Conventional homogeneous catalysts exhibit rapid reaction kinetics and aff ordability but face signifi cant challenges, including

the cumbersome separation of catalysts, complexities in product purifi cation, and the generation of wastewater. In this regard,

Na–graphitic carbon nitride (GCN) was previously developed as an eff ective heterogeneous catalyst for transesterifi cation. To

advance the industrial application of these catalysts, it is essential to incorporate a continuous production system and highquality

feedstock. Fixed bed reactors off er the advantage of simple operation and have been widely utilized in continuous

biodiesel production. In this study, Na–GCN was applied to the transesterifi cation of waste oils in a continuous fi xed bed

reactor. Various reaction conditions, including temperature, retention time, and the oil-to-methanol ratio, were compared

and optimized. The transesterifi cation of waste oil simulant, waste cooking oil, and waste food oil was conducted under the

optimized conditions. The fatty acid methyl ester (FAME) content was measured using gas chromatography equipped with

a fl ame ionization detector and HP-INNOWax, following an internal standard method. Notably, FAME yields exceeding

90% were maintained for 100 h of continuous operation using Na–GCN and waste cooking oil. The reaction system also

demonstrated enhanced stability over 100 h, even when processing waste food oil with high levels of impurities.