Sustainable hydrogen production via reforming of bio-oil using a novel spouted bed reactor
Sustainable process-product development & green chemistry
Sustainable & Clean Technologies - IIb: Energy Production (T1-5b)
Keywords: hydrogen, bio-oil, reforming, spouted bed reactor
Pollution of the environment due to the use of conventional fuels, in conjunction with the concern for the depletion of oil reserves, necessitates the intensification of research for alternative energy sources. Hydrogen is emerging as the energy carrier of the future since it can be used as a clean transport fuel as well as a means for the production of electricity via fuel cells. It is thus appearing as an attractive selection for sustainable development. Necessary requirement is to produce hydrogen from renewable energy sources, such as biomass, so as not to cause additional CO2 emissions to the environment. Reforming of the aqueous phase of bio-oil is one of the promising routes for the production of renewable hydrogen. One of the major hurdles to be overcome is the elimination of coke formed via thermal and/or catalytic reactions [1,2]. The design of a proper reactor in combination with active catalytic materials is the key component for the successful development of the process.
In the current work we present the experimental results of reforming of bio-oil using a novel spouted bed reactor. The particular type of reactor is characterized by the short residence time of the gas phase and the almost perfect mixing of the catalytic particles. Immediate mixing of catalyst and bio-oil is achieved using a properly designed nozzle that enables the injection of the liquids in small droplets that contact and react rapidly with the solid particles. The first phase of the experimental work was carried out in a pilot scale unit using ethylene glycol as a model compound. Parameters investigated were temperature, H2O/C ratio in the feed and the space velocity of reactants. Experiments were conducted in the presence of sand, olivine and a Ni/Olivine catalyst.
The thermal decomposition of ethylene glycol was investigated by loading the reactor with inert sand (SiO2). Runs were conducted in the absence and presence of steam. In the entire range of conditions studied, the main gaseous products were CO, CO2, CH4 and Η2. The presence of steam did not influence noticeably the selectivity of products or the total conversion, proving that the thermal decomposition of ethylene glycol dominates with catalytic actions totally absent. The production of coke was especially limited demonstrating the rapid and effective mixing of solid particles and reactants achieved using the spouted bed reactor. Increase of temperature from 650 C to 850 C led to an increase of ethylene glycol conversion to gases from 55% to 85%. Hydrogen yield compared to the maximum possible for the case of full reforming was very low fluctuating at 10-15%. The highest percentage of hydrogen was lost bound in CH4 and the liquid compounds produced.
A relative improvement was observed upon loading the reactor with olivine ((Mg,Fe)2SiO4), a mineral known for its mechanical strength. At equivalent conditions to the experiments using sand and in the presence of steam, carbon to gas conversion of ethylene glycol increased from 70% at 650 C to 95% at 850 C. Hydrogen yield at the highest temperature reached 35%. This increase in hydrogen production is not only due to the increased conversion but also due to the lower selectivity in CH4 compared to the experiments with sand. The presence of metals, Fe (5 wt%) and Ni (0.5 wt%) in olivine, explain this rise in hydrogen yield. Coke deposition on olivine was low averaging at 0.15 wt% of the bed for a typical experiment, percentage equivalent to 0.5 wt% of the total incoming carbon. The addition of oxygen in the feed in a ratio equal to Ο2/C=0.1 led virtually to complete elimination of carbonaceous deposits and a slight increase in carbon to gas conversion, without causing a noticeable difference in hydrogen yield.
Preliminary catalytic results over Ni/Olivine are especially promising. Conversion of ethylene glycol to gaseous products was complete for temperatures higher than 650 C. The yield in hydrogen was much higher as well, reaching 80% at 850 C, while thermodynamic equilibrium predicts at these conditions a yield equal to 85%. Coke generation in spite of the much higher space velocity used was practically nil (~0,02 wt% of the bed after 6h TOS). The suitability of the reactor for the successful reforming of bio-oil will be further investigated by conducting tests in a wide range of operating conditions, types of catalyst and model compounds of bio-oil and will conclude with the use of actual bio-oil.
References
1. Wang D., Czernik S., Chornet E., Energy & Fuels, 1998, 12, 12-19.
2. Kechagiopoulos P., Voutetakis, S., Lemonidou, A., Vasalos, I., Energy & Fuels, 2006, 20, 2155-2163.
See the full pdf manuscript of the abstract.
Presented Wednesday 19, 11:00 to 11:20, in session Sustainable & Clean Technologies - IIb: Energy Production (T1-5b).
