Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Organic polymerization
Patent
1997-04-24
2000-10-31
McMahon, Timothy
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Organic polymerization
422134, 366 83, 528137, 528138, 528230, 528250, C08F 612
Patent
active
061398047
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/JP95/02161 filed Oct. 20, 1995.
TECHNICAL FIELD
The present invention relates to a reactor used for production of a polyoxymethylene widely used as an engineering plastic in electrical parts, automobile parts, mechanical parts, etc., as well as to a process for producing a polyoxymethylene using the reactor. More particularly, the present invention relates to an improved process for producing a powdery polyoxymethylene continuously and efficiently using, as a main starting material, trioxane or a mixture of trioxane and a compound reactive therewith.
BACKGROUND ART
Polyoxymethylenes have been produced by a method of subjecting trioxane to bulk homopolymerization or subjecting trioxane with ethylene oxide or trioxane with a cyclic formal such as dioxolane, trioxepane or the like, to bulk copolymerization in the presence of a cationically active catalyst.
In conventional polyoxymethylene production, a reactor of two shafts self-cleaning type, such as disclosed in JP-A-51-84890 has been used mainly. In this reactor of two shafts self-cleaning type, the discharging port for reaction mixture is provided at the bottom of the reactor and consequently the polyoxymethylene formed as an intended product is recovered downward. This reactor, however, has had a problem in that the short residence time of reaction mixture gives a low conversion. Hence, a number of proposals have been made in order to make the residence time longer and the conversion higher.
For example, JP-A-56-59824 proposes a process wherein, in each two adjacent paddles fixed to a rotary shaft of a reactor, the angle of one (back) paddle is advanced by a given amount from the angle of the other (precedent) paddle to control the transfer speed of reaction mixture to increase the filling ratio of the reaction mixture and prolong the residence time of the reaction mixture. Also, JP-A-61-238812 proposes a process wherein a reactor is lifted at the discharging port side so that the reactor is tilted as a whole by 1-10.degree. from the horizontal state to prolong the residence time of the reaction mixture.
However, in the above process wherein the angle of one paddle is advanced from the angle of the other paddle to prolong the residence time, when the filling ratio is too high, the torque required for stirring increases sharply and surpasses the endurance limit of reactor (torque-out), making the continued reactor operation impossible. In the above process wherein a reactor is tilted slightly as a whole, both a very high conversion and very stable operation can be achieved; however, L/D (L: length of reactor, D: inside diameter of reactor) must be large in order to make sufficiently long the residence time, which requires a large reactor not suitable for industrial use.
The object of the present invention is to provide a process for producing a polyoxymethylene, wherein the residence time of reaction mixture in a reactor is long and thereby the conversion of trioxane can be increased.
DISCLOSURE OF THE INVENTION
The present inventors made a study in order to solve the above-mentioned problems of the prior art and, as a result, found out that the above object can be achieved by improving the structure of discharging port, discharging means for reaction mixture, of a reactor. The finding has led to the completion of the present invention.
The present invention provides a process for producing a polyoxymethylene using a reactor comprising: reaction which shafts are each provided with a plurality of paddles and rotated in the same direction, formed by the front ends of the individual paddles when the paddles are rotated, accommodating the two rotary shafts and provided with a heating and cooling jacket, trioxane and a compound reactive therewith, which is provided at one end of the case, and polyoxymethylene formed, which is provided at the other end of the case, said discharging means being a discharging port having a weir, which process comprises introducing trioxane or a mixture of trioxane and a compound reactive
REFERENCES:
patent: 4105637 (1978-08-01), Semanchik et al.
patent: 4343929 (1982-08-01), Sugio et al.
patent: 4625001 (1986-11-01), Tsubakimoto et al.
patent: 4769427 (1988-09-01), Nowakowsky et al.
Matumoto Hiromasa
Tanigawa Yukio
Asahi Kasei Kogyo Kabushiki Kaisha
McMahon Timothy
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