Evaporation distillation compared with

The efficiency of the SCC is illustrated in comparison with a traditional distillation-based essence recovery unit in Table 18.2. One can see that the aroma volatiles are preferentially stripped from the infeed in the SCC compared with the situation in a single-stage evaporator. Thus, highly concentrated aroma isolates can be produced. Flavortech [22] noted that essences of 1,500-fold maybe produced from juices if a double pass is used (the infeed is the flrst pass and the acquired essence the second pass). 

A question that arises in connection with distillation processes is How does a vapor-compression process compare with a multiple-effect evaporation process on the basis solely of energy cost This is readily answered as follows. The work of compression as kilowatt-hours per 1000 gallons is given by a specific form of Equation VIII. 134... 

In chemical process units such as reactors, distillation columns, evaporators, and heat exchangers, shaft work and kinetic and potential energy changes tend to be negligible compared with heat flows and internal energy and enthalpy changes. Energy balances on such units therefore usually omit the former terms and so take the simple form Q = U (closed system) or Q = AH (open system),... 

Helmholtz calculated the work done in the isothermal distillation of the solvent into the solution. The reversible dilution by dv of any solution containing in the volume v 1 mol. of solute and X mols. of solvent can be performed as follows. The quantity of pure solvent (dx mols.) which, when mixed with the solution, increases its volume by dv, is evaporated reversibly and isothermally at the temperature T and the vapour pressure jpQ. The vapour is then allowed to expand until its pressure has become equal to the lower vapour pressure p of the solution, and is then condensed so as to dilute the solution by dv. The quantities of work done in the evaporation and in the condensation are practically equal to one another, provided that the saturated vapour obeys the gas laws, and provided that the volume of the hquid is neghgible compared with the volume of the vapour. Hence the total work done dw is equal to the work done by the vapour in expanding from to p. 

At first, a slow reaction is considered. Slow means that the reaction rate is slow, compared with the residence times typical for separation equipment such as distillation trays. For residence time reasons a stirred vessel or, better, a cascade of stirred vessels is needed. Each vessel is supplied with energy to evaporate the component to be separated. If the relative volatility of this component is very high, a one-stage evaporation is sufficient. At a lower relative volatility, the separation... 

Because of the high temperatures used, it might be imagined that superheated water processes were costly in energy terms. However, this is not the case because water stays as a liquid and the latent heat of evaporation is not involved. As an example, we compare superheated water extraction with steam distillation. A greater mass of superheated water may be needed for a given mass of material to be extracted. However, only 505 kj kg is required to heat Hquid water from 30°C to 150°C, compared with 2550 kJ kg required to convert water at 30°C to steam at 100°C [8]. Moreover, it is relatively easy to recycle the heat in a superheated water process by... 

E4. A nonvolatile solute is dissolved in 1.0 kmol of methanol. We wish to switch the solvent to water. Because the solution is already concentrated, a first batch distillation to concentrate the solution is not required. We desire to have the solute in 1.0 kmol of solution that is 99.0 mol% water and 1.0 mol% methanol. This can be done either with a constant-level batch distillation or by diluting the mixture with water and then doing a sinple batch distillation. VLE data (ignore the effect of the solute) are in Table 2-7. Dilute the original pure methanol (plus solute) with water and then do a simple batch distillation with the goal of having Wfjnai = 1.0 and = 0.01. Find the moles of water added and the moles of water evaporated during the batch distillatiom Compare with constant-level batch distillation in Problem 9.D17. 

Membrane distillation (MD) has been successfully applied and demonstrated for effective removal of ethanol from the fermentation broth. In MD, volatile feed components are evaporated through air-fiUed pores of a hydrophobic membrane. In the ethanol production, the aqueous solution containing ethanol is heated and vapors are formed, which go through the porous hydrophobic membrane that favors the transport of ethanol as compared with water vapor. Thus, the membranes in MD separate two aqueous solutions differing in temperature and composition. The driving force for the mass transfer through the membrane is the gradient of partial pressure caused by the temperature difference across the membrane. 

In reactions 9.90 and 9.91, the precursor is the di(trifluoro-methylsulfonyl)amido salt of the metal rather than a halide as in eqs. 9.88 and 9.89. If M3 is reacted with [BMpyr][N(S02CF3)2] (compare with eq. 9.90), the product is [BMpyr]4[Prl6][N(S02CF3)2] containing the octahedral ion and a non-coordinated [N(S02CF3)2] ion. Separation of products from ionic liquid solvents is facile if the product is insoluble (separation is by filtration or removal of the solvent by cannula). However, if the product is soluble, separation may be difficult since the low volatility of ionic liquids prevents their ready evaporation. If the product is volatile, it can be separated by distillation because the ionic liquid has such a low vapour pressure. 

The most convenient way of separating phenols from the bulk of the material excreted in urine is steam distillation. Comparatively few compounds, however, are volatile in steam and a more general method which can be applied to almost all simple phenols is to extract the hydrolywd urine with ether in a continuous extractor for several hours. By adjusting the pH of the urine, it may be possible to separate phenols from phenolic acids a pH of 7.8 usually serves to prevent extraction of the acids while it permits extraction of other phenols. The phenolic acids can be subsequently extracted if the residual urine is adjusted to pH 1 (cf. Schmidt (80)). Tests may then be applied to the residue left after evaporation of the ether. If the phenols are liable to oxidation by atmospheric oxygen, e. g., aminophe-nols, the ether should be removed in vacuo or in a stream of nitrogen. The ether extract can be fractionated by conventional methods. Chromatographic separation of an ether extract on columns of powdered cellulose often provides a convenient method for the separation of mixtures of phenolic compounds (Section 11,4). 

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