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

Abstract

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.

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

“…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].…”

Present Advancement in Production of Carbon Nanotubes and Their Derivatives from Industrial Waste with Promising Applications

“…In addition, effect of synthesizing temperature on catalytic conversion of those plastic wastes to carbonaceous nanomaterials could be manifested through changes of catalyst particle size which is intentionally loaded into the synthesizing reactor (Bazargan and McKay, 2012;Altalhi et al, 2013). As a result, it should be noted that effluents of such plastic waste treating system are gases with substantial amounts of carbon monoxide, light hydrocarbons and hydrogen (Acomb et al, 2014). Therefore, it may be possible to utilize such gaseous by-products for power generation.…”

“…For example, in petrochemical downstream processing, the hydrocarbon gasses from the methane reformer would contain high content of CH 4 , CO and CO 2 , while those from refining units would consist of large compositions of BTEX, propane and ethylene. The current strategy for using these hydrocarbon gases is to install the carbon-material production unit on-board where the hydrocarbon sources are produced (Alves et al, 2011;Bazargan and McKay, 2012;Mankhand et al, 2012;Yang et al, 2012;Acomb et al, 2014). The use of suitable combustion equipment and catalyst as well as implementation of appropriate operating conditions, such as carbon source, flow of inert gas, and operating pressure, could realize controllable synthesis of CNTs with specifiable characteristics, such as diameter, length and purity Paradise and Goswami, 2007;Prasek, et al, 2011;Morales, et al, 2013).…”

“…Converting such plastic wastes into valuable products, such as carbon nanotubes (CNTs) could be an important and profitable option for industry and for environmental protection. Recently many research works focusing on synthesis of CNTs and other nanostructure derivatives through thermal decomposition of plastic wastes, such as polypropylene (PP), low density polyethylene (LDPE), high density polyethylene (HDPE), polyacrylate (PC), polyvinyl chloride (PVC), polystyrene (PS) and polyethyleneterephthalate (PET) with the presence of specific catalysts have been reported (Zhang et al, 2008;Quan et al, 2010;Zhuo et al, 2010;Mishra et al, 2012;Yang et al, 2012;Savant et al, 2013;Acomb et al, 2014;Bajad et al, 2015: Nahil et al, 2015. Within those previous works, usage of low-cost alternative feedstocks which are post-consumer plastic wastes for CNT production has been demonstrated.…”

“…plastics wastes), food wastes, and low value-added industrial by-products (red oil, glycerol, slop oil). Instead of using as alternative energy sources, such industrial wastes or by-products could be considered as one of good alternatives for production of carbonaceous nanomaterials Vijayaraghavan and Stevenson, 2007;Yuan et al, 2007;Zhang et al, 2008;Quan et al, 2010;Zhuo et al, 2010;Alves et al, 2011;Li et al, 2012;Yang et al, 2012;Altalhi et al, 2013;Acomb et al, 2014;Gong et al, 2014;Bajad et al, 2015). Table 2 summarizes some previous works which have made use of industrial waste as raw material for production of carbon nanotubes (CNTs) and derivatives.…”