Production of ethylene dichloride by direct chlorination and production of vinyl chloride monomer using chlorine recycle and apparatus

A process and a system uses a direct chlorination reactor for producing ethylene dichloride by direct chlorination, without the need for an oxychlorination unit. This ethylene dichloride may be used to make vinyl chloride monomer. In the process for making ethylene dichloride, ethylene and chlorine are both supplied to a direct chlorination reactor. The ethylene reacts with the chlorine to form ethylene dichloride. Chlorine is supplied to the direct chlorination reactor from an electrochemical cell which converts anhydrous hydrogen chloride to dry chlorine gas. This chlorine gas is purified and liquefied to form liquid dry chlorine, and the liquid dry chlorine is recycled to the direct chlorination reactor. The ethylene dichloride may be pyrolyzed to produce vinyl chloride monomer and anhydrous hydrogen chloride.

This application claims the priority benefit of U.S. Provisional 
Application 60/009,515, filed Dec. 28, 1995. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process and a system for producing 
ethylene dichloride by direct chlorination, and for producing vinyl 
chloride monomer from this ethylene dichloride using chlorine recycle. 
2. Description of the Related Art 
Ethylene dichloride (EDC) has value as a chemical intermediate. See 
Riegel's Handbook of Industrial Chemistry, Seventh Edition, Van Nostrand 
Reinhold Company, pp. 783-785. Most of the EDC produced goes into the 
manufacture of vinyl chloride monomer (VCM). Vinyl chloride monomer, 
CH.sub.2 .dbd.CHCl, by virtue of the wide range of applications for its 
polymers in both flexible and rigid forms, is one of the largest commodity 
chemicals in the United States and is an important item of international 
commerce. See Kirk Othmer, Encyclopedia of Chemical Technology, Third 
edition, Volume 23, pp. 865-866 (1983). For instance, vinyl chloride 
monomer is used to make poly(vinyl chloride). 
Hydrogen chloride (HCl), in either anhydrous form or aqueous form (also 
referred to as hydrochloric acid), is a reaction by-product of many 
manufacturing processes which use chlorine. For example, chlorine is used 
to manufacture polyvinyl chloride, isocyanates, and chlorinated 
hydrocarbons/fluorinated hydrocarbons, with hydrogen chloride as a 
by-product of these processes. Because supply so exceeds demand, hydrogen 
chloride, or hydrochloric acid, often cannot be sold or used, even after 
careful purification. Shipment over long distances is not economically 
feasible. Discharge of the chloride ions or the acid into waste water 
streams is environmentally unsound. Recovery and feedback of the chlorine 
to the manufacturing process is the most desirable route for handling the 
HCl by-product. 
Direct chlorination is a known process for making VCM. However, this 
process does not recover and feed the chlorine back to the VCM 
manufacturing process, and therefore, it is not used commercially. Because 
of the environmental considerations which make recovering and feeding 
chlorine back to a manufacturing process which uses chlorine particularly 
desirable, a balanced process using an oxychlorination process has been 
developed to make vinyl chloride from ethylene dichloride. In a typical 
plant producing vinyl chloride from ethylene dichloride, HCl is produced 
through pyrolysis of ethylene dichloride, and all the HCl produced in this 
pyrolysis is normally used as the feed for oxychlorination. In this 
process, EDC production is about evenly split between direct chlorination 
and oxychlorination, and there is no net production or consumption of HCl. 
A plant, or system, employing a currently used balanced oxychlorination 
process for ethylene-based vinyl chloride production is illustrated in the 
block flow diagram of FIG. 1. The plant is shown generally at 10. Plant 10 
includes a direct chlorination reactor as shown at 12 in FIG. 1. A first 
inlet feed line 14 as shown in FIG. 1 feeds ethylene (C.sub.2 H.sub.4) to 
the direct chlorination reactor. A second inlet feed line 16 feeds 
chlorine (Cl.sub.2) to the direct chlorination reactor. The ethylene and 
the chlorine are reacted in the reactor to produce ethylene dichloride 
(EDC). The EDC is sent through a line 17 to an ethylene dichloride (EDC) 
purification unit 18. 
The EDC purification unit purifies the ethylene dichloride, and light and 
heavy ends, which are a by-product of this purification, are released 
through a line 20 as shown in FIG. 1. Plant 10 also includes an ethylene 
dichloride (EDC) pyrolysis unit 22 as shown in FIG. 1. The purified EDC is 
delivered to the pyrolysis unit through a line 21. The pyrolysis unit 
pyrolyzes the ethylene dichloride to produce vinyl chloride monomer (VCM) 
and essentially anhydrous hydrogen chloride, which are both sent to a 
vinyl chloride monomer (VCM) purification unit 24 through a line 23 as 
shown in FIG. 1. The VCM purification unit separates the VCM and the 
essentially anhydrous hydrogen chloride. The VCM is sent through a line 26 
for further purification. A portion of the EDC is unreacted in the 
pyrolysis unit, and may be recycled back to the EDC purification unit from 
the VCM purification unit through a line 28. The essentially anhydrous 
hydrogen chloride is sent through a line 30 as shown in FIG. 1 to an 
oxychlorination reactor 32. Oxygen is added to the oxychlorination reactor 
through a line 34 as shown in FIG. 1. In addition, ethylene (C.sub.2 
H.sub.4) from first inlet feed line 14 is added to the oxychlorination 
unit through a line 36. Crude EDC, which has many impurities, and water 
are formed in the oxychlorination reactor, which are sent through a line 
38 to an ethylene dichloride (EDC) dryer 40 as shown in FIG. 1. The EDC is 
dried in the EDC dryer, and the water resulting from this drying is 
released from the EDC dryer through a line 42. The crude EDC from the EDC 
dryer is sent through a line 44 back to the EDC purification unit. 
Ethylene dichloride made from the oxychlorination process is generally less 
pure (.about.93 wt. % yield) than EDC produced by direct chlorination and, 
thus, is usually washed with water and then with caustic solution to 
remove water-extractable impurities. In contrast, direct chlorination 
generally produces EDC with a purity greater than 99.5 wt. % and, except 
for removal of the catalyst used in the formation of ethylene dichloride, 
such as ferric chloride, little further purification is necessary. 
Moreover, compared with direct chlorination, the oxychlorination process 
is characterized by higher capital investment and higher operating costs 
and less pure EDC product. However, the use of the oxychlorination process 
is dictated by the need to consume the HCl generated in EDC pyrolysis. 
Therefore, there exists a need to develop a system and a process for 
producing EDC by direct chlorination. Such a system and process could be 
used to make a wide variety of products from the EDC, including, in 
particular VCM. The VCM manufacturing process produces anhydrous hydrogen 
chloride (AHCl), which is difficult to dispose of, as noted above. 
Therefore, the need also exists to develop a system and a process for 
producing VCM which is able to use the AHCl from this process and recycle 
the chlorine from this AHCl back to the VCM manufacturing process. 
SUMMARY OF THE INVENTION 
The present invention solves the problems of the prior art by providing a 
process and a system for manufacturing EDC by direct chlorination. This 
EDC may be used in a process for making VCM which recycles chlorine to the 
VCM manufacturing process and which eliminates the need for an 
oxychlorination unit or an EDC dryer. This results in less capital 
investment and lower operating costs in producing EDC or VCM as compared 
to processes and systems of the prior art. 
Moreover, since the process and the system of the present invention produce 
EDC by direct chlorination alone, and not by oxychlorination, the EDC 
produced by the present invention is much cleaner, i.e., it has much less 
light and heavy ends, than that produced by the prior art. This results in 
a much purer product (i.e., purity greater than 99.5 wt. %, as opposed to 
about 93 wt. % for oxychlorination). In addition, less processing is 
necessary to achieve this purer product. Furthermore, by producing much 
purer EDC, the process and system of the present invention reduce the 
formation of undesirable by-products and thus the cost of disposal of such 
by-products. 
In addition, the oxychlorination process of the prior art consumes oxygen, 
thus adding expense to the process. In contrast, the process and the 
system of the present invention produce hydrogen, a valuable commodity, 
thereby increasing the profitability of making EDC or VCM. 
Thus, for all these reasons, the process and system of the present 
invention are more economical than processes and systems of the prior art 
for producing EDC or VCM. In addition, the process and system of the 
present invention are more environmentally acceptable than prior art 
processes and systems for manufacturing VCM, since they minimize or 
eliminate the environmental problems associated with the disposal of 
undesirable by-products in the VCM manufacturing process, such as 
anhydrous hydrogen chloride. 
To achieve the foregoing solutions, and in accordance with the purposes of 
the invention as embodied and broadly described herein, there is provided 
a system for producing ethylene dichloride from chlorine gas produced by 
the electrochemical conversion of anhydrous hydrogen chloride, comprising: 
a direct chlorination reactor; a first inlet supply line for supplying 
ethylene to the direct chlorination reactor; a second inlet supply line 
for supplying chlorine to the direct chlorination reactor, wherein the 
ethylene and the chlorine react in the direct chlorination reactor to 
produce ethylene dichloride; and an electrochemical cell including means 
for oxidizing anhydrous hydrogen chloride to produce dry chlorine gas and 
protons, an anode chamber disposed adjacent the oxidizing means, 
anode-side inlet means disposed in fluid communication with the anode 
chamber for introducing the anhydrous hydrogen chloride to the oxidizing 
means and anode-side outlet means also disposed in fluid communication 
with the anode chamber for discharging the chlorine gas, 
cation-transporting means for transporting the protons therethrough, 
wherein the oxidizing means is disposed in contact with one side of the 
cation-transporting means, means for reducing the transported protons, 
wherein the reducing means is disposed in contact with the other side of 
the cation-transporting means, a cathode chamber disposed adjacent the 
reducing means, cathode-side inlet means disposed in fluid communication 
with the cathode chamber for introducing a fluid to the other side of the 
cation-transporting means and cathode-side outlet means also disposed in 
fluid communication with the cathode chamber; a purification unit for 
liquefying the chlorine gas to liquid dry chlorine; and a recycle line 
connected to the outlet means at one end thereof and to the second inlet 
supply line at the other end thereof for recycling the liquid dry chlorine 
to the direct chlorination reactor. 
Further in accordance with the purposes of the invention, there is provided 
a system for producing vinyl chloride monomer from chlorine gas produced 
by the electrochemical conversion of anhydrous hydrogen chloride, 
comprising: a direct chlorination reactor; a first inlet supply line for 
supplying ethylene to the direct chlorination reactor; a second inlet 
supply line for supplying chlorine to the direct chlorination reactor, 
wherein the ethylene and the chlorine react in the direct chlorination 
reactor to produce ethylene dichloride; a pyrolysis unit for pyrolyzing 
the ethylene dichloride to produce vinyl chloride monomer; and an 
electrochemical cell including means for oxidizing anhydrous hydrogen 
chloride to produce dry chlorine gas and protons, an anode chamber 
disposed adjacent the oxidizing means, anode-side inlet means disposed in 
fluid communication with the anode chamber for introducing the anhydrous 
hydrogen chloride to the oxidizing means and anode-side outlet means also 
disposed in fluid communication with the anode chamber for discharging the 
chlorine gas, cation-transporting means for transporting the protons 
therethrough, wherein the oxidizing means is disposed in contact with one 
side of the cation-transporting means, means for reducing the transported 
protons, wherein the reducing means is disposed in contact with the other 
side of the cation-transporting means, a cathode chamber disposed adjacent 
the reducing means, cathode-side inlet means disposed in fluid 
communication with the cathode chamber for introducing a fluid to the 
other side of the cation-transporting means and cathode-side outlet means 
also disposed in fluid communication with the cathode chamber; a purifier 
for liquefying the chlorine gas to liquid dry chlorine; and a recycle line 
connected to the outlet means at one end thereof and to the second inlet 
supply line at the other end thereof for recycling the liquid dry chlorine 
to the direct chlorination reactor. 
Further in accordance with the purposes of the invention, there is provided 
a process for producing ethylene dichloride from chlorine gas produced by 
the electrochemical conversion of anhydrous hydrogen chloride, comprising 
the steps of: supplying ethylene to a direct chlorination reactor; 
supplying chlorine to the direct chlorination reactor, wherein the 
ethylene reacts with the chlorine in the direct chlorination reactor to 
form ethylene dichloride; supplying anhydrous hydrogen chloride to an 
anode-side inlet of an electrochemical cell, wherein the electrochemical 
cell comprises a cation-transporting membrane, an anode disposed in 
contact with one side of the membrane and a cathode disposed in contact 
with the other side of the membrane; applying a voltage to the 
electrochemical cell so that the anode is at a higher potential than the 
cathode, and so that the anhydrous hydrogen chloride is oxidized at the 
anode to produce chlorine gas and protons, the chlorine gas is released 
from the cell, the protons are transported through the cation-transporting 
membrane of the cell, and the transported protons are reduced at the 
cathode of the cell; liquefying the chlorine gas to liquid dry chlorine; 
and recycling the liquid dry chlorine back to the direct chlorination 
reactor to produce ethylene dichloride. 
Further in accordance with the present invention, there is provided a 
process for producing vinyl chloride monomer from chlorine gas produced by 
the electrochemical conversion of anhydrous hydrogen chloride, comprising 
the steps of supplying ethylene to a direct chlorination reactor; 
supplying chlorine to the direct chlorination reactor, wherein the 
ethylene reacts with the chlorine in the direct chlorination reactor to 
form ethylene dichloride; pyrolyzing the ethylene dichloride to produce 
vinyl chloride monomer and anhydrous hydrogen chloride; supplying the 
anhydrous hydrogen chloride to an anode-side inlet of an electrochemical 
cell, wherein the electrochemical cell comprises a cation-transporting 
membrane, an anode disposed in contact with one side of the membrane and a 
cathode disposed in contact with the other side of the membrane; applying 
a voltage to the electrochemical cell so that the anode is at a higher 
potential than the cathode and so that the anhydrous hydrogen chloride is 
oxidized at the anode to produce chlorine gas and protons, the chlorine 
gas is released from the cell, the protons are transported through the 
membrane of the cell, and the transported protons are reduced at the 
cathode of the cell; liquefying the chlorine gas to liquid dry chlorine 
and recycling the chlorine gas back to the direct chlorination reactor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Reference will now be made in detail to the present preferred embodiments 
of the invention as illustrated in the accompanying drawings. 
In accordance with the present invention, there is provided a system for 
producing ethylene dichloride from chlorine gas produced by the 
electrochemical conversion of anhydrous hydrogen chloride. The system of 
the present invention is shown generally at 100 in FIG. 2. This 
electrochemical conversion directly converts essentially anhydrous 
hydrogen chloride to dry chlorine gas. The term "direct" means that the 
electrochemical cell obviates the need to convert the essentially 
anhydrous hydrogen chloride to aqueous hydrogen chloride before 
electrochemical treatment. By "anhydrous", or "essentially anhydrous", is 
meant that the hydrogen chloride is molecular in form, as opposed to 
aqueous hydrogen chloride, which is ionic in form. 
The ethylene dichloride can be used to make various products. An example of 
such a product is vinyl chloride monomer, as will be described below. In 
addition, ethylene dichloride made by the present invention can be 
chlorinated to mainly tetrachloroethane; catalytic dehydrochlorination of 
the tetra gives trichloroethylene. With different chlorination conditions, 
mainly pentachloroethane can be formed, and with dehydrochlorination, 
perchloroethylene can be formed. Another modification of EDC chlorination 
is to adjust the conditions to maximize 1,1,2-trichloroethane as the 
product. This product, when dehydrochlorinated gives vinylidene chloride 
(1,1-dichloroethylene), a monomer used in a growing number of plastic 
polymers. This vinylidene chloride can be hydrochlorinated to methyl 
chloroform. The EDC produced by the present invention can also be used as 
a lead scavenger, or to produce ethylene amines. 
System 100 includes a direct chlorination reactor as shown at 102 in FIG. 
2. Direct chlorination of ethylene to ethylene dichloride is conducted by 
mixing ethylene and chlorine in direct chlorination reactor 102. A first 
inlet supply line 104 as shown in FIG. 2 supplies ethylene (C.sub.2 
H.sub.4) to the direct chlorination reactor. A second inlet supply line 
106 supplies liquid dry chlorine (Cl.sub.2) to the direct chlorination 
reactor. The ethylene and the chlorine react in the reactor to produce 
ethylene dichloride. The equation for this direct chlorination reaction is 
given by: 
EQU C.sub.2 H.sub.4 +Cl.sub.2 .fwdarw.C.sub.2 H.sub.4 Cl.sub.2 (1) 
Ferric chloride is a highly selective and efficient catalyst for this 
reaction and can be used with the present invention, although other 
catalysts may be used. It should be noted that the feeding of the ethylene 
and the chlorine may be simultaneous, or may be slightly spaced apart in 
time, as long as the conditions in the reactor are proper for the direct 
chlorination reaction to occur. 
By-products contained in EDC from the direct chlorination reaction and the 
ethylene dichloride pyrolysis as described above must be removed. The 
ethylene dichloride used for pyrolysis to vinyl chloride must be of high 
purity because the pyrolysis of ethylene dichloride is exceedingly 
susceptible to inhibition and fouling by trace quantities of impurities. 
It must also be dry (no separate water phase and very little total 
dissolved water) to prevent excessive corrosion downstream of the 
pyrolysis unit. Therefore, the system of the present invention may also 
include an ethylene dichloride (EDC) purification unit. Such an EDC 
purification unit is shown at 108 in FIG. 2. The EDC is delivered to the 
EDC purification unit through a line 107. The EDC purification unit 
purifies the ethylene dichloride. Light and heavy ends are a by-product of 
this purification. These light and heavy ends are released through a line 
110 as shown in FIG. 2. The purified EDC is sent through a line 111 for 
further processing, such as making VCM. Since the EDC produced by the 
present invention is much cleaner than that produced by the 
oxychlorination process of the prior art, the EDC purification unit of the 
present invention is much smaller than that of the oxychlorination 
process, thus reducing capital and operating costs. 
Essentially anhydrous hydrogen chloride, which is the by-product of an 
unrelated process, is sent via a line 116 as shown in FIG. 2 to an 
electrochemical cell which directly produces essentially dry chlorine gas. 
Such a cell is shown at 200 in FIGS. 2 and 3. The electrochemical cell of 
the present invention includes means for oxidizing the anhydrous hydrogen 
chloride to produce chlorine gas and protons. The oxidizing means 
comprises an electrode, or more specifically, an anode 204 as shown in 
FIGS. 3 and 3A. The oxidizing means oxidizes the anhydrous hydrogen 
chloride, which is molecular in form, to essentially dry chlorine gas and 
protons. This reaction is given by the equation: 
##STR1## 
The electrochemical cell of the present invention also comprises an anode 
chamber disposed adjacent the oxidizing means. An anode chamber is shown 
at 203 in FIGS. 3 and 3A disposed adjacent, meaning next to or near, the 
oxidizing means, or anode. The electrochemical cell of the present 
invention comprises anode-side inlet means disposed in fluid communication 
with the anode chamber for introducing the anhydrous hydrogen chloride to 
the oxidizing means. The inlet means comprises an anode-side inlet 202 as 
shown in FIG. 3. Anhydrous hydrogen chloride, which is a gas, is 
designated by AHCl in FIGS. 2-4. The electrochemical cell of the present 
invention also comprises anode-side outlet means also disposed in fluid 
communication with the anode chamber for discharging the chlorine gas. The 
anode-side outlet means comprises an anode-side outlet 206 as shown in 
FIG. 3. A portion of the anhydrous hydrogen chloride may be unreacted, and 
this unreacted portion leaves the electrochemical cell through the 
anode-side outlet, along with the essentially dry chlorine gas. Since 
anhydrous HCl, which is corrosive, is carried through the anode-side 
inlet, and chlorine gas is carried through the outlet, the inlet and the 
outlet may be lined with a copolymer of tetrafluoroethylene with 
perfluoro(alkyl)-vinyl ether, sold under the trademark TEFLON.RTM. PFA 
(hereinafter referred to as by E. I. du Pont de Nemours and Company of 
Wilmington, Del. (hereinafter referred to as "DuPont"). 
The electrochemical cell of the present invention also comprises 
cation-transporting means for transporting the protons therethrough, 
wherein the 10 oxidizing means is disposed in contact with one side of the 
cation-transporting means. Preferably, the cation-transporting means is a 
cation-transporting membrane 208, where the anode is disposed in contact 
with one side of the membrane as shown in FIGS. 3 and 3A. More 
specifically, membrane 208 may be a proton-conducting membrane. In the 
present invention, the membrane acts as the electrolyte. The membrane may 
be a commercial cationic membrane made of a fluoro- or perfluoropolymer, 
preferably a copolymer of two or more fluoro or perfluoromonomers, at 
least one of which has pendant sulfonic acid groups. The presence of 
carboxylic groups is not desirable, because those groups tend to decrease 
the conductivity of the membrane when they are protonated. Various 
suitable resin materials are available commercially or can be made 
according to the patent literature. They include fluorinated polymers with 
side chains of the type --CF.sub.2 CFRSO.sub.3 H and --OCF.sub.2 CF.sub.2 
CF.sub.2 SO.sub.3 H, where R is an F, Cl, CF.sub.2 Cl, or a C.sub.1 to 
C.sub.10 perfluoroalkyl radical. The membrane resin may be, for example, a 
copolymer of tetrafluoroethylene with CF.sub.2 .dbd.CFOCF.sub.2 
CF(CF.sub.3)OCF.sub.2 CF.sub.2 SO.sub.3 H. Sometimes those resins may be 
in the form that has pendant --SO.sub.2 F groups, rather than --SO.sub.3 H 
groups. The sulfonyl fluoride groups can be hydrolyzed with potassium 
hydroxide to --SO.sub.3 K groups, which then are exchanged with an acid to 
--SO.sub.3 H groups. Suitable perfluorinated cationic membranes, which are 
made of hydrated copolymers of polytetrafluoroethylene and poly-sulfonyl 
fluoride vinyl ether-containing pendant sulfonic acid groups, are offered 
DuPont under the trademark "NAFION.RTM." (hereinafter referred to as 
NAFION.RTM.). In particular, NAFION.RTM. membranes containing pendant 
sulfonic acid groups include NAFION.RTM. 115, NAFION.RTM. 117, NAFION.RTM. 
324 and NAFION.RTM. 417. The first and second types of NAFION.RTM. are 
unsupported and have an equivalent weight of 1100 g., equivalent weight 
being defined as the amount of resin required to neutralize one liter of a 
1M sodium hydroxide solution. NAFION.RTM. 324 and NAFION.RTM. 417 are both 
supported on a fluorocarbon fabric, the equivalent weight of NAFION.RTM. 
417 also being 1100 g. NAFION.RTM. 324 has a two-layer structure, a 125 
.mu.m-thick membrane having an equivalent weight of 1100 g., and a 25 
.mu.m-thick membrane having an equivalent weight of 1500 g. NAFION.RTM. 
115 in particular may be used with the electrochemical cell of the present 
invention. 
Although the present invention describes the use of a solid polymer 
electrolyte membrane, it is well within the scope of the invention to use 
other cation-transporting membranes which are not polymeric. For example, 
proton-conducting ceramics such as beta-alumina may be used. Beta-alumina 
is a class of nonstoichiometric crystalline compounds having the general 
structure Na.sub.2 O.sub.x.Al.sub.2 O.sub.3, in which x ranges from 500 
(.beta."-alumina) to 11 (.beta.-alumina). This material and a number of 
solid electrolytes which are useful for the invention are described in the 
Fuel Cell Handbook, A. J. Appleby and F. R. Foulkes, Van Nostrand 
Reinhold, N.Y., 1989, pages 308-312. Additional useful solid state proton 
conductors, especially the cerates of strontium and barium, such as 
strontium ytterbiate cerate (SrCe.sub.0.95 Yb.sub.0.05 O.sub.3-.alpha.) 
and barium neodymiate cerate (BaCe.sub.0.9 Nd.sub.0.01 O.sub.3-.alpha.) 
are described in a final report, DOE/MC/24218-2957, Jewulski, Osif and 
Remick, prepared for the U.S. Department of Energy, Office of Fossil 
Energy, Morgantown Energy Technology Center by Institute of Gas 
Technology, Chicago, Ill., December, 1990. 
The electrochemical cell of the present invention also comprises means for 
reducing the transported protons, where the reducing means is disposed in 
contact with the other side of the cation-transporting means. The reducing 
means comprises an electrode, or more specifically, a cathode 210, where 
cathode 210 is disposed in contact with the other side (as opposed to the 
side which is in contact with the anode) of membrane 208 as illustrated in 
FIGS. 3 and 3A. 
The electrochemical cell of the present invention also includes a cathode 
chamber disposed adjacent the reducing means. A cathode chamber is shown 
at 205 in FIGS. 3 and 3A disposed adjacent to, meaning next to or near, 
the reducing means, or cathode. The electrochemical cell of the present 
invention also comprises cathode-side inlet means disposed in fluid 
communication with the cathode chamber for introducing a fluid to the 
other side of the cation-transporting means. The cathode-side inlet means 
comprises a cathode-side inlet 212 as shown in FIG. 3. The cathode-side 
inlet means is connected to a line, such as line 115 as shown in FIG. 2. 
The cathode-side inlet introduces a fluid, such as water, to the 
cathode-side of the membrane in the first embodiment, or an 
oxygen-containing gas, such as oxygen gas, to the cathode and then to the 
cathode-side of the membrane in the second embodiment, as will be 
explained below. The electrochemical cell of the present invention also 
comprises cathode-side outlet means also disposed in fluid communication 
with the cathode chamber. The cathode-side outlet means comprises a 
cathode-side outlet 214 as shown in FIG. 3. The cathode-side outlet is 
connected to a line, such as line 117 as shown in FIG. 2. Since some 
chloride ions pass through the membrane and, consequently, HCl is present 
on the cathode-side of the cell, the cathode inlet and the outlet may also 
be lined with PFA. A passage 215 as shown in FIG. 3 is formed between the 
anode-side inlet and the cathode-side outlet, and a similar passage 217 is 
shown formed between the cathode-side inlet and the anode-side outlet. 
These passages carry the reactants into and the products out of the cell 
through the anode and cathode-side inlets, and the anode and cathode-side 
outlets, as will be further explained below. 
The anode and the cathode comprise an electrochemically active material. 
The electrochemically active material may comprise any type of catalytic 
or metallic material or metallic oxide, as long as the material can 
support charge transfer. Preferably, the electrochemically active material 
may comprise a catalyst material such as platinum, ruthenium, osmium, 
rhenium, rhodium, iridium, palladium, gold, titanium, tin or zirconium and 
the oxides, alloys or mixtures thereof. Other catalyst materials suitable 
for use with the present invention may include, but are not limited to, 
transition metal macro cycles in monomeric and polymeric forms and 
transition metal oxides, including perovskites and pyrochores. 
The anode and the cathode may be porous, gas-diffusion electrodes. Gas 
diffusion electrodes provide the advantage of high specific surface area, 
as known to one skilled in the art. A particular type of gas diffusion 
electrode, known as an ELAT, may be used as the anode and the cathode. An 
ELAT comprises a support structure, as well as the electrochemically 
active material. In one preferred embodiment, an ELAT comprising a support 
structure of carbon cloth and electrochemically active material comprising 
ruthenium oxide, commercially available from E-TEK, of Natick, Mass., may 
be used. Alternatively, an ELAT may be used which comprises a catalyst 
material mixed with carbon and particles of polytetrafluoroethylene, or 
PTFE, a tetrafluoropolymer resin which is sold under the trademark 
"TEFLON.RTM." (hereinafter referred to as "PTFE"), commercially available 
from DuPont. The catalyst material, carbon particles and PTFE are then 
sintered on a carbon cloth substrate, which is treated with a NAFION.RTM. 
solution. This ELAT is held mechanically against the membrane of the cell. 
Alternative arrangements of the electrochemically active material may be 
used for the anode and cathode of the present invention. The 
electrochemically active material may be disposed adjacent, meaning at or 
under, the surface of the cation-transporting membrane. For instance, the 
electrochemically active material may be deposited into the membrane, as 
shown in U.S. Pat. No. 4,959,132 to Fedkiw. A thin film of the 
electrochemically active material may be applied directly to the membrane. 
Alternatively, the electrochemically active material may be hot-pressed to 
the membrane, as shown in A. J. Appleby and E. B. Yeager, Energy, Vol. 11, 
137 (1986). 
If the electrodes are hot-pressed into the membrane, they have the 
advantage of having good contact between the catalyst and the membrane. In 
a hot-pressed electrode, the electrochemically active material may 
comprise a catalyst material on a support material. The support material 
may comprise particles of carbon and particles of PTFE. The 
electrochemically active material may be bonded by virtue of the PTFE to a 
support structure of carbon cloth or paper or graphite paper and 
hot-pressed to the cation-transporting membrane. The hydrophobic nature of 
PTFE does not allow a film of water to form at the anode. A water barrier 
in the electrode would hamper the diffusion of HCl to the reaction sites. 
The loadings of electrochemically active material may vary based on the 
method of application to the membrane. Hot-pressed, gas-diffusion 
electrodes typically have loadings of 0.10 to 0.50 mg/cm.sup.2. Lower 
loadings are possible with other available methods of deposition, such as 
distributing them as thin films from inks onto the membranes, to form a 
catalyst-coated membrane, as described in Wilson and Gottesfeld, "High 
Performance Catalyzed Membranes of Ultra-low Pt Loadings for Polymer 
Electrolyte Fuel Cells", Los Alamos National Laboratory, J. Electrochem. 
Soc., Vol. 139, No. 2 L28-30, 1992, where the inks contain solubilized 
NAFION.RTM. to enhance 10 the catalyst-ionomer surface contact and to act 
as a binder to the NAFION.RTM. perfluorinated membrane sheet. 
With such a system, loadings as low as 0.017 mg active material per 
cm.sup.2 have been achieved. 
In a preferred embodiment, a thin film of the electrochemically active 
material is be applied directly to the membrane to form a catalyst-coated 
membrane. In this preferred embodiment, the membrane is typically formed 
from a polymer as described above in its sulfonyl fluoride form, since it 
is thermoplastic in this form, and conventional techniques for making 
films from thermoplastic polymer can be used. The sulfonyl fluoride, or 
SO.sub.2 F, form means that the side chain, before the membrane is 
hydrolyzed, has the formula --OCF.sub.2 CF(CF.sub.3)!n-OCF.sub.2 CF.sub.2 
SO.sub.2 F. Alternately, the polymer may be in another thermoplastic form 
such as by having --SO.sub.2 X groups where X is CH.sub.3, CO.sub.2, or a 
quaternary amine. Solution film casting techniques using suitable solvents 
for the particular polymer can also be used if desired. 
A film of the polymer in sulfonyl fluoride form can be converted to the 
sulfonate form (sometimes referred to as ionic form) by hydrolysis using 
methods known in the art. For example, the membrane may be hydrolyzed to 
convert it to the sodium sulfonate form by immersing it in 25% by weight 
NaOH for about 16 hours at a temperature of about 90.degree. C. followed 
by rinsing the film twice in deionized 90.degree. C. water using about 30 
to about 60 minutes per rinse. Another possible method employs an aqueous 
solution of 6-20% of an alkali metal hydroxide and 5-40% polar organic 
solvent such as dimethyl sulfoxide with a contact time of at least 5 
minutes at 50.degree.-100.degree. C. followed by rinsing for 10 minutes. 
After hydrolyzing, the membrane can be converted if desired to another 
ionic form by contacting the membrane in a bath containing a 1% salt 
solution containing the desired cation or, to the acid form, by contacting 
with an acid and rinsing. The membrane used in the membrane-electrode 
assembly of the present invention is usually in the sulfonic acid form. 
The thickness of the membrane can be varied as desired. Typically, the 
thickness of the membrane is generally less than about 250 .mu.m, 
preferably in the range of about 25 .mu.m to about 150 .mu.m. 
The electrochemically active material is conventionally incorporated in a 
coating formulation, or "ink", which is applied to the membrane. The 
electrochemically active material in the form of particles having a 
particle diameter in the range of 0.1 micron (.mu.) to 10.mu.. The coating 
formulation, and consequently the anode and the cathode after the catalyst 
coated membrane is formed, also comprises a binder polymer for binding the 
particles of the electrochemically active material together. The particles 
of electrochemically active material, when coated with the binder polymer, 
have a tendency to agglomerate. By grinding the particles to a 
particularly small size, a better particle distribution may be obtained. 
Thus, the coating formulation is ground so that the particles have an 
average diameter of less than 5.mu., and in many cases, preferably less 
than 2.mu.. This small particle size is accomplished by ball milling or 
grinding with an Elger mini mill, which latter technique can produce 
particles of 1.mu. or less. 
The binder polymer is dissolved in a solvent. The binder polymer may be the 
same polymer as that used for the membrane, as described herein, but it 
need not be. The binder polymer may be a variety of polymers, such as 
polytetrafluoroethylene (PTFE). In a preferred embodiment, the binder 
polymer is a perfluorinated sulfonic acid polymer, and the side chain of 
the binder polymer, before hydrolyzation of the binder polymer, is 
represented by the formula -OCF.sub.2 CF(CF.sub.3)!n-OCF.sub.2 CF.sub.2 
SO.sub.2 F (i.e., the SO.sub.2 F, or sulfonyl fluoride form). The side 
chain, after hydrolyzation, is represented by the formula --OCF.sub.2 CF 
(CF.sub.3)!--OCF.sub.2 CF.sub.2 SO.sub.3 H (i.e., the SO.sub.3 H, sulfonic 
acid, or acid form). When the binder polymer is in the sulfonyl fluoride 
form, the solvent can be a variety of solvents, such as FLUORINERT FC-40, 
commercially available from 3M of St. Paul, Minn., which is a mixture of 
perfluoro(methyl-di-n-butyl)amine and perfluoro(tri-n-butylamine). In this 
embodiment, a copolymer polymerized from tetrafluoroethylene and a vinyl 
ether which is represented by the formula CF.sub.2 .dbd.CF--O--CF.sub.2 
CF(CF.sub.3)--O--CF.sub.2 CF.sub.2 SO.sub.2 F has been found to be a 
suitable binder polymer. In addition, ruthenium dioxide has been found to 
be a suitable catalyst. The sulfonyl fluoride form has been found to be 
compatible with FC-40 and to give a uniform coating of the ruthenium 
dioxide catalyst on the membrane. 
The viscosity of the ink can be controlled by (i) selecting particle sizes, 
(ii) controlling the composition of the particles of electrochemically 
active material and binder, or (iii) adjusting the solvent content (if 
present). The particles of electrochemically active material are 
preferably uniformly dispersed in the polymer to assure that a uniform and 
controlled depth of the catalyst layer is maintained, preferably at a high 
volume density with the particles of electrochemically active material 
being in contact with adjacent particles to form a low resistance 
conductive path through the catalyst layer. The ratio of the particles of 
electrochemically active material to the binder polymer may be in the 
range of about 0.5:1 to about 8:1, and in particular in the range of about 
1:1 to about 5:1. The catalyst layer formed on the membrane should be 
porous so that it is readily permeable to the gases/liquids which are 
consumed and produced in cell. The average pore diameter is preferably in 
the range of 0.01 to 50 .mu.m, most preferably 0.1 to 30 .mu.m. The 
porosity is generally in a range of 10 to 99%, preferably 10 to 60%. 
The area of the membrane to be coated with the ink may be the entire area 
or only a select portion of the surface of the membrane. If desired, the 
coatings are built up to the thickness desired by repetitive application. 
Areas upon the surface of the membrane which require no particles of 
electrochemically active material can be masked, or other means can be 
taken to prevent the deposition of the particles of electrochemically 
active material upon such areas. The desired loading of particles of 
electrochemically active material upon the membrane can be predetermined, 
and the specific amount of particles of electrochemically active material 
can be deposited upon the surface of the membrane so that no excess 
electrochemically active material is applied. In a preferred embodiment, 
the ink is deposited on the surface of the membrane by spraying. However, 
it should be noted that the catalyst ink may be deposited upon the surface 
of the membrane by any suitable technique, including spreading it with a 
knife or blade, brushing, pouring, metering bars and the like. 
Alternatively, the electrochemically active material may be applied to the 
membrane by using a screen printing process, as known in the art. An 
alternative to printing the electrochemically active material directly 
onto the membrane is the decal process, also known in the art, where the 
catalyst ink is coated, painted, sprayed or screen printed onto a 
substrate and the solvent is removed. The resulting decal is then 
subsequently transferred from the substrate to the membrane surface and 
bonded, typically by the application of heat and pressure. 
After depositing the catalyst layer of electrochemically active material, 
it is preferable to fix the ink on the surface of the membrane so that a 
strongly bonded catalyst layer and the cation-transporting membrane can be 
obtained. The ink may be fixed upon the surface of the membrane by any one 
or a combination of pressure, heat, adhesive, binder, solvent, 
electrostatic, and the like. A preferred method for fixing the ink upon 
the surface of the membrane employs pressure, heat or by a combination of 
pressure and heat. The catalyst layer is preferably pressed onto the 
surface of the membrane at 100.degree. C. to 300.degree. C., most 
preferably 150.degree. C. to 280.degree. C., under a pressure of 510 to 
51,000 kPa (5 to 500 ATM), most preferably 1,015 to 10,500 kPa (10 to 100 
ATM). 
If a catalyst-coated membrane as described above is used, the 
electrochemical cell must include a gas diffusion layer (not shown) 
disposed in contact with the anode and the cathode, respectively, (or at 
least in contact with the anode), on the side of the anode or cathode 
opposite the side which is in contact with the membrane. The gas diffusion 
layer provides a porous structure that allows the anhydrous hydrogen 
chloride to diffuse through to the layer of electrochemically active 
material of the catalyst-coated membrane. In addition, both the anode gas 
diffusion layer and the cathode gas diffusion layer distribute current 
over the electrochemically active material, or area, of the 
catalyst-coated membrane. The diffusion layers are preferably made of 
graphite paper, and are typically 15-20 mil thick. 
When using any type of membrane and electrodes with the present invention, 
the membrane must be kept hydrated in order to increase the efficiency of 
proton transport through the membrane. This keeps the conductivity of the 
membrane high. In the first embodiment, which has a hydrogen-producing 
cathode, the hydration of the membrane is obtained by keeping liquid water 
in contact with the cathode-side of the membrane, as will be explained 
below. For example, when using gas diffusion electrodes, liquid water is 
delivered to the cathode, and the liquid water passes through the 
gas-diffusion electrode and contacts the membrane. When using a 
catalyst-coated membrane, liquid water is delivered to the membrane 
itself, since the cathode is a thin layer of electrochemically active 
material applied directly to the membrane. 
In particular, in the first embodiment, water is added to the 
electrochemical cell through cathode-side inlet 212. The protons (2H+ in 
eq. (2) above) which are produced by the oxidation of the anhydrous 
hydrogen chloride are transported through the membrane and reduced at the 
cathode to form hydrogen gas, as given by equation (3) below. 
##STR2## 
This hydrogen gas is evolved at the interface between the cathode and the 
membrane. The hydrogen gas, which is shown as H.sub.2 (I) for the first 
embodiment in FIGS. 2 and 3, exits the cell through the cathode-side 
outlet and through a line 115 as shown in FIG. 1. The hydrogen gas may 
have some HCl therein due to chloride ion migration. The hydrogen gas may 
be used for other purposes, such as a fuel. 
In the second embodiment, membrane hydration is accomplished by the 
production of water and by the water introduced in a humidified 
oxygen-feed or air-feed stream. In particular, in the second embodiment, 
an oxygen-containing gas, such as oxygen, air or oxygen-enriched air 
(i.e., greater than 21 mol % oxygen in nitrogen) is introduced through 
cathode-side inlet 112. Although air is cheaper to use, cell performance 
is enhanced when enriched air or oxygen is used. This oxygen-containing 
gas should be humidified to aid in the control of moisture in the 
membrane, for purposes to be explained below. The oxygen gas (O.sub.2) and 
the transported protons are reduced at the cathode to water, as expressed 
by the equation: 
EQU 1/2O.sub.2 (g)+2e.sup.- +2H.sup.+ .fwdarw.H.sub.2 O(g) (4) 
The water formed, as illustrated by H.sub.2 O(II) in FIGS. 2 and 3, 
denoting the second embodiment, exits via the cathode-side outlet, along 
with any unreacted nitrogen and oxygen gas. The water may have some HCl 
therein due to chloride ion migration, as in the first embodiment. 
In the second embodiment, the cathode reaction is the formation of water. 
This cathode reaction has the advantage of more favorable thermodynamics 
relative to H.sub.2 production at the cathode in the first embodiment. 
This is because the overall reaction in this embodiment, which is 
expressed by the following equation: 
##STR3## 
involves a smaller free-energy change than the free-energy change for the 
overall reaction in the first embodiment, which is expressed by the 
following equation: 
##STR4## 
Thus, the amount of voltage or energy required as input to the cell is 
reduced in this second embodiment. 
Returning again to the description of FIG. 2, the electrochemical cell of 
the present invention further comprises an anode flow field 216 disposed 
in contact with the anode and a cathode flow field 218 disposed in contact 
with the cathode as shown in FIGS. 3 and 3A. The flow fields are 
electrically conductive, and act as both mass and current flow fields. 
Preferably, the anode and the cathode flow fields comprise porous graphite 
paper. Such flow fields are commercially available from Spectracorp, of 
Lawrence, Mass. However, the flow fields may be made of any material and 
in any manner known to one skilled in the art. For example, the flow 
fields may alternatively be made of a porous carbon in the form of a foam, 
cloth or matte. For the purpose of acting as mass flow fields, the anode 
mass flow field includes a plurality of anode flow channels 220, and the 
cathode mass flow field includes a plurality of cathode flow channels 222 
as shown in FIG. 3A, which is a cut-away, top cross-sectional view showing 
only the flow fields of FIG. 3. The anode flow fields and the anode flow 
channels, get reactants, such as anhydrous HCl in the first and second 
embodiments, to the anode and products, such as dry chlorine gas, from the 
anode. The cathode flow field and the cathode flow channels get catholyte, 
such as liquid water in the first embodiment, to the membrane, or an 
oxygen-containing gas to the cathode in the second embodiment, and 
products, such as hydrogen gas in the first embodiment, or liquid water in 
the second embodiment, from the cathode. 
The electrochemical cell of the present invention may also comprise an 
anode-side gasket 224 and a cathode-side gasket 226 as shown in FIG. 3. 
Gaskets 224 and 226 form a seal between the interior and the exterior of 
the electrochemical cell. Preferably, the anode-side gas is made of a 
fluoroelastomer, sold under the trademark VITON.RTM. (hereinafter referred 
to as VITON.RTM.) by DuPont Dow Elastomers L.L.C. of Wilmington, Del. The 
cathode-side gasket may be made of the terpolymer ethylene/propylene/diene 
(EPDM), sold under the trademark NORDEL.RTM. by DuPont, or it may be made 
of VITON.RTM.. 
The electrochemical cell of the present invention also comprises an anode 
current bus 228 and a cathode current bus 230 as shown in FIG. 3. The 
current buses conduct current to and from a voltage source (not shown). 
Specifically, anode current bus 228 is connected to the positive terminal 
of a voltage source, and cathode current bus 230 is connected to the 
negative terminal of the voltage source, so that when voltage is applied 
to the cell, current flows through all of the cell components to the right 
of current bus 228 as shown in FIG. 3, including current bus 230, from 
which it returns to the voltage source. The current buses are made of a 
conductor material, such as copper. 
The electrochemical cell of the present invention may further comprise an 
anode current distributor 232 as shown in FIG. 3. The anode current 
distributor collects current from the anode current bus and distributes it 
to the anode by electronic conduction. The anode current distributor may 
comprise a fluoropolymer which has been loaded with a conductive material. 
In one embodiment, the anode current distributor may be made from 
polyvinylidene fluoride, sold under the trademark KYNAR.RTM. (hereinafter 
referred to as "KYNAR.RTM.") by Elf Atochem North America, Inc. 
Fluoropolymers, and graphite. 
The electrochemical cell of the present invention may further comprise a 
cathode current distributor 234 as shown in FIG. 3. The cathode current 
distributor collects current from the cathode and for distributing current 
to the cathode bus by electronic conduction. The cathode distributor also 
provides a barrier between the cathode current bus and the cathode and the 
hydrogen chloride. This is desirable because there is some migration of 
hydrogen chloride through the membrane. Like the anode current 
distributor, the cathode current distributor may comprise a fluoropolymer, 
such as KYNAR.RTM., which has been loaded with a conductive material, such 
as graphite. 
The electrochemical cell of the present invention also includes an 
anode-side stainless steel backer plate (not shown), disposed on the 
outside of the cell next to the anode current distributor, and a 
cathode-side stainless steel backer plate (also not shown), disposed on 
the outside of the cell next to the cathode current distributor. These 
steel backer plates have bolts extending therethrough to hold the 
components of the electrochemical cell together and add mechanical 
stability thereto. 
When more than one anode-cathode pair is used, such as in manufacturing, a 
bipolar arrangement, as familiar to one skilled in the art, is preferred. 
The electrochemical cell of the present invention may be used in a bipolar 
stack. To create such a bi-polar stack, anode current distributor 232 and 
every element to the right of the anode current distributor as shown in 
FIG. 3, up to and including cathode current distributor 234, are repeated 
along the length of the cell, and current buses are placed on the outside 
of the stack. 
Returning again to the description of FIG. 2, the system of the present 
invention further comprises a purification unit 122, which liquefies and 
purifies the essentially dry chlorine gas. Liquid dry chlorine exits the 
purifier. As noted above, a portion of the anhydrous hydrogen chloride may 
be unreacted. This unreacted portion exits electrochemical cell 200, along 
with the essentially dry chlorine gas, and is sent to purification unit 
122. The purification unit separates out the unreacted anhydrous hydrogen 
chloride (AHCl as shown in FIG. 2) from the liquid dry chlorine and 
returns it through line 124 to line 116, which is connected to the 
anode-side inlet as shown in FIG. 2. 
The system of the present invention further comprises a recycle line 
connected to the electrochemical cell outlet means at one end thereof and 
to the second inlet supply line at the other end thereof for recycling the 
liquid dry chlorine to the direct chlorination reactor. A recycle line, 
shown at 126 in FIG. 2 joins second inlet feed line 106 to supply fresh 
liquid dry chlorine to the direct chlorination reactor. 
Further in accordance with the present invention, there is provided a 
system for producing vinyl chloride monomer from chlorine gas produced by 
the electrochemical conversion of anhydrous hydrogen chloride. Such a 
system is shown generally at 300 in FIG. 4. System 300 includes a direct 
chlorination reactor as shown at 302 in FIG. 4. Direct chlorination of 
ethylene to ethylene dichloride is conducted by mixing ethylene and 
chlorine in direct chlorination reactor 302. A first inlet supply line 304 
as shown in FIG. 4 supplies ethylene (C.sub.2 H.sub.4) to the direct 
chlorination reactor. A second inlet supply line 306 supplies liquid dry 
chlorine (Cl.sub.2) to the direct chlorination reactor. The ethylene and 
the chlorine react in the reactor to produce ethylene dichloride. The 
equation for this reaction is given by equation (1) above. As noted above, 
ferric chloride can be used as a catalyst with the present invention, 
although other catalysts may be used. It should be noted that the feeding 
of the ethylene and the chlorine may be simultaneous, or may be slightly 
spaced apart in time, as long as the conditions in the reactor are proper 
for the direct chlorination reaction to occur. 
By-products contained in EDC from the direct chlorination reaction and the 
ethylene dichloride pyrolysis as described above must be removed. The 
ethylene dichloride used for pyrolysis to vinyl chloride must be of high 
purity because the pyrolysis of ethylene dichloride is exceedingly 
susceptible to inhibition and fouling by trace quantities of impurities. 
It must also be dry (no separate water phase and very little total 
dissolved water) to prevent excessive corrosion downstream of the 
pyrolysis unit. Therefore, the system of the present invention may also 
include an ethylene dichloride purification unit connected to the direct 
chlorination unit for purifying the ethylene dichloride. Such an EDC 
purification unit is shown at 308 in FIG. 4. The EDC is brought to the EDC 
purification unit from the direct chlorination reactor through a line 309. 
The EDC purification unit purifies the ethylene dichloride. Light and 
heavy ends are a by-product of this purification. These light and heavy 
ends are released through a line 310 as shown in FIG. 4. As noted above 
for the EDC system, the EDC purification unit of the present invention is 
much smaller than that of the oxychlorination process, thus reducing 
capital and operating costs. 
The system of the present invention also includes a pyrolysis unit for 
pyrolyzing the ethylene dichloride to produce vinyl chloride monomer. Such 
a unit is shown at 312 in FIG. 4. The purified EDC is brought to the 
pyrolysis unit through a line 311. The pyrolysis unit pyrolyzes the 
ethylene dichloride from line 311 to produce vinyl chloride monomer, as 
well anhydrous hydrogen chloride, i.e., hydrogen chloride in molecular 
form (AHCl as shown in FIG. 4). This reaction is given by the following 
equation. 
EQU 2ClCH.sub.2 CH.sub.2 Cl.fwdarw.2CH.sub.2 .dbd.CHCl+2 AHCl (7) 
The system of the present invention also includes a vinyl chloride monomer 
purification unit connected to the ethylene dichloride purification unit 
for purifying the vinyl chloride monomer and for separating the vinyl 
chloride monomer from the anhydrous hydrogen chloride. Such a unit is 
shown at 314 in FIG. 4. The VCM is brought to the VCM purification unit 
from the EDC pyrolysis unit through a line 313. VCM purification unit 314 
purifies the VCM and separates the VCM from the anhydrous hydrogen 
chloride so that the VCM exits the VCM purification unit through a line 
317, and the anhydrous hydrogen chloride exits the VCM purification unit 
through a line 316 as shown in FIG. 4. 
In the production of vinyl chloride monomer in the present invention, a 
portion of the ethylene dichloride may be unreacted in pyrolysis unit 312. 
Therefore, the system of the present invention also includes a recycle 
line connected to the vinyl chloride monomer purification unit for 
recycling the unreacted ethylene dichloride to the ethylene dichloride 
purification unit. This recycle line is shown at 318 in FIG. 4. In the 
prior art as shown in FIG. 1, the unreacted portion is normally mixed with 
fresh ethylene dichloride supplied from the direct chlorination unit and 
the OHC reactor in the ethylene dichloride purification unit. However, 
since the ethylene dichloride produced according to the present invention 
is much cleaner than that produced by the OHC process of the prior art, 
the unreacted ethylene dichloride may be recycled back to the ethylene 
dichloride purification unit through recycle line 318. 
The anhydrous hydrogen chloride is sent through line 318 to an 
electrochemical cell, which is shown generally at 200 in FIGS. 3 and 4 and 
in detail in FIG. 3. The details of the cell are as described above. The 
anhydrous hydrogen chloride enters the cell through anode-side inlet 202 
as shown in FIG. 3. Either water in the first embodiment or an 
oxygen-containing gas in the second embodiment, as explained above, enters 
the cell through a line 319 as shown in FIG. 4 and through cathode-side 
inlet 212 as shown in FIG. 3. Hydrogen in the first embodiment, designated 
by H.sub.2 (I) in FIGS. 3 and 4, or water in the second embodiment, 
designated by H.sub.2 O(II) in FIGS. 3 and 4, leaves the cell through 
cathode-side outlet 214 which is shown in FIG. 3 and through a line 321 as 
shown in FIG. 4. Essentially dry chlorine gas (Cl.sub.2 as shown in FIG. 
4) exits the cell through anode-side outlet 206 which is shown in FIG. 3. 
The system of the present invention further includes a purification unit 
disposed in communication with the outlet means for purifying and 
liquefying the essentially dry chlorine gas. Such a purification unit is 
shown at 322 shown in FIG. 4. The chlorine entering purification unit 322 
is dry chlorine gas, whereas the chlorine gas leaving the purification 
unit is liquid dry chlorine. As noted above, a portion of the anhydrous 
hydrogen chloride may be unreacted. This unreacted portion exits 
electrochemical cell 200, along with the essentially dry chlorine gas, and 
is sent to the purification unit. The purification unit separates out the 
unreacted anhydrous hydrogen chloride (AHCl as show in FIG. 4) from the 
liquid dry chlorine and returns it through line 324 to line 316, which is 
connected to the anode-side inlet as shown in FIG. 4. 
The system of the present invention further comprises a recycle line 
connected to the electrochemical cell outlet means at one end thereof and 
to the second inlet supply line at the other end thereof for recycling the 
liquid dry chlorine to the direct chlorination reactor. A recycle line, 
shown at 326 in FIG. 4 recycles the liquid dry chlorine produced in 
electrochemical cell 200 to the direct chlorination reactor. Recycle line 
326 joins second inlet feed line 306 to supply fresh liquid dry chlorine 
to the direct chlorination reactor. 
Further in accordance with the present invention, there is provided a 
process for producing ethylene dichloride from chlorine gas produced by 
the electrochemical conversion of anhydrous hydrogen chloride. The 
operation of the system of the present invention as described above with 
respect to FIGS. 2, 3 and 3A will now be described as it relates to the 
process of the present invention. 
The process includes the step of supplying ethylene through a first inlet 
supply line, such as supply line 104 as shown in FIG. 2, to a direct 
chlorination reactor, such as reactor 102 as shown in FIG. 2. In addition, 
the process of the present invention includes the steps of supplying 
chlorine, that is liquid dry chlorine, through a second inlet supply line, 
such as line 106 as shown in FIG. 2, to the direct chlorination reactor. 
The ethylene and the chlorine gas may be supplied to the direct 
chlorination reactor simultaneously, or at different times. The ethylene 
reacts with the chlorine in the presence of a catalyst in the direct 
chlorination reactor to form ethylene dichloride according to equation (1) 
above. The ethylene dichloride may be sent to an ethylene dichloride 
purification unit, such as unit 108 as shown in FIG. 2. The light and 
heavy ends escape from the unit through a line, such as line 110. 
In addition, the process includes the step of supplying anhydrous hydrogen 
chloride, which is in molecular form, to an anode-side inlet of an 
electrochemical cell, such as anode-side inlet 202 of electrochemical cell 
200. The electrochemical cell comprises a cation-transporting membrane, 
such as membrane 208, an anode disposed in contact with one side of the 
membrane, such as anode 204 as shown in FIG. 3, and a cathode disposed in 
contact with the other side of the membrane, such as cathode 210. A 
voltage is applied to the electrochemical cell so that the anode is at a 
higher potential than the cathode and so that the molecular essentially 
anhydrous hydrogen chloride is transported through flow channels, such as 
channels 220 in anode mass flow field 216 and to the surface of the anode 
and is oxidized at the anode to produce chlorine gas and protons 
(H.sup.+). The chlorine gas is released from an anode-side outlet of the 
cell, such as anode-side outlet 206 as shown in FIG. 3. 
The process of the present invention further includes the step of recycling 
the chlorine gas back to the direct chlorination reactor through a recycle 
line, such as line 126, as shown in FIG. 2. A purification unit, such as 
unit 122 as shown in FIG. 2, is provided in the recycle line. The chlorine 
gas is essentially dry when it is released from the anode-side outlet of 
the cell. Thus, the present invention further includes the step of 
purifying and liquefying the essentially dry chlorine gas in a 
purification unit, such as unit 122, to form liquid dry chlorine, and 
supplying the liquid dry chlorine to the direct chlorination reactor. The 
liquid dry chlorine is supplied to the direct chlorination reactor through 
a recycle line, such as line 126 as shown in FIG. 2. In addition, a fresh 
supply of liquid dry chlorine is supplied to the direct chlorination 
reactor through a second inlet supply line, such as through line 106 as 
shown in FIG. 2. 
The protons produced in the electrochemical cell are transported through 
the membrane, which acts as an electrolyte. The transported protons are 
reduced at the cathode. A cathode current distributor 232 collects current 
from cathode 210 and distributes it to cathode bus 230. In the first 
embodiment, in order to maintain hydration of the membrane, water is 
delivered to the membrane at the cathode-side through a cathode-side 
inlet. such as inlet 212 as shown in FIG. 3. and through the channels in 
the cathode mass flow field, such as channels 222 in cathode mass flow 
field 218 as shown in FIG. 3A to hydrate the membrane and thereby increase 
the efficiency of proton transport through the membrane. The hydrogen gas 
which is evolved at the interface between the cathode and the membrane as 
described above exits via a cathode-side outlet, such as outlet 214 as 
shown in FIG. 3. In the second embodiment, in order to maintain hydration 
of the membrane, an oxygen-containing gas, such as oxygen (O.sub.2 (g)), 
which is preferably humidified, is introduced through a cathode-side 
inlet, such as inlet 212, and through the channels formed in the cathode 
mass flow field, such as channels 222 in flow field 218 as shown in FIG. 
3A. Oxygen and the transported protons are reduced at the cathode to form 
water, as explained above. The water exits via a cathode-side outlet, such 
as outlet 214 as shown in FIG. 3. 
A portion of the anhydrous hydrogen chloride may be unreacted in the 
electrochemical cell. This unreacted portion exits the electrochemical 
cell, along with the essentially dry chlorine gas, through an anode-side 
outlet, such as outlet 202, and is sent to a purification unit, such as 
unit 122 as shown in FIG. 2. The purification unit separates out the 
unreacted anhydrous hydrogen chloride. The present invention thus may 
further include the step of recycling the unreacted anhydrous hydrogen 
chloride to the anode-side inlet of the electrochemical cell through a 
recycle line, such as line 124 as shown in FIG. 2. 
Further in accordance with the present invention, there is provided a 
process for producing vinyl chloride monomer from chlorine gas produced by 
the electrochemical conversion of anhydrous hydrogen chloride. The 
operation of the system of the present invention as described above with 
respect to FIGS. 3, 3A and 4 will now be described as it relates to the 
process of the present invention. 
The process includes the steps of supplying ethylene through a first inlet 
supply line, such as first inlet line 304 as shown in FIG. 4 to a direct 
chlorination reactor, such as direct chlorination reactor 302 as shown in 
FIG. 4. In addition, the process includes the step of supplying liquid dry 
chlorine through a second inlet supply line, such as line 306 as shown in 
FIG. 4, to the direct chlorination reactor. The ethylene and the chlorine 
gas may be supplied to the direct chlorination reactor simultaneously, or 
at different times. The ethylene reacts with the chlorine in the presence 
of a catalyst in the direct chlorination reactor to form ethylene 
dichloride according to equation (1) above. 
The process of the present invention further includes the step of 
pyrolyzing the ethylene dichloride to produce vinyl chloride monomer and 
anhydrous hydrogen chloride. The ethylene dichloride is pyrolyzed in a 
pyrolysis unit, such as unit 312 as shown in FIG. 4, purifying the 
ethylene dichloride in an ethylene dichloride purification unit, such as 
unit 308 as shown in FIG. 4. 
The process of the present invention may further include the step of 
purifying the ethylene dichloride in an ethylene dichloride purification 
unit, such as unit 308 as shown in FIG. 4, before it is pyrolyzed. The 
light and heavy ends escape from the unit through a line, such as line 
310. The purified ethylene dichloride is sent to a pyrolysis unit, such as 
unit 312 as shown in FIG. 4. 
The process of the present invention may further include the step of 
purifying the vinyl chloride monomer in a vinyl chloride monomer 
purification unit, such as in a purification unit 314 as shown in FIG. 4. 
The purified VCM is sent for further purification, such as through line 
317 as shown in FIG. 4. 
In the pyrolysis unit, a portion of the ethylene dichloride may be 
unreacted. The unreacted ethylene dichloride is sent to the vinyl chloride 
purification unit. In the purification unit, the unreacted EDC is 
separated from the VCM. Thus, the present invention may further include 
the step of recycling the unreacted ethylene dichloride from the vinyl 
chloride monomer purification unit back to the ethylene dichloride 
purification unit. 
In addition, the VCM purification unit separates the unreacted essentially 
anhydrous hydrogen chloride from the VCM, and sends it to an 
electrochemical cell, such as electrochemical cell 200 as shown in FIGS. 3 
and 4 through a line, such as line 316 as shown in FIG. 4. The 
electrochemical cell converts anhydrous hydrogen chloride to dry chlorine 
gas and protons, as described above. 
The process of the present invention further includes the step of 
liquefying and purifying the dry chlorine gas in a purification unit, such 
as unit 322 as shown in FIG. 4, to form liquid dry chlorine and supplying 
this liquid dry chlorine to the direct chlorination reactor. The liquid 
dry chlorine is recycled to the direct chlorination reactor through a 
recycle line, such as line 326 as shown in FIG. 4. In addition, a fresh 
supply of liquid dry chlorine is supplied to the direct chlorination 
reactor through a second inlet supply line, such as through line 306 as 
shown in FIG. 4. 
In the process for producing vinyl chloride monomer according to the 
present invention, a portion of the anhydrous hydrogen chloride may be 
unreacted in the electrochemical cell. This unreacted portion exits the 
electrochemical cell, along with the essentially dry chlorine gas, and is 
sent to a purification unit, such as unit 322. The purification unit 
separates out the unreacted anhydrous hydrogen chloride. The present 
invention thus may further include the step of recycling the unreacted 
anhydrous hydrogen chloride to the anode-side inlet of the electrochemical 
cell through a recycle line, such as line 324 as shown in FIG. 4. 
Additional advantages and modifications will readily occur to those skilled 
in the art. The invention, in its broader aspects, is therefore not 
limited to the specific details and representative apparatus shown and 
described. Accordingly, departures may be made from such details without 
departing from the spirit or scope of the general inventive concept as 
defined by the appended claims and their equivalents.