Transient simulation of SO2 absorption into water in a bubbling reactor.

A bubbling reactor is an important type of gas scrubber to reduce SO2 emissions in maritime shipping. Both experiments and simulations were conducted to study the relationship between the periodic gas bubbling process and SO2 concentration at the outlet of the reactor, and the entrainment of liquid droplets on SO2 absorption. The accuracy of the model was verified by comparing the bubble size, the depth of bubbles injected into the water, and the SO2 concentration obtained in both experiments and simulations. The gas bubbling process is accompanied by bubble formation, rise, and collapse. The gas bubbling period is affected by the disturbance of the liquid level. The period of the SO2 concentration at the outlet of the gas bubbling reactor is smaller than that at the gas jar outlet which acts as the gas buffering region. The amounts of water carried out of the bubbling reactor by the gas bubbling process increase with the gas flow rates. The droplets and liquid film in the gas jar and the connecting tube play an important role in the absorption of SO2. This study encourages more research to reduce the fluctuation of SO2 concentration and consider droplet entrainment in the design of bubbling reactors.

Study of Catalytic CO2 Absorption and Desorption with Tertiary Amine DEEA and 1DMA-2P with the Aid of Solid Acid and Solid Alkaline Chemicals.

Studies of catalytic CO2 absorption and desorption were completed in two well-performed tertiary amines: diethylmonoethanolamine (DEEA) and 1-dimethylamino-2-propanol (1DMA-2P), with the aid of CaCO3 and MgCO3 in the absorption process, and with the aid of γ-Al2O3 and H-ZSM-5 in the desorption process. The batch process was used for CO2 absorption with solid alkalis, and the recirculation process was used for CO2 desorption with solid acid catalysts. The CO2 equilibrium solubility and pKa were also measured at 293 K with results comparable to the literature. The catalytic tests discovered that the heterogeneous catalysis of tertiary amines on both absorption and desorption sides were quite different from monoethanolamine (MEA) and diethanolamine (DEA). These results were illustrative as a start-up to further study of the kinetics of heterogeneous catalysis of CO2 to tertiary amines based on their special reaction schemes and base-catalyzed hydration mechanism.

Nitrosamine Formation in Amine-Based CO2 Capture in the Absence of NO2: Molecular Modeling and Experimental Validation.

A computational chemistry approach was used to elucidate and verify the different nitrosamine formation mechanisms and pathways. These included nitrosamine formation under acid or basic environments in the presence of NO, O2, SO2 and CO2 without NO2. The results clearly showed that nitrosamine could be formed without NO2 via 2 different types of mechanisms, namely, addition and elimination forming N-N bond before proton transfer and proton transfer before N-N bond formation, respectively. The essence of these mechanisms identified in this work was that two reaction steps were required to complete both reaction mechanisms with different nitrosating agents. Two steps were both necessary neither of which could be neglected, if the nitrosamine formation reaction was to be completed. Computational simulation performed on the reactant, intermediate, transition state, and product for each set of reactions also validated the proposed mechanisms. Experiment also detected nitrosamine from the reaction of diethylamine and NO, SO2, O2, and CO2 in both liquid and gas phase. Thus, NO2 is not necessary for nitrosamine formation to occur in the CO2 capture system.

Evaluating CO2 Capture Performance of Trisolvent MEA-BEA-AMP with Heterogeneous Catalysts in a Novel Bench-Scale Pilot Plant.

To reduce the huge energy cost of CO2 capture technology applicable in industry, the CO2 absorption-desorption performance was conducted in a novel bench-scale pilot plant with hot water as a heat source. The trisolvent MEA(monoethanol amine)-BEA(butylethanol amine)-AMP(2-amino-2-methyl-1-propanol) was prepared at a specific concentration to analyze the CO2 capture performance and compared with 5 M MEA as the benchmark. Meanwhile, several solid acid catalysts, blended H-ZSM-5/γ-Al2O3(1/2), or HND-8, were packed in the desorber, and the solid base catalyst, CaCO3 or CaMg(CO3)2, was packed in the absorber with random packing. The CO2 absorption efficiency (AE), cyclic capacity (CC), and heat duty (HD) were tested onto MEA-BEA-AMP and MEA under various operating conditions. Experimental results indicated that the performance of 4.3 mol/L MEA-BEA-AMP was significantly better than 5 M MEA under both catalytic and noncatalytic operation. The most energy efficient combination of this study was discovered as 0.3 + 2 + 2 mol/L MEA-BEA-AMP, with 50 g (CaCO3/CaMg(CO3)2) in the absorber and 150 g H-ZSM-5/γ-Al2O3(1/2) in the desorber. The heat duty reached as low as 2.4 GJ/tCO2 at a FG of 7.0 L/min and a FL of 70 mL/min. These results were highly applicable in an industrial amine scrubbing pilot plant for CO2 capture.

Enhanced hydrogen production from sludge anaerobic fermentation by combined freezing and calcium hypochlorite pretreatment.

A novel and high-efficiency sludge pretreatment method by combination of freezing and calcium hypochlorite (CH) for promoting the anaerobic fermentation performance was reported in this work. Experimental results indicated that a maximum biohydrogen production of 18.18 ± 0.43 mL/g volatile suspended solids (VSS) was realized by freezing (-5 °C) combined with CH (0.12 g/g VSS) pretreatment, which was 1.19, 4.05 and 11.36 times to that from the sole CH, sole freezing and control fermenters, respectively. Mechanism study showed that freezing + CH pretreatment efficiently disintegrated sludge flocs, producing abundant substrates for anaerobic fermentation. Model substances degradation experiment showed that the biochemical processes were all suppressed by freezing + CH method, but the suppressive degrees for hydrogen-consuming processes were greater than hydrogen-producing processes. 16S rRNA analysis revealed that the microbial community in freezing + CH treated reactor was more beneficial to hydrogen generation than that in the control, because the abundance of functional microbes was enriched from 6.81 % to 34.95 % by the co-treatment. Furthermore, sludge dewatering performance, including settleability, dewaterability and filterability, was enhanced by freezing + CH pretreatment.

Understanding the Impacts of Different Impurities on Elemental Mercury Removal by CaS in Chemical Looping Combustion of Coal: A First Principle Study.

CaSO4 has the advantages of abundant yield, high oxygen-carrying capacity, low cost, and no heavy metal pollution, making it promising as an oxygen carrier for chemical looping combustion (CLC). In comparison with other oxygen carriers, CaS as the reduced product of CaSO4 exhibits superior adsorption efficiency for Hg0 in the flue gas. In this paper, density functional theory (DFT) was used to investigate the adsorption mechanism of Hg0 on the adsorbent surface of CaS(001). The adsorption energies of different oxidized mercury species such as HgS, HgCl, and HgBr over the CaS surface were summarized. Furthermore, the effects of various flue gas components including SO2, H2S, S, HCl, Cl2, CO, H2, H2O, and C on Hg0 adsorption over the CaS(001) surface were evaluated. The results show that Hg0 can be adsorbed on the CaS(001) surface in a chemisorption manner with a reaction energy of -65.1 kJ/mol. The adsorption energy of different forms of mercury on the CaS(001) surface varies greatly, and mercury in the oxidized state is more easily captured by CaS. SO2 inhibits while other flue gas components promote Hg0 adsorption over the CaS surface. Overall, CaS tends to adsorb mercury in the reduction reactor and release mercury when CaS is re-oxidized to CaSO4 in the oxidation reactor. This is detrimental to mercury removal in the CLC of coal. This study sheds light on the migration and transformation of mercury in the CLC of coal with CaSO4 as the oxygen carrier.

Optimizing study on the NH3-SCR activity of Ce-W-Ti@g-C3N4 catalyst: influence of graphite carbon nitride types.

Herein, three g-C3N4(MCN/TCN/UCN), obtained by the direct pyrolysis of melamine/urea/thiourea respectively, were introduced as supports to optimize the NH3-SCR activity of Ce-W-Ti catalyst. Compared to CWT-400-Air, CWT@g-C3N4(2)-300-N2 exhibits lower crystalline anatase TiO2 and larger specific surface area, which improves the dispersion of Ce/W/Ti species on catalysts surface. Furthermore, the introduction of g-C3N4 as supports also contributes to doping C/N elements into Ce-W-Ti catalyst and increases the Ce3+/(Ce3++Ce4+) and Oα/(Oα+Oß) molar ratios on catalyst surface. These all are advantageous to the NH3-SCR activity. However, UCN shows better promotional effect than MCN and TCN. This might be mainly attributed to the loose and porous stacked layered fold structure of UCN, the larger BET surface area, higher dispersion of Ce/W/Ti species and moderate weak/medium-strong acid sites of CWT@UCN(2)-300-N2. At the same time, the influence of carbon nitride amount, calcination atmosphere and calcination temperature on the NH3-SCR activity of CWT@g-C3N4 catalyst were also investigated.

Modeling Study of the Slag Behaviors Based on Temperature-Time-Viscosity of Crystalline Slag in an Entrained-Flow Gasifier.

The crystal growth process has an important influence on the viscosity of the slag, which affects the characteristics of the slag layer on the wall of the gasifier. The slag flow and heat transfer model based on temperature-time-viscosity of crystalline slag were established, to predict the slag behaviors and protect gasifier. The results showed the overall viscosity of the slag after considering the residence time effect was higher than that when using the measured viscosity-temperature curve value. The liquid slag thickness, solid slag thickness, and residence time increased after the slag viscosity amendment, while the slag flow velocity and heat flux density decreased. Moreover, several types of crystallized slag were constructed to study the effects of crystal morphology and degree of crystallization difficulty on slag behaviors. The result indicated that the difficulty and crystal morphology of the slag crystallization cannot be ignored when using crystallized slag in gasification.

Facile access to high-efficiency degradation of tetracycline hydrochloride with structural optimization of TiN.

As a broad-spectrum antibiotic, tetracycline has become a potential ecological hazard. Herein, titanium nitride (TiN), with an advantageous structure, was synthesized by simple heating rate regulation and constructed for tetracycline hydrochloride (TC-HCl) degradation under light irradiation. All the samples were characterized by X-ray diffraction (XRD), N2-adsorption/desorption isotherm, ultraviolet-visible diffuse reflectometry (DRS), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). The results showed that the as-prepared TiN-x catalysts exhibited obviously enhanced photocatalytic property toward TC-HCl degradation compared with the commercial pure phase TiN (p-TiN). According to the results of photocatalytic degradation, TiN synthesized at 6 °C/min heating rate had the best removal rate of TC-HCl (90%) after dark reaction for 10 min and photo-degradation for 90 min. In addition, the trapping experiments have demonstrated that the photogenerated holes (h+) and superoxide radical ([Formula: see text]) are the main oxidation products of the present system. Strikingly, the reuse experiments showed high stability of TiN.

Experimental investigations and the modeling approach for CO2 solubility in aqueous blended amine systems of monoethanolamine, 2-amino-2-methyl-1-propanol, and 2-(butylamino)ethanol.

In this work, new CO2 solubility data on three types of aqueous amine blends were reported to complement existing databases. The experiments were conducted at temperatures of 313 K (absorption condition) and 363 K (desorption condition). The effect of the MEA concentration on the CO2 solubility in several amine blends at low CO2 partial pressure (8 to 50.65 kPa) were studied in this work, including 0.1, 0.3, 0.5 mol/L MEA + 2 mol/L AMP; 0.1, 0.3, 0.5 mol/L MEA + 2 mol/L BEA; and 0.1, 0.3, 0.5 mol/L MEA + 1, 2 mol/L AMP + 1, 2 mol/L BEA. Besides, an additional group of equilibrium CO2 solubility data were conducted at 298 K in order to estimate the heat of CO2 absorption of the blended solvents at a temperature range from 298 to 313 K. A new simplified Kent-Eisenberg model was developed for the predictions of blended solvents, and a multilayer neural network model with Levenberg-Marquardt backpropagation algorithm was developed upon five hundred reliable published experimental data. The predictions from two methods are both in good agreement with the experimental CO2 solubility data.

Facile self-assembly of carbon-free vanadium sulfide nanosheet for stable and high-rate lithium-ion storage.

Metal sulfides are recognized as potential candidates for the anode materials of lithium ion batteries (LIBs) because of their high theoretical capacity. However, the low reaction kinetics of metal sulfides leads to their poor cycle life and rate performance, which limits their practical application in the field of energy storage. In this work, we synthesized a self-assembled carbon-free vanadium sulfide (V3S4) nanosheet via a facile and efficient method. The unique mesoporous nanostructure of V3S4 can not only accelerate the migration of ions/electrons, but also alleviate the volume expansion during the lithium ion insertion/extraction process. When used as the anode material of LIBs, the carbon-free V3S4 electrode exhibits remarkable electrochemical performance with ultra-high charge capacity (1099.3 mAh g-1 at 0.1 A g-1), superior rate capability (668.8 mAh g-1 at 2 A g-1 and 588.8 mAh g-1 at 5 A g-1) and impressive cycling ability (369.6 mAh g-1 after 200 cycles at 10 A g -1), which is very competitive compared with those of most metal sulfides-based anode materials reported so far. The strategy in this work provides inspiration for the rational design of advanced nanostructured electrode materials for energy storage devices.

The CO2 absorption and desorption analysis of tri-solvent MEA + EAE + AMP compared with MEA + BEA + AMP along with "coordination effects" evaluation.

The slow kinetics of CO2 absorption and high energy cost of CO2 desorption were the main challenges for CO2 capture technology. To overcome these drawbacks, a novel tri-solvent MEA (monoethanolamine) + EAE (2-(ethylamino)ethanol) + AMP (2-amino-2-methyl-1-propanol) was prepared at different amine concentrations of 0.1 ~ 0.5 + 2 + 2 mol/L. The CO2 absorption and desorption experiments were conducted on MEA + EAE + AMP and their precursor MEA + EAE to evaluate the absorption-desorption parameters. Results demonstrated that the optimized concentrations of the bi-blend were 0.2 + 2 mol/L for absorption and 0.4 + 2 mol/L for desorption. For the tri-solvent, the optimized concentration was 0.2 + 2 + 2 mol/L, consistently for both abs-desorption sides. Compared with tri-solvent of MEA + BEA + AMP, MEA + EAE + AMP proved better in absorption but poorer in desorption, while its CO2 loading of operation line was 0.35 ~ 0.70 mol/mol, higher than that of 0.30-0.60 mol/mol MEA + BEA + AMP. These results led to another tri-solvent candidate of amine solvents in an industrial pilot plant.

Oxygen-Induced Elemental Mercury Oxidation in Chemical Looping Combustion of Coal.

Mercury emission is an important issue during chemical looping combustion (CLC) of coal. The aim of this work is to explore the effects of different flue gas components (e.g., HCl, NO, SO2, and CO2) on mercury transformation in the flue gas cooling process. A two-stage simulation method is used to reveal the reaction mechanism of these gases affecting elemental mercury (Hg0) oxidation. Furthermore, using this method, Hg0 oxidation by eight oxygen carriers (Co3O4, CaSO4, CeO2, Fe2O3, Al2O3, Mn2O3, SiO2, and CuO) commonly used in CLC are investigated and their Hg0 oxidation efficiencies were compared with the existing experimental results. The results show that HCl, NO, and CO2 promote Hg0 oxidation during flue gas cooling, while SO2 inhibits Hg0 oxidation. The stronger the oxygen release capacity of oxygen carriers, the higher the oxidation efficiency of Hg0 becomes. The order of Hg0 removal efficiency from high to low is Co3O4, CuO, Mn2O3, CaSO4, Fe2O3, CeO2, Al2O3, and SiO2, and this sequence is in good agreement with the existing experimental results. Different flue gas components directly or indirectly affect the O2 content, thus affecting the content of gaseous oxidized mercury (Hg2+). Different oxygen carriers have different oxygen release capacities and different Hg0 oxidation efficiencies. Therefore, O2 is the core species affecting the mercury transformation in CLC.

Synthesis of Cu3P/SnO2 composites for degradation of tetracycline hydrochloride in wastewater.

Antibiotic drugs have become dominating organic pollutants in water resources, and efficient removal of antibiotic drugs is the priority task to protect the water environment. Cu3P/SnO2 photocatalysts of various Cu3P loadings (10-40 wt% Cu3P) were synthesized using a combination of hydrothermal synthesis and a partial annealing method. Their photocatalytic activity was tested for tetracycline hydrochloride (TC-HCl) degradation under visible light irradiation. Cu3P/SnO2 samples were characterized by X-ray diffraction (XRD), N2-adsorption, ultraviolet-visible diffuse reflectance spectra (UV-vis DRS), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The results showed that the p-n type heterostructure between Cu3P and SnO2 was successfully constructed, and addition of Cu3P to SnO2 could improve its photocatalytic activity at an optimized loading of 30 wt% Cu3P. In photocatalytic degradation studies, removal rates of around 80% were found in 30 minutes of dark reaction and 140 min of photodegradation. The removal rate was superior to that of Cu3P and SnO2 alone under the same experimental conditions. According to trapping experiments and electron spin resonance (ESR) measurements, photogenerated holes (h+) and superoxide radicals ˙O2 - were considered as the main oxidation species in the present system. Finally, the reuse experiments showed high stability of Cu3P/SnO2. This study reports Cu3P as a cocatalyst combined with semiconductor SnO2 to form a highly efficient heterogeneous photocatalyst for the degradation of tetracycline hydrochloride for the first time.

The rainfall effect onto solidification and stabilization of heavy metal-polluted sediments.

Rainfall makes impacts on the process of solidification/stabilization (S/S) and the long-term safety of solidified matrix. In this study, the effect of rainfall on solidification/stabilization process was investigated by the rainfall test. The unconfined compressive strength (UCS) and toxicity characteristic leaching procedure (TCLP) were adopted to characterize the properties of S/S sediments before and after the rainfall test. The samples cured for 28 days were selected for semi-dynamic leaching tests with a simulated acidic leachant prepared at pH of 2.0, 4.0 and 7.0. The effectiveness of S/S treatment was evaluated by diffusion coefficient (De ) and leachability index (LX). The results indicated that UCS decreased at maximum deterioration rate of 34.23% after 7 days of curing, along with the minimum rate of 7.98% after 28 days by rainfall, with greater than 14 days referred. The rainfall had little effect on the leaching characteristics of heavy metals during the curing process. However, the simulated acid rain made significant impacts on the leaching behaviours of the heavy metals in the S/S materials. All the values of cumulative fraction of leached heavy metals were less than 2.0%, exhibition of good stabilization of cement. Furthermore, the calculated diffusion coefficient (De ) for Cu was 1.28 × 101 cm2 s-1, indicating its low mobility of heavy metal ions in S/S sediments. Furthermore, the calculated diffusion coefficients (Di ) for Cd, Cu and Pb were 7.44 × 10-11, 8.18 × 10-12 and 7.85 × 10-12 cm2 s-1, respectively, indicating their relatively low mobility of heavy metal in S/S sediments.

Eley-Rideal model of heterogeneous catalytic carbamate formation based on CO2-MEA absorptions with CaCO3, MgCO3 and BaCO3.

The mechanism was proposed of heterogeneous catalytic CO2 absorptions with primary/secondary amines involving 'catalytic carbamate formation'. Compared with the non-catalytic 'Zwitterion mechanism', this Eley-Rideal model was proposed for CO2 + RR'NH with MCO3 (M = Ca, Mg, and Ba) with four elementary reaction steps: (B1) amine adsorption, (B2) Zwitterion formation, (B3) carbamate formation, and (B4) carbamate desorption. The rate law if determining step of each elementary step was generated based on 'steady-state approximation'. Furthermore, the solid chemicals were characterized by SEM and BET, and this rate model was verified with 39 sets of experimental datasets of catalytic CO2-MEA absorptions with the existence of 0-25 g CaCO3, MgCO3 and BaCO3. The results indicated that the rate-determining step was B1 as amine adsorption onto solid surface, which was pseudo-first-order for MEA. This was the first time that the Eley-Rideal model had been adopted onto the reactions of CO2 + primary/secondary amines over alkaline earth metal carbonate (MCO3).

Photochemistry studied with ab initio orbital-correlation and state-correlation plots: Classic cyclobutene ring opening, and the reaction of N2 with photoexcited O2.

Pericyclic reaction theory arose from ideas presented in 1965, based on orbital-energy correlation diagrams (Woodward and Hoffmann) and state-energy correlation diagrams (Longuet-Higgins and Abrahamson). Here we have used ab initio complete-active-space self-consistent field (CASSCF) calculations to generate such diagrams. First we present diagrams for the classic case of cyclobutene ring opening, to demonstrate agreement between the CASSCF results and the classic diagrams of both Woodward/Hoffmann and Longuet-Higgins/Abrahamson. Then we present diagrams for the more difficult cases of N(2) + photoexcited O(2), to produce either 2 NO or NNO + O. These N(2) + O(2) cases feature significant electron reorganization, for which elementary pencil-and-paper diagrams are less accurate. Finally, the benefits and limitations of such diagrams for predicting photochemistry are briefly discussed.

Improved results for the excited states of nitric oxide, including the B/C avoided crossing.

The potential energy surfaces of ten electronic states of nitric oxide (NO) have been reexamined computationally, with state energies calculated using ab initio multireference methods. Our wave function expansions of 10x10(6) configurations improve upon the results of de Vivie and Peyerimhoff [J. Chem. Phys. 89, 3028 (1988)], who obtained excellent results from expansions of 16 000 configurations in 1988. We present results for the adiabatic properties r(e), B(e), T(e), and omega(e), demonstrating standard errors of 0.012 A, 0.026 cm(-1), 620 cm(-1), and 41 cm(-1), respectively. Vertical excitation energies and oscillator strengths are also presented, as are potential energy surface curves, with special attention to the B/C avoided crossing. The technical issue of state-averaging effects is also discussed.

Photodissociation dynamics of the NO dimer. I. Theoretical overview of the ultraviolet singlet excited states.

Molecular orbital theory and calculations are used to describe the ultraviolet singlet excited states of NO dimer. Qualitatively, we derive and catalog the dimer states by correlating them with monomer states, and provide illustrative complete active space self-consistent field calculations. Quantitatively, we provide computational estimates of vertical transition energies and absorption intensities with multireference configuration interaction and equations-of-motion coupled-cluster methods, and examine an important avoided crossing between a Rydberg and a valence state along the intermonomer and intramonomer stretching coordinates. The calculations are challenging, due to the high density of electronic states of various types (valence and Rydberg, excimer and charge transfer) in the 6-8 eV region, and the multiconfigurational nature of the ground state. We have identified a bright charge-transfer (charge-resonance) state as responsible for the broadband seen in UV absorption experiments. We also use our results to facilitate the interpretation of UV photodissociation experiments, including the time-resolved 6 eV photodissociation experiments to be presented in the next two papers of this series.