A heteroatom-modified titanium silicalite molecular sieve catalyst, its preparation method and application

Abstract

The present invention discloses a heteroatom-modified titanium silicalite molecular sieve catalyst, a preparation method thereof and an application thereof, which relates to the technical field of catalyst preparation. The method comprises the following steps: mixing a pretreated titanium silicalite molecular sieve and a heteroatom modification material, and performing ball milling to obtain a precursor; placing the precursor in an activation gas for activation to obtain the heteroatom-modified titanium silicalite molecular sieve catalyst. The present invention performs heteroatom modification on the titanium silicalite molecular sieve, which can effectively improve the surface electron cloud density of the molecular sieve, increase the basic functional groups on the material surface that are beneficial to the decomposition of hydrogen peroxide, and the heteroatoms will form new active sites with metal (Ti), which is beneficial to improving the activity and stability of the catalyst, and solves the problems of low catalyst activity and complex catalyst preparation process in the prior art when decomposing residual hydrogen peroxide in N-methylmorpholine N-oxide products.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and particularly relates to a heteroatom-modified titanium silicalite molecular sieve catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] As a green and environmentally friendly solvent, N-methylmorpholine N-oxide (NMMO) has been widely used in the processing and transformation of cellulose. This solvent not only has excellent solubility, but also its low toxicity makes it favored by the industry. When producing green and environmentally friendly Lyocell fibers, the process of dissolving wood pulp with NMMO as the solvent is crucial. This process has a huge demand for NMMO and extremely high requirements for its purity. It can be seen that obtaining high-quality NMMO is undoubtedly the key to developing Lyocell fibers. Therefore, improving the quality level of NMMO is crucial for meeting the development needs of the Lyocell fiber industry. Currently, the mainstream method for synthesizing NMMO industrially is to use N-methylmorpholine (NMM) as the raw material and H2O2 as the oxidant for tertiary amine oxidation reaction. To ensure sufficient reaction, hydrogen peroxide usually needs to be used in excess, which results in a certain amount of hydrogen peroxide remaining in the reaction-produced NMMO. The residual hydrogen peroxide will affect the spinning effect in the production process of Lyocell fibers and will also consume antioxidants during this process, leading to the decomposition of NMMO. Therefore, effectively removing the residual hydrogen peroxide in the NMMO product is of great significance for improving the product quality of NMMO.

[0003] Currently, the catalysts used for decomposing hydrogen peroxide can be mainly divided into two categories: metal-based catalysts and non-metal-based catalysts. Metal-based catalysts have high catalytic activity, but inevitably bring the problem of metal leaching, thus leading to the risk of secondary pollution; the catalytic activity of non-metal-based catalysts is relatively low, but due to their low cost, rich resources, and environmentally friendly characteristics, they have also been widely used. Aiming at the problem of possible residual hydrogen peroxide in the NMMO product, its effective removal has become a key link in improving the product quality. At the same time, the innovation of catalyst preparation technology aims to further improve the activity and stability of the catalyst, which not only concerns the final quality of the NMMO product but also is an important driving force for promoting the green and efficient development of related industries. Therefore, how to effectively control metal leaching, reduce production costs while ensuring catalytic efficiency, and explore a new and more environmentally friendly and efficient catalyst preparation method has become a major challenge and opportunity jointly faced by the current scientific research and industrial circles. Summary of the Invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a heteroatom-modified titanium silicalite molecular sieve catalyst, a preparation method thereof, and an application thereof, so as to solve the problems such as metal leaching, low activity, and high price in decomposing the residual hydrogen peroxide in N-methylmorpholine N-oxide products in the prior art.

[0005] The technical solution of the present invention for solving the above technical problems is as follows: A preparation method of a heteroatom-modified titanium silicalite molecular sieve catalyst is provided, including:

[0006] (1) Pretreat the titanium silicalite molecular sieve to obtain a pretreated titanium silicalite molecular sieve;

[0007] (2) Mix the pretreated titanium silicalite molecular sieve obtained in step (1) with a heteroatom modification material, and perform ball milling to obtain a precursor;

[0008] (3) Place the precursor obtained in step (2) in an activation gas for activation to obtain a heteroatom-modified titanium silicalite molecular sieve catalyst.

[0009] Based on the above technical solution, the present invention can also be improved as follows:

[0010] Further, in step (1), the titanium silicalite molecular sieve is placed in an acidic solution for pickling, then washed and dried to complete the pretreatment process of the titanium silicalite molecular sieve.

[0011] The beneficial effect of adopting the above further technical solution is: Pickling removes the ash and impurities on the surface of the titanium silicalite molecular sieve.

[0012] Further, the mass ratio of the titanium silicalite molecular sieve to the acidic solution is 1:50 - 200.

[0013] Further, the mass ratio of the titanium silicalite molecular sieve to the acidic solution is 1:100.

[0014] Further, the concentration of the acidic solution is 0.1 - 0.5 mol / L.

[0015] Further, the concentration of the acidic solution is 0.1 mol / L.

[0016] Further, the acidic solution is hydrochloric acid solution, sulfuric acid solution or nitric acid solution.

[0017] Further, the acidic solution is hydrochloric acid solution.

[0018] Further, the pickling time is 2 - 8 h.

[0019] Further, the pickling time is 4 h.

[0020] Further, in step (2), the mass ratio of the titanium silicalite molecular sieve to the heteroatom modification material is 40 - 100:1 - 7.

[0021] Further, in step (2), the ball milling time is 1 - 4 h, and the ball milling speed is 1000 - 1500 r / min.

[0022] Further, in step (2), the ball milling time is 1 - 4 h, and the ball milling speed is 1200 r / min.

[0023] Further, in step (2), after mixing the pretreated titanium silicalite molecular sieve, heteroatom modification material, and zirconium beads, ball milling is carried out.

[0024] The beneficial effect of adopting the above further technical solution is that mixing and ball milling the titanium silicalite molecular sieve and the modification material is beneficial for it to enter the internal pores of the molecular sieve and is beneficial for the doping modification in the subsequent sintering step.

[0025] Further, the mass ratio of the heteroatom modification material to the zirconium beads is 1 - 7:200.

[0026] Further, in step (2), the heteroatom modification material is melamine, dicyandiamide, urea, cysteine, thiourea, Na2S, Na2SO4, Na3PO4, Na2HPO4, or sodium borate.

[0027] Further, in step (2), the heteroatom modification material is melamine.

[0028] Further, in step (3), the activation gas is H2, CO2, NH3, water vapor, or HF.

[0029] The beneficial effect of adopting the above further technical solution is that activating the material with the activation gas can achieve doping modification on the surface of the titanium silicalite molecular sieve without damaging the titanium silicalite molecular sieve.

[0030] Further, in step (3), the activation gas is NH3.

[0031] The beneficial effect of adopting the above further technical solution is that using ammonia as the activation atmosphere can additionally provide a nitrogen source, ensuring the uniformity of heteroatom doping on the surface of the titanium silicalite molecular sieve, being beneficial for increasing the electron transfer speed and enhancing the catalytic activity.

[0032] Further, in step (3), activation is carried out at 600 - 1000 °C for 1 - 5 h.

[0033] Further, in step (3), activation is carried out at 600 - 800 °C for 1 - 5 h.

[0034] Further, in step (3), activation is carried out at 800 °C for 1 - 5 h.

[0035] The present invention also provides a heteroatom-modified titanium silicalite molecular sieve catalyst prepared by the above method.

[0036] The present invention also provides the application of the above heteroatom-modified titanium silicalite molecular sieve catalyst in decomposing residual hydrogen peroxide in N-methylmorpholine N-oxide products.

[0037] The present invention has the following beneficial effects:

[0038] 1. The present invention combines the advantages of metal-based catalysts and non-metal-based catalysts with catalytic activity. Moreover, this catalyst contains no heavy metal components, avoiding heavy metal pollution while ensuring catalytic activity and effectively reducing the cost of the catalyst.

[0039] 2. Nitrogen doping on the surface of titanium silicalite molecular sieve can form M-Nx active sites, which have strong stability and can effectively improve the stability of the catalyst.

[0040] 3. Heteroatom doping on the surface of titanium silicalite molecular sieve can increase the number of basic functional groups and the surface electron cloud density of the catalyst, which is beneficial to accelerating the decomposition of hydrogen peroxide. Description of the Drawings

[0041] Figure 1 Hydrogen peroxide removal rates of the catalysts of Examples 1-4 and Comparative Example 1.

[0042] Figure 2 Hydrogen peroxide removal rates of the catalysts of Examples 2 and 5-8.

[0043] Figure 3 Hydrogen peroxide removal rates of the catalysts of Examples 2, 9-10 and Comparative Example 2.

[0044] Figure 4 Stability test results of the 3N@TS1-NH catalyst of Example 9. Detailed Embodiments

[0045] The principles and features of the present invention are described below in conjunction with the drawings. The examples given are only used to explain the present invention and are not intended to limit the scope of the present invention. For those conditions not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0046] Example 1:

[0047] A heteroatom-modified titanium silicalite molecular sieve catalyst, and its preparation method includes the following steps:

[0048] (1) Place the titanium silicalite molecular sieve in an acidic solution (0.1 mol / L hydrochloric acid solution), carry out acid washing for 4 h, then wash and dry to remove surface ash and impurities, complete the pretreatment process, and obtain the pretreated titanium silicalite molecular sieve; wherein, the mass ratio of the titanium silicalite molecular sieve to the acidic solution is 1:100.

[0049] (2) Mix the pretreated titanium silicalite molecular sieve, heteroatom-modified material (melamine), and zirconium beads prepared in step (1), and then perform ball milling for 2 h at a ball milling speed of 1200 r / min. Separate the zirconium beads to obtain a precursor; wherein, the mass ratio of the titanium silicalite molecular sieve, heteroatom-modified material, and zirconium beads is 50:1:200;

[0050] (3) Place the precursor prepared in step (2) in an activation gas (H2) and activate it at 800 °C for 3 h to obtain a heteroatom-modified titanium silicalite molecular sieve catalyst (1N@TS1-800).

[0051] Example 2:

[0052] A heteroatom-modified titanium silicalite molecular sieve catalyst, and its preparation method includes the following steps:

[0053] In step (2), the mass ratio of the titanium silicalite molecular sieve, heteroatom-modified material, and zirconium beads is 50:3:200, and finally a heteroatom-modified titanium silicalite molecular sieve catalyst (3N@TS1-800) is obtained. The rest is the same as in Example 1.

[0054] Example 3:

[0055] A heteroatom-modified titanium silicalite molecular sieve catalyst, and its preparation method includes the following steps:

[0056] In step (2), the mass ratio of the titanium silicalite molecular sieve, heteroatom-modified material, and zirconium beads is 50:5:200, and finally a heteroatom-modified titanium silicalite molecular sieve catalyst (5N@TS1-800) is obtained. The rest is the same as in Example 1.

[0057] Example 4:

[0058] A heteroatom-modified titanium silicalite molecular sieve catalyst, and its preparation method includes the following steps:

[0059] In step (2), the mass ratio of the titanium silicalite molecular sieve, heteroatom-modified material, and zirconium beads is 50:7:200, and finally a heteroatom-modified titanium silicalite molecular sieve catalyst (7N@TS1-800) is obtained. The rest is the same as in Example 1.

[0060] Example 5:

[0061] A heteroatom-modified titanium silicalite molecular sieve catalyst, and its preparation method includes the following steps:

[0062] In step (3), the activation temperature is 600 °C, and finally a heteroatom-modified titanium silicalite molecular sieve catalyst (3N@TS1-600) is obtained. The rest is the same as in Example 2.

[0063] Example 6:

[0064] A heteroatom-modified titanium silicalite molecular sieve catalyst, and its preparation method comprises the following steps:

[0065] In step (3), the activation temperature is 700 °C, and finally a heteroatom-modified titanium silicalite molecular sieve catalyst (3N@TS1-700) is obtained. The rest is the same as in Example 2.

[0066] Example 7:

[0067] A heteroatom-modified titanium silicalite molecular sieve catalyst, and its preparation method comprises the following steps:

[0068] In step (3), the activation temperature is 900 °C, and finally a heteroatom-modified titanium silicalite molecular sieve catalyst (3N@TS1-900) is obtained. The rest is the same as in Example 2.

[0069] Example 8:

[0070] A heteroatom-modified titanium silicalite molecular sieve catalyst, and its preparation method comprises the following steps:

[0071] In step (3), the activation temperature is 1000 °C, and finally a heteroatom-modified titanium silicalite molecular sieve catalyst (3N@TS1-1000) is obtained. The rest is the same as in Example 2.

[0072] Example 9:

[0073] A heteroatom-modified titanium silicalite molecular sieve catalyst, and its preparation method comprises the following steps:

[0074] In step (3), the activation gas is NH3, and finally a heteroatom-modified titanium silicalite molecular sieve catalyst (3N@TS1-NH) is obtained. The rest is the same as in Example 2.

[0075] Example 10:

[0076] A heteroatom-modified titanium silicalite molecular sieve catalyst, and its preparation method comprises the following steps:

[0077] In step (3), the activation gas is CO2, and finally a heteroatom-modified titanium silicalite molecular sieve catalyst (3N@TS1-CO) is obtained. The rest is the same as in Example 2.

[0078] Example 11:

[0079] A heteroatom-modified titanium silicalite molecular sieve catalyst, and its preparation method comprises the following steps:

[0080] (1) Place the titanium silicalite molecular sieve in an acidic solution (0.3 mol / L sulfuric acid solution), carry out acid washing for 8 h, then wash and dry to remove surface ash and impurities, complete the pretreatment process, and obtain a pretreated titanium silicalite molecular sieve; wherein, the mass ratio of the titanium silicalite molecular sieve to the acidic solution is 1:50;

[0081] (2) Mix the pretreated titanium silicalite molecular sieve, heteroatom modification material (urea), and zirconium beads prepared in step (1), and then perform ball milling for 1 h at a ball milling speed of 1500 r / min. Separate the zirconium beads to obtain a precursor. The mass ratio of the titanium silicalite molecular sieve, heteroatom modification material, and zirconium beads is 40:1:200;

[0082] (3) Place the precursor prepared in step (2) in an activation gas (steam or HF), and activate it at 600 °C for 5 h to obtain a heteroatom-modified titanium silicalite molecular sieve catalyst.

[0083] Example 12:

[0084] A heteroatom-modified titanium silicalite molecular sieve catalyst, and its preparation method includes the following steps:

[0085] (1) Place the titanium silicalite molecular sieve in an acidic solution (0.5 mol / L nitric acid solution), perform pickling for 2 h, and then wash and dry to remove surface ash and impurities, completing the pretreatment process to obtain a pretreated titanium silicalite molecular sieve. The mass ratio of the titanium silicalite molecular sieve and the acidic solution is 1:200;

[0086] (2) Mix the pretreated titanium silicalite molecular sieve, heteroatom modification material (thiourea), and zirconium beads prepared in step (1), and then perform ball milling for 4 h at a ball milling speed of 1000 r / min. Separate the zirconium beads to obtain a precursor. The mass ratio of the titanium silicalite molecular sieve, heteroatom modification material, and zirconium beads is 100:7:200;

[0087] (3) Place the precursor prepared in step (2) in an activation gas (HF), and activate it at 1000 °C for 1 h to obtain a heteroatom-modified titanium silicalite molecular sieve catalyst.

[0088] Comparative Example 1:

[0089] A titanium silicalite molecular sieve catalyst, and its preparation method includes the following steps:

[0090] In step (2), the mass ratio of the titanium silicalite molecular sieve, heteroatom modification material, and zirconium beads is 50:0:200, and finally a heteroatom-modified titanium silicalite molecular sieve catalyst (0N@TS1-800) is obtained, and the rest is the same as in Example 1.

[0091] Comparative Example 2:

[0092] Do not treat the titanium silicalite molecular sieve.

[0093] Test Example

[0094] The heteroatom-modified titanium silicalite molecular sieve catalyst prepared by the present invention was subjected to hydrogen peroxide decomposition performance detection, and the titanium silicalite molecular sieve of Comparative Example 1 was used as a comparison. The specific detection method was as follows: Under the process conditions of 70 °C and a catalyst dosage of 0.2 g / L, the catalyst was used for the decomposition of residual hydrogen peroxide in the preparation of N-methylmorpholine N-oxide.

[0095] I. Different nitrogen doping amounts

[0096] The catalysts prepared in Examples 1-4 and Comparative Example 1 were subjected to catalytic activity detection, and the results are shown in Figure 1 .

[0097] It can be seen from Figure 1 that compared with the titanium silicalite molecular sieve catalyst without heteroatom modification in Comparative Example 1, the activity of the catalyst after heteroatom modification was improved. The group of catalysts with the highest activity was 3N@TS1-800, and the mass ratio of titanium silicalite molecular sieve to melamine was 50:3 (Example 2), and its hydrogen peroxide removal rate was 97.2%.

[0098] II. Different activation temperatures

[0099] The heteroatom-modified titanium silicalite molecular sieve catalysts prepared in Examples 2 and 5-8 were subjected to catalytic activity detection, and the results are shown in Figure 2 .

[0100] It can be seen from Figure 2 that the catalyst prepared at an activation temperature of 800 °C had higher activity (Example 2), and its hydrogen peroxide removal rate was 97.2%. The main reason was that when the activation temperature was low, nitrogen atoms were not completely doped into the interior of the titanium silicalite molecular sieve, resulting in fewer basic functional groups on the catalyst surface and lower activity; while when the temperature was too high, the structure of the titanium silicalite molecular sieve was damaged, the pores on the catalyst surface collapsed, resulting in the loss of catalytic active sites and a sharp decrease in activity.

[0101] III. Different activation gases

[0102] The heteroatom-modified titanium silicalite molecular sieve catalysts prepared in Examples 2, 9-10 and the titanium silicalite molecular sieve of Comparative Example 2 were subjected to catalytic activity detection, and the results are shown in Figure 3 .

[0103] It can be seen from Figure 3 that the catalyst prepared under an activation atmosphere of NH3 had better catalytic performance (Example 9), and the removal rate of residual hydrogen peroxide in the NMMO product was as high as 99.7%. This was mainly because sintering under an NH3 atmosphere introduced additional nitrogen doping, increasing the amount of nitrogen doping, increasing the electron cloud density on the catalyst surface and forming nitrogen-containing functional groups, which in turn formed Ti-Nx catalytic active centers with titanium. This structure was conducive to the catalytic oxidation and decomposition of hydrogen peroxide and could effectively improve the catalytic activity and stability.

[0104] IV. Stability

[0105] The heteroatom-modified titanium silicalite molecular sieve catalyst prepared in Example 9 was subjected to stability testing. The specific testing method was as follows: After catalytic activity testing, the catalyst was reused 4 times, and then the catalyst was separated using a solvent filter, dried, and placed under a N2 atmosphere, and heat-treated at 600 °C for 2 h to test the stability of the catalyst. The results are shown in Figure 4 .

[0106] As can be seen from Figure 4 , after four repeated experiments, the activity of the catalyst decreased to 89.1%, but the activity of the catalyst was restored after heat treatment under a N2 atmosphere. The main reason is that after 4 repeated experiments, some active sites on the surface of the catalyst were blocked by organic substances, resulting in a decrease in catalytic activity. After sintering at 600 °C, the organic substances were removed, and the catalytic active sites reappeared. It can be seen that the deactivation of this catalyst is renewable deactivation, indicating that the stability of the catalyst is good.

[0107] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a heteroatom-modified titanium silicalite molecular sieve catalyst, characterized in that, It includes the following steps: (1) Pretreat the titanium silicalite molecular sieve to obtain a pretreated titanium silicalite molecular sieve; (2) Mix the pretreated titanium silicalite molecular sieve obtained in step (1) with a heteroatom-modified material and perform ball milling to obtain a precursor; (3) Place the precursor obtained in step (2) in an activation gas for activation to obtain a heteroatom-modified titanium silicalite molecular sieve catalyst; In step (2), the heteroatom-modified material is melamine, dicyandiamide, urea, cysteine, thiourea, Na2S, Na2SO4, Na3PO4, Na2HPO4 or sodium borate; In step (3), the activation gas is H2, CO2, NH3, water vapor or HF; In step (3), activate at 600 - 1000 °C for 1 - 5 h.

2. The preparation method of the heteroatom-modified titanium silicalite molecular sieve catalyst according to claim 1, characterized in that, In step (1), place the titanium silicalite molecular sieve in an acidic solution for pickling, then wash and dry to complete the pretreatment process of the titanium silicalite molecular sieve.

3. The preparation method of the heteroatom-modified titanium silicalite molecular sieve catalyst according to claim 1, characterized in that, In step (2), the mass ratio of the titanium silicalite molecular sieve to the heteroatom-modified material is 40 - 100:1 - 7.

4. The preparation method of the heteroatom-modified titanium silicalite molecular sieve catalyst according to claim 1, characterized in that, In step (2), mix the pretreated titanium silicalite molecular sieve, the heteroatom-modified material and zirconium beads and then perform ball milling.

5. The preparation method of the heteroatom-modified titanium silicalite molecular sieve catalyst according to claim 1, characterized in that In step (3), activate at 600 - 800 °C for 1 - 5 h.

6. A heteroatom-modified titanium silicalite molecular sieve catalyst prepared by the preparation method of the heteroatom-modified titanium silicalite molecular sieve catalyst according to any one of claims 1 - 5.

7. Application of the heteroatom-modified titanium silicalite molecular sieve catalyst according to claim 6 in decomposing residual hydrogen peroxide in N-methylmorpholine N-oxide products.

Images