Cyclohexane entrainer

TABLE 17.7 Comparison of Benzene and Cyclohexane Entrainer Processes 80 mol% Case... 

The reaction rate is increased by using an entraining agent such as hexane, benzene, toluene, or cyclohexane, depending on the reactant alcohol, to remove the water formed. The concentration of water in the reaction medium can be measured, either by means of the Kad-Eischer reagent, or automatically by specific conductance and used as a control of the rate. The specific electrical conductance of acetic acid containing small amounts of water is given in Table 6. 

The above approach was confirmed in a recent study on design and control of a process for high-purity isopropyl palmitate by reactive distillation using cyclohexane as entrainer, with substantial energy reduction [21]. 

Liquid load Figure 6.9a is a plot of flood F-factor against liquid load. From Eq. (6,5), it also illustrates the effect of liquid load on the flood C-factor, or CSB. As liquid load increases, CSB first rises, then declines. The decline is slow, as illustrated by the cyclohexane-n-heptane curves in Fig. 6.9a, Some of the earlier flood correlations (18-20) predict that CSB rapidly diminishes at high liquid loads (as illustrated for the butane curves in Fig. 6,9a). Later work, first reported by Gerster et al. (21) and then by many others (15,22-26), however, showed that the rapid decline (such as that for the butane system) is associated with downcomer flooding, and not with entrainment flooding. 

Our final example of a complex column is an azeotropic system in which we add a light entrainer to facilitate the separation of two components. The classical example of this type of system is the use of benzene or cyclohexane to break the ethanol-water azeotrope. As shown in Fig. 6.26, the vapor from the top of the column is condensed and fed into a decanter in which the two liquid phases separate. The aqueous phase is removed as product. The organic phase (the light entrainer) is refluxed back to the column. Some of the organic may also be added to the feed stream to alter the composition profiles in the column (if more entrainer is needed lower in the column). Note that the organic level in the decanter is not controlled. A small stream of fresh entrainer ivould be added to make up for any losses of entrainer over a long period... 

Distillation, under nitrogen, with toluene as entrainer. This leads to a low-boiling azeotrope, the effect being similar to the well-known dehydration of ethanol with benzene or cyclohexane. 

All the configurations are designed such that a 99.0% conversion of myristic acid and a 99.9% product purity is obtained. The input parameters of the feed streams are based on a production of 1000 kg/hr (3697 mol/hr) isopropyl myristate and 99% conversion of the myristic acid. The ratio of myristic acid ipa was fixed at 1 1.15. The operating pressures are 1,5 and 10 bar and in simulations where an entrainer is used, this entrainer is cyclohexane. The kinetics of the reaction were experimentally determined. 

In the case of a still less reactive halide, or one with a tendency to undergo dehydrohalogenation, it is advantageous to add a reactive halide such as 1-bromo-naphthalene or n-butyl bromide for entrainment. Thus the reaction of 0.05 mole of eyclohexyl chloride and 0.05 mole of 1-bromonaphthalene with 0.33 g. atom of magnesium and isopropanol (0.3 mole) in 50 + 20 ml. of decalin afforded a mixture of 83% of cyclohexane and 10% of cyclohexene (removable with sulfuric acid). By this procedure cyclohexyl fluoride gives cyclohexane (33%) and benzotrifluoride gives toluene (10%). Fluorobenzene is inert. 

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. 

If the feed stream is 70 mole% benzene and 30 mole% cyclohexane, find the required acetone entrainer to feed ratio, assuming perfect separation between the azeotrope in the distillate and the benzene in the bottoms. 

The entrainer flow rate is determined by material balances. Cyclohexane material balance,... 

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 ... 

Typical of this process is the production of anhydrous ethanol from a concentrated ethanol solution in water, using benzene or cyclohexane or other components as the entrainer. 

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. 

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. 

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. 

Fig. 3.2-4 Extractive distillation process for the separation of benzene from cyclohexane using aniline as an entrainer.

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