Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Reexamination Certificate
1999-06-21
2001-05-01
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Process of treating scrap or waste product containing solid...
C521S040000, C521S149000
Reexamination Certificate
active
06225360
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to both method and system for recovering polyethylene from scrap material containing polyethylene.
2. Description of the Related Art
With the development of the the petrochemical industry, the production of various synthetic resins such as polyethylene, polypropyrene and polyvinylchloride, which originate from petroleum, has increased.
In particular, use of polyethylene among those synthetic resins has become widespread as a material for various household goods, protective cases for goods, parts thereof, other synthetic fibers, non-woven fabric or wrapping material.
Using products made of polyethylene enables humans to enjoy convenient daily life. However, industrial wastes originating from synthetic resins during the production of goods, or wastes goods made of synthetic resin raises a problem of environmental pollution. That is, air or soil pollution may become serious by incinerating or burying the waste of synthetic resin. Also, the continuous disposal of synthetic resin made from a limited amount of petroleum appears to be draining the petroleum supply, with a possible result being an end to growth in the synthetic resin industry.
Accordingly, a method for recovering synthetic resin from scrap material has been suggested so as to solve the above problems.
For example, Korean Patent Publication No. 89-4486 discloses methods for separating and recovering polyethylene from scrap thin metal plates coated with polyethylene resin. In the above disclosure, the thin metal plate covered with polyethylene resin is cut into an appropriate size for processing, and heated to a temperature higher than the melting point of polyethylene, to melt the polyethylene resin. As a result, the polyethylene resin is separated from the thin metal plate. However, in the polyethylene separation method, the entire system must be maintained at a high temperature to completely separate the molten polyethylene having a high viscosity from the thin metal plate, so that energy consumption increases. Also, the method is not suitable for scrap thermosetting resin or compound synthetic resin having synthetic resins whose difference in melting points is not great.
In addition, Korean Patent Publication No. 91-7451 and Laid-open Publication No. 95-8071 disclose methods for separating and recovering polyethylene resin using polyethylene-soluble solvent from scrap electric cables coated with polyethylene resin. Also, Japanese Patent Laid-open Publication No. 6-287350 discloses methods for separating and recovering polyolefin using polyolefin-soluble solvent from scrap materials containing polyolefin.
However, in the case of separating polyethylene from scrap materials only using a solvent as in the above disclosures, the polyethylene solution must be heated to a temperature higher than the boiling point of the polyethylene-soluble solvent, so as to separate the solvent. That is, if the polyethylene solution having only polyolefin-soluble solvent is cooled, polyethylene swells and is gelated in the solvent, thus it is difficult to separate polyethylene by filtration. However, evaporating the solvent requires much heat energy. Also, as the solvent evaporates, the concentration of polyethylene in the polyethylene solution relatively increases, so that the evaporation of solvent is hindered. Accordingly, a considerable amount of solvent remains in the recovered polyethylene. Thus, the quality of recovered polyethylene is lowered. Also, due to the incomplete recovery of the solvent, the production cost increases and the entire process becomes longer.
Japanese Patent Laid-open Publication No. 9-208738 discloses methods for depositing and recovering polyolefin from scrap materials containing polyolefin, in which polyolefin is dissolved in a polyolefin-soluble solvent, an insoluble component is removed from the mixture, and then a depositing agent or a poor solvent is added to polyolefin solution. However, extra processes for separating the polyolefin-soluble solvent and the depositing agent or poor solvent are required, so that energy consumption and the production cost increases in addition to the entire process being longer.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for recovering polyethylene from scrap materials containing polyethylene, in which a huge amount of scrap material containing polyethylene can be continuously disposed of without discharge of harmful substances, and high-quality polyethylene is easily recovered at low cost.
It is another object of the present invention to provide a system for recovering polyethylene from scrap materials containing polyethylene, in which a huge amount of scrap material containing polyethylene can be continuously disposed of without discharge of harmful substances, and high-quality polyethylene is easily recovered at low cost.
Accordingly, to achieve the first object of the present invention, there is provided a method for recycling polyethylene from scrap material containing polyethylene, comprising the steps of putting the scrap material containing polyethylene into a solvent mixture containing a polyethylene-soluble solvent and a polyethylene-insoluble solvent in a ratio of 1:1~1:3 based on volume, heating the mixture at a temperature of 60~145° C. to dissolve the polyethylene from the scrap material, resulting in a mixture of a polyethylene solution and insoluble substances. The resulting mixture is filtered to separate the polyethylene solution and the insoluble substances and polyethylene is deposited by cooling the separated polyethylene solution. Then, a mixture of the polyethylene deposition and the solvent mixture is filtered to separate the polyethylene deposition.
Preferably, the polyethylene-containing scrap material comprises at least one resin selected from the group consisting of polyvinylchloride, nylon and polyester.
To achieve the second object of the present invention, there is provided a system for recovering polyethylene from scrap material containing polyethylene, comprising a heating and dissolving unit, a first filter, a cooling and depositing unit and a second filter. The heating and dissolving unit is for dissolving the polyethylene from the polyethylene-containing scrap material into a solvent mixture, resulting in a mixture of a polyethylene solution and insoluble substances. The first filter filters the insoluble substances from the resulting mixture formed by the heating and dissolving unit, and the cooling and depositing unit cools the polyethylene solution contained in the heating and dissolving unit and the remaining polyethylene solution after filtration of the insoluble substances by the first filter, to deposit polyethylene, resulting in a mixture of the polyethylene deposition and the solvent mixture. The second filter filters the polyethylene deposition from the mixture obtained by the cooling and depositing unit.
Preferably, the recovery system further comprises a first drying unit for drying the insoluble substances obtained from the first filter by evaporating the remaining solvent mixture, a first condenser for condensing the remaining solvent mixture evaporated by the first drying unit, a second drying unit for evaporating the remaining solvent mixture from the polyethylene deposition obtained by the second filter, and a second condenser for condensing the remaining solvent mixture evaporated by the second drying unit.
Preferably, the system for recoverying polyethylene from a polyethylene-containing scrap material further comprises a heat exchanger for heat exchange between the polyethylene solution provided from the heating and dissolving unit and the first filter to the cooling and depositing unit, and the solvent mixture provided from a solvent tank to the heating and dissolving unit.
Preferably, at least one of the heating and dissolving unit, the first drying unit and the second drying unit further comprise an airtight screw feeder having a screw shaft with helical blade formed along only a part of
Cain Edward J.
Kim Kwang
Rothwell Figg Ernst & Manbeck
Wyrozebski-Lee Katarzyna
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