Process for producing a vanadium phosphorus oxide catalyst

Details Process for producing a vanadium phosphorus oxide catalyst Process for producing a vanadium phosphorus oxide catalyst

1999-05-21

2001-05-08

Bell, Mark L. (Department: 1755)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Phosphorus or compound containing same

C502S162000, C502S210000, C502S212000, C502S213000, C502S312000, C502S313000, C502S314000, C502S353000

Reexamination Certificate

active

06228798

ABSTRACT:

This invention relates to vanadium phosphorus oxide (VPO) catalysts. More particularly, the invention relates to a method of making VPO catalyst suitable for the oxidation of C
4
and C
5
paraffins and olefins to maleic anhydride, phthalic anhydride and acetic acid, especially paraffins and olefins produced by Fischer-Tropsch processes, and to a VPO catalyst made in accordance with the method.
According to the invention there is provided a method of making a vanadium phosphorus oxide (VPO) catalyst, the method comprising the steps of:
precipitating, from a solution comprising dissolved V
4+
ions and V
5+
ions at a total concentration of 45-65 g/l, a vanadium-containing and phosphorus-containing precipitate comprising a complex in accordance with the formula VOHPO
4
.½H
2
O; and
calcining the precipitate under an inert atmosphere, to produce a VPO catalyst having an active phase in accordance with the formula (VO)
2
P
2
O
9
, the solution from which the precipitate is precipitated comprising dissolved cations of at least two dopant metals selected from the group consisting of Bi, Zr, Cr, Ce, Co, Mn, Mg and Mo, said dissolved dopant metal cations being present in the solution in proportions such that the precipitate comprises 1-25% by mass of dopant metal cations in total, the balance being the VOHPO
4
.½H
2
O complex, each dopant metal forming 0.1-20% by mass of the precipitate.
Preferably, the proportion of dissolved V
4+
ions relative to the proportion of dissolved V
5+
ions is as high as practically feasible. Furthermore, the ratio of dissolved V
4+
ions:V
5+
ions in the solution may be such that the molar proportion of each of the V
4+
ions and the V
5+
ions in VPO catalyst, after calcining, is 0.1-10 mole %, typically 0.5-5%.
Preferably the total concentration of dissolved V
4+
ions and V
5+
ions in the solution is 50-60 g/l, the dissolved dopant metal cations being present in the solution in proportions such that the precipitate comprises 2-20% by mass of the dopant metals in total, each dopant metal forming 0.5-15% by mass of the precipitate, the ratio of dissolved V
4+
ions:V
5+
ions in the solution being such that the molar proportion of V
5+
ions in the VPO catalyst is 0.1-10 mole %, typically 0.5-6 mole %.
The solution from which the precipitate is precipitated may comprise dissolved cations of 2-3 dopant metals selected from said group consisting of Bi, Zr, Cr, Ce, Co, Mn, Mg and Mo.
One of the dopant metals may be Bi, Bi cations being present in the solution from which the precipitate is precipitated in a proportion such that Bi forms 1-15% by mass of the precipitate, the solution comprising, in addition to the Bi cations, cations of 1-2 other dopant metals selected from:
Zr;
Mn and Ce;
Co;
Ce;
Zr and Ce; and
Zr and Co.
Instead, one of the dopant metals may be Zr, Zr cations being present in the solution from which the precipitate is precipitated in a proportion such that Zr forms 1-15% by mass of the precipitate, the solution comprising, in addition to the Zr cations, cations of 1-2 other dopant metals selected from:
Bi;
Cr;
Ce and Cr;
Ce;
Co;
Bi and Ce; and
Bi and Co.
Instead, one of the dopant metals may be Cr, Cr cations being present in the solution from which the precipitate is precipitated in a proportion such that Cr forms 1-15% by mass of the precipitate, the solution comprising, in addition to the Cr cations, cations of 1-2 other dopant metals, selected from:
Zr; and
Ce and Zr.
Instead, one of the dopant metals may be Ce, Ce cations being present in the solution from which the precipitate is precipitated in a proportion such that Ce forms 1-15% by mass of the precipitate, the solution comprising, in addition to the Ce cations, cations of 1-2 other dopant metals, selected from:
Zr and Cr;
Zr;
Bi and Mn;
Bi;
Bi and Zr; and
Mn and Mg.
Instead, one of the dopant metals may be Co, Co cations being present in the solution from which the precipitate is precipitated in a proportion such that Co forms 1-15% by mass of the precipitate, the solution comprising, in addition to the Co cations, cations of 1-2 other dopant metals, selected from:
Zr;
Bi; and
Bi and Zr.
Instead, one of the dopant metals may be Mn, Mn cations being present in the solution from which the precipitate is precipitated in a proportion such that Mn forms 1-15% by mass of the precipitate, the solution comprising, in addition to the Mn cations, cations of 1-2 other dopant metals, selected from:
Bi and Ce;
Mg and Ce; and
Mo.
Instead, one of the dopant metals may be Mg, Mg cations being present in the solution from which the precipitate is precipitated in a proportion such that Mg forms 1-20% by mass of the precipitate, the solution comprising cations of Mn and Ce dopant metals in addition to the Mg cations. Instead, one of the dopant metals may be Mo, Mo cations being present in the solution from which the precipitate is precipitated in a proportion such that Mo forms 1-20% by mass of the precipitate, the solution comprising cations of Mn dopant metal in addition to the Mo cations.
The solution may comprise a solvent selected from alcohols and mixtures of two or more alcohols. When the solvent is a mixture of two alcohols, the alcohols may be present in a mass ratio of 1:2-2:1. In particular, the solvent may be anhydrous, the alcohol being selected from:
isobutanol;
benzyl alcohol;
ethanol;
octanol;
2-butanol;
isopropanol; and
mixtures of any two or more thereof.
More particularly, the solvent may be a mixture of two said alcohols.
The method may include the preliminary step of obtaining the solution of the V
4+
ions and V
5+
ions in the solution by dissolving V
5+
ions in the solvent and reducing a portion of the V
5+
ions to V
4+
ions. Reducing the V
5+
cations to the V
4+
cations may be by using a suitable reducing agent.
Dissolving the V
5+
ions in the solvent may be by admixing vanadium pentoxide (V
2
O
5
) with the solvent. When the solvent is an alcohol and is anhydrous, the reducing agent may be selected from benzyl alcohol, isobutanol or isopropranol, eg so that the solvent and reducing agent are the same alcohol. The reducing may be by refluxing the solution (conveniently at atmospheric pressure), optionally followed by stirring, at a suitable temperature, followed by the precipitation. In particular, the reducing of the V
5+
ions to V
4+
ions may be by means of a reducing agent, the method including refluxing the solvent containing the V
5+
ions dissolved therein with the reducing agent, the solvent and reducing agent optionally being the same alcohol.
The precipitation may be effected by adding phosphate ions to the solution, eg by adding phosphoric acid to the solution.
For the purpose of the reducing, routine experimentation can be employed to determine a suitable reducing agent and to determine a suitable proportion thereof to be used, to determine suitable periods respectively for refluxing and stirring, to determine a suitable stirring temperature, and to determine a suitable refluxing pressure and temperature if refluxing is at a pressure other than atmospheric pressure. After the refluxing has been carried out for a desired period, eg 3-20 hours, preferably 6-15 hours, and the stirring has been carried out for a desired period, eg 12-36 hours, preferably 18-30 hours, to take the reduction to a desired degree of completion, the solution may be cooled to room or ambient temperature, the precipitated complex then being collected and washed and dried, prior to calcining thereof.
Preferably, the calcining is carried out under an inert atmosphere for example under argon, eg in an oven flushed by argon, according to a suitable heating regime. Thus, heating rates, cooling rates, maximum temperature and the temperatures and durations of any temperature holds or plateaus may be determined by routine experimentation, a maximum temperature of 400-500° C., preferably 420-480° C., eg 450° C. being suitable. Thus the calcining may includ

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