Simulations supercritical extraction

Shing, K. S. Chung, S. T., Computer-simulation methods for the calculation of solubility in supercritical extraction systems, J. Phys. Chem. 1987, 91, 1674-1681... 

Effect of Unlike-Pair Interactions on Phase Behavior. No adjustment of the unlike-pair interaction parameter was necessary for this system to obtain agreement between experimental data and simulation results (this is, however, also true of the cubic equation-of-state that reproduces the properties of this system with an interaction parameter interesting question that is ideally suited for study by simulation is the relationship between observed macroscopic phase equilibrium behavior and the intermolecular interactions in a model system. Acetone and carbon dioxide are mutually miscible above a pressure of approximately 80 bar at this temperature. Many systems of interest for supercritical extraction processes are immiscible up to much higher pressures. In order to investigate the transition to an immiscible system as a function of the strength of the intermolecular forces, we performed a series of calculations with lower strengths of the unlike-pair interactions. Values of - 0.90, 0.80, 0.70 were investigated. 

The dynamics of adsorbed species over MgO(OOl) surface was studied by MD method. The migration of the adsorbed species was found to depend on the morphology of MgO and the thermal vibration of surface atoms in MgO lattice. Further, the situation where the supercritical fluid and adsorbed species exist together was simulated. The collision of supercritical fluid with the adsorbed species was identified as the primary cause of extraction. Additionally, the supercritical fluid form clusters around the desorbed species avoiding the readsorption. Thus, clustering is the secondary cause for the increased efficiency of supercritical extraction even above the critical conditions. The details of these simulation studies are given in the following section. 

Although CO2 is the most commonly used supercritical fluid for extraction, the solubility of certain solutes in CO2 is usually low and causes an inconvenience. The remedy for this problem is to add some entrainers such as water to facilitate the extraction. In this background, the MD simulations were carried out to study the supercritical extraction of nicotine by CO2 in the presence and absence of water as entrainer[40]. In the tobacco leaf, nicotine molecule is bonded to other organic molecules and forms organic acid salts. The malic salts of nicotine was chosen as the model with nicotine bonded to two malic molecules by hydrogen bonds[41]. It is assumed that when malic salts of nicotine are extracted from tobacco leaf, supercritical CO2 or entrainer molecule attacks the hydrogen bonds and decomposes the salt into three molecules. 

Griest WH, Ramsey RS, Ho CH, et al. 1992. Supercritical fluid extraction of chemical warfare agent simulants from soil. J Chromatogr 600(2) 273-277.. 

Our experimental set-up (described in ref. 7), allows us to record steady state absorption and emission spectra over a wide range of densities (10 5 to 20 at/nm3) in the Ar supercritical domain (Tc = 150.8 K, Pc = 49 bar). Representative absorption and emission spectra are shown in figure 1. These spectra could be reproduced with a good accuracy by means of equilibrium MD simulations performed with a standard procedure [8], In these simulations, the NO X-Ar and Ar-Ar interaction potentials were taken from the literature [9], We extracted an analytical NO A-Ar pair potential by an iterative fit of the experimental spectra, valid for the whole supercritical domain. 

John MS (2011) Monte Carlo simulation of solute extraction via supercritical carbon dioxide from polyethylene glycol). Fluid Phase Equilib 305(1) 76—82... 

A number of relatively new methods are being investigated to improve the recovery of small molecules. These methods include elec-trokinetic separators with bipolar membranes, simulated moving-bed chromatography and supercritical fluid extraction. The latter is practiced for food components. It has also been described for proteins but has not yet found wide acceptance in this field. A fastgrowing field is the production of bioethanol via fermentation processes either from milled com or from recycled biomass. The fermentation and saccharification processes can occur simultaneously in the fermenting tank by means of saccharification enzymes (amylases, cellulases). 

The simulated and experimental variations of the end-of-run (i.e., 8 hr.) isomerization rates with density are compared in Figure 1. Details of the experiments are provided elsewhere [2, 3]. At subcritical densities, the extraction of coke precursors is insignificant. Hence, an increase in the concentration of the hexene and coke precursors (i.e., oligomers) leads to lower isomerization rates. At near-critical densities, the extraction of coke precursors becomes significant. Hence, the isomerization rate increases. Both the experimental and simulated rates show a decreasing trend when the density is increased from near-critical to supercritical values. This is attributed to pore-diffusion limitations as the fluid changes from gas-like to liquid-like. Above 2.0 pc, the isomerization rate increases with density as the ability of the reaction mixture to extract the coke precursors increases. 

In front of the diversity and the complexity of supercritical fluid extraction, we dispose of all experimental and theoretical tools to compute and extrapolate pilot plant experimental data to an industrial unit. A lot of theoretical thermodynamic and kinetic data are now available, and experimental extractions carried out on pilot plants allow to build extrapolation models, from the very simple ones (like it is described in this case study) to the very sophisticated ones based on a numerical simulation software and taking into account hydrodynamic, thermodynamic and kinetic phenomena. 

The role of water as entrainer in the extraction of nicotine by supercritical CO2 fluid was studied by MD simulation. The following three systems were studied in detail ... 

Other exciting frontier areas of research in chemical engineering include molecular and nanoscale engineering, molecular simulation, surface modification, protein separation processes, supercritical fluid extraction, fluid particle systems, catalysis and reaction engineering, biochemical engineering, and computer-aided design, see also Careers in Chemistry. 

Supercritical CO2 can be effectively applied to the extraction of four hydrophobic disperse dyes from simulated dyebath. Quantitative removal of spiked dyes fi om aqueous solutions can be achieved by using 10% ethanol... 

They also follow expected effects of added ions (e.g. Li N03") via the reduction of the water activity ("salting-out effect"). The apparent discrepancy comes from our choice to model uranyl by its neutral U02(N03)2 salt instead of U02, in order allow for its possible extraction. In ct, it is very difficult to predict the status of ion pairs in pure solutions (see e.g. ref (53) for lanthanide salts in acetonitrile) and, a fortiori, at liquid-liquid interfaces. The formation of neutral salts may also be too slow to occur at the simulated time scales. Thus, this facet cannot be addressed by our simulations. In this context, the spontaneous formation of uranyl complexes with TBP is remarkable, and points to the importance of (micro)-heterogeneities of the systems and metastable conditions to form the complexes and promote their extraction to organic or supercritical phases. 

Clavier,. Y. Nicoud, R.M. Perrut, M. A new fractionation processes The supercritical fluid simulated moving bed. 7th Int. Symposium on Supercritical Fluid Chromatography and Extraction, Indianapolis, USA, 1996. 

E. Reverchon and C. Marrone, Modeling and simulation of the supercritical CO2 extraction of vegetable oils , / Supercrit Fluids, 2001,19,161-75. 

Serpil, T.(1997) Modeling and Simulation of Supercritical Fluid Extraction of Natural Materials from Plants, M.S. Tliesis, Bogazi9i University, Bebek, Istanbul, Turkey. 

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