The research of gasification/steam reforming of pyrolysis oil was initiated by the National Renewable Energy Laboratory (NREL) in the USA. In the nineties of the twentieth century, NREL published the first results30 on steam reforming of acetic acid (HAc) and hydroxyacetaldehyde (HAA) with the aim to produce hydrogen. HAc and HAA were chosen as model compounds because they represent a part of the pyrolysis oil, which was identified as a possible renewable biomass chemical and energy carrier. A fixed bed microreactor was used to convert the model compounds using grounded commercial catalysts (G-90C and C18HC from United Catalysts Inc.). The thermal stability of the compounds was given as an indicator for coke formation. Both HAc and HAA were catalytically converted to hydrogen-rich gas at a reactor temperature of ~700°C (for HAA a lower inlet temperature was chosen) and a steam over carbon ratio (S/C) > 2. Further tests with model compound reforming,31,32 including the vapors of cellulose, xylan and lignin, spraying of glucose, xylose and sucrose onto a fixed catalytic bed in combination with catalyst screening ultimately led to the first actual reforming of the aqueous soluble phase of pyrolysis oil.33

Two commercial naphtha/C2-C3 steam reforming catalysts (UCI G90C and the ICI 46-series) showed very promising results in their ability to convert the aqueous soluble phase of pyrolysis oil with only minor coking at high steam over carbon ratios (20-30).33 However, an increase of methane concentration during a test could be observed. To feed the aqueous soluble phase of pyrolysis oil, adjustments had to be made to the atomizer system in order to directly add the reactant to the catalytic bed. With the improvement of the feeding system, fixed bed reforming of the aqueous soluble phase of pyrolysis oil was still limited to 3-4 hours of operation due to carbonaceous deposits on the catalyst and in the freeboard.34 To overcome this run time barrier, the reactor bed was changed from a fixed to a bubbling fluidized bed where the commercial catalyst was grounded to a particle size of 300-500 pm. A different catalyst than the ones used before, namely the naphtha reforming catalyst C11-NK from Sud-Chemie, was now being used. The liquid feed was added to the reactor via an externally water cooled atomizer system which was either vertically or horizontally placed.16,34 The aqueous pyrolysis oil fraction was reformed in the fluidized bed.

Besides catalyst attrition (5%/day), also some catalyst deactivation was observed leading to a rising methane concentration which leveled off at roughly

1.5 vol%. Additionally, methane co-reforming experiments were done where, at co-reforming conditions, two times less unconverted methane was observed than when only methane was being steam reformed.

Steam reforming of the whole pyrolysis oil was done by Van Rossum et al. in a bubbling fluidized bed using both a dedicated35 and commercial reforming catalyst.36 Initially, a methane free syngas was being produced but in time the methane content increased till it reached the production level of noncatalytic pyrolysis oil gasification. The catalysts activity was then limited to enhancing the water gas shift reaction, coke/char gasification and some pre-reforming activity for C2-C3 hydrocarbons. The catalyst showed, similar to the catalyst used by the NREL, high levels of attrition.

Because the chemical mechanism of steam reforming oxygenated compounds is different37 than methane and naphtha, many research groups have been trying to develop new catalyst formulations using model compounds of pyrolysis oil and the aqueous phase of pyrolysis oil to produce hydrogen and synthesis gas while minimizing coke formation. The details of these investigations are beyond the scope of this chapter. Interested readers are referred to the following publications: Refs. 38, 39, 40, 41, 42, 43 and 44.