Preparation of vinyl chloride polymer

Details Preparation of vinyl chloride polymer Preparation of vinyl chloride polymer

2000-08-11

2001-08-14

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S062000, C526S344200

Reexamination Certificate

active

06274690

ABSTRACT:

This invention relates to a process for preparing a vinyl chloride polymer in a reactor and more particularly, to a process for preparing a vinyl chloride polymer of quality with minimal fisheyes batchwise in a closed large size reactor.
BACKGROUND OF THE INVENTION
In the prior art process for preparing a vinyl chloride polymer batchwise in a reactor, a polymer slurry is discharged from the reactor at the end of polymerization. Since a polymer scale has built up on the reactor inner wall, the reactor must then be cleaned for subsequent reaction. The following cleaning steps were used in the prior art.
(1) After the reactor is opened by disconnecting a manhole lid, pressurized water (water pressure 150 kg/cm
2
G=14.8 MPa·Gauge or higher) is injected through the manhole to wash away the polymer scale.
(2) After the reactor is opened by disconnecting a manhole lid, the worker enters the reactor and manually removes the polymer scale.
These cleaning steps (1) and (2) are performed while keeping the reactor open. This allows the unreacted monomer left in the reactor, though in a minor amount, to escape to the ambient air, causing air pollution. At the end of cleaning, the manhole must be closed again. A substantial labor and time are needed for opening and closing the manhole. The cleaning step deprives the process of continuity, leading to a lower productivity.
To solve these problems, the following cleaning steps were proposed.
(3) A nozzle is fixedly attached to the reactor at its top whereby pressurized water (water pressure 150 kg/cm
2
G =14.8 MPa·Gauge or higher) is injected from the nozzle into the reactor for cleaning while keeping the reactor closed without substantial opening.
(4) A special solvent is poured into the reactor for cleaning while keeping the reactor closed without substantial opening.
Currently, large size polymerization reactors having an internal volume of greater than about 40 m
3
are often used for the purpose of improving productivity. When the cleaning steps (3) and (4) are applied to such large size reactors, it is difficult from the apparatus and economical standpoints to fully clean the large size reactor in a closed state without substantially opening it. It is also difficult to solve the quality problem of vinyl chloride polymer products containing many fisheyes.
SUMMARY OF THE INVENTION
An object of the invention is to provide a novel and improved process for preparing a vinyl chloride polymer of quality with minimal fisheyes batchwise in a closed large size reactor, the process including washing the reactor with water without substantially opening the reactor.
It has been found that by providing a reactor at its top with a cylinder-guided lift type washer assembly having a vertically movable nozzle and injecting water into the reactor through the nozzle for cleaning the reactor, even a large size reactor having an internal volume of at least 40 m
3
can be effectively cleaned in a closed state, ensuring that vinyl chloride polymers of quality with least fisheyes are produced.
In one embodiment, the invention provides a process for preparing a vinyl chloride polymer by charging a reactor with a vinyl chloride monomer alone or a mixture of a vinyl chloride monomer and a monomer copolymerizable therewith, effecting polymerization to form a polymer, removing a slurry of the polymer from the reactor, and washing the interior of the reactor with water, and repeating a series of the foregoing steps. The reactor has an internal volume of at least 40 m
3
. A cylinder-guided lift type washer assembly having a nozzle is secured to the reactor at its top in a sealed manner such that the nozzle can be moved downward and upward in the reactor. The washing step is effected by feeding water to the nozzle through the assembly for injecting water from the nozzle into the reactor. Preferably, the nozzle is moved downward and then upward over a stoke of at least 1 meter. The reactor is preferably kept under an internal pressure of 0 to 7 kg/cm
2
G (0.101 to 0.788 MPa·Gauge) during the washing step. According to the invention, the large size reactor can be washed with water in the closed state, eliminating the potential of air pollution and significantly improving workability and productivity. The cylinder-guided lift type washer assembly having a vertically movable nozzle exerts an excellent cleaning effect. As a consequence, vinyl chloride polymers of quality with least fisheyes are effectively produced batchwise.


REFERENCES:
patent: 4374966 (1983-02-01), Fischer et al.

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