Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
BACKGROUND OF THE INVENTICN
In general, the field to which the present invention
relates is that of producing chlorinated derivatives of ethyl- -~
ene, such as vinyl and vinylidene halides, particularly vinyl
chloride. Also, closely connected therewith, is the synthesis
of chlorinated solvents from ethylene, chlorine and/or hydrogen
chloride. Among such solvents are the highly chlorinated ethyl-
enes, such as perchloroethylene which is made by a process in
which ethylene and/or partially chlorinated ethanes are sub-
~ected to one or more steps of catalytic oxyhydrochlorination
with hydrogen chloride and oxygen.
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 processes, a direct chlorination step
is a~so e~ployed wherein ethylene and elemental chlorine are
reacted in liquid phase to produce dichloroethanes which are
then cracked to vinyl chlorlde.
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 chlorohy-
drocarbon end product and, as a result, fairly large 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, etc.,
as well as aromatic compounds. Obviously, these undesirable
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chlorine-containing by-products pose economic, as well as ecolo-
gical, problems of disposal.
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 utilized
in the process and the production of unwanted chlorinated hydro-
carbon 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
.
We have unexpectedly found that the above problems of
prior processes can be overcome or substantially ellminated by
providing a process wherein the unwanted chlorohydrocarbon by- `
products are recovered for reuse in the form of hydrogen chlor- ~
ide essentially ~ree of elemental chlorine and chlorohydrocar- -
bon impurities and said hydrogen chloride is recycled to the
process for making chlorinated derivatives of ethylene. In addi-
tion, 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 said process. Specifically, the pro-
cess of the instant invention comprises passing the unwanted
chlorohydrocarbon contalnlng waste products through a heated
bed of an alumina-silica catalyst, which bed is fluidized by
air whereby said waste products are converted to a stream of ~-
combustion gases containing essentially only carbon oxides,
water, inert gases and hydrogen chloride.
DETAILED DESCRIPTION
As used herein, the terms "chlorlnated-ethylene deriva-
tives" and "chlorinated-ethylene synthesis" are generic terms
which encompass the various processes and their products wherein
ethylene is reacted with elemental chlorine and/or hydrogen
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. : . - :.. . , ., .. : ... . ..
104ZO~V
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, l,l-dichloro- -
ethane, l,2-dichloroethane, the trichloroethanes, the trichloro-
ethylenes, 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 ethylene or of
chlorinated-ethylene derivatives whereby ethylene, or a chlor-
inated derivative thereof, are converted to products of higher ~-
chlorine content, and the crackine (dehydrochlorination) or re-
arrangement of chlorinated-ethylene derivatives to produce
chlorinated-ethylene derivatives of lower chlorine content.
In the practice of the present invention the industrial
waste materials containing chlorohydrocarbons are passed into
.
and through a bed of an alumina-silica catalyst which is fluid-
ized by air and maintained at a temperature in the range of
about 400C. to about 500C. In the bed, the waste materials -
are burned and converted to a stream of combustion gases con-
taining essentially only carbon oxides, water, inert gases,
and most importantly, hydrogen chloride. 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 the hydrogen atoms attached to the
chlorine atoms of the hydrogen chloride. This enables the pro-
duction of a gas stream containing practically no elemental
chlorine. Elemental chlorine is undesirable and production
thereof must be avoided as far as possible. As complete com-
bustion as possible is al~o important since the presence of ~
chlorohydrocarbons in the combustion gases also tends to in- - ,
crease by-product formation in the oxyhydrochlorination step.
The waste materials, after enter~ng the fluid bed,
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are volatilized and then cleanly burned in the controlled man-
ner herein described. Even direct in~ection of the liquid waste
stream, which is often viscous and tarry and containing materials
comprised of suspended carbon, does not impair the bed or its
fluidization. Feeding the waste materials to the fluidized
catalytic bed may easily be accomplished utilizing standard
equipment, such as gear pumps, mechanical displacement pumps,
and the like. In view of the temperatures employed in the pre-
sent process, as described above, there are many conventional
materials that may be used to house the fluid bed which are ~ -
capable of withstanding the corrosive environment encountered -thereln.
The pressure employed in the bed of the combustion - ~
catalyst of the present invention is not critical. For exam- - ;
ple, the catalytic combustion reaction can be carried out at ~-
atmospheric pressure, particularly if the combustion gases are
not fed directly to the oxyhydrochlorination step or reaction.
When said gases are so fed, they will have to be prepressurized
to the same pressure existing in the oxyhydrochlorination re-
actor, since the oxyhydrochlorination reaction is normally oper- -
ated above atmospheric pressure. Accordingly, it is desirable
to maintain the gases in the combustion bed at a pressure in
the range of about 25 to 150 psig., and preferably in a range
of from about 40 to about 100 psig. In most cases, the pressure
should be maintained ~ust slightly higher than the pressure
maintained in the oxyhydrochlorination step in order to avoid
the necessity of compressing the combustion gases. Of course,
when one is running experiments testing the present catalytic ;
combustion reaction utilizing a simulated waste stream, atmos-
pheric pressure is satisfactory and convenient since it avoids
the necessity of pressurized equipment.
The alumina-silica combustion catalysts useful in the
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practice of the present invention are those containing from
about 13~ to about 94% by weight, based on the total weight of
catalyst, of A1203 and from about 87% to about 6~ by weight of
SiO2. Further, the catalysts must have a high surface area,
namely, a surface area of at least 10 square meters per gram
(m2/gm.). The most active catalysts of this type are those
having a surface area in the range of from about 175 m2/gm. to
about 600 m2/gm. We have found that the most useful alumina-
silica catalyst for our process is one containing pores averag- ~-
ing in size in the range of loA to 100~ in diameter and prefer-
ably, in the range of 20A to 80A. The most preferred catalyst
is one containing 94% Al203 and 6~ SiO2 and having a surface
area in the range of from about 175 to about 550 m2/gm.
The catalyst used herein is commercially available
since A1203 and SiO2 are each alone commonly utilized as sup- ~
ports for metal oxide catalysts employed in fluid bed processes -
in the oil refining industry and in chemical processes, suc'n as
oxyhydrochlorination, nitrile synthesis and maleic anhydride
synthesis. A1203 and SiO2 are readily available with the ran-
domly wide particle size distribution required for good fluidi-
zation, namely, with few, if any, particles finer than 20 mi-
crons or larger than about 200 microns in average diameter and
havlng the largest proportion of their particles in the range
of from about 40 to about 140 microns in average diameter. Very -
small particles, or "fines", having an average diameter below
about 20 microns should be avoided since they are too readily
lost from the fluid bed reactor. Similarly, large particles
having an average diameter greater than 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.
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In the present process the corrosive effect in the
fluid bed catalytic combustion chamber or reactor is very mild.
In view of this, normal heat exchange coils made of conven-
tional materials and design are inserted in the fluidized bed
where they serve either as steam generating coils or as pre-
heating coils for the raw or intermediate materials feed streams
in the process for making chlorinated derivatives of ethylene.
Even in those cases in making chlorinated derivatives of ethyl- ~ -
ene where only about 3% to 8% of the initial ethylene feed is
converted to by-products, the annual savings in heat energy is
very appreciable. Also, since the instant process is operated
at modest temperatures, the resulting combustion gases can be
fed directly to the oxyhydrochlorination reaction without inter-
stage cooling.
As pointed out hereinbefore, the present process is
carried out with the alumina-silica catalyst in fluidized form
and wherein air is utilized as the fluidizing agent or gas. 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 materials. In order
to insure complete combustion of the waste stream, it is ne-
cessary that at least two moles of oxygen (2) per mole of car- ~-
bon (C2) in the waste stream be supplied to the reaction. How-
e~er, in order to insure proper oxygen supply to the fluidizedcatalytic bed, sufficient air is fed to the bed to supply from
about 2.5 moles to about 10.0 moles of oxygen per mole of car-
bon (02/C2) or (0/C) in the waste stream. When air feed ratesare emplo~ed which provide an excess of about 10.0 moles of
3 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 hydrogen chloride to elemental
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chlorine which, as has previously been pointed out, 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.
Contact times of the waste materials or by-products
and the catalyst in the reactor may vary considerably without ~-
too much effect on the efficiency of combustion. When using a
fluid bed reactor, contact times between about 5 seconds and
about 50 seconds are satisfactory, keeping in mind that only
about one-half of the calculated contact time represents time
that the gases are in actual contact with the bed. This is be-
cause for the remainder of the time the gases are in the free
spacP above the bed in the catalyst disengaging and cyclone
separator portions of the reactor. Best results have been ob- -
tained when the contact time is in the range of about 15 to
about 35 seconds.
As previously pointed out, the most important variables
in the instant combustion process are the temperature of the
reaction and the catalytic efficiency of the catalyst. For ex-
ample, when the temperature of the reaction is below 350C.,
complete combustion cannot be achieved in reasonflble contact
times. When the reaction temperature is above 550C., the com-
bustion reaction mixture is very corrosive which, of course,
is detrimental.
We have found that most metal chlorides and metal ox-
ides have catalytic effect in the combustion reaction but to
varying degrees. The difficulty with most of these compounds
is that they function as Deacon catalysts thus convertin~ a
portion of the chlorine content of the waste materials to ele-
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mental chlorine. On the other hand, the alumina-silica cata-
lysts of this invention have the desired catalytic activity
and combustion gases produced therewith contain very little
and under optimum conditions, essentially no elemental chlorine
and essentially no chlorohydrocarbon materials. Furt~er, the
alumina-silica catalysts of this invention are inexpensive and
rugged in respect of their resistance to attrition and to foul-
ing by unburned carbon and by the trace metallic content of the
waste by-product feed streams.
By-product streams separated in various fractionation
steps in many chlorinated ethylene syntheses contain up to 1 or
2~ by weight of iron chlorides as impurities. In the catalyst
bed of the present invention, iron chlorides, and the like, are
oxidized to finely divided iron oxides the bulk of which are
carried out of the catalyst bed by the combustion gases and col-
lected in the cyclone separators. The small amount of iron -
oxides retained by the catalyst bed are without apparent harm-
ful effect 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 adversely affect the oxyhydrochlorination catalyst
which is normally on an alumina support. The only adverse ef-
fect, if any, of employing the combustion gases produced by the
instant invention 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.
When operating the present process, the combustion
reactor is first charged with the solid granular alumina-silica
3 catalyst. Upon the introduction of air, or fluidization, the
catalytic bed expands to nearly completely fill the internal
volume of the reactor. The catalyst bed is so fluidized before
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lO~Z~
the addition thereto o~ the waste by-product stream. In feed-
ing the by-product stream to the reactor, it is delivered to
the same at a position just slightly above the bottom air inlet.
Preferably, the waste stream is delivered to the reactor through
a water-cooled nozzle which prevents vaporization and/or char-
ring of the materials prior to contact of the materials with
the catalyst of the bed.
In order to more clearly define the pre~ent invention
the following specific examples are given, it being understood,
of course, that this is merely intended to be illustrative and
not limitative. In the Examples, all parts and percents are by
weight unless otherwise indicated.
EXAMPLE I
In this example 1500 grams of catalyst were charged
to a pressure reactor, the catalyst being composed of 94$ A12G3
and 6% SiO2. The surface area of the catalyst was approximately
175 square meters per gram and the bulk density (compacted) was
about 0.76 gm/cc. Pressure was applied to the reactor and
maintained therein at 75 psig. and the temperature in the reac-
tor was maintained at 450G. Air was fed into the bottom of
the reactor at a rate of 27.7 gram moles per hour. The chlorin-
ated by-product waste stream was fed into the reactor through a
spray nozzle situated above the air intake at a rate of 115 ml.
per hour. As the catalytic combustion of the waste stream took
place the effluent gases coming off the top of the reactor were
analyzed in a chromatograph with the exception of hydrogen
chloride which was analyzed by titration with NaOH. The efflu-
ent gas stream was found to contain the following: carbon
monoxide, carbon dioxide, water, nitrogen, oxygen, hydrogen
chloride, and inert materials, or "other" materials as reported
below. Based on the total carbon in the stream fed to the
reactor the yield was analyzed to be as follows:
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Yield to - C02 CO "Other"*
~ 9.LI~ o.9%
* "Other" included - perchloroethylene, chloro-
benzene, cis and trans l,2-dichloroethylene
More importantly, the amount of hydrogen chloride ob-
tained was high. Allowing for analytical inaccuracies and also,
not knowing the exact chlorohydrocarbon content of the waste
stream, the chlorine balance of the reaction, as hydrogen chlor-
ide, was 102%. This means, all factors considered, t~at essen-
tially 100% conversion or recovery to hydrogen chloride was ob-
tained. The effluent stream was subsequently used in an oxy-
hydrochlorination reaction.
EXAMPLE II
Here again the procedure of Example I was followed ~ -
employing a catalyst composed of 94% A1203 and 6% SiOz. The
catalyst had the same surface area and bulk density as that
described in Example I. The pressure applied to the reactor
and maintained therein was at 75 psig and the temperature was
450C. Air was fed into the bottom of the reactor at the rate
of 28.4 gram moles per hour. The chlorinated by-product waste -
stream was fed into the reactor at a rate of 120 ml. per hour. -
The effluent gas stream coming from the reactor contained the
same materials as in Example I. Upon analysis, the following
results were obtained: -
Yield to - C02 CO "Other"*
~.4~ 5~ --3.I~
* "Other" included - perchloroethylene, chloro-
benzene, cis and trans l,2-dichloroethylene
The chlorine balance expressed as hydrogen chloride was 101%.
Here again there was excellent conversion to useable hydrogen
chloride.
EXAMPLE III
In this example the procedure of Example I was again
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followed employing a catalyst composed of 87~ SiO2 and 13%
A1203 by weight. Several runs were made with pressure applied
to the reactor and maintained therein at 75 psig. The tempera-
ture was varied and the gram moles per hour of air fed into the
bottom of the reactor was varied. The chlorinated by-product
waste stream was fed into the reactor at a rate of 120 ml. per
hour. The effluent gas stream coming from the reactor contained
the same materials as in Example I. Particulars with respect
to feed and yield are given in the following Table I:
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:
~r~
N ~ ~1 O CD O ~1 0 ~1~ 0~ I~J
C.) C: . ... ... ....
o u~ o o a~oo o
~ I ~ ~0
O C~ ~ o 0 00 l
c~ O O O O O O a~
S::
0~) ~I t~J ~r)C~J N ~1 CS~ CO ~IJ
~1
N 0 ~ C~l O IS~ ~l ~N 0~)
C~ JO OOO ~1~11~ OOr~O :
N .-
C)
~1 ~ 0 O Lt~
C~ .. ... ... ....
o ~0~
h ~ r~l N OO ~ O ~I ~D 0
~! ~)1~ 0 N (~) Ir~l~N t ~ O~
_ 0~ ~ ~ N N ~r) C~J C~J ~)C~i
~0 ~ '~
~1~ ~ ~ Ir~N O mcs~ O 11
~1 O O ~ O C~.l 0 ~) N C~J O ~ O
rl ~ ~ 0--~ ~
~ ~ ~ 11~0 1~ L~
C\ :~
H N C~ J ~) O C~J H ~ O ~ ~
i3c o ~ l~t co ~I c~ ~\ c~ e- ~s) . . .,, -, .,,, ~,
~3c~ :i0 ~ omo
¢ ~ ~
,' :. -
O O O O - -:
C~l O O O O --~
~0 C)- ~i ,i ,-i ,i .. ..
d ' :
p:; ~r) ~) N ~ )
C~ 1~ 0 a~
'O :~
0 0 0 ~I
O
O ::1- (r) ~ ~ ,........ .
~ ~. ' '
U~
~-~ 0 ~0 C- ~ '
~ ~ V C) ~ '
O O O O
C~ ~
td ~ t' ~t ~ J ",, ~' ,,,
" ~ -
.' ' .
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Here again, as in the previous examples, there was
good conversion to useable hydrogen chloride.
Thus, it can be seen that the instant invention pro-
vides a new and improved method of disposing of undesirable
chlorinated by-products normally obtained when producing chlor-
inated derivatives of ethylene, such as in the production of
vinyl chloride. The present method goes even further in that
the catalytic oxidation permits recovering the contained chlor-
ine in the waste products as hydrogen chloride which is then
useable in the oxyhydrochlorination step in the production of
chlorinated derivatives of ethylene.
Heretofore, hydrogen chloride has been recovered from
the undesirable chlorinated by-products by incineration employ-
ing methane as a fuel. However, 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. On the other hand the present
process is economical in that no additional fuel is necessary
thus substantially reducing the cost of recovery. Also, the
new method 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 thè
production of chlorinated derivatives of ethylene. Another
advantage of the instant process 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.
While the present invention has been described in
terms of its specific embodiments, certain modifications and
equivalents will be apparent to those skilled in the art and
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are intended to be included within the scope of the present ~ -
invention, which is to be limited only by the reasonable scope
of the appended claims.
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