Search

The multi-objective optimization of methanol distillation is a critical and complex issue in the methanol industry. The three-column methanol distillation scheme is first simulated with Aspen Plus to provide the initial value of the NSGA-III algorithm. The operating parameters are optimized through the Python-Aspen platform. The total annual cost and CO2 emissions are considered the objective function. A small value of indicator generational distance can be achieved by increasing the number of generations, which is helpful in improving algorithm convergence. The NSGA-III algorithm has good convergence and distribution performance. By comparing the optimized results with the original ones, the total annual cost and CO2 emissions are, respectively, reduced by 5.35% and 12.80% when the operating parameters of the methanol distillation sequence are optimized through NSGA-III. As a result, substantial economic and energy savings can be made, offering great potential to improve the performance of the three-column methanol distillation.

The interfacial barrier of entry for light gas transport in a nanopore was a crucial factor to determine the separation efficiency in membrane technologies. To examine this effect, amorphous silica was prepared by sol-gel process, and its characterization results revealed that the commonly used cylindrical pore shape failed to represent the adsorption behavior of gases, but instead the pore shape had to be represented by a slit pore model. A finite element method (FEM) was developed to analyze the interfacial resistance by integrating a Lennard-Jones (LJ) potential over the layer area. It was found that the strong repulsion/attraction at the pore interface could be paired with the motion energy of guest molecules to predict the ideal selectivity between gases, thereby providing a solution to preliminarily screen the separation performance among a host of membrane candidates.

Porous mullite hollow fiber membranes were prepared with a combined phase-inversion and sintering method, using three sintering additives including yttrium stabilized zirconia (YSZ), small mullite particles (SMP), and titanium oxide (TiO2) to promote the particle sintering. The results indicated that all the three additives could improve the sintering performance of mullite hollow fiber membranes due to the decrease in activation energy of mullite grains. Both YSZ and TiO2 could react with mullite grains to generate composite oxides (e.g., ZrSiO4 and Al2TiO5) during sintering, following a reaction-sintering mechanism. Interestingly, the newly generated ZrSiO4 was instable and further decomposed into monoclinic ZrO2 and SiO2 in the sintering process. The decomposition could avoid excessive embedment of composite oxides among mullite grains which have negative impact on mechanical strength of mullite hollow fibers. Overall, the doping of YSZ provided a better promotion effect on the sintering of mullite hollow fiber membranes, where the microstructural and mechanical properties are insensitive to the doping content and sintering temperatures, so it could be used as the candidate for the large-scale preparation of mullite hollow fibers.

A pilot was used to experimentally study the ethanol dehydration process, based on the coupled process of distillation and vapor permeation by NaA zeolite membrane, and the effects of the water content in the feed, reflux ratio, mass flow, the product purity of the distill and the operating stability were systematically analyzed. It was found that due to the placement of NaA membrane, the operation zone of the original column could be significantly extended in the coupling, which in return could reduce the column facility investment. Based on the interplay among the operation parameters, it was found that the water content of the distilled product from the column could be used as a critical parameter to balance the energy consumption of the column and the membrane facility investment, and a value of 20 wt.% was recommended for the coupling. During the steady test of the coupling, the results indicated that the pilot plant could be continuously operated for 18 hours to dehydrate the feed (water/ethanol) from 60 wt.% to 8 wt.%, where the steady state was further validated in process simulation of Aspen plus. In summary, the parameters suitable for the stable operation of the distillation-vapor permeation coupling were investigated for the given condition. This research paves a foundation for the large-scale industrial design and application of the distillation-vapor permeation coupling.

We used a grand canonical Monte Carlo simulation to study the influence of impurities including water vapor, SO

Here, we use an electrospinning method to control the crystal structure, electronic structure and microstructure of catalysts simultaneously. The electrospun perovskite SmBa0.5Sr0.5Co2O6−δ (SBSC) possesses not only a large specific surface area but also an optimized crystal structure and electronic state, showing an excellent OER activity and durability.

T-type zeolite membranes were prepared on four-channel α-Al2O3 hollow fibers by secondary growth method with an ensemble synthesis strategy. Prior to the membrane synthesis, a bundle of α-Al2O3 hollow fibers were assembled on the ceramic bases by enamel sealing. The membrane modules with membrane areas of 0.03 m2 and 0.54 m2 were then seeded with ball-milled T-type zeolite crystals by dip-coating. A uniform and continuous T-type zeolite seed layer was obtained for a seed concentration of 1.5 wt% and a coating time of 15 s. The seeded modules were then immersed in synthesis solution for ensemble hydrothermal crystallization. After optimizing the synthesis parameters, high-quality hollow fiber zeolite membrane modules could be prepared with good reproducibility. The membrane module with 0.03 m2 exhibited a water permeation flux of 2.25 kg m−2 h−1 and a separation factor of 1348 for PV dehydration of 90 wt% ethanol/water mixture at 348 K. The membrane modules had long-term stability in acidic solution (pH~3) for 450 h as well. A pilot-scale apparatus composed of two 0.54 m2 membrane modules connected in series was further constructed for PV dehydration of 90 wt% isopropanol/water. The ensemble synthesis strategy paves a way for the industrialization of hollow fiber T-type zeolite membranes.

The single-chamber solid oxide fuel cell (SC-SOFC) represents an attractive alternative to batteries for micropower applications given its simplified stack design, easy gas management, lower operation temperature, and quicker start-up. Its stable operation over long duration relies on the availability of CO2-resistant cathode materials with high oxygen reduction reaction (ORR) activity. Here, we reported a novel perovskite oxide cathode SrSc0.075Ta0.025Fe0.9O3−δ (SSTF75), which provides CO2 resistance and high ORR activity. A peak power density of 1430 mW cm–2 was achieved with the SSTF75/Sm0.2Ce0.8O1.9 cathode at 650 °C with a methane and oxygen gas mixture (1:1 v/v ratio). It retained stable voltage performance at 600 °C for an over 90 h duration when discharged at a current density of 1000 mA cm–2. This work not only represents an advancing step in the SC-SOFC field but also authenticates an effective codoping strategy for the design of a CO2-resistant cathode for low-temperature applications.

In this work, the aggregation equation is developed to describe the aggregation number of copolymer molecules and micellar diameters from experimental data. Based on the regression parameters in the aggregation equation, it is concluded that the PO parts are beneficial to enlarge the micellar size and the EO parts suppress the formation of the micelles. By fitting the parameters with the EO and PO number, the aggregation equation was proposed to predict the aggregation behaviours of tri-block copolymers having EO units between 26 and 212, and with PO number between 30 and 70. By applying the equation to aqueous solution with salt additives, it can be extended to evaluate the impacts of the additives on the micelle formation.

This work studied the critical pore dimensions for different light gases in disordered microporous hybrid silica which was derived from 1,2-bis(triethoxysilyl)ethane (BTESE) precursor. The Lennard-Jones (LJ) parameters of the material, obtained from high pressure isotherms of light gases, were employed to evaluate dispersive interaction, diffusivity and adsorption coefficient in the nanopores of the hybrid silica, and the results demonstrated that the entrance barrier was the key factor to break down the separation limits confining the Graham law and the Knudsen model by gas kinetic theory. Finally, the critical pore dimensions for different resistance-dominated regions were evaluated, which theoretically explained why the separation capacity of the hybrid silica was less promising than pure silica for the purpose of gas separation.

Zeolite is widely used in the fields of adsorption, catalysis and membrane separation due to its well-defined structure. Equilibrium molecular dynamics (EMD) simulations were employed to investigate the effects of lattice flexibility on the transport diffusion of gases including CH4, Ar and H2 in LTA zeolite, associated with the effects of molecular size and gas loading being discussed. Our results reveal that the lattice vibration of zeolite leads to a pore breathing effect, which results in significantly enhanced interfacial resistance and much slower transport diffusion for CH4 and Ar, compared with the rigid lattices. Nevertheless, the diffusion of H2 with a small diameter, light weight and weak interactions, receives negligible impact from the lattice vibration. We find that the diffusivities of CH4, Ar and H2 increase with the thickness of zeolites and converge to constant values after the critical thicknesses, over which the interfacial resistance becomes negligible. For CH4 and Ar, the critical thicknesses are in the sub-micrometer scale and are around one order of magnitude higher than that of H2, emphasizing the interfacial resistance plays a dominant role for the molecules with diameters comparable to the aperture of zeolite and carrying relatively greater inertia. Further, as the loading increases from ~ 1 to ~ 3 mol per u. c., the interfacial resistances of CH4, Ar and H2 are reduced both in the rigid and flexible lattices, as a consequence of the prevalent fluid–fluid interactions. However, the ratios of the interfacial resistance to the total resistance, (Rf/Rt), and the critical thicknesses demonstrate different loading dependencies for CH4, Ar and H2. Our simulations essentially prompt the understanding of gases transport in nano-porous media, and benefit the optimal design of nano-porous membrane.

Grand canonical Monte Carlo (GCMC) and molecular dynamic (MD) simulations were systematically conducted to reveal the influence of volatile radionuclides, I2 and CH3I, on the adsorption of Xe/Kr/N2 mixtures in well-shaped carbon nanotubes (CNTs), stratified activated carbon fiber (ACF-15) and completely disordered silicon carbide derived carbon (SiC-DC). In the absence of radioactive impurities, the (6, 6) CNT with a pore size of 0.81 nm achieves adequately high adsorption of Xe (0.37 mol/kg) and Xe/Kr selectivity (45.3), presenting significantly superior performance than other CNTs and amorphous carbons. Albeit enhancing the amorphization of nanoporous carbons hardly impacts the sorption capacity, it hinders the adsorption kinetics dramatically by introducing the energy barriers to diffusion. However, when either I2 or CH3I presents in the gas phase, the adsorptions of Xe and Kr are severely excluded in nanoporous carbons due to the dominant adsorption of I2 and CH3I. For the Xe/Kr/N2/I2/CH3I mixture, the intense competitive adsorption occurs between I2 and CH3I in nanoporous carbons. It is found while the (6, 6) CNT demonstrates the greatest potential on separating CH3I from the quinary mixture, the (15, 15) CNT achieves the best performance on separating I2 among the carbon structures considered.

A dilute synthesis precursor was developed to prepare high-quality DDR zeolite membranes on α-Al 2 O 3 four-channel hollow fibers by secondary growth method. However, the as-membranes were susceptible to crack during high temperature activation (>873 K) for the template removal. A molecular simulation demonstrated that a large contraction of ~ 5% occurred for the DDR zeolite framework after template removal. Ozone environment was employed for membranes activation at low temperature (473 K) to prevent the formation of cracks. The occluded template in zeolite cages was successfully removed by this way and high quality DDR zeolite membranes were achieved reproducibly without any cracks. The membranes were further evaluated for single gas permeation and separation of CO 2 /CH 4 mixture. The ideal selectivities for CO 2 /CH 4 , CO 2 /N 2 , CO 2 /C 3 H 8 , CO 2 /H 2 , N 2 /CH 4 and O 2 /N 2 were 305, 32, 1500, 5, 10 and 1.7, respectively. For the separation of equimolar CO 2 /CH 4 mixture, a high selectivity of 500 and CO 2 permeance of 3.5×10 −8 mol m −2 s −1 Pa −1 could be achieved. The membranes also exhibited high stability in wet environment. A stable permeance of 3.5×10 −8 mol m −2 s −1 Pa −1 and selectivity of 140 could be achieved during 40 h test for the separation of CO 2 /CH 4 mixture containing 1.5% vapor at 353 K.

It is a great challenge for conventional NaA zeolite membrane to maintain stable water flux in pervaporation (PV) dehydration of polar aprotic solvents because the aggressive adsorption of these solvents on membrane surface restrain water adsorption and thereby reduce water flux gradually. To address this issue, a facile surface modification method was adopted to decorate the surface of NaA zeolite membrane with sol-gel derived TiO2 nanoparticles for PV dehydration of N, N-Dimethylacetamide (DMAc). Effect of TiO2 precursor composition on properties and separation performance of TiO2/NaA zeolite composite membranes was investigated extensively in terms of SEM, XRD, XPS, solvent adsorption and water contact angle. The results showed that the porous TiO2 layer on top of zeolite membrane not only hindered the electrostatic interaction between DMAc molecules and sodium cations from zeolite membrane but also allowed water permeation without large loss in flux. The minimum loss in water flux of TiO2/NaA zeolite membrane was about 17% after continuous PV dehydration of 10 wt% water/DMAc mixture for 24 h at 363 K while that of bare NaA zeolite membrane was over 95% within 15 h, indicating the effective improvement on separation stability of NaA zeolite membrane for PV dehydration of DMAc.

High-silica CHA (SSZ-13) zeolite membranes exhibit great potential for CO2 separation. However, the practical application is significantly hindered by the high investment cost. Here, we synthesized SSZ-13 zeolite membranes on four-channel hollow fibers with pore size of 150 nm, 370 nm and 600 nm, respectively. The CO2/CH4 selectivity of 127 ± 11 as well as CO2 permeance of (3.1 ± 0.6) × 10-7 mol m−2 s−1 Pa−1 was achieved on the membranes synthesized on the hollow fibers with 150 nm pore size at 433 K for 96 h. The single gas permeation was quantitively assigned to evaluate surface diffusion, Knudsen diffusion and viscous flow through the as-synthesized membranes. The permeation of small molecules (e.g., CO2 and N2) is mainly contributed by the zeolitic pores, however, the permeation of relatively big molecule (e.g., CH4) is more sensitive to the non-zeolitic pores. For the membranes with αCO2/CH4 of 130 and 48, the non-zeolitic pores contributed 24.7% and 69% of CH4 permeance, respectively.

Water diffusion in nanochannels is the basis of a variety of emerging nanotechnologies. The self and transport diffusions of water in carbon nanotubes (CNTs) having different pore sizes were investigated using equilibrium (EMD) and non-equilibrium molecular dynamics (NEMD) simulations. It is found that the formation of a depletion layer near the carbon wall in which water molecules lost hydrogen bonds accounts for the transforming of the self-diffusion mode. The reduced life time of hydrogen bond networks in larger CNTs stimulates the decorrelation of single water molecule from the center of mass of fluid, leading to the enlarged deviation between the self and transport diffusions. Our simulations reveal that the friction coefficient for water transporting in the CNT is enhanced by more than 60 times when the diameter of the CNT is increased from 8.1 to 33.9 A, leading to the transforming of the transport diffusion mode from ballistic into the Fickian mode. We show the smoothness of the CNT wall enhances the water flowrate in the CNT by orders of magnitude with respect to the value predicted by the Hagen-Poiseuille equation. However, this enhancement factor decreases from around 10,000 to 10 when the pore size of the CNT increases. We speculate that water transport in different CNTs experience different diffusion modes could be the explanation for the large discrepancies among the measured water flowrates in different studies. Our simulations also show that for the non-Fickian diffusion, the transport diffusivity calculated from EMD simulations is no longer effective in connecting the driving force and the driven flowrate.

A supported membrane and a xerogel derived from 1,2-bis(triethoxysilyl)ethane (BTESE) under the same conditions were characterized by a gas uptake technique and membrane permeation method, respectively, to investigate the transport mechanism inside the pores. The results indicated that the transport in both materials was governed by repulsive necks, with more adsorptive gases experiencing stronger restrictions. Furthermore, on the basis of a comparison between the two samples, the similarity of activation energies for spherical gases provided positive evidence for the commonly used assumption of pore network equivalence between xerogels and membranes derived under the same conditions. Finally, the neck dimensions in both materials were evaluated by the GT-based model, and a mean value of approximately 2.90 A (center-to-center distance) was obtained.

A postsynthetic covalent strategy involving dual-acyl chloride has been developed to introduce uncoordinated carboxyl groups into amine containing metal–organic frameworks (MOFs). The carboxyl group functionalized MOFs have been characterized by various techniques, including X-ray diffraction patterning, scanning electron microscopy, Fourier transform infrared spectroscopy, nuclear magnetic resonance, thermal gravimetric analysis, and gas adsorption. Results clearly indicated uncoordinated carboxyl groups were successfully grafted to the MIL-101(Cr)–NH2 framework. In addition, most of the amine groups (>80%) were grafted with carboxyl groups, which indicates this method is very effective. The thermal stability and adsorption selectivity of CO2/N2 were substantially enhanced, albeit the BET surface areas and total pore volumes were reduced. These observations could be explained by the effect of elimination of macropores in the framework due to the projecting of new functional groups in pore apertures. Here the successful fabrication of a MOF with uncoordinated carboxyl groups provides the possibility of efficiently modifying other MOFs.

In this study, two different particle sizes of Au nanoparticles (NPs) were synthesized using two different stabilizers, and then two different morphologies Au@TiO2 hollow spheres were obtained when the corresponding Au NPs solutions were added to the TiF4 ethanol–water solution under hydrothermal condition. The computational simulation is employed to provide the fundamental support to explain why different stabilizers yield different sizes of Au NPs, and the main cause for the experimental observation is contributed by the different interactive forces between Au and stabilizer molecules. The experimental strategy adopted different stabilizer in this work is expected to be generally applicable for the synthesis of many other types of micro-nanostructured materials.

The study of changes in the related mechanical property and microscopic structure of methane hydrate during the decomposition process are of vital significance to its exploitation and comprehensive utilization. This paper had employed the molecular dynamics (MD) method to investigate the influence of defects on the microscopic structure and mechanical property of the sI methane hydrate system, and to discover the mechanical property for the defect-containing hydrate system to maintain its brittle materials. Moreover, the stress-strain curve of each system was analyzed, and it was discovered that the presence of certain defects in the methane hydrate could promote its mechanical property, however, the system mechanical property would be reduced when the defects had reached a certain degree (particle deletion rate of 9.02% in this study). Besides, the microscopic structures of the sI methane hydrate before and after failure were analyzed using the F3 order parameter value method, and it was found that the F3 order parameters near the crack would be subject to great fluctuations at the time of failure of the hydrate structure. The phenomenon and conclusions drawn in this study provide a basis for the study of the microscopic structure and mechanical characteristics of methane hydrate.

Cobalt oxide silica membranes were prepared and tested to separate small molecular gases, such as He (dk = 2.6 Å) and H2 (dk = 2.89 Å), from other gases with larger kinetic diameters, such as CO2 (dk = 3.47 Å) and Ar (dk = 3.41 Å). In view of the amorphous nature of silica membranes, pore sizes are generally distributed in the ultra-microporous range. However, it is difficult to determine the pore size of silica derived membranes by conventional characterization methods, such as N2 physisorption-desorption or high-resolution electron microscopy. Therefore, this work endeavors to determine the pore size of the membranes based on transport phenomena and computer modelling. This was carried out by using the oscillator model and correlating with experimental results, such as gas permeance (i.e., normalized pressure flux), apparent activation energy for gas permeation. Based on the oscillator model, He and H2 can diffuse through constrictions narrower than their gas kinetic diameters at high temperatures, and this was possibly due to the high kinetic energy promoted by the increase in external temperature. It was interesting to observe changes in transport phenomena for the cobalt oxide doped membranes exposed to H2 at high temperatures up to 500 °C. This was attributed to the reduction of cobalt oxide, and this redox effect gave different apparent activation energy. The reduced membrane showed lower apparent activation energy and higher gas permeance than the oxidized membrane, due to the enlargement of pores. These results together with effective medium theory (EMT) suggest that the pore size distribution is changed and the peak of the distribution is slightly shifted to a larger value. Hence, this work showed for the first time that the oscillator model with EMT is a potential tool to determine the pore size of silica derived membranes from experimental gas permeation data.

The molecular orientation of permeating molecules crucially affects the gas transfer behavior in kinetic molecular sieving, particularly if the molecules are linear; however, this effect has been largely overlooked in the literature. To investigate this effect here we induce specific unfavourable molecular orientation of several linear gases based on adsorption effects in a hollow fiber NaA zeolite membrane, by anchoring a 3-dimensional alkali lignin molecule on the hydroxyls of the membrane surface. The results indicated that although the permeance was systemically reduced for all the gases investigated due to unfavourable orientation, the ideal selectivity for H2 relative to the linear molecules was consistently enhanced due to the presence of the alkali lignin molecule. On the other hand the permeation behavior for the spherically symmetric CH4 molecule was unaffected by the alkali lignin molecule, with the H2/CH4 unchanged and nearly constant over the operating temperature range. In addition to the defect healing, the enhancement in selectivity for H2 over the linear gases is strongly attributed to the normal orientation of the linear molecule relative to the pore axis on entry, induced by the adsorption force of the alkali lignin, leading to a repulsive potential at the pore mouth of the zeolite membrane. To validate the induced orientation effect of the linear molecules, ab initio method was employed to estimate the interaction energies between the pore mouth and linear molecules oriented parallel and normal to the pore axis. The computational results showed that the interaction energies were consistently higher for each specie when oriented normal to the pore axis (i.e. parallel to the pore cross-section), so that the tilted molecular orientation experienced stronger energy barriers; this is in accord with the experimental observation of increased selectivity for the more weakly-adsorbed H2 over the linear molecules. These findings can provide scientific guidance and facilitate new solutions to extend the separation boundaries of nanoporous membrane among gases.

Using 1, 2-bis (triethoxysilyl) ethane as a precursor, a hybrid organosilica membrane with high CO2 permselectivity, has been prepared by a two-step hot coating method. Here two sols with different sol particle sizes and microporous structures were prepared by tuning the dose of acid. By combining the two sols in the coating process using the two-step hot coating method, a thin and dense hybrid organosilica layer can be obtained. Single gas permeation experiments of the as-prepared membrane show a high permeance of 1.3×10−6 mol m−2 s−1 Pa−1 for CO2, with excellent CO2/N2 and CO2/CH4 separation factor of 23.5 and 31.5, respectively. Based on the mixture gas permeation experiments, the selectivities of CO2/N2 and CO2/CH4 at 20 °C were measured to be 10.5 and 17.5, respectively. The high perm-selectivity indicates that the as-prepared membrane contains only few defects. Furthermore, we demonstrate that the CO2 separation performance of the as-prepared membrane is greatly controlled by its CO2 adsorption properties.

Submicron NaA zeolite seeds were coated on the stainless steel (SS) hollow fiber support by self-assembly method, and then the hydrothermal crystallization and autoclave technique were used to synthesize NaA zeolite membranes. The effects of grafting temperature, grafting time and the size of induction seeds on the membrane performance were extensively investigated. The as-synthesized membranes and zeolite crystals were then characterized by X-ray diffraction, and the morphology and thickness of membranes were examined by scanning electron microscopy. The separation performance of the membrane was evaluated by pervaporation dehydration of 90 wt% ethanol/water mixtures at 75 °C. It was found that the seed-layer should be uniformly coated to induce good continuity for the NaA zeolite membrane layer, where the seeding effect was clearly affected by grafting time, grafting temperature and seed size. The optimal seeding condition was found for a grafting time of 6 h under a temperature of 110 °C, using a seed size of 150 nm. A continuous zeolite membrane layer could be obtained on the surface of the SS hollow fiber, with a separation factor above 10,000 and a permeation flux of 4.22 kg∙m−2∙h−1. The proposed self-assembly method could be readily operated and extended to the seeding process during the preparation of other supported zeolite membranes, providing a good prospect in batch-scale production of SS hollow fiber supported NaA zeolite membranes.

Intracellular amyloid fibrils linked to neurodegenerative disease typically accumulate in an age-related manner, suggesting inherent cellular capacity for counteracting amyloid formation in early life. Metazoan molecular chaperones assist native folding and block polymerization of amyloidogenic proteins, preempting amyloid fibril formation. Chaperone capacity for amyloid disassembly, however, is unclear. Here, we show that a specific combination of human Hsp70 disaggregase-associated chaperone components efficiently disassembles α-synuclein amyloid fibrils characteristic of Parkinson’s disease in vitro. Specifically, the Hsc70 chaperone, the class B J-protein DNAJB1, and an Hsp110 family nucleotide exchange factor (NEF) provide ATP-dependent activity that disassembles amyloids within minutes via combined fibril fragmentation and depolymerization. This ultimately generates non-toxic α-synuclein monomers. Concerted, rapid interaction cycles of all three chaperone components with fibrils generate the power stroke required for disassembly. This identifies a powerful human Hsp70 disaggregase activity that efficiently disassembles amyloid fibrils and points to crucial yet undefined biology underlying amyloid-based diseases.

We investigate gas adsorption and transport in a disordered microporous silica membrane having mean pore diameter 1.5 nm, coated on a porous tubular asymmetric support. The adsorption isotherms are found to be Langmuirian, with equilibrium constants that are accurately predicted for nonpolar gases, considering Lennard–Jones (LJ) interactions with a single layer of oxygen atoms on the pore surface. For the polar gas, CO2, the hydroxyls groups on the pore walls strongly increase the affinity with the pore walls, and a superposition of the LJ potential and an empirically represented electrostatic interaction is found to be adequate in correlating the Langmuirian equilibrium constant. The gas transport in the microporous silica layer is investigated using effective medium theory, with single pore transport represented by combination of pore mouth and internal pore diffusion resistances. Good agreement is observed for all the gases using different coordination numbers, indicating that the essential features of the transport in the silica micropores are captured in the approach. It is found that the overall transport resistance is dominated by the pore mouth barrier; however, the internal diffusion resistance in the relatively smaller pores is significant, especially for weakly adsorbed gases at higher temperature. In addition, the dependence of the pore mouth barrier coefficient on temperature and diffusing species are in good agreement with predictions of transition-state theory, with larger more strongly adsorbed molecules having higher activation energy. The proposed methodology is validated against experiment by comparison of the predicted flux for different gases in the supported membrane at various feed pressures in the low pressure range of 200–400 kPa, using the parameters obtained at 200 kPa.

The interpretation of experimental data on transport in porous materials is often based on the use of a single representative pore size, overlooking effects of the pore size distribution (PSD) and pore network connectivity, and fitting a tortuosity into which all such uncertainties are consigned. Using literature data on the diffusion of N2, Xe and i-C4H10 in mesoporous Shell silica spheres, we demonstrate that the tortuosity depends on the choice of the representative pore radius as well as gas species. Both the Knudsen model and the Oscillator model considering dispersive fluid–solid interactions, developed in this laboratory, are found to adequately interpret the data in conjunction with effective medium theory (EMT) by fitting a network coordination number instead of tortuosity. This insensitivity to model is due to the large mean mesopore radius of 7.4 nm for this silica; however, the Oscillator model is found to yield a value of the coordination number closer to the range of values expected for this material. Using the EMT we demonstrate that the tortuosity is dependent on temperature and diffusing species, because of differences in temperature dependence between the conductance at the representative pore radius and the true conductance which depends on the network connectivity and PSD. In the slip flow regime, which is obtained at large pore size, we show that the superposition of Knudsen and viscous mechanisms leads to temperature and species dependence of tortuosity, because of the different pore size dependence of the two contributions. This leads to different limiting tortuosities and PSD dependence in the Knudsen and viscous flow regimes. These critical aspects are largely unappreciated in the literature, and even systematic variations of tortuosity with temperature or diffusing species usually overlooked, often leading to misrepresentation of the underlying mechanism.

Understanding the transport behavior of fluid molecules in confined spaces is central to the design of innovative processes involving porous materials and is indispensable to the correlation of process behavior with the material structure and properties typically used for structural characterizations such as pore dimension, surface texture, and tortuosity. [...]

We investigate the low pressure transport of several gases in a disordered mesoporous silica membrane of mean pore diameter 3.70 nm, deposited on a porous tubular asymmetric support. The transport data for the supported membrane is examined using three different diffusion models, the classical Knudsen model, a version corrected for finite molecular size, as well as the Oscillator Model developed in this laboratory, using a representative pore size in each layer. We show that the correlation by the Knudsen approach, or its modification for finite molecular size, overestimates the diffusion coefficient in the membrane layer, and yields unrealistically high tortuosities, which vary with temperature and gas species. The apparent tortuosity is significantly reduced to a more reasonable range based on the Oscillator Model, which accounts for dispersive fluid–solid interaction and the effect of adsorption on the transport. In order to overcome the lack of transferability associated with fitting of a variable tortuosity, effective medium theory is used to model the transport in the different layers, while considering the entire pore size distribution for each layer, using only fundamental structural parameters. It is found that the classical and corrected Knudsen models yield significant deviations even with an unrealistically high thickness for the membrane layer, due to the overestimation of the diffusivity. The most satisfactory results are obtained with the Oscillator Model, in which the fitting error is significantly reduced with acceptable membrane thickness. The results indicate that the Knudsen model fails to represent the transport for the mesopores of mean size of 3.70 nm in silica, and that the Oscillator Model provides a more accurate apparent diffusivity which accounts for the effects of adsorption. We also show that use of the effective medium theory provides a satisfactory option to model the transport, using only fundamental structural parameters that are transferable.

We investigate the low pressure diffusion of several gases in a disordered mesoporous γ-alumina membrane of pore diameter 10.4. nm, coated on a macroporous α-alumina tubular support. Transport data for the uncoated support is also separately obtained and interpreted using the conventional slip flow correlation with a single representative pore size, and with effective medium theory while considering the entire pore size distribution. It is shown that the conventional correlation based on a single pore size yields significant anomalies in the tortuosity and pressure profile for all gases, which are eliminated on using the effective medium theory, demonstrating the importance of considering the pore size distribution (PSD). These anomalies lead to failure of the correlation for the membrane layer. The effective medium theory is also extended to the disordered membrane layer, using the classical slip flow model and a version corrected for finite molecular size, as well as the Oscillator Model developed in this laboratory. All the diffusion models fitted the experimental data accurately, without the artifacts observed with the commonly used single pore size model. The results make evident the importance of correctly taking the pressure profile into account, in any investigation for a multi-layered supported membrane (i.e. with a macroporous support and a mesoporous membrane layer). It is seen that the slip flow model leads to significantly higher apparent diffusivities than the Oscillator flow model at small pore sizes. Nevertheless, the performance of all three diffusion models is comparable, and it is not possible to distinguish between them for the large pore diameter of 10.4. nm of the mesoporous γ-alumina membrane layer. The results unequivocally show that it is critical to consider the full PSD for each layer rather than using a single representative pore size in modeling membrane transport, and in interpreting experimental permeability data.

On the basis of energy conservation law and surface pressure isotherm, the conformation energy changes of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG) in pure phospholipid monolayer at the air/water interface during compression are derived. The optimized conformations of phospholipids at absolute freedom state are simulated by Gaussian 98 software. Based on following assumptions: (1) the conformation energy change is mainly caused by the rotation of one special bond; (2) the atoms of glycerol near the water surface are active; (3) the rotation is motivated by hydrogen-bond action; (4) the rotation of bond is inertial, one simplified track of conformational change is suggested and the conformations of DPPC and DPPG at different states are determined by the plots of conformation energy change vs. dihedral angle. The thickness of the simulated phospholipid monolayer is consistent with published experimental result. According to molecular areas at different states, the molecular orientations in the compressing process are also developed.

The infiltration of fluids through the voids of porous materials is common place to several well established and emerging technologies, and optimizing their performance relies heavily on developing a deeper understanding of how the fluid flow is affected by the topology of the pore space. This is particularly challenging when the medium is unconsolidated, since it is not only the pore size distribution and pore network connectivity that must be considered, but also the pore aspect ratio distribution will often assume importance. In this work, we introduce a modified effective medium theory (EMT) where the effect of non-vanishing aspect ratios is considered in order to describe the transport mechanism of several light gases through unconsolidated macroporous α-alumina tubular supports. It is confirmed that the tortuosity is not just a property of the medium, but also depends (weakly) on the operating conditions due to the combined effect of viscous and Knudsen contributions. The coordination number and average pore length are the only adjustable parameters in the theory, which allowed adequate prediction of the variation of the apparent tortuosity with temperature for the investigated gases.

Micron-sized silica gel particles were first surface-modified with a coupling agent, γ-methacryloylpropyl trimethoxysilane (MPS), so polymerizable double bonds were introduced onto the surfaces of silica gel particles. Then, acrylonitrile (AN) was graft polymerized on the surfaces of the modified particles in the manner of “grafting from”, resulting in the grafted particles PAN/SiO2. In succession, the grafted PAN was transformed into the grafted poly (amidoxime) (PAO) via aminoximation transformation reaction with hydroxylamine hydrochloride as a reaction reagent, and the composite chelating particles PAO/SiO2 with graft-type were obtained. In this work, the effects of main factors on the graft polymerization of AN and on the aminoximation transformation reaction were investigated in depth. At the same time, the chelating adsorption property of PAO/SiO2 particles for heavy metal ions and rare ions was preliminarily examined. The experiments results show that: (a) In graft polymerization, the reaction tem...

The available surface equation of state for pure pulmonary surfactant monolayers is generalised to binary mixture monolayers by introducing a group of parameters, βi(i = 1–4) in the form of to express the influence of the components in new mixing rules and a new factor, I, is defined to represent the interaction intensity between two different components. The π − A isotherms getting by the surface equations of state agree with the experimental data for protein–lipid binary monolayers, and the average deviation is about 11.41%. The result shows the order of the interaction intensity between protein and lipid is SP-C/DPPG > SP-B/DPPG > SP-C/DPPC > SP-B/DPPC. L'equation d'etat de la surface disponible pour les monocouches de surfactant pulmonaire pures est generalisee en monocouches de melange binaire en introduisant un groupe de parametres, βi(i = 1–4) dans une forme qui permet d'exprimer l'influence des composantes dans de nouvelles regles de melange et un nouveau facteur, I , est defini pour representer l'intensite de l'interaction entre deux composantes differentes. Les isothermes π − A des equations d'etat de la surface concordent avec les donnees experimentales pour les monocouches binaires proteines-lipides et la deviation moyenne est d'environ 11,41%. Le resultat demontre que l'ordre de l'intensite de l'interaction entre les proteines et les lipides est SP-C/DPPG > SP-B/DPPG > SP-C/DPPC > SP-B/DPPC. Can. J. Chem. Eng. © 2010 Canadian Society for Chemical Engineering

Kinetics of synthesis of bis-(benzoxazolyl-2-methyl) sulfide (BBMS) is investigated under phase-transfer catalysis conditions. Thus, the reaction of 2-chloromethylbenzoxazole and sodium sulfide is carried out in a two-phase (organic/water) medium, and quaternary ammonium salt and quaternary phosphonium salt are used as phase-transfer catalyst (PTC) in the reaction. The conversion of 2-chloromethylbenzoxazole is dramatically enhanced by adding a small quantity of PTC and is also greatly affected by the reaction conditions. The effects of various reaction variables on the kinetics are investigated, including the amount of catalyst, the temperature, the kinds of catalysts, the kinds of solvents, and the agitation speed. An interfacial reaction mechanism is proposed to explain the characteristics of the reaction. A pseudo-first-order rate model is established to describe the relationship between the fractional conversion and the reaction time. The kinetics data demonstrate that the model is suitable to the reaction of synthesis of BBMS. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 296–302, 2009

Most neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease and other polyglutamine diseases are associated with degeneration and death of specific neuronal populations due to misfolding or aggregation of certain proteins. These aggregates often contain ubiquitin that is the signal for proteolysis by the ubiquitin-proteasome system, and chaperone proteins that are involved in the assistance of protein folding. Here we review the role of protein quality control systems in the pathogenesis of neurodegenerative diseases, and aim to learn more from the cooperation between molecular chaperones and ubiquitin-proteasome system responding to cellular protein aggregates, in order to find molecular targets for therapeutic intervention.

Protein aggregates are the hallmark of stressed and ageing cells, and characterize several pathophysiological states1, 2. Healthy metazoan cells effectively eliminate intracellular protein aggregates3, 4, indicating that efficient disaggregation and/or degradation mechanisms exist. However, metazoans lack the key heat-shock protein disaggregase HSP100 of non-metazoan HSP70-dependent protein disaggregation systems5, 6, and the human HSP70 system alone, even with the crucial HSP110 nucleotide exchange factor, has poor disaggregation activity in vitro4, 7. This unresolved conundrum is central to protein quality control biology. Here we show that synergic cooperation between complexed J-protein co-chaperones of classes A and B unleashes highly efficient protein disaggregation activity in human and nematode HSP70 systems. Metazoan mixed-class J-protein complexes are transient, involve complementary charged regions conserved in the J-domains and carboxy-terminal domains of each J-protein class, and are flexible with respect to subunit composition. Complex formation allows J-proteins to initiate transient higher order chaperone structures involving HSP70 and interacting nucleotide exchange factors. A network of cooperative class A and B J-protein interactions therefore provides the metazoan HSP70 machinery with powerful, flexible, and finely regulatable disaggregase activity and a further level of regulation crucial for cellular protein quality control. published

A fundamental understanding of the processes affecting fluid transport in the voids of porous materials constitutes a key step in numerous emerging applications in nanotechnology, materials design, membrane science and biology. By a purely hard sphere treatment of the diffusant, for over a century the Knudsen-based method has been the primary technique in our craft for investigating the transport of fluids in confined space, particularly in narrow disordered nanoporous adsorbents, catalysts and membranes. However, recent theoretical results and simulations, as well as experimental data on transport in well characterised narrow nanoporous materials indicate that the apparent success of the correlation is not necessarily a vindication of the Knudsen theory. Instead, these simulations, and the unrealistically high tortuosities obtained on application of the correlation, demonstrate the Knudsen model to substantially overestimate the diffusivity due to significant dispersive fluid-solid interaction. Besides affecting the molecular trajectories, which are no longer linear, the presence of the fluid-solid interaction leads to strong density profiles and adsorbate inhomogeneity in the direction normal to the pore walls. In this work, contributions are made involving such fundamental understanding of fluid transport in nanopores, and novel approaches are developed to facilitate the comprehensive analysis of transport in supported silica membranes. Firstly, an analysis of the transport of single gases in macroporous a-alumina substrates having a mean pore size of around 500 nm was conducted, and the results indicate that the tortuosity is dependent on the gas, and varies with operating conditions in the slip flow regime. A new effective medium theory (EMT) approach for modelling the transport in the substrate was developed to include the entire pore size distribution and the pore aspect ratio effect due to finite pore length. Theoretical results of the EMT provide an improvement on existing models that are based on empirical correlations using a representative pore size. The dependence of tortuosities on operating conditions in macroporous networks in slip flow regime is caused by the difference in dependence of Knudsen and viscous flow-based permeability on pore size, temperature and pressure; these yield different tortuosity limits for the pure Knudsen and viscous flow, respectively, in the presence of pore size distribution. Besides these, the importance of the choice of representative pore radius in determining the apparent tortuosity trends with temperature is also extensively provided in different nanoporous network. Moreover, a mesoporous g-alumina membrane having a mean pore size around of 10.4 nm was synthesized on the surface of the macroporous a-alumina substrate by dip-coating. The transport mechanism of single gases in the mesoporous g-alumina layer was investigated by the EMT approach to predict the macroscopic flow rate, using the classical slip flow model and a version corrected for finite molecular size, as well as the recent-developed Oscillator model in this laboratory. The analysis results indicate that all the three diffusion models describe the experimental data accurately and the interfacial pressure is correctly resolved in the approach, without the artifacts observed with the methodology using a single pore size. In addition, using literature data on the diffusion of N2, Xe and i-C4H10 in mesoporous Shell silica spheres (mean pore size 14.2 nm), the transport of gases was also analyzed to predict the pore coordination number for various diffusion models. It has found that both the Knudsen model and the Oscillator model adequately interpret the data in conjunction with EMT approach due to this large pore size. A mesoporous amorphous silica layer having mean pore size of around 3.7 nm was further synthesized on the asymmetric support comprising a macroporous substrate and mesoporous interlayer. The transport mechanism of single gases in the mesoporous silica layer was investigated to predict the membrane thickness. The most satisfactory results were obtained with the Oscillator model, in which the fitting error was significantly reduced using an acceptable membrane thickness, indicating that the Knudsen model fails to represent the transport for the mesopores in silica. Finally, a microporous amorphous silica layer was also synthesized on the asymmetric support, having a mean pore size around 1.5 nm. The adsorption and transport mechanism of single gases in the microporous silica membrane was examined, with the pore resistance represented by a combination of pore mouth and internal pore diffusion resistances. It has found that the pore mouth barrier dominates the overall transport resistance; and the internal diffusion resistance in the relatively smaller pores is significant, especially for weakly adsorbed gases at higher temperature. Overall, this thesis explored gas transport in different porous materials under low pressure limits, using modification of established diffusion models. The results provide fundamental understanding about how the adsorptive and diffusive behaviour of adsorbate is affected by the adsorbent structure at the nanoscales. These results are accompanied by detailed investigations to explain fluid-dependence of tortuosity under different transport mechanisms. While this work has predominantly focused on silica membranes, the results and models developed are generally applicable to transport in other nanoporous materials.