Process for the production of 1,3,3,3-tetrafluoropropene

This application claims domestic priority under 35 U.S.C. 119(e) to commonly owned U.S. Provisional Application Ser. No. 61/598,523, filed 14 Feb. 2012, the disclosure of which is hereby incorporated herein by reference.

The present invention describes a process for making the compound 1,3,3,3-tetrafluoropropene (CF 3 CH═CHF, HFO-1234ze or 1234ze). The described process is industrially applicable for making 1234ze from commercially available raw materials.

The tetrafluoropropene compound 1234ze is a useful compound with low global warming potential which is used in many applications. For example, CF 3 CH═CHF is useful as a foam blowing agent, refrigerant, and as monomer for homopolymers and copolymers.

Several methods for the preparation of CF 3 CH═CHF are known. For example, U.S. Pat. No. 6,548,719 describes the production of many fluoro-olefins including CF 3 CH═CHF from CF 3 CH 2 CF 2 H (245fa) by dehydrohalogenation in the presence of a phase transfer catalyst. U.S. Pat. Nos. 5,986,151 and 6,124,510 describe the gas phase catalytic dehydrofluorination of CF 3 CH 2 CF 2 H to afford CF 3 CH═CHF. These documents are hereby incorporated herein by reference.

Gas phase dehydrochlorination of CF 3 CH 2 CHFCl (244fa) is reported to give CF 3 CH═CHF as described in U.S. Pat. No. 7,829,748. Vapor phase fluorination of CF 3 CH═CHCl (1233zd) with HF with SbF 5 catalyst affords HFO-1234ze along with 245fa. See, for example, U.S. Pat. No. 7,829,748. This document is hereby incorporated herein by reference.

The main disadvantages of the above described methods are that in each case the starting materials, for example CF 3 CH 2 CF 2 H, typically need to be made in multiple reaction steps, and/or with relatively expensive raw materials, and thus there is a need to provide an improved (or alternate) process for the production of HFO-1234ze, at least from a cost effectiveness viewpoint. Accordingly, the present invention has been developed, namely a process which utilizes relatively inexpensive and commercially available starting materials for making HFO-1234ze as detailed below.

The present invention provides a simple three step process for the production of 1,3,3,3-tetrafluoropropene (HFO-1234ze). In the first step, carbon tetrachloride is added to vinyl fluoride to afford the compound CCl 3 CH 2 CHClF (HCFC-241fb). HCFC-241fb is then fluorinated with anhydrous HF to afford CF 3 CH 2 CHClF (HCFC-244fa) in the second step. Dehydrochlorination of HCFC-244fa, in the third step, affords the desired product, CF 3 CH═CHF (HFO-1234ze).

One embodiment of the present invention provides a simple three step process as depicted below:

CH 2 ═CHF+CCl 4 →CCl 3 CH 2 CHClF  (1)

(addition)

CCl 3 CH 2 CHClF→CF 3 CH 2 CHClF  (2)

(HF)

CF 3 CH 2 CHClF→CF 3 CH═CHF  (3)

(−HCl)

In another embodiment, vinyl chloride can be used in place of vinyl fluoride, such that the process has the following three steps:

CCl 4 +CH 2 ═CHCl→CCl 3 CH 2 CHCl 2   (1)

CCl 3 CH 2 CHCl 2 →CF 3 CH 2 CFHCl  (2)

CF 3 CH 2 CFHCl→CF 3 H═CHF  (3)

As shown in the above depicted reactions, the process comprises three steps:

Step (1)—addition of carbon tetrachloride to vinyl fluoride/chloride,

Step (2)—fluorination of the resultant product with HF, and

Step (3)—dehydrochlorination of the compound from step (2).

Thus, in one embodiment of the first step, carbon tetrachloride is added to vinyl fluoride to afford compound CCl 3 CH 2 CHClF (HCFC-241fb) which is then fluorinated with HF, preferably anhydrous HF, to afford CF 3 CH 2 CHClF (HCFC-244fa) in the second step. Fluorination reactions are typically carried out with hydrogen fluoride, preferably anhydrous HF (AHF) and a fluorination catalyst. These catalysts are well known, and one can fine tune the reaction conditions to afford mainly the desired product. Dehydrochlorination of CF 3 CH 2 CHClF (HCFC-244fa), in the third step, affords CF 3 CH═CHF (HFO-1234ze).

In certain embodiments, the addition reaction of CCl 4 to CH 2 ═CHF was conducted in the presence of triethylphosphate and iron powder at elevated temperature (120° C. to 130° C.) to afford CCl 3 CH 2 CHClF (HCFC-241fb), in good yield.

Iron nano particles and/or nano powder, which are commercially available, can also be employed for the addition reaction instead of iron powder. Iron nano particles can be on a support such as activated carbon. The advantage of Fe nanopowder is its large surface area thus reducing its amount as well as time required for the reaction.

In certain embodiments, the HCFC-241fb was fluorinated with three (3) equivalents of anhydrous HF in the presence of a fluorination catalyst such as SbCl 5 to afford CF 3 CH 2 CHClF (see for example U.S. Pat. No. 7,829,748). By-products such as CF 3 CH═CHCl (HCFO-1233zd) or CF 3 CH═CHF (HFO-1234ze) which may be formed can easily be separated from the higher boiling HCFC-244fa, for example, by distillation. Also, the fluorination reaction conditions may be fine-tuned in such a way that the desired CF 3 CH 2 CHClF is predominantly obtained.

In certain embodiments, the fluorination reaction is carried out in a Monel® tube reactor which is charged with a premade fluorination catalyst such as SbCl 5 (or SbF 5 or SbCl x F y , where x+y=5) on activated carbon (Togo Calgon PCB, 4×10 mesh) and heated to about 70° C. to 85° C. (see U.S. Pat. No. 7,829,748). Then a mixture of vaporized CCl 3 CH 2 CHClF and anhydrous HF (AHF) in a ratio of about 1:10 is passed through the heated catalyst bed in the reactor with a contact time of from 2 sec to 10 sec. Contact time=bulk volume of catalyst/volumetric flow rate of reactants in ml/sec. The flow rate of each reactant was controlled with a mass flow meter/controller in such a way that the contact time is maintained in the range of 2 sec. to 10 sec.

The effluent from the reactor was analyzed by GC/GC-MS for identification the products. CF 3 CH 2 CHClF (HCFC-244fa) was obtained as the main product; the by-products were CF 3 CH 2 CF 2 H (HFC-245fa) and CF 3 CH═CHCl (HCFC-1233zd) which could easily be separated from the higher boiling HCFC-244fa (bp=30° C. at 27 psi) by distillation.

Dehydrochlorination of CF 3 CH 2 CHClF can either be carried out in liquid or gas phase with an appropriate catalyst, as taught for example, in U.S. Patent Pub. No. 2007-0129580, U.S. Pat. No. 7,829,748 and PCT Publication No. WO 2009/0211542. Many catalysts can be used for dehydrochlorination depending on the reaction conditions. For liquid phase reactions, typical catalysts are sodium or potassium hydroxide with a phase transfer catalyst, as taught in U.S. Pat. No. 7,829,748. These documents are hereby incorporated herein by reference.

In certain embodiments, the vapor phase dehydrochlorination is conducted at a temperature range of from about 300° C. to 500° C. This process can be effected with a number of catalysts, including for example, acid treated activated carbon, or a mixture metal chloride and metal fluoride catalysts, for example CsCl+MgF 2 in a 1:9 ratio.

All processes described here can be run in a continuous manner either individually or as a combination of some or all of the individual process steps. As will be appreciated by those having ordinary skill in this art, various reaction modifications can be implemented for better selectivity and yield in each of the reaction steps described herein.