Regeneration of nickel-containing olefin oligomerization catalysts

Abstract

The invention relates to a method for regenerating a used catalyst that has been used for the oligomerization of C3 to C6 olefins, the catalyst in the fresh state having an active material composition of NiO in the range of 10% to 70% by weight, TiO2 and / or ZrO2 in the range of 5% to 30% by weight, Al2O3 in the range of 0% to 20% by weight, and SiO2 supplemented to 100% by weight, the process comprises the steps of: a) calcining the used catalyst in the presence of an oxygen-containing gas at a temperature of from 300 DEG C to 600 DEG C, b) applying nickel to the catalyst obtained in step a) in an amount of from 1% to 5% by weight corresponding to the mass of the used catalyst, and c) drying and calcining the catalyst obtained in step b).

Description

Technical Field

[0001] The present invention relates to a method for regenerating a spent catalyst that has been used for the oligomerization of C3 to C6 olefins, and the catalyst in its fresh state has an active material composition comprising 10% to 70% by weight of NiO, 5% to 30% by weight of TiO2 and / or ZrO2, 0% to 20% by weight of Al2O3, and SiO2 making up to 100% by weight. Background Art

[0002] Olefins having 3 to 6 carbon atoms or mixtures thereof are abundantly available from FCC (fluid catalytic cracking) units and steam crackers. They are used in various applications on an industrial scale, for example, for the oligomerization or co-oligomerization of olefins to higher olefins. Among C3 to C6 olefins, in particular, the C4 fraction (i.e., a mixture substantially containing butenes and butanes, and if applicable, after removal of isobutene) is known to be suitable for the preparation of oligomers, in particular octene and dodecene. Both octene and dodecene can be used, for example, for the preparation of plasticizers or surfactants after hydroformylation and subsequent hydrogenation to the corresponding alcohols.

[0003] The degree of branching of olefins plays a key role in some applications, such as for using olefins as plasticizer or surfactant alcohols. The degree of branching is described, for example, by the ISO index, which indicates the average number of alkyl side chains of the corresponding olefin fraction. As an example, in the C8 fraction, for the ISO index of this fraction, n-octene contributes 0, methylheptene contributes 1, dimethylhexene contributes 2, and trimethyl-pentene contributes 3. As another example, in the C12 fraction, for the ISO index of this fraction, n-dodecene contributes 0, methylundecene contributes 1, and dimethyldecene contributes 2. The lower the ISO index, the higher the molecular linearity in the corresponding fraction, and then, the higher the yield in hydroformylation and the better the properties of the plasticizer or surfactant prepared therefrom.

[0004] Oligomerization is carried out industrially under homogeneous or heterogeneous catalysis. Homogeneous catalytic methods have the disadvantage that the catalyst must be separated from the reaction mixture. This separation step generates a waste stream that must undergo complex post-treatment. In addition, homogeneous catalysts cannot be regenerated.

[0005] The described disadvantages do not occur in the heterogeneous catalyzed oligomerization of olefins. A process for the oligomerization of olefins to produce oligomers on a heterogeneous catalyst containing nickel is described, for example, in DE 43 39 713 A1. This document discloses a process for the oligomerization of unbranched C2-C6-olefins on a fixed bed catalyst at superatmospheric pressure and elevated temperature, wherein the catalyst contains 10% to 70% by weight of nickel oxide, 5% to 30% by weight of titanium dioxide and / or zirconium dioxide, 0% to 20% by weight of aluminum oxide, and as a complement, silicon dioxide, as important active components. The oligomerization of butene can be carried out by this process with very good selectivity to linear products.

[0006] However, this heterogeneous catalyzed process has the following disadvantages, namely, the nickel-containing catalyst deactivates over time, resulting in lower conversion, lower selectivity to dimers, and higher branching (i.e., higher ISO index). From a cost perspective, it is desirable to regenerate the deactivated catalyst and reuse it in further oligomerization reactions. A method known in the art for regenerating a used catalyst is calcination, i.e., heating the used catalyst to a temperature of 300 °C to 750 °C in the presence of oxygen and burning off the organic material on the catalyst surface. It is further known to impregnate the calcined used catalyst with additional nickel as another regeneration step. For example, document WO 2011 / 000697 A1 discloses a method for regenerating a nickel-containing catalyst that has been used for the oligomerization of olefins, the method comprising the steps of: calcination, impregnation with nickel, and activation by further temperature treatment. Positive results have been reported for used catalysts containing 5% to 50% by weight of Ni, 5% to 30% by weight of Al2O3, and 30% to 80% by weight of SiO2.

[0007] In practice, it has been found that the methods for regenerating used catalysts according to the prior art have different applicability for different types of catalysts. The object of the present invention is to provide a method for regenerating a used catalyst that improves the efficiency of the catalyst for olefin oligomerization reactions in terms of conversion and selectivity, while maintaining the desired degree of branching.

[0008] This object is achieved according to the invention by a method for regenerating a used catalyst according to claim 1 and a method for producing oligomers according to claim 8. Advantageous variants of these methods are presented in claims 2 to 7 and claim 9. Summary of the Invention

[0009] A first subject of the present invention is a method for regenerating a used catalyst that has been used for the oligomerization of C3 to C6 olefins. The catalyst in its fresh state has an active material composition consisting of 10% to 70% by weight of nickel(II) oxide (NiO), 5% to 30% by weight of titanium dioxide (TiO2) and / or zirconium dioxide (ZrO2), 0% to 20% by weight of aluminum(III) oxide (Al2O3), and silica (SiO2) making up the balance to 100% by weight. The method comprises the following steps: a) calcining the used catalyst in the presence of an oxygen-containing gas at a temperature of 300°C to 600°C, b) applying nickel to the catalyst obtained in step a) in an amount corresponding to 1% to 5% by weight of the mass of the used catalyst, and c) drying and calcining the catalyst obtained in step b).

[0010] A second subject of the present invention is a method for producing oligomers in which a feed mixture containing C3 to C6 olefins is fed into a reaction zone, wherein the oligomerization in the reaction zone is carried out in the presence of a catalyst that has been regenerated by the method according to the present invention. Preferably, the feed mixture contains C4 olefins.

[0011] It has been found that regenerating the used catalyst with a small amount of additional nickel shows an increase in conversion and a low degree of branching in subsequent methods for producing oligomers of C3 to C6 olefins.

[0012] Other technical features may be obvious to those skilled in the art from the following description and claims.

[0013] Definitions

[0014] "Active material" means the sum of the oxide substances, excluding the mass of graphite or other additives used to form the catalyst.

[0015] "ISO index" means a value calculated based on the composition of an isomer mixture as the average number of alkyl branches of the corresponding isomers. Isomers without alkyl branches are counted as 0 (zero), isomers with one alkyl branch are counted as 1 (one), isomers with two alkyl branches are counted as 2 (two), isomers with three alkyl branches are counted as 3 (three), etc. The calculation is based on the mass fractions of the corresponding isomers. For example, an isomer mixture containing 35% of isomers without methyl branches, 25% of isomers with one methyl branch, and 40% of isomers with two methyl branches results in an ISO index of 1.05.

[0016] "Oligomerization" means a chemical reaction in which at least two olefins form a new olefin, where the number of carbon atoms of the new olefin is equal to the sum of the carbon atoms of the reaction partners. This new olefin is also referred to as an "oligomer". Examples of oligomers are dimers, trimers and tetramers. The reaction partners can be of the same type, such as only C3 olefins, only C4 olefins, only C5 olefins or only C6 olefins. The reaction partners can also be of different types, such as C3 olefins and C5 olefins, or C4 olefins and C6 olefins. The latter type of reaction is also referred to as "co-oligomerization".

[0017] "Oxygen-containing gas" means a gas containing at least 5 vol.-% of oxygen. Preferably, the oxygen-containing gas mainly contains oxygen and nitrogen, such as air. Further preferably, the ratio of oxygen to nitrogen is selected such that the heat tone occurring during the treatment of the used catalyst is less than 50 °C.

[0018] Unless otherwise specified, throughout this document, "percentage (%)" means weight percentage (wt.-%), and the corresponding numbers are based on the total mass of the corresponding material.

[0019] "Used catalyst" means a nickel-containing catalyst that has been used at least once for the oligomerization of C3 to C6 olefins. Preferred embodiments

[0020] The calcination of the used catalyst in process step a) can be carried out in an oxygen-containing atmosphere, preferably in air. The preferred temperature range for calcination is from 300 °C to 650 °C, more preferably from 400 °C to 600 °C. The calcination can be carried out in a conventional furnace, such as in a muffle furnace, a rotary kiln or a shaft furnace. The used catalyst has carbon deposits. Therefore, carbon oxides and water are formed as oxidation products during the calcination.

[0021] In process step b), nickel is applied to the catalyst obtained in step a). Preferably, nickel is applied as a nickel compound. As nickel compounds, all nickel compounds are suitable, which can be converted into the oxide form of nickel when heated under calcination conditions in the presence of oxygen or an oxygen-containing gas mixture (such as air). Preferably, water-soluble nickel salts (such as nickel nitrate hydrate) or nickel salts having organic anions (such as formate, oxalate, acetate, acetylacetonate or 2-ethylhexanoate) are used as nickel compounds. Particularly preferred is nickel nitrate hydrate.

[0022] In a preferred embodiment of the regeneration method, the application of nickel in step b) is carried out by impregnating the used catalyst with a nickel-containing solution, in particular a solution containing nickel nitrate (such as a nickel nitrate hydrate solution). Preferably, the calcined catalyst is mixed with a solution containing the amount of nickel to be applied to the catalyst. In this case, the amount of the solution is advantageously chosen to correspond to 90% - 100% of the water absorption capacity of the catalyst material.

[0023] In method step c), the impregnated catalyst is dried and calcined. The drying can be carried out in air at a temperature of 50°C to 200°C. The calcination can be carried out as described above for step a). In a preferred embodiment of the regeneration method, the drying in step c) is carried out at a temperature of 80°C to 160°C, and the subsequent calcination is carried out at a temperature of 300°C to 600°C.

[0024] The regenerated catalyst can be further processed before being used again in the oligomerization process. In one embodiment, the catalyst is subjected to conditioning in a dry inert gas stream, preferably in a dry nitrogen stream, for example at atmospheric pressure and a temperature of 50°C to 500°C, preferably 100°C to 250°C, to remove trace amounts of moisture (which may originate from air) from the catalyst.

[0025] The used catalyst can have any form and geometry suitable for the corresponding application. In a preferred embodiment of the present invention, the used catalyst is provided in the form of extrudates or tablets, more preferably in the form of tablets. In a preferred embodiment of the regeneration method, the used catalyst has a mass fraction of carbon of 3% to 10% by weight of the total mass of the catalyst.

[0026] The used catalyst has been used at least once for the oligomerization of C3 to C6 olefins. Preferably, the used catalyst has been regenerated at least once and used again for the oligomerization of C3 to C6 olefins.

[0027] Preferably, the catalyst in the fresh state has an active material composition of 40% to 60% by weight of NiO, 5% to 20% by weight of TiO2 and / or ZrO2, 0% to 10% by weight of Al2O3, and the balance to 100% by weight of SiO2.

[0028] More preferably, the catalyst in the fresh state has an active material composition of 45% to 55% by weight of NiO, 8% to 18% by weight of TiO2 and / or ZrO2, 1% to 5% by weight of Al2O3, and the balance to 100% by weight of SiO2. Detailed Description

[0029] Comparative Example 1

[0030] Samples of the used catalyst were taken from the reactor of an industrial butene dimerization unit. In the fresh state before the first use, the catalyst had an active material composition of 46.5 wt% NiO, 13.9 wt% TiO2, 3.3 wt% Al2O3 and 36.3 wt% SiO2. The catalyst was provided in the form of 3×3 mm tablets, which were produced using 97% of the active material and 3% of graphite as a tableting aid. The catalyst had been regenerated once before and was in its second use. The used catalyst contained 5.1% carbon (C).

[0031] As a base case, the used catalyst was regenerated by calcination according to the prior art without adding additional substances such as nickel. 600 grams (g) of the used catalyst were heated in a rotary kiln from room temperature to a temperature of 450 °C at a rate of 5 Kelvin per minute (K / min). This temperature was maintained for two hours with an air supply to the rotary kiln of 100 liters per hour (l / h). After this time span, the catalyst was allowed to cool passively without additional measures. This procedure was repeated twice and the resulting catalyst samples were mixed to obtain approximately 1.7 kilograms (kg) of the calcined catalyst. The water absorption of the catalyst was 0.73 milliliters per gram (ml / g). Its carbon content decreased from 5.1% to 3.6%.

[0032] Example according to the present invention

[0033] In a series of experiments, parts of the calcined catalyst samples of the base case were impregnated with different amounts of nickel.

[0034] In a first experiment according to the present invention, 55.7 g of an aqueous nickel nitrate solution (with a nickel oxide content of 17.6% in the aqueous solution) was diluted with 167 g of water. This produced an impregnation solution with a volume of 208 milliliters (ml). 300 g of the calcined catalyst of the reference case was vigorously mixed with these 208 ml of the impregnation solution in a porcelain dish until the water absorption rate reached 95%. This corresponded to an amount of additional nickel of 2.5% of the mass of the used catalyst. The resulting impregnated tablets were dried in a convection oven at 120 °C for 16 hours (h). After the drying process, the tablets were calcined by heating in a muffle furnace from room temperature to 450 °C at a rate of 5 Kelvin per minute (K / min). This temperature was maintained for two hours. The total nickel content of the regenerated catalyst was determined by atomic spectrometry to be 37%. For the measurement, two aliquots of samples weighing approximately 0.10 to 0.15 g were digested with concentrated inorganic acid under heating. The mineralization residues were dissolved in dilute hydrochloric acid to 100 mL. Using external calibration, the nickel content of the solution thus prepared was analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES). The reported results are the average of the duplicates. Blank samples were prepared in a similar manner.

[0035] In a second experiment according to the present invention, 22.3 g of an aqueous nickel nitrate solution (with a nickel oxide content of 17.6% in the aqueous solution) was diluted with water, producing an impregnation solution with a volume of 138 ml. 200 g of the calcined catalyst of the reference case was vigorously mixed with the impregnation solution. All other parameters were the same as in the first experiment. A regenerated catalyst with an additional nickel amount of 1.5% was obtained.

[0036] In a third experiment according to the present invention, 60.4 g of an aqueous nickel nitrate solution (with a nickel oxide content of 17.6% in the aqueous solution) was diluted with water, producing an impregnation solution with a volume of 138 ml. 200 g of the calcined catalyst of the reference case was vigorously mixed with the impregnation solution. All other parameters were the same as in the first experiment. A regenerated catalyst with an additional nickel amount of 4% was obtained.

[0037] Comparative Example 2

[0038] In another experiment, the nickel concentration in the impregnation solution was further increased to obtain a regenerated catalyst with an additional nickel amount of 6%. 92.5 g of an aqueous nickel nitrate solution was diluted with water, producing an impregnation solution with a volume of 138 ml. 200 g of the calcined catalyst of the reference case was vigorously mixed with the impregnation solution. All other parameters were the same as in the first experiment.

[0039] Samples of these different regenerated catalysts were tested at technical scale in a reactor system for the dimerization of butenes. Two reactors were connected in series. The first reactor was fed with a raffinate-II feed stream. Since the feed was taken from a real plant, the feed composition varied between the experiments. Table 1 shows the composition by weight percentage of the three feed streams used in these experiments. Additional hydrocarbons, such as 1,3-butadiene, propylene, propane, cyclopropane, allene, methylcyclopropane, vinylacetylene, pentene and pentane, were present in trace amounts. Water and oxygenated organic compounds were removed by flowing the feed stream over molecular sieve (3A) and a purification catalyst before entering the reactor system.

[0040] Table 1:

[0041]

[0042] The outlet of the first reactor was fed to the inlet of the second reactor. A portion of the outlet of the second reactor was recycled to the second reactor. The remaining portion of the outlet of the second reactor was taken out as the product stream.

[0043] Each reactor comprised reaction tubes with an inner diameter of 15 mm and a tube length of 2200 mm. The two reaction tubes were each filled with 125 ml of catalyst and were delimited at each end by a layer of talc balls. The temperature inside the tubes was measured via a plurality of thermocouples. The operation of the reactors was quasi-isothermal.

[0044] Each reactor was equipped with 125 ml of regenerated catalyst. For this purpose, the catalysts obtained in the above examples were each provided in tablets of size 3×3 mm. Before each run, an inert nitrogen stream was passed through the reactor system at a temperature of 250 °C for 12 hours. For each reaction experiment, a raffinate-II feed stream of 250 g / h was fed to the first reactor. The recycle stream on the second reactor was set at 1.5 kg / h. The temperature in both reactors was set at 80 °C at a reactor internal pressure of 30 bar (absolute).

[0045] The composition of the feed stream, the outlet stream of the first reactor and the product stream of the second reactor was determined using an on-line gas chromatograph with two columns for the simultaneous determination of C4 isomers and olefins having 4, 8, 12 and more carbon atoms. The ISO index was determined by additional off-line analysis carried out in a hydrogenation gas chromatograph.

[0046] Table 2 shows the results of experiments carried out with five different regenerated catalysts. The percentage of nickel added is given in the first column of Table 2. The numbers in the second column refer to the feed composition given in Table 1. The values in the third and fifth columns show the conversion of C4 components in the respective reactors. The values in the fourth and sixth columns show the selectivity for C8 components in the respective reactors. The rightmost column shows the ISO index value of the C8 product obtained from the second reactor for each experiment. The first row of each pair of results refers to the analysis carried out after approximately two days of reactor run time, and the second row of each pair of results refers to the analysis carried out after approximately nine days of reactor run time.

[0047] Table 2:

[0048]

[0049] As expected, regeneration of the used catalyst by calcination alone gives moderate values of butene (C4) conversion, isooctene selectivity, and a rather high C8 ISO index. Reaction experiments carried out with three samples of the regenerated catalyst with a small amount (1.5%, 2.5%, 4%) of additional nickel show that the isooctene selectivity is increased and the degree of branching of isooctene (C8 ISO index) is within the desired range of 0.95 to 1.05. The butene conversion of the catalyst with a small amount of additional nickel is similar or higher compared to the catalyst without nickel addition. Adding a small amount of nickel to the used catalyst already rich in nickel proves to be beneficial. However, adding even more nickel (6%) shows a much lower butene conversion and an undesired increase in the formation of branched isooctenes, which can be inferred from the rather high ISO index.

Claims

1. A method for regenerating a used catalyst that has been used for the oligomerization of C3 to C6 olefins, the catalyst in its fresh state having an active material composition of 10% to 70% by weight of NiO, 5% to 30% by weight of TiO2 and / or ZrO2, 0% to 20% by weight of Al2O3, and the balance to 100% by weight of SiO2, the method comprising the following steps: a) calcining the used catalyst in the presence of an oxygen-containing gas at a temperature of 300°C to 600°C, b) applying nickel to the catalyst obtained in step a) in an amount corresponding to 1% to 5% by weight of the mass of the used catalyst, and c) drying and calcining the catalyst obtained in step b).

2. The method according to claim 1, wherein The application of nickel in step b) is carried out by impregnating the used catalyst with a nickel-containing solution, in particular a solution containing nickel nitrate.

3. The method according to claim 1 or 2, characterized in that, The drying in step c) is carried out at a temperature of 80°C to 160°C, and the subsequent calcining is carried out at a temperature of 300°C to 600°C.

4. The method according to any one of claims 1 to 3, characterized in that, The used catalyst has a mass fraction of carbon of 3% to 10% by weight.

5. The method according to any one of claims 1 to 4, characterized in that, The used catalyst has been regenerated at least once and is used again for the oligomerization of C3 to C6 olefins.

6. The method according to any one of claims 1 to 5, characterized in that, The catalyst in its fresh state has an active material composition of 40% to 60% by weight of NiO, 5% to 20% by weight of TiO2 and / or ZrO2, 0% to 10% by weight of Al2O3, and the balance to 100% by weight of SiO2.

7. The method according to any one of claims 1 to 5, characterized in that The catalyst in its fresh state has an active material composition of 45% to 55% by weight of NiO, 8% to 18% by weight of TiO2 and / or ZrO2, 1% to 5% by weight of Al2O3, and the balance to 100% by weight of SiO2.

8. A process for producing oligomers, in which a feed mixture containing C3 to C6 olefins is fed to a reaction zone, characterized in that, The oligomerization in the reaction zone is carried out in the presence of a catalyst regenerated by the method according to any one of claims 1 to 7.

9. The method for producing oligomers according to claim 8, characterized in that, The feed mixture contains C4 olefins.

Images