1. Field of the Invention
The present invention relates generally to producing maleic anhydride and more particularly to shaped catalyst structures containing catalytic material comprised of mixed oxides of vanadium and phosphorus which are useful for the production of maleic anhydride.
2. Background of the Invention
Various shapes for tablets of vanadium and phosphorus catalysts used in the production of maleic anhydride from butane have been described in the literature. For example, U.S. Pat. Nos. 4,283,307 and 5,168,090 describe catalyst tablets of various shapes that are used for the production of maleic anhydride.
One disadvantage of current tablet shapes is that they have relatively low side crush strengths. Side crush strength measures the weight or force needed to break a tablet. The side crush strength is important in catalyst manufacture since it directly impacts the durability of the catalyst during handling, shipment, and installation into a commercial reactor. With all other factors being equal, a catalyst tablet with a higher side crush strength is preferred to one with a lower crush strength.
Another disadvantage of current tablet shapes is that they have relatively high percent attrition. The percent attrition is a measurement (as detailed later) of the amount of catalyst lost to disintegration after subjected to a certain amount of wear and tear. The percent attrition is important in catalyst manufacture since it also directly impacts the durability of the catalyst during handling, shipment, and installation into a commercial reactor. With all other factors being equal, a catalyst tablet with a lower percent attrition is preferred to one with a higher percent attrition.
Catalyst tablets with lower crush strength and higher attrition tend to produce more broken catalyst tablets and more catalyst fines during handling, shipment, and installation into a commercial reactor. These broken catalyst pellets and catalyst fines create increased pressure drop in the commercial reactor tubes during normal operation and are thus undesirable.