Catalyst for preparing acetic acid through methanol carbonylation as well as preparation method and application of catalyst

Abstract

The invention discloses a catalyst for preparing acetic acid through methanol carbonylation as well as a preparation method and application thereof. The preparation method comprises the following steps: 1) mixing a silicon source, an aluminum source and an alkali source to form sol; 2) mixing quaternary ammonium salt and organic alkali, adding the mixture into the sol prepared in the step 1), and then aging, crystallizing, filtering, washing, drying and roasting; 3) dispersing the molecular sieve prepared in the step 2) in an NH4Cl aqueous solution, carrying out ammonium exchange, and then drying and roasting; and 4) carrying out pyridine adsorption on the molecular sieve prepared in the step 3) to obtain the catalyst. Wherein the quaternary ammonium salt in the step 2) is one or more of octalkyl trimethyl ammonium bromide, decyl trimethyl ammonium bromide, dodecyl trimethyl ammonium bromide, tetradecyl trimethyl ammonium bromide, hexadecyl trimethyl ammonium bromide and octadecyl trimethyl ammonium bromide. The prepared nanometer mordenite can improve diffusion of methanol and carbon monoxide and improve activity and selectivity of methanol carbonylation synthesis of acetic acid.

Description

Technical Field

[0001] The present invention relates to the field of catalysis for improving the reaction activity of methanol carbonylation to acetic acid, and in particular to a catalyst for preparing acetic acid by methanol carbonylation, and a preparation method and application thereof. Background Art

[0002] Acetic Acid (AA), as an important organic chemical raw material, can be derived into a series of high value-added chemicals, such as vinyl acetate monomer (Vac or VAM), acetic anhydride, chloroacetic acid (MCA), polyvinyl alcohol, acetate, etc. The downstream covers a wide range of fields, including synthetic fiber, medicine, printing and dyeing, textile, food processing, pesticide, fragrance and other industries. In recent years, the development prospects of acetic acid derivatives are good, entering a period of rapid growth in production capacity, and the market demand for acetic acid has also increased year by year.

[0003] The synthesis process of acetic acid includes anaerobic fermentation, light hydrocarbon liquid phase oxidation, acetaldehyde oxidation, methanol carbonylation, etc. Among them, the methanol carbonylation process for synthesizing acetic acid has high atomic economy and mild reaction conditions, which meets the requirements of green chemical industry. With the introduction of molecular sieve system catalysts, the advantages of this process are more prominent: it avoids the use of halides, the catalyst is cheap and easy to obtain and recycle, the selectivity of acetic acid is high, and it has great prospects for industrialization.

[0004] The reaction of this process is as follows: CH 3 OH + CO → CH 3 COOH. At present, the research on catalysts and processes for this reaction is increasing year by year, mainly focusing on two catalyst systems: heteropolyacids supported by precious metals and molecular sieves. However, considering the cost of catalytic reactions, most scholars focus on the research of molecular sieves, especially mordenite (MOR) and ZSM-5 with eight-membered ring structures. How to obtain catalysts with better reaction activity has attracted the attention of many researchers. Summary of the invention

[0005] The purpose of the present invention is to solve the above problems in the prior art and provide a catalyst for preparing acetic acid by carbonylation of methanol and a preparation method and application thereof. The catalyst prepared by the present invention has high activity, good selectivity, simple preparation process and is easy to industrially scale up.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] A method for preparing a catalyst for preparing acetic acid by carbonylation of methanol comprises the following steps:

[0008] 1) mixing a silicon source, an aluminum source and an alkali source uniformly to form a sol;

[0009] 2) mixing the quaternary ammonium salt and the organic base, adding the mixture to the sol prepared in step 1), and then aging, crystallizing, filtering, washing, drying and calcining;

[0010] 3) Disperse the molecular sieve prepared in step 2) in NH 4 Cl aqueous solution, ammonium exchange, followed by drying and calcination;

[0011] 4) adsorbing pyridine on the molecular sieve prepared in step 3) to obtain the catalyst;

[0012] Wherein, the quaternary ammonium salt in step 2) is one or more of octaalkyltrimethylammonium bromide, decanyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide and octadecyltrimethylammonium bromide.

[0013] The quaternary ammonium salt is preferably dodecyltrimethylammonium bromide.

[0014] The organic base is at least one of tetraethylammonium hydroxide and tetrapropylammonium hydroxide.

[0015] The molar ratio of the organic base to the quaternary ammonium salt is (1-10):1.

[0016] In step 1), the silicon source is silica sol, tetraethyl orthosilicate, water glass or silicon dioxide, the aluminum source is sodium aluminate, aluminum nitrate, aluminum sulfate, etc., and the alkali source is sodium hydroxide. When forming the sol, water is added and stirred to ensure sufficient and uniform mixing.

[0017] In step 2), the crystallization temperature is 140 to 200° C., preferably 150 to 180° C., and the crystallization time is 24 to 120 h, preferably 48 to 72 h.

[0018] In step 3), NH 4 The concentration of Cl is 0.1-1 mol / L, preferably 0.1-0.5 mol / L; the calcination temperature is 450-650° C., and maintained for 2-6 hours.

[0019] In step 4), the conditions for pyridine adsorption are to pass N 2 , heat up to 300-450℃ to dehydrate for 4-6h, then cool down to 200-350℃ to adsorb pyridine for 1-15h.

[0020] A catalyst for preparing acetic acid by carbonylation of methanol, the catalyst having a mordenite crystal phase.

[0021] The invention discloses an application of a catalyst for preparing acetic acid by carbonylation of methanol, which is used for preparing acetic acid by carbonylation of methanol and carbon monoxide. The catalyst is added into a fixed bed reactor, the molar ratio of the reaction raw materials methanol and carbon monoxide is 1:1-100, the temperature is 150-350°C, and the reaction pressure is 0.5-5.0MPa, preferably 2-3MPa.

[0022] The catalyst for preparing acetic acid by carbonylation of methanol prepared by the present invention has a significant influence on the performance and structure of the catalyst through a carefully designed preparation process, especially the change of the chain length of the quaternary ammonium salt.

[0023] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0024] 1) The molecular sieve catalyst prepared by the present invention has a mordenite crystal phase and high crystallinity. In the preparation process, an organic base and a quaternary ammonium salt of different chain lengths are used as a dual template agent to improve the crystallinity of the molecular sieve and reduce the non-framework Al and amorphous SiO 2 The catalyst has low cost, simple preparation process, simple post-treatment and is easy to repeat.

[0025] 2) Methanol conversion and acetic acid selectivity are significantly improved: When the chain length of the quaternary ammonium salt is moderate, especially when decanyl trimethyl ammonium bromide is used, the prepared catalyst exhibits the best methanol conversion and acetic acid selectivity. As shown in Example 2, the methanol conversion can reach 99.9%, and the acetic acid selectivity can reach 94.7%, which is much higher than the catalyst prepared without adding quaternary ammonium salt. This shows that the appropriate quaternary ammonium salt chain length can significantly improve the activity and selectivity of the catalyst.

[0026] 3) Accelerated reaction rate: Appropriate pore size distribution promotes rapid diffusion of reactants and products, thereby increasing the reaction rate. As shown in Table 2, as the chain length of the quaternary ammonium salt changes, the space-time yield of acetic acid also changes. When decanyl trimethyl ammonium bromide is used as a template, it shows an excellent space-time yield of acetic acid.

[0027] 4) Changes in catalyst morphology and crystallinity: The chain length of the quaternary ammonium salt directly affects the morphology and crystallinity of the catalyst. As the chain length changes, the morphology of the catalyst changes from nano-sized flower-like particles to micron-sized rod-like particles. This change in morphology not only affects the surface area and pore structure of the catalyst, but also further affects its catalytic performance.

[0028] 5) Optimization of pore size distribution: The chain length of the quaternary ammonium salt determines the occupation of the template in the pores, thereby affecting the pore size distribution of the catalyst. The data of the embodiment show that when decanyltrimethylammonium bromide is used as a template, the catalyst has a larger mesopore volume and micropore volume, and this pore size distribution is more conducive to the rapid diffusion of reactants and products.

[0029] 6) Regulation of acid sites: With the change of quaternary ammonium salt chain length, the silicon-aluminum ratio (Si / Al) and acid site distribution of the catalyst also changed. In particular, when decanyltrimethylammonium bromide was used as a template, the eight-membered ring B acid content of the catalyst accounted for the highest proportion, which was conducive to the methanol carbonylation reaction.

[0030] In summary, the change of quaternary ammonium salt chain length has a profound impact on the performance and structure of the catalyst. By selecting the appropriate quaternary ammonium salt chain length, a highly active and highly selective methanol carbonylation catalyst for acetic acid can be prepared, thereby improving the reaction efficiency and product quality. This catalyst is not only easy to prepare, but also low in cost, and has great prospects for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The XRD spectra of the mordenite molecular sieves prepared in Example 2 and Comparative Example 1 are shown.

[0032] Figure 2 This is a scanning electron microscope image of the mordenite molecular sieve prepared in Example 1.

[0033] Figure 3 This is a scanning electron microscope image of the mordenite molecular sieve prepared in Example 2.

[0034] Figure 4 This is a scanning electron microscope image of the mordenite molecular sieve prepared in Example 3.

[0035] Figure 5 This is a physical adsorption and desorption diagram of the mordenite molecular sieve prepared in Example 2.

[0036] Figure 6 NH is the mordenite molecular sieve prepared in Example 2 3 -TPD graph. DETAILED DESCRIPTION

[0037] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0038] Example 1

[0039] Weigh 10 g of silica sol (mass percentage of silica is 30 wt%), 1 g of sodium aluminate, and 2 g of sodium hydroxide in a plastic beaker, mix them evenly, and stir at room temperature for 4 h to obtain a uniform sol.

[0040] Weigh octaalkyltrimethylammonium bromide and organic base as dual template agents, so that the molar ratio of octaalkyltrimethylammonium bromide to silicon dioxide is 0.1, and the molar ratio of organic base to silicon dioxide is 0.1. After being fully mixed, add them to the above sol, continue stirring for 2 hours at room temperature for aging, put into a kettle, and start crystallization. The crystallization temperature is 150°C and the crystallization time is 72 hours. After the crystallization is completed, filter, wash with water until pH <10, roast for 5 hours at 600°C in air atmosphere to remove the template agent, repeat exchange in 0.1M ammonium chloride solution twice, and roast for 4 hours at 500°C in air atmosphere to remove ammonium, and obtain hydrogen-type mordenite, which adsorbs pyridine at 320°C in nitrogen atmosphere to obtain pyridine-adsorbed mordenite.

[0041] 0.3 g of the sieved catalyst sample (40-60 mesh) was reacted in a fixed bed reactor at 3 MPa, 310°C, with a raw material molar ratio of CO / methanol = 12:1. The product tail gas was kept warm and fed into the gas phase for online chromatographic analysis.

[0042] Embodiments 2 to 6

[0043] Under the same conditions as in Example 1, only the type of quaternary ammonium salt is changed, and octadecyl trimethyl ammonium bromide is replaced by decanyl trimethyl ammonium bromide (Example 2), dodecyl trimethyl ammonium bromide (Example 3), tetradecyl trimethyl ammonium bromide (Example 4), hexadecyl dimethyl benzyl ammonium bromide (Example 5), octadecyl trimethyl ammonium bromide (Example 6), and after being fully mixed, the mixture is added to the above-mentioned sol, stirred for 2 hours, and then the mixture is put into a kettle to start crystallization. After the crystallization is completed, the mixture is filtered, washed, roasted, ammonium exchanged, roasted, and adsorbed with pyridine.

[0044] Comparative Example 1

[0045] This comparative example 1 is the same as that in Example 2, in which no quaternary ammonium salt is added and other conditions remain unchanged.

[0046] The mordenite prepared in Example 2 was used as a relative standard, assuming that its crystallinity was 100%, and the sum of several crystal peak intensities was selected to calculate the crystalline phase diffraction intensity value. The selection principle of the crystalline phase diffraction peak was: good peak shape, no overlap, and the distance between the two peaks was more than 2° (2θ).

[0047] See also Figure 1 From the XRD analysis results, it can be seen that compared with the samples without adding quaternary ammonium salt, the crystallinity of the samples with quaternary ammonium salt added is significantly lower than that of the samples without adding quaternary ammonium salt, as shown in the relative crystallinity values ​​in Table 1. From the activity in Table 1, it can be seen that compared with the samples without adding quaternary ammonium salt, the samples with quaternary ammonium salt added have higher crystallinity, better crystallization and better performance, indicating that quaternary ammonium salt plays an important role as a template in the synthesis of MOR.

[0048] Table 1

[0049] sample Relative crystallinity <![CDATA[CH 3 OH conversion rate (%)]]> AA selectivity (%) MA selectivity (%) Example 2 100 99.9 94.7 4.2 Comparative Example 1 73 70.4 32.4 57.6

[0050] Table 2 shows the results of the carbonylation of methanol to acetic acid catalyzed by MOR prepared with different types of quaternary ammonium salts. It can be seen from the reaction activity that with the shortening of the chain length of the quaternary ammonium salt, the selectivity of acetic acid first increases and then decreases, and the selectivity of acetic acid with decanyltrimethylammonium bromide as the second template is the highest.

[0051] In addition, see Figures 2 to 4 As shown in Table 3, the morphology and crystallinity of the catalysts change with the change of the chain length of the quaternary ammonium salt.

[0052] Table 2

[0053]

[0054] Table 3

[0055] sample Relative crystallinity (%) Example 1 80 Example 2 100 Example 3 130 Example 4 121 Example 5 102 Example 6 104

[0056] In order to clearly indicate the reasons for the different reaction performances, the Si-Al ratio of the molecular sieves was characterized by XRF; NH 3 -TPD (2920) characterizes the total acid content of the molecular sieve. The specific procedure is to heat up to 500°C at 10°C / min and maintain for 60min for pretreatment to remove moisture and other impurities in the sample; then cool down to 100°C, pulse inject ammonia until adsorption saturation, purge for 30min under Ar atmosphere to remove physically adsorbed ammonia, then cool down to 50°C, wait for the baseline to stabilize, heat up to 800°C at 10°C / min, and record the peak signal with the thermal conductivity detector, see Figure 6 .

[0057] About NH 3 -TPD is used for peak fitting correction, and the peak area of ​​the high temperature peak is calculated The content of B acid (B acid) was then determined by hydroxyl infrared. The content of B acid in the twelve-membered ring and eight-membered ring of the MOR molecular sieve was determined. The specific procedure was as follows: the sample was vacuum pretreated at 400°C for 4 hours in an in-situ transmission cell, cooled to 50°C, and then scanned from 4000 to 600 cm -1 , with a resolution of 4cm -1 The FT-IR spectrum was recorded after 64 scans.

[0058] Table 4

[0059]

[0060] Table 4 shows the B acid content of the eight-membered ring and twelve-membered ring of the synthetic MOR molecular sieve. It can be seen from the table that as the chain length shortens, the amount of B acid in the eight-membered ring first increases and then decreases. When decanyltrimethylammonium bromide is used as the second template, the proportion of B acid is relatively high.

[0061] Table 5 shows the results of the pore structure characterization of the samples using low-temperature physical adsorption. The adsorption-desorption isotherms all show obvious hysteresis loops. The typical nitrogen adsorption-desorption isotherms are as follows: Figure 5 As shown in the figure, the samples of Examples 2 to 5 all have large mesopore volume and micropore volume, that is, the samples have mesopores and micropores. The samples of Examples 1 and 6 are mainly micropores and almost do not contain mesopores.

[0062] Table 5

[0063]

[0064] The mordenite molecular sieve catalyst prepared by the present invention has better stability and repeatability than traditional MOR due to the use of dual templates in the synthesis process, and can effectively improve the activity of methanol carbonylation to acetic acid reaction, wherein the methanol conversion rate can reach 99% and the acetic acid selectivity can reach 90%.

[0065] Among the present invention, along with the change of quaternary ammonium salt chain length, the crystallinity and morphology of catalyst change.When adopting decanyl trimethyl ammonium bromide, the molecular sieve of preparation is the flower-like particle of nanometer size, and along with the increase or reduction of chain length, morphology becomes the rod-like particle of micrometer size.The chain length of quaternary ammonium salt can directly affect the occupation situation of template agent in pore channel in the synthesis process, and then affect the pore size distribution of final catalyst.Suitable pore size is conducive to the rapid diffusion of reactant and product, thereby improves reaction performance and reaction rate.

Claims

1. A method for preparing a catalyst for carbonylation of methanol to produce acetic acid, It is characterized in that The following steps are involved: 1) mixing a silicon source, an aluminum source and an alkali source to form a sol; 2) mixing the quaternary ammonium salt and the organic base, adding the mixture to the sol prepared in step 1), and then aging, crystallizing, filtering, washing, drying and calcining; 3) Disperse the molecular sieve prepared in step 2) in NH 4 Cl aqueous solution, ammonium exchange, followed by drying and calcination; 4) adsorbing pyridine on the molecular sieve prepared in step 3) to obtain the catalyst; Wherein, the quaternary ammonium salt in step 2) is one or more of octaalkyltrimethylammonium bromide, decanyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide and octadecyltrimethylammonium bromide.

2. A method for preparing a catalyst for carbonylation of methanol to acetic acid as claimed in claim 1, Features: The quaternary ammonium salt is dodecyltrimethylammonium bromide.

3. The method for preparing a catalyst for preparing acetic acid by carbonylation of methanol as claimed in claim 1, Features: The organic base is at least one of tetraethylammonium hydroxide and tetrapropylammonium hydroxide.

4. The method for preparing a catalyst for preparing acetic acid by carbonylation of methanol as claimed in claim 1, Features: The molar ratio of the organic base to the quaternary ammonium salt is (1-10):

1.

5. A catalyst for preparing acetic acid by carbonylation of methanol, Features: Prepared by the preparation method according to any one of claims 1 to 4.

6. A catalyst for preparing acetic acid by carbonylation of methanol as claimed in claim 5, Features: The catalyst has a mordenite crystalline phase.

7. Use of the catalyst for preparing acetic acid by carbonylation of methanol as claimed in claims 5 and 6, Features: Used in the carbonylation reaction of methanol and carbon monoxide to produce acetic acid.

8. The use according to claim 7, Features: The catalyst is added into a fixed bed reactor, the molar ratio of the reaction raw materials methanol and carbon monoxide is 1:1-100, the temperature is 150-350° C., and the reaction pressure is 0.5-5.0 MPa.

Images