GB1601926A

GB1601926A - Manufacture of alumina sols

Info

Publication number: GB1601926A
Application number: GB26256/77A
Authority: GB
Original assignee: UOP LLC
Current assignee: Honeywell UOP LLC
Priority date: 1978-05-23
Filing date: 1978-05-23
Publication date: 1981-11-04

Description

(54) MANUFACTURE OF ALUMINA SOLS (71) We, UOP INC, a corporation organized under the laws of the State of Delaware, United States of America, of Ten UOP Plaza, Algonquin & Mt. Prospect Roads, Des Plaines, Illinois, 60016, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to the manufacture of alumina sols.

Alumina sols are utilized almost exclusively in the manufacture of alumina. However, the alumina product finds extensive use in the chemical and petroleum industries as a treating and purifying agent, and especially as a catalyst or as a support for other catalytic materials.

The alumina sol may be converted to alumina in many ways, virtually all of which require gelation of the sol and formation of a hydrogel which, upon drying, calcining and other miscellaneous processing steps, is converted to the desired alumina. The alumina is prepared in many shapes and sizes depending on its intended use. For example, spheres are a particularly useful form, and spheres are advantageously prepared by the technique of dispersing alumina sol droplets into a hot oil bath. The droplets are retained in the bath until they set into firm hydrogel spheroids, the spheroids being thereafter separated from the bath and subjected to a specific aging treatment designed to promote the development of desirable physical properties. The spheres are subsequently dried, usually at a temperature of from 35 to 200 C., and thereafter calcined, generally at a temperature of from 425 to 750 C.

In the manufacture of catalysts comprising alumina, it is frequently desirable to include a chlorine and/or fluorine component to enhance the acid function of the catalyst with respect to certain hydrocarbon conversion reactions, and it is generally considered that the halogen component is present in a combined form. Although the addition of chlorine and/or fluorine can be effected by various methods, for example by treating the calcined alumina with hydrochloric and/or hydrofluoric acid, a convenient and preferred method comprises utilizing an alumina sol formed by digesting aluminum metal in hydrochloric and/or hydrofluoric acid.

When necessary, the alumina subsequently produced therefrom may be treated with said acid(s) as aforesaid to add additional halogen, or treated with steam to lower the halogen concentration.

The manufacture of an alumina sol by the method whereby aluminum is digested in aqueous hydrochloric and/or hydrofluoric acid has heretofore been effected by charging an excess of metallic aluminum to a disgester together with water and said acid(s). The acidic solution is circulated in contact with the aluminum until a quantity has been digested in excess of that desired in the sol product. The resulting acidic sol is then separated from the digester and the aluminum and halogen concentration is adjusted to a desired level by the addition of hydrochloric and/or hydrofluoric acid thereto, the excess aluminum being retained in the digester as a portion of the subsequent aluminum charge thereto.

It has been recognized that the degree of subdivision of the aluminum reactant is a principal factor in determining the digestion rate; the smaller the particle size the greater the surface area in contact with the other reactants. Powdered aluminum would therefore appear to be ideal for use in the digestion process. However, due to the vigorous nature of the resulting reaction, the digestion process is difficult to effect in a controlled manner, and the practitioner has been relegated to the use of much larger aluminum particles, and to the use of a substantial excess thereof, to achieve effective control of the process.

In addition to a substantial slowing of the digestion process, the larger aluminum particles present an opportunity for the formation and accumulation of high molecular weight sol polymers detrimental to the sol product.

For example, as has been previously shown, the residual acidic sol remaining on the aluminum particles after the separation of the sol product, continues to digest the aluminum with the formation of said high molecular weight sol polymers. But for an intermediate washing step, a sufficient amount of said polymers is recovered in each succeeding sol product to yield a sol with a tendency to stratify into several distinct layers indicative of a non-homogeneous sol, and the alumina product is non-uniform as to composition and/or physical properties.

This invention seeks to present an improvement in the manufacture of an alumina sol by the method whereby aluminum is digested in aqueous hydrochloric and/or hydrofluoric acid, which improvement enables a finely divided aluminum reactant to be used to improve the digestion rate and/or obviates the formation of undesirable high molecular sol polymers and affords a sol of improved homogeneity and reproducibility.

According to the present invention there is provided a process for the manufacture of an alumina sol containing combined chloride and/or fluoride and from 10 to 16 wt. % aluminum, which comprises first digesting in hydrochloric and/or hydrofluoric acid an amount of solid alumina particles which provides from 5 to 25 wt. % of the final aluminum content of the sol product, and thereafter digesting metallic aluminum therein, preferably in finely divided form, to provide the required remaining amount of aluminum, the hydrochloride and/or hydrofluoric acid being employed in an amount which provides a sol containing combined chloride and/or fluoride and aluminum in an atomic ratio of A1: C1/F of from 0.5: 1 to 2: 1.

The alumina starting material may be any of the various hydrous aluminum oxides or alumina gels such as boehmite, bayerite or gibbsite. Activated aluminas, such as have been thermally treated at temperatures in excess of 400 C. with the elimination of at least a portion of the chemically and/or physically combined water and hydroxyl groups commonly associated therewith are also suitable starting materials. The high surface area gamma- and eta-aluminas prepared by the thermal treatment of boehmite and bayerite alumina respectively, generally at a temperature in the 400'-850' C. range, are particularly useful. The alumina product derived from the alumina sol of this invention is typically gamma-alumina, and the alumina starting material is advantageously a finely divided gamma-alumina resulting, at least in part, from the processing and breakage of, for example, the aforementioned calcined alumina spheres.

While higher or lower acid concentrations may be employed in the digestion process, a hydrochloric acid solution containing from 10 to 30 wt. % hydrogen chloride is most suitable for use in the present invention.

Lower acid concentrations tend to extend the digestion process, and generally do not lend themselves to the dissolution of large quantities of alumina and/or aluminum.

After digesting alumina in the aqueous acidic solution, the metallic aluminum reactant is added to the acidic reaction mixture in an amount to provide a total of from 10 to 16 wt. % aluminum therein. As heretofore noted, the degree to which the aluminum has been subdivided is a substantial factor determining the rate of digestion; the smaller the size of the particles, the greater the surface area exposed to the acidic solution and, therefore, the faster the rate of digestion. The present invention is particularly adapted to the use of a powdered aluminum to expedite the digestion process. Aluminum turnings, aluminum foil, or granulated aluminum may also be advantageously employed. Aluminum pellets which have been prepared by dropping molten alumunum into water have heretofore been employed, and may be used to advantage provided they are less than 1/4" in diameter.

Alumina sols of predetermined composition with respect to aluminum and chloride content are prepared by the process of this invention. It is usually preferred to maintain the chloride level of the sol product at from 8 to 12 wt. % thereof. Sols containing aluminum in excess of 16 wt. % are highly unstable, and it is therefore preferable to maintain the aluminum content at from 13 to 15 wt. %. The aluminum/halide atomic ratio in the sol product, which influences the physical properties of the ultimate alumina product, is maintained at from 0.5:1 to 2:1, preferably from 1:1 to 2:1. The aluminum and halide content of the sol, as well as the aluminum/halide atomic ratio, is substantially equivalent to the quantity and ratio of the aluminum/alumina and hydrohalic acid reactants charged to the digester and thus may be readily controlled.

The reaction conditions utilized in the digestion step of this invention generally include a temperature of from 50 to 125 C., a temperature of from 75 to 105 being preferred. It is highly desirable to effect the digestion under substantially liquid phase reaction conditions generally entailing the use of elevated pressures. Hydrogen, being a by-product of the digestion reaction, is' ad- vantageously employed to maintain a required pressure.

The present invention affords a substantially faster digestion rate than heretofore practiced in the manufacture of an alumina sol for use in the production of alumina. It generally precludes the formation of high molecular weight sol polymers and produces a sol having uniform physical appearance characteristics. Alumina produced from an alumina sol manufactured in accordance with the present invention possesses uniform physical properties and homogeneity of composition, particle to particle.

The following examples are presented in illustration of the improvement of this invention.

EXAMPLE I (Comparative) About 138 milliliters of concentrated hydrochloric acid was added to 263 milliliters of water in a glass vessel vented to the atmosphere through an overhead condenser.

The vessel was equipped with a stirrer as well as heating and cooling means to maintain the reaction mixture at approximately 105 C. In this example, representing prior art methods, 71.5 grams of high purity (99.9%) aluminum nodules, average size about 1/4 inch, were added to the acidic solution and digested therein-72 hours being required to effect substantially complete digestion of the aluminum. The resulting alumina sol product analyzed 14.38 wt. % Al and 12.7 wt. % Cl for an Al/Cl atom ratio of 1.18. The specific gravity of the sol at 15.5 C. was 1.4372.

EXAMPLE II In this example, representing one preferred embodiment of this invention, approximately 20.8 wt. % of the aluminum content of the sol product was derived from gammaalumina, and the remainder from powdered aluminum. Thus, 138 milliliters of concentrated hydrochloric acid was added to 170 milliliters of water in the described glass vessel. The powdered alumina (28.04 grams) was added to the acidic solution and digested therein within 4.5 hours to yield a clear solution. After the addition of 83 milliliters of water to the reaction mixture, 56.7 grams of powered aluminum was added thereto in increments, the rate of addition being determined by the heat of reaction. The addition and complete digestion of the aluminum was effected within about 6 hours, the total time required to produce the alumina sol being about 10.5 hours as opposed to the 72 hours of the preceding example. The resulting alumina sol product analyzed 14.27 wt. % Al and 11.69 wt. % C1 for an Al/Cl atom ratio of 1.22. The specific gravity of the sol at 15.5 C.

was 1.4282. The product was a clear sol, free of the milky-white appearance indicative of the undesirable high molecular weight sol polymers, and the product showed no tendency towards stratification on standing.

WHAT WE CLAIM IS: A A process for the manufacture of an alumina sol containing combined chloride and/or fluoride and from 10 to 16 wt. % aluminum which comprises first digesting in hydrochloric and/or hydrofluoric acid an amount of solid alumina particles which provides from 5 to 25 wt. % of the final aluminum content of the sol product, and thereafter digesting metallic aluminum therein to provide the required remaining amount of aluminum, the hydrochloric and/ or hydrofluoric acid being employed in an amount which provides a sol containing combined chloride and/or fluoride and aluminum in an atomic ratio of Al:Cl/F of from 0.5:1 to 2: 1.

2. A process as claimed in claim 1 wherein the metallic aluminum is a finely divided aluminum.

3. A process as claimed in claim 1 or 2 wherein hydrochloric acid is employed in an amount to provide a sol containing combined chloride and aluminum in an atomic ratio of Al:Cl/F of from 1:1 to 2: 1.

4. A process as claimed in any of claims 1 to 3 wherein the alumina and the aluminum are each digested at a temperature of from 50 to 125"C and at a pressure which maintains substantially liquid phase reaction conditions.

5. A process as claimed in claim 4 wherein the temperature is from 75 to 150"C.

6. A process as claimed in any of claims 1 to 5 wherein the alumina is a gamma- or etaalumina.

7. A process as claimed in any of claims 1 to 6 wherein hydrochloric acid solution having a hydrogen chloride content of from 10 to 30 wt. % is employed for the digestion.

8. A process for the manufacture of an alumina sol containing combined fluoride and/or chloride carried out substantially as hereinbefore specifically described or illustrated in the foregoing Example II.

9. An alumina sol containing combined chloride and/or fluoride and from 10 to 16 wt. % aluminum when manufactured by a process as claimed in any of claims 1 to 8.

10. Alumina containing combined chloride and/or fluoride when obtained from an alumina sol as claimed in claim 9 by a procedure involving gelation, formation of a hydrogel, drying and calcining.

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Claims

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with the present invention possesses uniform physical properties and homogeneity of composition, particle to particle.

The following examples are presented in illustration of the improvement of this invention.

EXAMPLE I (Comparative) About 138 milliliters of concentrated hydrochloric acid was added to 263 milliliters of water in a glass vessel vented to the atmosphere through an overhead condenser.

The vessel was equipped with a stirrer as well as heating and cooling means to maintain the reaction mixture at approximately 105 C. In this example, representing prior art methods, 71.5 grams of high purity (99.9%) aluminum nodules, average size about 1/4 inch, were added to the acidic solution and digested therein-72 hours being required to effect substantially complete digestion of the aluminum. The resulting alumina sol product analyzed 14.38 wt. % Al and 12.7 wt. % Cl for an Al/Cl atom ratio of 1.18. The specific gravity of the sol at 15.5 C. was 1.4372.

EXAMPLE II In this example, representing one preferred embodiment of this invention, approximately 20.8 wt. % of the aluminum content of the sol product was derived from gammaalumina, and the remainder from powdered aluminum. Thus, 138 milliliters of concentrated hydrochloric acid was added to 170 milliliters of water in the described glass vessel. The powdered alumina (28.04 grams) was added to the acidic solution and digested therein within 4.5 hours to yield a clear solution. After the addition of 83 milliliters of water to the reaction mixture, 56.7 grams of powered aluminum was added thereto in increments, the rate of addition being determined by the heat of reaction. The addition and complete digestion of the aluminum was effected within about 6 hours, the total time required to produce the alumina sol being about 10.5 hours as opposed to the 72 hours of the preceding example. The resulting alumina sol product analyzed 14.27 wt. % Al and 11.69 wt. % C1 for an Al/Cl atom ratio of 1.22. The specific gravity of the sol at 15.5 C.

was 1.4282. The product was a clear sol, free of the milky-white appearance indicative of the undesirable high molecular weight sol polymers, and the product showed no tendency towards stratification on standing.

WHAT WE CLAIM IS: A A process for the manufacture of an alumina sol containing combined chloride and/or fluoride and from 10 to 16 wt. % aluminum which comprises first digesting in hydrochloric and/or hydrofluoric acid an amount of solid alumina particles which provides from 5 to 25 wt. % of the final aluminum content of the sol product, and thereafter digesting metallic aluminum therein to provide the required remaining amount of aluminum, the hydrochloric and/ or hydrofluoric acid being employed in an amount which provides a sol containing combined chloride and/or fluoride and aluminum in an atomic ratio of Al:Cl/F of from 0.5:1 to 2: 1.
2. A process as claimed in claim 1 wherein the metallic aluminum is a finely divided aluminum.
3. A process as claimed in claim 1 or 2 wherein hydrochloric acid is employed in an amount to provide a sol containing combined chloride and aluminum in an atomic ratio of Al:Cl/F of from 1:1 to 2: 1.
4. A process as claimed in any of claims 1 to 3 wherein the alumina and the aluminum are each digested at a temperature of from 50 to 125"C and at a pressure which maintains substantially liquid phase reaction conditions.
5. A process as claimed in claim 4 wherein the temperature is from 75 to 150"C.
6. A process as claimed in any of claims 1 to 5 wherein the alumina is a gamma- or etaalumina.
7. A process as claimed in any of claims 1 to 6 wherein hydrochloric acid solution having a hydrogen chloride content of from 10 to 30 wt. % is employed for the digestion.
8. A process for the manufacture of an alumina sol containing combined fluoride and/or chloride carried out substantially as hereinbefore specifically described or illustrated in the foregoing Example II.
9. An alumina sol containing combined chloride and/or fluoride and from 10 to 16 wt. % aluminum when manufactured by a process as claimed in any of claims 1 to 8.
10. Alumina containing combined chloride and/or fluoride when obtained from an alumina sol as claimed in claim 9 by a procedure involving gelation, formation of a hydrogel, drying and calcining.