Catalytic pyrolysis of raw and hydrothermally carbonized Chlamydomonas debaryana microalgae for denitrogenation and production of aromatic hydrocarbons

Pyrolysis of raw and hydrothermally carbonized (HTC) Chlamydomonas debaryana with and without activated carbon (AC) or β-zeolite as the catalyst were studied. Monoaromatic hydrocarbon yields from the pyrolysis of raw and HTC treated algae without a catalyst were relatively low at optimum yields of 11.2% and 12.0% obtained at 600 °C, respectively. The maximum yields of monoaromatic hydrocarbons from the AC catalyzed pyrolysis of raw and HTC treated algae were 43.8% obtained at 600 °C and 43.5% obtained at 800 °C, respectively, compared to 32.3% and 32.7% for the maximum yields from the β-zeolite catalyzed pyrolysis at 500 °C and 600 °C, respectively. However, β-zeolite catalyzed pyrolysis produced higher yields of total hydrocarbons (aromatic + aliphatic) for raw and HTC algae compared to AC catalyzed pyrolysis. This means while β-zeolite was more effective in producing total hydrocarbon content, AC was more effective in aromatization of oxygenates. The combination of HTC pretreatment and catalytic pyrolysis were effective in reducing nitrogen content in bio-oil. The yields of nitriles and nitrogenous compounds were negligible for the AC catalyzed pyrolysis of HTC treated algae at 600 °C, compared to 8.3% using the β-zeolite at the same temperature. The AC catalyst had a lower tendency towards coking.