Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
2002-04-19
2004-03-16
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C528S275000, C528S308600, C528S488000, C528S490000, C528S495000, C528S501000, C528S50200C, C528S503000, C560S078000, C526S065000, C526S067000, C526S071000
Reexamination Certificate
active
06706843
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for separation of effective components from polyester waste (which may be either valuable or valueless substances). More specifically, the present invention relates to a process for separation and recovery of effective components such as dimethyl terephthalate and ethylene glycol from polyester waste which contains polyethylene terephthalate as the major component along with a foreign material, with a high efficiency.
BACKGROUND ART
Because of their excellent chemical stability, polyalkylene terephthalates are produced and used in large quantities for common materials such as fibers, films, resins and the like, as well as in the field of food packaging, and as bottles for drinking water, carbonated beverages and the like.
However, the costs of processing fiber, film and resin product waste or off-specification materials such as polyalkylene terephthalates (hereinafter also referred to simply as “polyester waste”), which are produced in large quantities with increasing production output and usage, are associated with higher product cost, while their processing is also a major problem for modern society, and therefore various recycling methods have been proposed for material recycling, thermal recycling, chemical recycling and the like.
Although material recycling whereby polyester waste is converted to low grade quality substances by melt molding has largely improved the situation for “disposables”, the obtained recycled products undergo further quality reduction when recycled again, and therefore their uses are limited and it has been difficult to avoid final disposal of polyalkylene terephthalates.
Another method employed is thermal recycling, whereby polyester waste is used as a fuel. This method offers the advantage of reutilizing the heat of combustion of the polyester waste, but since burn-off of the polyester waste cannot be avoided, it entails the problems of loss of the polyalkylene terephthalate starting material and generation of carbon dioxide, and is therefore not preferred from the standpoint of conservation of resources and preservation of the environment.
Chemical recycling is also being investigated as an alternative to the two types of recycling methods described above, whereby polyester waste is converted to its constituent components which are then recovered and again subjected to polymerization reaction to produce polyester for reuse.
Specifically, there is known a process in which the recovered polyester waste is reacted with methanol (hereinafter also abbreviated as “MeOH”) and is recovered as dimethyl terephthalate (hereinafter also abbreviated as “DMT”) and alkylene glycols, and a process in which the recovered polyester waste is hydrolyzed in the presence of an alkali compound and the resulting terephthalic acid and alkylene glycols are recovered. Such chemical recycling processes allow recycled reuse of compounds with essentially no loss, and thus offer advantages for reutilization of resources.
However, polyester waste delivered from the distribution industry and households usually contains foreign materials including chlorine-containing polymers such as polyvinyl chloride and polyvinylidene chloride (these will hereinafter be collectively referred to as “PVC”), colored polyester materials and polyolefins.
It has been difficult to avoid inclusion of such foreign materials even in the polyethylene/alkylene terephthalate portion (hereinafter also referred to as “polyalkylene terephthalate scrap”) which is sorted from polyester waste. These included foreign materials may cause various problems such as generation of decomposition gases (for example, hydrogen chloride gas) during the heating and reaction operations for the polyalkylene terephthalate scrap, or may melt and solidify in the recovery apparatus leading to damage to the instruments or clogging and adhesion inside the instruments. In addition, formation of organic chlorine compounds from hydrogen chloride gas can notably lower the quality of the recovered DMT and alkylene glycols.
For chemical recycling, therefore, effective reuse of polyalkylene terephthalates contained in polyester waste has required separation of the foreign materials in the polyester waste.
A conventional process for recovery of polyester waste, which is widely known as the glycolysis/transesterification reaction process and which is employed industrially, is a process of depolymerizing the polyalkylene terephthalates with ethylene glycol (hereinafter abbreviated as “EG”) and then subjecting them to a transesterification reaction with MeOH to obtain DMT.
During removal of the foreign materials, however, thermal decomposition of PVC, for example, becomes notable from about 195° C., and it has therefore been difficult to apply chemical recycling of PVC-containing polyalkylene terephthalate scrap as a result of the PVC decomposition that occurs by the above-mentioned glycolysis process that is usually carried out at 195 to 240° C. Moreover, when chemical recycling is applied to polyester waste containing colored polyalkylene terephthalates, partial decomposition of the colored substances reduces the quality of the recovered compounds.
In addition, in the case of polyolefin-containing polyester waste, melting or solidification of the polyolefins occurs under the processing conditions for the conventional glycolysis/transesterification reaction, causing such problems as clogging of the apparatus and hampered operation and, therefore, difficulties have plagued the industrial treatment of polyolefin-including polyester waste by conventional polyester recovery processes.
As a means of solving this problem, U.S. Pat. No. 5,504,122 proposes a process of adding an alkali compound to hydrogen chloride formed by thermal decomposition of a chlorine-containing resin to sequester it, and then subjecting the polyalkylene terephthalate to methanolysis and recovering the starting monomer.
Also, Japanese Unexamined Patent Publication HEI No. 8-259728 proposes a process whereby a mixture of a chlorine-containing resin and polyester waste is hydrolyzed in the presence of an alkali compound and then terephthalic acid and EG are recovered, i.e., similarly, an alkali compound is added to sequester generated chlorine compounds.
While all of these processes achieve the object of recovering the target substances, they are associated with various drawbacks. Specifically, in cases where a chlorine-containing resin and its decomposition product are included as foreign materials, the chlorine compounds sequestered by the alkali compound must be removed, and the removal of the chlorine compounds requires the additional steps of distillation, washing and ion-exchange, thus complicating the process. In cases where a colored polyester is included as an foreign material, the high temperature treatment of the polyalkylene terephthalate decomposes part of the colorant and lowers the quality of the target substance. In cases where a polyolefin is included as an foreign material, melting treatment of the polyalkylene terephthalate together with its decomposition product makes it inevitable that the component to be recovered will be included in the polyolefin when it is removed from the thermal decomposition tank.
Japanese Unexamined Patent Publication HEI No. 11-21374 also proposes a process of hydrolyzing polyester waste in the presence of an alkali compound. However, since the decomposition is carried out in an alkaline aqueous system, this process has the drawback of a high reaction pressure.
Finally, Japanese Unexamined Patent Publication HEI No. 11-302208 proposes a process in which polyester waste is hydrolyzed in water-containing ethylene glycol in the presence of an alkali compound and the resulting sodium terephthalate is dissolved in a large amount of water and subjected to acid precipitation. According to this process, the presence of the ethylene glycol allows the reaction pressure to be lowered during the hydrolysis, but a drawback is encountered in that the acid precipitation produces a miner
Hasegawa Hideo
Ishida Kenji
Ishihara Kenichi
Miyamoto Masanori
Nakashima Minoru
Acquah Samuel A.
Rader & Fishman & Grauer, PLLC
Teijin Limited
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