CS259978B1 - Method of acrylic and metacrylic acid's higher esters preparation - Google Patents

Abstract

Process for preparing higher acid esters acrylic and methacrylic using reoyolating the raw materials by interacting methyl acrylate, respectively. ethyl acrylate S1 of methyl methacrylate resp. ethyl methacrylate and alcohols having at least the acrylic chain two carbon atoms in the presence of a catalyst based on magnesium alcoholate, an inhibitor polymerization, at elevated temperature and current distilling off the releasing methanol, respectively. ethanol so that reactants react blends, i.e., alcohol and a recycled starting ester and solvent, is dried before the reaction (optionally outside reaction equipment) for water below 0.3 wt. after mixing the components in the reaction the device is azeotropically dried mixtures to a water content of less than 0.05% by weight, and immediately before the reaction began adds solid disperse in addition to the catalyst substance with abrasive and sorption effects, for example, activated carbon, soot, diatomaceous earth, clay and its modified forms.

Description

The invention relates to a process for the preparation of acrylic and methacrylic esters by re-esterification of methyl or ethyl acrylate in the presence of a magnesium alcoholate catalyst and by using recycled raw materials, which allows higher yields and a continuous operation of the production equipment.

. The preparation of higher acrylic and methacrylic esters by esterification of methyl or ethyl acrylate or methacrylate with the corresponding higher alcohols in the presence of a magnesium alcoholate catalyst has been described, for example, by Bondarjuk et al (GB Pat. 1 174 148), in Japan. No. 11,084 / 1973, Deguaseïde Patent 1,568,476) and longer by Berlin et al (Plaste Kat., 18, 1,12, 1971).

The advantage of this catalyst is that it can be easily separated from the reaction mixture by precipitation with carbon dioxide and filtration or extraction with mineral acids, so that, in most cases, the purification of the prepared higher ester by distillation, which is associated with a loss of yield, is largely eliminated. With this catalyst approximately the same reaction rates are achieved as when using titanium alcoholate or alkali metal alcoholates. At the same time, formation of by-products and polymerization reaction products is significantly reduced.

However, reesterification only takes place at high speed using fresh, non-recycled raw materials. If regenerated raw materials are used in the re-esterification, which is common in industrial production, but also in the case of large-scale re-esterification in at least several tens of liters, and in a metal plant, the reaction rate decreases significantly in successive operations and later even to stop re-esterification at a low degree of conversion. In most cases, the re-esterification may initially be continued after the addition of the next catalyst charge. These difficulties are greater when preparing lower molecular weight esters such as butyl methacrylate. After a few operations, a secondary phenomenon then occurs, which is passed through. No. 259978 slows down and later stops the distillation through the intensive heating medium supply to the heat exchanger.

It has been found that the cause of this phenomenon is the deposition of catalyst decomposition products on the internal surfaces of the reaction apparatus, including heat exchange surfaces. These products have the character of a gel which adheres firmly to the walls of the apparatus and, even with a low content of active substance which can be determined by gel drying, can greatly slow the flow of liquid in a wide environment and thereby substantially and unexpectedly reduce heat transfer in the apparatus. The sediment layer is naturally thicker at the locations where flow is slowed. However, it has been found that the decomposition of the catalyst decomposition products also occurs on the inner vertical surfaces of the tube heat exchanger, around which the reaction mixture flows at a high velocity exceeding 1 m / s at a Re value of the order of 4.10 ⁵ .

In such a case, it is necessary to drain the reaction mixture, flushing the apparatus with a clean solvent to remove esters and alcohols that would contaminate the waste water and to fill it with a dilute aqueous acid solution. After the deposits have dissolved, the device is rinsed with water, filled with solvent, dried by azeotropic distillation and the ester preparation is continued.

The disadvantages of this process are obvious: high consumption of solvent for rinsing and drying the equipment; the need for its regeneration and the resulting increased costs for equipment and energy; the production of large quantities of waste water containing sulfuric acid and its salts; the production of a certain amount of dissolved organic substances, of which, in particular, unsaturated esters make waste disposal difficult. In addition, it has been found that the azeotropic drying of the apparatus after purification using hydrocarbon solvents (e.g. cyclohexane), which are commonly diluted in reaction mixtures to prepare unsaturated esters, makes it difficult to achieve complete removal of water from the apparatus, particularly from pipe joints; filling of columns. This creates the prerequisites for accelerated decomposition of the catalyst in further re-esterification operations and shortens the diofl time of the apparatus between its cleaning.

It can be estimated that, for example, in the preparation of butyl methacrylate, it is possible to perform 5 to 10 operations before the distillation is stopped and the equipment needs to be cleaned. In the preparation of cetostearyl methacrylate le thus possible one after the other. 10 to 20 operations.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a process for preparing higher acrylic and methacrylic esters which avoids a decrease in the activity of magnesium alcoholate used as catalysts and serious heat exchange disturbances in the distillation removal of lower boiling alcohol. recycled raw materials and thus enable higher yields and a smooth running of the production equipment.

The principle of the invention is that the reaction mixture components, the starting alcohol, fresh and recycled acrylic or methacrylic acid methyl or ethyl ester and the solvent are dried outside the reaction apparatus to a water content of less than 0.3% by weight, after mixing the components in the reaction mixture. azeotropically drying the mixture for at least 20 minutes and into a mixture containing less than 0.05 wt. of water, a solid dispersant having an abrasive and sorptive effect is added in addition to the catalyst immediately before starting the reaction.

The cause of the decrease in catalyst activity during re-esterification is, as has been shown experimentally, the moisture present in the starting materials. Water hydrolyzes magnesium alcoholate to magnesium hydroxide (CH ₃ 0) ₂ Mg + 2 H ₂ O -> 2 0H ₃ 0H + Mg (OH) _g which can further react with methyl methacrylate to magnesium mstacrylene

Mg (0H) ₂ + 2 CH ₂ C (CH ₃ ) C00CH ₃ -9> (CH ₂ C (CH ₃ ) C00) _and Mg + 2 CH-jOH

In this way, the active catalyst is converted into inactive exhaust gases. Some sources do not consider the possibility of deactivating the catalyst in this manner (GB Pat. 1 174 148), according to others, the reaction mixture is only dried by azeotropic distillation (DAS 1 568 376) before the catalyst is added. Unrecycled feedstocks, acrylic and methacrylic esters and alcohols usually contain less than 0.2% (mostly less than 0.1) wt. water, hydrocarbons such as cyclohexane (used as co-solvents), even less water. Under these conditions, it is usually sufficient to maintain high catalyst activity and achieve near quantitative conversion by azeotropically drying the reaction mixture in the reaction apparatus prior to the reaction. In the industrial production of higher unsaturated esters, however, the excess of the lower ester, solvent and possibly alcohol (butanol) is recovered and are used in a batch of other manufacturing operations. A progressive method of regenerating and separating said volatile reactants from the ester to be distilled with steam (e.g. DAS) No. 2 317 226, Jap. 73-21929, 73-37011, 73-42044) to reduce thermal exposure of the product. In this case, the recovered raw materials contain emulsified water in addition to the dissolved water and the total water concentration in the batch during re-esterification usually exceeds

0.2% wt.

It has now surprisingly been found that at this and higher initial water concentration in the batch. the azeotropic removal of water in the reaction apparatus is insufficiently effective in achieving the required catalyst activity. The reaction mixtures were dried according to objective analytical analyzes, however, the conversions achieved were low, at a level of 75 to 90%, with a drying time of up to 1 hour. Longer drying times did not significantly affect the conversions achieved. The conversion was raised to 90-97% using a two to three times greater amount of catalyst (0.1 to 0.15 wt% Mg based on the reaction mixture). These conversions have also been satisfactory, since in the production of higher acrylates, respectively. methacrylates, unreacted alcohol cannot be separated from the product by technically acceptable means (high and near boiling components, ease of polymerization of unsaturated esters), and required. therefore, the conversion is greater than 98%. In addition, an increased amount of catalyst is undesirable as the catalyst decomposition reactions occur to a greater extent, the heat exchanger or heat exchange surfaces become clogged more quickly and it is necessary to shut down and clean the reaction equipment more frequently.

The deactivation of the catalyst by the water present in the recycle of the recovered raw materials was modeled to the same effect by adding water to the batch prepared from fresh raw materials containing initially less than 0.2 wt%. water. Conversely, re-esterification on a 200 L model was carried out using fresh raw materials not recycled at the same rate as in the laboratory. The described phenomenon is likely to be explained by the fact that water at higher concentrations is offset from the α »organic phase and can be deposited during drying in droplets on some parts of the apparatus. Upon subsequent esterification they dissolve with methanol or ethanol, flush into the reaction mixture and to decompose the catalyst.

The above disadvantages are overcome by the process of preparing the acrylic and methacrylic esters of the invention using recycled raw materials by the interaction of methyl or ethyl acrylate or methacrylate and higher alcohols having at least two carbon atoms in the alkyl chain in the presence of a magnesium alcoholate catalyst, polymerization inhibitor temperature and concomitant distillation of the liberated lower alcohol, characterized in that the components of the reaction mixture, higher alcohol, fresh and recycled lower ester and solvent are dried outside the reaction equipment to a water content of less than 0.3% by weight after mixing the components azeotropic drying is carried out in the reaction apparatus and into a mixture containing less than 0.05 wt. In the case of water, immediately before the start of the reaction, a solid dispersant is added in addition to the catalyst, with abrasive and absorption properties, preferably activated carbon, carbon black, diatomaceous earth, clays and their modified forms. Advantageously, only those reactants whose moisture content exceeds 0.3% by weight, preferably recycled raw materials, are subjected to drying outside the reaction apparatus. The azeotropic drying of the mixture in the reaction apparatus is preferably carried out only if the moisture content of the mixture exceeds 0.05% by weight.

Components of the reaction mixture whose moisture content exceeds 0.3% by weight are pre-dried either individually or together outside the reaction equipment itself.

This measure aims to prevent undetermined settling of water droplets in the reaction apparatus. Pre-drying applies primarily to recycled raw materials. The pre-drying may be carried out batchwise or continuously by rectification, preferably so that the dried feedstock is removed from the rectification column in vapors and does not entrain the separated water droplets. For example, it is not recommended that, in continuous drying, the raw material be taken as a liquid from the digester _f but as a vapor which is subsequently condensed.

Drying may also be considered to be the separation of water as a heterogeneous phase by sedimentation or centrifugation until a clear organic phase is obtained if the water solubility is less than 0.3% by weight. However, the components of the reaction mixture may be dried by treating anhydrous salts forming crystalline hydrates, solid hydroxides, or by treatment with sorbents such as silica gel or molecular sieves. However, these methods are more expensive.

'259978 ** £) · »

As already mentioned, the deactivation and decomposition of the catalyst are closely related to the deposition of decomposition products on the internal surfaces of the reaction apparatus and to the slowing down of the distillation during re-esterification. The higher initial water content of the batch and the difficulty of catalyst activity will subsequently result in a decrease in heat transfer efficiency, the need to increase the heating steam pressure, and finally in virtually complete stopping of the distillation. For example, in the preparation of butyl methacrylate and an initial water content of the batch of 0.5 to 0.7 wt%; after the second operation, the heat transfer coefficient was reduced by a factor of three.

By pre-drying recycled feedstocks outside the reaction equipment, it is possible to prevent the deactivation of the catalyst rapidly, its extensive decomposition and the rapid decrease in heat exchange in the equipment, but these phenomena cannot be completely excluded. On the one hand, if the water content in the batch is too low, less than 0.01% of the slurry, the rate of re-esterification is surprisingly slowed down, the viscosity of the mixture greatly increases and the reaction stops at a low degree of conversion. and this is the cause of the partial decomposition of the catalyst in the individual operations and the gradual deposition of decomposition products on the walls of the apparatus. In addition, moisture and carbon dioxide, which are contained in the air introduced into the reaction apparatus as a means of inhibiting polymerization, and also in the air that enters the apparatus during emptying, contribute to the decomposition of the catalyst. However, the drying of the air and the adsorption of carbon dioxide can substantially reduce the decomposition of the catalyst for these reasons.

Thus, by pre-drying recycled raw materials, the time between cleaning of the equipment can be substantially, more than 10-fold. Furthermore, it has been found that if a dispersive substance such as activated carbon, carbon black, diatomaceous earth, clays and treated forms is added to the dried reaction mixture prior to re-esterification prior to catalyst addition, the heat exchange surfaces of the re-esterification apparatus can be kept clean, These fumes are trapped by the added dispersant and kept in the reaction mixture soaring. The dispersant should not contain moisture, acidic or acidic substances which could reduce the activity of the catalyst.

For example, activated carbon and diatomaceous earth have been used with good results; carbon black, activated clays and their modified forms are also suitable.

The main advantage of the process according to the invention is up to 20% increased productivity of the re-esterification equipment, aS by 25% reduced investment costs for equipment and up to 30% reduced energy costs associated with cleaning the reaction equipment, reactant recovery and waste disposal. Another advantage is an increase in ester yields of up to 7%, which would otherwise be lost when the equipment is frequently cleaned »

The invention is further illustrated by the following examples, but its scope is not limited or exhaustive.

Example 1

For re-esterification, a reaction apparatus consisting of a 160 L stainless steel vessel connected to a circulation loop and a pump and an external tubular exchanger (8 tubes of 20 mm diameter and 2,000 mm length) was used. A column having a diameter of 200 mm and a height of 2000 mm was attached to the vessel _; filled with Raschig rings of 15 mm diameter. The column was followed by a condenser, a device for adjusting the reflux and distillate ratio, and a template for collecting the distillate.

27.2 kg of butanol (water content 0.05% w / w), 47 kg of methyl methacrylate (water content 0.1% w / w), 42.1 kg of cyclohexane (water content 0.01% w / w) were introduced into the rooster, and 100 g of di-tert-butyl-p-methylphenol, which was used as a polymerization inhibitor. The mixture was heated with the steam supplied to. to the boil. At a steam overpressure of 0.07 MPa, a column pressure drop of 1.5 kPa and a deatilate reflux ratio of 10: 1, the mixture was azeotropically dried for 30 minutes. After cooling to 70 ° C, the catalyst prepared by dissolution was added to the mixture

60.5 of magnesium metal in 2.6 L of methanol. The mixture was brought back to boiling and, at a reflux ratio of 10: 1, the methanol formed in the binary azeotropic mixture with cyclohexane was distilled off from the mixture. the rate of circulation of the reaction mixture in the tubes of the exchanger corresponded to the dimensionless dimension Re ~ 36,000. During the drying and reaction, air was introduced into the mixture at a rate of 40 l / h. The reaction was terminated after 3 h 45 min when the vapor temperature at the top of the column rose to

77.5 ^° C. Three resterification operations were performed as described above. The heating steam overpressure necessary to maintain an optimal 2 kPa rectification column load was 0.125 MPa in the last operation. After flushing the reactor with cyclohexane and disassembling the faces ~ 8 · * •

A whitish coating with a thickness not exceeding 0.1 mm was detected on the inner surface of the exchanger tubes.

Example 2

In the apparatus described in Example 1, methyl methacrylate was re-esterified with butanol using cyclohexane recycle containing 148 wt%, butyl methacrylate, 15 wt% butanol, 0.8 wt% butanol. water and 17.8 wt% methyl methacrylate. The recycle was obtained by stripping cyclohexane and methyl methacrylate from the reaction mixture after the reaction with steam and separating the aqueous phase of the distillate. 9.5 kg of butanol, 13.5 kg of methyl methacrylate, 2.3 kg of pure cyclohexane and 17.5 kg of recycled cyclohexane were introduced into the reactor. After the reaction mixture was dried by azeotropic rectification and after the addition of the catalyst, methanol liberating by reaction was distilled off as in Example 1. In this way, five operations were performed in succession. In the fourth operation, the methanol distillation was stopped, i.e. the reaction was stopped, but the distillation rate was not reduced, even after 60% butanol conversion had been achieved. After addition of another catalyst charge, the re-esterification was complete. Vprvé third operation during the fifth rising steam pressure required for maintaining the optimum and constant speed distillation until 0.28 MPa _0. Further steam pressure has been increased to avoid overheating of the mixture. Due to the rapidly decreasing level of heat transfer through fouling of the heat exchanger tubes, the amount has decreased. of distillate until the distillation practically stopped when 70% conversion was reached. The reaction mixture was cooled and discharged into a reservoir. Pure cyclohexane was charged into the reactor, which was heated and kept under reflux for 1 hour. By boiling the apparatus with solvent, the heat transfer was improved to such an extent that the reaction mixture could be recharged into the reactor and the esterification was complete after the addition of a new catalyst charge. Two further re-esterification operations were performed at a steam overpressure of 0.2 to 0.28 MPa _{. The} clogged exchanger tubes were then cleaned as follows:

Flushing the reactor with cyclohexyne at the boiling point for 0.5 hour; removing the heat exchanger lids and treatment with 0.5% sulfuric acid ^{0 0} P ° for 2 hours; by rinsing the pipes with water and · drying with air and refitting the lids. After disassembling the lids, a white, adhering pellet-shaped deposit of 0.5 to 1 mm thickness was detected on the inner surface of the tubes. These deposits were virtually completely dissolved by the action of acid. However, the other reactor spaces, in particular the vessel in which the deposit layer was considerably larger, were not cleaned by said procedure.

Example 3

In the apparatus described in Example 1, methyl methacrylate butanol was re-etherified using the recycled solvent as described in Example 2, with the recycled solvent being dried azeotropically in an enamel boiler with a 100 mm diameter and 2000 mm height glass column attached before use. to the distillate 10 1 l until the vapor temperature on the head stabilizes. The dried recycle was clear and contained less than 0.05% water. In addition, 0.2 wt% carboraffin (activated carbon) based on the initial weight of the batch was added to the reaction mixture.

Under these conditions, 10 re-esterification operations were carried out without stopping the low-conversion re-esterification and without decreasing the distillation rate at a heating steam overpressure of 0-105 to 1.115 MPa and a column pressure drop of 2 kPa. After removing the heat exchanger faces, the inner surface of the tubes was found without any deposits *

Claims (3)

The process for preparing higher acrylic and methacrylic esters using recycled raw materials by the interaction of methyl acrylate and methacrylic acid, respectively. ethyl acrylate or methyl methacrylate, respectively. ethyl methacrylate and alcohols having at least two carbon atoms in the alkyl chain, in the presence of a magnesium alcoholate catalyst, a polymerization inhibitor, at elevated temperature, while at the same time distilling off the liberated methanol and the carbon monoxide, respectively. ethanol, characterized in that the components of the reaction mixture, the starting alcohol, the fresh and recycled starting ester and the solvent are optionally dried outside the reaction apparatus to a water content of less than 0.3% by weight, optionally after mixing the components in the reaction apparatus azeotropic drying of the mixture to a water content of less than 0.05 wt. and immediately prior to the start of the reaction, a solid dispersant is added in addition to the catalyst, with abrasive and greasy effects, preferably activated carbon, carbon black, quartz, clays and their modified forms. 2. Process according to claim 1, characterized in that only those reactants whose moisture content is higher than 0.3% by weight, preferably recycled feedstock, are preferably subjected to drying outside the reaction apparatus. 3. Process according to claim 3, characterized in that the azeotropic drying in the reaction apparatus is preferably carried out only if the moisture content of the mixture exceeds 0.05% by weight.