Investigation Of Hydrogen Production From Steam Reforming Of Bio-oil And Catalytic Deactivation By Carbon Deposition

Hydrogen energy has attracted much attention in industrial countries as a kind of clean energy or energy carrier. More financial resources have been put in the area of hydrogen energy research and development. Renewable energy sources are environmental friendly and can significant reduce the green house CO2 emition. Compared with biomass itself, bio-oil from biomass pyrolysis has much higher energy density and can be easily collected, stored and transported. It can be facilely collected from scattered areas and transported to produce hydrogen intensively. Now catalytic steam reforming of bio-oil for hydrogen production is proven an economically feasible method. In this paper, Ni based catalysts used in steam reforming of bio-oil were prepared, the catalyst performance was studied, and the carbon deposition model of catalyst was set up.In this study, Ni was selected as the active metal and Al2O3 as support based on the consideration. Some additives such as MgO,La2O3 were intruduced to improve the catalytic performance. Ni-based catalyst was prepared using impregnation method. The optimal catalyst preparation conditions can be concluded as:Ni content of 18%, calcination temperature of 850℃, and calcination time duration of 6h.Thermodynamic analysis was carried out based on steam reforming of butanol via Gibbs free energy minimization method. Complete conversion of butanol can produce high quality hydrogen. Operation parameters were S/B value, temperature and pressure. The optimal reaction conditions can be concluded as:pressure 0.1 MPa, temperature 600-800℃, and S/B= 9-12. Under these conditions, hydrogen yield can be maximized to 74.93%-80.96% with the methane yield keeping the lowest level and the CO selectivity of 45.01%-51.98%.The intrinsic kinetics characteristics of acetic acid (selected as model bio-oil) steam reforming were studied in fixed-bed with Ni/MgO-La2O3-Al2O3. Dynamic model parameters were calculated using MATLAB software. The power function of dynamic model were lined firstly during regression. Then, kinetic parameters were estimated by regress () function for multi-variable linear regression methods. The kinetic model parameters were directly simulated by non-linear fitting with lsqnonlin().The dynamic model was established to reveal the kinetic characteristics, and to provide an important theoretical basis for the selection of reactor, simulation, amplification, optimizing technology and catalyst design.The prepared Ni-based catalysts were applied in steam reforming different bio-oil model compounds such as acetic acid, butanol, furfural, adipinketone and m-cresol. The results showed that support played important role in reforming efficiency. Hydrogen yield increased by adding MgO and La2O3. The catalyst activity can be showed in the following order: Ni/MgO-La2O3-Al2O3> Ni/MgO-Al2O3 - Ni/La2O3-Al2O3> Ni/Al2O3. With using mixture model compounds as feedstock, the catalyst Ni/MgO-La2O3-Al2O3 showed the optimal precessing parameters of the reaction temperature 750-850℃, S/C 5-9, and LHSV 1.5-2.5 h-1. Under this reaction condition, the maximum hydrogen yield of 88.14% can be achieved.Fixed-bed reactor and fluidized-bed reactor were investigated in the steam reforming of bio-oil to H2 with using Ni/MgO-La2O3-Al2O3 as catalyst, respectively. The results indicated that the optimal reaction conditions for fixed-bed reactor can be concluded as:temperature 750-850℃, S/C 7-12, and WHSV 0.8-1.5 h-1. The maximum hydrogen yield was 68.27%. And for fluidized-bed reactor, the optimal reaction conditions were temperature 700-800℃, S/C 15-20, and WHSV 0.5-1.0 h-1. The maximum hydrogen yield was 75.88%. Fixed-bed reactor required higher temperature (100℃higher) than that for fluidized-bed for the steam reforming. However, the fluidized-bed required higher S/C. LHSV for fluidized-bed reactor was lower. And the hydrogen yield obtained by fluidized-bed reactor was 7% higher than that for fixed-bed.The deactivation mechanism of Ni based catalyst was analyzed dependent of the steam reforming of bio-oil, and the apparent carbon deposition rate equation can be builded as follows:The activity energy of carbon deposition E1=28 kJ/mol, which was relatively lower. The activity energy of carbon elimination E2=71 kJ/mol.