CHAPTER 3:Low-Temperature Microwave Pyrolysis and Large Scale Microwave Applications

Abstract

The following chapter discusses the potential uses of microwave technology in the low temperature decomposition of biologically derived materials and its application on both laboratory and commercial scales. In so doing, we examine the historic development of microwave technology from its origins (with Kassner in 1937) to the present day. The mechanism of microwave heating is examined, with specific attention given to dielectric losses and the dipolar polarisation mechanism, with further emphasis on the changing interaction of microwaves with increased material temperature. Further to this, the specific application of microwaves on the laboratory scale is reviewed with focus given to the microwave decomposition of the constituent components of biomass (cellulose, hemicellulose and lignin) and real life examples, such as the decomposition of barley, wheat, wood, etc. The resulting decomposition materials and chemicals are reviewed, for example the production of levoglucosan and levoglucosenone from cellulose. Finally, consideration is given to current large scale commercial applications of microwave technology, looking at both 915 MHz and 2450 MHz applications, which include microwave drying, exfoliated vermiculite, chemical extraction and pasteurisation. Specific attention is given to large scale microwave activation of biomass for the production of bio-chars and bio-oils.