuously in the form of a methanol/methyl (meth) acrylate azeotrope (13) via a distillation column (2) and also:

-the reaction mixture is continuously conducted away from the reaction apparatus into a distillation column (3) or an evaporator (5), in which the volatile components, which are compounds of the general formula (a), compounds of the general formula (B), methanol, and a very low proportion of the product amide (C) are removed via the top by distillation under reduced pressure and returned to the reaction apparatus, and the product amide (C) is removed from the bottom of the column together with the catalyst, polymerization inhibitor and high-boiling by-products;

-feeding the bottom stream (15) originating from the distillation column (3) continuously to the purification distillation process.

In a preferred embodiment of the above process, the vapor stream of the evaporator (5) is continuously fed to a further distillation column in which the high-purity product amide (C) is discharged via the top by distillation under reduced pressure, and the catalyst, polymerization inhibitor and high-boiling by-products are removed via the bottom together with a small portion of the product amide (C).

Description of the method

The process of the present invention is depicted schematically in FIG. 1.

Explanation of reference symbols in fig. 1:

1. reaction equipment

2. Azeotrope distillation column

3. Low boiling point compound distillation column

5. Thin film evaporator

Methyl (meth) acrylate and catalyst feed

12. Amine feed

13. Methanol/methyl (meth) acrylate azeotrope

14. Low boiling point compound recycle stream

15. Crude product

The reactants, methyl (meth) acrylate (MMA)11, are fed continuously to a suitable reaction apparatus 1, in which either a single reaction vessel or a cascade of a plurality of reaction vessels connected in series may be used. It is significant that all reaction vessels have a vapor outlet to azeotrope distillation column 2 to remove methanol liberated in the reaction.

The amine 12 is continuously fed to the column for dehydration during the azeotrope distillation. The molar ratio of MMA to amine in the reactor feed is from 1 to 2, preferably from 1.05 to 1.15.

The desired tetraalkoxy titanate is metered as catalyst (the tetraalkoxy titanate content, based on MMA used, is preferably from 0.1 to 10% by weight, more preferably from 0.2 to 7% by weight, particularly preferably from 0.2 to 4% by weight), likewise preferably continuously, as is one or more polymerization inhibitors, into the reaction apparatus 1. However, it is also possible to use all transesterification catalysts known from the prior art as transesterification catalysts. Useful catalysts are, for example, zirconium acetylacetonate and also zirconium 1, 3-diketonates; mixtures of alkali metal cyanates or alkali metal thiocyanates and alkali metal halides may also be used; and zinc compounds, e.g. dioctylzinc oxide, alkaline earth metal oxides or hydroxides, e.g. CaO, Ca (OH)₂、MgO、Mg(OH)₂Or mixtures of the above, also alkali metal hydroxides, alkali metal alkoxides and lithium chloride and hydroxide; the above compounds may also be usedA mixture with the above alkaline earth metal compound and lithium salt; dialkyltin oxides, such as dioctyltin oxide, alkali metal carbonates together with quaternary ammonium salts, such as tetrabutylammonium hydroxide or cetyltrimethylammonium bromide, and furthermore mixed catalysts composed of diorganotin oxide and organotin halides, acidic ion exchangers, phosphorus-molybdenum heteropolyacids, titanium alkoxides, such as isopropyl titanate, chelate compounds of metallic titanium, zirconium, iron or zinc with 1, 3-dicarbonyl compounds, lead compounds, such as lead oxides, lead hydroxides, lead alkoxides, lead carbonates or lead salts of carboxylic acids. A catalyst mixture consisting of dialkyltin oxide and alkyl titanate is particularly preferred, for example dioctyltin oxide and isopropyl titanate in a ratio of about 1: 1 (wt%/wt%), which is used in amounts of 0.1 to 10 wt%, preferably 0.2 to 7 wt%, based on MMA used. The catalyst mixture is used in an amount of 0.1 to 10% by mass, based on the amine used.

Useful polymerization inhibitors are, for example, hydroquinone, 4-hydroxy-2, 2, 6, 6-tetramethylpiperidinooxy or bis (2-methoxycarbonylpropyl) sulfide, phenothiazine, tert-butylcatechol, hydroquinone monomethyl ether or mixtures thereof, the amount of polymerization inhibitor being 100-5000ppm, based on the reaction mixture. Combinations of hydroquinone monomethyl ether with oxygen are contemplated.

The amine used may contain water. In the case of amines, the amines used have a water content of from 50 to 500ppm (0.05 to 0.005% by weight). The amine is preferably distilled off via an azeotrope column 2 before entering the reaction apparatus. In this column, the water contained in the amine is removed overhead. In order to avoid contamination of the methanol/MMA azeotrope 13 by the amine used, the amine is preferably fed in the lower part of the distillation column 2. The amines used can also be dehydrated in other ways:

by an upstream dehydration-distillation column or

By treatment with dehydrating agents, e.g. molecular sieves or

By membrane separation methods, such as pervaporation.

Dehydration is therefore important because the water present in the amine may cause irreversible damage to the catalyst (e.g. tetraalkyl titanate) in the reactor. The presence of water in the amine leads to the formation of by-products and should therefore be strictly avoided. Hydrolysis of the catalyst and the costs due to increased catalyst usage and solid precipitation problems are avoided by this dehydration step. In addition, the product purity is also increased due to the reduced proportion of by-products.

In the reaction apparatus 1, the reaction is carried out at a temperature in the range of 80 to 160 ℃. Preferably 110 ℃ and 135 ℃. In order to increase the reaction rate, the methanol liberated in the reaction is removed from the reaction mixture via the distillation column 2 as an azeotrope 13 with MMA. After a reactor residence time of about 0.5 to 3 hours, preferably a residence time of 0.75 to 1.5 hours, the reaction mixture, which consists in the largest part of the products alkyl (meth) acrylamide, unconverted MMA and amine, and also small amounts of methanol, catalyst, polymerization inhibitor and small amounts of by-products, is fed to a continuously running falling-film evaporator 5. The vapor of the falling film evaporator 5 is fed to the low boiler distillation column 3. There, the components having a low boiling point relative to the product ester, predominantly methanol, MMA and unconverted reactant amine, are separated off under reduced pressure, preferably at a pressure of from 10 to 500 mbar, more preferably from 20 to 500 mbar. These components are removed via the top of the distillation column and returned as low boiler recycle stream 14 to the reactor zone or to azeotrope distillation column 2. From this recycle stream it is ensured that the MMA and amine reactants involved are almost completely converted based on the overall process. The crude amide 15 preferably contains more than 93 wt.% of product ester, wherein the crude amide 15 is present in the effluent of the falling-film evaporator 5 and is still admixed with catalyst, polymerization inhibitor and high-boiling by-products, and the crude amide 15 is fed to a further work-up in a vacuum distillation stage, which is preferably operated at a pressure in the range of 20 to 200 mbar. The high-purity product amine is separated off here by distillation as top product.

The by-products formed in the process are components which have a high boiling point relative to the reactants amine and methyl methacrylate and thus enter the product ester as impurities, thereby significantly reducing the product quality. This problem can be solved by using a device 5 with a manageable membrane evaporation process to separate the product amine from the catalyst, the polymerization inhibitor and the high-boiling by-products. Suitable devices known for this purpose are falling film, thin layer and short path evaporators.

After the preparation of the alkylamino (meth) acrylamides, a purification distillation apparatus can optionally also be provided, which can also be operated under reduced pressure, for example at 500 to 50 mbar.

The process according to the invention is illustrated in detail by the following examples without being restricted thereto.

Example (b):

aminolysis to amino esters as described in succession

For the continuous, descriptive preparation of N-dimethylaminopropyl methacrylamide (amino ester), 235kg/h of an MMA/catalyst feed, which contains 3.8% by weight of isopropyl titanate and 3.0% by weight of dioctyltin oxide of the azeotrope column, and 244kg/h of N-Dimethylaminopropylamine (DMAPA), were metered into the first reactor. In addition, the recycle return stream from the top of the low boiler distillation column also flowed continuously into the first reactor via the azeotrope distillation column (195kg/h of a catalyst having a composition of 78.9 wt.% MMA, 2.12 wt.% methanol, 10.1 wt.% DMAPA and 8.88 wt.% by-product). The molar ratio of MMA to DMAPA in the reactor feed was 1.23: 1. Furthermore, the vapor of the stirred tank, from which methanol has been removed in the azeotrope distillation column, is fed to the first reactor via the bottom of the azeotrope distillation column. Under these reaction conditions, a reaction temperature of 107 ℃ was adjusted in the first reactor. The distillate removed from the azeotrope distillation column was 117kg/h and contained 56.54 wt% methanol, 39.12 wt% MMA, 4.02 wt% isopropyl alcohol and 0.5 wt% by-products.

The effluent from the first reactor flows into the second reactor and the effluent from the second reactor flows into the third reactor. The following compositions were obtained in the reactors with a residence time of about 15 minutes in the first reactor, a residence time of about 30 minutes in the second reactor and a residence time of about 60 minutes in the third reactor.

	T(℃)	MMA(wt％)	DMAPA(wt％)	Amino ester (wt%)	Methanol (wt%)	By-product (wt%)
							First reactor	107	62.7	10.23	22.07	0.62	4.38
Second reactor	111	55.6	10.15	27.69	0.59	5.97
							Third reactor	130	46.8	4.86	41.29	1.24	5.81

The vapors from each reactor were fed continuously to the azeotrope distillation column.

The effluent of the third reactor continuously flows into the thin-layer evaporator of the low boiler distillation column, where unconverted DMAPA, MMA and methanol are removed as distillate (195kg/h) and fed back into the first reactor as a return stream. The bottom starting stream of the thin-layer evaporator of the low boiler distillation column was 426kg/h and had the following composition: 93% amino ester product, 0.5% DMAPA, 0.2% MMA, 2.15 wt% MMA-amine adduct and 4.25 wt% other by-products.

Claims (17)

1. A process for the preparation of compounds of the general formula (C) in continuous operation,

in the formula, R₁Is H or CH₃A group, and R₂Is a linear, branched or cyclic alkyl or aryl group having 2 to 12 carbon atoms, and optionally may be substituted with-NR³R⁴OR-OR⁵Mono-or polysubstituted, hereinR³Or R⁴Can be hydrogen, and furthermore R³、R⁴Or R⁵Identical or different and is an alkyl radical having from 1 to 12 carbon atoms, by reacting a compound of the general formula (B) with a compound of the general formula (A) in the presence of a transesterification catalyst and in the presence of at least one polymerization inhibitor in a device for continuous reaction,

R₂NH₂ (B)

in the formula, R₂Has the above-mentioned definition, and can be used for making various foods,

in the formula, R₁Is H or CH₃A group, and R³Is a methyl group, and the compound is,

the method is characterized in that: the reactants are fed continuously into a suitable reaction apparatus (1) and the alcohol formed in the reaction is removed continuously in the form of a methanol/methyl (meth) acrylate azeotrope (13) via a distillation column (2) and also:

-the reaction mixture is continuously conducted away from the reaction apparatus into a distillation column (3) or an evaporator (5), in which the volatile components, which are compounds of the general formula (a), compounds of the general formula (B), methanol, and a very low proportion of the product amide (C) are removed via the top by distillation under reduced pressure and returned to the reaction apparatus, and the product amide (C) is removed from the bottom of the column together with the catalyst, polymerization inhibitor and high-boiling by-products;

-feeding the bottom stream (15) originating from the distillation column (3) continuously to the purification distillation process.

2. A method according to claim 1, characterized in that: the vapor stream of the evaporator (5) is continuously fed to a further distillation column in which the high-purity product amide (C) is discharged via the top by distillation under reduced pressure and the catalyst, polymerization inhibitor and high-boiling by-products are removed via the bottom together with a small portion of the product amide (C).

3. A method according to claim 1, characterized in that: the amine (B) is fed to the reaction apparatus for dehydration via a distillation column (2).

4. A method according to claim 1, characterized in that: the molar ratio of methyl (meth) acrylate, i.e. MMA, to amine in the reactor feed is 1-2.

5. The method according to claim 4, characterized in that: the molar ratio of methyl (meth) acrylate, i.e. MMA, to amine in the reactor feed is from 1.05 to 1.15.

6. A method according to claim 1, characterized in that: the transesterification catalyst used was a tetraalkyl titanate.

7. The method according to claim 6, characterized in that: the catalyst is used in amounts of from 0.1 to 10% by weight, based on MMA used.

8. The method of claim 7, wherein: the catalyst is used in amounts of from 0.2 to 7% by weight, based on MMA used.

9. A method according to claim 1, characterized in that: the catalyst mixture employed was a mixture of dioctyltin oxide and isopropyl titanate in a 1: 1 (wt%) ratio.

10. A method according to claim 9, characterized in that: the catalyst mixture is used in amounts of from 0.1 to 10% by weight, based on MMA used.

11. A method according to claim 10, characterized in that: the catalyst mixture is used in amounts of from 0.2 to 7% by weight, based on MMA used.

12. A method according to claim 1, characterized in that: the polymerization inhibitor used is phenothiazine, tert-butylcatechol, hydroquinone monomethyl ether, hydroquinone or mixtures thereof, the amount of polymerization inhibitor being 100-5000ppm, based on the reaction mixture.

13. A method according to claim 1, characterized in that: oxygen is additionally used as a polymerization inhibitor.

14. A method according to claim 1, characterized in that: the amine used is dimethylaminopropylamine.

15. A method according to claim 1, characterized in that: the pressure in the first distillation column (3) is from 20 to 500 mbar.

16. A method according to claim 1, characterized in that: the residence time in the reaction apparatus is from 0.5 to 1.5 hours.

17. A method according to claim 1, characterized in that: the evaporator (5) is a thin film evaporator.