Apparatus and method for handling easily polymerizable compound

Abstract: The present invention provides an apparatus for handling an easily polymerizable compound such as (meth)acrylic acid which comprises a tubular member that is furnished to a side wall of the apparatus and opened to the inside of the apparatus, specifically, for example, an apparatus and a method which effectively inhibit the polymerization of (meth)acrylic add in a distillation column for (meth)acrylic acid wherein the distillation column has such as an inlet or outlet of gas or liquid, a manhole, or a tube into which an instrument is inserted. The tubular member (e.g. an inlet or outlet, a manhole, a tube into which an instrument is inserted) is set so as to have a downward gradient (α) (e.g. in the range of 3° to 70°) toward the inside of the apparatus.

Description: BACKGROUND OF THE INVENTION A. TECHNICAL FIELD The present invention relates to a method for handling an easily polymerizable compound, specifically, relates to: a method which can effectively inhibit the polymerization of (meth)acrylic acid etc. when the (meth)acrylic acid etc. are handled by distillation etc.. B. BACKGROUND ART It is well-known that: (meth)acrylic acid etc. so easily polymerize that their polymerization often occurs in their production process, with the result that stopping the apparatus cannot be helped. For countermeasures against it, when (meth)acrylic acid etc. are produced, polymerization inhibitors such as hydroquinone, phenothiazine, and molecular-oxygen-containing gases are added, and further, the inner surface of the apparatus which is used is subjected to surface treatment for preventing solids such as polymers and deposits from attaching to the apparatus. However, even if the above countermeasures are made, the occurrence of the polymerization cannot sufficiently be inhibited, but is unavoidable. Therefore, in the case where tubes are clogged with the resultant polymers, the operation is stopped to remove them manually or chemically. As to an apparatus used, a tubular member that serves for example as an outlet or inlet through which substances are discharged from or charged into the inside of the apparatus or as a portion to which an instrument seat is fitted is usually furnished to a side wall of the apparatus, and the polymerization easily occurs particularly in this tubular member. Document US-A-4 369 097 discloses a method for distillation of an easily polymerizable liquid. The tubular members penetrating the side wall of and opening into the evaporator utilized according to this document have a downward gradient. SUMMARY OF THE INVENTION A. OBJECT OF THE INVENTION The present invention has been made under the above circumferences, and an object of the present invention is to provide a method which effectively inhibits the occurrence of the polymerization of easily polymerizable compounds such as (meth)acrylic acid when they are produced. B. DISCLOSURE OF THE INVENTION The present inventors diligently studied and, as a result, completed the present invention by finding that, when the easily polymerizable compounds such as (meth)acrylic acid are distilled, gases condense either in a tubular member that is furnished to a distillation column or on surfaces of instruments as inserted into this tubular member, and liquids as formed by this condensation reside unavoidably to cause the occurrence of the polymerization, and further that, for inhibiting this residence of the condensates in the tubular member or on the surfaces of the instruments, it is enough to proceed according to claim 1. The present invention thus relates to a method for handling an easily polymerizable compound according to claim 1. These and other objects and the advantages of the present invention will be more fully apparent from the following detailed disclosure. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional illustration of a tubular member as furnished to an apparatus as utilised according to the present invention (injection inlet not shown). Fig. 2 is a sectional illustration of another tubular member as furnished to an apparatus as utilised according to the present invention (injection inlet not shown). Fig. 3 shows sectional illustrations of three forms (a), (b), (c) of manholes. Fig. 4 shows sectional illustrations of two forms (a), (b) of instrument seats. Fig. 5 is a sectional illustration of a tubular member of which the out-of-apparatus portion is equipped with an inlet for injecting a molecular-oxygen-containing gas and/or a polymerization inhibitor. Fig. 6 is a sectional illustration of a tubular member as equipped with a temperature-raising or heating means (injection inlet not shown). Fig. 7 is a sectional illustration of a state where a polymerization-inhibitor-containing liquid is sprayed to a tubular member. Fig. 8 is a sectional illustration of a state where an opening of a tubular member to the inside of the apparatus is equipped with a cover (injection inlet not shown). Fig. 9 is a sectional illustration of a tubular member having a flange to the inside of the apparatus (injection inlet not shown). Fig. 10 is a sectional illustration of a conventional tubular member having a flange to the inside of the apparatus. DETAILED DESCRIPTION OF THE INVENTION The "easily polymerizable compound" as referred to in the present invention means a compound which easily polymerizes to form a polymer when being handled by such as its reaction or distillation, and typical examples thereof include (meth)acrylic acid and their esters such as methyl esters, ethyl esters, n-propyl esters, isopropyl esters, n-butyl esters, isobutyl esters, 2-hydroxyethyl esters, and N,N-dimethylaminoethyl esters. These are handled alone respectively or in forms of their mixtures or liquids containing them. The "apparatus" used according to the present invention implies those which are used to carry out reaction, distillation, extraction, absorption, storage, and/or heat-exchange, such as reactors, distillation columns, tanks and heat-exchangers. An explanation is given below about the tubular member that is furnished to a side wall of the apparatus according to the present invention and opened to the inside of the apparatus. Figs. 1, 2, 6, 8, 9 illustrate typical examples of the tubular member used according to the present invention. The tubular member 1 of Fig. 1 is a so-called inlet nozzle or outlet nozzle for introducing a gas, liquid, or solid, or a fluid that is their mixture phase, into the apparatus 2 or getting them out therefrom. This fluid may be either the easily polymerizable compound itself or another. The tubular member 1 is furnished to a side wall 21 of the apparatus 2 and opened to the inside of the apparatus 2 and, as shown in the figure, this tubular member is set so as to have a downward gradient (α) toward the inside of the apparatus 2. The tubular member 1 is set so as to have a downward gradient (α) toward the inside of the apparatus 2. If the tubular member is given such a gradient, a condensate 3 on an inner wall surface 11 of the tubular member 1 rapidly falls downward and is therefore prevented from residing. In such a respect, the gradient (α) is in the range of 3° to 70°, more preferably in the range of 5° to 60°. In the case where the gradient (α) is too little, the condensate does not rapidly fall, therefore the polymerization inhibition effect is not sufficiently obtained. Incidentally, in the case where the gradient (α) is too much, there are unfavorable problems about the connection to such as piping. In the present invention, all the tubular members that are furnished to a side wall of the apparatus do not need to be given the gradient (α), but it is preferable to give the gradient (α) to, particularly among the tubular members, those which is under an atmosphere under which a gas phase or a gas-liquid mixed phase easily condenses on the inner and outer wall surfaces of the in-apparatus portion and/or the inner wall surface of the out-of-apparatus portion. The tubular member 1 of Fig. 2 does not only have a portion 1a as projects out of the apparatus 2 like in the case shown in Fig. 1, but also has a portion 1b as inserted in the apparatus 2. Namely, this tubular member comprises an out-of-apparatus portion and an in-apparatus portion of the tubular member. Fig. 3 illustrates (a) a conventional manhole or handhole, (b) a pad type manhole or handhole, and (c) a manhole with an inner lid 22, respectively. Figs. 4(a) and (b) show insertion tubes or seats for an instrument 4 such as a pressure gauge or a liquid level indicator. As to the tubular member 1, it is preferable that a portion 1a as projects out of the apparatus 2 is shortened as much as possible, because the inner wall surface area of the out-of-apparatus portion of the tubular member is thereby reduced to prevent the condensate from residing on the inner wall surface, with the result that the polymerization can effectively be inhibited. According to the present invention, it is possible to add a molecular-oxygen-containing gas and/or a polymerization inhibitor, which are conventionally used as polymerization inhibitors, into the out-of-apparatus portion 1a of the tubular member for the purpose of inhibiting the polymerization inside the out-of-apparatus portion 1a. Fig. 5 explicitly illustrates that the out-of-apparatus portion 1a is equipped with an inlet 12 for injecting a molecular-oxygen-containing gas and/or a polymerization inhibitor. For example, in the case where, as shown in Fig. 5, an instrument 4 such as a diaphragm type liquid level indicator is inserted into the tubular member 1 of Fig. 1, a small clearance is made between the inner wall surface of the tubular member 1 and the outer wall surface of the instrument 4, and the liquid tends to reside in this clearance, therefore it is preferable to inhibit the polymerization by injecting the molecular-oxygen-containing gas and/or the polymerization inhibitor from the inlet 12 as shown in Fig. 5. In Fig. 6, the out-of-apparatus portion 1a of the tubular member 1 is equipped with a temperature-raising or heating means 13 such as a steam jacket. If the out-of-apparatus portion 1a of the tubular member 1 is temperature-raised or heated, then the gas is prevented from condensing on the inner wall surface of the tubular member, therefore not only the residence of the condensate, but also the occurrence of the polymerization can more effectively be inhibited. It is not only permissible that the temperature-raising or heating means 13 is provided to the whole of the out-of-apparatus portion 1a, but it is also permissible that the temperature-raising or heating means 13 is provided to only a part of the out-of-apparatus portion 1a. Examples of the temperature-raising or heating means 13 include an electric or steam heater tracing as well as a jacket through the inside of which a heating medium can be circulated. As to the tubular member 1 of Fig. 2, the condensate tends to reside on the periphery of a portion where the in-apparatus portion 1b of the tubular member is in contact with an inner wall surface 21 of the apparatus, therefore it is preferable that the whole peripheral portion is welded and that the resultant welded portion 14 is surface-smoothed. This smoothing is preferably to such an extent that beads can disappear from the surface of the weld, specifically, Rmax according to JIS B0601 (-1994) can be 12.5S or lower. Also in the case of Fig. 4(b) where a thermometer seat is inserted in the tubular member of Fig. 2, it is preferable that, as is shown in this figure, the whole peripheral portion where an instrument seat which is a tubular member 1 is in contact with the inner wall surface 21 of the apparatus is welded and that the resultant welded portion 14 is surface-smoothed. It is also effective that a means 5 of spraying a polymerization-inhibitor-containing liquid to an opening 15 of the tubular member 1 to the inside of the apparatus is equipped (Fig. 7), or that the opening 15 of the tubular member 1 to the inside of the apparatus is equipped with a cover 6 to lessen the influence of the condensate falling on the inside wall of the apparatus (Fig. 8). Fig. 9 illustrates a tubular member 1 having a flange-bonded portion 16 on the in-apparatus portion 1b. As to a conventional tubular member 1 of Fig. 10, a gasket 17 which is fitted to a flange-bonded portion 16 does not have the same diameter as that of the flange, so a concave (clearance) portion c is present. Therefore, the condensate tends to reside in this clearance portion c to form a polymer. In contrast, in the present invention, as is shown in Fig. 9, a gasket 17 having the same diameter as that of the flange is used to make substantially no concave (clearance) portion c. In this way, in the present invention, it is preferable that the in-apparatus portion 1b of the tubular member 1 is substantially free of concave (concave-free). The place where the tubular member according to the present invention is furnished is not especially limited, but can be selected according to its use purpose. Next, an explanation is made about the method for handling an easily polymerizable compound which involves the use of the above apparatus according to the present invention. This handling method is carried out according to claim 1. Effects and Advantages of the Invention: The method according to the present invention can effectively prevent the residence of the condensate and therefore can effectively inhibit the polymerization of the easily polymerizable compound. Thus, the easily polymerizable compound can be produced in a high yield. Especially, the easily polymerizable compound can be handled stably for a long period of time. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention is more specifically illustrated by the following examples of some preferred embodiments in comparison with comparative examples not according to the invention. However, the invention is not limited to the below-mentioned examples. EXAMPLE 1 A liquid containing an acrylic ester was purified with a stainless-steel-made (SUS316) rectifying apparatus as equipped with a distillation column, a condenser, and a reboiler. The below-mentioned tubular members were furnished to the distillation column, the condenser, and the reboiler so as to have their respective gradients below. Incidentally, as to the manhole or handhole, a pad type was used. Distillation column: Seats for instruments (thermometer, pressure gauge, liquid level indicator): 3° Pressure-equalizing vent, pressure measurement seat (column top, column bottom): 6° Manhole (column top, column bottom): 5° Condenser: Gas outlet: 10° Pressure measurement seat: 60° Reboiler: Manhole or handhole: 6° The feed composition of the acrylic ester was 2-ethylhexyl acrylate 60 weight %, 2-ethylhexanol 32 weight %, and acrylic acid 7 weight %. The apparatus was operated continuously for 3 months under conditions where column top absolute pressure = 30 mmHg (= about 4.00 kPa), column top temperature = 98 °C, column bottom absolute pressure = 65 mmHg (= about 8.67 kPa), column bottom temperature = 135 °C, reflux ratio = 0.9. After the operation had been stopped, the inside of the apparatus was inspected. As a result, the attachment of the resultant polymer was not found on any tubular member. COMPARATIVE EXAMPLE 1 The liquid containing the acrylic ester was distilled in the same way as of Example 1 except that all the tubular members were furnished horizontally to the same apparatus as that used in Example 1. The apparatus was operated continuously for 3 months. After the operation had been stopped, the inside of the apparatus was inspected. As a result, the attachment of the resultant polymer was found on some of the tubular members. In addition, the manhole which was set on the column bottom was entirely clogged with the resultant polymer, and therefore could not manually be opened. Various details of the invention may be changed without departing from its spirit not its scope. Furthermore, the foregoing description of the preferred embodiments according to the present invention is provided for the purpose of illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

Claims: A method for inhibiting polymerisation of an easily polymerizable compound during handling thereof, which involves during handling of the easily polymerizable compound the use of an apparatus comprising: an interior space with a vertical side wall (21), and a tubular member (1) furnished to said side wall (21) of the interior space and having an opening towards the interior space, wherein said tubular member (1) is set so as to have a downward gradient (α) in the range of 3° to 70° relative to the horizontal toward the inside of the interior space, wherein the whole peripheral portion where an interior space portion (1b) of the tubular member (1) is in contact with an inner wall surface (21) of the interior space is welded and the resultant welded portion (14) is surface-smoothed, wherein an out-of-interior space portion (1a) of the tubular member (1) is equipped with an inlet (12) adapted to allow injecting a molecular-oxygen-containing gas and/or a polymerization inhibitor into the interior of the tubular member (1), and wherein the handling of the easily polymerizable compound comprises reaction, distillation, extraction, absorption, storage, and/or heat-exchange in connection with producing the easily polymerizable compound. The method according to claim 1, wherein the gradient (α) is in the range of 5° to 60° relative to the horizontal. The method according to claim 1 or 2, wherein an out-of-interior space portion (1a) of the tubular member (1) is shortened as much as possible. The method according to anyone of claims 1 to 3, wherein an out-of-interior space portion (1a) of the tubular member (1) is equipped with a temperature-raising or heating The method according to claim 1-4, wherein the resultant welded portion (14) is surface-smoothed so that Rmax according to JIS B0601(-1994) is 12.5S or lower. The method according to anyone of claims 1 to 5, which further comprises a means (5) for spraying a polymerization-inhibitorcontaining liquid from the inside of the interior space towards the opening (15) of the tubular member (1). The method according to anyone of claims 1 to 6, wherein the opening of the tubular member (1) towards the inside of the interior space is equipped with a cover (6). The method according to anyone of claims 1 to 7, wherein an interior space portion (1b) of the tubular member (1) is substantially free of concave portions or clearances. The method according to anyone of claims 1 to 8, wherein said apparatus is a reactor, destillation column, tank, or heat-exchanger for use in connection with producing the easily polymerizable compound.

Inventors: MATSUMOTO YUKIHIRO, NISHIMURA TAKESHI, MATSUMOTO, YUKIHIRO, NISHIMURA, TAKESHI
Applicants: NIPPON CATALYTIC CHEM IND, NIPPON SHOKUBAI CO., LTD.
Application year: 2000
Main classification: B01D3
IPC codes: B01D3, C07C57, C07C51, B01J19, C07C67, B01J4, C07B63, C07C69, C08F2