BORON-CONTAINING MOLECULAR SIEVE MTT
The present invention relates to boron-containing zeolites having the MTT framework topology defined by the connectivity of the tetrahedral atoms in the zeolite, such as boron-containing SSZ-32 and boron-containing AZM-23 zeolites.
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This application is a continuation-in-part of application Ser. No. 11/216,546, filed Aug. 30, 2005.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to boron-containing zeolites having the MTT framework topology defined by the connectivity of the tetrahedral atoms in the zeolite (referred to herein sometimes simply as “B-MTT”.
2. State of the Art
Zeolites having the MTT framework topology defined by the connectivity of the tetrahedral atoms (referred to herein simply as MTT) are known. See, for example, Ch. Baerlocher et al., Atlas of Zeolite Framework Types, 5th Revised Edition, 2001 of the International Zeolite Association. Examples of MTT zeolites include the zeolite designated “SSZ-32”. SSZ-32 and methods for making it are disclosed in U.S. Pat. No. 5,053,373, issued Oct. 1, 1991 to Zones. This patent discloses the preparation of zeolite SSZ-32 using an N-lower alkyl-N′-isopropylimidazolium cation as an organic structure directing agent (SDA), sometimes called a templating agent. It does not, however, disclose boron-containing MTT zeolite. U.S. Pat. No. 4,076,842, issued Feb. 28, 1978 to Plank et al., discloses the preparation of the zeolite designated “ZSM-23”, a zeolite with a structure similar to SSZ-32, using a cation derived from pyrrolidine as the SDA. U.S. Pat. No. 4,076,842 does not disclose boron-containing MTT zeolite. Zeolites SSZ-32 and ZSM-23 are commonly referred to as having the MTT framework topology. Both of the aforementioned patents are incorporated herein by reference in their entirety. Other MTT zeolites include EU-13, ISI-4 and KZ-1.
U.S. Pat. No. 5,707,600, issued Jan. 13, 1998 to Nakagawa et al., discloses a process for preparing medium pore size zeolites, including SSZ-32, using small, neutral amines. The amines contain (a) only carbon, nitrogen and hydrogen atoms, (b) one primary, secondary or tertiary, but not quaternary, amino group, and (c) a tertiary nitrogen atom, at least one tertiary carbon atom, or a nitrogen atom bonded directly to at least a secondary carbon atom, wherein the process is conducted in the absence of a quaternary ammonium compound. Examples of the small amines include isobutylamine, diisobutylamine, trimethylamine, cyclopentylamine, diisopropylamine, sec-butylamine, 2,5-dimethylpyrrolidine and 2,6-dimethylpiperidine. U.S. Pat. No. 5,707,600 does not disclose boron-containing MTT zeolite.
U.S. Pat. No. 5,707,601, issued Jan. 13, 1998 to Nakagawa, discloses a process for preparing MTT zeolites using small, neutral amines. The amines contain (a) only carbon, nitrogen and hydrogen atoms, (b) one primary, secondary or tertiary, but not quaternary, amino group, and (c) a tertiary nitrogen atom, at least one tertiary carbon atom, or a nitrogen atom bonded directly to at least one secondary carbon atom, wherein the process is conducted in the absence of a quaternary ammonium compound. Examples of the small amines include isobutylamine, diisobutylamine, trimethylamine, cyclopentylamine, diisopropylamine, sec-butylamine, 2,5-dimethylpyrrolidine and 2,6-dimethylpiperidine. U.S. Pat. No. 5,707,601 does not disclose boron-containing MTT zeolite.
U.S. Pat. No. 5,332,566, issued Jul. 26, 1994 to Moini, discloses a method of synthesizing ZSM-23 (i.e., MTT) using an organic directing agent having the structure:
It is disclosed that the ZSM-23 can contain boron oxide. However, it has been found that when this organic directing agent is used in an attempt to prepare boron-containing MTT zeolites, a zeolite having the MTW topology (e.g., ZSM-12) is produced.
U.S. Pat. No. 5,405,596, issued Apr. 11, 1995 to Moini et al., discloses the MTT zeolite ZSM-23 and a method of making it using a directing agent having the following formula:
(CH3)3N30(CH2)12N+(CH3)3.
It is disclosed that the ZSM-23 can contain boron oxide. However, it has been found that when this organic directing agent is used in an attempt to prepare boron-containing MTT zeolites, a zeolite other than MTT zeolite is produced.
It has now been found that boron-containing MTT zeolites, such as boron-containing SSZ-32, can be prepared using certain nitrogen-containing organic compounds.
SUMMARY OF THE INVENTIONIn accordance with the present invention there is provided a boron-containing zeolite having the MTT crystal topology and comprising (1) silicon oxide and (2) boron oxide. The boron-containing MTT zeolite can have a silicon oxide to boron oxide mole ratio of about 20 to about 500.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The present invention comprises a boron-containing zeolite having the MTT crystal topology and comprising (1) silicon oxide and (2) boron oxide. The boron-containing MTT zeolites are prepared using a structure directing agent (“SDA”) selected from the following:
SDA's A, D, E, F, O, T, U, Y, BB, EE and FF above are referred to collectively herein as “B-MTT SDA's”.
When the SDA is a cation, it is associated with an anion, A−, which is not detrimental to the formation of the boron-containing MTT zeolites. Representative of such anions include halogens, such as fluoride, chloride, bromide, and iodide; hydroxide; acetate; sulfate and carboxylate. Typically, hydroxide is the anion. It may be beneficial to ion exchange, for example, a halide for hydroxide ion, thereby reducing or eliminating the alkali metal or alkaline earth metal as a source of hydroxide.
The boron-containing MTT zeolites can be prepared as follows:
(a) preparing a reaction mixture comprising (1) source(s) of silicon oxide; (2) source(s) of boron oxide; (3) optionally, source(s) of an alkali metal oxide, alkaline earth metal oxide or mixtures thereof; (4) at least one B-MTT SDA; and (5) water;
(b) maintaining the reaction mixture under conditions sufficient to form crystals of the zeolite; and
(c) recovering the crystals of the zeolite.
The process of the present invention comprises forming a reaction mixture from source(s) of silicon oxide; sources(s) of boron oxide; optionally, source(s) of alkali and/or alkaline earth metal (M) cations with valences n (i.e., 1 or 2); at least one B-MTT SDA (X); and water, said reaction mixture having a composition in terms of mole ratios within the following ranges:
The reaction mixture is prepared using standard molecular sieve preparation techniques. Typical sources of silicon oxide include fumed silica, silicates, silica hydrogel, silicic acid, collodial silica, tetra-alkyl orthosilicates, and silica hydroxides. Sources of boron oxide include borosilicate glasses and other reaction boron compounds. These include borates, boric acid and borate esters.
it has been found that seeding the reaction mixture with boron-containing MTT crystals both directs and accelerates the crystallization, as well as minimizing the formation of undesired contaminants. In order to produce pure phase boron-containing MTT crystals, seeding may be required. When seeds are used, they can be used in an amount that is about 2-3 weight percent based on the weight of SiO2.
The reaction mixture is maintained at an elevated temperature until boron-containing MTT crystals are formed. The temperatures during the hydrothermal crystallization step are typically maintained from about 120° C. to about 160° C. It has been found that a temperature below 160° C., e.g., about 120° C. to about 140° C., is useful for producing boron-containing MTT crystals without the formation of secondary crystal phases.
The crystallization period is typically greater than 1 day and preferably from about 3 days to about 7 days. The hydrothermal crystallization is conducted under pressure and usually in an autoclave so that the reaction mixture is subject to autogenous pressure. The reaction mixture can be stirred, such as by rotating the reaction vessel, during crystallization.
Once the boron-containing MTT crystals have formed, the solid product is separated from the reaction mixture by standard mechanical separation techniques such as filtration. The crystals are water-washed and then dried, e.g., at 90° C. to 150° C. for from 8 to 24 hours, to obtain the as-synthesized crystals. The drying step can be performed at atmospheric or subatmospheric pressures.
Due to the unpredictability of the factors which control nucleation and crystallization in the art of crystalline oxide synthesis, not every combination of reagents, reactant ratios, and reaction conditions will result in crystalline products. Selecting crystallization conditions which are effective for producing crystals may require routine modifications to the reaction mixture or to the reaction conditions, such as temperature, and/or crystallization time. Making these modifications are well within the capabilities of one skilled in the art.
The mole ratio of silicon oxide to boron oxide in the final product can be from about 20 to about 500.
Typically, the zeolite is thermally treated (calcined) prior to use as a catalyst.
Usually, it is desirable to remove the alkali metal cation, if present, by ion exchange and replace it with hydrogen, ammonium, or any desired metal ion.
The X-ray diffraction patterns of Tables I, IA, IIA below are representative of B-MTT zeolite made in accordance with this invention. Minor variations in the diffraction pattern can result from variations in the silica-to-boron mole ratio of the particular sample due to changes in lattice constants. In addition, sufficiently small crystals will affect the shape and intensity of peaks, leading to significant peak broadening. The variation in the scattering angle (two Theta) measurements, due to instrument error and to differences between individual samples, is estimated at +/−0.10 degrees.
The X-ray powder diffraction patterns were determined by standard techniques. The radiation was the K-alpha/doublet of copper. A diffractometer with a scintillation counter detector was used. The peak heights I and the positions, as a function of 2Theta where Theta is the Bragg angle, were read from the relative intensities, 100×I/Io where Io is the intensity of the strongest line or peak, and d, the interplanar spacing in Angstroms corresponding to the recorded lines, can be calculated.
The X-ray diffraction pattern of Table I below shows the major peaks of an as-synthesize B-MTT zeolite made in accordance with this invention. As used herein, the term “as-synthesized” refers to B-MTT prior to removal of any SDA from the pores of the zeolite, e.g., prior to calcination.
Table IA below shows the major peaks of a typical X-ray diffraction pattern for as-synthesized B-MTT zeolite made in accordance with this invention, including the relative intensities of the peaks or lines.
The X-ray diffraction pattern of Table II below shows the major peaks of a calcined B-MTT zeolite made in accordance with this invention.
aThe X-ray patterns provided are based on a relative intensity scale in which the strongest line in the X-ray pattern is assigned a value of 100: W(weak) is less than 20; M(medium) is between 20 and 40; S(strong) is between 40 and 60; VS(very strong) is greater than 60.
Table IIA below shows an X-ray diffraction pattern representative of a calcined B-MTT zeolite made in accordance with this invention. In Table IIA, the intensity (I) of the peaks or lines is expressed as the intensity relative to the strongest peak or line in the pattern, i.e., I/Io×100 where Io is the intensity of the strongest peak or line.
Calcination can result in changes in the intensities of the peaks as well as minor shifts in the diffraction pattern. The zeolite produced by exchanging the metal or other cations present in the zeolite with various other cations (such as H+ or NH4+) yields essentially the same diffraction pattern, although again, there may be minor shifts in the interplanar spacing and variations in the relative intensities of the peaks. Notwithstanding these minor perturbations, the basic crystal lattice remains unchanged by these treatments.
The boron-containing MTT zeolites of this invention are useful in catalysts for hydroconverting heavy normal paraffins into lighter normal paraffin products with minimal formation of isoparaffins, such as the hydroconversion process of copending application Ser. No. 11/501,087, filed Aug. 7, 2006 entitled “Catalyst and Process for Selective Hydroconversion of Normal Paraffins to Normal paraffin-Rich Lighter Products” which is incorporated by reference herein in its entirety.
The following examples demonstrate, but do not limit, the present invention.
EXAMPLESThere are numerous variations on the embodiments of the present invention illustrated in the Examples which are possible in light of the teachings supporting the present invention. Carbosil M-5 fused silica was used as the silica source. All reactions were performed within a Blue-M convection oven on a spit rotating at 43 rpm. Synthesis were performed with H2O/SiO2 mole ratio=42.
For synthesis of boron-containing MTT zeolites, a typical example is as follows (with SDA E): 1.0 g 1N KOH, 0.70 g N-isopropyl-1,3-propanediamine, and 10.4 deionized H2O were mixed together in a 23 mL Teflon cup. Next 0.035 g potassium tetraborate tetrahydrate was dissolved in the mixture. Finally 0.90 g of Cabosil M-5 was added, and the resultant gel was thoroughly mixed to create a uniform gel. The Teflon reactor was then capped and sealed inside a Parr autoclave. The autoclave was placed in an oven with a rotating spit (43 rpm) and heated at 150° C. for 10 days. After the reaction was completed, the reaction mixture was removed, cooled to room temperature, and then the reactor contents were filtered under vacuum in a glass filtration funnel. The solids were then washed with 500-1500 mL deionized water and either dried overnight at room temperature or in an oven at 90-150° C.
In examples in which seeds were added in borosilicate reactions, 0.02 g of the as-synthesized MTT borosilicate zeolite prepared with SDA E was used as the seed material.
Examples 1-17
aMole ratios
bSi/B ratio
Claims
1. A boron-containing zeolite having the MTT crystal topology and comprising (1) silicon oxide and (2) boron oxide.
2. The boron-containing zeolite of claim 1 having a silicon oxide to boron oxide mole ratio of about 20 to about 500.
Type: Application
Filed: Dec 18, 2006
Publication Date: Jun 7, 2007
Applicant:
Inventor: ALLEN BURTON (Richmond, CA)
Application Number: 11/612,275
International Classification: C01B 39/00 (20060101);
