Process distillation

The second class of distillation operation using an extraneous mass-separating agent is extractive distillation. Here, the extraneous mass-separating agent is relatively involatile and is known as a solvent. This operation is quite different from azeotropic distillation in that the solvent is withdrawn from the column bottoms and does not form an azeotrope with any of the components. A typical extractive distillation process is shown in Fig. 3.11. ... 

When a mixture contains components with a broad range of volatilities, either a partial condensation from the vapor phase or a partial vaporization from the liquid phase followed by a simple phase split often can produce an effective separation. This is in essence a single-stage distillation process. However, by its very nature, a single-stage separation does not produce pure products hence further separation of both liquid and vapor streams is often required. 

Example 6.1 The flowsheet for a low-temperature distillation process is shown in Fig. 6.19. Calculate the minimum hot and cold utility requirements and the location of the pinch assuming AT, m = 5°C. 

TABLE 6.4 Stream Data for Low-Temperature Distillation Process... 

Example 6.6 Determine the refrigeration requirements for the low-temperature distillation process from Example 6.1 shown in Fig. 6.19 for AT , = 5 C. 

Set-up for vac-distillation. She wraps the flask and still head with aluminum foil to act as an insulator. Speeds up the distillation process. Begin to heat the DCM extraction slowly under maximum... 

This carbon dioxide-free solution is usually treated in an external, weU-agitated liming tank called a "prelimer." Then the ammonium chloride reacts with milk of lime and the resultant ammonia gas is vented back to the distiller. Hot calcium chloride solution, containing residual ammonia in the form of ammonium hydroxide, flows back to a lower section of the distiller. Low pressure steam sweeps practically all of the ammonia out of the limed solution. The final solution, known as "distiller waste," contains calcium chloride, unreacted sodium chloride, and excess lime. It is diluted by the condensed steam and the water in which the lime was conveyed to the reaction. Distiller waste also contains inert soHds brought in with the lime. In some plants, calcium chloride [10045-52-4], CaCl, is recovered from part of this solution. Close control of the distillation process is requited in order to thoroughly strip carbon dioxide, avoid waste of lime, and achieve nearly complete ammonia recovery. The hot (56°C) mixture of wet ammonia and carbon dioxide leaving the top of the distiller is cooled to remove water vapor before being sent back to the ammonia absorber. 

The cmde product from the gasifier contains CO2 and H2S, which must be removed before the gas can be used to produce chemicals. The Rectisol process is used to remove these contaminants from the gas. This is accompHshed by scmbbing the product with cold methanol which dissolves the CO2 and H2S and lets the H2 and CO pass through the scmbber. The H2S is sent to a Claus sulfur plant where over 99.7% of the sulfur in the coal feed is recovered in the form of elemental sulfur. A portion of the clean H2 and CO are separated in a cryogenic distillation process. The main product from the cryogenic distillation is a purified CO stream for use in the acetic anhydride process. The remaining CO and hydrogen are used in the methanol plant. 

Fig. 9. Methanol-to-olefins (MTO) and Mobil olefins-to-gasohne (MOGD) and distillate process schematic.

Essential Oils. Essential oils are produced by distillation of flowers, leaves, stems, wood, herbs, roots, etc. Distillations can be done directly or with steam. The technique used depends mosdy on the desired constituents of the starting material. Particular care must be taken in such operations so that undesired odors are not introduced as a result of pyrolytic reactions. This is a unique aspect of distillation processing in the flavor and fragrance industry. In some cases, essential oils are obtained by direct expression of certain fmits, particular of the citms family. These materials maybe used as such or as distillation fractions from them (see Oils, essential). 

Physicochemical relationships are such that soHd potassium chloride can be converted to soHd potassium nitrate ia a one-stage operation of the simplest kiad. The conversion takes place ia a stirred reaction system (Fig. 10). The overall separation is analogous to a rectification and stripping operation ia a distillation process. 

Subsequent separation of this solvent imposes substantial capital and operating cost penalties. A Bayer AG patent (37) claims use of a solvent in which DNT is soluble, but in which the TDA is practically insoluble. This allows separation and recycle of the solvent to the reactor without any distillation process. 

Lower Pressure. Usually, relative volatdity increases as pressure drops. For some systems, a 1% drop in absolute pressure cuts the requited reflux by 0.5%. Again, if operating at reduced pressure looks promising, the process can be evaluated by simulation. In a complete study of distillation processes, other questions that need to be asked include. Is the separation necessary Is the purity necessary Are there any recycles that could be eliminated Can the products be sent directly to downstream units, thereby eliminating intermediate heating and cooling ... 

Distillation processes typically reduce the IDS concentration to levels weU below the required specifications. Because the product water from the two processes is combined, the RO process can produce water at higher I DS concentrations and stiU meet the potable water specifications. In addition, the power produced from the MSF process can be used in the RO process, cutting energy costs. 

Japan, Canada, and the United States accounted for 70% of the 1995 estimated world production of 2000 t (Table 5). At least 100 t of selenium was also available to Western markets from the former Soviet bloc. Selenium production is expected to rise in South America, particularly Chile, as the copper industry continues rapid expansion. A considerable amount of unrefined selenium is also shipped to Chile and the Philippines for conversion to final commercial product by either hydrometaHurgical or distillation processes. 

Electrolytic and distillation processes are used to produce primary slab zinc at smelters from ores and concentrates, whereas redistillation is used to recover zinc from secondary zinc materials at both primary and secondary smelters (see Table 13) (64,65). In 1965, neady 60% of the primary slab zinc was manufactured by the distillation process. However, in 1975, electrolytic slab zinc became dominant and by 1996 its share increased to 78%. 

Pure zirconium tetrachloride is obtained by the fractional distillation of the anhydrous tetrachlorides in a high pressure system (58). Commercial operation of the fractional distillation process in a batch mode was proposed by Ishizuka Research Institute (59). The mixed tetrachlorides are heated above 437°C, the triple point of zirconium tetrachloride. AH of the hafnium tetrachloride and some of the zirconium tetrachloride are distiUed, leaving pure zirconium tetrachloride. The innovative aspect of this operation is the use of a double-sheU reactor. The autogenous pressure of 3—4.5 MPa (30—45 atm) inside the heated reactor is balanced by the nitrogen pressure contained in the cold outer reactor (60). However, previous evaluation in the former USSR of the binary distiUation process (61) has cast doubt on the feasibHity of also producing zirconium-free hafnium tetrachloride by this method because of the limited range of operating temperature imposed by the smaH difference in temperature between the triple point, 433°C, and critical temperature, 453°C, a hafnium tetrachloride. 

Generally, most asphalts are 79—88 wt % C, 7—13 wt % H, trace-8 wt % S, 2—8 wt % O, and trace-3 wt % N (Table 7). Trace metals such as iron, nickel, vanadium, calcium, titanium, magnesium, sodium, cobalt, copper, tin, and 2inc, occur in cmde oils. Vanadium and nickel are bound in organic complexes and, by virtue of the concentration (distillation) process by which asphalt is manufactured, are also found in asphalt. 

SourM sh. Sour mash is made with a lactic culture and not less than 20% stillage added back to the fermentor and fermented for at least 72 h. Spirits. Spirits are distilled spirits including all singular whiskeys, gin, brandy, mm, cordials, and others made by a distillation process for nonindustrial use. 

Within each type of distilled spidts, wide vadations of flavor can be achieved by the type and amount of starting grains or other fermentable matedals, methods of preparation, types of yeasts, fermentation conditions, distillation process, maturation time and temperature, blending, and use of new technologies such as membrane separation. 

Whole grains means grains of cereals from which no part has been intentionally removed. The unique taste characteristics and smokey flavor of Scotch is developed from peat used in the whisky production process. The character and amount of peat used in malting the barley have a critical affect on the flavor intensity of the final product. The aroma of the burning peat is absorbed by the barley malt and is carried through the distillation process. 

Extractive distillation, using similar solvents to those used in extraction, may be employed to recover aromatics from reformates which have been prefractionated to a narrow boiling range. Extractive distillation is also used to recover a mixed ben2ene—toluene stream from which high quaUty benzene can be produced by postfractionation in this case, the toluene product is less pure, but is stiU acceptable as a feedstock for dealkylation or gasoline blending. Extractive distillation processes for aromatics recovery include those Hsted in Table 4. 

Separation and Purification. Separation and purification of butadiene from other components is dominated commercially by the extractive distillation process. The most commonly used solvents are acetonitrile and dimethylformarnide. Dimethylacetamide, furfural, and... 

Table 7. Distillation Process Requirements for the Production of Deuterium ...

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