JP6458922B2 - Method for producing butyl acrylate - Google Patents

Description

  The present invention relates to a method for producing butyl acrylate.

  The most common production method of commercial butyl acrylate is a production method by an esterification reaction using acrylic acid and butanol as raw materials. Most of them are liquid phase reactions, and organic acids and inorganic acids different from acrylic acid or ion exchange resins are used as homogeneous or heterogeneous catalysts.

  When the produced butyl acrylate is present in the presence of the catalyst and water, a reverse reaction that returns to the raw acrylic acid and butanol also occurs, so that the esterification reaction proceeds efficiently while distilling off the water produced by the esterification reaction. Reactive distillation, which performs an esterification reaction, is most commonly used.

  As a method of reactive distillation, a batch system is used in which the raw materials and auxiliaries are supplied to the reactor, the reaction and the contents of the reactor are taken out while removing by-products by distillation (Non-patent Document 1). And a continuous type in which all these operations are continuously performed (Patent Document 1).

  Compared to continuous reactive distillation, batch reactive distillation has the advantage that fewer equipment is required and capital investment can be kept low. However, compared to the continuous type in which the operating conditions such as temperature, pressure, composition, and flow rate are substantially constant, the batch type in which these change with time becomes complicated in operation management and more often for the recovery of raw materials. Intermediate tanks are required, the raw material recovery rate is low, and the like.

  In general, the larger the production scale, the more the continuous process tends to be selected due to its economic advantage. Also in the production of butyl acrylate, the scale of individual production facilities tends to increase with the expansion of the market scale, and the proportion of continuous reactive distillation increases.

  High reaction conversion is not essential for continuous reactive distillation of common compounds. This is because the unreacted raw material contained in the contents of the most downstream reactor is continuously separated and recovered in the downstream separation step, and the recovered unreacted raw material is circulated in the reactive distillation.

  However, in the case of butyl acrylate production, the boiling point of the raw acrylic acid is in the vicinity of the boiling point of the product butyl acrylate, and its distillation separation is difficult. It is extracted and separated by alkaline water (Patent Document 2). Reusing the separated acrylic acid as a raw material is almost economically disadvantageous and is usually discarded.

  As mentioned above, from the viewpoint of suppressing the loss of acrylic acid, it is desired that the reaction conversion rate of acrylic acid in the production of butyl acrylate is as high as possible. On the other hand, acrylic acid and butyl acrylate are easily polymerizable compounds, and the higher the operating temperature such as the reaction temperature, and the longer the operating time such as the reaction time, the higher the risk of blockage due to polymerization, etc. Reaction conditions must be avoided.

As measures for reducing the polymerization risk, it is common to lower the temperature by reducing the pressure and to add a polymerization inhibitor (Patent Document 2). In order to shorten the operation time, the reactor is made into multistage in series, and an appropriate amount of an appropriate catalyst is added (Patent Document 1). Moreover, in order to increase the reaction conversion rate of acrylic acid more efficiently, an excessive amount of butanol relative to acrylic acid is supplied to the reactor (Patent Document 3).

  In addition to the polymerization of acrylic acid and butyl acrylate, several side reactions proceed in parallel with the esterification reaction. The main by-product is butyl 3-butoxypropionate, which is produced by adding butanol to butyl acrylate.

  The production rate of butyl acrylate is proportional to (acrylic acid concentration) × (butanol concentration). That is, although the production rate of butyl acrylate decreases as the reaction conversion rate of acrylic acid increases, the production rate of butyl 3-butoxypropionate is proportional to (butyl acrylate concentration) × (butanol concentration). The reaction conversion rate of acrylic acid increases, and it increases as the butyl acrylate concentration increases.

  In other words, when the reaction conversion rate is increased for the purpose of reducing the loss of acrylic acid, a dilemma occurs in which the loss of acrylic acid and butanol due to the formation of 3-butoxypropionic acid increases.

  By-produced butyl 3-butoxypropionate is known to be recoverable by thermal decomposition as acrylic acid, butanol and butyl acrylate, but not all can be recovered. The smaller the amount, the better.

  In the prior art, in a method of continuously producing butyl acrylate by reactive distillation having a plurality of reactors in series using acrylic acid and butanol as raw materials, the temperature in each reactor is controlled by controlling the temperature of each reactor. Although the acrylic acid concentration and the 3-butoxypropionic acid amount were controlled, the acrylic acid concentration and the 3-butoxypropionic acid amount were varied even when the temperature control was kept constant.

Special Table 2002-507194 JP 2008-266159 A Japanese Examined Patent Publication No.59-12102

Ulmann's Enclopedia of Industrial Chimistry, 5th edition, A1 volume, P168

  The present invention has been made to solve the above problems. That is, in order to perform a more efficient esterification reaction in series multistage reactive distillation with acrylic acid and butanol, the production amount of butyl 3-butoxypropionate is suppressed and the reaction conversion rate of acrylic acid is increased. It is an object of the present invention to provide a method for continuously producing butyl acrylate.

  As a result of intensive studies to solve the above problems, the present inventor has shown that 3-butoxypropion can maintain a constant amount of heat supplied to at least the most downstream reactor when the reaction conversion rate of acrylic acid is high. The present inventors have found that it is effective for improving the reaction conversion rate of acrylic acid without increasing butyl acid acid, and have completed the present invention.

That is, the present invention
From the reaction step of reacting acrylic acid and butanol using a multistage reactor in series to form a reaction mixture containing butyl acrylate, and the reaction mixture containing butyl acrylate generated in the reaction step, the butyl acrylate And a distillation step of separating by distillation using a distillation column,
In the reaction step, the amount of heat of a heat source supplied to at least the most downstream reactor among the multistage reactors in series is made substantially constant.

  Preferably, the heat source is steam, and the amount of heat is a steam amount determined based on the acrylic acid concentration in the outlet liquid of the most downstream reactor, and the heat source may be an organic solution or an inorganic solution. preferable. Further, the series multistage reactor preferably has 3 to 8 stages, and the temperature of each of the series multistage reactors is preferably 80 to 110 ° C. In the series multistage reactor, It is preferable that the temperature of the reactor is higher as the reactor, the top pressure of the distillation column is preferably 10 to 40 kPa, the distillation column is preferably one stage or multistage, and the distillation column is In the case of multiple stages, the column top pressure is preferably lower in the downstream distillation column.

  According to the present invention, in order to perform a more efficient esterification reaction in series multistage reactive distillation with acrylic acid and butanol, the amount of butyl 3-butoxypropionate is suppressed, and the reaction of acrylic acid A continuous production method of butyl acrylate that increases the conversion rate can be provided.

It is a figure which shows an example of an esterification reaction distillation apparatus. It is a figure which shows an example of the reaction liquid composition in each reactor in an esterification reaction distillation apparatus. It is a figure which shows an example of the relationship between the acrylic acid density | concentration and water density | concentration in the most downstream reactor in an esterification reaction distillation apparatus. It is a figure which shows an example of the relationship between the butyl 3-butoxypropionate density | concentration and acrylic acid density | concentration in the most downstream reactor in an esterification reaction distillation apparatus. It is a figure which shows an example of the relationship between the butyl 3-butoxypropionate density | concentration and water density | concentration in the most downstream reactor in an esterification reaction distillation apparatus. It is a figure which shows an example of the boiling point computed by the calculation which used butanol concentration and water concentration as a variable about the ternary system of butyl acrylate / butanol / water in the most downstream reactor in the esterification reaction distillation apparatus. It is a figure which shows an example of the relationship between the temperature of the most downstream reactor in the esterification reaction distillation apparatus, and the water concentration in this most downstream reactor. It is a figure which shows an example of the relationship between the acrylic acid density | concentration according to reactor temperature and water density | concentration in the most downstream reactor in an esterification reaction distillation apparatus. It is a figure which shows an example of the relationship between the temperature of the most downstream reactor in the esterification reaction distillation apparatus, and the steam supply amount to this most downstream reactor. It is a figure which shows an example of the relationship according to the load to this most downstream reactor about the temperature of the most downstream reactor in an esterification reaction distillation apparatus, and the steam supply amount to this most downstream reactor. It is a figure which shows an example of the relationship according to the water concentration in this most downstream reactor about the load in the esterification reaction distillation apparatus, and the steam supply amount to the most downstream reactor. The figure which shows an example of the relationship between the steam supply amount to the most downstream reactor, the water concentration in the most downstream reactor, and the temperature of the reaction liquid in the most downstream reactor in the esterification reaction distillation apparatus. It is.

In this specification, unless otherwise specified, steam refers to water vapor.
Hereinafter, the method of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a flow sheet showing an example of a reactive distillation apparatus used in the butyl acrylate reaction step in the present invention.

  The raw acrylic acid (1), butanol (2), and acid catalyst (3) are supplied to the most upstream reactor (R1) of the reactors (R1 to R5) arranged in series.

As the number of reactors increases, the reaction conversion rate of acrylic acid can be increased efficiently, but the equipment costs associated with the increase in the number of reactors and their associated equipment increase, and the labor required for operation control and maintenance Therefore, an appropriate number is selected in consideration of these matters. Usually, the number of reactors is 3-8.
The reactor may be an individual container, a shape divided into a plurality of reaction chambers by a partition plate, or a combination thereof.

  The water produced by the esterification reaction is azeotroped with butanol and butyl acrylate by heating and sent to the distillation column (C1). One distillation column may exist for each of the reactors, or one distillation column may exist for a plurality of reactors. For the same reason as the number of reactors, the number of distillation columns is usually 1 to 4.

  The distillate gas from the distillation tower is condensed by a condenser (E1) and separated into an organic layer and an aqueous layer by a decanter (D1). The organic layer is circulated (16) as a reflux liquid to the distillation column (C1), and the aqueous layer (17) is discharged out of the system. Since the water layer (17) contains a small amount of butanol, it may be sent to a butanol recovery distillation column (not shown) for the purpose of recovery.

The same applies to the second and subsequent distillation columns (C2).
In the plurality of series reactors, the reaction conversion rate of acrylic acid is higher in the downstream reactor, and the reaction conversion rate reaches 95% or more in the most downstream reactor. It is difficult to separate and recover unreacted acrylic acid from butyl acrylate. Therefore, the higher the conversion rate of the reaction, the higher the reaction conversion rate in terms of the basic unit of the acrylic acid raw material. Usually, the reaction conversion is 99.5% or less. Since butanol supplied to the reactor is a little excessive with respect to acrylic acid, the composition of the liquid in the reactor on the most downstream side is mainly composed of butyl acrylate, 5 to 15% by weight of butanol and a small amount of acrylic acid, Contains acid catalyst and a small amount of by-products.

  The higher the temperature, the higher the esterification reaction rate, which is more efficient. However, there are problems such as easier polymerization of acrylic acid and butyl acrylate, and relatively faster side reaction. The temperature of the reactor is usually kept in the range of 80 to 110 ° C, more preferably 85 to 105 ° C. In order to perform distillation at the reactor temperature, a reduced pressure is required, and the pressure at the top of the distillation column is usually 10 to 40 kPa.

Hereinafter, the operation control method of each reactor will be described.
The vacuum apparatus is controlled so that the pressure becomes a constant value. Although it is most desirable to control the pressure of the reaction apparatus itself, it is desirable to control the pressure at the top of the reaction distillation apparatus in order to avoid clogging of the measurement section due to butyl acrylate and erroneous indication due thereto. As a vacuum apparatus to be used, a liquid ring vacuum pump, a steam ejector, or a combination thereof is generally used, and pressure control is performed by opening / closing a vacuum line valve. Although the pressures in the reactors may all be the same, since the boiling point of the reaction solution on the downstream side becomes higher, it is desirable that the pressure on the downstream side is lower in order to efficiently carry out the reactive distillation.

Heat input to the reactor is performed by supplying a heat source to an inner coil provided inside the reactor, a jacket provided on the outer wall surface of the reactor, or a heat exchanger provided in a circulation path outside the reactor. . Steam is the most common heat source, but organic or inorganic heat medium solutions can also be used. It is desirable to adjust the supply amount of the heat source for each reactor so that the liquid temperature in the reactor becomes a set value. The set temperature of the reactor may be the same in all the reactors, but since the boiling point is higher in the downstream reaction solution, it is desirable that the temperature is higher in the downstream side in order to proceed the reactive distillation efficiently. The temperature difference between the most upstream reactor and the most downstream reactor is preferably 2 to 15 ° C.

Thus, by controlling the temperature and pressure, the liquid composition in each reactor can be controlled. However, different control is required in a state where the reaction conversion rate of acrylic acid is high.
In a state where the reaction conversion rate of acrylic acid is high, the reaction conversion rate does not become constant even if the temperature and pressure of the most downstream reactor or the like are accurately controlled. Although it is possible to increase the reaction conversion rate by increasing the reaction temperature sufficiently, by-product of butyl 3-butoxypropionate is increased. In addition, since the esterification reaction is a reversible reaction and water is required for hydrolysis of the reverse reaction, it is necessary to efficiently distill off water.

In a state where the reaction conversion rate of acrylic acid is high, butyl 3-butoxypropionate is controlled by controlling the amount of heat to at least the most downstream reactor substantially constant, rather than the conventional method of controlling the temperature of the reactor. The amount of water produced can be suppressed, and water can be distilled off efficiently.
At this time, the amount of heat of the heat source supplied from the most downstream reactor to the one upstream reactor may also be controlled to be substantially constant.

Note that the constant amount of heat means that the amount of heat per unit time transferred from the heat medium supplied to the heat exchanger of the reactor to the process fluid in the reactor is constant. In the case of a medium that does not undergo a phase change in the process of heat transfer, the amount of heat is [heat medium flow rate per unit time] × [specific heat of the heat medium] × ([heat medium heat exchanger inlet temperature] − [heat medium Heat exchanger outlet temperature]).
When the heat medium is steam and condenses due to heat exchange, the amount of heat is [steam flow rate per unit time] × {[water evaporation latent heat] + [specific heat of steam] × ([steam supply temperature] − [steam Condensation temperature]) + [specific heat of water] × ([condensation temperature of water vapor] − [water temperature at the outlet of the heat exchanger])}.
The amount of heat does not prohibit fluctuation within a minute time, but a constant amount of heat is supplied to the process fluid continuously supplied and discharged into the reactor. Means an average value of the supplied heat amount at θ, preferably θ / 2, more preferably an average value of the supplied heat amount at θ / 4.
“Substantially constant” means that the average value of the supplied heat amount is substantially constant, and the fluctuation is at most 15%, preferably 10% or less, more preferably 5% or less.

EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, the scope of the present invention is not limited to these.
The numerical values in the charts shown below are based on operation and analysis data for about two years in commercial facilities of butyl acrylate when steam is used as a heat source unless otherwise specified. It should be noted that things that are considered to have not reached a steady state, such as at the start of operation or immediately after changing the operating conditions, are excluded.

Table 1 and FIG. 2 show butyl acrylate, butanol, acrylic acid, butyl 3-butoxypropionate in the first to fifth stage reactors in the production of butyl acrylate by conventional operation performed at a controlled temperature, and Each concentration (% by weight) of water. These were sampled and analyzed all at the same time. It is confirmed that the acrylic acid concentration decreases exponentially and the butyl 3-butoxypropionate concentration increases gradually.

  Next, Table 2 shows the average value and standard deviation of the liquid composition in the most downstream reactor.

  From Table 2, it can be confirmed that the one having a large coefficient of variation (a value obtained by dividing the standard deviation by the average value) is acrylic acid and then water.

  FIG. 3 shows the relationship between the acrylic acid concentration and the water concentration with respect to the liquid composition in the most downstream reactor. From FIG. 3, the acrylic acid concentration and the water concentration show a positive correlation, and it can be confirmed that the smaller the water concentration, the smaller the acrylic acid concentration.

  Here, for example, the result of FIG. 3 shows that the residence time is long because of the low amount of acrylic acid supplied, and as a result, the acrylic acid concentration in the most downstream reactor is low (acrylic acid conversion rate is increased). Conceivable. If the conversion rate of acrylic acid increases due to an increase in residence time, acid catalyst, reaction temperature, etc., the amount of by-produced butyl 3-butoxypropionate is also considered to have increased. FIG. 4 shows the relationship between the butyl 3-butoxypropionate concentration and the acrylic acid concentration.

  From FIG. 4, no correlation is confirmed between the butyl 3-butoxypropionate concentration and the acrylic acid concentration. That is, it is assumed that the reason why the coefficient of variation of the acrylic acid concentration is large is not due to the residence time or the like.

Similarly, FIG. 5 shows the relationship between the butyl 3-butoxypropionate concentration and the water concentration. From FIG. 5, it can be confirmed that there is no correlation between the butyl 3-butoxypropionate concentration and the water concentration.
From the above, it is considered that the decrease in the water concentration in the most downstream reactor contributes to the increase in the acrylic acid conversion rate.

  In order to increase the acrylic acid conversion rate, the concentration of water, which is a light-boiling component, may be lowered, and for that purpose, it is considered that the temperature may be increased. Fig. 6 shows the boiling point calculated under reduced pressure (30 kPa) in a ternary system of butyl acrylate / butanol / water using the water concentration and the butanol concentration which is another major light boiling component as variables. is there.

  From FIG. 6, it can be confirmed that the water concentration decreases by about 0.04 wt% by raising the boiling point of 2 to 2.5 ° C. The butanol concentration is reduced by about 2% by weight at a boiling point of 1 ° C. Here, the change in the concentration of butanol is ± 0.86% by weight from the standard deviation in Table 2, that is, the influence on the temperature due to the variation of the butanol concentration during operation is ± 0.5 ° C. at most.

  Therefore, the relationship between the water concentration and the temperature in the most downstream reactor (FIG. 7) and the relationship between the acrylic acid concentration and the temperature (not shown) were examined, but no correlation was found between them. That is, it can be confirmed that the water concentration does not decrease just because the temperature of the most downstream reactor is increased.

Next, FIG. 8 is a plot of the data used in FIG. 3 divided into regions of 90 ° C. or higher and lower than 93 ° C. and 96 ° C. or higher and 99 ° C. or lower according to the temperature of the reactor.
In each of the two temperature ranges, there is a correlation that the lower the water concentration, the lower the acrylic acid concentration, but when comparing the two, it was not possible to confirm the relationship that the higher the temperature, the lower the water concentration.

Next, FIG. 9 shows the relationship between the temperature of the most downstream reactor and the amount of steam supplied to the inner coil (reboiler) in the reactor.
From FIG. 9, it can be confirmed that there is a positive correlation between the temperature of the most downstream reactor and the steam supply amount. Further, it can be confirmed that the steam supply amount has a considerable range even when the temperature is kept constant.

FIG. 10 shows a low state (load 70 to 80%) and a high state (95 to 105%) of the load of the butyl acrylate production plant (the ratio between the production amount per unit time and the design production amount, also referred to as the operation rate). 9 is a plot of the relationship between the amount of steam supplied to the most downstream reactor and the temperature of the most downstream reactor, as in FIG.
From FIG. 10, it can be confirmed that even if the plant load is within a certain range and the most downstream reactor is controlled to be in a specific temperature range, the steam supply amount can take a wide range. That is, even if the temperature of the reactor is controlled, it can be confirmed that there is a considerable fluctuation in the steam supply amount.

FIG. 11 is a plot of the relationship between the plant load and the steam supply amount divided into a high water concentration (≧ 0.1 wt%) and a low water concentration (≦ 0.07 wt%).
In each load, it can be confirmed that the water concentration decreases as the steam supply amount increases.

From the above, in order to reduce the water concentration, the steam supply amount should be set large. This is very different from the conventional operation performed by controlling the temperature, which is an absolute index. In the conventional operation performed by controlling the temperature, the steam supply amount has a considerable fluctuation and is not controlled. The fact that the amount of steam supply is not controlled may be present when the water concentration is low, but also when the water concentration is high. As a result, the fluctuation width of the residual acrylic acid concentration is considered to increase.
That is, in order to keep the water concentration in the most downstream reactor always low, the steam supply amount should be controlled, not the temperature.

For example, in FIG. 11, as the steam supply amount for making the water concentration less than 0.07% by weight,
Steam supply (kg / h) = ( load (%)-15 ) (kg / h)
The degree is necessary. FIG. 12 shows the distillation calculation of the influence of steam that is 10-20 kg / h more than this average value.
The liquid composition to be heated is a butyl acrylate solution containing 0.2% by weight of water and 6% by weight of butanol, and the distillation calculation when heated / distilled under 30 kPa in accordance with the plant scale. went.
From FIG. 12, it can be confirmed that the water concentration decreases by 0.01 to 0.02% by weight when the steam supply amount increases by 20 kg / h. Although it can be confirmed that the temperature rises by 1 ° C., as described above, the reality is not certain.

It is considered that the amount of heat supplied to the most downstream reactor varies depending on the configuration of the reactor and the reaction conditions. As described above, there is a point that cannot be predicted by calculation. Therefore, for example, the following optimization is preferably performed as an embodiment of the present invention.
When there is an operation record by temperature control, the correlation corresponding to FIG. 11 is obtained by the same method as described above.
On the other hand, when there is no track record or when building a new one, design with a margin (≧ 20%) in the capacity of the heat exchanger, perform a constant heat operation, and reflect the analysis result of the process liquid, Make an optimal heat supply.

  From the above, it was confirmed that in the conventional operation performed by controlling the temperature, a large fluctuation occurred in the steam supply amount of the most downstream reactor, which had an influence on the acrylic acid conversion rate. On the other hand, about the reactor which consists of all five stages, it investigated also about the thermal load of reactors other than the most downstream reactor.

  From Table 3, it can be confirmed that the downstream reactor has a smaller amount of heat. According to the present invention, the amount of heat supplied to the most downstream reactor is increased, but the ratio is sufficiently small compared to the amount of heat of the entire reactor. It can be confirmed that the coefficient of variation in the amount of heat supplied to each reactor increases toward the downstream side and becomes maximum in the most downstream reactor.

  The temperatures of the five reactors are set to 90 ° C., 92 ° C., 92 ° C., 94 ° C., and 96 ° C. in order from the first stage as reference conditions. The pressure is set to 25 kPa on the upstream side and 20 kPa on the downstream side as the top pressure of the distillation column.

Example 1
The temperature control of R5 was stopped, the steam supply amount (kg / h) was set to ( load (%)-10 ) (kg / h), and the operation was continued for about 6 months. The average temperature of R5 was 96.3 ° C. (0.3 ° C. increase), the water concentration was 0.06 wt%, the acrylic acid concentration was 0.27 wt% (standard deviation 0.05 wt%), 3-butoxy The butyl propionate concentration was 3.38% by weight.
The residence time of the process liquid in R5 was about 2 hours, and the average amount of supplied steam for 30 minutes was ± 7% at the maximum with respect to the above relational expression and 3% or less with a standard deviation. There is a maximum difference of 20 ° C. in the temperature of the supply steam, which corresponds to less than 2% of the heat supply by the steam. Therefore, the fluctuation of the heat supply amount was less than 5%.

(Comparative Example 1)
Based on the analysis results, all the set temperatures of the reactors R1 to R5 were changed with the same amount of change so that the acrylic acid concentration at the exit of R5 was 0.30% by weight, and the operation was continued for about 2 months.
The maximum temperature increase was 3.6 ° C. The acrylic acid concentration was 0.30% by weight (standard deviation 0.34% by weight), and the butyl 3-butoxypropionate concentration was 4.22% by weight.
The average amount of steam supplied for 30 minutes in R5 was ± 26% at maximum with respect to the average value at a load of 100%, and 17% with standard deviation.

(Example 2)
As in Example 1, except that the temperature control of R4 was stopped, the steam supply amount to R4 was 2.2 times the supply amount to R5, and the operation was continued for one month.
The water concentration was 0.05% by weight, acrylic acid was 0.26% by weight (standard deviation 0.05% by weight), and the butyl 3-butoxypropionate concentration was 3.47% by weight.
The variation in the amount of heat supplied in R5 was less than 5%.

DESCRIPTION OF SYMBOLS 1 Acrylic acid 2 Butanol 3 Acid catalyst 11, 20, 21, 22 Reactor bottoms 12, 13, 23, 24, 25 Distillate gas 14 from reactors 26, Distillation tower bottoms 15, 27 Distillation bottom Outlet gas 16, 28 Organic layer (reflux)
17, 29 Water layer 30 Reactor bottoms (crude butyl acrylate)
C1, C2 Distillation column D1, D2 Decanter E1, E2 Condenser R1, R2, R3, R4, R5 Reactor

Claims (7)

A reaction step comprising reacting acrylic acid and butanol to form a reaction mixture containing butyl acrylate using a multistage reactor in series, and water from the reaction mixture containing butyl acrylate produced in the reaction step, A method for producing butyl acrylate, comprising a distillation step of azeotropically distilling with butyl and sending it to a distillation column, and separating water by distillation, and a step of separating crude butyl acrylate ,
In the reaction step, the amount of steam as a heat source to be supplied to at least the most downstream reactor among the multistage reactors in series is made constant (however, including a fluctuation of 15% or less). A method for producing butyl acrylate, wherein the concentration of acrylic acid in the outlet liquid of a downstream reactor is reduced.   The process of claim 1, wherein the series multistage reactor is 3 to 8 stages.   The method according to claim 1 or 2, wherein all the temperatures of the series multistage reactor are 80 to 110 ° C.   The method according to any one of claims 1 to 3, wherein the temperature of the reactor is higher in the downstream multi-stage reactor.   The method according to any one of claims 1 to 4, wherein a top pressure of the distillation column is 10 to 40 kPa.   The method according to any one of claims 1 to 5, wherein the distillation column has one stage or multiple stages.   The method according to claim 6, wherein when the distillation column is multistage, the column top pressure is lower in the downstream distillation column.