Conductive Monolithic Catalysts: Development and Industrial Pilot Tests for the Oxidation of o-Xylene to Phthalic Anhydride

We present herein results from a campaign (>1500 h) of o-xylene oxidation runs in a 1 in. single-tube technical fixed-bed pilot reactor (i.d. = 24.6 mm) loaded with 16 washcoated (V2O5/TiO2) monolithic catalysts with Al honeycomb supports (each 10 cm long) and operated at typical industrial conditions for PA (phthalic anhydride) production. The highly conductive monolithic supports afforded substantially reduced axial T-gradients in comparison with reference runs in the same pilot reactor loaded with conventional egg-shell ring catalyst pellets, the maximum T-difference with the salt bath being halved at the same hot spot temperature (∼440 °C) and the mean bed temperature being about 20 °C higher. Temperature gradients were still moderate at an o-xylene feed concentration of 80 g/Nm3 (at Qair = 4 N m3/h), which represents an upper limit for industrial PA packed-bed reactors loaded with the same V2O5/TiO2 catalyst coated onto ring pellets. Operation at higher o-xylene feed contents (up to 95 g/Nm3) was fou...