Note: Descriptions are shown in the official language in which they were submitted.
~47540
BACKGROUND OF THE INVENTION
The general field to which the present invention re-
liates is that of producing chlorinated derivati~es of etnylene,
such as vinyl and vinylidene chlorides, particularly vinyl
chloride. Also, closely connected therewith is the synthesis
of chlorinated solvents from ethylene, chlorine and/or hydrogen
chloride. Among such solvents are t~e highly chlorinated ethyl-
en~s, such as perchloroethylene which is made by a process in
which ethylene and/or partially chlorinated ethanes are sub-
jected to one or more steps of catalytic oxyhydrochlorination
with hydrogen chloride and oxygen. Such a process is shown in
British Patent No. 962,872.
Vinyl chloride is prepared by various processes from
ethylene, elemental chlorine, and/or hydrogen chloride in most
all of which a cracking step is employed wherein ethylene di-
chloride is thermally cracked in the vapor phase under pressure
to vinyl chloride and by-product hydrogen chloride. The latter
is recovered by an oxyhydrochlorination step wherein the hydro-
gen chloride is reacted with additional ethylene and oxygen to
produce dichloroethanes which in turn are recycled to the
cracking step. In many procesees, a direct chlorination step
is also employed wherein ethylene and elemental chlorine are
reacted in liquid phase to produce dichloroethanes which are
then cracked to vinyl chloride.
In all of these known solvent and monomer processes,
the desired direct chlorination, oxyhydrochlorination, and/or
- cracking steps are not 100% selective to the desired chloro-
hydrocarbon end product and, às a result, significant quantities
of undesired chlorine-containing by-products are obtained as
complex mixtures which range in composition from chloroform or
ethyl chloride to trichloroethanes and trichloroethylenes,
tetrachloroethanes, hexachloroethanes, hexachlorobutadiene,
1047540
etc., as well as aromatic compounds. Obviously, these undesir-
able chlorine-containing by-products pose economic, as well as
ec:ological, problems of disposal.
A known and useful process ~or the production of vinyl
chloride involves the so-called "adiabatic" or "one-step" reac-
tion of mixed vapors of ethylene and elemental chlorine at
superatmospheric pressure and hightemperatures. It is believed
that in such a process the ethylene and chlorine react to form
ethylene dichloride which in turn is simultaneously thermally
and catalytically cracked to vinyl chloride and a hydrogen
chloride by-product. The term "adiabatic process" is derived
from the nature of the two process steps ~ust referred to.
That is, the reaction of ethylene and chlorine is exothermic
in nature while the cracklng of the product thus obtained is
endothermic in nature. Therefore, it is theoretically possible
to balance the heat yield and heat consumption of the two reac-
tions and thereby operate nearly adiabatically with reduced
heat input. Tne hydrogen chloride generated in such an adiaba-
tic process is recovered in an oxyhydrochlorination step wherein
a mixture of the by-product hydrogen chloride, ethylene and
oxygen are catalytically reacted to form ethylene dichloride
which is then recycled to the first stage adiabatic reactor.
A process of this type is shown in U.S. Patent No. 3,291,846.
One undesirable characteristic of the known forms of
the adiabatic vinyl chloride process is the relatively higher
proportion of polychlorinated by-product formed in the first
stage chlorinator/cracking step which represents not only a
loss of the ethylene, chlorine and/or hydrogen chloride raw
materials, but also, a significant loss of heat energy in a pro-
cess which is supposedly intended to be an adiabatic procedure.
Unfortunately, in come cases, such chlorine-containing by-
products can amount to as much as about 10 to 20 mol percent
~047540
based on the starting raw materials. Accordingly, unless a
means is provided to accommodate such large losses of raw mater-
ials in unwanted by-products and loss of heat energy, an other-
wLse potentially attractive process becomes unattractive econom-
ically.
Further, prior art methods for making dichloroethanesas precursors for both monomers and solvents have, for the most
part, involved the direct interaction of ethylene and elemental
chlorine in the liquid phase using ethylene dichloride as a
solvent and at low temperatures. Such a reaction is extremely
exothermic but, unfortunately, its 'neat yield is liberated at
such low temperatures that the only practical method of temper-
ature control involves the use of large volumes of process
cooling water. Thus, the heat of reaction can only be liberated
in large water-coollng towers or by discharging the heated water
to a natural water course. Neither of such methods of heat
disposal is satlsfactory from an ecological and economic point
of view.
Therefore, it would be most desirable and beneficial
to have a process for producing chlorinated derivatives of
ethylene and chlorinated solvents from ethylene, chlorine and/
or hydrogen chloride wherein the heat energy produced is util-
ized in the overall process and the production of unwanted
chlorinated hydrocarbon by-products is substantially eliminated,
or the end result is insignificant, due to reutilization of the
waste products in the process.
SUMMARY OF THE INVENTION
~ e have unexpectedly found that the above problems
of prior processes can be overcome or substantially eliminated
by providing a process wherein the unwanted chlorohydrocarbon
by-products are recovered for reuse in the form of hydrogen
chloride essentially free of elemental chlorine and cnlorohydro-
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~47S40
carbon impurities and said hydrogen chloride is recycled to
the process. In addition, the intrinsic heat energy values of
the crude by-products are returned to the process to preheat raw
material feeds and intermediate feeds in the process for pro-
ducing chlorohydrocarbons from ethylene.
According to the invention there is provided in the
process of producing chlorinated derivatives of ethylene which
includes the step of oxyhydrochlorination whereby hydrogen
chloride is reacted with oxygen and ethylene or a chlorinated
ethylene derivative, the improvement which comprises separating
in a stream from said process any unwanted chlorinated ethylene
derivatives and other by-products, injecting said stream into
a fluidized bed of an alumina combustion catalyst which is being
fluidized by air and maintained at a temperature in the range
of about 400C. to about 500C. to produce a mixture of hot
combustion gases containing essentially hydrogen chloride and
being essentially free of both elemental chlorine and chloro-
hydrocarbon materials, recycling said mixture of gases to said
oxyhydrochlorination step, and wherein at least a portion of
the raw materials fed to said process is employed to remove
heat from said fluidized bed of combustion catalyst.
Specifically the new and novel process has been
developed for the production of vinyl chloride, which is based
mainly on ethylene and elemental chlorine as the raw materials,
but which can just as easily employ hydrogen chloride. The steps
of this process include (a) a reaction between ethylene and
chlorine to form vinyl chloride and hydrogen chloride;
, . ~ --
~047540
(b) an oxyhydrochlorination step wherein hydrogen
chloride from step (a) and also step (c) below, is reacted with
e1:hylene over a Deacon catalyst in the presenceof oxygen to pro-
duce dichloroethanes which can be recycled to step (a), and (c)
S a low temperature (about 400 to 500C) fixed or fluid bed
catalytic combustion step wherein unwanted hydrocarbon-containing
by-products, incuding chlorohydrocarbon by-products, are burned
in a highly controlled fashion to form a stream of combustion
gases containing hydrogen chloride essentially free of both
elemental chlorine and chlorohydrocarbon materials, which stream
of combustion gases is recycled to the oxyhydrochlorination step
(b) to recover the hydrogen chloride content thereof as di-
chloroethanes and wherein the raw material feed streams of step
(a) and/or (b) are employed to absorb the heat of combustion in
step (c) and return heat energy to the vinyl chloride synthesis.
The handling of the heat energy in step (c) can really be
considered as a fourth step, namely, a closed heat loop.
Step (a) is conveniently an adiabatic one-step
reaction between ethylene and elemental chlorine at high
temperatures. This reaction may be carried out in the vapor
phase at 325 to 460C to form ethylene dichloride, with
simultaneous cracking of the ethylene dichloride to form a
mixture of vinyl chloride and by-product hydrogen chloride.
The chlorination of the ethylene may also be carried
out at low temperatures in a liquid phase, whereafter the
ethylene dichloride may be cracked under pressure in a vapor
phase at a temperature of 450 to about 650C to form a
mixture of vinyl chloride and by-product hydrogen chloride.
DETAILED DESCRIPTIO~
As used in this specification, the terms "chlorinated-
ethylene derivatives" and "chlorinated-ethylene synthesis" are
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generic terms which encompass the various processes and their
p~oducts wherein ethylene is reacted with elemental chlorine
an,d/or hydrogen chloride in one step or in a plurality of steps
to produce a chloroethylene or chloroethane type compound, such
as vinyl chloride, vinylidene chloride, ethyl chloride, 1,1-
dichloroethane, l,2-dichloroethane, the trichloroethanes, the
trichloroethylenes, the tetrachloroethanes, perchloroethylene,
and many others, Thus, chlorinated-ethylene synthesis includes
any of the steps of direct chlorination of ethylene or of
chlorinated-ethylene derivatives, oxyhydrochlorination of ethyl-
ene or of chlorinated-ethylene derivatives w~.e reby ethylene,
or a chlorinated derivati~e thereof, are converted to products
of higher chlorine content, and the cracking (dehydrochlorin-
ation) or rearrangement of chlorinated-ethylene derivatives to
produce chlorinated-ethylene derivatives of lower chlorine con-
tent.
In general, the process of the present invention com-
prises combining a synthesis of chlorinated-ethylene derivatives
which includes at least one step of oxyhydrochlorination, then
separating unwanted by-products from the chlorine-containing
intermediates and from the desired chlorinated-ethylene product,
and thereafter sub~ecting the thus separated unwanted by-products
to catalytic combustion which is exothermic. It is this com-
bustion step which is an essential part of the present invention.
The catalytic combustion is accomplished by bringing
the said by-products into contact with air and/or oxygen at
atmospheric or superatmospheric pressures in a fixed or fluidlzed
bed of solid alumina-containing combustion catalyst, which bed
of catalyst is maintained at a temperature in the range of about
400C. to about 500C. thereby producing a stream of combustion
gases comprised ess~ntially of hydrogen chloride, carbon oxides,
water and inert gases. Inasmuch as these combustion gases are
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lQ4'~5~0
to be recycled to an oxyhydrochlorination step or reaction, it
is necessary that the gases do not contain elemental chlorine
or chlorohydrocarbon materials since they will increase the
complexity of the process by producing unwanted high boiling
polychlorinated by-products in the gases leaving the oxyhydro-
chlorination step or reactor. Further, elemental chlorine at
these temperatures is highly corrosive to all common metals and
alloys, Thus, any elemental chlorine in these combustion gases
would greatly increase the cost of equipment (replacement) and
therefore might make the process impractical. Therefore, the
temperature of the catalyst bed is important since it has been
found that when the temperature of said bed is below 400C. in-
complete combustion results thus producing a stream of gases
containing hydrogen chloride contaminated with unreacted and/or
partlally pyrolyzed chlorohydrocarbon materials. When the
temperature of the catalyst bed is above 500C., oxidation of
the hydrogen chloride results in the formation of elemental
chlorine.
Under the conditions specified, the fluidized bed of
solid alumina-containing combustion catalyst provides essen-
tially complete oxidation of the most complex and discolored
high boiling stillbottom by-product streams with the formation
of hydrogen chloride. Many stillbottom materials, produced in
the purification of chlorinated solvents, in the purification
f ethylene dichloride and in the purification of vinyl chlor-
ide monomer may contain benzene and/or more complex aromatic
- ~ompounds and are heavily contaminated with iron chlorides,
tarry materials, and dispersed or suspended carbon. However,
even the most viscous and tarry residues can be heated to re-
duce their viscosity and then in~ected under pressure into the
bed of solid alumina-containing combustion catalyst without
impairing the operation of the catalyst bed.
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l(J47540
The pressure employed in the ~ixed or fluidized bed
of solid alumina-containing combustion catalyst is not critical
since atmospheric or superatmospheric pressure may be employed.
~owever, since an oxyhydrochlorination reaction is normally
operated above atmospheric pressure, it is usual to feed the
combustion gases to said reaction at an equal or comparable
pressure. Accordingly, it is desirable to maintain the gases
in the combustion bed at a pressure in the range o~ about 25
to 150 psig., and preferably in a range of from about 40 to about
lO0 psig. In any event, the pressure should be maintained
~ust slightly higher than the pressure obtaining in the o~yhy-
drochlorination step in order to avoid the necessity of com-
pressing the combustion gases.
The alumina combustion catalyst employed herein must
have a high surface area, namely, a surface area of at least
10 square meters per gram (m2/gm.). The most active alumina
catalyst of this type is one having a surface area in the range
of from about 80 m2/gm. to about 400 m2/gm. It has been ~ound
that the most useful alumina combustion catalyst for the pre-
sent process is one containing pores averaging in size in the
range of 30A to 60A in diameter and having a sur~ace area in
the range o~ from about lO0 m2/gm. to about 200 m2/gm.
The alumina combuction catalyst o~ the present inven-
tion is readily available with the randomly wide particle size
distribution required for good ~luidization, namely, with few,
if any, particles ~iner than 20 microns or larger than about
200 microns in average diameter and having the largest propor-
tion of particles in the range of from about 40 to about 140
microns in average diameter. Very small particles, or ~Ifines~
having an average diameter below &bout 20 microns should be
avoided since they are too readily lost from the reactor. Simi-
larly, large particles having an average diameter greater than
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1~)47540
about 200 microns are to be avoided since they are too difficult
to fluidize, It is apparent, due to the nature of the present
process, that the catalytic material must not be friable and
should be resistant to attrition to the maximum extent possible.
In the fluid bed combustion catalyst system of the
present invention, the air must be employed in a sufficient
quantity and at a rate of flow not only to completely fluidize
the catalyst bed but also, to furnish sufficient oxygen for the
controlled combustion of the hydrocarbons of the waste or by-
product stream. In order to insure complete combustion of the
waste stream, it is necessary that at least two moles of oxy~en
(2) per mole of carbon (C2) in the waste stream be supplied
to t~e reaction. J~owever, in order to lnsure proper oxygen
supply to the fluidized catalytic bed, sufficient alr is fed
to the bed to supply from about 2.5 moles to about 10.0 moles
of oxygen per mole of carbon (02/C2) or (0/C) in the waste
stream. When air feed rates are employed which provide an ex-
cess of about 10.0 moles of oxygen per mole of carbon in the
waste stream, reduced capacity and catalyst losses result and,
more importantly, it increases the risk of oxidation of the hy-
drogen chloride to elemental chlorine which is to be avoided.
When the air feed rates are such that less than about 2.0 moles
of oxygen per mole of carbon in the waste stream are provided,
only about 80% to 85% of complete combustion results. The
preferred air feed rates are such that about 2.5 moles to about
5.5 moles of oxygen are provided for each mole of carbon in the
waste feed stream.
In the alumina combustion catalyst bed, the time of
contact of the waste materials with the bed is about 10 seconds
3o to about 50 seconds. The catalyst, at the temperatures employed,
causes essentially complete combustion of the chlorohydrocarbons
in the waste stream but limiting said combustion so as to leave
_g_
7540
the hydrogen atoms attached to the chlorine atoms of the hydro-
gen chloride. This enables the production of a gas stream con-
taining practically no elemental chlorine. Elemental chlorine
is undesirable and production thereof must be avoided as-far
as possible. As complete combustion as possible is also impor-
tant since the presence of chlorohydrocarbons in the combustion
gases also tends to increase by-product formation in the oxyhydro-
chlorination step.
The waste materials, after entering the alumina com-
bustion catalyst bed, are volatilized and then cleanly burned
in the controlled manner herein descrlbed. Even direct injec-
tion of the liquid waste stream. which is often viscous and
tarry and containing materials comprised of suspended carbon,
does n~t impair the catalyst bed and when employing a fluid bed,
does not impair the fluidization thereof. Feeding the waste
materials or stream to the catalyst bed may easily be accom-
plished utilizing standard equipment, such as gear pumps, mech-
anical displacement pumps, and the like. In view of the temp-
eratures employed, there are many conventional materials that
may be used to house the catalyst bed which are capable of
withstanding the corrosive environment encountered therein.
However, in the present process, the corrosive effect in the
catalytic combustion chamber or reactor is very mild. In view
of this, normal heat exchange coils made of conventional mater-
ials and design are inserted in the catalyst bed where they
serve either as steam generating coils or as preheating coils
- for the raw or intermediate materials feed streams in the pro-
cess for making chlorinated derivatives of ethylene. Even in
those cases in making chlorinated derivatives of ethylene where
only about 3% to 8~ of the initial ethylene feed is converted
to by-products, the annual savings in heat energy is appreci-
able. Also, since the combustion step is operated at low temp-
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-
7540
eratures the resulting combustion gases can be ~ed directly to
the oxyhydrochlorination reaction without interstage cooling.
It has been found that most metal chlorides and metal
oxides, when used alone, have some catalytic effect in the com-
bustion reaction step but to varying degrees. The difficulty
with most of these compounds when used alone is that they func-
tion as Deacon catalysts thus converting or rearranging at
least a portion of the chlorine content o~ the waste materials
to ~orm new polychlorinated hydrocarbons some of which are more
resistant to oxidation. When so using such metallic catalysts,
the combustion gases generally contain appreciable amounts of
polychlorinated and unsaturated by-products. On the other hand,
we have unexpectedly found that the alumina (A1203) catalyst
employed in the present invention has the desired catalytic
activity and the combustion gases produced therewith contain
very little, and under optlmum conditions, essentially no ele-
mental chlorine and essentially no chlorohydrocarbon materials.
Further, the alumina catalyst of this invention is inexpensive
and rugged in respect of its resistance to attrition and to
~ouling by unburned carbon and by the trace metallic content
of the waste by-product ~eed streams. By-product streams sep-
arated in various ~ractionation steps in many chlorinated ethyl-
ene syntheses contain up to 1 to 2% by weight of iron chlorides
as impurities. In the alumina combustion catalyst bed of the
present invention, iron chlorides, and the like, are oxidized
to ~inely divided iron oxides the bulk of which are carried out
of the catalyst bed by the combustion gases and collected in
the cyclone separators. However, when the iron oxides are
extremely fine, they will pass through the cyclone separators
and oxyhydrochlorination reactor and captured in a water scrubber
following said reactor. The small amQunt of iron oxides re-
tained by the catalyst bed are without apparent harmful effect
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~4'7540
on the catalyst bed efficiency. Also, any small amount of iron
oxides carried out of the combustion reactor by the combustion
gases to the subsequent oxyhydrochlorination step do not affect
the oxyhydrochlorination catalyst which is normally on an alumina
support. The only adverse effect, if any, of employing the
combustion gases in the oxyhydrochlorination step is a very
small decrease in capacity due to increased loadings of inert
gases from the combustion gases, in the oxyhydrochlorination
feed.
In any chlorinated ethylene process it is essential
to have an oxyhydrochlorination step in order to consume by-
product hydrogen chloride formed in any cracking or rearrange-
ment step and, as is the case in the present invention, to con-
vert the hydrogen chloride content of the by-product combustion
gases to useful intermediates or final products. A suitable
oxyhydrochlorination reaction or step to produce ethylene di-
chloride or EDC, is one in which a mixture of ethylene, oxygen
and hydrogen chloride, having a low moisture content, is passed
through a bed of a fluldizable Deacon catalyst under superatmos-
pheric pressure and at a velocity which fluidizes the catàlyst.
The catalyst employed is a copper chloride on an alumina 8Up-
port. The catalyst, on the other hand, employed in the fluid
bed catalytic combustion step, described above, is all alumina,
The concentration of the copper chloride on the alumina support
is usually between about 3% and 12% by weight as copper and
preferably, is between about 3.5% and 7% by weight as copper.
Internally disposed steam generating coils in direct contact with
the fluidized bed remove the heat of the exothermic reaction
whereby the temperature in the bed is maintained in the range
3o of about 190C. to about 250C and preferably, in the range
of about 220C. to about 240C. The fluidized bed reaction is
essentially isothermal if the temperature in said range and a
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~047540
pressure between about 10 and about 50 psig. are balanced to
stay above the dew point of the reactants, product and inert
materials.
With reference to dew point, it is essential that the
f:Luidized bed oxyhydrochlorination reactor receiving recycle
combustion gases be operated at a pressure and temperature above
the dew point of the gases in the bed. The combustion gases con-
tain water formed in the combustlon of the hydrogen content of
the by-product feed. Normally, a fluidized bed of Deacon type
oxyhydrochlorination catalyst must be operated with incoming
gas mixtures which are as low as practical in moisture in order
to prevent condensation of moisture and/or other liquids in
the bed. Such condensation could leach the active copper cata-
lyst content thus formine localized areas of high concentration
wh~ch could lead to hot-spot formation. Since water is also
one of the by-products of the oxyhydrochlorination reaction,
and unless care is exercised, it may be possible for the total
moisture content of the gases, including intermixed recycle
combustion gases, to become too high. This is especially true
in the upper regions of the bed in a large commerc~al size
fluid bed oxyhydrochlorination reactor.
Another important feature of the instant invention
i~ the utilization in other stages of the process of the heat
energy generated during the combustion of chlorine-containing
by-products in the fluid bed catalytic combustion step. The
fluid bed catalytic combustion reactor is operated at low com-
bustion temperatures, namely, in the range of about 400 to
500C. while the fluid bed of the oxyhydrochlorination step is
operated at a temperature in the range of about 190 to 250C.
3o The temperature differental between the recycle combustion gases
and the oxyhydrochlorination step is not too great. When the
heat content of the combustion æases is lntermingled with the
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i()47540
feed streams to the oxyhydrochlorination reaction, the need for
outside heat for feed preQeating is greatly reduced and in many
inlstances eliminated.
Further, since heat must be removed from the combus-
tion bed to effect control of the temperature of combustion in
the range indicated, a substantial portion of the heat gener-
ated in the by-product fluid bed catalytic combustion step can
be recovered and returned to the process by passing incoming
raw materials or one or more of the intermediate feed streams
into heat exchange relationship with the fluid bed catalyst of
the combustion reactor. While the more usual steam generating
coils disposed in the fluid bed combustion reactor can be em-
ployed for removal of heat, it has been found to be more desir-
able to recover the heat of combustion by passlng reactant
feed materials through coils and/or other heat exchangers in
contact with the catalyst of the combustion bed. In con~unc-
tion with a preferred step of the instant invention, namely,
the adiabatic type of ethylene/chlorine to vinyl chloride re-
actor, a more nearly adiabatic style of operation can be achieved
by preheating the ethylene/chlorine feed streams in heat ex-
change with the fluid bed combustion catalyst.
The preferred combination of steps of the present
inventive process, such as the one step chloro-cracking or
adiabatic ethylene/chlorine to vinyl chloride reaction and the
low temperature fluid bed catalytic combustion of by-products
in closed heat-loop operation, provides a new and unique solu-
tion to heat wastage or heat energy loss. The one step vapor
phase hot chlorination of ethylene is strongly exothermic and
liberates its heat at temperatures sufficiently high to crack
3o the ethylene dichloride (EDC) to form vinyl chloride. The
cracking of EDC is an endothermic reaction. Theoretically the
two reactions should supply a small excess o~ heat but due to
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1~)475~0
various heat losses and the heat required to preheat feed
streams, it is necessary to maintain a net heat input into the
process. The closed heat loop, whereby the ethylene and chlor-
lne feeds are preheated by the by-product combustion reactor,
significantly reduces the net heat input required for the chlor-
inator/cracker operation.
The oxyhydrochlorination reaction is also strongly
exothermic and, as commonly carried out in a fluidized bed re-
actor, is a significant net low pressure steam generator. The
EDC produced in the oxyhydrochlorination reaction, however,
is fed back to the chlorinator/cracker where it is cracked to
vinyl chloride. The heat absorbed in cracking such recycled
EDC has to be supplied to the chlorinator/cracker and such heat
load, plus the heat energy requirements of the vinyl c~loride
recovery and purification train, are the main heat requirements
of the overall process. The overall process is thus signifi-
cantly lower in required heat energy costs than presently known
vinyl chloride processes where large amounts of natural gas
are required to operate the known forms of the direct fired
tube-type cracking furnaces and gas-fired burner type by-product
disposal furnaces.
Also useful in the present process is a vinyl chlor-
ide cracking step, such as the well-known process shown in U.S.
patent No. 2,724,oo6. In such a process, the material commonly
known as "EDC", which is a mixture comprised essentially of
1,2-dichloroethane and some l,l-dichloroethane, is vaporized
and the vapors passed through a tube-type cracking furnace
which usually is directly heated by gas burners to a temperature
in the range of about 450 to 650C. Usually no cracking
catalyst is employed but there are prior art processes which
disclose the use of cracking tubes packed with either porous
inert solids or with other type catalysts which are alleged to
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1047S40
facilitate the reaction. In the absence of a catalyst, the re~
action is a thermally induced cracking whereby one molecule of
hydrogen chloride issplit out of each EDC molecule forming one
molecule of vinyl chloride.
In the cracking reaction, pressures will range any-
where from 1 atmosphere, or slightly below, up to 28 to 48
atmospheres. The mixed vapors from the cracking furnace are
cooled to condense the bulk of the chlorohydrocarbons. The re-
covered chlorohydrocarbons are then fractionated in one or more
columns to separate hydrogen chloride, vinyl Ghloride, EDC and
impurities. In this fractionation, low and high boiling im-
purities, or by-products, are also separated out which are then
fed to the catalytic combustion step of the present process.
The by-product hydrogen chlorlde i8 recycled to the oxyhydro-
chlorination ~tep to produce additional EDC which, along with
the recovered unreacted EDC, is returned to the cracking step.
There are also other known thermal cracking processes
all of which may be employed in conjunction with or as a step
in the present process. In any event~ in each case the effluent
gases leaving the cracking furnace are treated to recover and
purify the desired cracked chlorohydrocarbon product, such as
vinyl chloride In the recovery and purification treatment,
the product is condensed, washed with water, if desired, and
distilled and fractionated to produce an overhead stream of
purified product and one or more often dark-colored and viscous
stillbottoms streams containing high-boiling polychlorinated
derivatives of ethylene, unsaturated dienes, such as butadiene
and chloroprene, aromatic hydrocarbons, such as benzene, tarry
residues and iron chloride impurities. t~hile the proportions,
3o based on the stoichiometry of the reaction, of unwanted by-
products produced by cracking are small, they are nevertheless
higher than is produced in the oxyhydrochlorination step and as
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lV4'~S40
a result, the cumulative total produced in a commercial vinyl
chloride installation is substantial and poses a serious dis-
po~;al problem Thus, the present invention offers a distinctly
`advantageous process since such stillbottoms streams are an
ideal feed to the catalytic combustion step thus essentially
eliminating the disposal problem.
Further, the so-called direct chlorination reaction
may be employed as a step in the present process, particularly
in con~unction with the catalytic combustion step. In direct
chlorination, ethylene, or a chlorinated derivative of ethylene,
is reacted with elemental chlorine in liquid phase at low temp-
eratures in the range of 20 to 50C. to produce a chlorinated
derivative of increased chlorine content. Catalysts may be
employed in the reaction, such as iron chlorides, and the like.
In the reaction, about one mole each of ethylene and chlorine
dissolved in liquid ethylene dichloride react vigorously witn
liberation of heat to produce l,2-dichloroethane or ethylene
dichloride (EDC). Likewise, and at slightly higher temperatures
in the range of 40 to 75C., about equimolar proportions of
EDC and elemental chlorine react to form tetrachloroethane which
is a precursor of both perchloroethylene, and especially tri-
chloroethylene. These products are usually ~actionally dis-
tilled to remove the unwanted by-products as stillbottoms
streams. These streams, being particularly suitable, are then
cycled to the catalytic combustion step in the present invention.
I~hen operating the present process utilizing a fluid
bed in the catalytic combustion step, the combustion reactor is
first charged with the solid granular alumina catalyst. Upon
the introduction of air, inducing fluidization, the catalytic
bed expands so that the internal volume of the reactor may vary
from half full to nearly completely full, depending on the
volume of catalyst and volume of air employed. The catalyst
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~04~'7~40
bed is fluidized before the addition thereto of the waste by-
product stream. In feeding the by-product stream to the reac-
tor, it is delivered to the same at a position just slightly
above the bottom air inlet. Pre~erably, the waste stream is
delivered to the reactor through a water-cooled nozzle which
prevents vaporization and/or charring of the materials prior to
contact of the materials with the catalyst of the bed.
In order to more clearly define the present invention
the following specific example is given, it being understood,
of course, that this is merely intended to be illustrative and
not limitative. In the example, all parts and percents are by
weight unless otherwise indlcated.
EXAMPLE I
The alumina catalyst employed in this run had a sur-
face area of 150 m2/gm. and was charged to a fluid bed main-
tained at atmospheric pressure. Atmospheric pressure was em-
ployed for simplicity of operation in the pilot plant. How-
ever, in a plant, superatmospheric pressure would preferably
be employed. The amount of catalyst used was 265 grams. Air
was ~ed to the reactor at a rate of o.685 moles~nour and the
waste stream was fed to the reactor at a rate of 2.82 cc./hour.
The reaction was continued for a period of 55 hours and the
feed rate of the waste stream was fixed so as to give a contact
time between the waste stream and the catalyst varying from
31.8 to 29.5 seconds. The temperature in the reactor was varied
from 450C. to 500C. The waste stream was comprised essen-
- tially of the following materials: trans 1,2-dichloroethylene,
l,l-dichloroethane, cis l,2-dichloroethylene, CHC13, ethylene
dichloride, l,l,l-trichloroethane, carbon tetrachloride, 1,1,2-
trichloroethylene, 1 ~,2-trichloroethane, and tetrachloroethyl-
ene. As the catalytic combustion of the waste stream took
place, the effluent gases coming off the top of the reactor
-18-
~ (?~7540
were analyzed in a chromatograph with the exception of hydrogen
chloride which was analyzed by titration with NaOH. The data
with respect to the run is given in the following table:
-19-
~)47S40
. . . . . . . .
o C~l ~oo C~ o
V o ~ ~ U~ ..~ U~
CU O~
~CO Ct~ ~CO
~ v ~ o~ ~o
t~ ~ ~ o ~o ~ ~
~o ~
~1 CU C~~0 0 0
o ~ ,~ .
~c~J ~ ~a.
~1 ~O C\J C- ~ 0 ~D C~J
P: o~oo a~
o ,.
~
o o co ~ ~ ~o ~ ~ ~
CO~O Jt~O OCO
t~ CO
~t J Ll~ J U~J J
:~ O 000 000 00
O V ........
a) o~ ~c-~ oco
C~.l OJ ~
O 000 000 00
I O O O
V I ~
o
~1 1~ I C~J- - C~J,, _ C~J=
m c~ cu c~
:~;
I ~ ~ ~
N = = = . ._
O ~ ~ ~
~ ~ I --I ~ ,1
~ ~
O O O
~1 N (U C~l
,0. ~1 ~1 ~1
~; ~= = ~- = ~=
C`J L~
:~
U~ U~
C~J C~J CU
CU J = = J = - J _
O .
~d CO
a) .
~I = - o = . a~,=
V E~ u~ ~ ~ cu
~ O lS~ O
L~= = ~= - O =
~ ~; .
a) ~v
o
~n Ll~ ~
~ ... ..
c) ~ ~1 u~ o
--20--
~4'7540
The effluent gas stream was ready for use, as obtained, in an
o~yhydrochlorination reaction.
The important advantage of the instant invention is
th~at it provides a new and improve~ method of disposing of un-
desirable chlorinated by-products normally obtained when pro-
ducing chlorinated derivatives of ethylene, such as in the
production of vinyl chloride. The present process goes even
further in that the catalytic oxidation step permits recovering
the contained chlorine in the waste products as hydrogen chlor-
ide which is then useable in the oxyhydrochlorination step in
the production of chlorinated derivatives of et'.~ylene.
Heretofore, hydrogen chloride has been recovered from
the undesirable chlorinated by-products by incineration. How-
ever, this method is very costly and unreliable. Further, such
a process is highly impractical since the cost of recovery is
more than five times the market price of the hydrogen chloride.
The main element of cost in methods such as this is related to
the highly corrosive hydrochloric acid formed. When hydrogen
chloride is dissolved in water, the suitable materials of con-
struction are expensive and fragile resulting in high mainten-
ance costs. On the other hand, the catalytic combustion step
of the present process is economlcal in that no additional fuel
is necessary thus substantially reducing the cost of recovery.
Also, the catalytic combustion step is advantageous in that
the temperatures employed permit heat exchange for generating
steam or the heat energy produced can be utilized in preheating
- the feed streams in the production of chlorinated derivatives
of ethylene. Another advantage is the fact that substantially
no elemental or free chlorine is produced thus resulting in
only an insignificant amount of corrosion of equipment. Numer-
ous other advantages of the present invention will be readily
apparent to those skilled in the art.
-21-
i~47S40
While the present invention has been described in
te]~ns of its specific embodiments, certain modifications and
equivalents will be apparent to those skilled in the art and
are intended to be included within the scope of the present in-
vention, which is to be limited only by the reasonable scope
of the appended claims.
-22-
