KR20040016035A - Degradation method of waste-polymr using ozone - Google Patents

Abstract

PURPOSE: A method for degrading the waste polymer is provided, to degrade the waste polymer into small molecules by using ozone without using an expensive catalyst or without pyrolysis. CONSTITUTION: The method comprises the steps of dissolving the waste polymer in a solvent; and injecting ozone at a high temperature to degrade the waste polymer into small molecules. The waste polymer is the thermoplastic polymer generated from the plastic industry as by-products. Preferably the solvent is selected from the group consisting of ethylene glycol, diethylene glycol, 1,4-butanediol, methanol, water and trichlorobenzene; the reaction is performed at a temperature of 110-150 deg.C for 1-6 hours, and the concentration of ozone is 50-1,000 ppm based on 1 g of the waste polymer. Preferably the small molecules have a molecular weight of 50-35,000 Dalton.

Description

Decomposition of Waste Polymer Using Ozone {DEGRADATION METHOD OF WASTE-POLYMR USING OZONE}

The present invention relates to a method of decomposing waste polymers by dissolving the waste polymers in a solvent and then decomposing them into low molecules by adding ozone, a powerful oxidizing agent.

Until now, waste polymer has been treated by landfilling or incineration, but since it is not easily decomposed, it is difficult to secure landfill and pollutes soil when landfilling is not appropriate. Some can be recovered, but polluting the atmosphere with the generation of toxic gases. From this point of view, a simple recycling method for pulverizing, melting and re-producting waste polymer materials is very desirable in terms of low pollution and efficient recycling of resources. Since most polymeric materials are hydrocarbons consisting of carbon and hydrogen, they can be broken down and converted to low molecular weight hydrocarbon mixtures.

Methods of decomposing the polymer material include pyrolysis which decomposes at high temperature by applying heat, and catalytic decomposition which uses a catalyst to obtain a specific range of products at low temperature. The pyrolysis process is easy to operate, but requires a lot of energy, and generates a lot of lower hydrocarbons such as methane and ethane, and thus the economic value of the product is low. On the other hand, since the catalytic decomposition process is performed at a low temperature, the energy requirement is small and the product distribution can be controlled to some extent. However, there are disadvantages in that the activity of the catalyst is lowered during use and the process operation is complicated.

The decomposition process of the existing polymer materials uses catalysts and additives, and then requires a recovery process and takes a lot of time. For example, the decomposition treatment technology of polymer materials such as polystyrene and polyethylene terephthalate has a disadvantage of requiring a liquid solvent (methanol, ethylene glycol, etc.), a long reaction time of 4-5 hours or more, and a catalyst.

On the other hand, ozone is the second strongest oxidizing gas after fluoride in nature, and already uses ozone to treat wastewater of certain harmful substances (plating wastewater), to treat organic and inorganic synthetic wastewater (especially from pharmaceutical companies), Various attempts have been made to disinfect water and sterilize and prevent odors and pathogens from livestock, such as barns, houses and pigs. However, no research has been done on the decomposition of polymers.

By applying ozone to the decomposition of waste polymers, the present inventors have conducted various studies to decompose to monomer level without a catalyst and to shorten reaction temperature and reaction time. Therefore, when the waste polymer was pulverized and dissolved in a solvent and treated with ozone at a predetermined temperature or more, it was found that the decomposition of the waste polymer proceeded, and the study was conducted to obtain the optimal conditions. As a result, it is possible to suggest the content of waste polymer, the concentration of ozone, the reaction temperature and reaction time, and the optimum conditions of the solvent.

It is an object of the present invention to provide a method for converting waste polymers into low molecules.

Still another object of the present invention is to provide a method for converting low molecular weight molecules at low temperatures and high yields.

It is another object of the present invention to provide a recycling method of waste polymers.

1a to 1d are graphs showing the decomposition rate of spent polymers with temperature.

2 is a graph showing the decomposition rate according to the content of the waste polymer.

3 is a graph showing the decomposition rate of the waste polymer according to the concentration of ozone.

The present invention provides a method for dissolving the waste polymer to a low molecule by dissolving the waste polymer pulverized to a suitable size in a solvent, and then injecting ozone, a powerful oxidizing agent.

Hereinafter, the present invention will be described in detail.

The present invention adopts a method of using ozone, a powerful oxidizing agent, instead of pyrolyzing at high temperature or using a catalyst to decompose waste polymers.

As used throughout the specification, 'waste polymer' refers to all waste polymers generated as by-products in the plastics industry, and does not limit the type thereof, and preferably uses a thermoplastic polymer that can be dissolved in a solvent. For example, polyolefin general purpose resins, such as polyethylene and a polypropylene; Polyurethane, polystyrene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polypropylene, etc. can be used.

The waste polymer is cut into a size of 10 mm to 100 μm using a grinder commonly used in the art in order to increase solubility in a solvent. The size of the waste polymer may be appropriately adjusted according to the size and solubility of the reactor used.

The low molecules referred to below include monomer and oligomer levels and refer to a range of 50 to 35,000 Daltons. .

Specifically, in order to decompose the waste polymer into low molecules, the waste polymer pulverized to an appropriate size is injected into a reactor filled with a solvent.

At this time, the solvent is different depending on the type of waste polymer to be treated, and can be used to completely dissolve or swell the waste polymer, for example ethylene glycol, diethylene glycol, 1,4-butanediol, methanol, TCB (trichlorobenzene) is used. According to a preferred embodiment, ethylene glycol is used to decompose the waste polyurethane and waste polyethylene terephthalate and methanol is used to decompose the waste polystyrene.

The type and content of the solvent to be used as a factor that greatly affects the decomposition reaction of the waste polymer can be decomposed the waste polymer in high yield through the selection and content of the appropriate solvent. The solvent is for facilitating contact between the waste polymer and ozone, and any solvent that can dissolve the waste polymer may be used, and the solvent may be appropriately selected by those skilled in the art. One example is described in detail in the POLYMER HANDBOOK.

The content of the selected solvent depends on the solubility with the waste polymer, and the amount of the solvent is used so that the waste polymer is completely dissolved. In some cases, physical processes such as heating, stirring, an ultrasonic grinder, and pressurization may be performed. For example, according to the embodiment for determining the decomposition according to the content of the waste polymer, the decomposition was performed while changing the content of polystyrene to 0.5 to 5 g under the same treatment conditions, the initial reaction time (less than 1 hour) A similar yield was obtained, but after 6 hours of completion of the reaction, there was a large difference in decomposition rate ranging from 64 to 92%. These results indicate that the lower the content of the waste polymer in the solvent, the higher the decomposition rate is, which is actually the basis for scale-up to a pilot scale.

At this time, in order to increase the solubility of the waste polymer and increase the reactivity with ozone, an appropriate stirrer is installed in the reactor, and the speed is appropriately adjusted according to the size of the reactor.

After raising the temperature of the reactor in which the waste polymer is injected, ozone is injected to decompose the waste polymer.

The temperature of the reactor depends on the type of solvent used, and is performed for 1 to 6 hours in the range of 110 to 150 ℃. Such reaction temperature and time can also decompose the waste polymer in high yield by controlling the appropriate reaction temperature and time as a factor influencing the decomposition reaction of the waste polymer. According to the preferred embodiment, the polystyrene was decomposed by varying the reaction temperature at 110 to 150 ° C. under the same conditions, and as the reaction temperature was higher, the degradation yield increased proportionally. Shows that the decomposition occurs in a high yield at a relatively low temperature compared to that performed at 400 ℃ to 500 ℃ in the conventional pyrolysis method to decompose the waste polymer through the method of the present invention. Specifically, as the temperature increases, the polymer chain scission increases, and at the beginning of the reaction, the branch or terminal is decomposed and the main chain is broken over time. In addition, as the cutting proceeds randomly, hydrogen extraction and b-scission increase. (G. Madras et al., Thermal degradation kinetics of polystyrene in solution, Polymer Degradation and Stability , 58 (1997) 131-138; Oxidative degradation kinetics of polystyrene in solution, Chemical Engineering Science , Vol. 52, No. 16, PP 2707-2713)

The injected ozone is in the radical state and reacts with the terminal or the active site of the waste polymer to promote the decomposition of the polymer chain. In the present invention, the ozone is adjusted to 50 ppm to 1000 ppm with respect to 1 g of the waste polymer. If the concentration of the injected ozone is less than the above range, the desired degree of decomposition of the waste polymer cannot be achieved, and if it exceeds, the purification of the remaining ozone becomes difficult and undesirable. According to a preferred embodiment, the decomposition degree of polystyrene was measured by varying the concentration of ozone under the same treatment conditions, the higher the concentration of ozone, the higher the decomposition rate, which was different from the initial reaction (less than 1 hour). An increase in the concentration of ozone means an increase in the amount of ozone radicals reacting with the waste polymers, leading to an increase in the rate of decomposition as a result of decomposition of the waste polymers by such ozone radicals. As a result, looking at the yield after 6 hours after the reaction was completed, a relatively wide range of yield difference was shown to 43 ~ 81%, and showed a similar decomposition rate above a certain concentration. According to another preferred embodiment, the measurement of the activation energy according to the concentration of ozone, the higher the concentration showed a lower activation energy, these results show that ozone is an excellent oxidant compared to other catalysts or pyrolysis.

Ozone, used to decompose waste polymers, is produced via an ozone generator and is typically produced using oxygen or air. In terms of yield, it is preferable to use oxygen, and in terms of economics, it is more efficient to use air, which can be appropriately selected depending on the situation.

The low molecular weight decomposed from the waste polymer through the above method was found to be capable of degrading to the level of the monomer, with a molecular weight ranging from 50 to 35,000.

Hereinafter, the present invention will be described in more detail with reference to Examples.

However, the following examples are only examples of the present invention and the present invention is not limited by these examples.

A three-necked flask containing a solution (solvent + waste polymer) was added to the mantle and agitated. The cooler was fixed to the top of the flask to prevent backflow of steam. At this time, the reaction temperature was read through a thermometer in the flask, and the thermocouple was inserted between the mantle and the flask to enable temperature control.

Example 1 Degradation of Hard Polyurethane

Rigid polyurethane foams (molecular weight 300,000) were crushed into powder so as to have an average diameter of about 1-2 mm with a crusher in the form of a mixer. 40 g of ethylene glycol was added to a small reactor equipped with a cooler, and the temperature inside the reactor was raised to 200 ° C., and then 50 g of the polyurethane foam powder was added thereto while blowing air having an ozone concentration of 300 ppm. The decomposition reaction was performed.

At this time, since the density of the rigid polyurethane is about 0.4 g / cm 3, it is about 4 times the volume of ethylene glycol to be reacted. For this example the glycol-decomposition reaction was completed in about 3.5 hours. At this time, the completion of the reaction does not mean 100% decomposition of the waste polymer, but when 3.5 hours or more, it means a maximum decomposition state in which decomposition does not progress any more.

The decomposition rate at this time was 87%, the saponification degree was OH value 450 mg KOH / g. The safflower value means that the larger the value, the greater the presence of low molecular weight.

Example 2 Degradation of Hard Polyurethane

The hard polyurethane was decomposed in the same manner as in Example 1 except that the concentration of ozone was 500 ppm. At this time, the reaction time was 2.5 hours (decomposition rate: 92%), and the saponification degree of the obtained regenerated polyol was 490 mg KOH / g.

Example 3 Degradation of Rigid Polyurethane

The hard polyurethane was decomposed in the same manner as in Example 1 except that the reaction was performed at 180 ° C. At this time, the reaction time was 3 hours (degradation rate: 84%), and saponification degree was 495 mg KOH / g.

Example 4 Degradation of Rigid Polyurethane

The hard polyurethane was decomposed in the same manner as in Example 1 except that the reaction was performed at 160 ° C. At this time, the reaction time was 5 hours (decomposition rate: 79%), and saponification degree was 485 mg KOH / g.

Example 5 Degradation of Waste Polyurethane

As waste polyurethane foam in the reactor, a system seat foam having a molecular weight of about 158,000 and mounted on an actual vehicle was used as a raw material. 30 g of the waste polyurethane foam powder and 10 g of diethylene glycol were added thereto, and the reaction temperature was raised to 160 ° C. while the reaction mixture was stirred. Then, the ozone concentration was 300 ppm and reacted for 4 hours (degradation rate: 94%). The degree of saponification was 520 mg KOH / g.

Example 6 Degradation of Soft Waste Polyurethane

A soft waste polyurethane was carried out in the same manner as in Example 5, except that 30 g of a soft waste polyurethane foam (molecular weight: 200,000) powder and 20 g of ethylene glycol were added to the reactor to carry out the reaction at 200 ° C. Was decomposed. The decomposition was carried out for 4 hours to complete the reaction. The decomposition rate was 82%, and the saponification degree of the obtained regenerated polyol was 460 mg KOH / g.

<Example 7>

30 g of soft waste polyurethane foam powder and 30 g of 1,4-butanediol were introduced into the reactor, except that the reaction was carried out at 180 ° C., and the soft waste polyurethane was decomposed in the same manner as in Example 5. The reaction time was 5.5 hours and the saponification degree of the regenerated polyol was 400 mg KOH / g.

In Examples 1 to 7, the reaction conditions for decomposing the waste polymer and the physical properties of the obtained polyol are summarized in Table 1 below.

According to Table 1, as the ozone concentration and the reaction temperature increases, it was found that decomposition into low molecules increased, and it was also found that the kind of solvent was affected under the same conditions. This result is explained in more detail by the following examples.

Example 8 Degradation Rate of Waste Polymer According to Reaction Temperature and Solvent

In order to determine the degree of decomposition of the waste polymer into low molecules according to the reaction temperature and the type of solvent was carried out as follows.

1) Decomposition of waste polystyrene: trichlorobenzene solvent

2 g of waste polystyrene (molecular weight 350,000 Aldrich) and 200 cc (TCB (trichlorobenzene) having a molecular weight of 350,000 were injected into the reactor and heated, followed by decomposition of polystyrene by injecting ozone at a concentration of 780 ppm. The reaction temperature was carried out at 110 ℃, 120 ℃, 130 ℃, 140 ℃, 150 ℃ each.

2) Degradation of Waste Polyethylene Terephthalate

Polyethylene terephthalate (PET) (molecular weight 1.9 × 104 g / g mol) was used as waste polymer in the same manner as above, and ethylene glycol was used as a solvent, and decomposition reaction was performed by injecting 300 ppm of ozone. At this time, the reaction temperature was carried out by changing to 190 ℃, 200 ℃, 210 ℃, 220 ℃, 230 ℃.

3) Degradation of Waste Polyethylene Terephthalate

20 g of polyethylene terephthalate and 200 ml of methanol were injected into the high-pressure reactor, and then decomposition was performed while injecting 300 ppm of ozone under 8 MPa pressure. At this time, the reaction temperature was carried out by changing to 220 ℃, 230 ℃, 240 ℃, 250 ℃, 260 ℃.

4) Degradation of Waste Polyethylene Terephthalate

3 g of polyethylene terephthalate and 200 ml of water were injected into the high-pressure reactor, and then decomposition was performed while injecting 300 ppm of ozone under 8 MPa pressure. At this time, it was carried out by changing the reaction temperature to 70 ℃, 80 ℃, 90 ℃.

At this time, the decomposition rate was calculated through the following equation, and the results are shown in Table 2 and FIGS. 1A to 1D.

According to Table 2, Figures 1a to 1d, it can be seen that the decomposition rate also increases as the reaction temperature increases. These results show that while conventional pyrolysis is performed at a high temperature of 673 to 773 K (400 to 500 ° C.), high decomposition rates are obtained even at relatively low temperatures of 383 to 423 K (110 to 150 ° C.) in oxidative decomposition using ozone of the present invention. Shows that it can. Moreover, even when methanol and water were used as solvents in order to decompose polyethylene terephthalate, it was found that the decomposition rate was high, and in particular, when water was used, decomposition was possible at low temperature. As such, since water can be used to decompose waste polymers, waste solvents are not generated in the decomposition process, thereby achieving environmentally friendly processes.

Example 9 Degradation Rate According to Content of Waste Polymer

In order to determine the degree of decomposition into low molecules according to the content of the waste polymer was carried out as follows.

The reaction was carried out in the same manner as in Example 8, but the reaction temperature was fixed at 130 ℃ and the reaction was carried out for 6 hours while only changing the amount of the waste polymer, and the sample was taken at each time to measure the decomposition rate. And shown in FIG. 2.

According to Table 3 and Figure 2, it can be seen that the decomposition rate is lowered as the content of the waste polymer is increased, because the less the molar ratio of ozone radicals in contact with the waste polymer, the less reaction occurs.

Example 10 Degradation Rate of Waste Polymer According to Ozone Concentration

In order to determine the decomposition of polystyrene according to the concentration of ozone was carried out as follows.

In the same manner as in Example 8, but the reaction temperature was fixed at 130 ℃ and the reaction was carried out for 6 hours while changing only the concentration of ozone, each sample was taken to measure the decomposition rate, the results obtained Table 4 And shown in FIG. 3.

According to Table 4 and Figure 3, it can be seen that the decomposition rate is lowered as the concentration of ozone to be treated is increased, which is the same as the result of Example 9, the more the ozone radicals in contact with the waste polymer as the concentration of ozone increases, the random This is because a large amount of chain cutting occurs.

From the above experiments, decomposition of waste polymer using ozone shows the following results.

1) The waste polymer to be treated is preferably in a crushed form, and as the content thereof increases, the decomposition rate of the low molecules decreases.

2) When the decomposition reaction is performed, the higher the temperature of the reactor, the more random the chain cutting proceeds, the higher the decomposition rate to low molecules.

3) The higher the concentration of ozone treated, the higher the ozone radicals in contact with the spent polymers, and the lower the activation energy, the stronger the oxidation reaction.

Therefore, the present invention can be easily decomposed into low molecules by ozone treatment of the waste polymer, and can overcome various waste stages due to the conventional waste plastic treatment as the low molecules can be recycled. In particular, it reduces the consumption of thermal energy used, and the process is simpler than the process using the catalyst, resulting in lower fixed and operating costs such as facility investment, minimizing the size of the facility, and reducing manufacturing costs. There is an effect to improve the productivity by allowing the product to be produced.

Claims (6)

After dissolving waste polymer in a solvent, ozone is injected at high temperature to decompose it into low molecules. The method of claim 1, wherein the waste polymer is a thermoplastic polymer generated as a by-product in the plastics industry. The method of claim 1, wherein the solvent is ethylene glycol, diethylene glycol, 1,4-butanediol, methanol, water. Trichlorobenzene (TCB) characterized in that the method selected from the group consisting of. The method of claim 1, wherein the reaction is carried out at 110 to 150 ° C for 1 to 6 hours. The method according to claim 1, wherein the concentration of ozone is 50 to 1000 ppm with respect to 1 g of waste polymer. The method of claim 1, wherein the low molecular weight is 50 to 35,000 Daltons.