Process for the production of chlorinated hydrocarbons

A process of the type for producing 1,1,1,2,3-pentachloropropane by introducing 1,1,1,3-tetrachloropropane, chlorine, and Lewis acid catalyst, optionally in the presence of carbon tetrachloride, the improvement comprising introducing the Lewis acid as a slurry within a chlorinated hydrocarbon.

FIELD OF THE INVENTION

Embodiments of the present invention provide processes for the production of chlorinated hydrocarbons, particularly 1,1,1,2,3-pentachloropropane and 1,1,2,3-tetrachloropropene.

BACKGROUND OF THE INVENTION

Hydrofluoroolefins (HFOs) have been proposed as “fourth generation” refrigerants. These compounds have also been proposed for use as blowing agents, biocides, and monomer feedstock. Most industrially useful synthetic techniques require chlorinated hydrocarbon feedstocks to produce the HFOs. In particular, 2,3,3,3-tetrafluoropropene (HFO-1234yf) can be produced by employing 1,1,2,3-tetrachloropropene (HCC-1230xa) feedstock.

U.S. Publication No. 2009/0216055A1 teaches a method for producing 1,1,2,3-tetrachloropropene by dehydrochlorinating 1,1,1,2,3-pentachloropropane (HCC-240db). This patent publication teaches that 1,1,1,2,3-pentachloropropane can be produced in a single reaction vessel by heating a reaction mixture of 1,1,1,3-tetrachloropropane (HCC-240fa), chlorine, and a Lewis acid catalyst. The Lewis acid catalyst dehydrochlorinates the 1,1,1,3-tetrachloropropane to form 1,1,3-trichloropropene, and then the 1,1,3-trichloropropene reacts with chlorine in the presence of the catalyst to produce 1,1,1,2,3-pentachloropropane. The catalyst (e.g. ferric chloride) is added to the reactor either continuously or periodically and is generally maintained at 30 to 1000 ppm. The product is fed, either continuously or periodically, to a reactive distillation system where the 1,1,1,2,3-pentachloropropane is dehydrochlorinated to 1,1,2,3-tetrachloropropene in the presence of a Lewis acid catalyst such as the ferric chloride. The distillation system employed includes a reaction zone, a separation zone, and a condensing zone. The liquid in the reaction zone is heated and agitated. Heat can be provided through a jacket on the vessel, by internal heat exchangers, or by external heat exchangers, and the agitation can be provided via pump circulation or stirring.

Because 1,1,2,3-tetrachloropropene is an important feedstock for the synthesis of certain HFOs, there is a desire to improve the efficiency of the processes for the production of 1,1,2,3-tetrachloropropene.

SUMMARY OF THE INVENTION

One or more embodiments of the present invention provide a process of the type for producing 1,1,1,2,3-pentachloropropane by introducing 1,1,1,3-tetrachloropropane, chlorine, and Lewis acid catalyst, optionally in the presence of carbon tetrachloride, the improvement comprising introducing the Lewis acid as a slurry within a chlorinated hydrocarbon.

Other embodiments of the present invention provide a process of the type for converting 1,1,1,2,3-pentachloropropane to 1,1,2,3-tetrachloropropene by reactive distillation in the presence of a Lewis acid catalyst, the improvement comprising heating a crude product stream including 1,1,1,2,3-pentachloropropane and Lewis acid catalyst within a reboiler operating at conditions that inhibit the reaction or formation of deposits within the distillation column and the reboiler.

Yet other embodiments of the present invention provide a process for producing 1,1,1,2,3-pentachloropropane, the process comprising (i) providing a slurry of a Lewis acid catalyst within a chlorinated hydrocarbon; (ii) continuously circulating the slurry through a slurry loop in fluid communication with a reactor; and (iii) introducing into the reactor 1,1,1,3-tetrachloropropane, chlorine, and the slurry.

Still other embodiments of the present invention provide a process for converting 1,1,1,2,3-pentachloropropane to 1,1,2,3-tetrachloropropane, the process comprising (i) providing a mixture of 1,1,1,2,3-pentachloropropane and Lewis acid catalyst; (ii) heating the mixture within a forced recirculation reboiler; and (iii) introducing the heated mixture from the forced recirculation reboiler to a column to thereby vaporize 1,1,2,3-tetrachloropropene formed by heating the 1,1,1,2,3-pentachloropropane in the presence of Lewis acid catalyst.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Embodiments of the invention are based, at least in part, on the discovery of a process for the synthesis of 1,1,1,2,3-pentachloropropane by chlorinating 1,1,1,3-tetrachloropropane, wherein one or more Lewis acid catalysts, such as ferric chloride, is delivered to a reaction vessel from a slurry system wherein the catalyst is slurried within a chlorinated hydrocarbon (e.g. carbon tetrachloride). It is believed that by separately preparing a catalyst slurry, efficiencies can be achieved and problems associated with the Lewis acid catalysts, such as handling problems and its propensity to absorb water, can be avoided. This process also will advantageously allow for more finite controls on the introduction of the catalyst to the reactor.

According to other embodiments, 1,1,1,2,3-pentachloropropane crude is dehydrochlorinated to 1,1,2,3-tetrachloropropene by reactive distillation through a distillation technique that heats the crude within a forced circulation reboiler. The flow velocity and heat flux within the reboiler are maintained to prevent fouling within the distillation system. Indeed, it has been discovered that localized hot spots within the distillation system cause catalyst residues to bake onto the surface of the system. Thus, while the prior art teaches that 1,1,1,2,3-pentachloropropane crude can be directly treated by reactive distillation to form 1,1,2,3-tetrachloropropene, it has now been contemplated that specific distillation systems can give rise to process efficiencies. Additionally, since the reactive distillation takes place in the presence of threshold levels of Lewis acid catalyst (e.g. ferric chloride), further efficiencies are contemplated by employing the same or similar slurry system employed for delivering the Lewis acid catalyst to the chlorination reactor.

According to embodiments of the present invention, 1,1,1,2,3-pentachloropropane is prepared by introducing 1,1,1,3-tetrachloropropane, chlorine, Lewis acid catalyst, and optionally carbon tetrachloride. In this respect, U.S. Publication Number 2009/0216055A1 is incorporated herein by reference. As the skilled person appreciates, the 1,1,1,3-tetrachloropropane is a liquid at reaction conditions, and therefore the chlorine and the Lewis acid catalyst are added to the 1,1,1,3-tetrachloropropane liquid, which may be included within a mixture with carbon tetrachloride. In one or more embodiments, the chlorine is added as a gas and can be added to the 1,1,1,3-tetrachloropropane liquid through, for example, a tube submerged into the liquid or via one or more gaseous dispersing elements within the liquid. As the skilled person appreciates, several Lewis acid catalysts have been employed as chlorination catalysts, and practice of embodiments of the invention are not limited to specific Lewis acid catalysts. Ferric chloride is a common chlorination catalyst and/or dehydrochlorination catalyst, and therefore specific embodiments of the invention are described with reference to ferric chloride, although the skilled person can readily extend the teachings herein to other chlorination catalysts.

According to embodiments of the present invention, the Lewis acid, such as ferric chloride, which is partially soluble in the reaction medium at reaction conditions, is introduced to the 1,1,1,3-tetrachloropropane liquid as a slurry dispersed (and partially dissolved) within a chlorinated hydrocarbon liquid, such as carbon tetrachloride. In one or more embodiments, the catalyst is maintained within a liquid dispersion through continuous agitation that may be provided by, for example, a continuous circulation loop that is in communication with the vessel that contains the 1,1,1,3-tetrachloropropane liquid.

The process of one or more embodiments of the present invention can be described with reference toFIG.1. As shown, system11includes Lewis acid mix tank21, which is in fluid communication with reactor51(which may be referred to as chlorination reactor51) through a circulation loop41. Slurry tank21receives chlorinated hydrocarbon (e.g. carbon tetrachloride)31through inlet22and Lewis acid catalyst33through inlet23. Slurry tank21may also optionally receive other materials34, such as additional solvents, catalysts, catalyst ligands, or recycle streams captured downstream in the process, through inlet26. In one or more embodiments, carbon tetrachloride31may be fed continuously, or in other embodiments it may be periodically injected, into slurry tank21through inlet22. Likewise, Lewis acid catalyst33may be periodically added to slurry tank21, or in other embodiments, Lewis acid catalyst33may be continuously charged to slurry tank21by employing continuous feeding apparatus. For example, Lewis acid catalyst33can be charged to slurry tank21by employing a dustless bucket tipper.

A slurry35of carbon tetrachloride31and Lewis acid catalyst33is formed by agitating the mixture within slurry tank21via one or more mixing elements24, which may include agitation devices or baffles. Mixing elements24may be operated in a manner to substantially disperse the Lewis acid catalyst within the chlorinated hydrocarbon liquid (e.g. carbon tetrachloride); in particular embodiments, agitation is sufficient to achieve a substantially homogeneous concentration of the Lewis acid within the chlorinated hydrocarbon.

Slurry35is continuously circulated through a circulation loop41via one or more pumps43that are upstream of reactor51, which pumps may also advantageously maintain pressure within loop41. Adequate pressure may also be maintained within loop41through the assistance of a back-pressure valve49, which is downstream of where loop41delivers slurry35to reactor51(i.e. downstream of valve47within loop41). Slurry35moving through loop41may be heated or cooled by heating or cooling elements45. Other materials34, such as those described above, may also optionally be injected into loop41. In one or more embodiments, the mixing of the various constituents within slurry35can be enhanced by one or more in-line mixers, which are not shown. Circulation loop41also includes a valve47that, when in the open position, allows slurry35to feed reactor51. When valve47is in its closed position, slurry35circulates through loop41back to mix tank21. Valve47may include a control valve or solenoid valve that can be controlled by a signal flow sensor or similar device.

In one or more embodiments, the flow of slurry35into reactor51, which flow is at least partially regulated by valve47, can be proportional to the 1,1,1,3-tetrachloropropane65and chlorine61feed rate into reactor51.

In one or more embodiments, loop41is maintained at a pressure that is greater than the pressure within reactor51; in particular embodiments, the pressure within loop41is sufficient to create flow into reactor51(when valve47is open) while taking into account potential gravitational assistance. As the skilled person will appreciate, sufficient pressure can be maintained within loop41while valve47provides flow into reactor51by back-pressure valve49. Valve49may include a control valve or solenoid valve that can be controlled by a signal flow sensor or similar device. In one or more embodiments, temperature controls (e.g. element45) provide cooling to maintain the temperature of slurry35below the boiling point of the chlorinated hydrocarbon (e.g. below 77° C. for carbon tetrachloride). In particular embodiments, the loop temperature is maintained at from about 0 to about 80° C., in other embodiments from about 5 to about 60° C., and in other embodiments from about 10 to about 40° C.

In one or more embodiments, the concentration of Lewis acid (e.g. ferric chloride)33within slurry35may be represented as a percent solids (both dispersed and soluble) within the weight of liquid. In one or more embodiments, the percent solids ferric chloride within slurry35may be from about 1 to about 15 wt %, in other embodiments from about 2 to about 10 wt %, and in other embodiments from about 3 to about 7 wt %.

According to embodiments of the present invention, 1,1,1,2,3-pentachloropropane crude stream can be directly treated by reactive distillation to form 1,1,2,3-tetrachloropropene. This procedure is generally known in the art, and therefore U.S. Publication Number 2009/0216055A1 is incorporated herein by reference in this regard. As suggested above, according to embodiments of the present invention, reactive distillation takes place by heating the crude product stream within a forced circulation reboiler.

The reactive distillation process of one or more embodiments can be described with reference toFIG.2, which shows reactive distillation system101including distillation column103and reboiler123. As generally known in the art, column103includes a bottom zone103A, where column bottoms106in the form of liquid (which general includes about 3-5% solids) collect and form liquid level106A. Column103also includes a packing zone103B, where packing materials104(e.g. grid material) and/or trays104are located, as well as a draw tray108. At the upper end thereof, column103includes head space103C through which vapor passes out of column103.

In one or more embodiments, reboiler123, which may also be referred to as forced recirculation boiler123, may include a single or multi-pass reboiler. In particular embodiments, as will be described herein below, a heating fluid or media travels shell side through reboiler123. Practice of the present invention is not limited by the type of heating fluid employed and may include, for example, steam.

Distillation column103and reboiler123are in fluid communication via reboiler loop111. 1,1,1,2,3-pentachloropropane crude71enters column103, and more specifically, bottom103A, at or near liquid level106A, where crude71becomes included in column bottoms106. Additional Lewis acid catalyst can be introduced to crude71through, for example, slurry35(which is described above). Column bottoms106enter loop111through outlet105. The velocity of column bottoms106flowing through loop111is regulated by, for example, pump115. In one or more embodiments, the velocity of column bottom106flowing through loop111is maintained at a rate sufficient to reduce tube wall temperatures within reboiler123and thereby inhibit reactions and/or the formation of deposits within reboiler123. Column bottoms106enter reboiler123at inlet125and circulate tube side within reboiler123. In one or more embodiments, the velocity of column bottoms106through reboiler123is at least 1, in other embodiments at least 3, and in other embodiments at least 5 m/s. In these or other embodiments, the velocity of column bottoms106through reboiler123is from about 1 to about 20, in other embodiments from about 2 to about 12, and in other embodiments from about 3 to about 9 m/s.

As suggested above, column bottoms106travel tube side through reboiler123where they are subjected to heat that is transferred from heating fluid127(e.g. steam) introduced through inlet126shell side of bottoms106. In one or more embodiments, heat flux across the tubes within reboiler123is less than 44, in other embodiments less than 33, and in other embodiments less than 22 kW/m2. In these or other embodiments, the heat flux across the tubes within reboiler123is from about 5 to about 44 kW/m2, in other embodiments from about 7 to about 33 kW/m2, and in other embodiments from about 10 to about 22 kW/m2.

The heating of column bottoms106, which includes 1,1,1,2,3-pentachloropropene and Lewis acid catalyst (e.g. ferric chloride), causes the dehydrochlorination of the 1,1,1,2,3-pentachloropropane to produce 1,1,2,3-tetrachloropropene.

Column bottoms106exit reboiler at exit129, as a heated liquid, and are injected into column103at inlet107, which is positioned below packing zone103B; in particular embodiments, column bottoms106enter at or near liquid level106A. Column bottoms106leaving reboiler123through outlet129are heated to an extent that at least certain target constituents, such as the 1,1,2,3-tetrachloropropene, will flash (i.e. boil) due to pressure differentials experienced upon entry into column103, and at least portions thereof will travel through packing space103B toward head space103C and ultimately exit vapor outlet109. Also, in one or more embodiments, reboiler123may be located at a lower elevation relative to the bottom of distillation column103to thereby provide sufficient hydrostatic pressure and thereby prevent premature boiling of the column bottoms within reboiler123. Accordingly, the combination of fluid velocity through loop111, heat reflux within reboiler123, and the pressure maintained within loop111serve to inhibit reactions and/or the formation of deposits onto the tube walls or within distillation column103.

In one or more embodiments, vapor (from the heating of column bottoms106) may partially condense at packing space103B and at least portions thereof may be removed from column103through draw tray108. This condensate, which is rich in 1,1,2,3-tetrachloropropene, can be recirculated back to the process for several advantageous uses. For example, draw stream117B, which may be referred to as seal face flush117B, can be routed to one or more pumps, such as pump117A, to provide a constant seal flush, which advantageously maintains constant pressure on the rotary seal face and maintains the seal in proper working order for long periods of time. Also, draw stream117C, which may also be referred to as instrument flush117C, can be routed to one or more instruments, such as level instrumentation within bottom zone103A, which can provide constant flush on instrumentation and thereby inhibit solids build up on the instruments. In these or other embodiments, condensate from draw tray108can also be collected in tank117, which advantageously allows for volume build up that can be subsequently used, for example, during startup of the reactor.

As the skilled person will appreciate, the desired 1,1,2,3-tetrachloropropene will exit distillation column103as a vapor stream132through vapor outlet109of distillation column103. Vapor stream132may then be routed through condenser136, which causes the condensation of the desired chlorinated hydrocarbon138(i.e. 1,1,1,2,3-pentachloropropane), which may also be referred to as condensate stream138, while allowing lighter materials (as well as uncondensable materials) to exit as a light-end stream140. A portion of condensate stream138may be routed back to column103via a distributor (not shown) through stream139and into head space103C to reflux the packing. The remainder of condensate138is collected as the desired product. Depending on the desired level of purification, further distillation and purification of condensate138can be accomplished in downstream processing.

Additionally, as shown in bothFIGS.1and2, slurry35, which includes Lewis acid from circulation loop41, can be combined with 1,1,1,2,3-pentachloropropane crude stream71through valve48to provide sufficient Lewis acid to catalyze the dehydrochlorination reaction. As specifically shown inFIG.2, slurry35can be combined with 1,1,1,2,3-pentachloropropane crude stream71prior to crude stream71entering column103. In other embodiments, which are not shown, slurry35can be directly introduced to column103or to loop111.