JPS6338977B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing butyl methacrylate by transesterifying methyl methacrylate and butanol in the presence of a transesterification catalyst and a polymerization inhibitor. It is known to use an acidic or basic catalyst when producing butyl methacrylate by a transesterification method, and examples of acidic catalysts include sulfuric acid, p-toluenesulfonic acid, and the like. On the other hand, examples of basic catalysts include various alkali metal alcoholates, lithium hydroxide, barium hydroxide, etc. Examples of alkali metal alcoholates include sodium, potassium, magnesium, calcium,
Metal alcoholates such as aluminum are shown, and titanium alcoholates, thallium alcoholates, and the like are also known. However, according to the findings and experimental results of the present inventors, basic catalysts, especially metal alcoholate catalysts represented by sodium methylate, titanium tetraisopropylate, etc. It has serious drawbacks such as the tendency to produce by-products such as methanol produced in the exchange reaction.Other than this, with the exception of sodium methylate and titanium tetraisopropylate, catalytic activity is low and the reaction is difficult. In addition to being slow, they are generally expensive and have little practical use. On the other hand, although acidic catalysts, especially sulfuric acid, cause some side reactions, the effect is small, and because of their low cost, they are the most commonly used transesterification catalysts. However, the biggest drawback of the sulfuric acid catalyst is its corrosivity, and it is therefore impossible to use other metals other than ultra-expensive metals such as Hastelloy and zirconium, such as the most commonly used SUS stainless steel, as the material for the reactor. Yes, glass-lined equipment is usually used. For this reason, the construction cost of manufacturing equipment is inevitably much higher than when SUS stainless steel is used. Furthermore, the following points can be mentioned as disadvantages of the sulfuric acid catalyst. That is, since the sulfuric acid catalyst does not necessarily have high catalytic activity, a large amount is required to be used. On the other hand, this transesterification reaction is shown by equation (1), and the equilibrium is In order to obtain butyl methacrylate in high yield, the reaction must proceed to the right, and the methanol produced must be distilled off by azeotropic distillation with methyl methacrylate. Furthermore, in order to increase the reaction rate and suppress the polymerization, an excess amount of methyl methacrylate relative to butanol is used, but this is distilled off, and then the crude butyl methacrylate is distilled to obtain purified butyl methacrylate. It is common, and for this reason, the manufacturing format is often batch-wise.
As the reaction progresses and the distillation progresses, the amount of liquid in the reaction tank decreases, the concentration of sulfuric acid increases, and the temperature in the reaction tank increases, making it easier for methacrylic acid ester to polymerize. In order to suppress this polymerization, sodium hydroxide, etc. A method is adopted in which sulfuric acid is removed in the form of a salt by water extraction using an alkaline aqueous solution.
For this reason, it is necessary to perform a separation operation between each of the above-mentioned organic layers and the water dissolved therein, resulting in a disadvantage that the process becomes complicated. The present inventors have conducted extensive studies to solve the above-mentioned problems with conventional basic catalysts and acidic catalysts, and as a result,
The present invention has been completed, and its purpose is to make it possible to use SUS stainless steel as the equipment material for producing butyl methacrylate.
The object of the present invention is to develop a catalyst that has high catalytic activity, causes few side reactions, and is inexpensive. That is, the present invention provides ``In producing butyl methacrylate by transesterifying methyl methacrylate and butanol in the presence of a transesterification catalyst and a polymerization inhibitor, sodium hydroxide and/or A method for producing butyl methacrylate characterized by using potassium hydroxide. In the method of the present invention, the amount of methyl methacrylate used is in the range of 1.2 to 10 moles, preferably 1.5 to 5 moles, per mole of butanol. As a polymerization inhibitor, phenothiazine, hydroquinone, hydroquinone monomethyl ether, etc. can be used, and the amount added is determined based on the reaction solution.
A range of 0.05 to 1 weight is preferred. Next, sodium hydroxide and/or potassium hydroxide is used as a catalyst, but its purity is sufficient to be equivalent to that of an industrial chemical. Among these, in the case of potassium hydroxide, the purity according to JIS standards is about 85%, with most of the remainder being water, but the presence of this amount of water does not affect the reaction in any way. This point is in sharp contrast to the case where the presence of water is not allowed when a metal alcoholate catalyst, which is a typical conventional catalyst, is used. Sodium hydroxide and potassium hydroxide can be used alone, but they can also be used in combination in any proportion. The amount of catalyst used is based on the raw material butanol.
In the range of 0.1 to 20 mol%, more preferably 0.5
~10 mol% range. If it is less than 0.1 mol %, the effect as a catalyst is small, and even if it is used more than 20 mol %, the effect remains unchanged. The catalyst is used by being dissolved in the raw material butanol in advance, but it may also be used by adding it in a solid state to a mixed system of butanol and methyl methacrylate. In the method of the present invention, the transesterification reaction is usually carried out under normal pressure, but in some cases, reaction under reduced pressure is also an effective method, and a range of 200 Torr to 760 Torr is preferred. In the case of a reaction under reduced pressure, the reaction rate decreases somewhat because the temperature of the reaction tank decreases, but
This is a preferred embodiment from the viewpoint of suppressing polymerization. The reaction tank temperature is about 95 to 120℃ in the normal pressure method.
In the reduced pressure method, it decreases somewhat. The reaction format is preferably a super-necessary partial type where the reaction is completed by breaking the equilibrium as shown in equation (1). Here, one aspect of the reaction operation when batch operation is adopted is that a reaction tank with a distillation column is used as the reaction tank, and the temperature at the top of the distillation column is
A range of about 66 to 70°C is preferable. In order to bring the distillate gas from the top of the column close to the azeotropic composition of methanol and methyl methacrylate, and to minimize the distillation of butanol, the temperature at the top of the column is maintained and reflux is carried out at an appropriate ratio. It is necessary to carry out, and the reflux ratio is 2~
A range of about 10 is preferable. As the reaction progresses, the production of methanol decreases, so the temperature at the top of the column increases. By monitoring this temperature, the progress of the reaction can be grasped. Next, the target product is separated and purified, and this step can be performed either batchwise or continuously. First, excess methyl methacrylate is distilled off, but this step suppresses the polymerization of methacrylate ester.
Distillation conditions in the range of 50 to 300 torr are preferred. Methyl methacrylate recovered in this step can be used as a raw material for the next reaction. This step can be carried out without any problems in either a batch or continuous method, but it is usually preferable to distill the azeotropic fraction of methanol and methyl methacrylate in a reaction tank, followed by subsequent distillation. . Next, the butyl methacrylate product is distilled out from the crude butyl methacrylate layer after distilling off the methyl methacrylate. In this step as well, distillation under reduced pressure is essential to suppress polymerization of butyl methacrylate, and vacuum distillation in the range of several torr to 100 torr is preferred. Therefore, this step can be carried out continuously in the reaction tank after the distillation of methyl methacrylate, but as the butyl methacrylate is distilled off, the liquid volume decreases and eventually reaches almost zero. Therefore, the efficiency of the device is extremely reduced. For this reason, it is practical to carry out distillation of butyl methacrylate using a separate small-capacity distillation vessel, and distillation using a thin film evaporator is a particularly preferred embodiment. Therefore, the yield of butyl methacrylate in the above series of operations is approximately 96 to 98 mol% as the reaction rate of butanol (mol of reacted butanol/mol of raw material butanol), and the yield of butyl methacrylate (produced methacrylic acid Butyl mol/raw material butanol mol) is 94-96 mol% and its purity is 99.3-99.7
reach %. The selectivity of butanol to butyl methacrylate (produced butyl methacrylate moles/reacted butanol moles) is approximately 98.0%, and most of the remainder is a polymer and is discarded as a residue after distilling butyl methacrylate, but it is not handled properly. The above characteristics are not so problematic. According to the method of the present invention, SUS stainless steel is used as the material for equipment such as reaction vessels, pumps, and piping.
SUS304 steel, which is cheaper than SUS316, can be fully used and construction costs can be reduced. Furthermore, its catalytic activity is quite satisfactory compared to other catalysts, and there is only a slight decrease in yield due to side reactions, resulting in higher yields and higher purity than other catalysts. Butyl methacrylate can be obtained. Also, in terms of catalyst cost, it is clearly overwhelmingly cheaper than other catalysts. In summary, by employing the method of the present invention, it becomes possible to produce butyl methacrylate at a considerably lower cost than conventional methods. Hereinafter, the present invention will be explained in more detail with reference to Examples. However, this example does not limit the present invention. Example 1 Two flasks equipped with a stirrer and equipped with a glass column having an inner diameter of 50 mm and a length of 55 cm filled with 50 cm of glass tubes having an outer diameter of 5 mm and a length of 5 mm were placed in an oil bath. The outside of the glass column could be heated with a ribbon heater, and a splitter-type reflux distributor was attached to the top of the column. In the above flask, 74.1 g of n-butanol, 400.4 g of methyl methacrylate, and first-class caustic soda as a reagent.
1.2g and 1g of phenothiazine as polymerization inhibitor,
Add 1g of hydroquinone monomethyl ether,
The oil bath temperature was set at 110°C while stirring. Total reflux was carried out until the top temperature fell to 65.5 to 66°C, and after reaching the above temperature, the methanol produced by the reaction was distilled off by azeotropic distillation with methyl methacrylate while appropriately changing the reflux ratio to maintain the temperature. Ta. The reflux ratio during this period is generally in the range of 2 to 6, and the tower top temperature is 70
The reaction was terminated when the temperature and reflux ratio reached 10°C. The reaction time from distillation of the methanol fraction to this point was approximately 4 hours. Next, the inside of the system was set to 100 mmHg (100 Torr) using a vacuum pump.
At a reflux ratio in the range of 0.5 to 1, the top temperature is 45 to 50°C.
Methyl methacrylate was distilled out. This distillate contained 2.0g of unreacted norbutanol. Then, the pressure in the system was set at 5 mmHg (5 torr), and butyl methacrylate was distilled out without reflux. The top temperature during this period was 40-43°C. The liquid volume of this distillate was 136.1 g, and the purity of butyl methacrylate was 99.5%. As a result of analysis, the reaction rate of n-butanol was 96.8%, the yield of butyl methacrylate was 95.2%, and the selectivity from n-butanol to butyl methacrylate was 98.3%. After completing a series of operations, weigh the flask and subtract the polymerization inhibitor and catalyst to find out the amount remaining in the flask.
It was 1.5g. Examples 2 to 3 Comparative Examples 1 to 4 In Example 1, experiments were conducted in exactly the same manner as in Example 1, except that some of the compositions and the like were changed. The results are shown in Table 1.

[Table] As is clear from Table 1, when the catalyst of the present invention is used, the yield of product BMA is higher than in the case of conventional alcoholate catalysts, and the product has the effect of particularly high purity. As a result of various studies on the cause of this, we found that when an alcoholate catalyst is used, a substance represented by the following molecular formula (2) in which CH ₃ OH is added to the double bond of MMA (3) (hereinafter referred to as (A)) but, It was found that 0.5 to 1% of BMA was produced as a by-product, and this was mixed into the product. That is,
When using a metal alcoholate catalyst such as Mg methylate, Na methylate, or Ti isopropylate, it is inevitable that the product (A) will be produced as a by-product, and the boiling point of (A) is between that of butanol and BMA. A part of this is recovered to the MMA/BuOH layer, but the rest is distilled to the n-BMA layer, resulting in a decrease in product purity. Also, regarding (A) distilled into the MMA/BuOH layer,
Since this fraction is used repeatedly, (A) accumulates and reaches an equilibrium concentration, which inevitably lowers the purity of the product. On the other hand, when using the catalyst of the present invention,
Since (A) is not substantially produced, the above problem does not occur. Comparative Example 5 In Example 1, an experiment was conducted in exactly the same manner as in Example 1, except that some of the compositions were changed. The results are shown in Table 2. As is clear from Table 2, LiOH as a catalyst
When using KOH/NaOH, the butanol reaction rate and product are
It can be seen that the results are far inferior in terms of BMA yield, BMA purity, and amount remaining in the pot.

【table】

Claims (1)

[Claims] 1. In producing butyl methacrylate by transesterifying methyl methacrylate and butanol in the presence of a transesterification catalyst and a polymerization inhibitor, sodium hydroxide and A method for producing butyl methacrylate, characterized in that / or potassium hydroxide is used. 2. The method for producing butyl methacrylate according to claim 1, wherein the butanol is normal butanol. 3. The method for producing butyl methacrylate according to claim 1, wherein the butanol is isobutanol. 4 Sodium hydroxide to raw material butanol
The method according to any one of claims 1 to 3, wherein 0.5 to 10 mol% is used. 5 Potassium hydroxide to raw material butanol
The method according to any one of claims 1 to 3, wherein 0.5 to 10 mol% is used.