查看更多>>摘要：The separation of enantiomers in a continuous manner represents a nontrivial task. Identical physical properties of an enantiomeric pair render the standard separation methods unusable, and its separation traditionally relies on the use of a chiral environment. Here, we theoretically analyze lateral electrochromatography as a potential method for continuous steady-state enantiomer separation. The developed mathematical model of a lateral electrochromatography device (LEC) treats the stationary (selective) phase as a pseudo-homogeneous environment. The intensity of the solute transport in that phase is given by an effective diffusion coefficient which depends on the degree of solute-stationary phase interactions. Under the assumptions of phase equilibrium and neglected diffusion/dispersion transport, we derived simplified algebraic expressions determining the slopes (deflections) of solute concentration trajectories allowing the solute separation. These expressions may assist in optimizing the LEC geometry and setting the control parameters such as the applied voltage or pressure difference. Numerical simulations on spatially two- and three-dimensional domains are in good agreement with both simplified algebraic predictions and available experimental observations. We show that LEC can separate enantiomers continuously in a steady-state regime under optimized operating conditions. However, the separation efficiency strongly depends on the enantioselectivity of the stationary phase. The results of the simulations also offer basic designing rules for a LEC that is compatible with continuous synthesis and separation of pharmaceuticals and other special chemicals.
查看更多>>摘要：In this report, thermo-separating magnetic ionic liquids (MILs) were discovered for the first time. Two Polypropylene glycol 600 (PPG_(600)) based thermo-separating MILs were synthesized, characterized and successfully applied to construct the first reported thermo-separating magnetic ionic liquid aqueous two-phase system (MILATPS). This novelly proposed thermo-separating MILATPS combined the advantages of rapid extraction, volatile organic solvent free, magnetic separation and thermo-recovery of MIL in an extraction process. Phase behaviors and extraction-recovery processes of phenol, o-cresol and m-cresol were systematically studied. Several influencing factors on phenolic compound extraction efficiencies were detailedly investigated and optimized. Under optimal conditions, both two synthesized thermo-separating MILs revealed good performances with extraction efficiencies higher than 90%. Scale-up studies were also satisfactory. Additionally, both high purities of MILs and phenolic compounds could be ideally recovered simply by heating and the recoveries of phenolic compounds were higher than 95% for all systems. Furthermore, the two MILs could be recycled for at least 6 times with steadily high extraction efficiencies. This novelly proposed thermo-separating MILATPS is simple and green method which is showing great potential in an extraction-recovery process and the industrial treatment of phenolic wastewater.
查看更多>>摘要：Two series of 6FDA-based co-polyimide membranes were synthesized by adding different diamine monomer containing special functional groups: APAF (containing -OH) and DABA (containing -COOH). The ODA/APAF and ODA/DABA series were heat treated at 450 °C and 350 °C, respectively. Thermal rearrangement of polymer chain segments is confirmed in ODA/APAF membranes by infrared spectroscopy, while addition of DABA in ODA/DABA membranes causes decarboxylation crosslinking. Positron lifetime measurements reveal existence of ultramicropores in polyimides. The thermal rearrangement in ODA/APAF membranes induces remarkable increase in both size and number of ultramicropores and therefore increase in fractional free volume (FFV), but the crosslinking in ODA/DABA causes significant decrease in both size and number of ultramicropores. The increase in FFV is favorable for gas permeation, but too large size of the micropore drastically deteriorates the gas selectivity. Finally, the ODA/APAF(3:7) shows a high CO2 permeability of 127.4 Barrer with CO2/CH4 selectivity of 34.2, which surpasses the 1991 Robeson upper bound. Besides, the ODA/DABA(3:7) exhibits a H2 permeability of 22.6 Barrer with H2/CH4 selectivity of 256.8, which also exceeds the 1991 Robeson upper bound. Our results indicate that the gas permeability and selectivity of polymer membranes can be effectively adjusted by tailoring the ultramicropore structures, and positron can provide precise information about micropores.
查看更多>>摘要：This study proposes an onboard membrane carbon capture and liquefaction system for LNG-fueled ships to satisfy the IMO's 2050 greenhouse gas reduction targets. The exhaust gas from a natural gas ship has a low CO2 fraction (~3%) and high O2 fraction (~16%) compared to the flue gas from power plants. Herein, considering the above distinguishing features, a membrane carbon capture and liquefaction system has been proposed that is energy efficient and compact for the application of ships. To ascertain the performance of the proposed membrane-based system, it is compared to an amine-based onboard system in terms of energy consumption and major equipment size. This work evaluates four process configurations by varying the number of membrane stages and associated liquefaction processes at different CO2/N2 selectivity and CO2 permeance. The results show that energy consumption (3.98 GJ_e/t_(LCO2)) is higher than the amine-based system (3.07 GJ_e/t_(LCO2)) at the CO2/N2 selectivity of 50, but it can be decreased to 3.14 and 2.82 (GJ_e/t_(LCO2)) with an improved selectivity of 100 and 150, respectively. The major equipment size decreases to 54%, 28%, and 20% of the amine-based system when the permeance is 1000, 2000, and 3000 GPU, respectively. The results indicate that the new onboard membrane carbon capture and liquefaction system can be a competitive solution for the IMO's greenhouse gas reduction targets for 2050.
查看更多>>摘要：Transition metal oxides and transition metal containing oxides have been extensively researched in heteroge-neous catalytic ozonation for water treatment. However, catalytic mechanism for typical transition metal oxide -manganese oxide (MnO2) in catalytic ozonation is still ambiguous. Herein, MnO2 and magnesium manganese oxides (MgMn_xO_y) with different molar ratios of Mg to Mn were analysed by linear sweep voltammetry (LSV) test to explore a necessary condition for electron transfer reaction between ozone and acid sites of the catalysts in aqueous solution. And their catalytic performances were investigated in ozonation of acetic acid aqueous so-1 lution at a neutral pH. It is found that electron transfer reaction occurs in manganese containing oxides catalytic ozonation when ozone is adsorbed on protonated surface hydroxyl groups of acid sites (Mn~(2+)/Mn~(3+) in the lattice). But ozone that is absorbed on protonated hydroxyl groups of Mg~(2+) in the lattice cannot react with acid sites to generate reactive oxygen species in MgMn_xO_y catalytic ozonation. Protonation of hydroxyl groups on acid sites can be achieved by enhancement in point of zero charge (pH_(PZC)) of the catalysts or decrease in initial pH of aqueous solution. Protonation ability of hydroxyl groups on acid sites and electron transfer ability of acid sites are positively related to Mg content in MgMn_xO_y. MgMn_xO_y with 2:1 molar ratio of Mg to Mn (Mg2MnO_y) exhibits the highest catalytic activity and good stability in ozonation of acetic acid. On basis of catalytic mechanism on acid sites of manganese containing oxides, modification and application of manganese containing oxides would be further developed in heterogeneous catalytic ozonation for water treatment.
Alex Christopher BarksdaleJunghyo YoonHyukjin J. Kwon
8页
查看更多>>摘要：The surge of electric vehicle deployment in response to the global climate crisis has marked tremendous increase in the demand of lithium-ion batteries. Lithium brine has gained much attention as a critical primary lithium resource over mineral sources due to cheaper processing and greater abundance. However, reducing the Mg~(2+): Li~+ ratio of brines remains a challenge, as magnesium contaminates lithium precipitates. Solar evaporation ponds are traditionally employed to concentrate Li and reduce Mg content to tackle this issue, but typically require 1-2 years to process a batch of feed solution, and require much land area disturbing the local environment near brine resources. Here we present a continuous, scalable ion separation technique for reducing the Mg~(2+):Li~+ ratio of brine as an alternative to solar evaporation. The device utilizes ion concentration polarization to induce a locally amplified electric field. The amplified electric field separates ions into streams according to electrophoretic mobility. We demonstrate reduction of a 25:1 Mg~(2+):Li~+ lab brine to below 10:1 Mg~(2+):Li~+, which is an acceptable lithium production purity by industrial standards. Reduction of a 60:1 Mg~(2+):Li~+ to ~ 10:1 and a 100:1 Mg~(2+):Li~+ brine to approximately 20:1 are also demonstrated. The system suffers a high specific energy consumption (8.804 kWh/g Li~+ for 25:1 reduction to 9:1) due to low lithium recovery (9.9%) and microfluidic system size. However, an economic scaling analysis shows that this work is within an order of magnitude of the state-of-the-art separation technologies in the literature after various process parameters are normalized. Ultimately, this work demonstrates a potential novel process for continuous lithium extraction from brines, which is a generalizable ion separation tool utilizing differences in electrophoretic mobility.
查看更多>>摘要：A degassing contactor using a flat sheet membrane module (FM) was operated in sweep gas mode to study the performance of several commercial polymer membranes, both dense (polydimethylsiloxane, PDMS) and microporous (polypropylene, PP, and polyvinylidenefluoride, PVDF), for the recovery of dissolved methane from water. Non-steady state experiments were conducted at different liquid (Q_L, 3.5-40.5 L h~(-1)) and gas flow rates (Qn2, 0.05-15.00 L h~(-1)). In the case of PDMS, PP, and when PVDF was operated at moderate high Q_L (>=21 L h~(-1)), similar methane removal efficiencies (RE) were obtained. In the case of PVDF operated at relatively low Q_L (3.5 L h_1), a lower RE was observed. A model for the mass transfer of methane has been selected that is adequate in predicting the experimental results. These results concluded that the mass transfer resistance was mainly located in the liquid phase. Microscopy and especially contact angle measurements were used to monitor the structural and surface stability on the membranes. The membranes were altered during the operation, especially for Q_L > 21 L h~(-1), showing a decrease (PDMS and PP) or an increase (PVDF) in hydrophobicity and even cleavages (PDMS). The combination of the FM and contact angle technique has demonstrated to be very versatile and useful for monitoring the variation of the membrane properties during operation.
查看更多>>摘要：A biomass-based carbon fiber/metal-organic frameworks (MOFs/CF) electrode, with excellent electro-catalytic activity, was used for design the electro-Fenton (EF) process. The carbon fiber membrane (CF) was prepared from regenerated cotton fiber membrane through carbonization, and the MOFs were successfully introduced on the surface of the CF by the solvothermal method to obtain MOFs/CF electrode. Through the oxygen reduction reaction (ORR), the continuous on-site generation of H2O2 was achieved over the MOFs/CF electrode. Moreover, the MOFs could efficiently catalyse H2O2 to form hydroxyl radicals OOH), which can degrade organic pollutants in the EF process. Excellent electrocatalytic performance was exhibited when the electrode was applied to degrade tetrabromobisphenol A (TBBPA). The total organic carbon removal efficiency for TBBPA reached 80% in 240 min, which demonstrated TBBPA was also rapidly mineralized by the constructed EF system.
查看更多>>摘要：Rapid degradation of petroleum hydrocarbons by chemical oxidation is currently facing lots of environmental concerns, and green activation methods are highly needed. This study investigated the degradation of total petroleum hydrocarbons (TPHs), polycyclic aromatic hydrocarbons (PAHs), and n-alkanes in soil by FeS@BC and FeS activated persulfate (PS). Various controlling factors including FeS to biochar (BC) mass ratio, PS dosage, FeS@BC dosage, and initial pH were examined. The optimal parameters were obtained by single-factor experiments. Under the optimal condition, the removal rates of TPHs, PAHs, and n-alkanes by a FeS@BC/PS system were 61.83 %, 78.17 %, and 91.56 %, respectively, which were much higher than those of a FeS/PS system (47.91 %, 51.20 %, and 79.31 %, respectively). Radical quenching experiment and Electron Paramagnetic Resonance (EPR) revealed that the dominant active substance is sulfate free radical (SO_4~(·-)) produced by PS during activation. Based on the characterization and data analysis, a possible activation mechanism is proposed: the reduction of Fe~(2+)/Fe~(3+) and the activation of BC as an electron transfer mediator promote the generation of SO_4~(·-). This study demonstrates that the FeS@BC/PS system has a promoting effect on the degradation of petroleum hydrocarbons in soil, which has great potential for remediation of petroleum-contaminated soil.
查看更多>>摘要：The excessive release of CO2 from the burning of fossil fuels is of great concern, and effective treatment methods are urgently needed to solve the resulting crisis. Membrane-based separation processes have attracted significant attention due to their advantages, such as low investment cost, low energy consumption, and ease of operation. Herein, composite organosilica membranes were fabricated via co-polymerization reactions between bis(trie-thoxysilyl)acetylene (BTESA), bis(triethoxysilyl)benzene (BTESB), and 4,4'-bis(triethoxysilyl)-1,1'-biphenyl (BTESBPh). Then, dynamic light scattering (DLS), Fourier-transform infrared (FT-IR) spectrometry, and sorption measurements were used to assess the evolution of the network structures. We found that the addition of BTESB into BTESA densified membrane structures, while the co-polymerization reactions between BTESA and BTESBPh increased membrane pore sizes. Thus, all membranes exhibited great potential for CO2 capture and would be competitive candidates as suitable membrane materials for CO2 treatment applications.
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