JPH09263772A - Apparatus and method for treating waste plastic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover fuel oils or chemical raw materials from plastics not easily convertible into oils and wastes containing foreign matter, etc., at good efficiency by using an apparatus consisting of a specified pressure vessel, a specified heating means and a specified extracting means. SOLUTION: This apparatus for treating waste plastic comprizing of a pressure vessel 1 for mixing waste plastics containing at least C, H and other elements with water, a heating means 3 for heating the vessel 1 until the water is converted into supercritical water which can function as a solvent for the heat decomposition reaction of the waste plastics, and means 6 and 7 for extracting oils and solid chemical substances from the solvent. Desirably, an oxygen source such as oxygen, air or H2 O2 is mixed with waste plastics and water, Namely, the number of hydrogen bonds and the orientation force which determine the properties of water depend on the temperature. When the temperature is high, the effect of thermal movement preponderates. It can therefore dissolve nonpolar compounds at the critical point or higher and can further dissolve various gases. Therefore, water can function as a reaction solvent which accelerates the oxidation reaction of organic compounds.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for thermally decomposing discarded plastic (referred to as waste plastic in the specification) and recovering it as oil. More specifically, it is an unsuitable material for oilization using supercritical water. The present invention relates to a method for efficiently removing oil and recovering high-quality oil.

[0002]

2. Description of the Related Art A technique for pyrolyzing waste plastics by pyrolysis to recycle them as fuel oil has attracted attention because the value of recycled products is relatively high. However, if pyrolysis of mixed waste plastics containing foreign substances such as vinyl chloride resin, polyethylene terephthalate and other elements other than C and H, and foreign substances such as paper, the decomposition efficiency decreases, and the oil containing halogen (chlorine) However, there are various problems, such as the formation of solids, the condensing tube is blocked by solid matter, and the like.

Therefore, by adding alkali and water to carry out thermal decomposition, halogen is prevented from being mixed in the produced oil,
Attempts have also been made to prevent the precipitation of solid substances such as phthalic anhydride on the condensing tube (Japanese Patent Laid-Open No. 4-35334), but this method cannot prevent the degradation of decomposition efficiency due to paper, etc. Since a large amount of thermal decomposition residue remains, there is a problem that volume reduction efficiency is poor.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for recovering a good quality fuel oil and a solid chemical raw material from a mixed plastic waste containing a difficult-to-oil plastic and a foreign substance. And

[0005]

In order to solve the above-mentioned problems, the invention of claim 1 provides a pressure vessel for mixing waste plastic containing at least an element other than C and H with water, and the water is supercritical water. A treatment device for waste plastic, comprising: heating means for heating the pressure resistant container until it becomes a solvent for thermal decomposition reaction of the waste plastic; and means for extracting oil and solid chemical substances from the solvent. It is provided.

The invention according to claim 2 is at least C,
First, mixing waste plastic containing elements other than H with water
A second step of heating the mixture until the water becomes supercritical water to make it a reaction solvent of the waste plastic, and a third step of extracting oil and solid chemicals from the solvent. The present invention provides a method for treating waste plastic, which comprises:

Further, the invention of claim 3 is characterized in that in the first step of the invention of claim 2, an oxygen source such as oxygen, air or hydrogen peroxide is mixed with the waste plastic and water. A method of processing plastics is provided.

Further, the invention of claim 4 provides a method for treating waste plastic, characterized in that after the third step in the invention of claim 2, the extracted solid chemical substance is further decomposed by heating. It is a thing.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have made a waste plastic containing halogen such as vinyl chloride resin and Teflon, such as Cl, which is an element other than C and H, waste plastic containing O element such as polyethylene terephthalate, and paper. We conducted a thorough study on the method of thermal decomposition and oilification of mixed waste plastic containing foreign substances such as (carbohydrate). As a result, it was found that by heating with water and maintaining the temperature and pressure in the vicinity of the critical point of water, the dehalogenation decomposition of vinyl chloride resin etc. can be promoted first, and secondly the polycondensation of polyethylene terephthalate etc. (Dehydration polymerization) It was found that the plastic can be hydrolyzed, and the present invention was completed.

Further, it has been found that, in some cases, by adding an oxygen source in addition to water and heating, foreign matter such as paper adhering to the surface of the waste plastic can be easily oxidized and removed.

The decomposition principle of the above-mentioned waste plastic of the present invention is as follows. Water has a high boiling point and a critical point despite its small molecular weight, and has a large specific heat and latent heat. Further, since it has a large dielectric constant, it dissolves many elements in the form of ions and selectively dissolves many polar compounds, but it does not melt oil at relatively low temperatures such as room temperature. However, the number of hydrogen bonds and the orientation force (the force that acts between permanent dipoles due to the uneven distribution of electrons in the molecule) that determine the properties of water depend on temperature, and the effect of thermal motion is dominant at high temperatures. Therefore, in the temperature range above the critical point (temperature 374.2 ° C, pressure 22.1MPa), non-polar compounds generally called "oils" can be dissolved in water. Furthermore, since it also dissolves with various gases, if, for example, oxygen gas, water and an organic compound are mixed in appropriate amounts and operated so as to satisfy the temperature, pressure and density conditions near the critical point of water, water will oxidize the organic compound. It acts as a reaction solvent that accelerates the reaction. In the present invention, this property of critical water is applied.

However, this is a condition that the organic compound is dissolved in water in the form of fluid, and in other cases, in the case of solid such as plastic, the reaction proceeds only on the surface. Therefore, for waste plastic raw materials that have foreign matter such as paper adhered to the surface, only the foreign matter on the surface is removed by adjusting the amount of oxygen added and the reaction time, and the decomposition of plastic is suppressed. Will be possible.

The reaction of each resin in the waste plastic proceeds as follows. First, vinyl chloride resin is usually decomposed at 300 ° C or lower to desorb hydrogen chloride, and the remaining molecular chains cross-link with adjacent molecules. Therefore, the oily substance is hardly recovered even if the heat treatment is performed. Not only that, but some vinyl chloride resins used for practical purposes may contain tens of percent of plasticizer depending on the application, and solid substances such as phthalic anhydride are generated by the thermal decomposition of this plasticizer. There is a problem that collection is difficult. Further, alcohol-based and olefin-based oily substances are obtained by the thermal decomposition of the plasticizer.Since this olefin easily undergoes an addition reaction with hydrogen chloride, chlorinated organic substances are produced and mixed with the oil, so the produced oil is used as a fuel. In this case, it is necessary to treat the combustion exhaust gas, which causes a problem that high quality fuel oil cannot be produced. When heat treatment is performed in supercritical water, hydrogen chloride, phthalic acid, and alcohols are decomposed, and the problem of addition reaction between hydrogen chloride and organic compounds is solved. When the temperature is further lowered to around room temperature after the treatment, hydrogen chloride separates as an aqueous solution, phthalic acid separates as a precipitated solid, and an alcohol system separates as an oil.
Each can be easily recovered.

Polyethylene terephthalate is produced by alternately polycondensing (dehydrating) terephthalic acid and ethylene glycol. Even if this is thermally decomposed, an oily substance is not obtained, but only a phthalic acid-based or ester-based solid substance is obtained. Therefore, when treated in supercritical water, it is completely decomposed into terephthalic acid and ethylene glycol. When the temperature is returned to room temperature after the treatment, terephthalic acid can be recovered as a precipitated solid, and ethylene glycol can be recovered as an aqueous solution.

Further, the paper is manufactured from natural polymer compounds such as cellulose. When heat-treated, it decomposes to produce water, leaving a carbonaceous residue. When heated together with plastic, energy is required to decompose the paper itself, resulting in a long processing time and reduced economic efficiency. Further, when trying to prevent the formation of an organic chlorine compound from a vinyl chloride resin by adding an alkali, it has been obtained experimental data that the efficiency is deteriorated when paper is mixed. Therefore, when heated together with oxygen in supercritical water, it is completely decomposed to generate water and carbon dioxide.

Furthermore, polyolefin plastics, that is, polyethylene, polypropylene, and polystyrene are polymer compounds composed of only carbon and hydrogen, and produce a high proportion of oily substance by thermal decomposition. When treated in supercritical water without adding oxygen, polystyrene has a low decomposition temperature and thus decomposes to produce an oily substance.
The other two types hardly react. When cooled to room temperature after the treatment, polyethylene and polypropylene have a small specific gravity and are recovered in a state of being suspended in water.

In practice, the waste plastic processing apparatus shown in FIG. 1 is used to carry out the present invention. 1 is a pressure-resistant autoclave for charging waste plastic raw materials, 2 is a vacuum pump for reducing the pressure in the autoclave, 3
Is a molten salt bath, and a heater 10 as a heating means for heating the autoclave 1 until the water becomes supercritical water and causing it to become a solvent for thermal decomposition reaction of waste plastic is attached to the outer periphery thereof. The heater 10 is resistance heating, but may be induction heating or the like. 4 is a water tank for cooling the autoclave 1, 5 is an oxygen cylinder for supplying oxygen to the autoclave, 6 is a condenser for returning the gas evaporated from the autoclave to a liquid, 7
Is a recovery container for recovering a liquid substance such as oil obtained in the condenser 6 and a solid chemical substance in some cases.
Further, the condenser 6 and the recovery container 7 are means for extracting oil and solid chemical substances, and 8 is a refrigerant passed through the inside of the condenser. Also, autoclave 1, vacuum pump 2, condenser 6
The line connecting the lines and the like indicates the line of the gas passage.

[0018]

【Example】

(Embodiment 1) In the following embodiment, the waste plastic processing apparatus shown in FIG. 1 is used to obtain an organic substance such as oil which can use waste plastic as a fuel or a chemical raw material, a chemical product which can be used as a chemical raw material, and the like.

First, 100 parts by weight of mixed waste plastic (soft vinyl chloride resin wire coating material: 40, polyethylene terephthalate beverage bottle: 20, foam polystyrene food tray: 20, polyethylene shopping bag: 20 parts by weight)
Then, 200 parts by weight of water and 200 parts by weight of water were sealed in the autoclave 1 at room temperature, and the air was removed using the vacuum pump 2. Here, the evacuation was performed to the vapor pressure of water at room temperature: 3.5 kPa. The purpose of this is to eliminate the influence of oxygen, but the presence of oxygen is positive in terms of accelerating the reaction, so that evacuation is not actually required. If the pressure is less than 3.5kPa, the added water will evaporate. Therefore, it is preferably in the range of 3.5 kPa to 101 kPa.

Next, the container is immersed in a molten salt bath 3 and 375 ° C.
Heated up. At this time, the heat medium of the molten salt bath 3 is Super-
A ternary molten salt called Salt was used, but it is liquid at 375 ° C. and can be used in an open system, for example, a mixed salt of potassium nitrite salt, sodium nitrite salt or the like, or metallic sodium may be used. The heating temperature is 370 from the viewpoint of exerting the reaction solvent characteristics of supercritical water as much as possible.
It is desirable to be in the range of ℃ to 400 ℃.

Then, after reaching the set temperature of 375 ° C., the reaction was carried out for 30 minutes, the container was taken out, placed in a water tank 4 and rapidly cooled. At this time, the reaction time is sufficient if the dechlorination reaction of the vinyl chloride resin, the decomposition reaction of the plasticizer and the hydrolysis reaction of polyethylene terephthalate can be carried out, and a sufficient reaction can be obtained if it is between 5 minutes and 1 hour. As a result, the pressure inside the autoclave 1 rises as the temperature rises and finally reaches 20MP.
It was over a. The reaction product was a yellow transparent oily liquid mainly composed of styrene, a solid suspended in water (hydrochloric acid), hydrochloric acid having a concentration of about 6%, and a solid substance precipitated in hydrochloric acid. As a result of the analysis, it was found that the suspended solids were polyethylene and the precipitated solids were a mixture of phthalic acid, terephthalic acid and carbonaceous residue. Little gas was produced. The material balance is summarized as follows.

(1) Before reaction: waste plastic 100, water 200 (2) After reaction: oily substance 33, floating solid 20, aqueous solution 213, precipitated solid 34 Since these reaction products can be easily separated and collected, there is no waste. It can be recycled. That is, oil can be used as fuel oil, suspended solids can be fuel oil if pyrolyzed at higher temperature, aqueous solution can be reused for addition to process plastics again, and precipitated solids can be heated to phthalate. It can be recovered as a chemical raw material by melting the acid and separating it from the carbonaceous residue.

(Comparative Example 1) Using the same apparatus and sample as in Example 1, the waste plastic raw material was treated in exactly the same manner as in the treatment conditions except that water was not added.

As a result, the pressure inside the autoclave after being placed in the water tank 4 and rapidly cooled did not exceed 10 MPa. The reaction products were hydrogen chloride-based gas, viscous gums and solids. Gum-like substance is styrene 2
The main component was the monomer, and the monomer and trimer were also included.
The solid was a mixture of polyethylene, esters, phthalic acids, and carbonaceous residue. The material balance is (1) before the reaction: waste plastic raw material 100 (2) after the reaction: gas 12, gum-like substance + solid substance 88. Although dechlorination decomposition of polyvinyl chloride, decomposition of plasticizer, decomposition of polystyrene, and decomposition of poly (ethylene terephthalate) were confirmed in this reaction, it is difficult to separate and recover the product, and therefore it is not only difficult to recycle the product. When the solid matter was pyrolyzed at a higher temperature, there was a problem of pipe clogging due to phthalic acid or the like.

(Example 2) The same apparatus and sample as in Example 1 were used, but after evacuation, heating was performed after adding 1 MPa of oxygen gas from the cylinder 5 to the gas. Conditions and the like not described here are the same as those in the first embodiment.

After reaching the set temperature, it was taken out in about 1 minute and rapidly cooled. As a result, the properties of the reaction product were almost the same as in Example 1, but there was a gas containing mainly carbon dioxide. Mass balance is (1) before reaction: plastic 100, water 200, oxygen gas 14 (2) after reaction: gas 10, oil 30, floating solids 20, aqueous solution 22
1 and the precipitated solid was 33. Since a partial oxidation reaction occurred in this reaction, decomposition proceeded sufficiently even in a short reaction time, and a recyclable product was obtained as in Example 1. However, the reaction time is preferably in the range of 30 seconds to 10 minutes, as long as the dechlorination reaction, the hydrolysis reaction and the partial oxidation reaction are performed, and it is not necessary to perform the thermal decomposition of the polymer. Among the products obtained as a result, the contents of oil, suspended solids, aqueous solution, and precipitated solids are as follows.

(1) The gas is carbon dioxide, (2) the oil is a hydrocarbon oil containing styrene monomer as a main component,
(3) Floating solids are polyethylene, (4) Aqueous solution is about 6%
The concentration of hydrochloric acid, (5) solids, was a mixture of phthalic acids and carbonaceous residues.

(Embodiment 3) Using the same apparatus and sample as in Embodiment 1, after carrying out thermal decomposition for 30 minutes, the internal fluid is introduced into the recovery container 7 through the condenser 6 without taking out the autoclave from the molten salt bath. The internal pressure of the autoclave was lowered to atmospheric pressure by, and further heated to 500 ° C. in a molten salt bath.

As a result, a yellow transparent oily liquid and hydrochloric acid were recovered in the recovery container, phthalic acids were recovered in the condenser, and carbonaceous residue was recovered in the autoclave. The material balance is summarized as follows.

(1) Before reaction: waste plastic 100, water 200 (2) After reaction: gas 2, oil 50, aqueous solution 213, deposit 2
6 and residue 9. The contents of each product were as follows.

(1) The gas is a lower hydrocarbon, (2) the oil is a hydrocarbon oil mainly containing olefins, (3) the aqueous solution is hydrochloric acid having a concentration of about 6%, and (4) the deposit is , Phthalates,
(5) The residue was a carbonaceous residue.

As a result, the decomposition reaction was completed, and a large amount of fuel oil was obtained. The aqueous solution can be used as an additive when decomposing the plastic again, and can also be used as concentrated hydrochloric acid if the concentration of hydrogen chloride increases. The deposits (phthalic acids) can be used as chemical raw materials.

[0033]

As described above, according to the present invention, it is possible to obtain high-quality oils and organic compounds as fuel oils or chemical raw materials from plastics unsuitable for oiling and mixed waste plastics containing foreign substances. Since chemical raw materials such as can be easily separated and collected, efficient recycling becomes possible.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an oil treatment device suitable for carrying out the present invention.

[Explanation of symbols]

 1: Autoclave 2: Vacuum pump 3: Molten salt bath 4: Water tank 5: Oxygen gas cylinder 6: Condenser 7: Recovery container 8: Refrigerant 10: Heater

Claims (4)

[Claims] 1. A pressure-resistant container for mixing waste plastic containing at least an element other than C and H with water, and heating the pressure-resistant container until the water becomes supercritical water so as to be used as a solvent for the thermal decomposition reaction of the waste plastic. An apparatus for treating waste plastic, comprising: heating means; and means for extracting oil and solid chemical substances from the solvent. 2. A first step of mixing waste plastic containing at least an element other than C and H with water, and heating the mixture until the water becomes supercritical water to become a reaction solvent for the waste plastic. A method for treating waste plastic, comprising a second step and a third step of extracting oil and solid chemical substances from the solvent. 3. The method for treating waste plastic according to claim 2, wherein an oxygen source such as oxygen, air, or hydrogen peroxide is mixed with the waste plastic together with water in the first step. 4. The method for treating waste plastic according to claim 2, wherein after the third step, the extracted solid chemical substance is further decomposed by heating.