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•Subcritical water hydrolysis produced up to 18 wt% reducing sugars from rice husks.•Conversion efficiency of 39 g/100 g carbohydrates was obtained at 220 °C.•The maximum content of ...levulinic acid (2.3 g/L) was obtained at 260 °C.•Dissociation of hemicelluloses is more efficient than dissociation of cellulose.
This work aimed at producing fermentable sugars and bioproducts from rice husks by subcritical water hydrolysis at 25 MPa in a semi-continuous mode. The influences of temperature (180 °C; 220 °C; 260 °C) and liquid/solid ratio (7.5 g water/g husks; 15 g water/g husks) on reducing sugar yield (YRS), efficiency (E), kinetic profiles (0–15 min), composition of sugars, inhibitors and organic acids, and physicochemical characteristics of the remaining solid material were evaluated and discussed in the work. The highest YRS (18.0 ± 2.9 g/100 g husks) and E (39.5 ± 1.7 g sugars/100 g carbohydrates) were obtained at 220 °C and 7.5 gwater/g husks. In such condition, the hydrolyzed solutions presented cellobiose (18.0 g/L), xylose 17.7 g/L), arabinose (3.6 g/L), glucose (1.5 g/L), and levulinic acid (0.7 g/L). The fermentable sugars and bioproducts can be applied in several industrial fields, especially for the production of bioethanol and other higher value-added chemical compounds.
•Sewage sludge combustion was conducted in a moving bed combustor.•Exhaust gas from combustion was used in the drying process.•The gaseous emissions from the combustion and drying process were ...evaluated.•The study found low concentrations of BTEX, PAH and PCDD/PCDF.
Substantial increase in sewage sludge generation in recent years requires suitable destination for this residue. This study evaluated the gaseous emissions generated during combustion of an aerobic sewage sludge in a pilot scale moving bed reactor. To utilize the heat generated during combustion, the exhaust gas was applied to the raw sludge drying process. The gaseous emissions were analyzed both after the combustion and drying steps. The results of the sewage sludge characterization showed the energy potential of this residue (LHV equal to 14.5MJkg−1, db) and low concentration of metals, polycyclic aromatic hydrocarbons (PAH), polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF). The concentration of CO, NOx, BTEX (benzene, toluene, ethylbenzene and xylenes) emitted from the sludge combustion process were lower than the legal limits. The overall sludge combustion and drying process showed low emissions of PCDD/PCDF (0.42ng I-TEQNm−3). BTEX and PAH emissions were not detected. Even with the high nitrogen concentration in the raw feed (5.88% db), the sludge combustion process presented NOx emissions below the legal limit, which results from the combination of appropriate feed rate (A/F ratio), excess air, and mainly the low temperature kept inside the combustion chamber. It was found that the level of CO emissions from the overall sludge process depends on the dryer operating conditions, such as the oxygen content and the drying temperature, which have to be controlled throughout the process in order to achieve low CO levels. The aerobic sewage sludge combustion process generated high SO2 concentration due to the high sulfur content (0.67wt%, db) and low calcium concentration (22.99gkg−1) found in the sludge. The high concentration of SO2 in the flue gas (4776.77mgNm−3) is the main factor inhibiting PCDD/PCDF formation. Further changes are needed in the pilot plant scheme to reduce SO2 and particulate matter emissions, such as the installation of exhaust gas-cleaning systems. According to previous studies, the efficient operation of such cleaning systems is also effective for metals emission control, which makes the combustion of sewage sludge a feasible treatment method from both energetic and environmental perspectives.
The reduction of carbon dioxide emissions from flue gases can be achieved using post-combustion capture technologies such as adsorption. In this paper, we report experimental data for the fixed-bed ...adsorption of carbon dioxide and nitrogen on activated carbon. The breakthrough curves were obtained at different temperatures – 301–306, 323, 373 and 423
K – using CO
2/N
2 mixtures. XPS and FTIR measurements were used to identify chemical changes in the adsorbent after CO
2 adsorption. A model based on the Linear Driving Force (LDF) approximation for the mass transfer was used, considering the energy and momentum balances, to satisfactorily reproduce the breakthrough curves.
The kinetics of the ozonation of graphite with different particle sizes (106 μm, G106; 6.20 μm, G6.2) was studied at several temperatures under a flow of O3 diluted in O2. The reaction was ...first-order with respect to graphite and to the consumption of ozone. X-ray photoelectron spectrum (XPS) showed that the reactions occurring in the solid under steady-state conditions maintain the original stoichiometry, as predicted by the postulated mechanism for SO2. The deoxygenation reaction occurred along with the ozonation reaction at 100 °C. The rate of oxygen elimination in the flow system has the same rate-determining kinetic barrier as ozone insertion. Ozonation and deoxygenation reactions are sequentially related. Ozonation occurs with the insertion of O3, forming a 1,2,3-trioxolane followed by an oxygen transfer that produces a peroxide valence tautomer in equilibrium with 1,3-dicarbonyl, peroxide ↔ dicarbonyl, and an oxirene that eliminates atomic oxygen. The decarboxylation reaction was studied at 600 °C from the ozonated G106 (ΔG ≠ = 83.60 ± 0.08 kcal·mol–1). Total decarboxylation at 600 °C matched the number of moles of CO2 removed and the oxygen content after ozonation, showing that the reduction of ozone on graphite was essentially a clean reduction with no secondary oxidations. When ozonized graphite was heated to 600 °C, only peroxide ↔ dicarbonyl species remained in the matrix. The peroxide tautomer isomerized to dioxirane and eliminated CO2 as a dioxicarbene. Total deoxygenation of decarboxylated graphite G106 was obtained by pyrolysis. There was residual oxygen that arose from the atomic oxygen eliminated from the oxirene, intercalated in graphite layers, and formed basal epoxy groups. Also, incoming O atoms reacted with the intercalated O atoms to produce O2 molecules. Thermal annealing deintercalated molecular oxygen (600–900 °C).
Oil emulsified in water is one of the most difficult mixtures to treat due to the good stability of emulsions, so there is a growing demand for more efficient methods for separating immiscible ...oil/water mixtures. In this context, the focus of this study was to obtain an adsorbent for the selective treatment of a simulated oily wastewater. To this aim, a modified hydrotalcite sample with hydrophobic and magnetic characteristics was prepared and characterized. Initially, the effect of sodium dodecyl sulfate (SDS) amount on the adsorbent characteristics was evaluated (266-800 mg
SDS
g
−1
LDH
). The hydrophobic hydrotalcite (LDH-SDS) containing 533 mg
SDS
g
−1
LDH
(LDH-SDS2) presented a higher interlayer space where the surfactant molecules were arranged perpendicular to the lamellae, allowing better access to the hydrotalcite pores and facilitating the selective adsorption of oil compounds. Moreover, the synergistic association of hydrophobic properties with super-wetting and effective adhesion oil to Fe
3
O
4
favoured the selective adsorption of the simulated oily wastewater onto the hydrophobic and magnetic hydrotalcite (LDH-MSDS), facilitating the post-treatment separation. The kinetic analysis demonstrated that the adsorption equilibrium was attained in 120 min and the pseudo-second order model was the most suitable for predicting the removal of total organic carbon (TOC) from the simulated oily wastewater. The Langmuir model described very well the equilibrium experimental data, with a maximum adsorption capacity for TOC removal using LDH-MSDS of 659.9 mg g
−1
. Therefore, the modified hydrotalcite prepared in this study showed intrinsic characteristics that make it a promising adsorbent for the selective treatment of oily wastewaters.
In this study, silver molybdate was used as a catalyst in different oxidation processes to degrade pantoprazole (PAN) from aqueous suspension. The catalyst was synthesized using a controlled ...precipitation method and characterized by XRD, FTIR spectroscopy, BET analysis, Zeta potential, FEG-SEM/EDS, DRS and EPR. The α- and β-phases of Ag2MoO4 were identified as crystalline structure of the butterfly-shaped particles. The metastable α-phase could be completely converted into β-Ag2MoO4 by thermal treatment at 300 °C. The band gap energy of β-Ag2MoO4 (Eg = 3.25 eV) is slightly higher than for as-prepared catalyst (α-Ag2MoO4 + β-Ag2MoO4) (Eg = 3.09 eV), suggesting that as-prepared catalyst should be active under visible light. PAN is sensible to UV light irradiation, and the addition of H2O2 as electron acceptor enhanced the mineralization rate. In the catalytic UV-based reactions, high PAN oxidation efficiencies were obtained (>85%) but with low mineralization (32-64%). Catalytic peroxidation and photo-catalytic peroxidation under visible light showed the highest PAN oxidation efficiency, leading to its almost complete mineralization (>95%), even under dark conditions (98% in 120 min). Several degradation byproducts were identified and three mechanistic routes of PAN decomposition were proposed. The identified byproducts are less toxic than the parent compound. EPR coupled with the spin trapping method identified •OH radicals as the main ROS species in both photocatalytic and catalytic peroxidation reactions. Ag2MoO4 showed to be a promising catalyst to promote the decomposition of hydrogen peroxide into ROS.1
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•Facile synthesis of Ag2MoO4 with both α and β-phases.•α-Ag2MoO4 + β-Ag2MoO4 catalyst showed photocatalytic activity under visible light.•Efficient oxidation of pantoprazole by catalytic peroxidation with Ag2MoO4.•Mechanistic route for pantoprazole degradation via.•OH radicals is proposed.•Almost complete toxicity removal of PAN and its by-products was observed in 2 h.
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•Removal of Cu(II), Ni(II), Zn(II) using derivatized chitosan.•Selectivity on the adsorption of metals using derivatized chitosan.•The order of the affinity of adsorbent for the metal ...ions was: Cu(II) > Zn(II)∼Ni(II).
The preconcentration of metal ions present at low concentration levels in aqueous systems and the selective removal of potentially toxic metals are important applications of adsorption processes. In this study, a heptadentate dinucleating ligand was anchored to chitosan for use in adsorption studies on Zn(II), Cu(II) and Ni(II) ions. The novel adsorbent was characterized by 13C NMR and FT-IR spectroscopy, TGA and BET surface area analysis. The degree of substitution of the ligand in chitosan, obtained from CHN analysis, was 0.73. The adsorption kinetics followed a pseudo-second-order model. The rate constants and the adsorption capacities for multicomponent systems decreased in the order Cu(II) >> Ni(II) ∼ Zn(II), indicating the preferential adsorption of Cu(II). For Cu(II) ions, the Langmuir model provided the best fitting to the experimental data, and the monolayer Cu(II) adsorption capacity was 0.404 mmol g−1, while the linear isotherm described Zn(II) and Ni(II) ion adsorption.
► Selected Brazilian agroindustrial solid residues were characterised as solid fuels. ► The fuel properties were assessed aiming their use as alternative energy sources. ► Biomass properties ...influence the thermochemical conversion processes. ► The agroindustrial solid residues studied can potentially be used as energy sources.
In the present work, selected agroindustrial solid residues from Brazil – biosolids from meat processing wastewater treatment and mixture of sawdust with these biosolids; residues from apple and orange juice industries; sugarcane bagasse; açaí kernels (Euterpe oleracea) and rice husk – were characterised as solid fuels and an evaluation of their properties, including proximate and ultimate composition, energy content, thermal behaviour, composition and fusibility of the ashes was performed. The lower heating value of the biomasses ranged from 14.31MJkg−1 to 29.14MJkg−1, on a dry and ash free basis (daf), all presenting high volatile matter content, varying between 70.57wt.% and 85.36wt.% (daf) what improves the thermochemical conversion of the solids. The fouling and slagging tendency of the ashes was predicted based on the fuel ash composition and on the ash fusibility correlations proposed in the literature, which is important to the project and operation of biomass conversion systems. The potential for application of the Brazilian agroindustrial solid residues studied as alternative energy sources in thermochemical processes has been identified, especially concerning direct combustion for steam generation.
In this study, treatment for the removal of 1,4-dioxane by ozone and by catalytic ozonation using CuO as the catalyst was investigated. While the removal of 1,4-dioxane was small (20%) and ...mineralization negligible after 6 h of ozonation treatment, the removals of 1,4-dioxane and total organic carbon increased by factors of 10.35 and 81.25, respectively, after catalytic ozonation in the presence of CuO. The mineralization during catalytic ozonation was favoured at pH 10 (94.91 min
−1
), although it proceeded even at pH 3 (54.41 min
−1
). The CuO catalyst decreased the equilibrium concentration of soluble ozone and favoured its decomposition to reactive oxidative species. Radical scavenging experiments demonstrated that superoxide radicals were the main species responsible for the degradation of 1,4-dioxane. Further scavenging experiments with phosphate confirmed the presence of Lewis active sites on the surface of CuO, which were responsible for the adsorption and decomposition of ozone. The reaction mechanism proceeded through the formation of ethylene glycol diformate, which quickly hydrolyzed to ethylene glycol and formic acid as intermediate products. The stability of CuO indicated weak copper leaching and high catalytic activity for five recycling cycles. The toxicity of the water, assessed by Vibrio fischeri bioluminescence assays, remained the same (low toxicity) after catalytic ozonation while it increased after treatment with ozonation alone.
The desulfurization of carbons modified with SO2 was studied as a dispersion in boiling cyclohexane (81°C) using activated carbon (mAC) and graphene oxide (mGO), modified by SO2. The steady‐state ...species in the carbon matrix after the catalytic reduction of SO2 was considered a trisulfane. For mAC, there was a burst of a sulfur species identified as S2 by UV spectrum with a maximum at 217 nm (εM at 217 nm = 2.56 × 103) that showed a second‐order decay of absorbance with
kS2 = 47.29 M‐1·sec‐1 (
ΔG354‡= 18.1 kcal·mol‐1). The product was postulated to be S4. No other consecutive reaction was observed because of the possible adsorption of S4 in the carbon matrix. The desulfurization of mGO was shown by XPS and the kinetics were a second‐order decay up to 16 min (
kS2= 18.41 M‐1·sec‐1;
ΔG354‡= 18.8 kcal·mol‐1) followed by a second‐order increase of absorbance with
kS4 = 3.84 M‐1·sec‐1 (
ΔG354‡= 19.9), where the product showed a double maximum at 260‐285 nm typical of S8. These results are consistent with a mechanism of consecutive thermodynamically favorable dimerizations of S2 and S4 and with the desulfurization mechanism that has been previously postulated.
The desulfurization of carbons modified with SO2 occurred in boiling cyclohexane from a trisulfane inserted in the carbon matrix, with a burst of disulfur S2 that dimerized to tetrasulfur and finally to S8. The desulfurization path is largely more energetically favorable than the decarboxylation route.
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