Cyclohexanol azeotropes

Cyclohexanol [108-93-0] M 100.2, m 25.2", b 161.1", d 0.946, n 1.466, n s 1.437, n 1.462. Refluxed with freshly ignited CaO, or dried with Na2C03, then fractionally distd. Redistd from Na. Further purified by fractional crystn from the melt in dry air. Peroxides and aldehydes can be removed by prior washing with ferrous sulfate and water, followed by distillation under nitrogen from 2,4-dinitrophenylhydrazine, using a short fractionating column water distils as the azeotrope. Dry cyclohexanol is very hygroscopic. 

Finally, mention should be made of the two effects of interaction of the mathematical model whose negative coefficients show minima of flashpoints for the binary butanol/cyclohexanol and butanol/pentanol combinations. Can they be explained by the presence of azeotropes in these substances The tables examined did not list these mixtures and there was no time to do an experimental check with the students. 

CeHsBr Bromobenzene 156.1 CeHnO Cyclohexanol 160.65 CioHis a-Pinene 155.8 Azeotropic 243... 

Some physical properties of the main species are listed in Table 5.2. Bringing phenol in reaction conditions implies vaporization at low partial pressure. Vacuum is necessary for carrying out separations by distillation. Phenol forms azeotropes with both cyclohexanol and cyclohexanone. If unconverted phenol should be recycled this could affect the global yield by recycling desired product too. If water appears as a byproduct, it gives azeotropes with both cyclohexanone and cyclohexanol. Because these azeotropes are low boilers they can be removed easily by distillation. 

Handling the separation problem involves essentially the ternary mixture phenol/ cyclohexanone/cyclohexanol. As Table 5.10 indicates, phenol is the highest boiler (181.9°C), followed by cyclohexanol (160.8°C) and cyclohexanone (155.4°C). Phenol forms positive azeotropes with cyclohexanone and cyclohexanol, of similar composition (roughly 75% mol phenol) and very similar boiling points. 

Figure 5.7 displays the RCM of the ternary mixture cyclohexanone/cyclohexa-nol/phenol at 0.1 bar. Note the existence of a distillation boundary that prevents recycling pure phenol, as well as the fact that the difference between the boiling points of azeotropes is only 1 °C. The RCM suggests that cyclohexanone will separate easily by distillation, while phenol will be recycled as an azeotrope, most probably with cyclohexanol. 

The separation section receives liquid streams from both reactors. For assessment the residue curve map in Figure 5.7 is of help. The first separation step is the removal of lights. This operation can take place in a distillation column operated under vacuum (200mmHg) with a partial condenser. Next, the separation of the ternary mixture cyclohexanone/cyclohexanol/phenol follows. Two columns are necessary. In a direct sequence (Figure 5.15) both cyclohexanone and cyclohexanol are separated as top products. The azeotrope phenol/cyclohexanol to be recycled is the bottoms from the second split In an indirect sequence (Figure 5.16) the azeotropic phenol mixture is a bottom product already from the first split. Then, in the second split cyclohexanone is obtained as the top distillate, while cyclohexanol is taken off as the bottom product The final column separates the phenol from the heavies. 

The column (C-3) delivers cydohexanol as top and a phenol/cyclohexanol mixture to be recycled as bottoms. The column is designed to ensure bottoms as close as possible to the azeotrope phenol/cyclohexanol, while minimizing losses in cyclohexanone. This column has 30 theoretical stages and operates at moderate reflux, below 3 1, which leads to diameters of 2.5/1.8m. 

In the two-step process the two reactors are coupled by the same separation system. Phenol gives azeotropes with both cyclohexanone and cyclohexanol. The relative volatility of cyclohexanone to cyclohexanol is very low at normal pressure, but it rises significantly under high vacuum. Alternative separation schemes are evaluated based on direct and indirect sequences. Both are equivalent in energy consumption, although the indirect sequence is more suitable by a decoupling effect. 

Dehydrogenation of the cyclohexanol/n clohexanone mixture to phenol. The alcohol forms with the phenol an azeotrope with a high phenol content (for example, 75 molar per cent at 12 kPa absolute). In order to employ distillation as a means of purification, this means that the reactor output must have a phenol content higher than that of the azeotrope. In practice, conversion takes place in the vapor phase with platinum base... 

The first stage in the production of anthracene is the recovery of a 25 to 30% anthracene concentrate by crystallization, which can be carried out in two stages to increase the yield. The crystallizate, known as anthracene cake , is generally concentrated to around 50% by vacuum distillation. The main co-boiling compound of 50 s anthracene is phenanthrene while carbazole is reduced to below 2%. Subsequent refining to yield pure anthracene , containing over 95%, is normally achieved by recrystallization in polar solvents, such as acetophenone, mixtures of cyclohexanol/cyclohexanone or N-methylpyrrolidone in addition, distillation or azeotropic distillation with ethylene glycol can be used for purification. 

Azeotrope Datcn binarcr Gemische von Cyclohexanol mit den Xylol-Isomcren... 

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