JP3225238B2 - Thermal decomposition method of synthetic polymer compound - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to industrial and domestic wastes that are discarded in large quantities without being used, and in particular to synthetic polymer compounds (hereinafter, referred to as "high-molecular-weight") whose proportion in these wastes increases.
Process that can be processed at high speed and in large quantities to recover reusable low-to-medium molecular useful compounds, and in particular, water in a supercritical or subcritical state is good. The present invention relates to a method capable of efficiently decomposing polymers into constituent units or conjugates as small as oligomers thereof by utilizing the formation of a suitable ionic reaction region.

[0002]

2. Description of the Related Art Industrial and domestic wastes contain a large amount of biopolymers and synthetic polymers, but most of them are discarded without being reused. Since these polymers can be valuable chemical raw materials and energy resources, there is a demand for the development of a technology capable of treating these polymers in large quantities and effectively utilizing them.

One of the most promising polymer resources is a large amount of cellulose and lignin contained in agricultural and forestry products such as paper, wood and straw. As a technique for producing glucose from cellulose, various methods are basically known, such as a pyrolysis method, a high-temperature hydrolysis method using an acid catalyst, and an enzymatic hydrolysis method. It is difficult to say that this method is effective in terms of mass production.

[0004] The above-mentioned method has the drawback that the reaction cannot be controlled and the production rate of glucose is low. The other methods have problems such as equipment corrosion due to the added acid and removal of the acid from the product, and the drawback that if the concentration of the acid is suppressed to avoid such inconvenience, the rate of glucose production is reduced. is there. Further, the reaction rate is too slow to be used as an industrial production technique.

[0005] As a specific example of the hydrolysis method using an acid (the above-mentioned method) among the above-mentioned prior arts, a study by JFSaeman of Forest Products Laboratory conducted during World War II, In the decomposition reaction of cellulose with acid,
It has been reported that the rate of glucose production is almost equal to the rate of undesired glucose decomposition reaction, and high glucose yield improvement is not expected.

In order to improve the yield of glucose, a technique has been proposed in which a cellulose-containing substance is pretreated with ethylenediamine, cadmium hydroxide, water and the like, followed by acid treatment (JP-A-59-160755). ), The yield of glucose was still not sufficient. Furthermore, Japanese Unexamined Patent Publication No.
As seen in JP-A-9-500648, a technique for obtaining a high yield by increasing the concentration of an acid has been proposed.
Complicated treatments such as an acid decomposition step are further required.

On the other hand, Hans E. Grethlein's paper (Comparison o) described in "Biotechnology and Bioengineering" [Vol.XX P503-525 (1978)]
f the Economics of Acid and Enzymatic Hydrolysis o
f According to Newsprint), when the hydrolysis reaction rate at high temperature is evaluated based on the decomposition reaction rate of cellulose and glucose measured at low temperature, the amount of sulfuric acid added is 2% at high temperature (300 ° C or lower). It has been shown that a reaction time of 0.035 seconds can result in a glucose yield of about 90%. On the basis of this idea, an apparatus and a method as disclosed in, for example, JP-A-57-129699 have been proposed.

However, the present inventors have confirmed by experiments that the dielectric constant and ionic product of water under high temperature and high pressure are significantly different from those under low temperature and normal pressure, and the hydrolysis reaction rate evaluated at low temperature is extrapolated. It has been found that the reaction rate under high temperature and high pressure cannot be directly evaluated. Furthermore, the technique disclosed in the above publication has a difficulty in operability,
Not applicable to industrial mass processing technology.

In the above description, the case of cellulose has been mainly described. However, the above-mentioned various polymer wastes, such as plastic films, plastic bottles, plastic trays, and other various plastic molded products, have similar problems. Is useful to selectively decompose low
Recovering medium molecular compounds has become one of the important issues in saving resources or protecting the global environment.

[0010]

SUMMARY OF THE INVENTION The present invention has been made under such a circumstance, and its object is to include a large amount in industrial and domestic waste without causing inconvenience in the prior art. It is an object of the present invention to provide an optimal method for recovering low to medium molecular compounds that can be used for efficiently decomposing and reusing various synthetic polymer compounds.

[0011]

Means for Solving the Problems The present invention, which has achieved the above object, comprises a step of preparing a synthetic polymer compound using supercritical or subcritical water as a solvent without adding an oxidizing agent.
The gist lies in the fact that the synthetic polymer compound is thermally decomposed into constituent units or oligomers thereof. The synthetic polymer compounds targeted in the present invention include polystyrene,
Synthetic polymers such as polyethylene and polypropylene are exemplified. In the present invention, waste containing one or more of these polymers can be effectively thermally decomposed.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors first studied from various angles a method for effectively decomposing cellulose. As a result, they found that glucose can be produced in a high yield of 20% or more with good controllability without using an acid by decomposing cellulose using water in a supercritical or subcritical state. The application was filed earlier (Japanese Patent Application No. 2-238085). It was also found that when an acid is added, glucose can be obtained in a high yield (for example, 30% or more) even when the acid concentration of the reaction solution is 1/10 or less of the conventional value.

The rationale for the action and effect of water in a supercritical or subcritical state has not been fully elucidated, but can be considered as follows. Supercritical or subcritical water can easily and drastically change its dielectric constant and ionic product (Kw) by controlling temperature and pressure. FIG. 1 is a graph showing the temperature dependence of the ionic product (Kw) of water at each pressure. The higher the pressure, the higher the ionic product (Kw) is maintained up to a high-temperature region. It can be expected to form a region for favorable ionic reactions (hydrolysis reaction and dehydration reaction). That is, since the ionic product and dielectric constant of water in a supercritical state or a subcritical state are large, and these can be adjusted in a wide range by controlling temperature and pressure, water in such a state is used as a solvent for the hydrolysis reaction. Thus, for example, glucose, 5
-It was thought that an optimal environment was provided for decomposition into HMF and various carboxylic acids.

The present inventors have repeatedly studied the usefulness of the above method for various synthetic polymer compounds even after the completion of the above invention. As a result, when decomposed using water in a supercritical or subcritical state as a solvent, various polymers such as polystyrene, polyethylene, and polypropylene are effectively and selectively decomposed, and useful structural unit molecules or oligomers thereof are useful. The present inventors have found that such species can be recovered and completed the present invention.

The decomposition of cellulose is thought to proceed mainly by a hydrolysis reaction.
The decomposition of polypropylene, polystyrene and the like is considered to be due to radical reaction (thermal decomposition or oxidation reaction) decomposition. In other words, the decomposition of these polymers is different from the thermal decomposition under low pressure, because the generation of gas is small, and the controlled thermal decomposition or another reaction involving a high concentration of hydrogen radicals occurs due to the presence of high pressure water. In the present invention, this is referred to as pyrolysis for convenience.

The control mechanism of the thermal decomposition reaction in the present invention can be considered as follows. Thermal decomposition (bond cleavage) under normal pressure depends on temperature, surrounding molecules, and radical concentration, but the primary products generated by decomposition decompose into secondary substances or combine with other radicals. Thus, the decomposition proceeds further. However, if a high-density inert molecule is present in the thermal decomposition reaction field, the thermal decomposition reaction and the secondary decomposition of the primary product are also suppressed, and the reaction rate and the reaction path are changed. Further, since water molecules also serve as a supply source of hydrogen radicals, they form a reaction system different from thermal decomposition under normal pressure, and the contribution of ionic reactions increases. In the supercritical state, the density of water and radicals can be largely controlled by manipulating the pressure and temperature, so that it is considered that thermal decomposition in such a field can be controlled to a considerable extent.

In practicing the present invention, in order to form water in a supercritical state or a subcritical state, the temperature and pressure must be appropriately adjusted at least in the range of 200 to 800 ° C. and pressure of 2.0 to 90 MPa. I just need. In addition, the decomposition reaction in the present invention effectively proceeds without adding an acid. However, adding a small amount of an acid so as to have an acid concentration of 2% or less is effective in increasing the yield. Since the concentration is low, corrosion of the apparatus does not occur, and removal of the acid after the completion of the reaction is relatively easy. Examples of the above-mentioned acid include sulfuric acid, hydrochloric acid, phosphoric acid and the like, and the more preferable acid concentration is 0.05% or less in consideration of the effect of addition and post-treatment. That is, according to the present invention, even when the acid concentration is about 0.05%, the effect of the acid addition can be sufficiently exhibited.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples do not limit the present invention. It is included in the technical scope.

[0019]

EXAMPLES The present inventors carried out the present invention with respect to each polymer of polystyrene, polyethylene and polypropylene, conducted a decomposition experiment, and examined the effects of the present invention. The decomposition reaction experiment at this time was performed using a batch type apparatus. That is, about 0.5 g of each polymer and 3 ml of water were charged into a reaction tube (volume: 6 ml, made of SUS), and the inside of the reaction tube was replaced with nitrogen. Then, the reaction tube was put into a metal bath heated to 400 ° C., and rapidly (800 K / min). ). 400 ° C,
After reacting at 30 MPa for 1 minute, the reaction tube was quenched by putting it in cold water, polymer residue in the reaction tube was recovered, its weight was measured, and the conversion was calculated. In addition, the conversion is
It indicates the rate at which the polymer decomposed and changed into another substance. For example, a conversion of 1.0 means 100% of the polymer.
Means decomposed.

The results are shown in Table 1. As can be seen from Table 1, selective pyrolysis of all the polymers proceeded quickly and in a short period of time, suggesting the effectiveness of the technique as a technique for treating a large amount of polymers. At this time, the generation of a large amount of gas as seen in the thermal decomposition reaction under normal pressure was hardly observed, and it was considered that the thermal decomposition reaction controlled by the presence of high-density water occurred. Table 1 also shows the bonding type of each polymer.

[0021]

[Table 1]

[0022]

Industrial Applicability The present invention is constituted as described above. By using supercritical or subcritical water as a solvent, a synthetic polymer compound can be effectively and selectively decomposed. . Such a method of the present invention can be greatly expected as a technique for treating industrial and domestic waste containing a large amount of a synthetic polymer compound in a large amount, particularly a technique for selectively recovering a useful compound therefrom.

[Brief description of the drawings]

FIG. 1 is a graph showing the temperature dependence of the ionic product of water at each pressure.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Ryuichi Fukusato 9-1-1912, Takahama-cho, Ashiya-shi (56) References JP-A-61-66789 (JP, A) JP-B-60-54119 (JP, B2) JP-A-56-501205 (JP, A) U.S. Pat. No. 4,113,446 (US, A) WO 91/11394 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J 11/00- 11/28 B09B 3/00 302-304

Claims (2)

(57) [Claims] 1. A synthetic polymer compound prepared by using supercritical or subcritical water as a solvent without adding an oxidizing agent.
In the structural unit of the synthetic polymer compound or their
A method for thermally decomposing a synthetic polymer compound, which is thermally decomposed into oligomers . 2. The thermal decomposition method according to claim 1, wherein the synthetic polymer compound is at least one selected from the group consisting of polystyrene, polyethylene, and polypropylene.