Carbon nanotubes from catalytic pyrolysis of polypropylene

252

134

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.

Section: Effect Of Catalyst Temperature On Carbon Nanotubes Productionmentioning

confidence: 99%

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

Yao

Zhang

Williams

et al. 2018

252

134

“…Current mass production of CNTs comes from chemical vapour deposition of hydrocarbon gases such as methane and acetylene, however the pull of a low cost alternative which tackles waste management problems has encouraged research into production from plastic sources. As a result, a number of studies have started to tailor their pyrolysis processes towards carbon nanotube production, achieving large yields with temperatures up to 900°C [17,[20][21][22][23][24][25][26][27]. Using a two stage process also enables large yields of hydrogen gas and carbon nanotubes can be produced simultaneously from a plastic source [20,26,28].…”

Section: Introductionmentioning

confidence: 99%

The use of different metal catalysts for the simultaneous production of carbon nanotubes and hydrogen from pyrolysis of plastic feedstocks

Acomb

Williams

2016

229

120

Nickel, iron, cobalt and copper catalysts were prepared by impregnation and used to produce carbon nanotubes and hydrogen gas from a LDPE feedstock. A two stage catalytic pyrolysis process was used to enable large yields of both products. Plastics samples were pyrolysed in nitrogen at 600°C, before the evolved gases were passed to a second stage and allowed to deposit carbon onto the catalyst at a temperature of 800°C. Carbon nanotubes were successfully generated on nickel, iron and cobalt but were barely observed on the copper catalyst. Iron and nickel catalysts gave the largest yield of both hydrogen and carbon nanotubes as a result of metal-support interactions which were neither too strong, like cobalts, nor too weak like copper. These metal support interactions proved a key factor in CNT production. A nickel catalyst with a weaker interaction was prepared using a lower calcination temperature. Yields of both carbon nanotubes and hydrogen gas were lower on the Ni-catalyst prepared at the lower calcination temperature, as a result of sintering of the nickel particles. In addition, the catalyst prepared at a lower calcination temperature produced metal particles which were too large for CNT growth, producing amorphous carbons which deactivate the catalyst instead. Overall the iron catalyst gave the largest yield of CNTs, which is attributed to both its good metal-support interactions and irons large carbon solubility.

“…CNT production from plastics has been demonstrated [27][28][29][30][31][32][33][34][35][36][37][38], however the effect of the steam injection rate on CNT and hydrogen has not been considered. The potential to produce CNTs from the pyrolysis of plastics was demonstrated by Kukovitsky et al [27].…”

Section: Introductionmentioning

confidence: 99%

“…Chung et al [35] investigated the use of both polypropylene (PP) and polystyrene (PS) as CNT precursors. CNTs were produced from each of the plastics, however the morphology of the CNTs varied depending on the feedstock due to the aromatic and olefinic nature of the precursors.…”

Section: Introductionmentioning

confidence: 99%

Control of steam input to the pyrolysis-gasification of waste plastics for improved production of hydrogen or carbon nanotubes

Acomb

2014

165

102

Carbon nanotubes (CNTs) have been proven to be possible as high-value by-products of hydrogen production from gasification of waste plastics. In this work, steam content in the gasification process was investigated to increase the quality of CNTs in terms of purity.Three different plastics -low density polyethylene (LDPE), polypropylene (PP) and polystyrene (PS) were studied in a two stage pyrolysis-gasification reactor. Plastics samples were pyrolysed in nitrogen at 600°C, before the evolved gases were passed to a second stage where steam was injected and the gases were reformed at 800°C in the presence of a nickelalumina catalyst. To investigate the effect that steam plays on CNT production, steam injection rates of 0, 0.25, 1.90 and 4.74 g h -1 were employed. The CNTs produced from all three plastics were multiwalled CNTs with diameters between 10 and 20 nm and several microns in length. For all the plastic samples, raising the steam injection rate led to increased hydrogen production as steam reforming and gasification of deposited carbon increased. High quality CNTs, as observed from TEM, TPO and Raman spectroscopy, were produced by controlling the steam injection rate. The largest yield for LDPE was obtained at 0 g h -1 steam injection rate, whilst PP and PS gave their largest yields at 0.25 g h -1 . Overall the largest CNT yield was obtained for PS at 0.25 g h -1 , with a conversion rate of plastic to CNTs of 32% wt.