Thermal Behavior of Pyrolysis Oil-Diesel Oil Emulsion in Evaporating Micronic Droplets

The transformations thermally induced in emulsion 70/30 w/w diesel oil/pyrolysis oil droplets of 82?m have been studied. This was possible by thanks to the application of the Generalized Scattering Imaging laser technique for determining simultaneously size and optical properties of emulsion droplets. Arrays of calibrated droplets of emulsion were injected in pre-heated air flow inside a tubular reactor. Four thermal regimes were analyzed: room temperature, 150°C, 250°C and 350°C. For comparison, droplets of the same diesel oil used to form the emulsion were studied in identical experimental conditions. During heating, the emulsion droplets suffer progressive depletion of the diesel oil phase. The pyrolysis oil, dispersed in the diesel oil matrix in the form of microdroplets 2?m sized, undergoes partial evaporation, liquid phase pyrolysis and polymerization. The formation of heavier compounds in the pyrolysis oil microdroplets was inferred by measuring the increase of absorption of the droplets. Due to the depletion of the diesel oil matrix, the concentration of pyrolysis oil microdroplets increases with the temperature. At 350°C almost the totality of diesel oil is evaporated and the pyrolysis oil microdroplets dispersed in an emulsion droplet coalesce to form one single droplet. These residual droplets showed a very narrow size distribution and absorption greater than the original PO in agreement with the fact that they represent the outcome of combined evaporation, liquid phase pyrolysis and polymerization of the pyrolysis oil. Sample of residual droplets were also captured at the exit of the reactor and analyzed by means of optical microscopy. The microscope analysis was consistent with the laser diagnostic results.