Liquids in Separation Processes

Separation processes are not only of great importance in refineries, but also in the chemical, petrochemical, gas processing, and pharmaceutical industries. Although the reactor can be regarded as the heart of a chemical plant, in most cases, 60-80% of the total cost is taken up by the separation step. This step involves one or more thermal separation processes such as distillation, extraction, absorption, crystallization, adsorption, membrane processes, c/c., which are used to obtain the products at the required purity. 

Other separation processes can become advantageous, when separation problems such as unfavorable separation factors (0.95 aj2 1.05) or azeotropic points occur. In these cases, a special distillation process (extractive distillation) may be used. Extraction processes do not depend on a difference of vapor pressure between the compounds to he separated hut on the relative magnitudes of the activity coefficients of the compounds. As a result, extraction processes are particularly useful in separating the different aromatic compounds (Cg to C[2) from the different aliphatic compounds (Cg to C12). Absorption processes are ideally suited for the removal of undesired compounds from gas streams, e.g., sour gases (HjS, COj) from natural gas. 

For extractive distillation, extraction and absorption processes, highly selective solvents are required. The economic importance of extraction and extractive distillation processes can be recognized from the fact that the worldwide production of the BTX aromatics (benzene, toluene, xylenes, ethylbenzene) as important primary petrochemical products for the industrial manufacturing of many chemical products 

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The acquisition of experimental phase equihbrium data for ionic hquid-organic mixtures has displayed that ionic liquids are suitable for the separation of industrially relevant organic mixtures, in particular, for aromatic-ahphatic separation problems. Ionic hquids are indeed a very promising class of solvents that offer numerous advantages over commercially applicable solvents, most notably in flexibility, separation efficiency and economy. However, considerable challenges (biotoxicity, viscosity, solvent production cost and purity) have to be addressed before the full scale industrial implementation of ionic liquids in separation processes can be realized. 

Radioactive waste disposal problems Ionic liquids in separation processes Biodegradable polymers... 

Membrane processes offer another attractive option to apply ionic liquids in separation processes. Two general approaches have been reported the use of ionic liquids as bulk ionic liquid membranes (BILM) [131,132] or as supported ionic liquid membranes (SILM) [133, 134]. In the former case, the ionic liquid acts as selective separation layer in the latter case, the membrane supports the liquid separation layer and separates two conpartments, resulting in a very efficient ionic liquid use and separation unit. Reported exanples for SILMs include reactions with in situ product removal [135], extraction of bioorganic substances [136,137] and removal of CO2 and SO2 from gas streams [138,139]. SILMs have also been successfully... 

Ordinary diffusion involves molecular mixing caused by the random motion of molecules. It is much more pronounced in gases and Hquids than in soHds. The effects of diffusion in fluids are also greatly affected by convection or turbulence. These phenomena are involved in mass-transfer processes, and therefore in separation processes (see Mass transfer Separation systems synthesis). In chemical engineering, the term diffusional unit operations normally refers to the separation processes in which mass is transferred from one phase to another, often across a fluid interface, and in which diffusion is considered to be the rate-controlling mechanism. Thus, the standard unit operations such as distillation (qv), drying (qv), and the sorption processes, as well as the less conventional separation processes, are usually classified under this heading (see Absorption Adsorption Adsorption, gas separation Adsorption, liquid separation). 

Centrifugation is a well-established liquid-solid separation process popular in commercial and municipal waste treatment facilities. It is usually used to reduce slurry and sludge volumes and to increase the solids concentration in these waste streams. It is a technically and economically competitive process and is commonly used on waste sludges produced from water pollution control systems and on biological sludges produced in industry and municipal treatment facilities. 

NGL are those portions of natural gas which are recovered as liquids in separators, field facilities or gas processing plants. Natural gas liquids include, but are not limited to, heavier hydrocarbon components, natural gasoline and condensate they may include small quantities of nonhydrocarbons. 

Before leaving ionic liquids it is worth mentioning their potential value in separation processes. Organic solvents are frequently used in multiphase extraction processes and pose the same problems in terms of VOC containment and recovery as they do in syntheses, hence ionic liquids could offer a more benign alternative. Interesting applications along this line which have been studied include separation of spent nuclear fuel from other nuclear waste and extraction of the antibiotic erythromycin-A. 

The groups incorporating the liquid and vapour flow-rates and the equilibrium constants have a general significance in separation process calculations. 

The coimnerdal liquid adsorptive separation process of Ciq-Ch -olefins from Cio-Ci4 n-paraffins is another unique example of how zeolite adsorption can be applied. As shown in Table 6.1, distillation is not an option to separate C10-C14 olefins from Ciq-Cu paraffins because of their close boiling points. In this case, the UOP Olex process using NaX adsorbent is used to separate Ciq-Cm olefins from Cio-Ci4 paraffins. 

In the chromatographic liquid adsorptive separation process, the adsorption and desorption processes must occur simultaneously. After the desorption step, both the rejected product (product with lower selectivity, resulting in less adsorption by adsorbent) and the extracted product (product with higher selectivity, resulting in strong adsorption by adsorbent) contain desorbent In general, the desorbent is recovered by fractionation or evaporation and recycled back into the system. 

Operational characteristics of the required filtration equipment, like other liquid-solid separation processes, should be relatively simple in operation and offer excellent reliability with full automation. This hands-off operation would reduce health and safety concerns to an absolute minimum. 

This article reviews the phase behavior of polymer blends with special emphasis on blends of random copolymers. Thermodynamic issues are considered and then experimental results on miscibility and phase separation are summarized. Section 3 deals with characteristic features of both the liquid-liquid phase separation process and the reverse phenomenon of phase dissolution in blends. This also involves morphology control by definite phase decomposition. In Sect. 4 attention will be focused on flow-induced phase changes in polymer blends. Experimental results and theoretical approaches are outlined. 

Micelles and other organized surfactant aggregates are increasingly utilized in analytical applications (1.)- They interact with reagents and alter spectroscopic and electrochemical properties which, in turn, often results in increased sensitivities. Organized assemblies have also been employed in separation processes. Gas, liquid and thin layer micellar chromatographic techniques have been developed (2). 

Example 4.9 Entropy production in separation process Distillation Distillation columns generally operate far from their thermodynamically optimum conditions. In absorption, desorption, membrane separation, and rectification, the major irreversibility is due to mass transfer. The analysis of a sieve tray distillation column reveals that the irreversibility on the tray is mostly due to bubble-liquid interaction on the tray, and mass transfer is the largest contributor to the irreversibility. 

Solvents are used in separation processes, such as in solvent extraction and gas absorption, and in liquid-phase reactions. The solvents are usually recovered within the process and reused, but losses occur because of leaks, incon5)lete recovery, and degradation. Leaks, however, are strictly regulated by the Environmental Protection Agency (EPA). 

The pore connectivity r of two types of silica (highly porous beads, monolithic silicas) was calculated according to the pore network model proposed by Meyers and Liapis. Nt was proportional to the particle porosity in the case of highly porous beads. The differences in the pore connectivity for both types of silica were reflected in the mass transfer kinetics in liquid phase separation processes by measuring the theoretical plate height-linear velocity dependencies. In a future study, monolithic silicas possessing different macro- as well as mesopores will be investigated and compared with the presented results. 

The use of supercritical fluids in separation processes has received considerable attention in the past several years and the fundamentals of supercritical fluid (SCF) extraction and potential applications have been described in a recent review article (p. It is generally known that supercritical conditions enhance the dissolution of solid particles. In comparison with liquid solvents, supercritical fluids have a high diffusivity, a low density and a low viscosity, thus allowing rapid extraction and phase separation. Little information is available in the literature however, on mass transfer coefficients between supercritical fluids and solids. 

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