Separations processes example

Solubilitiesattemperaturesand pressures above the critical values of the solvent liave important applications for supercritical separation processes. Examples are extraction of caffeine from coffee beans and separation of asplraltenes from heavy petroleum fractions. For a typical solid/vapor equilibrium (SVE) problem, tire solid/vapor saturation pressure P is very small, and the saturated vapor is for practical purposes an ideal gas. Hence 0 for pure solute vapor at this pressure is close to unity. Moreover, exceptfor very low values of the system pressure P, the solid solubility yj is small, and can be approximated by j, the vapor-phase fugacity coefficient of the solute at infinite dilution. Finally, since is very small, the pressure difference P — in the Poyntingfactor is nearly equal to P at any pressure where tins factor... 

Table 1-5. Selected thermal separation processes. Examples of the Gibb s phase rule. 

Topcoat (PVD technology) A film or coating that is put on a deposited film structure, generally by a separate process. Example Lacquer coating on a deposited gold film to provide abrasion resistance. 

The value of many chemical products, from pesticides to pharmaceuticals to high performance polymers, is based on unique properties of a particular isomer from which the product is ultimately derived. Eor example, trisubstituted aromatics may have as many as 10 possible geometric isomers whose ratio ia the mixture is determined by equiHbrium. Often the purity requirement for the desired product iacludes an upper limit on the content of one or more of the other isomers. This separation problem is a compHcated one, but one ia which adsorptive separation processes offer the greatest chances for success. 

Fluidized-bed appHcations in the 1990s may be separated into catalytic reactions, noncatalytic reactions, and physical processes. Examples of fluidized-bed appHcations include the foUowing ... 

The early developments of solvent processing were concerned with the lubricating oil end of the cmde. Solvent extraction processes are appHed to many usefiil separations in the purification of gasoline, kerosene, diesel fuel, and other oils. In addition, solvent extraction can replace fractionation in many separation processes in the refinery. For example, propane deasphalting (Fig. 7) has replaced, to some extent, vacuum distillation as a means of removing asphalt from reduced cmde oils. 

An enrichment is defined as a separation process that results in the increase in concentration of one or mote species in one product stream and the depletion of the same species in the other product stream. Neither high purity not high recovery of any components is achieved. Gas enrichment can be accompHshed with a wide variety of separation methods including, for example, physical absorption, molecular sieve adsorption, equiHbrium adsorption, cryogenic distillation, condensation, and membrane permeation. 

Reversible Processes. Distillation is an example of a theoretically reversible separation process. In fractional distillation, heat is introduced at the bottom stiUpot to produce the column upflow in the form of vapor which is then condensed and turned back down as Hquid reflux or column downflow. This system is fed at some intermediate point, and product and waste are withdrawn at the ends. Except for losses through the column wall, etc, the heat energy spent at the bottom vaporizer can be recovered at the top condenser, but at a lower temperature. Ideally, the energy input of such a process is dependent only on the properties of feed, product, and waste. Among the diffusion separation methods discussed herein, the centrifuge process (pressure diffusion) constitutes a theoretically reversible separation process. 

Transfer of material between phases is important in most separation processes in which two phases are involved. When one phase is pure, mass transfer in the pure phase is not involved. For example, when a pure liqmd is being evaporated into a gas, only the gas-phase mass transfer need be calculated. Occasionally, mass transfer in one of the two phases may be neglec ted even though pure components are not involved. This will be the case when the resistance to mass transfer is much larger in one phase than in the other. Understanding the nature and magnitudes of these resistances is one of the keys to performing reliable mass transfer. In this section, mass transfer between gas and liquid phases will be discussed. The principles are easily applied to the other phases. 

Process Unit or Batch Unit A process unit is a collection of processing equipment that can, at least at certain times, be operated in a manner completely independent from the remainder of the plant. A process unit normally provides a specific function in the production of a batch of product . For example, a process unit might be a reactor complete with all associated equipment (jacket, recirculation pump, reflux condenser, and so on). However, each feed preparation tank is usually a separate process unit. With this separation, preparation of the feed for the next batch can be started as soon as the feed tank is emptied for the current batch. 

However, total quantities of hazardous materials do not, on their own, provide an entirely reliable measure of potential hazard. It is more useful to consider quantities of material within sections of the plant that can be isolated. The amount of material within these individual plant sections usually represents the largest credible release that could occur. Some examples of plant sections that may be isolated include tank farms, unloading racks, and separate process buildings. 

When ionic liquids are used as replacements for organic solvents in processes with nonvolatile products, downstream processing may become complicated. This may apply to many biotransformations in which the better selectivity of the biocatalyst is used to transform more complex molecules. In such cases, product isolation can be achieved by, for example, extraction with supercritical CO2 [50]. Recently, membrane processes such as pervaporation and nanofiltration have been used. The use of pervaporation for less volatile compounds such as phenylethanol has been reported by Crespo and co-workers [51]. We have developed a separation process based on nanofiltration [52, 53] which is especially well suited for isolation of nonvolatile compounds such as carbohydrates or charged compounds. It may also be used for easy recovery and/or purification of ionic liquids. 

Example 8-19 Continuous Steam Flash Separation Process Separation of Non-Volatile Component from Oi anics... 

Batch with Constant Reflux Ratio, 48 Batch with Variable Reflux Rate Rectification, 50 Example 8-14 Batch Distillation, Constant Reflux Following the Procedure of Block, 51 Example 8-15 Vapor Boil-up Rate for Fixed Trays, 53 Example 8-16 Binary Batch Differential Distillation, 54 Example 8-17 Multicomponent Batch Distillation, 55 Steam Distillation, 57 Example 8-18 Multicomponent Steam Flash, 59 Example 8-18 Continuous Steam Flash Separation Process — Separation of Non-Volatile Component from Organics, 61 Example 8-20 Open Steam Stripping of Heavy Absorber Rich Oil of Light Hydrocarbon Content, 62 Distillation with Heat Balance,... 

The area of interest covered by this paper is limited to processes in which chemical conversion occurs, as in the processes noted above. Gas-liquid-particle processes in which a gaseous phase is created by the chemical reaction between a liquid and a solid (for example, the production of acetylene by the reaction between water and carbide) are excluded from the review. Also excluded are physical separation processes, such as flotation by gas-liquid-particle operation. Gas absorption in packed beds, another gas-liquid-particle operation, is not treated explicitly, although certain results for this operation must necessarily be referred to. 

It may finally be pointed out that certain separation processes in addition to packed-bed gas absorption are gas-liquid-particle operations. Examples are flotation and a special type of fluidized crystallization process (Z2). 

For multielectron-transfer (reversible) processes, the cyclic voltammogram consists of several distinct peaks if the E° values for the individual steps are successively higher and are well separated. An example of such a mechanism is the six-step reduction of the fullerenes C60 and C70 to yield the hexaanion products and C7q. Such six successive reduction peaks are observed in Figure 2-4. 

Chemical forces are normally irreversible in nature (at least in chromatography) and thus, the distribution coefficient of the solute with respect to the stationary phase is infinite or close to infinite. Affinity chromatography is an example of the use of chemical forces in a separation process. The stationary phase is formed in such a manner that it will chemically interact with one unique solute present in the sample and thus, exclusively extract it from the other materials... 

The second use of Equations (2.36) is to eliminate some of the composition variables from rate expressions. For example, 0i-A(a,b) can be converted to i A a) if Equation (2.36) can be applied to each and every point in the reactor. Reactors for which this is possible are said to preserve local stoichiometry. This does not apply to real reactors if there are internal mixing or separation processes, such as molecular diffusion, that distinguish between types of molecules. Neither does it apply to multiple reactions, although this restriction can be relaxed through use of the reaction coordinate method described in the next section. 

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