JP2000178249A - Depolymerization of nylon 6 - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain caprolactam in good yield without causing various kinds of problems by controlling the amount of sticking chlorides to a prescribed value or below according to a simple means such as washing with water when depolymerizing a thermoplastic material consisting essentially of nylon 6 and containing the alkali(ne earth) metal chlorides sticking thereto with an acidic catalyst. SOLUTION: When a thermoplastic material consisting essentially of nylon 6 (preferably containing >=90 wt.% of the nylon 6) and containing an alkali metal chloride and/or an alkaline earth metal chloride sticking thereto is preferably washed with water and then depolymerized with an acidic catalyst (preferably a phosphoric acid catalyst) to afford caprolactam, the amount of the sticking chlorides is controlled so as to be an equivalent amount of <=0.20 based on the catalyst. The sticking chlorides are preferably derived from common salt. The thermoplastic material is preferably a fibrous structure and/or a fiber waste, e.g. a fishing net, a rope and clothes. Thereby, the depolymerization of the nylon 6 can industrially and advantageously be carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for depolymerizing nylon 6. More specifically, the present invention relates to a method for depolymerizing a fiber structure or fiber waste containing nylon 6 as a main component.

[0002] The caprolactam obtained according to the present invention is
It is a useful compound that can be used as a raw material for fibers, a raw material for resins, or a raw material intermediate.

[0003]

2. Description of the Related Art With respect to acid-catalyzed depolymerization of a thermoplastic material containing nylon 6 as a main component and containing an inorganic salt, in a wet-type phosphoric acid-catalyzed depolymerization of carpet, it is contained as a filler in a carpet backing, There is known a method of mechanically removing alkaline calcium carbonate, which neutralizes carbon dioxide, using a separator before depolymerization (Japanese Patent Laid-Open No. 5-11 / 1990).
No. 7441).

[0004]

This method is excellent in that it can mechanically remove an alkaline salt that is contained in a thermoplastic containing nylon 6 as a main component and reduces the catalytic activity of phosphoric acid. . However, the need to remove nearly neutral alkali metal chlorides and / or alkaline earth metal chlorides in acid catalyzed depolymerization is generally unknown, and metal chlorides adhered to thermoplastics are not known. Is difficult to remove mechanically.

An object of the present invention is to depolymerize a thermoplastic material containing nylon 6 as a main component and having an alkali metal chloride and / or an alkaline earth metal chloride attached thereto with an acid catalyst to obtain caprolactam in a high yield. It is to provide a means that can be advantageously used.

[0006]

The present inventors studied acid-catalyzed depolymerization of a thermoplastic containing nylon 6 as a main component and having an alkali metal chloride and / or an alkaline earth metal chloride attached thereto. The chloride undergoes a salt exchange reaction with the catalyst in the heat-melted nylon 6 to generate hydrogen chloride gas, and the acid catalyst becomes a neutral alkali metal salt and / or alkaline earth salt and is deactivated. It was found that the yield of the mixture decreased and the viscosity of the reaction mixture increased. Furthermore, it was found that the generated chlorine roots such as hydrogen chloride gas significantly corrode the depolymerization apparatus.

Accordingly, the present inventors have conducted intensive studies and as a result,
A thermoplastic material to which an alkali metal chloride and / or an alkaline earth metal chloride is adhered with nylon 6 as a main component,
In the case of depolymerization with an acid catalyst, caprolactam can be obtained in good yield, without problems in handling and equipment corrosion by controlling the amount of the chloride adhered to a certain level or less by simple means such as washing with water. And arrived at the present invention.

That is, according to the present invention, a thermoplastic material having nylon 6 as a main component and having an alkali metal chloride and / or an alkaline earth metal chloride attached thereto is depolymerized with an acid catalyst.
In obtaining caprolactam, there is a nylon 6 depolymerization method or the like, wherein the amount of the attached chloride is 0.20 equivalent times or less of the catalyst.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail.

The nylon 6 referred to in the present invention may be any one as long as caprolactam is polymerized. Usually, it is polycaprolactam, an oligomer of caprolactam, or the like, and may be a copolymer with another monomer. Hexane methylene diamine as a copolymer component,
1,4-diaminobutane, p-phenylenediamine, p
Diamine components such as xylylenediamine; dicarboxylic acid components such as adipic acid, sebacic acid, succinic acid, terephthalic acid and isophthalic acid; and aminocarboxylic acid components such as laurolactam. Preferred are polycaprolactam and oligomers of caprolactam. These nylons 6 may contain, for example, a polymerization degree regulator such as acetic acid and benzoic acid, and a terminal group regulator.

The adhered alkali metal chloride referred to in the present invention is:
Salt (sodium chloride), potassium chloride, lithium chloride and the like can be mentioned. Examples of the alkaline earth metal chloride include magnesium chloride and calcium chloride. Preferably, it is salt.

The thermoplastic nylon 6 used in the present invention
The raw material / material composition other than the alkali metal chloride and / or the alkaline earth metal chloride may be any organic or inorganic substance. Thermoplastics include other polymers,
An additive, a face / dye, a processing agent, a metal fiber, a filler, and the like may be included. For example, polyethylene terephthalate, nylon 66, resin additives (antioxidants,
UV absorbers, flame retardants, heat resistant agents, antistatic agents, lubricants, etc.), carbon black pigments, various dyes, polyolefin resin processing agents, fiber processing oil agents, lead fibers, glass fibers, titanium oxide, silica, etc. It may be. Usually, the content of nylon 6 in the thermoplastic material is 80% by weight or more, preferably 90% by weight or more, and more preferably 95% by weight or more.
% By weight. When the content of nylon 6 is small, the amount of waste composed of other components increases.

[0013] The thermoplastic used in the present invention includes a product containing nylon 6 as a main component, raw material production, material processing, and the like.
Examples include industrial waste generated in the process of assembling and manufacturing the product, or waste product used. For example, industrial, clothing, indoor / outdoor fiber structures, or fiber wastes thereof, and industrial, household equipment / appliance resin structures, or resin wastes thereof can be exemplified. More specifically, as textile structures, fishing nets, industrial goods such as ropes for ships, uniforms, innerwear, stockings, knitwear, clothing such as swimwear, curtains, indoor goods such as carpets, ropes, nets, Outdoor products such as tire cords, belts, sheets, and the like, and fiber wastes include polymer yarn wastes, cut fabric wastes, defective wastes, used products, and the like generated during the manufacturing process. Resin structures include molded parts for household appliances, molded parts for drinking water, molded parts for toys, molded parts for household goods, molded parts for houses, etc., household goods, molded parts for automobiles, molded parts for industrial machinery, packages, films Examples of industrial products such as resin waste and resin waste include polymer molding waste, film waste, cutting waste, defective waste, and used products. Preferable examples include fishing nets and ship mooring ropes to which salt is attached by seawater, clothing to which salt is attached by sweat, and the like. Further, these can be used together with polycaprolactam or an oligomer of caprolactam as a raw material for depolymerization.

In the present invention, it is important to control the amount of alkali and / or alkaline earth metal chloride attached to the thermoplastic containing nylon 6 as a main component to a certain amount or less relative to the acid catalyst. The adhesion amount of the chloride is 0.1.
It is 20 equivalents or less, preferably 0.10 equivalents or less, more preferably 0.05 equivalents or less. In addition, the content is preferably 0.01% by weight or less based on the thermoplastic material. More preferably, 0.0
Not more than 01% by weight. When the chloride is present in a certain amount or more, the acid catalyst is deactivated as described above, and the yield decreases and the viscosity of the reaction mixture increases. In addition, equipment corrosion occurs.

As a method for reducing the amount of the chloride adhered to the thermoplastic material to a certain amount or less, any physical or chemical means may be used. For example, the chloride may be water-soluble, and may be washed with water, or if the chloride adheres significantly, may be shaken off by vibration. Preferably, a method of removing by washing with water or the like, and more preferably, a method of cutting a thermoplastic material into small pieces and then washing with water to remove excess moisture adhered, or making it rain outdoors can be mentioned.

The acid-catalyzed depolymerization method used in the present invention may be any method. Usually, nylon 6 is depolymerized by heating with an acid catalyst, and may be in the absence (dry) or presence (wet) of water.

The depolymerization pressure may be any of reduced pressure, normal pressure, and pressurized. The depolymerization temperature is usually from 100 to 40
0 ° C., preferably 200 to 350 ° C., more preferably 220 to 300 ° C. If the temperature is low, the nylon 6 does not melt, and the depolymerization rate becomes slow. If the temperature is high, unnecessary decomposition of nylon 6 occurs, resulting in a decrease in the purity of the recovered caprolactam.

The acid catalyst used in the present invention includes phosphoric acid,
Examples include boric acid, sulfuric acid, organic acids, organic sulfonic acids, solid acids, and salts thereof. Preferably, phosphoric acid,
Examples include boric acid, organic acids, and alkali salts. More preferably, phosphoric acid, sodium phosphate, potassium phosphate and the like can be mentioned. The amount of the catalyst used is usually 0.01 to 5 with respect to 6 components of nylon contained in the thermoplastic.
0% by weight. Preferably from 0.1 to 20% by weight,
More preferably, it is 1 to 10% by weight. If the amount of the catalyst used is small, the reaction rate becomes slow, and if it is large, the side reaction increases and the cost of the catalyst increases, which is economically disadvantageous.

When performing dry depolymerization, the produced caprolactam is usually recovered from the reactor by distillation under reduced pressure.
After the depolymerization reaction is completed, caprolactam may be taken out by distillation under reduced pressure, or may be taken out continuously as the reaction proceeds.

When performing wet depolymerization, the produced caprolactam is usually distilled out of the reactor together with water to obtain a recovered aqueous solution of caprolactam. After the depolymerization reaction is completed, the aqueous solution of caprolactam may be taken out by distillation, or may be taken out continuously as the reaction proceeds. Preferably, water is continuously supplied to the reactor, and the resulting aqueous solution of caprolactam is continuously removed from the reactor. More preferably, at ordinary pressure, steam is continuously supplied to the reactor, and the resulting aqueous solution of caprolactam is continuously removed from the reactor.

In the case of wet depolymerization, the amount of water used is usually 0.1 to 50 times the weight of the nylon 6 component contained in the thermoplastic. Preferably, it is 0.5 to 20 times by weight, more preferably 1 to 10 times by weight. If the amount of water used is small, the reaction rate will be low, and if it is large, the concentration of the recovered caprolactam aqueous solution will be low, which is disadvantageous in obtaining caprolactam.

The material of the depolymerization apparatus used in the present invention may be any as long as it is durable with respect to the reaction mixture containing the acid catalyst under depolymerization conditions such as reaction temperature and pressure. Normally, stainless steel is used from the viewpoint of durability and cost.

The recovered caprolactam obtained in the present invention can be easily purified by adding a purification means. Other purification means include distillation, crystallization, ion exchange, activated carbon treatment, oxidizing agent treatment, reducing agent treatment, hydrogenation treatment and the like. Preferably, crystallization or distillation is performed.

[0024]

The present invention will be described in more detail with reference to the following examples. The examples do not limit the invention in any way. Example 1 A used mooring rope (100% by weight nylon 6; hereinafter abbreviated as a rope)
1000 g of ion-exchanged water is added to 250 g,
After heating and stirring for an hour, the rope and the filtrate were separated by a centrifuge. 500 g of ion-exchanged water is newly added to the separated rope.
And the same operation was repeated once. The obtained rope was 250 g, and the total weight of the filtrate was 1500 g.

Ion-exchanged water was added to 18.3 g of the filtrate to make 50.0 g, and chlorine ions were analyzed. The amount of salt in the filtrate is 0.20% by weight, the amount of salt attached to the rope is 3.0 g, and 1.2% by weight based on the rope.

The salt in the filtrate is a value obtained by converting inorganic chlorine in the filtrate into salt, and is AT-11 manufactured by Kyoto Electronics Industry Co., Ltd.
In 8, using a silver electrode as a measurement electrode and a mercury sulfate electrode as a reference electrode, a 0.1 mol / L silver nitrate aqueous solution, a burette of 20 ml, and a 60% by weight nitric acid aqueous solution were added to the titrant, and the filtrate was subjected to potentiometric titration. analyzed.

[0027] Ion exchange water 5
00 g was added and the same operation was repeated once. The obtained rope weighed 250 g and the filtrate weighed 500 g.

When 25 g of the rope was centrifuged for the third time, it was washed with 50 g of ion-exchanged water and separated in the same manner, and chloride ions were analyzed in the same manner. As a result, no salt was detected in the filtrate. The detection limit of salt is equivalent to 0.001% by weight of the rope.

The third centrifugation of the rope, 160 g, confirmed that no salt was detected, and 6.4 g of 75% by weight phosphoric acid.
(4.8 g of phosphoric acid) was charged into a 1 L depolymerization can. (From the detection limit of salt, the content is 0.0002
Less than equivalent times. NaCl / H ₃ PO ₄ = (0.0016 / 58.44)
÷ (4.8 / (98.00 / 3)) = approximately 0.0002 equivalent) Heated to 260 ° C. under a nitrogen atmosphere.

The reaction was started by injecting heated steam at a rate of 250 ml / hour into the depolymerization vessel. The depolymerization reaction was continued for 6 hours while cooling caprolactam / water vapor distilled from the depolymerization vessel and recovering the aqueous solution of caprolactam.

During the depolymerization reaction, the pressure inside the depolymerization vessel is 0.01
0.03 kg / cm ² , and there was no blockage in the can.

The total weight of the obtained aqueous solution of recovered caprolactam was 1640 g, the concentration of caprolactam was 9.15% by weight, the recovered caprolactam was 150 g, and the depolymerization yield was 94.
%Met. Example 2 160 g of nylon 6 clothing waste adhering to 0.43 g of sodium chloride and 6.4 g of phosphoric acid of 6.4 g (4.8 g of phosphoric acid) were charged into a 1-L depolymerization can. (The salt content is 0.1% relative to phosphoric acid.
05 equivalent times. NaCl / H ₃ PO ₄ = (0.43 / 58.44) ÷
(4.8 / (98.00 / 3)) ≒ 0.05 equivalent times) Under nitrogen atmosphere, 2
Heated to 60 ° C.

The heating steam was introduced at a rate of 250 ml / hour into the depolymerization vessel to start the reaction. The depolymerization reaction was continued for 6 hours while cooling caprolactam / water vapor distilled from the depolymerization vessel and recovering the aqueous solution of caprolactam.

During the depolymerization reaction, the pressure inside the depolymerization vessel was 0.01
0.03 kg / cm ² , and there was no blockage in the can.

The total weight of the obtained aqueous solution of recovered caprolactam was 1640 g, the concentration of caprolactam was 8.78% by weight, the recovered caprolactam was 144 g, and the depolymerization yield was 90%.
%Met. Comparative Example 1 Same as Example 1, rope 1 with 1.2% by weight of salt attached thereto
60 g (1.9 g of salt) and 6.4 g of 75% by weight phosphoric acid
(4.8 g of phosphoric acid) was charged into a 1 L depolymerization can. (The salt content is 0.22 equivalent times relative to phosphoric acid. NaCl
/ H ₃ PO ₄ = (1.9 / 58.44) ÷ (4.8 / (98.00 / 3)) ≒ 0.22 equivalent times) Heated to 260 ° C. under a nitrogen atmosphere.

Heating steam was introduced into the depolymerization vessel at an introduction rate of 250 ml / hour, and the reaction was started. The depolymerization reaction was continued for 6 hours while cooling caprolactam / water vapor distilled from the depolymerization vessel and recovering the aqueous solution of caprolactam.

During the depolymerization reaction, the pressure inside the depolymerization vessel was 0.01
From 0.08 kg / cm ² with time. After the completion of the reaction, the residue was highly viscous, and the steam blowing line to the depolymerization reactor was almost blocked. In addition, the reaction rate decreased and the phosphoric acid catalyst was deactivated.

The total weight of the obtained aqueous solution of recovered caprolactam was 1590 g, the concentration of caprolactam was 5.91% by weight, the recovered caprolactam was 94 g, and the depolymerization yield was 59%.
Met. Example 3 As in Example 1, the third centrifugation of rope 160g and 75% by weight of phosphoric acid, which was confirmed to be in the absence of salt, was carried out.
4 g (4.8 g of phosphoric acid) in a 1 L depolymerization can (SUS316)
(Made of stainless steel). The detection limit for salt content is
It is equivalent to 0.001% by weight with respect to the rope and 0.0002 equivalent times with respect to the phosphoric acid. Under nitrogen atmosphere, 26
Heated to 0 ° C.

The reaction was started by injecting heated steam at a rate of 250 ml / hour into the depolymerization vessel. The depolymerization reaction was continued for 6 hours while cooling caprolactam / water vapor distilled from the depolymerization vessel and recovering the aqueous solution of caprolactam.

During the depolymerization reaction, the pressure inside the depolymerization vessel was 0.01
0.03 kg / cm ² , and there was no blockage in the can. After the completion of the first reaction, the depolymerization apparatus was dismantled and washed.

Similarly, the second and third reactions were repeated. After the completion of the third reaction, the depolymerization apparatus was disassembled and washed, and the inside of the reactor was visually observed. As a result, no change was observed from before the start of the reaction, and it was confirmed that no corrosion occurred.

The total weight of the aqueous solution of recovered caprolactam obtained by the three reactions was 4,900 g, the concentration of caprolactam was 9.2% by weight, the recovered caprolactam was 450 g, and the depolymerization yield was 93%. Comparative Example 2 Same as Example 1, rope 1 with 1.2% by weight of salt attached thereto
60 g (1.9 g of salt) and 6.4 g of 75% by weight phosphoric acid
(4.8 g of phosphoric acid) was charged into a 1 L depolymerization can (SUS316 stainless steel autoclave). The salt content is 0.22 equivalent times of phosphoric acid. Under nitrogen atmosphere,
Heated to 260 ° C.

The heating steam was introduced at a rate of 250 ml / hour into the depolymerization vessel to start the reaction. The depolymerization reaction was continued for 6 hours while cooling caprolactam / water vapor distilled from the depolymerization vessel and recovering the aqueous solution of caprolactam.

During the depolymerization reaction, the pressure inside the depolymerization vessel was 0.01
From 0.08 kg / cm ² with time. After the completion of the reaction, the residue was highly viscous, and the steam blowing line to the depolymerization reactor was almost blocked. In addition, the reaction rate decreased and the phosphoric acid catalyst was deactivated. After the completion of the first reaction, the depolymerization apparatus was dismantled and washed. After obstruction of the line was removed by heating and melting, it was burned and decomposed by a portable burner.

Similarly, the second and third reactions were repeated. After the completion of the third reaction, the depolymerization apparatus was dismantled and washed, and the inner surface of the reactor was visually observed. As a result, spot-like corrosion was observed on the smooth surface of the upper lid.

The total weight of the recovered caprolactam aqueous solution obtained by the three reactions was 4,800 g, the caprolactam concentration was 5.9% by weight, the recovered caprolactam was 280 g, and the depolymerization yield was 58%.

[0047]

According to the present invention, a thermoplastic material containing nylon 6 as a main component and having an alkali metal chloride and / or an alkaline earth metal chloride attached thereto is depolymerized with an acid catalyst to give caprolactam in good yield. It can be manufactured in an industrially advantageous manner without handling problems and device corrosion problems.

Claims (11)

[Claims] 1. A caprolactam is obtained by depolymerizing a thermoplastic material containing nylon 6 as a main component and having an alkali metal chloride and / or an alkaline earth metal chloride attached thereto to obtain caprolactam. Is 0.20 for the catalyst
Nylon 6 depolymerization method characterized by being not more than equivalent times. 2. The thermoplastic material having nylon 6 as a main component and having an alkali metal chloride and / or an alkaline earth metal chloride attached thereto contains nylon 6 in an amount of 90% by weight or more. Nylon 6 depolymerization method. 3. The thermoplastic resin according to claim 1, wherein the chloride of the thermoplastic containing nylon 6 as a main component and having an alkali metal chloride and / or an alkaline earth metal chloride attached thereto is derived from common salt. The nylon 6 depolymerization method according to any one of the above. 4. A thermoplastic material comprising nylon 6 as a main component and having an alkali metal chloride and / or an alkaline earth metal chloride attached thereto is a fiber structure and / or fiber waste. 4. The nylon 6 depolymerization method according to any one of the above items 3 to 3. 5. The nylon 6 depolymerization method according to claim 4, wherein the fiber structure and / or fiber waste is at least one selected from a fishing net, a rope, and clothing. 6. The thermoplastic material according to claim 1, wherein the thermoplastic containing nylon 6 as a main component and having an alkali metal chloride and / or an alkaline earth metal chloride attached thereto is washed with water before depolymerization. 5. The nylon 6 depolymerization method according to any one of the above items 5. 7. A thermoplastic material containing nylon 6 as a main component and having an alkali metal chloride and / or an alkaline earth metal chloride attached thereto is obtained by cutting before washing with water and removing water after washing. The nylon 6 according to claim 6, wherein
Depolymerization method. 8. A thermoplastic material containing nylon 6 as a main component and having an alkali metal chloride and / or an alkaline earth metal chloride attached thereto is depolymerized with a phosphoric acid catalyst in the presence of water. Item 8. The nylon 6 depolymerization method according to any one of Items 1 to 7. 9. A process for continuously supplying steam to a depolymerization reactor for a thermoplastic material having nylon 6 as a main component and having an alkali metal chloride and / or an alkaline earth metal chloride attached thereto, and The nylon 6 depolymerization method according to claim 8, wherein the recovered caprolactam aqueous solution is continuously distilled from the vessel and depolymerized. 10. A thermoplastic material having nylon 6 as a main component and having an alkali metal chloride and / or an alkaline earth metal chloride attached thereto, wherein the amount of the chloride attached to the catalyst is 0.
10. It is 10 equivalent times or less.
The nylon 6 depolymerization method according to any one of the above. 11. The nylon 6 depolymerization method according to claim 10, wherein the amount of the chloride adhered is 0.01% by weight or less based on the thermoplastic material.