Process for preparing synthetic clay minerals

Details Process for preparing synthetic clay minerals Process for preparing synthetic clay minerals

2000-12-21

2003-05-20

Koslow, C. Melissa (Department: 1755)

Compositions: coating or plastic

Materials or ingredients

Pigment, filler, or aggregate compositions, e.g., stone,...

C423S325000, C423S326000, C423S327100, C423S328100, C423S329100, C423S330100

Reexamination Certificate

active

06565643

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for preparing synthetic clay minerals.
2. Prior Art
U.S. Pat. No. 3,803,026 describes a process for preparing a clay-type material in which an amorphous gel comprising silicon oxide, aluminum oxide, and, e.g., magnesium oxide is subjected to a high-temperature ageing step in an autoclave.
C.R. Acad. Sc. Paris 7 292 describes a process for preparing, int. al., clays comprising aluminum, silicon, and, e.g., magnesium by way of a co-precipitation process.
EP 0 605 044 describes a process in which a glass type material, e.g., boron glass is reacted with a source of layered ions, e.g., aluminum or magnesium.
The use of synthetic clay minerals as cracking component in catalytic applications is described, e.g., in WO 96/07477. There, catalysts are disclosed which at least comprise a hydrogenation metal component and a swelling synthetic clay composed of clay platelets having an average diameter not exceeding 1 &mgr;m and an average degree of stacking not exceeding 20 sheets per stack. This reference refers to the synthetic clays of WO 96/07613 as being particularly attractive for use in catalytic applications, particularly in hydroprocessing, in view of their small particle size and low degree of stacking, which is accompanied by a large surface area and high accessibility.
In WO 96/07613 mentioned above, the synthetic clay minerals are prepared by bringing the pH of an aqueous liquid containing precursors for the clay to be prepared to a value of 3-9 and the temperature of the liquid to a value of from 60° to 350° C. The resulting clays have a crystalline structure with distinct peaks in the X-ray diffraction pattern at about 2&THgr;=20°, 2&THgr;=35°, and 2&THgr;=60°. They are made up of elementary three-layer platelets with dimensions from 0.01 &mgr;m to 1 &mgr;m, which are optionally stacked to up to 20 platelets. One particular example of such a clay material is a saponite, which, as indicated above, is a clay in which the tetravalent silicon ions of the tetrahedron layers are at least partly replaced by trivalent aluminum ions and in which the octahedral layer contains divalent ions almost exclusively.
The clay minerals prepared in accordance with WO 96/07613 typically have a sodium content of more than 0.5 wt. %. This is too high to be acceptable in hydroprocessing, and therefore the clay minerals need to be subjected to the ion exchange described above. A disadvantage of the clay minerals prepared in accordance with this reference is their poor filterability, which typically is above 2000 seconds (s), expressed as normalised filtration time. Because of this low filterability, the ion exchange takes a long time and so is difficult to perform on a commercial scale. Therefore there is need for a process to prepare synthetic clay minerals with a small platelet size and a low degree of stacking in which the problem of low filterability in effecting the ion exchange is circumvented.
SUMMARY OF THE INVENTION
The present invention fulfils the above need by providing a process which comprises the steps of
a) providing a silica-alumina with a total content of sodium and potassium of less than 2.0 wt. %
b) combining the silica-alumina with an octahedron ion source in such a manner that less than 0.1 mole of the total of sodium or potassium is added per mole of octahedron ion,
c) if necessary, adjusting the pH to a value of at least 7, with less than 0.1 mole of the total of sodium and potassium being added per mole of octahedron ion during the pH adjustment,
d) ageing the precipitate formed in c) at a temperature of 0-350° C. in an aqueous environment
e) optionally isolating the resulting material, optionally followed by washing.
Other embodiments of the present invention encompass further details relating to the synthetic clay mineral preparation process, including further ingredients in the composition and further details concerning the process for preparation, all of which are hereinafter disclosed in the following discussion of each of those facets of the invention.
DETAILED DISCRIPTION OF THE INVENTION
Clays minerals are layered silicates, also known as phyllosilicates. The individual clay platelets are composed of a central layer of octahedrally coordinated metal ions interlinked by oxygen ions. On either side of this so-called octahedral layer there are so-called tetrahedral layers composed of tetrahedrally coordinated metal ions linked to one another and to the octahedral layer by oxygen atoms. The metal ions in the tetrahedral layers are tetravalent. The metal ions in the octahedral layer can be trivalent or divalent. Two types of octahedral layers exist, namely the trioctahedral layer, in which all octahedral sites are filled with divalent cations, and the dioctahedral layer, in which two thirds of the octahedral sites are filled with trivalent cations and one third of the octahedral sites remain unfilled.
The above-described structure is electroneutral. However, if the structure comprises lower valency cations at the location of the tetravalent tetrahedral ions or the tri- or divalent octahedral ions, the clay platelet is negatively charged. This phenomenon is known as isomorphous substitution. For instance, in a dioctahedral layer divalent metal ions such as magnesium, zinc, or nickel may be present instead of trivalent metal ions such as aluminum. Materials with such a structure are called montmorillonites. Alternatively, in a trioctahedral layer monovalent metal ions such as lithium may be present instead of divalent metal ions such as magnesium or zinc. Materials with such a structure are called hectorites. In the tetrahedral layer trivalent metal ions, e.g., aluminum atoms, may be present instead of the tetravalent ions, generally silicon. In the case of a clay with a trioctahedral layer this material is called saponite, for a clay with a dioctahedral layer this material is called beidellite.
The negative charge resulting from isomorphous substitution is counterbalanced by the presence of cations, also known as counter-ions, in the space between the clay platelets. These counter-ions often are sodium or potassium. It is because of the negative charge caused by isomorphous substitution that clays can be advantageous for use in catalysis, since it gives them the potential to function as solid acids. However, to be able to function as solid acids, it is essential that the clay minerals comprise Brønsted acid groups, since these are at least partially responsible for the cracking ability of these compounds. Brønsted acid sites can be achieved by replacing the non-hydrolyzable counter-ions such as sodium or potassium with ammonium ions and then heating the whole. This process will result in ammonia desorption, leaving a proton to form a Brønsted site. Brønsted sites can also be introduced by replacing the counter-ions with hydrolyzable metal ions. Hydrolysis will then give hydrogen ions.
By the process of the present invention a clay material can be obtained which has a total content of sodium and potassium of below 0.5 wt. %. Therefore, it is not necessary to subject it to an ion exchange step. This is advantageous, because, as indicated above, carrying out an ion exchange on the final clay material is not attractive in view of its high normalised filtration time.
In the process of the present invention, if an ion exchange is carried out, it is carried out on the silica-alumina, before addition of the octahedron ion. Silica-aluminas can be selected to have a much better filterability than the final clay materials produced by the process of this invention, and therefore carrying out the ion exchange on the silica-alumina instead of on the final clay results in a more efficient process. The process according to the invention thus makes it possible to use relatively cheap alumina and silica sources which contain substantial amounts of the total of sodium and potassium without a cation exchange of the final clay being necessary.
Incidentally, it is noted that non

Affiliated with

Also associated with

Rating

Process for preparing synthetic clay minerals does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Process for preparing synthetic clay minerals, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for preparing synthetic clay minerals will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3075461