2.3. Catalytic activity tests and biodiesel analytical methods Water scale-derived catalysts were used in transesterification reactions carrying out in a batch reactor for the catalytic activity. Soybean oil and methanol were placed in a round-bottom glass flask equipped with a reflux condenser. Next, the designated amount of prepared catalyst was placed in and stirred at 50–80 C for 2–6 h. After the reaction, centrifugation was used to separate the layers (methyl ester, glycerol, and catalyst). The product was directly measured by gas chromatography. Then, the treated sample (0.2 lL) was injected into the GC-122 gas chromatograph, which was equipped with a SE-54 capillary column (0.32 mm 30 m). The column temperature was kept at 160 C for 2 min, raised to 220 C at a rate of 10 C/min, then to 260 C at a rate of 8 C/min, and finally maintained at this temperature for 10 min. The internal standard method for determinating the yield of biodiesel was used, with methyl salicylate as internal standard.
In our work, the composition of biodiesel was 56.5% methyl linoleate, 23.2% methyl oleate, 10.6% methyl palmitate, 6.6% methyl linolenate and 3.1% methyl stearate from the gas chromatogram.