Preparation method of co-based c4 selective hydrogenation catalyst

Abstract

The application relates to a Co-based C4 selective hydrogenation catalyst preparation method and belongs to the technical field of low-carbon olefin selective hydrogenation catalyst preparation methods. In the prior art, the problem of crystal SnO2 or nano tin oxide particle generation in a hydrogenation catalyst with a Co active center loaded on an Sn-containing MCM-41 molecular sieve seriously affects the catalytic efficiency of Co and the butene selectivity. In the application, before a tin source is added, hydrochloric acid is used to acidify organic alkoxysilane, and Cl ‑ The rapid hydrolysis of the tin source can be inhibited to some extent, the formation of Sn-O-Sn bonds is avoided, the formation of Si-O-Sn bonds, i.e. the generation of skeleton SnOx, is effectively promoted, the generation of crystal SnO2 is avoided, the combination of metal Sn and Co to form an alloy phase is avoided during the reaction at high temperature, the catalyst activity is remarkably improved, the butene selectivity of the catalyst is improved, and the butene loss rate is reduced.

Description

Technical Field

[0001] A method for preparing a Co-based C4 selective hydrogenation catalyst belongs to the technical field of preparation methods for low-carbon olefin selective hydrogenation catalysts. Background Technology

[0002] Mixed C4 hydrocarbons (C4) typically contain butadiene in addition to alkanes and monoolefins, ranging from several thousand ppm. Due to the more reactive carbon-carbon double bonds, butadiene undergoes polymerization under acid catalysis when used as a feedstock in mixed C4. The presence of these polymerizable compounds leads to catalyst deactivation in alkylation, affecting stable plant operation and product quality. Therefore, selective hydrogenation units are often required to remove these polymerizable components. Currently, the industrially used selective hydrogenation catalyst for butadiene is alumina-supported Pd catalyst. However, Pd is expensive, resulting in high catalyst costs and hindering large-scale initial deployment. Therefore, in recent years, researchers have conducted more extensive research on inexpensive, non-precious metal alternative catalysts.

[0003] Patent CN105709786A discloses a method for preparing a selective hydrogenation catalyst for 1,3-butadiene. This catalyst is a P-modified Ni-based catalyst supported on alumina. Under reaction conditions of 95°C, 1.8 MPa, and a hydrogen / butadiene molar ratio of 1.8, the butadiene conversion rate in the mixed C4 mixture is 71.4%, and the butene loss rate is 1.7%. CN105399593A discloses a method for preparing a Raney copper catalyst and using it in the butadiene hydrogenation reaction. After hydrogenation, the butadiene content in the mixed C4 mixture is >1000 ppm, and the butene selectivity is around 76%. The above patents exhibit low selectivity for butene, and the conversion rate from butadiene to butene is also low.

[0004] In addition, the transition metal Co is also a commonly used hydrogenation catalyst. CN108404916A discloses a method for preparing a cobalt catalyst, using sodium hypophosphite as a reducing agent to directly synthesize the cobalt catalyst under atmospheric pressure and low temperature conditions. In the hydrogenation reaction of butadiene, this catalyst achieves a butadiene conversion of 45.1% and a 1-butene selectivity of 78.2%. However, due to the excessively strong hydrogenation ability of Co, some monoolefins are hydrogenated to butane. Since monoolefins are the main raw materials and target products in alkylation reactions, the presence of alkanes reduces the product yield in the alkylation reaction. Numerous studies have shown that introducing Sn as a promoter into non-noble metals (such as Ni and Co) produces geometric and electronic effects, which help to reduce the adsorption of monoolefins on the catalyst surface, thereby inhibiting excessive hydrogenation to form alkanes and improving catalyst selectivity. However, due to the weak interaction between Sn and the support, Sn is prone to forming a metallic state during high-temperature reduction, resulting in a low metal / Sn atomic ratio in the metal-Sn alloy phase after reduction. This reduces the number of exposed active metal phases, which in turn inhibits the hydrogenation reaction of butadiene and decreases catalyst activity.

[0005] Introducing Sn into the framework of molecular sieves (such as ZSM-5, MCM-41, SOPA-34, etc.) can suppress the Sn reduction process by utilizing the strong interaction between the molecular sieve framework and Sn. Existing Sn-molecular sieve systems are typically prepared using a method of alkaline source co-precipitation followed by hydrothermal crystallization. Due to the different hydrolysis rates of Sn and Si sources, non-framework tin species such as crystalline tin oxide or tin oxide nanoparticles inevitably form under high Sn / Si molar ratio conditions. Their weak interaction with the molecular sieve makes them easily reduced to the metallic state during the reduction process. Patent CN109364979A provides a method for preparing Sn-MCM-41 molecular sieves. It involves mixing tin tetrachloride pentahydrate and tetraethyl orthosilicate, then adding the mixture to a solution containing a template and ammonia. After hydrothermal crystallization, Sn-containing MCM-41 molecular sieves are obtained. However, the method does not explain the coordination state and reduction performance of Sn in the molecular sieve. Those skilled in the art will recognize that this catalyst still does not solve the problem of Sn self-crystallization and polymerization, generating crystalline SnO2 or nano-tin oxide particles. This SnO2 easily forms metallic Sn after high-temperature reduction and combines with Co to form an alloy phase, severely affecting the catalytic efficiency of Co and the selectivity of butene. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art, and to solve the problems of the high Sn / Co atomic ratio in the alloy phase of the supported non-precious metal Co-Sn catalytic system, which leads to a reduction in the number of hydrogenation activities, as well as the problems of high single olefin loss rate and high cost of Pd-based catalysts in non-precious metal catalytic systems. The present invention provides a low-cost method for preparing a nickel-based C4 fraction selective hydrogenation catalyst that has high butadiene selective hydrogenation activity and single olefin yield.

[0007] The technical solution adopted by this invention to solve its technical problem is: a method for preparing a Co-based C4 selective hydrogenation catalyst, characterized by comprising the following steps: 1) The template agent, hydrochloric acid, and organoalkoxysilane are dissolved in water to prepare a mixture; 2) Add the tin precursor solution and mix thoroughly; 3) Add ammonia water, stir evenly, and then perform hydrothermal crystallization at 90~110℃ for 10~15 hours; 4) The solid obtained in step 3) is washed, dried, and calcined to obtain a catalyst support; 5) The catalyst support is impregnated with a cobalt precursor solution, and then dried and calcined to obtain a Co-based C4 selective hydrogenation catalyst.

[0008] This invention employs an acidification treatment of the organoalkoxysilane with hydrochloric acid before adding a tin source. The principle is that since the hydrolysis rate of the alkoxysilane source is much lower than that of the tin source, the added tin source will preferentially undergo a hydrolysis-condensation reaction, that is, the Sn-OH bonds preferentially condense to form a non-framework SnO. x Nanoparticles. When using the pre-hydrolysis scheme of this invention, i.e., preferentially adding a silicon source and hydrochloric acid to a solution containing a template agent, the alkoxysilane source will... + Under the influence of [the substance], a hydrolysis reaction occurs to generate Si-OH monomers. Simultaneously, when a tin source is subsequently added, the Cl in the hydrochloric acid [is affected]. - This can, to some extent, suppress the excessively rapid hydrolysis of the tin source and prevent the formation of Sn-O-Sn bonds. Therefore, when an alkaline source is added, the condensation hydrolysis rates of tin and silicon are comparable, which can effectively promote the formation of Si-O-Sn bonds, i.e., the formation of the framework SnOx, and avoid the formation of crystalline SnO2. This avoids the formation of an alloy phase by combining metallic Sn with Co during high-temperature reduction in the reaction, thus preventing a serious impact on the catalytic efficiency of Co and the selectivity of butene.

[0009] The sample in this invention mainly exists in the form of isolated Sn species with four-coordinate framework. Sn is stabilized in the oxidized state. Sn-MCM-41 is prepared in steps 1) to 4). When Co is loaded on Sn-MCM-41, the overflow hydrogen dissociated on the surface of metallic Co causes Sn near Co to be forcibly reduced to the metallic state, forming a Co3Sn2 alloy phase with Co. Sn that is farther away from Co is stabilized in the oxidized state by the molecular sieve, thereby reducing the Sn / Co atomic ratio in the Co-Sn alloy phase, exposing more active Co, significantly improving the catalyst activity, improving the butene selectivity of the catalyst, and reducing the butene loss rate.

[0010] Preferably, the preparation process of the mixture in step 1) is as follows: after the template agent is dissolved in water, hydrochloric acid is added, the mixture is mixed evenly, and then an organic alkoxysilane is added.

[0011] Adding hydrochloric acid in advance provides stable H+ for organoalkoxysilanes. + The reaction environment ensures that all alkoxysilane sources are in H+. + Under the action of [something], a hydrolysis reaction occurs to generate Si-OH monomers.

[0012] Preferably, in the mixture described in step 1), the molar amounts of the template agent, hydrochloric acid, and organoalkoxysilane are 0.15~0.25 parts, 0.03~0.06 parts, and 1 part, respectively.

[0013] Under the preferred molar ratio, organoalkoxysilanes can fully utilize H + The reaction ensures the full generation of Si-OH monomers, guaranteeing the rate of silicon condensation hydrolysis after the subsequent addition of ammonia.

[0014] Based on 1 molar part of organoalkoxysilane, the molar part of water in step 1) is 120-141 parts.

[0015] Preferably, the template agent in step 1) is one of the alkyl trimethyl ammonium halide long-chain alkane quaternary ammonium cationic surfactants of C12 to C18.

[0016] Preferably, the template agent in step 1) is hexadecyltrimethylammonium bromide.

[0017] Preferably, the organoalkoxysilane in step 1) is tetraethyl orthosilicate.

[0018] Preferably, the tin precursor solution in step 2) is an ethanol solution of tin tetrachloride pentahydrate.

[0019] Given the hydrolytic nature of tin chloride, tin chloride pentahydrate is selected because it is readily soluble in water and has a slow hydrolysis rate. The addition method of first dissolving it in ethanol and then adding it to the reaction system can effectively alleviate the hydrolysis of tin, ensure the hydrolysis rate of tin and silicon, and prevent the crystallization of tin oxide.

[0020] More preferably, the tin precursor solution in step 2) contains 0.02 to 0.04 parts of tin in molar fraction.

[0021] Preferably, in the ammonia water described in step 3), the molar amount of NH3 is 0.8 to 1.4 parts.

[0022] Preferably, after preparing the mixture in step 1), it is stirred for 1.5 to 2.5 hours.

[0023] Allow sufficient time to ensure that the organoalkoxysilanes react fully under the action of hydrogen ions.

[0024] Compared with the prior art, the beneficial effects of this invention are: low raw material cost, short reaction time, high catalytic activity of the final Co-based C4 selective hydrogenation catalyst, high butadiene conversion rate, strong butene selectivity, and low butene loss rate. Attached Figure Description

[0025] Figure 1 The XRD patterns are of the Co-based C4 selective hydrogenation catalyst (a) of Example 1, the Co-based C4 selective hydrogenation catalyst (b) of Comparative Example 1, and the Co-based C4 selective hydrogenation catalyst (c) of Comparative Example 2.

[0026] Figure 2 UV-vis spectra of MCM-41 (a), Sn-MCM-41 prepared in Example 1 (b), Sn-MCM-41 prepared in Comparative Example 1 (c), and Sn-MCM-41 prepared in Comparative Example 2 (d).

[0027] Figure 3 XPS spectra of the Co-based C4 selective hydrogenation catalysts prepared in Examples 1(c), 1(b), and 2(a) after reduction. Detailed Implementation

[0028] The present invention will be further described below with reference to the embodiments, wherein Embodiment 1 is the preferred embodiment of the present invention.

[0029] Example 1 A method for preparing a Co-based C4 selective hydrogenation catalyst comprises the following steps: 1) Weigh 17.5 g of CTAB and dissolve it in 600 g of deionized water.

[0030] 2) Add 1.4 g of concentrated hydrochloric acid (0.014 mol HCl) and 50.00 g of TEOS in sequence, and continue stirring for 2 h.

[0031] 3) Dissolve 3.4 g of SnCl4∙5H2O in 10 g of anhydrous ethanol and slowly add it to the solution in step 2), then stir for 12 h.

[0032] 4) Add 22.9 g of concentrated ammonia solution and stir continuously for 3 hours, then dilute at 100 °C. o C hydrothermal crystallization for 12 h.

[0033] 5) The solid product obtained in step 4 is filtered and washed several times with deionized water until the filtrate is neutral. Then, it is heated at 60°C. o Dry at C for 12 h, 550 o Sn-MCM-41 was obtained by calcining at C for 6 h.

[0034] 6) Dissolve 2.8 g of cobalt nitrate hexahydrate in 12 g of deionized water, and impregnate the precursor obtained in step 5 with it for 60 minutes. o After drying at C for 12 hours, at 500 o The final catalyst was obtained by calcination at C for 3 h. The molar ratio of the main components used in this embodiment is 1 TEOS: 0.04 SnCl4∙5H2O: 0.06 HCl: 1.4NH3: 0.2 CTAB: 141 H2O.

[0035] Example 2 A method for preparing a Co-based C4 selective hydrogenation catalyst, based on Example 1, except that in step 2), the concentrated hydrochloric acid is replaced with 0.7 g and the hydrochloric acid with 0.007 mol. Other conditions are the same as in Example 1.

[0036] Example 3 A method for preparing a Co-based C4 selective hydrogenation catalyst, based on Example 1, except that in step 2), TEOS is replaced with tetramethyl silicate, and the mass is replaced with 36.5 g (0.24 mol). Other conditions are the same as in Example 1.

[0037] Example 4 A method for preparing a Co-based C4 selective hydrogenation catalyst, based on Example 1, involves replacing TEOS with tetramethyl silicate (36.5 g, 0.24 mol) in step 2). In step 3), the weight of SnCl4∙5H2O is set to 1.7 g, 0.048 mol. Other conditions are the same as in Example 1.

[0038] Example 5 A method for preparing a Co-based C4 selective hydrogenation catalyst, based on Example 1, involves the following modifications: Step 1) CTAB is replaced with 21.9 g (0.06 mol); Step 2) TEOS is replaced with tetramethyl silicate (36.5 g (0.24 mol); Step 3) SnCl4∙5H2O is set to 3.4 g (0.0096 mol). All other conditions remain the same as in Example 1.

[0039] Example 6 A method for preparing a Co-based C4 selective hydrogenation catalyst, based on Example 1, except that in step 2), the concentrated hydrochloric acid is replaced with 1.0 g and 0.01 mol. Other conditions are the same as in Example 1.

[0040] Example 7 A method for preparing a Co-based C4 selective hydrogenation catalyst, based on Example 1, except that in step 2), the concentrated hydrochloric acid is replaced with 0.85 g and 0.0086 mol. Other conditions are the same as in Example 1.

[0041] Example 8 A method for preparing a Co-based C4 selective hydrogenation catalyst, based on Example 1, involves adding TEOS first, followed by hydrochloric acid in step 2).

[0042] Comparative Example 1 A method for preparing a Co-based C4 selective hydrogenation catalyst, based on Example 1, except that hydrochloric acid is not added in step 2), while other conditions are the same as in Example 1.

[0043] Comparative Example 2 A method for preparing a Co-based C4 selective hydrogenation catalyst is disclosed. The method is the same as that used in Example 1 to synthesize MCM-41 molecular sieve, except that tin tetrachloride pentahydrate is not added during the synthesis. The resulting molecular sieve is used to prepare a Co-Sn catalyst by impregnation. As a comparison, the content of Co and Sn in the catalyst is the same as that in Example 1.

[0044] Performance testing The Co-based C4 selective hydrogenation catalysts prepared in the examples and comparative examples were packed into a fixed-bed reactor and subjected to selective hydrogenation of the catalytic C4 fraction containing 0.56% butadiene by mass in a continuous manner (the composition of the C4 fraction is shown in Table 1).

[0045] Table 2. Composition of C4 fraction (wt%) .

[0046] The operating conditions are as follows: Reaction temperature: 40℃.

[0047] Reaction pressure: 1.5 MPa.

[0048] Raw material weight hourly space velocity: 10 h -1 .

[0049] Hydrogen / butadiene molar ratio: 5.

[0050] The results of the hydrogenation performance evaluation of the selected catalyst are shown in Table 2.

[0051] Table 2 Evaluation results of hydrogenation performance of catalyst selection .

[0052] Reference Figure 1 ,from Figure 1 The XRD patterns of the samples show that, compared to samples prepared by the impregnation method and the traditional hydrothermal method, the Co / Sn atomic ratio in the sample used in this invention is significantly increased. Experimental evaluation results indicate that the catalyst of this invention possesses higher catalytic activity while also exhibiting good catalytic selectivity. Figure 2 As shown, the UV-Vis spectra indicate that the sample in this invention mainly exists as isolated Sn species with a four-coordinate framework, while the samples prepared by the conventional hydrothermal and impregnation methods contain some crystalline tin oxide or tin oxide nanoparticles. Furthermore, XPS analysis of the three Sn-MCM-41 samples prepared before Co impregnation, after high-temperature reduction, revealed that Sn in the sample of this invention is stabilized in the oxidized state, while the presence of metallic Sn was detected in both samples of the comparative examples. (Refer to...) Figure 3 In this invention, the Sn synthesized using this method remains in the oxidized state after high-temperature reduction. This is attributed to the strong interaction between Sn-O-Al in the framework Sn species, which inhibits excessive reduction of Sn to the metallic state. In contrast, the presence of metallic Sn was detected in the samples of Comparative Examples 1 and 2, indicating that the non-framework SnOx is easily reduced to its lowest valence state during high-temperature reduction due to the weaker interaction between the supports. Therefore, in the samples of this invention, when Co is loaded onto Sn-MCM-41, the overflow hydrogen dissociated on the surface of metallic Co forces Sn near Co to be reduced to the metallic state, forming a Co3Sn2 alloy phase with Co. Sn farther from Co is stabilized in the oxidized state by the molecular sieve, thereby reducing the Sn / Co atomic ratio in the Co-Sn alloy phase, exposing more active Co and improving catalyst activity. Simultaneously, the low butene loss rate demonstrates stronger butene selectivity and high butadiene conversion.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a Co-based C4 selective hydrogenation catalyst, characterized in that: Includes the following steps: 1) The template agent, hydrochloric acid, and organoalkoxysilane are dissolved in water to prepare a mixture; 2) Add the tin precursor solution and mix thoroughly; 3) Add ammonia water, stir evenly, and then perform hydrothermal crystallization at 90~110℃ for 10~15 hours; 4) The solid obtained in step 3) is washed, dried and calcined to obtain the catalyst support Sn-MCM-41; 5) The catalyst support is impregnated with a cobalt precursor solution, and then dried and calcined to obtain a Co-based C4 selective hydrogenation catalyst; The preparation process of the mixture in step 1) is as follows: after the template agent is dissolved in water, hydrochloric acid is added, the mixture is mixed evenly, and then an organic alkoxysilane is added; In the mixture described in step 1), the molar amounts of the template agent, hydrochloric acid, and organoalkoxysilane are 0.15~0.25 parts, 0.03~0.06 parts, and 1 part, respectively. The organoalkoxysilane mentioned in step 1) is tetraethyl orthosilicate; After preparing the mixture as described in step 1), stir for 1.5 to 2.5 hours; The tin precursor solution mentioned in step 2) is an ethanol solution of tin tetrachloride pentahydrate.

2. The method for preparing a Co-based C4 selective hydrogenation catalyst according to claim 1, characterized in that: Step 1) The template agent is one of the alkyl trimethyl ammonium halide long-chain alkane quaternary ammonium cationic surfactants of C12 to C18.

3. The method for preparing a Co-based C4 selective hydrogenation catalyst according to claim 1, characterized in that: The template agent mentioned in step 1) is hexadecyltrimethylammonium bromide.

4. The method for preparing a Co-based C4 selective hydrogenation catalyst according to claim 1, characterized in that: In step 2), the tin precursor solution contains 0.02 to 0.04 molar amounts of tin.

5. The method for preparing a Co-based C4 selective hydrogenation catalyst according to claim 1, characterized in that: In the ammonia water described in step 3), the molar amount of NH3 is 0.8 to 1.4 parts.

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