True atmospheric distillation

Feed analyses in terms of component concentrations are usually not available for complex hydrocarbon mixtures with a final normal boihng point above about 38°C (100°F) (/i-pentane). One method of haudhug such a feed is to break it down into pseudo components (narrow-boihng fractions) and then estimate the mole fraction and value for each such component. Edmister [2nd. Eng. Chem., 47,1685 (1955)] and Maxwell (Data Book on Hydrocarbons, Van Nostrand, Princeton, N.J., 1958) give charts that are useful for this estimation. Once values are available, the calculation proceeds as described above for multicomponent mixtures. Another approach to complex mixtures is to obtain an American Society for Testing and Materials (ASTM) or true-boihng point (TBP) cui ve for the mixture and then use empirical correlations to con-strucl the atmospheric-pressure eqiiihbrium-flash cui ve (EF 0, which can then be corrected to the desired operating pressure. A discussion of this method and the necessary charts are presented in a later subsection entitled Tetroleum and Complex-Mixture Distillation. ... 

In addition to the whole crude oil tests performed as part of the inspection assay, a comprehensive or full assay requires that the crude be fractionally distilled and the fractions characterized by the relevant tests. Fractionation of the crude oil begins with a true boiling point (TBP) distillation using a fractionating column with an efficiency of 14-18 theoretical plates and operated at a reflux ratio of 5 1 (ASTM D-2892). The TBP distillation may be used for all fractions up to a maximum cut point of about 350°C atmospheric equivalent temperature (AET), but a low residence time in the still (or reduced pressure) is needed to minimize cracking. 

H -I- HD is the only mixture of compounds of hydrogen that has a separation factor as favorable as in conventional industrial distillation. In this case, however, the true separation factor is less favorable than here calculated from the vapor-pressure ratio, because of nonidealities in gaseous and liquid mixtures of hydrogen and HD. Moreover, it is desirable to operate above atmospheric pressure, to preclude in-leakage of air. Under practical conditions, at... 

A nearly equimolar mixture of ethylene and ethane is to be separated. The stream is available at about 3 atm, and high-purity (greater than 99%) ethylene is desired at greater than 95% recovery. An adsoibent with reasonable selectivity has been found which will desorb ethylene either at pressures well below atmospheric, or in the presence of a Cj hydrocaibon or heavier, or in the presence of various inert gases. Ethylene in turn cannot displace hydrocarbons with more than four carbons, however. In Table 12.6-1, the tme statements are 1,6, 7, and 9. Statement 9 is considered to be true because ciyogenic distillation would be required to separate the ethylene from the inert or purge material. In Table 12.6-2 we see that PSA is the most likely choice, using vacuum desorption. 

Assay analyses of whole crudes are done by combining an atmospheric and vacuum distillation run. These two runs when combined will provide a TBP (True Boiling Point Curve). While these batch distillation methods are labor intensive, taking between three to five days, they allow the collection of distillation fractions that can be utilized for testing. While each of the distillations techniques have been standardized by ASTM, cut schemes tend to mimic Refinery product classifications and there is no standardization of the individual inspection formats. Each corporation tends to perform both physical and chemical testing that best meet the needs of their refining operations and product suites. 

Essential oil. Traditionally, essential oil is recovered from plant materials by steam distillation at atmospheric pressure. This was also true of hops until about 1980. Clearly, prolonged heating at 100°C in water or steam is likely to damage some of the more labile constituents of the essential oil and it had to be acknowledged that the oil so recovered from hops differed in aroma from fresh, dried hops. 

Distillation of the leaves in the Straits Settlements is carried out in stills with htlse-bottom cylinders, usually with steam at a pressure of about 1 3 atmospheres, when a yield of about 1 5 per cent, is obtained. By using higher pressure a larger yield of oil results, but the quality is inferior. By very prolonged distillation up to 2 6 per cent, has been obtained in the native distilleries, but in Europe, where most of the leaves are distilled for perfumery purposes, a yield of 4 per cent, is obtained from the true patchouli leaves, and of about 1 to 1 5 per cent, from the Java leaves. There appears to be no doubt that the question of fermentation of the leaves has an important bearing on the yield of oil. 

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