Channel Intersections Research Articles

Sorption, Structure and Dynamics of CO₂ and Ethane in Silicalite at High Pressure: A Combined Monte Carlo and Molecular Dynamics Simulation Study.

Silicalite is an important nanoporous material that finds applications in several industries, including gas separation and catalysis. While the sorption, structure, and dynamics of several molecules confined in the pores of silicalite have been reported, most of these studies have been restricted to low pressures. Here we report a comparative study of sorption, structure, and dynamics of CO2 and ethane in silicalite at high pressures (up to 100 bar) using a combination of Monte Carlo (MC) and molecular dynamics (MD) simulations. The behavior of the two fluids is studied in terms of the simulated sorption isotherms, the positional and orientational distribution of sorbed molecules in silicalite, and their translational diffusion, vibrational spectra, and rotational motion. Both CO2 and ethane are found to exhibit orientational ordering in silicalite pores; however, at high pressures, while CO2 prefers to reside in the channel intersections, ethane molecules reside mostly in the sinusoidal channels. While CO2 exhibits a higher self-diffusion coefficient than ethane at low pressures, at high pressures, it becomes slower than ethane. Both CO2 and ethane exhibit rotational motion at two time scales. At both time scales, the rotational motion of ethane is faster. The differences observed here in the behavior of CO2 and ethane in silicalite pores can be seen as a consequence of an interplay of the kinetic diameter of the two molecules and the quadrupole moment of CO2.

Conversion of chloromethane to propylene over fluoride-treated H-ZSM-35 zeolite catalysts

H-ZSM-35 with 2D channel intersections has been first found to be an effective catalyst over chloromethane transformation into propylene. Fluoride treatment is further introduced to improve the catalytic performance. With a proper concentration of fluoride treatment, the selectivity and yield of propylene can be enhanced significantly while a high propylene/ethylene ratio is achieved. Detailed characterizations demonstrate that dealumination caused by fluoride treatment results in a reduction in acidic sites, which is responsible for the improvement of catalytic performance.

On-chip valley topological materials for elastic wave manipulation.

Valley topological materials, in which electrons possess valley pseudospin, have attracted a growing interest recently. The additional valley degree of freedom offers a great potential for its use in information encoding and processing. The valley pseudospin and valley edge transport have been investigated in photonic and phononic crystals for electromagnetic and acoustic waves, respectively. In this work, by using a micromanufacturing technology, valley topological materials are fabricated on silicon chips, which allows the observation of gyral valley states and valley edge transport for elastic waves. The edge states protected by the valley topology are robust against the bending and weak randomness of the channel between distinct valley Hall phases. At the channel intersection, a counterintuitive partition of the valley edge states manifests for elastic waves, in which the partition ratio can be freely adjusted. These results may enable the creation of on-chip high-performance micro-ultrasonic materials and devices.

Location and chemical speciation of Cu in ZSM-5 during the water-gas shift reaction

Cu/ZSM-5 catalysts were found to exhibit activity for the water-gas shift (WGS) reaction at temperatures over 300 °C. Nominal Cu loadings of 1, 5, and 10% on ZSM-5 were synthesized using the wetness impregnation technique and evaluated for WGS activity; with a clear trend favoring increased Cu loading (10% > 5% > 1%). X-ray diffraction (XRD) confirmed high dispersion of small Cu at low loadings while CuO crystallized at higher loadings. In-situ XRD showed an evolving transformation of CuO → Cu metal, with the appearance of a metallic copper phase at the optimum reaction conditions, particularly at the highest copper loading. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed the ability of the surface to activate H2O and adsorb CO, by the presence of HO-Al/Si and transient CO-Cu+ surface species in two distinct locations (5 membered rings (2157 cm−1) vs channel intersections (2138 cm−1) within the ZSM-5 framework, that likely formed during the CuO → Cu transition. The lowest loaded Cu-ZSM-5 (1%) showed only the 5 membered ring occupied Cu+ while the higher loadings showed both, with comparable temperature dependent behavior for the channel intersection Cu+. The amounts of Cu+ species in each location were observed to be dependent on temperature while the 5-membered ring showed better thermal stability. In-situ ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) was used to further confirm the gradual changes to the chemical state of copper (CuO → Cu2O → Cu) under reaction conditions.

Selective Introduction of Acid Sites in Different Confined Positions in ZSM-5 and Its Catalytic Implications

Controlling the location of acid sites in zeolites can have a great effect on catalysis. In this work we face the objective of directing the location of Al into the 10R channels of ZSM-5 by taking advantage of the structural preference of B to occupy certain positions at the channel intersections, as suggested by theoretical calculations. The synthesis of B-Al-ZSM-5 zeolites with variable Si/Al and Si/B ratios, followed by B removal in a postsynthesis treatment, produces ZSM-5 samples enriched in Al occupying positions at 10R channels. The location of the acid sites is determined on the basis of the product distribution of 1-hexene cracking as a test reaction. The higher selectivity to propene and lower C4=/C3= ratio in the samples synthesized with B and subsequently deboronated can be related to a larger concentration of acid sites in 10R channels, where monomolecular cracking occurs. Finally, several ZSM-5 samples have been tested in the methanol to propene reaction, and those synthesized through the B-...

Understanding the unique sorption of alkane-α, ω-diols in silicalite-1.

Adsorption equilibria of alkane-α, ω-diols (propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol, and hexane-1,6-diol) from aqueous solution onto an all-silica zeolite of the type mordenite framework inverted (MFI, also known as silicalite-1) are obtained by simulations and experiments at T = 323 K and also for pentane-1,5-diol (C5) at 348 and 383 K. After an initial slow rise, isotherms at T = 323 K exhibit steep changes in loading, reaching saturation at 10, 9, 8, and 7 molec/uc as the number of carbon atoms of the diols increases from 3 to 6. The abrupt change in loading corresponds to a minimum in the free energy of adsorption (from vapor to zeolite) that is associated with a rapid rise in the number of hydrogen bonds per sorbate molecule due to the formation of large clusters. For C5 at low loading, the centers-of-mass primarily occupy the channel intersections with oxygens oriented along the straight channels where intermolecular hydrogen bonds are formed. At saturation loading, the C5 centers-of-mass instead occupy the straight and zig-zag channels, and nearly all C5 molecules are involved in a percolating hydrogen-bonding network (this also occurs for C6). With increasing temperature, the C5 isotherm decreases in steepness as the minimum in free energy of adsorption decreases in depth and a less-ordered structure of the adsorbed molecules results in a lower number of diol-diol hydrogen bonds. However, the C5 isotherm does not shift significantly in concentration of the adsorption onset, as the free energies of solvation and adsorption increase by similar and compensating amounts. At T = 323 and 348 K, the steep change for the C5 adsorption isotherm is found to be a phase transition (as indicated by a bimodal distribution of unit cell occupancies at intermediate loading) from a less-dense phase with only small hydrogen-bonded clusters to an ordered solid phase with loadings of 8 molec/uc. At T = 383 K, the sorbates are less ordered, the distribution of occupancies becomes unimodal at intermediate loading, and the loading rises more gradually with concentration. Several different enhanced sampling methods are utilized for these simulations.

Effect of Next-Nearest-Neighbor Aluminum Atoms in the HZSM-5 Framework Synthesized with Various Aluminum Sources on Liquefied Petroleum Gas Transformation to Light Olefins

HZSM-5 catalysts with various aluminum distributions in their frameworks and different Si/Algel ratios were synthesized to investigate the product distribution in liquefied petroleum gas cracking. The characterization of synthesized zeolites was performed by X-ray diffraction (XRD), Brunauer, Emmett, and Teller (BET) method, (scanning electron microscopy) SEM, NH3-TPD, X-ray fluorescence (XRF), and direct reflectance (DR) UV–visible, and 27Al MAS NMR analyses. The maximum proportion of 0NNN aluminum atoms (90.6–92.6%) were found in HZSM-5 synthesized with aluminum nitrate. The higher 0NNN aluminum atoms in the zeolite framework and lower content of aluminum at channel intersections enhanced the olefin yield and decreased the C5+ yield. The amount of coke increased with increase of the 1NNN Al atoms. The optimum olefin yields for HZSM-5 synthesized with aluminum nitrate, aluminum chloride and aluminum hydroxide were found to be 47.22% with Si/Algel 50, 45.47% with Si/Algel 30, and 44.32% with Si/Algel 30, ...

Learning a River Network Extractor Using an Adaptive Loss Function

We have created a deep-learning-based river network extraction model, called DeepRiver, that learns the characteristics of rivers from synthetic data and generalizes them to natural data. To train this model, we created a very large database of exemplary synthetic local channel segments, including channel intersections. Our model uses a special loss function that automatically shifts the focus to the hardest-to-learn parts of an input image. This adaptive loss function makes it possible to learn to detect river centerlines, including the centerlines at junctions and bifurcations. DeepRiver learns to separate between rivers and oceans, and therefore, it is able to reliably extract rivers in coastal regions. The model produces maps of river centerlines, which have the potential to be quite useful for analyzing the properties of river networks.

Butylene catalytic cracking to propylene over a hierarchical HZSM-5 zeolite: Location of acid sites controlling the reaction pathway

A hierarchical ZSM-5 zeolite was prepared by steam-assisted crystallization (SAC) method and then the acidity of zeolites was modified by using organic silane compounds (catalytic cracking of silane, or the CCS method). The obtained zeolite was finally applied in the process of butylene catalytic cracking to produce propylene. High yield of propylene, 40 wt%, was achieved and it was much higher than that achieved on other prepared zeolites. This rise in propylene yield is mainly ascribed to the specific location of framework aluminum of zeolite in crystal sphere. Compared with the ZSM-5 zeolite synthesized by hydrothermal method, the ZSM-5 zeolite prepared from SAC method shows more acid sites in straight and sinusoidal channels rather than the intersection of channels, which is beneficial to reinforcing the reaction pathway of producing propylene and simultaneously suppressing the main side reactions in butylene catalytic cracking. And since the external acid sites of zeolite were covered by using the CCS method, the main side reactions were further inhibited. These results also help to elucidate the catalytic behavior of acid sites in different locations of HZSM-5 in butylene catalytic cracking and better understand the processing of SAC method.

Effect of framework single and close (pairs and un-pairs) aluminum atoms on phosphorous modification of HZSM-5 in cracking of liquefied petroleum gas to ethylene and propylene

To investigate the effects of framework single and close Al atoms on modification of HZSM-5 with phosphorus and steam in liquefied petroleum gas (LPG) cracking to light olefins, HZSM-5 zeolites were synthesized with two Al sources including Al(NO3)3 and Al(OH)3. The unmodified, P-modified HZSM-5 and steam-treated P/HZSM-5 zeolites were characterized by XRD, BET, 27Al MAS NMR and NH3-TPD techniques. The Al locations in the HZSM-5 zeolites were determined by combining the results of XRF and diffuse reflectance UV–visible spectroscopy. The catalytic performance showed that the olefin yields and catalytic stability of HZSM-5(1) synthesized with higher single Al atoms and lower Al atoms at channel intersections (β sites) was greater than that of HZSM-5(2) synthesized with higher close and pair Al atoms. The reduction of acid site strength and increment of weak to strong (W/S) acid ratio after P modifications and steam treatment resulted in a significant increase of olefin yields and a decrease of C5+ yields and coke amount. The catalytic stability and propylene to ethylene (P/E) ratio for P/HZSM-5(1) with lower strong acid sites was greater than that of P/HZSM-5(2). The P/E ratio, deactivation rate, propylene yield and olefin yields were found to be 1.005, 13.58%, 23.42% and 46.72% for P/St/HZSM-5(1) and 0.959, 15.49%, 20.09% and 41.04% for P/St/HZSM-5(1) after 240 min. The catalytic results showed that the highest and lowest catalytic stability were related to the P/St/HZSM-5(1) and HZSM-5(2) catalysts, respectively.

Instantaneous simulation of fluids and particles in complex microfluidic devices.

Microfluidics researchers are increasingly using computer simulation in many different aspects of their research. However, these simulations are often computationally intensive: simulating the behavior of a simple microfluidic chip can take hours to complete on typical computing hardware, and even powerful workstations can lack the computational capabilities needed to simulate more complex chips. This slows the development of new microfluidic chips for new applications. To address this issue, we present a microfluidic simulation method that can simulate the behavior of fluids and particles in some typical microfluidic chips instantaneously (in around one second). Our method decomposes the chip into its primary components: channels and intersections. The behavior of fluid in each channel is determined by leveraging analogies with electronic circuits, and the behavior of fluid and particles in each intersection is determined by querying a database containing nearly 100,000 pre-simulated channel intersections. While constructing this database takes a nontrivial amount of computation time, once built, this database can be queried to determine the behavior of fluids and particles in a given intersection in a fraction of a second. Using this approach, the behavior of a microfluidic chip can be simulated in just one second on a standard laptop computer, without any noticeable degradation in the accuracy of the simulation. While our current technique has some constraints on the designs of the chips it can simulate (namely, T- or cross-shaped intersections, 90 degree channel turns, a fixed channel width, fluid flow rates between 0 and 2 cm/s, and particles with diameters between 1 and 20 microns), we provide several strategies for increasing the range of possible chip designs that can be simulated using our technique. As a proof of concept, we show that our simulation method can instantaneously simulate the paths followed by particles in both simple and complex microfluidic chips, with results that are essentially indistinguishable from simulations that took hours or even days to complete using conventional approaches.

Ethylene formation by dehydration of ethanol over medium pore zeolites

In this work, the role of pore arrangement of 10-ring zeolites ZSM-5, TNU-9 and IM-5 on their catalytic properties in ethanol transformation were investigated. Among all the studied catalysts, the zeolite IM-5, characterized by limited 3-dimensionality, presented the highest conversion of ethanol and the highest yields of diethyl ether (DEE) and ethylene. The least active and selective to ethylene and C3+ products was zeolite TNU-9 with the largest cavities formed on the intersection of 10-ring channels. The catalysts varied, however, in lifetime, and their deactivation followed the order: IM-5>TNU-9>ZSM-5. The processes taking place in the microporous zeolite environment were tracked by IR spectroscopy and analysed by the 2D correlation analysis (2D COS) allowing for an insight into the nature of chemisorbed adducts and transition products of the reaction. The cage dimension was found as a decisive factor influencing the tendency for coke deposition, herein identified as polymethylated benzenes, mainly 1,2,4-trimethyl-benzene.

Optically monitored segmented flow for controlled ultra-fast mixing and nanoparticle precipitation

Nanoparticles of drugs or colloidal carrier systems are capable of providing substantial advantages for drug bioavailability, but manufacturing nanoparticulate drugs or drug carriers remains a challenge because traditional mechanical or chemical batch mode processes might lack precise control of nanoparticle sizes. Microfluidic approaches are believed to give advantages but often do not provide chemically inert environments and lack controllable operation. Here, segmented flow devices with symmetrical design for centered organic phase injection and for nanoparticle precipitation in transparent and chemically inert glass microchannels are presented. Femtosecond laser fabrication was used to structure borosilicate glass wafers with hydrophilic microchannels of nearly circular cross section. They allow for ultra-fast mixing of solvents with aqueous fluids and subsequent precipitation of poorly water soluble drug nanoparticles or colloidal carrier particles. The best results for mixing and controlled precipitation were obtained with flow focusing and gas segmentation occurring at the same channel intersection point. In such systems, early interdiffusion of the solvent and aqueous solution before ultra-fast convective mixing in the plug is suppressed. A novel optical analysis technique revealed that the speed of mixing can be well controlled by simply adjusting the volume flow rate of the gas phase where changes in the liquid flow rate have practically no influence. In a controlled and stable Taylor flow, smallest plug volumes of 3.8 nl can be generated, which allows complete mixing in 9 ms. The production of lipid nanoparticles down to a diameter of 74 nm could already be demonstrated.

A Straightforward Descriptor for the Deactivation of Zeolite Catalyst H-ZSM-5

ZSM-5 is a widely used zeolite catalyst and is employed industrially for the methanol to gasoline (MTG) process. Even so, deactivation of ZSM-5 by coke formation constitutes a major technical and also fundamental challenge. We investigate the deactivation of a range of ZSM-5 catalysts through catalytic testing, physicochemical characterization, and powder X-ray diffraction (XRD). It is demonstrated that the unit cell changes upon deactivation. Periodic density functional theory is used to show that the change is induced by certain methyl substituted benzenes in the channel intersection in ZSM-5. This finding is corroborated by Rietveld refinement of XRD data obtained for deactivated catalysts. We are able to establish a direct correlation between the difference in the length of the a- and b-unit cell vectors and the total amount of coke, the remaining acidity, and the remaining surface area of the catalysts. This a- minus b-parameter is a straightforward descriptor that carries the essential information r...

Capturing channelized reservoir connectivity uncertainty with amalgamation curves

During reservoir characterization all the geological uncertainties affecting the quantity and distribution of hydrocarbons should be captured to assess the risks affecting final recovery.In a typical modeling workflow the geological uncertainties are accounted for through the construction of a sufficiently large set of 3-D static models. Out of this set, a few representative models are selected and dynamically simulated so as to correlate the geological characteristics of the reservoir with its dynamic performance and to propagate the uncertainty onto the final recovery factors, yet maintaining the computational run time acceptable. In channelized depositional environments, which are strongly heterogeneous, the selection approach must also account for channel connectivity, which plays a key role in the possibility of efficiently draining the reservoir for a reasonable number of wells.This study can be seen as a step forward in the assessment of the risks associated to the development of channelized reservoirs under the assumption that a way to express the concept of channel connectivity is channel amalgamation. Channel amalgamation is here defined through amalgamation curves which are numerically described using a set of indexes whose combination provide spatial information of channel intersections. These indexes were calculated for a full set of 3-D geological models and used to steer the selection of a representative model sub-set for subsequent fluid flow simulations.The validity of the index-based selection was verified on different sets of synthetic reservoir models through the evaluation of the representativeness of the model sub-set in reproducing the uncertainty of the original dataset. Eventually, the existence of a strong correlation between channel amalgamation and production performance was proved. From a practical perspective, the possibility to include channel amalgamation in the assessment of the geological models can considerably improve the representativeness of the selected models for uncertainty propagation thus reducing significantly the number of geological models to be considered.

Fluoride-mediated synthesis of TON and MFI zeolites using 1-butyl-3-methylimidazolium as structure-directing agent

In this work, 1-butyl-3-methylimidazolium (1B3MI) cation has been employed as a structure-directing agent for the synthesis of pure silica and Ti-containing zeolites in fluoride media. The 1B3MI OSDA exhibited distinct phase selectivity depending on the synthesis conditions, and particularly the concentration of the synthesis gel. Thus, under more diluted conditions (H2O/SiO2 = 14), the 1B3MI cation yielded pure silica TON zeolite with high crystallinity. Attempts to obtain Ti-containing zeolites, however, failed at this diluted condition even after 15 days of synthesis. In contrast, highly crystalline Ti-MFI was the only phase obtained upon reducing the H2O/SiO2 molar ratio from 14 to 7. The presence of Ti in the MFI zeolite framework was confirmed by both infrared and DRS UV-vis spectroscopies. The presence of intact OSDA molecules within the micropores was inferred from elemental analysis and 13C CP-MAS NMR spectroscopy. On the other hand, thermogravimetric analyses showed a different packing of the 1B3MI cation in the pure silica TON and Ti-MFI samples. Moreover, the environments for Si and F species in the as-made materials were investigated by means of 29Si and 19F MAS NMR, respectively. Finally, molecular simulations showed that the most stable arrangement of the 1B3MI cations involves the location of the imidazolium rings on the channel intersections and of the butyl chains on the sinusoidal channels.

MOPSA: A microfluidics-optimized particle simulation algorithm.

Computer simulation plays a growing role in the design of microfluidic chips. However, the particle tracers in some existing commercial computational fluid dynamics software are not well suited for accurately simulating the trajectories of particles such as cells, microbeads, and droplets in microfluidic systems. To address this issue, we present a microfluidics-optimized particle simulation algorithm (MOPSA) that simulates the trajectories of cells, droplets, and other particles in microfluidic chips with more lifelike results than particle tracers in existing commercial software. When calculating the velocity of a particle, MOPSA treats the particle as a two-dimensional rigid circular object instead of a single point. MOPSA also checks for unrealistic interactions between particles and channel walls and applies an empirical correcting function to eliminate these errors. To validate the performance of MOPSA, we used it to simulate a variety of important features of microfluidic devices like channel intersections and deterministic lateral displacement (DLD) particle sorter chips. MOPSA successfully predicted that different particle sizes will have different trajectories in six published DLD experiments from three research groups; these DLD chips were used to sort a variety of different cells, particles, and droplets. While some of these particles are not actually rigid or spherical, MOPSA's approximation of these particles as rigid spheres nonetheless resulted in lifelike simulations of the behaviors of these particles (at least for the particle sizes and types shown here). In contrast, existing commercial software failed to replicate these experiments. Finally, to demonstrate that MOPSA can be extended to simulate other properties of particles, we added support for simulating particle density to MOPSA and then used MOPSA to simulate the operation of a microfluidic chip capable of sorting cells by their density. By enabling researchers to accurately simulate the behavior of some types of particles in microfluidic chips before fabricating the chips, MOPSA should accelerate the development of new microfluidic devices for important applications.

TNU‐9 Zeolite: Aluminum Distribution and Extra‐Framework Sites of Divalent Cations

The TNU-9 zeolite (TUN framework) is one of the most complex zeolites known. It represents a highly promising matrix for both acid and redox catalytic reactions. We present here a newly developed approach involving the use of 29 Si and 27 Al (3Q) MAS NMR spectroscopy, CoII as probes monitored by UV/Vis and FTIR spectroscopy, and extensive periodic DFT calculations, including molecular dynamics, to investigating the aluminum distribution in the TUN framework and the location of aluminum pairs and divalent cations in extra-framework cationic positions. Our study reveals that 40 and 60 % of aluminum atoms in the TNU-9 zeolite are isolated single aluminum atoms and aluminum pairs, respectively. The aluminum pairs are present in two types of six-membered rings forming the corresponding α and β (15 and 85 %, respectively, of aluminum pairs) sites of bare divalent cations. The α site is located on the TUN straight channel wall and it connects two channel intersections. The suggested near-planar β site is present at the channel intersection.

Pressure Losses in Hydraulic Manifolds

Hydraulic manifolds are used to realize compact circuit layout, but may introduce a high pressure drop in the system. Their design is in fact oriented more toward achieving minimum size and weight than to reducing pressure losses. This work studies the pressure losses in hydraulic manifolds using different methods: Computational Fluid Dynamic (CFD) analysis; semi-empirical formulation derived from the scientific literature, when available; and experimental characterization. The purpose is to obtain the pressure losses when the channels’ connections within the manifold are not ascribable to the few classic cases studied in the literature, in particular for 90° bends (elbows) with expansion/contraction and offset intersection of channels. Moreover, since CFD analysis is used to predict pressure losses, general considerations of the manifold design may be outlined and this will help the design process in the optimization of flow passages. The main results obtained show how CFD analysis overestimates the experimental results; nevertheless, the numerical analysis represents the correct trends of the pressure losses.

Effect of the quasi-continuous equal-channel angular pressing on the structure and functional properties of Ti–Ni-based shape-memory alloys

The effect of severe plastic deformation by equal-channel angular pressing (ECAP) under normal and quasi-continuous regimes on the structure and the mechanical and functional properties of a Ti–50.2 at % Ni shape-memory alloy (SMA) has been studied. ECAP was carried out at an angle of intersection of channels of 120° in the normal regime with heating between passes at 450°C for 20 passes and in the quasi-continuous regime at the temperature of 400°C for three, five, and seven passes. The hot screw rolling with subsequent annealing at 750°C for 30 min and cooling in water was used as a control treatment (CT). A mixed submicrocrystalline and nanosubgrained structure was formed. The increase in the number of passes from three to seven led to a decrease in the average size of structural elements from 115 ± 5 to 103 ± 5 nm and to an increase in the fraction of grains/subgrains having a size less than 100 nm. After ECAP (seven passes) and post-deformation annealing at the temperature of 400°C for 1 h, a completely recoverable strain was 9.5%; after normal ECAP, 7.2%; after CT, 4.0%.