Bio-Char from Microwave Hybrid Heating Pyrolysis as a Contribution to The Circular Economy

Microwave Hybrid Heating Pyrolysis (MHHP) is a technology that couples classical electrical heating with MW heating, and in this chapter, several examples of the formation of bio-char and bio-attributed-char from MHHP of contaminated/waste products are reported. The process is carried out in the first step using electrical heating because in this stage, the microwave heating has a low efficiency. When the oven temperature reaches a prefixed value, the Microwave heating is activated, displaying its maximum efficiency. In this way, the MHHP process is usually more efficient than classic thermal pyrolysis because the reaction time and the energy required are reduced. Several biomasses have been employed in the MHHP: cellulose, lignin, residues from agricultural productions such as olive pruning residue, and crops from Vitis vinifera. In addition, wood pellets in general or wood residues from municipal solid waste or short rotation coppice of poplar, as well as an invasive species (Arundo Donax), were also used to produce bio-char. The char may be employed as a soil amendment, as support for catalysts, as filler for plastics, for energy storage, or as a solid fuel for the production of energy. In all cases, a very strong reduction of carbon footprint is obtained.