Peter Geoffrey Gray

The reformer lineout phenomenon and its fundamental importance tocatalyst deactivation

Abstract The transient kinetic behaviour of a fresh or pre-sulphided catalystbrought on-line, which is termed ‘lineout’, is found to be due to an initial deposition of coke on the metal sites of the catalyst (~ 1 wt %), the quantity of this deposition being essentially constant over the length of reformer operation. The coke deposition during long term reformer operation (~ 20 wt %) is found to be on the alumina; however the observed deactivation in octane yields is due to the change in nature of coke (gradual graphitization) on the metal sites of the catalyst. Thus two types of coke on the metal sites are distinguished, one being easily removed by hydrogen (reversible coke), and the other less readily removed (irreversible coke). The quantity of irreversible coke is increased by operation at high temperatures and/or low pressures. Mechanisms of coking are given and it is shown that catalyzed hydrogenation and hydrogasification limit metal site catalyst deactivation. These coke removal mechanisms are discussed in detail and a model is developed to predict the unsteady coking during lineout and the graphitization behaviour at longer times.

CHARACTERIZATION OF TITANIUM PHOSPHATE AS ELECTROLYTES IN FUEL CELLS

Titanium phosphate is currently a promising material for proton exchange membrane fuel cells applications (PEMFC) allowing for operation at high temperature conditions. In this work, titanium phosphate was synthesized from tetra iso-propoxide (TTIP) and orthophosphoric acid (H3PO4) in different ratios by a sol gel method. High BET surface areas of 271 m2.g-1 were obtained for equimolar Ti:P samples whilst reduced surface areas were observed by varying the molar ratio either way. Highest proton conductivity of 5.4×10-2S.cm-1 was measured at 20°C and 93% relative humidity (RH). However, no correlation was observed between surface area and proton conductivity. High proton conductivity was directly attributed to hydrogen bonding in P-OH groups and the water molecules retained in the sample structure. The proton conductivity increased with relative humidity, indicating that the Grotthuss mechanism governed proton transport. Further, sample Ti/P with 1:9 molar ratio showed proton conductivity in the order of 10-1 S.cm-1 (5% RH) and ~1.6×10-2S.cm-1 (anhydrous condition) at 200°C. These proton conductivities were mainly attributed to excess acid locked into the functionalized TiP structure, thus forming ionisable protons.