Synthesis of large crystal zeolites

#This invention relates to a method of preparing crystalline zeolites wherein the crystalline zeolites are crystallized in the form of large crystals.

#Crystalline microporous molecular sieves, both natural and synthetic, such as zeolites, have been demonstrated to have catalytic properties for various types of hydrocarbon conversion processes. In addition, the crystalline microporous molecular sieves have been used as adsorbents and catalyst carriers for various types of hydrocarbon conversion processes, and other applications. These molecular sieves are ordered, porous, crystalline material having a definite crystalline structure as determined by x-ray diffraction, within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. The dimensions of these channels or pores are such as to allow adsorption of molecules with certain dimensions while rejecting those with larger dimensions. The interstitial spaces or channels formed by the crystalline network enable molecular sieves, such as crystalline aluminosilicates, to be used as molecular sieves in separation processes and catalysts and catalyst supports in a wide variety of hydrocarbon conversion processes.

#Zeolites are comprised of a lattice of silica and optionally alumina combined with exchangeable cations such as alkali or alkaline earth metal ions. Although the term "zeolites" includes materials containing silica and optionally alumina, it is recognized that the silica and alumina portions may be replaced in whole or in part with other oxides. For example, germanium oxide, tin oxide, phosphorous oxide, and mixtures thereof can replace the silica portion. Boron oxide, iron oxide, titanium oxide, gallium oxide, indium oxide, and mixtures thereof can replace the alumina portion. Accordingly, the terms "zeolite", "zeolites" and "zeolite material", as used herein, shall mean not only molecular sieves containing silicon and, optionally, aluminum atoms in the crystalline lattice structure thereof, but also molecular sieves which contain suitable replacement atoms for such silicon and aluminum, such as silicoaluminophosphates (SAPO) and aluminophosphates (ALPO). The term "aluminosilicate zeolite", as used herein, shall mean zeolites consisting essentially of silicon and aluminum atoms in the crystalline lattice structure thereof.

#The following examples exemplify the process of the present invention.

#A sodium aluminate solution was prepared by dissolving alumina hydrate (201 parts by weight, 65% Al.sub.2 O.sub.3 content) in a caustic solution comprising NaOH (369.1 parts by weight) and water (825 parts by weight) at 100.degree. C. The solution was cooled and then added with vigorous stirring to a slurry containing colloidal silica (15400 parts by weight), tetrapropylammonium bromide (TPABr) (2457 parts by weight), water (16747 parts by weight), and 54 by weight MFI seeds to provide a synthesis mix. The mix was stirred until a homogeneous consistency was obtained. The molar composition of the mix, excluding seeds, was 80 SiO.sub.2 /1 Al.sub.2 O.sub.3 /3.6 Na.sub.2 O/7.2 TPABr/1168 H.sub.2 O. The mix (10 L) was placed in an autoclave and heated while stirring with a single blade turbine (0.8 M/sec tip speed). In 6 hours a temperature of 150.degree. C. was reached at autogenous pressure. The heat up time between 140.degree. C. and 150.degree. C. was 20 min. The stirring was stopped and the mixture was allowed to crystallize without further agitation at 150.degree. C. for 20 hours. After crystallization, a sample was taken. X-ray diffraction analysis showed the product was fully crystalline. Laser light scattering was used to determine the crystal size of the resulting crystals. The mass mean crystal diameter of the crystals and the amount of crystals less than 1 micron diameter is shown below in Table I.

#A synthesis mix was prepared as described in Example 1. The mix (36 L) was placed in an autoclave and heated while stirring with a single blade turbine (0.8 M/sec tip speed). In 5 hours, a temperature of 130.degree. C. was reached at autogenous pressure. The stirring was stopped and heating was continued in a static mode for 7 hours until a temperature of 150.degree. C. was reached. The mixture was allowed to crystallize without further agitation at 150.degree. C. for 20 hours. After crystallization, a sample was taken. X-ray diffraction analysis showed the product was fully crystalline. Laser light scattering was used to determine the crystal size of the resulting crystals. The mass mean crystal diameter of the crystals and the amount of crystals less than 1 micron diameter is shown below in Table I.