JPS6020379B2 - Polylactam depolymerization method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for thermally depolymerizing polylactam.

More specifically, the present invention relates to an improved continuous depolymerization method for recovering gaseous lactam by thermally depolymerizing polylactam in the presence of a catalyst. It is important to thermally depolymerize polylactam, especially polycaprolactam scraps, and recover lactam, which is a raw material for polylactam production, in order to reduce the production cost of polylactam, and also from the perspective of saving resources. . In the conventional polylactam depolymerization method, polylactam is introduced in solid form together with phosphoric acid, brought into contact with steam and heated, melt-polymerized, and the obtained lactam is taken out of the system together with steam.

However, the above method has the following drawbacks.
First of all, raw materials are introduced together with the catalyst in a constant state while controlling the liquid level in the device. Therefore, the temperature within the apparatus drops considerably each time a charging operation is performed, resulting in a reduction in the reaction rate. After the charging operation is completed, the temperature gradually recovers, but once the temperature has recovered, the next operation is performed, causing the temperature to drop further. In this way, the temperature inside the apparatus is constantly fluctuating, making the reactor extremely inefficient. Second, when a volatile substance such as phosphoric acid is used as a depolymerization catalyst, the catalyst is combined with polylactam in the depolymerization system, but as mentioned above, water vapor is added to the depolymerization system to remove the lactam. is also supplied, so that the catalyst comes into contact with steam before acting on the polylactam.

By contacting with steam, the catalyst is steam-distilled and dissipated from the depolymerization system, resulting in an unnecessarily high consumption of the catalyst. Thirdly, since the heating source in the above method is steam, the consumption of steam is enormous and the lactam concentration in the cracked gas is quite low.

Therefore, in order to separate only the lactam, it is necessary to remove a considerable amount of water, and the burden on the subsequent process becomes enormous.
In general, in order to remove separated unreacted substances from the system,
Periodically, the bond is suspended, the bottom of the device is opened, and the bond is removed. However, this method significantly reduces the transfer rate and the removal operation is extremely dangerous.

In order to solve the above-mentioned drawbacks, the present inventor conducted intensive research and completed the present invention.

That is, the present invention uses a vertical reactor having an outer cylinder having a heating device and an inner cylinder installed in the outer cylinder when thermally depolymerizing polylactam in the presence of a catalyst. The polylactam is supplied from a supply port provided at the lower part of the gap between the inner cylinder and the polylactam in the gap, while being heated by the heating device, moved to the upper part of the reactor and depolymerized. The resulting reaction mixture overflows into the inner cylinder through the gap and is brought into contact with steam blown out from a steam blowing nozzle provided below the middle part of the inner cylinder, so that the obtained lactam is transferred to the reactor. This is a method for depolymerizing polylactam, which is characterized in that the residual liquid produced by depolymerization is taken out from the upper part, and the residual liquid created by the depolymerization is discharged from the residual groove outlet provided at the lower part of the inner cylinder. Before explaining aspects of the present invention in detail, a depolymerization apparatus preferred for use in the present invention will first be explained with reference to the drawings.

FIG. 1 is a longitudinal sectional view of one embodiment of the depolymerization apparatus used in the present invention. 1 is a vertical reactor outer cylinder (hereinafter abbreviated as outer cylinder),
Heating jacket 2, gas-liquid separator 3, lactam outlet 4
have.

There is an inner cylinder 5 inside the outer cylinder 1, a water vapor blowing nozzle 6 is provided below the middle part inside the inner cylinder 5, and a residual liquid discharge port 7 is provided.
is placed below it. Also, the gap 8 between the outer cylinder and the inner cylinder
A polylactam supply port 9 is provided at the lowest part of the polylactam supply port 9.
Further, the supply port 9 has a catalyst addition row 0. FIG. 2 is a longitudinal sectional view of one embodiment of the depolymerization apparatus used in the present invention, which is further improved than the apparatus shown in FIG.

A circulation pipe 11 is provided for external circulation from below the inner cylinder 5 to the bottom of the gap 8, and the circulation pipe 11 has a catalyst addition port 12 and a heating screw 13. Next, embodiments of the present invention will be explained using the drawings.

In the case of a tablet using the depolymerization apparatus shown in FIG.
The reaction mixture is heated to the depolymerization temperature by the heating jacket 2 and depolymerized, while the resulting reaction mixture moves to the upper part and overflows into the inner cylinder 5. Next, the reaction mixture is brought into contact with water vapor blown from a water vapor blowing nozzle provided below the middle part of the inner cylinder 5, and the lactam in the reaction mixture is quantitatively taken out from the upper lactam outlet 4 along with the water vapor. On the other hand, the residual liquid produced by depolymerization is discharged from the residual groove discharge port 7. Next, when using the apparatus shown in FIG.
It is externally circulated to the bottom of the gap 8 through the circulation pipe 11.

At this time, the catalyst is added from the catalyst addition row 2, heated by the heating sled 13, and fed. Also, the inner cylinder 5
It is preferable that the circulation pipe 11 provided at the bottom is provided below the steam blowing nozzle 6 and above the residual oak discharge port 7. The improved method described above results in continuous polylactam depolymerization because the reaction mixture is recycled quantitatively. In the present invention, the polylactams to be depolymerized are polycaprolactam, polyenanthulactam, and polylau.

It refers to lactams or copolyamides containing them, and is particularly suitable for use in blind polymerizing polycaprolactam. Further, the polylactam to be depolymerized in the present invention may contain additives such as pigments and stabilizers. In addition, in the present invention, the polylactam should be melted so that it can be quantitatively supplied to the reaction vessel, but the temperature of the melt should be 200 oo or higher, especially 230 q
Preferably, the temperature is maintained at a constant temperature of 0 to 280 qC.

Next, in the present invention, the polylactam supplied to the gap is heated to a depolymerization temperature while moving upward, and the heating temperature at this time is 270 to 330 qo.

If it is less than 270 qo, the rate of the depolymerization reaction will be 4.0 qo, whereas if it is more than 33 qo, a large amount of depolymerization residue will be produced, which is not preferable.

In order to heat the reaction mixture to the above temperature range, the reaction vessel may be heated with a jacket or with an electric heater. Next, in the present invention, the depolymerized reaction mixture is brought into contact with steam to evaporate the lactam, and the temperature of the steam used is preferably 300 to 450 oo. In addition, the amount of water vapor supplied to the reaction vessel is 0% by weight relative to the weight of the molten polylactam added to the reaction vessel.
．． 05-2. It is sufficient within the pitch range. In addition, in order to bring the water vapor into contact with the reaction mixture, it is preferable to blow out the water vapor into the reaction mixture from a water vapor blowing nozzle as shown in Figure 1. It is preferable to eject water vapor from multiple nozzles. At this time, it is preferable that the position at which steam is spouted into the reaction mixture is 5 to 20 degrees below the level of the reaction mixture. At a shallow position of 5 degrees or less below the level, it becomes difficult to make sufficient contact between the steam and the reaction mixture, while at a depth of 2 degrees or more below the level, the polymerization of the reaction mixture does not proceed sufficiently. This is not preferable because it has the disadvantage that the catalyst may be extracted from the reaction mixture. Next, in the improved method of the present invention, a part of the reaction mixture is externally circulated from the lower part of the inner cylinder to the bottom of the gap, but the amount of the reaction mixture that is externally circulated is the amount of reaction mixture remaining in the inner cylinder per minute. The amount is preferably 0.05 to 0.5 times the weight of the mixture.

If the circulating amount exceeds the above range, a large amount of the lactam that has fully reacted will be withdrawn at the same time, resulting in a decrease in the apparent reaction rate, which is not preferable. On the other hand, if the circulation rate is small, the movement of the polylactam in the gaps is slow, resulting in poor heat transfer efficiency and slow depolymerization rate, which is also not preferable. In addition, in the present invention, the catalyst is orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid, polyphosphoric acid,
oxyacids of phosphorous, such as phosphorous acid, or their esters;
Salts of weak bases or alkaline compounds can be used, but in the present invention, those that easily convert into orthophosphoric acid, such as orthophosphoric acid, pyrophosphoric acid, and metaphosphoric acid, are particularly preferred.

These phosphoric acid catalysts are preferably used as they are or as concentrated aqueous solutions or lactam solutions. The amount of catalyst supplied into the reaction mixture varies depending on the amount of molten polylactam supplied to the gap, the amount of depolymerization residue taken out from the reaction vessel, etc. On the other hand, the amount of catalyst incorporated in the recycled reaction mixture is preferably selected to be between 0.05 and 3%. In the present invention, as a device for externally circulating the reaction mixture, for example, a screw feeder, a Milton Roy pump, a gear pump, etc., as shown in FIG. 2, are used.

On the other hand, as a device for feeding the catalyst into the reaction mixture, for example a Milton Roy or a diaphragm pump is used. Next, in the present invention, the high-density depolymerization residue produced as a by-product when molten polylactam is depolymerized is constantly discharged from the discharge port at the bottom of the inner cylinder. , 2, a screw extruder or the like is used.

When discharging the above-mentioned depolymerization residue, it is preferable to reduce the amount of active ingredients that can be depolymerized into lactam contained therein as much as possible, but by reducing the amount of active ingredients, the melt viscosity of the residue increases. Please be careful as this will make it more difficult to remove. In reality, it is possible to determine the amount of active ingredient by measuring the load required to operate the extrusion device as shown in Figure 1, so the rotation speed of the extruder can be changed or controlled depending on the load. It is preferable to take out a residual liquid containing a certain active ingredient by stopping the operation of the extractor. In the present invention, constantly discharging the residue means removing the residue containing a certain amount of active ingredient as much as possible, and it is preferable to take out the residue as continuously as possible.
Depending on the situation, it may be intermittent.

The polylactam depolymerization method of the present invention is as described above, but by adopting the method of the present invention, the first
Since the polylactam reaches the depolymerization reaction chamber through the heating section, the temperature inside the device is kept constant and the reaction rate is constant.

Second, thermal energy is used for melting and depolymerization, whereas in the present invention it is used only for depolymerization, resulting in much higher efficiency and significantly lower water vapor consumption. Also, as a result, the concentration of lactams discharged becomes even higher. Thirdly, since the catalyst is not directly added to the depolymerization reaction region, it has various effects such as solving the problem of scattering, and is a great contribution to industry. Examples will be shown below, but the present invention is not limited thereto.

EXAMPLE Using the depolymerization apparatus shown in FIG. 2, continuous depolymerization of polycapramide was carried out under the conditions shown below.

The outer cylinder 1 in FIG. 2 has an inner diameter of 0.41 mm and a volume of 27.3 mm, and the inner cylinder 5 has an inner diameter of 0.34 mm and a volume of 21.5 mm. First, outer cylinder 1
temperature is maintained at 350°C, and the steam blowing nozzle is
265 oo of molten polycapramide was fed at a rate of 150 to 200 m/min so as to cause the mixture to immerse in water for about 0.5 oz.

During that time, 350 qo of superheated steam was blown out at 200 t/min.
The reaction mixture was externally circulated at a rate of 50-100 min/min. Orthophosphoric acid, which is a depolymerization catalyst, was added through the addition port 12 in an amount of 0.2% by weight based on the polycapramide. On the other hand, 3 to 10 portions of the depolymerization residue was extracted from the residual groove discharge port 7. As a result, water vapor with a lactam content of 50 to 60% by weight was
0-40M/min was obtained. Moreover, the phosphorus content in the obtained steam was 14 m.

[Brief explanation of the drawing]

1 and 2 are longitudinal sectional views of a depolymerization apparatus used in the present invention. 1 is an outer cylinder, 5 is an inner cylinder, 6 is a water holly air blowing nozzle, 9 is a polylactam supply port, 7 is a liquid discharge port, and 11 is a circulation pipe. Figure 1 Figure 2

Claims (1)

[Claims] 1. When thermally depolymerizing polylactam in the presence of a catalyst, a vertical reactor having an outer cylinder equipped with a heating device and an inner cylinder installed inside the outer cylinder is used, and the outer cylinder and inner cylinder of the reactor are Polylactam is supplied from a supply port provided at the bottom of the gap, and in the gap, the polylactam is moved to the top of the reactor while being heated by the heating device and depolymerized, and then the polylactam is obtained by depolymerization. The reaction mixture is allowed to overflow into the inner cylinder from the gap and is brought into contact with steam blown out from a steam blowing nozzle provided below the middle part of the inner cylinder, so that the obtained lactam is transferred to the upper part of the reactor. 1. A method for depolymerizing polylactam, which comprises taking out a polylactam, and discharging a residue by-produced by the depolymerization from a residue outlet provided at the bottom of an inner cylinder.