Catalytic Partial Oxidation of Iso-octane over Rh/α-Al₂O₃ in an Adiabatic Reactor: An Experimental and Modeling Study

Catalytic partial oxidation (CPO) of hydrocarbons represents an interesting technology for hydrogen production on mobile systems. We investigated the CPO of 2,2,4-trimethyl pentane (iso-octane), chosen as surrogate for gasoline. CPO experiments were carried out in a laboratory scale autothermal reformer with honeycomb monolith catalysts (2% Rh/α-Al₂O₃), equipped with probes for spatially resolved measurements of temperature and concentration. The iso-octane CPO process follows a reaction pathway which mainly consists of the exothermic combustion reaction and the endothermic steam reforming. The chemical reaction is very fast, and sharp gradients of temperature and concentration establish at the catalyst inlet. Similarly to the CPO of light hydrocarbons, the consecutive reaction mechanism results in the formation of a hot spot of temperature at the catalyst inlet. However, compared to light hydrocarbons, this phenomenology is specifically emphasized in the case of iso-octane, because of the higher overall exothermicity and the lower diffusion rate, which limits the steam reforming reaction rate. The reactor design strategy previously suggested in the CPO of methane, based on the enlargement of the channel opening to selectively limit the rate of oxygen consumption, does not work for the CPO of iso-octane where the consumption of the fuel is also considerably limited by mass transfer

Sustainable Hydrogen Production via Sorption Enhanced Reforming of Complex Biorefinery Side Streams in a Fixed Bed Adiabatic Reactor

In this work, sorption enhanced steam reforming is explored as a potential solution for the valorization of gaseous streams recovered from biorefinery hydrogenation processes. The hydrogen content of such streams limits the hydrocarbon conversion in conventional steam reforming due to thermodynamic and kinetic constraints. A previously developed 1D dynamic heterogeneous model of an adiabatic reactor was thus applied to evaluate the effect of H2 dilution on the performance indicators of the sorption enhanced reforming process. The mathematical model analysis highlights that despite of CO2 capture by the sorbent favorably modifies the thermodynamics of syngas production, H2 dilution worsens the performance of the sorption enhanced reforming of model H2/CH4 streams with respect to pure CH4. Results show a drop of 17% for CH4 conversion and a reduction of 15.4% of the captured CO2 on passing from pure methane to a H2/CH4 feed with a 40/60 molar ratio. However, on increasing the heat capacity of the bed, by replacing part of the sorbent with an inert heat carrier, better performances are calculated for the H2/CH4 feed matching the pure CH4 case. The presence of C2+ hydrocarbons is assessed as well and the results show a significant improvement in the reformer’s performance; in the case of a stream composed of H2/CH4/C3H8 with a molar ratio 40/45/15, the total hydrocarbon conversion grows to 92.8%, CO2 capture ratio to 82.6%, and H2 purity to 95.6%. The positive effect is associated with thermal factors that promote the reaction kinetics. Thus, the suitability of the sorption enhanced reforming technology to H2-rich and C-poor streams is strictly composition dependent; by cofeeding of C2+ hydrocarbons, the process turns into a remarkable solution for converting gaseous streams in pure H2