hydrogen, transferring the radical site to a tertiary carbon atom of an other macromolecule or that of its own chain. The intermolecular radical transfer of 2 is followed by the β-scission reaction drawn in Scheme 12.3, resulting in a vinyl terminal group 3 and reproducing 2. This chain reaction produces n-propyl and 2-methylvinylene terminal groups in the fragments, which can be isoalkanes, 1-isoalkenes (oligomers) and α, ωisoalkadienes. The series of peaks above pentamer represent these fragment compounds in the pyrogram of PP in Figure 12.2. The considerably superior yield of trimer, tetramers and pentamers to that of the larger oligomers indicates the contribution of another reaction. Intramolecular radical transfer of a secondary macroradical to a tertiary carbon atom of its own chain leads to these oligomers, drawn in Scheme 12.5. The two possible directions of β-scission explain the occurrence of n-pentane among the wholly isoalkanoic products of PP. In the pyrolysis process of PP the intramolecular radical transfer is preferred to the intermolecular one, thus the low oligomer formation predominates. Consequently the pyrolysis oil of PP is much more volatile than that of PE, decomposing mainly through intermolecular radical transfer. The difference of the backbone structure of the products of these polymers is more important from the point of view of fuel properties. The isoalkanoic structure of PP is held in the thermal decomposition products, in this way the octane number of the pyrolysis oil might be high. In a batch reactor [26] the gasoline fraction (44–220◦C) of the pyrolysis oil obtained from 100 g PE and PP mixture at 440◦C has an octane number of 88.6 with 5.6 wt% aromatic content, and the diesel oil (151–347◦C boiling point range) had 56◦C ignition temperature, −4◦C cloud point and a cetane index of 59.5. Pyrolysing waste PP in an 1 L autoclave at 430◦C for 20 min

Feedstock recycling and pyrolysis of waste plastics : converting waste plastics into diesel and other fuels

The present review is aimed at exploring the field of the catalytic cracking of polyolefins over solid acids, focusing on the role played by the catalysts toward the synthesis of fuels and chemicals as well as on the reaction systems currently used. Initially, conventional solid acids, such as micrometer sized crystal zeolites and silica–alumina, were used to establish the relationship among their activity, selectivity, and deactivation in the polyolefin cracking and the inherent properties of the catalysts (acidity, pore structure); however, the occurrence of steric and diffusional hindrances for entering the zeolite micropores posed by the bulky nature of the polyolefins highlighted the importance of having easily accessible acid sites, either through mesopores or by a high external surface area. This fact led toward the investigation of mesoporous materials (Al-MCM-41, Al-SBA-15) and nanozeolites, which allowed increasing the catalytic activities, especially for the case of polypropylene. Further advan...

Developing Advanced Catalysts for the Conversion of Polyolefinic Waste Plastics into Fuels and Chemicals

Pyrolysis of a fraction of waste polypropylene and polyethylene for the recovery of BTX aromatics using a fluidized bed reactor

Feedstock recycling of polymers by pyrolysis in a fluidised bed

Feedstock recycling of plastic waste by thermal and catalytic processes is a promising route to eliminate this refuse (which is harmful to the environment) by obtaining, at the same time, products that are useful as fuels or chemicals. During the past decade, this option has undergone an important evolution from a promising scientific idea to an alternative that is very close to reality with commercial opportunities. Thus, several commercial processes have been developed worldwide, most of them especially addressed toward the preparation of diesel fuel. The present review highlights the most remarkable achievements of the field, providing a fundamental insight into this fascinating area and highlighting the main milestones that should be achieved in the next future for this alternative to become applied commercially on a large scale.

Fuels from Waste Plastics by Thermal and Catalytic Processes: A Review

Recycling of mixed plastics by pyrolysis in a fluidised bed

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Recycling of mixed plastics by pyrolysis in a fluidised bed