Gasification of pyrolysis oil was studied in a fluidized bed over a wide temperature range (523−914 °C) with and without the use of nickel-based catalysts. Noncatalytically, a typical fuel gas was produced. Both a special designed fluid bed catalyst and a crushed commercial fixed bed catalyst showed an initial activity for syngas (H2 and CO) production at T > 700 °C. However, these catalysts lost activity irreversibly and elutriation from the fluid bed occurred. The equilibrium catalytic activity suffered from incomplete reforming of hydrocarbons (CH4). In all the experiments the carbon to gas conversion was incomplete, which was mainly caused by the formation of deposits and the slip of microcarbonaceous particles. A two-stage reactor concept, which consisted of a sand fluidized bed followed by a fixed catalytic bed, was proposed and tested. This system uncouples the atomization/cracking of the oil and the catalytic conditioning of the produced gases, enabling protection of the catalyst and creating opportunities for energy efficiency improvements. In a bench scale unit of this reactor (0.5 kg oil/h), methane and C2−C3 free syngas (2.1 Nm3 CO + H2/kg dry oil, H2/CO = 2.6) with a low tar content (0.2 g/Nm3; dry, N2 free gas) was produced in a long duration test (11 h).

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The evaporation of pyrolysis oil was studied at varying heating rates (∼1–106°C/min) with surrounding temperatures up to 850°C. A total product distribution (gas, vapor, and char) was measured using two atomizers with different droplet sizes. It was shown that with very high heating rates (∼106°C/min) the amount of char was significantly lowered (∼8%, carbon basis) compared to the maximum amount, which was produced at low heating rates using a TGA (∼30%, carbon basis; heating rate 1°C/min). The char formation takes place in the 100–350°C liquid temperature range due to polymerization reactions of compounds in the pyrolysis oil. All pyrolysis oil fractions (whole oil, pyrolytic lignin, glucose and aqueous rich/lean phase) showed charring behavior. The pyrolysis oil chars age when subjected to elevated temperatures (≥700°C), show similar reactivity toward combustion and steam gasification compared with chars produced during fast pyrolysis of solid biomass. However, the structure is totally different where the pyrolysis oil char is very light and fluffy. To use the produced char in conversion processes (energy or syngas production), it will have to be anchored to a carrier. © 2010 American Institute of Chemical Engineers AIChE J, 2010

The liquefaction of lignocellulosic biomass is studied for the production of liquid (transportation) fuels. The process concept uses a product recycle as a liquefaction medium and produces a bio-oil that can be co-processed in a conventional oil refinery. This all is done at medium temperature (≈ 300 °C) and pressure (≈ 60 bar). Solvent-screening experiments showed that oxygenated solvents are preferred as they allow high oil (up to 93% on carbon basis) and low solid yields (≈ 1-2% on carbon basis) and thereby outperform the liquefaction of biomass in compressed water and biomass pyrolysis. The following solvent ranking was obtained: guaiacol>hexanoic acid ≫ n-undecane. The use of wet biomass results in higher oil yields than dry biomass. However, it also results in a higher operating pressure, which would make the process more expensive. Refill experiments were also performed to evaluate the possibility to recycle the oil as the liquefaction medium. The recycled oil appeared to be very effective to liquefy the biomass and even surpassed the start-up solvent guaiacol, but became increasingly heavy and more viscous after each refill and eventually showed a molecular weight distribution that resembles that of refinery vacuum residue.

Lignocellulosic feedstock can be converted to bio-oil by direct liquefaction in a phenolic solvent such as guaiacol with an oil yield of >90 C% at 300–350 °C without the assistance of catalyst or reactive atmosphere. Despite good initial performance, the liquefaction was rapidly hindered by the formation of heavy components (molecular weight > 1000 Da), which increased the viscosity of the bio-oil upon recycling the bio-oil or a fraction of it as a liquefaction solvent. This paper explores the possibility to minimize the production of this undesirably heavy fraction by optimizing the process parameters such as temperature, heating rate, reaction time, and concentration of water. This study allowed us to find a compromise between maximizing the bio-oil yield and minimizing its heavy fraction. It also provides insight onto the reaction network of the liquefaction reaction, showing for instance that all product fractions, including the heaviest products and the char, are mainly direct liquefaction products rather than secondary reaction products, e.g. from bio-oil recondensation. However, the resulting heavy fraction is still too high to allow effective recycling of the bio-oil. Complementary approaches need to be investigated.