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Flow scheme of gas extraction from solids Chapter 3 Supercritical Fluid Extraction from Solids

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Mechanisms of Transport in the Solid Phase

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Elementary membrane Mechanisms of Transport in the Solid Phase

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Model of an Elementary Membrane

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Integral Extraction Curve

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Extraction Rate Curves

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Remaining amount of extract in the solid

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Folie 10 Concentration of extract in SC-solvent

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Caffeine from raw coffee beans, N 2 O Dependence of amount of extract on pressure

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Caffeine from raw coffee beans, N 2 O Dependence of extraction rate on temperature

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Caffeine from raw coffee beans, N 2 O Dependence of amount of extract on density

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Caffeine from raw coffee beans, N 2 O Dependence of extraction on solvent ratio

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Caffeine from raw coffee beans, N 2 O Dependence of extraction rate on solvent ratio

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Caffeine from raw coffee beans, N 2 O Dependence of extraction rate on size of particles

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Extraction of theobromine from cocoa seed shells Limited mass transfer by small particles

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Extraction of oil from rape seeds Influence of pretreatment

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Fluid phase (extract phase) Concentration of the extract: accumulated quantity of extract; quantity of extract per unit of time; composition of extract in dependence of time. Concentration of the extract in the extraction vessel: medium concentration over the total volume; concentration in the extraction vessel (plug flow); local concentrations: radial distribution (no backmixing, but no plug flow); local concentrations: radial and axial distributions (backmixing). Modeling the Extraction

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Solid phase (raffinate phase) Concentration of extractible substances in bulk solid: accumulated depletion of the solid (mean value); depletion of solid related to the remaining content; remaining concentration of extractible substances: radial and axial distribution. Concentration of substances in single particles: mass transport by diffusion; mass transport resistance by chemical reactions and/or phase transitions; simple geometric particles, complex shape; monodispersity of solid particles (size), multidispersity of the solid particles (size distribution). Modeling the Extraction

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Operating parameters Pressure, temperature, density of the fluid, quantity of solvent per unit of time and mass of solid (solvent ratio); chemical composition of the extracting solvent. Modeling the Extraction

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Pretreatment of the solid size reduction and enlargement of surface; destruction of the plant cells adjustment of the water content; chemical reactions for setting free the extract compounds. Modeling the Extraction

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m = mass of extract components; m s = mass of the solid substrate; c m = mean concentration of extractible components in the solid. Transport of extract in the solid to the interface and the fluid: Steady State Approximation

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No phase transition at the interface: s = mass transfer coefficient in the solid phase; F = mass transfer coefficient in the fluid phase; k = total mass transfer coefficient; c 0 = initial mean concentration of extractible components in the solid; c = concentration of extracted components in the bulk of the fluid; A = mass transfer area. For k = const.: Mass transport resistance in the solid dominant: Steady State Approximation

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Constant rate of extraction: The extraction can be calculated by dimensionless correlations, e.g. for a fixed bed (Wakao and Kaguei): F = mass transfer coefficient solid-fluid; d = diameter of a volume equivalent sphere; D G = self diffusion coefficient of the fluid; = viscosity of fluid; u = linear flow velocity of fluid. Steady State Approximation

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Radial distribution of porosity in a fixed bed

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Tubular reactor Radial distribution of flow velocity

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Influence of direction of flow

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Numerical solution for breakthrough curves

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Axial and radial concentration profiles Extraction of caffeine from coffee beans

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Determination of effective diffusion coefficient Extraction of sugar from coffee grounds

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Extraction of oil from soja bean flakes Determination of effective diffusion coefficient

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Depletion in a spherical particle

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Determination of effective diffusion coefficient

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Constant effective diffusion coefficient, calculated from total amount of extract Extraction of theobromine from cocoa seed shells Modeling the extraction

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Extraction of theobromine from cocoa seed shells Constant effective diffusion coefficient, incl. Mass transfer resistance to fluid Modeling the extraction

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Extraction of theobromine from cocoa seed shells Experimental results

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The VTII-Model for the Extraction from Solids Using Supercritical Solvents equilibrium distribution between solid and supercritical solvent (adsorption isotherm); diffusion in the solid (effective diffusion coefficient or effective transport coefficient as defined by the transport model); mass transfer from the surface of the solid to the bulk of the fluid phase (supercritical solvent); axial dispersion (effective dispersion coefficient, taking into account inhomogeneities of the fixed bed, the solvent distribution and the influence of gravity). Modeling the Extraction

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Mass balance for the fluid phase: Mass balance for the solid phase: Equilibrium between fluid phase and solid phase: Overall mass transfer coefficient: Modeling the Extraction: VT II-Model

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c s = mean concentration of extract components in solid phase; c F = concentration of extract in the fluid (supercritical solvent); D ax = axial dispersion coefficient; u z = void volume linear velocity of supercritical solvent; K( c s ) = equilibrium distribution coefficient solid and fluid phase; D es = effective diffusion coefficient in the solid phase; k oG = overall mass transfer coefficient related to the fluid phase; z = coordinate in axial direction; = void volume fraction (porosity of the fixed bed); t = time of extraction; a = specific surface of solid phase (mass transfer surface area); s = density of solid; k 1, k 2 = coefficients of the sorption isotherm (Freundlich-isotherm); F = mass transfer coefficient for the fluid phase. Modeling the Extraction: VTII-Model

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Extraction of theobromine from cocoa seed shells with CO 2 Fitting of laboratory experiment to VT II-model

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Extraction of theobromine from cocoa seed shells with CO 2 Prediction of scale-up (40) with VT II-model

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Solubility of theobromine in CO 2

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Solubility of theobromine. Influence of water

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Extraction of theobromine from cocoa seed shells with CO 2 Influence of water on extraction

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Extraction of theobromine from cocoa seed shells with CO 2 Influence of fluid flow velocity, solvent ratio

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Extraction of theobromine from cocoa seed shells with CO 2,, Pilot plant experiments Concentration profiles

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Extraction of theobromine from cocoa seed shells with CO 2,,, VT II - model Simulation of concentration profiles

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Extraction of oil from rape seeds

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Influence of solvent ratio on loading of gas phase Extraction of oil from rape seeds

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Extraction of oil from palm fruits

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Extraction of oil from a wild species of oil palm

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Different supercritical solvents, different entrainers Extraction of soy bean flakes

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Enriching by precipitation

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Substrate: Aparisthmium cordatum Extracts obtained with different solvents

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Multistage extraction

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Gas extraction plant

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Flow scheme of simple laboratory plant

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Flow scheme of laboratory plant

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Laboratory Plant: Penang

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Flow scheme of a laboratory plant

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Flow scheme of pilot plant

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