Incinerator bottom ash derived from municipal solid waste as a potential catalytic support for biomass tar reforming

Ni-FeOx synergy induced by metal-support interaction on Ni-impregnated incineration bottom ash for effective tar reforming

The incineration bottom ash (IBA) was impregnated with nickel to catalyze toluene (tar surrogate) steam reforming. A toluene conversion of >80 % was achieved at 800℃ without activity decay in a 100-h test for 15 %Ni/IBA. An activation stage was observed for Ni/IBA catalysts in the initial 50 ∼ 400 min under different reaction conditions. A series of experiments and characterizations were performed to explore the possible mechanisms for the activation. It was found that the iron species in IBA gradually migrated to the catalyst surface and formed a Ni-FeOx complex owing to the metal-support interaction. The synergy of Ni-FeOx played an important role in improving the activity of Ni/IBA due to the enhanced lattice oxygen activity. Additionally, Ni/IBA catalysts showed a much lower coke deposition rate than Ni/Al2O3 (1.12 vs. 3.45 mg-C/gcat∙h) because of the variable states of FeOx and the abundant basic sites caused by the alkali and alkaline earth metals contained in IBA.

MSW pyrolysis volatiles' reforming by incineration fly ash for both pyrolysis products upgrading and fly ash stabilization

The effective disposal of municipal solid wastes (MSW) and its incineration-derived fly ash (IFA), which contains large amounts of heavy metals (HMs) and chlorine (Cl), is an urgent task. In this study, IFA was used to reform MSW pyrolysis volatiles within 500-800 °C. The changes of reformed pyrolysis products, the migration characteristics of HMs and Cl between IFA and pyrolysis products were investigated. The results indicated that the O- and Cl-containing compounds in pyrolysis oil tended to decrease, light hydrocarbons and its calorific value increased accordingly after reforming; more CH₄ and H₂ gases were produced concurrently. The increase in reforming temperature enhanced these trends. The IFA absorbed Cl from volatiles during reforming, which reduced HCl in the gas product. The toxicity equivalent (TEQ) of PCDD/Fs in IFA decreased dramatically from 0.47 μg/kg to 0.0055 μg/kg after reforming at 500 °C, and it decreased with increasing reforming temperature. Some of the HMs' concentrations in the used IFAs increased, but their leaching capacity all decreased significantly at 800 °C except for Cr. The used IFA at 800 °C (IFA-800) corresponded to the lowest HMs leaching concentrations and could meet the landfill requirements; while the used IFA at 500 °C (IFA-500) corresponded to the maximum carbon deposition of 14.63 wt%, providing the energy source for its melting. Therefore 800 °C was recommended for harmless disposal of IFA, and 500 °C was better for a further melting of IFA., The contamination of pyrolysis liquid caused by inorganic Cl-containing compounds at 500 and 800 °C with much lower levels than the original. This study showed the hazardous properties of IFA can be dampened after interacting with MSW pyrolysis volatiles within the tested temperature range, and provided a good chance for the simultaneous disposal of IFA and recovery of high-quality MSW pyrolysis products.

MSWIBA Formation and Geopolymerisation to Meet the United Nations Sustainable Development Goals (SDGs) and Climate Mitigation

Sustainable Development Goals (SDGs) constitute an action plan for the environment and people. One of the main goals is to limit the increase in global average temperature to 2 °C and aim for a stop at 1.5 °C. The goals of the circular economy (CE) are in line with the SDGs. In the waste management chain, the last CE element is a recovery in the municipal solid waste incineration plant (MSWIP). However, during recovery, municipal solid waste bottom ash (MSWIBA) is created (in about 30% of the bunch). The development of MSWIBA in the construction industry is a possibility of closing the cycle. This article shows the MSWIBA formation process, alkali pre-treatment of MSWIBA, and its geopolymerisation. Studies have determined the mechanical properties of geopolymer with MSWIBA and leachability from crushed and from monolith geopolymer. Alkali pre-treatment improves MSWIBA mechanical properties and upgrades immobilisation. Moreover, geopolymerisation is a better solution than concreting, because of the lack or low consumption of high-emission and energy-intensive cement. A SWOT analysis was carried out for the proposed solution.

Carbon Formation in the Reforming of Simulated Biomass Gasification Gas on Nickel and Rhodium Catalysts

Biomass gasification gas contains hydrocarbons that must be converted to CO and H2 prior to the utilization of the gas in a synthesis unit. Autothermal or steam reforming operating with a nickel or noble metal catalyst is a feasible option to treat the gas, but the harsh reaction conditions may lead to the formation of solid carbon. This study discusses the effects of pressure, time-on-stream, and ethylene content on the carbon formation on nickel and rhodium catalysts. The experiments were carried out with laboratory-scale equipment using reaction conditions that were closely simulated after a pilot-scale biomass gasifier. The results indicated that ethylene content above 20,000 vol-ppm and the increased pressure would increase the carbon formation, although there were differences between the rhodium and nickel catalysts. However, carbon formation was significantly more pronounced on the nickel catalyst when the reaction time was increased from 5 h to 144 h. The type of carbon was found to be primarily encapsulating and graphitic. The formation of whisker carbons (also known as carbon nanotubes) was not observed, which is consistent with the literature as the feed gas contained H2S. It was concluded that utilizing a noble metal catalyst as the front layer of the catalyst bed could lower the risk for carbon formation sufficiently to provide stable long-term operation.

Modification strategies of heterogeneous catalysts for water-gas shift reactions

Featured by high energy density, hydrogen has been deemed as a clean and renewable energy source compared with conventional fossil fuels. Water-gas shift reaction (WGSR) exhibits great potential in the...

Municipal Solid Waste Incineration Ash-Incorporated Concrete: One Step towards Environmental Justice

Municipal solid waste and cement manufacture are two sources of environmental justice issues in urban and suburban areas. Waste utilization is an attractive alternative to disposal for eliminating environmental injustice, reducing potential hazards, and improving urban sustainability. The re-use and recycling of municipal solid waste incineration (MSWI) ash in the construction industry has drawn significant attention. Incorporating MSWI ash in cement and concrete production is a potential path that mitigates the environmental justice issues in waste management and the construction industry. This paper presents a critical overview of the pretreatment methods that optimize MSWI ash utilization in cement/concrete and the influences of MSWI ash on the performance of cement/concrete. This review aims to elucidate the potential advantages and limitations associated with the use of MSWI ash for producing cement clinker, alternative binder (e.g., alkali-activated material), cement substitutes, and aggregates. A brief overview of the generation and characteristics of MSWI ash is reported, accompanied by identifying opportunities for the use of MSWI ash-incorporated products in industrial-scale applications and recognizing associated environmental justice implications.

Arming wood carbon with carbon-coated mesoporous nickel-silica nanolayer as monolithic composite catalyst for steam reforming of toluene

Steam reforming is an effective measure for biomass tar elimination as well as H₂-rich syngas (H₂ + CO) production. However, the granular or powdery Ni-based catalysts are prone to deactivation, which is caused by inappropriate mass transfer and clogging of catalyst bed. Herein, monolithic wood carbon (WC) with low-tortuosity microchannels is armed with a carbon-coated mesoporous nickel-silica nanocomposite (Ni-SiO₂@C) layer via an evaporation-induced self-assembly and calcination procedure for toluene (tar model compound) steam reforming. The quality of the Ni-SiO₂@C layer growing on the surface of WC microchannel is affected by the molar ratios of Si/Ni feed. A uniform thin-layer coverage is obtained on the Ni-15SiO₂@C/WC (Si/Ni = 15) catalyst, where highly dispersed Ni nanoparticles (average size of 6.6 nm) with appropriate metal-support interaction and remarkable mechanical strength are achieved. The mass transfer, coke resistance, and hydrothermal stability of the Ni-15SiO₂@C/WC catalyst were significantly improved by the multilevel structure assembled from the WC microchannels and the secondary ordered SiO₂ mesopores. A stable toluene conversion over 97% with an H₂ yield of 135 μmol/min was obtained at 600 °C on the Ni-15SiO₂@C/WC catalyst. This work opens a new window for facilely constructing high-performance wood carbon-based monolithic tar reforming catalyst.

In situ catalytic reforming of plastic pyrolysis vapors using MSW incineration ashes

The valorization of municipal solid waste incineration bottom and fly ashes (IBA and IFA) as catalysts for thermochemical plastic treatment was investigated. As-received, calcined, and Ni-loaded ashes prepared via hydrothermal synthesis were used as low-cost waste-derived catalysts for in-line upgrading of volatile products from plastic pyrolysis. It was found that both IBA and air pollution control IFA (APC) promote selective production of BTEX compounds (i.e., benzene, toluene, ethylbenzene, and xylenes) without significantly affecting the formation of other gaseous and liquid species. There was insignificant change in the product distribution when electrostatic precipitator IFA (ESP) was used, probably due to the lack of active catalytic species. Calcined APC (C-APC) demonstrated further improvement in the BTEX yield that suggested the potential to enhance the catalytic properties of ashes through pre-treatment. By comparing with the leaching limit values stated in the European Council Decision, 2003/33/EC for the acceptance of hazardous waste at landfills, all the ashes applied remained in the same category after the calcination and pyrolysis processes, except the leaching of Cl^- from the ESP, which was around the borderline. Therefore, the use of ashes in catalytic reforming application do not significantly deteriorate their metal leaching behavior. Considering its superior catalytic activity towards BTEX formation, C-APC was loaded with Ni at 15 and 30 wt%. The Ni-loading favored an increase in overall oil yield, while reducing the gas yield when compared to the benchmark Ni loaded ZSM catalyst. However, Ni addition also caused the formation of more heavier hydrocarbons (C20-C35) that would require post-treatment to recover favorable products like BTEX.

Research on synergistically hydrothermal treatment of municipal solid waste incineration fly ash and sewage sludge

To explore a feasible method of utilizing municipal solid waste incineration fly ash (IFA) rather than releasing it into solidified landfill, in this work, IFA was pretreated by mixing it with municipal sewage sludge (MSS) and applying hydrothermal treatment (HTT). The influences of the IFA dosage, HTT temperature, HTT time, and liquid to solid ratio (L/S) on the dewatering, chlorine migration, solidification, and leaching of heavy metals (HMs) in MSS were investigated. The results show that the synergistic effect was obtained, IFA enhanced the dewatering of MSS and in return, MSS improved the release of chlorine in IFA. The optimal pretreatment conditions were an IFA dosage of 5%, HTT temperature of 180 °C and HTT time of 60 min. The moisture of the solid residue after HTT could be controlled below 40%. Under a fixed IFA dosage, the chlorine content of the liquid could be reached almost 50% with increasing HTT temperature, and the chlorine distribution exhibited a strong positive correlation with the L/S ratio (R² > 0.90). The migrating chlorine was mainly derived from its soluble state, which was controlled by the HTT liquid volume. After the soluble chlorine was dissolved, bound chlorine compounds, such as CaCl(OH), gradually neutralized and released chlorine into the liquid during HTT, and finally reached an equilibrium as the L/S ratio continued to increase. In addition, during HTT, satisfactory HM immobilization performance was achieved and the fraction of HMs, such as Cr, Ni, Cu and Zn, stabilized.