METHOD FOR THE REGENERATION OF HYDRATING CATALYTIC CONVERTERS

Description

[0001] The present invention relates to a process for the regeneration of a catalyst used for the nuclear hydrogenation of an aromatic ester, wherein a gas stream containing a certain amount of oxygen is used for the regeneration.

[0002] The hydrogenation of aromatics, and especially aromatic esters, in which the aromatic ring is hydrogenated, is well known and is also referred to as core hydrogenation. In such core hydrogenation, catalysts containing transition metals, for example, are used. Suitable catalysts are known to those skilled in the art. Corresponding hydrogenation processes are also used on an industrial scale.

[0003] As the core hydrogenation process progresses, the catalysts used can lose activity, either due to blockage, loss, or poisoning of the catalyst's active sites. If the loss of activity is too high and / or the hydrogenation process can no longer be operated economically, the catalyst's activity must be increased. This is achieved by a regeneration process in which the catalyst is freed of deposits and adhesions. Calcination of the catalyst is possible, in which the deposits are removed at high temperatures (> 200 °C), but this can be problematic for certain catalysts or purely from an energy perspective due to the high temperatures.

[0004] Catalysts can also be regenerated by passing a gas stream over them, which entrains and removes the deposits. One such process for regenerating ruthenium catalysts is described, for example, in WO 2008 / 015103 A1. The regeneration disclosed therein is characterized by flushing the catalyst with an inert gas until the catalyst has partially or even completely regained its activity. The reason for the regenerating effect described therein using benzene hydrogenation is the removal of water, i.e., the drying of the catalyst.

[0005] WO 02 / 100536 A1 describes a process for hydrogenating at least one aromatic compound by bringing it into contact with a hydrogen-containing gas in the presence of a catalyst which comprises ruthenium as active metal alone or together with at least one other metal of transition group I, VII or VIII of the Periodic Table, applied to a support material based on amorphous silicon dioxide.

[0006] WO 2006 / 136541 A1 discloses a coated catalyst which contains ruthenium alone or together with at least one other metal of transition groups IB, VIIB or VIII of the Periodic Table of the Elements (CAS version) and is applied to a support containing silicon dioxide, and a process for hydrogenating a carbocyclic aromatic group to the corresponding carbocyclic aliphatic group using the coated catalyst.

[0007] BE 882.279 A further discloses a process for reactivating a catalyst with a gas having a volume fraction of oxygen in the range of 1 to 100% for the hydrogenation of sugars, which catalyst is based on at least one of the six metals of the platinum group, namely ruthenium, rhodium, palladium, osmium, iridium and platinum.

[0008] However, the known process has the problem that the regeneration effect may be too low, especially when not only water has to be removed from the catalyst or when not only water but also other substances that reduce the hydrogenation activity are present on the catalyst.

[0009] Accordingly, the object of the present invention was to provide processes for the regeneration of a catalyst used for the nuclear hydrogenation of an aromatic, in particular an aromatic ester, with which an acceptable activity can be achieved more quickly and better.

[0010] The object is achieved by the process mentioned in claim 1. Preferred embodiments are specified in the subclaims. The process according to the invention is a process for the regeneration of a catalyst used for the ring hydrogenation of an ester of a benzenecarboxylic acid, a benzenedicarboxylic acid, a benzenetricarboxylic acid or a benzenetetracarboxylic acid, which catalyst comprises at least one transition metal from the group consisting of iron, ruthenium, nickel, rhodium, platinum, palladium or mixtures thereof on a support material, in at least one reactor, wherein the regeneration by passing a gas stream having an oxygen content of 380 ppm to 9000 ppm over the catalyst to be regenerated; at a temperature of 15 to 170 °C, preferably 25 to 150 °C, particularly preferably 25 to 120 °C, very particularly preferably 25 to 110 °C; and without removing the catalyst from the at least one reactor is carried out.

[0011] The process according to the invention, in which small amounts of oxygen are present in the gas stream, the regeneration medium, enables advantageous regeneration of the hydrogenation catalyst. The regeneration improves the catalyst activity, which according to the present invention can be achieved even at low oxygen concentrations. The regeneration described here enables the core hydrogenation, through which the actual valuable products are produced, to be subsequently restarted at increased conversions and thus carried out more effectively. At the same time, the relatively low oxygen concentration prevents oxidation processes from leading to greatly increased (possibly even only locally) temperatures in the reactor, which could damage the catalyst or, in the worst case, lead to damage to the reactor.

[0012] The core hydrogenation of aromatic esters described here is usually carried out in at least one reactor, i.e., the core hydrogenation can be carried out in one or more reactors, each containing a suitable catalyst. The inventive regeneration of the catalyst used can be carried out in any of the reactors present. If several reactors are present, the regeneration can be carried out simultaneously or staggered for each reactor, with simultaneous regeneration of all catalysts in all reactors present being preferred.

[0013] According to the invention, the process is suitable for all catalysts used in the ring hydrogenation of aromatic esters. The catalyst comprises at least one transition metal on a support material or consists of at least one transition metal on a support material. Suitable catalysts are also familiar to the person skilled in the art and can be found, for example, in WO 03 / 103830 A1.

[0014] The transition metal of the catalyst to be regenerated is a metal selected from the group consisting of iron, ruthenium, nickel, rhodium, platinum, palladium, or mixtures thereof. Ruthenium is the particularly preferred transition metal of the catalyst used in the present invention. The transition metal content in the catalyst to be regenerated is generally 0.1 to 30 mass%. The ruthenium content, calculated as metal, is preferably in the range of 0.1 to 10 mass%, in particular in the range of 0.3 to 5 mass%, very particularly in the range between 0.4 and 2.5 mass%.

[0015] The support material on which the transition metal is located is preferably selected from the group consisting of activated carbon, silicon carbide, aluminum oxide, silicon dioxide, aluminosilicate, titanium dioxide, zirconium dioxide, magnesium oxide, zinc oxide, or mixtures thereof. Preferred support materials are aluminum oxide, silicon dioxide, titanium dioxide, and mixtures thereof. These support materials may additionally contain alkali metals, alkaline earth metals, and / or sulfur. In a particularly preferred embodiment of the present invention, the catalyst to be regenerated is a coated catalyst.

[0016] According to the invention, a gas stream is used as the regeneration medium. This gas stream preferably consists of an inert gas and oxygen, with the gas stream having an oxygen content of 380 ppm to 9000 ppm. The inert gas can be nitrogen, helium, neon, argon, carbon dioxide, or a mixture thereof. Nitrogen is particularly preferably used as the inert gas. The gas stream during regeneration can be passed over the catalyst in the same or reverse flow direction, relative to the flow direction during core hydrogenation, preferably in the same flow direction.

[0017] If multiple hydrogenation reactors are present, the regeneration medium can be fed exclusively to the first reactor. The regeneration medium would then also be fed from the first reactor to the subsequent reactor(s) to regenerate the catalysts there as well. However, it is preferred that the regeneration medium be fed to each individual reactor if multiple reactors are present. The regeneration medium is thus fed directly to each individual reactor and does not first pass through the previous reactor(s).

[0018] The regeneration is preferably carried out at a temperature of 15 to 170 °C, preferably 25 to 150 °C, particularly preferably 25 to 120 °C. It is important in this context that no burn-off of the catalyst occurs, in which the impurities are removed at high temperatures. The pressure during regeneration is preferably in the range of 0.5 to 200 bar, preferably 1 to 110 bar.

[0019] The length of time the regeneration described here must be carried out to sufficiently improve catalyst activity depends on various factors. Examples of these factors are the type and amount of impurities, the nature of the reactors (size, diameter), or the nature of the catalyst particles (in particular size, shape, surface area, pore structure, metal loading, and penetration depth of the metal in the support). In a preferred embodiment of the present invention, the regeneration duration is at least 24 hours. If regeneration is terminated too early, it may happen that the catalyst has to be regenerated again after only a relatively short period of use in core hydrogenation.

[0020] The regeneration according to the invention takes place using a catalyst used in the ring hydrogenation of an aromatic ester. The aromatic ester is an ester of a benzenecarboxylic acid, an ester of a benzenedicarboxylic acid, an ester of a benzenetricarboxylic acid, or an ester of a benzenetetracarboxylic acid, preferably an ester of benzenedicarboxylic acid or benzenetricarboxylic acid. These include phthalates, isophthalates, terephthalates, and trimellitates. Esters of benzenedicarboxylic acid, i.e., phthalates, isophthalates, and terephthalates, are preferred. Of these, the C8 to C10 alkyl esters, in particular the C8 to C10 alkyl esters of phthalic acid (e.g. dioctyl phthalate, diethylhexyl phthalate, diisononyl phthalate, dipropylheptyl phthalate) or the C8 to C10 alkyl esters of terephthalic acid (e.g. dioctyl terephthalate, diethylhexyl terephthalate, diisononyl terephthalate, dipropylheptyl terephthalate) are particularly preferred.

[0021] The core hydrogenation is preferably carried out in the liquid phase. The core hydrogenation can be carried out continuously or discontinuously over suspended or particulate catalysts arranged in a fixed bed. In the process according to the invention, continuous core hydrogenation over a catalyst arranged in a fixed bed, in which the product / reactant phase is predominantly in the liquid state under reaction conditions, is preferred. The reactor(s) are preferably operated as trickle-bed reactors, which may be fully or partially flooded.

[0022] If core hydrogenation is carried out continuously on a catalyst arranged in a fixed bed, it is advisable to convert the catalyst into the active form before the core hydrogenation is carried out for the first time. After regeneration, such activation is not absolutely necessary. Activation can be achieved by reducing the catalyst with hydrogen-containing gases according to a temperature program. If necessary, the reduction can be carried out in the presence of a liquid phase trickling over the catalyst. A solvent or the hydrogenation product can be used as the liquid phase. Under appropriate hydrogenation conditions, such activation can also be omitted, since it also occurs under reaction conditions.

[0023] Different process variants can be selected for core hydrogenation. It can be carried out adiabatically, polytropically, or virtually isothermally, i.e. with a temperature rise of typically less than 10 °C, in one or more stages. In the latter case, all reactors, preferably tubular reactors, can be operated adiabatically or virtually isothermally, or one or more can be operated adiabatically and the others virtually isothermally. Furthermore, it is possible to hydrogenate the aromatic polycarboxylic acid esters in straight pass or with product recirculation. It is also possible to have two reactors, with the first reactor operating with product recirculation and the second reactor in straight pass. It is also possible to carry out core hydrogenation as a trickle bed. The reactor can also be partially or fully flooded.

[0024] Nuclear hydrogenation can be carried out in the liquid / gas mixed phase or in the liquid phase in three-phase reactors in cocurrent flow, with the hydrogenation gas being distributed in the liquid reactant / product stream in a conventional manner. In the interest of uniform liquid distribution, improved reaction heat removal, and a high space-time yield, the reactors are preferably operated at high liquid flow rates of 15 to 120, in particular 25 to 80 m³ per m² of cross-section of the empty reactor per hour. If a reactor is operated in a straight-pass configuration, the specific catalyst hourly velocity (LHSV) can assume values ​​between 0.1 and 10 h³.

[0025] The core hydrogenation can be carried out in the absence or, preferably, in the presence of a solvent. Any liquid that forms a homogeneous solution with the reactant and product, is inert under hydrogenation conditions, and can be easily separated from the product can be used as a solvent. The solvent can also be a mixture of several substances and may optionally contain water.

[0026] For example, the following substances can be used as solvents: straight-chain or cyclic ethers, such as tetrahydrofuran or dioxane, as well as aliphatic alcohols in which the alkyl radical has 1 to 13 carbon atoms. Preferred alcohols include isopropanol, n-butanol, isobutanol, n-pentanol, 2-ethylhexanol, nonanols, technical nonanol mixtures, decanol, technical decanol mixtures, and tridecanols.

[0027] When using alcohols as solvents, it may be advantageous to use the alcohol or alcohol mixture that would be produced during saponification of the product. This eliminates the formation of byproducts due to transesterification. Another preferred solvent is the hydrogenation product itself.

[0028] By using a solvent, the aromatics concentration in the reactor feed can be limited, allowing for better temperature control in the reactor. This can minimize side reactions and thus increase product yield. The aromatics content in the reactor feed is preferably between 1 and 35%, especially between 5 and 25%. In reactors operated in loop mode, the desired concentration range can be adjusted by the circulation rate (ratio of recycled hydrogenation effluent to reactant).

[0029] The core hydrogenation can be carried out in a pressure range of 20 to 300 bar, preferably 40 to 200 bar. The hydrogenation temperatures are preferably in the range of 60 to 200°C, in particular in the range of 80 to 180°C.

[0030] Any hydrogen-containing gas mixture that does not contain harmful amounts of catalyst poisons such as carbon monoxide or hydrogen sulfide can be used as hydrogenation gases. The inert gas components can be, for example, nitrogen or methane. Hydrogen with a purity of greater than 95%, especially greater than 98%, is preferred.

[0031] The invention is explained below using examples. These examples show exemplary embodiments and are not to be understood as limiting. Example 1 - same oxygen concentration

[0032] For the present experiments, a reproducible catalyst had to be produced first, which then had to be regenerated. In this case, diisononyl terephthalate (DINT) was continuously hydrogenated. The core hydrogenation of DINT took place in a tubular reactor in recirculating operation. The recirculating tubular reactor was flowed through in cocurrent flow with a liquid phase (DINT and hydrogenation product) and a gas phase (hydrogen) in a trickle bed. In Example 1, a commercially available ruthenium catalyst (Specialyst®< 102: 1% Ru on a TiO 2 support, Evonik Operations GmbH) was used as the hydrogenation catalyst. This catalyst was diluted with an equivalent amount of inert material (TiO 2 ) and used in the tubular reactor with an internal diameter of 40 mm and a length of 378 mm. The DINT feed rate used in core hydrogenation was always 130 g / h, and the recycle flow was 80 L / h. H2 control was achieved via a constant exhaust gas flow rate of 0.5 L / h.The experiments were conducted at a system pressure of 100 bar and a tubular reactor temperature of 110 °C. The DINT concentration was measured using inline Raman analysis. The DINT conversion decreased continuously over time. Regeneration was performed after approximately 3700 to 5700 hours.

[0033] Before regeneration, the circulation pump and reactant feed were stopped, and the liquids were drained from the circulation reactor. Subsequently, the respective regeneration conditions (e.g., pressure, temperature) were set, and regeneration was carried out for a specific period of time (see Table 1). After regeneration, the circulation pump and reactant feed were restarted to perform core hydrogenation again, as described in the previous paragraph. The effectiveness of regeneration was assessed based on sampling immediately before the reactant feed was shut off (DINT conversion before regeneration) and approximately 20 to 40 hours after the reactant feed was restarted (DINT conversion after regeneration). The results are listed in Table 1 below. Table 1: Test data for Example 1 Regeneration Pressure / bar T / °C Duration / Days O 2 - Concentration / ppm Circular reactor turnover / % Previously Afterward difference 1 100 110 3 400 91,0 94,3 3,3 2 10 110 3 400 90,6 94,1 3,5 3 10 110 1 400 90,8 93,9 3,1

[0034] From Table 1 it can be seen that neither the pressure nor the duration of regeneration have a significant influence on the regeneration. Example 2 - different oxygen concentrations

[0035] The experiments for Example 2 were conducted in a similar manner to those for Example 1. Therefore, only the differences from the process in Example 1 are listed below. A ruthenium catalyst with a larger amount of Ru was used as the hydrogenation catalyst (2% Ru on TiO 2 support). The feed rate of DINT used in the core hydrogenation was always 180 g / h, and hydrogenation was carried out at a temperature of 92.5 °C. In contrast to Example 1, in addition to the temperature and pressure, the oxygen concentrations were also varied during regeneration. To avoid problems (oxyhydrogen gas), the reactor was first inertized with N 2 before the regeneration experiments with higher O 2 concentration. The results are shown in Table 2. Table 2: Test data for Example 2 Regeneration Pressure / bar T / °C Duration / days O 2 - Concentration / ppm Circular reactor turnover / % Previously Afterward difference 1 100 110 3 400 90 92,5 2,5 2* 10 110 4 36 89,4 89,8 0,4 3* 1 RT 1 20000 88,2 90,2 2 4* 100 RT 1 20000 88,5 90,6 2,1 5 1 110 1 5000 88,1 91,0 2,9 6 100 RT 1 5000 86,8 88,7 1,9 * not according to the invention

[0036] Table 2 shows that poorer regeneration results were achieved at very low oxygen concentrations. At high oxygen concentrations, regeneration is better even in a short time. However, it should be noted that such high concentrations pose the risk of calcination or catalyst burn-off, which is why only low temperatures or lower pressures could be used. Even higher oxygen concentrations (> 20,000 ppm) proved ineffective in this case for safety reasons.

Claims

1. Process for regenerating a catalyst which is used for the ring hydrogenation of an ester of a benzenecarboxylic acid, of a benzenedicarboxylic acid, of a benzenetricarboxylic acid or of a benzenetetracarboxylic acid and comprises at least one transition metal from the group consisting of iron, ruthenium, nickel, rhodium, platinum, palladium and mixtures thereof on a support material in at least one reactor, wherein the regeneration is conducted - by passing a gas stream having an oxygen content of 380 ppm to 9000 ppm over the catalyst to be regenerated; - at a temperature of 15 to 170°C; and - without deinstalling the catalyst from the at least one reactor.

2. Process according to any of the preceding claims, wherein the regeneration is conducted at a temperature of 25°C to 150°C.

3. Process according to Claim 1 or 2, wherein the support material is selected from the group consisting of activated carbon, silicon carbide, aluminium oxide, silicon dioxide, aluminosilicate, titanium dioxide, zirconium dioxide, magnesium oxide, zinc oxide and mixtures thereof.

4. Process according to any of Claims 1 to 3, wherein the catalyst used is an eggshell catalyst.

5. Process according to any of the preceding claims, wherein the gas stream is an inert gas, preferably nitrogen, helium, neon, argon, carbon dioxide and mixtures thereof, having an oxygen content according to Claim 1.

6. Process according to Claim 1, wherein the aromatic ester is an ester of benzenedicarboxylic acid or of benzenetricarboxylic acid, preferably an ester of benzenedicarboxylic acid.

7. Process according to Claim 6, wherein the aromatic ester is a C8- to C10-alkyl ester of phthalic acid or a C8- to C10-alkyl ester of terephthalic acid.

8. Process according to any of the preceding claims, wherein the regeneration is conducted at a pressure in the range of 0.5 to 200 bar.

9. Process according to any of the preceding claims, wherein the duration of the regeneration is at least 24 hours.

10. Process according to any of the preceding claims, wherein the gas stream in the regeneration is guided over the catalyst in the same or in the reverse flow direction, based on the flow direction in the hydrogenation, preferably in the same flow direction.