Aqueous film formation on irregularly shaped inorganic nanoparticles before deliquescence,as revealed by a hygroscopic differential mobility analyzer–Aerosol particle mass system

A hygroscopic tandem differential mobility analyzer (H-TDMA) and a hygroscopic coupled DMA and aerosol particle mass (H-DMA-APM) were coupled to examine aqueous film formation and the deliquescence behavior of inorganic nanoparticles. The two systems complement each other because H-DMA-APM measures mass change, while H-TDMA measures mobility diameter (volume) change of nanoparticles upon water uptake. The former mass change was, in particular, more capable to discern minute particle phase changes than the latter size change at moderate RHs. The mass and diameter changes were used to derive the particle effective density for evaluation of aqueous film formation on the nanoparticle surface before and after deliquescence transition. The measurements further showed that approximately 3–5 and 12–20 monolayer equivalents of water molecules formed on the respective surface of 50- and 100-nm inorganic aerosols (ammonium sulfate and sodium chloride) before deliquescence relative humidity (DRH). These findings support the physical basis of the coated-surface model given by Russell and Ming in 2002, and suggest that the phase transition of inorganic nanoparticles near deliquescence is a gradual process instead of an abrupt change. This phenomenon changed the surface energy values, thus confirming the explanation that the DRH of nanoparticles increases as the particle size decreases. This is the first direct observation of nanoparticle deliquescence phase transition using the H-DMA-APM system, and the detailed characterization of aqueous film formation on inorganic nanoparticles is feasible with the presented measurement systems.

© 2016 American Association for Aerosol Research     

Characterization of the TSI model 3086 differential mobility analyzer for classifying aerosols down to 1 nm

Measurement systems for particle sizing starting at 1 nm are used to bridge the gap between mass spectrometer measurements and traditional aerosol sizing methods, and thus to enable measurement of the complete size distribution from molecules and clusters to large particles. Such a measurement can be made using a scanning mobility particle sizer equipped with a diethylene glycol growth engine (e.g., TSI Model 3777 Nano Enhancer) along with a condensation particle counter, and a differential mobility analyzer (DMA) appropriate for such small sizes. Previous researchers have used high-resolution DMA (HRDMA) and also the TSI Nano-DMA (Model 3085) in such a scanning mobility particle sizer system. In this study, we evaluate the performance of the recently introduced TSI 1 nm-DMA (Model 3086). The transfer function was characterized using 1–2 nm monomobile molecular ion standards. The same measurements were repeated on a TSI Nano-DMA, with good agreement to previously published values. From the measured transfer function, the resolution of each DMA model was determined as a function of particle size and sheath flow rate. Resolution of the TSI 3086 in the 1–2 nm range was 10–25% higher than the TSI 3085. Measured resolutions of the TSI 3086 were 10–20% lower than theoretically predicted values, whereas those of the Model 3085 were 0–10% lower.

Copyright © 2018 TSI Inc.     

Dispersion of liquid–liquid phase by a jet-induced gas–liquid–liquid mixing column developed for separation of organic pollutants

This article presents the gas and liquid entrainment and its dispersion in a gas–liquid–liquid mixing column. The variations in phase entrainment is observed with the change in the paraffin liquid and kerosene volume fraction from 5% to 35% due to the increase in the flow resistance with increase in the effective viscosity of the liquid–liquid mixture. The degree of dispersion is enunciated based on the axial dispersion model and the flow resistance of the phases in the column. A correlation is proposed to interpret the entrainment of phase as a function of operating variables within the range of experimental conditions.     

Accurate mass determination of melamine–formaldehyde synthetic polymers after separation on preparative HPLC

Separation of 57 species from solutions of commercial melamines and analysis by high resolution mass spectrometry using electrospray ionisation and atmospheric pressure chemical ionisation is reported. Structures for melamine-based crosslinked polymers were also confirmed with two orthogonal techniques for characterisation of polymers: Fourier Transform Infrared Spectrometry (FTIR) and Nuclear Magnetic Resonance spectroscopy (NMR), respectively.Accurate mass measurements of melamine–formaldehyde resin structures were achieved in the ppm range, using an internal calibration standard reserpine. Results were within 5 ppm of calculated formulae. Relative isotopic abundances of [M+H]⁺ ions were evaluated for different fractions. Results were independent of the mobile phase used. NMR studies also confirmed structures of fractions and their thermal stability up to 70 °C. Differences in NMR spectra were explained by change of conformation and it was confirmed that this is a reversible process by reheating samples. Stability at 70 °C was confirmed by MS, since when the temperature of the ion transfer capillary in MS was set above this temperature decomposition occurred.     

Simulation of the separation of a helium–methane mixture in a flat membrane module

The problem of the membrane separation of a helium–methane mixture containing 0.1 wt % He, which imitates the composition of a helium-rich natural gas field, has been numerically analyzed. The helium and methane flux distribution along the length of a flat-sheet membrane module have been calculated. The distribution of the average mass concentration of helium in the channels is presented. The gas pumping expenditures have been estimated. The optimal working parameters of the gas mixture have been determined. Heating the mixture above 400 K does not enhance the helium–methane separation efficiency.     

Analysis of triacylglycerols of seeds and berries of sea buckthorn (Hippophaë rhamnoides) of different origins by mass spectrometry and tandem mass spectrometry

TAG of seeds, berries, and fruit pulp/peel of different subspecies of sea buckthorn (Hippophaë rhamnoides) were analyzed by MS and tandem mass spectrometry (MS/MS). The seeds contained mainly TAG with acyl carbon number (ACN) of 52 with 2–6 double bonds (DB) (20–30%), and TAG of ACN 54 with 3–9 DB (70–80%). In the pulp/peel fraction, the major TAG were species with ACN:DB of 48∶1 to 48∶3 (19–49%), 50∶1 to 50∶4 (31–41%), and 52∶1 to 52∶6 (9–19%). The molecular weight species of whole berries largely resembled those of fruit pulp/peel with additional species of ACN 54 from the seeds (5–24%). Subspecies (spp.) sinensis differed from ssp. mongolica and rhamnoides by having a higher proportion of TAG of ACN 52 (27% vs. 21% and 22%, P<0.05) and a lower proportion of ACN 54 (71% vs. 79% and 78%, P<0.01) in seed TAG. Seed TAG of ssp. mongolica contained a higher proportion of more unsaturated species compared with those of the two other subspecies. Berry TAG of ssp. mongolica had the highest proportion of molecular species of ACN 48 due to the higher proportion of palmitic and palmitoleic acids and the lower seed content of the berries. Overall, palmitic acid favored the sn-1 and sn-3 positions. The order of preference of unsaturated FA for the sn-2 position depended at least partially on the FA combination of TAG. Seed TAG of ssp. mongolica contained a higher proportion of α-linolenic acid in the sn-2 position than those of ssp. sinensis. In berry TAG, ssp. mongolica had the highest proportions of palmitoleic and linoleic acids in the sn-2 position, and the lowest proportion of oleic/cis-vaccenic acid in the sn-2 position, among the three subspecies.     

Novel solution for acceleration motion of a vertically falling non-spherical particle by VIM–Padé approximant

In this paper, the acceleration motion of a vertically falling non-spherical particle in incompressible Newtonian media was investigated. The velocity and acceleration were carried out using analytical solution techniques i.e., the variational iteration method (VIM) and a Padé approximant. The results were also compared with VIM and the established fourth order Runge–Kutta method in order to verify the accuracy of the proposed method. It was shown that this method can lead into more accurate results compared with VIM.     

Numerical simulation and experimental study of gas cyclone–liquid jet separator for fine particle separation

To address the shortcomings of existing particulate matter trapping technology, especially the low separation efficiency of fine particles, herein, a novel gas cyclone–liquid jet separator was developed to research fine particle trapping. First, numerical simulation methods were used to investigate the flow field characteristics and dust removal efficiency of the separator under different working conditions,and to determined suitable experimental conditions for subsequent dust removal experiment...     

Synthesis of polycyclic polyfunctionalized carbocycles by a cobalt(I)-initiated tandem diels–alder reaction sequence

The cobalt(I)-catalyzed neutral Diels–Alder reaction of acyclic 1,3-dienes with conjugated enynes can be used to generate secondary dihydroaromatic 1,4,8-trienes containing a 1,3-diene substructure, in good yields under mild reaction conditions. These 1,3-dienes can be converted, with reactive dienophiles in a tandem normal Diels–Alder reaction, into polycyclic compounds. In a similar tandem Diels–Alder sequence, the cobalt-catalyzed neutral homo Diels–Alder reaction of 2,5-norbornadiene can be used to generate polycyclic cycloaddition adducts. A sequential triple Diels–Alder reaction sequence can be realized when norbornadiene is reacted with the excess of the conjugated enynes under cobalt(I) catalysis. In a homo Diels–Alder, neutral Diels–Alder, normal Diels–Alder reaction sequence, the intermediately formed adducts are reacted with activated dienophiles to yield polycyclic compounds in a short sequence. The structures of several products were established by X-ray analysis. This showed that predominantly endo-products are formed in the tandem reaction sequences, while the exo-product becomes predominant in the triple Diels–Alder reaction sequence.     

Modeling of gas–liquid separation inside a slightly inclined annular duct

Electrical submersible pumping (ESP) is an artificial lift system used in the petroleum industry. ESP skid is an equipment in which the pump is housed inside a pipe forming a slightly inclined annular duct through which two-phase gas–liquid flows from inlet to pump intake. Part of the gas is pulled by the pump and part is separated and flows to the equipment top. This article analyses and models the observed separation process. Experiments showed good qualitative but poor quantitative agreement with literature models. Starting from a two-dimensional drift-flux model, radial and axial slips are modeled through phases' momentum transfer, showing the importance of drag, virtual mass and Basset's forces, leading to a semi-analytical model. As there is no model for such forces for the case of annular duct in the literature, experimental data is used for closure. The proposed model produced satisfactory and physically coherent results.     

Experimental study of a vane-type pipe separator for oil–water separation

An experimental study of a new vane-type pipe separator (VTPS) was conducted for the possible application in the well-bore for oil–water separation and reinjection. Results by using particle image velocimetry (PIV) reveal a better flow field distribution for oil–water separation, which is formed in VTPS than that in hydrocyclone. The effects of split ratio, the oil content, guide vanes’ installation and number of guide vanes on oil–water separation performance have been investigated experimentally. Compared to a traditional single hydrocyclone, VTPS shows a good separation performance as the water content at the inlet of VTPS reaches 79.9%, the oil content at the water-rich outlet is about 400 ppm while the split is near 0.70. These results are helpful to provide a possibly new design for downhole oil–water separation.     

Dynamic modelling of a bubble column for particle formation via a gas–liquid reaction

This paper presents a dynamic model of a bubble column reactor with particle formation, accomplished by adopting a hybrid CFD-reaction engineering approach. CFD is employed for estimating the hydrodynamics and is based on the two-phase Eulerian–Eulerian viewpoint. The reaction engineering model links the penetration theory to a population balance that includes particle formation and growth with the aim of predicting the average particle size. The model is then applied to the precipitation of CaCO₃ via CO₂ absorption into Ca(OH)₂aq in a draft tube bubble column and draws insight into the phenomena underlying the crystal size evolution.     

Discrete particle simulation of solids motion in a gas–solid fluidized bed

The solids motion in a gas–solid fluidized bed was investigated via discrete particle simulation. The motion of individual particles in a uniform particle system and a binary particle system was monitored by the solution of the Newton's second law of motion. The force acting on each particle consists of the contact force between particles and the force exerted by the surrounding fluid. The contact force is modeled by using the analogy of spring, dash-pot and friction slider. The flow field of gas was predicted by the Navier–Stokes equation. The solids distribution is non-uniform in the bed, which is very diluted near the center but high near the wall. It was also found that there is a single solids circulation cell in the fluidized bed with ascending at the center and descending near the wall. This finding agrees with the experimental results obtained by Moslemian. The effects of the operating conditions, such as superficial gas velocity, particle size, and column size on the solids movement, were investigated. In the fluidized bed containing uniform particles better solids mixing was found in the larger bed containing smaller size particles and operated at higher superficial gas velocity. In the system containing binary particles, it was shown that under suitable conditions the particles in a fluidized bed could be made mixable or non-mixable depending on the ratios of particle sizes and densities. Better mixing of binary particles was found in the system containing particles with less different densities and closer sizes. These results were found to follow the mixing and segregation criteria obtained experimentally by Tanaka et al.     

The efficiency of diffusional particle collection onto wire grids in the mobility equivalent size range of 1.2–8 nm

The diffusional deposition efficiency of monomobile, singly charged nanoaerosols onto electrically grounded metal wire mesh was measured on the basis of electrometer current data. The overall experimental uncertainty was of the order of 1% of measured penetration and 1% of measured particle mobility. The aerosol was either WO_x produced by evaporation/condensation and classified with a special high flow DMA into mobility classes between 1.2 and 8 nm—or electrosprayed THAB ions with a mobility equivalent diameter of 1.44 or 1.76 nm for the monomer and dimer, respectively.The experimental data were compared first to a model by Cheng and Yeh for diffusion deposition onto wire screens. Very good agreement was found down to approximately 3–4 nm, however, with a progressive deviation toward lower than predicted penetration values (predicted by pure diffusion theory (over ?25% at 1.2 nm)). The WO_x data agree very well with penetration data obtained for THAB monomer and dimer. For the larger size range above 4 nm, our data are also in excellent agreement with recent data by Thomas et al. It can be concluded that, no thermal rebound effect exists for charged particles in the electrical mobility diameter size range down to 1.2 nm. Lower than predicted penetrations measured below about 3 nm are most likely due to a small contribution by the image charge effect coupled with diffusion. Comparisons between the electrical and diffusional mobility of THAB ions show that the monomer is split into at least two different electrical mobility peaks, however, with the same diffusion coefficient, thus indicating the possible existence of structural isomers for the THAB monomer.     

Preparation of macroporous cordierite monoliths via the sol–gel process accompanied by phase separation

Monolithic cordierite with a cocontinuous macroporous structure has been successfully prepared by the sol–gel process accompanied by phase separation in the presence of poly(acrylamide) (PAAm). Propylene oxide (PO) acts as an acid scavenger to mediate the gelation of MgO–Al₂O₃–SiO₂ ternary system, while PAAm works as a phase-separation inducer as well as a network former. The dried gel and that heat-treated at 800 °C are amorphous, and the sapphirine begins to precipitate at 900 °C, then transforming to orthorhombic β-cordierite at 1100 °C. After heat-treated at and above 1200 °C, the resultant β-cordierite further transforms to stable hexagonal α-cordierite. Heat-treatment changes the macroporous structure of cordierite monoliths such as macropore size and its distribution. The macroporous cordierite monolith after heat-treated at 1200 °C is found to possess a total porosity of 54%, interconnected macropores and dense solid skeletons.     

Remarkable improvement of gas–liquid mass transfer by modifying the structure of conventional T-junction microchannel

Enhancing the mass transfer performance just by modifying the channel structure without external energy input is one of the most important topics for microchemical technology development. This work reports the high-performance gas–liquid mass transfer in a novel step T-junction microchannel. The liquid-side mass transfer coefficient in the step T-junction has been significantly improved by one order of magnitude when compared with the conventional T-junction, which is higher up to 60 × 10⁻⁴ m/s. To our knowledge, it might be the highest value obtained in the microchannel without external energy input. The parameters of bubble generation frequency and gas–liquid interface movement velocity in different microdevices are explored to reveal the mechanism behind the ultra-high mass transfer coefficient in the step T-junction. Finally, two models considering the gas absorption are developed for the bubble generation frequency and volume, and two models are proposed for the gas–liquid mass transfer coefficient.     

Comment on “The effects of molecular weight and thermal decomposition on the sensitivity of a thermal desorption aerosol mass spectrometer”

Copyright © American Association for Aerosol Research     

Intensification of liquid–liquid two-phase mass transfer in a capillary microreactor system

A convenient strategy to intensify the liquid–liquid mass transfer performance in a capillary microreactor system was developed by narrowing the inlet channel of T-micromixer or adding baffles into the capillary. Various geometrical parameters such as the inlet mode and diameter of the modified T-micromixer, the number of baffles and interval distance between baffles in the modified capillary were investigated to elaborate the mass transfer intensification mechanism. The liquid–liquid two-phase flow patterns in new capillary microreactors were captured by a high-speed camera. Moreover, pressure drops and specific energy dissipation of these modified microreactor systems were studied and a new parameter indicating the ratio of the mass transfer coefficient to the energy dissipation was proposed. This work highlights the modified capillary microreactor systems with embedding baffle units for achieving high mass transfer rates with its advantages over other types of reactors or microreactors considering specific energy dissipation and effective energy utilization efficiency. © 2018 American Institute of Chemical Engineers AIChE J, 65: 334–346, 2019