Ernesto Reverchon

Supercritical fluid extraction and fractionation of essential oils and related products

Supercritical CO2 extraction of essential oils is one of the most widely discussed applications in the supercritical fluid literature. Nevertheless, a comprehensive overview of the analytical, processing and modeling aspects has never been attempted. This is partly due to the difficulties involved in isolating essential oils from the other products which supercritical CO2 can dissolve. Moreover, only a limited number of studies provide quantitative data on the parameters governing this process. In this review, solubility data on pure compounds belonging to essential oils are analyzed. Processes proposed to isolate and fractionate essential oils by supercritical CO2 and the corresponding modelling aspects are discussed critically.

Supercritical antisolvent precipitation of micro- and nano-particles

Abstract Traditional micronization processes can be improved by taking advantage of the unique characteristics of the supercritical antisolvents that include very large diffusivities when compared with those of liquids and the one step complete elimination of the solvent from the precipitates. The application of supercritical antisolvent processing has until now been explored in a variety of different fields including: explosives, polymers, pharmaceutical compounds, coloring matter, superconductors, catalysts and inorganic compounds. In this review the experimental techniques currently available, results and present perspectives of application of this technique are critically examined and discussed.

Modeling and simulation of the supercritical CO2 extraction of vegetable oils

Abstract The model of broken and intact cells has been applied to the experimental results on oil seed supercritical extraction obtained by various authors and on several species of seeds. The results analyzed are related to various extraction apparatus ranging from very low laboratory scale to pilot plants. Moreover, a wide range of operating conditions has been covered, CO2 flow rates ranging between 1.5 and 750 g/min, extraction pressures from 240 to 550 bar, temperatures between 25 and 50°C and particle diameters from 0.25 to 4 mm have been considered. Besides, the experimental results existing in the literature, systematic scanning electron microscope (SEM) analysis have been performed on seed particles belonging to the different seed species studied, thus obtaining data about the microscopic cells that bear the oil that are characteristic of the different seed structures. Operating in this manner the differential mass balances that characterize this kind of models have been supported by microscopic information on seed structure and the number of adjustable parameters in the model has been reduced to only one, the internal mass transfer coefficient (ki). A fair good fitting of all the available experimental results has been obtained using best fit ki values ranging between 2.4×10−7 and 9.2×10−8 m/s and producing a coherent description of the extraction process. Some simulation tests have also been performed that evidenced the role of particle size and of internal mass transfer and of their interaction on the overall performance of the extraction process.

Production of antibiotic micro- and nano-particles by supercritical antisolvent precipitation

Abstract Supercritical antisolvent precipitation (SAS) has been used to produce micronized particles of some antibiotics. Griseofulvin, ampicillin, amoxicillin, and tetracycline have been tested in N-methylpyrrolidone, dimethylsulfoxide, ethyl alcohol and methylene chloride. Some coupled antibiotic–liquid solvent have been successfully processed. Amorphous particles have been obtained at all successful SAS conditions while crystals have been sometimes observed when the micronization process failed. For example, spherical nanoparticles have been observed for tetracycline in N-methylpyrrolidone. These particles tend to coalesce in small aggregate-forming groups. The effect of the SAS process parameters on morphology, particle size and particle size distribution have been studied for the system tetracycline/N-methylpyrrolidone. The coalescence of tetracycline particles decreases with the increase in operating pressure; whereas the diameter of the aggregates increases with tetracycline concentration in the liquid solvent. Operating at 180 bar, 40°C and at different concentrations, aggregates with mean diameters between 0.6 and 0.8 μm have been observed.

Almond oil extraction by supercritical CO2: experiments and modelling

Oil from crushed almond seeds was extracted with supercritical CO2 at 350 bar and 40°C. Almond particles of three different mean sizes were tested. Extraction of the smaller particles was performed at two different solvent flow rates. Oil yields were obtained with asymptotic values at large extraction times that were close to the values obtained by Soxhlet extraction. An extraction model based on the physical evidence of broken and intact oil cells has been developed. It accounts for a former equilibrium regime and a latter finite mass transfer regime. All model parameters except the internal mass transfer coefficient and the oil concentration at solvent saturation have been determined with independent experiments. The model solution was calculated with a finite difference numerical technique. A good agreement was obtained between model curves and the experimental data for an internal mass transfer coefficient of 7.5×10-9m/s. Solute concentration profiles within the extractor were evaluated with our model.

Supercritical antisolvent micronization of some biopolymers

Abstract We processed various biopolymers by semi-continuous supercritical antisolvent precipitation (SAS) to evaluate the possibility of producing nano and micro-particles of controlled size and distribution. First, some liquid expansion curves were experimentally produced to study the general behavior of the ternary systems antisolvent-solvent-biopolymer. A condition that guarantees a successful SAS micronization is that solute does not modify the expansion curves of the solvent-antisolvent binary system. SAS experiments were performed by varying the process parameters; we mainly studied the influence of pressure, temperature and liquid solution concentrations. SEM images of the processed material were used to study morphologies, mean particle size and particle size distribution. We successfully processed by SAS dextran, poly- l -lactide (PLLA) and poly-(hydroxypropylmethacrylamide) (HPMA), using dimethylsulfoxide (DMSO) and dichloromethane (DCM) as liquid solvents.

Salicylic acid solubilization in supercritical CO2 and its micronization by RESS

Abstract Salicylic acid solubilization in supercritical CO 2 and its micronization by rapid expansion of the supercritical solution (RESS) have been studied. Solubilities at 40 and 60 °C in the range from 100 to 350 bar have been measured using the flow method. Experimental results have been compared with those obtained by other authors and have been successfully correlated using the Peng-Robinson equation-of-state. The influence of some process parameters on salicylic acid crystals morphology has been evaluated by analyzing the crystals precipitated in the expansion chamber by optical microscopy. Preexpansion temperature and expansion chamber temperature both have a great influence on the morphology of salicylic acid crystals. Analysis of particle-size distributions showed that the preexpansion temperature influence particle dimensions, while the temperature of the expansion chamber seemed mainly to modify the particle size distribution.

Process parameters and morphology in amoxicillin micro and submicro particles generation by supercritical antisolvent precipitation

Continuous supercritical antisolvent precipitation (SAS) has been used to produce micro and sub-micro particles of amoxicillin. Liquid solutions of amoxicillin in N-methyl pyrrolidone (NMP) or dimethylsulfoxide (DMSO) have been continuously sprayed using supercritical CO2 as the antisolvent. When DMSO has been used, the precipitation of amoxicillin has been only partly successful and two different particle morphologies have been observed during the same experiment. When amoxicillin has been solubilized in NMP, spherical and non-agglomerated microparticles have been obtained by SAS with mean diameters ranging between 0.25 and 1.2 μm obtained at various precipitation temperatures and solute concentrations in the liquid solution. The effect of the ratio of CO2/liquid solution flow rates has also been studied.

Rifampicin microparticles production by supercritical antisolvent precipitation

Semi-continuous supercritical antisolvent (SAS) precipitation has been used to produce Rifampicin micro- and nanoparticles with controlled particle size (PS) and particle size distribution (PSD). SAS experiments were performed using different liquid solvents. The best micronization results have been obtained using dimethyl sulfoxide (DMSO); using this solvent and operating at 40 degrees C, we obtained nanoparticles with mean diameters ranging from 0.4 to 1 microm at a pressure of 120 bar or more, and microparticles with mean diameters ranging from 2.5 to 5 microm at pressures between 90 and 110 bar. The morphology of Rifampicin precipitates was different too. Nanoparticles connected in small aggregates were obtained at pressures higher than 120 bar, whereas, spherical single microparticles were obtained operating at lower pressures. We also investigated the effect of the concentration of Rifampicin in the liquid solution on particles diameter: we observed that, increasing the liquid concentration, the mean PS increased and the PSD enlarged. XRD and HPLC analysis on treated Rifampicin showed that particles are amorphous and no degradation occurred as a consequence of supercritical processing. We attempted an explanation of the different morphologies observed considering the modification of the high pressure vapor-liquid equilibria of the ternary system Rifampicin-DMSO-CO(2) with respect to the behavior of the binary system DMSO-CO(2).

Fractional separation of SCF extracts from marjoram leaves: Mass transfer and optimization

Abstract Carbon-dioxide SCF extraction from herbaceous substrates produces nearly solid extracts because of simultaneous solubilization of essential oil components and cuticular waxes. Fractionation of the extract is required to isolate the essential oil. A mechanism is proposed to explain coextraction of essential oil and leaf and cuticular waxes, based on different mass transfer mechanisms for the two compound families. Cuticular waxes are hypothesized as mainly solubilized by leaching, while essential oil extraction is supposed dependent on complex diffusion phenomena. If extraction mechanisms operate as modeled, fractional separation of supercritical solution can be realized in a series of separators, taking advantage of the different solubilities of the two compound families and of their different concentrations in the solution. Marjoram leaf (Origanum Majorana L.) essential oil isolation by SCF has been studied as an application of fractional separation procedure. A nearly complete fractionation has been realized and a high quality essential is oil produced.