Microwave Pyrolysis for Conversion of Materials to Energy: A Brief Review

The disposal of wastes, such as municipal solid waste, wastewater treatment sludge, agricultural waste, plastics, and tires, is becoming a serious problem in many industrialized and public sectors. Although these wastes are reused, there are still an abundant amount left posing environmental and health problems. A thermal treatment method to convert such wastes to energy, such as pyrolysis, has recently become an attractive alternative for the wastes disposal because both energy and usable by-products can be produced. The use of microwave for pyrolysis, although at its infancy for waste treatment, has several advantages compared to conventional heating, especially time saving due to volumetric heating. Several microwave pyrolysis of wastes has been investigated, including coffee hulls, wood, coal, sewage sludge, hospital waste, plastic wastes, corn cobs, and rice straw. The most important factors influencing the yield of product during the pyrolysis is temperature in a range from 200 to 1,000 degrees C according to product preference. High temperature favors gas products, whereas lower temperature favors liquid products. Comparatively, microwave pyrolysis produced gas with higher hydrogen and carbon monoxide (syngas) content compared to conventional heating. Liquid product also has shown a considerable decrease in polycyclic aromatic hydrocarbons production, which is of known carcinogens. Solid products also showed promising characteristics for adsorbent and carbon sequestration.