Process for preparing zeolite beta and use thereof

Abstract

Method for preparing zeolite beta which method comprises crystallization of zeolite beta from a solution comprising a template, a silicon source and an aluminum source in which the template is polymeric compound comprising ionizable polydiallyldimethylammonium (PDADMA) cationcrystallization. Furthermore, the present invention provides the use of thus prepared zeolite beta in catalysts for hydrocarbon conversions.

Claims

1. A method for preparing zeolite beta which method comprises crystallization of zeolite beta from a solution consisting essentially of a template, a silicon source and an aluminum source in which the template is a polymeric compound comprising a ionizable polydiallyldimethylammonium (PDADMA) cation.

2. A method according to claim 1, wherein the zeolite beta is prepared by hydrothermal crystallization of a solution comprising PDADMA and a silicon source which are present in a molar ratio SiO.sub.2/PDADMA between the silicon source calculated as SiO.sub.2 and the polymeric compound calculated as the cationic PDADMA monomer is 1-10, the molar ratio SiO.sub.2/M.sub.2O between the silicon source calculated as SiO.sub.2 and the base source calculated as alkali metal oxide M.sub.2O is of 1-10.

3. A method according to claim 1, wherein the hydrothermal crystallization is carried out at a temperature of 150-230 C.

4. The method according to claim 1, wherein the molar ratio SiO.sub.2/Al.sub.2O.sub.3 between the silicon source calculated as SiO.sub.2 and the aluminum source calculated as Al.sub.2O.sub.3 is of 20-100.

5. The method of claim 1, comprising dissolving the aluminum source and the base source in the water, adding the polymeric PDADMA compound and stirring for a time period of 0.2-1.5 h.

6. The method of claim 1, wherein the product obtained by crystallization is filtered, dried and calcined sequentially to obtain a final zeolite beta with a composite pore structure.

7. The method of claim 1, wherein the templating polymeric PDADMA compound has a molecular weight of 110.sup.5-510.sup.5.

8. The method of claim 1, wherein the templating polymeric PDADMA compound is PDADMA salt.

9. The method of claim 8, wherein the templating PDADMA salt is added to the preparation solution in the form of an aqueous solution with a solid content of 10-60 wt %.

10. A hydroconversion catalyst, comprising from 5 to 95 wt % zeolite beta prepared by crystallization of zeolite beta from a solution comprising a template, a silicon source and an aluminum source in which the template is polymeric compound comprising ionizable polydiallyldimethylammonium (PDADMA) cation; from 5 to 95 wt % refractory oxide binder; and from 0.01 to 30 wt % catalytically active metal, wherein the percentages are based on the total dry weight of the catalyst.

11. A hydrocarbon conversion process, which comprises contacting hydrocarbon compounds with the hydroconversion catalyst of claim 10 and hydrogen at a reaction temperature in the range of from 250 to 500 C. and reactor inlet pressure in the range of from 310.sup.6 to 310.sup.7 Pa.

12. The process of claim 11, wherein the hydrocarbon conversion process is chosen from the group consisting of pyrolysis of polyethylene, alkylation of benzene with benzyl alcohol (ABB), condensation of benzaldehyde with hydroxyacetophenone (CBH), and alkylation of phenol with tert-butyl alcohol (APT).

13. The hydroconversion catalyst according to claim 10, wherein the zeolite beta is prepared by hydrothermal crystallization of a solution comprising PDADMA and a silicon source which are present in a molar ratio SiO.sub.2/PDADMA between the silicon source calculated as SiO.sub.2 and the polymeric compound calculated as the cationic PDADMA monomer is 1-10, the molar ratio SiO.sub.2/M.sub.2O between the silicon source calculated as SiO.sub.2 and the base source calculated as alkali metal oxide M.sub.2O is of 1-10.

14. The hydroconversion catalyst according to claim 10, wherein the hydrothermal crystallization is carried out at a temperature of 150-230 C.

15. The hydroconversion catalyst according to claim 10, wherein the molar ratio SiO.sub.2/Al.sub.2O.sub.3 between the silicon source calculated as SiO.sub.2 and the aluminum source calculated as Al.sub.2O.sub.3 is of 20-100.

16. The hydroconversion catalyst according to claim 10, comprising dissolving the aluminum source and the base source in the water, adding the polymeric PDADMA compound and stirring for a time period of 0.2-1.5 h.

17. The hydroconversion catalyst according to claim 10, wherein the product obtained by crystallization is filtered, dried and calcined sequentially to obtain a final zeolite beta with a composite pore structure.

18. The hydroconversion catalyst according to claim 10, wherein the templating polymeric PDADMA compound has a molecular weight of 110.sup.5-510.sup.5.

19. The hydroconversion catalyst according to claim 10, wherein the templating polymeric PDADMA compound is PDADMA salt.

20. The hydroconversion catalyst according to claim 19, wherein the templating PDADMA salt is added to the preparation solution in the form of an aqueous solution with a solid content of 10-60 wt %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Now the present invention is further described with reference to the figures, wherein:

(2) FIG. 1 shows X-ray diffraction (XRD) spectra of the zeolite product synthesized by the present invention;

(3) FIG. 2 shows isothermal nitrogen absorption-desorption curves of the zeolite product synthesized by the present invention;

(4) FIG. 3a-3d shows TEM images of the zeolite product synthesized by the present invention, wherein FIGS. 3a and 3b are low magnification images, FIGS. 3c and 3d are high resolution images, and the inserted at left bottom of FIG. 3b is an electron diffraction image of zeolite particle;

(5) FIG. 4 shows the curves for conversions versus temperatures of PDPE pyrolyses over beta MS (zeolite beta according to the present invention) and beta (conventional zeolite beta) as well as without any catalyst (blank), wherein the conversions are determined from thermogravimetric data; and

DETAILED DESCRIPTION OF THE INVENTION

(6) In the present invention, the following measurements are involved:

(7) Ratio Si/Al was determined by a PW1400 X ray fluorescence spectrometer XRF analysis;

(8) XRD spectra were measured by a Rigaku X-ray diffractometer using Cu K (=1.5418 ) radiation; Isothermal nitrogen absorption-desorption curves were measured at 196 C. using a Micromeritics ASAP 2020M and 3020M system, wherein the sample was degassed for 10 h at 150 C. before being measured;

(9) TEM images were obtained on a JEOL JEM-2100F electron microscope operated at 200 kV and JEOL JEM-3010 instrument operated at 300 kV;

(10) Pore size distribution for mesopores was calculated using Barrett-Joyner-Halenda (BJH) model; and

(11) Thermogravimetric analysis (TG) and differential thermal analysis (DTA) were performed with SDT Q600 V8.2 Build 100 instrument in air with a heating rate of 10 C./min.

(12) Now the present invention is described by reference to a specific example, which is provided to demonstrate the present invention only, rather than to limit the present invention in any way.

Example

(13) In this example, all the reaction agents are of technical grade, wherein:

(14) The template is polydiallyldimethylammonium chloride (aqueous solution with a solid content of 20 wt % and a molecular weight of 110.sup.5-210.sup.5) purchased from Sigma-Aldrich Company, Ltd. (USA);

(15) The silica source is fumed silica purchased from Shenyang Chemical Co.;

(16) The base source is NaOH and the aluminum source is NaAlO.sub.2, both of them were purchased from Sinopharm Chemical Reagent Co.;

(17) Benzene, benzyl alcohol, benzaldehyde, 2-hydroxyacetophenone, phenol, tert-butyl alcohol and dodecane were purchased from Aladdin Industrial Co (China); and

(18) Low-density polyethylene (LDPE) was purchased from Alfa Aesar.

(19) Synthesis of Zeolite Beta with a Composite Pore Structure

(20) In this example, single crystals of zeolite beta according to the invention were synthesized by use of PDADMA chloride as template, wherein the silicon source calculated as SiO.sub.2, the template calculated as cationic PDADMA monomer, the aluminum source calculated as Al.sub.2O.sub.3, the base source calculated as Na.sub.2O and H.sub.2O were used at a molar ratio of 45SiO.sub.2/7.5PDADMA/Al.sub.2O.sub.3/10Na.sub.2O/2258H.sub.2O.

(21) Specifically, 0.08 g NaAlO.sub.2 and 0.3 g NaOH being dissolved in 12.1 mL deionized water, then 2.0 g PDADMA chloride (calculated on the basis of the aqueous solution with a solid content of 20 wt %) being added and stirring being continued for about 0.5 h to form a clear solution; then, 0.935 g fumed silica being added to the clear solution and stirring being continued for 12-24 h to form a gel; and the resultant gel being transferred into an autoclave to be crystallized at about 180 C. for about 96 h; finally, the resultant crystallization product being filtered at room temperature, dried at about 100 C., and calcined at about 550 C. for about 5 h to remove the template, thereby the zeolite product beta-MS being obtained.

(22) Characterization, Confirmation and Properties of the Product

(23) The zeolite product beta-MS was measured for XRD spectra, isothermal nitrogen absorption-desorption curves and TEM images respectively. Specifically:

(24) XRD spectra are shown in FIG. 1. It can be seen that the shown spectra are of typical zeolite beta, thus, it can be confirmed that the presently synthesized product is zeolite beta indeed;

(25) Isothermal nitrogen absorption-desorption curves are shown in FIG. 2. It can be seen that the isothermal nitrogen absorption-desorption curves exhibit a hysteresis loop at a relative pressure of 0.50<P/P.sub.0<0.90, thereby the presence of meso-pores in the presently synthesized zeolite beta can be confirmed.

(26) TEM images are shown in FIG. 3a-3d, wherein low magnification images (FIGS. 3a and 3b) show obvious mesopores in the sample, thus it is further confirmed that the presently synthesized zeolite beta is with a composite pore structure; and wherein high resolution TEM images (FIGS. 3c and 3d) show very ordered micropores in same direction and this is in good agreement with the characteristics of single crystals of zeolite beta, thereby it is determined that the presently synthesized zeolite beta with a composite pore structure is its single crystals, furthermore, this regard can be demonstrated by that the electron diffraction of zeolite beta particle, inserted at left bottom of FIG. 3b, is a single set of diffraction spectra, which indicated that zeolite beta particle is a single crystal rather than a nanocrystal aggregation.

(27) Finally, for the presently synthesized zeolite beta with a composite pore structure, the following properties, i.e. ratio Si/Al of 10.2, BET surface area of 724 m.sup.2/g, pore volume of 0.90 cm.sup.3/g, and the calculated central value of BJH pore size distribution of 7 nm, were obtained through further analyses and measurement.

(28) Test of Hydrothermal Stability

(29) After being exposed to 100% steam at 700 C. for 2 h, the synthesized zeolite product beta-MS has BET surface area of 538 m.sup.2/g, pore volume of 0.87 cm.sup.3/g, and the calculated central value of BJH pore size distribution of 11.4 nm. Compared with the above-mentioned original data, it can be known that the presently synthesized zeolite beta-MS with a composite pore structure has good hydrothermal stability, i.e. keeping high BET surface area and large pore volume even after hydrothermal treatment. Thus, the presently synthesized zeolite beta with a composite pore structure has a good properties for industrial applications.

(30) Test of Catalytic Ability

(31) The presently synthesized zeolite beta MS with a composite pore structure is tested for its catalytic ability in comparison with the conventional zeolite beta, which conventional zeolite beta was purchased from Nankai University and is with ratio Si/Al of 12.2, BET surface area of 587 m.sup.2/g and pore volume of 0.36 cm.sup.3/g, and after hydrothermal treatment, i.e. after being exposed to 100% steam at 700 C. for 2 h, is with BET surface area of 487 m.sup.2/g and pore volume of 0.36 cm.sup.3/g, that is to say, this conventional zeolite beta is with good hydrothermal stability and suitable for industrial application either. Table 1 shows a summary about the properties of the presently synthesized zeolite beta MS with a composite pore structure and the conventional zeolite beta before and after hydrothermal treatment.

(32) TABLE-US-00001 TABLE 1 BET Total surface pore area volume Zeolites (m.sup.2/g) (m.sup.3/g) beta MS Before hydrothermal 724 0.90 (presently treatment synthesized, After hydrothermal 538 0.87 Si/Al = 10.2) treatment beta Before hydrothermal 587 0.36 (conventional, treatment Si/Al = 12.2) After hydrothermal 480 0.36 treatment

(33) All the zeolite samples used in the tests of catalytic ability are in hydrogen form. For this purpose, the zeolite samples were ion-exchanged with 1M NH.sub.4NO.sub.3 at 80 C., then calcined at 500 C. for 5 h, and this procedure was repeated twice, thereby both zeolite beta MS with a composite pore structure and the conventional zeolite beta in hydrogen form were obtained.

(34) Herein, the obtained zeolite beta MS with a composite pore structure and the conventional zeolite beta in hydrogen form were used in bulky molecular hydrocarbon conversions such as low-density polyethylene (LDPE) pyrolysis, alkylation of benzene with benzyl alcohol (ABB), condensation of benzaldehyde with hydroxyacetophenone (CBH), and alkylation of phenol with tert-butyl alcohol (APT).

(35) Firstly, low-density polyethylene (LDPE) pyrolysis was carried out in a HENVEN HCT-3 (Beijing) differential thermal balance under a nitrogen flow of 50 cm.sup.3/min and a reaction temperature ramping from 30 C. to 600 C. at a rate of 10 C./min, wherein the polymer powder and the zeolite were carefully weighed and intimately mixed at a mass ratio 10:1 in the -Al.sub.2O.sub.3 crucibles of the differential thermal balance. FIG. 4 shows the curves for conversions versus temperatures of PDPE pyrolyses over beta MS (zeolite beta with a composite pore structure) and beta (conventional zeolite beta) as well as without any catalyst (Blank), wherein the conversions are determined from thermogravimetric data of LDPE.

(36) As can be known from FIG. 4, the presently synthesized zeolite beta MS with a composite pore structure has much higher catalytic activity than the conventional zeolite beta, specifically, zeolite beta MS with a composite pore structure can reach a relatively high conversion at a relatively low reaction temperature. Of course, both zeolite beta MS and zeolite beta show significant catalytic activity over that without any catalyst (shown as Blank in FIG. 4).

(37) Furthermore, in alkylation of benzene with benzyl alcohol (ABB), condensation of benzaldehyde with hydroxyacetophenone (CBH), and alkylation of phenol with tert-butyl alcohol (APT) (their reaction formula are shown in FIG. 5), the obtained products were analyzed by gas chromatography Shimazu 2010C with a flame ionization detector (FID), wherein a column DB-1 (30 m) was used, the flame ionization detector (FID) is at a temperature of 280 C., and the separated product was determined by .sup.1H NMR technology.

(38) All the above-mentioned three reactions are carried out in a three-necked round flask equipped with a condenser and a magnetic stirrer, wherein the reaction temperature is ramping from an initial value of 80 C. to a final value of 280 C. at a heating rate of 10 C./min. In all the three reactions, a stirring rate of higher than 800 rpm and catalyst particles smaller than 400 mesh were required.

(39) Specifically, the alkylation of benzene with benzyl alcohol (ABB) was carried out by mixing 0.02 g catalyst with 57 mmol benzene and 2.9 mmol benzyl alcohol at about 80 C. for a time period of about 5 h; the condensation of benzaldehyde with 2-hydroxyacetophenone (CBH) was carried out by mixing 0.10 g catalyst with 14 mmol benzaldehyde and 7 mmol 2-hydroxyacetophenone at about 150 C. for a time period of about 18 h; and the alkylation of phenol with tert-butyl alcohol (APT) was carried out by mixing 0.15 g catalyst with 5 mmol phenol, 10 mmol tert-butyl alcohol, and 10 ml cyclohexane solvent at about 100 C. for a time period of about 4 h.

(40) The conversions of each reaction over the two catalysts are shown in Table 2.

(41) TABLE-US-00002 TABLE 2 Conversions of each reaction (%) Zeolites ABB CBH APT Zeolite beta MS (Si/Al = 10.2) 48 59 61 Zetolite beta 27 35 44 (comprative, Si/Al = 12.2)

(42) As can be known from the data in table 2, in terms of alkylation of benzene with benzyl alcohol (ABB), condensation of benzaldehyde with hydroxyacetophenone (CBH), and alkylation of phenol with tert-butyl alcohol (APT), the presently synthesized zeolite beta MS with a composite pore structure reached much higher conversions than the conventional zeolite beta.

(43) Thus, the presently synthesized zeolite beta with a composite pore structure is much better than the conventional zeolite beta when being used as the catalyst for bulky molecular hydrocarbon conversions.