Phase Transitions of Single Salt Particles Studied Using a Transmission Electron Microscope with an Environmental Cell

The hygroscopic behavior of 0.1 to 4 μ m NaBr, CsCl, NaCl, (NH₄)₂SO₄, and KBr particles were monitored using a transmission electron microscope (TEM) equipped with an environmental cell into which gases can be introduced. This instrument, commonly called an environmental transmission electron microscope or ETEM, allowed us to observe phase transitions and behavior of small particles at relative humidities between 0 and 100%. We used deliquescence relative humidity and efflorescence relative humidity values from the literature for each salt to calibrate the relative humidity in the environmental cell. Using our methodology, we reliably and accurately measured the phase transitions and hygroscopic behavior of inorganic particles with the ETEM.     

Nanosize Effect on the Deliquescence and the Efflorescence of Sodium Chloride Particles

The deliquescence and efflorescence relative humidity values of 6- to 60-nm NaCl particles were measured using a tandem nano-Differential Mobility Analyzer. The deliquescence relative humidity (DRH) increased when the dry particle mobility diameter decreased below approximately 40 nm. The efflorescence relative humidity (ERH) similarly increased. For example, the DRH and ERH of 6-nm particles were 87% and 53%, respectively, compared to 75% and 45% for particles larger than 40 nm. Power law fits describing the nanosize effect are: DRH(d _m) = 213 d _m ^?1.6+ 76 and ERH(d _m) = 213 d _m ^?1.65+ 44, which are calibrated for 6 < d _m < 60 nm with less than 1% RH uncertainty and where d _m is the dry particle mobility diameter (nm). Two independent methods were used to generate the aerosol particles, namely by vaporizing and condensing granular sodium chloride and by electrospraying a high-purity sodium chloride aqueous solution, to investigate possible effects of impurities on the results. The DRH and ERH values were the same within experimental uncertainty for the particles generated by the two methods. The physical explanation for the nanosize effect of increasing DRH and ERH for decreasing dry particle mobility diameter is that the free energy balance of NaCl increasingly favors smaller particles (i.e., those without water) because the surface areas and hence surface free energies per particle are less for small, anhydrous particles than for bloated, aqueous particles. [Supplementary materials are available for this article. Go to the publisher's online edition of Aerosol Science and Technology for the following free supplemental resources: Graphs and data of the size distribution measurements of the deliquescence- and the efflorescence-mode experiments of the 6-, 8-, 15-, 20-, 30-, and 60-nm dry mobility diameter particles.]     

Effect of Surface Tension from MD Simulations on Size-Dependent Deliquescence of NaCl Nanoparticles

The deliquescence of sodium chloride is size dependent for particles smaller than 100 nm, with some discrepancies between measured and predicted deliquescence relative humidity as a function of size. Two sources of uncertainty in current models are the solid–liquid/solid–vapor surface tensions and the curvature dependence of surface tension. Molecular Dynamics simulations are used to calculate surface tensions and their corresponding upper bounds, which compare well with measured values of liquid–vapor (LV) interfaces and significantly reduce uncertainty compared to experimental estimates of solid–liquid (SL) and solid–vapor (SV) interfaces. Surface tensions calculated for nanoparticles in the 2–10 nm size range are related to the corresponding flat interface values using the first-order Tolman length ( δ ). At 1 atm and 300 K, the Tolman length determined from the test-area method is of the order of 0.1 nm with a precision between 5% and 10%. The δ ^LV (water–air) is 0.15 nm, δ ^LV (soln–air) is 0.10 nm, δ ^SL (NaCl–soln:) is 0.13 nm, and δ ^SV (NaCl–air) is 0.14 nm, with positive values corresponding to a decrease in surface tension for smaller particles. The size-dependent deliquescence relative humidity is calculated using a thermodynamic model of water uptake with these new surface tension estimates and with Tolman length corrections. The reduced uncertainties in surface tension significantly improve agreement with measured deliquescence relative humidity of sodium chloride nanoparticles with 5–150 nm diameters. The size-dependent corrections to surface tension produce a minor improvement in the comparison of predicted and measured deliquescence relative humidity of particles smaller than 3 nm.     

The 1-by-3 Tandem Differential Mobility Analyzer for Measurement of the Irreversibility of the Hygroscopic Growth Factor

A new instrument, namely the 1 × 3 tandem differential mobility analyzer (1 × 3-TDMA), has been developed. Its primary measurement is the irreversibility of the hygroscopic growth factor of aerosol particles. The instrument uses the hysteresis of phase transitions to infer the solid or aqueous state of the particles. A first DMA passes particles of a selected electric mobility at relative humidity RH₀. Exiting this DMA, the particles are split into three separate flows. The first flow is exposed to RH ₀  → (RH ₀ +  δ ) → RH ₀ in a deliquescence test before passing through a second DMA that is set to the same electric mobility as the first DMA. The second flow passes directly to a third DMA without change in RH, thereby serving as a reference arm. This DMA is also set to the same electric mobility as the first DMA. The transmission ratio of the 1 × 3-TDMA is defined as the particle concentration passing the deliquescence test divided by that passing through the reference arm. The transmission ratio is unity in the absence of deliquescence and zero when a phase transition occurs, at least for ideal instrument performance in application to a test aerosol of fully deliquesceable particles. For the third flow passing out of the first DMA, an efflorescence test is run by using the RH profile of RH ₀  → (RH ₀ ? δ ) → RH ₀ before passing through a fourth DMA. A full data set for the 1 × 3-TDMA is obtained by scanning RH₀, typically from 20 to 85%. In the present paper, the 1 × 3-TDMA instrument is described, and laboratory data are presented for the phase transitions of externally mixed aerosols of aqueous and solid sodium chloride particles, aqueous and solid ammonium sulfate particles, and their mixtures, as well as a mixture of aqueous and solid sea salt particles. The observed transmission ratio is compared to a model analysis. The intent behind the development of this instrument is to deploy it for field measurements and use observations of the irreversibility of the growth factors of atmospheric particles as markers of their physical state.     

Rebounding hygroscopic inorganic aerosol particles: Liquids,gels, and hydrates

Particle rebound was studied for ten atmospherically relevant inorganics. Experiments were conducted with submicron particles in aerosol form to a relative humidity (RH) of <5% followed by progressive exposure to RH up to 95% for 2 s. At low RH, particles of MgCl₂, NaCl, NH₄Cl, KCl, (NH₄)₂SO₄, and Na₂SO₄ crystallized. As RH increased, these particles completed the transition from rebounding to adhering close to their deliquescence RH (DRH). The onset of decreased rebound, however, was below the DRH. Rebound curves for particles of MgCl₂, NH₄NO₃, MgSO₄, and NaNO₃ had different features than explained by water adsorption and deliquescence. Particles of MgCl₂ had rebound curves characterized by two domains, corresponding to its two hydrates. At low RH, particles of MgSO₄ and NaNO₃ did not crystallize but rebound occurred, suggesting a glassy or high-viscosity though noncrystalline state. Gel formation for MgSO₄ can increase viscosity, affecting rebound behavior. Particles of NH₄NO₃ adhered even to <5% RH, suggesting a low-viscosity state even to low RH. Particles of NH₄HSO₄ were investigated as a special case by exposure to 5 ppm ammonia at 10% and 90% RH. At low RH, these particles still had sufficient molecular diffusivity to maintain active heterogeneous chemistry, although with some kinetic limitations. The different behaviors between nitrates and sulfates suggest different roles of heterogeneous chemistry in regions affected by NO_x compared to SO₂ emissions. The results of this study could have implications for the use of different wet and dry seed particles in chamber experiments.

Copyright © 2017 American Association for Aerosol Research     

Hygroscopic Behavior of Aerosol Particles Emitted from Biomass Fired Grate Boilers

This study focuses on the hygroscopic properties of submicrometer aerosol particles emitted from two small-scale district heating combustion plants (1 and 1.5 MW) burning two types of biomass fuels (moist forest residue and pellets). The hygroscopic particle diameter growth factor (Gf) was measured when taken from a dehydrated to a humidified state for particle diameters between 30–350 nm (dry size) using a Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA). Particles of a certain dry size all showed similar diameter growth and the Gf at RH = 90% for 110/100 nm particles was 1.68 in the 1 MW boiler, and 1.5 in the 1.5 MW boiler. These growth factors are considerably higher in comparison to other combustion aerosol particles such as diesel exhaust, and are the result of the efficient combustion and the high concentration of alkali species in the fuel. The observed water uptake could be explained using the Zdanovski-Stokes-Robinson (ZSR) mixing rule and a chemical composition of potassium salts only, taken from ion chromatography analysis of filter and impactor samples (KCl, K₂SO₄, and K₂CO₃). Agglomerated particles collapsed and became more spherical when initially exposed to a moderately high relative humidity. When diluted with hot particle-free air, the fractal-like structures remained intact until humidified in the H-TDMA. A method to estimate the fractal dimension of the agglomerated combustion aerosol and to convert the measured mobility diameter hygroscopic growth to the more useful property volume diameter growth is presented. The fractal dimension was estimated to be ～ 2.5.     

Comparative Study of Selective Separation of Magnesium from Brine and Seawater

Abstract

A highly selective, sensitive, and inexpensive procedure for the separation of magnesium from brine and seawaters is proposed. The method is based on the separation of the harmful major constituent (calcium) of saline water. This is achieved by floating both calcium and magnesium as their oleates at the pH of saline water (7.5–8.5) to avoid the effect of NaCl on the precipitation of Ca as CaSO₄. The float is dissolved in HNO₃/methanol, precipitated as CaSO₄, and the mother liquor is refloated as pure magnesium oleate. This purity is confirmed by infrared measurements.     

FTIR Characterization of Polymorphic Transformation of Ammonium Nitrate

Solid ammonium nitrate (NH ₄ NO ₃ ) exists in five stable polymorphic forms (designated as phases I, II, III, IV, and V) below its melting point at around 170°C. Phase IV is stable in a temperature range of ?17°C ～ 32°C and is the only phase that has been considered by the atmospheric research community until recently. In this study, we examine the IV ? III phase transition of NH ₄ NO ₃ and how relative humidity (RH) affects the transition path and the transition temperatures using in-situ microscopic Fourier Transform InfraRed spectroscopy. Two kinds of NH ₄ NO ₃ samples, powder produced from grinding commercially produced chemicals and single particles obtained by efflorescence of droplets on PTFE filters, were studied. The powder samples exhibit the IV?III phase transition and the transition temperature depends on the RH while the single particle samples exhibit only the IV?II transition at about 52°C (forward) and 48°C (reverse), bypassing phase III, with transition temperatures independent of the RH. However, grinding of the particles produced through efflorescence results in the IV?III transitions. Differences in crystal structure and moisture content may explain the distinct phase transition behaviors of the two types of samples. These results suggest that solid and pure NH ₄ NO ₃ aerosol particles are stable in phase IV under ambient conditions.     

New hyperdispersant agent for polypropylene/CaSO4 composites

A new hyperdispersant agent with Si? OH as an anchoring group and poly(butyl acrylate) as a solvatable chain was synthesized, and its effect on the properties of polypropylene (PP)/CaSO₄ composites was investigated. Fourier transform infrared spectroscopy results showed that the hyperdispersant agent reacted on the CaSO₄ surface and the modified CaSO₄ particles. The tensile strength and impact strength of the PP/CaSO₄ composites increased about 14 and 34%, respectively, versus that of PP/CaSO₄ (filled with the same unmodified fraction). According to surface analysis by scanning electron microscopy, the CaSO₄ particles were buried well in the PP matrix when CaSO₄ was coated with the hyperdispersant agent. CaSO₄ significantly increased the crystallization temperature and crystallization rate of PP by differential scanning calorimetry, but the addition of hyperdispersant‐agent‐modified CaSO₄ did not lead to the formation of crystalline PP through X‐ray diffraction. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Phase Transition and Hygroscopic Properties of Internally Mixed Ammonium Sulfate and Adipic Acid (AS-AA) Particles by Optical Microscopic Imaging and Raman Spectroscopy

We studied the phase transition and hygroscopicity of particles of a mixture of two atmospherically relevant species, ammonium sulfate and adipic acid. We conducted extensive investigations on ammonium sulfate–adipic acid (AS-AA) particles deposited on a hydrophobic substrate with the weight percentage (wt%) of AA ranging from 3 to 90%. Crystallization and deliquescence were observed through an optical microscope, which enabled multiple particles to be examined simultaneously. At an initial relative humidity (RH) of 94%, which was the highest RH setting, AA solids were formed from the deposited solution droplets, leading to the presence of mixed-phase particles prior to the complete crystallization recorded between 31% and 42% RH of all mixtures. The complete crystallization RH values were close to that of pure AS, indicating that the AA solids did not promote effective heterogeneous nucleation of AS. When the RH was increased, partial deliquescence in all mixtures was observed at 80% RH, which was attributed to the dissolution of the AS fractions. Full deliquescence was only observed in 3 wt% AA particles at 91% RH. We also used Micro-Raman Spectroscopy to determine the hygroscopicity of mixtures with up to 50 wt% AA. The hygroscopic behavior of the AS fraction in the mixed particles was found to resemble that of pure AS particles. However, there was observable water uptake in the solid particles at about 70% RH in mixtures with up to 70 wt% AA. This early water uptake was more pronounced in mixtures with lower weight percentages of AA (AA less than 30 wt%).     

高氯酸钠试剂过饱和电导率的测定研究

通过对直径约200～500μm的NaClO4微液滴在风化和潮解过程的研究,观测到NaClO4微液滴在相对湿度为20%时发生结晶析出和在相对湿度为45%时结晶发生潮解,表明NaClO4微液滴在相对湿度20%～45%间处于过饱和状态。设计了包含微电极、观测池和湿度调节装置的微液滴电导率测量系统,并将其应用于NaClO4微液滴风化和潮解过程(相对湿度变化范围为79%～20%)的测量,取得了过饱和状态下NaClO4微液滴的电导值。本工作对溶液临界状态过饱和电导率的测量工作进行了有益的探索性研究。     

Flux Synthesis of Na2Ca2Nb4O13: The Influence of Particle Shapes,Surface Features,and Surface Areas on Photocatalytic Hydrogen Production

The layered perovskite (n = 4) Ruddlesden‐Popper phase Na₂Ca₂Nb₄O₁₃ was prepared within molten NaCl and Na₂SO₄ fluxes, yielding either rod‐shaped or platelet‐shaped particles, respectively. The flux‐to‐reactant molar ratios of 5:1 or 20:1 were found to significantly influence particle sizes and surface areas, while still maintaining the overall particle shapes. Measured surface areas of flux‐prepared Na₂Ca₂Nb₄O₁₃ particles ranged from ～0.36 to 4.6 m²/g, with the highest surface areas obtained using a 5:1 (NaCl‐to‐Na₂Ca₂Nb₄O₁₃) molar ratio. All samples exhibited a bandgap size of ～3.3 eV, as determined by UV–Vis diffuse reflectance measurements. Photocatalytic rates for hydrogen production under ultraviolet light for platinized Na₂Ca₂Nb₄O₁₃ particles in an aqueous methanol solution ranged from ～230 to 1355 μmol H₂ g ^{? 1} h ^{? 1} when using the photochemical deposition (PCD) method of platinization, and ～113–1099 μmol H₂ g ^{? 1} h ^{? 1} when using the incipient wetness impregnation (IWI) method of platinization. The higher photocatalytic rates were obtained for the rod‐shaped particles with the highest surface areas, with an apparent quantum yield (AQY) measured at ～6.5% at 350 nm. For the platelet‐shaped particles, the higher photocatalytic rates were observed for the sample with the lowest surface area but the largest concentration of stepped edges and grooves observed at the particle surfaces. The latter origin of the photocatalytic activity is confirmed by the significant enhancement of the photocatalytic rates by the PCD method that allows for the preferential deposition of the surface Pt cocatalyst islands at the stepped edges and grooves, while the photocatalytic enhancement is much smaller when using the more general IWI platinization method.     

An Analysis of Four Models Predicting the Partitioning of Semivolatile Inorganic Aerosol Components

A comparison is conducted between 4 atmospheric equilibrium mod els: GFEMN, ISORROPIA, SCAPE2, and SEQUILIB. While ISORROPIA, SCAPE2, and SEQUILIB simplify the problem at hand in an effort to reduce computational rigor, GFEMN does not employ many of the simplifying assumptions used in previous models, thus allowing it to accurately predict multistage aerosol behavior and deliquescence depression. We examine model performance for representative atmospheric environments over an extended composition, temperature, and RH domain and against observations in Southern California. The predictions of GFEMN, ISORROPIA, SCAPE2, and SEQUILIB are in general agreement, but the latter 3 do not adequately reproduce multistage deliquescence behavior for multi component systems. The most notable differences in model predictions occur for H⁺ and aerosol water concentrations; discrepancies in predictions of aerosol nitrate and total dry inorganic PM concentrations are not as significant. The models predict different deliquescence relative humidities for multicomponent systems, but for ammonia poor environments, these discrepancies do not introduce differences in total dry inorganic PM predictions. Against measurements taken during the Southern California Air Quality Study (SCAQS), all models qualita tively reproduce but generally underpredict aerosol nitrate concentrations. Finally, based on its overall agreement with GFEMN and its computational efficiency, ISORROPIA appears to be the model of choice for use in large-scale aerosol transport models. In places where crustal material comprises a significant portion of total PM, SCAPE2 is an alternative.     

Reactivity of a CaSO<Subscript>4</Subscript>-oxygen carrier in chemical-looping combustion of methane in a fixed bed reactor

Chemical-looping combustion (CLC) is a promising technology for the combustion of gas or solid fuel with efficient use of energy and inherent separation of CO₂. A reactivity study of CaSO₄ oxygen carrier in CLC of methane was conducted in a laboratory scale fixed bed reactor. The oxygen carrier particles were exposed in six cycles of alternating reduction methane and oxidation air. A majority of CH₄ reacted with CaSO₄ to form CO₂ and H₂O. The oxidation was incomplete, possibly due to the CaSO₄ product layer. The reactivity of CaSO₄ oxygen carrier increased for the initial cycles but slightly decreased after four cycles. The product gas yields of CO₂, CH₄, and CO with cycles were analyzed. Carbon deposition during the reduction period was confirmed with the combustible gas (CO+H₂) in the product gas and slight CO₂ formed during the early stage of oxidation. The mechanism of carbon deposition and effect was also discussed. SO₂ release behavior during reduction and oxidation was investigated, and the possible formation mechanism and mitigation method was discussed. The oxygen carrier conversion after the reduction decreased gradually in the cyclic test while it could not restore its oxygen capacity after the oxidation. The mass-based reaction rates during the reduction and oxidation also demonstrated the variation of reactivity of CaSO₄ oxygen carrier. XRD analysis illustrated the phase change of CaSO₄ oxygen carrier. CaS was the main reduction product, while a slight amount of CaO also formed in the cyclic test. ESEM analysis demonstrated the surface change of particles during the cyclic test. The reacted particles tested in the fixed bed reactor were not uniform in porosity. EDS analysis demonstrated the transfer of oxygen from CaSO₄ to fuel gas while leaving CaS as the dominant reduced product. The results show that CaSO₄ oxygen carrier may be an interesting candidate for oxygen carrier in CLC. This work was presented at the 7 ^th China-Korea Workshop on Clean Energy Technology held at Taiyuan, China, June 26–28, 2008.     

Growth inhibition in calcium sulfate crystal using a copolymer in oil fields: theoretical study and experimental evaluations

A poly(itaconic acid-co-sodium vinylsulphonate) (PIASVS) was theoretically studied and experimentally evaluated as an inhibitory agent against the growth of calcium sulfate (CaSO₄) crystals, in both non-saline and saline solutions. Density functional theory revealed that the CaSO₄ crystal precipitation could be precluded through the effective pairing of Ca²⁺ and SO₄^2? ions by carboxylic group polymer heads and that, moreover, the Na⁺ cations of the sulphonate polymer heads could be easily replaced by Ca²⁺. With PIASVS concentration of 50 ppm, lower than what is required in oil recovery processes, the polymer inhibited 33% in CaSO₄ crystals growth in non-saline solution, but the salt increased the inhibitory performance of PIASVS up to 54%. Thermogravimetric analysis, scanning electron microscopy and X-ray diffractometry techniques showed that PIASVS changed the CaSO₄ crystal morphology from a bassanite phase in non-saline solution to a bassanite/gypsum mix. The crystal morphology observations along with the conductivity measurements confirmed the pairing of ions from dissolved CaSO₄ by NaCl and PIASVS. Dynamic light scattering revealed that, the PIASVS cluster size increased in non-saline solution but decreased in saline solutions, suggesting that NaCl increases the PIASVS solubility in aqueous solution. The performance of PIASVS as anti-scaling agent was found to be suitable for the conditions found in the Mexican oil reservoirs.     

Determination of Particle Effective Density in Urban Environments with a Differential Mobility Analyzer and Aerosol Particle Mass Analyzer

Effective densities of atmospheric aerosols in various locations of the Los Angeles Basin were determined by a DMA-APM technique. Effective density was calculated by comparing voltage distributions of sampled atmospheric aerosols with PSL particles of known density. The five sites chosen for field experiments were: (1) Interstate-710 Freeway, impacted by heavy-duty diesel vehicles; (2) State Route CA-110, open only to gasoline vehicles; (3) Riverside, a receptor site known for secondary particle formation; (4) University of Southern California, a typical urban and industrial environment; and (5) Coast for marine aerosol. The size range selected for this study was from 50 nm to 414 nm. While 50 nm particles exhibited a single effective density multiple effective densities were measured for each of the other particle sizes as significant fractions of these particles are transported from background sources. Regardless of location, 322–414 nm particle effective densities were considerably lower than unity. The lowest effective densities (～ 0.1 g cm ^{? 3} ) were reported for I-710, confirming that diesel combustion aerosols are rich in chain agglomerates with large void spaces. Riverside exhibited high effective densities (～ 1.2–1.5 g cm ^{? 3} ) for 50–202 nm particles, which we hypothesize is due to transformations that occur during advection from Los Angeles. Measurements of diurnal variation of effective density at Riverside support this hypothesis. Overall, our results suggest that effective density declines as the particle mobility diameter increases irrespective of location. Fractal dimensions calculated from average effective densities were lowest for I-710 ( D _f = 2.41) and CA-110 (D _f = 2.54) aerosols, presumably due to the influence of vehicular combustion emission on these sites. By contrast, average fractal dimensions at USC, Riverside and Coast were found to be 2.79, 2.83, and 2.92, respectively. High fractal dimensions at these sites may be the effects of aging, moisture absorption and/or organic vapor condensation on the particles, which fills void space and makes particles more spherical.     

Comparison of Fouling Mechanism by CaSO4 and CaHPO4 on Nanofiltration Membranes

Abstract

We investigated the mechanism of CaSO₄ and CaHPO₄ scaling on nanofiltration membranes by observing the flux decline behavior. It was found that CaSO₄ fouling contributed a greater resistance than CaHPO₄ fouling under the same operating conditions. CaSO₄ fouling was characterized by reversible cake growth caused by both bulk and surface crystallization at a lower operating pressure, and by surface crystallization at a higher operating pressure. CaHPO₄ fouling was characterized by both irreversible pore/surface adsorption and reversible cake growth through surface crystallization regardless of operating conditions. These findings indicate that both fouling solutes and operating parameters should be considered when evaluating inorganic fouling of a nanofilter.     

Linking micro‐scale predictions of capillary forces to macro‐scale fluidization experiments in humid environments

The effects of increasing relative humidity (RH) on fluidization/defluidization are investigated experimentally and understood via particle‐level predictions for the resulting capillary force. Experimentally, defluidization is found to be more sensitive to small changes in RH than fluidization. This sensitivity is captured by a new defluidization velocity U_df, which characterizes the curvature of the defluidization plot (pressure drop vs. velocity) observed between the fully‐fluidized (constant pressure drop) and packed‐bed (linear pressure drop dependence on velocity) states; this curvature is indicative of a partially‐fluidized state arising from humidity induced cohesion. Plots of U_df vs. RH reveal two key behaviors, namely U_df gradually increases with a relatively constant slope, followed by an abrupt increase at RH ～55%. Furthermore, the bed transitions from Group A to Group C behavior between RH of approximately 60–65%. From a physical standpoint, these macro‐scale trends are explained via a theory for capillary forces that, for the first time, incorporates measured values of particle surface roughness. Specifically, a model for the cohesive energy of rough surfaces in humid environments shows the same qualitative behavior as U_df vs. RH for RH <55%, unlike predictions of the cohesive force. Furthermore, the abrupt transition at RH ～60–65% is explained via the previously observed onset of liquid‐like water adsorption, rather than crystal/ice‐like adsorption, onto glass surfaces. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3585–3597, 2016     

Development of balloon-borne impactor payload for profiling free tropospheric aerosol

Size-segregated aerosol vertical profiles in the troposphere are critically important for source attribution, transformation processes, atmospheric stability, and radiative forcing. For the first time, the development of a 6-stage impactor for real-time balloon-borne measurements of size-segregated (cutoff diameter [D_ae]: 0.15–5?µm) aerosol mass concentrations in the free troposphere was tested during spring 2016 over Hyderabad, India, is presented. Total aerosol mass concentrations obtained with the 6-stage impactor (M_TI) and a co-located optical particle counter (M_TOPC) measurements at the surface under ambient conditions agreed to within 15%. The effect of aerosol particle growth on the M_TI data are assessed using an urban aerosol particle model by scaling mass concentration of water-soluble (hydrophilic) aerosol particles at ambient relative humidity (RH) to that at RH = 50%. An overall uncertainty of the measurement of the M_TI was estimated to be about 19%. The altitude variation of size-segregated mass concentrations of aerosol particles along with thermodynamic variables depicted convectively well-mixed layer extending up to about 4.5?km within which aerosol particles showed two distinct layers, one at ～2?km and another at about 4.5?km. The size-resolved air samples containing aerosol particles collected using the balloon-borne 6-stage impactor will be useful for their chemical characterization and also long-range transport studies.

Copyright © 2019 American Association for Aerosol Research     

Plugging problems observed in severe hydrocracking of vacuum residue

Carbons deposited on the filter after the reactor of hydrocracking (US-Sludge) and in the heat exchanger (DS-Sludge) in a commercial H-Oil process were analyzed through the elemental analysis, XRD, SEM, optical microscope, ¹³C-NMR and Raman spectroscopy to elucidate their formation mechanism. Heat treatment of sludge and oil products recovered from the commercial process was performed at 698 K of a reaction temperature. XRD showed the presence of Fe_1−xS, NaCl, and CaSO₄ as well as carbon (2Θ = 26.6°) in US-Sludge. The carbon showed medium and fine mosaic textures surrounding the isotropic grains. DS-Sludge showed mixed texture of domain and flow surrounding the fine mosaic grains. The sludge consisted of stacked carbon flakes with a number of pores on the surface. EDX showed dominant presence of NaCl and CaO particles in the mosaic region. Heat treatment of asphaltene in the product mixed with US-Sludge gave the same appearance to that of DS-Sludge. US- and DS-Sludge are concluded to be formed through the respective carbon formation in the reactor and to be separated on the filter and on the heat exchanger surface, respectively. The carbon particles produced in the reactor collect contaminant Fe_1−xS and CaSO₄ particles to form the agglomerate where the growth and coalescence of the anisotropic spheres are very restricted to form the fine mosaic texture as observed in the US-Sludge. In contrast, the carbonization of the major precipitated heavy aromatic component leads to the domain or flow anisotropic texture through rather free growth and coalescence of anisotropic spheres on the surface of the heat exchanger wall. Although some parts of precipitated component together with US-Sludge give mosaic texture through the restricted growth and coalescence of anisotropic sphere by the presence of reactive fine solids.