Pressure distillation theoretical stages

Heat Sensitivity. The heat sensitivity or polymerization tendencies of the materials being distilled influence the economics of distillation. Many materials caimot be distilled at their atmospheric boiling points because of high thermal degradation, polymerization, or other unfavorable reaction effects that are functions of temperature. These systems are distilled under vacuum in order to lower operating temperatures. For such systems, the pressure drop per theoretical stage is frequently the controlling factor in contactor selection. An exceUent discussion of equipment requirements and characteristics of vacuum distillation may be found in Reference 90. 

We may encounter problems in the purification of substances with a high normal boiling point. If purification only requires a small number of theoretical stages. Short Path Distillation (SPD), in which pressures can be as low as 0.001 bar, can prove useful. Many vitamins and pharmaceuticals can be processed without deterioration of quality. It is now common to use mechanical vacuum pumps with proper condensers preceding the pump. 

Packed fractional distillation columns run in the batch mode are often used for low-pressure drop vacuum separation. With a trayed column, the liquid holdup on the trays contributes directly to the hydraulic head required to pass through the column, and with twenty theoretical stages that static pressure drop is very high, e.g., as much as 100-200 mm Hg. 

A column with partial condenser and reboiler is to be used for the separation of benzene (1) from toluene (2), giving a distillate with 0.95 mole fraction benzene and a bottoms product with 0.10 mole fraction benzene. The column will operate at 105 kPa pressure and a reflux ratio of 4. The feed, at 55°C and a flow rate of 100 kmol/h containing 45 mol% benzene and 55 mol% toluene, enters the column at the fifth theoretical stage from the top. The estimated average relative volatility (benzene relative to toluene) is assumed constant, and estimated at 2.41. Based on the column conditions and thermodynamic properties, the predicted q-value is 1.2. It is required to determine the number of theoretical stages below the feed to complete the separation. 

A mixture of n-butane and n-pentane is loaded into a batch distillation reboiler to produce a distillate at constant rate and composition. The column pressure is constant at 500 kPa, the initial charge is 100 kmol, and the distillate rate is 10 kmol/h. The column has three theoretical trays plus the reboiler, giving it four theoretical stages. The initial charge composition, the required distillate composition, and the component relative volatilities, assumed constant, are as follows ... 

Due to the increased difficulty of separating THF and ethylacetate in the presence s of water, it was necessary to dewater the THF/ ethylacetate-mixture before the rectification. The ethylacetate/ THF rectification column (119) was designed for 60 theoretical stages and a reflux ratio of 15. The column was operated at 0.5 bar since the VLE-data are slightly more favorable under vacuum.3 A further reduction of the rectification pressure was not possible since water was used for condensing the distillate. 

A batch distillation column with three theoretical stages (the first stage is the still pot) is charged with 100 kmol of a 20 mol% n-hexane in n-octane mixture. At a constant reflux ratio R - 1.0, how many moles of the charge must be distilled if an average product composition of 70 mol% n-hexane is required If the boilup ratio is 10 kmol/h, calculate the distillation time. The equilibrium distribution curve at column pressure is given in Figure 6.27. 

A water-isopropanol mixture at its bubble point containing 10 mol% isopropanol is to be continuously rectified at atmospheric pressure to produce a distillate containing 65 mol% isopropanol. Eighty-five percent of the isopropanol in the feed must be recovered. VLE data are given in Problem 6.13. If a reflux ratio of 1.5 times the minimum is used, how many theoretical stages will be required ... 

A batch distillation column with eight theoretical stages (the first stage is the still pot) is charged with 500 kmol of a 48.8 mol% A in B mixture at atmospheric pressure (relative volatility aA B = 2.0). The boil-up ratio is constant at 213.5 kmol/h. If the distillate composition is to be maintained con-... 

Determine the number of theoretical stages required and the optimum stage locations for the feed and liquid side stream for the distillation process shown below assuming that methanol (M) and ethanol (JB) form an ideal solution. Use the Antoine equation for vapor pressures. 

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