AUTOTHERMIC CATALYTIC REACTOR WITH FLAT TEMPERATURE PROFILE FOR THE PRODUCTION OF HYDROGEN FROM LIGHT HYDROCARBONS

摘要

The present invention relates to the make of a heterogeneous gas-solid catalytic reactor operated in autothermic conditions, but characterised by a flat temperature profile, to be used in the distributed production of hydrogen, obtained by catalytic conversion of light hydrocarbons, air and water. The autothermic reactor (ATR) as a whole consists of a central zone where the structured catalyst is positioned, of a zone where the reactants, pre-heated beforehand by the effluent gases of the reactor, meet up and mix, and of two heat exchangers for recovering the sensitive heat of output gases by the cold reactants. This system configuration allows feeding the reactor directly with cold reactants at room ambient temperature, in particular with water in liquid phase, which is vaporised and heated directly by the sensitive heat of the reaction products. The operating conditions of the reactor in terms of temperature are clearly fixed by the choice of the feeding ratios O2/C(x), H2O/C(y) and by spatial velocity (GHSV). Typical values of feeding ratios fall within the ranges 0.3-1 and 0.5-2, respectively for x and y, whereas spatial velocity is comprised between 10000 and 200000 h-1, corresponding to contact times variable within the range 20-400 thousandths second. Generally, in typical ATR reactors used industrially, temperature profiles in the catalytic bed are characterised by large gradients between the inlet and the outlet section (usually even higher than 200°C). The forming of such gradients is due to at least three factors that operate in a concurrent manner. In fact, the first factor is related to the intrinsic mechanism by which the autothermic reforming reaction takes place on the catalyst surface, a second one to the typical features of bad heat conductors of the catalyst supports normally used, and the third one to the fluid-dynamic conditions that set in the catalytic bed, typically consisting of packed particles. This invention concurrently uses three actions aimed at limiting the negative effects of the three factors listed above, in order to obtain the temperature profile flattening so as to optimise the operation of the ATR reactor both in terms of energy and of catalytic activity. In particular, the proposal relates to the following three actions: 1. the adoption of a specifically formulated catalyst so as to favour a "direct type" reaction mechanism, as opposed to commonly used catalysts that operate through an indirect mechanism 2. the use and the make of the catalyst on a structured support with a high porosity and tortuosity, and characterised by a high thermal conductivity such as fecralloy and/or silicon carbide coated with noble elements inserted in a chemical structure of the perovskite type with formula BaZr1-x(noble Metal) XO3. 3. the adoption of a radial flow geometry catalytic bed rather than axial, so as to locally optimize the contact time in the catalytic bed.