Attempted Separation of Isomeric Hexenes by Fractional Distillation

Abstract

Attempted Separation of Hexenes by Distillation 795 of magnitude of the number of plates required, but consideration of the holdup and the 30 to 1 reflux ratio actually used in these distillations would certainly increase the estimates considerably.9Consideration of Holdup and Reflux Ratio.-All the above computations are on the assumption that reflux was nearly total and that holdup was zero so that the conclusions are for maximum sharpness of separation and minimum plates required. No statement of the holdup in the Podbielniak-Simons-Taylor® column is given but it must be appreciable compared with the amount of any one component and quite large compared (9) Arthur Rose, L. M. Welshans and . H. Long, Ind. Eng.Che.m., 32, May (1940).with the amounts of the components present in small amount so that the separations involving these would be expected to be much less sharp than the above discussion indicates. SummaryCalculations have been made to show that a minimum of 400 or more theoretical plates are required for sharp separation of certain close boiling hexenes, and that the use of a fractionating column with a small number of theoretical plates can produce no appreciable separation in such cases even with low holdup and high reflux ratio.

Review of Olefin Isomerization

“…Goldwasser and Taylor (24) report extensive studies on the hexenes. Their methods of analyses are such that considerable doubt is cast on their results (59,87). An example of their results showed that alumina at 398°C.…”

“…Further, Rose (59) showed by calculation and Whitmore et al (87) by experimental evidence that it is impossible to separate many of the isomeric products of n-hexene by present methods of fractional distillation. Literature reports that are based on questionable analytical methods are reviewed in this paper only in the absence of data obtained by more credible methods.…”

Perforated Plate Columns for Analytical Batch Distillations

“…Stedman column and that the perforated plate column has a higher maximum reflux rate or capacity. Comparison with the helix-packed type of column (8) shows that the perforated plate column has a lower average holdup per theoretical plate per 100 ml. of reflux per minute.…”

“…from the data given in Tables I and II and Bragg's data (I) on the Stedman type packing which has been included for purposes of comparison. Similar data on columns of the helix-packed type (3,7,8) could not be calculated from the information given in the literature. Data on the Bruun column (2) were also omitted, since the operating holdup was not given for a specified reflux rate.…”

Efficient Low-Holdup Laboratory Column

“…Although the problem of devising such a column has been a common one throughout the history of organic chemistry, it has only been in the past few years that successful investigations have been carried out in this field. Of the several recent comprehensive articles concerning laboratory fractionation columns, those of Whitmore et al (11) and Podbielniak (8) are the most important, since these two articles contain a critical discussion of all recently developed fractionating columns.…”