Distillation columns Oldershaw

The ether extracts were separated into acidic and nonacidic fractions by extraction with a 10% aqueous sodium carbonate solution. The ether solutions of acidic and nonacidic fractions were dried over anhydrous sodium sulfate and subjected to a preliminary concentration using a 30-plate Oldershaw distillation column. The ether extracts from both fractions were concentrated to final volumes of 5 ml using a spinning band distillation apparatus. 

Geelen and Wijffels (19) investigated the reaction of vinyl acetate with stearic acid in a distillation column to form vinyl stearate and acetic acid. A modified form of the McCabe-Thiele diagram was employed to obtain the number of theoretical plates for a given conversion. This was tested experimentally using a bubble-cap Oldershaw column for the distillation reactor followed by a packed column for separation of top products (vinyl acetate acetic acid). Theoretical considerations agreed reasonably well with experimental findings. 

Example 8.3.1 Laboratory sieve-plate crossflow distillation columns, called Oldershaw columns, having diameters around 2.54 cm to 5.08 cm, have been found to yield plate efficiencies which generally agree with those in columns larger in diameter in the range of 45-120 cm (Fair et ai, 1983). The plates in Oldershaw columns are generally well-mixed. Consider now the benezene-toluene distillation illustrated in Examples 8.1.11 and 8.1.12, where benzene-toiuene = 2.5. The value of E v for this System in an Oldershaw column is 0.6. 

Oldershaw, C. F. (1941) Ind. Eng. Chem. (Anal, ed.) 13, 265. Perforated plate columns for analytical batch distillations. 

As might be expected, the vapour phase may offer the controlling resistance to mass transfer in high pressure distillations. Values for tray efficiencies at elevated pressure are scarce [23, 24]. The prediction of tray efficiency may be approached in several ways. One way is to utilize field performance data taken for the same system in very similar equipment. Unfortunately such data are seldom available. When they are available, and can be judged as accurate and representative, they should be used as a basis for efficiency specification [25], Another way is to utilize laboratory-or pilot-plant efficiency data. For example a small laboratory-Oldershaw tray-column can be used with the same system. Of course, the results must be corrected for vapour-and liquid mixing effects to obtain overall tray efficiencies for large-scale design [26], Another approach is the use of empirical or fundamental mass-transfer models [27-30],... 

FIG. 14-44 An Oldershaw column. (From H. Z. Kister, Distillation Design, copyright 1992 by McGraw-Hill reprinted by permission.)... 

Uses of Oldershaw columns to less conventional systems and applications were described by Fair, Reeves, and Seibert [Topical Conference on Distillation, AIChE Spring Meeting, New Orleans, p. 27 (March 10-14, 2002)]. The applications described include scale-up in the absence of good VLE, steam stripping efficiencies, individual component efficiencies in multicomponent distillation, determining component behavior in azeotropic separation, and foam testing. 

GC-Mass Spectrometry. The ether extracts were concentrated using an Oldershaw column with 30 theoretical plates followed by a 200-plate spinning band distillation apparatus (Kontes Glass Co., Vineland,... 

Direct Scale-Up of iMboratory Distillation Efficiency Measurements It has been found by Fair, Null, and Bolles [Ind. Eng. Chem. Process Des. Dev., 22,53 (1983)] that efficiency measurements in 25- and 50-mm- (1- and 2-in-) diameter laboratory Oldershaw columns closely approach the point efficiencies [Eq. (14-129)] measured in large sieve-plate columns. A representative comparison of scales of operation is shown in Fig. 14-37. Note that in order to achieve agreement between efficiencies it is necessary to ensure that (1) the systems being distilled are the same, (2) comparison is made at the same relative approach to the flood point, (3) operation is at total reflux, and (4) a standard Oldershaw device (a small perforated-plate column with downcomers) is used in the laboratory experimentation. Fair et al. made careful comparisons for several systems, utilizing as large-scale information the published efficiency studies of Fractionation Research, Inc. 

J.R. Fair, B.E. Reeves and A.F. Seibert, The Oldershaw column Useful for solving distillation problems, Proc. AIChE Meeting, New Orleans, March... 

Perfluorobutyric acid (heptafluorobutyric acid) [375-22-4] M 214.0, m -17.5 , b 120 /735mm, df 1.651, Up 1.295, pK -0.17. Fractionally distil the acid twice in an Oldershaw column (p 10) with an automatic vapour-dividing head, the first distillation being in the presence of cone H2SO4 as a drying agent. (Take care with the hot acid.) [Beilstein 2IV 810.]... 

Extractive Distillation of Liquid-Liquid Extract. The extract portion was fed into a continuous still, 2 inches in diameter, made up of the following sections in ascending order a 100-ml capacity reboiler, a vacuum-jacketed, silvered column 3 feet long containing helipak, an intermediate feed section, and a vacuum-jacketed silvered 15-plate Older-shaw column, another feed section and a 10-plate Oldershaw column, topped off with a solenoid operated liquid dividing reflux head. The extract entered the still through a preheater at the lower feed section. The reflux ratio and boil-up rate were adjusted to fix the bottoms compo-... 

The fact that the properties of the substance undergoing distillation have an appreciable influence on the pressure drop is apparent from the curves shown in Fig. 108 [229] and from Table 33 [200]. The data listed in the latter table were determined in an Oldershaw sieve-plate column (28 mm diameter) with 30 actual plates. 

It is difficult to detect foaming in a works-scale column and pilot and laboratory scale work should be done on a tray column if it is intended that the full scale job will be done on trays. An Oldershaw glass column which allows observation of what is happening inside the column is useful in this respect. In a batch distillation the surface tension of column contents may alter throughout the batch. 

Hirata (22) also studied the behaviour of an Oldershaw column, a packed column and a sieve-tray column as distillation reactors for the esterification of ethanol and acetic acid. He found reflux ratio to be an important factor affecting not only separation but also conversion. 

For very complex mixtures, the entire distillation design can be done using the Older-shaw column by changing the number of trays and the reflux rate until a combination that does the job is found. Since the commercial column will have an overall efficiency equal to or greater than that of the Oldershaw column, this combination will also work in the commercial column. This approach eliminates the need to determine vapor-liquid equilibrium (VLE) data (which maybe quite costly), and it also eliminates the need for complex calculations. The Oldershaw column also allows one to observe foaming problems TKister. 19901. 

Copolymerization. 2,3-Dimethy1-1,3-butadiene (Aldrich Chemical Company) was purified by distillation through a 40 plate Oldershaw column, bp 69°, at a 5/1 reflux ratio. G.C. analysis indicated 99.9% purity. Copol3mierization was carried out in a 3.79 1 continuous flow well-stirred reactor at -98°. Separate streams of monomers and AICI3 in methyl chloride were fed to the reactor. Reactant concentrations in the combined feed were (mol/L) ISB, 3.15 DMB, 0.107 AICI3, 0.003. Monomer conversion in the reactor was 88%. The rubber product was isolated by precipitation with 2-propanol/ acetone, dried on a hot rubber mill, then a vacuum oven. The sample used in this work had an Mn (membrane osmometry) of 200000 and a M (diisobutylene, 20°) of 550000. 

The sieve tray developed by Oldershaw [22, 23] is recognized as the common distillation tray to be used for representing the point efficiency. The construction parameters are given in Table 4.2, and the column is shown in Fig. 4.26. The simulation of which is the convenient way to find the point efficiency of the corresponding separating system. 

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