Heteroatom modified titanium silicalite molecular sieve catalyst as well as preparation method and application thereof

Abstract

The invention discloses a heteroatom modified titanium silicalite molecular sieve catalyst as well as a preparation method and application thereof, and relates to the technical field of catalyst preparation. The method comprises the following steps: mixing a pretreated titanium silicalite molecular sieve and a heteroatom modified material, and carrying out ball milling to obtain a precursor; and placing in an activation gas for activation to prepare the heteroatom modified titanium silicalite molecular sieve catalyst. The titanium silicalite molecular sieve is subjected to heteroatom modification, so that the electron cloud density on the surface of the molecular sieve can be effectively improved, alkaline functional groups, favorable for catalyzing decomposition of hydrogen peroxide, on the surface of the material are increased, and heteroatoms can form new active sites with metal (Ti), so that the activity and stability of the catalyst are improved; the problems that in the prior art, when residual hydrogen peroxide in an N-methylmorpholine oxide product is decomposed, the activity of a catalyst is low, and the preparation process of the catalyst is complex are solved.

Description

Technical Field

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

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

[0003] At present, the catalysts used to decompose 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 they inevitably bring about the problem of metal dissolution, which in turn causes the risk of secondary pollution; non-metal-based catalysts have relatively low catalytic activity, but due to their low cost, abundant resources and environmentally friendly characteristics, they have also been widely used. In view of the problem of hydrogen peroxide that may remain in NMMO products, its effective removal has become a key link in improving product quality. At the same time, the innovation of catalyst preparation technology aims to further improve the activity and stability of the catalyst, which is not only related to the final quality of NMMO products, but also an important driving force for promoting the green and efficient development of related industries. Therefore, how to effectively control metal dissolution, reduce production costs, and explore new methods for preparing more environmentally friendly and efficient catalysts while ensuring catalytic efficiency has become a major challenge and opportunity faced by the current scientific research and industry. 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 silicon molecular sieve catalyst and its preparation method and application, so as to solve the problems of metal dissolution, low activity and high price in the residual hydrogen peroxide in the decomposition of N-methylmorpholine oxide product in the prior art.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: a method for preparing a heteroatom-modified titanium silicon molecular sieve catalyst is provided, comprising: (1) pretreating the titanium silicate molecular sieve to obtain a pretreated titanium silicate molecular sieve; (2) mixing the pretreated titanium silicon molecular sieve obtained in step (1) and the heteroatom modified material, and ball milling to obtain a precursor; (3) Placing the precursor obtained in step (2) in an activation gas for activation to obtain a heteroatom-modified titanium silicon molecular sieve catalyst.

[0006] On the basis of the above technical solution, the present invention can also be improved as follows: Furthermore, in step (1), the titanium silicon molecular sieve is placed in an acidic solution for acid washing, and then washed and dried to complete the titanium silicon molecular sieve pretreatment process.

[0007] The beneficial effect of adopting the above further technical solution is: acid washing removes ash and impurities on the surface of the titanium silicon molecular sieve.

[0008] Furthermore, the mass ratio of titanium silicalite to acidic solution is 1:50-200.

[0009] Furthermore, the mass ratio of titanium silicalite to the acidic solution is 1:100.

[0010] Furthermore, the concentration of the acidic solution is 0.1-0.5 mol / L.

[0011] Furthermore, the concentration of the acidic solution is 0.1 mol / L.

[0012] Furthermore, the acidic solution is a hydrochloric acid solution, a sulfuric acid solution or a nitric acid solution.

[0013] Furthermore, the acidic solution is a hydrochloric acid solution.

[0014] Further, pickling is performed for 2-8 hours.

[0015] Further, pickling was performed for 4 hours.

[0016] Furthermore, in step (2), the mass ratio of titanium silicon molecular sieve and heteroatom modified material is 40-100:1-7.

[0017] Furthermore, in step (2), the ball milling time is 1-4 hours, and the ball milling speed is 1000-1500 r / min.

[0018] Furthermore, in step (2), the ball milling time is 1-4 h, and the ball milling speed is 1200 r / min.

[0019] Furthermore, in step (2), the pretreated titanium silicon molecular sieve, the heteroatom modified material and the zirconium beads are mixed and then ball milled.

[0020] The beneficial effect of adopting the above further technical solution is that ball milling the titanium silicon molecular sieve and the modified material is conducive to their entry into the pores of the molecular sieve, which is conducive to doping modification in the subsequent sintering step.

[0021] Furthermore, the mass ratio of the heteroatom modified material to the zirconium beads is 1-7:200.

[0022] Furthermore, in step (2), the heteroatom-modified material is melamine, dicyandiamide, urea, cysteine, thiourea, Na2S, Na2SO4, Na3PO4, Na2HPO4 or sodium borate.

[0023] Furthermore, in step (2), the heteroatom-modified material is melamine.

[0024] Furthermore, in step (3), the activation gas is H2, CO2, NH3, water vapor or HF.

[0025] The beneficial effect of adopting the above further technical solution is: by activating the material with an activated gas, the doping modification can be achieved on the surface of the titanium silicon molecular sieve without damaging the titanium silicon molecular sieve.

[0026] Furthermore, in step (3), the activation gas is NH3.

[0027] The beneficial effect of adopting the above further technical solution is: using ammonia as the activation atmosphere can provide an additional nitrogen source, ensuring the uniformity of heteroatom doping on the surface of the titanium silicon molecular sieve, which is beneficial to improving the electron transfer speed and increasing the catalytic activity.

[0028] Furthermore, in step (3), activation is performed at 600-1000° C. for 1-5 h.

[0029] Furthermore, in step (3), activation is performed at 600-800° C. for 1-5 h.

[0030] Furthermore, in step (3), activation is performed at 800° C. for 1-5 h.

[0031] The present invention also provides a heteroatom-modified titanium silicon molecular sieve catalyst prepared by the method.

[0032] The present invention also provides the use of the heteroatom-modified titanium silicon molecular sieve catalyst in decomposing residual hydrogen peroxide in N-methyl morpholine oxide products.

[0033] The present invention has the following beneficial effects: 1. The present invention combines the advantages of metal-based catalysts with catalytic activity and non-metal-based catalysts, and the catalyst does not contain heavy metal components, thereby avoiding heavy metal pollution while ensuring catalytic activity, and effectively reducing the cost of the catalyst; 2. Nitrogen doping on the surface of titanium silicon molecular sieve can form M-Nx active sites, which have strong stability and can effectively improve the stability of the catalyst; 3. Heteroatom doping on the surface of titanium silicon molecular sieve can increase the number of basic functional groups of the catalyst and the surface electron cloud density, which is beneficial to accelerate the catalytic decomposition of hydrogen peroxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The removal rate of hydrogen peroxide by the catalysts of Examples 1-4 and Comparative Example 1; Figure 2 is the removal rate of hydrogen peroxide by the catalysts of Examples 2 and 5-8; Figure 3 is the removal rate of hydrogen peroxide by the catalysts of Examples 2, 9-10 and Comparative Example 2; Figure 4 The stability test results of the 3N@TS1-NH catalyst of Example 9 are shown in FIG. DETAILED DESCRIPTION

[0035] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not used to limit the scope of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0036] Embodiment 1: A heteroatom-modified titanium silicon molecular sieve catalyst, the preparation method of which comprises the following steps: (1) placing the titanium silicate molecular sieve in an acidic solution (0.1 mol / L hydrochloric acid solution) for pickling for 4 hours, then washing and drying to remove surface ash and impurities, completing the pretreatment process to obtain a pretreated titanium silicate molecular sieve; wherein the mass ratio of the titanium silicate molecular sieve to the acidic solution is 1:100; (2) mixing the pretreated titanium silicalite, heteroatom modified material (melamine) and zirconium beads obtained in step (1), and then ball milling the mixture for 2 h at a speed of 1200 r / min, separating the zirconium beads and obtaining a precursor; wherein the mass ratio of the titanium silicalite, heteroatom modified material and zirconium beads is 50:1:200; (3) The precursor prepared in step (2) is placed in an activation gas (H2) and activated at 800°C for 3 hours to obtain a heteroatom-modified titanium silicalite catalyst (1N@TS1-800).

[0037] Embodiment 2: A heteroatom-modified titanium silicon molecular sieve catalyst, the preparation method of which comprises the following steps: In step (2), the mass ratio of titanium silicalite, heteroatom-modified material and zirconium beads is 50:3:200, and finally a heteroatom-modified titanium silicalite catalyst (3N@TS1-800) is obtained. The rest is the same as in Example 1.

[0038] Embodiment 3: A heteroatom-modified titanium silicon molecular sieve catalyst, the preparation method of which comprises the following steps: In step (2), the mass ratio of titanium silicalite, heteroatom-modified material and zirconium beads is 50:5:200, and finally a heteroatom-modified titanium silicalite catalyst (5N@TS1-800) is obtained. The rest is the same as in Example 1.

[0039] Embodiment 4: A heteroatom-modified titanium silicon molecular sieve catalyst, the preparation method of which comprises the following steps: In step (2), the mass ratio of titanium silicalite, heteroatom-modified material and zirconium beads is 50:7:200, and finally a heteroatom-modified titanium silicalite catalyst (7N@TS1-800) is obtained. The rest is the same as in Example 1.

[0040] Embodiment 5: A heteroatom-modified titanium silicon molecular sieve catalyst, the preparation method of which comprises the following steps: In step (3), the activation temperature is 600° C., and a heteroatom-modified titanium silicon molecular sieve catalyst (3N@TS1-600) is finally obtained. The rest is the same as in Example 2.

[0041] Embodiment 6: A heteroatom-modified titanium silicon molecular sieve catalyst, the preparation method of which comprises the following steps: In step (3), the activation temperature is 700° C., and a heteroatom-modified titanium silicon molecular sieve catalyst (3N@TS1-700) is finally obtained. The rest is the same as in Example 2.

[0042] Embodiment 7: A heteroatom-modified titanium silicon molecular sieve catalyst, the preparation method of which comprises the following steps: In step (3), the activation temperature is 900° C., and a heteroatom-modified titanium silicon molecular sieve catalyst (3N@TS1-900) is finally obtained. The rest is the same as in Example 2.

[0043] Embodiment 8: A heteroatom-modified titanium silicon molecular sieve catalyst, the preparation method of which comprises the following steps: In step (3), the activation temperature is 1000° C., and a heteroatom-modified titanium silicon molecular sieve catalyst (3N@TS1-1000) is finally obtained. The rest is the same as in Example 2.

[0044] Embodiment 9: A heteroatom-modified titanium silicon molecular sieve catalyst, the preparation method of which comprises the following steps: In step (3), the activation gas is NH3, and the heteroatom-modified titanium silicon molecular sieve catalyst (3N@TS1-NH) is finally obtained. The rest is the same as in Example 2.

[0045] Embodiment 10: A heteroatom-modified titanium silicon molecular sieve catalyst, the preparation method of which comprises the following steps: In step (3), the activation gas is CO2, and finally a heteroatom-modified titanium silicon molecular sieve catalyst (3N@TS1-CO) is obtained. The rest is the same as in Example 2.

[0046] Embodiment 11: A heteroatom-modified titanium silicon molecular sieve catalyst, the preparation method of which comprises the following steps: (1) placing the titanium silicate molecular sieve in an acidic solution (0.3 mol / L sulfuric acid solution) for pickling for 8 hours, then washing and drying to remove surface ash and impurities, completing the pretreatment process to obtain a pretreated titanium silicate molecular sieve; wherein the mass ratio of the titanium silicate molecular sieve to the acidic solution is 1:50; (2) mixing the pretreated titanium silicon molecular sieve, heteroatom modified material (urea) and zirconium beads obtained in step (1), and then ball milling the mixture. The ball milling time is 1 h and the ball milling speed is 1500 r / min. The zirconium beads are separated to obtain a precursor. The mass ratio of the titanium silicon molecular sieve, the heteroatom modified material and the zirconium beads is 40:1:200. (3) The precursor prepared in step (2) is placed in an activation gas (water vapor or HF) and activated at 600° C. for 5 h to obtain a heteroatom-modified titanium silicon molecular sieve catalyst.

[0047] Embodiment 12: A heteroatom-modified titanium silicon molecular sieve catalyst, the preparation method of which comprises the following steps: (1) placing the titanium silicate molecular sieve in an acidic solution (0.5 mol / L nitric acid solution) for pickling for 2 hours, then washing and drying to remove surface ash and impurities, completing the pretreatment process to obtain a pretreated titanium silicate molecular sieve; wherein the mass ratio of the titanium silicate molecular sieve to the acidic solution is 1:200; (2) mixing the pretreated titanium silicalite, heteroatom modified material (thiourea) and zirconium beads obtained in step (1), and ball milling them for 4 h at a ball milling speed of 1000 r / min, separating the zirconium beads and obtaining a precursor; wherein the mass ratio of the titanium silicalite, heteroatom modified material and zirconium beads is 100:7:200; (3) The precursor prepared in step (2) is placed in an activation gas (HF) and activated at 1000° C. for 1 h to obtain a heteroatom-modified titanium silicalite catalyst.

[0048] Comparative Example 1: A titanium silicon molecular sieve catalyst, the preparation method of which comprises the following steps: In step (2), the mass ratio of titanium silicalite, heteroatom modified material and zirconium beads is 50:0:200, and finally a heteroatom modified titanium silicalite catalyst (0N@TS1-800) is obtained. The rest is the same as in Example 1.

[0049] Comparative Example 2: Titanium silicate molecular sieve is not treated.

[0050] Test example The heteroatom-modified titanium silicalite catalyst prepared in the present invention was tested for its hydrogen peroxide decomposition performance, with the titanium silicalite of Comparative Example 1 used as a comparison. The specific testing method was as follows: under process conditions of 70° C. and a catalyst dosage of 0.2 g / L, the catalyst was used to decompose residual hydrogen peroxide in the preparation process of N-methylmorpholine oxide.

[0051] 1. Different Nitrogen Doping Amounts The catalysts prepared in Examples 1-4 and Comparative Example 1 were tested for catalytic activity. Figure 1 .

[0052] Depend on Figure 1 It can be seen that compared with the titanium silicalite catalyst in comparative example 1 which has not been modified with heteroatoms, the activity of the catalyst after heteroatom modification is improved. The most active group of catalysts is 3N@TS1-800, in which the mass ratio of titanium silicalite to melamine is 50:3 (Example 2), and its removal rate for hydrogen peroxide is 97.2%.

[0053] 2. Different activation temperatures The heteroatom modified titanium silicon molecular sieve catalysts prepared in Examples 2 and 5-8 were tested for catalytic activity. The results are shown in Figure 2 .

[0054] Depend on Figure 2It can be seen that the catalyst prepared at an activation temperature of 800 °C has higher activity (Example 2), and its removal rate of hydrogen peroxide is 97.2%. The main reason is that when the activation temperature is low, nitrogen atoms are not completely doped into the interior of the titanium silicon molecular sieve, resulting in fewer basic functional groups on the catalyst surface and lower activity; when the temperature is too high, the structure of the titanium silicon molecular sieve is destroyed, and the pores on the catalyst surface collapse, resulting in the loss of catalytic active sites and a sharp drop in activity.

[0055] 3. Different Activation Gases The heteroatom modified titanium silicon molecular sieve catalysts prepared in Examples 2, 9-10 and the titanium silicon molecular sieve of Comparative Example 2 were tested for catalytic activity. The results are shown in Figure 3 .

[0056] Depend on Figure 3 It can be seen that the catalyst prepared when the activation atmosphere is NH3 has better catalytic performance (Example 9), and the removal rate of residual hydrogen peroxide in the NMMO product is as high as 99.7%. This is mainly because the sintering in the NH3 atmosphere introduces additional nitrogen doping, increases the amount of nitrogen doping, increases the electron cloud density on the catalyst surface and forms nitrogen-containing functional groups, which then form Ti-Nx catalytic active centers with titanium. This structure is conducive to catalyzing the oxidative decomposition of hydrogen peroxide and can effectively improve the catalytic activity and stability.

[0057] 4. Stability The heteroatom-modified titanium silicon molecular sieve catalyst prepared in Example 9 was subjected to stability testing. The specific testing method was as follows: after the catalytic activity test, the catalyst was reused 4 times, and then the catalyst was separated by a solvent filter, dried, placed in a N2 atmosphere, and heat treated at 600°C for 2 h to test the stability of the catalyst. The results are shown in Table 1. Figure 4 .

[0058] Depend on Figure 4 It can be seen that after four repeated experiments, the activity of the catalyst dropped to 89.1%, but after heat treatment in N2 atmosphere, the activity of the catalyst was restored. The main reason is that after four repeated experiments, some active sites on the catalyst surface were blocked by organic matter, resulting in a decrease in catalytic activity. After sintering at 600 °C, the organic matter was removed and the catalytic active sites reappeared. It can be seen that the deactivation of the catalyst is regenerative deactivation, indicating that the catalyst has good stability.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a heteroatom-modified titanium silicon molecular sieve catalyst, characterized in that: The following steps are involved: (1) pretreating the titanium silicate molecular sieve to obtain a pretreated titanium silicate molecular sieve; (2) mixing the pretreated titanium silicon molecular sieve obtained in step (1) and the heteroatom modified material, and ball milling to obtain a precursor; (3) Placing the precursor obtained in step (2) in an activation gas for activation to obtain a heteroatom-modified titanium silicon molecular sieve catalyst.

2. The method for preparing the heteroatom-modified titanium silicon molecular sieve catalyst according to claim 1, characterized in that: In step (1), the titanium silicon molecular sieve is placed in an acidic solution for acid washing, and then washed and dried to complete the titanium silicon molecular sieve pretreatment process.

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

4. The method for preparing the heteroatom-modified titanium silicon molecular sieve catalyst according to claim 1, characterized in that: In step (2), the pretreated titanium silicon molecular sieve, the heteroatom modified material and the zirconium beads are mixed and then ball milled.

5. The method for preparing the heteroatom-modified titanium silicon molecular sieve catalyst according to claim 1, characterized in that: In step (2), the heteroatom-modified material is melamine, dicyandiamide, urea, cysteine, thiourea, Na2S, Na2SO4, Na3PO4, Na2HPO4 or sodium borate.

6. The method for preparing the heteroatom-modified titanium silicon molecular sieve catalyst according to claim 1, characterized in that: In step (3), the activation gas is H2, CO2, NH3, water vapor or HF.

7. The method for preparing the heteroatom-modified titanium silicon molecular sieve catalyst according to claim 1, characterized in that: In step (3), activation is performed at 600-1000°C for 1-5h.

8. The method for preparing the heteroatom-modified titanium silicon molecular sieve catalyst according to claim 1, characterized in that: In step (3), activation is performed at 600-800°C for 1-5h.

9. The heteroatom-modified titanium silicon molecular sieve catalyst prepared by the preparation method of the heteroatom-modified titanium silicon molecular sieve catalyst according to any one of claims 1 to 8.

10. Use of the heteroatom-modified titanium silicon molecular sieve catalyst according to claim 9 in decomposing residual hydrogen peroxide in N-methylmorpholine oxide products.

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