Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Reexamination Certificate
1999-07-13
2001-04-10
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...
C521S048500
Reexamination Certificate
active
06214893
ABSTRACT:
TECHNICAL FIELD
This invention relates to a process for the decomposition of a polyester which can accelerate the reaction for decomposing the polyester to form monomers serving as raw materials or raw material derivatives, and a system for the monomerization of a polyester.
BACKGROUND ART
The methods for reusing a polyester as the same type of polyester material include a material cycle and a chemical cycle. In the material cycle, a polyester is softened, for example, by the application of heat and then re-formed. This method of reuse is simple in process construction and involves low recycling costs per cycle. However, since the properties (e.g., moldability) of the original material are deteriorated as the re-forming is repeated, the number of recycles is limited. Moreover, the material must inevitably be changed over to applications having lower property requirements.
On the other hand, the chemical cycle comprises returning a polyester to the form of raw materials, purifying them, and synthesizing a polyester again. Consequently, this method requires a complicated system and involve high recycling costs per cycle. However, it can provide much value added because the number of recycles is markedly increased and the application of the recycled material is not limited.
DISCLOSURE OF THE INVENTION
Although a large number of processes for the monomerization of polyesters are known, a satisfactorily high reaction rate cannot be achieved because they are based on a surface reaction. Typical processes include solvolysis with methanol and hydrolysis with water. However, since polyesters are insoluble in methanol or water, the reaction is carried out in a system having two separated phases. Accordingly, none of them has been satisfactory from the viewpoint of reaction conditions such as reaction time and temperature.
For example, it has been reported by Sako et al. in the Institute for Material Science, the Agency of Industrial Science and Technology that the decomposition of PET in methanol requires treatment at 300° C. and 80 atmospheres for 30 minutes. However, the present inventors have confirmed that the decomposition rate of PET depends on its specific surface area. Specifically, when a test was carried out by grinding an equal weight of PET finely and dividing the reaction vessel so as not to cause the PET to agglomerate again during melting, the PET could be completely decomposed in a period of 10 to 20 minutes. Thus, it would be desirable to provide a simple method which permits the effective specific surface area for reaction to be increased in actual plants.
According to the present invention, in the decomposition of a polyester, the decomposition products obtained by solvolysis, together with the polyester, are added to the reaction system. For example, in the decomposition of a polyester, the dimethyl carboxylate and dihydroxy compound corresponding to the decomposition products obtained by solvolysis with methanol, together with the polyester, are added to the reaction system. Thus, the decomposition rate can be enhanced. The reason for this is considered to be that the aforesaid dimethyl carboxylate corresponding to a decomposition product dissolves the polyester at temperatures higher than its melting point to increase the effective area for reaction or to aid in the dissolution of the polyester in methanol or its mixing with methanol.
That is, the present invention provides a process for the decomposition of a polyester which comprises decomposing the polyester by solvolysis to form monomers, wherein the decomposition products obtained by solvolysis are recycled as solvents for the polyester. For example, according to a preferred embodiment of the present invention, a polyester is decomposed by solvolysis with methanol to form a dimethyl carboxylate and a dihydroxy compound, and these decomposition products are previously added to and mixed with a melt of the polyester for the purpose of decomposing the polyester by solvolysis.
The solvent used in the aforesaid solvolysis generally comprises a polar solvent. Alcohols are preferred, lower alkyl alcohols (commonly alkyl alcohols having 1 to 5 carbon atoms) are more preferred, and methanol is most preferred.
As described above, the present invention is characterized in that the decomposition products are recycled as solvents for the polyester. When a lower alkyl alcohol is used as the polar solvent, the decomposition products being recycled are a dialkyl carboxylate and a dihydroxy compound. When methanol is used as the polar solvent, the decomposition products being recycled are a dimethyl carboxylate and a dihydroxy compound.
The polyesters which can be monomerized or decomposed according to the present invention include, for example, polyethylene-butylene terephthalate (PEBT), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycyclohexanedimethylene terephthalate (PCT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN) and polycarbonate (PC).
In the examples which will be given later, the effectiveness of the present invention was confirmed for all of the polyesters tested. Accordingly, it is believed that the process of the present invention is universally useful for polyesters.
In the practice of the present invention, it is preferable to recover the aforesaid decomposition products with progressive reduction in pressure and recycle them.
Moreover, the present invention also provides a system for the monomerization of a polyester which comprises a high-pressure reaction vessel for receiving a molten polyester and reacting it with a solvent, pressure reducing means and recovery means for progressively reducing the pressure of the decomposition products formed in the high-pressure reaction vessel and thereby recovering the decomposition products, and lines for recycling the decomposition products from the recovery means to the high-pressure reaction vessel as solvents for the polyester. It is to be understood that an insufficiently decomposed oligomer and/or the solvent may also be recycled.
It may be expected that this monomerization system can achieve high recoveries in a short period of time. Generally, recovery tanks are used as the aforesaid recovery means.
As is evident from the above description, the present invention provides a process for the decomposition of a polyester wherein the decomposition products obtained by the solvolytic decomposition of a polyester, together with the polyester, are added to the reaction system, so that its monomerization can be achieved under satisfactory reaction conditions such as reaction time and temperature.
Moreover, the present invention also provides a process for the decomposition of a polyester and a system for the monomerization of a polyester, wherein the aforesaid decomposition products are recovered with progressive reduction in pressure and recycled, so that high recoveries can be achieved in a short period of time.
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Ishihara Nobuo
Kawamura Wataru
Kishi Masahiro
Okazaki Kikuo
Cain Edward J.
Mitsubishi Heavy Industries Ltd.
Myers Bigel Sibley & Sajovec P.A.
Wyrozebski-Lee Katarzyna
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