Chromium catalyst materials and methods for making and using the same from chromium(VI) free sources
The present disclosure relates to methods for making chromium-containing dehydrogenation catalysts using chromium feedstocks that need not include chromium(VI). The disclosure also relates to the catalysts made thereby, as well as to dehydrogenation methods using such catalysts. In one aspect of the disclosure, a method includes providing a formable mixture comprising, on a dry basis, an aluminum hydroxide, present in an amount within the range of about 40 wt. % to about 90 wt. %; an acid (e.g., nitric acid), present in an amount within the range of about 2 wt. % to about 15 wt. %; and a chromium(III) source, present in an amount within the range of about 2 wt. % to about 35 wt. %; forming the formable mixture; and calcining the formed mixture. In certain embodiments, the method further includes impregnating the calcined mixture with an aqueous impregnation solution including a chromium(III) salt; and calcining the impregnated mixture.
1. A method for preparing a chromium catalyst, the method comprising
providing a solid aluminum hydroxide and a solid chromium(III) source selected from chromium(III) oxide, chromium(III) hydroxide, chromium(III) halide, chromium(III) acetate or chromium(III) stearate;
preparing a formable mixture by directly mixing the solid aluminum hydroxide, the solid chromium(III) source and an acid and, if necessary, sufficient water to make the mixture formable, the formable mixture comprising, on a dry basis,
the aluminum hydroxide, present in an amount within the range of about 40 wt. % to about 90 wt. %;
the acid, present in an amount within the range of about 2 wt. % to about 15 wt. %; and
the chromium(III) source, present in an amount within the range of about 10 wt. % to about 35 wt. %;
forming the formable mixture via extrusion or tabletting; and
calcining the formed mixture to provide a calcined mixture comprising Al 2 O 3 and Cr 2 O 3 impregnate the calcined mixture with an aqueous impregnation solution comprising a chromium (III) salt; and calcining the impregnated mixture, chromium content being present in a calcined catalyst in an amount in the range of 15-50 wt %, as Cr 2 O 3 on a calcined basis,
wherein the formable mixture before the calcining step comprises less than 1% chromium(VI) as a molar fraction of total chromium.
2. The method according to claim 1 , wherein formable mixture before the calcining step comprises less than 0.5% chromium(VI) as a molar fraction of total chromium.
3. The method according to claim 1 , wherein the formable mixture includes the aluminum hydroxide present in an amount within the range of about 60 wt. % to about 90 wt. % on a dry basis.
4. The method according to claim 1 , wherein the acid is nitric acid, formic acid or acetic acid.
5. The method according to claim 1 , wherein the acid is present in the formable mixture in an amount within the range of about 4 wt. % to about 10 wt. %.
6. The method according to claim 1 , wherein the chromium(III) source is chromium(III) oxide or chromium(III) hydroxide.
7. The method according to claim 1 , wherein the chromium(III) source is present in the formable mixture in an amount within the range of about 10 wt. % to about 25 wt. % on a dry basis.
8. The method according to claim 1 , wherein the formable mixture comprises water in an amount within the range of about 3 wt. % to about 20 wt. % on a wet basis.
9. The method according to claim 1 , wherein the formable mixture further comprises a pore forming organic compound in an amount within the range of about 0.1 wt. % to about 5 wt. % on a dry basis.
10. The method according to claim 1 , wherein the aluminum hydroxide, the acid and the chromium(III) source make up at least about 80 wt. % of the formable mixture on a dry basis.
11. The method according to claim 1 , wherein the formed mixture is calcined at a temperature within the range of about 300° C. to about 900° C.
12. The method according to claim 1 , wherein
the formable mixture includes the aluminum hydroxide present in an amount within the range of about 60 wt. % to about 90 wt. % on a dry basis;
the acid is present in the formable mixture in an amount within the range of about 4 wt. % to about 10 wt. %;
the chromium(III) source is present in the formable mixture in an amount within the range of about 3 wt. % to about 25 wt. % on a dry basis; and
the aluminum hydroxide, the acid and the chromium(III) source make up at least about 95 wt. % of the formable mixture on a dry basis.
13. The method according to claim 1 , wherein the materials included in the aqueous impregnation solution comprise less than 1% chromium(VI).
14. The method according to claim 1 , wherein the aqueous impregnation solution further comprises one or more of
a sodium salt, present in an amount sufficient to provide the catalyst with sodium within the range of about 0.1 wt. % to about 5 wt. % calculated as sodium oxide on a calcined basis;
a potassium salt, present in an amount sufficient to provide the catalyst with sodium within the range of about 0.1 wt. % to about 5 wt. % calculated as potassium oxide on a calcined basis;
a zirconium salt, present in an amount sufficient to provide the catalyst with sodium within the range of about 0.1 wt. % to about 5 wt. % calculated as ZrO 2 on a calcined basis;
a magnesium salt, present in an amount sufficient to provide the catalyst with sodium within the range of about 0.1 wt. % to about 5 wt. % calculated as MgO on a calcined basis.
15. The method according to claim 1 , wherein chromium is present in the calcined catalyst in an amount within the range of about 25 wt. % to about 50 wt. %.
16. The method according to claim 1 , wherein the formable mixture before the calcining step comprises less than 0.1% chromium(VI) as a molar fraction of total chromium.