Mohamad A. Nahil

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 H2 g(-1) 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).

Novel bi-functional Ni–Mg–Al–CaO catalyst for catalytic gasification of biomass for hydrogen production with in situ CO2 adsorption

Catalytic gasification of biomass in the presence of CaO is a promising route for CO2 capture and thereby high yield hydrogen production. However, the instability of the CaO sorbent for CO2 adsorption is a challenge for the process. A novel bi-functional Ni–Mg–Al–CaO catalyst has been prepared with different contents of CaO by integration of the catalytic and CO2 adsorbing materials to maximise hydrogen production. The prepared catalysts were tested for hydrogen production via the pyrolysis-gasification of wood biomass using a two-stage fixed-bed reaction system. The carbonation/calcination results using thermogravimetric analysis (TGA), in an atmosphere of N2 or CO2, showed that the reactivity of CaO with CO2 decreased even after several cycles of carbonation/calcination, while the Ni–Mg–Al–CaO catalyst showed a comparatively stable CO2 adsorption even after 20 cycles. Adding CaO to the Ni–Mg–Al catalyst leads to an increase in hydrogen production and selectivity due to the enhancement of the water–gas shift reaction by in situ CO2 adsorption. An optimal content of CaO was suggested to be 20 wt% (weight ratio of CaO/Ni–Mg–Al) which gave the highest hydrogen production (20.2 mmol g−1 biomass) in the presence of the Ni–Mg–Al–CaO catalyst. Temperature-programmed oxidation (TPO) showed that carbon deposition was significantly decreased with the addition of CaO in the Ni–Mg–Al catalyst, and with the increase of CaO content, coke deposition on the reacted catalyst was further decreased.

Thermal processing of plastics from waste electrical and electronic equipment for hydrogen production

Plastic waste from waste electrical and electronic equipment (WEEE) produced from a real-world commercial WEEE recycling centre has been processed using pyrolysis–gasification using a two-stage reaction system to produce hydrogen. In the first stage, the plastic fraction was pyrolysed at 600 °C and the evolved pyrolysis gases were passed directly to a second reactor at 800 °C and reacted with steam in the presence of a Ni/Al2O3 catalyst. In addition, high impact polystyrene (HIPS) and acrylonitrile–butadiene–styrene (ABS) which were the main components of the WEEE plastic were reacted to compare with the WEEE plastic. The results showed that the introduction of steam and the catalyst increased the yield of hydrogen. Increasing the nickel content in the catalyst also resulted in higher hydrogen yield. The comparison of the results of WEEE with those of HIPS and ABS showed that WEEE plastic was mainly composed of ABS. The catalyst, after reaction, showed significant deposition of coke composed of filamentous and layered type carbon. Overall the novel processing of waste plastic from electrical and electronic equipment using a two stage pyrolysis–gasification reactor shows great promise for the production of hydrogen.

High temperature pyrolysis of solid products obtained from rapid hydrothermal pre-processing of pinewood sawdust†

A sample of pinewood sawdust was rapidly pre-processed in a torrefaction-type procedure, separately in subcritical water (neutral) and with added Na2CO3 (alkaline compound) and Nb2O5 (solid acid) in a batch reactor. The original sawdust and the three friable solid recovered products from the hydrothermal procedure were characterized in detail. The solid recovered products (SRPs) gave higher C/O and C/H ratios, higher calorific values and reduced moisture contents compared to the original sawdust. The four solid samples were then subjected to rapid high temperature pyrolysis in a fixed-bed reactor to investigate the effect of the pre-processing routes on the yields and compositions of the pyrolysis products. With increasing pyrolysis temperature, the pre-processed samples produced more CO and H2, far more char and less tar than the original sawdust. The trends in the composition of gases and the yields of char suggested a combination of Boudouard reaction and CO2 dry reforming as the predominant reactions during pyrolysis. For all samples, increased temperature led to reduced tar production with an increase in the aromatic oxygenates and aromatic hydrocarbon contents of the tar. At 800 °C, the ratio of aromatic hydrocarbons increased dramatically particularly from the sample pre-processed with Nb2O5 indicating possible deoxygenation catalysis.

Novel application of biochar from biomass pyrolysis for low temperature selective catalytic reduction

Biomass pyrolysis is regarded as a promising technology to produce bio-oils for future energy. Biochar generated from the biomass pyrolysis is normally combusted to provide extra heat to the pyrolysis process. In this work, the novel application of the biochar in the field of low temperature selective catalytic reduction (SCR) of NOx has been investigated in order to increase the economic value of the biochar. Biochar produced from the pyrolysis of cotton stalk agriculture waste was steam activated and used as a catalyst support for Ce–Mn. The influence of the steam activation on SCR experiment was investigated. The results show that there are two temperature windows during the SCR. The first is between 180 and 240°C, where the material (Ce–Mn–AC1) with less mesoporous shows the highest NO conversion (∼20%). The second is after 260°C, where the catalysts with more mesopores and higher acidity show better NO conversion (∼55%).

Pyrolysis–catalysis of waste plastic using a nickel–stainless-steel mesh catalyst for high-value carbon products

ABSTRACT A stainless-steel mesh loaded with nickel catalyst was produced and used for the pyrolysis–catalysis of waste high-density polyethylene with the aim of producing high-value carbon products, including carbon nanotubes (CNTs). The catalysis temperature and plastic-to-catalyst ratio were investigated to determine the influence on the formation of different types of carbon deposited on the nickel–stainless-steel mesh catalyst. Increasing temperature from 700 to 900°C resulted in an increase in the carbon deposited on the nickel-loaded stainless-steel mesh catalyst from 32.5 to 38.0 wt%. The increase in sample-to-catalyst ratio reduced the amount of carbon deposited on the mesh catalyst in terms of g carbon g−1 plastic. The carbons were found to be largely composed of filamentous carbons, with negligible disordered (amorphous) carbons. Transmission electron microscopy analysis of the filamentous carbons revealed them to be composed of a large proportion (estimated at ∼40%) multi-walled carbon nanotubes (MWCNTs). The optimum process conditions for CNT production, in terms of yield and graphitic nature, determined by Raman spectroscopy, was catalysis temperature of 800°C and plastic-to-catalyst ratio of 1:2, where a mass of 334 mg of filamentous/MWCNTs g−1 plastic was produced.