CS208316B1 - A method for continuously producing polyphenylene oxide - Google Patents

Abstract

The invention relates to the continuous production of polyphenylene oxide by oxidative polycondensation of phenols in the presence of catalytic metal complexes with amines. In a cascade of at least three stirred reactors with different mixing regimes, mixing in the first members of the cascade ensures optimal aeration of the reaction mixture, in the middle members of the cascade the precipitation of polymer particles from a mixture of polar and non-polar solvents in which polyphenylene oxide is only partially soluble, and in the last members of the cascade the growth of polymer particles.

Description

The invention relates to the continuous production of polyphenylene oxide by oxidative polycondensation of phenols in the presence of catalytic metals with amines in a cascade of stirred reactors.

Prior art processes for the continuous production of polyphenylene oxide in a cascade of stirred reactors lead by oxidative polycondensation as a homogeneous reaction. The reaction medium is usually a non-polar solvent such as benzene or a solvent mixture containing a high performance polyphenylene oxide solvent.

The resulting polyphenylene oxide is kept in solution throughout the reaction and is only separated after passing through a cascade of reactors in special equipment. The disadvantage of these methods is the impossibility to influence the size and properties of the polymer particles, which have a large influence on the mechanical and processing properties of the plastic.

Also known is the process for the continuous production of polyphenylene oxide by heterogeneous polycondensation in piston flow columns described in U.S. Pat. Certificate No. 192 278.

Two feeds, one with a monomer and the other with a catalyst, are fed to the head of the column absorber with a large trap volume and about 50 theoretical plates, and an oxygen stream is fed countercurrently to the column. A disadvantage of this process compared to the cascade of stirred reactors is the low specific column performance.

Now the disadvantages have been eliminated. The present invention relates to a process for the continuous production of polyphenylene oxide by oxidative polycondensation of phenols in the presence of catalytic metal complexes with amines in a cascade of stirred reactors, in which the reaction medium is a mixture of polar and non-polar solvents. Agitation ensures agitation in the first cascade members by optimizing the aeration of the reaction mixture, in the middle cascade members, the dropping of polymer particles, and in the last cascade members by their growth.

The present invention provides a continuous process of oxidative polycondensation of 2.6 xylenol on a cascade of mixed oxygen oxygenated aeration reactors in a polymerization medium consisting of a binary mixture of polar and non-polar solvents in the presence of a catalyst system. The monomer (2,6-xylenol) solution and the catalyst components are fed to the tempered cascade of the reactors inlet separately so that the mean residence time of the reactive batch in the cascade corresponds to the desired molecular weight.

In practical terms, it is important that in the polymerization medium of this type, the reactive system has a characteristic pre-precipitation point, that is, a point determined by the molecular weight of the polymer from which the polymer falls out of solution in the form of a solid phase suspension. The numerical value of the pre-precipitation point is mainly influenced by the polarity of the polymerization medium, the original conoentraoi monomer and the temperature. This has the consequence that in the first part of the stirred reactor cascade, the reaction in the two-component liquid-gas region takes place in a high kinetic reaction rate, i.e. at high specific oxygen consumption and generation

208 316 reaction heat. After the precipitation point, it is a three-component system where the precipitated solid phase of the product is already present. The specific kinetic parameters decrease substantially (reaction rate, generation of reaction heat and oxygen consumption), but there are risks associated with the degree of product dispersity and deposits on the internal surfaces of the reactors and connecting pipes.

From the last cascade solution, the polyphenylene oxide slurry is discharged to a mixing member connected to a dosing pump for dosing the stop-reagent and further to a stirred tank upstream of the product and mother liquor separator (centrifuge or continuous overpressure or vacuum filter).

A stop agent is a chemical agent that inactivates the catalyst system and thereby stops the polymerization reaction.

Against an analogous batch process of polyphenylene oxide synthesis on a stirred batch reactor, the continuous process on the cascade of stirred reactors of the invention has these essential advantages; '

1) The productivity of the reactor unit increases substantially. This effect is achieved by eliminating the so-called manipulation times of the batch reactor (emptying, filling, batch tempering, purging and flushing), which are a waste time for the reactor utilization. and the polymer obtained is of the same quality as the one prepared by the batch process according to the conventional polyphenylene oxide evaluation criteria.

In a continuous cascade polymerization arrangement, there is no observable competitive reaction to diphenoquinone,

3) Continuous cascade polymerization allows the specialization of individual members (built-in, heat exchange surfaces, mixers) and the specialization of each member.

In a batch process, each reactor must have universal properties, covering the full range of operating conditions from start to consolation. In contrast to the batch process, each reactor operates in a cascade in a stationary mode and with a constant feed.

4) the issue of temperature regulation is simplified, ie isothermal regime is adhered to, and the same applies to the chemical engineering solution of the heat exchange problem.

5) For operational capacities, it is possible to anticipate some savings of labor force xx and operation of the equipment in a continual process.

6) Solution of continualization of the main technological node of polyphenylene oxide synthesis technology - polymerization enables to continualize the whole technology as a whole.

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The polyphenylene oxide reactor cascade of the invention may consist of 4 to 6 members, preferably of the same size, and the member in which the polyphenylene oxide precipitates may and preferably be doubled. Indeed, it has been found experimentally that this member has the greatest build-up of deposits and that the parallel reserve eliminates the need for cascade downtime due to solvent cleaning. This purification can be limited to the reserve member during polymerization. The oxygen supply to the cascade members is preferably parallel, and the entire cascade operates at a slight oxygen overpressure, the overflow from the member to the next member by gravity. For reactors in a cascade in which the polyphenylene oxide slurry (second part in the downstream direction), the overflow connection tubes are preferably equipped with a meohanioclean cleaning device enabling the overflows to be cleaned while the polymerization is running. All members are equipped with a small venting device in the upper lid to prevent the accumulation of inert (nitrogen) in the free space above the surface.

It is advantageous to use jacketed cylindrical vaulted bottom reactors equipped with bottom-drive stirrers for safety reasons. Intermediate jacket spaces of the reactors are connected to regulated tempering circuits. For the first members operating in a stationary state without the excluded polymer slurry in the high reaction rate mode, high-speed agitators with an axial outlet flow directed to the bottom of the vessel, such as propeller with constant helix or six- or possibly three-blade propellers with straight oblique blades, are preferred. cases with stops on the internal walls of the reactors. Indeed, at this stage of the reaction, the most important is to ensure heat and mass transfer (oxygen dispersion) and to homogenize the temperature and concentration according to the charge.

In a station where the polyphenylene oxide precipitates in the stationary mode, the criteria for mixing are the shear stress limitation criteria of the agitator to obtain a well filterable suspension, to keep the polymer suspension in the fluid, and to prevent deposits on the internal surfaces of the device.

In the last members of the cascade, the mixing task concentrates mainly on keeping the suspension suspended. For the steady-state members filled with the polyphenylene oxide slurry, the above-mentioned high-speed agitators with an axial outlet flow directed to the bottom of the vessel, but without hints at the internal walls of the reactors, are most preferred.

The reactor cascade should be connected to a system of at least four metering pumps (with the necessary reserve), preferably to a multi-component metering machine. To the first member of the cascade are separately led from the tanks:

a) a stream of a solution of monomer (2,6-xylenol) in the polymerization medium

b) a stream of catalyst components in a polymerization medium

o) fault margin

208 316, it is naturally possible to lead the individual components separately to two or more component catalyst systems.

It will be dosed into the outlet piping section behind the last cascade member

d) the stop reagent stream, optionally diluted with polymerization medium, streams a) b) c) d) must satisfy both the molar ratios of the active substances to the polymerization regulation and the resulting concentration of these components in the reaction mixture, or the composition of the polymerization medium must be maintained. The ratio of the stationary system containment (with the mixing mode set in each member) to the total feed rate (streams a) b)) gives a mean residence time which, together with the concentration ratios of the active reaction components and the reaction temperature, determines the resulting molecular weight of polyphenylene oxide. the desired molecular weight of the product is in the range of 50,000 to 60,000.

The following examples illustrate the invention.

Example 1

Solutions of 2,6-xylenol, cupric chloride dihydrate and morpholine are metered in to a five-member stirred reactor cascade that complies with the principles outlined in the general section when aerated with pure oxygen at 35 ° C using the polymerization medium of the azeotropic ethanol-benzene mixture to give a final concentration in The reaction mixture was 100 g of 2,6-xylenol (1,1,5 S cupric chloride dihydrate), 20 g of morpholine (l) and 2,035 g of diethanolamine (i) as a stop agent. feed rate to the exit of the reactor cascade; and a feed rate such that the mean residence time was 35 minutes. We obtain a polyphenylene oxide product having a molecular weight of 50,000 with a yield of between 91 and 93% (depending on the purity of the monomer).

Example 2

Reaction coolant solutions are fed to a six-member stirred reactor cascade at 50 ° C under aeration with pure oxygen using the ethanol-benzene azeotrope to produce a final concentration of 100 g of 2,6-xylenol / l, 0.85 g copper chloride dihydrate, 20 g morpholine / l, 0.658 g acetic acid / l (stop reagent dosed to the 6-member outlet) and dosing rate such that the mean residence time was 35 minutes. A product with a molecular weight of 60,000 is obtained with a yield of between 92 and 94%.

Claims (1)

Object of the invention Process for the continuous production of polyphenylene oxide by oxidative polycondensation of phenols in the presence of catalytic metal complexes with amines in a cascade of mixed reactors characterized in that the reaction medium is a mixture of polar and non-polar solvents in which polyphenylene oxide is sparingly soluble. mixing in the first cascade members optimal aeration of the reaction mixture, in the middle cascade members the polymer particle loss and in the last cascade members their growth.