Or extractive distillation

Dehydrogenation of Tertiary Amylenes, The staiting material here is a fiaction which is cut from catal57tic clacking of petroleum. Two of the tertiary amylene isomers, 2-methyl-l-butene and 2-methyl-2-butene, are recovered in high purity by formation of methyl tertiary butyl ether and cracking of this to produce primarily 2-methyl-2-butene. The amylenes are mixed with steam and dehydrogenated over a catalyst. The cmde isoprene can be purified by conventional or extractive distillation. 

Extraction and Extractive Distillation. The choice of an extraction or extractive distillation solvent depends upon its boiling point, polarity, thermal stabiUty, selectivity, aromatics capacity, and upon the feed aromatic content (see Extraction). Capacity, defined as the quantity of material that is extracted from the feed by a given quantity of solvent, must be balanced against selectivity, defined as the degree to which the solvent extracts the aromatics in the feed in preference to paraffins and other materials. Most high capacity solvents have low selectivity. The ultimate choice of solvent is deterrnined by economics. The most important extraction processes use either sulfolane or glycols as the polar extraction solvent. 

Often it is called, reasonably enough, benzene concentrate or aromatics concentrate. Benzene concentrate is about 50% benzene, plus some other C5 s, Ce s, and Cys. All of them boil at about 176°F, the boiling point of benzene. Since the boiling temperature of the benzene is so close to that of the other hydrocarbons in the concentrate stream, simple fractionation is not a very effective way of isolating the benzene from benzene concentrate. Instead, one of two processes is used to remove the benzene, solvent extraction process or extractive distillation. The two differ in the primary mechanism they use. One operates on a liquid-liquid basis, the other on a vapor-liquid basis. 

The benzene leaves the olefins plant fractionator mixed with the other gasoline components so it is handled the same way as a refinery stream. An aromatics concentrate is made and run through one of the two separation processes you just read about, solvent extraction or extractive distillation. 

Separation of toluene from the other components can be by solvent extraction or extractive distillation, just as described in the benzene chapter. The boiling points of benzene and toluene are far enough apart that the feed to separation unit of choice can be split (fractionated) rather easily into benzene concentrate and a toluene concentrate. Alternatively, the separation unit can be thought of as aromatics recovery unit. Then an aromatics concentrate stream is fed to the solvent extraction unit, and, the aromatics outturn can be split into benzene and toluene streams by fractionation. Both schemes are popular. 

The usual procedures of fractional, azeotropic, or extractive distillation under inert gases, crystallization, sublimation, and column chromatography, must be carried out very carefully. For liquid, water-insoluble monomers (e.g., styrene, Example 3-1), it is recommended that phenols or amines which may be present as stabilizers, should first be removed by shaking with dilute alkali or acid, respectively the relatively high volatility of many of these kinds of stabilizers often makes it difficult to achieve their complete removal by distillation. Gaseous monomers (e.g., lower olefins, butadiene, ethylene oxide) can be purified and stored over molecular sieves in order to remove, for example, water or CO2. 

Acetic acid is one of the oldest known chemicals. Dilute acetic acid, vinegar, has been made by aerobic bacterial oxidation of ethanol. It has also been reclaimed by extraction or extractive distillation from pyroligneous acid, which was obtained from the extractive distillation of wood (J ). In the early nineteen hundreds, oxidation of acetaldehyde became the main source of acetic acid. The acetaldehyde has been obtained from acetylene ( ). ethylene (3) or ethanol as indicated below. 

Extractions or extractive distillations with supercritical solvent need to be performed at as high as possible a solubility of oil in the extract or vapor phase in order to reduce the solvent or carrier gas requirement. From our lemon oil-carbon dioxide phase diagrams, it appears that the highest practical solubility level is 0.9 mole % (2.8 wt ) essential oil. This is obtainable at 313 K. At lower temperature, sensitivity of solubility to pressure requires that solubility be lower (e.g., 0.3 mole % at 308 K). 

A separation process is sought that can satisfy both our present economic and enviromental constraints. It would also provide an alternative to present practice that relies on expensive azeotropic or extractive distillation processes used in the recovery of products from low relative volatility streams. As an example, virtually all industrial butadiene recovery processes now rely on extractive distillation using acetonitrile or other equivalent agent to enhance the relative volatility of the C4 components. The use of supercritical or near critical separation of these streams may satisfy these requirements provided certain pressure, temperature and recompression criteria can be met. Such a process would also reduce the need for a complex train of distillation towers. 

Hydrazine is produced in the hydrated form with one mole of water added. Although a significant fraction of hydrazine is used as the hydrate, numerous applications (such as rocket propulsion) require anhydrous hydrazine. Because of the azeotrope at 68% hydrazine, reactive distillation or extractive distillation must be used to produce pure hydrazine. 

UOP/Shell BTX, purification Reformate, pyrolysis gasoline Shell Sulfolane process liquid extraction and/or extractive distillation with sulfolane solvent 123 1998... 

The reactor effluent is quenched by water injection, and then by passage through a series of heat exchangers in which steam is produced. It is then cooled by a second water quench or by means of a heavy hydrocarbon. The condensates are separated, and the gases are compressed and sent to a train of simple or extractive distillation stages to... 

The design of azeotropic or extractive distillation columns, as with con-A ventional columns, demands a knowledge of the vapor-liquid equilibrium properties of the system to be distilled. Such knowledge is obtained experimentally or calculated from other properties of the components of the system. Since the systems in azeotropic or extractive distillation processes have at least three components, direct measurement of the equilibrium properties is laborious and, therefore, expensive, so methods of calculation of these data are desirable. 

The success of the NRTL equation in undergoing this test would suggest that it will be a powerful tool in the design of processes involving azeotropic or extractive distillation. The effect of the addition of a third... 

If the equilibrium ratios are functions of phase compositions as occurs in liquid extraction or extractive distillation, it is necessary to include more variables in the iterative process. It was later shown (3) that for liquid extraction problems with known stage temperatures, the minimum number of iteration variables for quadratic convergence is nm, the n vapor flow rates, and n(m — 1) of the phase compositions. The total number of variables is n(2m + 2) because the temperatures are known. The iteration sequence is completely different for this case as compared with the previous case with composition independent equilibrium ratios. 

To separate solutions of both liquids and of solids in a liquid (particularly water), two methods usually are considered first (1) vaporization—i.e., evaporation or distillation—to utilize the different relative volatilities of the components, either normally or accentuated by another liquid in azeotropic or extractive distillation and (2) liquid-liquid extraction to take advantage of the relative preferential solubility of one component in an added liquid. 

Derivation Interaction of methanol and ammonia over a catalyst at high temperature. The mono-, di-, and trimethylamines are all produced and yields are regulated by conditions. They are separated by azeotropic or extractive distillation. 

The terms entrainer and solvent are commonly used interchangeably to refer to the separating agent used to enhance the separation of close boilers or azeotropes by azeotropic or extractive distillation. For consistency, the term entrainer will be used to designate the azeotropic distillation agent and solvent, the extractive distillation agent. 

While solvent volatility at ambient conditions has little effect on liquid-liquid equilibria [because the pure component vapor pressure cancels out in Equation (10.9)], solvent volatility nonetheless can be important in solvent regeneration, particnlarly if simple or extractive distillation is used to recycle solvent. These techniqnes are commonly nsed in solvent regeneration when extraction is applied to the recovery of many organic chemicals (e.g., acetic acid [34] recovery, which typically involves extractive distillation to regenerate the solvent and prodnce glacial acetic acid). Then the latent heat of vaporization is also an important consideration. Usnally, however, it is desirable to have regeneration withont solvent distillation, as that approach is often inefficient and expensive. 

Formic add displays an unusual behavior, however, significantly complicating the scheme for the separation of the different products formed and for the purification of the acetif acid. Formic acid, which boils at a temperature approaching that of water (bpi.013 - 100.7°Q forms an azeotrope with water, with a boiling point higher than those of the pure components ( ,.ou = 107.2°C, water content, percent weight, 2Z6). Hence its separation requires azeotropic or extractive distillation. 

A second alternative for the separation of hydroformylation products from a rhodium [8] or cobalt [9] catalyst is to perform the catalytic reaction in a polar solvent using complexes of monosulfonated trialkyl- or triarylphosphines (e.g., TPPMS). Addition of both water and an apolar solvent such as cyclohexane gives a biphasic system. After separation of the apolar layer, the added apolar solvent must be stripped from the products. In order to form a homogeneous system with new substrate alkene, the polar catalytic phase must be freed from water, e.g., by azeotropic or extractive distillation. Clearly, these extra co-distillation steps are energy-consuming. 

---