CA1067917A - Production of 1,2-dichloroethane with purification of dichloroethane recycle - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An improved process is provided for the production of 1,2-dichloroethane by chlorination of ethylene with chlorine in a liquid medium comprising 1,2-dichloroethane at a temperature of between 85°C.
and 160-C., and in which a stream of 1,2-dichloroethane containing a minor amount of chloroprene is available for introduction into the ethylene chlorination reaction zone, the improvement whereby introduction of chloroprene, chlorinated derivatives thereof or mixtures thereof into the ethylene chlorination reaction zone is substantially avoided. The improvement comprises subjecting the stream of 1,2-dichloroethane to a controlled prechlorination by contacting it with a chlorination agent selected from the group consisting of chlorine and aluminum chloride, wherein between 0.5 and 2 moles of chlorine chloride is utilized per mole of chloroprene, at a temperature of between 0°C. and 100°C., so as partially to chlorinate the chloroprene therein to produce one or more further chlorinated derivatives thereof; separating the further chlorinated derivatives of chloroprene from the 1,2-dichloroethane; and introducing the 1,2-dichloroethane substantially free of chloroprene or chlorinated derivatives thereof, into the ethylene chlorination reaction zone. This process provides a more efficient utilization of the chlorination agent and production of more chlorinated product.

Description

10t~'7~31'7 This application relates to an improvement in a process for production of l,2-dichloroethane by reaction of chlorine and ethylene in a liquid medium at temperatures between 85 and 160C. One process of this type if disclosed, for instance, in Canadian Patent No. 1,021,803 issued November 29, 1977. Another process of this general type is dis-closed in British patent 1,231,127 of Solvay et Cie published May 12, 1971.
In the process as described in the aforesaid Canadian Patent No. 1,021,803, the liquid medium for the chlorination reaction comprises a liquid chlorinated hydrocarbon having two carbon atoms, or mixtures of two or more such compounds. Preferably, the liquid medium comprises 1,2-dichloroethane, 1,1,2-trichloroethane, or a mixture of these two compounds.
In one embodiment disclosed in the above-identified Canadian Patent No. 1,021,803, as well as in the above-identified British patent 1,231,127, a stream of 1,2-dichloroethane recovered from the fractiona-tion section of a process for pyrolysis of 1,2-dichloroethane to produce vinyl chloride, is introduced into the chlorination reaction system. In the process of the above-identified Canadian Patent No. 1,021,803, the 1,2-dichloroethane is introduced as make-up for the circulating liquid medium. In addition, a fractionation column associsted with the chlorination reactor serves to fractionate the 1,2-dichloroethane in .
the chlorination~reactor, as well as such 1,2-dichloroethane as may be recycled from the pyrolysis process, or other sources, to remove ~impurities therefrom. The purified 1,2-dichloroethane from this fractionation column can be returned to the pyrolysis furnace.
:: ~
The dichloroethane stream being recycled from the pyrolysis .
fractionation section to the chlorination reactor often contains minor , ~ .
but signiicant amountæ of chloroprene and may also contain small amounts of other chlorinated C~ hydrocarbons. For example, this stream ", , ~,"" , ~ ,, " , , " ,,~ "~ , " ", ~- 1067917 may contain from 0.01 to 0.3 mole per cent chloroprene. This chloro-prene can polymerize further in the process, particularly in the over-head of fractionation columns, resulting in plugging of the columns and/or associated lines.
The aforesaid Canadian Patent No. 1,021,803 discloses that this polymerization can be substantially prevents by sub~ecting the recycle dichloroethane stream to a pre-chlorination step for chlorination of the chloroprene prior to introducing this recycle stream into the main chlorination reactor system. The chloroprene is converted to heavier boiling chlorinated compounds which will not polymeriæe and which are said to be separated either in the fractionation column asso-ciated with the main chlorination reactor (from the bottom of the fractionation column) or from the bottom of the chlorination reactor itself.
British patent 1,266,676 of Knapsack A.G. published March 15, 1972 discloses a process for removing products, e.g., chloroprene, from 1,2-dichloroethane in a combination process in which ethylene is first chlorinated to produce dichloroethane, the dichloroethane is cracked to produce vinyl chloride, and cracked dichloroethane can be recycled to the chlorination reactor. The chloroprene is removed from the dichloro-ethane (to prevent plugging up of equipment) by chlorinating it in the presence of ferric chloride to form a high boiler with respect to di-chloroethane, and which can be readily separated from it. The patent discloses three procedures for chlorinating the chloroprene: (a) intro-ducing the dichloroethane containing chloroprene into the main chlorina-~ .tion reactor, in which the chloroprene will be chlorinated by chlorine and ferric chloride simultaneously with the chlorination of ethylene to produce dichloroethane; (b) chlorinating at least a portion of the over-head from the light ends column to convert the chloroprene to higher ~; ~ 30 boiling compounds, and secycling the~chlorinated overhead to the column, ~ 3 ~

~0~'7~L'7 the higher boiling compounds being removed at the bottom and passed to a heavy ends column; and (c) chlorinating the overhead of the light ends column and recycling the chlorinated overhead to the column, with removal of dichloroethane as a side-stream from this column. The main chlorina-tion reactor operates at a temperature of 50C.
It has now been found that introduction of either chloroprene (as proposed in the above-identified British patent 1,266,676) or chlorinated derivatives of chloroprene (as proposed in the above-identified Canadian Patent No. 1,021,803) into a chlorination reactor operating at a temperature of above 85C., results in a loss of yield of 1,2-dichloroethane based on chlorine at temperatures above 85~C., and particularly between 85 and 160C. Surprisingly, in the main chlorina-tion reactor, the chloroprene is not merely chlorinated to the next highest boiling derivative (mainly trichlorobutenes), but is further chlorinated to form higher boiling derivatives ~hich may range up to fully chlorinated butane. Similarly, partially chlorinated derivatives of chloroprene are further chlorinated under these conditions to more highly chlorinated compounds. These more highly chlorinated compounds represent a yield loss of chlorine as they are removed from the chlorina-tion reactor as heavy ends and disposed of as waste. The above-identified Canadian Patent No. 1,021,803 suggests that up to 3 moles of chlorine per mole of chloroprene may be used in the pre-chlorination step before introducing the recycled dichloroethane through the main chlorination reactor. The use of 3 moles of chlorine per mole of chloro-prene represents an e~cessive use of chlorine in the process and, in addition, the more highly chlorinated compounds may be still further chlorinated in the main chlorination reactor, using up additional chlorine.
The introduction of the partially chlorinated recycle 1,2-dichloroethane into the fractionation column associated with the main _4 ~675~'7 chlorination reactor, rather than into the reactor itself, as suggested in the prior art, does not alleviate the situation. The partially chlorinated derivatives of chloroprene do not leave the column in the overhead or side streams; rather they pass downwards through the column, ultimately entering the chlorination reactor, and further chlorinated.
It is an ob~ect, therefore, of one broad aspect of the present invention to provide an improved process for the removal of chloroprene from 1,2-dichloroethane which is being recycled to a reactor for chlorination of ethylene at a temperature of above 85C.
An object of a further aspect of the present invention is to provide a process for minimizing chlorine losses in a process of chlorinating ethylene utilizing chlorine in which 1,2-dichloroethane is to be recycled to the reactor.
By a broad aspect of this invention, an improvement is provided in a process for production of 1,2-dichloroethane by chlorination of ethylene with chlorine in a liquid medium comprising 1,2-dichlorethane at a temperature of betwe~n 85C. and 160C., and in which a stream of 1,2-dichloroethane containing a minor amount of chloroprene is available for introduction into the ethylene chlorination reaction zone, the improvement whereby introduction of chloroprene, chlorinated derivatives thereof or mixtures thereof into the ethylene chlorination reaction zone is substantially avoided, comprlsing: (a) subjecting the stream of 1,2-dlchloroethane to a controlled prechlorination by contacting it with a chlorinatlon agent selected from the group consisting of chlorine and aluminum chloride, wherein between 0.5 and 2 moles of chIorine chloride is utilized per mole of chloroprene, at a temperature of between 0C. and 100C., so as partially to chlorinate the chloroprene therein ~o produce one~or more further chlorinated derivatives thereof; (b) separating the further chlorinated derlvatives of chloroprene from the 1,2-dichloro-ethane; and (c) introducing the 1,2-dichloroethane substantially free - 1067~7 of chloroprene or chlorinated derivatives thereof~ into the ethylene chlorination reaction zone.
In one variant, the chlorination agent is aluminum chloride, while in another varian~, the chlorination agent is chlorine.
In another variant, the chlorine utilized is introduced in an amount of 0.5 to 2 moles, preferably 0.05 ~o 1.5 and most desirably 0.95 to 1.3 moles of chlorine per mole of chloroprene.
In yet another variant, the chlorine is introduced in the form - of a gas, while in another variant,the chlorine is introduced in the form of a liquid.
By another variant, the stream of 1,2-dichloroethane further - contains a minor amount of an incompletely chlorinated C~ hydrocarbon other than chloroprene.
By yet another variant, vapor generated in the ethylene -` chlorination zone is utilized to furnish heat for the conduct of step (b), ~` the vapor being thereby condensed, and the condensed vapor recycled to the ethylene chlorination zone.
`;~ By yet another variant, heat for the conduct of step (b) is -supplied by indirect heat exchange with steam. ~ -By another vsriant, the ethylene chlorination reaction is con-ducted at 85C. to 140C., preferably at 85C. to 120C.
::
By another variant, the chloroprene chlorination reaction is conducted at a temperature of 20C. to 60C.
By another variant, the ethylene chlorination reaction is con-ducted in a circulating liquid medlum selected from the group consisting of 1,2~-dichloroethane, 1,1,2-trichloroethane and mixtures thereof.
By a variation thereof, the ethylene chlorination ~one i~
operated~at a temperature and pressure 8uch ~hat the circulating liquid medium is maintalnsd at a temperature below its boiling point in the chlorination rsactlon zone.
' :1 : : ' :

~ - 6 ~ ~ -~o~t7s~7 As mentioned above, the present invention herein can be utilized in any one of a number of processes for producing 1,2-dichloro-ethane from ethylene and chlorine at temperatures of above 85C. ~or convenience, the invention will be described in terms of its utilization in connection with a process as disclosed in the above-identified Canadian Patent No. 1,021,803.
In the accompanying drawings, Figure 1 represents the use of a process of one aspect of this invention in combination with a generalized process for chlorination of ethylene to produce 1,2-dichloroethane; and Figure 2 represents a more detailed embodiment of an aspect of this invention in combination with a process as described in the above-identified Canadian Patent No. 1,021,803.
Referring to the general flow scheme of Figure 1, ethylene in .
line 5 and chlorine in line 6 are introduced into a chlorination zone 1, which generally comprises a chlorination reactor, and which may be one of the various types as are known in the art, together with such asso-ciated fractionation equipment as may be necessary to separate the pro-ducts of this reactor into one or more fractions. At least three main fractions are recovered from the chlorination zone: a 1,2-dichloroethane fraction (stream 7), a light ends fraction, comprising primarly compon-- ents boiling ,:

: .
~ .

: -, .-.
: :~ : . .

: 30 :
~ 7 -1~6'~

below 1,2~dichlor~ ~hane (s~ream 8) and a heavy ends raction comprising primarily components boiling above 1,2-dichloroethane (stream 9). In generaL, the chlor~-lnation reactor will operate at a temperature of . 85 to about 1 60C, preferably about 85 to about 140C, and most preferably 85 to 120C. As hereto-fore mentioned, the liquid in which the chlorination reaction is cond~cted is composefl primarily o~ one or more C~ chlorina~ed hydrocarbons, preerably 1,2-1~ ~ichloroethane, 1,L,2-trichloroethane or mixtures thereof.
Some of the liquid medium ~ill be removed along with the product 1,2-diohloroethane in the fractionation sect~on associated with the chlorination reactor.
If the chlorina~ion-reactor9 for example, is :.15 located in a plan~ producing vinyl chloride ~y pyrolysis of 192-di~hloroethane, it may. be considered advantageous to recycle ?art or all of the unpyrolyæed dichloroe~hane to the chLorina~ion section for ~r~ctionation and purifi-ca~ion ~n the fraction~ting column ar columns a~sociated wlth the chlorination reactor ~his str~am of uncracked . 192-dichloroethcne wlll often contain minor amounts o chloroprene~ generally from 0.~ to 0..3 ~nole per cent `~ and may also contain as impurities mlnor amQunts of other incomplet~Ly chlorlnated C4 hydrocar~ons é~ 4 ' 25 dichlorobute~e-2. As men~ioned previouslq, ~t has been fo~md that in~crotuction of chloro2rene and/ox othex inco~-.- pletely chlorinated C4 h7drocarbons (e.g. ,part~a~ly ;chlori-nated derivatives of. chloroprene) into a chlorination zone . operating a~ 2 t~mperature of above 85C~ results in a use .
. .
.: .
_ 8 ~
;- ~ r-. ~. . .
~ ~ - . ', . .

;

'79~'7 .... .
of excess amounts of chlorine in producing highly chlorinated C4 hydrocaxbons which, in any case, must be disposed of as waste. Similarly, chlorinating the f~chloroprene in a pre-chlorination step as suggested in German patent application 2,427,045 ~ould ~150 result in additional chlorine being utilized ~o produce waste products if the products o~ this pre-chlorina~ion ~ep were introduced into the main chlorina~ion reaction zone.
0 ' According to an aspect o the invention, the unpyrolyzed 192-dichloroethane stream in line 10 is contacted ~Ji~h, a chlor;na~ing agen~ in such a m~nner as hereinafter described to convert the chloroprene by partial chlori- ~
: nation to compounds which are high boilers with respect ~ .
-. 15 ~o 1,2-dichloroethane.
The partial chlor~na~ion may:be pexform~d according to any of the processes known ln the ar~ for this purpose as long as the process empl~yed does not s~gn~fica~tly.a~fect the desired components i~ the stre~m or introduce other undesirable impuri~ies. The -p~eferred chlorina~îng agent is chlorine, which may be in~roduced i~ either the liquid or g2seous sta~e. Other ~ -chlor~nat~ng ag~nts for chlorinating chloroprene may b~
used, e:g,O alumin~m chloride. In additio~ to chlsro-prene, other C4 chlori~ted hydrocarbons present as i~purities in the 192-dichloroeth~ne may also be fur~her :-chlorin~ed i~ ~his s tep.. - . .. ; :
;. .. .. ... ..
.. . In gener ~, the partial chlorinatlon will be conduc~ed at ~emperatures of be~een 0G, nd lOQC~r .
g _ , . . .

, . ' . ' ' ' ' ' ,'.' ..' ,','.'' . ' . ,' '' ,' . ": , , '''' '.: ' ' ', ' ' ' ' "' ." ' '' "

~L067~

preferably between 20C and 6QC. At ~emperatures much over 100C., selectivity of the chlorination may be lessene~l, and some 1"2~dichioroe~hane may be-'~come further chlorina~ed. I:f chlorine is employed as the chlorinating aOent5 the chlorination may be conducted either with or without any of the knowrl chlorination catalys~s, ~- g- ferric chloride. The amount o~ chlorine used is be~7een . 0.5 and

2, preferably be~een about 0.85 and 1~75a m~lee .0 of chlorine per mole of chloroprene. Most preferred ~ ~s an amoun~ o 2bout 0.95 - 1.3 moles of chlorine per ., mole of chloroprene~ The reaction is generally con-ducted at ambient pre~sure; how~ver the pressur2 may be ~aried if desirable.
Though the de~ailed description of this aspect of ~nvention which follows is phrased in terms of partial i _. ~.
, chlorination of chloroprene with chlorine, as discussed previously other chlorination agents can be u~ilized `, în a generally similar manner.
O The partial chlorina~ion may he carried out in a separate pre-chlorina~ion zone42, or may be carried out ~y simply introd~ucing chlorine or another chlori-j .
nating agent into the 1,2-dichloroethane line 40 witho~t any special a~paratus. .The 1,2-dichloroe~hane, now con-tzirling chlorinated del:iv2tives of chloro2rene and other . C4 co~pounds (if present) is passed in li~le 13 into a distlllatio~ apparatus ~, ~7hich ma~J b~- a ~in~le pla~e . evapora~or. In apparatus 4j 1,2-dichloroethane is .
r adil~ sep~rated. ~rom chlorina~d derivatives of chloro-.~30 . ~pre~e; 1,2-dichloroethane is rem.oved. as overhead from the ; i . . ~-~ , . . .
,:
. ~ 1~._. . . ..
;~ . - . . . - .
,i. , , . - . , .
~ 1 ~l6~7~
....... ~ . . .. .. .

column and conveyed into th~ main chlorination reactor 1, via line l~. The chlorinated derivatives of chloroprene tand o ther C4 compounds i presen t) are removed as a botSoms product fxom apparatu~3 4 in line 15, and preferably are combined ~Ji~h the heavy ellds fraction from the chlori-nation zone 1, in line 9, and the combined products passed through a heavy ends/tar still 2 in which 1,2-dichloro-e~hane is removed and returned to the chlorinatio~ r~actor in line 16 . Heavy ends 9 including chlorinated derivatives 10 of chloroprene, are removed. from the tar still i~ line 17 and passed to waste disposal or recovery.
Re~erring now ~o Figure 2, the chlorination re-actor 20 ~s preferably composed of a c~rcula~ing loo~p re-ac~or haviag a down leg ~1, up leg 23" a~d cro~s-o~rer legs 22 and 24. Chlor~nation reactor 20 i~ gen~rally shown schematically as beir.g s~ilar ~o Figure 2 o German appli-catio~ 2,~ ,045; however, any of the co~a~tructions d~s-.
closed ~n that application and any equi~Jalen~ constructions kno~Jn in ~he art may be ut~ l~zed., Chlorine iTl 1 ine 25 2û and ethylen~ in 1 ine 26 are intro~uced into ~he reactor a~ appropriate points . The reac~or 20 contains . a cir culatin~ liq~id medium which ~a~ be 1,2-dichloroe~llane9 1,1,2-tr~ch~oroethaneg or mixtures ther~of, and cont~ining an approp~i~te catalys~, ~or example~ f~rric chloride~
~s disclosed in the said German ?ate~t a~plication, ~hero is preerabl~ a slig~ exress o eth;rle;le over and above - the a~ount req~ e~ to react uith the chlorine; how~ver~
chlorine m~r be present in a sma~l excess. Temperztures Qf ~he chlorina~io~ re2c~0r ar~ those at which ~he clrcu- .
lat~ng liquid medi-~ does not vaporize in the reac~;o~t :

^, ~ - 11 ~

' 7~
zone under the conditions e~ployed. In general, the temperature is maintained at bet~7een 8-5Co ~nd 180C., Dreerabl~ 851,. to 160C., under I suficient s~s~em 2ressure so that the 1,2-dichloro-e~hane liquid medium (which nonmally boils at about 83.5C.) will not vapoxize in ~he ~eaction zone 20.
.- The pressures employed may va~ considerably provided they ara suf~icient ~o prevent vaporization of the 1~2-dichloroe~h2ne at the temperature o the reac~ion zone.
Associated wi~h the chlorination reactor 20 is fractionation or d~stillation column 30 ~Jhich is used ~o fractionate the products of the chlorination re~ction - as ~ell as ~her substances as disc:ussed belo~J. A
- pressure diferential ~-s maintained be~Jeen the chlori-.. 15 nat~on zone 20 and the~ ractionation column 30 such that a~ the tem~e~atures employed, the heat o xeaction of ~:he c~lorination: of ethy~ene is u~il~ed ~o vaporize a portion.
o ~he circula~ing liq~id ~edium in ~}:2e fract~ona~ion zone in or~er to ~onduct a :~raction~tion of the l~qu~d mediu~, reaction products and unreacted startinO materials. The frac~io~ion zone produces a light ends ~raction 29 as . overhe~d.. The light ends ~raction in line 29 can b~ sent ~o ~urther fraction2tion (not sh~wn) to recover 1~2-: dichloroe~hane and light hydrocarbons~ A side s~ream 28 .
. 25 is withdr2T.~r.3 comprising 1"2 dichlor~ethane ?roduct o the chlorina~ion reac tion, ~Jhich,, in a plan~ for production of . ; ~ :
vingl chloride9 is most advantageously.c~rLve~J~d ~b the cracking s~ep to be pyrolyzed. Heavy ends~ tha~ is, com-. pone~ hoiling :hi~,her than 17 2-dichloroethan~, are re - .

~0~'7?17..... .

turned from the bottom o the fractionation column in~o the chlorination reac~or and eventually removed from this reactor in line 27.
: A stream o 1,2-dichloroethane, recovered from the frac~ionation sect:ion o~ a pyrclysis u'nit, which may be ln the same plant or in another plan~, an~ containing -minor amounts of chloroprene and possi~ly other incompletely chlorinated C4 hydrocarbons enters the system in line 40 ~
and is contacted ~h chlorine (o~ another chlorination age~) introduced in line 41. As in Figure 1, ~h~ chlorine may be mixed with the dichloroethane in a pre-chlorination . zone 42, or the chlorine may s~ply be introduced into line 40 and mixed ~1ith the dichloroethane in ~he line. The d~chloroeth~ne stream5, a~ter contact w~th ~he chlorine, 1~ is passed thxough line 44, preferably m~xed wi~h recycle , in line 45 and introduced into distilla~ion ~P2ar tus 45.
Apparatus 45 may be a singl~-plate evapora~or or may be more compl~cated s~s~mO The products leave app2ratu~
45 in overhead line 47 and are separa~ed in a ~ ocl~-out d~ ~8 into liquid and gaseo~--s products. Tie Oaseous products com?rise substantially ?uri~ied 1~2-dichloro-ethane containing littLe or no chloropre~e or chlo*inated .~, .
derivat~ves thereof. I~sis Oas~ous pr~duct is conveyed hrou h ~:ine 49 in~o a condenser 49a. and then into a liquid-gas separator 52J ~ich is opera~ed at atmospheric : pressure9 ~ith~gaseous products vented ~hrough line 5~a, , : and the ~iquid product, containing primarily 1,2-dic~1~ro-ethane, is introduced in~ rractiona~ion column 30 thro~h : li~e:53. If de~ired, a.portion of th~s dichloroethane ~0 ma~ be ta~en off in Line S~ a~d combîned ~ith the dichloro . - . ~ , ~ e~ha~e product or the colum~ in ~ine 289 and ~he combined ;~ . ' . .

~a~7~3fl~7 - dichloroe thane s treams forwarded to the pyrolysis unit O
The liqllid product from knockout drum 48 is removed in line 503 a portion o~ it returned to distilla~ion apparatus 45 in line 46, and the remainder passed through line 51, pre~erably combined with heavy ends frorn the chlorination reactor in line 27, and introduced in~ tar still 32~ 192-diehloroethane contained in streams 27 and 51 is removed by distillation of the combined heav~ ends stxeam. This .
d~chloroe thane is returned to the chlorination zone in . line 34 . ~lea~r ends are removed from the tar s till in lin~
36 and passed ~o waste disposal or~or f~rther processingO
In one embodimentg ~e heat utilized to conduct ~he separation in distillation azpara~us 45 is supplied by reaction heat from the chlorination reactor 20. Th~s ~5 is most advantageously perfsnmed by heat exchange with ; a ~apor dra~ off fr~m the top of the chlorination reactor i~ line 559 ~ntroduced in indire~t heat exchange ; - with the combined ~eeds Co the dis~iLlation col~mn 45, recover d as a li~uid and returned i~ 1~ne 5~ to the :~20 chlorination reactor. ~lternatively3 ~hè heat for oper-ation of the dis~illation eolumn 4$ ca~ be whol~y or `: partly suppl~ed by steam or any other hi~h temperature gas which is cooled or co~ldensed in ~ndirect heat exchange . . . .
with the zroduc ts being dis tilled in the colurnn O
The heav~ ends removed in ~n~3s 50 and 51 com-pr~se chlorinated derivatives of chloroprene and/or such other C4 hydroc~rbons a~ may be present, toget~er with i ~2-dichloroe~hane . 95% of the chloropre;le ~rld such other chlorina~ed hydroearbons as r;lay be oriOinally presen t i;l ~he dichloroe thane s tream in lille 40 are re-.
4 ~ . :

., .

moved by the combination o~ partial chlorination and - dis~illation . The vapor produc ts from distillation apparatus 45 in line 49 c~mprise be~7een about 90 and ; abou~ 98% of ~he stream introd~lced in line 40; thus the stream in line 51 cont2ilning chlorin~ted ~rivatives o4 chlo~oprene and s~milar compounds comprises abou~
2 ~o 10% of the original 1,2-dich~oroe~hane streæm in line 40.
As is known in ~he ar~, processes conducted lQ . similar to Figures L and 2 ~Jill utilize pumps, compressors, hea~ exchangers and similar apparatus which are not : - ~hn~n in these diagr~ms.
The follow~ng ex&mples present comparative . data on ~hQ operation of a process as described in ~igure 2 and as described in ~he Genman patQnt application~

~ (Prior Art) - Th~s e~ample shows ~he operation of the process as sho~ in Figure 1 of German patent application 2,4~7,045, in which the rec7cle dic~loroet'n2;le in line 40`is con-- tac~ed w~h chlorine, snd t7.-le produc~s are introduced into the chlorination reactor 20.
Rec~cle 1,2-dichloroethane containing 2700 ppm r chioropreDe was partiall~ chlorinated ~lsing L.~0 ~oles o~
ch~orine ?er mole o~ chloroprene (0.0246 l~ chlorine/
- gallon o~ dichloroethanQ) i The rec.ction ~.7as carried out- 25 ~t a~bie;lt temperature ( 20C) by c~rc~lating th~ dichloro-~thane by means OT a pumE~ and injecting ~h_ chlorine zs a .. ..
gzs into the p~p dischar~e. At the cr:mpletion OI ~he ;. ~ . .
chlorine add~ tion, ~he chloroprene concen~ration was l"s5 than 10 ppm.

, ~0~'753~ 7 The partially chlorinated recycle dichloroethane was fed to the distillation column 30 of the chlorinator 20 at a rate of 20 gallons/
hour. The chlorinator was operated at the following conditions:

, C2H4 Feed rate 534 g moles/hr 2 4/ 2 Ratio 1.05 % Oxygen in Chlorine 1.0%
Pressure at Top of Reactor 11 PSIG
Reaction Temperature 111C Maximum The hydrogen chloride generation rate was 19 g moles/hour. Material balances over the chlorinator gave the following results:
moles of 1,2-dichloroethane produced/mole of chlorine - fed = 0.958 of the ethylene reacted, 99.1% was converted to 1,2-dichloroethane Thus, the yield of 1,2-dichloroethane was 95.8%, based on total chlorine feed (to both the partial chlorinator and the main chlorinator).
; Exam~le 2 This E~ample shows results obtained utilizing the process of an aspect of the present invention, in which the partial chlorination of the chloroprene is carried out with chlorine, and the chlorinated derivatives of `; chloroprene are separated from the 1,2-dichloroethane prior to its introduc-, tion into the chlorlnation reactor 20.

.' .
, :~" ~ ' `i, ~
., .

, . . .

'7~7 Recycle 1,2-dichloroethane was partially chlorinated using the procedure outlined in Example 1. The recycle originally contained 1130 ppm chloroprene. By reaction with 1.10 moles of chlorine/mole of chloroprene (0.0103 lb. chlorine/gallon of dichloroethane), the chloroprene content was reduced to less than 10 ppm.
~ The partially chlorinated recycle dichloroethane was fed to a - single plate distillation unit operating at atmospheric pressure and a pot temperature of 85C. Of the feed to the unit, 95% was taken off as a distilled product and 5% was removed as a heavy ends stream. The distilled product was condensed and collected and fed to the chlorinator 20 as described in Example 1.
The chlorinator was operated as described in Example 1. The hydrogen chloride generation rate was 5 g moles/hour. Material balances gave the following results:
- moles of EDC produced/mole of chlorine fed = 0.986 of the ethylene reacted, 99.2% was converted to 1,2-dichloroethane .! Thus, the yield of 1,2-dichloroethane was 98.6% based on total chlor~ne fed 1 to both the partial chlorinator and the main chlorinator.
- Operation utilizing the principle of aspects of the present invention, :, in a typical plant producing about l billion pounds of vinyl chloride per year, will result in a saving of chlorine of 17.5 milIion pounds per year.
.~., .
. . .

'':
.. ..

,.., -i :.~

~ - 17 -.., `

Claims (16)

The embodiments of the invention in which an exclusive prop-erty or privilege is claimed are defined as follows:

1. In a process for production of 1,2-dichloroethane by chlorination of ethylene with chlorine in a liquid medium comprising 1,2-dichloroethane at a temperature of between 85°C. and 160°C., and in which a stream of 1,2-dichloroethane containing a minor amount of chloro-prene is available for introduction into the ethylene chlorination reac-tion zone, the improvement whereby introduction of chloroprene, chlorin-ated derivatives thereof or mixtures thereof into the ethylene chlorina-tion reaction zone is substantially avoided, comprising:
(a) subjecting the stream of 1,2-dichlorethane to a controlled prechlorination by contacting it with a chlorination agent selected from the group consisting of chlorine and aluminum chloride, wherein between 0.5 and 2 moles of chlorine chloride is utilized per mole of chloroprene, at a temperature of between 0°C. and 100°C. so as partially to chlorinate the chloroprene therein to produce one or more further chlorinated derivatives thereof;
(b) separating said further chlorinated derivatives of chloroprene from the 1,2-dichloroethane; and (c) introducing the 1,2-dichloroethane substantially free of chloroprene or chlorinated derivatives thereof, into the ethylene chlorination reaction zone.

2. A process according to claim 1 in which the chlorination agent is aluminum chloride.

3. A process according to claim 1 in which the chlorination agent is chlorine.

4. A process according to claim 3 in which the amount of chlorine introduced into step (a) is from 0.85 to 1.5 moles of chlorine per mole of chloroprene.

5. A process according to claim 3 in which the amount of chlorine introduced into step (a) is between 0.95 and 1.3 moles of chlorine per mole of chloroprene.

6. A process according to claim 3 in which the chlorine is introduced into step (a) in the form of gas.

7. A process according to claim 3 in which the chlorine introduced into step (a) in the form of liquid.

8. A process according to claim 1 in which the stream of 1,2-dichloroethane further contains a minor amount of an incompletely chlorinated C4 hydrocarbon other than chloroprene.

9. A process according to claim 1 in which vapor generated in the ethylene chlorination zone is utilized to furnish heat for the conduct of step (b), the vapor being thereby condensed, and the condensed vapor recycled to the ethylene chlorination zone.

10. A process according to claim 1 in which heat for the con-duct of step (b) is supplied by indirect heat exchange with steam.

11. A process according to claim 1 in which the ethylene chlori-nation reaction is conducted at a temperature between 85°C. and 140°C.

12. A process according to claim 1 in which the ethylene chlorination reaction is conducted at a temperature between 85°C. and 120°C.

13. A process according to claim 1 in which step (a) is con-ducted at a temperature of between 20°C. and 60°C.

14. A process according to claim 1 in which the chlorination agent comprises chlorine and a chlorination catalyst.

15. A process according to claim 1 in which the ethylene chlorination reaction is conducted in a circulating liquid medium selected from the group consisting of 1,2-dichloroethane, 1,1,2-tri-chloroethane and mixtures thereof.

16. A process according to claim 15 in which the ethylene chlorination zone is operated at a temperature and pressure such that the circulating liquid medium is maintained at a temperature below its boiling point in the chlorination reaction zone.