Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Removing and recycling removed material from an ongoing...
Reexamination Certificate
2003-02-24
2004-11-30
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Removing and recycling removed material from an ongoing...
C526S067000, C526S344000, C526S344200, C526S345000
Reexamination Certificate
active
06825288
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a vinyl chloride-based polymer using suspension polymerization, in which the heat removal efficiency can be improved without affecting the quality of the product polymer.
2. Description of the Prior Art
In the production of vinyl chloride-based polymers, large scale polymerization vessels and reduced polymerization times are used to improve the productivity. In one technique, a method is employed in which heat removal is performed using both a polymerization vessel jacket and a reflux condenser, in order to increase the reaction heat removal capability per unit of time. Particularly in cases in which the maximum value of the total heat removed per unit of time exceeds 10,000 MJ/hr, it is typical for a coolant which has been cooled using a cooling apparatus such as a refrigeration device to be used as a cooling medium and passed through the polymerization vessel jacket, and for a reflux condenser to also be used. In these types of methods requiring the use of a coolant, from an economic viewpoint it is desirable to reduce the proportion of heat removal performed by the jacket, in order to economize on the power costs associated with operating the refrigeration device. As a result, it is necessary to increase the proportion of heat removal performed by the condenser, without requiring the use of the coolant cooled by the refrigeration device.
However, in those cases in which a vinyl chloride-based polymer is produced by a suspension polymerization method using a dispersant (such as a partially saponified polyvinyl alcohol, or a cellulose ether), if heat removal is conducted so that the proportion of the total heat removal performed by the reflux condenser per unit of time exceeds 30%, then not only are the particle size distribution, the bulk specific gravity and the porosity of the product polymer all affected, but foaming of the polymerization reaction liquid increases during the polymerization, and in some cases the polymerization reaction liquid may erupt up into the reflux condenser causing particles of polymer to become deposited on the inside of the condenser, and these particles may then fall back into the polymerization reaction liquid, causing an increase in fish eyes and defects within the molded polymer film. Accordingly, in order to prevent these types of problems, the quantity of heat removed by the reflux condenser per unit of time during the polymerization reaction is typically restricted to less than 30% of the total quantity of heat removed.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of producing a vinyl chloride-based polymer by suspension polymerization using a polymerization vessel equipped with both a reflux condenser and a jacket, wherein the proportion of the total heat removal performed by the reflux condenser per unit of time can be increased, and the proportion of the total heat removal performed by the jacket can be reduced, without affecting the quality of the product polymer.
The present invention provides a method of producing a vinyl chloride-based polymer by suspension polymerization of vinyl chloride or a monomer mixture comprised of vinyl chloride using a polymerization vessel equipped with a reflux condenser and a jacket, in which a maximum value of total quantity of heat removed per unit of time is at least 10,000 MJ/hr, said method comprising:
(1) commencing heat removal when or after a polymerization conversion rate reaches 15%,
(2) controlling said reflux condenser so as to remove a fixed quantity of heat per unit of time during a period from a point where said polymerization conversion rate reaches a preset polymerization conversion rate within a range from 20 to 35%, until a point where said polymerization conversion rate reaches another preset polymerization conversion rate within a range from 50 to 65%, wherein a ratio of a quantity of heat removed by said reflux condenser (A MJ/hr) relative to a total quantity of heat removed, per unit of time, is within a range from 30 to 60%,
(3) controlling said reflux condenser so as to remove a fixed quantity of heat per unit of time during a period from a point where said polymerization conversion rate reaches a preset polymerization conversion rate within a range from 70 to 75%, until a point where said polymerization conversion rate reaches another preset polymerization conversion rate of at least 80%, wherein a ratio of a quantity of heat removed by said reflux condenser (B MJ/hr) relative to a total quantity of heat removed, per unit of time, is within a range from 20 to 30%,
wherein a ratio of said quantity of heat removed (A MJ/hr)/said quantity of heat removed (B MJ/hr) is in a range from 1.2 to 2.0.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As follows is a more detailed description of the present invention.
<Heat Removal Pattern Using a Reflux Condenser>
As a result of intensive investigations, the inventors of the present invention discovered that when a polymerization reaction is conducted using a reflux condenser, during the period when the polymerization conversion rate is between 20 and 65%, even if the quantity of heat removed by the reflux condenser per unit of time (under a fixed rate operation) exceeds 30% of the total heat generated by the polymerization per unit of time, little foaming occurs in the polymerization reaction liquid, and effects on the quality of the polymer such as the bulk specific gravity, the porosity and the occurrence of fish eyes are minimal.
In other words, in a reflux condenser heat removal pattern according to the present invention, heat removal using the reflux condenser is commenced at or after the point where the polymerization conversion rate reaches 15%, and then fixed rate heat removal operation of the reflux condenser is performed over two subsequent stages, during a preset range (a first stage) when the polymerization conversion rate is between 20 and 65%, and during a preset range (a second stage) when the polymerization conversion rate exceeds 70% (and is preferably between 70 and 90%), and by setting the quantity of heat removed by the reflux condenser during the first stage of the heat removal pattern to a larger value than that of the second stage, the quantity of coolant required for the heat removal performed by the polymerization vessel jacket can be reduced, thereby conserving energy by reducing the operational load on the refrigeration device, while the quality of the product vinyl chloride-based polymer remains unaffected.
The polymerization vessel used in the present invention is a jacketed vessel with a reflux condenser attached either directly or indirectly at the top of the vessel. There are no particular restrictions on the structure of the polymerization vessel jacket, and known systems can be used. Furthermore, in the case of a large scale polymerization vessel, the vessel may also include a cooling baffle or a cooling coil or the like inside the vessel in order to increase the area of heat removal surfaces. A stirrer is provided either through the upper portion of the vessel or in the base of the vessel.
In a heat removal pattern of the present invention, initial commencement of heat removal using the reflux condenser must occur when or after the polymerization conversion rate has reached 15%. If heat removal is commenced before the polymerization conversion rate has reached this level, then heat removal starts at a stage in which the apparent particle size distribution is yet to be determined, and consequently the quantity of refluxing monomers is large, and the distribution within the suspension system becomes very non-uniform, making control of the particle size distribution of the product polymer very difficult. In addition, dispersion of the catalyst also becomes non-uniform, resulting in an unfavorable increase in the occurrence of fish eyes.
Furthermore, if the heat removal quantity is raised instantaneously from the commencement of heat removal to the fixed
Amano Tadashi
Kuniyasu Toyotaro
Usuki Masahiro
Shin-Etsu Chemical Co. , Ltd.
Teskin Fred
LandOfFree
Method of producing of vinyl chloride-based polymer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of producing of vinyl chloride-based polymer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of producing of vinyl chloride-based polymer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3294189