Difference between revisions of "Pyrolysis"

<onlyinclude>'''Pyrolysis''' (from greek ''pyr,'' "fire" and ''lysis,'' "loosing/unbind") is a conversion technology that utilises a thermochemical process to convert organic compounds in presence of heat and absence of oxygen into valuable products which can be solid, liquid or gaseous. The chemical transformations of substances are generally accompanied by the breaking of chemical bonds which leads to the conversion of more complex molecules into simpler molecules which may also combine with each other to build up larger molecules again. The products of pyrolysis are usually not the actual building blocks of the decomposed substance, but are structurally modified (e.g. by cyclization and aromatisation or rearrangement).</onlyinclude>

Since all kind of [[biowaste]] contains hydrocarbonaceous material it can also be processed via pyrolysis. However, the composition of the feedstock has an impact on the pyrolysis process and therewith on the products which can be obtained. Usually wood and herbaceous feedstocks are processed which are composed differently<ref name=":2">{{Cite journal|author=Carpenter, D., Westover, T. L., Czernik, S. and Jablonski, W.|year=2014|title=Biomass feedstocks for renewable fuel production: a review of the impacts of feedstock and pretreatment on the yield and product distribution of fast pyrolysis bio-oils and vapors|journal=Green Chemistry|volume=16|issue=2|page=384-406|doi=10.1039/C3GC41631C}}</ref> which qualifies [[garden and park waste]] as suitable feedstock.       

The pre-treatment of the feedstock has an impact on the pyrolysis process, its efficiency, and the yield of certain products. The following pre-treatments may be considered <ref name=":0" />:

Produced pyrolysis oil is a multiphase emulsion composed of water and and hundrets of organic molecules such as acids, alcohols, ketones, furans, phenols, ethers, esters, sugars, aldehydes, alkenes, nitrogen- and oxygen- containing molecules. A longer storage or exposure to higher temperature increases the viscosity due to possible chemical reactions of the compounds in the oil which leads to the formation of larger molecules<ref name=":1">{{Cite journal|author=Czernik, S. and Bridgwater|year=2004|title=Overview of Applications of Biomass Fast Pyrolysis Oil|journal=Energy & Fuels|volume=18|issue=2|page=590-598|doi=10.1021/ef034067u}}</ref>. The presence of oligomeric species with a molecular weight >5000 decreases the stability of the oil<ref name=":0" />, furthermore the formation of aerosols from volatile substances accelerates the aging process in which the water content and phase separation increases. The application as fuel in standard equipment for petroleum fuels (e.g. boilers, engines, turbines) may be limited due to poor volatility, high viscosity, coking, and corrosiveness of the oil<ref name=":1" />. To overcome these problems the pyrolysis oil has to be upgraded in a post-treatment to be used as fuel and/or the equipment for the end-application has to be adapted.