KR20020030944A - The contiunous transport equipments for PTFE pyrolysis - Google Patents

Abstract

PURPOSE: Provided is a device for continuously transferring polytetrafluoroethylene, for developing a process capable of industrially producing a TFE by pyrolysis of PTFE. CONSTITUTION: The device comprises at least two major reservoir(10) for PTFE capable of storing particles or powders of PTFE and operating alternately; a minor reservoir(11) for PTFE which temporarily stores PTFE supplied from the major reservoir(10); a vertical screw feeder(13) which quantitatively introduces PTFE supplied from the minor reservoir(11) into process by duct(14); and a heat exchanger(15) which blocks and cools a heat transmitted from a vertical pyrolysis reactor(16). The device can conveniently and economically mass-produce a TFE.

Description

The contiunous transport equipments for PTFE pyrolysis

The present invention relates to a continuous polytetrafluoroethylene (PTFE) pyrolysis transport apparatus, and particularly in the case of producing tetrafluoroethylene (TFE) by pyrolyzing PTFE in a vacuum atmosphere, handling and transport are very dangerous. It provides a continuous polytetrafluoroethylene (PTFE) pyrolysis transfer apparatus that provides a means to effectively deliver difficult TFE, thereby enabling mass production of industrially highly available TFE in a convenient way at the desired place of use.

In general, there are two methods for preparing TFE: pyrolysis of CFC-22 and pyrolysis of PTFE.

Since the pyrolysis method of CFC-22 includes a large amount of impurities including hydrochloric acid generated after pyrolysis, hydrochloric acid absorption tower, Ca (OH) ₂ neutralization tower, purification sulfuric acid tower for removing trace impurities, and reactions are generated. A large-scale purification process is required, such as distillation to separate TFE, such as HFP (hexafluoropropylene), OFCB (octafluorocyclobutane), etc. It is known that it is suitable for the mass production process of at least 3,000 annually due to the high equipment investment and operating costs.

On the other hand, the process of producing TFE by pyrolysis of PTFE under vacuum is much simpler than the CFC-22 pyrolysis process, and consists of PTFE injection process, pyrolysis process, and condensation of the produced TFE. In view of the stability of the impossible TFE, there is an advantage in that the desired TFE can be obtained through small scale production, but in most cases, a very small amount of PTFE is experimentally obtained by a batch reaction, or a powder is injected even in continuous operation. And due to the blockage of the conveying device by agglomeration of the PTFE in the form of particles in the conveying device has a disadvantage that it is difficult to mass-produce the TFE commercially for a long time.

The process of producing TFE by pyrolysis of PTFE under vacuum is as follows.

① The whole system is maintained at a vacuum of 10 ^-2 torr or less, ② The powder, particulate or scrap PTFE is introduced into the reactor, ③ The TFE by thermal decomposition of PTFE at a pressure of 5torr or less and a high temperature of 500 ℃ or more Generating FE, ④ condensing and solidifying the generated TFE at a temperature of -142 ° C. or lower, and ⑤ converting the obtained TFE to a gas phase and passing it through an absorption tower into which a polymerization inhibitor is added and storing it as a gas. Consists of.

According to the steps of ① and ②, the process is divided into a continuous process (① → ② → ③ → ④ → ⑤) or a batch process (② → ① → ③ → ④ → ⑤).

In order to achieve a continuous process which is a commercially available process in this step, it is necessary to add the powder or particulate PTFE in a quantitatively / continuously high temperature into the reactor while the whole system is maintained in a vacuum state.

Here, the glass transition temperature of PTFE is 19 ℃ and 30 ℃, before 19 ℃ the molecular structure is twisted 13 carbon atoms, the unit length is 16.9Å, after 19 ℃ 15 carbon atoms constitute a unit molecule, hexagonal It shows the structural form and the unit length is 15.9Å, increasing volume by 1%.

Moreover, at 30 degreeC or more, it has a characteristic changed into a flat plate form.

Therefore, the low glass transition temperature of PTFE is extremely difficult to continuously and quantitatively input due to phase change caused by mechanical heat generated during transfer of PTFE for PTFE pyrolysis or conducted heat during high temperature pyrolysis. have.

In addition, in the case of PTFE in the form of powder or granules, pores are formed in the particles during the manufacturing process, so that they are agglomerated even at extremely low pressures, and thus, natural transfer is difficult.

Therefore, in order to commercially complete a TFE manufacturing process by continuous injection of PTFE and pyrolysis, a continuous quantitative injection method and apparatus for powder or particulate PTFE have to be solved.

Accordingly, the present invention has been made in view of the above, and the present invention provides a continuous feed apparatus of PTFE for developing a process capable of commercial production of TFE by pyrolysis of PTFE.

The conveying apparatus provided by the present invention is characterized by being capable of continuously producing a large amount of TFE by continuously injecting powder or particulate PTFE into a high-temperature pyrolysis reactor without interruption of PTFE conveying under high vacuum. According to the conveying apparatus of the present invention, It is convenient and economical by overcoming the degradation of productivity due to the interruption of the pyrolysis reaction and frequent dismantling and maintenance of the device due to batch reaction, which is a disadvantage of the method of producing TFE by the conventional PTFE pyrolysis, and poor transfer of PTFE (welding, fixing, etc.). The effect of enabling the commercial mass production of TFE can be expected.

1 is a schematic view showing a continuous PTFE pyrolysis transport apparatus according to the present invention

<Explanation of symbols for main parts of drawing>

10: PTFE primary reservoir 11: PTFE secondary reservoir

12 ball valve 13 vertical screw feeder

14 introduction tube 15 heat exchanger

16 vertical pyrolysis reactor 17 transparent hose for vacuum

It is an object of the present invention to provide a pyrolysis transfer apparatus of powder or particulate PTFE for continuously producing a large amount of TFE compared to a conventional TFE production process by batch PTFE pyrolysis.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 schematically shows the overall configuration of a continuous PTFE pyrolysis transport apparatus according to the present invention.

Here, reference numeral 10 denotes a PTFE main reservoir.

The PTFE main reservoir 10 is a jacket-mounted reservoir, the lower portion of which has a circular cone shape for the natural transfer of PTFE.

At this time, the conical shape is preferably to have an angle of 60 ° or more horizontal, and more preferably to have an angle of 70 ± 5 °.

Also, reference numeral 11 denotes a PTFE auxiliary reservoir.

The PTFE auxiliary storage tank 11 is a conical auxiliary storage tank is equipped with a confirmation window for confirming the smooth flow of the PTFE is fitted and put into the jacket.

The PTFE auxiliary reservoir 11 is preferably set to a total height of 50 cm or less, and more preferably 30 ± 5 cm in order to prevent the pressing by the weight of the PTFE to be introduced and smooth transfer.

At this time, the conical shape is preferably to have an angle of 60 ° or more horizontal, and more preferably to have an angle of 70 ± 5 °.

In addition, reference numeral 12 denotes a ball valve.

The ball valve 12 is installed between the PTFE primary reservoir 10 and the PTFE secondary reservoir 11, and serves to interrupt the flow of vacuum operation and powder or particulate PTFE.

Reference numeral 13 also denotes a vertical screw feeder.

The vertical screw feeder 13 is a motor-driven metering means equipped with a magnetic drive for metering PTFE, and an introduction tube 14 for conveying PTFE powder is provided at one side.

At this time, it is preferable to use the step motor etc. which can adjust a rotation speed.

The driving direction of the introduction pipe 14 and the screw feeder is preferably maintained at an angle of 60 ° or more horizontal, more preferably to have an angle of 75 ± 5 °.

The entire system of the vertical screw feeder 13 is provided with a jacket for cooling.

Reference numeral 15 denotes a heat exchanger.

The heat exchanger 15 is a kind of cooling means for blocking and cooling the heat transferred by conduction, convection or radiation in the vertical pyrolysis reactor 16 at which the high temperature is maintained.

The heat exchanger 15 prevents the generation of PTFE scale in the transfer pipe by the heating of the PTFE injected into the vertical pyrolysis reactor 16 and the blockage of the transfer pipe, and the horizontal direction of the top surface of the vertical pyrolysis reactor 16. It is installed to have an angle of 70 ° or more.

Reference numeral 17 denotes a transparent hose for vacuum.

Therefore, all devices equipped with a jacket in the conveying apparatus according to the present invention are cooled with cooling water of 19 ° C. or lower, which is the glass transition temperature of PTFE, for cooling the PTFE, and more preferably, transferred using a refrigerant of −5 ± 5 ° C. It prevents the coagulation and fixation of PTFE in the device by the temperature rise above the glass transition temperature of PTFE by the external mechanical force, and induces the smooth flow of PTFE.

On the other hand, when described the thermal decomposition process using the transfer device of the present invention as follows.

Lock the PTFE secondary reservoir and fill the PTFE primary reservoir with either powder or particulate PTFE.

In order to remove oxygen in the reaction system using a vacuum pump, the pressure of the PTFE main reservoir, the PTFE auxiliary reservoir, the vertical screw feeder, the heat exchanger, the vertical pyrolysis reactor, and the TFE measuring tank is lowered to 10 ^-3 torr.

A circulating refrigerant is operated to cool the PTFE primary reservoir, PTFE secondary reservoir, vertical screw feeder and heat exchanger, and the reactor is slowly heated to the desired pyrolysis temperature.

After checking the vacuum level of the whole system, the vacuum pump is stopped and the whole system is sealed.

Open the ball valve to transfer the PTFE particles in the PTFE primary reservoir to the PTFE secondary reservoir by gravity.

By controlling the number of revolutions of the vertical screw feeder, the desired amount of PTFE particles are introduced into the vertical pyrolysis reactor and pyrolyzed.

At this time, the pressure of the vertical pyrolysis reactor is operated to be 5torr or less.

As PTFE particles are pyrolyzed in a vertical pyrolysis reactor, the TFE obtained is transferred to a TFE condensing tank maintained below -142 ° C to condense and solidify.

It is preferable that the PTFE main reservoir is provided with at least two tanks so that one side of the PTFE main tank can be alternately operated when one of the PTFE is exhausted.

Hereinafter, various embodiments of a method for manufacturing a TFE using the apparatus of the present invention configured as described above will be described.

EXAMPLE 1

Fill the PTFE main reservoir with 50 kg of PTFE (M-292, Daikin, Japan), vent the entire system to 10 ^-3 torr and seal.

At this time, the temperature of the reactor was raised to 650 ° C at the same time as the exhaust gas, and a circulating refrigerant of -5 ° C was operated to cool the PTFE main reservoir, the vertical screw feeder, and the cooler. Cool to below.

The ball valve is opened to feed PTFE from the PTFE main reservoir into the PTFE secondary reservoir, and the PTFE is introduced into the pyrolysis reactor at a rate of 15 kg / hr by operating a vertical screw feeder.

At this time, the pressure of the reactor was 3torr or less.

Pyrolyzed PTFE is continuously stored in a TFE condensing bath cooled with liquid nitrogen.

According to the PTFE exhaust and TFE storage of the two PTFE main reservoirs, the filling / exhaust operation of PTFE and the evaporation / recooling of TFE were repeated for 40 hours, and no clogging in the PTFE feeder occurred during the operation.

The gas obtained was analyzed using GC and GC / MS, resulting in 96.5% TFE and 3.5% HFP, producing trace amounts of carbon and OFCB.

EXAMPLE 2

PTFE was added to the vertical pyrolysis reactor at a rate of 15 kg / h in the same manner as in Example 1, and the pyrolysis reaction was performed while changing the temperature of the vertical pyrolysis reactor to 550 to 950 ° C.

Table 1 shows the results of analyzing the composition of the obtained gas.

EXAMPLE 3

In the same manner as in Example 1, the shredded PTFE scrap (average diameter 3mm) was introduced into the vertical pyrolysis reactor at a rate of 15 kg / h, and pyrolysis reaction was performed.

The maximum pressure during the pyrolysis reaction was 4.5torr, and the analysis of the gas composition showed TFE 94% and HFP 6%, and trace amounts of PFCB and carbon were produced.

[Comparative Example 1]

PTFE pyrolysis was carried out under the same conditions as in Example 1 using a horizontal screw feeder in the same apparatus as in FIG.

10 minutes after the addition of PTFE, the blockage of PTFE introduced in the screw feeder occurred, thereby stopping the reaction.

As a result of analysis of the obtained gas, it was TFE 95% and HFP 5%.

[Comparative Example 2]

PTFE pyrolysis was carried out with the jacket of the PTFE main reservoir, the PTFE secondary reservoir, the vertical screw feeder, and the heat exchanger removed in the same apparatus as in FIG. 1.

After 20 minutes of PTFE injection, the reaction was stopped due to PTFE blockage in the heat exchanger section, PTFE main / secondary reservoir and vertical screw feeder.

As a result of analysis of the obtained gas, it was 94.3% of TFE and 5.7% of HFP.

As described above, the present invention provides a transfer apparatus that can be applied to a process of thermally decomposing TFE having high industrial utilization in PTFE, thereby mass-producing high purity TFE having various commercially available applications through an easy method at a desired place of use. There is an advantage that can be.

Claims (4)

At least two PTFE main reservoirs (10) capable of storing powder or particle-shaped PTFE and capable of alternating operation, and the PTFE main reservoirs (10) are connected by a ball valve (12) and a transparent hose for vacuum (17). The PTFE auxiliary reservoir 11 temporarily stored before the PTFE supplied from the main reservoir 10 is introduced into the process, and operated by the motor and the magnetic driver driving means, and operated in a state where the rotation speed can be controlled. Between the vertical screw feeder 13 for metering the PTFE supplied from the PTFE auxiliary reservoir 11 into the process, and the vertical screw feeder 13 and the vertical pyrolysis reactor 16 for pyrolyzing the PTFE. Continuous polytetrafluoroethylene pyrolysis transfer device, characterized in that it comprises a heat exchanger (15) installed in the high temperature vertical pyrolysis reactor (16) to block and cool the heat transferred. The continuous polytetrafluoroethylene pyrolysis transfer apparatus according to claim 1, wherein the PTFE main reservoir (10) and the PTFE auxiliary reservoir (11) are provided with a jacket for circulating refrigerant. The continuous polytetrafluoroethylene pyrolysis transfer apparatus according to claim 1, wherein the heat exchanger (15) is installed to have an angle of 70 ° or more with the top horizontal direction of the vertical pyrolysis reactor (16). The continuous polytetrafluoroethylene pyrolysis transport apparatus according to claim 2, wherein the circulating refrigerant of the jacket uses a refrigerant maintained at -5 ° C.