Although biocrude from HTL of algae offers better elemental ratios compared to lignin based fuels (Patel and Hellgardt, 2013), the oxygen and nitrogen content is still problematic. Biocrude with high N cannot be blended with R1530 crude unless an additional denitrogenation step is added prior to blending, resulting in additional costs. Catalytic deoxygenation or hydrotreating is also necessary to improve fuel quality, but the presence of nitrogen heterocycles, as identified by GC–MS usually causes catalyst poisoning making denitrogenation challenging.
3.4. Molecular weight analysis – SEC
SEC analysis of the biocrude samples shows the average molecular weight of the compounds present in the oil. Supplementary Information 1 – Fig. 3 infers that processing condition has a noticeable, but not significant impact on the average molecular weight of the species present in the biocrude. At reaction condition of 380 °C and 4 min, the average Mw of 200 is detected. For all other analysed biocrudes, a Mw range between 500 and 1000 is observed. The four samples from 30 s RT at 380 °C and 300 °C and the 4 min RT sample at the same temperatures show that a lower Mw distribution is achieved, confirming that the effect of temperature is greater at producing lower average Mw compounds opposed to the RT.