Search

Co-refining of fast pyrolysis bio-oil together with fossil oil in existing refinery infrastructure is an attractive and cost-efficient route to conversion of lignocellulosic biomass to transportation fuel. However, due to large differences in properties between the two oils, special notice is needed to reduce process-related issues. Here, fast pyrolysis bio-oil produced from lignocellulosic biomass was co-refined with vacuum gas oil at a 20:80 weight ratio in continuous operation in a pilot-scale slurry hydrocracker in order to investigate the impact of process parameters on product quality and process performance. Mass balances together with product characterization were used to investigate product yields, product composition, and hydrodeoxygenation. Best conversion and hydrodeoxygenation of the fast pyrolysis bio-oil was achieved using an unsupported catalyst loading of 900 ppm Mo with either a low temperature (410 °C) and long residence time (2 h) or higher temperature (435 °C) and shorter residence time (1 h). These settings resulted in about 94% hydrodeoxygenation but also led to highest yield of biogenic carbon to gas phase (40–43 wt %) and lowest yield of biogenic carbon to oil fractions (53–56 wt %) as well as the water fraction (3–5 wt %). Successfully, coke yield remained low at around 0.07–0.10 wt % for all performed runs, which was comparable to the insoluble particle content in the feed due to the presence of particles in the untreated fast pyrolysis bio-oil. Co-processing pyrolysis oil with fossil oil in a slurry hydrocracker seems to be a robust process with regard to coke formation, which should lead to reduced plugging issues compared to fixed bed hydrotreaters. Although this study gives a brief understanding of the effect of process parameters on the processing of fast pyrolysis bio-oil, further research is required to find optimal process parameters and to fully comprehend the possibilities and limitations for production of transportation fuels from fast pyrolysis bio-oil using this technology.

Pyrolysis conditions and the presence of ash-forming elements significantly influence char properties and its oxidation or gasification reactivity. In this study, intrinsic gasification rates of char from high heating rate pyrolysis were analyzed with isothermal thermogravimetry. The char particles were prepared from two biomasses at three size ranges and at two temperatures. Reactivity dependence on original particle size was found only for small wood particles that had higher intrinsic char gasification rates. Pyrolysis temperature had no significant effect on char reactivity within the range tested. Observations of ash formation highlighted that reactivity was influenced by the presence of ash-forming elements, not only at the active char sites but also through prohibition of contact between char and gasification agent by ash layer formation with properties highly depending on ash composition.

Particles filtered out of pyrolysis oil produced through fast pyrolysis of stem wood, willow, reed canary grass, bark, and forest residue were characterized using scanning electron microscopy and energy-dispersive spectroscopy with the aim of identifying particle categories and discussing transport mechanisms of particles and inorganics into the oil. Particles filtered out of both the condensed and the aerosol fractions of the oil displayed three types of morphology: (i) char-like structures (1–15 μm), (ii) spheres (100 nm to 1 μm), and (iii) irregularly shaped residue (50–500 nm). The char-like structures were identified as char. The spheres and irregularly shaped residue shared morphology and composition with tar balls and organic particles with inorganic inclusions. These particles could have formed either during the fast pyrolysis stage or through precipitation from the oil during storage. All particles consisted mainly of C and O but also small amounts of inorganics. The particles from the aerosol fraction of the oil had higher inorganics content than the particles from the condensed fraction. The results were discussed, and suggested transport mechanisms of inorganics into particles were presented.