JPS61209002A - Recovery of monomer - Google Patents

Abstract

PURPOSE:To simply and economically recover a monomer from a polymer suspension or dispersion containing an org. polymer up to 50wt%, by utilizing a column packed with a packing material having a specific structure in a definite range of a volume/space ratio. CONSTITUTION:A polymer suspension or dispersion containing an org. polymer up to 50wt% is flowed downwardly through a column packed with a packing material, which is a perforated hollow structure capable of being received in a sphere with a diameter of 20-300mm, so as to set the volume/space ratio thereof to 50% or more on the basis of the total packing volume. In order not only to prevent the sedimentation of the polymer by holding the transmitted solution to a sufficient mobile state but also to move the unreated monomer in said solution to a gaseous phase by utilizing gas-liquid equilibrium relation before recovering the same, steam is flowed upwardly through the column so as to be countercurrently contacted with said solution.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention allows a polymer suspension or emulsion to flow down into a packed column packed with a packing material, and countercurrently contacts the column with water vapor, thereby producing monomers. Regarding how to recover.

PRIOR ART In general, in the homopolymer production reaction of acrylonitrile by suspension polymerization or emulsion polymerization method, or the production reaction of copolymers of acrylonitrile and various copolymers, unreacted monomers are suspended. Or it is recovered from the emulsion. These polymer products or their processed products are widely used in daily life as raw materials for acrylic fibers or acrylic resins, such as clothing and plastics.

Techniques for recovering monomer bars from such suspensions or emulsions include (4) multi-stage reactions or patch reactions to increase the reaction yield and reduce the content of unreacted monomers; (B) A method in which unreacted monomers are recovered using an evaporator type method under vacuum; (C) A method in which unreacted monomers are recovered under vacuum using a tray distillation method using trays made of perforated plates. There are known methods for collecting such substances (Japanese Patent Application Laid-Open No. 122902/1983).

Problems to be Solved by the Invention However, the techniques (4), (B), and (Q) each have their own problems. In other words, the technique (4) has a wide molecular weight distribution of the polymer, which is particularly difficult for fibers. As for the products for which it is used, it causes defects in quality.Although the technology of (B) is simple, it causes the current uneconomical situation.The technology of (C) Particularly in the case of suspensions containing polymer particles with large sedimentation properties, there are areas of poor fluidity in some portions of the trays, and the polymer particles may settle at these locations, causing blockages and other problems. There was a problem.

In addition to the above methods, methods have also been considered in which a packed column is filled with a packing material, and these methods also prevent precipitation of polymer particles and repolymerization reactions in the packing layer caused by unreacted monomers. There has been a problem in that people hesitate to use it due to concerns about scaling or occlusion. In consideration of the problems of the prior art, the present invention has been developed to easily and easily recover unreacted monomers remaining in the reaction solution without making the molecular weight distribution wider than necessary for product quality. , have found a method that does not cause other sedimentation problems in the recovery equipment.

Means to solve the problem, the present invention consists of flowing a polymer suspension or emulsion containing at most 50 percent organic polymer into a packed column packed with packing material and directing water vapor in the opposite direction. In a method for recovering monomers by contacting with a flow,
The portion of the total volume of the packing that is not occupied by the solid portion (referred to as the volumetric porosity of the packing) is 50% or more,
In addition, the packing, which is a perforated hollow structure that can fit into a sphere with a diameter of 20 to 300 mm, is placed in a packed column such that the volumetric void ratio of the packing to the total packing volume is 50% or more. This is achieved by a monomer recovery method characterized by filling a plurality of monomers.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a simple and economical method for recovering unreacted monomer from polymer suspensions or emulsions containing up to 10% by weight of polymer. The liquid is caused to flow downward through a column filled with a packing, which is a perforated hollow structure that can fit into a sphere with a diameter of zθ ~ 300 mm, and the liquid is given a sufficient degree of movement. Ninth, to maintain the state and prevent polymer deposition, and to move unreacted monomers in the liquid into the gas phase by utilizing the gas-liquid equilibrium relationship (hereinafter referred to as rectification), For subsequent recovery, a method is used in which water vapor is directed upward from the bottom of the column in countercurrent flow with the liquid.

It is natural from the basic characteristics of distillation that it is desirable for the packing to have high rectifying performance and low pressure drop as much as possible, but furthermore, the larger the volumetric porosity of the packed packing, the more the polymer liquid It is preferable to prevent sedimentation, and a volumetric void ratio of 5 ofb or more is required to ensure sufficient motion of the polymerization solution. The smaller the packing size, the greater the pressure loss, and conversely, the larger the packing size, the lower the rectification performance.
It is necessary that the structure be a perforated hollow structure that can fit into a 0 mm sphere. The shape of the filling is 20 to 300 mm in diameter.
It can have any shape as long as it can fit inside a millimeter sphere, but commonly used ones include hollow cylinders with the top and bottom sides cut out and multiple holes drilled on the sides; Hollow spheres with multiple holes punched on the surface, and hollow cubes with multiple holes punched on the sides are also used.

Further, the volumetric porosity of the packing with respect to the total volume of the packing packed in the packed column needs to be 50% or more. If it is less than 50%, it becomes impossible to ensure sufficient motion of the polymerization solution as described above.

The filling height of the packing is determined by the degree of monomer recovery, but if it is stacked too high, the pressure loss will be large and the utility of the heat source will be uneconomical.It also depends on the performance of the packing, but in general The filling height is preferably 1 to 10 meters, more preferably 2 to 5 meters.
A meter or so is good. It goes without saying that high performance is desirable in terms of rectification performance of the packing, but it is currently preferable that the filling height per theoretical plate be 100 to 400 mm. More preferably, it is economical to have a filling height of 1000 mlJ meters or more per theoretical plate.

A schematic diagram of one example of the apparatus used to carry out the method of the invention is shown in FIG. In FIG. 1, a suspension or emulsion flowing down from a polymerization tank flows through a pump inlet pipe 1, a pump 2, a feed pipe 3, and a distillation recovery vessel 4. There is a packed bed 5 filled with fillers inside the distillation recovery vessel 4, in which unreacted monomers move to the gas phase and pass through the top steam pipe 7 to the steam condenser IO. The suspension or emulsion from which the reaction monomer has been removed is transferred to tank 9 via bottom pipe 8t.

Further, the heat source is supplied through the heat source steam piping 6 by direct or indirect heat transfer. 11 is a vacuum generator. A more detailed explanation will be given below based on examples.

EXAMPLE In an apparatus such as the flow shown in FIG. Tests were conducted on liquids. The conditions and results are shown in Table 1. The suspension was supplied at a temperature of about 50°C, and steam was supplied as a heat source in an amount of 1/10 of the weight of the suspension. I did an experiment. In addition, in the experimental section 5, a thick Raschig ring was used. The results also show that the concentration of acrylonitrile in the tank 9 was measured, and the pressure drop was measured as the pressure difference between the upper and lower parts of the packed layer 5. As a result, the example of the present invention had a better pressure than the comparative example. 0 Effects of the Invention According to the method of the present invention, there is no deposition of polymer particles in the packed bed, no scaling or blockage from the repolymerization reaction of unreacted monomers, and The pressure loss due to the packed bed can be reduced, and the monomer can be recovered more economically than conventional methods, which is highly effective.

Margin below

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of an apparatus used to carry out the method of the present invention. 1... Pump inlet piping 2... Pump 3... Feed piping 4... Distillation recovery device 5... Packed bed 6... Heat source steam piping 7... Tower steam piping 8...・Bottom piping 9...Tank 10...Steam condenser 11...Vacuum generator Patent applicant Asahi Kasei Corporation Figure 1

Claims (1)

[Claims] (1) A polymer suspension or emulsion containing at most 50 percent organic polymer is allowed to flow down into a packed column, and the monomers are removed by countercurrent contact with water vapor in the opposite direction. In the recovery method, the portion that is not occupied by the solid portion with respect to the total volume of the packing (referred to as the volumetric porosity of the packing) is 50% or more, and the diameter is 20%.
A plurality of packings that are perforated hollow structures that can fit into a sphere of ~300 mm are packed in a packed column such that the volumetric porosity of the packings is 50% or more with respect to the total filling volume of the packings. A method for recovering a monomer characterized by