Review of kinetic models for supercritical fluid extraction

Influence of Ethanol Parametrization on Diffusion Coefficients Using OPLS-AA Force Field

Molecular dynamics simulations employing the all-atom optimized potential for liquid simulations (OPLS-AA) force field were performed for determining self-diffusion coefficients (D11) of ethanol and tracer diffusion coefficients (D12) of solutes in ethanol at several temperature and pressure conditions. For simulations employing the original OPLS-AA diameter of ethanol's oxygen atom (σOH), calculated and experimental diffusivities of protic solutes differed by more than 25%. To correct this behavior, the σOH was reoptimized using the experimental D12 of quercetin and of gallic acid in liquid ethanol as benchmarks. A substantial improvement of the calculated diffusivities was found by changing σOH from its original value (0.312 nm) to 0.306 nm, with average absolute relative deviations (AARD) of 3.71% and 4.59% for quercetin and gallic acid, respectively. The new σOH value was further tested by computing D12 of ibuprofen and butan-1-ol in liquid ethanol with AARDs of 1.55% and 4.81%, respectively. A significant improvement was also obtained for the D11 of ethanol with AARD = 3.51%. It was also demonstrated that in the case of diffusion coefficients of non-polar solutes in ethanol, the original σOH=0.312 nm should be used for better agreement with experiment. If equilibrium properties such as enthalpy of vaporization and density are estimated, the original diameter should be once again adopted.

Recent Advances in Supercritical CO2 Extraction of Pigments, Lipids and Bioactive Compounds from Microalgae

Supercritical CO₂ extraction is a green method that combines economic and environmental benefits. Microalgae, on the other hand, is a biomass in abundance, capable of providing a vast variety of valuable compounds, finding applications in the food industry, cosmetics, pharmaceuticals and biofuels. An extensive study on the existing literature concerning supercritical fluid extraction (SFE) of microalgae has been carried out focusing on carotenoids, chlorophylls, lipids and fatty acids recovery, as well as the bioactivity of the extracts. Moreover, kinetic models used to describe SFE process and experimental design are included. Finally, biomass pretreatment processes applied prior to SFE are mentioned, and other extraction methods used as benchmarks are also presented.

Diffusion of Squalene in Nonaqueous Solvents

Capillary flow techniques have been used to determine the translational diffusion constant, D, of squalene in seven alkanes and five cyclohexanes. The alkanes are n-hexane, n-octane, n-decane, n-dodecane, n-tetradecane, 2,2,4,4,6,8,8-heptamethylnonane (isocetane), and 2,6,10,14-tetramethylpentadecane (pristane). The cyclohexanes are cyclohexane, n-butylcyclohexane, n-hexylcyclohexane, n-octylcyclohexane, and n-dodecylcyclohexane. When combined with published data in CD₂Cl₂, ethyl acetate, n-hexadecane, squalane, n-octane-squalane mixtures, and supercritical CO₂, the 35 diffusion constants and viscosities, η, vary by factors of ∼230 and ∼500, respectively. A fit to the modified Stokes-Einstein equation (MSE, D/T = A _SE/η ^p ) gives an average absolute percentage difference (AAPD) of 7.72% between the experimental and calculated D values where p and A _SE are constants, T is the absolute temperature, and the AAPD is the average value of (10²) (|D _calcd - D _exptl|/D _exptl). Two other MSE fits using subsets of the 35 diffusion constants may be useful for (a) estimating the viscosity of the hydrophobic core of lipid droplets, where squalene is a naturally occurring component, and (b) providing estimates of the D values needed to design extraction processes by which squalene is obtained from plant oils. The Wilke-Chang equation also was considered and found to give larger AAPDs than the corresponding MSE fits.

Optimization of Oil Recovery from Japonica Luna Rice Bran by Supercritical Carbon Dioxide Applying Design of Experiments: Characterization of the Oil and Mass Transfer Modeling

This study presents an optimization strategy for recovery of oil from Japonica Luna rice bran using supercritical carbon dioxide (scCO2), based on design of experiments (DoE). Initially, a 24−1 two level fractional factorial design (FFD) was used, and pressure, temperature, and scCO2 flow rate were determined as the significant variables; while the yield, total flavonoids content (TFC), and total polyphenols content (TPC) were the response functions used to analyze the quality of the extracts recovered. Subsequently, central composite design (CCD) was applied to examine the effects of the significant variables on the responses and create quadratic surfaces that optimize the latter. The following values of pressure = 34.35 MPa, temperature = 339.5 K, and scCO2 flow rate = 1.8 × 10−3 kg/min were found to simultaneously optimize the yield (6.83%), TPC (61.28 μmol GAE/g ext), and TFC (1696.8 μmol EC/g ext). The fatty acid profile of the oils was characterized by GC-FID. It was demonstrated that the acids in largest quantities are C16:0 (15–16%), C18:1 (41%), and C18:2 (38–39%). Finally, three mass transfer models were applied to determine the mass transfer coefficients and assess the cumulative extraction curves, with an AAD% of 4.16, for the best model.

Chemical Properties and Therapeutic Potential of Citral, a Monoterpene Isolated from Lemongrass

BACKGROUND

Citral is one of the main components of lemongrass oil present at a concentration of 65-85% approximately and is generally separated by steam refining. It is an important component in the manufacturing of scents, citrus chemicals, cosmetics, food and pharmaceutical products.

OBJECTIVES

This article aims at reviewing the published literature to highlight the metabolism, extraction strategies and therapeutic significance of citral for improving the scope of its application in the food and pharma industry.

DISCUSSIONS

Apart from steam refining, there are other techniques like solvent extraction, supercritical fluid extraction and ultrasonication by which citral can be extracted and the method of extraction defines its quality. It is an unstable molecule and undergoes rapid deterioration on exposure to air. Citral is biosynthesized by the plants through the 5 carbon precursor isopentenyl diphosphate (IPP) units utilizing two diverse biochemical pathways, acetate- mevalonate (acetate- MVA) pathway or 2C-methylerythritol-4-phosphate (MEP). Orally Citral was absolutely digested in the gastrointestinal tract and its metabolism leads to the discharge of metabolites which include a number of acids and a biliary glucuronide. There is no scientific evidence about the long term bioavailability of citral in the body and it has no adverse effect on tissue related to its accumulation and delayed excretion. Citral exhibits various important therapeutic properties like antimicrobial, antioxidant, anticancer, anti-diabetic and anti-inflammatory.

CONCLUSION

Citral is a potent biomolecule with various important biological activities and therapeutic implications. Strategies are required to increase the stability of citral which could increase its applications.

Extraction of natural products using supercritical fluids and pressurized liquids assisted by ultrasound: Current status and trends

Natural products are a source of a wide range of chemical compounds, from pigments to bioactive compounds, which can be extracted and used in different applications. Due to consumer awareness, the interest in natural compounds significantly increased in the last decades, prompting the search for more efficient and environmentally friendly extraction techniques and methods. Pressurized liquids and fluids (sub and supercritical) are being explored to extract natural compounds within the green process concept. The combination of these techniques with ultrasound has emerged as an alternative to intensify the extraction process efficiently. In this context, this work presents a comprehensive review and current insights into the use of high-pressure systems, specifically supercritical fluid extraction and pressurized liquid extraction assisted by ultrasound, as emerging technologies for extracting bioactive compounds from natural products. The extraction mechanisms, applications, and the influence of operational parameters in the process are addressed, in addition to an analysis of the main challenges to be overcome for widespread application.

Predictive Models for the Binary Diffusion Coefficient at Infinite Dilution in Polar and Nonpolar Fluids

Experimental diffusivities are scarcely available, though their knowledge is essential to model rate-controlled processes. In this work various machine learning models to estimate diffusivities in polar and nonpolar solvents (except water and supercritical CO₂) were developed. Such models were trained on a database of 90 polar systems (1431 points) and 154 nonpolar systems (1129 points) with data on 20 properties. Five machine learning algorithms were evaluated: multilinear regression, k-nearest neighbors, decision tree, and two ensemble methods (random forest and gradient boosted). For both polar and nonpolar data, the best results were found using the gradient boosted algorithm. The model for polar systems contains 6 variables/parameters (temperature, solvent viscosity, solute molar mass, solute critical pressure, solvent molar mass, and solvent Lennard-Jones energy constant) and showed an average deviation (AARD) of 5.07%. The nonpolar model requires five variables/parameters (the same of polar systems except the Lennard-Jones constant) and presents AARD = 5.86%. These results were compared with four classic models, including the 2-parameter correlation of Magalhães et al. (AARD = 5.19/6.19% for polar/nonpolar) and the predictive Wilke-Chang equation (AARD = 40.92/29.19%). Nonetheless Magalhães et al. requires two parameters per system that must be previously fitted to data. The developed models are coded and provided as command line program.

Prediction of methane diffusion coefficient in water using molecular dynamics simulation

Diffusion coefficient is one the most effective factors in mass transfer calculation, which plays an important role in study at the molecular scale. In this study, Material Studio software was used to simulate the diffusion coefficient of methane in water through molecular dynamics. COMPASS force field was also used for optimization of atomic structures of methane and water, and Group-Based method was applied to model to calculate both van der Waals and electrostatic forces. In addition, Universal force field was used to optimize of amorphous cell, while Ewald and Atom-Based methods were applied for modeling and calculation of van der Waals and electrostatic potential energy at constant temperatures. The simulation duration for equilibrium of amorphous cell in both state of NVT and NVE was assumed 5ps. The impact of temperature as well as concentration on diffusion coefficient were investigated and results showed that the diffusion coefficient had linear relationship with temperature and third-degree polynomial relationship with concentration. As a result, of the simulation, the diffusion coefficient function versus temperature and concentration was developed.

Kinetics Study of Microwave-Assisted Brine Extraction of Lipid from the Microalgae Nannochloropsis sp

The kinetics of lipid extraction utilizing microwave-assisted extraction (MAE) from Nannochloropsis sp. microalgae were studied using a low cost and green solvent, namely brine (NaCl) solution. The kinetic modelling of the lipid extraction was performed to evaluate the mechanism of the lipid mass transfer using different extraction models, including Fick’s Law, First and Second-order Rate Law and the Patricelli mathematical model. The Patricelli mathematical model described the kinetics of lipid extraction well, with the highest average values of determination coefficient (R² ≥ 0.952) and the lowest average values of mean relative percentage deviation (MRPD ≤ 8.666%). The lipid analysis indicated a positive influence of the microwave temperature and time on the quantity and quality of extracted lipids. SEM analysis of spent microalgae clearly shows an increase in the distorted cell with increase microwave temperature and time, which could be directly correlated to the mechanism of the MAE-brine technique.

Supercritical CO2 Extraction of Extracted Oil from Pistacia lentiscus L.: Mathematical Modeling, Economic Evaluation and Scale-Up

In this study, the extracted oil of Pistacia lentiscus L. the Tunis region was extracted using supercritical carbon dioxide (SC-CO₂) extraction containing different major components in the oil such as α-pinene (32%) and terpinene-4-ol (13%). The investigation of the effect of different variables on the extraction yield with 5% level of confidence interval showed that the CO₂ pressure was the main significant variable to influence the oil yield. In order to better understand the phenomena, three parameters were considered to adjust all parameters of broken and intact cell (BIC) model: grinding efficiency (G), the internal mass transfer parameter (kSa0), and the external mass transfer parameter (kfa0), which were estimated by experimental extraction curves to calculate the diffusion coefficient. From an economic point of view, we found out that the high cost of production of the extracted oil was due to the low mass of extracted oil obtained from this type of plant.

Extraction of Triterpenic Acids and Phytosterols from Apple Pomace with Supercritical Carbon Dioxide: Impact of Process Parameters, Modelling of Kinetics, and Scaling-Up Study

Apple pomace, a byproduct of juice production, is a rich source of bioactive compounds and nutrients. Supercritical fluid extraction was proposed as a method for a fast and selective extraction of hydrophobic compounds with a pharmaceutical potential from this matrix. Chromatographic analysis showed that the pomace contained significant amounts of such substances, the most abundant of them were ursolic acid, oleanolic acid, and β-sitosterol. The solubility was chosen as a primary factor for a selection of the extraction conditions; the best results were acquired for a temperature of 80 °C and a pressure of 30 MPa. The equation proposed by Chrastil was applied for the description of the impact of the process parameters on the solubility of the analytes; the obtained values of coefficients of determination were satisfactory, despite the fact that the equation was developed for binary systems. The extraction curves obtained during the experiments were used for the description of the process kinetics using the Broken plus Intact Cell model. The impact of the temperature, pressure, and flow rate of carbon dioxide on the mass transfer phenomena was investigated. The data obtained allowed the prediction of the extraction curve for the process conducted on the larger scale.