**6. Acknowledgments**

262 Biodiesel – Feedstocks and Processing Technologies

alcohol to oil molar ratio of 24:1 and a reaction time over 30 min. The biodiesel product, which typically exceeds the 96.5% alkyl esters content of the international standard for

For future research involving the low-temperature approach, the use of low-grade feedstocks and/or heterogeneous catalysts are very interesting topics. Alternatively, studies on scale up continuous reactors which are more suitable for an industrial scale are required. These have been successfully evaluated in lab-scale tubular reactors (Bunyakiat et al., 2006; He et al., 2007b; Minami & Saka, 2006), but an evaluation on a scaled-up reactor is presently lacking. An optimal reaction time to achieve over 96.5% alkyl esters content is the most important finding for the low-temperature approach studies because it corresponds with

The high-temperature approach uses supercritical transesterification at temperatures over 400 ºC, as described in Section 3.4. Even though the mono-alkyl esters content in the product from the high-temperature process is always lower than the biodiesel specification value of 96.5%, it can be proposed as an alternative biofuel that would require further studies on engine testing and fuel properties itself. Improved fuel properties, such as the viscosity and density of the biofuel product, from the hightemperature approach have been proposed (Marulanda et al., 2009). Furthermore, the operating temperature and pressure used in the high-temperature approach are close to those for catalytic hydrocracking in conventional petroleum refining, so it has a high

Since the high-temperature approach, as recently initiated, has evaluated the triglycerides found in soybean oil (Anitescu et al., 2008) and chicken fat (Marulanda et al., 2009; Marulanda et al., 2010) only, then additional research into other triglycerides are needed. In addition, studies on the economical feasibility and environmental impact are also required. Indeed, the complete fuel properties need examining along with engine testing for the biofuel product for the high-temperature approach (Basha et al., 2009). On the other hand, the fine studies on the reactions pathways and/or chemical kinetics are also attractive works

Supercritical transesterification is a promising method for a more environmentally friendly biodiesel production as a result of its feedstock flexibility, production efficiency and environmentally friendly benefits. For extended details, the review articles on supercritical transesterification with methanol (de Boer & Bahri, 2011; Sawangkeaw et al., 2010), or ethanol (Balat, 2008; Pinnarat & Savage, 2008) and other supercritical technologies (Lee &

Even though the knowledgebase of this process has been growing the past decade, more work is still required for an adequate understanding of the process. In spite of its advantage of feedstock flexibility, there has so far been very little research on the use of low-grade feedstocks in supercritical transformation. Furthermore, prospective studies for both the low-temperature and high-temperature approaches, as mentioned previously, are required

biodiesel (EN14214), can be used as biodiesel.

**4.2 The high-temperature approach** 

reactor sizing and reflects on the economical feasibility.

possibility that it can be realized in an industrial scale.

to better understand the high-temperature approach.

Saka, 2010; Tan & Lee, 2011) are also available elsewhere.

to realize supercritical transesterification at an industrial scale.

**5. Conclusion** 

The authors would like to acknowledge the financial support from Postdoctoral Fellowship (Ratchadaphiseksomphot Endowment Fund) and the Thai Government Stimulus Package 2 (TKK2555), under the Project for Establishment of Comprehensive Center for Innovative Food, Health Products and Agriculture. We also express thanks to Dr. Robert Douglas John Butcher from the Publication Counseling Unit, Faculty of Science, Chulalongkorn University, for English language editing.
