Ternary blends of biodiesel with petro-diesel and diesel from direct coal liquefaction for improving the cold flow properties of waste cooking oil biodiesel

• Ternary blends of PD, DDCL and BWCO exhibited better cold flow properties.
• Ternary phase diagrams presented the relationship between the compositions and cold flow properties of ternary blends.
• PD and DDCL effectively changed the crystallization way of crystals in ternary blends.
• Ternary blends with no more than 20 vol.% BWCO satisfied the ASTM D7467.

This study aims to reduce the cloud point (CP), cold filter plugging point (CFPP) and pour point (PP) of biodiesel from waste cooking oil (BWCO) by ternary complementary blending 0# petro-diesel (PD) and diesel from direct coal liquefaction (DDCL) with BWCO. The cold flow properties of BWCO–PD–DDCL ternary blends, and BWCO–PD, BWCO–DDCL binary blends were comparative evaluated. Ternary phase diagrams were used to present the blending effect on the CP, CFPP, and PP of biodiesel. Results indicated that PD and DDCL exhibited positive synergistic effects on improving the cold flow properties of ternary blends. Ternary blends containing 20% BWCO and 10–40% PD have lower CFPP with respect to BWCO–PD and BWCO–DDCL blends in volume ratio of 20:80. When blends contain up to 60% DDCL and less than 15% BWCO, such fuels could be used in extremely low temperature areas. Other fuel properties were also determined and compared with the ASTM D7467. In addition, to explore the performance mechanism, differential scanning calorimetry and polarizing optical microscopy were used to observe the crystallization behavior and crystal morphology of blends fuel.