CA1206723A - Selective conversion of chlorinated alkanes to hydrogen chloride and carbon dioxide - Google Patents

Abstract

Abstract A method of converting saturated aliphatic chlori-nated hydrocarbons to carbon dioxide and hydrogen chlo-ride which comprises contacting a preheated mixture of the hydrocarbon, water, and, optionally, oxygen with a molecular sieve catalyst at temperatures of from 180°C
to 400°C. Simple chlorinated hydrocarbons can thus be completely converted to HCl and CO2 at low temperatures without the production of undesired by-products.

Description

7~

SELECTIVE CONVERSION OF
CHLORINATED ALK~NES ~O HYDROGEN
CHLORIDE AND CARBON DIOXIDE

This invention relates to a method of pro-ducing hydrochloric acid from chlorinated alkanes.

Hydrochloric acid is generally Gbtained as a by-product from the synthesis of other compounds. How-ever, many uses for hydrochloric acid are very distantfrom the production site, causing transportation problems.
Shipment of gaseous HCl is hazardous and difficult, and shipment of hydrochloric acid requires the shipment of large amounts of wa-ter.

The present.invention.is advantageous in that with a relatively small capital expenditure, equip-ment can be set up at remote locations (such as an oil field) for the production of hydrochloric acid.

. In the present invention, saturated ali-phatic chlorinated hydrocarbons are reacted with water and, where necessary, oxygen to produce carbon dioxide ~k 27,815B-F -1-and HC1 without substantial formation oE undesired by-products. q~is method com-prises contacting at reactive conditions a vaporized mixture of the chlorinated hydrocarbon, at least a stoichiometric quantity of water and at least a stoichio-metric quan-tity of oxygen with a suitable molecular sieve catalyst to convert at least 10 mole percent of said chlorinated hydrocarbon -to carbon dioxide and hyd-rogen chloride.
Chloromethanes and other simple saturated chlorinated aliphatic hydro-carbons (hereinafter sometimes referred to as RCl's) can be selectively thermally reacted with water and oxygen at relatively low temperatures to yield CO2 and HCl in essentially quantitative amounts. In this process no more than about ten mole percent of the chlorinated hydrocarbon reacted is converted to chlorine, COC12 and other chlorocarbon compounds.
The method of the present invention concerns the conversion of a satur-ated aliphatic chlorinated hydrocarbon to carbon dioxide and hydrogen chloride without substantial formation of free chlorine or phosgene. This method compri-ses contac-ting a vaporized mixture containing said chlorinated hydrocarbon, at least a stoichiometric amount of water and, where necessary, at leas-t a stoichio-metric amount of oxygen with a catalytically effecti.ve amount of a suitable mole-cular sieve catalyst at a temperature and for a period of time sufficient to re-act said hydrocarbon selectively. Nitrogen or some other diluent inert in the re-action is optionally present in the vaporized mixture.

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:~2~'7~3 As used herein, the term suitable molecular sieve catalyst refers to an acid resistant molecular sieve catalyst which either is in the hydrogen form or is loaded with an alkali earth or rare earth metal, with the hydro-gen form of the catalyst being preferred. As used herein,the term effective amount refers to that amount of cata-lyst which must be presen~ for the desired reaction to occur at a rate such that the period of time re~uired to react to the RCl is not unreasonably long.

10Illustrative RCl's which can be reacted in accordance with the present invention are saturated, ali-phatic chlorinated hydrocarbons such as, for example, tetrachloromethane (carbon tetrachloride), trichlorometh~
ane (chloroform), 1,2 dichloropropane, 1,2-dichlorobutane, and the like, or mixtures thereof. The -term "chlorinated hydrocarbon" as used herein includes compounds derived from aliphatic hydrocarbons wherein at least one of the hydrogens on the carbon backbone has been replaced with chlorine. Optionally, the so-called "chlorinated hydro-carbon" may contain only carbon and chlorine moieties.~referably, the RCl treated according to the present invention is selected from the group consisting of tetra-chloromethane, trichloromethane and 1,2-dichloropropane.
The most preferred RCl is tetrachloromethane.

The chlorinated hydrocarbons correspond to ~H~(2n+2~_b~Clb, wherein n is a whole number preferably from 1 to 10 inclusive, more preferably no more than 5j most preferably no more than 3, and b is a whole number from 1 to 2n+2 inclusive. It i5 preferred to use greater than a stoichiometric amount of water, preferably 27,815B-F-3-67~3 at least a 25 mole percent excess, more preferably at least about 50 mole percen-t excess, most preferably at least a 100 mole percenk excess. Where oxygen is required in the reaction, i.e., where the chlorinated hydrocarbon bears one or more hydrogen moieties, i-t is preferred that an excess of oxygen be employed. Preferably at leas-t an 80 mole percent excess of oxygen is employed, more prefer-ably at least about a 100 mole percent excess. Generally, the RCl content of the vaporized eed mixture is in the range from about 1 to about 30 mole percent, preferably from about 4 to about 15 mole percent.

Conveniently, a separate preheater appa-ratus is utilized to prepare the vaporized mixture.
Streams of li~uid RCl, air and water vapor are intro-duced into the preheater where the resulting mixture issimultaneously intermixed and heated to a temperature above about 100C. Preferably the vaporized mixture is heated to a temperature in the range from about 120C to the operating temperature of the catalyst. Apparatus suitable for this purpose are well-known in the art.

The preheated, vaporized RCl mixture is contacted with the catalyst in any reaction vessel affording the desired contact time and an othexwise suitable environ-ment for the reaction. The manner in which the catalyst is disposed in the reactor is not generally critical so long as intimate con-tact between the catalyst and vapor-ized mixture occurs. ~enerally, a fixed bed or packed column is preferred, but. a fluidized bed is also operable.
The catalyst used in the subject process is preferably preheated to the desired temperature range prior to intro-duction of the vaporized RCl mixture. Inasmuch as the 27,815B-F

reaction ls exothermic, the reaction vessel is advanta-geously equipped with some conventional means for cooling to maintain the desired catalyst tempe:rature. The temper-ature of the catalyst is advantageously permitted to increase during the reaction until analysis of the exit stream indicates the desired conversion of the RCl has been achieved. Samples of the inlet and outlet gas streams are conveniently analyzed by gas chromatographic (~C) methods to provide a means for monitoring the degree and completeness of the oxidation. In addition to exter-nal cooling, the feed rate and ratio can be varied to moderate the temperature of the catalyst.

The catalyst is usually maintained at tem-peratures of from 160C to 400C during the reaction of RCl's. For example, 1,2-dichloropropane can be com-pletely converted to C02 and HCl at temperatures of 190C, while tetrachloromethane and trichloromethane are likewise completely converted at temperatures of about 240C and 310C, respectively. A preferred catalys-t reaction temper-ature is from 180C to 340C, more preferably from 190C
D to 3~5 C.

The vaporized RCl mixture is desirably con-t~cted with the catalyst at a pressure of at least one atmosphere (101 kPa). A pressure somewhat greater than atmospheric pressure is generally preferred, with a pres-sure of from 10 to 30 pounds per square inch gauge (psig) (69 to 207 kPa) being especially preferred.

The feed rate of the RCl mixture can be varied to provide a contact period with the catalyst which sub-stantially converts the RCl to CO2 and HCl. The contact 27,815B-F

~2t~7~3 time necessary to effect essentially complete conversion will vary depending on the RCl, the reaction temperature, the catalyst and other factors. In general, a contact time of from less than 1 second to lO seconds will be suf-ficient to effect essentially complete conversion at tem-peratures above 300C.

The subject method can be operated batchwise, but preferably is operated continuously. If the conver-sion of the RCl to C02 and HCl is undesirably low in a single pass, then either the residence time can be increased or multiple passes of the vaporized mixture through the catalyst bed can be utilized.

The catalysts which are employed in the pres-ent invention are acid-resistant type molecular sieves which are effective to convert a significant percentage or substantially all of the RCl being treated to C02 and HCl under the conditions of this invention. Catalysts which are not effective in so selectively converting ~he RCl to C02 and HCl, and chlorinated hydrocarbons which cannot be so converted by an effective catalyst as described herein are not deemed to be within the scope of the subject invention.

Molecular sieve catalysts of the Y-type, mor-denite, zeolite, etc., in the hydrogen form or loaded with an alkali earth or rare earth metal can be employed in the present invention. Representative of these are the commer-cially available Linde Molecular Sieve Catalysts, such as Linde*SK 609, LZ-Y 82, and the like (available from Union Carbide Corporation), Zeolons*(available from Norton Chem-ical Process Products), and the like.

* Trade Mark 27,815B-F -6-,~
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.~2Q~7~3 An ammonium form of the catalyst is operable but is advantageously first converted to the hydrogen form.
One convenient m thod for conversion of the ammonium form of the catalyst to the hydrogen form is to load the cata-lyst into the reactor and heat it at high temperatures, e.g., from 320C to ~20C, under a nitrogen gas purge for a period of about 16 hours. The catalys-t is then treated with dry 2 for about 2 hours while the catalyst is gradu-ally cooled to the temperature at which the RCl mixture is introduced.

In a preferred embodiment of this invention, a preheated vaporized mixture of the RCl containing amounts of water and oxygen in excess of the stoichio-metric is contacted with a non-metal loaded, hydrogen form of a molecular sieve catalyst at temperatures of from 190C to 340C. The vaporized mixture is intro-duced at a flow rate which provides a catalyst contact time of about 10 seconds. In conversion of CC14 the above-described procedure is operable, except only CC14 and H2O need be introduced and the temperature is pref-erably from 190C to 340C, more preferably from 220C
to 310C.

The following examples further illustrate the practice of the subject invention.

Example 1 A glass tubular reactor (13 mm X 45 mm) was sharged with about 100 ml of a molecular sieve catalyst, Linde LZ-Y82, available from Union Carbide Corp. LZ-Y82 is a type Y zeolite havlng a faujasite structure and an alumi-num to silicon ratio of about two. LZ-Y82 is described 27,815B-F -7-as an 1/8 inch extrudate of the base catalysts 33-411 group purchased from Linde. It is purchased in the ammo-nium (NH4 ) form and converted to the hydrogen form by known thermal procedures. The packed reactor was then heated to about ~50C in the presence of a dry nitrogen purge for a period of abou-t 16 hours. Dry oxygen was then fed into the reactor as the catalyst was cooled to about 150C. The oxygen feed was continued for a period of about two hours before the RCl mixture was contacted with the catalyst.

A vaporized, pre-heated RCl mixture was pre pared by thoroughly mi~ing streams of water vapor, tetra-chloromethane and air in a packed glass tube equipped with temperature control means and preheated to about 120C. The vaporized mixture was then fed into the catalyst reactox at a pressure of about one atmosphere (101 kPa) and contacted with the catalyst. Samples of the mixture entering and exiting the catalyst reactor were taken for gas chromatographic analysis. The temper-ature of the catalyst was slowly permitted to increaseuntil analysis of the exit stream indicated all of the CCl4 had been converted to HCl and CO2. The analysis was conducted by analyzing 5-ml portions of the feed and exit gas streams for CCl4 content, the samples being injected directly into the entry port of an H~ 5840A Gas Chromatograph. Mass balance calcula-tions were also made by quenching the exit stream in chilled tetrachloroethene ~perchloroethylene) and water, followed by absorption into neutral aqueous KI, and finally by scrubbing with NaOH. Gas chromatographic analysis of the quench solu-tion indicated the amount of any unreacted RCl. The HCl absorbed in the quench water and the neutral KI was 27,815B-F -8--g titrated with AqNO3 and NaOH and added to the amount found in NaOH scrub solution. The amount of CO2 found in the NaOH scrub solution was determined by titration with HCl.

As a result of these operations, it was deter-min~d that a vaporized CCl4 feed mixture fed at a rate of 9.89 gxams/hr of CCl4 and 5.79 grams/hr of water (mole ratio of 1:5) was completely converted only to HCl (9.37 grams/hr) and CO2 l3.09 grams/hr) at temperatures of at least about 240C or higher. No free Cl2 was detected.

Example 2 The operations of Example l above were repeated, using other RCl mixtures, with air also being mixed with the vaporized RCl mixture. The RCl mixtures and catalytic temperatures required to obtain 100 percent conversion of the RCl's to HCl and CO2 are set forth in the following table, no free Cl2 being detected:

27,815B-F -9-6~7~3 TABLE I

*RCl Mixture Catalyst % Con-(mole ratio) Temp. (C) version Products ~Hcl34)2o 2 310 100 HCl, CO2

2 PDC:H 2 190 100 HCl, CO
(1:5:~) 2

3 PDC/CCl ***:H O:O 240 100 HCl, CO2 (1:5:4)

4 CHC13/Ccl4** ~2 2 100 HCl, CO2 *Average contact time of about 10 seconds.
**2 feed as compressed air in all runs.
***RCl wt. % CompQSitiOn was ~5% CC14 and 15%
PDC (1,2-dichloropropane) for ~un 3 and 85% CC14 and 15% CHC13 for Run 4.

A ten--fold increase in the feed rate indi-cated all but trace amounts of CC14 and CHC13 were reacted, with a greater reaction temperature resulting from increased heat release.

E~ample 3 Using essentially the same procedure set out in Example 1 above except that the catalyst employed was ZEOLON 900 (trademark of Norton Company) in the sodium form. A vaporized tetrachloromethane feed mixture being fed at a rate of 0.33 g/minute of tetrachloromethane and 27,815B-F -10-3L~

0.56 g/minute of wa-ter was completely converted to hydro-gen chloride and carbon dioxide at 250C. No free chlo-rine gas was detected.

ZEOLON 900 is a synthetic mordenite having a five-membered ring system which is characterized by a collection of one-dimensional pores of 67 nm diameter.
ZEOLON 900 has a silica to alumina ratio of ten. It is described as self bonded and is available from Norton Chemical Company as either a 1/8 inch (3.2 mm) or 1/16 inch (1.6 mm) extrudate. It is available in either the hydrogen or the sodium form.

Example 4 A steel tubular reactor having an internal diameter of 2 inches (50.8 mm) and a length of 6 feet (1.8 m) was packed with 3680 cubic centimeters of ZEOLON
900 in the hydrogen form. The reactor was equipped with a cooling jacket through which a heat transfer fluid could be conducted and a means for sensing temperature.

Two liquid feed streams were separately pre-heated to a temperature of 250C. The first stream con-sisted of tetrachloromethane introduced to the preheater at a rate of 9.47 g/minute. The second stream consisted of water introduced at a rate of 17.37 g/minute, a 680 mole percent excess over the stoichiometric amount. The resulting heated vaporiæed streams of water and tetrachlo-romethane were thoroughly intermixed as they were produced.

27,815B-F

7~3 The vaporized mixture was introduced into one end of the tubular reactor and passed through the packed catalyst at a pressure of about 8.5 psig (58.6 kPa gauge).
The catalyst temperature varies during the reaction and along the length of the reactor reaching a maximum temper-ature of about 332C in the first thixd of the bed. The contact time with the catalyst was about 10 seconds.

Analysis of the product gas by conventional analytical methods indicated the CCl4 in the feed had been essentially completely convexted to HCl and CO2.
No chlorine gas was detected in the product.

The foregoing examples illustrate the method of the present invention in completely converting RCl's to desired HCl and CO2 products. Other like RCl's or mix-tures can also be oxidized by the method of the presentinvention.

27,815B-F -12-

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of reacting at least one saturated aliphatic chlorinated hyd-rocarbon to selectively produce carbon dioxide and hydrogen chloride without the formation of free chlorine or phosgene which comprises contacting a vaporized mixture containing said chlorinated hydrocarbon and at least a stoichiometric quantity of water with a catalytically effective amount of a suitable molecular sieve catalyst at a temperature of from 180°C -to 350°C and for a sufficient per-iod of time to convert at least 10 mole percent of said chlorinated hydrocarbon to carbon dioxide and hydrogen chloride without substantial formation of free chlorine and phosgene, wherein the molecular sieve catalyst is an acid resistant molecular sieve catalyst which either is in the hydrogen form or is loaded with an alkali earth or rare earth metal.

2. The method of Claim 1 wherein said vaporized mixture further contains at least a stoichiometric quantity of oxygen.

3. The method of Claim 2 wherein the vaporized mixture further comprises an inert diluent.

4. The method of Claim 2 wherein said catalyst is employed in hydrogen form.

5. The method of Claim 4 wherein said catalyst comprises a Y-type or mor-denite zeolite catalyst.

6. The method of Claim 2 wherein the chlorinated hydrocarbon is selected from the group consisting of tetrachloromethane, trichloromethane, 1,2-dichloro-propane, and 1,2-dichlorobutane.

The method of Claim 2 wherein the chlorinated hydrocarbon has from 1 to 10 carbon atoms inclusive.

8. The method of Claim 2 wherein the chlorinated hydrocarbon has no more than 3 carbon atoms.