Refinement of crude glycerol from biodiesel fuel production using a small solar thermal collector

The efficient utilization of crude glycerol (CG) derived from biodiesel fuel (BDF) production remains an important challenge, especially in the case of smaller BDF plants. This work demonstrated a simple, carbon-neutral approach for adding value to CG. In this approach, CG was refined at temperatures in the vicinity of 500 °C that limited volatilization, using a small solar thermal collector (STC) with a parabolic trough as its heat source. The resulting products were composed of pyrolysis oil derived from unreacted triglycerides, refined glycerol containing surplus methanol left over from BDF production, solid residue incorporating a high level of potassium derived from the original catalyst, and some gaseous pyrolysis compounds. The oil contained hydrocarbons, BDF, and fatty acids that could be blended with BDF as fuel additives. The refined glycerol was purified and converted to solketal as a fuel additive. Potassium could be recovered from the solid residue as potassium carbonate. The STC used in this work was a simple device composed of a receiver, double-glazed vacuum component with a selective absorption coating, and a collector with a thin Al mirror coating. The temperature inside the receiver exceeded 500 °C within 20 min on a clear day during trials in Japan at solar intensities of ∼1000 W/m 2 . This STC potentially refined ∼1 kg of CG daily and would be suitable for a BDF plant with a daily fuel output on the order of 10 L. • Heating crude glycerol from biodiesel fuel production could remove its impurities. • Heating crude glycerol to 500 °C provided pyrolysis oil containing n-hydrocarbon. • Heating crude glycerol also provided glycerol that could be converted to solketal. • The potassium could be recovered from the solid residue as potassium carbonate. • Design of small solar thermal reactor was proposed for refinery of crude glycerol.