WO1999007470A1

WO1999007470A1 - Fluorination catalysts and process for their preparation

Info

Publication number: WO1999007470A1
Application number: PCT/US1997/013941
Authority: WO
Inventors: John Stephen Bass; Addison Miles Smith; Paul Gene Clemmer; Mark Kaiser; Li Wang
Original assignee: Alliedsignal Inc.
Priority date: 1997-08-08
Filing date: 1997-08-08
Publication date: 1999-02-18
Also published as: AU3912397A

Abstract

Processes for the preparation of a vapor phase fluorination catalyst, its regeneration, and its use are provided. The catalyst of the invention is prepared by contacting a fluorination catalyst to chlorine during pretreatment of the catalyst, which serves to maintain catalyst life. The catalyst of the invention may be used in the vapor phase fluorination of hydrocarbons, halocarbons, and hydrohalocarbons to prepare fluorinated products in improved yield and with improved selectivity.

Description

FLUORINATION CATALYSTS AND PROCESS FOR THEIR PREPARATION Field of Invention

The present invention relates to vapor phase fluorination catalysts and processes for their preparation and use. In particular, the invention relates to fluorination catalysts which are pretreated with chlorine in order to maintain catalyst life and improve product yields and selectivity. Further, the invention relates to a process for the production of hydrofluorocarbons, hydrochlorofluorocarbons, chlorofluorocarbons, and fluorocarbons by vapor phase fluorination of hydrocarbons, halocarbons, or hydrohalocarbons with hydrogen fluoride in the presence of a chlorine pretreated fluorination catalyst.

Background of the Invention

Processes for the vapor phase fluorination of hydrocarbons, halocarbons and hydrohalocarbons using hydrogen fluoride in the presence of a fluorination catalyst are well known. However, such processes suffer from substantial catalyst deactivation resulting in low yields and poor selectivity.

Many methods for maintaining catalyst activity have been proposed. For example, it is known that the addition of a continuous oxidant cofeed during the fluorination process will aid in maintaining catalyst life. Shinsuke et al.. in .TP 2017137, disclose the fluorination of trihalogenopropanes with hydrogen fluoride in which catalyst activity is maintained by the continuous addition of either oxygen or chlorine to the reaction system. However, such continuous cofeeds are disadvantageous because their addition may produce yield losses and may pose flammability problems. US Patent No. 4,155,881 to Sullivan discloses a process for activating chromic fluoride catalysts by contacting the catalysts with hydrogen chloride and chlorine. The disclosed process is disadvantageous because it requires temperatures, during catalyst regeneration, which may be detrimental to fluorination catalysts other than chromic fluoride, such as chromia. Additionally, the disclosed process is disadvantageous because catalyst regeneration is preferably carried out at superatmospheric pressures.

The present invention provides a fluorination catalyst that has improved performance in that it has an improved life, good selectivity, and good fluorination process yields.

Description of the Invention and Preferred Embodiments The present invention provides processes for the preparation of fluorination catalysts with improved performance in fluorination reactions and use of the catalysts. The catalysts of this invention are prepared by contacting the catalysts with chlorine. It has been discovered that this chlorine treatment improves the fluorination catalysts' performance in fluorination reactions in that catalyst deactivation is substantially reduced while at the same time, product yields and selectivity are good compared to catalysts untreated with chlorine.

The fluorination catalysts useful in the present invention may be any one of the vapor phase fluorination catalysts known in the art. Exemplary fluorination catalysts include, without limitation, metal based catalysts such as metal oxides, metal fluorides and halides, and lanthanide and actinide catalysts. Typically, the fluorination catalyst is a chromium based catalyst such as chromium oxide, also known as chromia, halogenated chromium catalysts such as chromium fluoride and chromium oxyfluoride, or chromium based catalysts containing other metals. Preferably, the catalyst is chromia catalyst.

Amounts of the catalysts of this invention useful in fluorination reactions are readily ascertainable by those of ordinary skill in the art. Typically, the amount of catalyst used will be an amount effective to drive the reaction to completion, which amount will be a function of the desired, or required, productivity, e_^, the amount of product to be formed.

The fluorination catalyst useful in this invention may be in bulk form or may be supported on any known support system. Exemplary support systems include, without limitation, activated carbon, alumina, aluminum fluoride, aluminum oxyfluoride, and other oxides such as titania and magnesia. Further, a catalyst promoter may be used in conjunction with the catalyst. Any of the known promoters may be used, including a metal or metals from groups VIII, VIIB, IIIB, LB and/or a metal having an atomic number of 58 through 71 as disclosed in US Patent No. 4,922,037 which is incorporated herein by reference in its entirety.

The catalysts useful in the present invention are commercially available or may be made by any method known to those ordinarily skilled in the art of catalyst synthesis. For example, chromia catalysts may be made by any number of processes such as heating Cr(OH)₃ or chromium oxide gel precipitated from an aqueous solution of Cr(III) compounds by the addition of base. As another example, mixtures of urea and Cr(III) salts in aqueous form may be heated to form a hydrated chromium oxide gel which, in turn, may be heated to provide chromia catalysts. Yet another example is the reacting of CrO₃ with a reducing agent such as alcohol to form a chromia catalyst. Further exemplary methods for the preparation of chromia catalysts include the oxidation of chromium oxalate or chromium acetate and the thermal decomposition of compounds such as

Prior to using a fluorination catalyst in a vapor phase fluorination reaction, it is desirable to pretreat the catalyst before introducing the reaction feed stock. By "pretreat" is meant to chemically or physically alter a catalyst in order to create active sites on the catalyst at which a reaction may occur. The precise pretreatment used will depend on the specific reaction that the catalyst will be used in. For example, the catalyst may be calcined under a flow of inert gas at temperatures from about 200° C to about 450° C for from about 2 to about 100 hours. Subsequently, the catalyst may be exposed to hydrogen fluoride, either alone or mixed with up to about 5 to about 95 weight percent of an inert gas at temperatures from about 200° C to about 450° C for about 1 to about 50 hours. For purposes of this invention, the foregoing methods as well as other pretreatment methods, such as standard calcination and fluorination treatments, well known to those ordinarily skilled in the art, may be used.

It has been discovered that when a fluorination catalyst is contacted with chlorine as a part of the pretreatment process, improved catalyst performance, as evidenced by improved reactant conversion, reduced catalyst deactivation, and good selectivity, is achieved. Further, the improved performance is achieved without the need for a continuous oxidant cofeed during the fluorination reaction. The chlorine may be introduced at any point in the pretreatment process used. Preferably, the catalyst is contacted with the chlorine after the catalyst has been dried under an inert gas or vacuum and after it has been contacted with hydrogen fluoride

The chlorine may be introduced, either in liquid or gaseous form, into the pretreatment process and may be added at conditions appropriate to the pretreatment process being utilized. Preferably, the chlorine is diluted with from about 60 to about 75 percent hydrogen fluoride and/or from about 20 to about 30 percent of an inert gas. Dilution may occur prior to, or simultaneously with, the chlorine being passed over the catalyst.

The chlorine may be passed over the catalyst at a total volume of chlorine to total volume of catalyst of from about 1 to about 3,000 v/v. More preferably, the chlorine to catalyst volume is from about 10 to about 1,000 v/v, most preferably from about 50 to about 500 v/v. The chlorine may be exposed over a period of time that is convenient for the equipment being utilized. Generally, the chlorine exposure may be for a period of time from about 1 to about 200 hours, more preferably from about 5 to about 70 hours, and most preferably from about 10 to about 30 hours.

Chlorine exposure may be conducted at any temperature and pressure convenient to the fluorination process to be used. Preferably, the temperature of exposure is identical to the temperature of the fluorination reaction, typically from about 100° C to about 400° C. Preferably, exposure pressures range from atmospheric to the pressure of the fluorination reaction, typically up to about 500 psig, for which the catalyst will be used.

Following pretreatment of the catalyst with chlorine, the flow of chlorine is discontinued and the feed material, along with hydrogen fluoride, can be introduced and the fluorination reaction initiated. One ordinarily skilled in the art will recognize that the catalyst of this invention may be used to produce any fluorinated product. Thus, the feed material used in the fluorination reaction will depend on the desired fluorinated product. Generally, the feed material may be any hydrocarbon, halocarbon, or hydrohalocarbon of from 1 to 6 carbon atoms, both saturated and olefinic. Exemplary feed materials include, without limitation, methylene chloride, chloroform, tetrachloroethylene, trichloroethylene, vinyl chloride, 1, 1, 1-trichloroethane, acetylene, 1, 1-dichloroethane, vinylidene chloride, 1,1, 1 ,3 ,3 ,3-hexachloroethane, 1 , l-dichloro-2,2,2-trifluoroethane, 1 -chloro- 1 ,2,2,2- tetrafluoroethane, l-chloro-2,2,2-trifluoroethane, l-fluoro-l, l-dichloroethane, and 1 -chloro- 1, 1-difluoroethane.

By using the catalyst of the invention, the need for the continuous addition of any material that is typically used to extend catalyst life during the fluorination reaction is eliminated. If catalyst deactivation, or a decrease in catalyst activity and selectivity, occurs during the course of the fluorination reaction, the catalyst may be regenerated, preferably by the non-continuous addition of chlorine to the reactants. By "regenerate" is meant to restore reaction sites to the catalyst. The non-continuous addition, or addition that does not proceed uninterrupted for the duration of the fluorination reaction, of chlorine may be at flows of from about 0.1 to about 10 mol percent based on organic content. More preferably, the amount of chlorine is from about 2 to about 8 mol percent. Alternatively, the flow of feed materials may be discontinued and the fluorination catalyst contacted with chlorine, either alone or in dilute form. In either the preferred or alternate method, the addition or contacting of chlorine is carried out for a period of time sufficient to regenerate the catalyst, preferably from about 1 to about 50 hours, more preferably from about 10 to about 25 hours.

The vapor phase fluorination reactions in which the catalysts of this invention are used are generally known. Typically, the reaction will be carried out in a corrosion resistant reactor at temperatures from about 100° C to about 450° C, preferably, from about 250° C to about 400° C and at a pressure from about 0 psig to about 300 psig, preferably from about 50 psig to about 200 psig depending on the specific reaction and productivity requirements. The mole ratio of HF/feed will be from about 50/1 to about 1/1, preferably about 10/1 to about 2/1. The liquid hourly space velocity for a fixed bed reactor will be about 0.5 to about 5.0 hr^"1, preferably from about 0.75 to about 2 hr^'1 based on the feed material. Typically, product will be separated from the byproduct by distillation and purified as required depending on the end use. Suitable reaction conditions are determinable by those ordinarily skilled in the art by a consideration of the feed material as well as the desired conversion of the feed consistent with a high selectivity.

The catalysts of this invention may be advantageously used to produce any of a wide variety of fluorinated hydrocarbons, halocarbons, or hydrohalocarbon products including, without limitation, difluoromethane, pentafluoroethane, and 1,2,2,2-tetrafluoroethane. For example, the typical vapor phase process for the production of difluoromethane from methylene chloride and hydrogen fluoride suffers from substantial catalyst deactivation during the process as well as low yields and poor selectivity. The catalyst of this invention may be used in this reaction to increase yields and provide improved selectivity.

The present invention will be further clarified by a consideration of the following examples.

Examples

Example 1 An INCONEL™ reactor was charged with 60 cc chromia catalyst and heated to 350° C under a 550 seem flow of dry nitrogen over a period of 5 hours and then held for 12 hours. The pressure was maintained at atmospheric pressure. The temperature was then reduced to 200° C and the nitrogen flow decreased to 275 seem. Anhydrous hydrogen fluoride was added to the nitrogen flow at 33 g/hr and the rate maintained until the initial exotherm subsided. The temperature was then raised to 350° C over a period of 3 hours and the hydrogen fluoride feed rate increased to 43 g/hr. Both temperature and feed rates were held for 9 hours.

After this pretreatment, the temperature was reduced to 250° C and the reaction started by adding methylene chloride and discontinuing the nitrogen flow. Feeds were maintained at 64 g/hr HF and 33 g/hr CH₂C1₂ to give a HF:CH₂C1₂ mole ratio of 8: 1. The pressure was maintained at 50 psig and contact time was 6 seconds. Conversion was measured as the percent methylene chloride fluorinated, Le, CH₂C1₂ fluorinated/moles CH₂C1₂ throughput. Selectivity was measured as the percent moles of a fluorination product divided by the moles of CH₂C1₂ converted. Difluoromethane was the desired product and chlorofluoromethane the under fluorinated byproduct. The results are listed on Table I.

Table I

Example 2 An INCONEL™ reactor was charged with 60 cc chromia catalyst pretreated as in Example 1. The feeds were started and reaction run as described in Example 1 except that air was added to the reaction mixture at a flow rate of 10 seem. This resulted in an oxygen:CH₂Cl₂ ratio of 0.012. Results are listed on Table II Table II

Example 3 An TNCONEL™ reactor was charged with 285 cc chromia catalyst and the catalyst heated to 350° C under a 350 seem flow of nitrogen over a period of 7 hours. The pressure was maintained at atmospheric pressure and catalyst held at 350° C for 8 hours. The reactor temperature was reduced to 200° C and anhydrous hydrogen fluoride added to the nitrogen flow at 50 g/hr. The temperature was increased to 350° C over a period of 5 hours and held at that temperature for 2 hours. The reactor temperature was reduced to 250° C and chlorine gas added to the mixture at 50 seem. The chlorine pretreatment was continued for 13 hours after which the chlorine flow was discontinued and CH₂C1 was added to the HF/N₂ mixture. The nitrogen flow was discontinued and feedrates of CH₂C1₂ and HF were adjusted to 140 g/hr and 250 g/hr, respectively. These conditions resulted in a contact time of 8 seconds and an HF:CH₂C1₂ mole ratio of 7.6 : 1. The results are listed on Table III.

Table III

After 152 hours on stream, the CH₂C1₂ conversion decreased from 85% to 61%. At this point, chlorine gas was added to the reaction mixture at a rate of 40 seem for a period of 19 hours. The resulting Cl₂ : CH₂C1₂ mole ratio was 0.065. The results are listed on Table IV.

Table IV

Following the 19 hour regeneration period, the chlorine flow was discontinued and the reaction allowed to continue at the same reaction conditions used initially for an additional 80 hours. The results are listed on Table V. Table V

The foregoing examples demonstrate that pretreatment of the fluorination catalyst with chlorine provides improved product yield and good selectivity in comparison to catalysts that are not pretreated with chlorine and catalysts subjected to continuous oxidant cofeeds. Additionally, Example 3 demonstrates that catalyst regeneration is achieved readily by the subsequent, non-continuous addition of chlorine to the deactivated catalyst.

Example 4 An INCONEL™ reactor was charged with 60 cc chromia catalyst pretreated as in Example 1. The feeds were started and reaction run as for Example 1 except that chorine gas was added to the reaction mixture at a flow rate sufficient to equal a Cl₂ : CH₂C1₂ mole ratio of 0.100. After 88 hours on stream, the chlorine cofeed was discontinued and the reaction allowed to proceed for an additional 66 hours with no oxidant cofeed. The results are listed on Table VI.

Table VI

Example 4 illustrates that the continuous addition of chlorine during the fluorination reaction is inferior in performance to the catalyst of this invention in both reaction yield and selectivity. Notably, yield and selectivity markedly improved after discontinuation of the chlorine flow in Example 4.

Prospective Examples

Prospective Example 1 An INCONEL™ reactor is charged with 300 cc chromia catalyst and the catalyst is heated to 350° C under a 350 seem flow of nitrogen over a period of 7 hours. The pressure is maintained at atmospheric pressure and the catalyst held at 350° C for 8 hours. The reactor temperature is then reduced to 250° C and anhydrous hydrogen fluoride is added to the nitrogen flow at 50 g/hr. The temperature is increased to 350° C over a period of 5 hours and held at that temperature for 2 hours. Chlorine gas is then added to the mixture at 50 seem. The chlorine pretreatment is continued for 13 hours after which the chlorine flow is discontinued and 1,1, 1-trifluorochloroethane, HCFC-133a, is added to the HF/N₂ mixture. The nitrogen flow is discontinued and feed rates of HCFC-133a and HF are adjusted to result in a contact time of 10 seconds at a pressure of 50 psig and an HF:HCFC-133a mole ratio of 4: 1. The expected results are: Time on Stream (hr) Conversion CF₃CC1H₂ Selectivity CF₃CFH₂ Deactivation Rate

(% conversion hr) 10 22 % 97 %

100 12 % 90 % 0.11

Prospective Example 2 An INCONEL™ reactor is charged with 300 cc chromia catalyst and the catalyst is heated to 350° C under a 350 seem flow of nitrogen over a period of 7 hours. The pressure is maintained at atmospheric pressure and the catalyst held at 350° C for 8 hours. The reactor temperature is then reduced to 250° C and anhydrous hydrogen fluoride is added to the nitrogen flow at 50 g/hr. The temperature is increased to 360° C over a 5 hour period and held at that temperature for 2 hours. Chlorine gas in then added to the mixture at 50 seem. The chlorine pretreatment is continued for 13 hours after which the chlorine flow is discontinued and tetrachloroethylene is added to the HF/N mixture. The nitrogen flow is discontinued and feed rates of tetrachloroethylene and HF are adjusted to result in a contact time of 20 seconds at a pressure of 100 psig and an HF:tetrachloroethylene mole ratio of 24: 1. The expected results are:

Time on Stream (hr) Conversion CC1₂CC1; Selectivity Deactivation Rate

CF₃CHF₂ CFjCHClF (% conversion hr) 10 80 % 40 % 55 %

100 78 % 35 % 60 % 0.02

Other embodiments of the invention will be apparent from a consideration of the specification or practice of the invention disclosed. It is intended that the specification and examples be considered as exemplary with the true scope and spirit of the invention being indicated in the following claims.

Claims

What is claimed is:

1. A process for pretreating a fluorination catalyst, comprising: contacting the fluorination catalyst with chlorine under conditions suitable to improve the fluorination catalyst's performance in a fluorination reaction.

2. The process of claim 1 further comprising the steps of:

(A) drying the fluorination catalyst; and

(B) contacting the fluorination catalyst with hydrogen fluoride prior to contacting the fluorination catalyst with chlorine.

3. The process of claims 1 or 2 wherein the fluorination catalyst is a chromium based catalyst.

4. The process of claim 3 wherein the chromium based catalyst is a chromia catalyst.

5. The process of claim 1 wherein the chlorine contacted with the fluorination catalyst is in dilute form.

6. A process for regenerating a deactivated fluorination catalyst while the fluorination catalyst is used in a fluorination reaction, comprising the step of adding chlorine non-continuously to the fluorination reaction reactants under conditions suitable to regenerate the fluorination catalyst.

7. A process for regenerating a deactivated fluorination catalyst after use in a fluorination reaction, comprising the step of contacting the fluorination catalyst with chlorine under conditions suitable to regenerate the fluorination catalyst.

8. The process of claims 6 or 7 wherein the fluorination catalyst is a chromium based catalyst.

9. A process for preparing a fluorinated product, comprising the steps of: (A) contacting a fluorination catalyst with chlorine during pretreatment of the fluorination catalyst under conditions suitable to improve the fluorination catalyst's performance in a fluorination reaction;

(B) initiating the fluorination reaction by contacting a feed material with hydrogen fluoride in the presence of the catalyst of step (A); and (C) carrying out the fluorination reaction in step (B) under reaction conditions suitable to produce a fluorinated product.

10. The process of claim 11 further comprising the step of:

(D) adding chlorine non-continuously to the feed materials and hydrogen fluoride of step (B) under conditions suitable to regenerate the fluorination catalyst as the fluorination catalyst becomes deactivated.