Performance and kinetics of iron-based oxygen carriers reduced by carbon monoxide for chemical looping combustion

Chemical looping combustion is a promising technology for energy conversion due to its low-carbon, high-efficiency, and environmental-friendly feature. A vital issue for CLC process is the development of oxygen carrier, since it must have sufficient reactivity. The mechanism and kinetics of CO reduction on iron-based oxygen carriers namely pure Fe₂O₃ and Fe₂O₃ supported by alumina (Fe₂O₃/Al₂O₃) were investigated using thermo-gravimetric analysis. Fe₂O₃/Al₂O₃ showed better reactivity over bare Fe₂O₃ toward CO reduction. This was well supported by the observed higher rate constant for Fe₂O₃/Al₂O₃ over pure Fe₂O₃ with respective activation energy of 41.1±2.0 and 33.3±0.8 kJ·mol⁻¹. The proposed models were compared via statistical approach comprising Akaike information criterion with correction coupled with F-test. The phase-boundary reaction and diffusion control models approximated to 95% confidence level along with scanning electron microscopy results; revealed the promising reduction reactions of pure Fe₂O₃ and Fe₂O₃/Al₂O₃. The boosting recital of iron-based oxygen carrier support toward efficient chemical looping combustion could be explained accurately through the present study.     

Distribution of labile and residual particulate carbon in the Baltic Sea

During the September 1971 cruise of F. K. Alkor in the central Baltic Sea, the surface or summer water layer down to a depth of about 30 m was found to contain 187.4 g/l of particulate organic carbon, with a C:N (atoms) ratio of 8.97. This carbon was 44% (89.9 g/l) labile to bacterial decomposition, as determined by burning an aliquot of each sample in a CHN-analyser before and after maintenance in nutrientenriched sea water at 20°C for 3 months. The particulate material from the intermediate or winter water layer, with a depth ranging from 30 to 70 m, contained only 48% (43.1 g/l) of the labile carbon found in the summer surface layer, and had a significantly higher C:N ratio (11.25). These two facts indicate that a considerable breakdown of the organic material had taken place. The material, removed from the particulate state during this process, was 48% (89.7 g/l) of the original total particulate carbon, and was relatively nitrogen-rich, with a C:N ratio of 6.49. In this material, 52% (46.8 g/l) of the organic carbon was labile. The particulate material in the rest of the water column showed no significant changes until it reached the sediment. The slurry immediately above the sediment had a C:N ratio of 9.15, indicating the introduction of nitrogen from either dissolved or colloidal material. Labile carbon (44% of the total) was also present in sufficient quantities to support life and to make this an important diagenetic site.     

Mechanism of dry detoxification of chromium slag by carbon monoxide

Environmental Chemistry Letters - Dry detoxification is a major technology used at the industrial scale for remediation of chromium slag. However, the mechanism of this reaction is poorly known, in...     

Anaerobic degradation kinetics of reactive dye with different carbon sources

This study aims to investigate the anaerobic degradation kinetics of reactive dye, C.I. Reactive Red 141 (Evercion Red H-E7B) by partially granulated anaerobic mixed culture using three carbon sources, namely modified starch (MS), polyvinyl alcohol (PVA) and acrylic size (AS) during batch incubation. There is a first-order kinetics reaction in the decolorization processes using MS and PVA as carbon sources, while a zero-order kinetics relationship describes the decolorization process for the AS carbon source. The k values and color removal rate of decolorization with MS carbon source was higher than those of PVA and AS carbon sources. This is because the MS carbon source was well degraded in comparison to AS and PVA, respectively This study also found dye reduction could be enhanced through the addition of MS as a carbon source. The decolorization rates increased with decrease in dye concentrations of RR 141. In contrast, the decolorization rates increased with increase in COD concentration.     

Modeling of adsorption kinetics and equilibria of acid dyes onto activated carbon in single- and binary-component systems

Adsorptive removal of Acid Blue 127 and Acid Yellow 17 from their single and binary solutions has been studied using powdered activated carbon (PAC). The dyes used extensively for dying of nylon fiber in textile industry are known as Nylomine Blue P-B (NB) and Nylomine Yellow P-4G (NY), respectively. Time-dependent results obtained from single-component system have been better predicted by two resistance diffusion model rather than homogeneous surface diffusion. The magnitudes of film- and intraparticle diffusion coefficients calculated from McKay equation are ～10^?9 and ～10^?15 m² s^?1, whereas surface diffusion coefficients have been estimated as ～10^?13 m² s^?1 using Vermeulen approximation. Experimental equilibrium isotherms have been evaluated by changing initial dye concentrations in the range of 0.02–1.00 of mmol L^?1. Freundlich isotherm parameters for individual solutions of the dyes have been used to predict their equilibrium behaviors in binary solutions by applying extended Freundlich model. Langmuir isotherm model and its extended form have also been fitted to the data for single- and binary-dye solutions, respectively. Thermodynamic functions derived from the temperature dependence of adsorption equilibrium constants in 298–318 K range show that adsorption processes are endothermic but spontaneous.     

Steam activation,characterisation and adsorption studies of activated carbon from maize tassels

In this paper, steam-produced activated carbon (STAC) from maize tassel (MT) was evaluated for its ability to remove basic dye (methylene blue MB) from aqueous solution in a batch adsorption process. The equilibrium experiments were conducted in the range of 50–300 mg/L initial MB concentrations at 30°C, for effect of pH, adsorbent dosage and contact time. The experimental data were analysed by Langmuir, Freundlich and Temkin isotherm models of adsorption. Freundlich adsorption isotherm was found to have highest value of R²(R²=0.97) compared to other models of Langmuir and Temkin having (0.96 and 0.95 respectively). STAC has a high adsorptive capacity for MB dye (200 mg/g) and also showed favourable adsorption for the dye with the separation factor (R_L<1) for the dye-activated carbon system. The kinetic data obtained were analysed using pseudo first-order kinetic equation and pseudo second-order kinetic equation. The experimental data fitted well into pseudo second-order kinetic equation, as demonstrated by the high value of R².     

Ozonation of the 5-fluorouracil anticancer drug and its prodrug capecitabine: Reaction kinetics,oxidation mechanisms,and residual toxicity

Specific second-order rate constants were determined for 5-FU and CAP with ozone. Reaction sites were confirmed by kinetics, Fukui analysis, and products. The olefin moiety was the main ozone reaction site for 5-FU and CAP. Carboxylic acids comprised most of the residual TOC for 5-FU. Ozonation removed the toxicity associated with 5-FU and products but not CAP. Anticancer drugs (ADs) have been detected in the environment and represent a risk to aquatic organisms, necessitating AD removal in drinking water and wastewater treatment. In this study, ozonation of the most commonly used antimetabolite ADs, namely 5-fluorouracil (5-FU) and its prodrug capecitabine (CAP), was investigated to determine reaction kinetics, oxidation mechanisms, and residual toxicity. The specific second-order rate constants between aqueous ozone and 5-FU, 5-FU⁻, 5-FU²⁻, CAP, and CAP⁻ were determined to be 7.07(±0.11)×10⁴ M⁻¹·s⁻¹, 1.36(±0.06)×10⁶ M⁻¹·s⁻¹, 2.62(±0.17)×10⁷ M⁻¹·s⁻¹, 9.69(±0.08)×10³ M⁻¹·s⁻¹, and 4.28(±0.07)×10⁵ M⁻¹·s⁻¹, respectively; furthermore, the second-order rate constants for ^•OH reaction with 5-FU and CAP at pH 7 were determined to be 1.85(±0.20)×10⁹ M⁻¹·s⁻¹ and 9.95(±0.26)×10⁹ M⁻¹·s⁻¹, respectively. Density functional theory was used to predict the main ozone reaction sites of 5-FU (olefin) and CAP (olefin and deprotonated secondary amine), and these mechanisms were supported by the identified transformation products. Carboxylic acids constituted a majority of the residual organic matter for 5-FU ozonation; however, carboxylic acids and aldehydes were important components of the residual organic matter generated by CAP. Ozone removed the toxicity of 5-FU to Vibrio fischeri, but the residual toxicity of ozonated CAP solutions exhibited an initial increase before subsequent removal. Ultimately, these results suggest that ozone is a suitable technology for treatment of 5-FU and CAP, although the residual toxicity of transformation products must be carefully considered.     

Adsorption of methylene blue onto activated carbon derived from periwinkle shells: kinetics and equilibrium studies

Periwinkle shell, an abundant and inexpensive natural resource, was used to prepare activated carbon by physicochemical activation with potassium hydroxide (KOH) and carbon dioxide (CO₂) as the activating agents at 850 °C for 2 h. The adsorption equilibrium and kinetics of methylene blue dye on such carbon were then examined at 25 °C. Adsorption isotherm of the methylene blue (MB) on the activated carbon was determined and correlated with common isotherm equations. The equilibrium data for methylene blue adsorption well fitted to the Langmuir equation, with maximum monolayer adsorption capacity of 500.00 mg/g. Two simplified kinetic models including pseudo-first-order and pseudo-second-order equation were selected to follow the adsorption processes. The adsorption of methylene blue on activated carbon derived from periwinkle shell could best be described by the pseudo-second-order equation. The kinetic parameters of this best-fit model were calculated and discussed.     

磷酸活化活性炭对Cu~（2＋）的吸附特征研究

寻求廉价而高效的吸附材料为目的,研究向日葵秸杆基活性炭对铜离子的吸附性能。以向日葵秸秆为原料,经H3PO4活化制备活性炭,通过静态实验研究了其对水溶液中Cu2＋的吸附特性,考察了溶液pH值、吸附温度和离子强度对吸附的影响,探讨了吸附热力学、动力学和吸附机理。结果表明：溶液pH值为5～6时活性炭对Cu2＋的去除效果最好;向50 mL 170 mg·L-1的溶液中加入0.5 g活性炭,温度为45℃、吸附时间为1 h时,对Cu2＋的去除率可达98.3%;Langmuir方程能更好地描述Cu2＋在活性炭上的等温吸附特征,静态吸附容量可达41.03 mg·g-1;吸附过程符合拟二级动力学过程,且为吸热的化学吸附过程,膜扩散为速率控制步骤,离子交换可能在吸附过程中起了重要作用。     

施用钢渣对水稻土硅素肥力的影响

施用钢渣种植水稻的盆栽试验结果表明,与对照相比,施用钢渣使土壤pH升高,土壤水溶态硅和无定形硅的含量下降,活性硅及有效硅含量上升,水稻植株含硅量增加.除水溶态硅外,上述影响均随钢渣用量增加或粒度变细而增强.