Method of decomposing a polyurethane

Details Method of decomposing a polyurethane Method of decomposing a polyurethane

2001-04-02

2003-02-04

Sergent, Rabon (Department: 1711)

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

Synthetic resins

Process of treating scrap or waste product containing solid...

C521S049000, C564S437000, C564S469000, C564S488000, C564S497000, C564S498000, C568S621000, C568S623000, C568S624000, C568S854000, C568S858000, C568S868000, C252S182130, C252S182240, C252S182270

Reexamination Certificate

active

06515036

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method of chemically decomposing the cuttings made in molding or fabricating articles of polyurethane resins and waste of such resin articles for industrially advantageous recovery of a polyamine compound and a polyol compound useful as the raw materials of the polyurethane resin.
BACKGROUND OF THE INVENTION
Polyurethane resins are widely used in large quantities as materials for flexible, semi-rigid or rigid urethane foams which are useful as cushion materials in sofas and like furniture or in beds and like beddings, in automotive seats and the like, as heat insulating materials in refrigerators, or as elastomers in shoe soles, tires, belts and the like. In recent years, methods of recycling or reusing articles of plastics, not excepting polyurethane resins, have been investigated because the protection of resources and preservation of the environment are considered more important. Known methods of recycling polyurethane resins include, if roughly classified, (1) a material recycling technique, (2) a chemical recycling technique and (3) an energy recycling technique.
The material recycling technique (1) is investigated on methods of reusing polyurethane resins as cushion materials by rebonding or compression molding of polyurethane foams and methods of using polyurethane resins by grinding foams and elastomers and incorporating the fragments as a filler into a new material.
The chemical recycling technique (2) includes methods of decomposing a polyurethane into the raw materials or into chemical compounds usable as the raw materials to make reuse thereof. The methods are known as a glycol decomposition method, an amine decomposition method or a hydrolysis method.
The energy recycling technique (3) is intended for recovery as heat or a vapor (steam) given off by using a polyurethane resin as a fuel.
The technique (1) poses a problem as to the quality of obtained product and is unavoidably applied only for limited purposes. It was suggested that the technique (3) will involve a risk of raising a new pollution problem on the generation of a detrimental substance by combustion of a polyurethane resin.
If the chemical recycling technique (2) is economically and industrially feasible, it may be an ideal recycling technique since the recovered compounds find wide applications.
However, the glycol decomposition method and the amine decomposition method comprise breaking urethane bonds with a glycol or amine compound, the urethane bond being relatively susceptible to decomposition among a variety of bonds present in the polyurethane resin such as urethane bonds, urea bonds, biuret bonds and allophanate bonds, followed by liquefaction of urethane bonds by exchange reaction. In the methods, the glycol or amine compound used as the decomposer newly generates urethane bonds and urea bonds which are included as a urethane or urea derivative into the liquid decomposition product.
Consequently according to the technique (2), the polyurethane resin is not decomposed sufficiently to provide a polyol as the starting material of polyurethane resin and a polyamine compound as an intermediate of polyisocyanate so that the recycled material is used for limited applications.
JP-B-42-10634, JP-B-43-21079 and JP-B-48-5280 disclose recovery methods in which a urethane polymer is subjected to heat decomposition with an amine compound and an alkali metal or alkaline earth metal to recover a polyether and an amine derivative having an amino group converted from the isocyanate group of polyisocyanate, namely to recover the raw material of a urethane polymer. The disclosed methods necessitate removing and disposing of the salts derived from the alkali metal or alkaline earth metal. Further the methods give the decomposition product in the form of a liquid and entail a problem of taking a cumbersome separation procedure. Actually the methods have not been commercially applied yet since the recycled product can not be used as the raw material due to a small amount of amine present in the polyether. Therefore, there is a demand for developing a treatment method to be conducted subsequent to the decomposition with an amine.
The proposals include a method of hydrolyzing a polyurethane resin using water as a decomposer. For example, JP-A-54-70377 describes a method in which polyurethane foam is hydrolyzed in the presence of an alkali metal or an alkaline earth metal at a temperature of 300° C. using a heated water vapor (steam) at 0.4 to 10 atm. When a water vapor is used under such a low pressure, the reaction is retarded. Thus this method suggests that the presence of a catalyst is inevitable.
A method was recently reported for converting a high molecular weight compound to a low molecular weight compound using water retained at a high temperature and high pressure (WO 98/34904). This method may be worthy to be carried out if the urethane refuse used as the starting material in the method consists of a polyurethane resin alone and is free of non-hydrolyzable contaminants. However, the shredder dust from automotive seats is available in the largest quantities among the polyurethane resin-containing waste and contains a large quantity of cuttings of non-hydrolyzable contaminants such as fibers and leathers used as the surface layer materials (fabrics) for automotive seats. Therefore, insofar as the shredder dust is used as the material to be treated in the method, the hydrolyzate contains the contaminants remaining after the hydrolysis. For removal of the contaminants from the hydrolyzate, it becomes necessary to filter the hydrolyzate after the reactor is returned to a normal pressure. Consequently it is difficult to continuously perform the hydrolysis.
However, polyurethane resins are hydrophobic and are usually mixed with fibers to provide a composite material. For example, the shredder dust from automotive seats is unavoidably provided as mixed with a fibrous material used as the surface layer material. If this method is conducted in a batchwise manner, the hydrolysis must be performed at a high added water ratio (ratio of water/compound to be hydrolyzed) for the decomposition of a bulky foam article. Consequently large-size high pressure equipment is required so that the method incurs a high energy cost and is uneconomical.
A continuous operation is considered necessary, of course, for compacting the equipment and for enhancing the energy efficiency. Even if a continuous supply is enabled, the hydrolysis needs a prolonged period because of hydrophobicity of polyurethane resin, and the largest problem arises as follows. When articles of polyurethane resin contain contaminants such as fibers and cloths as in the case of the foregoing shredder dust, the pressure regulating valve may be clogged with the contaminants and the valve disk may be blocked therewith so that the state of liquid layer may not be held at a high temperature and a high pressure. To overcome this problem, liquefaction may be required prior to taking a hydrolysis procedure.
JP-A-11-80419 discloses a method in which the refuse of polyurethane is hydrolyzed in a closed state in the presence of water in a larger amount than saturated water vapor to give a water-soluble product, which is then subjected to supercritical hydration decomposition. This method practically requires an organic alkaline compound because the reaction is retarded due to the presence of water alone and is inefficient. Further, pressure must be applied because of reaction in a closed state, and limitation is imposed on the equipment.
The prior patent application filed by the same applicant as in the present application (Japanese Patent Application No.11-263424) proposes a method of decomposing a polyurethane resin for recovery of components, the method comprising the steps of dissolving a polyurethane resin in a solubilizing agent such as a polyamine compound, a low molecular weight glycol or an amino alcohol, removing the insolubles when so required, hydrolyzing the solution with liquid water retained at 200 to 320° C. and

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