Thermal degradation of real-world waste plastics and simulated mixed plastics in a two-stage pyrolysis-catalysis reactor for fuel production

Real-world postconsumer mixed plastics and a simulated mixture of plastics were processed in a two-stage pyrolysis-catalysis fixed bed reactor in the presence of a zeolite HZSM-5 catalyst. In addition, single plastic polyethylene, polypropylene, polystyrene, and polyethylene terephthalate were also processed in the two-stage reactor. The product yield, composition, and hydrocarbon distribution of the product oil was obtained in relation to plastic type. Noncatalytic pyrolysis of the plastics produced a high yield of an oil/wax product in the 81-97 wt % range. Addition of the catalyst reduced the yield of oil to between 44 and 51 wt %, with an increase in gas yield from cracking of the oil volatiles. However, the condensed oils produced from pyrolysis-catalysis were enriched with lower molecular weight (C5-C15) hydrocarbons and were markedly more aromatic in composition with a high proportion of single-ring aromatic hydrocarbons. Comparison of the results from pyrolysis and pyrolysis-catalysis of the simulated mixture of plastics with the data obtained for the individual plastics showed that significant interaction between the plastics occurred in the mixture with higher C2-C4 gas yield and higher aromatic content in the oils than expected from the proportions of the individual plastics in the mixture

Chemical Recycling of Printed Circuit Board Waste by Depolymerization in Sub- and Supercritical Solvents

Disposal of waste printed circuit boards is regarded as a potential major environmental problem due to their heavy metal content. Therefore, recycling waste printed circuit boards represents an opportunity to recover the high value resin chemicals and the high value metals that are present. In this study, the solvo-thermal depolymerisation of waste printed circuit boards obtained from desktop computer monitors was carried out using water, ethanol and acetone between 300 and 400 °C. Alkalis (NaOH, KOH) were used as additives to promote the removal of the resin fraction of the printed circuit boards. At 400 °C, 94 % resin removal was achieved when water was used as the solvent, in the presence of NaOH. The liquid produced in the process was analysed by GC/MS and the results showed that it was mainly composed of phenol, and some phenolic compounds, with up to 62.5 wt% present as phenol in the liquid phase

Characterization and evaluation of Ni/SiO catalysts for hydrogen production and tar reduction from catalytic steam pyrolysis-reforming of refuse derived fuel

A series of Ni/SiO catalysts have been prepared and investigated for their suitability for hydrogen production and tar reduction in a two-stage pyrolysis-reforming system, using refuse derived fuel (RDF) as the raw material. Experiments were conducted at a pyrolysis temperature of 600°C, and a reforming temperature of 800°C. The product gases were analysed by gas chromatography (GC) and the condensed fraction was collected and quantified using gas chromatography-mass spectrometry (GC-MS). The effects of the catalyst preparation method, nickel content and the addition of metal promoters (Ce, Mg, Al), were investigated. Catalysts were characterised using BET surface area analysis, temperature programmed oxidation (TPO), and scanning electron microscopy (SEM). The TPO and SEM analysis of the reacted catalysts showed that amorphous type carbons tended to be deposited over the Ni/SiO catalysts prepared by impregnation, while filamentous type carbons were favoured with the sol-gel prepared catalysts. The influence of catalyst promoters (Ce, Mg, Al) added to the Ni/SiO catalyst prepared by the sol-gel method was found not to be significant, as the H production was not increased and the tar formation was not reduced with the metal-added catalyst. The highest H concentration of 57.9vol.% and lower tar amount produced of 0.24mg/g; were obtained using the 20wt.% Ni/SiO catalyst prepared by sol-gel. On the other hand a low catalytic activity for H production and higher tar produced were found for the impregnated series of catalysts, which might be due to the smaller surface area, pore size and due to the formation of amorphous carbons on the catalyst surface. Alkenes and alcohol functional groups were mainly found in the analysed tar samples, with major concentrations of styrene, phenol, indene, cresols, naphthalene, fluorene, and phenanthrene

Enhanced methane and hydrogen yields from catalytic supercritical water gasification of pine wood sawdust via pre-processing in subcritical water

A two-stage batch hydrothermal process has been investigated with the aim of enhancing the yields of hydrogen and methane from sawdust. Samples of the sawdust were rapidly treated in subcritical water and with added Na2CO3 (alkaline compound) and Nb2O3 (solid acid) at 280 °C, 8 MPa. Each pre-processing route resulted in a solid recovered product (SRP), an aqueous residue and a small amount of gas composed mainly of CO2. In the second stage, the SRP and the liquid residues were gasified in supercritical water in the presence of Ru/Al2O3 catalyst for reaction times of up to 60 min for the SRP at 500 °C, 30 MPa. Using the catalyst, carbon gasification efficiencies and methane selectivity increased with increasing reaction time. Overall, SRP from the Na2CO3 pre-processing route produced 51% more hydrogen and 61% more methane than the original sawdust under identical reaction conditions. The cumulative yields of methane and hydrogen were 57.1 mol kg−1, 42.5 mol kg−1 and 47.7 mol kg−1, from Na2CO3, Nb2O5 and neutral pre-processing routes, respectively. The combined yield of the two gases from direct SCWG of the original sawdust was 24.6 mol kg−1. The entire process may represent a step-change in future energy production from biomass as the products from the first stage can be used as feedstocks for various other biomass conversion technologies

Catalytic Supercritical Water Gasification of Refuse Derived Fuel for High Energy Content Fuel Gas

Refuse derived fuel (RDF) was processed using hydrothermal gasification at high temperature to obtain a high energy content fuel gas. Supercritical water gasification of RDF was conducted at a temperature of 500 °C and 29 MPa pressure and also in the presence of a solid RuO2/γ-Al2O3 catalyst. The effect of residence time (0, 30 and 60 min) and different ruthenium loadings (5, 10, 20 wt% RuO2/γ-Al2O3) were investigated. Up to 93 % carbon gasification efficiency was achieved in the presence of 20 wt% RuO2/γ-Al2O3 catalyst. The fuel gas with the highest energy value of 22.5 MJ Nm−3 was produced with the 5 wt% RuO2/γ-Al2O3 catalyst after 30 min reaction time. The results were compared with the use of NaOH as a homogeneous catalyst. When NaOH was used, the maximum gross calorific value of the product gas was 32.4 MJ Nm−3 at 60 min reaction time as a result of CO2 fixation. High yields of H2 and CH4 were obtained in the presence of both the NaOH and RuO2/γ-Al2O3 catalysts

Supercritical water oxidation of dioxins and furans in waste incinerator fly ash, sewage sludge and industrial soil

Three environmental samples containing dioxins and furans have been oxidized in the presence of hydrogen peroxide under supercritical water oxidation conditions. The samples consisted of a waste incinerator fly ash, sewage sludge and contaminated industrial soil. The reactor system was a batch, autoclave reactor operated at temperatures between 350°C and 450°C, corresponding to pressures of ~20-33.5 MPa and with hydrogen peroxide concentrations from 0.0 to 11.25 vol%. Hydrogen peroxide concentration and temperature/pressure had a strong positive effect on the oxidation of dioxins and furans. At the highest temperatures and pressure of supercritical water oxidation of 450°C and 33.5 MPa and with 11.25 vol% of hydrogen peroxide, the destruction efficiencies of the individual polychlorinated dibenzo-ρ-dioxins/polychlorinated dibenzofurans (PCDD/PCDF) isomers were between 90% and 99%. There did not appear to be any significant differences in the PCDD/PCDF destruction efficiencies in relation to the different sample matrices of the waste incinerator fly ash, sewage sludge and contaminated industrial soil

Potential applications of nanotechnology in thermochemical conversion of microalgal biomass

The rapid decrease in fossil reserves has significantly increased the demand of renewable and sustainable energy fuel resources. Fluctuating fuel prices and significant greenhouse gas (GHG) emission levels have been key impediments associated with the production and utilization of nonrenewable fossil fuels. This has resulted in escalating interests to develop new and improve inexpensive carbon neutral energy technologies to meet future demands. Various process options to produce a variety of biofuels including biodiesel, bioethanol, biohydrogen, bio-oil, and biogas have been explored as an alternative to fossil fuels. The renewable, biodegradable, and nontoxic nature of biofuels make them appealing as alternative fuels. Biofuels can be produced from various renewable resources. Among these renewable resources, algae appear to be promising in delivering sustainable energy options. Algae have a high carbon dioxide (CO2) capturing efficiency, rapid growth rate, high biomass productivity, and the ability to grow in non-potable water. For algal biomass, the two main conversion pathways used to produce biofuel include biochemical and thermochemical conversions. Algal biofuel production is, however, challenged with process scalability for high conversion rates and high energy demands for biomass harvesting. This affects the viable achievement of industrial-scale bioprocess conversion under optimum economy. Although algal biofuels have the potential to provide a sustainable fuel for future, active research aimed at improving upstream and downstream technologies is critical. New technologies and improved systems focused on photobioreactor design, cultivation optimization, culture dewatering, and biofuel production are required to minimize the drawbacks associated with existing methods. Nanotechnology has the potential to address some of the upstream and downstream challenges associated with the development of algal biofuels. It can be applied to improve system design, cultivation, dewatering, biomass characterization, and biofuel conversion. This chapter discusses thermochemical conversion of microalgal biomass with recent advances in the application of nanotechnology to enhance the development of biofuels from algae. Nanotechnology has proven to improve the performance of existing technologies used in thermochemical treatment and conversion of biomass. The different bioprocess aspects, such as reactor design and operation, analytical techniques, and experimental validation of kinetic studies, to provide insights into the application of nanotechnology for enhanced algal biofuel production are addressed

Anaerobic digestion and gasification of seaweed

The potential of algal biomass as a source of liquid and gaseous biofuels is a highly topical theme, with over 70 years of sometimes intensive research and considerable financial investment. A wide range of unit operations can be combined to produce algal biofuel, but as yet there is no successful commercial system producing such biofuel. This suggests that there are major technical and engineering difficulties to be resolved before economically viable algal biofuel production can be achieved. Both gasification and anaerobic digestion have been suggested as promising methods for exploiting bioenergy from biomass, and two major projects have been funded in the UK on the gasification and anaerobic digestion of seaweed, MacroBioCrude and SeaGas. This chapter discusses the use of gasification and anaerobic digestion of seaweed for the production of biofuel

Catalytic conversion of bio-oil in supercritical water: Influence of RuO2/γ-Al2O3 catalysts on gasification efficiencies and bio-methane production

Catalytic supercritical water gasification of heavy (dewatered) bio-oil has been investigated in a batch reactor in the presence of ruthenium catalysts in the form of RuO2 on γ-Al2O3 support. The reactions were carried out at temperatures of 400 °C, 450 °C and 500 °C and reaction times of up to 60 min using 15 wt% of bio-oil feed. Increased ruthenium oxide loading led to increased carbon gasification efficiencies (CGE) and bio-methane production. Hence, using the 20 wt% RuO2/γ-Al2O3 catalyst, CGE was 97.4 wt% at 500 °C and methane yield reached nearly 30 wt% of the bio-oil feed, which gave a CH4/CO2 molar ratio of 1.28. There was evidence that the RuO2 was involved in the initial conversion of the bio-oil to carbon oxides and hydrogen as well as the reduction of the CO2 to methane via CO methanation. However, competition for CO consumption via the water-gas shift reaction was also possible due to the large presence of water as the reaction medium. This work therefore demonstrates that high concentrations of heavy fraction of bio-oil can be catalytically converted to a methane-rich gas product under hydrothermal conditions at moderate temperatures. The calorific values of the gas product reached up to 54 MJ kg−1, which is nearly 3 times the HHV of the bio-oil feed

Catalytic pyrolysis of waste plastic from electrical and electronic equipment

Plastic waste collected from waste electrical and electronic equipment (WEEE) was pyrolysed in the presence of zeolite catalysts to produce a gasoline range aromatic oil. The plastic was from equipment containing cathode ray tubes (CRTs) and also plastic waste from refrigeration equipment. In addition, for comparison the main plastics contained in the WEEE, in the form of high impact polystyrene (HIPS) and acrylonitrile-butadiene-styrene (ABS) were also pyrolysed in the presence of the zeolite catalysts. Two zeolite catalysts; Y zeolite and ZSM-5 were used. Catalytic pyrolysis took place in a two stage fixed bed, batch reactor with the plastic pyrolysed in the first stage and the evolved pyrolysis gases catalysed in the second stage reactor. The quantity of oil produced from uncatalysed pyrolysis of plastics from CRTs and refrigerators was more than 80 wt%. The gases consisted of hydrogen, methane and C2-C4 hydrocarbons. When the zeolite catalysts were introduced there was a decrease of between 5 and 10 wt% in oil yield and a corresponding increase in gas yield. The composition of the oils derived from the uncatalysed pyrolysis of WEEE plastics were mainly aromatic with high concentrations of styrene, derived from the HIPS and ABS present in the plastic waste. Addition of the zeolite ZSM-5 and Y zeolite to the pyrolysis process resulted in significant concentrations of benzene, toluene and ethylbenzene in the product oil but reduced concentrations of styrene. The oils from both thermal and catalysed pyrolysis also contained significant concentrations of polycyclic aromatic hydrocarbons for example, naphthalene, phenanthrene and pyrene