3.2. Continuous process
3.2.1. Effect of molar ratio of methanol to PFAD and reaction temperature on the conversion of FAME
It can be seen in Fig. 6 that the FAME conversion was raised when the molar ratio of methanol to PFAD was increased for both reaction temperatures of 70 and 75 °C. Table 3 shows the levels of residual FFA and glycerides with increasing molar ratio of methanol.
3.2.2. Purification processes
The FAME obtained from esterification process still had 1.4 wt% residual FFA, which must be removed to meet the biodiesel standards.
When the FAME was neutralized with NaOH–MeOH solution there was no residual FFA, lower glycerides and higher FAME content product. Hundred percent FAME was obtained using 5.48 ml of 1 M NaOH–MeOH solution. However, this method produced high levels of waste methanol and soap.
When the FAME was neutralized with NaOH–H2O solution, the method required higher amount of NaOH than the first method. However, with salt addition removal of soap from water was easily obtained. It was also found that increasing levels of NaOH could increase the amount of FAME and decrease the amount of glycerides. To meet quality standard of biodiesel, 9.13 v/wt% of 3 M NaOH–H2O solution (9.13 ml of the solution/100 g of FAME phase) was required and to get 100% FAME 11.87 v/wt% of 3 M NaOH–H2O solution was needed (Fig. 7).
The FAME phase can also be purified by neutralization with NaOH–H2O solution followed by transesterification process. Neutralization with 1.83 v/wt% of 3 M NaOH–H2O solution could get rid of all residual FFA; however, the residual glycerides needed to be transformed to FAME by transesterification process. The purity of FAME met quality standard for biodiesel when the amount of 0.396 M NaOH–MeOH solution was 3.85 wt% (3.85 g of solution/100 g of neutralized FAME phase) and to get 100% FAME 4.46 wt%, the 0.396 M NaOH–MeOH solution was required (Fig. 8).
3.2.3. Fuel properties of PFAD biodiesel
The fuel properties of biodiesel obtained in this work are summarized in Table 4. It can be seen that most of its properties are in the range of fuel properties prescribed in the latest Thai and American standards for biodiesel, except cloud point and pour point. PFAD mainly consists of saturated FFA (>49 wt%) which results in high values of cloud point and pour point of PFAD biodiesel. However, a blend of diesel and PFAD biodiesel is possible in practice.
4. Conclusion
A process for the production of biodiesel from relatively low cost PFAD a residual product from the refining of crude palm oil has been evaluated. The final product is a light brown material meeting the requirements of the Thai biodiesel standard. A range of methanol to PFAD ratios and acid catalyst concentrations were established that would produce a high-quality product in reasonable CSTR residence times, and at lower temperatures which we considered to be a more economic solution.