Micronization of salicylic acid and taxol (paclitaxel) by rapid expansion of supercritical fluids (RESS)

The particle sizes of the pharmaceutical substances are important for their bioavailability. The bioavailability can be improved by reducing the particle size of the drug. In this study, salicylic acid and taxol were micronized by the rapid expansion of supercritical fluids (RESS). Supercritical CO₂ and CO₂ + ethanol mixture were used as solvent. Experiments were carried out to investigate the effect of extraction temperature (318–333 K) and pressure (15–25 MPa), pre-expansion temperature (353–413 K), expansion chamber temperature (273–293 K), spray distance (6–13 cm), co-solvent concentration (ethanol, 1, 2, 3, v/v, %) and nozzle configuration (capillary and orifice nozzle) on the size and morphology of the precipitated salicylic acid particles. For taxol, the effects of extraction pressure (25, 30, 35 MPa) and co-solvent concentration (ethanol, 2, 5, 7, v/v, %) were investigated. The characterization of the particles was determined by scanning electron microscopy (SEM), optical microscopy, and LC–MS analysis.The particle size of the original salicylic acid particles was L/D: 171/29–34/14 μm/μm. Depending upon the different experimental conditions, smaller particles (L/D: 15.73/4.06 μm/μm) were obtained. The particle size of taxol like white crystal powders was reduced from 0.6–17 μm to 0.3–1.7 μm The results showed that the size of the precipitated salicylic acid and taxol particles were smaller than that of original particles and RESS parameters affect the particle size.     

Computational fluid dynamics simulations of submicrometer and micrometer particle deposition in the nasal passages of a Sprague-Dawley rat

Computational fluid dynamics (CFD) simulations were conducted in a model of the complete nasal passages of an adult male Sprague-Dawley rat to predict regional deposition patterns of inhaled particles in the size range of 1 nm to 10 μm. Steady-state inspiratory airflow rates of 185, 369, and 738 ml/min (equal to 50%, 100%, and 200% of the estimated minute volume during resting breathing) were simulated using Fluent?. The Lagrangian particle tracking method was used to calculate trajectories of individual particles that were passively released from the nostrils. Computational predictions of total nasal deposition compared well with experimental data from the literature when deposition fractions were plotted against the Stokes and Peclet numbers for micro- and nanoparticles, respectively. Regional deposition was assessed by computing deposition efficiency curves for major nasal epithelial cell types. For micrometer particles, maximum olfactory deposition was 27% and occurred at the lowest flow rate with a particle diameter of 7 μm. Maximum deposition on mucus-coated non-olfactory epithelium was 27% for 3.25 μm particles at the highest flow rate. For submicrometer particles, olfactory deposition reached a maximum of 20% with a particle size of 5 nm at the highest flow rate, whereas deposition on mucus-coated non-olfactory epithelium reached a peak of approximately 60% for 1–4 nm particles at all flow rates. These simulations show that regional particle deposition patterns are highly dependent on particle size and flow rate, indicating the importance of accurate quantification of deposition in the rat for extrapolation of results to humans.     

Production of bioethanol from corn meal hydrolyzates

The two-step enzymatic hydrolysis of corn meal by commercially available α-amylase and glucoamylase and further ethanol fermentation of the obtained hydrolyzates by Saccharomyces cerevisiae yeast was studied. The conditions of starch hydrolysis such as substrate and enzyme concentration and the time required for enzymatic action were optimized taking into account both the effects of hydrolysis and ethanol fermentation. The corn meal hydrolyzates obtained were good substrates for ethanol fermentation by S. cerevisiae. The yield of ethanol of more than 80% (w/w) of the theoretical was achieved with a satisfactory volumetric productivity P (g/l h). No shortage of fermentable sugars was observed during simultaneous hydrolysis and fermentation. In this process, the savings in energy by carrying out the saccharification step at lower temperature (32 °C) could be realized, as well as a reduction of the process time for 4 h.     

Filtration of fly ash using fluidized bed at 300–500 °C

The filtration of the coal-burning fly ash using fluidized beds with silica sand of 770 μm under temperatures of 36, 300, 400, and 500 °C was studied. The variations of the outlet concentration and particle size distribution (PSD) with time were measured to evaluate the dynamic characteristics of the process. Experimental results showed that the overall collection efficiency decayed with the operation time, revealed the effect of the elutriation of fly ash on particle filtration. The collection efficiency rose when the temperature increased from 36 °C to 500 °C. The strong attrition at high temperature released more small particles than that at room temperature, increased the concentration of the particles less than 10 μm (PM₁₀) at high temperature. The removal efficiency of the particles in a size of 4–7 μm, not the submicron particles, is the lowest because they are most easily elutriated from fluidized beds.     

Supercritical anti-solvent micronization of marigold-derived lutein dissolved in dichloromethane and ethanol

This work aims to study supercritical anti-solvent (SAS) micronization of lutein derived from marigold flowers. Lutein solution in dichloromethane (DCM) or ethanol was atomized into the stream of supercritical carbon dioxide (SC-CO₂) through a concentric nozzle in a pressurized vessel. The effects of pressure and SC-CO₂ flow rate on morphology, mean particle size (MPS) and particle size distribution (PSD) were investigated. The reduction in lutein MPS from 202.3 μm of unprocessed lutein to 1.58 μm and 902 nm could be achieved by SAS micronization using DCM and ethanol, respectively. In both solvent systems, no significant effects of pressure and SC-CO₂ flow rate on particle morphology were observed. However, pressure was found to have a significant effect on MPS and PSDs of lutein particles.     

Diamond-like carbon sintered compacts formed by spark plasma sintering

A spark plasma sintering (SPS) method was utilized for the novel production of diamond-like carbon (DLC) compacts. Two amorphous carbon powders with different particle sizes (45 μm and 24 nm diameter) were employed as starting materials for the sintering experiments. The carbon powders were sintered using a SPS system at various sintering temperatures and holding times. The structural properties of the sintered compacts were evaluated using X-ray diffraction (XRD) analysis and high-resolution transmission electron microscopy (HRTEM). Disk-shaped compacts were obtained by sintering the powder with a particle diameter of 45 μm, although the compacts were very brittle and easily broken. However, sintering of the 24 nm diameter powder particles at temperatures of 1473 to 1573 K with a holding time of 300 s led to the successful production of sintered compacts without breakage. Reflection peaks related to graphite structure were observed in XRD patterns of the compacts sintered from the 24 nm diameter particles. HRTEM analysis revealed that the compacts sintered at 1473 K with a holding time of 300 s had an amorphous structure and consisted of 34% sp³ carbon bonding. Evaluation of the structural properties indicated that sintered compacts with DLC structure could be created by the SPS method with 24 nm diameter amorphous carbon particles.     

Micronization of ketoprofen by the rapid expansion of supercritical solution process

The particle size of the pharmaceutical substances is important for their bioavailability (the percentage of the drug absorbed compared to its initial dosage). The absorption rate can be increased by reducing particle size of the drug particles. This study was conducted to investigate the effects of the extraction pressure (140–220 bar), extraction temperature (308–338 K), nozzle length (2–15 mm), effective nozzle diameter (450–1700 μm), and collection distance (1–10 cm) on the size and morphology of the precipitated ketoprofen particles. The characterization (size and morphology) of the particles was investigated using scanning electron microscopy (SEM). The average particle size of the original material was 115.42 μm, while the average particle size of the micronized particles is between 0.35 and 7.03 μm near to quisi-spherical, needle and irregular shape depending upon the experimental conditions.     

Ultrasonochemical coating and characterization of TiO2-coated zirconia fine particles

Zirconia fine particles were prepared by ultrasonic spray pyrolysis (USP) and employed as a substrate for titanium/titania coating by ultrasonochemistry. The effects of several process factors on the characteristics of the prepared particles were investigated and the particles were then characterized by various techniques. This substrate was coated with various titanium concentrations (0.025–0.1 M) for two ultrasonication time periods (30 min, 2 h) by sonochemistry, and finally calcined at 1100 °C. Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), particle size analysis (PSA), Fourier transformation infrared spectroscopy (FT-IR) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) comprised the techniques used to characterize them. The particles were prepared in a monodispersed spherical form with no interior cavity; their average size was shown to be 0.62 μm before calcination and 2.57 μm after calcination. The titania surface coating acted to partially stabilize the particles to a tetragonal phase. Based on the analytical results, the optimum conditions for preparing the particles were shown to be 7.5 wt% of titania as an initial solution concentration and 0.5 h of coating time.     

Synthesis of titanium oxide particles in supercritical CO2: Effect of operational variables in the characteristics of the final product

A new chemical precursor is proposed for the synthesis of TiO₂ anatase nanoparticles in supercritical CO₂: the organometallic diisopropoxititanium bis(acetylacetonate) (DIPBAT). DIPBAT thermohydrolysis in supercritical carbon dioxide (SC-CO₂) has been studied in the range 10.0–20.0 MPa and 200–300 °C, and compared with that of titanium tetraisopropoxide (TTIP). The proposed reaction mechanism is a thermohydrolysis, where the hydrolysis of acetylacetonate groups is the limiting step of the reaction rate. The addition of water directly to the reaction favours the growth of formed particles, whereas ethanol offers better results as hydrolysing reactant, leading to smaller particles. Experiments have been performed first in a batch process and secondly in a semi-continuous one, varying the residence time in the reactor from 30 s to 2 min. The effect of operational variables in the final product and their influence in the different steps of the process have been studied. Results have shown that product crystallinity is related with temperature, and temperatures higher than 250 °C are necessary to obtain well-crystallized TiO₂ anatase. In the same sense, area Brunauer–Emmett–Teller (BET) is connected with crystallinity, and amorphous product, Ti(OH)₄, shows the highest surface area. Particle size and particle size distribution (PSD) are controlled by instantaneously supersaturation degree, and precursor concentration together with pressure are the main responsible of particle size control. Operational conditions influence solubility of species, mass transfer, chemical reaction and nucleation and particle growth and they mark the final characteristics of the product and its application. In such a way, good crystallized TiO₂ anatase particles of about 200 nm in diameter have been obtained working at 300 °C, 20.0 MPa and residence time of 2 min, with a reaction medium composed by CO₂/ethanol (80/20, v/v). Such particles present good optical properties and specific surface area BET of around 150 m²/g. At lower working temperatures the obtained particles present worse crystallinity; however, their specific surface area increases to 350 m²/g and they are suitable as support of metal clusters in heterogeneous catalysis.     

Extraction of bioactive components from Centella asiatica using subcritical water

Bioactive components, asiatic acid and asiaticoside, were extracted from Centella asiatica using subcritical water as an extraction solvent. Extraction yields of asiatic acid and asiaticoside were measured using high-performance liquid chromatography (HPLC) at temperatures from 100 to 250 °C and pressures from 10 to 40 MPa. As temperature or pressure increased, the extraction yield of asiatic acid and asiaticoside increased. At the optimal extraction conditions of 40 MPa and 250 °C, the extraction yield of asiatic acid was 7.8 mg/g and the extraction yield of asiaticoside was 10.0 mg/g. Extracted asiatic acid and asiaticoside could be collected from water as particles with a simple filtering process. Dynamic light scattering (DLS) was used to characterize particle size. Particles containing asiatic acid were larger (1.21 μm) than particles containing asiaticoside (0.76 μm). The extraction yields of asiatic acid and asiaticoside using subcritical water at 40 MPa and 250 °C were higher than extraction yields using conventional liquid solvent extraction with methanol or ethanol at room temperature while the subcritical water extraction yields were lower than extraction yields with methanol or ethanol at its boiling point temperature.     

Micronization and characterization of squid lecithin/polyethylene glycol composite using particles from gas saturated solutions (PGSS) process

Lecithin was isolated from squid viscera residues after supercritical carbon dioxide (SC-CO₂) extraction at 25 MPa and 45 °C. The particle formation of squid lecithin with biodegradable polymer, polyethylene glycol (PEG) was performed by PGSS using SC-CO₂ in a thermostatted stirred vessel. By applying different temperatures (40 and 50 °C) and pressures (20–30 MPa), conditions were optimized. Two nozzles of different diameters (250 and 300 μm) were used for PGSS and the reaction time was 1 h. The average diameter of the particles obtained by PGSS at different conditions was about 0.74–1.62 μm. The lowest average size of lecithin particle with PEG was found by the highest SC-CO₂ density conditions with the stirring speed of 400 rpm and nozzle size of 250 μm. The inclusion of lecithin in PEG was quantified by HPLC. Acid value and peroxide value was measured after micronization of lecithin.     

Rheology and sedimentation velocity of alkaline suspensions of hematite particles at elevated temperature

This study aims to characterize the sedimentation velocity and the rheology of suspensions of hematite particles suspended in strongly alkaline media at 100 and 110 °C, as done for an alternative electrochemical process in development for iron production by direct electrode reduction of hematite. Considering the medium used in the process, i.e. 12% (v/v) suspension of hematite particles in 50% sodium hydroxide aqueous, the sedimentation velocity of hematite particle at 110 °C is 0.010 mm/s, which is very slow because the average size of the solid particles is around 10 μm and the significant collisions and interactions occuring between the particles in the concentrated suspension. Two geometries were used to characterize the rheological behavior of the apparent viscosity of the suspension of 12% (v/v) (i.e. 33 wt%) at 100 °C: a conventional Couette geometry and a helical ribbon mixer. The suspension was found shear thinning in the range of shear rate studied. The rheological behavior of the suspension can be described by a power-law model. The apparent viscosity of the hematite suspension estimated at a shear rate between 0.5 and 10 s⁻¹ is between 100 and 20 mPa s for the two geometries. The apparent viscosity calculated from the terminal velocity of 10 μm particles is of the same order of magnitude of the results obtained with the two rheometer configurations. The effect of the particle concentration on the sedimentation velocity and viscosity of the hematite suspensions was also studied.     

Preparation of porous silver particles using ammonium formate and its formation mechanism

Here we report the preparation of two different types of macroporous silver particles (round and coral) by simple chemical reduction using ammonium formate. We also discuss the chemical mechanism of silver particle and macroporous silver particle formation. The synthesized round type and coral-type porous silver particles were 20–50 μm and 30–150 μm in size and their pores were 100–200 nm and 1–2 μm across, respectively. They were characterized by particle distribution analysis, X-ray diffraction, and scanning electron microscopy.     

Preparation of poly-lactic acid nano/microparticles using supercritical anti-solvent with enhanced mass transfer

Supercritical anti-solvent precipitation with enhanced mass transfer (SAS-EM) was applied for the production of micro and sub-microparticles of poly-lactic acid (PLA). SAS-EM technique uses an ultrasonic vibrating surface to enhance mass transfer rate between supercritical CO₂ and solvent. Without applying ultrasonic power, which is same as SAS process, PLA particles with average diameters ranging between 1 μm and 3 μm were obtained. Using SAS-EM with the power supply of 200 W, spherical PLA particles smaller than 1 μm were obtained. The particle size was able to be controlled in the range of 0.4 μm–1.0 μm, by adjusting the power supply of ultrasonic field, the system pressure and temperature.     

Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities

A new expiratory droplet investigation system (EDIS) was used to conduct the most comprehensive program of study to date, of the dilution corrected droplet size distributions produced during different respiratory activities.Distinct physiological processes were responsible for specific size distribution modes. The majority of particles for all activities were produced in one or more modes, with diameters below 0.8 μm at average concentrations up to 0.75 cm^?3. These particles occurred at varying concentrations, during all respiratory activities, including normal breathing. A second mode at 1.8 μm was produced during all activities, but at lower concentrations of up to 0.14 cm^?3.Speech produced additional particles in modes near 3.5 and 5 μm. These two modes became most pronounced during sustained vocalization, producing average concentrations of 0.04 and 0.16 cm^?3, respectively, suggesting that the aerosolization of secretions lubricating the vocal chords is a major source of droplets in terms of number.For the entire size range examined of 0.3–20 μm, average particle number concentrations produced during exhalation ranged from 0.1 cm^?3 for breathing to 1.1 cm^?3 for sustained vocalization.Non-equilibrium droplet evaporation was not detectable for particles between 0.5 and 20 μm, implying that evaporation to the equilibrium droplet size occurred within 0.8 s.     

Purification and isolation of β-glucans from barley: Downstream process intensification

The purpose of this work was to study the purification and isolation (downstream process) of the β-glucan extracted from barley in an ultrasound assisted extraction (UAE) process. The co-extracted starch (average concentration 5.2 ± 0.1 g/L) was hydrolyzed by means of α-amylase. The optimization of the hydrolysis length, temperature and enzyme dose led to removal efficiencies higher than 90% (9 min hydrolysis length and enzyme doses of 100 μL/g at 55 °C), compared to the traditional hydrolysis processes (1 h at 95 °C). In a second step, a significant intensification of the process has been achieved by dosing the enzyme during the UAE step (7 min at 55 °C), resulting in a starch removal of 90%.Dextrins and other oligosaccharides were formed as a consequence of the enzymatic hydrolysis. In order to separate these low molecular weight molecules from the β-glucan (239 kDa), an ultrafiltration process (polysulfone membrane, nominal MWCO 100 kDa) was tried in a tangential flow cell: diafiltration successfully eliminated more than 45% of the oligosaccharides present in the liquid, providing a significant increase in the concentration of β-glucan and with the possibility of improving the percentage of elimination.The combination of these three technologies (UAE, enzymatic hydrolysis and diafiltration) allows getting high purity β-glucan concentrates (greater than 70%).     

Sinter forging of rapidly quenched eutectic Al2O3–ZrO2(Y2O3)-glass powders

Spray dried agglomerates of Al₂O₃–ZrO₂ (1% Y₂O₃) with 4 wt.% borosilicate glass were arc plasma sprayed and rapidly quenched into water. Because of the rapid quenching the particles <25 μm were mostly amorphous. After annealing 1 h at 1200 °C the scale of the microstructure of the particles was on the order 30 nm. Hot forging of this powder yielded dense specimens with the width of the ZrO₂ phase still less than 100 nm. Since the particle size ranged from 5 to 25 μm and the scale of the particle microstructure was <100 nm, densification was controlled by creep of the particles rather than by the typical hot pressing mechanism of diffusion along the neck between particles to fill the pores. Thus, the scale of the microstructure controls densification rather than the particle size. These powders offer an alternate source for manufacturing nanostructured parts and should be more suitable for hot pressing or forging than nanoparticulate powders.     

Production of concentrated natural beta-carotene from buriti (Mauritia vinifera) oil by enzymatic hydrolysis

The present work aimed at the extraction and concentration of β-carotene from crude and refined buriti oils using enzymatic hydrolysis as a process strategy. The performance of two commercial lipolytic preparations (Lipozyme TL IM and CALB L), as well as lipases from Yarrowia lipolytica, was evaluated. The parameters considered in the hydrolysis process were: temperature, enzyme loading and ratio buriti oil/water. Based on a previously conducted statistical design, the experimental conditions were set in order to maximize the free fatty acids (FFA) content in the oil, and simultaneously, minimize the loss of carotenoids. Lipozyme TL IM showed to be the most appropriate enzyme source for the hydrolysis of both oils. The optimized conditions determined for the crude buriti oil processing were 31 °C, 0.0047 g lipase mL^?1 (0.47 g lipase per 100 mL reactional mixture) and 2.33 (ratio oil/water), while for the refined oil, 45 °C, 0.0066 g lipase mL^?1 and 1.80 were the best conditions. At the optimized conditions, the maxima FFA release were 73.0% and 74.8% and the total carotenoids contents were 1578 and 793 mg kg^?1, respectively for the crude and the refined buriti oils, after 4 h of reaction agitated at 300 rpm. Following hydrolysis, oils were deacidified by winterization or phases partition with ethanol.     

Growth mechanism and field emission behavior of carbon nanotubes grown over 300 nm thick aluminium interlayer

The influence of thick aluminium (Al) ~ 300 nm interlayer on the growth and field emission (FE) properties of carbon nanotubes (CNTs) deposited on silicon coated with a 2 nm iron (Fe) catalyst was studied. The CNTs were grown over silicon substrate with and without Al-interlayer via CVD. It was observed that the presence of such high thickness of the interlayer on the substrate resulted in higher growth rate, narrower diameters and longer height of CNTs compared to CNTs grown on silicon (Si) substrate coated only with Fe. Al-interlayer hinders the diffusion of Fe into silicon, hence promotes the growth rate. Literature reports that a thick layer of Al causes Fe to diffuse into it, negatively affecting the growth. However, in our experiments, no evidence of depletion of Fe from the substrate was observed. Unique patterns of grown CNTs could be attributed to anisotropic Al-melting over the silicon substrate resulting in Al/Fe rich and deficient regions. The drastic improvement of current density from 0.41 mA/cm² to 20 mA/cm² at a field of 3.5 V/μm was found with Al-interlayer CNT grown samples. These mechanisms of improvements in field emission characteristics have been discussed in detail.     

Ballistic properties and burning behaviour of an ammonium perchlorate/guanidine nitrate/sodium nitrate airbag solid propellant

An experimental investigation on the determination of ballistic properties and burning behavior of a composite solid propellant for airbag application was conducted. The experimental results were obtained using a high-pressure optical strand burner. Steady-state burning rates were determined for a pressure range of 20.8–41.5 MPa and initial propellant temperatures of −30 to +80 °C. For the pressure and temperature ranges tested, the temperature sensitivity was on the order of 1 × 10⁻³ K⁻¹. The pressure exponent was found to be a function of the initial propellant temperature and was 0.75 at 25 °C. The activation energy and the pre-exponential factor of the Arrhenius equation are 2.735 kcal/mol and 15.06 cm/s, respectively. The pressure deflagration limit for this propellant was found to be in the range of 8.37–8.72 MPa. During combustion, small condensed-phase spherical particles were ejected from the burning surface. The size of the particles decreased with either increasing the pressure or the initial propellant temperature. For pressures below 41.4 MPa, average particle size was on the order of 900 μm, and at 84.4 MPa, the bead size was much smaller, on the order of 300 μm. A chemical analysis on these particles using both the ESEM and the X-ray diffraction method indicated that the material of the beads was mostly sodium chloride with a small amount of silicon-containing compounds.