KR101139475B1 - Method of recycling crosslinked waste pipes of high density polyethylene - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of regenerating crosslinked waste-crosslinked high density polyethylene (HDPE) pipe, which is mostly incinerated, into a reformable high density polyethylene pipe by decrosslinking with supercritical methanol. The waste crosslinked high density polyethylene pipe is a high density polyethylene resin that can be reshaped by decrosslinking reaction using supercritical methanol for 5 to 10 minutes under a reaction temperature of 370 to 390 ° C. and a reaction pressure of 5 to 30 MPa. It is characterized by regeneration.

Waste Crosslinked High Density Polyethylene, Crosslinked Pipe, Recycled, Supercritical Reaction, Decrosslinking

Description

Recycling method of waste crosslinked high density polyethylene pipe {METHOD OF RECYCLING CROSSLINKED WASTE PIPES OF HIGH DENSITY POLYETHYLENE}

The present invention relates to a method of regenerating crosslinked waste-crosslinked high density polyethylene pipes using a supercritical methanol to a high density polyethylene resin that can be reshaped by decrosslinking.

In the recent era of low carbon green growth, waste plastics, especially urethane resins, phenolic resins, urea resins, epoxy resins, melamine resins, unsaturated polyester resins, etc. Technology development is emerging as an important social problem. However, for the recycling of the waste crosslinked polymer, only some R & D and commercialization are in progress in developed countries such as the United States and Japan, and incineration or landfilling is mostly carried out in Korea.

In general, crosslinked polymers are widely used in various fields that are closely related to real life, such as small marine materials, structural materials for automobiles and aerospace, and sporting goods. However, due to the insoluble and infusible properties of the intramolecular crosslinked network, they are simply crushed, crushed and discarded due to the lack of proper treatment or regeneration methods. There is no recycling, which causes many environmental problems.

In order to recycle the waste crosslinked polymer resin, which is mostly incinerated, a complex system for decrosslinking the crosslinked structure of the thermosetting resin and organic / inorganicizing the decrosslinked reaction product is required. As such, the recycling of waste cross-linked polymer resins is very urgent in terms of recycling waste resources and resource efficiency. However, some developments have been reported only in advanced countries such as Japan and the United States.

In particular, the waste crosslinked high density polyethylene-based pipes having a long-term durability of 90% or more of the crosslinking degree used for high-temperature, high-pressure hot water ondol are not melted even when heated due to the crosslinked network structure, and thus cannot be remolded. Thus, waste crosslinked high density polyethylene based pipes are mostly incinerated, which causes serious environmental problems.

Regarding the recycling of the waste crosslinked polymer resin, Korean Patent No. 10-0733941 discloses a method of regenerating a multilayer waste packaging film in which aluminum is deposited using a compatibilizer and a functional resin, and Korean Patent No. 10-0728087 Disclosed is a method for recycling waste high density polyethylene by reactive extrusion using a peroxide crosslinking agent. EP 0897783A2 also discloses a method for partially decrosslinking waste low density polyethylene foams by increasing shear stress at high temperatures using a twin screw extruder.

In addition, Japanese Laid-Open Patent Publication Nos. 2005-281429, 2004-161983, 2003-96233, 2001-253968 and 2001-98107 use supercritical water to selectively crosslink the crosslinked polyolefin. Although some attempts have been made, the critical temperature and critical pressure of the water are so high that an expensive reactor is required, making it economically difficult to commercialize.

Accordingly, the present inventors have diligently researched to develop an economical method for effectively recycling the waste crosslinked high density polyethylene pipe, which is mostly incinerated, and as a result, the supercross methanol is used as a reaction solvent to remove the waste crosslinked high density polyethylene pipe. The present invention has been completed by developing a method of regenerating a high-density polyethylene resin that can be reformed and remolded.

Accordingly, an object of the present invention is to provide a method of re-crosslinking a crosslinked high-density polyethylene-based pipe to be recycled to a high-density polyethylene-based resin that can be re-molded in an environmentally friendly and economical manner to recycle the waste crosslinked high-density polyethylene-based pipe.

In order to achieve the above object, the present invention is a cross-linking reaction of the waste crosslinked high density polyethylene pipe using supercritical methanol for 5 to 10 minutes under a reaction temperature of 370 to 390 ° C. and a reaction pressure of 5 to 30 MPa. Provided is a method for regenerating waste crosslinked high density polyethylene based pipes, the method comprising the step of converting to a reformable high density polyethylene based resin.

The present invention also provides a regenerated high density polyethylene resin regenerated according to the above method.

In addition, the present invention provides a molded article manufactured using the recycled high density polyethylene resin.

Recycling method of waste crosslinked high density polyethylene pipe according to the present invention is an environmentally-friendly and economical method with low commercialization cost because it can perform decrosslinking reaction at lower reaction pressure than supercritical water because supercritical methanol is used as a reaction solvent. to be. Therefore, according to the present invention, it is possible to significantly reduce the amount of waste crosslinked high density polyethylene pipe which is mostly incinerated, thereby preventing secondary environmental pollution due to its incineration, and the recycled high density polyethylene recycled therefrom is superior to new high density polyethylene. Due to its mechanical properties, it can be usefully recycled into various molded products.

The present invention provides a high-density polyethylene recyclable by decrosslinking the waste crosslinked high density polyethylene pipe using supercritical methanol for 5 to 10 minutes under a reaction temperature of 370 to 390 ° C. and a reaction pressure of 5 to 30 MPa. It provides a method for regenerating waste cross-linked high density polyethylene pipe, comprising the step of converting to a resin.

The recycling method of the waste crosslinked high density polyethylene pipe according to the present invention is characterized by applying an environmentally friendly supercritical fluid process to recycling the waste crosslinked polymer resin, wherein the critical temperature and the critical pressure are relatively mild compared to the supercritical water. And converting the waste crosslinked high density polyethylene pipe, which is a crosslinked polymer resin, into a high density polyethylene resin that can be reshaped by a decrosslinking reaction using supercritical methanol, which is easy to equip, as a reaction solvent.

Supercritical fluid refers to a substance in which a liquid or gaseous substance has reached a "critical state" in which gas and liquid are indistinguishable beyond the limits of a certain high temperature and high pressure called a supercritical point. The density of supercritical fluid molecules is close to liquid, but the viscosity is low, close to gas, and the diffusion is fast, so the thermal conductivity is as high as water. Accordingly, the use of supercritical fluid as a solvent results in extremely high concentrations of dissolved molecules, i.e., solvents around the solute. Because of this feature, supercritical fluids are often used in the process of extracting and separating certain components from a mixture.

In the present invention, a supercritical fluid having all of the advantages of low surface tension, low viscosity, high diffusion rate and excellent dissolving ability of a liquid, and supercritical methanol which can cut a polymer chain in a high temperature and high pressure state above a critical point. Was selected. Supercritical methanol is a supercritical fluid with a molecular weight of 32.04 g / mol and has a lower critical point than a supercritical water having a critical temperature of 512.6 ° C and a critical pressure of 8.09 MPa and a critical temperature of 647.3 ° C and a critical pressure of 7.38 MPa. Since the equipment construction cost is low at the time of commercialization, it can be effectively used to convert waste crosslinked high density polyethylene pipe, which is a crosslinked polymer resin, into a high density polyethylene resin by a decrosslinking reaction.

Hereinafter will be described in detail the regeneration method of the waste cross-linked high density polyethylene pipe according to the present invention.

In the present invention, a method for recycling waste cross-linked high density polyethylene pipes by a supercritical fluid process using a high pressure batch reactor and a supercritical methanol as a reaction solvent is illustrated.

In the regeneration method according to the present invention, all the waste crosslinked high density polyethylene pipes which are not recycled due to insolubility and incompatibility of the crosslinked polymer chain and simply discarded by incineration may be applied. Preferably, it may be a waste crosslinked high density polyethylene pipe of organic peroxide crosslinking method or electron beam crosslinking method or a mixture thereof, and a waste crosslinked high density polyethylene pipe having a gel fraction of 85 to 95% may be advantageously applied.

In addition, according to the regeneration method of the present invention, regardless of the type of waste crosslinked high density polyethylene pipe, all kinds of wastes can be recycled, and in particular, the waste crosslinked high density polyethylene pipe used for hot water ondol at high temperature and high pressure may have a predetermined size or less. More effective when applied after grinding. This is because the waste-crosslinked high density polyethylene resin has high crystallinity, high crosslinking degree, high density and excellent durability, and the diffusion rate of the reaction fluid may be influenced by the particle size during the decrosslinking reaction using the supercritical fluid, which may influence the overall reaction efficiency. . Therefore, for efficient decrosslinking reaction, the waste-crosslinked high density polyethylene pipe is pulverized to have a predetermined size or less, preferably 11 mm or less, as a pretreatment process before being applied to the decrosslinking reaction. At this time, the grinding of the waste crosslinked high density polyethylene pipe may be performed according to a conventional method in the art.

The high pressure batch reactor illustrated in FIG. 1 may be manufactured using stainless steel, Hastelloy steel, Inconel steel, etc., but since methanol is almost non-corrosive in a supercritical state, it is economical to use stainless steel having a low cost. It is advantageous.

In a preferred embodiment of the present invention, after the finely pulverized crosslinked high density polyethylene pipe and supercritical methanol are put into the above-described high pressure batch reactor, the reaction temperature is 370 to 390 ° C. and the reaction pressure is 10 to 15 MPa. The decrosslinking reaction is carried out for 10 minutes to convert the waste crosslinked high density polyethylene pipe into a high density polyethylene resin.

The supercritical methanol used as the reaction solvent is preferably used in an amount of 100 to 500 parts by weight based on 100 parts by weight of the waste crosslinked high density polyethylene pipe. If the amount of supercritical methanol is less than 100 parts by weight, the supercritical conditions are not established and decrosslinking is not performed. If the amount is more than 500 parts by weight, the reactor is thicker due to the explosion risk due to high vapor pressure. Problems that must be produced can arise.

The reaction pressure is adjusted according to the amount of waste crosslinked high density polyethylene pipe and supercritical methanol injected into the reactor within the above range, and the reaction temperature is controlled by using an electric furnace installed outside the reactor. After the decrosslinking reaction is completed, it is preferable to control the cooling rate to within 15 minutes by quenching the cooler in the reactor as well as the flange part in order to reduce the residence time of the reactants in the reactor. If the cooling rate exceeds 15 minutes, there may be a problem in that physical properties due to degradation of the polymer decrease due to an increase in the reaction residence time.

As a result of analyzing the degree of crosslinking after recovering the high density polyethylene resin recycled through the above method, the waste crosslinked high density polyethylene pipe has a gel fraction of 0.5% or less by decrosslinking reaction using supercritical methanol according to the present invention. It was confirmed that the conversion to a high density polyethylene-based resin as possible.

In conclusion, the recycling method of the waste crosslinked high density polyethylene pipe according to the present invention uses supercritical methanol, which is an environmentally friendly solvent, as the reaction solvent, so that the crosslinking reaction can be carried out at a lower reaction pressure than the supercritical water. It's a friendly way. Therefore, according to the present invention, the amount of waste crosslinked high density polyethylene pipe which is mostly incinerated can be significantly reduced, thereby preventing secondary environmental pollution due to its incineration, and the recycled high density polyethylene recycled therefrom has a gel fraction of 0.5% or less. Has excellent mechanical properties corresponding to new high density polyethylene and can be usefully recycled into various molded articles.

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are only for illustrating the present invention more specifically, it will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples in accordance with the gist of the present invention.

Example  One

In consideration of the characteristics of the waste-crosslinked high density polyethylene pipe having high crystallinity and structure, a pretreatment process of grinding waste crosslinked high density polyethylene pipe for high temperature and high pressure hot water ondol under a predetermined size was performed. At this time, the waste crosslinked high density polyethylene-based pipes having a gel fraction of about 90% were ground to have particle sizes of 10 to 11 mm, 5 to 6 mm, and 0.6 to 1 mm, respectively. In a 500 ml stainless steel batch reactor (SUS316), a pulverized product having respective particle size and 125 parts by weight of supercritical methanol were added to 100 parts by weight of the pulverized powder, followed by 365 ° C., 370 ° C. under a reaction pressure of 15 MPa and The decrosslinking reaction was performed at a reaction temperature of 375 ° C. for 5 minutes. After the decrosslinking reaction was terminated, a high density polyethylene resin was recovered by rapidly cooling the temperature of the reactant to room temperature using a cooler.

The crosslinking degree of the high density polyethylene-based resin recovered after each reaction was measured according to ASTM D2765. Briefly, the pulverized sample of 30 to 60 mesh was put into a 120 mesh wire mesh bag and boiled at 1 atmosphere (0.1 MPa) at 110 ° C. for 12 hours using xylene contained in a round flask connected to a condenser. It was. After extraction, the amount of the sample remaining in the wire mesh bag (mg) was measured, and the gel fraction (%) was calculated using this, and the results are shown in Table 1 below.

Reaction temperature (℃) Reaction pressure (MPa) Particle size (mm) XLPE: Methanol Weight Ratio (g: g) Response time (minutes) Gel fraction (%) 365 15 10-11 1: 1.25 5 40.7 5-6 33.6 0.6-1 24.5 370 15 10-11 1: 1.25 5 12.4 5-6 8.9 0.6-1 3.9 375 15 10-11 1: 1.25 5 7.1 5-6 3.1 0.6-1 0.6

Table 1 shows the results of measuring the gel fraction according to the particle size of the waste crosslinked high density polyethylene during the decrosslinking reaction according to the present invention. As shown in Table 1, in the samples having a particle size of 10 to 11 mm of the pulverized product, the decrosslinking reaction was poor due to the high crystallinity of the crosslinked high density polyethylene resin, while the particle size of the pulverized product was 6 mm or less, especially 0.6 to In the sample of 1.0 mm, the decrosslinking reaction was well performed, and it was confirmed that the gel fraction was reduced to 1% or less. Therefore, for efficient decrosslinking reaction, it is preferable to crush the waste crosslinked high density polyethylene pipe to have a particle size of 11 mm or less and then decrosslink it.

Example  2

The waste crosslinked high density polyethylene pipe for high temperature, high pressure hot water ondol having a gel fraction of about 90% was crushed to a particle size of about 0.6 to 1.0 mm, and then 125 weights of supercritical methanol was added to this pulverized product and 100 parts by weight of the pulverized product. Part was added to a 500 ml volume stainless steel batch reactor. The decrosslinking reaction was performed for 5 minutes while varying the reaction temperature of the reactor to 320 ° C, 340 ° C, 360 ° C, 365 ° C, 370 ° C, 380 ° C and 400 ° C under a reaction pressure of 15 MPa. After the decrosslinking reaction was terminated, a high density polyethylene resin was recovered by rapidly cooling the temperature of the reactant to room temperature using a cooler.

The gel fraction (%) of the high density polyethylene-based resin recovered after each reaction was measured according to the method described in Example 1 above, and the results are shown in Table 2 below.

Reaction temperature (℃) Reaction pressure (MPa) XLPE: Methanol
Weight ratio (g: g) Response time (minutes) Gel fraction (%) 320 15 1: 1.25 5 85.9 340 15 1: 1.25 5 82.6 360 15 1: 1.25 5 53.0 365 15 1: 1.25 5 24.5 370 15 1: 1.25 5 3.9 375 15 1: 1.25 5 0.6 380 15 1: 1.25 5 0 400 15 1: 1.25 5 0

As shown in Table 2, in the crosslinked high density polyethylene pipe having a 90% gel fraction, the decrosslinking reaction was actively carried out as the reaction temperature was increased, but the change in the gel fraction was not large at the reaction temperature below 360 ° C. The gel fraction decreased sharply at 365 ° C. and the gel fraction decreased rapidly at 370 ° C., and the gel fraction decreased below 0.5% at 380 ° C. or higher.

Example  3

As described in Example 2, the supercritical methanol was used as a reaction solvent except for using a 2000 mL volume stainless steel batch reactor and varying the reaction temperature, reaction pressure and reaction time as shown in Table 3 below. Decrosslinking reaction of the waste crosslinked high density polyethylene pipe with 90% gel fraction was carried out.

Reaction temperature (℃) Response time (minutes) Reaction pressure (MPa) Gel fraction (%) 360 One 10 55.6 5 10 54.3 15 53.8 10 10 52.7 15 10 50.6 365 One 10 30.4 5 10 25.4 15 24.5 10 10 21.3 15 10 19.8 370 One 10 13.8 5 10 6.9 15 3.9 10 10 3.5 15 10 3.4 375 One 10 3.4 5 10 1.2 15 0.6 10 10 0.3 15 10 0.2

As shown in Table 3, it was found that the gel fraction of the waste crosslinked high density polyethylene pipe decreased in proportion to the reaction pressure and the reaction time when the decrosslinking reaction proceeded at the reaction temperature of 370 ° C. or higher, as shown in Example 2. .

According to the present invention, when the crosslinked waste crosslinked high density polyethylene pipe using supercritical methanol as a reaction solvent, the gel fraction was remarkably reduced, and it was confirmed that the waste crosslinked high density polyethylene pipe could be effectively recycled to the high density polyethylene resin. It was.

The specific parts of the present invention have been described in detail, and it is apparent to those skilled in the art that such specific descriptions are merely preferred embodiments, and thus the scope of the present invention is not limited thereto. something to do. Thus, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Figure 1 shows a schematic diagram of a high pressure batch reactor that can be used in the decrosslinking reaction according to the present invention.

<Description of the symbols for the main parts of the drawings>

A: pressure gauge, B: nitrogen inlet

C: Hurenji, D: Reactor

E: coolant inlet, F: temperature gauge

G: nitrogen outlet, H: coolant outlet

Claims (9)

The waste crosslinked high density polyethylene pipe having a gel fraction of 85 to 95% in the reactor was subjected to decrosslinking reaction with supercritical methanol for 5 to 10 minutes under a reaction temperature of 370 to 390 ° C. and a reaction pressure of 5 to 30 MPa. step; And And quenching the reactant after completion of the decrosslinking reaction. The method for regenerating the waste crosslinked high density polyethylene pipe according to claim 1, wherein the waste crosslinked high density polyethylene pipe is an organic peroxide crosslinked or electron beam crosslinked waste crosslinked high density polyethylene pipe or a mixture thereof. delete The method for regenerating the waste crosslinked high density polyethylene pipe according to claim 1, wherein the waste crosslinked high density polyethylene pipe is pulverized to have a particle size of 11 mm or less before the decrosslinking reaction. The method of claim 1, wherein supercritical methanol is used in an amount of 100 to 500 parts by weight based on 100 parts by weight of the waste crosslinked high density polyethylene pipe. The method of claim 1, wherein the decrosslinking reaction is performed for 5 to 10 minutes under a reaction temperature of 370 to 380 ° C and a reaction pressure of 10 to 15 MPa. Regenerated high density polyethylene-based resin recycled according to the method of claim 1. The regenerated high density polyethylene resin according to claim 6, wherein the regenerated high density polyethylene resin has a gel fraction of 0.5% or less. A molded article manufactured using the recycled high density polyethylene resin according to claim 6.

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