Evaporation or Simple Distillation

For a mixture of ethane, n-butane, and n-pentane, the bubblepoint and dewpoint temperatures at lOOpsia, a flash at 100°F and lOOpsia, and an adiabatic flash at lOOpsia of a mixture initially liquid at 100°F will be determined. The overall composition z, the coefficients A, B, and C of Eq. (13.21) and the coefficients a, b, c, and d of Eqs. (13.27) and (13.28) are tabulated  

Results for successive iterations for j8 and the final phase compositions are 

Adiabatic flash calculation Liquid and vapor enthalpies off charts in the API data book are fitted with linear equations 

The inlet material to the flash drum is liquid at 100°F, with Ha = 8, 575.8 Btu/lb mol. The flash Eq. (13.42) applies to this part of the example. The enthalpy balance is 

The numerical results were obtained with short computer programs which are given in Walas (1985, p. 317). 

As a mixture of substances is evaporated, the residue becomes relatively depleted in the more volatile constituents. A relation for binary mixtures due to Rayleigh is developed as follows The differential material balance for a change dL in the amount of liquid remaining is 

Simple distillation is not the same as flashing because the vapor is removed out of contact with the liquid as soon as it forms, but the process can be simulated by a succession of small flashes of residual liquid, say 1% of the original amount each time. After n intervals. 

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For transformations of inexpensive chemicals, cost is most important, so researchers use acids and simple esters, for example, methyl or glyceryl. Acylations with these donors are often slow and reversible with an equilibrium constant near one. To drive reactions to completion, researchers removed the water or alcohol by evaporation or azeotropic distillation. In other cases, crystallization of the product drives the reaction. 

Distillation is a method of separation that is based on the difference in composition between a Hquid mixture and the vapor formed from it. This composition difference arises from the dissimilar effective vapor pressures, or volatihties, of the components of the Hquid mixture. When such dissimilarity does not exist, as at an a2eotropic point, separation by simple distillation is not possible. Distillation as normally practiced involves condensation of the vaporized material, usually in multiple vaporization/condensation operations, and thus differs from evaporation (qv), which is usually appHed to separation of a Hquid from a soHd but which can be appHed to simple Hquid concentration operations. 

Methods have been described for the determination of total fatty acids in raw sewage sludge. These methods [30-32] require a concentration steps such as simple distillation, steam distillation, evaporation, or extraction [33-35] which resulted in great losses of the volatile matter [36, 37],... 

As an alternative to simple distillation, pervaporation could be used [124], This technique makes use of non-porous membranes with a selective layer consisting of hydrophilic or hydrophobic polymer. Those compounds, which are volatile and soluble in the membrane, are evaporated into the vacuum on the permeate side. By this means, selective separation, for example of volatile impurities from volatile auxiliary agents in the ionic liquid, should be possible. 

Such an explosion may be avoided by taking a few simple precautions. Ethers should be bought in small quantities, kept in tightly sealed containers, and used promptly. Any procedure requiring evaporation or distillation should use only peroxide-free ether. Any ether that might be contaminated with peroxides should be discarded or treated to destroy the peroxides. 

Furthermore, acetone, which remains dissolved in the raffinate solution after extraction, may be distilled readily therefrom because of its high volatility from aqueous solutions and particularly from the solution with its high concentration of solute. This high concentration greatly reduces the vapor pressure of water, and for the same reason, acetone can be evaporated or distilled readily from the extract layer. In fact, a substantial portion of that used as the solvent for the acetic acid can be evaporated from the extract layer in a simple pot still without distilling over an appreciable amount of acetic acid. 

To design or control an evaporation or condensation process, you must know the conditions at which the transition from liquid to vapor or vapor to liquid takes place. Design or control of other separation processes such as distillation, absorption, and stripping also requires information on the conditions at which phase transitions occur and on the compositions of the resulting phases. This section outlines the required calculations for a relatively simple class of mixtures. 

Remove the ether by simple distillation or by evaporation on the steam bath under an aspirator tube. See Fig. 5 in Chapter 5 or Fig. 9 in Chapter 3 or use a rotary evaporator (Fig. 7 in Chapter 10). When evaporation ceases, add 2-3 g of anhydrous sodium sulfate to the residual oil and heat for about 5 min longer. Then decant the methyl benzoate into a 50-mL round-bottomed flask, attach a stillhead, dry out the ordinary condenser and use it without water circulating in the jacket, and distill. The boiling point of the ester is so high (199°C) that a water-cooled condenser is liable to crack. Use a tared 25-mL Erlenmeyer as the receiver and collect material boiling above 190°C. A typical student yield is about 7 g. See Chapter 36 for the nitration of methyl benzoate. 

Pervaporation is most competitive in situations where simple evaporation or distillation lacks separation power because of low volatility differences. It was first... 

A simple distillation involves applying heat to vaporize a liquid and then cooling the vapor until it condenses as a liquid. The separation of water from the salts in sea water is one example. See Figure 3-5, p. 24. The sea water is placed in a container called a still pot, or simply a pot, and heat is applied. The water will evaporate easily, but the salt will not and is left behind. However, the water will be lost unless something is done to collect it. A condenser is added to the system to cool the water vapor and condense it back to a liquid. The pure water then is collected in a container called a receiver. 

The first separation example is seawater desalination. Traditionally, desahnation was done by distillation or simple evaporation/condensation [55]. Today, thermally driven desalination has been largely replaced by the membrane process reverse osmosis. In reverse osmosis an applied pressure exceeding the osmotic pressure of the salt solution causes water to permeate through a dense membrane. Hydrated salt ions are relatively large compared to water and have a lower permeability through the membrane resulting in relatively salt-free water being collected as the reverse osmosis permeate. 

Procedure Put alcohol in 25-mL rb flask and add H2SO4. Mix, add stirbar, attach to fractional dist. apparatus. Heat with oil bath heating rate such that head temp, stays below 90 °C. Stop when 2.5 mL remain in rxn. flask. Put distillate in 25-mL Erlenmeyer and add 1-2 g K2CO3. Occasionally swirl mix. for 15 min and transfer liquid to 10-mL rb by decantation or pipet. Add stirbar and do simple distillation (no flames ) receiver must be close to drip tip of adapter to minimize losses by evaporation. Collect product at 80-85 °C (760 torr). 

Separate the Neutral Compound from the drying agent by decantation (Fig. 2.56) or gravity filtration through a cotton plug (Fig. 5.5) into a 100-mL round-bottom flask. Remove the solvent by simple distillation (Fig. 2.37). Alternatively, use rotary evaporation or one of the other techniques described in Section 2.29. Allow the residue to cool to room temperature to solidify, scrape the contents of the flask onto a piece of weighing paper to air-dry, and then transfer it to a dry. fared vial. 

Transfer the dried ethereal solution to a 50-mL round-bottom flask equipped for simple distillation and concentrate the solution by distillation. Alternatively, rotary evaporation or other techniques may be used to concentrate the solution. Transfer the residue to a 25- or 50-mL filter flask. 

Work-Up and Isoiation Transfer the reaction mixture to a small separatory funnel. Add 5 mL of water and separate the layers. Extract the aqueous layer with two separate 10-mL portions of diethyl ether. Wash the combined organic layers sequentially with two 10-mL portions of water and two 10-mL portions of saturated brine, and dry them over several spatula-tips full of anhydrous sodium sulfate. Add additional portions of anhydrous sodium sulfate if the liquid remains cloudy. Filter or decant the dried solution into a dry 50-mL round-bottom flask and remove the volatile solvents by simple distillation. Alternatively, rotary evaporation or other techniques may be used to remove the solvents. The final traces of solvents may be removed by attaching the flask to a vacuum source... 

Decant the solution into a 50-mL round-bottom flask and remove most of the dichloromethane by simple shortpath distillation cool the receiving flask in an ice-water bath. Alternatively, use rotary evaporation or other techniques to remove most of the dichloromethane. Using a Pasteur pipet to minimize material loss, transfer the crude product into a 10-mL round-bottom flask. Remove the last traces of dichloromethane from the crude product by connecting the flask to a vacuum source. Then continue the distillation using the shortpath apparatus fitted with a clean, tared receiving flask. Since the volume of product is likely to be only 1-2 mL. an accurate boiling point may be difficult to obtain, and all material that distills above 110-115 °C should be collected in order to obtain a reasonable yield. 

Decant about one-half of the ethereal solution into a 5-mL conical vial equipped for simple distillation and concentrate the solution to about half its original volume, removing the distillate from the Hickman stillhead as necessary. Allow the solution to cool below the boiling point, add the remainder of the dried ethereal extracts, and again concentrate the solution to about one-half its original volume. Alternatively, use rotary evaporation or other techniques to concentrate the solution. Cool the concentrated solution to room temperature. Once crystallization has begun, further cool the solution in an ice-water bath, and then collect the product 15 by vacuum filtration. Recrystallize it from 50% aqueous ethanol and air-dry the purified product. 

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