may require the use of a mixture of non-edible oils and third-generation feedstocks like microalgal lipids. Efficient processes need to be developed to convert these feedstocks into biodiesel in a cost-effective way that requires R&D in both chemistry and reactor design and engineering. Lab-scale research in academic institutions and universities and the pilot-scale trials in the industry should go hand-in-hand to develop an energy-efficient, sustainable, and economically attractive commercial biodiesel process.
References
1. Moholkar, V.S., Choudhury, H.A., Singh, S., Khanna, S., Ranjan, A., Chakma, S., and Bhasarkar, J., Physical and chemical mechanisms of ultrasound in biofuel synthesis, in Production of Biofuels and Chemicals with Ultrasound (eds. Fang, Z., Smith, R.L.J., and Qi, X.), pp. 35–86. Springer, Dordrecht, 2015.
2. Abomohra, A.E.F., Elsayed, M., Esakkimuthu, S., El-Sheekh, M., and Hanelt, D., Potential of fat, oil and grease (FOG) for biodiesel production: A critical review on the recent progress and future perspectives. Prog. Energy Combust. Sci., 81, 100868, 2020.
3. Chuah, L.F., Klemeš, J.J., Yusup, S., Bokhari, A., Akbar, M.M., A review of cleaner intensification technologies in biodiesel production. J. Clean. Prod., 146, 181–193, 2017.
4. Elbashir, N.O., Ahmed, W. Choudhury, H.A., Nasr, N.M., et al., GTL Derived Synthetic Fuels: Potentials and Challenges in Global Market, in Water-Food-Energy Nexus: Processes, Technologies and Challenges, CRC Press Taylor & Francis Group, 2016.
5. Basha, S.A., Gopal, K.R., Jebaraj, S., A review on biodiesel production, combustion, emissions and performance. Renew. Sustain. Energy Rev., 13 (6–7), 1628–1634, 2009.
6. Mahlia, T.M.I., Syazmi, Z.A.H.S., Mofijur, M., Abas, A.P., Bilad, M.R., Ong, H.C., Silitonga, A.S., Patent landscape review on biodiesel production: Technology updates. Renew. Sustain. Energy Rev., 118, 109526, 2020.
7. Damanik, N., Ong, H.C., Tong, C.W., Mahlia, T.M.I., Silitonga, A.S., A review on the engine performance and exhaust emission characteristics of diesel engines fueled with biodiesel blends. Environ. Sci. Pollut. Res., 25 (16), 15307–15325, 2018.
8. Knothe, G., and Razon, L.F., Biodiesel fuel. Prog. Energy Combust. Sci., 58, 36–59, 2017.
9. Malani, R.S., Sardar, H., Malviya, Y., Goyal, A., Moholkar, V.S., Ultrasound-Intensified Biodiesel Production from Mixed Nonedible Oil Feedstock Using Heterogeneous Acid Catalyst Supported on Rubber De-oiled Cake. Ind. Eng. Chem. Res., 57 (44), 14926–14938, 2018.
10. Malani, R.S., Choudhury, H.A., Moholkar, V.S., Waste biorefinery based on waste carbon sources: case study of biodiesel production using carbon based catalysts and mixed feedstocks of nonedible and waste oils, in Waste Biorefinery Volume-II (eds. Bhaskar, T., Pandey, A., Rene, E.R., and Tsang, D.C.W.), Elsevier B.V., pp. 337–378, 2020.
11. Badday, A.S., Abdullah, A.Z., Lee, K.T., Khayoon, M.S., Intensification of biodiesel production via ultrasonic-assisted process: A critical review on fundamentals and recent development. Renew. Sustain. Energy Rev., 16 (7), 4574–4587, 2012.
12. Wang, T., Global biodiesel production by country 2018. https://www.statista.com/statistics/271472/biodiesel-production-in-selected-countries/, 2019.
13. IEA, Biofuel Production Growth by Country. IEA Paris, https://www.iea.org/data-and-statistics/charts/bio, 2019.
14. Renewable energy policy Network 21st Century steering committee. Renewables 2014: global status report. REN 21, https://www.ren21.net/wp-content/uploads/2019/05/, 2014.
15. Abbaszaadeh, A., Ghobadian, B., Omidkhah, M.R., Najafi, G., Current biodiesel production technologies: A comparative review. Energy Convers. Manag., 63, 138–148, 2012.
16. Aransiola, E.F., Ojumu, T. V., Oyekola, O.O., Madzimbamuto, T.F., Ikhu–Omoregbe, D.I.O., A review of current technology for biodiesel production: State of the art. Biomass and Bioenergy, 61, 276–297, 2014.
17. Tabatabaei, M., Aghbashlo, M., Dehhaghi, M., Panahi, H.K.S., Mollahosseini, A., Hosseini, M., Soufiyan, M.M., Reactor technologies for biodiesel production and processing: a review. Prog. Energy Combust. Sci., 74, 239–303, 2019.
18. Choudhury, H.A., Malani, R.S., Moholkar, V.S., Acid catalyzed biodiesel synthesis from Jatropha oil: Mechanistic aspects of ultrasonic intensification. Chem. Eng. J., 231, 262–272, 2013.
19. Choudhury, H.A., Srivastava, P., Moholkar, V.S.,Single-step ultrasonic synthesis of biodiesel from crude Jatropha curcas oil. AIChE J., 60 (5), 1572–1581, 2014.
20. Choudhury, H.A., Goswami, P.P., Malani, R.S., Moholkar, V.S., Ultrasonic biodiesel synthesis from crude Jatropha curcas oil with heterogeneous base catalyst: Mechanistic insight and statistical optimization. Ultrason. Sonochem., 21 (3), 1050–1064, 2014.
21. Malani, R.S., Patil, S., Roy, K., Chakma, S., Goyal, A., Moholkar, V.S., Mechanistic analysis of ultrasound-assisted biodiesel synthesis with Cu2O catalyst and mixed oil feedstock using continuous (packed bed) and batch (slurry) reactors. Chem. Eng. Sci., 170, 743–755, 2017.
22. Malani, R.S., Shinde, V., Ayachit, S., Goyal, A., Moholkar, V.S., Ultrasound-assisted biodiesel production using heterogeneous base catalyst and mixed non-edible oils. Ultrason. Sonochem., 52, 232–243, 2019.
23. Maddikeri, G.L., Pandit, A.B., Gogate, P.R., Intensification approaches for biodiesel synthesis from waste cooking oil: A review. Ind. Eng. Chem. Res., 51 (45), 14610–14628, 2012.
24. Ranjan, A., Singh, S., Malani, R.S., Moholkar, V.S., Ultrasound-assisted bioalcohol synthesis: Review and analysis. RSC Adv., 6 (70), 65541–65562, 2016.
25. Malani, R.S., Goyal, A., Moholkar, V.S., Ultrasound-Assisted Biodiesel Synthesis: A Mechanistic Insight, in Biofuels (eds. Agrawal, A.K., Agarwal, R.A., Gupta, T., Gurjar, B.R., Springer, Singapore, pp. 103–135, 2017.
26. Ghayal, D., Pandit, A.B., Rathod, V.K., Optimization of biodiesel production in a hydrodynamic cavitation reactor using used frying oil. Ultrason. Sonochem., 20 (1), 322–328, 2013.
27. Moholkar, V.S., Sable, S.P., Pandit, A.B., Mapping the cavitation intensity in an ultrasonic bath using the acoustic emission. AIChE J., 46 (4), 684–694, 2000.
28. Moholkar, V.S., and Pandit, A.B., Modeling of hydrodynamic cavitation reactors: A unified approach. Chem. Eng. Sci., 56 (21–22), 6295–6302, 2001.
29. Shah, Y.T., Pandit, A.B., Moholkar, V.S., Cavitation Reaction Engineering, Plenum Press, New York, 1999.
30. Suslick, K.S. Sonochemistry. Science (80-. ), 247 (4949), 1439–1445, 1990.
31. Leighton, T.G. The acoustic bubble, Academic Press, San Diego, 1994.
32. Mason, T.J., and Lorimer, J.P. Applied sonochemistry: The uses
