Abstract
Hydrogen production from waste plastics is an important alternative for managing waste plastics. This work addresses a promising technology for co-producing high value carbon nanotubes (CNTs) in addition to the production of hydrogen; thus significantly increasing the economic feasibility of the process. Catalyst design is a critical factor to control the production of hydrogen and CNTs. NiMnAl catalysts, prepared by a co-precipitation method, with different metal molar ratios were developed and investigated using a two-stage fixed-bed reactor. It was found that the NiMnAl catalyst with the higher Mn content produced a higher yield of carbon (57.7wt.%). Analysis of the carbon on the NiMnAl catalysts showed it to consist of ⿼90wt.% of carbon nanotubes. The CNTs were recovered from the catalyst and added at 2wt.% to LDPE plastic to form a composite material. The tensile and flexural strength and the tensile and flexural modulus of the CNT composite material were significantly improved by the addition of the recovered CNTs. Thus it is suggested that cost-effective CNTs could be produced from waste plastics as by-product of the production of hydrogen, enhancing the potential applications of CNTs in the composite industry.
Highlights
Plastic is an essential material widely used in both everyday life and manufacturing processes since their commercial development in the 1930s and 1940s (PlasticsEurope, 2014)
We propose the following mechanism for carbon nanotubes (CNTs) and hydrogen production from the pyrolysis-catalytic steam reforming of waste plastic: (i) at the initial stage of the experiment, the catalyst has high catalytic activity for steam reforming of pyrolysis vapours to produce hydrogen and other gases; (ii) due to the saturation of carbon sources, carbon deposition on the surface of catalyst occurs; (iii) in this work, the NiMnAl 444 catalyst generated a large fraction of amorphous carbons compared with the NiMnAl 424 catalyst due to the effect of promoter Mn
This work has demonstrated the co-production of valuable CNTs and clean hydrogen energy carrier as a promising process for the management of waste plastics
Summary
Plastic is an essential material widely used in both everyday life and manufacturing processes since their commercial development in the 1930s and 1940s (PlasticsEurope, 2014). Among the current technologies, advanced thermo-chemical processes including pyrolysis and gasification have shown the most promise (Acomb et al, 2014; Lopez-Urionabarrenechea et al, 2011; Straka and Bicakova, 2014). Waste plastics can be converted into transportation grade liquid fuels (Lopez-Urionabarrenechea et al, 2011); gasification of waste plastics, can produce a hydrogen enriched syngas for producing energy, fuel and power (Acomb et al, 2013, 2014; Kannan et al, 2013; Straka and Bicakova, 2014)
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