US2590426A - Process for photochemical chlorination of hydrocarbons - Google Patents

Description

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penetration of the actinic light. progress of the reaction is thus rendered difiicult Patented Mar. 25, 1952 UNITED STATES: PATENT OFFICE PR-CESS FOR PHCTOCHEMICAL CHLORIN- ATION F HYDROCARBONS Anthony Loverde, Niagara Falls, N. Y., assignor to the United States of America as represented by the United States Atomic Energy Commission . 7 a, Drawing. Application May 23, 1945, l Serial No. 596,217

3 Claims. 1 This invention relates to a process for the photochemical chlorination of hydrocarbons. More particularly it relates to the production of chlorinated parafiinic hydrocarbons of five or more carbon atoms in which a major portion, e. g.

fifty to approximately ninety per cent, of the hydrogen atoms have been replaced by chlorine.

An object of the present inventionis a process for chlorinating parafiinic hydrocarbons of five 'or more carbon atoms to a chlorinated product in which a major portion of the hydrogen atoms, e. g. fifty to approximately ninety per cent, have been replaced by chlorine atoms, while substantially eliminating difficulties usually encountered in controlling the course of the highly exothermic reaction. Another object is a process for obtaining a chlorinated product of the aforementioned kind in which the starting material comprises an initially partially chlorinated paraffinic hydrocarbon of five or more carbon atoms per molecule and a chlorine content insuilicient in amount to prevent violent reaction upon further chlorination. A further object is a process of the foregoing nature wherein the reaction is conducted under liquid phase conditions.

In the photochemical chlorination of hydrocarbons the reaction is frequently so vigorous that, evensvith cooling to relatively low temperatures, e. g, 25 C. to 30 C., miniature explosions 'I he reaction may become so violent as to result in destruction of the hydro carbon molecule, scttingcarbcn free. When the operation is conducted in liquid phase, the free carbon darkens the liquid and this obstructs The further and in some cases a point may be reached at .which further chlorination becomes virtually im- 'possible.'. This is the chief reason for the well known diiiiculty of carrying photochemical chlorination of parafiinic hydrocarbons to the higher ranges ofchlorine content, particularly in liquid phase.

The problem of controlling the violence of the reaction has been recognized in several early patents, and a variety of proposals to overcome this difficulty have ensued. Probably the most satisfactory of these proposals is the use of a diluent for the chlorine such as an inert gas. Such useof a diluent facilitated to some degree the control of the reaction since it prevented or decreased excessive decomposition and carbon formation by absorbing a large part of the heat of reaction, thus preventing occurrence of ignition and explosions. Among the diluents most 2 commonly proposed are nitrogen and carbon dioxide.

While an inert gas, such as nitrogen or carbon dioxide, is very effective for the purpose of preventing explosions, as the reaction proceeds it becomes less and less vigorous, even when there is no obscuring of the liquid by carbon or dark colored products from side reactions. It has therefore not been possible with the use of diluted chlorine to replace a major portion, e. g. fifty to approximately ninety per cent, of the hydrogen by chlorine. This is particularly true when parafiinic hydrocarbons having five or more carbon atoms are chlorinated in liquid phase;

According to the present invention, there is provided an improved process for the production of chlorinated parailinic hydrocarbons of five or more carbon atoms in which a major portion of the hydrogen atoms have been replaced by chlorine atoms, which comprises subjecting the material, under actinic light; to the action of chlorine diluted with an inert gas during the'initial stage of the reaction and to the action of undiluted chlorine during the remainder of the reaction. Inert gases, such as nitrogen, carbon dioxide, or mixtures thereof may be used as diluents for the chlorine.

Now having indicated in a general way the nature and purpose of my invention, the following example is given. not by way of limitation, but rather in illustration of a preferred method of carrying out my invention. In the example the parts are given by weight unless otherwise indicated.

' Example Three thousand six hundredgrams of heptane were placed in a glass flask equipped with a thermometer and reflux condenser,'andsubjectedto actinic light. Carbon dioxide was admitted to sweep out the air. Chlorine was then admitted, mixed With approximately an equal volume of carbon dioxide, the temperature being held at 25 to 30 C. After 24 hours the temperature was allowed to start rising; At the end of 48 hours the temperature had risen to 50 C. The carbon dioxide was then shut off and thereafter undiluted chlorine was fed to thereactor. At the end of '72 hours the temperature had risen to '70 C. The temperature was allowed to continue to rise at the rate of C. per day until it had reached 150 0., \vliereit Was held. After a total elapsed time of hours, the product had a specific gravity of 1.810 at 25 C. and the chlorine content was 79.5 per cent by weight.

While in the example carbon dioxide has been shown in illustration of an inert gas as the dilient, other inert gases such as nitrogen, and the like are equally operable in the process.

Similarly, while heptane has been used in the example in illustration of a normally liquid parafiinic hydrocarbon having fiveor more carbon atoms, other hydrocarbons which are equally operable are pentane, hexane, octane, nonane, decane and higher hydrocarbons.

While my invention has been described in de- 10 lamp,

tail in connection with the chlorination of paraflinic hydrocarbons as starting materials, it is within the scope of the invention to employ as starting material an initially. partially chlorinated parafiinic hydrocarbon having five or more carbon atoms per molecule and having a chlorine;

content insufficient in amount to prevent violent reaction upon further chlorination. Examples of such starting materials are partially chlorinated parafiinic hydrocarbons having five or more carbon atoms and preferably not over two chlorine atoms per molecule.

While I prefer to carry out my invention with the aid of cooling, I do not wish to be limited thereto, as with sufiicient dilution of the chlorine and a reactor of relatively large radiation surf ace per unit of volume the temperature may be made self-regulating.

F'urthermore, if cooling is used, although I prefer to maintain the temperature during the initial stage of the reaction between about 25 C. and about 30 0., this temperature may be varied over a considerable range, as may the later temperatures as the reaction progresses.

In the carrying out of this process the chlorine is preferably initially diluted with an equal volume of the inert gas. However, the ratio of the diluent to the chlorine may bevariedover a wide range depending upon the violence of the reaction, etc.

It will be understood that the time of the reaction shown in the example is illustrative only and with a change in the conditions of the reaction, reactants, etc., a similar change may be made in the time of the reaction. It further may vary somewhat with the choice of diluent used.

By the term initial stage of the reaction" within the intention of the specification and claims is meant that period in which sufficient chlorine atoms are substituted so that when undiluted chlorine is then introduced the reaction rate has been sufficiently retarded to eliminate danger of explosions. This point is generally reached, for example in the chlorination f heptane, when about twenty per cent or the hydrogen atoms have been replaced by chlorine.

While in the example, the dilution of the Cl: with CO2 was continued for 48 hours, ordinarily from to 24 hours of dilution with the inert gas is sufficient. However, as illustrated, the dilution may be continued for an additional time to insure that the danger of explosion is eliminated.

To produce the actinic light necessary in the carrying out of this process, as illustrated in the example, any of the well known types of commercial lights may be used which will induce or speed the reaction in the chlorination of a paraffinic hydrocarbon, such as tungsten filament mercury vapor arc lamp, and the like.

By my process I accomplish the following objectives: namely, moderation and avoidance of decomposition during the early stage of the reaction; and chlorination to a higher chlorine content than heretofore possible.

Qther advantages will be apparent from the ioregoin adisglgsure to those skilled in the art.

and while a spefiilirexample has been used to illustrate my invention, it is to be understood that the scope of this invention is not limited to this embodiment, but is defined hy the appended claims.

W hat I claim is:

1. The process for photochemical chlorination of heptane to approximately eighty per cent chlorine which comprises bringing the heptane, under actinic light, in contact with chlorine diluted with approximately an equal volume of an inert gas at a temperature rising gradually from about 25 to about 50 C. for approximately 48 hours, then in contact with undiluted chlorine for a further period of approximately hours at a temperature rising gradually to approximately C.

2. The process of claim 1 wherein the inert gas is nitrogen. I

3. The process for photochemical chlorination of heptane to approximately eighty per cent chlorine which comprises bringin the heptane, under actinic. light, in contact with chlorine diluted with approximately an equal volume of carbon dioxide at a temperature rising gradually. from about 25 to about 50 C. for approximately48 hours, then in contact with undiluted chlorine for a further period of approximately 80 hours at a temperature rising gradually to approximately 150 C.

ANTHONY LOVERDE.

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

UNITED STATES PATENTS Number

Claims (1)

1. THE PROCESS FOR PHOTOCHEMICAL CHLORINATION OF HEPTANE TO APPROXIMATELY EIGHTY PER CENT CHLO-RINE WHICH COMPRISES BRINGING THE HEPTANE, UNDER ACTINIC LIGHT, IN CONTACT WITH CHLORINE DILUTED WITH APPROXIMATELY AN EQUAL VOLUME OF AN INERT GAS AT A TEMPERATURE RISING GRADUALLY FROM ABOUT 25* TO ABOUT 50* C. FOR APPROXIMATELY 48 HOURS, THEN IN CONTACT WITH UNDILUTED CHLORINE FOR A FURTHER PERIOD OF APPROXIMATELY 80 HOURS AT A TEMPERATURE RISING GRADUALLY TO APPROXIMATELY 150*. C.