US3528900A - Photochlorination process - Google Patents

Description

Sept. 15, 1970 Filed May 31, 1966 D. S. ROSENBERG ET AL PHOTOCHLORINATION PROCESS 2 Sheets-Sheet 1 l I I9 rwnnocAnaoN r STORAGE SEPARATION ZONE F PRODUCT RECOVERY v ZONE 25 gljb 21 HEAT A HEAT excmmesnms RE CT'ON CHANGER zone \i w ,L V M 1 5 9 j 9 FLOW I v METER FLOW METER 9 7 5 V M CH LORI N E STORAG E Sept. 15, 1970 s, ROSENBERG ET AL 3,528,900

PHOTOCHLORINATION PROCESS Filed May 31, 1966 2 Sheets-Shoat 2 '9 HYDROCARBON SEPARATION zowz - PRODUCT RECOVERY 12 f5 ZON E 25 [1]) 21 u EAT u EAT EXCHANGEQ/J5 ggi EXQHANGEQ CHLORIN E STORAGE Fig 2 United States Patent US. Cl. 204-163 8 Claims ABSTRACT OF THE DISCLOSURE A continuous process for photochemical chlorination of saturated aliphatic and alicyclic hydrocarbons of 3 to 5 carbon atoms per molecule comprises maintaining liquid polychlorohydrocarbon in a circulating stream in communication with an external two stage reaction zone containing a main body of liquid polychlorohydrocarbon, adding liquid hydrocarbon into the externally circulating stream of liquid polychlorohydrocarbon, adding gaseous chlorine to the mixture of liquid hydrocarbon and liquid polychlorohydrocarbon, and irradiating the mixture, whereby chlorination is efiected, after which the desired polychlorohydrocarbon is withdrawn as a liquid and is recovered from the externally circulating stream leaving the reaction zone.

This invention relates to a process for the chlorination of aliphatic and alicyclic hydrocarbons. More particularly, this invention relates to a continuous process for the photochlorination of aliphatic and alicyclic hydrocarbons in partially chlorinated hydrocarbon derivatives thereof, containing three to five carbon atoms in the molecule. Most preferably, the invention relates to a continuous process for the photochlorination of pentane.

It is known in the art that the photochemical chlorination of aliphatic and alicyclic hydrocarbons containing three to five carbon atoms in the molecule may be effected in chlorinators wherein gaseous hydrocarbons and gaseous chlorine are introduced continuously into a liquid mixture of the product in a reaction zone by diffusion means at points removed by one another so as to minimize the possibility of an explosion. The usual method of dilfusion provided is the dispersion of the gaseous feeds by use of a porous thimble or sintered glass plate. Mechanical dispersion with a turbo-mixer can also be employed. The disadvantages inherent in the use of a diffuser for the introduction of hydrocarbons are numerous. For example the pore-size of the diifusers normally used is about 15-20 microns and pores of this size are readily plugged by contaminants entrained in the hydrocarbon gas. Gaseous hydrocarbon feeds require the use of an elaborate evaporating system operating under pressure to force the starting material through the small pores of the diffuser. Further, when both reactants are introduced in the gaseous state into the photochemical chlorinator, bubbles of gaseous reactants may coalesce and may form explosive mixtures. These conditions have imposed severe restrictions on operation of chlorinators using a feed based on gaseous difiusion of both reactants.

It has been known in the art that chlorination of hydrocarbons may be eifected by using liquid reactants. One such process involves introducing liquid chlorine directly into a body of liquid hydrocarbon or partially chlorinated hydrocarbon under conditions of extremely low temperature in order to avoid the risk of explosions which is even greater when using liquid reactants in this manner than 'when using gaseous reactants. To our knowledge, the risk and danger in these processes have been so great that none has been put to use on a large commercial scale. Another such process for the photochemi- 3,528,900 Patented Sept. 15, 1970 cal chlorination of hydrocarbons comprises separately injected liquid chlorine and liquid hydrocarbon into an externally recirculating stream of liquid polychlorohydrocarbon, so that, at least percent of the reactants entering the radiation or reaction zone are in the liquid phase.

The principal object of this invention is to provide an improved continuous process for the photochlorination of aliphatic and alicyclic hydrocarbons and partially chlorinated hydrocarbon derivatives thereof, wherein increased overall efficiency and economy as well as smoother and less hazardous operations are realized from improved operating methods.

Another object of this invention is to provide a process wherein the danger of explosion encountered in the use of liquid chlorine is eliminated.

A further object of the invention is to provide an improved continuous circulating chlorination process Wherein the explosion hazard caused by bubbles of reactants coalescing is substantially eliminated.

A still further object is to provide a method for eliminating the need to circulate the stream of reactants at a rate which maintains at least 90 percent of the reactants entering the reaction zone in the liquid phase.

It has now been found that these and related objects may be accomplished in a continuous process for the photochemical chlorination of aliphatic and alicyclic hydrocarbons and partially chlorinated derivatives thereof containing from three to five carbon atoms by providing a circulating stream of liquid polychlorinated hydro carbon which is in communication with a reaction zone and introducing gaseous chlorine through a diffusion area into said circulating stream of liquid polychlorohydrocarbon near the entrance of the reaction zone and continuously injecting liquid hydrocarbon into the externally circulating stream of liquid polychlorohydrocarbon at a point sufliciently removed from said dilfusion area and said reaction zone so that thorough mixing with the liquid polychlorohydrocarbon is obtained prior to introduction to the photochlorinator.

It has been found that when the above conditions are maintained, large quantities of chlorine bubbles can be tolerated without chances of explosion. Under these conditions, up to 40 percent of the chlorine feed can be out of solution and still not have a hazardous condition.

Further, in view of the fact that the hydrocarbon is introduced as a liquid into the externally circulating stream of polychlorohydrocarbon and uniformly mixes therewith prior to its being circulated with chlorine to the reaction zone, the reaction proceeds much more smoothly and a considerably more uniform product is obtained than had been obtained by the prior art processes. The manner in which the process of the invention is carried out will be more clearly understood from the following description of the accompanying drawings in which FIG. 1 is a partially schematic flow sheet showing an embodiment of this invention wherein the gaseous chlorine is introduced to the reactor at and around the introduction point of the circulating stream; and FIG. 2 is a partially schematic flow sheet showing another embodiment which may be employed in performing the process of this invention, comprising the separate introduction of the reactants into the circulating system.

Referring to FIGS. 1, wherein the reaction zone is shown as a partial sectional view, gaseous chlorine 1, passing through flow meter 11, is introduced to the photochlorinator through a nozzle or dispenser 3, and liquid hydrocarbon starting material 5, passing through flow meter 7, is separately injected through a nozzle into a circulating system 9 of liquid polyhydrocarbon having a specific gravity between about 1.3 and about 1.8. The external stream is circulated through the system by means of pump 24. The temperature of the reaction medium in the photochlorinator 13 is maintained between 25 degrees and 150 degrees centigrade by means of external heat exchangers 15 and 17. A portion of the polychlorohydrocarbon is withdrawn from the separation zone 19 to a product recovery zone 21 wherein the desired product is recovered. Efiluent gases, such as chlorine and hydrogen chloride are removed from the separation zone and vented 23 to a recovery system. The photochemical energy is supplied by a mercury vapor lamp suspended in a light well 25.

Referring to FIG. 2, wherein the reaction zone is shown in partial section, gaseous chlorine 1 and liquid hydrocarbon starting material 5, passing through flow meters 11 and 7 respectively, are separately injected by means of nozzles into a circulating system of liquid polychlorohydrocarbon 9 having a specific gravity between about 1.3 and about 1.8. The external stream is circulated through the system by pump 25 means, such as a centrifugal pump. The temperature of the reaction medium in the photochlorinator 13 is maintained between 25 degrees and 150 degrees centigrade by means of external heat exchangers 15 and 17. A portion of the polychlorohydrocarbon 9 is withdrawn from the separation zone 19 to a product recovery zone 21, wherein the desired product is recovered and the remaining portion is recycled to the photochlorinator as the externally circulating stream. Effluent gases such as chlorine and hydrogen chloride are removed from the separation zone and vented 23 to a recovery system. The photochemical energy is supplied by a mercury vapor lamp suspended in a light well 25.

The mole ratio of chlorine to hydrogen starting material is maintained between about 3 to 1 and about 12 to 1. The circulating stream is passed through an irradiated reaction zone to effect the chlorination of the hydrocarbon in a reaction medium of liquid polychlorohydrocarbon. The reaction is catalyzed by exposing the main liquid body of polychlorohydrocarbons to the action of actinic light having a wave length from about 3,000 to about 5,000 A. The temperature of the liquid body of polychlorohydrocarbon employed as a reaction medium for the chlorination is maintained between about 25 degrees and about 150' degrees centigrade and preferably between about 50 degrees and about 125 degrees centrigrade by means of external heat exchangers located in the circulating stream which remove the heat of reaction and the heat of the mercury lamps. A portion of the liquid polychlorohydrocarbon stream leaving the reaction zone is withdrawn continuously to maintain a constant liquid volume in the reaction system.

The liquid hydrocarbon reactant and gaseous chlorine reactant may be injected separately through nozzles into the circulating stream of liquid polychlorohydrocarbon. It is also within the scope of this invention to inject the liquid hydrocarbon reactant into the circulating stream of liquid polychlorohydrocarbon at a point external to the chlorination zone at a point around, or preferably above, the point of introduction of the polychlorohydrocarbon stream containing hydrocarbon and causing the stream to move away from such region.

The liquid hydrocarbon may be added to the circulating stream by any suitable and known method for adding liquid materials and the gaseous chlorine may be introduced to the circulating stream or the photochlorinator by any suitable and known method for introducing gaseous materials to liquids. Preferably, the chlorine gas is introduced to the circulating stream of the photochlorinator through a disperser.

The photochemical chlorinator contains liquid polychlorohydrocarbons having a specific gravity between about 1.3 and about 1.8, preferably between about 1.5 and about 1.8, as the coolant and diluent for the chlorination of hydrocarbons.

Since undesired chlorinolysis of the polychlorohydrocarbons is initiated at temperatures of about 150 degrees centigrade, it is preferred to maintain the reaction medium temperature below about 125 degrees centigrade, and is most preferred to maintain the reaction temperature between about degrees centigrade and about degress centigrade. The volume of mixed polychlorohydrocarbons in the chlorinator is kept substantially constant by continuous Withdrawal of liquid polychlorohydrocarbon from the external circulating stream as the reaction proceeds.

The flow rate of the circulating stream of liquid polychlorohydrocarbons having a specific gravity between about 1.3 and about 1.8 is maintained by pumping means, such as a centrifugal pump, and is dependent upon the available heat exchanger capacity and the chlorine feed rate required for the desired production. It is assumed that all heat of reaction is removed in the heat exchanger, as is consistent with sound design principles. Beneficially, the utilization of liquid pentane feed in the process of the invention reduces the heat load on the system, which contributes to greater effective heat exchanger output and ultimately to increased flow rate. The economics of heat exchanger capacity dictate the maximum flow rate while the minimum flow rate is dictated by the chlorine feed rate required.

The reaction between chlorine and a hydrocarbon is especially sensitive to certain impurities. Therefore, the starting materials should be free from harmful inhibitors or materials which may delay or slow down the reaction between the hydrocarbon and the chlorine. Presence of reaction inhibitors such as free oxygen or oxygenated organic compounds in the system will inhibit chlorination and they should be eliminated before starting chlorination.

By the procedure of this invention, the operational hazard encountered in the utilization of liquid chlorine with liquid hydrocarbon or gaseous chlorine with gaseous hydrocarbon, that is, the accumulation of an explosive mixture of chlorine and hydrocarbon, is substantially reduced. This reduction was unexpectedly obtained by the utilization of a liquid hydrocarbon feed and a gaseous chlorine feed in combination.

The above description of the drawings and the following examples further illustrate our invention, but it is to be understood that the specific details given in the drawing and examples have been chosen for the purpose of illustration and are not intended to limit our invention except as defined in the appended claims. All temperatures are in degrees centigrade and all parts are by weight, unless otherwise mentioned.

EXAMPLE 1 This example illustrates the embodiment set forth by FIG. 1

The chlorination apparatus employed to obtain the data for the following example consisted of a nickel pipe fitted with a jacketed light well assembly which consisted of a Pyrex pipe mounted inside a second Pyrex pipe supported on the vertical axis of the chlorinator. A 3000 watt Westinghouse BH-9 mercury vapor lamp suspended in the light well was used to furnish photochemical energy for this run. The chlorinator had a conical bottom section wherein the circulating liquid streams entered the chlorinator through a nickel pipe. A drain valve was provided at the bottom. A liquid overflow at the top of the chlorinator was provided. Exit gases were withdrawn through a nickel pipe mounted above the liquid overflow. A thermometer well extended into the body of the chlorinator for measuring the liquid temperature.

After the light source had been turned on and had reached normal operating temperature, the circulating stream of polychloropentanes Was started at a maximum flow rate. Both chlorine and pentane feeds, during the induction period, are set forth below in Table I.

TABLE I.FEED RATES hi/lolar Moles er hour Parts per hour propor ions p G Clz/Cs l liztln Time Li Gas Liq. as p 0- 51 1 1; 01; 05111; 01; chlormator The liquid pentane flow was regulated through a flow controller and passed into the polychloropentane circulating line, the inlet point of which was in a laminar flow region, through a Lunkenheimer 906 BS needle valve. The molar ratio of chlorine feed to pentane feed was about 9.0 to 1. Following the 124 minutes induction period set forth above, the flow rate of reactants into the circulating stream of liquid polychlorohydrocarbon was maintained for a period of three hours at about 103 parts per hour of llquid pentane and about 908 parts per hour of gaseous chlorine.

During the reaction period of three hours, the molar proportion of chlorine to pentane was thus kept at 9.0 to 1. The temperature of the photochlorinator was kept at about 99-101 degrees centigrade during the reaction period. The hydrogen chloride and chlorine gas stream leaving the reaction zone of the photochlorinator contained about 24.6-27.6 percent of chlorine while the same stream contained from 0.02 to 0.06 percent of unreacted pentane. The product recovered had a specific gravity of 1.688 at degrees centigrade corresponding to composi- 11011 of C5CI7 4ZH5.

EXAMPLE 2 The apparatus and procedure of Example 1 were used to obtain the following data.

After the light source had been turned on and had reached an operating intensity, the circulating stream of polychloropentanes was started at a maximum flow rate provided by the circulating pumps.

Following the induction period, 908 parts per hour of chlorine and 103 parts per hour of pentane were iniected, respectively, into a circulating stream of liquid polychloropentane. During the reaction period of 36 hours, the chlorine to pentane molar proportion was kept at about 9.0 to- 1. The temperature of the photochlorinator reaction zone was maintained at about 102-107 degrees centrigrade. The hydrogen chloride and chlorine gas stream leaving the reactor contained about 23.9 percent of chlorine and 0.14 percent of pentane based on pentane feed. The product obtained had a specific gravity of 1.684 at 20 degrees centigrade corresponding to an average composition of C CI H EXAMPLE 3 The following example was run for comparison and as a control.

Employing the apparatus and procedures of Example 2, a gaseous pentane feed was used in place of liquid pentane. The total operating time was 36 hours. This run operated at specific gravities ranging from 1.666-1.673 at TAB LE II Example 2 3 Running time (hours) 36 36 Temperature of photochlorinator 102-107 102-109 Pressure in photochlorinator (atmospheres) 2. 29 2. 36 Specific gravity of product 1. 684 1. 669

It is clearly evident from the specific gravities of the reaction products that the process of this invention results in the more effective and eflicient chlorination of the hydrocarbon reactant.

What is claimed is:

1. A continuous process for the photochemical chlorination of aliphatic and alicyclic saturated hydrocarbons containing three to five carbon atoms in the molecule, comprising maintaining a circulating stream of liquid polychlorohydrocarbon in communication with an external to a reaction zone containing the main body of liquid polychlorohydrocarbon, injecting liquid hydrocarbon into said externally circulating stream of liquid polychlorohydrocarbon, introducing gaseous chlorine to the mixture of liquid hydrocarbon and liquid polychlorohydrocarbon, passing the mixture so produced through an irradiated reaction zone to effect chlorination of hydro carbon and a polychlorohydrocarbon, and withdrawing a portion of the externally circulating stream leaving the reaction zone and recovering said portion as product.

2. A process in accordance with claim 1 wherein the circulating stream is maintained at a temperature between about 25 degrees centigrade and degrees centigrade.

3. A process in accordance with claim 2 wherein gaseous chlorine and liquid pentane are passed to the reaction zone in molar proportions in the range of about 6 to 1 and about 10 to 1.

4. A process in accordance with claim 3 wherein the liquid polychlorohydrocarbon reaction medium has a specific gravity between about 1.3 and about 1.8.

5. A process in accordance with claim 4 wherein the gaseous chlorine is introduced to circulating stream of liquid polychlorohydrocarbon and liquid hydrocarbon.

6. A process in accordance with claim 4 wherein the gaseous chlorine is introduced to the reaction zone, around the point at which the circulating stream is passed into said reaction zone.

7. A process in accordance with claim 4 wherein the liquid hydrocarbon is pentane and the liquid polychlorohydrocarbon starting material is a mixture of partially chlorinated pentane derivatives.

8. A process in accordance with claim 1 wherein the liquid hydrocarbon is pentane and the liquid polychlorohydrocarbon starting material is a mixture of partially chlorinated pentane derivatives.

References Cited UNITED STATES PATENTS 2,899,370 8/ 1959 Rosenberg 204163 2,997,508 8/1961 Stretton et a1. 204-163 3,405,046 10/1968 Sennewald et al. 204-163 HOWARD S. WILLIAMS, Primary Examiner

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