State of the art of applied fast pyrolysis of lignocellulosic materials — a review

Pyrolysis is the degradation of macromolecular materials with heat alone in the absence of oxygen. It has both analytical and applied aspects. The development of advanced fast pyrolysis processes for liquids production has gained much attention in the last decade, because they offer a convenient way to convert low value woody residues into liquid fuels and value-added products. This review describes the new pyrolysis reactors under development. The systems based on (bubbling) fluidized bed and circulating fluidized bed reactors are presented. Moreover, the principles of ablative pyrolysis techniques such as the rotating blade and rotating cone reactors including the vortex system are outlined and a vacuum pyrolysis system, a recent technical development, is also presented. The international activities within the International Energy Agency and European Union are shortly outlined with special emphasis on the chemical and physical properties of pyrolysis oils and the methods for their upgrading and utilization as fuel and chemical feedstock. The pyrolysis liquids obtained in a yield of ca. 70% (based on dry wood) are complex mixtures of oxygenated aliphatic and aromatic compounds. Their energetic utilization is being tested in burners, Diesel engines and turbines. Commercial applications exist in the field of production of food aromas. Emerging areas of utilization are: additives for flue gas cleaning of coal combustion; acetic acid for chip production; adhesives; fuel enhancers; specialty chemicals; and fertilizers.