JP3759467B2 - Manufacturing method and manufacturing apparatus of ethylene-vinyl acetate copolymer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for producing an ethylene-vinyl acetate copolymer (EVA).
[0002]
[Prior art]
Since polymerization of ethylene and vinyl acetate involves a large heat of reaction, it is necessary to efficiently remove the heat of reaction in the continuous production of EVA. For removing the reaction heat, a cooler installed in the polymerization tank, for example, a jacket and a coil (J & C), is usually used. However, as the operation time elapses, the polymer scale adheres to the surface of the cooler and the heat removal capability decreases. Therefore, it is necessary to periodically stop the operation and remove the scale from the cooler.
[0003]
The polymer scale adheres not only to the cooler in contact with the polymerization solution but also to the top plate of the polymerization tank. When the scale attached to the top plate falls into the polymerization solution, a defect called fish eye is induced when EVA saponified product (ethylene-vinyl alcohol copolymer: EVOH) is formed into a film, a container or the like.
[0004]
In order to prevent this defect, Japanese Patent Application Laid-Open No. 11-116636 discloses a method of performing polymerization while cooling the top plate of the polymerization tank and keeping the temperature of the top plate lower than the polymerization temperature. In this publication, as an example, an example in which a cooling coil installed on the outer surface of the top plate is used and the inner surface temperature of the top plate is maintained about 10 ° C. lower than the polymerization temperature (65 to 77 ° C. in the left example) is described. Has been. By using this method, the polymerization reaction on the inner surface of the top plate is suppressed, and adhesion of polymer scale can be prevented. However, here, the top plate is simply cooled to prevent the scale from adhering. For this reason, in order to remove reaction heat from the polymerization solution, a cooler is still required, and polymer scale adheres to the cooler.
[0005]
In Japanese Patent Publication No. 2-52922, ethylene gas derived from a polymerization tank is brought into contact with vinyl acetate (or vinyl acetate solution) as a copolymerization monomer in a heat exchanger to dissolve ethylene in vinyl acetate. The method of introducing into a polymerization tank in a heated state is disclosed. When this method is used, the polymerization solution is cooled by the vaporization of ethylene accompanying the temperature increase after being introduced into the polymerization tank. In this method, vinyl acetate (solution) is used as a solvent for circulating ethylene. According to the publication, if the ethylene is simply cooled and condensed, a cooling medium having a very low temperature is required. In this publication, it is necessary to circulate a large amount of ethylene using a booster for cooling the polymerization solution by condensation of ethylene, and the condensation operation itself becomes impossible when the ethylene is boosted to a critical point or higher. Has also been pointed out.
[0006]
[Problems to be solved by the invention]
The method described in Japanese Examined Patent Publication No. 2-52922 makes it possible to remove heat of reaction without using J & C by utilizing both the heat of condensation and the heat of dissolution of ethylene. To achieve continuous operation. However, since ethylene is circulated using a monomer (vinyl acetate) supplied to the polymerization tank, the application has certain limitations.
[0007]
That is, first, it has been difficult to apply to a batch polymerization apparatus in which raw materials are not continuously supplied. The batch polymerization apparatus has an advantage that it is more suitable for production of a small variety of products than the continuous apparatus. Secondly, even a continuous polymerization apparatus has a problem in stability when operating conditions such as the start and end of the apparatus operation change extremely. For example, when the supply of vinyl acetate is stopped during an emergency stop, the circulation of ethylene acting as a coolant is also stopped.
[0008]
Accordingly, an object of the present invention is to provide a new manufacturing method and manufacturing apparatus for EVA that can realize a stable continuous operation over a long period of time without continuously supplying raw materials.
[0009]
[Means for Solving the Problems]
The present inventor has found that the gas present above the polymerization solution condenses at a temperature higher than the condensation temperature of ethylene alone. Surprisingly, the cooling effect of adding the resulting condensate to the polymerization solution is greater than expected based on the heat of condensation of ethylene. Based on this new finding, the present invention has been completed.
[0010]
That is, the production method of the present invention is a method for producing an ethylene-vinyl acetate copolymer in a polymerization solution containing ethylene, vinyl acetate, methanol and a polymerization initiator in a polymerization tank, and vaporized from the polymerization solution. In order to cool the gas containing steam and condense at least a part of the gas, at least a part of the gas is cooled to a temperature higher than the condensation temperature of ethylene alone, and a condensate of at least a part of the gas a step of generating a said condensate is introduced into the polymerization solution, and a step of vaporizing at least one component of the condensate, the vapor saw including the at least one component, outside the polymerization tank in An EVA manufacturing method characterized in that a condensate is generated .
[0011]
The method of the reference example of the present invention is a method for continuously producing EVA,
(A) Continuously introducing ethylene, vinyl acetate-containing liquid, methanol and a polymerization initiator into a polymerization tank to form a polymerization solution in the polymerization tank,
(B) continuously cooling a gas containing vapor evaporated from the polymerization solution, generating a condensate of at least a part of the gas,
(C) continuously introducing the condensate into the polymerization solution, vaporizing at least one component of the condensate, and including the at least one component in the vapor in step (b);
And (d) continuously discharging a portion of the polymerization solution from the polymerization tank.
As the vinyl acetate-containing liquid, vinyl acetate or a vinyl acetate solution may be used. As the vinyl acetate solution, an alcohol solution of vinyl acetate, for example, a methanol solution of vinyl acetate is suitable.
[0012]
According to the production method of the present invention, stable continuous operation over a long period of time can be realized without continuously supplying raw materials. It can also be applied to batch-type devices. Since the cooling effect by the gaseous condensate is sufficiently large, it is not necessary to directly cool the polymerization solution, which is advantageous in suppressing the adhesion of the polymer scale. As apparent from the size of the cooling effect by the condensate and the high condensation temperature of the gas, it is considered that the condensate is not produced by condensation of ethylene alone. When the gas containing the component vaporized from the polymerization solution is cooled, components other than ethylene (vinyl acetate, methanol, etc.) contained in the gas are probably condensed before the ethylene is condensed. And ethylene melt | dissolves in this liquefied component and a condensed liquid produces | generates.
[0013]
In another aspect, the present invention provides a method for producing an ethylene-vinyl alcohol copolymer (EVOH) by saponifying EVA obtained by the above-described method, and further includes EVA obtained by the above-described method. .
[0014]
The present invention further provides an apparatus for producing EVA. The manufacturing apparatus includes a polymerization tank that holds a polymerization solution containing ethylene, vinyl acetate, methanol, and a polymerization initiator, and a cooler, and the cooler is in contact with vapor evaporated from the polymerization solution, and An apparatus for producing an ethylene-vinyl acetate copolymer disposed at a position not in contact with a polymerization solution,
The cooler is a heat exchanger that is connected to a cooling medium supply source and is not connected to a liquid supply source other than the cooling medium supply source;
A first conduit connecting the cooler and the polymerization tank so that a gas to be cooled is introduced from the polymerization tank to the cooler; and
A second conduit connecting the cooler and the polymerization vessel so that condensate is introduced from the cooler into the polymerization vessel;
A third conduit connecting the vinyl acetate source and the polymerization vessel without passing through the cooler ;
In order to condense at least a part of the gas containing vapor evaporated from the polymerization solution, at least a part of the gas is cooled to a temperature higher than the condensation temperature of ethylene alone, and at least a part of the gas is condensed. A means for generating a liquid is provided .
Another EVA production apparatus of the present invention includes a polymerization tank that holds a polymerization solution containing ethylene, vinyl acetate, methanol, and a polymerization initiator, and a cooler, and the cooler vaporizes from the polymerization solution. An ethylene-vinyl acetate copolymer production apparatus disposed at a position that is in contact with the polymerization solution and not in contact with the polymerization solution,
The cooler is a heat exchanger connected to a cooling medium supply source, not connected to a liquid supply source excluding the cooling medium supply source, and the cooler is disposed in the polymerization tank ;
In order to condense at least a part of the gas containing vapor evaporated from the polymerization solution, at least a part of the gas is cooled to a temperature higher than the condensation temperature of ethylene alone, and at least a part of the gas is condensed. A means for generating a liquid is provided .
[0015]
The cooler may be disposed inside the polymerization tank or may be disposed outside thereof. When the cooler is arranged inside the polymerization tank, the “position not in contact with the polymerization solution” is, for example, 50% or more of the height inside the polymerization tank, preferably 60% or more, depending on the design of the apparatus. . Therefore, the position not in contact with the polymerization solution is, for example, the position inside the polymerization tank and 50% or more of the height, or the outside of the polymerization tank.
[0016]
In the apparatus of the present invention, a cooler is arranged so that a gas containing vapor vaporized from the polymerization solution can be condensed. On the other hand, when the cooler is placed in contact with the polymerization solution, most of the cooling capacity of the cooler is spent on a liquid having a high heat transfer coefficient. The direct cooling target of the heat exchanger described in Japanese Patent Publication No. 2-52922 is also vinyl acetate (solution) that flows along the tube wall, not ethylene. This device is suitable for dissolving the gas in a solvent, but is also not suitable for producing a “condensate”. In Japanese Patent Application Laid-Open No. 11-116636, the cooler is in contact with the top plate of the polymerization tank from the outside of the polymerization tank, and is not “in contact with vapor vaporized from the polymerization solution”. In addition, if the wide top plate is cooled to condense the gas, a cooler having a very high cooling capacity is required. In this method, as described in JP-A-11-116637, the cooling temperature of the top plate having a large heat capacity is stopped to such an extent that the polymer scale can be prevented from sticking, and does not reach the temperature at which the gas is condensed.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described.
In the method of the present invention, it is preferable that at least one component vaporized from the condensate contains ethylene. In addition to ethylene, it is more preferable to contain at least one component other than ethylene and selected from vinyl acetate and methanol, such as vinyl acetate and methanol. Polymerization heat generated in the polymerization solution by generating a condensate from at least a part of the gas containing ethylene present in the gas phase in the polymerization tank and adding the condensate to the polymerization solution in a state containing ethylene Is absorbed.
[0018]
The temperature of the polymerization solution (polymerization temperature) is preferably 30 ° C. or more and 80 ° C. or less, more preferably 40 ° C. or more and 80 ° C. or less, although it depends on the polymerization rate of the target raw material and the degree of polymerization of the polymer. The temperature of the condensate returned to the polymerization solution is preferably −5 ° C. or higher and 30 ° C. or lower. If the temperature of the condensate is too high, a sufficient cooling effect may not be obtained. On the other hand, if the temperature of the condensate is too low, temperature non-uniformity may occur in the polymerization tank. In order to set the temperature of the condensate within this range, the cooling temperature of the gas is preferably set to −10 ° C. or more and 25 ° C. or less. Here, the gas cooling temperature is, for example, the temperature of the cooling medium to be supplied when using a heat exchanger. The temperature T _{2 of the} condensate is preferably controlled so as to be lower than the temperature T _{1 of the} polymerization solution (T ₁ <T ₂ ).
[0019]
The condensate may be generated outside the polymerization tank or may be generated inside the polymerization tank. In the former, for example, it is easy to remove a gas that is difficult to condense, such as nitrogen, and in the latter, since no external device is required, the cost of the device can be reduced. A condensate may be generated inside and outside the polymerization tank. In order to condense the components while homogenizing them, the gas may be stirred in the polymerization tank.
[0020]
When the gas containing the vapor from the polymerization solution is condensed outside the polymerization tank, a cooler outside the polymerization tank and the polymerization tank may be connected by the first and second conduits. The first conduit connects the cooler and the polymerization vessel so that the gas to be cooled is introduced from the polymerization vessel to the cooler, and the second conduit connects the cooler and the polymerization vessel to the condensate. It connects so that it may introduce into a superposition | polymerization tank from a cooler. In this case, it is preferable that the third conduit connecting the vinyl acetate supply source and the polymerization tank is arranged so as not to pass through the cooler. This is because the supply of the vinyl acetate-containing liquid is separated to condense the gas. With this arrangement, at least a portion of the gas can be condensed before it contacts the vinyl acetate-containing liquid. It is preferable that the cooler further includes a fourth conduit that is connected to the cooler at one end and discharges at least a part of the gas residue after condensation from the cooler. This is because inert gas such as nitrogen is discharged out of the system.
[0021]
In order to condense the gas in the polymerization tank, the cooler may be disposed in the polymerization tank so as to be in contact with the gas phase in the polymerization tank and not in contact with the polymerization solution. The cooler is preferably arranged so that its heat exchange surface does not contact the polymerization solution or the polymerization tank. When the heat exchange surface is disposed so as to be in contact with only the gas phase, at least a part of the gas can be efficiently condensed.
[0022]
By applying the present invention, it is possible to absorb all of the heat of polymerization generated in the polymerization solution by vaporizing at least one component of the condensate. However, in the present invention, other cooling methods may be used in combination, for example, cooling of the polymerization solution by J & C may be performed auxiliary.
[0023]
The present invention can be applied to continuous EVA production, and can be carried out, for example, as a method including the steps (a) to (d). In this case, it is preferable that the condensate is generated by a cooler disposed outside the polymerization tank in the step (b), and the vinyl acetate-containing liquid is introduced into the polymerization tank in the step (a) without passing through the cooler. Alternatively, in the step (b), the gas may be condensed by a cooler disposed in the polymerization tank so as to be in contact with the gas phase in the polymerization tank and not in contact with the polymerization solution.
[0024]
In the apparatus of the present invention, the cooler may be a heat exchanger that is in contact with a cooling medium supply source and is not connected to a liquid supply source other than the supply source. Examples of the liquid supply source include a vinyl acetate (containing liquid) supply source and a methanol supply source. These liquid supply sources are preferably connected directly to the polymerization tank without going through a cooler.
[0025]
Hereinafter, materials used for EVA polymerization will be described. However, in the present invention, basically, conventionally used raw materials, catalysts and the like can be used without any particular limitation.
[0026]
Methanol is used as a polymerization solvent. Components other than methanol may be used together with methanol as the polymerization solvent. As a component other than methanol, a solvent containing an aliphatic alcohol having 4 or less carbon atoms such as ethanol, n-propanol, i-propanol, n-butanol, and t-butanol is suitable. The amount of the polymerization solvent is suitably 0.1 to 50 parts by weight, particularly 1 to 30 parts by weight with respect to 100 parts by weight of vinyl acetate.
[0027]
Although it does not restrict | limit especially as a polymerization initiator, Use of at least 1 sort (s) chosen from a diacyl peroxide type | system | group initiator, a valeronitrile type | system | group initiator, and a peroxydicarbonate type | system | group initiator is suitable. Examples of diacyl peroxide polymerization initiators include acetyl peroxide, dipropyl peroxide, isobutyryl peroxide, benzoyl peroxide, and dilauroyl peroxide. Examples of valeronitrile polymerization initiators include 2 2,2'-azobis (2,4,4'-trimethylvaleronitrile), 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (4-methoxy-2,4-dimethyl) Valeronitrile), 2,2'-azobis (4-ethoxy-2,4-diethylvaleronitrile), 2,2'-azobis (4,4'-diethoxy-2-methylvaleronitrile), and peroxy Examples of dicarbonate polymerization initiators include dicyclohexyl peroxydicarbonate, bis- (4- - butylcyclohexyl) peroxydicarbonate, di -n- propyl peroxydicarbonate and the like. Among these, acetyl peroxide, 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), di-n-propyl peroxydicarbonate, and dicyclohexyl peroxydicarbonate are preferable, and 2,2 ′. -Azobis (4-methoxy-2,4-dimethylvaleronitrile) is more preferred.
[0028]
In the present invention, in order to efficiently remove the heat of polymerization, it is preferable that the polymerization solution has a predetermined concentration or more of ethylene concentration. Accordingly, the EVA from this solution preferably contains 5 mol% or more, more preferably 10 mol% or more, and even more preferably 20 mol% or more of ethylene. In order to continuously produce EVA containing less than 5 mol% of ethylene, it is necessary to reduce the supply amount of vinyl acetate and increase the supply amount of the polymerization solvent in order to sufficiently remove the heat of polymerization. This leads to a decrease in productivity and an increase in manufacturing cost.
[0029]
In order to obtain EVA having a considerably high ethylene content, it is necessary to increase the ethylene concentration of the solution in the polymerization tank. For this reason, it is necessary to increase the partial pressure of ethylene gas in the polymerization tank. An excessively high internal pressure increases the load on the polymerization tank. Therefore, in consideration of safety, the ethylene content of EVA from the polymerization solution is preferably 60 mol% or less, more preferably 55 mol% or less, and particularly preferably 50 mol% or less. The pressure in the gas phase in the polymerization tank (polymerization pressure) is preferably 20 kg / cm ² or more and 80 kg / cm ² or less, although it depends on the target ethylene content.
[0030]
In addition to ethylene and vinyl acetate, a monomer copolymerizable therewith may coexist. Examples of such monomers include (1) α-olefins such as propylene, n-butene, i-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and 1-dodecene, and (2) Unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, salts thereof, anhydrides or esters thereof (for example, mono- or dialkyl esters), nitriles such as (3) acrylonitrile, methacrylonitrile, (4) Amides such as acrylamide and methacrylamide; (5) Olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid and methallyl sulfonic acid or salts thereof. In addition, alkyl vinyl ethers, vinyl ketone, N-vinyl pyrrolidone, vinyl chloride, vinylidene chloride and the like may coexist. However, it is preferable to add these third monomers within a range that does not impair the object of the present invention.
[0031]
FIG. 1 is a cross-sectional view showing an embodiment of the manufacturing apparatus of the present invention. A plurality of introduction pipes 5, 6, and 7 are connected to the polymerization tank 1 (the number and arrangement of the introduction pipes are not limited to those shown in the figure). From these introduction pipes, at least (1) ethylene, (2) methanol (3) Vinyl acetate or vinyl acetate solution and (4) polymerization initiator (polymerization catalyst) are supplied into the tank, and the gas phase part 2 and the liquid phase part 3 are formed in the tank. Methanol may be introduced into the polymerization tank as part of the vinyl acetate solution. Stirrers 22 and 23 are installed in the gas phase portion and the liquid phase portion, respectively. These may share a rotation axis. In this apparatus, raw materials such as vinyl acetate and methanol are directly supplied to the polymerization tank 1 without passing through the heat exchanger 12 installed outside the polymerization tank. The polymerization solution constituting the liquid phase portion 3 is taken out from the drain tube 8 connected to the bottom of the tank after completion of the copolymerization (or continuously while the copolymerization is in progress).
[0032]
A gas condensing device 10 is connected to the polymerization tank 1 in order to remove heat generated by the polymerization reaction. The gas condensing device 10 includes a heat exchanger 12 and pipes (a gas introduction pipe 11 and a condensate introduction pipe 13) that connect the heat exchanger and the polymerization tank. The gas introduction pipe 11 supplies the gas above the polymerization solution from the gas phase part 2 of the polymerization tank to the heat exchanger 12. The heat exchanger 12 condenses the gas by heat exchange between the gas and the cooling medium. The condensate introduction pipe 13 flows the produced condensate into the polymerization tank. The cooling medium is supplied to the heat exchanger from the cooling medium supply pipe 15 and is recovered from the recovery pipe 16. The supply direction of the cooling medium may be reversed.
[0033]
The gas condensing device 10 may be a closed gas-liquid conversion system in which no substance enters or exits, but as shown in FIG. 1, in order to release the remainder of the gas condensed in the heat exchanger 12 to the outside of the system, A gas release pipe (exhaust pipe) 17 may be provided in the heat exchanger. When copolymerization is carried out while releasing at least a part of the gas residue out of the system, accumulation of low-activity nitrogen or the like can be suppressed during continuous production. As a result, a decrease in ethylene partial pressure in the polymerization tank is prevented, and the copolymerization ratio of ethylene and vinyl acetate can be easily kept constant. As shown in the figure, the gas release pipe 17 is located above the junction between the gas introduction pipe 11 and the heat exchanger 12 and the junction between the condensate introduction pipe 13 and the heat exchanger 12. It is good to connect to.
[0034]
As the heat exchanger 12, various types of exchangers such as a coil type and a plate type can be used without particular limitation, but a multi-tube type heat exchanger is preferable from the viewpoint of both efficiency of gas condensation and discharge. The heat exchanger of FIG. 1 has a high degree of design freedom because it is not necessary to separately introduce a liquid for dissolving the gas. In order to supply the liquid sufficiently and uniformly in order to efficiently dissolve the gas in the liquid, for example, in a multitubular heat exchanger, it is necessary to keep the diameter and interval of the narrow tubes large to some extent. However, the heat exchanger of FIG. 1 does not require such consideration and can be easily formed into a compact shape. In addition to the heat exchanger outside the tank described above, other heat exchangers such as a coil arranged to cool the polymerization solution and a jacket arranged to cool only the polymerization solution may be used. .
[0035]
Also in the production apparatus of FIG. 2, a plurality of introduction pipes 5, 6, and 7 are connected to the polymerization tank 1, and the polymerization tank includes a gas phase part 2 and a liquid phase part 3, and a stirrer installed in each phase. 22 and 23 and a drainage pipe 8.
[0036]
In the apparatus of FIG. 2, a heat exchanger (coil) 20 is installed in the gas phase portion 2 in the polymerization tank, instead of the gas condensing apparatus 10 outside the polymerization tank. This coil is arranged so as not to contact the liquid phase part (polymerization solution) 3 but only to the gas phase part 2. The coil 20 is supplied from a cooling medium supply pipe 25 provided with a valve, and condenses the gas above the polymerization solution by heat exchange with the cooling medium recovered from the recovery pipe 26. As the coil 20, it is preferable to install a coil having a heat exchange efficiency that removes all of the heat generated by the copolymerization. However, also in this apparatus, if necessary, a coil for directly cooling the polymerization solution may be supplementarily used.
[0037]
If the apparatus shown in FIG. 1 and FIG. 2 is used, the heat generated by the polymerization reaction can be efficiently removed by utilizing the condensation heat of ethylene and the heat of dissolution of other components such as vinyl acetate and methanol. For this reason, EVA can be manufactured stably for a long period of time.
[0038]
The gas existing above the polymerization solution itself condenses to become a condensed liquid, is returned to the liquid phase part of the polymerization tank, and is vaporized again. This cooling operation involving gas-liquid circulation can be carried out independently from the supply of the raw material, and therefore can be easily applied to a batch polymerization apparatus. In addition, in a continuous polymerization apparatus, the start, end, emergency stop, etc. of the operation can be stably performed. In addition, the adhesion of the polymer scale to the inner wall of the polymerization tank can be suppressed as compared with the case of relying on the direct cooling of the polymerization solution.
[0039]
The EVA obtained by the present invention may be converted to EVOH by a known saponification method using an alkali catalyst. EVA may be saponified by either a continuous method or a batch method. The saponification degree of EVOH is preferably 95 mol% or more, more preferably 99 mol% or more. If the degree of saponification is not sufficient, the gas barrier properties deteriorate. In order to improve interlayer adhesion and the like, the degree of saponification may be about 80 to 95 mol%. This EVOH can be used alone or blended with EVOH having a saponification degree of 99 mol% or more.
[0040]
The melt flow rate (MFR) of EVOH obtained as described above is generally in the range of 0.1 to 100 g / 10 minutes. Here, the MFR of EVOH refers to a value measured under a load of 2160 g at 190 ° C. based on JISK7210. However, when the melting point is around 190 ° C or over 190 ° C, it is measured under a load of 2160g and at a plurality of temperatures above the melting point. And a value extrapolated to 190 ° C.
[0041]
Various additives may be added to EVOH as necessary. Examples of such additives include antioxidants, plasticizers, heat stabilizers, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, and other thermoplastic resins. The EVOH resin thus obtained can be formed into various molded products such as films, sheets, pipes, tubes, bottles and the like by a known molding method.
[0042]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited to the following Example.
Example 1
Polymerization of ethylene-vinyl acetate copolymer (EVA) is continuously carried out using a polymerization tank with an internal capacity of 660 L in which a heat transfer area of 3 m ² and a vertical multi-tube heat exchanger with 8 tubes are arranged outside the tank. Went to. A pipe was arranged between the heat exchanger and the polymerization tank so that the gas in the polymerization tank and the condensate generated in the heat exchanger circulated. Raw materials such as vinyl acetate and ethylene were directly introduced into the polymerization tank without going through a heat exchanger. Moreover, the coil was not installed in the polymerization tank, and the jacket of the polymerization tank was set to the polymerization temperature. Thus, all the heat generated by the polymerization was removed by the heat exchanger.
[0043]
Using this apparatus, continuous polymerization was carried out at a polymerization pressure of 58 kg / cm ² , a polymerization temperature of 60 ° C., a vinyl acetate supply rate of 34 kg / hour, and a polymerization rate (vinyl acetate standard) of 35%. During the polymerization, the gas phase part in the tank and the liquid phase part were stirred by a stirrer in the apparatus. The inlet temperature of the brine passed through the multitubular heat exchanger was 4.5 ° C., and the outlet temperature was 11 ° C. The amount of brine was adjusted to maintain the above temperature, but was constant at 1100 L / hour during continuous polymerization. The temperature of the condensate returning from the heat exchanger to the polymerization tank was 20 ° C.
[0044]
In the above continuous polymerization, the calorific value calculated from the heat of polymerization of ethylene and vinyl acetate is about 5350 kcal / hour (about 22.4 MJ / hour), and the amount of heat removed by the heat exchanger is about 6500 kcal / hour (about 27.27). 2 MJ / hour). Thus, EVA (ethylene content: 42 mol%) was produced while removing heat generated by the polymerization with a heat exchanger outside the polymerization tank. During continuous operation for 20 days, heat removal did not become difficult and stable production could be realized. After the operation was stopped, the inside of the polymerization tank was inspected, and no polymer scale was deposited from the liquid phase part.
[0045]
(Example 2)
Continuous polymerization was carried out under the same conditions as in Example 1 except that instead of the vertical multitubular heat exchanger, a coil having a heat transfer area of 3 m ² provided in the gas phase portion in the polymerization tank was used. . The coil was placed so as not to contact the polymerization solution. The inlet temperature of the brine passing through the coil was 4.0 ° C., and the outlet temperature was 11 ° C. The amount of brine was adjusted to maintain the above temperature, but was constant at 1100 L / hour during continuous polymerization.
[0046]
In the above continuous polymerization, the calorific value calculated from the polymerization heat of ethylene and vinyl acetate is about 5350 kcal / hour (about 22.4 MJ / hour), and the heat removal amount by the heat exchanger is about 7000 kcal / hour (about 29.29). 3 MJ / hour). Thus, EVA was manufactured while removing heat generated by the polymerization by the coil disposed in the gas phase portion in the polymerization tank. During continuous operation for 20 days, heat removal did not become difficult and stable production could be realized. After the operation was stopped, the inside of the polymerization tank was inspected, and no polymer scale was deposited from the liquid phase part.
[0047]
(Comparative example)
Continuous polymerization was carried out under the same conditions as in the Examples using a polymerization tank with a coil (J & C) installed in the jacket and the liquid phase part without using a heat exchanger for cooling the gas phase part. The heat transfer area of this J & C was 10 m ² . By heat removal with the J & C temperature being 45 ° C., the copolymerization initially progressed, but the temperature of the J & C had to be lowered with the passage of time, eventually approaching the temperature of the refrigerant for J & C temperature control, Heat removal became difficult. Therefore, the same continuous polymerization as described above was performed with the heat transfer area of J & C being 15 m ² . However, the heat removal ability of J & C decreased with the passage of time. For this reason, continuous operation had to be interrupted in about 10 days. When the inside of the polymerization tank was inspected after the operation was stopped, a large amount of polymer scale adhered to the J & C surface.
[0048]
Furthermore, continuous polymerization was attempted by passing brine at the same temperature as in Example 1 through J & C. Although the heat removal capability improved, the heat removal capability decreased as the operation continued. For this reason, continuous operation had to be interrupted in about 7 days. When the inside of the polymerization tank was inspected after the operation was stopped, a large amount of polymer scale adhered to the J & C surface.
[0049]
【The invention's effect】
By applying the present invention, EVA can be stably produced over a long period of time without continuously supplying raw materials. The present invention can also be applied to batch production, and is excellent in stability at the start, end, or emergency stop even in continuous production.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a manufacturing apparatus of the present invention.
FIG. 2 is a cross-sectional view showing another embodiment of the production apparatus of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Polymerization tank 2 Gas phase part 3 Liquid phase part 5-8, 11, 13, 15-17, 25, 26 Conduit 10 Gas condenser 12 Heat exchanger 20 Coil 22,23 Stirrer

Claims (13)

A method for producing an ethylene-vinyl acetate copolymer in a polymerization solution containing ethylene, vinyl acetate, methanol and a polymerization initiator in a polymerization tank,
In order to cool the gas containing the vaporized vapor from the polymerization solution and condense at least a part of the gas, the gas is cooled to a temperature higher than the condensation temperature of ethylene alone to cool the gas. Producing at least a portion of the condensate;
Introducing the condensate into the polymerization solution and vaporizing at least one component of the condensate,
The steam comprises the at least one component;
A method for producing an ethylene-vinyl acetate copolymer, wherein a condensate is generated outside a polymerization tank.   The method for producing an ethylene-vinyl acetate copolymer according to claim 1, wherein at least one component vaporized from the condensate contains ethylene.   The method for producing an ethylene-vinyl acetate copolymer according to claim 2, wherein the at least one component vaporized from the condensate is other than ethylene and further contains at least one component of the polymerization solution.   The manufacturing method of the ethylene-vinyl acetate copolymer in any one of Claims 1-3 which hold | maintains the temperature of a polymerization solution at 30 to 80 degreeC.   The method for producing an ethylene-vinyl acetate copolymer according to any one of claims 1 to 4, wherein at least a part of the gas is cooled to -10 ° C or higher and 25 ° C or lower for condensation.   The method for producing an ethylene-vinyl acetate copolymer according to any one of claims 1 to 5, wherein the gas is stirred in a polymerization tank.   The ethylene-vinyl acetate according to claim 1, further comprising introducing a vinyl acetate-containing liquid into the polymerization solution, wherein the at least part of the condensate is generated before at least part of the gas contacts the liquid. A method for producing a copolymer.   The method for producing an ethylene-vinyl acetate copolymer according to any one of claims 1 to 6, wherein a condensate is produced even in a polymerization tank.   9. The ethylene-vinyl acetate according to claim 8, wherein at least a part of the gas is condensed on a surface of a cooler disposed in the polymerization tank so as to be in contact with a gas phase in the polymerization tank and not in contact with a polymerization solution. A method for producing a copolymer.   The method for producing an ethylene-vinyl acetate copolymer according to any one of claims 1 to 9, wherein all of the heat of polymerization generated in the polymerization solution is absorbed by vaporization of at least one component of the condensate. An ethylene-vinyl acetate copolymer produced by producing an ethylene-vinyl acetate copolymer by the method according to any one of claims 1 to 10, and saponifying the obtained ethylene-vinyl acetate copolymer. Production method. A polymerization tank for holding a polymerization solution containing ethylene, vinyl acetate, methanol and a polymerization initiator; and a cooler, wherein the cooler is in contact with vapor vaporized from the polymerization solution and does not come into contact with the polymerization solution. An apparatus for producing an ethylene-vinyl acetate copolymer disposed at a position,
The cooler is a heat exchanger that is connected to a cooling medium supply source and is not connected to a liquid supply source other than the cooling medium supply source;
A first conduit connecting the cooler and the polymerization tank so that a gas to be cooled is introduced from the polymerization tank into the cooler; and
A second conduit connecting the cooler and the polymerization vessel so that condensate is introduced from the cooler into the polymerization vessel;
A third conduit connecting the vinyl acetate source and the polymerization vessel without passing through the cooler;
In order to condense at least a part of the gas containing vapor evaporated from the polymerization solution, at least a part of the gas is cooled to a temperature higher than the condensation temperature of ethylene alone, and at least a part of the gas is condensed. An apparatus for producing an ethylene-vinyl acetate copolymer comprising means for producing a liquid.   The ethylene-vinyl acetate copolymer according to claim 12, further comprising a fourth conduit having one end connected to a cooler and discharging at least a part of the gas residue after condensation from the cooler. Manufacturing equipment.

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