WO2018192530A1 - Compound structure molecular sieve and preparation method and application thereof - Google Patents

Abstract

The invention discloses a compound molecular sieve and preparation method thereof. The compound molecular sieve takes an MTT micropore molecular sieve as a core and takes an MCM-41 mesopore molecular sieve as a shell. The catalyst supported on the composite molecular sieve can be used in a hydroisomerization reaction.

Description

Composite structure molecular sieve and preparation method and application thereof Technical field

The invention belongs to the technical field of catalysts, and in particular relates to a composite structure molecular sieve and a preparation method and application thereof.

Background technique

Petroleum products, such as lubricating oil, jet fuel point, freezing point, pour point, etc. are the focus of attention. In recent years, the products obtained by the Fischer-Tropsch synthesis method have been more clean, and have the characteristics of sulfur-free, nitrogen-free, and low aromatic hydrocarbons, and have attracted attention as raw material oils for producing jet fuels and lubricating oils. However, due to the presence of high levels of normal paraffins, Fischer-Tropsch products have disadvantages such as higher freezing point and poor low temperature fluidity. In order to reduce the pour point and the pour point, a hydroisomerization process can be employed to rearrange the linear alkane to produce a branched product to achieve the desired effect.

The catalyst plays an important role in the hydroisomerization reaction. The catalyst used in the hydroisomerization mostly uses a molecular sieve as a catalyst carrier to provide an acid site, and a hydrodehydrogenation function is achieved by supporting a noble metal.

Patent CN 104334271 A discloses a process for producing a hydroisomerization catalyst and a process for producing a lubricating base oil selected from the group consisting of ZSM-22 zeolite (TON structure), ZSM-23 zeolite (MTT structure), SSZ-32. At least one of zeolite (MTT structure) and ZSM-48 zeolite is subjected to specific caulking treatment to finally obtain a hydroisomerization catalyst; and patent CN 104220169 A discloses a ZSM-22 zeolite hydroisomerization catalyst And a method for producing the same, the zeolite carrier of the hydroisomerization catalyst is at least one of ZSM-22 zeolite, ZSM-23 zeolite, SSZ-32 zeolite, and ZSM-48 zeolite; Patent CN200680036697.1 discloses a An isomerization dewaxing process using zeolite MTT and MTW, wherein the catalyst is preferably a combination of a hydrogen type zeolite MTT and MTW, and the MTT and MTW zeolites have a crystal size of less than 0.1 micron; and the patent US7390763 B2 discloses a The preparation method of small-grain MTT structure molecular sieve and its application in the isomeric pour point condensation of C ₁₀ + normal paraffins can increase the target product yield by 7.14% by using small-grain MTT structure molecular sieve.

Due to its unique pore structure and acidity and alkalinity, MTT molecular sieves are very suitable for the catalytic hydrogenation of alkane. The regular ten-membered ring structure and adjustable acid properties in MTT molecular sieves provide a prerequisite for the hydrogen-isomerized pour point depressing reaction, and the change of grain size and morphology can further regulate its catalytic performance; 103153860 A proposes a process for preparing small-grain molecular sieves in the absence of an amine component. The pore size of MTT molecular sieve is 0.52nm×0.45nm. Due to its unique pore structure and suitable acidity, it can optimize the pore properties and rational configuration of the active catalyst, and the heterogeneous pour point depressing reaction for normal paraffins Excellent catalytic performance. However, the pore structure of the molecular sieve of MTT structure has a restrictive effect on the formation and diffusion of multi-branched isomerization products, which leads to a secondary reaction of the isomerized product, that is, a cracking reaction, and the cracked product promotes the formation of carbon deposits, which easily blocks the catalyst pores. Therefore, the activity, selectivity and stability of the MTT molecular sieve catalyst used in the hydrogen isomerization reaction are not ideal and need to be further improved.

Summary of the invention

In order to solve the above problems, the present invention provides a core-shell molecular sieve having a micro-mesoporous composite structure and a high external specific surface area, a preparation method thereof and a hydroisomerization catalyst prepared therefrom. The microporous-mesoporous composite molecular sieve has a micropore and mesoporous double model pore distribution, which combines the pores of the mesoporous material with the advantages of strong acidity and high hydrothermal stability of the microporous molecular sieve, so that the two materials can complement each other. Synergistic effect; the number of pores of the molecular sieve is closely related to the size of its external surface area. The composite molecular sieve exhibits higher activity and selectivity in the hydroisomerization reaction due to its higher specific surface area and larger pore structure. And stability, reducing the formation of carbon deposits, increasing the heterogeneity of normal paraffins and the yield of target products, thereby reducing the freezing point of the product and improving the performance of the product.

The first aspect of the present invention provides a composite molecular sieve catalyst, which uses MTT microporous molecular sieve as a core and MCM-41 mesoporous molecular sieve as a shell, which can be abbreviated as MCM-41@MTT molecular sieve.

Wherein the MTT microporous molecular sieve and the MCM-41 mesoporous molecular sieve are molecular sieves of a known type in the molecular sieve field, and the pore size and pore structure type and molecular sieve crystal form are already well-known information, and those skilled in the art can refer to the field. Known by patents and papers.

A second aspect of the present invention provides a method for preparing the composite molecular sieve, comprising the steps of:

(1) Mix the MTT molecular sieve powder, the lye and the surfactant uniformly, and raise the temperature to 150-180 ° C for 12 to 48 hours, then cool down, add the acid solution to make the pH 8-9, and then heat up to 110-130 ° C. After ~72h, the temperature is lowered, the solid is separated, washed with deionized water until neutral, and dried at 110-130 ° C to obtain a solid;

(2) The solid obtained in the step (1) is calcined at 500 to 600 ° C for 3 to 5 hours, and then cooled to obtain the composite molecular sieve.

Preferably, the alkali solution described in the step (1) is an inorganic alkali solution such as NaOH, KOH solution or the like; or an organic alkali solution such as tetramethylammonium hydroxide or tetraethylammonium hydroxide solution, the alkali solution The concentration of the alkali solution and the MTT molecular sieve is 5:1 to 25:1;

Preferably, the surfactant described in the step (1) is a long-chain alkyltrimethylammonium bromide (CTAB) having three or more carbon atoms: such as decamethyltrimethylammonium bromide, twelve The alkyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecane and trimethylammonium bromide are added in an amount of from 1 to 4 times the mass of the MTT molecular sieve.

A third aspect of the present invention provides a hydroisomerization catalyst comprising a support and a hydrogenation-dehydrogenation active component, wherein the support is MCM-41@MTT composite molecular sieve, and the hydrogenation-dehydrogenation active group Divided into Pt or Pd, the hydrogenation-dehydrogenation active component loading is 0.5 wt% of the total mass of the hydroisomerization catalyst.

The fourth aspect of the present invention provides the hydroisomerization catalyst for the hydroisomerization of normal paraffins to isoparaffins (such as isomeric depressing and isomerization dewaxing), hydrocracking and hydrodeoxygenation. Use for increasing catalytic activity and/or increasing selectivity and/or reducing carbon deposits and/or prolonging catalyst life.

The invention has the beneficial effects that the core-shell molecular sieve catalyst MCM-41@MTT with micro-mesoporous composite structure and high specific surface area provided by the invention has suitable acidity, a large number of orifices and a high specific surface area. And pore volume, larger active sites. The suitable acid concentration and acid strength are beneficial to reduce the occurrence of secondary reaction-cracking reaction, reduce the formation of cracking products while increasing the isomerization selectivity, reduce the formation of carbon deposits, and improve the isomerization rate of the catalyst and Stability; at the same time, the number of orifices of the catalyst increases, and the diffusibility of the pores is enhanced, which facilitates the diffusion of reactants and products out of the molecular sieve pores; increases the heterogeneous selectivity, reduces the formation of carbon deposits, and prolongs the life of the catalyst.

DRAWINGS

Figure 1 is a powder XRD pattern of the molecular sieve prepared in Comparative Example and Example 1;

2 is a N ₂ adsorption-desorption isotherm curve of the molecular sieve prepared in Comparative Example and Example 1;

Figure 3 is a TEM image of the molecular sieve prepared in the comparative example;

Figure 4 is a TEM image of the molecular sieve prepared in Example 1;

Figure 5 is a graph comparing the hydrodeoxygenation conversion of fatty acids in the comparative examples and examples.

Figure 6 is a graph comparing the hydrodeoxygenation selectivity of fatty acids in the comparative examples and examples.

detailed description

In order to more clearly understand the technical features, objects, and advantages of the present invention, the technical solutions of the present invention are described in detail below. The following embodiments embody the processes described in the present invention, but the present invention is not limited to these examples.

Comparative example 1:

The present comparative example provides a preparation method of a noble metal Pt catalyst supported by an MTT structure molecular sieve, and the specific steps are as follows:

1.53 g of 1,3-diisopropylimidazolium chloride (1 mol/L) was weighed into a polytetrafluorocarbon lining, and 22.52 g of high-purity water was added thereto, and shaken; then 12.03 g of potassium hydroxide solution (1 mol) was added. /L), stirring at room temperature for 30 min; 7.62 g of a silica sol, 2.5 g of a silica alumina sol, and 0.9 g of isobutylamine were added to the above alkaline solution, and the mixture was uniformly stirred. Then, the reactant gel was placed in a polytetrafluoroethylene-lined hydrothermal synthesis kettle, sealed, and crystallized at 175 ° C for 8 days under autogenous pressure; the crystallized product was taken out, cooled, centrifuged, and washed with deionized water to the middle. Drying in an oven at 120 ° C; then placing it in a muffle furnace and calcining at 600 ° C for 6 h to obtain the desired product. The precious metal Pt was loaded, and the loading amount was 0.5% by weight.

The powder XRD diffraction pattern of this type of molecular sieve is shown in the curve of Fig. 1, and the N ₂ adsorption-desorption isotherm curve is shown in the curve of Fig. 2, and the TEM image is shown in Fig. 3.

Example 1

The present embodiment provides a core-shell MCM-41@MTT molecular sieve having a micro-mesoporous composite structure, and the preparation method thereof is as follows:

2g MTT molecular sieve core, 20ml 0.3mol / L lye was added to the reaction kettle, stirred for 30min, then 4g of surfactant was added, stirring was continued for 30min, and the reaction was stirred in a 150 °C homogeneous reactor for 24 hours; 3 mol/L hydrochloric acid solution was added dropwise, the pH of the mixed solution was adjusted to be between 8 and 9, and then crystallized at 120 ° C for 48 hours; the crystallized product was taken out, and the mixture was taken out after centrifugation by water cooling, and washed with deionized water. Neutral, dry in an oven at 120 °C.

The molecular sieves were then placed in a muffle furnace and calcined at 550 ° C for 4 h to obtain MCM-41@MTT molecular sieves. The precious metal Pt was then loaded using an equal volume impregnation method with a loading of 0.5 wt%.

Example 2

2 g of MTT molecular sieve core, 20 ml of 0.2 mol/L inorganic base (NaOH or KOH) solution was added to the reaction vessel, stirred for 30 min, and then 3 g of surfactant was added. Other operations were similar to those of Example 1, and MCM-41 was obtained. @MTT molecular sieve. The precious metal Pt was loaded, and the loading amount was 0.5% by weight.

Example 3

2 g of MTT molecular sieve powder and 4 g of surfactant were added to 20 mL of a 0.5 mol/L organic base TAAOH (tetramethylammonium hydroxide or tetraethylammonium hydroxide) solution, thoroughly mixed, and stirred at room temperature for 30 min. Then, it was transferred to a crystallization vessel, and the reaction was stirred at 180 ° C for 24 hours. After cooling, the pH of the mixed system was adjusted to 8.5 by dropwise addition of 3 mol/L HCl solution, followed by crystallization at 120 ° C for 24 h; the crystallization vessel was taken out, and after cooling with water, the mixture was taken out for centrifugation and washed with solid water. To neutral. Finally, the solid powder was dried in an oven at 120 ° C, and then the molecular sieve was placed in a muffle furnace and calcined at 550 ° C for 4 h to obtain MCM-41@MTT molecular sieve. The precious metal Pd was supported by an excessive impregnation method using ethanol as a solvent, and the loading amount was 0.5% by weight.

The powder XRD diffraction pattern of this type of molecular sieve is shown in the curve of Fig. 1, and the N ₂ adsorption-desorption isotherm curve is shown in the curve of Fig. 2, and the TEM image is shown in Fig. 4.

Example 4: Hydrogenation of normal paraffins

The comparative example and the catalyst prepared in Example 1 were applied to the hydroisomerization pour point condensation reaction of nC ₁₂ -nC ₂₃ mixed normal paraffins; comparison was obtained at different reaction temperatures, Pt/MCM-41@ The conversion and isomerization ratio of the MTT catalyst are greatly improved compared with the conversion and the isomerization amount of the Pt/MTT catalyst, indicating that the micro-mesoporous composite molecular sieve MCM-41@MTT catalyst having the core-shell structure prepared by the present invention is applied to the positive In the isomeric reaction of an alkane, an isoparaffin mixture can be obtained with high activity and high selectivity, as shown in Table 1. Moreover, the micro-mesoporous composite molecular sieve MCM-41@MTT catalyst having the core-shell structure prepared by the invention has stable isomerization yield for 7 days of continuous operation, as shown in Table 2. The micromolecular composite molecular sieve MCM-41@MTT catalyst with core-shell structure of the invention has good stability performance, few carbon deposits are formed, and the isomerization yield of the catalyst is stable for 7 days.

Table 1 Catalytic performance evaluation results

Table 2 Stability evaluation of Pt/MCM-41@MTT catalyst

operation hours	270 ° C, liquid phase yield of isomers, %
1d	96.0%
2d	96.2%
3d	95.7%
4d	95.8%
5d	96.4%
6d	95.5%
7d	96.1%

Example 5: Heterogeneous dewaxing of normal paraffins

The Pt/MCM-41@MTT catalyst prepared in the examples was applied to the isothermal dewaxing of nC ₂₀ -nC ₄₀ mixed normal paraffins to prepare a lubricating base oil, and the yield of the class III + lubricating base oil was obtained. above 50. The micro-mesoporous composite molecular sieve MCM-41@MTT catalyst with core-shell structure prepared by the invention is applied to the isomerization dewaxing reaction of normal paraffins, and the lubricating base oil can be obtained with high activity and high selectivity.

Example 6: Hydrodeoxygenation of fatty acids

The comparative examples and the catalysts prepared in the examples (Examples 1 and 3) were applied to the hydrodeoxygenation of palmitic acid and stearic acid to produce a high quality diesel reaction, as shown in Figure 5, at low temperatures. The total conversion of fatty acids was higher than that of the comparative examples (the conversion rates of Example 1 and Example 3 were the same), and the selectivity of the target carbon number C ₁₅ -C ₁₈ of the MCM-41@MTT catalyst was significantly higher than that of the MTT catalyst, as shown in Fig. 6. Shown. The micromolecular composite molecular sieve MCM-41@MTT catalyst with core-shell structure prepared by the invention is applied to the hydrodeoxygenation reaction of fatty acids, and high-quality diesel oil can be prepared with high activity and high selectivity.

Claims (7)

1. A composite molecular sieve characterized in that the composite molecular sieve has a MTT microporous molecular sieve as a core and a MCM-41 mesoporous molecular sieve as a shell.
2. A method for preparing a composite molecular sieve according to claim 1, comprising the steps of:

   (1) Mix the MTT molecular sieve powder, the lye and the surfactant uniformly, and raise the temperature to 150-180 ° C for 12 to 48 hours, then cool down, add the acid solution to make the pH 8-9, and then heat up to 110-130 ° C. After ~72h, the temperature is lowered, the solid is separated, washed with deionized water until neutral, and dried at 110-130 ° C to obtain a solid;

   (2) The solid obtained in the step (1) is calcined at 500 to 600 ° C for 3 to 5 hours, and then cooled to obtain the composite molecular sieve.
3. The preparation method according to claim 2, wherein the alkali liquid in the step (1) is an inorganic alkali liquid or an organic alkali liquid, and the concentration of the alkali liquid is 0.2 to 1.0 mol/L, and the alkali liquid The mass ratio to the MTT molecular sieve is from 5:1 to 25:1.
4. The preparation method according to claim 2, wherein the surfactant in the step (1) is a long-chain alkyltrimethylammonium bromide having three or more carbon atoms, and the amount of the surfactant is The mass of the MTT molecular sieve is 1 to 4 times.
5. The method according to claim 4, wherein the long-chain alkyltrimethylammonium bromide is decamethyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and fourteen. Alkyltrimethylammonium bromide or cetyltrimethylammonium bromide.
6. A hydroisomerization catalyst comprising a carrier and a hydrogenation-dehydrogenation active component, wherein the carrier is the composite molecular sieve of claim 1, the hydrogenation-dehydrogenation active component For Pt or Pd, the hydrogenation-dehydrogenation active component loading is 0.5% of the total mass of the hydroisomerization catalyst.
7. Use of a hydroisomerization catalyst according to claim 6 for the hydroisomerization of normal paraffins to isoparaffins for increasing catalytic activity and/or increasing selectivity and/or reducing carbon deposition and / or extend the life of the catalyst.

Images