CA1051929A - Process for the separation of cis- and trans-1,2-dichloroethylene from 1,1-dichloroethane by distillation and isomerization process for preparing 1,1,1-trichloroethane and method for the removal of cis- and trans-1,2-dichloroethylene from 1,1-dichloroethane by selective chlorination - Google Patents

Abstract

ABSTRACT
Methylchloroform is prepared by reacting ethy-lene and hydrogen chloride in the presence of AlCl3 to producc ethyl chloride, which is then reacted with Cl2 and ethyl chloroform at 400-550°C; this reaction mix-ture is cooled to produce a gaseous fraction and a liquid fraction; a minor portion of the liquid fraction is re-turned to the cooling zone and the remainder ie mixed with the gaseous fraction and hydrochlorinated to form low boiling materials and polychlorinated ethanes; the low boiling materials are removed, and then sequentially there are separated 1,1-dichloroethane, cis- and trans--1,2-dichloroethylenes and methylchloroform.

Description

~.o.~,~9Z9 The present invention is a process for preparing l,l,l-trichloroethane.
The hydrochlorination of ethylene in the pre-sence of a Friedel-Crafts metal halide cataly~t is an old and well known procedure. The art employs prinicpally ethylene and a substantially high purity hydrogen chloride in a boiling bed reactor. The composition of the boiling bed is substantially the product of the hydrochlorination.
Many of the Friedel-Crafts metal halide catalysts have been suggested and depending upon the conversionJ tempera-ture of reaction, pressure, etc., the entire scope is employed. Aluminum chloride or ferric chloride, however, are the preferred and most commonly referred-to metal halide Friedel-Crafts catalysts. The principal product of this reaction with ethylene is ethyl chloride. It has become common practice to purify the ethyl chloride from this reaction prior to its use in preparing any number of more highly chlorinated materials. Likewise, the thermochlorination of ethyl chloride is a well known process. The temperatureS pressure, and the ratio of chlorine, with or without catalysts, dictate the product which is obtained. Many processes are known which integrate a di- and trichloro- product such as, for example, chlori-nating ethyl chloride to l,l-dichloroethane recycling the l,l-dichloroethane with the ethyl chloride feed and producing therefrom l,l,l-trichloroethane. Several techniques have been disclosed for carrying out such a process. Again in each of these processes, it is normal that the effluent product of the chlorination is separated into the desired product and recycle streams. Some desired product may be -~

17,182/183/198-F -1-105~929 recycled as a temperature control, thus a chlorination control medium. The hydrochlorination of unsaturated partially chlorinated hydrocarbons such as vinyl chloride, vinylidene chloride, cis- and trans-dichloroethylenes, are each documented in the prior art. The use of ferric chloride and/or aluminum chloride as the metal halide Friedel-Craft~ catalyst for these hydrochlorinations is also well known. The separation of each of the products of the hydrochlorination of one or more of the unsaturated, partially chlorinated hydrocarbons is a rather lengthy pro-cedure requiring several distillations to obtain high purity products. It is evident from the prior art that the skilled technician approaches the preparation of polychlorinated ethylenes and ethanes in a stepwise manner, preferring to separate the intermediate products and purify them before employing them in the next step. This procedure necessitates several large pieces of purification equipment intermediate to the various steps and oftentimes results in compounds being present as impurities in the desired product, which create problems in the next step unless removed by chemical means.
It would therefore be advantageous if there were p~ovided a process whereby ethylene and chlorine were the two external reactants introduced into a process, and therefrom produce l,l,l-trichlorethane with a minimum of intermediate separations of reaction products in order to provide feeds for each of the steps of a multi-step process.

17,182/183/19S-F -2-10519'~9 The present invention provides a process for preparing l,l,l-trichloroethane comprising:
(a) reacting ethylene and hydrogen chloride, wherein the hydrogen chloride is obtained from another step in the process, in the presence of aluminum chloride catalyst to produce ethyl chloride;
(b) reacting said ethyl chloride, recycle ethyl chloride and l,l-dichloroethane with chlorine at a temper-ture of 400-550C;
(c) subjecting the reaction mixture from (b) to a liquid quench, thus producing (1) a gaseous product mixture comprising hydrogen chloride, vinyl chloride, and vinylidene chloride, and (2) liquid product;
(d) returning a minor portion of said liquid product to the quench zone, mixing the remaining portion of said liquid product with the gaseous product mixture formed in (c)(l), and hydrochlorinating this latter mixture to form a second product mixture comprising hydrogen chloride, ethylene, ethyl chloride, vinyl chloride, vinylidene chloride, ;
l,l-dichloroethane, cis- and trans-1,2-dichloroethylenes, l,l,l-trichloroethane, ethylene dichloride, trichloroethylene, 1,1,2-trichloroethane and unsymmetrical tetrachloroethane; -~
(e) separating the hydrogen chloride ethylene : :
ethyl chloride vinyl chloride and vinylidene chloride from ~ :
said second product mixture;
(f) separating from the remaining portion of said -second product mixture l,l-dichloroethane and the cis- and trans-1,2-dichloroethylenes;
(g) separating l,l,l-trichloroethane from the portion remaining after the separation in (f).

~ ' .
17182/183/198-F ~ -2a-lOS~9Z9 Figure 1 represents a flow chart in accordance with the present invention. The present invention will now be described having regard to Figure 1, wherein ethylene 17182/183/198-F -2b-105~9Z9 (1) is mixed with hydrogen chloride (15) and fed to a hydrochlorinator (A) wherein the ethylene is hydrochlor-inated to ethyl chloride (3). The reaction is conducted in a boiling bed of ethyl chloride containing aluminum chloride catalyst dispersed throughout. The resulting gaseous product (ethyl chloride) stream (3) of this first hydrochlorination is then admixed with a recycle fraction (20) and chlorine and thermally chlorinated in thermal chlorinator (B). The recycle fraction (20), obtained from the separation of products in latter steps, has a boiling point be~ween about 37C. and about 60C.
and is principally l,l-dichloroethane. The thermal chlorination is carried out at between about 400 and 550C. The resulting product stream (5) of this thermal chlorination is subjected to a liquid quench (C) wherein ~
those chlorinated hydrocarbons boiling above about 40C. -are converted from the gaseous state to the liquid state. ;
The nonliquefied gases (6) of the product effluent stream ;
resulting from the quench, primarily hydrogen chloride, vinyl chloride and vinylidene chloride, and any unreacted ethylene, are taken overhead. The liquid (7) resulting from the quench (C) of the product effluent from the thermal chlorinator is in part used as the quench liquid and in the greater part is admixed with the vinyl chloride, vinylidene chloride and hydrogen chloride and any unreacted ethylene overhead fraction from the quench, and the resulting mixture (10) introduced into a liquid hydro-chlorinator (D) in which ferric chloride is the metal halide Friedel-Crafts catalyst. Thus, effectively, the entire effluent from the thermal chlorinator is quenched 17,182/183/198-F -3-lOS19Z9 and passed directly to the ferric chloride hydrochlorina-tion reactor (D~. This procedure eliminates a di~tilla-tion between steps in the process; however, it increases the severity of the final product purification step because the 1,2-dichloroethane produced in the reactions and which will now appear with the product, l,1,1-tri-chloroethane as an impurity, must be removed. The purification may consist of a distillation of the product stream tll) from the hydrochlorinator (D). As illustrated, the first distillation (E) separates the lights (14), predominantly hydrogen chloride, and minor proportions of ethylene, vinyl chloride, ethyl chloride, and vinyli-dene chloride. The undistilled portions (bottoms) from this distillation (~) are further distilled at (F) to lS separate the l,l-dichloroethane and the cis- and trans-1,2--dichloroethylenes, stream (17). The bottoms from this still (F) are further distilled (G) to obtain l,l,l-tri-chloroethane (18) and a bottoms of higher boiling compon-ents (19) mostly ethylene dichloride, trichloroethylene, 1,1,2-trichloroethane and unsymmetrical tetrachloroethane.
The cis- and trans-dichloroethylenes, produced in small amounts in the thermal chlorinator, have boiling points such that the cis isomer is practically impossible to separate from the recycle l,l-dichloroethane by

2~ distillation. If both isomers or the cis isomer alone are allowed to remain with the recycle l,l-dichloroethane, they pass through the thermal chlorinator and hydrochlori-nator essentially unaffected, thereby continuously increasing in concentration in the recycle l,l-dichloroethane.

17,182/183/198-F -4-10519,Z9 The efficiency of the thermal chlorinator and the ferric chloride hydrochlorinator are improved if the cis- and trans-dichloroethylenes are maintained at a relatively low level by removal ~rom the recycle 1,1--dichloroethane stream (20) prior to its use in the thermal chlorinator. Two procedures are provided for this removal: one consists of separating the trans isomer by distillation and allowing the cis isomer, at the thermal chlorination temperature, to partially isomerize to a mixture consisting of approximately 60 percent cis and 40 percent trans. The trans isomer is then removed by distillation, and the remaining cis isomer can be passed to the thermal chlorinator where the partial isomerization is repeated. The other procedure is to cold chlorinate the recycle stream during its return to the thermal chlorinator and convert the cis- and trans-dichloro-ethylenes into high boiling compounds.
The recycled fraction (14) consists of any ethylene that has not reacted or which is produced in the thermal chlorination, hydrogen chloride which has not reacted in the hydrochlorinator, ethyl chloride and small amounts of vinyl chloride and vinylidene chloride.
These components are returned to the process, about 1/2 of the stream (14) represented by stream (15) providing the hydrogen chloride for the hydrochlorination of the ethylene in hydrochlorinator (A). The excess hydrogen chloride (16) is withdrawn from the process.
In an alternative procedure (see dotted lines Figure 1) in accordance with the present invention, the above principal steps are carried out with the single 17,182/183/198-F -5-10519Zg exception that the liquid (7) resulting ~rom the quench of the product effluent from the thermal chlorinator (B) is in part used as the quench liquid and in the greater part is forwarded to a boiling bed dehydrochlorinator (H) containing a Friedel-Crafts catalyst, particularly ferric chloride, and more particularly about 1000 ppm ferric chloride. The dehydrochlorination reactor (H) is operated at conditions which primarily dehydrochlorinate 1,1,1--trichloroethane to vinylidene chloride, thus permitting separation of 1,2-dichloroethane from the reaction stream.
The gaseous products (8) resulting from the dehydrochlorination in (H), (those boiling below about 60C.) are admixed with the vinyl chloride, vinylidene chloride and hydrogen chloride and any unreacted ethylene overhead fraction stream (6) from the quench tower (C) and the resulting mixture (10) introduced into the liquid hydrochlorinator (D) in which ferric chloride is the metal halide Friedel-Crafts catalyst. The high boiling materials (9) from (H) are delivered to a still (I) to recover the recyclable chlorinated materials, predominantly l,l-dichloroethane (12) which are mixed with recyclables from product finishing system (17). The remainder of this high boiling material is removed from the process (13) and may be combined with the heavies (19) from the l,l,l-trichloroethane product still (G) and these heavies either separated and/or cracked as appropriate to obtain usable higher polychlorinated hydrocar~ons.
It follows that elimination of 1,2-dichloroethane fr~m the process following its formation in the thermal chlorinator (B), as proposed in the description above, 17,182/183/198-F -6-materially reduces the severity of the purification steps to obtain the desired product, 1,1,1-trichloroethane, in a high purity.
In accordance with the present invention, about 33.9 pounds (15.4 kg.) ethylene (4.4 pounds (2.0 kg.) of which may be separated as a product of the overall process) and about 74.6 pounds (33.0 kg.) of hydrogen chloride are reacted at about 50C and about 35 psig(2.47 kg/cm2.) in the presence of aluminum chloride catalyst in a boiling bed hydrochlorinator (A) producing about 74.9 pounds (34.0 kg.) of ethyl chloride and about 30.4 pounds (13.8 kg.) excess hydrogen chloride. This is mixed together with about 21.8 pounds (9.9 kg.) ethyl chloride and about 98.9 pounds (44.8 kg.) l,l-dichloroethane obtained as products of the overall reaction. This mixture is reacted in a thermal chlorination reaction zone (B) for about two seconds at 475C. and 40 psig (2.82 kg./cm.2) with 153.7 pounds (69.8 kg.) chlorine. The resulting product stream is passed into a liquid bed hydrochlorinator reactor (D) operating at 45C. and 35 psig (2.47 kg./cm.2) where it is contacted with ferric chloride (10.4 pounds (4.72 kg.) in 50.2 pounds (22.8 kg.) of perchloroethylene)to produce, in pounds (kg.):
134.9 (61.0) HCl (hydrogen chloride) 254.39 (1.98) C2H4 (ethylene) 0.74 (0.34) C2H3Cl (vinyl chloride) 21.77 (9.85) C2H5Cl (ethyl chloride) 0-95 (0.43) 1'1-C2H2C12 (vinylidene chloride) 2.21 (1.00) t-C2H2C12 (trans-1,2-dichloroethylene) 30102.09 (46.6) 1,1-C2H4C12 (l,l-dichloroethane) 17,182/183/198-F -7-5.27 (2.39) c-C2H2C12 (ci4-1,2-dichloroethyleneJ
106.49 (48.2) 1,1,1-C2H3C13 (l,l,l-trichloroethane) 1.57 (0.71) C2HC13 ~1,1,2-trichloroethylene) 1.68 (0.76) 1,2-C2H4C12 (1,2-dichloroethane) 4.50 (2.04) 1,1,2-C2H3C13 (1,1,2-trichlorethane) 1.25 (0.57) 1,1,1,2-C2H2C14 (unsym. tetrachloroe~hane) This product stream is separated in several stills (E, F, and G) to obtain product (l,l,l-trichloro-ethane), recycle streams and heavies, of which the latter are removed from the system. The hydrogen chloride, vinyl chloride, ethyl chloride, and vinylidene chloride and any unreacted ethylene are spearated as overhead on a first still (E) and sent to the aluminum chloride hydrochlori-nator (A); the 1,1-C2H2C12, cis-1,2-C2H2C12 and trans-1,2--C2H2C12 overhead from a second still (F) are sent to the thermal chlorination reactor (B) and while enroute are chlorinated at 25C., with care being taken to exclude light or other radiation, to react the cis- and trans--dichloroethylenes to make heavies and prevent their building up in the reactors. The l,l,l-trichloroethane is product from the third still (G) and the bottoms from the third still are the heavies.
Further, to illustrate the use of the present invention in such a multi-reaction train for producing l,l,l-trichloroethane from ethylene and chlorine as the sole feeds as set forth in the drawing (Figure 1), the overall feed of ethylene of about 231.7 lb-mols/day (105 kg.-moles) and about 499.2 lb.-mols/day (226 kg.-m.) of chlorine to produce about 183.9 lb.-mols/day (83.0 kg.--m.) of l,l,l-trichloroethane, about 34.5 lb.-mols/day 17,182/183/198-F -8- `

~0519Z9 t15.6 kg.-m.) of heavies (1~2-dichloroethane, cis- and tranQ-1,2-dichloroethylenes, trichloroethylene, 1,1,2--trichloroethane and unsymmetrical tetrachloroethane).
These latter compounds, the heavies, with about 381.7 lb.-~ols/day (173 kg.-m.) of hydrogen chloride are removed from the process. Each can be employed in other processes.
To illustrate the use of dehydrochlorination step (Figure 1 dotted lines) a liquid such as would be obtained from the quench of a thermal chlorinator effluent (Stream 7, Figure 1) and anhydrous ferric chloride are fed to a 1000-cc vessel fitted with a 30--tray distillation column. The rate of take-off from the top tray of the column is adjusted such that the overhead temperature is maintained at about 40C. The temperature of the material remaining in the reboiler ranges between 62 and 78C.
At the end of 7 hours, the feed pump is shut off and the system-allowed to cool. During the 7 hour period, 418 grams of liquid and 0.5 grams FeC13 were fed. The table below shows the quantities of the various compounds fed and recovered:

17,182/183/198-F -9-105~9Z9 ~a O ~ D O u~
~ . . ~ . . . . . . . . . .
P~ ~ ~ ~ ~ ~ lo ) ~ ~ O ~5) ~ N ~
O ) ~1 ~9 ~1 S~

~ ~ ~ O ~9 0 l` ~i 1` ~ -i O 0 00 ;~ ~ l d' a o a o ~ ~ o ~ 3 ~ 3 o ~ ~
o ~ ~ o ~
a s~ ~ u ~ O ~
o o ~ I o u ~ o ~ u ~ o_l o ~rl o I ~ ~u E~ I O~u ~0 E~
I ~ ~ ~, ~q ~ _I _I ~ ~ ~ ~ ~ o _I
I U I U
1 h ~ a) ~ O
~ l U E~

17 ~182/183/198--F --10-lOSl9Z9 From the above, it is obvious that 1,1,1-trichloroethane can be converted to vinylidene chloride in high yields, thus, simplifying its separation from compounds with which it i8 admixed in the thermal chlorinator reaction product.

17,182/183/198-F -11-

Claims (4)

1. A process for preparing 1,1,1-trichloroethane comprising:
(a) reacting ethylene and hydrogen chloride, wherein the hydrogen chloride is obtained from another step in the process, in the presence of aluminum chloride catalyst to produce ethyl chloride;
(b) reacting said ethyl chloride, recycle ethyl chloride and 1,1-dichloroethane with chlorine at a temper-ature of 400°-550°C;
(c) subjecting the reaction mixture from (b) to a liquid quench, thus producing (1) a gaseous product mixture comprising hydrogen chloride, vinyl chloride, and vinylidene chloride and (2) liquid product;
(d) returning a minor portion of said liquid product to the quench zone, mixing the remaining portion of said liquid product with the gaseous product mixture formed in (c)(1), and hydrochlorinating this latter mixture to form a second product mixture comprising hydrogen chloride, ethylene, ethyl chloride, vinyl chloride, vinylidene chloride, 1,1-dichloroethane, cis- and trans-1,2-dichloro-ethylenes, 1,1,1-trichloroethane, ethylene dichloride, tri-chloroethylene, 1,1,2-trichloroethane and unsymmetrical tetrachloroethane;
(e) separating the hydrogen chloride ethylene ethyl chloride vinyl chloride and vinylidene chloride from said second product mixture;
(f) separating from the remaining portion of said second product mixture 1,1-dichloroethane and the cis- and trans-1,2-dichloroethylenes;
(g) separating 1,1,1-trichloroethane from the portion remaining after the separation in (f).

2. A process as in Claim 1 wherein the major portion of the liquid product formed in (c) (2) is dehydrochlorinatedJ thus converting the major portion of the 1,1,1-trichlorethane to vinylidene chloride, and the remainder of the product from the dehydrochlorination is distilled to recover 1,1-dichloroethane.

3. A process as in Claim 1 wherein the second product mixture formed in (d) is distilled to remove the trans-1,2-dichloroethylene, the remaining portion is returned to the thermal chlorination zone where the cis-1,2-dichloroethylene is partially isomerized to form a mixture consisting of approximately 60 percent cis-1,2-dichloroethylene and 40 percent trans-1,2-dichloroethylene, the trans-1,2-dichloroethylene is removed by distillation and the cis-1,2-dichloroethylene is returned to the thermal chlorination zone.

4. A process as in Claim 1 wherein the second product mixture formed in (d) is chlorinated in the absence of both light and a catalyst to convert the cis- and trans-1,2-dichloroethylenes to trichloro- and tetrachloroethanes and this thus-produced product mixture is returned to the thermal chlorination zone.