The conversion of biomass to fuels at 100 to 250 oC is the first stage of pyrolysis, 300-600 is the medium whereas 600-1000 oC is the final and high temperature pyrolysis.
You can find detail information in my article: Alma, M. H., Salan, T., & Temiz, A. (2016). A novel approach for the liquefaction of wood powder: usage of pyrolytic bio‐oil as a reaction medium. International Journal of Energy Research, 40(14), 1986-2001.
It was extensively reported in the literature that the thermal decomposition of the wood biopolymers started at about 280 °C with the generation of active cellulose via the exothermic degradation under the inert atmosphere. At the higher temperatures (e.g., 350 °C - 550 °C), the longer chains of the biopolymers were broken down via primary phase decomposition and secondary phase cracking reactions into smaller fragments, which were condensable (i.e., tars and oils) and non-condensable pyrolytic vapors, and solid charcoal. The low temperatures resulted in the high amount of char while the higher temperatures promoted a significant amount of bio-oil production. Moreover, the temperatures elevated to 700 °C enhanced the formation of non-condensable gasses, which affected the proportion of bio-oil enormously. Hence, the yield and content of these three main products of the pyrolysis varied significantly depending on the process temperature. The increasing cleavage of the bonds of C-H, O-H, C-O, C-N and N-H in the functional groups of the main wood polymers into non-condensable gasses (e.g., carbon monoxide and hydrogen) at an elevated temperature of 600 °C.
Dear Abdul,
From my observation of recent in dealing with biomass of different types apart from literature . Generally, the temperature range given in your question might not be observable as we have unbounded moisture loss and evaporation taking place below 150 degrees C. Moisture loss and light volatile matter content often occur at the reactive drying stage where biomass will be unable to return to its original stage (150-220 degrees C thereabout). After which hemicellulose will begin to decompose at 220 degrees and above with partial degradation of lignin. So biochar produced at this point will still be with low energy density, high C-O and H-O bonds and the grindability will be low. However, going to 300- 600 degrees C, you might have had complete decomposition of your biomass polymers even lignin where in the formation of condensable gases becomes prominent. For biochar with high energy density and low volatiles, you can obtain that with this stage but with lower mass and energy yield.
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