US2567759A - Fluorination of high molecular compounds - Google Patents

Description

Sept. 11, 1951 A. F. BENNING FLUORINATION OF HIGH MOLECULAR COMPOUNDS Filed March 17, 1945 4 5 C andenser 04/8 1 Separafor Res/due Anfhony E Banning mam,

Patented Sept. 11, 1951 FLUORINA'I'ION OF HIGH MOLECULAR COMPOUNDS Anthony F. Bennlng, Woodstown, N. J assignor to the United States of America. as represented by the United States Atomic Energy Commission Application March 11, 1945, Serial No. 533,216

4 Claims. (01. 260-653) the production of fluorocarbon lubricant oils from high-boiling hydrocarbon oils.

In the past it has been proposed to produce fluorocarbons by reaction of hydrocarbon vapors and fluorine diluted with a suitable inert gas in contact with a fluorination catalyst such as silver fluoride. The production of fluorocarbon lubricants by the fluorination of high-boiling hydrocarbon oils by this method has been successfully conducted but the yields of fluorocarbons corresponding to the original hydrocarbons are characteristically low. Thus the fluorination of a lubricant oil fraction yields a fluorocarbon product containing an amount of fluorocarbons corresponding to 16% to 25% of the original hydrocarbons in the oil. The rest of the oil is converted into shorter chain scission products during the fluorination. As a consequence far greater proportions of the total fluorine and hydrocarbon employed go into by-products than into the desired fluorinated lubricant.

It has also been proposed to fluorinate hydrocarbons in vapor phase by fluorinating agents such as silver difluoride, cobalt trifluoride, and manganese trifluoride. For application to oils boiling in the lubricant oil boiling range this process requires reduced pressure or dilution with an inert gas or vapor. The use of reduced pressures involves special equipment and is complicated by the production of volatile by-products during the reaction. The use of inertgases results in very substantial losses of the desired fluorocarbons.

. It is an object of the present invention to provide an improved fluorination process for the manufacture of highly fluorinated lubricant oils, whereby substantially higher yields of the desired products are obtained and substantially less fluorine is necessary for carrying out the process. A further object is to provide a process which is relatively easy to control and operate compared to processes previously employed for manufacture of fluorinated lubricant oils. Further objects of the invention will be evident from the following description.

In accordance with the process of my invention a high-boiling hydrocarbon oil vapor is mixed with a greater volume of vapor of a relatively inert volatile fluoride and the mixture of vapors is brought into contact with a fluorinating agent of the group consisting of cobalt trifluoride, manganese trifluoride, and silver difluoride at a temperature between 150 C. and 400 C. The volatile fluoride vapor moderates the reaction and at the same time facilitates retention of hydrocarbon oils. intermediate fluorinated oil products, and flnal fluorinated oil products in vapor phase durin the reaction.

Suitable fluorides for accomplishing the purposes of the invention are hydrogen-fluoride and substantially inert volatile organic fluorides such as fluorinated hydrocarbons having at least 90% of the original hydrogen content replaced by fluorine. Because they are nearly inert under the conditions of reaction, substantially completely fluorinated organic compounds are preferred; for example; perfluoro-heptane, perfluoro-octane. perfluoro methylcyclohexanes, perfluoro dimethylcyclohexanes, perfluoro dimethylcyclo pentanes. perfluoro-ethyl-cyclopentanes, highly fluorinated kerosene or distillate fractions distilling in the kerosene range, highly fluorinated light lubricant oil fractions and volatile fluorocarbon by-products obtained in the fluorination of high-boiling lubricant oils.

I prefer to carry out the process of the invention by mixing hydrogen fluoride vapor and highboiling hydrocarbon vapor in a weight ratio between about 1:1 and about 5:1 and to pass the vapor mixture into contact with cobalt trifluoride maintained at a temperature between 300 and 350 C. The process is particularly applicable to petroleum derivative fractions boiling above 300 C. at normal atmospheric pressure (760 mm); petroleum lubricant oil fractions distilling at temperatures between 200 C. and 300 C. at 10 mm. of mercury absolute pressure are illustrative of this type of material.

The process of my invention is to be distinguished from vapor phase processes involving elemental fluorine in that in my process the presence of fluorine in elemental form is avoided. I have found that the elemental fluorine attacks the hydrocarbons and partially fluorinated hydrocarbons with such vigor that a large proportion of scission products is invariably formed. Consequently greater yields are obtainable by carefully avoiding the presence of fluorine during the fluorination of the hydrocarbons. The absence of fluorine during the fluorination process also eliminates the possibility of explosions resulting from the reaction of fluorine with hydrocarbons and their fluorinated derivatives.

The process may be conducted advantageously by passing a mixture of high-boiling hydrocarbon vapor and volatile fluoride vapor through a reactor containing a constantly agitated body of cobalt trifluoride in comminuted form. The desired high temperature in the reactor may be maintained by external heating when necessary. Normally the heat evolved during the fluorination is adequate to maintain the desired temperature. External cooling may be provided to prevent a temperature rise above the most suitable operating temperature range.

Products of the fluorination are withdrawn from the fluorinating chamber in vapor phase,

60 dust of inorganic fluorides is separated by settling or screeningfand the product is then condensed; The volatile fluoride diluent may be condensed along with the. fluorination product, or ii desired, it may be condensed later in a separate condenser. when the diluent employed is a fluorinated hydrocarbon of relatively highboiling point such as a per-fluorinated kerosene fraction, a single condensation may be employed to condense the diluent along with the fluorocarbon lubricant. On the other hand when a volatile fluoride, such as hydrogen fluoride, is employed as diluent, it is more advantageous to employ a second condenser operated at a lower temperature in order to recover the diluent.

In the fluorination of hydrocarbons by means of a fluorinating agent such as cobalt trifluoride, it is customary to regenerate the fluorinating agent periodically by treating it with elemental fluorine. This expedient may be employed in the process of the present invention. The fluorine may be introduced into the reactor with or without a diluent, such as hydrogen fluoride, to convert the cobalt difluoride to cobalt trifluorlde. It is important in conducting a regeneration by this method to be sure that no hydrocarbon is present when fluorine is introduced into the reactor. The reactor is therefore flushed with hydrogen fluoride vapor before each run with hydrocarbon and before each regeneration with fluorine. By an adequate flushing step the absence of fluorine in elemental form during the hydrocarbon fluorination process is insured.

By use of my process as described above, 55% to 65% of the total amount of hydrocarbons initially present in a lubricant oil can be converted to the corresponding fluorocarbons to produce a highly fluorinated lubricant. Similarly advantageous results can be obtained in the fluorination or high-boiling kerosene fractions.

The attached drawing illustrates diagrammatically a suitable form of apparatus for carrying out the process of the invention.

The apparatus comprises hydrogen fluoride vaporizer I, oil vaporizer 2, jacketed reactor 3, dust separator 4, and oil and hydrogen fluoride condensers and 6. The hydrogen fluoride vaporizer I has an inlet 1 for hydrogen fluoride and is provided with suitable heating means such as steam coil 8. The HF vaporizer is connected to oil vaporizer 2 by conduit 9, which may be wrapped with an electric heating element N, or other suitable heating means, to superheat the HF vapor. The oil vaporizer 2 is a vertical tube wrapped with an electrical resistance heating element l2 and lagged. It is provided, at the top, with a distributing box l3, having oil inlet H, for distributing ingoing oil uniformly on all sides, and at the bottom, with a trap l5 for collecting any unvaporized oil, which may be withdrawn by way of outlet I6. From trap l5 vapor line H leads, by way of a series of separate inlets ll, l9, etc., into reactor 3. Conduit 20 leads fro line 9 directly to vapor line IT. This line is provided also with a fluorine inlet 2| for use in regenerating spent fluorinating agent. All of the lines through which hot oil vapors pass to the reactor are provided with heating means to avoid any temperature drop in these lines.

Reactor 3 is of generally cylindrical crosssection, disposed horizontally and provided with gas jacket 22 for heating and cooling the reactor. It has a scraping and distributing mechanism 23 for presenting fresh surfaces of fluorinating agent during the fluorination process.

4. Conventional means (not shown) for securing access to the interior of the reactor and for introducing fresh fluorinating agent and removing spent or deteriorated reagent are provided.

The dust separator 4 may be a simple lagged or jacketed vertical cylinder having a sufliciently large cross-section to reduce the gas velocity and permit solid particles to settle back into the reactor 3.

Condenser 5 is mounted above dust separator 4 and is connected to it by vapor conduit 2|. Condenser 5 may be a conventional heat exchanger cooled by circulation of water or another suitable cooling medium. It is provided at the bottom with an outlet 25 for withdrawal of condensate therefrom. Condenser 5 is connected by conduit 26 to condenser B for recovery of hydrogen fluoride.

Condenser 6 has outlet 21 for liquid products and outlet conduit 28 leading to a suitable vent for gases and uncondensed vapors. Condenser B is cooled by a low temperature cooling medium, such as brine solution, in order to provide a flnal temperature below the boiling point of hydrogen fluoride at the operating pressure.

The operation of this apparatus for the production of a fluorocarbon lubricant may be as follows:

Reactor 3 is charged with a quantity of cobalt difluoride suflicient to flll about one-fourth the volume of the reactor.

Hydrogen fluoride is introduced to vaporizer I and vaporized therein and the vapors are passed through conduit 9, vaporizer 2, inlets l8, l9, etc., reactor 3, and dust separator 4 to expel air from the system. When the passage of hydrogen fluoride has been continued for a sufllcient period to accomplish this purpose, fluorine is introduced at inlet 2| to convert the cobalt difluoride to cobalt trifluoride. After most of the cobalt difluoride has been converted to the trifluoride, the introduction of fluorine is stopped and the passage of hydrogen fluoride vapor is resumed until a test of the exhaust vapors shows no'fluorine. The production of cobalt trifluoride causes sumcient heat evolution to raise the temperature of reactor 3 to the temperature desired for the fluorination. If during flushing of the reactor with hydrogen fluoride the reactor is cooled below the desired reaction temperature, it may be reheated by passing combustion gas through jacket 22.

The hydrogen fluoride vapor conduit 9 is now heated to maintain the temperature of hydrogen fluoride between 200 and 300 C. at the superheater outlet. Oil is introduced through line ll to oil vaporizer 2, which is controlled thermostatically to provide an outlet temperature of about 350 C. so that all of the oil flowing into the vaporizer passes out as vapor. The flow of hydrogen fluoride is maintained to provide approximately two parts by weight of hydrogen fluoride for each one part by weight of oil. The mixture of vapors passes into reactor 3 by way of the inlets l8, l9, etc. It is preferred to introduce the vapors through a series of inlets along the reactor as indicated in order to distribute the heat of the reaction and prevent an excessive temperature rise locally in any single zone. A large proportion of the-mixture is introduced at the inlets most remote from the outlet to dust separator 4. During this operation the agitator'23 is operated slowly to turn over the solid matter in reactor 3 and to con:

8 tinually expose fresh surfaces to the gases and vapors passing through the reactor.

Reaction gases and vapors pass from reactor 3 up through dust separator 4. Solid matter separates out and falls back into the reactor. The vapors and gases then continue up into con denser 5, which is cooled by water to condense out normally liquid reaction products. The gas stream, cooled to about 30 0., passes from condenser 5 to brine-cooled condenser 6, which effects further cooling to about 0., thus condensing hydrogen fluoride, which is drawn of! through outlet 21.

In the following example quantities are expressed in terms of weight unless otherwise indicated.

Example 1 The initial material employed was a lubricant oil of petroleum origin having the following distillation characteristics at 10 mm. of mercury absolute pressure:

0. Initial boiling p in 183 2% (by volume) over 226 50% (by volume) over 242 95% (by volume) over 253' Into a steel reactor which contained about 4500 parts of COFs and which had been swept with hydrogen fluoride, 64 parts of the lubricant oil vapor mixed with 77 parts of hydrogen fluoride vapor were passed at a substantially constant rate in about 8 hours. During this period the temperature of the gases in the reactor was held between 300 and 360 C. After this reaction period 19 parts of hydrogen fluoride vapor was passed through in about 1% hours to remove organic material from the reactor. The evolved gases and vapors from the reaction and subsequent sweeping were cooled to condense organic products and hydrogen fluoride. 169 parts of HF-i'ree fluorinated hydrocarbon was obtained, distilling as follows (in a still having a column equivalent to about 5 theoretical plates):

(a) 16% (by volume) over at 185 C. at 760 mm. (b) 41% (by volume) over at 140 C. at 10 mm. (c) 86% (by volume) over at 213 C. at 10 mm. Fractions (b) and (0) combined had a viscosity at 100 C. less than 30 centipoises and a vapor pressure at 60 0. less than 0.01 mm. It passed 5 specifications as a material inert to highly reactive inorganic fluoride.

\ Example 2 The initial material was a high-boiling kerosene fraction having therollowing distillation characteristics at 760 mm. of mercury absolute pressure:

C. Initial boiling point 236% 5% (by volume) over -1 242 95% (by volume) over 322 my poin 333 Example 3 The process of Example 2 was duplicated except that, in place 01 hydrogen fluoride, perfiuoro-dimethylcyclohexane was employed in a ratio of -11 kilograms of the fluorocarbon per liter of oil fed to the vaporizer. The proportion of hydrocarbon oil converted to fluorocarbon oil 5 distilling above 180 C. was 45%.

When the same process was carried out using an equal volume of nitrogen in place of the fluorocarbon vapor under otherwise substantially identical conditions a yield of less than 38% was obtained.

It will be understood that I intend to include variations and modifications of the invention and that the preceding example is illustrative only and in no wise to be construed as a limitation upon the invention, the scope of which is defined in the appended claims, wherein I claim:

1. The method of preparing a highly fluorinated high molecular product, which comprises passing a mixture of vapor or a high-boiling hyhydrogen fluoride into contact with a fluorinating agent of the group consisting of cobalt trifluoride, silver difluoride, and manganese trifluoride at a temperature between 150 C. and 400 C.

2. The method of preparing a highlyfluorinated lubricant, which comprises passing a mixture of vapors of a high-boiling hydrocarbon oil comprising principally hydrocarbons distilling above 300 C. and at least an equal weight of hydrogen fluoride into contact with fluorinating agent of the group consisting of cobalt trifluoride, silver di fiuoride, and manganese trifluoride at a temperature between 150 C. and 400 C.

3. The method of preparing a .highly fluorinated lubricant, which comprises passing a mixture of vapors of a high-boiling hydrocarbon oil comprising principally hydrocarbons distillin above 300 C. and between one and five times its weight of hydrogen fluoride into contact with a fluorinating agent of the group consisting of cobalt trifluoride, silver difluoride, and manganese trifluoride at a temperature between 150 C. and 400 C.

4. The method of preparing a highly fluorinated lubricant which comprises passing a mixture of vapors of a high-boiling hydrocarbon oil comprising principally hydrocarbons distilling above 300 C. and at least an equal weight 0 of hydrogen fluoride into contact with an agitated body of cobalt trifluoride maintained ata temperature between 280 C. and 360 0., and separating the highly fluorinated lubricant from hydrogen fluoride by condensation.

ANTHONY F. BENNING.

REFERENCES CITED The following references are of record in the file or this patent:

OTHER REFERENCES Mellor, "Comprehensive Treatise on Inorganic v and Theoretical Chemistry, vol. 12, page 344: vol. 14, pages 603-9.

Rufl, Angewandte Chemie," vol. 47, page 480 Jockusch, "Naturwissenschaften," vol. 22, page 561 (1922). Adams et 91., "Organic Reactions," vol. 11. We 70.

drocarbon oil and a larger volume of vapor of

Claims (1)

1. THE METHOD OF PREPARING A HIGHLY FLUORINATED HIGH MOLECULAR PRODUCT, WHICH COMPRISES PASSING A MIXTURE OF VAPOR OF A HIGH-BOILING HYDROCARBON OIL AND A LARGER VOLUME OF VAPOR OF HYDROGEN FLUORIDE INTO CONTACT WITH A FLUORINATING AGENT OF THE GROUP CONSISTING OF COBALT TRIFLUORIDE, SILVER DIFLUORIDE, AND MANGANESETRIFLUORIDE AT A TEMPERATURE BETWEEN 150* C. AND 400* C.

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