The method of producing ptfe

 

(57) Abstract:

The invention relates to the production of polytetrafluoroethylene by polymerization of tetrafluoroethylene. The method includes purging the reactor with an inert gas until the oxygen content of from 0.01 to 0.005%, the purification of water for polymerization of the organic and inorganic impurities by filtration through two successively arranged membrane located so that the space above the first membrane is constantly given to 25-50% of the flow coming at her with concentrated impurities, and from the space above the second membrane 20-30% of the flow coming at it from a return this portion to the first membrane. The process of filing on tetrafluoroethylene polymerization is carried out with speed, providing the temperature in the gas phase reactor 40-60°C. Supplied to the polymerization of the tetrafluoroethylene contains 0.05-0.4 mg of the alkylamine per liter of gaseous tetrafluoroethylene. As the alkylamine used tertiary alkylamines followed from the group triethyl - tripropyl or tributylamine. The method according to the invention improves the security of the process and the polymer yield, reduce the consumption of system initiation. 4 C.p. f-crystals, 4 tab., 1 Il.

The invention alsacia tetrafluoroethylene (TPV).

There is a method of instruction PTFE polymerization of TPV in the environment of demineralized water in the presence of a polymerization initiator at 2.17 MPa and a temperature of 20-40oC [Pat. USA 5405923, CL 08 F 2/18, C 08 F 14/26]. The disadvantage of this method is the high pressure polymerization, resulting in an increased probability of explosive decomposition of the TPV, which increases the risk process, increased accumulation of the formed PTFE on the walls of the reactor, and hence the complexity of the technology because of the need for periodic cleaning of the internal surface of the reactor [Y. A. Panshin, S., Malkevich, U. S. Dunaevskaya. Fluoropolymers. L., Chemistry, 1978, p 19-35].

The closest in technical essence of the present invention is a method of obtaining described in the patent of the Russian Federation [the Patent of Russia 2056437, class C 08 F 114/26]. He adopted for the prototype. In accordance with this method the process of obtaining PTFE is carried out by polymerization of the TPV in liquid medium (in particular, water, subjected to demineralization in the presence of the initiator. Before serving TPV in the reactor it is blown with an inert gas until the oxygen content in the exhaust of the inert gas is less than 0.05% in order to prevent explosive decomposition TPV (safety improvement process). Obtained as a result of the ku combine with flour.

The disadvantages of the prototype method include the following:

- not fully secure the polymerization process, as removal from the reactor of oxygen by purging with an inert gas to a residual oxygen content of less than 0.05% is a necessary but not sufficient condition for security. In addition, the upper limit of the content of residual oxygen in the reactor is such that the process of explosive decomposition TPV remains potentially possible;

- application for the polymerization of demineralized water, i.e. water, purified only from mineral impurities. It Is Known [J. A. Panshin, S., Malkevich, U. S. Dunaevskaya. Fluoropolymers. L., Chemistry, 1978, S. 29-31] that the quality of the obtained PTFE, stable quality from the polymerization process to process, exit PTFE spent on TPV, depend on the presence in water of organic impurities determined quantitatively by titration of water with potassium permanganate solution. In the case of standard procedures for obtaining demineralized water these organic impurities are in the water treated according to the law of the case and in significant quantities [L. A. Kul. Fundamentals of chemistry and technology of water. Kiev, Naukova Dumka, 1991, S. 407], which leads to following the progress of the initiator due to its interaction with organic impurities; 2) reduction of yield of PTFE; 3) reducing the molecular weight of the PTFE and the change in molecular mass distribution, and therefore, deterioration in the quality PTFE; 4) contact with additional quantities of organic impurities in the process of washing and grinding the obtained PTFE, which has a negative effect upon receipt of the products like PTFE, especially at the stage of sintering at 370-390o(May be cracking products) and changes colour from white to yellowish interspersed with dark inclusions. The latter does not meet the requirements of the international standard ASTM d 4894 "specifications for materials based on PTFE granular structure produced by the method of molding and plunger extrusion". In this regard, the present invention is to eliminate the disadvantages inherent in the prototype.

This goal is achieved through the use of the following technical solutions:

- purge the reactor with an inert gas is made up of oxygen content in the inert gas from 0.01 to 0.005%. When the oxygen content exceeding 0.01% chance of explosive decomposition of the TPV in contact with oxygen remains high. Providing oxygen content below 0.005% of the causes of beings of which are described below;

- submission of the TPV in the reactor-polymerization is carried out with speed, providing the temperature of the gas phase in the reactor 40-60oC. When the temperature is below 40oC there is a decrease in the performance of the process, at temperatures above 60oC increases the probability of explosive decomposition TPV;

- TPV fed to the reactor-polymerization, contains 0.05-0.4 mg per liter of gaseous TPV alkylamine, which ensures the stability of the rate of polymerization in time and thereby reduces the risk of the polymerization process. As the alkylamine used triethylamine, tributylamine or other similar compounds;

as the source water, the treatment which received clean water to conduct polymerization TPV was used river water, which was subjected to the standard pre-treatment:

- coagulation suspended in river water impurities by adding coagulants type of aluminum sulfate, hydroxochloride aluminium;

sucks water for the purpose of deposition of the resulting sludge;

filtering attorney water through bulk consistently spaced filters with quartz sand and activated carbon to further remove estato type of trisodium phosphate, sodium hexametaphosphate and other translating hardness salts in the sediment.

After standard procedures pre-treatment water containing the number of soluble organic and inorganic impurities, is passed through two consecutive reverse osmosis membrane element. And part of the water (25-50%), supplied to the first as the membrane is continuously removed from namebrands space together with organic and inorganic impurities, not passed through the membrane, including hardness salts. The flow of water that passes through the first membrane, and served during the second membrane so that namebrands space is constantly given to 20-30% of the specified flow together with impurities, is not passed through the second membrane, and served in the line of flow at first along the membrane. Water that passes through both the membrane element and purified from organic and inorganic impurities, is used to conduct polymerization processes TPV (Fig. 1). As the material of the membranes used for water purification, can be used polyamide-polysulfone, cellulose acetate, etc. In case of receiving a special high grades of PTFE water, purified the

The upper bound of the magnitude of water flows, which contain concentrated organic and inorganic impurities and disposed of, without passing through the first (50% of the total flow) and second (30% of the flow to the second membrane element of the membrane, due to the fact that a further increase in the portion of the exhaust flow does not reduce impurities in the filtrate after the second membrane.

Lower limit value selection part flows with concentrated impurities not passed through the first (25% of the total flow of water on the 1st membrane) and second (20-30% of the water flow on the 2nd membrane), due to the fact that when the values of flows less than the above, there is a decrease in the level of water treatment, especially from organic impurities, which leads to a lowering of the yield of PTFE and deterioration of its quality when used in the polymerization of the water of such quality.

The invention is illustrated by the following examples.

EXAMPLE 1 (control)

Demineralized (demineralized water) for the polymerization of TPV were prepared using standard procedures demineralization described in [L. A. Kul. Fundamentals of chemistry and technology of water. Kiev, Naukova Dumka, 1991] and consisting in passing eschatological United H-cationite (filled with ion exchange resin Ky-2) and anionite (filled with ion exchange resin AB-17-8) filters. The height of the resin layer in the apparatus of 1.5 m feed Rate of 10 m3/PM

Characteristics of raw and treated water are shown in table. 1.

EXAMPLE 2

The treatment of the source water (see table. 1) were made using reverse osmosis plants, the scheme of which is shown in the drawing. As membrane elements, used elements from Dow Chemical of the two brands BW 30LE-440 and SWHR 30-4040. The process parameters and the quality of the purified water are given in table. 2 and 3, respectively.

As can be seen from the table. 1 and 3, the level of salt in the water (p. 3), purified on ion exchange resins and reverse osmosis membranes, about the same, but the content of organic impurities in water, purified by ion exchange, 1.7-2.3 times higher than in water, purified by the proposed method (table. 3, op. 1, 2, 5, 6).

EXAMPLE 3

Polymerization TPV carried out in a reactor with a volume of 3.2 m3fitted with a stirrer, a jacket, a device for the emergency release of pressure. As the initiation system used a system of 3 components: salt nadkarni acid, ferrous iron salt and an inorganic acid (sulfuric or hydrochloric). The reactor was loaded 1800 liters of water purified of impurities (example 2), two Yanou or sulfuric acid with a concentration of 4%). The reactor was closed, felt the tightness was purged with an inert gas to remove oxygen. Liquid tetrafluoroethylene containing alkylamine, from the collection of TPV pipeline was applied to the polymerization reactor. As they flow through the pipeline TPV with alkylamino evaporated and, entering the reactor, creating the necessary pressure. Then the reactor was added to 2 l of the third component of the system initiating salt of iron (II) with a concentration of 0.5 g/L. decreasing the pressure in the reactor (due to the process of polymerization in the reactor was periodically applied TPV from liquid TPV. As the polymerization proceeded in the gas phase, analysis of the content of the alkylamine in TPV was carried out from the gas phase. The resulting PTFE powder was separated from the mother liquor, washed with water, purified according to example 2, was milled in the presence of a specified water, dried in a current of hot air until the moisture content of 0.02%.

The parameters and characteristics of the process are given in table. 4.

Thus from table. 4 it follows that the maximum process security is achieved when the temperature of the gas phase reactor is in the range of 40-70oC, the content of the alkylamine is 0.05-0.4 mg/l katowicach and inorganic impurities by the method of passing the source water through two successively arranged membrane (example 4-16 table. 4) allows to increase the output of PTFE compared with the prototype by about 3-10%, and decrease the consumption of system initiation salt nadkarni acid + inorganic acid + salt of iron (II) approximately 1.9-6.8 times (the comparison is made with experiments of the prototype, providing the maximum possible output PTFE).

1. The method of producing PTFE by purging the reactor with an inert gas to obezkislorazhivaniya volume of the reactor, polymerization of tetrafluoroethylene in the reactor in an environment free from organic and inorganic impurities in water, containing the initiation system, separation of the resulting suspension of polymer powder with subsequent washing, grinding and drying, characterized in that the quality of treated water use water filtered after standard cleaning procedures from suspended impurities, chlorine and decarbonization, via two series-arranged the reverse osmosis membrane, and from the space above the first membrane is constantly given 25 to 50% by weight of flow to it, with concentrated organic and inorganic impurities, and from the space above the second membrane 20 to 30% of the mass flow flowing on her return this portion to the first meta in the exhaust from the reactor gas 0,005 - of 0.01%.

3. The method according to PP.1 and 2, characterized in that the supply of tetrafluoroethylene perform with speed, providing the temperature in the gas phase of the reactor 40 - 60oC.

4. The method according to p. 3, characterized in that the use of tetrafluoroethylene containing 0.05 to 0.4 kg of the alkylamine per liter of gaseous tetrafluoroethylene.

5. The method according to p. 4, characterized in that the use of tetrafluoroethylene containing tertiary alkylamines followed selected from the group triethyltetramine or tributylamine.

 

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