This study aims to develop a two-stage fluidized catalytic bed reactor system for continuous co-production of carbon nanotubes (CNTs) and hydrogen from waste plastics gasification. Ni/Al-SBA-15 and ...Ni–Cu/CaO–SiO2 catalysts have been synthesized and granulated for CNTs synthesis and hydrogen production in the first- and second-stage reactor, respectively. The operating parameters, including reaction temperature and equivalence ratio (ER), were investigated to confirm the feasibility for CNTs and hydrogen production of this system. The Ni/Al-SBA-15 added in the first-stage reactor enhanced the waste plastics degradation to produce CH4 and C2–C5 hydrocarbons with increasing temperature, which could be used as the source for CNTs synthesis. Lowering the ER promoted the catalytic thermal cracking and reforming of hydrocarbons that contributed to the CNTs and hydrogen production. Nevertheless, the H2 production rate showed a significant increase to 857.6 mmol/h-g catalyst with the assistance of Ni–Cu/CaO–SiO2 in the second-stage reactor. The produced smaller-molecule hydrocarbons from the second-stage reactor with higher temperatures could benefit the co-production of CNTs and hydrogen. The two-stage fluidized catalytic bed gasification system exhibited an optimal performance of high fraction CNTs and H2 when temperatures of first- and second-stage reactor were controlled at 600 and 800 °C, respectively, with 0.1 ER.
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•A two-stage fluidized catalytic bed is developed to produce carbon nanotubes and H2.•Ni/Al-SBA-15 and Ni–Cu/CaO–SiO2 were granulation to use in the pilot-scale system.•Ni/Al-SBA-15 and Ni–Cu/CaO–SiO2 highly enhanced carbon nanotubes and H2 production.•Operating parameters of the fluidized bed were evaluated for catalytic performance.•The system gave 857.6 mmol H2/h-g catalyst and carbon nanotubes fraction of 48.0%.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
The waste plastic gasification in a fluidized bed for a continuous carbon nanotube (CNT) and hydrogen coproduction is a potential method for sustainable management. Ni/Al2O3 catalysts have been ...synthesized by the impregnation method to upgrade hydrogen production and CNT synthesis. However, few studies investigated the effect of operating parameters for upcycling waste plastics into CNTs and hydrogen in the fluidized-bed system. The reaction temperature and the equivalence ratio (ER) were evaluated for CNT and hydrogen coproduction. Increasing the reaction temperature and lowering the ER enhanced the methane dry reforming, hydrocarbon dry reforming, and hydrocarbon direct decomposition for hydrogen and CNT coproduction. While increasing the reaction temperature from 500 to 700 °C can obtain higher CNT yield and H2 production rate, the system heated to 700 °C and maintained at this temperature should provide more energy. Moreover, the gas composition at 600 °C with 0.1 ER contained more CH4 and C2–C5 hydrocarbons compared with that with a higher ER, which could be used as the carbon source of CNTs. The reaction temperature of the fluidized bed in the waste plastic gasification system controlled at 600 °C with 0.1 ER and the gasified products upgraded through a catalytic fixed-bed reactor at 680 °C exhibited an optimal catalytic performance of less-defective CNTs in 22.0% yield and H2 production rate (385.1 mmol/h-g catalyst).
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Upcycling waste plastics into carbon nanotubes (CNTs) and hydrogen is attractive for its efficient disposal. Although Ni-based catalysts are typically used in both hydrogen production and CNT ...synthesis, few studies have investigated the catalytic active site for the co-production of CNTs and hydrogen by waste plastic gasification. To evaluate the effect of nickel species distribution of the Ni/Al2O3 catalyst, it was prepared by an impregnation method using different calcination atmospheres to determine their feasibility for the co-production of CNTs and hydrogen. For comparison, various Ni/Al2O3 catalysts for CNT growth were examined by CH4 thermal chemical vapor deposition (CVD). Ni/Al2O3 calcined under a reductive H2 atmosphere (H–Ni/Al2O3) gave smaller nickel nanoparticles containing metallic nickel species, which showed optimal performance for CNT and hydrogen co-production by waste plastic gasification. In addition, the quality of the CNTs was higher using this process compared to the CNTs synthesized by CH4 thermal CVD. Further examination of the catalysis temperature found that the H–Ni/Al2O3 catalyst gave higher quality CNTs in a 24.3% yield, along with a hydrogen production rate of 325.4 mmol h–1 g–1 of catalyst at 680 °C. The produced H–Ni/Al2O3 contained metallic nickel, demonstrating an improved catalytic activity for CNT and hydrogen production from waste plastics.
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Biomass gasification for hydrogen production was performed in a continuous-feeding fluidized-bed with the use of Fe/CaO catalysts. The relationship between catalyst properties and biomass ...gasification efficiencies was studied. The findings indicated that only CaO was involved in the enhancement of char gasification, resulting in an increased hydrogen production. However, CaO was also easily deactivated by biomass tar. The characterization results indicated that when CaO was impregnated with Fe, Ca2Fe2O5 formed on the surface of the support. Ca2Fe2O5 decomposed polyaromatic tar but was not effective in char gasification. The synergistic effects between Fe and CaO that effectively enhanced biomass gasification mainly involved combustion and pyrolysis, and the biomass gasification products, i.e., char and tar, were further gasified, indicating that tailor-made Fe/CaO catalysts prevented CaO deactivation by tar, thus promoting biomass gasification and hydrogen production.
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► Sawdust was gasified with less char formation with the assistance of CaO. ► Ca2Fe2O5, as the main reactive sites, decomposed polyaromatic tar. ► Ca2Fe2O5, as a protection, prevented CaO deactivation by biomass tar. ► Fe/CaO catalyst with well-designed enhanced H2 production and biomass gasification.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
The influence of the polymerization temperature upon the bulk‐structure‐doped conductive polymer polyaniline (emeraldine‐salt, PANI) on the semiconducting, optical, and electrical properties of the ...photocatalyst is investigated. When the B‐PANI polymerization temperature increases from 5 to 60 °C, the crystallinity and conductivity of Pt/N‐TiO2/B‐PANI (PNT/B‐PANI) decreases. To rectify the problems of recycling convenience and secondary pollution, this study combines a photocatalyst and a porous polystyrene film for sustainable hydrogen production. The photocatalytic performance of the polystyrene/PNT/B‐PANI‐5 (PS/PNT/B‐PANI‐5) photocatalyst film (27 047 μmol h−1 g−1) under simulated sunlight irradiation is enhanced by a factor of up to 1.6 compared to that of PS/PNT. Therefore, the PS/PNT/B‐PANI photocatalyst film is a visible‐light photocatalyst which is a promising candidate for enhancing photocatalytic recycling convenience.
This study focuses on enhancing photocatalyst recycling by developing polystyrene/Pt/N‐TiO2/polyaniline (PS/PNT/PANI) films. These films facilitate hydrogen production under simulated sunlight. Results indicate that porous PS/PNT/B‐PANI blended films exhibit the highest photocatalytic activity, achieving 27 047 μmol h−1 g−1, particularly at a polymerization temperature of 5 °C.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
This study investigated the stabilization efficiencies of using an aluminum-rich precursor to incorporate simulated cadmium-bearing waste sludge and evaluated the leaching performance of the product ...phase. Cadmium oxide and γ-alumina mixtures with various Cd/Al molar ratios were fired at 800–1000 °C for 3 h. Cadmium could be crystallochemically incorporated by γ-alumina into CdAl4O7 monoclinic phase and the reaction was strongly controlled by the treatment temperature. The crystal structure details of CdAl4O7 were solved and refined with the Rietveld refinement method. According to the structural refinement results, the stabilization efficiencies were quantified and expressed as a transformation ratio (TR) with optimized processing parameters. The preferred treatment temperature was found to be 950 °C for mixtures with a Cd/Al molar ratio of 1/4, as its TR value indicated the cadmium incorporation was nearly completed after a 3 h treatment scheme. Constant-pH leaching tests (CPLT) were conducted by comparing the leachability of the CdO and CdAl4O7 phases in a pH 4.0 environment. A remarkable reduction in cadmium leachability could be achieved via monoclinic CdAl4O7 structure formation to effectively stabilize hazardous cadmium in the waste stream. The CPLT and X-ray photoelectron spectroscopy (XPS) results suggested incongruent dissolution behavior during the leaching of the CdAl4O7 phase.
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This study involved the reuse of residues, including fly ash (FA) and bottom ash (BA), from municipal solid waste (MSW) incineration and reservoir sediment (RS) to make lightweight aggregates (LWAs) ...and to evaluate the effects of the incinerator type, material mixing ratio, and preparation conditions on the properties of the resulting aggregates. The MSW incineration ashes were mixed in three different ratios (65% BA + 15% FA, 70% BA + 10% FA, and 75% BA + 5% FA) with reservoir sediment and were sintered at temperatures of 950–1050 °C. The ash samples were obtained from an incineration plant equipped with fluidized-bed (FB) and mechanical-bed (MB) furnaces. The ash from the FB incinerator could be turned into LWAs at a relatively low temperature (1000 °C). Compressive strength measurements indicated that these aggregates were stronger than those manufactured using the ash from the MB incinerator. The BA and FA from the FB incinerator showed good chemical stabilities due to the operating conditions of the incinerator, suggesting that they are suitable for fabricating LWAs. Thus, the thermal synthesis of LWAs from mixtures of incineration residue and RS is a highly effective method for the recycling/disposal of MSW incinerator ash.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
This study aims to develop polystyrene/polyaniline/Pt/N-TiO2 (PS/PANI/PNT) photocatalytic films for hydrogen production under simulated sunlight to improve the efficiency of photocatalyst recycling. ...The effects of the molar ratio of aniline monomer (AN) to oxidizing reagent (ammonium peroxydisulfate, APS) and the weight ratio of AN to PNT on the conductivity of synthesized nanofiber PANI (F-PANI) materials were investigated. PS/PANI/PNT with F-PANI/PNT were synthesized for photocatalytic hydrogen production. An AN/APS molar ratio of 1:2 in F-PANI/PNT was suitable for AN oxidation. The conductive pathway of PANI chains was enhanced by PNT addition at a AN/PNT weight ratio of 1:0.25, which was favorable for enhancing conductivity, facilitating the faster migration of electron–hole pairs to the photocatalyst surface to improve the hydrogen production rate. The F-PANI/PNT photocatalyst effectively separates its electron–hole pairs and has strong electron reduction and hole oxidation abilities, which is suitable for improving the photocatalytic hydrogen production capacity. The contact angle of PS/F-PANI/PNT-2–0.25 was lower than that of PS/PNT, indicating that the hydrophilicity and active sites of PS/F-PANI/PNT-2–0.25 increased. The optimal photocatalytic hydrogen production of F-PS/PANI/PNT (28,580 μmol h-1 g-1) was reached when the polymerization temperature, AN/APS molar ratio, and AN/PNT weight ratio were 5 °C, 1:2, and 1:0.25, respectively. The PS/F-PANI/PNT film showed excellent recyclability, with comparable photocatalytic activity even after five cycle repetition tests. This approach provides a promising alternative to traditional photocatalytic systems and contribute to a more efficient photocatalyst recycling process.
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•F-PANI/PNT photocatalyst was successfully synthesized.•Effects of oxidant molar concentrations and PNT weight concentrations of F-PANI/PNT were discussed.•Optimal H2 production efficiency of PS/F-PANI/PNT-2–0.25 was 28,580 μmol h-1 g-1.•H2 production efficiency of PS/F-PANI/PNT-2–0.25 was 1.6-times higher than that of PS/F-PANI-2.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
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•QXRD indicated that more than 90% of Pb were extracted from CRT glass.•The formation of viscous semi-liquid glass facilitated Pb extraction.•87.3% of Pb were recovered by Na2CO3 ...addition through thermal reduction with C.•Re-vitrification of lead back to silicate-glass was detected with further heating.
This study quantitatively determined the extraction of lead from CRT funnel glass and examined the mechanisms of thermally reducing lead in the products of sintering Pb-glass with carbon in the pre-heated furnace. The experimentally derived results indicate that a 90.3 wt% lead extraction efficiency can be achieved with 20 wt% of C addition at 950 °C for 3 min under air. The formation of viscous semi-liquid glass blocked the oxygen supply between the interaction of C and Pb-glass, and was highly effective for the extraction of metallic Pb. A maximum of 87.3% lead recover was obtained with a C to Na2CO3 ratio of 1/3 at 1200 °C. The decrease of C/Na2CO3 ratio enhanced the metallic lead recovery by increasing the glass viscosity for effective sedimentation of metallic lead in the bottom. However, with the further increase of temperature and treatment time, re-vitrification of lead back to silicate-glass matrix was detected in both Pb-glass/C and Pb-glass/C/Na2CO3 systems. The findings indicated that with proper controls, using C as an inexpensive reagent can effectively reduce treatment time and energy, which is crucial to a waste-to-resource technology for economically recovering lead from the waste CRT glass.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
The purpose of this research was to study the influence of the aluminum content of Ni/Al-SBA-15 catalysts on catalytic performance in the production of carbon nanotubes (CNTs) and hydrogen (H
2
) ...during waste plastic gasification. The effects of the preparation method (
i.e.
, impregnation (IM) or the polyol process (P)) and Ni loading on CNT production were also discussed. Al-SBA-15 supports were synthesized by a two-step "pH-adjusting" hydrothermal method with various Si/Al ratios. The surface acidity of the Ni/Al-SBA-15 catalysts could be altered without destroying the mesoporous hexagonal structure by varying the Si/Al ratio. The catalytic performance indicated that the catalyst loaded with 10 wt% Ni on Al-SBA-15 with an Si/Al molar ratio of 10 prepared by the polyol process (10Ni/Al-SBA-15(10)-P) produced higher quality CNTs with uniform diameter in 74.1% yield. The mesoporous hexagonal structure and the more strongly acidic sites of 10Ni/Al-SBA-15(10)-P enhanced the CNT quality and promoted the dehydrogenation and aromatization of the waste plastic. Moreover, the Ni/Al-SBA-15(10) catalysts prepared
via
the polyol process with higher Ni loadings possessed better Ni dispersion and more active sites for high CNT yield compared to impregnated catalysts. Increasing the aluminum content of the Ni/Al-SBA-15 catalyst also enhanced the dry reforming of methane and hydrocarbons to generate more H
2
in the waste plastic gasification process.
The acidic sites of Ni/Al-SBA-15 catalysts strikingly promoted the activity of carbon nanotubes and H
2
production in waste plastic gasification.
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