Fractional Condensation of Biomass Pyrolysis Vapors

In this paper, we have investigated the possibilities to steer the composition and, thus, the quality of pyrolysis liquids by the reactor temperature and the pyrolysis vapor condenser temperature. Pine wood was pyrolyzed in a 1 kg/h fluidized-bed pyrolysis reactor operated at 330 or 480 °C. The pyrolysis vapors produced were condensed using a condenser train of two counter-current spray columns arranged in series. In this paper, the temperature of the first condenser was varied between 20 and 115 °C, while the second condenser temperature was kept at 20 °C. To describe the composition of the oils, we have integrated several analytical techniques into a novel characterization scheme that can account for 77−82 wt % of the oils. The effects of the condensation conditions on fractions of light compounds in the oils can be predicted with a simple equilibrium stage condensation model. It has been observed that pyrolysis at 330 °C gives a light oil with a low amount of mid-boilers [normal boiling point (nbp) of 150−300 °C] and heavy compounds (water insolubles and mono- and oligosugars). Sugars, mid-boilers, and water-insoluble lignin-derived oligomers are more present in the oil obtained at 480 °C, while the yields of light organics are approximately the same for 330 and 480 °C. It can be concluded that fractional condensation is a promising cheap downstream approach to concentrate compounds (classes) and, thus, to control the quality of pyrolysis oils. For instance, operating the first condenser around 70−90 °C gives an aqueous liquid in the second condenser containing 40 wt % light organics, which are interesting for extraction (e.g., 10 wt % acetic acid) and supercritical water gasification to produce hydrogen. Under these conditions, the oils from the first condenser have a high content of sugars (20 wt %) and lignin-derived oligomers (40 wt %), which are attractive fractions for fermentation/sugar chemistry and gasoline production via fluidized catalytic cracking (FCC)/hydrotreatment, respectively.