MXPA06001446A

MXPA06001446A - Process for regenerating a hydrogenation catalyst.

Info

Publication number: MXPA06001446A
Application number: MXPA06001446A
Authority: MX
Inventors: Michel Strebelle
Original assignee: Solvay
Priority date: 2003-08-08
Filing date: 2004-08-05
Publication date: 2006-05-19
Also published as: EA008672B1; UA84436C2; EA200600378A1; EP1658137A1; WO2005014168A1; KR20060056980A; NO20060496L; EG24366A; CA2534760A1; CN1832801A; TW200510062A; AR045336A1; BRPI0413286A; JP2007501691A; MY149389A

Abstract

Process for regenerating a spent hydrogenation catalyst comprising at least one catalytic metal selected from the group consisting of Ru, Rh, Pd, Os, Ir and Pt on an inert support, the said process essentially consisting of a thermal treatment in the presence of oxygen at a temperature of between 300 and 700 degree C.

Description

PROCEDURE FOR THE REGENERATION OF TJN HYDROGENATION CATALYST FIELD OF THE INVENTION The present invention relates to a process for the regeneration of a specific hydrogenation catalyst, as well as an industrial process using such a regenerated catalyst. BACKGROUND OF THE INVENTION Numerous industrial processes use a catalytic hydrogenation step. Catalysts that agree well in this respect are those that comprise a group VIII metal of the periodic system chosen from the following elements: Ru, Rh, Pd, Os, Ir and Pt; and on an inert support (silica, alumina, ...). An example of such a procedure consists in the production of vinyl chloride monomer (VC) by coupling a direct chlorination and an oxychlorination of ethylene '(C2H4) to form 1,2-dichloroethane (DCEa) which is subjected to pyrolysis to form VCM on the one hand and HCl on the other hand. During this pyrolysis a small amount of acetylene (C2H2) is produced, in the order of approximately 2,000 ppm (by volume with respect to the volume of HCl), which can not be easily separated from HCl due to its very close volatilities. Therefore, the HCl of the pyrolysis is recycled in the oxychlorination and, during the course of this, the C2H2 reacts to give various non-recoverable secondary products that tax the profitability of the process. A known and elegant method to eliminate this < ¾H2 consists in transforming it into ethylene (C2H4) by hydrogenation using a suitable catalyst. Such a catalyst is described in patent application DE 24 38 153 which illustrates in particular a Pd-based catalyst on non-porous silica support. However, this catalyst undergoes a progressive deactivation during its use and although the aforementioned request mentions the theoretical possibility of regenerating it, in practice it has been found that such regeneration is unsuccessful, taking into account mainly the contamination of this catalyst by heavy metals ( H. üller et al., Chem.-Ing. -Tech. 59 (1987) N ° 8, pp. 645-7). The Applicant has noted, however, that, surprisingly, under the condition that such a polluted catalyst is treated in the presence of oxygen at a temperature sufficient to remove the contaminants, but not too high in order not to deteriorate the catalyst, the latter could , despite everything, regenerate satisfactorily. SUMMARY OF THE INVENTION Accordingly, the present invention relates to a process for the regeneration of a hydrogenation catalyst comprising at least one catalytic metal chosen from the following group: Ru, Rh, Pd, Os, Ir and Pt, on a inert support, said regeneration process being essentially constituted by a thermal treatment in the presence of oxygen at a temperature comprised between 300 and 700 ° C.

Among the catalytic metals mentioned above, Pt and Pd are preferred. Pd is particularly preferred in view of its high hydrogen adsorption capacity. The concentration of the catalytic metal in the catalyst is generally greater than or equal to 0.01% by weight (based on the total weight of the catalyst), preferably greater than or equal to 0.05%, even 0.1%. This concentration is, however, generally less than or equal to 10%, even 5% and even 1%. DETAILED DESCRIPTION OF THE INVENTION 1 The inert support of the regenerable catalyst by the process according to the present invention is preferably chosen from silica, alumina and silica-alumina, porous or not. Substrates based mainly on silica (that is to say, constituted by more than 50%, preferably more than 95% of Si02) give good results. It is preferably a non-porous or low-porous support, ie having a specific surface (measured according to the BET method with nitrogen) of less than 5 m2 / g, and preferably 3 m2 / g and even 1 m2 / g. The average pore volume of this support is advantageously less than 0, 01 mL / g. Its particle size is advantageously between 1 and 20 ram, even between 2 and 10 mm, and preferably between 3 and 7 mm. On this support, the catalytic metal is generally present in a layer less than or equal to the micron. It is generally in the form of crystallites having a size between 0.1 and 0.5 Dra. In particular, the non-porous silica as described in the references cited above (DE 2,438,153 and the article by Müller). ) gives good results. Because the process according to the invention is "essentially constituted by a heat treatment" it is understood that most of the regeneration of the catalyst (i.e., at least 50% of the gain in selectivity and / or in the rate of conversion) is carried out by the heat treatment. Preferably, at least 75% of the regeneration is a result of the heat treatment, even at least 90% and particularly preferably, the entire regeneration is a result of that, which implies that the process according to this variant of the invention it is done in the absence of any regenerative treatment (with steam or with H2, for example) prior to or after said thermal treatment and, therefore, that the catalyst produced in the heat treatment is reused as it is in a hydrogenation reaction. However, generally care is taken to eliminate, before the thermal regeneration according to the invention, the reagents still present on the surface of the catalyst (for example, by flushing with nitrogen) Similarly, by "reusing the catalyst as such", it is understood use identical to that of a fresh catalyst. This may include, for example, a previous activation by sweeping with H2. The heat treatment in question consists of a stay at an elevated temperature (between 300 and 700 ° C) in the presence of oxygen. Preferably, the temperature during the heat treatment is greater than or equal to 400 ° C, even at 500 ° C, and this in order to increase the efficiency of the regeneration. However, it is preferably less than or equal to 600 ° C, even at 550 ° C and this in order not to deteriorate the catalyst (in fact, it is known that at too high a temperature the supported catalysts may undergo a "sintering" or agglomeration of the catalytic metal that produces a loss of activity by reduction of the active surface). The heat treatment can be done in the presence of pure oxygen. However, the oxygen is preferably diluted, for example with an inert gas. Therefore, the air gives good results. In fact, it is therefore typically what is generally termed an oxidizing atmosphere and this can be fixed or mobile (i.e., a gaseous stream containing oxygen is passed over the catalyst to be regenerated). A mobile oxidizing atmosphere gives good results. Simply a stay in a stove or an electric oven, preferably ventilated, can serve as a heat treatment according to the present invention. Another form that gives good results consists in passing the oxidizing atmosphere through the catalyst bed, for example, in situ, in the hydrogenation reactor. Generally better results are obtained when the catalyst is dispersed during the treatment, i.e. it offers a maximum surface area to the oxidizing atmosphere. Therefore, the catalyst will advantageously be distributed in a layer that goes from the catalyst monolayer (whose thickness depends on the size of the catalyst particles) to a layer of approximately 20 cm, although preferably the thickness of this layer does not exceed 10. cm, even 5 cm. The duration of said treatment is easily determined by the professional and will be adapted to the desired regeneration rate. It is generally greater than or equal to 1 hour, even 5 hours. This duration is, however, generally less than or equal to 48 hours, even 24 hours. The same applies to the flow rate of ventilation, which is preferably greater than or equal to 0.01 L / min-kg catalyst (or liter per minute and kg of catalyst), even at 0.1 L / min-kg catalyst, more generally less than or equal to 100 L / min-kg catalyst and even at 10 L / min-kg catalyst. The catalyst that is intended to be regenerated by the process according to the invention is a "used" catalyst, that is to say, it has served in a hydrogenation reaction on the basis of which its catalytic activity (from the point of view of selectivity and / or This drop in catalytic activity is generally attributed to a deposit of carbonaceous substances and / or contaminations by chlorinated compounds and / or traces of at least one heavy metal. One of the following metals: Al, As, Cd, Cr, Ni, Cu, Sn, Fe, n, Hg, Pb, Zn and Ti (although the latter is not generally considered as a heavy metal, it is, however, a annoying contamination for hydrogenation catalysts and as such is considered as heavy metal within the framework of the present invention.) Traces of heavy metals are particularly troublesome and, among them, Fe and Ti in particular when they are generally present in industrial fluids, taking into account the nature of the equipment used to transport / treat them. Similarly, traces of Hg that can be found in some sources of ¾ are equally annoying. By "traces" are meant quantities of the order of ppm, even of the tens of ppm. It is not uncommon for the initial catalyst to already contain traces of some heavy metals (mainly Fe, but generally less than 50 ppm) but during use an increased content of these (for example, a content higher than 50 ppm in the case of iron) generally contributes to a decline in catalytic activity. The hydrogenation reaction in which the catalyst has been used is preferably a hydrogenation reaction of the acetylene. It is preferably traces of acetylene (C2H2) present in a fluid, and preferably, in a gaseous mixture consisting essentially of HCl and product of the pyrolysis of DCEa, as described above. Such a mixture generally contains between 1,500 and 2,500 ppm of acetylene. It often also contains in the order of tens to hundreds of ppm of chlorinated organic products, such as VCM and ethyl or methyl chloride, and / or non-chlorinated organic products, such as ethylene (C2H4), methane and butadiene. These contaminants result from an imperfect separation, during the separation operations of the products of the HCl pyrolysis, said separation generally being carried out by distillation. For this type of reaction, as described above, the Pd-based catalysts on non-porous silica support give good results and are easily regenerable by the process according to the invention. The catalyst regenerated by the process according to the present invention can be used in any hydrogenation reaction for which it has a catalytic activity. Preferably, it is reused in a process similar to that in which it was previously used. In addition, the present invention also relates to a process for the synthesis of VC by coupling direct chlorination and oxychlorination of ethylene to form DCEa which is transformed mainly into VCM and HCl by pyrolysis, said HCl containing traces of acetylene and recycling in the oxychlorination after the hydrogenation of these traces of acetylene in the presence of a catalyst regenerated by a process as described above. The present invention is illustrated in a non-limiting manner by the following example: E39H catalyst (silica balls 3 to 5 mm in diameter having 0.15% Pd supported on the surface and a specific surface less than 1 m2) has been used. / g) marketed by DEGUSSA and as described in the Müller article cited above, for 4 and a half years (54 months) in contact with HCl containing approximately 2,000 ppm of C2¾ at a pressure of 10 bar and a temperature between 120 and 180 ° C. The residence time (ratio between the normal m3 of HCl / hour and the volume of the catalytic bed in m3) was 1680 h "1. The amount of H2 used was 3.8 moles per mole of C2H2. it has been analyzed and compared with the virgin catalyst, the results of these analyzes are shown in the table below: A load of 150 kg of this used catalyst has been distributed in 18 trays of 0.3 m2 each. The oven temperature has been brought to 500 ° C and has been maintained for 18 hours. The ventilation of the oven is controlled by an air supply of 100 L / minute. This charge has then been reused under conditions similar to those described above, at a temperature of 173 ° C and its catalytic activity has been compared with that of the catalyst used at the end of its life (used at 180 ° C) in the following table : Catalyst Catalyst used regenerated Conversion rate 82 94, 6 C2H2 (%) Yield (% mole 48, 7 62.9 C2H / C2H2) It is found that the catalytic activity has been significantly regenerated (improved conversion and performance even though the operating temperature is lower).

Claims

NOVELTY OF THE INVENTION Having described the present invention, it is considered as novelty, and therefore the content of the following is claimed as property: CLAIMS

1. - Process for the regeneration of a used hydrogenation catalyst comprising at least one catalytic metal selected from the following group: Ru, Rh, Pd, Os, Ir and Pt, on an inert support, characterized in that the catalyst used has been used in a hydrogenation reaction of traces of acetylene present in a gaseous mixture essentially constituted by HC1 and product of the pyrolysis of 1,2-dichloroethane (DCEa) and because said process consists essentially of a heat treatment in the presence of oxygen at a temperature comprised between 300 and 700 ° C.

2. Method according to the preceding claim, characterized in that the catalytic metal is Pd.

3. Method according to any one of the preceding claims, characterized in that the inert support is mainly silica-based.

4. Method according to any one of the preceding claims, characterized in that the inert support has a BET surface of less than 5 m2 / g.

5. Method according to any one of the preceding claims, characterized in that the temperature during the heat treatment is between 400 and 600 ° C.

6. - Method according to any one of the preceding claims, characterized in that the heat treatment is done in the presence of air.

7. - Method according to the preceding claim, characterized in that the heat treatment consists of a stay in an oven or a ventilated electric oven.

8. - Procedure according to any one. of the preceding claims, characterized in that the catalyst is contaminated with traces of heavy metals.

9. - Procedure for the synthesis of vinyl chloride monomer (VCM) by coupling direct chlorination and oxychlorination of ethylene to form DCEa that is transformed mainly in VCM and in HC1 by pyrolysis, said HC1 containing traces of acetylene and being recycled in oxychlorination after the hydrogenation of these traces of acetylene in the presence of a catalyst regenerated by a process according to any one of the preceding claims.