Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Sulfur or compound containing same
Reexamination Certificate
1999-08-11
2001-01-30
Yildirim, Bekir L. (Department: 1764)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Sulfur or compound containing same
C502S219000, C502S221000, C502S222000, C502S223000
Reexamination Certificate
active
06180556
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to solid, superacid catalysts, based on zirconia and mixed sulfated oxides, obtained directly via sol-gel, with a non-alkoxide synthesis method, in the forms of use, microspheres, or spheres having dimensions of up to 3 mm and over, and with textural and mechanical characteristics which make them suitable for isomerization processes of hydrocarbons, verified by means of the model conversion reaction of n-butane to iso-butane.
2. Description of the Background
Interest in solid (super)acid catalysts derives from considerations of an environmental nature, associated with improvements in industrial isomerization and alkylation processes of hydrocarbons, which use large quantities of sulfuric or hydrofluoric acid in emulsion.
If solid acids can be compared with the known liquid superacids, the question will remain open until a clear definition of solid superacid is formulated [J. Sommer et al., Catal. Today, 38 (1997)309]. In fact, whereas the definition of liquid superacid is based on the definition of R. J. Gillespie [Adv. Phys. Org. Chem., 9 (1972)1]: any acid stronger than sulfuric acid at 100% (H
0
=−12 in Hammett's acidity scale), the most convincing evidence of the superacid nature of a solid should be, viceversa, its capacity to reversibly protonize an alkane, exploiting the &sgr;- basicity of the C—H or C—C bond [G. A. Olah, Angew. Chem. Int. Ed. Engl., 12 (1973) and J. Sommer et al., J. Am. Chem. Soc., 19 (1997)3274].
Among all linear alkanes, n-butane is the most difficult to isomerize, requiring the formation of a primary isobutyl cation. On the other hand, isobutane is an essential intermediate for the production of alkylated and oxygenated products for fuel.
It has been known for some time that sulfated zirconia is a solid acid, active in the isomerization of n-butane [M. Hino et al., Chem. Lett., (1979)1259]. The tetragonal, rather than monoclinic sulfated phase, seems to be the active crystalline phase of this material [C. Monterra et al., J. Catal., 157 (1995) 109].
The doping of sulfated zirconia with transition elements favourably influences the isomerization rate of n-butane, in particular the combination of mixed oxides of iron and manganese [F. C. Lange et al., Catal. Lett., 41 (1996)95]. The addition of 0.4% Pt to a sulfated zirconia, doped with iron and manganese oxides, produces an increase in the activity with respect to sulfated zirconia alone [X. M. Song et al., Catal. Lett., 37 (1996)187]. The role of the metal consists in favouring the hydrogenation/dehydrogenation mechanism, by inhibiting the formation of carbonaceous substances, which can deactivate the system. Its role therefore consists in establishing a bifunctional mechanism, by increasing the surface concentration of the olefins, rather than increasing the acid strength of the sites [F. Garin et al., J. Catal., 151 (1995)26]. As a consequence, a considerable increase in the life of the catalyst is observed [J. C. Yori et al., Appl. Catal., 129 (1995)83] and, following this scheme, doping with iridium and platinum allows more active sulfated zirconias to be obtained [M. Hino et al., Catal. Lett. 30 (1995)25 and J. C. Yori et al., Appl. Catal.:A, 129 (1995)83]. A promoting role of aluminum has recently been observed, which is different from that of transition metals, in stabilizing the surface sulfated complex and increasing the number of acid sites with intermediate acid strength, the most effective for the isomerization of n-butane [Z. Gao et al., Topics in Catalysis, 6 (1998)101].
Finally, WO
3
also makes zirconia a strong solid acid [M. Hino et al., Chem. Commun., (1987)1259] and Pt (0.3%) promotes the selective hydroisomerization of alkanes, from n-heptane upwards, at 373-473K, without the formation of carbonaceous substances [E. Inglesia et al., J. Catal., 144 (1993)238].
U.S. Pat. No. 5,750,459 of the same applicant describes a sol-gel process for the production of spheres and microspheres of pure zirconia or mixed oxides based on zirconia, obtained starting from a basic zirconium carbonate, and useful as catalysts or carriers for catalysts. This patent provides a detailed description of the procedure for obtaining pure zirconia spheres, example 1, pure zirconia microspheres, example 2, and spheres of mixed zirconia-alumina oxides (10% by weight), example 4.
PCT/US97/07424 describes a sol-gel process for the production of sulfated zirconia, obtained starting from zirconium alkoxides mixed with acetylacetone in a solution of ethanol, and precipitated in an acidified mixture of a C
8
-C
18
alkylamine and water. The sulfation process with diluted sulfuric acid takes place on powders dried at 110° C., after precipitation, aging, centrifugation and extraction with ethanol. The end-catalyst, sulfated zirconia in powder form, is obtained after calcination of the solid at temperatures ranging from 600 to 750° C. for about two hours. As an alternative, the same patent describes a process in which sulfated zirconia in powder form is obtained by hydrolysis of a solution of zirconyl chloride in diluted ammonia, washing with water and drying at 110° C., powdering and impregnation in diluted sulfuric acid for 5 hours, filtration and calcination at about 650° C.
CA-2069373 describes a process in which the life of the superacid catalyst is prolonged if the isomerization is carried out under supercritical conditions or almost critical conditions. Example 1 of this patent describes a procedure in which the superacid catalyst in powder form is obtained by hydrolyzing at pH 7-8, with an ammonia solution, a solution of a zirconium salt, obtained starting from a zirconium carbonate dissolved in nitric acid. The precipitate is separated, washed, filtered, dried and ground. It is then impregnated using the “incipient wetness” method with a solution of ammonium sulfate, dried and calcined at 725° C. The sulfated zirconia thus obtained contains a percentage of sulfates of 4%. Optionally, the example also describes the incorporation of one or more transition metals, for example Fe and Mn, onto the sulfated zirconia. The catalyst is obtained, alternatively, by impregnating a salt of the metal either onto dried zirconium hydroxide or sulfated hydroxide.
A similar superacid catalyst, based on sulfated zirconia, obtained however starting from a solution of zirconium oxychloride, hydrolyzed with a solution of ammonia, and then impregnating the dry powder with sulfuric acid, and others based on sulfated titania and sulfated iron oxide are described in U.S. Pat. No. 5,017,699. These catalysts are claimed in the synthesis of polyalkyl ethers of polymethylolmelamine compounds.
EP-0759423 describes a superacid catalyst obtained, again starting from a solution of zirconium oxychloride, as in the previous patent, but impregnating the dry product with a solution of ammonium sulfate and calcinating at 650° C. This catalyst is useful in the synthesis of isobornyl methacrylate or acrylate.
JP-01/245853 describes a process for obtaining a catalyst with a high alkylation activity. Metals of group IIb, such as Zn, Cd, or of group Va, such as V, or of group VIa, such as Cr, Mo or of group VIIa, such as Mn, or their compounds, and a radical of sulfuric acid or one of its precursors, are supported on a hydroxide or oxide of metals of group III, such as Al, Ga and/or of group IV, such as Ti and Zr, followed by calcination and stabilization at temperatures of about 400-800° C.
EP-0653397 discloses a method for the preparation of superacids based on sulfated zirconia, which incorporates, by means of “incipient wetness” impregnation, heteropolyacid (HPA) components or polyoxoanionic (POA) components, which give advantageous properties for effecting alkylation processes in liquid phase of isoparaffins to olefins. In the invention, preference is given to HPA or POA having the Keggin structure, represented by the f
Marella Marcello
Meregalli Letizia
Pinna Francesco
Tomaselli Michele
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
VeneziaTecnologie S.p.A.
Yildirim Bekir L.
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