CA1042020A

CA1042020A - Low temperature fluid bed catalytic combustion of chlorohydrocarbon waste stream

Info

Publication number: CA1042020A
Application number: CA226,042A
Authority: CA
Inventors: Ronald M. Kovach; Henry J. Essig
Original assignee: BF Goodrich Corp
Current assignee: Goodrich Corp
Priority date: 1974-07-22
Filing date: 1975-05-01
Publication date: 1978-11-07
Also published as: JPS5113708A; FR2279701A1; FR2279701B1; NL7506866A; SE7508289L; IT1036389B; SE425309B; DE2532075A1; AU8080575A; BE831590A; JPS6012326B2; ES439003A1; GB1505869A

Abstract

LOW TEMPERATURE FLUID BED CATALYTIC COM-BUSTION OF CHLOROXYDROCARBON WASTE STREAM
ABSTRACT OF THE DISCLOSURE
There is disclosed an improved method of making chlor-inated derivatives of ethylene wherein chlorine-containing by-products are burned in a fluid bed catalytic combustion reactor to produce primarily a hydrogen halide which is recycled to the chlorinated derivative reaction and the heat of combustion from said reactor is utilized to preheat the materials in said chlor-inated derivative reaction. The fluid bed catalyst is one con-taining 13% to 94% Al2O3 and 87% to 6% SiO2 and having a surface area of at least 10 square meters per gram. The fluid bed catalytic combustion reaction is carried out under superatmos-pheric pressure and at temperatures in the range of about 350°C.
to about 550°C. to produce a mixture of gases containing essen-tially hydrogen chloride and carbon oxides, water and inert materials, said mixture being substantially free of elemental chlorine and chlorohydrocarbon compounds.

Description

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 ' .

.

1~4;~0~) 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 ~ ., . . :

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

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, 10~0~
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 i~2QZo 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.

0~
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 .

ZQZ~3 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-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 _9_ : . .

- - .- . ~ . : ~ :

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:

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 ~o~ v 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:

:

~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 ",, ~' ,,, " ~ -.' ' .

-13- :- -.

- . .
- . .~ ~ .

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 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.

.~ , . .

.. . .

.

Claims

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

1. 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 com-prises separating in a stream from said process any unwanted chlorinated ethylene derivatives and other by-products, inject-ing said stream into a fluidized bed of an alumina-silica combustion catalyst comprised of 13% to 94% by weight of Al2O3 and 87% to 6% by weight of SiO2 which is being fluidized by air and maintained under superatmospheric pressure and at a tempera-ture in the range of about 350°C. to about 550°C. to produce a mixture of hot combustion gases containing essentially hydrogen chloride and being essentially free of both elemental chlorine and chlorohydrocarbon materials.

2. A process as defined in claim 1, wherein said tempera-ture is in the range of about 400°C. to about 550°C.

3. A process as defined in claim 2, wherein said catalyst has a surface area of at least 10 square meters per gram.

4. A process as defined in claim 1, 2 or 3, wherein the catalyst is comprised of 94% by weight of Al2O3 and 6% by weight of SiO2.

5. A process as defined in claim 2, including recycling the produced mixture of hot combustion gases to said oxyhydro-chlorination step.

6. A process as defined in claim 1, 2 or 3, wherein the pressure is in the range of 25 to 150 psig.

7. A process as defined in claim 1, 2 or 5, wherein said combustion catalyst has a surface area of at least 175 square meters per gram.

8. A process as defined in claim 1, 3 or 5, wherein the chlorinated derivative of ethylene is vinyl chloride.

9. A process as defined in claim 1, 3 or 5, wherein said stream is in contact with said catalyst bed for a period in the range of about 5 to about 50 seconds.

10. A process as defined in claim 1, wherein the heat energy produced in said fluidized bed is employed to preheat the material feed streams in said process of producing chlori-nated derivatives of ethylene.

11. A process as defined in claim 1, wherein the pressure is in the range of 25 to 100 psig, and said catalyst has a sur-face area of at least 175 square meters per gram, and said catalyst is comprised of 94% by weight of Al2O3 and 6% by weight of SiO2.

12. A process as defined in claim 11, wherein the chlori-nated derivative of ethylene is vinyl chloride.

13. A process as defined in claim 10, wherein the combus-tion catalyst is comprised of 94% by weight of Al2O3 and 6% by weight of SiO2, and has a surface area of at least 175 square meters per gram.

14. A process as defined in claim 13, wherein the pressure is in the range of 25 to 100 psig.

15. A process as defined in claim 14, wherein said stream is in contact with said catalyst bed for a period in the range of about 5 to about 50 seconds.

16. A process as defined in claim 10, 13 or 15, wherein the chlorinated derivative of ethylene is vinyl chloride.

17. A process as defined in claim 13, wherein the chlori-nated derivative of ethylene is vinyl chloride, the pressure is 75 psig, and the temperature is 450°C.

18. A process as defined in claim 17, wherein said stream is in contact with said catalyst bed for a period in the range of about 15 to about 35 seconds.