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

Dingding Yao,Yeshui Zhang,Paul T Williams,Haiping Yang,Hanping Chen

doi:10.1016/j.apcatb.2017.09.035

Abstract

The 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-Al2O3 produced the highest hydrogen yield (22.9mmol H2/gplastic) and carbon nanotubes yield (195mgg−1plastic) among the monometallic catalysts, followed by Fe/α-Al2O3, Ni/γ-Al2O3 and Ni/α-Al2O3. The bimetallic Ni-Fe catalyst showed higher catalytic activity in relation to H2 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 (287mgg−1plastic) and hydrogen production (31.8mmol H2/gplastic) were obtained at 800°C in the absence of steam and in the presence of the bimetallic Ni-Fe/γ-Al2O3 catalyst.

Highlights

The worldwide demand for plastics grows rapidly and inevitably produces large quantities of waste plastics
Since the filamentous carbons deposited on these catalysts, observed from TEM data, were identified as carbon nanotubes (CNT), the results suggest that Ni/γ-Al2O3 produced more CNTs than Ni/α-Al2O3
The results show that the hydrogen yield increased from 27.2 to 43.7 mmol H2/gplastic when the catalyst temperature was increased from 700 to 900 °C, while carbon deposition on the catalyst remained high and in the range of 40–44 wt.%

Summary

Introduction

The worldwide demand for plastics grows rapidly and inevitably produces large quantities of waste plastics. 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]. Due to their extraordinary properties including chemical stability, electric conductivity, high surface area, etc., carbon nanotubes have been attracting worldwide attention [7,8,9]. Hydrogen, which will be an important clean fuel in the future, can be generated during this process

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