Armando T. Quitain, Mitsuru Sasaki and Motonobu Goto

Abstract Pretreatment has been considered an important step for efficient and effec­tive biomass-to-biofuel conversion. One of many promising methods of pretreatment includes the use of microwave (MW). MW-based pre-treatment approach utilizes both thermal and non-thermal effects generated by an extensive intermolecular col­lision as a result of realignment of polar molecules with MW oscillations. Compared to conventional heating, electromagnetic field generated by MW has the ability to directly interact with the material to produce heat, thereby accelerating chemical, physical, and biological processes. The advantages of employing MW rather than the conventional heating include reduction of process energy requirements, selective processing, and capability for instantaneous start and ceasing of a process. This also offers enormous benefits such as energy efficiency due to rapid and selective heating, and the possibility for developing a compact process. This chapter reviews recent advances on the utilization of MW irradiation for pretreatment of biomass for more efficient biofuel (bioethanol, biogas (methane), and biodiesel) production.

Keywords Microwave ■ Biomass ■ Sludge ■ Bioethanol ■ Biogas ■ Methane ■ Biodiesel ■ Free ■ fatty acids

6.1 Introduction

Pretreatment is an extremely important step in the synthesis of biofuels from ligno- cellulosic biomass or plant oils containing high fraction of free fatty acids (FFAs). Thorough knowledge of the fundamentals underlying various processes is necessary

M. Goto (H)

Bioelectrics Research Center, Faculty of Engineering, Kumamoto University, 2-39-1 Kurokami, 860-8555 Kumamoto, Japan e-mail: mgoto@kumamoto-u. ac. jp

A. T. Quitain ■ M. Sasaki

Graduate School of Science and Technology, Faculty of Engineering, Kumamoto University, 2-39-1 Kurokami, 860-8555 Kumamoto, Japan

Z. Fang (ed.), Pretreatment Techniques for Biofuels and Biorefineries,

Green Energy and Technology,

DOI 10.1007/978-3-642-32735-3_6, © Springer-Verlag Berlin Heidelberg 2013 in choosing a suitable pretreatment method appropriate for a particular structure of the biomass substrate and the hydrolysis agent [1].

The pretreatment process for the lignocellulosic biomass targets the breakdown of the lignin structure and the disruption of the crystalline structure of cellulose for an easy access of acids or enzymes into the matrix resulting into more efficient hydrol­ysis of the cellulose [2]. Comprehensive review of several methods of pretreatment including physical, pyrolysis, physicochemical, and biological has been reported by Kumar et al. [1], while pretreatment technologies based on the use of enzymes have been extensively summarized by Alvira et al. [3]. Mtui [4] also highlighted recent advances in the treatment of lignocellulosic wastes focusing on domestic and agro-industrial wastes. Mechanical, physical, and biological treatment systems were discussed, and among the systems mentioned, physicochemical and biological treatments seem to be most favored options for production of biofuel or bio-based products. In these published reviews, limited information has been reported regarding the use of microwave (MW), which is considered to be a very promising pretreatment technique.

Research on the development of pretreatment methods utilizing MW irradiation has reached a significant level during the past few years. Literature search using Scopus resulted into heavy turn outs. This dramatic increase in the number of pub­lished research literatures is due to the introduction of scientific MW equipment to the market in the 1980s, the search for a more energy efficient methods for bio­fuel production, and the increasing interests of the academe, research institutes, and industry on its utilization for biomass-to-biofuel conversion.

This chapter summarizes recent advances on the utilization of MW irradiation for pretreatment of biomass for more efficient biofuel (bioethanol, biogas (or methane), and biodiesel) production. The fundamentals of MW technology and its benefits are also discussed, while introducing some challenges of the technique, prospects, and future outlook.