JP2007277389A - Recovery process of plastic waste by type - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To recover reworked materials for every types by batch processing of plastic wastes without beforehand classification. <P>SOLUTION: This recovery process by types comprises a step of crushing the plastic wastes into a controlled size, a step of hydrolyzing the crushed plastics, a step of extracting a crude lactic acid aqueous solution formed from a plant-derived biodegradable plastic contained in the hydrolyzed plastic wastes, a step of sorting a petroleum-derived powdery biodegradable plastic by sorting a residual solid component by a particle size after the extraction of the crude lactic acid aqueous solution, and a step of sorting a petroleum-derived chemical synthetic plastic by removing an impurity from the residual solid component after sorting the petroleum-derived powdery biodegradable plastic. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for separating used plastics, and more particularly to a method for separating plant-derived plastics from other plastics and recovering them effectively.

  In recent years, the production and usage of petroleum-derived chemically synthesized plastics, which are petrochemical products such as PE (polyethylene), PP (polypropylene), and PS (polystyrene), have been enormous, and the treatment after use has been domestic and overseas. Regardless of the cause, it is a major cause of environmental pollution and a major social problem.

  This is a problem, and chemical synthetic plastics do not decompose naturally, that is, do not return to nature. In order to deal with this problem, researches on naturally decomposable plastics (biodegradable plastics) have been actively conducted in Japan and overseas, and some of them have been put into practical use.

  Also, in recent expositions, biodegradable plastics are taken up as one major theme. Judging from this situation, it is expected that many replacements for petroleum-derived plastics will appear in the next few years.

  However, although this biodegradable plastic can be naturally decomposed, it can be relied on when it is a small amount of waste, but it takes a long time for natural decomposition. If it is used in a large amount like chemical synthetic plastics and then disposed of in large quantities, it will soon face the problem of waste disposal, and eventually it will have to rely on incineration or landfill again. It is clear that the situation has resulted in repeated vicious circles where initial expectations are betrayed and become a major cause of environmental pollution and a major social problem.

  However, various proposals have been made for the recycling method of waste containing biodegradable plastics. For example, Patent Document 1 discloses that methane gas produced by fermentation by efficiently decomposing and fermenting organic waste containing biodegradable plastics in a short period of time including biodegradable plastics using methane fermentation technology. The technology to collect is introduced.

  The recovered methane gas is used as clean fuel energy. Patent Document 2 describes a method of regenerating biodegradable waste containing biodegradable plastics and food residues as resources such as fertilizer and feed. According to this method, when the biodegradable waste is only the biodegradable plastic, it can be regenerated into lactic acid as a raw material.

  However, it is a special case that the waste treatment is only biodegradable plastic. Usually, biodegradable plastic waste contains various types of waste including other types of plastic. For this reason, in order to regenerate lactic acid, which is a raw material, from biodegradable plastic waste, it is necessary that the waste be sorted according to type.

  However, when the waste is plastic, it is difficult to distinguish whether the waste is a chemically synthetic plastic that cannot be decomposed or a biodegradable plastic. Strictly speaking, even biodegradable plastics are different from those derived from plants and those derived from petroleum. Conventionally, when processing plastics, regardless of the type, they are landfilled or incinerated at the same time. When plastic is recycled from waste, it cannot be decomposed by chemical-synthetic plastics, which are derived from decomposable plants. It is necessary to separate into biodegradable plastics and degradable petroleum-derived biodegradable plastics.

Separately recovered petroleum-derived chemical synthetic plastics are crushed and recycled to new resources by mixing with other materials via chemical treatment. In addition, both plant-derived and petroleum-derived biodegradable plastics can be decomposed by hydrolysis treatment or microbial treatment, but the conditions are not necessarily the same.
Patent Publication 2005-95729 Patent Publication 2005-131631

  The problem to be solved is that when plastic waste is recycled, it is difficult to recycle if the waste contains only a specific plastic or if the waste is not sufficiently separated. Is a point.

  The most important feature of the present invention is that plastic waste can be collectively processed without being manually sorted in advance, and finally the recycled material can be recovered for each type of plastic.

  According to the method for separating and recovering plastic waste of the present invention, plastic waste is collectively processed, and finally the biodegradable plastic derived from plant and petroleum using the difference in characteristics of plastic waste and derived from petroleum These can be separated and collected into plastics of chemical synthesis system and recycled as raw materials for the respective plastics.

  Extraction of crude lactic acid aqueous solution by hydrolysis treatment of plastic waste in batches and residual solid particles for the purpose of separating and recovering biodegradable plastics derived from plants and petroleum and chemical synthetic plastics derived from petroleum By separating the diameter and removing impurities, we realized the separation and recovery of plant-derived, petroleum-derived biodegradable plastics and petroleum-derived chemically synthesized plastics without sorting plastic waste in advance.

  FIG. 1 shows the configuration of a system used in the method of the present invention. In FIG. 1, the system according to the present invention comprises a combination of a hydrolysis treatment device A, a particle size sorting device B, and an impurity removal device C.

  The hydrolysis processing apparatus A includes a combination of a processing chamber 1, an extraction pipe 2, a cooling tower 3, and a circulation pump 4. The processing chamber 1 is a kettle that heats a workpiece to be processed and performs a hydrolysis treatment. The outer wall of the processing chamber 1 is equipped with a heater 5, and the extraction pipe is disposed between the processing chamber 1 and the cooling tower 3. 2 are connected.

  The extraction pipe 2 is a circulation pipe that connects between the lower steam return port 6 of the processing chamber 1 and the upper steam outlet 7, and the cooling tower 3 is connected in the pipe, and the circulation pump 4 is It is connected in the pipe line on the upstream side of the cooling tower 3. Further, the processing chamber 1 has an input port 8 and a discharge port 9 for the object to be processed, in which the object to be processed input into the processing chamber 1 is agitated while rotating about the vertical axis. A stirring blade 10 is provided.

  The cooling tower 3 is a heat exchanger that cools the air (steam) in the extraction pipe 2, and the circulation pump 4 forcibly blows water vapor in the processing chamber 1 to the cooling tower 3 after hydrolysis of the object to be processed. To do. The cooling tower 3 includes a drain 11 in which the extracted crude lactic acid aqueous solution that is a hydrolysis component in water vapor is stored in the cooling tower 3, and the crude lactic acid aqueous solution stored in the cooling tower 3 is used as an extract. It is collected in the container V1. The crude lactic acid eluted by hydrolysis in the chamber 1 is recovered in the container V2 by opening the drain 11 '.

  The particle size sorting apparatus B is a device that sorts solids in the processing chamber 1 into powder and granular materials by particle size sorting. In this example, the impurity removing device C is a device that mainly separates the remaining material other than the powder sorted by the particle size sorting device B using a method such as magnetic separation or specific gravity separation into a metal component and a non-metal component. is there. The powder selected by the particle size sorting apparatus B is mainly a biodegradable plastic derived from petroleum, and the residue from which the metal has been removed by the impurity removing apparatus C is a chemical synthetic plastic derived from petroleum.

  The present invention is a method for separating and recovering plastic from plastic waste by sequentially performing a hydrolysis process, a particle size selection process, and an impurity removal process. Hydrolysis treatment is a treatment that selectively hydrolyzes biodegradable plastic contained in plastic waste. As a result of the hydrolysis treatment, plant-derived biodegradable plastic is extracted as a solution, and petroleum-derived biodegradable plastic is extracted. The degradable plastic becomes powdery by hydrolysis treatment.

  The particle size selection process is a process of selecting the particle size of petroleum-derived biodegradable plastics that have been hydrolyzed into a powder form from the solids extracted and remained as plant-derived biodegradable plastic solutions. The impurity removal process is a process of selecting a petroleum-derived chemically synthesized plastic from remaining solids in addition to the petroleum-derived biodegradable plastic whose particle size is selected.

  The impurity removal process is a process for removing metal components that are not hydrolyzed other than petroleum-derived chemically synthesized plastics from impurities contained in plastic waste.

  Next, a procedure for recovering recycled plastic materials from plastic waste using the above system will be described with reference to FIG.

(1) Crushing process (step S1)
In the present invention, the object to be treated is a crushed plastic waste mainly composed of plant-derived biodegradable plastic. Here, plastic waste mainly composed of plant-derived plastics is mostly plant-derived plastics, including petroleum-derived biodegradable plastics and petroleum-derived chemical synthetic plastics. This means that other types of plastics may be included.

  That is, it is used in the sense that it is not necessary to separate these by hand in advance and to limit the raw material to only plant-derived plastic. Plastic waste mainly composed of plant-derived plastic is crushed to a size of 3 to 5 cm.

(2) Raw material input (step S2)
An object to be processed crushed to a size of 3 to 5 cm is put into the processing chamber 1 and filled to the full capacity of the processing chamber 1.

(3) Water supply (Step S3, Step S4)
In the processing chamber 1, 20% of the total weight of the object to be processed is added, and the processing chamber 1 is sealed.
(4) Heating mode start (step S5)
A timer is set and the heater 5 is energized to start the heating mode while heating the inside of the processing chamber 1 to about 140 ° C. In the heating mode, the pressure in the processing chamber 1 is maintained at a saturated water vapor pressure at a heating temperature of about 140 ° C. Further, the stirring blade 10 is rotationally driven about once every fixed interval (for example, 2 seconds) to stir the raw material in the processing chamber 1.

(5) Hydrolysis treatment (step S6)
In this state, the workpiece is exposed to an atmosphere of saturated water vapor generated in the processing chamber 1 while heating the workpiece in the processing chamber 1 over a certain period of time, and the hydrolysis reaction proceeds. Depending on the heating mode, the hydrolysis reaction of the lactic acid-based biodegradable plastic proceeds to generate a vapor of the crude lactic acid aqueous solution, and the vapor fills the processing chamber 1. After elapse of a predetermined time, the heater 5 is turned off to complete the heating mode.

  Although the time required for the hydrolysis treatment of the object to be treated depends on the capacity of the treatment chamber 1, it is usually 5 to 8 hours. That is, when heated in a sealed processing chamber 1 at about 140 ° C., the biodegradable plastic in the object to be processed can be hydrolyzed within a few hours under a saturated water vapor pressure at 140 ° C. .

FIG. 3 is a diagram showing a decomposition mechanism of organic substances by hydrolysis. In FIG. 2, hydrolysis basically means that water ions (H ⁺ and OH ⁻ ) act between oxygen and other atoms (for example, carbon C) that are organically coupled to each other to break the electrical coupling. That is.

That is, so-called polarization occurs in which electrons move between carbon “C” and oxygen “O” and are unevenly distributed, and water ions “H ⁺ ” and “OH ⁻ ” are attracted and electrically coupled therewith. Although it is a phenomenon, the energy of each electron and atom is closely related, and temperature and pressure directly act as excitation energy of this electron and atom. Accordingly, the reaction rate of the hydrolysis reaction slightly changes depending on the temperature and pressure applied to the reaction at this time.

  For example, lactic acid, which is a raw material for polylactic acid, is sublimated into a gas within a certain temperature range, melted into a liquid, or evaporated into a gas. However, melting itself is a reaction accompanied by decomposition. When lactic acid decomposes, it is not pure lactic acid and is difficult to be a raw material for polylactic acid. However, it is possible to pass through this delicate reaction region by controlling the temperature and pressure of the atmosphere.

  Here, by controlling temperature and pressure, polylactic acid is hydrolyzed into a lactic acid oligomer. Under high pressure, it sublimes even at a relatively low temperature, and once it becomes a gas, this gas is water-soluble and therefore dissolves in a large amount in hot water. This makes it possible to recover a large amount of lactic acid as a solution.

  The time set by the timer is the heating mode time of the hydrolysis treatment. In the heating mode, with the steam delivery port 7 and the steam return port 6 of the extraction pipe 2 closed and the inside of the processing chamber 1 sealed, the object to be treated is heated and pressurized, and under the saturated water vapor pressure at the heating temperature. The hydrolysis of the workpiece is advanced. When the set time has elapsed, a buzzer will notify you. In addition, even before the set time, when a heating mode abnormality (temperature abnormality, pressure abnormality) occurs, a buzzer can also notify.

(6) Cooling mode (step S7)
When the time of the heating mode set by the timer has elapsed, the heating mode is terminated, and then the mode is shifted to the cooling mode (step S7). In the cooling mode, the temperature is lowered while controlling the pressure and temperature in the processing chamber 1 according to the saturated water vapor pressure curve shown in FIG. In the cooling mode, the valves of the extraction pipe 2 on the delivery side and the return side are opened, the circulation pump 4 is activated, the water vapor in the processing chamber 1 is sucked into the extraction pipe 2, and a part is passed through the cooling tower 3. The dried air after the condensation and cooling is returned to the processing chamber 1 again, and the solution remaining in the processing chamber 1 is recovered while circulating the water vapor in the processing chamber 1 between the cooling tower 3 and the processing chamber 1.

  In the cooling mode, an aqueous solution of crude lactic acid and a dried solid matter are left in the processing chamber 1, and the extract extracted from the object to be processed and contained in the steam is sent into the cooling tower 3, It is cooled in the cooling tower 3 and condensed and stored in the cooling tower 3 as a crude lactic acid aqueous solution.

(7) Solution recovery (step S8)
The water vapor in the processing chamber 1 gradually decreases in temperature and pressure due to repeated cooling, and after confirming that the processing chamber 1 is at room temperature and normal pressure, the drain 11 of the cooling tower 3 is opened. The crude lactic acid aqueous solution extracted inside is collected in the container V1, and the solution in the processing chamber 1 is collected in the container V2 by opening the drain 11 ′. The solid product is recovered from the discharge port 9. The crude lactic acid aqueous solution collected in the containers V1 and V2 becomes the raw material of the biodegradable plastic product again.

(8) Execution of drying process (step S9)
The solid matter remaining in the processing chamber 1 is further dried to a humidity of 4% or less and recovered from the processing chamber 1.
(9) Grain size selection process (step S10)
The solid matter collected from the processing chamber 1 is taken out to the particle size sorting device B, the particle size is sorted, and sorted into powder and granules, and the fine particle size is collected in the container V3. Although the particle size of the screen cannot be specified, the fine powder is mainly a biodegradable plastic derived from petroleum. As long as petroleum-derived biodegradable plastics are also biodegradable, they are hydrolyzed into fine powders, and those that are not hydrolyzed remain in the originally crushed size. Petroleum-derived biodegradable plastics obtained as powders are processed into, for example, plastic recycled materials and soil conditioners.

(10) Impurity removal process (step S11)
After the particle size sorting process, the solid matter having a large particle size remaining in the particle size sorting device B is sorted by the impurity removal processing device C. In this example, the metal particles are selected, the metal particles are collected in the container V4, and the remaining particles are collected in the container V5. The remaining granules are mainly petroleum-derived plastics. The recovered petroleum-derived plastic is recycled as a raw material for plastic products. In the above-described embodiments, an example in which a heater is used as a means for raising the temperature in the processing chamber 1 has been described. However, in a large system, it is more efficient to use heated steam as a heat source using a boiler.

  According to the present invention, plastic waste can be collectively processed without being manually sorted in advance, and finally collected for each type of plastic. In the above embodiments, the temperature is lowered in the biodegradable plastic processing chamber under the conditions of constant temperature and pressure, particularly in the heating mode at the saturated steam pressure at the heating temperature of 140 ° C. and the cooling mode after the end of the heating mode. An example in which the hydrolysis treatment is physically performed is shown. According to this method, the hydrolysis treatment can be completed in a relatively short time of 5 to 8 hours, but the hydrolysis treatment in the present invention is not necessarily limited to the case where the treatment is physically performed. Hydrolysis treatment is possible in principle by microbial treatment, chemical reaction treatment and other existing methods, but with the existing methods, hydrolysis takes too much time and has practical problems. Naturally, hydrolysis treatment by microbial treatment or chemical reaction treatment can also be used if the treatment time can be cleared in practice.

  The method of the present invention is applied to the processing of a large amount of plastic waste generated from the distribution industry such as fresh food products, preserved processed products, cooked products, and cooked dishes, restaurants, supermarkets, convenience stores, etc. In addition, the plastic raw materials can be recycled efficiently.

It is a block diagram of the system used for the method of this invention. It is a figure which shows the flow of this invention method. It is a figure explaining the hydrolysis mechanism of organic substance. It is a graph which shows a saturated water vapor pressure curve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Processing chamber 2 Extraction pipe 3 Cooling tower 4 Circulation pump 5 Heater 6 Steam return port 7 Steam delivery port 8 Input port 9 Outlet port 10 Stirring blade 11, 11 'Drain V1, V2, V3, V4, V5 Container

Claims (3)

A method for separating and recovering plastic from plastic waste having a hydrolysis process, a particle size selection process, and an impurity removal process,
Hydrolysis treatment is a treatment that selectively hydrolyzes biodegradable plastic contained in plastic waste.
Plant-derived biodegradable plastics are extracted as a solution by hydrolysis, and petroleum-derived biodegradable plastics are powdered by hydrolysis.
The particle size selection process is a process for selecting the particle size of powdery petroleum-derived biodegradable plastic from the solid matter extracted and remaining as a plant-derived biodegradable plastic solution,
The method for separating and collecting plastic waste, wherein the impurity removal process is a process of selecting a chemical synthetic plastic derived from petroleum from solids other than the biodegradable plastic derived from petroleum whose particle size is selected.   2. The plastic waste according to claim 1, wherein the impurity removal treatment is a treatment for removing metal components other than petroleum-derived chemically synthesized plastics that are not hydrolyzed from impurities contained in the plastic waste. Separation collection method.   A step of crushing plastic waste to a certain size, a step of hydrolyzing the crushed plastic, and a crude lactic acid aqueous solution generated from biodegradable plastics derived from plants contained in the plastic waste by hydrolysis And after the extraction of the crude lactic acid aqueous solution, the remaining solid components are subjected to particle size selection to select powdery petroleum-derived biodegradable plastics, and powdery petroleum-derived biodegradable plastics are selected. The method for separating and recovering plastic waste according to claim 1, further comprising a step of removing impurities from the remaining solid components and selecting a chemical synthetic plastic derived from petroleum.

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