Hydrogen production via reforming of pyrolysis oil aqueous fraction

Abstract

Increase in energy demands and the need of new and renewable energy sources pushes the development of biomass utilization. One of the new emerging interests is hydrogen production from pyrolysis oil aqueous fraction using catalytic steam reforming. Although it is known firstly as a source of valuable chemicals and sugars, hydrogen production via reforming is indicated to be the most cost-effective way for utilizing pyrolysis oil aqueous fraction. The literature review revealed that wide range of catalysts and process conditions have been tested and main challenges revolved around catalyst stability, feeding system and reactor design. Based on the stability issue, oxidative steam reforming and testing of different types and combinations of reforming catalysts was chosen as a topic of the experimental part master’s thesis.

In the experimental part, oxidative steam reforming of pyrolysis oil aqueous fraction from condenser unit in fast pyrolysis of forest thinning was tested using three different catalysts and catalyst combination and four different oxygen concentrations —represented by different O/C ratios. The experiments were carried out in a fixed bed steel reactor with process conditions set up as reaction temperature of 650oC, atmospheric pressure and S/C of 3.84. It was found that combination of zirconia monolith as pre-reformer and commercial nickel catalyst (Reformax) to be the best catalyst combination that enhanced the stability of carbon-to-gas conversions and hydrogen production. With this combination, the carbon-to-gas conversions remained above 80% for 4 hours and hydrogen productions above 70% in any O/C ratio used. This catalyst combination also showed role in suppressing the rate of C2 formation side reactions. It was also found that increase of oxygen fed into in the system benefited to create more stable carbon-to-gas conversions and hydrogen production profiles. The observed main problem with the experiments was carbon coking at the top of the reactor as a result of feed depolymerisation and decomposition during the spraying process.