Chemistry of inorganic compounds – Silicon or compound thereof – Oxygen containing
Reexamination Certificate
1997-02-11
2001-02-27
Dunn, Tom (Department: 1754)
Chemistry of inorganic compounds
Silicon or compound thereof
Oxygen containing
C423S328200, C423S329100, C502S240000
Reexamination Certificate
active
06193943
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to the synthesis of novel metal-substituted mesoporous molecular sieves and to their use as a catalysts for peroxide hydroxylation of benzene and oxidation of large substituted aromatics. Specifically the mesoporous molecular sieve catalysts of the present invention are prepared by a neutral S° I° self-assembly method comprising steps of hydrogen H-bonding between neutral amine (S°) or diamine (S°—S°) template and neutral inorganic oxide precursors (I°), followed by hydrolysis and crosslinking under mild reaction conditions. The new templating approach ensures the preparation of hexagonal or hexagonal-like oxidation catalysts exhibiting large framework wall thickness of at least about 17 Å, small elementary particle size (≦400 Å), and unique combinations of framework-confined uniform mesopores and textural mesopores. In addition, the invention provides for the synthesis of thermally stable pillared lamellar metallosilicates by neutral templating method involving neutral metallosilicate precursors (I°) and neutral diamine surfactants (S°—S°). The invention also provides for efficient recovery and recycling of the neutral template by simple solvent extraction methods. This invention also demonstrates the preparation of transition metal-substituted hexagonal MCM-41 silica using mediated S
+
X·I
+
templating route and mild reaction conditions.
The invention also relates to a catalytic application of these mesoporous metallosilicates for peroxide oxidation of substituted aromatics with kinetic diameters that are too large (larger than 6 Å) to access the pore structure of the conventional microporous transition metal-substituted silicates such as titano- and vanadosilicalites.
(2) Description of Related Art
One of the most important methods for converting hydrocarbons to useful industrial chemicals, intermediates and pharmaceuticals is catalytic oxidation. Currently, stoichiometric oxidations with inorganic oxidants, such as permanganate and dichromate, are carried out on a large scale in the manufacture of fine chemicals. However, these oxidation routes generate large amounts of waste inorganic salts (pollutants) that are extremely difficult to dispose of and economically impractical to recycle. In addition, these classical oxidation processes exhibit low selectivity and thus involve as an indispensable part of the synthesis a costly separation of the side products. Therefore, there is a growing demand for developing cleaner, catalytic and much more selective alternatives to existing oxidation processes. For example, the classical multistep process of production of hydroquinone from benzene involves the following steps: (i) preparation of aniline from benzene by nitration and reduction in order to generate a functional group that can be easily oxidized; (ii) oxidation with stoichiometric amounts of MnO
2
and (iii) reduction with Fe/HCl (Sheldon R. T. in
New Developments in Selective Oxidation,
Eds. Centi G. and Trifiro F., Elsevier Sci. Publ. B. V., Amsterdam, (1990) pp. 1-29). The amount of generated waste is huge—about 10 kg of inorganic salts (MnSO
4
, FeCl
2
, Na
2
SO
4
, NaCl) per kg of hydroquinone product.
The current catalytic process on the other hand, uses three steps with the initial step being benzene alkylation to 1,4-diisopropylbenzene followed by catalytic oxidation and acid catalyzed rearrangement of the bis-hydroperoxide. It is estimated that the latter process produces about 10% of inorganic salts formed by the classical process (i.e. >1 kg inorganic salts per kg hydroquinone). It is clear that the classical multistep process leads to huge production of waste by-products. On the other hand the existing catalytic process still generates some waste and organic by-products as a result of oxidatively eliminating the isopropyl groups from the 1,4-diisopropylbenzene. In summary, the disadvantages of the classical method are that it generates large amount of pollutants, the oxidant is difficult if not impossible to recover and the selectivity is very low. On the other hand the disadvantages of the existing catalytic process are that it involves multistep transformations, still generates significant amount of pollutants and difficult to separate by-products. Therefore, a one or two step selective catalytic oxidation process to hydroquinone is highly desirable. Such a catalytic process has been recently disclosed (U.S. Pat. No. 4,410,501) and industrially implemented in Italy by Enichem. The high selectivity toward hydroquinone was achieved by performing a liquid phase peroxide oxidation of phenol in the micropores (approximately 6 Å in size) of the titanium substituted molecular sieve—silicalite (denoted TS-1). Another important advantage of this heterogeneous catalytic system is that the catalyst is stable and can be recovered and recycled.
However, the catalytic oxidation of a much larger organic entities such as 2,6-di-tert-butylphenol (with kinetic diameter of approximately 10 Å) is currently performed only by a homogeneous catalytic routes employing different organometallic complex catalysts such as: Co(disalicyl-idenepropylenetriamine) disclosed by Nishinaga, A. et al.
Chem. Lett.
4, 817-820 (1994); binuclear Cu(II).mu.-hydroxo complexes with nitrogen chelating ligands (Mari et al.
Chemom. Intell. Lab. Syst.
22(2) 257-263 (1994)); a phase-transfer catalysts such as 18-crown-6, 18-dibenzocrown-6, triethylbenzylammonium chloride (U.S. Pat. No. 1,747,434) and metalloporphyrins or intercalated metalloporphirins such as Cobalt(II) phthalocyaninetetrasulfonate intercalated into a Mg
3
Al
25
-layered double hydroxide (LDH)—Chibwe et al.,
J. Chem. Soc., Chem. Commun.
3, 278-280 (1993). However, the use of homogeneous catalysts has the following major disadvantages: (i) these catalysts are usually very expensive, highly toxic and difficult to separate and to recover from the reaction product and (ii) the catalytic oxidation of the 2,6- di-tert-butylphenol over these metal complexes proceeds primarily to the 3,3′,5,5′-tetra(tert-butyl)-4,4′-diphenoquinone dimer rather to the more desirable 2,6-di-tert-butylbenzoquinone monomer, i.e. the selectivity to the corresponding monomer is very low. One way to solve the separation problem, as taught by Chibwe et al., ibid, is to encapsulate these metal complex catalysts in inorganic matrix (such as LDH) and to be able to recover and recycle the catalyst. However, the large scale industrial application of the above processes and the use of expensive and toxic catalysts is still little justified due to the low selectivity toward mono-benzoquinone and separation problems. A very promising way to improve the selectivity toward monomeric benzoquinone would be to limit the size of the active complex, i.e. the size of the reaction product, by performing the oxidation of the large aromatic substrate into the uniform mesopores of a transition metal-substituted porous molecular sieve material.
Porous materials created by nature or by synthetic design have found great utility in all aspects of human activity. The pore structure of the solids is usually formed in the stages of crystallization or subsequent treatment. Depending on their predominant pore size, the solid materials are classified as: (i) microporous, having pore sizes<20 Å; (ii) macroporous, with pore sizes exceeding 500 Å; and (iii) mesoporous, with intermediate pore sizes between 20 and 500 Å. The use of macroporous solids as adsorbents and catalysts is relatively limited due to their low surface area and large non-uniform pores. Microporous and mesoporous solids, however, are widely used in adsorption, separation technology and catalysis. Owing to the need for higher accessible surface area and pore volume for efficient chemical processes, there is a growing demand for new highly stable mesoporous materials. Porous materials can be structurally amorphous, paracrystalline, or crystalline. Amorphous materials, s
Chibwe Malama
Pinnavaia Thomas J.
Tanev Peter T.
Wang Jialiang
Zhang Wenzhong
Board of Trustees operating Michigan State University
Dunn Tom
Hendrickson Stuart L.
McLeod Ian C.
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