Specific Process Knowledge/Thermal Process/Pyrolysis
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General description of pyrolysis
The pyrolysis process consists of multiple steps of carbonization of organic polymers at high temperature in inert atmosphere. This process includes many different parameters such as the number of thermal processing steps, temperatures, atmospheres (nitrogen, argon, gas mixture) and pressure (ambient, vacuum). During the process, the polymers chains undergo large changes. The reactions of the polymer chain take place in a multi-step process (Figure below), including dehydrogenation, cyclization, condensation, hydrogen transfer and isomerization. Below 300oC is the pre-carbonization phase. In this phase, unreacted monomers and solvent are removed from the polymeric precursor structure. During phase I of carbonization (between 300oC and 500oC), all halogens and heteroatoms are eliminated. In this phase, most mass of polymer precursor is lost and meanwhile the carbon network is formed. After further increase of the temperature (from 500oC to 1200oC), the carbonization phase II is reached. The remaining hydrogen, oxygen and nitrogen atoms attached to carbon atoms are removed, thus forcing the aromatic network to become interconnected. In the final step, the so-called ‘annealing stage’ (above 1200oC), most of the remaining impurities are eliminated. This clearly means that the final temperature of the pyrolysis process will determine the carbon product both in term of structure and properties.
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