Solvents entrainers

Labor and maintenance costs can usually be kept to the order of a few cents per pound of metal produced. However, where a circuit has been improperly designed and several manual operations are required, then labor and maintenance costs can be high. Excessive solvent entrainment losses, mentioned earlier, are added to labor costs. Any crud that forms and has to be removed can result in additional costs from labor requirements. For example, if incorrectly designed contacting equipment is chosen, which results in periodic shutdowns necessary for cleaning because of formation of cruds and precipitates, a major maintenance problem could arise. 

The mixture to be separated is fed, together with the entrainer, to the middle of the first column. Flere, the solvent, carbon dioxide and acetone, is supercritical to provide high solubility of the monoglycerides. The supercritical phase leaves the top of column I and goes to the lower part of column II. In column II, the binary solvent entrainer is subcritical and in the bottom of this column, the monoglyceride leaves, together with the entrainer. Part of it is returned as reflux to column I, whereas the rest goes to distillation for the separation of acetone. With a bottom temperature of... 

Ethanol as a Co>Solvent with SC>C02 for Extracting Cholesterol from Beef Tallow. Figure 4 contains data for comparing the extraction of lipid and cholesterol with 5% ethanol as a co-solvent (entrainer) compared to extracting with SC-CO2 alone. 

Arafat, H. A., M. C. Hash, A. S. Hebden, and R. A. Leonard. 2001. Characterization and Recovery of Solvent Entrained During the Use of Centrifugal Contactors. Argonne National Laboratory Report ANL-02/08, Argonne, IL. 

Other variations of flows are possible in each case if more solvent-entrainer is added to the emulsion in advance, it is recovered by drawing off a corresponding percentage of the entrainer layer which discharges from the decanter and recycling it back to solution tank where it is added to the optimum proportional amount of feed emulsion. Thus, if kerosene and an aromatic solvent—e.g., toluene or xylene—are used in dissolution of the emulsion, the aromatic chosen as the entrainer is continuously... 

In all cases, the selective solvents (entrainers) have the task of altering the partition coefficients in a way that high separation factors and selectivities for the different phase equilibria (extractive distillation vapor-liquid equilibrium (VLE), extraction liquid-liquid equilibrium (LLE), absorption gas-liquid equilibrium (GLE)) are achieved, resulting in a separation of compounds. The required partition coefficients, separation factors and selectivities can be calculated with the help of thermodynamic models (g -models, equations of state). 

Extractive distillation is a suitable distillation process for the separation of azeotropic systems or systems with separation factors tti2 close to unity. A typical extractive distillation process for the separation of aliphatics firom aromatics is shown in Figure 1. In extractive distillation processes, the high boiling selective solvent (entrainer), introduced not far from the top of the extractive distillation column, has to alter the volatilities in such a way that the separation factor attains a value very different from unity. Typical entrainers for the separation of aliphatics from aromatics are Ai-Methyl-pyrrolidone (NMP) or //-Formylmorpholine (NFM). In the presence of NMP or NFM,... 

Contamination of effluent gas due to incomplete gas absorption or solvent entrainment... 

Extractive distillation uses a selective solvent (entrainer). Here the entrainer influences the ratio of the activity coefficients of the components in order to alter the separation factor far from unity. Often about 70% of the liquid phase inside the column consist of the entrainer. A typical extractive distillation process for separating aromatics (benzene) from aliphatics (cyclohexane) is show in Fig. 3.2-4. 

In extractive distillation a solvent is added to the mixture to be separated, its boiling point is higher than that of the components of the mixture. In the case of a binary mixture, the added solvent must interact more strongly with one of the components to lower its volatility. The other more volatile component can thus be distilled off, leaving the added solvent and the higher-boiling component at the bottom of the column. The added solvent (entrainer) must be miscible with the mixture at all temperatures, concentrations, and pressures. 

While for azeotropic distillation the knowledge of the azeotropic points and of the miscibility gap is most important, for the selection of solvents (entrainers) for extractive distillation the knowledge of the influence of the entrainer on the separation factor is required. 

After extraction, the expended aqueous raffinate stream may have an undue proportion of the organic solvent entrained in it, sufficient to warrant the use of a phase separator. This is normally only a delay vessel with provision for removal of the two phases separately. With normal care in design and operation, entrainment losses of solvent can be reduced below 0 1 per cent of the solvent usage, for each circuit of the plant. 

Tortoise-like basket vertical speed — to reduce solvent entrainment (Chapter 1.22). 

The purpose of the solvent entrainer in this extractive distillation column is to alter the relative volatility between IPA and water, making IPA go to the top of the column and water go to the bottom of the column. The upper section of the column (above the entrainer feed location) is called the rectifying section, and its purpose is to separate the IPA and the entrainer. The middle section of the column (between the entrainer feed stage and the fresh feed stage) is called the extractive section. The purpose of this section is to suppress water from going up the column. The bottom section of the column (below the fresh feed location) is called the stripping section, and its purpose is to keep IPA from going down the column. The bottoms product of the column is the mixture of water and the entrainer, and it is fed to another downstream entrainer recovery column to separate these two components, so the entrainer can be recycled back to the extractive distillation column. 

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