Microwave irradiation was applied to syntheses of ETBE from biomass-deriveable alcohols (TBA and EtOH). The maximum yield obtained under atmospheric conditions was low at around 30%, which agreed with our previous studies on reactive distillation and the results obtained by other researchers. Performing the experiments in a sealed reactor at a micro­wave power of 350W, and irradiation time of 1 min, the mixture reached pressurized condi­tions obtaining EtOH conversion closed to 90%. The conversion and yield were found to be also dependent on operating parameters such as temperature, microwave irradiation power, time and amount of catalysts. Preliminary studies on combined reaction and separation process inside the cavity showed promising results but need further investigation for con­trol and optimization of its operation.

The application of microwave irradiation to the synthesis of this promising biofuel offer benefits including energy efficiency, development of a compact process, rapid heating and instant on-off process (instant heating-cooling process), among others. Unlike the conven­tional heating, the heat is generated within the material, thus rapid heating occurs. Besides, microwave effects on reaction also likely occur, thus obtaining dramatic increase in the yield even at low bulk temperatures.

The benefits have been indicated by the above mentioned results. However, there are some drawbacks including the problems with non-homogeneous heating that would require thor­ough investigation prior to its commercialization. Although the field is in its infancy, the outlook is bright for the proposed methods due to foreseen high global demands for bio­fuels. The next few years should see development of continuous compact process, along with cheap, effective and stable solid catalysts.

As the demand for biofuels continue to increase in the near future, and while the search for an efficient and low-cost production process continues, the global outlook is positive for the use of microwave irradiation to the synthesis of ETBE. To overcome the limitations for scal­ing up microwave-assisted technology for ETBE production, development of a compact con­tinuous process is suggested, but still poses several challenges that require detailed investigation. The future also calls for the development of cheap, effective and stable solid catalysts for the synthesis of the abovementioned fuels. While the use of microwave irradia­tion offers great benefits with regards to rapid reaction or synthesis, safety is a big factor to consider in designing a large scale production plant. However, this can be avoided if multi­layered compact reactors operating under microwave irradiation can be developed instead.

Acknowledgments

Most of the research works were supported financially by the Japan Science and Technology carried out at the Research Institute for Solvothermal Technology, Kagawa Industry Support Fundation. The MARS 5 apparatus was donated by AIST-Shikoku through the kindness of Dr. Akinari Sonoda. This work was also partly supported by Kumamoto University Global COE Program "Global Initiative Center for Pulsed Power Engineering".

Author details

Armando T. Quitain1, Shunsaku Katoh2 and Motonobu Goto2

1 Graduate School of Science and Technology, Kumamoto University, Japan

2 RIST Kagawa, Kagawa Industry Support Foundation, Japan Department of Chemical Engineering, Nagoya University, Japan