Concomitant extraction of bio-oil and value added polysaccharides from Chlorella sorokiniana using a unique sequential hydrothermal extraction technology

To make algal bio-fuel economically viable, extraction of value added co-products along with oil, appears absolutely necessary. The major barrier in algal co-product development is the lack of an efficient separation technology. To address this issue a unique two-step sequential hydrothermal liquefaction (SEQHTL) technology for the simultaneous production of value-added polysaccharides and bio-oil from algal-biomass was developed. The first step involves the subcritical water extraction of valuable algal (Chlorella sorokiniana) polysaccharides at 160 °C. The polysaccharide rich water extract was removed and precipitated with ethanol. In the next step, the extracted biomass was liquefied to bio-oil at 300 °C. The yield of bio-oil by SEQHTL was 24% of the dry weight. In addition, this method also extracted 26% of the polysaccharides present whereas; direct hydrothermal liquefaction (DIRHTL) only generated 28% bio oil. In the SEQHTL method bio-char formation was remarkably low, and as such, SEQHTL produce 63% less bio-char than DIRHTL. The yield of bio-char production is negatively correlated to polysaccharide content (p > 0.98) suggesting majority of carbohydrates present in algal biomass were converted into bio-char. This conversion did not significantly influence the bio-oil production. Comparative GC-FID, GC–MS, NMR, FT-IR analysis and ESI-MS of the bio-oil extracted by SEQHTL with DIRHTL showed no significant differences. Elemental analysis of the SEQHTL bio-oil demonstrated that it contained 70% carbon, 0.8% nitrogen, and 11% oxygen. This method demonstrates an important proof-of-concept step towards the concomitant production of value added co-products, along with bio-oil, from algal biomass.