Synthetic Halloysites

1. Field of the Invention

This invention relates to a novel composition of matter useful as a catalyst and/or catalyst base in hydrocarbon conversion reactions. More particularly, this invention relates to synthetic halloysite, its preparation and its use in hydrocarbon conversion reactions such as cracking, hydrocracking, hydrofining, desulfurization, and demetallization.

2. Description of the Prior Art

Halloysite is a well-known kaolin clay mineral having the empirical formula Al.sub.2 O.sub.3 :2SiO.sub.2 :2H.sub.2 O. A complete chemical analysis for halloysite is given in the "Encyclopedia of Chemical Technology," 2nd Edition, Vol. 5, page 545 (Interscience Publishers). Further descriptions concerning the properties and characteristics of naturally-occurring halloysite may be found in the literature such as, for example, Thomas F. Bates et al. (1950), Morphology and Structure of Endellite and Halloysite, The American Mineralogist, Vol. 35, pages 463-484; Thomas F. Bates et al., Further Observations on the Morphology of Chrysotile and Halloysite, Proceedings National Conference on Clays and Clay Minerals, VI, Berkeley, 1957 pages 237-248; and G. Brown, The X-Ray Identification and Crystal Structures of Clay Minerals, Mineralogical Society (Clay Minerals Group), London, 1961, pages 68-77.

Natural halloysite has been used heretofore in the petroleum art as a catalytic cracking catalyst. Unfortunately, naturally-occurring halloysite contains various metals, such as iron, which are detrimental to its effectiveness as a hydrocarbon conversion catalyst. It has been found, therefore, necessary to subject the naturally occurring halloysite to acid treatment in order to reduce the iron content and thereby increase its effectiveness as a hydrocarbon conversion catalyst. Unfortunately, acid treatment often does substantial damage to the crystalline structure of the halloysite which drastically limits its use as a catalyst in hydrocarbon conversion processes.

In accordance with the present invention, a synthetic halloysite which is substantially iron-free is obtained by crystallization from a reaction mixture containing hydrous alumina gel and aqueous silica sol. In a further embodiment of the invention, metal substituted synthetic halloysites are prepared by coprecipitation of metal hydroxides with the alumina gel.

In general, the halloysite of the invention is prepared by crystallization from an aqueous mixture containing a mixture of alumina gel and a silica source maintained at a pH of 4 to 10 for at least about 16 hours at a temperature in excess of 200.degree. C. A preferred reaction scheme is given by the following equations:

metal substituted synthetic halloysites can be prepared in accordance with the invention by coprecipitation of a hydroxide of the metal with the alumina gel. The empirical formula for such metal substituted synthetic halloysites, which may have an SiO.sub.2 /Al.sub.2 O.sub.3 ratio greater than the stoichiometric amount, can be expressed by the following formula:

where

M is a metal selected from Groups IIA, IIIB, VIB and VIII of the Periodic Table

n is valence of M

x=0 to 1, preferably 0.8 to 1.0

y=0 to 1.

Preparation of the synthetic halloysite of the Invention involves the reaction of hydrous alumina gel, i.e., Al(OH).sub.3, and a source of silica. The hydrous alumina gel is prepared in accordance with known techniques such as by the reaction of aqueous mixtures of aluminum chloride or aluminum sulfate and an inorganic base such as NH.sub.4 OH, NaOH or NaAlO.sub.2, and the like. Preparation of alumina gel by use of ammonium hydroxide is preferable to the use of sodium hydroxide since it is desirable to maintain the soda (Na.sub.2 O) content to a low level and because the more alkaline gels tend to form crystalline boehmite.

The silica source may include those sources which are conventionally used for the preparation of crystalline aluminosilicate zeolites. These include silicic acid, silica sol, silica gel, sodium silicate, etc. Silica sols are particularly useful. These are colloidal dispersions of discrete spherical particles of surface-hydroxylated silica such as is sold by E. I. du Pont de Nemours & Company, Inc. under the trademark "Ludox."

The proportions of the reactants employed in the initial reaction mixture are determined from the following molar ratio of reactants.

The pH of the reaction mixture should be adjusted to a range of about 4 to 10, preferably 6 to 8. The temperature of the reaction mixture should preferably be maintained at between about 230.degree. and 270.degree. C., more preferably 240.degree. to 250.degree. C., for a period from about 2 hours to 100 hours or more. The time necessary for crystallization will depend, of course, upon the temperature of the reaction mixture. By way of example, the crystallization of the synthetic halloysite occurs in about 24 hours at a temperature of about 250.degree. C.

The catalytic activity of the synthetic halloysites of the invention can be improved by incorporating therein metals selected from Groups IIA, IIIB, VIB, and VIII of the Periodic Table as given in "Websters Seventh New Collegiate Dictionary," (1963) published by G. C. Merriam Company. Specific examples of such metals include, among others, magnesium, lanthanum, molybdenum, cobalt, nickel, palladium, platinum and rare earths. Particularly preferred metals include magnesium, nickel, cobalt and lanthanum. The metals are incorporated into the synthetic halloysite structure by adding soluble salts of the metal to the reaction mixture or by coprecipitation of the metal hydroxide with Al(OH).sub.3. The metals are most conveniently added to the reaction mixture in the form of their hydroxides. The synthetic halloysite of the invention, particularly when substituted with the afore-described metals, is useful for catalytic cracking, hydrocracking, desulfurization, demetallization and other hydrocarbon conversion processes. For example, substituted halloysites of the invention containing metals such as magnesium, lanthanum and rare earths such as cerium, praseodymium, neodymium, gadolinium, etc., are useful in catalytic cracking of petroleum feedstocks. Synthetic halloysite containing nickel, cobalt, palladium, platinum, and the like are particularly useful for hydrocracking petroleum feedstocks.

The feedstocks suitable for conversion in accordance with the invention include any of the well-known feeds conventionally employed in hydrocarbon conversion processes. Usually they will be petroleum derived, although other sources such as shale oil are not to be excluded. Typical of such feeds are heavy and light virgin gas oils, heavy and light virgin naphthas, solvent extracted gas oils, coker gas oils, steam-cracked gas oils, middle distillates, steam-cracked naphthas, coker naphthas, cycle oils, deasphalted residua, etc.

The operating conditions to be employed in the practice of the present invention are well-known and will, of course, vary with the particular conversion reaction desired. The following table summarizes typical reaction conditions effective in the present invention.

The halloysite structure of the composition of this invention has been confirmed by X-ray diffraction and electron microscopy. However, there are a number of significant differences between naturally occurring halloysite and the synthetic halloysite of this invention. For example, the synthetic halloysites of the invention have surface areas ranging from about 85 sq. meters/gram to about 200 sq. meters/gram (BET Method as used, for example, in U.S. Pat. No. 3,804,741) as compared to naturally occurring halloysite which has a surface area generally within the range of 40-85 sq. meters/gram (BET Method). Further, the synthetic halloysite of the invention will be substantially iron-free, i.e., less than 0.05% iron, as compared to naturally occurring halloysite which contains significant amounts of iron. The synthetic and naturally occurring halloysites also differ in that the physical form of the synthetic halloysite is flakes, while the physical form of the natural halloysite has a tube-like configuration. Furthermore, it has been discovered that the synthetic halloysite has considerably better catalytic activity than natural halloysite under analogous hydrocarbon conversion conditions. Although the synthetic halloysite has the same empirical formula as naturally occurring halloysite, the higher surface area, the elimination of iron and the presence of selective metals makes the synthetic halloysite a more effective hydrocarbon conversion catalyst.

The following examples further illustrate the present invention. Unless otherwise specified, all percentages and parts are by weight.

This example illustrates a general procedure for the preparation of the synthetic halloysite of the invention.

A solution consisting of 962 grams of AlCl.sub.3.6H.sub.2 O in 3,200 cubic centimeters (cc) of water were added to a 1 gallon stainless steel vessel. The solution was stirred at ambient conditions and neutralized with about 740 cc. of a 28% ammonia solution, thereby producing a pH greater than 8. The Al(OH).sub.3 gel produced was washed with water until it was substantially chloride-free. The washed Al(OH).sub.3 gel was then blended with 790 grams of silica sol sold under the trade name "LS-30 Ludox" by E. I. du Pont de Nemours & Company. The blend of silica sol and alumina gel was then transferred to a 200 cc. Monel autoclave where it was heated at 246.degree. C. for 48 hours to produce synthetic halloysite.

Using the general procedure of Example 1, a number of synthetic halloysites were prepared to determine the surface area of synthetic halloysite prepared in accordance with the invention. The results given below in Table I show that the surface area expressed in square meters per gram is higher than naturally occurring halloysite.

Using the general preparation procedure given in Example 1, a number of metal-substituted synthetic halloysites were prepared by precipitating insoluble hydroxides of various metals with aluminum hydroxide and blending the resultant washed gel with the silica sol. The reaction conditions and the amount of substituted metal in the synthetic halloysite product are given in Table II.

The catalysts prepared in the previous example were pressed on a hydraulic ram, the compacted forms of the catalyst then crushed to 14-35 mesh (Tyler series), and then calcined at 540.degree. C. for 16 hours. Portions of this granular catalyst were charged to reactors and the temperature adjusted to 280.degree. C. A stream of helium was passed through a saturator filled with cumene at 18.degree. C. and passed into the reactor and contacted with the catalyst. The effluent from the reactor was analyzed by gas chromatography to determine the amount of conversion of the cumene to benzene and propylene. The results obtained were compared with natural halloysite (API Standard No. 13). The results obtained were given below in Table III.

The above data show the effectiveness of the synthetic halloysites of the invention as cracking catalyst. Synthetic halloysite is more active than natural halloysite and the activity of synthetic halloysite is significantly improved by substituting such metals as magnesium and nickel in the structure. Conversely, the incorporation of iron in synthetic halloysites acts as a catalyst poison, just as it does in natural halloysites.

This example compares in Table VI the X-ray powder diffraction pattern of a typical synthetic halloysite of the invention with the published patterns for naturally occurring halloysite (ASTM 13-375) and the closely related mineral kaolinite (ASTM 14-164).

In obtaining the X-ray powder diffraction pattern, standard procedures were employed. The radiation source was the K-alpha doublet for copper. A Geiger counter spectrometer with a strip chart pen recorder was used in recording the data. The peak heights I, and the positions as a function of 2.theta., where .theta. is the Bragg angle, were read from the spectrometer chart. From these, the relative intensities I were observed. Also, the interplanar spacing, d, in Angstrom units, corresponding to the recorded lines, were determined by reference to standard tables. The more significant interplanar spacings, i.e., d values, for a typical synthetic halloysite of the invention, natural halloysite and kaolinite are shown below in Table IV. As regards the synthetic halloysite of the invention, the relative intensities of the lines are expressed as s. (strong), m. (medium) and w. (weak).

As regards synthetic halloysite and the related kaolinite mineral, the d line at 4.43 A is significant. Kaolinite has d lines at 4.48 A and 4.37 A, but no strong intensity d line at 4.43 A as in the case of the synthetic halloysite of the invention. The synthetic halloysite of the invention can also be distinguished on the basis that the d line at 4.43 A is of stronger intensity than either the 001 line (d=7.3) or the 002 (d=3.56). Accordingly, the significant X-ray diffraction characteristics of the synthetic halloysite of the invention are as follows: