MXPA97003302A - Procedure for the regeneration of a catalyst based on trivale chrome compounds - Google Patents

Abstract

Process for the regeneration of a fluorination catalyst, based on optionally supported Cr (III) compounds, comprising: a) the treatment at 350-400 ° C, with an air / inert gas mixture and b) the treatment at 300 ° C-380 ° C, with a mixture of an inert gas containing 1 to 10% by volume of hydrogen

Description

PROCEDURE FOR THE REGENERATION OF A CATALYST FL BASE DF COMPOUNDS OF TRIVALENT CHROME The present invention relates to a process for the regeneration of fluorination catalysts, based on Cr (III) compounds, optionally supported. The use of Cr (?) Based ore in various reactions of organic compounds that contain halogen, high temperatures, is well known in the art. In particular, various fluids are known to be used for industrial fluorides, which are based on oxides / oxy fluorides of Cr (IIl), optionally supported on alumina, fluorinated alumina, aluminum tri-luoride, in the reactions in gaseous phase, at high temperatures, between HF and hydrocarbons that have halogen, with the purpose of injecting fluorine lathes. US Pat. No. 5,262,574 and EP 408,005, the use of supported on RIF3 in the fluorination in fa?, and gaseous with HF, respectively, of CCla = CCl; a to obtain OFaCHOl ^ 0 (HCFC-123) and CHCl-CCla and CFaCHaCl (HCFC-133a) to obtain CFJBCHJÜF (HFC-13 a). Said catalysts, during their use in an industrial heating plant, tend to be deactivated due to the deposit on their surface, of organic contaminants that! *. they comprise carbonaceous residues and / or organic olí gomers that are derived from the catalytic disintegration and / or olgomepzacion of the reacted organic compounds. In order to restore the catalytic activity, the spent catalyst is usually treated with oxidizing gas, such as air or oxygen / nitrogen mixtures at sufficiently high temperatures (300-500 ° C) in order to cause combustion of the contaminants org nicos. However, the above traffic also causes the partial oxidation of Or.TTT) to Cr (VT) and consequent loss of the active metal Or (III), so that the catalyst is active and has a short life. In addition, the formation of toxic and volatile Cr (VI) compounds is a highly undesirable result, since their dispersion in the environment is regulated by the laws in force that do not allow concentrations of Cr (VI) greater than 1 ppm in the Effluent wastewater and even lower concentrations are in the gaseous effluents. In the case of the use of the so-called reactivated lifts in fluorination procedures with HF, the presence of Cr (VT) gives all the undesirable results, since it reacts with the HF forming Cr (VI), O OuFi, oxyfluoride. , which is gaseous at room temperature and toxic, which contaminates the process effluents. To obviate the loss of chromium in the catalyst-during regeneration with air and in the successive reactions with HF, it has been proposed in EP 475,693, to regenerate the catalyst based on chromium compounds by treatment with a mixture of HF / .ure that contains up to 30 molar% of air, at temperatures of 300 to 500 ° C. However, said process shows the drawback that, in order to avoid the loss of the significant amounts of HF used in the regeneration mixture, it is necessary to employ two reactors which, alternatively, in a reactor * occurs the regeneration of the spent catalyst and , contemporaneously in the other reactor, the fluorination of the halogen-containing organic compound occurs, by r-circulating the hot HF coming directly from the reactor under regeneration. We have now discovered a procedure for the regeneration of depleted or deactivated catalysts, based on Or compounds (IIT), which can be carried out in the same reactor that contains the catalytic bed, which does not show the disadvantages or the disadvantages of the tecmca above and allows to obtain a highly active, regenerated catalyst, which does not contain Cr (VI) compounds. The method according to the invention comprises: a) a first phase of treatment with an oxidizing gas, in particular air, carried out with methods known in the art; and b) a successive phase of hydrogen treatment, mixed in par- ticular proportions with an inert gas and at particular temperatures, until the disappearance of the compounds of Or (VI), formed during the previous oxidation phase. Accordingly, it is an object of the present invention a method for the regeneration of a fluorination catalyst, which is based on Or (I?) Compounds, optionally supported, depleted due to the presence on its surface of organic contaminants, which comprises: a) the treatment of spent catalyst with a flow of air or with an oxygen / inert gas mixture, at temperatures of 350 ° C to 400 ° C, until contaminants disappear org rucos; and b) the treatment of the catalyst obtained after step a), with a flow of a gaseous mixture formed by an inert gas and from 1 to 10% by volume of hydrogen, at temperatures of 300 ° C to 380 ° C, until complete disappearance of Cr (VE) compounds, formed during the oxidation phase. The dead gas used in phases a) and b) is preferably nitrogen. The amount of hydrogen in mixture with the inert gas preferably ranges from 3 to 6% on volume. The treatment temperature in phase b) varies preferably from 310 ° C to 340 ° C, while the pressure is not critical, since it can vary from atmospheric to approximately * > relative barias. The treatment time of phase b) is generally less than one hour. The process according to the invention is particularly suitable for the regeneration of a fluorination catalyst, based on Cr (III) oxide and / or oxyfluoride supported on AlFa, AlaOa or ni «03 which has been used in the fluor * ation in gas phase with HF or hydrocarbons containing 5 halogen. In particular, a catalyst based on Cr (III) oxide and / or oxi lutein supported on AlFa can be used continuously for extended periods in an industrial plant to prepare HCFC-123 from perchlorethylene and HF, such as it is described in USP 5,262,574, alternating periods of production with cycles of regeneration, according to the method of the invention, without suffering substantial chromium losses or catalytic activity. On the contrary, if regeneration is carried out L5 using only the oxidation phase a), already after a few production / regeneration cycles, substantial chrome losses are seen in the catalyst, as well as a drop in its catalytic activity. Some examples are given below for illustrative purposes of the invention. The catalysts used in the examples were determined: the content of carbonaceous substances by 1P0 analysis (oxidation at programmed temperature); J i- the content of compounds of Cr (VT) by oxidunetric analysis, by the wet route; the catalytic activity, by means of catalytic test. The TPO analysis, well known in the art, was carried out by letting an oxidizing gas flow over a catalyst sample *, while progressively heating from room temperature to 700 ° C, at a programmed speed of 10 ° C / m, and determining the variation of the analysis gas composition, compared to a reference gas flow that does not pass over the sample. For the TPO, a flow of 40 cc / minute was used, of an oxygen / helium mixture with 5% by volume of oxygen. In the wet oxidation analysis, well known in the art, the compounds were extracted from a catalyst sample by washing with acidified water and, successively, titrating with KT / tulose. The catalytic test comprises the use of a catalyst sample in the normal fluorination of HCFC-133a (CFaCHaCL) with anhydrous HF in a molar ratio of I33a / HF of 1: 4, at a temperature of 320 ° C.

EXAMPLE A catalyst based on Cr (rtt) oxide, supported on A1F3, prepared as described in USP 5,262,574, which contained 7.4% chromium, was used in the continuous synthesis of HCFC-123 from perchloroeti log and HF, according to with the operating conditions described in example i of the above mentioned US patent. Fll catalyst, after continuous operation until its catalytic activity, determined by the catalytic test, had dropped to 70% of its initial value, is regenerated m situ by means of the following treatments, in sequence: a) treatment with a flow of a mixture of mitogen / air containing 30% by volume of air, at a temperature of 380 ° C, until the disappearance of organic contaminants, as by TPO analysis, and the restoration of catalytic activity. The TPR analysis and the wet oxidirnetic analysis show that the catalyst contains 0.2% by weight of Cr.VI). h) The successive treatment with a nitrogen / hydrogen mixture containing 5% by volume of hydrogen, with a flow rate of 150 ni (hour per kg of catalyst, at a temperature of 325 ° C for 50 minutes. The catalyst does not show the presence of Cr (VI) .The catalytic test shows that the catalyst has the same activity as the initial fresh catalyst.The catalyst thus regenerated is then placed back into operation in the synthesis of HCFC- 123, where it behaves in the same way as the initial fresh catalyst.

Claims (7)

1. - A process for the regeneration of a fluoridation catalyst *, based on Cr (TTI), b-opconally supported compounds, exhausted by the presence on its surface of organic contaminants, characterized in that it comprises: (a) the treatment of spent catalyst with an air flow or a mixture of oxygen / inert gas, at temperatures of 350 ° C to 400 ° C, until the organic contaminants disappear; and (b) the treatment of the catalyst obtained after step (a) with a flow of a gaseous mixture formed by an inert gas and from 1 to 10% by volume of hydrogen, at temperatures of 300 ° C to 380 °. C, until the complete disappearance of Cr (VT) compounds, formed during the oxidation phase a).

2. Process according to claim 1, further characterized in that the compounds of Cr (III) are oxides and / or oxy fluorides and the support is selected from fluorinated A1F3, 1003 and Ale »0

3. 0 3 .-- Method according to claim 1, further characterized in that the catalyst consists of Cr (III) oxide and / or oxy luoride supported on AlFa.

4. Method according to claim 1, further characterized in that the amount of hydrogen in r. Mixture with inert gas varies from 3 to 6% by volume.

5. Method according to claim 1, further characterized in that the inert gas used in phases a) and b) is neither reactive.

6. Method according to claim 1, further characterized in that phase b) is carried out at temperatures of 310 ° C to 340 ° C.

7. Process for the fluorination of halogen-containing hydrocarbons with HF in the gas phase, in the presence of a catalyst, based on optionally supported Cr (III) compounds, which has been regenerated according to the procedure of claim 1.