JPH08151349A - Method for heating polymerizable liquid - Google Patents

Abstract

PURPOSE: To heat a polymerizable liquid readily deteriorated by heating under stable operating conditions while suppressing the occurrence of coloring or polymerized substances by using a forced circulation type heat exchanger. CONSTITUTION: A polymerizable liquid such as acrylic acid and (meth)acrylic esters is heated by using and operating a forced circulation type heat exchanger so as to regulate the flow velocity of the polymerizable liquid circulated through the interior of the heat exchanger to 1.0-2.0m/g. A polymerrzation inhibitor e.g. phenothiazine) can be used in combination. The contact surface of a heater in the forced circulation type heat exchanger is always washed away with the circulating liquid without retaining the liquid on the contact surface. Thereby, trouble such as occurrence of coloring, by-products or polymerization is reduced and stable operations are regarded as possible without deteriorating the performances of the heat exchanger by preventing the liquid retained on the contact surface from polymerizing or scales from depositing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to acrylic acid or methacrylic acid (hereinafter acrylic and methacrylic are combined.
(Referred to as (meth) acrylic), a method for heating a polymerizable liquid such as (meth) acrylic acid ester, which suppresses coloring and generation of a polymerized product, and which does not deteriorate the performance of the heater. The present invention provides an industrially advantageous method for heating a liquid, and can be used in various industries including the chemical industry dealing with polymerizable liquids.

[0002]

2. Description of the Related Art Polymerizable liquids such as (meth) acrylic acid and (meth) acrylic acid ester are widely used as raw materials for synthetic resins, paints, adhesives and other polymer products. In particular, colorless and transparent products are required in order to prevent accidental coloring of these products. However, these polymerizable liquids are liable to cause problems such as coloration and formation of polymerized products under high temperature, and particularly in the vicinity of the contact surface with the high temperature portion such as the heat transfer surface of the heater, the polymerizable liquid Is colored and a polymer is generated, which is a big problem. On the other hand, the operation of heating the polymerizable liquid is to purify the polymerizable liquid by distillation, or to carry out the reaction of esterification reaction or transesterification reaction.
It is an essential operation, and the above-mentioned problems that occur at that time are one of the major causes of making those operations difficult. Generally, a jacket type heat exchanger or a thermosiphon type external heating type heat exchanger is used to heat the polymerizable liquid, but the liquid does not accumulate on the heat transfer surface of those heat exchangers. Since the heat transfer surface is likely to occur and the heat transfer surface is at a high temperature, a polymer is easily generated, and the generated polymer adheres to the heat transfer surface to form a scale, which deteriorates the performance of the heater. Furthermore, in a heater with degraded performance, the method of raising the temperature of the heating source to promote heat transfer is adopted to secure the same amount of heating, but it is necessary to further raise the contact temperature on the heat transfer surface. Therefore, the polymerization reaction is further accelerated, and the generation of scale becomes more remarkable. If the vicious cycle method as described above is adopted, the performance of the heater deteriorates rapidly and becomes unusable, and ultimately the operation is stopped and the heater is cleaned.・ You will have to check. Then, the polymerizable liquid heated in such a state is often colored unsuitably as a product. As a means for solving these problems, it has been proposed to use a large amount of a polymerization inhibitor or a method using a polymerization inhibitor as disclosed in JP-A-58-174346. Further, as in the method disclosed in Japanese Examined Patent Publication No. 6-53711, a stirring thin film evaporator is used, and the heating surface is continuously scraped by a wiper attached to the inside of the evaporator. A method of preventing polymerization due to retention of the polymerizable liquid and adhesion of scale such as a polymer is also proposed.

[0003]

However, the above-mentioned conventional methods have the following problems. The addition of a large amount of the polymerization inhibitor tends to increase the coloration due to heat and has a problem that the product quality is deteriorated. Further, when a special polymerization inhibitor having a low coloring property disclosed in JP-A-58-174346 is used, the polymerization inhibitor has to be removed in order to obtain a final product. Have a point. This is the same when the coloring substance is removed with activated carbon or activated clay. On the other hand, the method of using the stirring thin film evaporator not only increases the equipment cost because it is a special heater, but also generates a polymer in the gap between the wiper movable part and the fixed part,
It often makes long-term driving impossible. The present inventors have conducted various studies in order to solve the drawbacks of the conventional methods as described above, which occur when the polymerizable liquid is heated for purification or reaction by distillation, to complete the present invention. It has arrived.

[0004]

DISCLOSURE OF THE INVENTION The inventors of the present invention have investigated the causes of coloring and formation of a polymer when heating a polymerizable liquid, and as a result, the temperature of the polymerizable liquid and the polymerizable liquid at that temperature have been investigated. The residence time is significantly involved, and the effect of the temperature at the part where the polymerizable liquid is in contact with the heating source is also significant, and the higher the temperature at that part, the more marked the coloring and the formation of the polymer. The present inventors have found the above findings, and have utilized this finding to obtain a method for reducing the coloring and the formation of the polymer when heating the polymerizable liquid, and as a result of intensive studies, the present invention has been completed. . Furthermore, the present inventors, when heating the polymerizable liquid by the forced circulation type heat exchanger, the ability of the forced circulation type heat exchanger (overall heat transfer coefficient U:
It is an index that indicates the ease with which heat can be transferred from the heat exchanger. It decreases when the heat exchanger becomes dirty due to the adhesion of scale, etc. and it becomes difficult to transfer heat.) It was also found that the temperature of the heated liquid and the flow velocity of the polymerizable liquid (hereinafter referred to as the circulating liquid) in the heat exchanger are greatly related, and when the polymerizable liquid is heated by the forced circulation heat exchanger. In addition, as a result of extensive studies to find a method for reducing the coloring and the formation of a polymer, the present invention has been completed.

That is, the present invention relates to an invention relating to a method for heating a polymerizable liquid characterized in that it is heated using a forced circulation type heat exchanger, and a polymerizable liquid passing through the forced circulation type heat exchanger in the heating method. The invention relates to a method for heating a polymerizable liquid, characterized in that the flow velocity of the liquid is 1.0 to 2.0 m / s.

The present invention will be described in more detail below. The heat exchanger used for heating the polymerizable liquid in the present invention is a forced circulation type heat exchanger that evaporates a part of the circulating liquid while forcibly circulating the reaction liquid through the heat exchanger by a pump or the like. , As the type of heat exchanger, multi-tube heat exchanger,
Examples include a spiral heat exchanger and a plate heat exchanger. Further, a generally known one having a ratio of the evaporation amount to the total circulation amount in the heat exchanger of about 1 to 20% is used. The heat transfer area A [m ² ] of the heat exchanger is, as shown in the equation (1), the overall heat transfer coefficient U [kj / of the heat exchanger using the required heating amount Q [kj / Hr]. m ² / Hr / ° C.] and the temperature difference Δt [° C.] between the temperature of the polymerizable liquid and the heat source. A small value is preferable, but if it is too small, the heat transfer area A becomes too large and the facility cost becomes high, which is economically disadvantageous.
It is preferable that the heat transfer area is such that t is 1 to 30 ° C, and more preferably 3 to 20 ° C. Further, when the temperature of the heating medium is 200 ° C. or higher, coloring on the surface of the heater and formation of a polymer become remarkable, so it is preferable to set it so as not to do so.

[0007]

[Formula 1] A = Q / (U × Δt) (1) Formula

It is necessary to operate the heat exchanger so that the flow rate of the polymerizable liquid circulated inside the heat exchanger used in the present invention is in the range of 1.0 to 2.0 m / s. It is preferable for the purpose of preventing coloration of the product and preventing the formation of a polymer. 1.0 m / s
If it is less than the above value, the flow velocity of the circulating liquid is slow, so that the scale is remarkably generated on the heat transfer surface and the capacity of the heat exchanger is reduced. It is preferable that the flow rate of the circulating fluid is as high as possible,
If it exceeds 2.0 m / s, the pump that circulates the circulating fluid becomes large, which increases the equipment cost and is economically disadvantageous. The polymerizable liquid that can be heated by the method of the present invention is diverse, and specific examples thereof include (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and Butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate,
Octyl (meth) acrylate, alkyl or cycloalkyl esters of acrylic acid such as nonyl (meth) acrylate, ethylene glycol di (meth) acrylate, glycerin tri (meth) acrylate and other polyfunctional
Examples thereof include (meth) acrylate and the like, or various liquids containing these polymerizable liquids. In the method of the present invention,
A polymerization inhibitor is used in combination in the same manner as the conventional technique for handling a polymerizable liquid, and as the polymerization inhibitor to be used, aromatic amines such as phenothiazine and hydroquinone, which are generally used when handling the polymerizable liquid, and A polymerization inhibitor such as a phenol compound such as a derivative thereof can be used. Oxygen is also widely used as a polymerization inhibitor, and oxygen dissolved in the polymerizable liquid has a great effect as a polymerization inhibitor, and it is necessary to operate in an atmosphere of a gas containing oxygen or to contain oxygen. By introducing gas into the polymerizable liquid and bubbling (aeration), oxygen is introduced into the liquid, and dissolved oxygen in the liquid effectively acts as a polymerization inhibitor. The oxygen-containing gas used to dissolve oxygen is not particularly limited, but if the oxygen concentration is high, such as air, an explosive mixed gas (explosive gas) is formed, which is dangerous. Since it increases, it is preferable to use a gas whose oxygen concentration is suppressed to 21% by volume (air) or less. Further, when the oxygen concentration is lower than 3% by volume, the oxygen partial pressure decreases, and it is difficult to obtain a high dissolved oxygen concentration.
The oxygen concentration is preferably 3% by volume or more.

[0009]

The method of the present invention reduces the occurrence of coloring and polymerized substances,
The details of why it is superior to heating the polymerizable liquid without degrading the performance of the heater are unknown, but the contact surface with the heater in the forced circulation heat exchanger is constantly washed with circulating liquid. Therefore, it is considered that since the liquid does not stay on the contact surface, troubles such as coloring, by-products and polymerization are reduced. Furthermore, it is considered that the polymerization of the liquid stagnant on the contact surface and the adhesion of scale are prevented, so that the performance of the heat exchanger is not deteriorated and stable operation is possible.

[0010]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples. The overall heat transfer coefficient U used as an index indicating the capacity of the heater in this specification is calculated by the following equation.

[0011]

[Formula 2] U = Q / (A × Δt), Δt = t ₁ −t ₀ Q: Required heating amount [kj / Hr], Δt: Temperature difference [° C.], A:
Heat transfer area [m ² ], t ₁ : Temperature of heating source [° C], t ₀ : Temperature of liquid to be heated [° C].

Example 1 1150 Mj / Hr as heat transfer amount Q
As the evaporator for distilling the crude acrylic acid containing 100%, a forced circulation type heat exchanger using a multi-tube heat exchanger (stainless steel, heat transfer area A is 15 m ² ) was used. Circulating fluid flow rate 1.
When operating at 5 m / s, the temperature difference Δt immediately after the start of operation is 1
8.6 ℃ (t ₀ is 90.9 ℃, t ₁ is 109.5 ℃),
The overall heat transfer coefficient U was 4122 kj / m ² / Hr / ° C. 1
Even after continuous operation for 1 year, Δt is 19.0 ° C and U is 40
It was 35 kj / m ² / Hr / ° C, and almost no decrease in U was observed.

Examples 2 to 8 As shown in Tables 1 and 2, when heating was performed under the same apparatus and conditions as in Example 1, the results shown in Tables 1 and 2 were obtained. In addition,
In Tables 1 and 2, symbols such as BA and HA in the column of the polymerization liquid (abbreviation of the polymerization liquid) indicate the following polymerization liquids. BA: Butyl acrylate HA: 2-Ethylhexyl acrylate DM: Dimethylaminoethyl methacrylate AA: Acrylic acid

[0014]

[Table 1]

[0015]

[Table 2]

COMPARATIVE EXAMPLE 1 2-Ethylhexyl acrylate, which requires 1000 Mj / Hr as a heat transfer amount Q, and crude acrylic acid 2-containing 70% of acrylic acid 2-
As an evaporator for distilling ethylhexyl, a stirring thin film evaporator (made of stainless steel, heat transfer area A is 9.6 m ² ) was used. The temperature difference Δt immediately after the start of operation is 15.0 ° C (t ₀ is 1
25.0 ° C., t ₁ was 140.0 ° C.), and the overall heat transfer coefficient U was 6942 kj / m ² / Hr / ° C., which was three times the value in the case of Example 3. However, after two months, a polymer was generated in the gap between the wiper movable part and the fixed part, and the operation could not be continued. Therefore, the evaporator was stopped and cleaning and inspection were performed.

Example 9 As a vaporizer for distilling crude methyl acrylate containing 80% of methyl acrylate required for heat transfer amount Q of 1800 Mj / Hr, a multi-tube heat exchanger (stainless steel, heat transfer area A
Used 25 m ² ). When operating at a circulating fluid flow rate of 1.6 m / s, the temperature difference Δt immediately after the start of operation was 17.0 ° C (t ₀ was 8
2.0 ° C., t ₁ was 99.0 ° C.), and the overall heat transfer coefficient U was 4235 kj / m ² / Hr / ° C. Δt was 17.5 ° C, U was 4114 kj / m ² / Hr / even after 1 year of continuous operation
C. and almost no decrease in U was observed.

Comparative Example 2 1800 Mj / Hr as heat transfer amount Q 1800 Mj / Hr As a vaporizer for distilling crude methyl acrylate containing 80% of required methyl acrylate, a thermosiphon heat exchanger (stainless steel,
The heat transfer area A used was 20 m ² . The temperature difference Δt immediately after the start of operation is 17.2 ° C (t ₀ is 82.0 ° C, t ₁ is 99.2 ° C)
Therefore, the overall heat transfer coefficient U was 5250 kj / m ² / Hr / ° C., which was 1.2 times the value of the case of Example 9. However, after 1 month of continuous operation, Δt was 20.6 and U was 52.
The value decreased to 50 kj / m ² / Hr / ° C. and was almost the same value as in Example 9. After three months, the required heat transfer amount could not be obtained, so the operation was stopped and the heat exchanger was cleaned and inspected.

[0019]

EFFECTS OF THE INVENTION According to the present invention, there is provided a method for heating a polymerizable liquid such as (meth) acrylic acid ester under stable operation while suppressing coloring and formation of a polymer.
The effect of contributing to the chemical industry that manufactures polymerizable liquids such as (meth) acrylic acid ester and the industry that handles them is very large.

Claims (2)

[Claims] 1. A method for heating a polymerizable liquid, which comprises heating using a forced circulation heat exchanger. 2. The method for heating a polymerizable liquid according to claim 1, wherein the flow rate of the polymerizable liquid passing through the forced circulation type heat exchanger is set to 1.0 to 2.0 m / s.