Cyclohexane azeotropic distillation

A solution of quinoline 1-oxide (0.29 g, 2 mmol) in cyclohexane (1 L) was dehydrated by azeotropic distillation in the reaction vessel. The solution was purged with dry N2 and irradiated with a Hanau high-pressure Hg lamp. The resulting solution was evaporated and the residue was extracted with a little cyclohexane. The insoluble part contained carbostyril (3). The cyclohexane extract was evaporated and the residue purified by short-path distillation at 50°C/0.1 Torr yield 0.174g (60%) moisture-sensitive oil. 

Weichbrodt et reported on the use of focused open-vessel microwave-assisted extraction (EOV-MAE) for the determination of organochlorine pesticides in high-moisture samples such as fish. The results were comparable to those with closed-vessel microwave-assisted extraction (CV-MAE) and ASE. The main advantage of FOV-MAE is that the use of Hydromatrix is unnecessary as the solvent mixture of ethyl acetate and cyclohexane allows the removal of water from the sample matrix via azeotropic distillation. 

This conjugated ketone is prepared from cyclohexane-1,3-dione (1) via the enol ethyl ether (2), which is prepared by azeotropic distillation of a solution of (1)... 

EXAMPLE 10.3 SEPARATING BENZENE AND CYCLOHEXANE BY AZEOTROPIC DISTILLATION... 

The boiling points of benzene and cyclohexane are 80.1 °C and 80.8°C, respectively, and they form a minimum boiling azeotrope at 100 kPa, 77°C, and 54 mole% benzene. It is proposed to separate them by adding acetone as an entrainer, which forms a minimum boiling azeotrope with cyclohexane at 100 kPa, 53°C, 73.9 mole% acetone and 25.1 mole% cyclohexane. The azeotrope is taken as the overhead stream in a distillation column, and the benzene is recovered as the bottoms product. Further processing will be used to separate the cyclohexane and acetone in the azeotrope distillate. 

Here F and D are the feed and distillate molar flow rates, and X r arid Xcz are the mole fractions of cyclohexane in the feed and azeotropic distillate. Another material balance results from the fact that all the cyclohexane in the feed and all of the entrainer make up the distillate rate ... 

Benzene and cyclohexane are separated by azeotropic distillation using acetone as an entrainer. At the column pressure of 1 atm, acetone forms a minimum boiling azeotrope with cyclohexane at 74.6 mole% acetone and 25.4 mole% cyclohexane. The feed contains 75 kmol/h benzene and 25 kmol/h cyclohexane. The entrainer, pure acetone, is mixed with the feed and sent to the column. The distillate is 99.5 mole% azeotrope and 0.5 mole% benzene. The bottoms is 99 mole% benzene and 1 mole% cyclohexane. Determine the entrainer flow rate. 

The temperature is adjusted to remove the alcohol by-produced by azeotropic distillation as soon as it is formed, with the ester from which it is derived (ethanol/ethyl acrylate azeotrope, for example). A third compound may be used, such as cyclohexane (ethanol/cyclohexane azeotrope j. After the catalyst system is separated, the liquid stream from the reactor is fractionated and purified under vacuum in the presence of a polymerization inhibitor (such as phenothiazine). 

Liquid-liquid extraction can be used to recover one of the components to be separated, as well as the entrainer to be recycled. A typical process is the separation of cyclohexane/benzene, with nbp s at 80.8 °C and 80.1 °C and minimum-boiling azeotrope at 77.6 °C (Seader and Henley, 1998). If acetone is used as entrainer (nbp 56.2 °C), then an azeotrope appears between acetone and cyclohexane (nbp 53.1 °C). RCM shows a distillation boundary between the components to be separated (Fig. 9.32). To simplify the process, consider an initial azeotropic mixture. After mixing with entrainer the feed f, is separated in two products, benzene in bottoms and acetone-cyclohexane azeotrope in top. From the last mixture cyclohexane can be extracted with water. Finally acetone and water are separated by simple distillation. 

For the production of fuel-grade ethanol, the ethanol has to be dried . Anhydrous ethanol cannot be produced by simple distillation because ethanol forms an azeotropic mixture with water. The maximum ethanol content achievable by distillation is approximately 97.2vol.%, which is usually not sufficient for the application as fuel-ethanol. The residual water can be removed either by azeotropic distillation by the addition of, e.g., cyclohexane or by the application of molecular sieves. Today, state-of-the-art plants operate with molecular sieves which provide considerable advantages in terms of investment and operating costs. 

Cyclohexane is stable at its boiling point and so is suitable as an entrainer for azeotropic distillation. It is produced in large quantity as a raw material for nylon manufacture, and therefore costs httle more than benzene, from which it is derived. 

One method for ethanol dehydration is heterogeneous azeotropic distillation, which has been used for many decades. A suitable light entrainer component (benzene, cyclohexane, isooctane, ethylene glycol, and so on) is added to modify the relative volatilities. The water is driven overhead with the entrainer and a high-piu ity ethanol bottoms stream is produced in the azeotropic column. The overhead vapor is condensed and fed to a decanter. The organic phase is refluxed back to the column. The aqueous phase is fed to another column that produces a bottoms product of high-purity water and a distillate that is recycled back to the azeotropic column. A third column in the front end of the process is used to preconcentrate the low-concentration stream from the fermenter up to a concentration closer to the azeotrope before feeding this into the azeotropic column. 

Azeotropic distillation. A further development involves the addition of an entrainer, either another solvent or water, to the mixture of liquids to be separated. The purpose of this material is to form a selected azeotrope with one of the components. This results in a difference in relative volatility between the azeotrope and the non-azeotropic component allowing separation to be achieved. Typically the azeotrope will be of higher volatility and becomes the distillate, although the azeotrope can be such that it is removed as bottoms. An effective entrainer therefore must be selective for the solvent to be recovered, stable under the conditions of use, chemically compatible with all components, relatively inexpensive, readily available and must be easily separable from the desired product. Water is an ideal entrainer when used to form azeotropes with solvents which separate on condensation. Guidelines for entrainer selection have been provided by Berg and Gerster [28,29]. Many examples of azeotropic distillation can be cited [23]. Examples include the separation of benzene from cyclohexane by the azeotrope of the latter with acetone followed by liquid-liquid extraction with water to yield the cyclic hydrocarbon. Similarly the use of methylene chloride as an entrainer for separation of an azeotropic mixture of methanol and acetone is achieved by addition of methylene chloride followed by the distillation of the selective azeotrope between the alcohol and chlorinated hydrocarbon. 

In this section, you will prepare N-cinnamyl-m-nitroaniline (9) by a sequence beginning with the condensation of cinnamaldehyde (5) with nx-nitroaniline (6), followed by reduction of the intermediate imine 7 with sodium borohydride, as shown in Equations 17.12-17.14. The formation of the imine is reversible, but the reaction is driven to completion by azeotropic distillation. Because cyclohexane and water form a minimum-boiling azeotrope (Sec. 4.4), the water generated by the condensation of 5 and 6 is continuously removed by distilling the cyclohexane-water azeotrope throughout the course of the reaction. 

Figure 3.3.19 Homogeneous azeotropic distillation of cyclohexane and benzene at 1 bar ...

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