Development of Ni- and Fe- based catalysts with different metal particle sizes for the production of carbon nanotubes and hydrogen from thermo-chemical conversion of waste plastics

Co-production of valuable hydrogen and carbon nanotubes (CNTs) has obtained growing interest for the management of waste plastics through thermo-chemical conversion technology. Catalyst development is one of the key factors for this process to improve hydrogen production and the quality of CNTs. In this work, Ni/SiO2 and Fe/SiO2 catalysts with different metal particle sizes were investigated in relation to their performance on the production of hydrogen and CNTs from catalytic gasification of waste polypropylene, using a two-stage fixed-bed reaction system. The influences of the type of metals and the crystal size of metal particles on product yields and the production of CNTs in terms of morphology have been studied using a range of techniques; gas chromatography (GC); X-ray diffraction (XRD); temperature programme oxidation (TPO); scanning electron microscopy (SEM); transmission electron microscopy (TEM) etc. The results show that the Fe-based catalysts, in particular with large particle size (∼80 nm), produced the highest yield of hydrogen (∼25.60 mmol H2 g−1 plastic) and the highest yield of carbons (29 wt.%), as well as the largest fraction of graphite carbons (as obtained from TPO analysis of the reacted catalyst). Both Fe- and Ni-based catalysts with larger metal particles produced higher yield of hydrogen compared with the catalysts with smaller metal particles, respectively. Furthermore, the CNTs formed using the Ni/SiO2-S catalyst (with the smallest metal particles around 8 nm) produced large amount of amorphous carbons, which are undesirable for the process of CNTs production

Pyrolysis-catalytic dry (CO2) reforming of waste plastics for syngas production: Influence of process parameters

Catalytic dry (CO2) reforming of waste plastics was carried out in a two stage, pyrolysis-catalytic reforming fixed bed reactor to optimise the production of syngas (H2 + CO). The effects of changing the process parameters of, catalyst preparation conditions, catalyst temperature, CO2 input rate and catalyst:plastic ratio were investigated. The plastics used was a mixture of plastics simulating that found in municipal solid waste and the catalyst used was Ni-Co-Al2O3. The results showed that changing each of the process conditions investigated, all significantly influenced syngas production. An increase of 17% of syngas production was achieved from the experiment with the catalyst prepared by rising-pH technique compared to preparation via the impregnation method. The optimum syngas production of 148.6 mmolsyngas g−1swp was attained at the catalytic dry reforming temperature of 800 °C and catalyst:plastic ratio of 0.5. The increase of CO2 input rate promoted a higher yield of syngas

Investigation of nickel-impregnated zeolite catalysts for hydrogen/syngas production from the catalytic reforming of waste polyethylene

Catalytic steam reforming of waste high density polyethylene for the production of hydrogen/syngas has been investigated using different zeolite supported nickel catalysts in a two-stage pyrolysis-catalytic steam reforming reactor system. Experiments were conducted into the influence of the type of zeolite where Ni/ZSM5-30, Ni/β-zeolite-25 and the Ni/Y-zeolite-30 catalysts were compared in relation to hydrogen and syngas production. Results showed that the Ni/ZSM5-30 catalyst generated the maximum syngas production of 100.72 mmol g‾¹ plastic , followed by the Ni/β-zeolite-25 and Ni/Y-zeolite-30 catalyst. In addition, the ZSM-5 supported nickel catalyst showed excellent coke resistance and thermal stability. It was found that the Y type zeolite supported nickel catalyst possessed narrower pores than the other catalysts, which in turn, promoted coke deactivation of the catalyst. Large amounts of filamentous carbons were observed on the surface of the Ni/Y-zeolite-30 catalyst from scanning electron microscope images. In addition, the influence of Si:Al molar ratio for the Ni/ZSM-5 catalysts in relation to hydrogen and syngas yield was inv estigated. The results indicated that hydrogen production was less affected by the Si:Al ratio than the type of zeolite support. Also, the Ni/ZSM5-30 catalyst was further investigated to determine the influence of different process parameters on hydrogen and syngas yield via different reforming temperatures (650, 750, 850 °C) and steam feeding rate (0, 3, 6 g h‾¹). It was found that increasing both the temperature and steam feeding rate favoured hydrogen production from the pyrolysis-catalytic reforming of waste polyethylene. The optimum catalytic performance in terms of syngas production was achieved when the steam feeding rate was 6 g h‾¹ and catalyst temperature was 850 °C in the presence of Ni/ZSM5-30 catalyst, with production of 66.09 mmol H 2 g‾¹(plastic) and 34.63 mmol CO gg‾¹(plastic)

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

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 nickel-alumina catalyst. To investigate the effect that steam plays on CNT production, steam injection rates of 0, 0.25, 1.90 and 4.74gh-1 were employed. The CNTs produced from all three plastics were multiwalled CNTs with diameters between 10 and 20nm 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 0gh-1 steam injection rate, whilst PP and PS gave their largest yields at 0.25gh-1. Overall the largest CNT yield was obtained for PS at 0.25gh-1, with a conversion rate of plastic to CNTs of 32wt%

Processing real-world waste plastics by pyrolysis-reforming for hydrogen and high-value carbon nanotubes

Producing both hydrogen and high-value carbon nanotubes (CNTs) derived from waste plastics is reported here using a pyrolysis-reforming technology comprising a two-stage reaction system, in the presence of steam and a Ni-Mn-Al catalyst. The waste plastics consisted of plastics from a motor oil container (MOC), commercial waste high density polyethylene (HDPE) and regranulated HDPE waste containing polyvinyl chloride (PVC). The results show that hydrogen can be produced from the pyrolysis-reforming process, but also carbon nanotubes are formed on the catalyst. However, the content of 0.3 wt.% polyvinyl chloride in the waste HDPE (HDPE/PVC) has been shown to poison the catalyst and significantly reduce the quantity and purity of CNTs. The presence of sulfur has shown less influence on the production of CNTs in terms of quantity and CNT morphologies. Around 94.4 mmol H g plastic was obtained for the pyrolysis-reforming of HDPE waste in the presence of the Ni-Mn-Al catalyst and steam at a reforming temperature of 800 C. The addition of steam in the process results in an increase of hydrogen production and reduction of carbon yield; in addition, the defects of CNTs, for example, edge dislocations were found to be increased with the introduction of steam (from Raman analysis)

Hydrogen and Carbon Nanotubes from Pyrolysis-Catalysis of Waste Plastics: A Review

More than 27 million tonnes of waste plastics are generated in Europe each year representing a considerable potential resource. There has been extensive research into the production of liquid fuels and aromatic chemicals from pyrolysis-catalysis of waste plastics. However, there is less work on the production of hydrogen from waste plastics via pyrolysis coupled with catalytic steam reforming. In this paper, the different reactor designs used for hydrogen production from waste plastics are considered and the influence of different catalysts and process parameters on the yield of hydrogen from different types of waste plastics are reviewed. Waste plastics have also been investigated as a source of hydrocarbons for the generation of carbon nanotubes via the chemical vapour deposition route. The influences on the yield and quality of carbon nanotubes derived from waste plastics are reviewed in relation to the reactor designs used for production, catalyst type used for carbon nanotube growth and the influence of operational parameters

MONOCHROMATOR FOR THE VACUUM ULTRAVIOLET II. HIGH RESOLUTION MONOCHROMATOR (APPLICATION OF OFF-PLANE EAGLE MOUNTING)

Author Institution: Laboratory of Molecular Structure and Spectra, Department of Physics, The University of ChicagoThe possibility of constructing a high resolution monochromator for the vacuum ultraviolet is examined; the off-plane Eagle mounting is chosen as the most suitable one. Considering all optical restrictions arising from an off-plane setting, the resolving power of the grating in the off-plane Eagle mounting is calculated numerically for the following conditions; 3-meter concave grating $(5 \times 3^{\prime}$ ruled area) with 30,000 lines/inch or 15,000 lines/inch, 0 to 5800 \AA in the first order, and distance of the entrance slit from the Rowland plane 6 cm. In order to have compactness, a link mechanism introduced by Bair et al. is chosen in the scanning system and a tentative design of a 3-meter vacuum monochromator Will be shown schematically. Therefore, it is recommended to use the off-plane Eagle mounting in constructing a high resolution monochromator for the vacuum ultraviolet

Current research activities in the field of multilayers for soft X-rays in Japan

The present status of studies on soft X-ray multilayers in Japan is briefly reviewed. This includes the design concepts, optical constants of substrates and thin films, fabrication techniques, evaluation methods, and some applications