One-step conversion of microalgae to alcohols and esters through co-pyrolysis with biodiesel-derived glycerol

Nowadays, efficient conversion of wastes and biomass has attracted increasing attention in the context of waste recycling and energy production. The present study aimed to enhance the production of combustible oxygenated organics (alcohols and esters) in the bio-oil through co-pyrolysis of Chlorella vulgaris and biodiesel-derived glycerol (WG). WG showed significant higher volatiles and moisture contents (91.6% and 8.4%, respectively) than those of C. vulgaris (71.8% and 7.0%, respectively). In addition, C. vulgaris showed 14.6% ash content and 6.5% fixed carbon, which were not recorded in WG. TG analysis confirmed that increase of C. vulgaris blend ratio enhanced the solid residues, while WG reduced the solid residues and enhanced the thermal decomposition rate at early stages of the reaction. Pyrolysis of C. vulgaris individually resulted in 56.9% bio-oil yield, while 50% and 70% WG blends increased the bio-oil yield to 58.5% and 65.2%, respectively. Due to blending with WG, both bio-oil and pyrolytic gas yields increased in favor of bio-char, which reduced significantly from 24.0% from pyrolysis of pure C. vulgaris to 17.4% using 50% WG blend ratio. FTIR analysis confirmed a synergistic effect of WG and C. vulgaris during pyrolysis which resulted in significant impact on the functional groups of the bio-oil. GC MS analysis of the produced bio-oil confirmed the enhancement of alcohols and esters from 1.41% and 0.0% in the bio-oil of C. vulgaris to 53.1% and 28.7%, respectively, in the bio-oil of WG. However, 50% WG blend ratio showed the maximum alcohol content of 71.8%. In addition, 50% blend ratio of WG reduced the nitrogen-containing compounds by 82.2% below that of C. vulgaris individually, while acids were completely disappeared. In conclusion, co-pyrolysis of C. vulgaris and WG could be a potential approach for stable and combustible oxygenated organics.