MXPA97001158A - Procedure for preparing peroxidi perfluoropolieteres - Google Patents

Abstract

Procedure for the oxidation of tetrafluoroethylene at temperatures between -80 ° C and -50 ° C in the presence of UV radiation and pentafluoroethane as solvents

Description

PROCEDURE PñRfl PREPARE PERQXIDIC PERFLUOROPOLIETERES The present invention relates to a process for preparing peroxidic perfluoropolyethers obtained by photo-oxidation of tetrafluoroethylene in the presence of solvents. More particularly, it relates to a process that does not use chlorofluorocarbon solvents which, as is well known, have a dangerous impact on ozone (ODP) and cause greenhouse effect (GUP). It is well known that low temperature TFE photoxidation processes for producing peroxidic perfluoropolyethers are carried out industrially in CFC solvents, for example R12. In accordance with international agreements that refer to the reduction and elimination of CFCs from the market, the need to find substitute solvents has been created. Said substitute solvents must allow the synthesis to be carried out without causing problems in comparison with the current solvents, in particular with R12 (CF2CI2 dichlorodifluoromethane) which is the solvent most used due to its optimum yields. The solvent must not produce a chain transfer, since, if desired, it must also be able to obtain a control in the molecular weight. Moreover, a substitute solvent of R12 must allow obtaining a polymer that has a low content of peroxide units (PO) with good productivity. An ideal solvent is that which allows obtaining yields similar to those obtainable with the R12 operating in the same conditions as reactor volume, gas flow velocity, radiant lamp power and reaction temperature. In fact, it is known that in the process of photoxidation of tetrafluoroethylene (TFE) in the presence of CFC solvents, polymers with a lower PO can be obtained if the radiant power of the UV lamp increases, or if working at higher temperatures , that the flow velocity of the TFE and the reactor volume are equal. However, the increase in radiant power includes higher process costs and the increase in temperature implies lower yields. Therefore, the substitute solvents must be considered with the same radiant power, reactor configuration, temperature and flow rate of the reactants. An optimum solvent will be the one that provides the highest productivity with the lowest PO, with the same reaction. In the patents of the art, such as the solvents used in the photoxidation of tetrafluoroethylene, mention is made especially of specific chlorofluorocarbon or perfluorinated solvents, optionally containing oxygen atoms and CFCs are mainly used in the synthesis as the preferred solvents. See for example USP patents 4,451,646, USP 5,354,922, USP 3,847,978 and USP 3,715,378. The Applicant has unexpectedly and surprisingly found a specific solvent that does not contain chlorine, which is capable of giving a polymer with a low content of peroxide units (PO) and with good productivity, even compared to those obtained with R12. The object of the present invention is a process for the oxidation of tetrafluoroethylene at temperatures between -80 ° C and -50 ° C, preferably between -70 ° C and -SCC, in the presence of UV radiation and pentafluoroethane (125) as a solvent. The radiation used and the flow rate of oxygen and TFE are those well known in the CFC solvent art and are described for example in USP 3,715,378, incorporated herein by reference. The polymers obtained have the following general formula: A-0- (CF2-CF2-0) p- (CF2-0 -), - (0) r-B wherein terminals fi and B may be the same as or different from each other and consist of -CF3, -COF, -CF2COF, -CF2X wherein X denotes a radical group that is derived from the type of transfer agent used, for example it may be F, Cl, etc .; the indices p, q and r, equal or different from each other, are integers, the sum p + q is a number between 2 and 1000, preferably 10 and 400, the ratio q / p is between 0.1 and 10, preferably between 0.2 and 5; the ratio r / (p + q) is such that it leads to a perfluorop > Peroxydic ether having a PO generally lower than 4.5-5, preferably less than 4, generally consists of between 1 and 3.5. The PO value is expressed as grams of active oxygen (16 amu) (unit of atomic mass) per 100 grams of polymer. The TFE concentration generally varies between 0.005 and 1 mol per liter of solution, preferably 0.01-0.5 rnoles / 1; therefore the flow velocity of TFE is such that it gives these concentrations. The amount of oxygen used is sufficient to saturate the solution, it is generally operated with an excess of oxygen with respect to TFE and the partial pressures of oxygen are generally between 0.1 and 2 atm, preferably 0.2 and 1. The method of the invention, if if desired, it can be carried out in the presence of a chain transfer agent if molecular weight control is desired. As transfer agents, well known in the art, mention may be made, for example, of fluorine, chlorine, chlorotrifluoroethylene (CTFE), etc. The peroxidic perfluoropolyethers can then be transformed into products without peroxidic oxygen by means of a thermal treatment at temperatures generally between 100-250 [deg.] C. or by UV radiation, in the presence or absence of solvents. The product thus obtained can be subjected to fluorination treatment to obtain a perfluoropolyether with perfluoroalkyl terminals. alternatively, the crude peroxidic product can be subjected to chemical reduction and successive transformation reactions to obtain functional products. See for example USP 3,715,378. The chemical reduction is carried out for example in accordance with methods described in USP 4,451,646, 3,847,978. The derivative thus obtained in the carboxylic acid salt form can be subjected to decarboxylation procedures in the presence of hydrogen donating substances, among which are glycols, water, etc., to obtain perfluoropolyethers having both terminals -OCF2H. See, for example, the European patent application EP 95111906.4 in the name of the applicant. A further object of the present invention is a solvent containing co or essential component pentafluoroethane in mixture with perfluoroalkanes, linear or branched for example from 3 to 7 carbon atoms among which can be mentioned perfl? Oropropane and / or perfluoroheptane. The proportions by volume between 125 and the other perfluorinated solvent indicated generally ranges from 9: 1 to 1: 7, preferably from 1: 1 to 4: 1. Solvent mixtures show PO and productivity values similar to those of 125. This is very unexpected if one considers that, for example, perfluoroheptane only leads to very high PO values and therefore has very low productivity if comparisons are made with the same PO.

In the case of the synthesis of peroxidic polymers having a high molecular weight, it is preferable, according to a preferred embodiment of the invention, to use the solvent mixtures indicated above. According to the present invention, when the molecular weight is mentioned, it means a number-average molecular weight. The following examples are given for illustrative and non-limiting purposes of the present invention.

EXAMPLE 1 It is cooled to -50 ° C in a cylindrical reactor for photosynthesis, equipped inside with coaxial protectors, containing a high pressure mercury lamp of 150 U, cooled by recirculation of transparent fluid to UV radiation, also equipped with refrigerant maintained at the temperature of -75 ° C and supply ducts to feed the reaction gas, and it is charged with 415 ce of hydropentafluoroethane (R125). It begins to load 12.0 Nl / h of oxygen and after a few minutes the mercury lamp is turned on. Then 6.0 Nl / h of tetrafluoroethylene and 0.040 Nl / h of chlorine diluted with 2.4 Nl / h of nitrogen are charged. This input is kept constant throughout the test, equal to 300 minutes, as well as the temperature (~ 50 ° C). At the end of the reaction, the lamp is switched off, Reagent streams are closed and the solvent and gaseous by-products are allowed to evaporate until they reach room temperature. The oil remaining in the reactor is discharged and degassed under vacuum to remove residual traces of solvent and by-products; heavy, it is equal to 67.8 grams, which correspond to a specific productivity of 33 g / h / 1. The iodometric analysis of the peroxide content indicates a PO equal to 1.84 (expressed as grams of active oxygen / 100 grams of product). The kinematic viscosity at 20 ° C of the product is equal to 600 cSt. The i * F-NMR analysis confirms the following structure: T- (CF2CF2?) N (CF2?) «(CF2CF200) p (CF2? O), - T where T = a OCF2CI, OCF2CF2CI, OCF3, OCF2COF, OCOF . The ratio (p + n) / (q + rn) is equal to 0.94 and the ratio n / m is equal to 0.74. The number average molecular weight calculated by the 19F-NMR spectrum is equal to 12800.

EXAMPLE lfl (COMPARATIVE) In the same reactor of example 1, employed at -50 ° C, 440 cc of dichlorodifluoromethane are introduced. 12.0 Nl / h of oxygen are charged and after a few minutes the mercury lamp is turned on. Then 6.0 Nl / h of tetrafluoroethylene during the whole test (300 minutes) keeping the temperature at -50 ° C. When the reaction ends the lamp goes out, the reactant flows and the solvent are closed and the reaction byproducts are allowed to evaporate. The oil remaining in the reactor, after degassing, is equal to 70.8 g corresponding to a specific productivity of 32 g / h / 1. The PO is equal to 1.66 and the viscosity at 20 ° C equals 350 cSt. The i ^ F-RIN indicates a structure similar to that reported in example 1, with the same type of terminals. The ratio (p + n) / (l + m) is equal to 0.81 and the n / m equals 0.67. The average molecular weight calculated by NMR is equal to 10300.

EXAMPLE 2 420 ce of hydropentafluoroethane (R125) is introduced into the reactor of example 1 at a temperature of -50 ° C. One operates with the same procedure as in Example 1, charging 18.8 Nl / h of oxygen, 9.0 Nl / h of tetrafluoroethylene and 0.040 Nl / h of diluted chlorine in a stream of 2.4 Nl / h of nitrogen. After 300 minutes of reaction, 99.5 g of product are obtained (corresponding to a specific productivity of 47 g / h / 1), having PO = 1.88 and viscosity equal to 4700 cSt. The RNH analysis indicates a structure similar to that of Example 1 with propulsion (p + n) / (q + m) equal to 1.27 and n / m = 1.04 and weight molecular equals 26700.

EXAMPLE 2A (COMPARATIVE) 440 cc of dichlorodifluorornetan are introduced into the reactor of Example 1 at a temperature of -50 ° C. One operates with the same procedure as in example 1, charging 18.0 Nl / h of oxygen and 9.0 Nl / h of tetrafluoroethylene for 300 minutes. 103.5 grams of oil are obtained (corresponding to a specific productivity of 47 g / h / 1), having PO = 2.02 and viscosity equal to 1380 cSt. The NMR analysis indicates a structure similar to that of Example 1, with proportion (p + n) / (q + m) equal to 1.07 and n / m = 0.84 and molecular weight equal to 17300.

EXAMPLE 3 400 ce of hydropentafluoroethane is introduced into the reactor of example 1 at a temperature of -50 ° C. It is operated with the same procedure as in Example 1, charging 24.0 Nl / h of oxygen, 12.0 Nl / h of tetrafluoroethylene and 0.060 Nl / h of chlorine, diluted in a current of 2.4 Nl / h of nitrogen. After 300 minutes of reaction, 144.4 grams of product are obtained (corresponding to a specific productivity of 73 g / h / 1), having PO = 2.45 and viscosity equal to 2300 cSt. NMR analysis indicates a structure similar to that of Example 1 with proportion (p + n) / (q + m) equal to 1.55 and n / m = 1.21 and average molecular weight equal to 20700.

EXAMPLE 3 (COMPARATIVE) 440 cc of dichlorodifluoroethane are introduced into the reactor of example 1 at a temperature of -5 ° C. One operates with the same procedure as in example 1, charging 24.0 Nl / h of oxygen and 12.0 Nl / h of tetrafluoroethylene for 300 minutes. 166 grams of product are obtained (corresponding to a specific productivity of 76 g / h / 1), having PO = 2.65 and viscosity equal to 7160 cSt. The NMR analysis indicates a structure similar to that of Example 1, with proportion (p + n) / (q + m) equal to 1.44 and n / m = 1.04 and molecular weight equal to 31000.

EXAMPLE 4 430 cc of a 1: 1 by volume mixture of perfluoropropane and R125 are introduced into the reactor of example 1 at the temperature of -50 ° C, where 5.3 g of product obtained in example 1, used as activator, were previously dissolved . One operates with example 1, charging 12.0 Nl / h of oxygen, 6.0 Nl / h of TFE and 0.021 Nl / h of chlorotrifluoroethylene diluted in a current of 0.7 Nl / h of nitrogen. After 240 minutes of reaction, 77.9 grams of polymer are obtained (corresponding to a specific productivity of 45 g / h / 1), having P0 = 2.57 and viscosity equal to 2500 cSt. The NMR analysis indicates a structure similar to that of Example 1 with ratio (p + n) / (q + m) equal to 1.69 and n / m = 1.18 and average molecular weight equal to 21400.

EXAMPLE 4 (COMPARATIVE) 420 cc of R12 are introduced into the reactor of example 1 at the temperature of -60 ° C, where 5.3 grams of the product obtained in example 1, used as activator, were previously dissolved. The procedure is as in Example 1, charging 12.0 Nl / h of oxygen and 6.0 Nl / h of TFE. After 240 minutes of reaction, 76.9 grams of polymer are obtained (corresponding to a specific productivity of 46 g / h / 1, having P0 = 2.53 and viscosity equal to 2100 cSt.) NMR analysis indicates a structure similar to that of Example 1 with proportion (p + n) / (q + m) equal to 1.65 and n / m = 1.17 and average molecular weight equal to 20000. EXAMPLE 5 430 cc of a 1: 1 by volume mixture of perfluoropropane and R125 are introduced into the reactor of example 1 at the temperature of -60 ° C, where 6.6 grams of product obtained in example 1, used as activator, were previously dissolved . One operates with example 1, loading 18.0 Nl / h of oxygen, 9.0 Nl / h of TFE and 0.021 Nl / h of chlorotrifluoroethylene diluted in a current of 0.7 Nl / h of nitrogen. After 240 minutes of reaction, 123.8 grams of polymer are obtained (corresponding to a specific productivity of 72 g / h / 1), having P0 = 3.48 and viscosity equal to 10000 cSt. The NMR analysis indicates a structure similar to that of Example 1 with ratio (p + n) / (q + m) equal to 2.87 and n / m = 1.73.

EXAMPLE 6 410 ce of a 20:80 volume mixture respectively of perfluoropropane and R125 were introduced into the reactor of example 1 at the temperature of -60 ° C, where 4.5 grams of the product obtained in example 1, used as activator, was dissolved previously. The procedure is as in Example 1, charging 18.0 Nl / h of oxygen, 9.0 Nl / h of TFE and 0.030 Nl / h of chlorotrifluoroethylene, diluted in a current of 1.0 Nl / h of nitrogen. After 240 minutes of reaction, 116.9 grams of the polymer were obtained (corresponding to a specific productivity of 71 g / h / 1), having P0 = 3.21 and viscosity equal to 25000 cSt. The NMR analysis indicates a structure similar to that of Example 1 with ratio (p + n) / (q + rn) = 2.49 and molecular weight equal to 48000.

EXAMPLE 7 430 cc of a 20:80 volume mixture respectively of perfluoropropane and R125 were introduced into the reactor of example 1 at the temperature of -60 ° C, where 5.6 grams of the product obtained in example 1, used as activator, was dissolved previously. The procedure is as in Example 1, charging 18.0 Nl / h of oxygen, 9.0 Nl / h of TFE and 0.030 Nl / h of chlorotrifluoroethylene, diluted in a current of 1.0 Nl / h of nitrogen. After 240 minutes of reaction, 125.8 grams of the polymer were obtained (corresponding to a specific productivity of 73 g / h / 1), having P0 = 3.75 and viscosity equal to 24000 cSt. The NMR analysis indicates a structure similar to that of Example 1 with ratio (p + n) / (q + m) equal to 3.50 and n / m = 1.95 and molecular weight equal to 47000.

EXAMPLE 7A (COMPARATIVE) 430 cc of R12 are introduced into the reactor of example 1 at the temperature of -60 ° C, where 6.0 g of the product obtained in example 1, used as activator, were previously dissolved. The procedure is as in Example 1, charging Nl / h of oxygen, 9.0 Nl / h of TFE and 0.021 Nl / h of chlorotrifluoroethylene diluted in a stream of 0.7 Nl / h of nitrogen. After 240 minutes of reaction, 125.5 g of polymer were obtained (corresponding to a specific productivity of 75 g / h / 1), which has PO = 3.44 and viscosity equal to 5500 cSt. The NMR analysis shows a structure similar to that of Example 1, with proportion (p + n) (q + m) = 2.48 and n / m = 1.65, and molecular weight equal to 28000.

Claims (14)

NOVELTY OF THE INVENTION CLAIMS

1. - Oxidation procedure of tetrafluoroethylene at temperatures between -80 ° C and -50 ° C in the presence of UV radiation and pentafluoroethane (125) with solvent.

2. Process for oxidation of tetrafluoroethylene according to claim 1, at temperatures between -70 ° C and -50 ° C. 3.- Oxidation process of tetrafluoroethylene according to claims 1 and 2 further characterized in that the polymers obtained have the following general formula, A-0- (CF2-CF2-0) P- (CF2-0-) < , ~ (0) r -B, where terminals A and B, equal or different from each other, comprise -CF3, -COF, -CF2OF, -CF2X wherein X denotes a radical group derived from the type of the transfer agent used; the indices p, qyr, equal or different from each other, are integers, the sum p * q is a number between 2 and 1000, the ratio q / p is between 0.1 and 10, the proportion r / (? + q) it is such that it leads to a peroxidic perfluoropolyether having a PO of less than 4.5-5. 4. Process for oxidation of tetrafluoroethylene according to claim 3, further characterized in that X is F or Cl; p + q is between 10 and 400; the q / p ratio is between 0.2 and 5; the ratio r / (p + q) is such that it leads to a peroxidic perfluoropolyether that It has a PO between 1 and 3.5. 5.- Oxidation process of tetrafluoroethylene according to claims 1-4, further characterized in that the concentration of TFE varies from 0.005 and 1 mol per liter of solution and the partial pressures of oxygen are between 0.1 and 2 atm. 6. The oxidation process according to claims 1-5, further characterized in that the peroxidic perfluoropolyethers are subjected to a heat treatment at temperatures between 100 and 250 ° C or by UV radiation, in the presence or absence of solvents. 7. Process for oxidation of tetrafluoroethylene according to claim 6, further characterized in that the perfluoropolyethers obtained are subjected to a fluorination treatment to obtain perfluoropolyethers with perfluoroalkyl ends. 8. Process for oxidation of tetrafluoroethylene according to claim 6, further characterized in that the perfluoropolyetherer obtained are subjected to chemical reduction and subsequent transformation reactions to obtain functional products. 9. Oxidation process of terefluoroethylene according to claim 8, further characterized in that the functional perfluoropolyethers are the carboxylic acid salts, optionally subjected to decarboxylation procedures in the presence of donor substances. hydrogen to obtain perfluoropolyethers having both terminals -OCF2H. 10.- Oxidation process of tetrafluoroethylene according to claims 1-9, further characterized in that the solvent contains in linear or branched perfluoroalkane mixture. 11. Process for the oxidation of tetrafluoroethylene according to claim 10, further characterized in that the perfluoroalkanes have from 3 to 7 carbon atoms. 12. Process for oxidation of tetrafluoroethylene according to claim 11, further characterized in that the perfluoroalkane is selected from perfluoropropane and / or perfluoroheptane. 1

3. Process for oxidation of tetrafluoroethylene according to claim 10-12, further characterized in that the proportions in volume between pentafluoroethane and the perfluorinated solvent vary between 9: 1 and 1: 7 1

4. Process for oxidation of tetrafluoroethylene according to claim 13, further characterized in that the proportions by volume between pentoflorethane and the perfluorinated solvent vary between 1: 1 and 4: 1.