Processing Real-World Waste Plastics by Pyrolysis-Reforming for Hydrogen and High-Value Carbon Nanotubes

Abstract

Producing both hydrogen and high-value carbon nanotubes (CNTs) derived from waste plastics is reported here using a pyrolysis-reforming technology comprising a two-stage reaction system, in the presence of steam and a Ni-Mn-Al catalyst. The waste plastics consisted of plastics from a motor oil container (MOC), waste commercial high density polyethylene (HDPE) and regranulated HDPE waste containing polyvinyl chloride (PVC). The results show that hydrogen can be produced from the pyrolysis-reforming process, but also carbon nanotubes are formed on the catalyst. However, the content of 0.3 wt.% polyvinyl chloride in the waste HDPE (HDPE/PVC) has been shown to poison the catalyst and significantly reduce the quantity and purity of CNTs. The presence of sulphur has shown less influence on the production of CNTs in terms of quantity and CNT morphologies. Around 94.4 mmol H 2 g -1 plastic was obtained for the pyrolysis-reforming of HDPE waste in the presence of the Ni-Mn-Al catalyst and steam at a reforming temperature of 800 °C. The addition of steam in the process results in an increase of hydrogen production and reduction of carbon yield; in addition, the defects of CNTs e.g. edge dislocations were found to be increased with the introduction of steam (from Raman analysis).

Hydrogen production from catalytic reforming of the aqueous fraction of pyrolysis bio-oil with modified Ni–Al catalysts

“…The largest coke formation on the reacted Ni-Mn-Al catalyst is consistent with former reports that Ni-Mn-Al catalyst generated a large amount of carbon nanotubes during plastics gasification [48].…”

Co-production of hydrogen and carbon nanotubes from real-world waste plastics: Influence of catalyst composition and operational parameters

“…The gas compositions at different steam to plastic ratios show ( Table 2) that the product gases consist of H 2 , CO, CH 4 and a lower content of CO 2 and hydrocarbons. The hydrogen concentration remained stable in the range of 62-65 vol.%.…”

“…Thermal recycling via pyrolysis and gasification of waste plastics, into fuels and chemical products has been identified as a promising technology for tackling waste issues related to plastics [2,3]. In recent years, an attractive method of producing high value nanomaterials such as carbon nanotubes (CNTs) from waste plastics has been reported [4,5]. The produced CNTs were further utilised to produce reinforced materials which exhibited improved strength characteristics, implying the potential of the process in industrial applications [6].…”

High-value resource recovery products from waste tyres

“…Figure 3 shows that the main weight loss of the reacted catalysts resulting from carbon oxidation occurred between temperatures of 450 and 600°C and was assigned to the oxidation of amorphous carbon. The oxidation that occurred after a temperature of 600°C was assigned to the oxidation of filamentous/whisker-type carbon (Wu and Williams, 2010;Wu et al, 2013). Table 2 shows that carbon formation on the catalyst (coke deposits) for the catalyst used in the pyrolysis-catalysis of waste tyre samples was significant, being up to 14 wt% depending on the process conditions.…”

“…It is the amorphous carbons that primarily deactivate the catalyst by encapsulating the active metal sites of the catalyst. The whiskertype carbons are solid and filamentous in nature but in some cases hollow carbon nanotubes (CNTs) have been identified (Wu et al, 2013). CNTs comprise a tubular material composed of a graphitic hexagonal carbon structure with diameters ranging from 1 to 50 nm and lengths ranging from several microns to several centimetres.…”