Catalyst-precursor for the production of maleic acid anhydride and method for the production thereof
A process for preparing a vanadium, phosphorus, and oxygen catalyst precursor for preparing maleic anhydride by heterogeneously catalyzed gas-phase oxidation of a hydrocarbon having at least four carbon atoms, which comprises (a) reacting vanadium pentoxide with from 102 to 110% strength phosphoric acid in the presence of a primary or secondary, noncyclic or cyclic, unbranched or branched, saturated alcohol having from 3 to 6 carbon atoms in a temperature range from 80 to 160° C.; (b) isolating the precipitate formed; (c) setting an organic carbon content of ≦1.1% by weight in the isolated precipitate by heat treatment in a temperature range from 250 to 350° C., the heat-treated product, following the addition of 3.0% by weight of graphite, giving a powder X-ray diffraction diagram which in the 2θ region features a ratio of the height of the peak of any pyrophosphate phase present at 28.5° to the height of the peak due to the graphite at 26.6° of ≦0.1; and (d) shaping the heat-treated product obtained from step (c) into particles having an averaged diameter of at least 2 mm; a catalyst precursor obtainable from this process; a process for preparing a catalyst from the catalyst precursor; a catalyst obtainable from that process; and also a process for preparing maleic anhydride over that catalyst.
1. A process for preparing a vanadium, phosphorus, and oxygen catalyst precursor for preparing maleic anhydride by heterogeneously catalyzed gas-phase oxidation of a hydrocarbon having at least four carbon atoms, which comprises
(a) reacting vanadium pentoxide with from 102 to 110% strength phosphoric acid in the presence of a primary or secondary, noncyclic or cyclic, unbranched or branched, saturated alcohol having from 3 to 6 carbon atoms in a temperature range from 80 to 160° C.;
(b) isolating the precipitate formed;
(c) setting an organic carbon content of ≦1.1% by weight in the isolated precipitate by heat treatment in a temperature range from 250 to 350°, the heat-treated product, following the addition of 3.0% by weight of graphite as internal standard and using CuKα radiation (λ=1.54·10 −10 m), giving a powder X-ray diffraction diagram which in the 2θ region features a ratio of the height of the peak of any pyrophosphate phase present at 28.5° to the height of the peak due to the graphite at 26.6° of ≦0.1; and
(d) shaping the heat-treated product obtained from step (c) into particles having an averaged diameter of at least 2 mm.
2. A process as claimed in claim 1 , wherein heat treatment in step (c) is conducted at from 270 to 340° C.
3. A process as claimed in claim 1 , wherein an organic carbon content of ≦0.8% by weight is set in step (c).
4. A process as claimed in claim 1 , wherein the heat-treated product from step (c), following the addition of 3.0% by weight of graphite as internal standard and using CuKα radiation (λ=1.54·10 −10 m), gives a powder X-ray diffraction diagram which in the 2θ region features a ratio of the height of the peak of any pyrophosphate phase present at 28.5° to the height of the peak due to the graphite at 26.6° of 0.05.
5. A process as claimed in claim 1 , wherein particles of substantially hollow cylindrical structure are shaped in step (d).
6. A process as claimed in claim 1 , wherein said primary or secondary, noncyclic or cyclic, unbranched or branched, saturated alcohol having from 3 to 6 carbon atoms is isobutanol.
7. A catalyst precursor for preparing maleic anhydride by heterogeneously catalyzed gas-phase oxidation of a hydrocarbon having at least four carbon atoms, obtainable as claimed in claim 1 .
8. A process for preparing a vanadium-phosphorus-oxygen catalyst for preparing maleic anhydride by heterogeneously catalyzed gas-phase oxidation of a hydrocarbon having at least four carbon atoms by treating a vanadium, phosphorus, and oxygen catalyst precursor in at least one atmosphere comprising oxygen (O 2 ), hydrogen oxide (H 2 O), and/or inert gas in a temperature range from 250 to 600° C., which comprises using a catalyst precursor as claimed in claim 7 .
9. A catalyst for preparing maleic anhydride by heterogeneously catalyzed gas-phase oxidation of a hydrocarbon having at least four carbon atoms, obtainable as claimed in claim 8 .
10. A process for preparing maleic anhydride by heterogeneously catalyzed gas-phase oxidation of a hydrocarbon having at least four carbon atoms with oxygenous gases, which comprises using a catalyst as claimed in claim 9 .