Multilayer catalytic bed for the partial oxidation of n-butane to maleic anhydride
A catalytic bed for the partial oxidation of n-butane to maleic anhydride which comprises at least one first catalytic layer and at least one second catalytic layer, wherein each catalytic layer consists of a vanadium and phosphorus mixed oxide (VPO) catalyst and only the catalyst of the second catalytic layer further comprises tungsten, and wherein the second catalytic layer constitutes 25% to 45% of the total length of the catalytic bed and is arranged consecutively after the first catalytic layer along the direction in which the mixture of gases comprising the oxidation reagents flows. The present invention also relates to a process for producing maleic anhydride by partial oxidation of n-butane which uses the catalytic bed.
1. A catalytic bed for the partial oxidation of n-butane to maleic anhydride comprising a first catalytic layer and a second catalytic layer, wherein
the first catalytic layer and the second catalytic layer consist of a vanadium and phosphorus mixed oxide (VPO) catalyst comprising vanadyl pyrophosphate (VO) 2 P 2 O 7 as main component and only the VPO catalyst of the second catalytic layer further comprises tungsten,
the second catalytic layer constitutes 25% to 45% of the total length of the catalytic bed and is arranged consecutively after the first catalytic layer, so that a mixture of gases comprising n-butane and oxygen flows first through the first catalytic layer and then through the second catalytic layer, and
the VPO catalyst of the second catalytic layer comprises tungsten in an amount corresponding to an atomic ratio of vanadium to tungsten between 250:1 and 60:1.
2. The catalytic bed according to claim 1 , wherein the second catalytic layer constitutes 36% of the total length of the catalytic bed.
3. The catalytic bed according to claim 1 , wherein the VPO catalyst of the second catalytic layer comprises tungsten in an amount corresponding to an atomic ratio of vanadium to tungsten of 100:1.
4. The catalytic bed according to claim 1 , wherein the VPO catalyst of at least one of the first catalytic layer and the second catalytic layer further comprises at least one promoter element selected from the group consisting of magnesium, manganese, iron, cobalt, nickel, niobium, molybdenum, lanthanum, cerium, and bismuth.
5. The catalytic bed according to claim 4 , wherein the at least one promoter element is bismuth.
6. The catalytic bed according to claim 1 , wherein:
the catalytic bed consists of the first catalytic layer and the second catalytic layer;
the second catalytic layer constitutes 25% to 45% of the total length of the catalytic bed;
the VPO catalyst of the second catalytic layer comprises tungsten in an amount corresponding to an atomic ratio of vanadium to tungsten of 100:1; and
the VPO catalyst of the first catalytic layer and the VPO catalyst of the second catalytic layer further comprise bismuth.
7. The catalytic bed according to claim 6 , wherein the second catalytic layer constitutes 36% of the total length of the catalytic bed.
8. The catalytic bed according to claim 1 , wherein the VPO catalyst of the first catalytic layer and the VPO catalyst of the second catalytic layer have, independently of each other, a phosphorus/vanadium atomic ratio between 1:1 and 1.8:1.
9. The catalytic bed according to claim 8 , wherein the VPO catalyst of the first catalytic layer and the VPO catalyst of the second catalytic layer have, independently of each other, a phosphorus/vanadium atomic ratio between 1.1:1 and 1.6:1.
10. A process for the production of maleic anhydride by partial oxidation of n-butane, comprising the step of feeding in a reactor a mixture of gases comprising n-butane and oxygen in the presence of a catalytic bed according to claim 1 .
11. The process according to claim 10 , wherein the mixture of gases comprises n-butane at a concentration from 1.65 to 1.95 mol %.