Zeolite beta and process for producing the same

#The present invention relates to a zeolite beta and a process for producing a zeolite beta without using an organic compound as a structure directing agent.

#Synthetic zeolites are crystalline aluminosilicate, and have uniform pores of a size in angstrom attributed to the crystal structure of each zeolite. Utilizing the characteristic, the synthetic zeolites have been industrially used as molecular sieve adsorbents for adsorbing only molecules having a specific size, adsorption separating agents for adsorbing highly affinitive molecules, and catalyst base. One of such zeolites, i.e., zeolite beta is abundantly used in the world as a catalyst in the petroleum chemical industry and an adsorbent for treating automobile exhaust gas. The characteristic of the zeolite beta is that the zeolite beta has pores of a 12-membered ring in a three-dimensional direction as described in Non Patent Literature 1 below. Moreover, the X-ray diffraction diagram showing the structural characteristics is described in Non Patent Literature 2 below.

#A variety of processes for synthesizing a zeolite beta has been proposed. A general process uses tetraethylammonium ion as a structure directing agent (hereinafter abbreviated to an “SDA.”). Such a process is described in Patent Literature 1 and 3 and Non Patent Literature 3 below, for example. According to these processes, the zeolite beta having a SiO2/Al2O3 ratio 10 to 400 is obtained. Unfortunately, a compound containing tetraethylammonium ion is expensive, and most of it is decomposed after crystallization of the zeolite beta is completed. For this reason, the compound cannot be recovered and reused. For this reason, the zeolite beta produced by the process is expensive. Further, because tetraethylammonium ions are taken into crystals, the tetraethylammonium ions need to be calcined and removed when the zeolite beta produced by the process is used as an adsorbent or a catalyst. The exhaust gas in the calcination causes environmental pollution, and many chemicals are needed for the treatment for detoxifying a synthesis mother solution. Thus, the process for synthesizing a zeolite beta using tetraethylammonium ion is a production process that costs high and impose a large environmental load. Accordingly, realization of a production process without using the SDA has been desired.

#FIG. 1 is a process chart for implementing a production process according to the present invention.

#FIG. 2 is a scanning electron microscope image of a zeolite beta used for a seed crystal synthesized in Reference Example and having a SiO2/Al2O3 ratio=24.0.

#FIG. 3 is a scanning electron microscope image of a zeolite beta used for a seed crystal synthesized in Reference Example and having a SiO2/Al2O3 ratio=18.4.

#Hereinafter, the present invention will be described according to the preferred embodiments. As one of the characteristics, the zeolite beta according to the present invention has a large BET specific surface area, a large micropore specific surface area, and a large micropore volume while the zeolite beta has a low SiO2/Al2O3 ratio and is aluminum-rich. Although a zeolite beta having a low SiO2/Al2O3 ratio is known, the BET specific surface area, the micropore specific surface area, and the micropore volume of the zeolite beta is not large. If the BET specific surface area, the micropore specific surface area, and the micropore volume are made larger in the conventionally known zeolite beta, the SiO2/Al2O3 ratio is inevitably made larger.

#The zeolite beta according to the present invention has a SiO2/Al2O3 ratio of 10 to 16, preferably 10 to 14, and is aluminum-rich. Such an aluminum-rich zeolite beta according to the present invention has a large BET specific surface area measured in the state of the sodium type, i.e., 500 to 700 m2/g and preferably 550 to 700 m2/g. The zeolite beta according to the present invention has a large micropore specific surface area measured in the state of the sodium type, i.e., 350 to 500 m2/g and preferably 380 to 500 m2/g. Additionally, the zeolite beta according to the present invention has a large micropore volume measured in the state of the sodium type, i.e., 0.15 to 0.25 cm3/g and preferably 0.18 to 0.25 cm3/g.

#The zeolite beta according to the present invention includes the sodium type zeolite, and further includes an H+ type zeolite in which sodium ion is ion-exchanged with a proton. In the case where the zeolite beta is the H+ type, the measurement of the specific surface area and the like are performed after the proton is substituted by sodium ion. To convert the sodium type zeolite beta to the H+ type, for example, the sodium type zeolite beta is dispersed in an aqueous solution of an ammonium salt such as ammonium nitrate, and the sodium ion in the zeolite is substituted by ammonium ion. The ammonium type zeolite beta is calcined to obtain the H+ type zeolite beta.