A Typical Column

A typical column chromatography experiment is outlined in Figure 12.4. Although the figure depicts a liquid-solid chromatographic experiment similar to that first used by Tswett, the design of the column and the physical state of the... 

If long distillation time is a problem, one can move to continuous distillation with conventional shell and tube heaters accompanied by a typical column bottom (often called a sump) which is a high temperature holdup, or better yet a short path evaporator (falling film, thin film, or wiped film) with usually a smaller receiver (called an accumulator in this case). The most chemical damage is in the thin liquid film at the heat transfer surface, so the short path evaporators do the least thermal damage. 

This example focuses on the design and optimization of a steady-state staged column. Figure El 2.1 shows a typical column and some of the notation we will use, and Table El2.1 A lists the other variables and parameters. Feed is denoted by superscript F. Withdrawals take the subscripts of the withdrawal stage. Superscripts V for vapor and L for liquid are used as needed to distinguish between phases. If we number the stages from tihe bottom of the column (the reboiler) upward with k= 1, then V0 = L1 = 0, and at the top of the column, or the condenser, Vn = Ln+l = 0. We first formulate the equality constraints, then the inequality constraints, and lastly the objective function. 

Figure 10.1 A typical column (or newspaper) layout for a scientific poster.

A typical column setup is shown in Figure 3.6. The heart of the system is, of course, the column of adsorbent. In general, the longer the column, the better the resolution of components. However, a compromise must be made because flow rate decreases with increasing column length. The actual size of a column depends on the nature of the adsorbing material and the amount of chemical sample to be separated. For preparative purposes, column heights of 20 to 50 cm are usually sufficient to achieve acceptable resolution. Column inside diameters may vary from 0.5 to 5 cm. 

Table 4.1 summarizes the potential quantity of a crude mixture that could be processed annually in comparison to column diameter. This assumes a typical column loading of approximately 60 g per kg of stationary phase, which would not be unusual, and 24 h operation. It is important to note that the figures given are for throughput of crude starting material and that yield will depend upon the initial product purity. 

Some people feel that columns cost too much and, therefore, purchase the lowest-price column. This is one strategy for choosing the best column. However, when the nature of a column in a chromatographic system is considered, it makes sense that there should be little to no price sensitivity in the user. For instance, if an instrument sells for 20,000, a typical column sells for 300. Therefore, a column is only 300/ 20,000, or 1.5% of the cost of an instrument installation. This is a minor part even if repeat buying is calculated. Second, keep in mind that without the column performance the entire instrument is worth precisely zero. Third, it is very hard to evaluate how a column will perform without prior experience with it—there is no easy believability to competitive claims that one C 8 column will work as well as, or even the same as, another. In essence, a column is nothing more and nothing less than a user s attempt to solve an analytical problem. Users should not be sensitive to price, they should be concerned with time, effort, and repeatability. Therefore, most individuals should gladly pay for these benefits, because the best column does your separation. 

Figure 2.2 contrasts a typical column with a variable feed rate as set by an upstream unit to an on-demand column with bottoms flowrate set by a downstream operation. Further examples are given in later chapters when specific plants are considered (Chap. 8 for the Eastman process and Chap. 11 for the vinyl acetate process). 

The syrup liquor at 60% concentration is then passed upward through cylindrical columns packed with carbon. A typical column has a diameter of 12 ft. (3.66 m) and a height of 30 ft. (9.14 m), and holds 90,000 lbs (40,823 kg) of carbon. In a typical operation, the syrup liquor is passed through such carbon columns at a rate of 100 gallons (379 liters) per minute at a temperature of 71°C (160°F) and a pH of 4.5. The average residence-time is 90 minutes. 

Figure 2 shows a typical column operation used to soften a hard water containing calcium magnesium and sodium salts. 

Scaling within one mode disturbs prior centering across the same mode, but not across other modes [ten Berge 1989], This holds for two-way arrays as well as higher order arrays. The reason for this is illustrated in Figure 9.8. The vertical arrow shows a typical column vector and the horizontal line a typical row-vector. When scaling within the first mode, the elements of any column are multiplied by different numbers and hence prior centering across the first mode is destroyed. 

The physical content of the requirement (38) is that any electronic variable in the problem should have exactly the same relationship to the nuclear variables as does any other electronic variable. The physical content of the requirement (39) is that every member of a set of identical nuclei must enter into the definition of te in the same way. Thus (38) is satisfied by requiring all the columns of Vne to be identical and from now on a typical column will be denoted v. If the entries in v are identical for identical nuclei then (39) is also satisfied. 

What is a typical column efficiency, and what are normal detection limits ... 

The ratio P aIP b does not change much over the range of temperatures encountered in a typical column, so the relative volatility is taken as constant in the following derivation. 

The volume of sample injected onto the column is an important parameter for the detectability. It is possible to improve the detection limit by using quite large sample volumes without spoiling the column performance. For a typical column of 4 mm... 

In summary, beside flows, five variables are controlled in a typical column. Three of these (pressure and two levels) are controlled to set stable conditions, and two (compositions) are controlled to achieve the desired product purities. 

We choose 1.5 for the B term on the basis of our data. Therefore the normal performance of a typical column should follow the following equation ... 

Let us take a typical column of 15 cm length and packed with S-/im particles. This column would have a plate count of about 10,000 plates under normal running conditions. Table 3.1 shows the standard deviation of a peak as a function of the retention factor for several internal diameters of the column. 

The mixed flow dryer is a continuous dryer shown in Figure 24.15. The dryer consists of one or two rectangular columns. A typical column is 762 mm thick. A series... 

The treated carbons that remove mercury from hydrogen are also effective with air. Operating conditions are similar. The higher density of air causes the pressure drop through a typical column to be higher (about 80 mm w.c. vs 30 mm with hydrogen). Alternatively, a larger column can offer lower gas velocities and therefore reduced pressure drops. 

A typical column would use silica gel adsorbent (particle size = 40 to 63 ixm) packed to a height of 5 inches in a glass column of 20-mm diameter. The pressure applied to the column would be adjusted to achieve a solvent flow rate such that the solvent level in the column would decrease by about 2 in./min. This system would be appropriate to separate the components of a 250-mg sample. 

The dimensions of the column that you use depend upon the application. For analytical applications, a typical column is constructed of tubing that has an inside diameter of between 4 and 5 mm, although analytical columns with inside diameters... 

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