Distillation theory,

D. B. Van Dongen, Distillation ofMc otropic Mixtures The Application of Simple-Distillation Theory to Design of Continuous Trocesses, Ph.D. dissertation. University of Massachusetts, Amherst, 1983. 

Solute equilibrium between the mobile and stationary phases is never achieved in the chromatographic column except possibly (as Giddings points out) at the maximum of a peak (1). As stated before, to circumvent this non equilibrium condition and allow a simple mathematical treatment of the chromatographic process, Martin and Synge (2) borrowed the plate concept from distillation theory and considered the column consisted of a series of theoretical plates in which equilibrium could be assumed to occur. In fact each plate represented a dwell time for the solute to achieve equilibrium at that point in the column and the process of distribution could be considered as incremental. It has been shown that employing this concept an equation for the elution curve can be easily obtained and, from that basic equation, others can be developed that describe the various properties of a chromatogram. Such equations will permit the calculation of efficiency, the calculation of the number of theoretical plates required to achieve a specific separation and among many applications, elucidate the function of the heat of absorption detector. 

The lack of satisfactory solvent recovery methods prior to 1930 prevented the use of selective solvents more suitable for lubricating oils. The major part of any solvent extraction plant is its complex solvent recovery system. Chemical engineering s contributions to distillation theory and process design resulted in the development of efficient solvent recovery techniques. In 1933, as illustrated by Figure 3, large commercial plants were... 

The term plate height comes from distillation theory. Some high-performance distillation columns contain discrete units called plates, in which liquid and vapor equilibrate with each other. As a teenager, A. J. R Martin, coinventor of partition chromatography, built distillation columns in discrete sections from coffee cans. (We don t know what he was distilling ) When he formulated the theory of partition chromatography, he adopted terms from distillation theory. 

Separations that take place in a chromatographic column are very similar to other types of separation, and it is for this reason that we will cover several of the more important separation techniques. A chromatographic column may be likened to a distillation column in many respects in fact, some of the terminology in chromatography is taken from distillation theory. 

SEPARATION FACTOR. The reader will recall that the separation factor, a, in Section 2.1.4, is the same as the relative volatility term used in distillation theory. In 1959, Purnell (32,33) introduced another separation factor (S) term to describe the efficiency of a column. It can be used very conveniently to describe efficiency of open tubular columns ... 

Distillation Theory and Practice—an Intensive Course, University of New South Wales/University of Sydney, August 9-11,1977. 

A key physical property in distillation theory is the vapor pressure. Each pure component has a characteristic vapor pressure at a particular temperature, and vapor pressure increases with temperature and generally with a reduction in molecular weight. Vapor pressure is defined as the pressure at which a liquid and its vapor can coexist in equilibrium at a particular temperature. 

Petlyuk, Distillation Theory and its Applications to Optimal Design of Separation Units Rao and Nott, An Introduction to Granular Flow... 

What is H anyway The original interpretation, taken from distillation theory, was height equivalent to a theoretical plate, or HETP. We have seen that this concept was inadequate, and the preceding discussion of the van Deemter equation has presented it as a measure of the extent of spreading of an analyte zone as it passes through a column. Thus, a more appropriate term might be column dispersivity. In fact, another, independent approach to the theory of chromatography defines H as... 

In the form of equation (2-8) the definition of // is exactly identical to the plate height as it evolved from the distillation theory and was brought to chromatography by Martin and Synge [2]. If // is the theoretical plate height, we can determine the total number of the theoretical plates in the column as... 

The plate theory assumes that the solute is in equilibrium with the mobile and stationary phases. Due to the continuous exchange of solute between the two phases as it progresses down the column, equilibrium between the phases can never actually be achieved. To accommodate this nonequilibrium condition, a technique originally introduced in distillation theory is adopted, where the column is considered to be divided into a number of cells or plates. Each cell is allotted a finite length and, thus, the solute spends a finite time in each cell. The size of the cell is such that the solute is considered to have sufficient residence time to achieve equilibrium with the two phases. Thus, the smaller the plate, the more efficient the solute exchange between the two phases and, consequently, the more plates there are in the column. As a result, the number of theoretical plates contained by a column has been termed the column efficiency. The plate theory shows that the peak width (the dispersion or peak spreading) is inversely proportional to the square root of the efficiency and, thus, the higher the efficiency, the narrower the peak. Consider the equilibrium that is assumed to exist in each plate then... 

F.B. Petlyuk, 2004, Distillation Theory and Its Applieation of Optimal Design of Separation units, Cambridge series in ehemical engineering... 

F. Petl)aik, Distillation Theory and Its Application to Optimal Design of Separation Units, Cambridge University Press UK, 2004. ISBN 9780521820929. 

Savarit Arts et metiers, Definition of Distillation, Simple Discontinuous Distillation, Theory and Operation of Distillation Column, and Exhausting and Concentrating Columns for Liquid and Gaseous Mixtures and Graphical Methods for Their Determination, (1922), pp. 65, 142, 178, 241, 266, 307. 

The peak width is obtained from the intersection of the baseline with the tangents drawn through the inflection points on the sides of each peak. The theoretical-plate model, a carryover from distillation theory, assumes a column to be made up of a series of plates. At each plate, one equilibrium distribution of solute between the mobile phase and stationary phase occurs. Thus, the higher the value of N, the more chance there is for separation to occur (that is, the better the separating power of the column). 

The nomenclature also reflects the origin of the concept the distillation theory of gas chromatography. In this concept, a certain length of the chromatographic column was occupied by a theoretical plate. This length was the height equivalent to the theoretical plate. If we divide the column length... 

Petl)nik, F.B., Distillation Theory and its Application to Optimal Design of Separation Unit. 2004, Cambridge Cambridge University Press. 

My own technical experience has pretty much followed this history of distillation simulation. My practical experience started back in a high-school chemistry class in which we performed batch distillations. Next came an exposure to some distillation theory and running a pilot-scale batch distillation column as an undergraduate at Penn State, learning from Arthur Rose and Black Mike Cannon. Then, there were five years of industrial experience in Exxon refineries as a technical service engineer on pipestills, vacuum columns, light-ends units, and alkylation units, all of which used distillation extensively. 

In AR theory (as well as in distillation theory), the region of concentrations that obey mass balance constraints is often referred to as the mass balance triangle— this is because S takes the shape of a scalene or right-angled triangle in and a tetrahedron in We prefer to use the term stoichiometric subspace , however, as S is not always represented by these shapes, particularly for unusual reaction stoichiometry. 

Theoretical plate a concept borrowed from distillation theory and countercurrent extraction a chromatographic column is modeled as a series of discrete plates in each of which local equilibrium of analyte partitioning between stationary and mobile phases is established. The Plate Theory accounts for retention of analytes, i.e., retention times, but not the peak shapes (widths), for isocratic elution. 

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