Difference between revisions of "Pyrolysis"

The pyrolysis is an endothermal process which requires the input of energy in form of heat which can either be directly (direct pyrolysis) applied via hot gases or indirectly (indirect pyrolysis) via external heating of the reactor. Compared to gasification, the process takes place in an atmosphere without oxygen or at least under a limitation of oxygen.

The pyrolysis process and the formation of products can be controlled to a certain extend via different temperature ranges and reaction times as well as by utilising reactive gases, liquids, catalysts, alternative forms of heat application (e.g. via microwaves or plasma), and a variety of reactor designs.

A range of different reactions occur during the process such as dehydration, depolymerisation, isomerisation, aromatisation, decarboxylation, and charring<ref name=":0">{{Cite journal|author=Hu, X. and Gholizadeh, M.|year=2019|title=Biomass pyrolysis: A review of the process development and challenges from initial researches up to the commercialisation stage|journal=Journal of Energy Chemistry|volume=39|issue=|page=109-143|doi=doi:https://doi.org/10.1016/j.jechem.2019.01.024}}</ref>.

A range of solid, liquid, and gaseous products can be obtained from the pyrolysis process including char, pyrolysis oil, and pyrolysis gas. Depending on the feedstock origin and composition as well as the pre-treatment and process the yield as well as the chemical and physical properties of the products can vary.

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.

* Fischer-Tropsch-Synthesis