JPH0632762A - Recovery of carboxylic ester reaction product - Google Patents

Abstract

PURPOSE: To recover a carboxylate ester reaction product through specified processes from a reaction mixture contg. an azeotrope-forming alcohol precursor and further impurities.

CONSTITUTION: The reaction mixture contg. a carboxylate ester reaction product mixed with at least one azeotrope-forming alcohol precursor, e.g. an alkanol and further impurities is drawn and fractionated and the carboxylate ester reaction product is recovered from the reaction system as follows; the reaction mixture is first fractionated into a carboxylate ester product-contg. stream and a 1st azeotrope stream, an additional azeotrope-forming alcohol precursor is sufficiently added to the 1st azeotrope stream so as to provide a total concn. of the alcohol in excess of its azeotropic concn. and the resultant alcohol- enriched stream is fractionated into a 2nd azeotrope stream for recycle to the reaction system and a 1st residue stream for disposal.

COPYRIGHT: (C)1994,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the removal of a reaction mixture containing at least one azeotrope-forming alcohol precursor and a carboxylic acid ester further mixed with impurities and fractionation thereof from the reaction zone. The present invention relates to a method for collecting a reaction product. More specifically, the present invention relates to the recovery of a purified carboxylic acid ester, preferably an alkyl ester of acrylic acid or methacrylic acid, from a reaction effluent in a continuous production process,
The reaction effluent may or may not form an azeotrope with the carboxylic ester and / or the carboxylic ester and / or alcohol mixed with the corresponding alcohol to form an azeotrope with the ester. It contains further impurities.

[0002]

BACKGROUND OF THE INVENTION Various carboxylic acid ester production processes have been carried out using alcohol precursors to the carboxylic acid ester in the reaction zone in excess of the required stoichiometric amount. For example, in an equilibrium reaction, the reaction can thus be run to near completion. Alternatively, the conversion, expressed as product produced per unit catalyst and time in the catalytic reaction, can be increased. Alcohol precursors that are used in excess of the required stoichiometric amount may be discarded if they are cheap, but are preferably added to the reaction zone in the continuous or semi-continuous mode of operation of the process. Be recycled. In any case, it is
It must be separated from the reaction product, for example by fractionation.

For reaction mixtures containing a mixture of carboxylic acid ester reaction product and an excess of alcohol precursor in liquid form under the conditions of temperature and pressure applied, this fractionation is carried out, for example by distillation. It is convenient to take advantage of the different volatility of the components to be separated. This does not cause any problems for azeotropic reaction mixtures where each component has discontinuous volatility. Also, the topping and / or tailing of reaction products and / or recycled alcohol precursors from light-end and / or heavy-end contaminants can be done using standard chemistry techniques.

However, if the carboxylic acid ester reaction product and the alcohol precursor form an azeotrope, the azeotrope will have a volatility higher or, at times, lower than that of the carboxylic acid ester reaction product. Separated by. This azeotrope contains some of the reaction products and is usually recycled into the reaction for economic reasons. In a continuous process, when recycling a portion of the reaction effluent, measures should be taken to avoid the accumulation of contaminants such as those resulting from reactants, side reactions or catalyst residues.
Therefore, a bleed stream containing such contaminants should be removed from the process. Heavy ends having a volatility lower than that of the reaction product or azeotrope and light ends having a higher volatility can be used by conventional methods, by flashing or by bleed flow and / or
Alternatively, it can be separated off at a position suitable as a distillation overhead or bottom, preferably at the position where the maximum concentration of the contaminant occurs. These topping or tailing processes have a volatility between that of the azeotrope and that of the reaction product, or intermediate to form a further azeotrope with the reaction product in this volatility range. It does not remove body contaminants.

US Pat. No. 4,280,0010 discloses a continuous process for the production of alkyl acrylates by reacting acrylic acid with an excess of a lower alcohol, in which a product consisting of an acrylate ester and a precursor alcohol is formed. The organic phase of the product stream is fed to the distillation column,
Fractionation into an azeotrope stream of alcohol and ester from the top of the column recycled to the reactor and a crude ester product stream from the bottom of the column which undergoes purification by distillation until more pure. Heavy ends are removed from the system with the bleed stream from the reactor, while contaminants boiling between the ester / alcohol azeotrope and pure ester are obviously removed in the final purification step.

US Pat. No. 4,250,328 discloses the production of methyl isobutyrate or methacrylate by a direct esterification process, in which an excess of isobutyric acid or methacrylic acid precursor drives the reaction equilibrium in the reaction zone. It has been used to minimize the amount of alcohol in the staggered reaction effluent and attempts have been made to overcome the problems associated with azeotrope formation. However, this method is not applicable to processes that use precursors other than free acids such as transesterification and carbonylation; resulting in the loss of methacrylic acid due to the required bleed flow; and also in the methacrylic acid recycle stream. Can cause problems.

Other processes aimed at separating components of close volatility have been described, for example, in US Pat. No. 407.
No. 0254, US Pat. No. 4,518,462 and EP-A-390577, which produce an azeotrope with the impurities to be removed and thus can be more easily separated from the product to be purified. The exogenous component is added to the mixture.

[0008]

Due to azeotrope formation, known recovery processes commonly have a separated stream containing an excess of alcohol precursor also containing a portion of the carboxylic ester product. In practice, the concentration of the carboxylic ester reaction product in the azeotrope stream will be much higher than the azeotrope concentration. First, in commercially operating distillation columns, the theoretical degree of separation can only be approximated using economically acceptable equipment. Second, since purification of the carboxylic ester product is the main goal of the recovery process, distillation provides the most effective separation for carboxylic esters between the volatility of the ester and that of the azeotrope. Preference is given to operating so that further impurities present in the reaction effluent having a volatility in the range are also achieved. Therefore, if the azeotrope has a volatility higher than that of the pure carboxylate ester, it is desirable to cut the reaction effluent at a volatility just above the volatility of the pure carboxylate ester to obtain lighter impurities. Is substantially free of azeotrope, and fractionation into an azeotrope stream containing a significant amount of all azeotrope-forming alcohol precursor and intermediate impurities and carboxylic acid esters is preferred. In principle, the carboxylic acid ester product of this part is not lost since it is recycled to the reaction zone. However, the presence of intermediate impurities leads to unwanted accumulation in the continuous process. This is done by bleeding a portion of the recycle stream or by applying further fractionation to the bottoms material containing the substantially pure azeotrope recycled and the intermediate impurities discarded.
Should be avoided.

After separation of the substantially pure azeotrope, this bottoms material stream will have some of its carboxylic ester product as its major component, which is due to the content of intermediate impurities. It is discarded in view of this, resulting in a reduction in the overall yield of this carboxylic ester production process. Moreover, some impurities in this bottoms stream, such as water, cause miscibility problems.

The present invention aims to solve these problems by providing a recovery process which avoids the use of valuable reaction products as carriers for intermediate impurities to be bleed from the process. To do.

[0011]

Accordingly, a recovery process as described above is provided, which comprises: a) a reaction mixture, a carboxylic ester product-containing stream, and a first azeotrope stream. B) Addition of sufficient additional azeotrope-forming alcohol precursor to the stream of the first azeotrope obtained in step a) to bring the total alcohol concentration above that azeotrope concentration. Providing; and c) fractionating the alcohol-enriched stream obtained in step b),
A second azeotrope stream for recycling to the reaction zone,
And a step of making the first residue stream for disposal.

[0012]

By the process of the present invention, it is achieved that the first retentate stream containing the intermediate impurities to be removed from the carboxylic ester production process contains an alcohol precursor as its major carrier component. Thus, less expensive amounts of alcohol precursor than the valuable ester product are wasted, resulting in an overall increase in product yield. Furthermore, since alcohols generally have more versatile solvent properties than esters, miscibility problems with the aqueous component of the first residue stream are avoided.

The present recovery method is also very conveniently incorporated into the carboxylic acid ester production process. Step b)
A portion of the additional azeotrope-forming alcohol precursor added in step c) is recycled to the reaction zone due to the relative increase in the amount of azeotrope stream obtained in step c), and the carboxylic acid ester production process Serves as (part of) a supply. This particular amount can be easily compensated by a corresponding decrease in the regular alcohol precursor feed. Furthermore, since the present method does not introduce any foreign component, the purification step is not complicated at all.

The present recovery method can be applied to reaction effluents from various carboxylic ester production processes that use an alcohol that forms an azeotrope with the carboxylic ester product as one of the precursors. Such processes typically involve the direct esterification of a carboxylic acid with an alcohol, transesterification of a carboxylic acid ester with a different alcohol, and the presence of an alcohol of an ethylenically and / or acetylenically unsaturated compound. Carbonylation of

Preferably, such a process is carried out with a stoichiometric excess of alcohol precursor in the reaction zone, eg to shift the equilibrium or increase the efficiency of the catalyst. However, also when using an equivalent amount of alcohol precursor feed, the reaction effluent may contain residual alcohol precursor due to incomplete reaction, in which case the present recovery method can be applied. The latter mode of operation is not preferred because such effluents also contain corresponding unreacted amounts of other precursors which complicate the purification process.

Typical examples of carboxylic acid ester and corresponding alcohol pairs are methanol / methyl acetate, methanol / methyl isobutyrate, methanol /
Methyl acrylate, methanol / methyl methacrylate, n-butanol / n-butyl formate and n-
Pentanol / n-pentyl formate are mentioned, both of which form a binary azeotrope. This recovery method also
Where the carboxylic acid ester and the corresponding alcohol form a ternary or higher azeotrope with further components present in the reaction effluent, for example water / methanol / methylchloroacetate, water / ethanol It is also applicable to / ethyl acetate, water / n-propanol / n-propyl acetate and water / isoamyl alcohol / isoamyl acetate.

Extensive literature data is available on reliable empirical formulas for azeotropic compositions and correction factors for specific physical conditions. On this basis, the additional minimum amount of azeotrope-forming alcohol precursor required to achieve a total concentration of alcohol that exceeds its azeotropic concentration can be readily calculated. Larger amounts may be added and may contribute to a higher degree of purification. The upper limit is essentially determined by economic considerations.

The fact that the reaction products to be recovered by the process of the present invention are esters of unsaturated carboxylic acids means that such products impose stringent standards on their impurities in a wide range of polymerization processes. It is preferable because it has the use of Typical unsaturated carboxylic acid is 3
May have from 6 to 6 carbon atoms.

The azeotrope-forming alcohol precursor in the process of the present invention is preferably an alkanol, which typically has from 1 to 6, more typically from 1 to 4 carbon atoms. Thus, the corresponding reaction product is an alkyl ester of unsaturated carboxylic acid.

The most preferred reaction products consist of the class of C ₁ -C ₄ alkyl acrylates and methacrylates, in which case the azeotrope-forming alcohol precursor is the corresponding C ₁ -C ₄ alkanol. Examples of the most preferred reaction products are methyl acrylate, ethyl acrylate, n-butyl acrylate, methyl methacrylate and n-butyl methacrylate.

The most preferred reaction products such as methylmethacrylate are the cationic palladium / methoxides by direct esterification of methacrylic acid with methanol, for example in the presence of an acid catalyst, or with propyne with carbon monoxide and ethanol. It has been made by reaction in the presence of a phosphine catalyst. As mentioned above, the alcohol was usually in stoichiometric excess with respect to methacrylic acid or propyne, respectively, in the reaction zone.
Whether all methacrylic acid or propyne is converted, the reaction effluent will then contain residual alcohol in addition to the methylmethacrylate product.

According to the present invention, the reaction mixture from which the carboxylic acid ester reaction product is to be recovered may contain, in addition to intermediate impurities, high and / or low boiling point endo, which is the reaction product or the azeotrope, respectively. Impurities with lower or higher volatility than the mixture, or if the azeotrope is a negative azeotrope, have the opposite volatility. In order to obtain a pure product, it is desirable to remove such impurities.

Therefore, according to a preferred embodiment of the present invention, the process further comprises the step of separating the stream containing the reaction product and the heavy end having a volatility lower than that of the azeotrope. This heavy-end tailing can be done using conventional chemical techniques such as distillation. This heavy end may be disposed of in a reliable manner. The heavy ends often contain catalysts or catalyst residues, in which case recycling of the catalyst or its components, which may be after regeneration, may be considered for economic reasons. The heavy-end tailing step may occur prior to or after separation of the azeotrope stream.

According to another preferred embodiment of the process of the present invention, the process further comprises the step of separating a stream containing an azeotrope and a light end having a volatility higher than that of the reaction product. This light end topping can be done using conventional chemical techniques such as distillation or flushing. In the sorting according to the present invention,
Several streams are differentiated and separated by their different volatility. This fractionation can be done by applying a temperature gradient under isobaric conditions. It can also be done by multi-stage pressure release under isothermal or quasi-isothermal conditions. This fractionation is preferably performed by distillation.

[0025]

EXAMPLES Taken as an example for illustrative purposes, methanol (M) for the production of methyl methacrylate (MMA).
The reaction effluent of the carbonylation of propyne in the presence of (eOH) contains, in addition to water and minor impurities such as acetone, 5
It may contain 2 mol% MMA and 46 mol% MeOH. When the MMA product is to be recovered according to the present invention,
The reaction effluent was tray no. 1 with 6 feed inlets
In a first distillation column with 6 trays, a pressure of 0.5 bar (absolute), 80 ° C. at the bottom and 43 at the top, respectively.
It can be fractionated at a temperature of ° C. This results in a stream cut at a temperature slightly below the boiling point of pure MMA, with a heavy end-containing MMA product stream from the bottom of the column, at the top.
In addition to trace amounts of impurities that are more volatile than MMA, 9.34
This results in a first azeotrope stream comprising mol% MMA, 90.45 mol% MeOH and 0.21 mol% water. If desired, impurities with boiling points below the boiling point of the azeotrope may be removed from the process at this point, for example by flashing or distillation. The azeotrope composition under the applied conditions is 4 mol% MMA and 96
Mol% MeOH.

A second column of trace impurities, such as acetone, boiling in the range between the azeotrope and pure MMA (10 trays: feed inlet: tray No. 6, p =
0.5 bar (absolute), T _bot = 59 ° C, T _top = 45
Direct tailing of the azeotrope stream for distillative removal from C. C.) (without applying the teachings of the invention) is substantially free of intermediate impurities at 7.59 mol% MM.
A, 92.37 mol% MeOH and 0.04 mol%
57.5 in addition to the recycle overhead product containing water and intermediate impurities removed from the process at this point.
This gives a waste bottoms product containing 9 mol% MMA, 37.11 mol% MeOH and 5.30 mol% water.

According to the invention, additional MeOH is added to the stream of the first azeotrope in order to raise its molar concentration to 94.60 mol%, whereby, in addition to trace impurities, An alcohol-enriched first azeotrope stream is obtained having a composition of 5.28 mol% MMA, 94.60 mol% MeOH and 0.12 mol% water. Second tower of this stream (10 trays, feed inlet: tray N
o. 6, p = 0.5 bar (absolute), T _bot = 55 ° C.,
(T _top = 45 ° C.), practically no intermediate impurities, 5.33 mol% MMA, 94.66 mol% M
3.26 mol% in addition to the recycle overhead product containing OH and 0.01 mol% water, and intermediate impurities
MMA, 91.72 mol% MeOH and 5.00
A waste bottom product containing mol% water is obtained.

In the present invention, M is discarded from the bottom of the second tower.
It can be seen that this results in a significant reduction in the proportion of MA. Furthermore,
The high proportion of methanol in the bottoms stream obtained according to the invention eliminates miscibility problems with the amount of water present. The first azeotrope stream was added to MMA 380.5
The following table lists the molar composition data, expressed as a flow for the process occurring at a rate of 0 kg / hr.

[0029]

The present invention Other than the invention The first azeotropic mixture MMA 380.5 kg / hr 380.5 kg / hr MeOH 1179.9 kg / hr 1179.9 kg / hr water 1.6 kg / hr 1.6 kg / hr MeOH (addition ) 1000 kg / hr recycle stream MMA 375.2 kg / hr 298.7 kg / hr MeOH 2132.1 kg / hr 1163.0 kg / hr water 0.1 kg / hr 0.2 kg / hr waste stream MMA 5.3 kg / hr 81. 8 kg / hr MeOH 47.8 kg / hr 16.9 kg / hr Water 1.5 Kg / hr 1.4 Kg / hr

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Douwe Kristian van der Beek Holland 2596 H.A.R., The Hague, Karel van Bilantran 30 (72) Inventor Peter Bastien De・ Blank Country 2596 H.A.R., The Hague, Karel Juan Villantran 30 (72) Inventor Kishjor Giararia The Netherlands 4791 A.R.S., Krundelt, Vesterike Landvueg 1

Claims (7)

[Claims] 1. A method for recovering a carboxylic acid ester reaction product from a reaction zone by taking out and fractionating a reaction mixture containing an azeotrope-forming alcohol precursor and a carboxylic acid ester further mixed with impurities. ,
A method comprising the steps of: a) fractionating the reaction mixture into a carboxylic ester product-containing stream and a first azeotrope stream; b) the first azeotrope obtained in step a). To the stream of the azeotrope with sufficient additional azeotrope-forming alcohol precursor to add,
Providing a total alcohol concentration above its azeotrope concentration; and c) the alcohol-enriched stream obtained in step b) to a second azeotrope stream for recycling to the reaction zone and for disposal. The step of separating into the first residual flow of. 2. The method of claim 1 further comprising the step of separating a stream containing the reaction product and a heavy end having a volatility less than that of the azeotrope. 3. A process according to claim 1 or 2 further comprising the step of separating a stream comprising a light end having a volatility higher than that of the azeotrope and the reaction product. 4. The method according to claim 1, wherein the reaction product is an ester of an unsaturated carboxylic acid. 5. The azeotrope-forming alcohol precursor comprises:
The method according to claim 4, which is an alkanol. 6. The method of claim 5 wherein the reaction product is an alkyl acrylate or methacrylate and the azeotrope-forming alcohol precursor is the corresponding alkanol. 7. The method according to claim 1, wherein the fractionation is performed by distillation.
The method described in any one of.