Particle formation of an edible fat (rapeseed 70) using the supercritical melt micronization (ScMM) process

The supercritical melt micronization (ScMM) process, also known as particles from gas saturated solutions (PGSS) was applied, in a continuous operated pilot plant, for the particle formation of the edible fat, rapeseed 70 (RP70). The effect of variables like the CO₂ concentration, the melt temperature and the atomization pressure were studied in order to investigate particle morphology, density and the particle size distribution. The experiments were performed at CO₂ concentrations between 0 and 50 wt%, atomization pressure between 70 and 180 bar and melt temperature between 60 and 100 °C. Particles obtained as a function of the CO₂ concentration, showed completely solid, spherical–hollow and aggregated particles with a decrease in particle mean size as the concentration of CO₂ was increased. The results obtained as a function of atomization pressure showed no significant influence on particle morphology and size distribution. Experiments carried out as a function of the melt temperature showed distorted, spherical–hollow and aggregated particles. Furthermore, a theory was developed to explain the mechanism for particle formation as a function of the CO₂ concentration and the melt temperature. The crystallinity of the final product of RP70, showed an alpha polymorph with a crystallinity of 84%.     

Anti-solvent effect in the production of lysozyme nanoparticles by supercritical fluid-assisted atomization processes

Particles of lysozyme in the range of 0.1–5 μm were generated by high pressure CO₂ or N₂ (at pressures between 8 MPa and 25 MPa) from aqueous ethanol solutions using an atomization process similar to the supercritical assisted atomization technology. Perfect nanosized spheres of lysozyme were produced using both supercritical fluids. However, while N₂ assisted atomization-produced spheres at all experimental conditions reported here, supercritical CO₂ assisted atomization produced particles of two distinct morphologies depending on the pre-mixing conditions. This work shows that CO₂ assisted atomization produces particles by two different mechanisms depending on the mixture pre-expansion phase equilibria conditions: anti-solvent crystallization and spray drying crystallization. Depending on the governing precipitation mechanism (anti-solvent or spray drying), fibers or spherical particles were obtained with CO₂. Lysozyme activity was severely affected by pure anti-solvent processing, while N₂ processed lysozyme conserved mostly its activity.     

Theophylline polymorphs by atomization of supercritical antisolvent induced suspensions

The Atomization of Supercritical Antisolvent Induced Suspensions (ASAIS) is a small volume supercritical antisolvent process characterized by the inline dissolution of the antisolvent before the liquid atomization for the solvent extraction step. The antisolvent (CO₂) is mixed with the solute-containing solution in a small volume mixer immediately before the nozzle orifice in conditions such that cause the precipitation of the solutes. The generated suspension is then spray-dried for solvent separation. Compared to other similar particle-producing techniques, this approach allows a more efficient control of the antisolvent process and reduces the volume of the high-pressure precipitator by several orders of magnitude. Theophylline (TPL) particles produced by ASAIS are the polymorph previously obtained elsewhere by conventional SAS. Yet, the normal (non-polymorph) crystal form is obtained under non-antisolvent conditions. The required phase equilibria of the system TPL/tetrahydrofuran/CO₂ between 308 K and 328 K were also obtained. The results presented here demonstrate that, under selected conditions, ASAIS is a continuous-regime alternative to conventional SAS for the production of unique products, such as crystal polymorphs.     

Controllable preparation and formation mechanism of BSA microparticles using supercritical assisted atomization with an enhanced mixer

Supercritical fluid assisted atomization introduced by a hydrodynamic cavitation mixer (SAA-HCM) was used to prepare bovine serum albumin (BSA) microparticles. Water was used as the sole solvent. A hydrodynamic cavitation mixer was applied to improve mass transfer and achieve a continuous near-thermodynamic-equilibrium solubilization of SC-CO₂ in the liquid solution. Under the different conditions, the prepared BSA microparticles had various morphologies, such as corrugated particles, smooth hollow spherical particles and cup particles, with particle diameters ranging from 0.3 to 5 μm. The microparticle formation process was elucidated with the shell formation and central bubble mechanism. Compared to native BSA, BSA microparticles did not show significant change in primary structure, according to the results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The secondary structure of BSA was characterized by Fourier transform infrared spectroscopy (FT-IR). No new peaks were observed after SAA-HCM processing. In addition, the crystalline structure of the BSA microparticles was demonstrated to be amorphous because of the sudden supersaturation in the precipitation process. The SAA-HCM process is expected to be a promising technique for producing microparticles suitable for pulmonary delivery of therapeutic macromolecules.     

Absorption of carbon dioxide in aqueous MDEA solution coupling dust suppression under atomization

ABSTRACT

Large amounts of CO₂ and dust particles coming from power plant flue need to be captured and removed before flue is discharged into the air. In present work, absorption of carbon dioxide in aqueous N-methylidiethanolamine (MDEA) solution coupling dust suppression has been studied in an atomization absorption column, with MDEA concentrations ranging from 0.1 to 0.5mol/L, and with atomization frequencies ranging from 50 to 80 HZ. The obtained experimental results show that absorption rate of CO₂ in aqueous MDEA solution can be enhanced when the absorption process couples a dust suppression one under the condition of atomization. The reason for it is attributed to the adsorption of droplets on the solid particles which restrains the amount of entrainment and makes more droplets contact with gas so as to increase effective mass transfer area, thus resulting in the increase of CO₂ absorption rate. The range of obtained enhancement factor is from 1.1 to 1.7. Mass transfer enhancement factor increases with the increase of MDEA concentration and atomization frequency at a certain range. Effective mass transfer areas and entrainment ratios suppressed have been calculated based on theoretic research. The results calculated agree with our experimental phenomena, and support the enhancement mass transfer mechanism proposed.     

Elaboration of PEG/PA66 blends in a twin-screw batch-type mini-extruder: Process study and modelling

This paper deals with the development of the morphology in polyethylene glycol (PEG) and polyamide 66 (PA66) immiscible blends exhibiting an extremely low viscosity ratio (η_PEG/η_PA66=3-4×10^-5). These materials were obtained by melt mixing, under different operating conditions, using a twin-screw batch-type DSM mini-extruder.Scanning electron microscopy, followed by quantitative image analysis was used to determine PEG particles size distribution (PSD) as a function of blends composition and screw rotation speed. Experiments carried out with two mixing time (5 and 10 min) showed no significant difference of PSD. So, to avoid thermal degradation of the products, the mixing time was set up at 5 min for all experiments. The influence of PEG concentration and screw rotation speed on PSD appeared to be similar to that obtained in a previous study for the same blends elaborated in a Haake internal mixer. The results clearly showed that the average particle diameters decreased as screw rotation speed increased and as PEG concentration decreased. However, this decrease is less important using the twin-screw batch-type mini-extruder with which the particle sizes are smaller. The particles sizes were then correlated to blend composition, shear rate and viscosity ratio owing to an extension of Serpe's model. The unknown parameters of the corresponding model were estimated on the basis of experimental data. This enabled then to predict with a good precision the influence of the process operating conditions on the morphology of the dispersed phase.     

Modeling of precipitation of ultra-fine particles by pressure reduction over CO2-expanded liquids

A mathematical model has been developed to describe the process of precipitation of ultrafine particles by pressure reduction over gas (CO₂)-expanded liquids. A rapid pressure reduction over a CO₂-expanded organic solution, from 30–70 to 1 bar at 303 K decreases the solution temperature by 30–80 K in a very short span of time (0.5–1.5 min), which generates a rapid, high, and uniform supersaturation of the dissolved solute in the solution and facilitates precipitation of ultrafine particles. The model developed in this work estimates the supersaturation attained, nucleation and growth rates obtained during the pressure reduction over CO₂-expanded organic solutions, and the particle size distribution of the precipitated particles. Cholesterol has been chosen as a model solute to be precipitated, and acetone has been chosen as a solvent. A new method has been developed for prediction of equilibrium solubility of solute which is affected by a decrease in CO₂ mole fraction as well as a simultaneous decrease in solution temperature during pressure reduction. This method combines the semi-empirical approach of using the partial molar volume fraction of solvent in a CO₂-solvent binary mixture and solid–liquid equilibrium data for a solute–solvent system. Size distributions of the precipitated particles have been calculated assuming primary nucleation (homogeneous as well as heterogeneous nucleation) and diffusion-limited growth kinetics. The predicted mean average particle sizes are then compared with the size of cholesterol particles precipitated by pressure reduction of a CO₂-expanded acetone solution of cholesterol. The particle sizes predicted assuming heterogeneous nucleation are found to be closer to the experimentally observed particle sizes, indicating that the heterogeneous nucleation could be the main mechanism of nucleation, which could occur at the gas–liquid interface of the CO₂ bubbling out of CO₂-expanded solution during pressure reduction.     

Instrument for ceramic particle dispersion II: Computational fluid dynamics analysis

A planetary-type mixer using a container equipped with stainless steel mesh has been developed. For various slurries (Al₂O₃ in water), each modeled as Newtonian fluid, the shear stress was calculated using computational fluid dynamics (CFD) under various mixing conditions and with different equipment properties. The meshed-geometry included more than 100,000 nodes with hexahedral cells in one zone, with quadrilateral cells in the remaining zones. The fluid viscosity, rotation rate, and mesh opening affected the maximum shear stress. The shear stress increased concomitantly with increasing fluid viscosity. The container rotation rate and the maximum shear stress share a proportional relation. For a fluid with 9.2 mPa s, the shear stress was 134 Pa or more for a 0.81 mm and larger mesh opening, as observed at the bottom of the container. Mesh having an opening smaller than 0.81 mm generated high shear stress on the mesh surface. The maximum shear stress increased with decreasing mesh opening size. The particle size distributions of the Al₂O₃ particles in the slurries after treatment by the mixer were estimated under conditions similar to those of the calculations. Results show peaks in the particle size distributions of the Al₂O₃ particles in the slurries before treatment at 0.2 and 2-70 μm because of the primary particle size and agglomerates. The amounts of the agglomerate decreased concomitantly with the decreased mesh opening size. When slurries pass through the small mesh openings, high shear stress is generated. That achieves the good dispersion of the sub-micron sized Al₂O₃ particles in the slurry.     

Production of microparticles from milk fat products using the Supercritical Melt Micronization (ScMM) process

The ScMM (Supercritical Melt Micronization) process was applied for the production of microparticles from anhydrous milk fat (AMF) and a diacylglycerol-based modified milk fat (D-AMF). Both fats were able to dissolve ca. 30 wt% CO₂ in the studied pressure and temperature ranges, being the CO₂ amount slightly higher for AMF. A melting point depression was observed in both systems in the presence of CO₂. Two powder morphologies were obtained (spherical hollow particles and a mass sponge-like broken particles) depending on the ScMM process conditions. The concentration of CO₂ in the fat melt was the main process variable affecting the particle morphology, followed by the temperature of the melt. The small broken particles originated from the breakage of spherical fat particles that solidified before all CO₂ could escape from the atomized droplets. While the hollow spheres had a tendency to agglomerate, the broken microparticles constituted a free-flowing powder as long as they were stored at low temperatures (up to −18 °C). Both types of particles have a potential for being incorporated in refrigerated or frozen food products as a structuring agent.     

An analysis of liquid CO2 drop formation with and without hydrate formation in static mixers

The formation process of CO₂ drops in various types of Kenics Static Mixers was analyzed from the perspective of energy dissipation in the mixer, focusing on the formation of drop surfaces. Experimental studies on CO₂ drop formation were conducted under varying temperatures, pressure, and flow rates, with and without hydrate formation. Analysis of the CO₂ drop size and distribution at several locations within the static mixer was conducted, as of pressure drop in the mixer, to determine dissipation energies. In all the experimental conditions, by considering the surface energy for hydrate formation, the energy required for the formation of CO₂ drops correlated well with total energy dissipation by mixer flow, which is represented by a pressure drop along the mixer. This process has important applications to the formation of liquid CO₂ for ocean disposal as a countermeasure to global warming. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

The effect of CO2 dissolved in a diesel fuel on the jet flame characteristics

This paper is concerned with an experimental study of the jet diffusion flame characteristics of fuel containing CO₂. Using diesel fuel containing dissolved CO₂ gas, experiments were performed under atmospheric conditions with a diesel hole-type nozzle of 0.19 mm orifice diameter at constant injection pressure. In this study, four different CO₂ mass fraction in diesel fuel such as 3.13%, 7.18%, 12.33% and 17.82% were used to study the effect of CO₂ concentration on the jet flame characteristics. Jet flame characteristics were measured by direct photography, meanwhile the image colorimetry is used to assess the qualitative features of jet flame temperature. Experimental results show that the CO₂ gas dilution effect and the atomization effect have a great influence on the flame structure and average temperature. When the injection pressure of diesel fuel increased from 4 MPa to 6 MPa, the low temperature flame length increased from 18.4 cm to 21.7 cm and the full temperature flame length decreased from 147.6 cm to 134.7 cm. With the increase of CO₂ gas dissolved in the diesel fuel, the jet flame full length decreased for the jet atomization being improved greatly meanwhile the low temperature flame length increased for the CO₂ gas dilution effect; with the increase of CO₂ gas dissolved in the diesel fuel, the average temperature of flame increases firstly and then falls. Experimental results validate that higher injection pressure will improve jet atomization and then increased the flame average temperature.     

Separation and capture of carbon dioxide from CO2/H2 syngas mixture using semi-clathrate hydrates

The relation between anthropogenic emissions of CO₂ and its increased levels in the atmosphere with global warming and climate change has been well established and accepted. Major portion of carbon dioxide released to the atmosphere, originates from combustion of fossil fuels. Integrated gasification combined cycle (IGCC) offers a promising fossil fuel technology considered as a clean coal-based process for power generation particularly if accompanied by precombustion capture. The latter includes separation of carbon dioxide from a synthesis gas mixture containing 40 mol% CO₂ and 60 mol% H₂.A novel approach for capturing CO₂ from the above gas mixture is to use gas hydrate formation. This process is based on selective partition of CO₂ between hydrate phase and gas phase and has already been studied with promising results. However high-pressure requirement for hydrate formation is a major problem.We have used semiclathrate formation from tetrabutylammonium bromide (TBAB) to experimentally investigate CO₂ capture from a mixture containing 40.2 mol% of CO₂ and 59.8 mol% of H₂. The results shows that in one stage of gas hydrate formation and dissociation, CO₂ can be enriched from 40 mol% to 86 mol% while the concentration of CO₂ in equilibrium gas phase is reduced to 18%. While separation efficiency of processes based on hydrates and semi-clathrates are comparable, the presence of TBAB improves the operating conditions significantly. Furthermore, CO₂ concentration could be increased to 96 mol% by separating CO₂ in two stages.     

Flow and mixing efficiency characterisation in a CO2-assisted single-screw extrusion process by residence time distribution using Raman spectroscopy

Hot-melt extrusion of a bio-sourced polyamide has been implemented in a single-screw extruder with supercritical carbon dioxide injection. CO₂ acts as a plasticiser in the extruder barrel and as a physical blowing agent at the die. To insure a better mixing and dissolution of the CO₂ into the polymer melt, addition of a static mixer between the screw tip and the die was tested. The effect of both the static mixing element and the CO₂ injection on the melt flow behaviour has been elucidated. A recent technique of in-line Raman spectroscopy was implemented to make a residence time distribution study, using titanium dioxide as a tracer. The use of a static mixer exerts a major modification on the flow behaviour: it improves mixing by enhancing dispersion. In addition, the structure of the manufactured products was studied: the static mixer led to more homogeneous porous structure. The broad range of CO₂ incorporation (up to 25%, w/w) into the melt led to the manufacture of foams with adjustable porosity from 15 to 70%.     

Effects of chlorine and sulphur on particle formation in wood combustion performed in a laboratory scale reactor

Fine particle formation in wood combustion was studied in a laboratory scale laminar flow reactor at various flue gas chlorine and sulphur concentrations. Aerosol samples were quenched at around 850 °C using a porous tube diluter. Fine particle number concentrations, mass concentrations, size distributions and chemical compositions were measured. In addition, flue gas composition, including SO₂ and HCl, was monitored. Experimental results were interpreted by thermodynamic equilibrium calculations.Addition of HCl clearly raised fine particle mass concentration (PM1.0) which was because of increased release of ash-forming material to fine particles. Especially the release of K, Na, Zn and Cd to fine particles increased. These species form chlorides which apparently increases their volatilization from the fuel. When a sufficient amount of SO₂ was supplied in a chlorine rich combustion (S/Cl molar ratio from 4.7 to 7.5), most of the HCl stayed in the gas phase, release of ash-forming elements decreased and also fine particle concentrations dropped significantly. The sulphation of alkali metals is suggested to play a key role in the observed decrease in the fine particle concentration. It seems that the formation of sulphates leads to alkali metal retention in the coarse particle fraction.     

Poly(ethylene terephthalate) nanoparticles prepared by CO2 laser supersonic atomization

Poly(ethylene terephthalate) (PET) particles were prepared by the irradiation of PET fibers with a carbon dioxide (CO₂) laser while atomizing them at supersonic velocities. A supersonic jet was generated by blowing air into a vacuum chamber through a fiber injection orifice. The fibers are melted by laser heating and atomized by the supersonic jet at the outlet of the orifice. The PET particles produced by CO₂ laser supersonic atomization conducted at a laser power of 34 W and at a chamber pressure of 10 kPa have an average particle size of 0.619 μm, high circularity, and a smooth surface that is not roughened by laser ablation. The novel CO₂ laser supersonic atomization technique can be used to easily prepare polymeric nanoparticles of various thermoplastic polymers using only CO₂ laser irradiation without the need for solvents and additives. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40909.     

pH-Controlled association of PEG-containing terpolymers of N-isopropylacrylamide and 1-vinylimidazole

Temperature- and pH-controlled association of terpolymers of N-isopropylacrylamide (NIPA) with 1-vinylimidazole (VI) and polyethylene glycol (PEG) has been investigated by light scattering and atomic force microscopy (AFM) in situ. The polymers contained 0-15 mol% VI and 0-2 mol% PEG. The phase transition temperatures (T_p) have been in the range of 32-45 °C and exhibited significant dependence on the pH of solution in the pH range between 5 and 8. The T_p of the polymers increased with increasing VI content and with decreasing pH, confirming major effect of VI ionization status on T_p. The presence of PEG grafts in the polymer structure had augmenting effect on the magnitude of pH-responsiveness and on the pH-independent colloidal stability of the polymer particles formed above T_p. Incorporation of VI into the polymer structure had similar, but pH-dependent effect on colloidal stabilization of the polymer particles. The size of the particles formed after the phase transition is driven by the association of the collapsed NIPA segments in the globule conformation and it decreased with decreasing pH. The phase transition temperature of the polymers could be adjusted to increase from temperatures below, to temperatures above body temperature upon decreasing pH from 7 to 6, suggesting that such polymers could provide a material platform for a variety of biomedical applications. AFM analysis in situ showed a fully reversible formation of particles in the solutions of the polymers above their T_p.     

Absorption of carbon dioxide into aqueous solutions of piperazine activated 2-amino-2-methyl-1-propanol

In this work, new experimental data on the rate of absorption of CO₂ into piperazine (PZ) activated aqueous solutions of 2-amino-2-methyl-1-propanol (AMP) are reported. The absorption experiments using a wetted wall contactor have been carried out over the temperature range of 298-313 K and CO₂ partial pressure range of 2-14 kPa. PZ is used as a rate activator with a concentration ranging from 2 to 8 wt%, keeping the total amine concentration in the solution at 30 wt%. The CO₂ absorption into the aqueous amine solutions is described by a combined mass transfer-reaction kinetics-equilibrium model, developed according to Higbie's penetration theory. Parametric sensitivity analysis is done to determine the effects of possible errors in the model parameters on the accuracy of the calculated CO₂ absorption rates from the model. The model predictions have been found to be in good agreement with the experimental results of rates of absorption of CO₂ into aqueous (PZ+AMP). The good agreement between the model predicted rates and enhancement factors and the experimental results indicates that the combined mass transfer-reaction kinetics-equilibrium model with the appropriate use of model parameters can effectively represent CO₂ mass transfer in PZ activated aqueous AMP solutions.     

Process performances and characteristics of powders produced using supercritical CO2 as solvent and antisolvent

A carbon dioxide (CO₂) soluble compound (cholesterol) was successfully precipitated either by rapid expansion of SCCO₂ solutions (RESS process, acronym for Rapid Expansion of Supercritical Solution), or from methylene chloride solutions by antisolvent precipitation (SAS-process, acronym for Supercritical Antisolvent process). The same fluid was thus used either as a solvent or as an antisolvent to precipitate cholesterol. Performances of RESS and SAS were compared through the analysis of the particle characteristics and production rates. Differences were related to supersaturation and time scale of nucleation/growth involved in both processes. Polydispersity, large size and elongated shape were characteristics of particles produced by SAS, especially when experiments were performed under conditions of total miscibility of CO₂ and organic solvent. Conditions where vapor-liquid equilibrium exists promoted a confinement of the growth that consequently reduced the final particle size. RESS, by comparison, produced smaller and monodispersed particles. Production of small particles is a key advantage for RESS, but lower production rates and yield might be disadvantages. The combination of the two processes offers the opportunity of tunable sizing of powder, switching from a large production of particles ranging from 10 to 100 μm, to a limited production of fine crystals below 10 μm.     

Batch production of micron size particles from poly(ethylene glycol) using supercritical CO2 as a processing solvent

The major advantage of using supercritical carbon dioxide (CO₂) as a solvent in polymer processing is an enhancement in the free volume of a polymer due to dissolved CO₂, which causes a considerable reduction in the viscosity. This allows spraying the polymer melt at low temperatures to produce micron size particles. We have used supercritical CO₂ as a solvent for the generation of particles from poly(ethylene glycol) (PEG) of different molecular weights. Since PEG is a hydrophilic compound, it is a most commonly used polymer for encapsulating a drug. PEG particles with different properties may allow keeping a good control over the release of the drug. It has been possible to produce particles with different size, size distribution, porosity and shape by varying various process parameters such as molecular weight, temperature, pressure and nozzle diameter. A flow and a solidification model have been applied in order to have a theoretical insight into the role of different parameters.     

Coenzyme Q10 nanoparticles prepared by a supercritical fluid-based method

A supercritical fluid-based method is proposed to produce coenzyme Q₁₀ (CoQ₁₀) nanoparticles. First, CoQ₁₀/polyethylene glycol 6000 composite particles are prepared by a modified PGSS (particles from gas-saturated solutions) process with controlling the flow rate of the gas-saturated solution. Then, CoQ₁₀ nanoparticles are obtained by dissolving the composite particles into water. The effect of experimental variables of the modified PGSS process, including pressure, temperature, flow rate of the gas-saturated solution, and mass fraction of CoQ₁₀, on the CoQ₁₀ particle size and particle size distribution was investigated. Results show that CoQ₁₀ slurry product with a median diameter of 190 nm and yield of 89.8% can be prepared at an optimum condition (operating pressure of 25 MPa, operating temperature of 80 °C, gas-saturated solution flow rate of 1.02 mL/min, CoQ₁₀ mass fraction of 40% and nozzle diameter of 100 μm) via the supercritical fluid-based method.