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

Abstract

A B S T R A C TThe use of Ni-Fe catalysts for the catalytic pyrolysis of real-world waste plastics to produce hydrogen and high value carbon nanotubes (CNT), and the influence of catalyst composition and support materials has been investigated. Experiments were conducted in a two stage fixed bed reactor, where plastics were pyrolysed in the first stage followed by reaction of the evolved volatiles over the catalyst in the second stage. Different catalyst temperatures (700, 800, 900°C) and steam to plastic ratios (0, 0.3, 1, 2.6) were explored to optimize the product hydrogen and the yield of carbon nanotubes deposited on the catalyst. The results showed that the growth of carbon nanotubes and hydrogen were highly dependent on the catalyst type and the operational parameters. Fe/ γ-Al 2 O 3 produced the highest hydrogen yield (22.9 mmol H 2 /g plastic ) and carbon nanotubes yield (195 mg g −1 plastic ) among the monometallic catalysts, followed by Fe/α-Al 2 O 3 , Ni/γ-Al 2 O 3 and Ni/α-Al 2 O 3 . The bimetallic Ni-Fe catalyst showed higher catalytic activity in relation to H 2 yield than the monometallic Ni or Fe catalysts because of the optimum interaction between metal and support. Further investigation of the influence of steam input and catalyst temperature on product yields found that the optimum simultaneous production of CNTs (287 mg g −1 plastic ) and hydrogen production (31.8 mmol H 2 /g plastic ) were obtained at 800°C in the absence of steam and in the presence of the bimetallic Ni-Fe/γ-Al 2 O 3 catalyst.

Coke formation and deactivation during catalytic reforming of biomass and waste pyrolysis products: A review

“…In this regard, some authors observed by TEM that the coke deposited on Ni catalysts in the H2 production by in-line pyrolysis-reforming of several plastic feedstock (HDPE, LDPE, PP) comprises both amorphous (or encapsulating) and filamentous coke, the former being presumably favored by the olefinic nature of the stream entering into the reforming step [6,7,95,160,241]. Some of these authors aimed a co-production of H2 and filamentous coke in the form of CNTs due to their commercial interest.…”

“…Concerning reforming of hydrocarbons, a simultaneous production of H2 and carbon deposits with filamentous morphology is gaining interest in the nanotechnological research field, due to the potential use of these carbon materials (such as carbon nanotubes) in a number of mechanical, thermal and electronic applications. In this regard, the group of Williams in the University of Leeds (UK) has envisioned applications for the filamentous coke deposited on the catalyst during the steam reforming/gasification of the volatiles from the pyrolysis of waste plastics, such as low density polyethylene [6,312,313], polypropylene [241,314], tires [315] or real-world waste plastics [7,316], as well as in bio-oil reforming [317], based on the fact that this filamentous coke resembles high-value CNTs. Nevertheless, the feasibility of a co-production of coke with filamentous morphology together with H2 production during the reforming of hydrocarbons needs further study on the properties and formation/growth mechanism of the coke, aiming to advance in their understanding and thus to enhance the economical throughput of the reforming process within refinery.…”

“…Considering it is one of the most abundant renewable energy sources and its usage implies a null CO2 net generation, its valorization technologies show a noticeable development degree [2,3]. On the other hand, recycling of wastes from fossil fuels derivatives, such as plastic wastes, has aroused a great deal of interest in H2 production within a waste refinery framework, considering the following facts: (1) the world plastic production shows a continuous increasing trend, with a global production of 335·10 6 t in 2016 [4]; (2) their dumping involves a severe environmental issue due to their slow biodegradability [5]; and (3) their chemical composition is favorable toward the production of H2 and carbon materials [6,7].…”

Ab initio modelling of molecular hydrogen rotation in the outside of carbon nanotubes

“…Remarkably, both experimental and theoretical evidences for hydrogen solid-like packing have been very recently reported [3,4]. Accordingly, the research on methods to produce CNTs has been intensified over the last few years, including synthesis techniques from waste plastics [5] with hydrogen co-production [6].…”

Sustainable Steel Carburization by Using Snack Packaging Plastic Waste as Carbon Resources

“…Their rapidly-growing consumption in modern society has inevitably given rise to a large quantity of corresponding waste accumulation [6]. Over the past few decades, the urgency to recover resources from waste plastics has gained unprecedented attention around the world [7][8][9].…”