Column distillation pressure

Distillation columns are controlled by hand or automatically. The parameters that must be controlled are (/) the overall mass balance, (2) the overall enthalpy balance, and (J) the column operating pressure. Modem control systems are designed to control both the static and dynamic column and system variables. For an in-depth discussion, see References 101—104. 

Regardless of the procedure used, certain initial steps must be taken for the determination or specification of certain product properties and yields based on the TBP distillation curve of the column feed, method of providing column reflux, column-operating pressure, type of condenser, and type of side-cut strippers ana stripping requirements. These steps are developed and ilhistrated with several detailed examples by Watkins (op. cit.). Only one example, modified from one given by Watkins, is considered briefly here to indicate the approach taken during the initial steps. 

A distillation column is operating at 27.5 inches mercury vacuum, referenced to a 30-inch barometer. This is the pressure at the inlet to the ejector. Due to pressure drop through a vapor condenser and trays of a distillation column, the column bottoms pressure is 23 inches vacu-... 

Pj = pure component vapor pressure, mm Hg R = reflux ratio (liquid returned to column)/(distillate drawoff) subscripts indicate number of plates, Rjnin... 

A low-pressure process has been developed by ICl operating at about 50 atm (700 psi) using a new active copper-based catalyst at 240°C. The synthesis reaction occurs over a bed of heterogeneous catalyst arranged in either sequential adiabatic beds or placed within heat transfer tubes. The reaction is limited by equilibrium, and methanol concentration at the converter s exit rarely exceeds 7%. The converter effluent is cooled to 40°C to condense product methanol, and the unreacted gases are recycled. Crude methanol from the separator contains water and low levels of by-products, which are removed using a two-column distillation system. Figure 5-5 shows the ICl methanol synthesis process. 

Make a preliminary design for a vertical thermosyphon for a column distilling crude aniline. The column will operate at atmospheric pressure and a vaporisation rate of 6000 kg/h is required. Steam is available at 22 bar (300 psig). Take the column bottom pressure as 1.2 bar. 

A reboiler of a distillation column is required to supply 10 kg-s 1 of toluene vapor. The column operating pressure at the bottom of the column is 1.6 bar. At this pressure, the toluene vaporizes at 127°C and can be assumed to be isothermal. Steam at 160°C is to be used for the vaporization. The latent heat of vaporization of toluene is 344,000 J-kg 1, the critical pressure is 40.5 bar and critical temperature is 594 K. Steel tubes with 30 mm outside diameter, 2 mm wall thickness and length 3.95 m are to be used. The film coefficient (including fouling) for the condensing steam can be assumed to be 5700 Wm 2-K 1. Estimate the heat transfer area for ... 

The residue is cooled to room temperature and transferred into a 200-mL round-bottomed flask equipped with a 6 -Vigreux column, distillation head, condenser and a cow receiver to be purified by distillation under reduced pressure. 

Monomers. High grade monomers were carefully purified by chemical methods and dried. Before preparing each emulsion, the monomer was rectified by a column distillation in an argon atmosphere under reduced pressure, and then freed from traces of oxygen by a series of freeze-thaw cycles in vacuo. Purity of the monomers was checked by gas chromatography. 

As already pointed out, it is possible to monitor the purity of the fractions by methods such as vapor pressure (see below) or gas phase infrared spectroscopy (Chapter 9). In planning an experiment, solvents and reactants are often chosen such that their vapor pressures facilitate the separation of reactants, products, and solvent. For compounds of similar volatility, more advanced separation techniques are required, such as fractional codistillation, low temperature column distillation, or gas chromatography, all of which are described in Chapter 9. 

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