JP2006131652A - Method for making waste plastic material mixture containing chlorine-containing resin harmless - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a waste plastic material mixture containing chlorine-containing resins harmless without discharging harmful materials. <P>SOLUTION: This method for making the waste plastic material mixture containing the chlorine-containing resins harmless is provided by mixing a necessary amount of zinc oxide to the waste plastic material mixture containing the chlorine-containing resins, thermally decomposing at 180-300°C and washing to remove chlorine components. The produced zinc chloride is reused by returning to zinc oxide. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention belongs to the field of waste plastic decomposition and recycling technology.

  Plastic waste discharged in large quantities as industrial waste or household waste is often a mixture of polyethylene, polyethylene terephthalate, etc., and chlorinated resins such as polyvinyl chloride, polyvinylidene chloride. Such plastic waste may not only generate harmful hydrogen chloride gas during pyrolysis and incineration, but also by-produce toxic chlorine compounds such as dioxins. For this reason, landfilling has been the mainstream for the treatment of plastic mixtures containing chlorine-containing resins. However, now that waste landfills are saturated, detoxification and recycling of waste plastic mixtures containing chlorine-containing resin is an urgent and important issue facing Japan. For this reason, development of various decomposition and recycling technologies for detoxifying plastic waste has been attempted (for example, see Patent Document 1).

Japanese Patent Application Laid-Open No. 2004-296552

  Attempts have been made to separate chlorine-containing resins and other plastics by a specific gravity separation method or a selective dissolution method using a solvent as a treatment method for waste plastic mixtures containing chlorine-containing resins. However, these methods may have problems such as incomplete separation of the chlorine-containing resin and other resins and the need for a large amount of solvent. By the way, in the case of a polyvinyl chloride resin, a method of dechlorinating by reacting with zinc oxide has been tried. This method is known to proceed at a low temperature of about 200 ° C. If this method can be applied to waste plastic mixtures and only the chlorine-containing resin contained can be selectively dechlorinated and detoxified, there is no longer any need for landfill treatment, which is highly desirable from the viewpoint of effective use of resources and environmental conservation. Here is the problem to be solved by the present invention.

  The invention of claim 1 of the present invention is that only zinc-containing resin contained in the mixture is obtained by mixing zinc oxide (ZnO) into the waste plastic mixture and thermally decomposing it at normal temperature and low temperature (180 to 300 ° C). Is a dechlorination detoxification method for a waste plastic mixture mixed with chlorine-containing resin, which is characterized by selectively dechlorination detoxification.

  The invention of claim 2 is a detoxification treatment of various waste plastic mixtures containing chlorinated resins such as polyvinyl chloride, polyvinylidene chloride and copolymers thereof in polyethylene, polypropylene, polystyrene, polyethylene terephthalate and the like and mixtures thereof. It is characterized by.

The invention of claim 3 is the cause of environmental pollution by regenerating and repeatedly using zinc chloride (ZnCl ₂ ), which is produced when the chlorine-containing resin-mixed waste plastic mixture is rendered harmless by the above method. This is a method that does not discharge the zinc compound to the environment.

  According to the invention of claim 1, the carbonaceous solid (hydrocarbon) obtained by mixing the required amount (more than the equivalent chlorine content) of zinc oxide with the chlorine-containing resin-mixed waste plastic mixture and dechlorinating at low temperature is substantially reduced. Since it does not contain chlorine, it can be thermally recycled as it is, or it can be oiled and recycled using existing pyrolysis oil conversion technology, eliminating the need for landfill. Further, since the present invention can be applied to various types of waste plastic mixtures according to claim 2, the practical significance is extremely large. According to the invention of claim 3, the unreacted portion of zinc oxide used for detoxifying the waste plastic mixture and zinc chloride as a by-product are once dissolved in dilute hydrochloric acid or the like, and an alkaline aqueous solution such as sodium hydroxide or calcium hydroxide is added. When neutralized, the zinc component precipitates as zinc hydroxide. When the precipitate is heated and dried at 300 ° C or higher, it returns to zinc oxide, so it can be recovered and reused without causing environmental pollution.

  Next, an embodiment of the present invention will be described based on the drawings. In FIG. 1, reference numeral 1 denotes a waste plastic mixture and zinc oxide mixing tank. Waste plastic and zinc oxide are introduced from the inlet 1a and mixed uniformly by a stirrer or the like.

  The mixture is sent to the decomposition tank 2 and heated to 200 to 300 ° C. with a heater or the like while stirring. As a result, the chlorine-containing resin is selectively pyrolyzed, chlorine and hydrogen are removed at a ratio of 1: 1, and converted into a carbonaceous solid (hydrocarbon) and zinc chloride and water are produced.

  The resulting heat treatment mixture is sent to the washing / separation tank 3 and thoroughly washed with an acid solution (for dissolving zinc oxide) 3a and then with water (for dissolving zinc chloride) 3b while stirring with a stirrer 3c, and then solidified with a filter 3d. And the cleaning solution are separated. Zinc chloride and unreacted zinc oxide are dissolved in the cleaning solution. The solid component is taken out from the outlet 3e, which has been converted to a plastic mixture containing no chlorine.

  On the other hand, the cleaning liquid is sent to the neutralization tank 4 by the pump 3f. In the neutralization tank 4, the washing solution is stirred with a stirrer 4b, and alkali 4c such as caustic soda and calcium hydroxide is added and neutralized (pH = 7) while monitoring with a pH meter 4d. By this treatment, substantially all of the zinc component in the cleaning solution is precipitated as zinc hydroxide. This reaction solution is sent to the filtration / drying tower 5 by a pump 4e. In the filtration / drying tower 5, the solid component (zinc hydroxide) is separated by the filter 5a and taken out from the outlet 5b after drying. The zinc hydroxide is returned to zinc oxide by heat treatment and reused.

  The remaining liquid phase (aqueous salt solution such as sodium chloride and calcium chloride) is sent to the waste liquid tank 6. Sodium chloride, calcium chloride, and the like can be easily obtained from the waste liquid by evaporation to dryness, but these can be reused as industrial raw materials.

  Thermal analysis of plastic mixtures in the presence of zinc oxide.

Next, the results of concrete implementation of the present invention will be described. Polyvinyl chloride (PVC), zinc oxide (ZnO), and polyethylene (PE) (or polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET)) are mixed at a weight ratio of 1: 1: 1. The decomposition characteristics were measured using a thermal analyzer. Examples of results are shown in FIGS. Figure 2 shows PVC
The thermal analysis result of the / ZnO mixture is shown. An exothermic peak with weight loss is observed in the range of 190 to 300 ° C, suggesting that the dehydrochlorination reaction of PVC proceeds. In addition, an exothermic peak with weight loss is observed again above 380 ° C, indicating that the decomposition reaction (main chain cleavage reaction) due to the cleavage of the carbon-carbon bond proceeds. FIG. 3 shows the thermal analysis results of the PE / ZnO mixture. An endothermic reaction with weight loss occurs above 400 ° C, indicating that the degradation reaction of the polyethylene (main chain cleavage reaction) proceeds due to the cleavage of the carbon-carbon bond. In addition, weight loss is not observed below this temperature, indicating that polyethylene does not decompose below 400 ° C. FIG. 4 shows the thermal analysis results of the PVC / ZnO / PE mixture. Comparing with Fig. 2, it can be seen that the exothermic peak with weight loss around 200-310 ° C corresponds to dehydrochlorination reaction of PVC. Moreover, weight loss above 400 ° C suggests that the main chain cleavage reaction proceeds.

  Table 1 summarizes the results of decomposition of mixtures of polyvinyl chloride and various plastics in the presence of zinc oxide. It was revealed that the dechlorination reaction proceeded at 190 to 330 degrees in any mixture. On the other hand, it became clear that the decomposition reaction (main chain cleavage reaction) by cleavage of carbon-carbon bond proceeds at 330 ° C or higher. Therefore, it can be seen that when PVC-containing waste plastic mixture is heat-treated at an appropriate temperature of 200 to 300 ° C, polyvinyl chloride can be selectively dechlorinated without decomposing the coexisting plastic.

  Next, polyvinyl chloride, zinc oxide, and polystyrene (or polyethylene, polypropylene, polyethylene terephthalate) were mixed at a weight ratio of 1: 1: 1, and heat-treated at 200 ° C. in a nitrogen atmosphere. FIG. 5 shows an example of infrared absorption spectrum measurement results of a carbonaceous solid obtained by washing with a dilute acid solution and water using a Fourier transform infrared spectrophotometer. Curve A is the spectrum of the untreated mixture, but it is a spectrum that combines the polystyrene spectrum shown by curve D and the PVC spectrum shown by curve E. A spectrum different from A is obtained for the 200 ° C. treated product shown by curve B, and only a spectrum derived from polystyrene is observed in the sample washed after heat treatment shown by curve C. Therefore, it can be concluded that chlorine in PVC was removed as zinc chloride by heat treatment at 200 ℃. Similar results were obtained in infrared absorption spectra after heat treatment of PVC and other plastic mixtures. Therefore, it was clarified that polyvinyl chloride can be selectively dechlorinated without decomposing coexisting plastic by heat-treating the PVC-containing waste plastic mixture at an appropriate temperature of 200-300 ° C.

  Next, polyvinyl chloride, zinc oxide, and polystyrene were mixed at a weight ratio of 1: 1: 1, and the organic matter produced when the temperature was decomposed in a nitrogen atmosphere was analyzed. Compared to the case of decomposition. The results are shown in FIG. In the temperature decomposition of the mixture, no organic substance is generated at 350 ° C. or lower. Therefore, it has been clarified that organic substances are not substantially generated in the dechlorination reaction (200-300 ℃). This result is important because it suggests that virtually no harmful organochlorine compounds are produced during the dechlorination reaction. On the other hand, organic substances such as styrene and toluene are generated at 350 ° C or higher. Since these organic substances are known to be generated by main chain decomposition of polystyrene and PVC, it shows that thermal decomposition of polystyrene and dechlorinated PVC proceeds at 350 ° C. or higher.

  From the above results, it is clear that the PVC can be selectively dechlorinated without decomposing coexisting plastic by heat treating the PVC-containing waste plastic mixture at an appropriate temperature of 200-300 ° C. It was.

1 shows an overview of the best apparatus for carrying out the invention. The thermal analysis result of a polyvinyl chloride-zinc oxide mixture is shown. The thermal analysis result of a polyethylene-zinc oxide mixture is shown. The thermal analysis result of a polyvinyl chloride-polyethylene-zinc oxide mixture is shown. 2 shows an infrared absorption spectrum of a thermal decomposition product of a zinc oxide-plastic mixture. The analysis result of the thermal decomposition product of the plastic mixture in the presence of zinc oxide is shown.

Explanation of symbols

1 ... Waste plastic and zinc oxide mixing tank
2 ... Dechlorination reactor
3 ... Cleaning / separation tank
4 ... Neutralization tank
5 ... Filtration / drying tank
6 ... Waste liquid tank

Claims (3)

  Waste plastics characterized by selectively dechlorinating and detoxifying only the chlorinated resin contained in this plastic mixture by mixing zinc oxide with the waste plastic mixture and thermally decomposing it in the range of 180-300 ° C. Detoxification method for mixtures.   The waste plastic mixture according to claim 1, wherein the plastic mixture contains polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and the like, and the mixture contains chlorine-containing resins such as polyvinyl chloride, polyvinylidene chloride, and copolymers thereof. Detoxification method for plastic mixtures. The zinc oxide used in claim 1 and zinc chloride, which is one of the products, are dissolved in an acidic aqueous solution, adjusted to pH, separated as a precipitate, reconverted into zinc oxide, and repeatedly used. To detoxify waste plastic mixture.