The Minimum Solvent Consumption

The minimum solvent consumption will be obtained from the product of the optimum flow rate and the analysis time. 

The amount of gas employed in a GC analysis is not usually important, particularly where open tubular columns are used. In LC, however, solvent use presupposes a solvent disposal difficulty if not a toxicity problem and, thus, solvent consumption can be extremely important. 

For an LC column, substituting for (tmin) from equation (31) and for (Qopt) from equation (42) in equation (43), 

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The maximum permissible charge that can be placed on an LC column was discussed in chapter 5 and is given by the following equation, 

The above equation reduces to a surprisingly simple function. 

Graph of Solvent Consumption against Separation Ratio 

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The analysis must be completed with the minimum solvent consumption. 

Little has been said concerning the column diameter which, unfortunately, is an aspect of column technology that involves extensive theoretical discussion which is probably not appropriate here. Each column that is optimized to analyze a particular sample in the minimum time and with the minimum solvent consumption will also have an optimum diameter. The optimum column diameter... 

The amount of solvent needed for the purification of a unit amount of target compound is conveniently described by the term specific production. Thus, the minimum solvent consumption can be determined for a given purification. The amount of solvent pumped through the column during one cycle is proportional to the mobile phase flow rate and the cycle time. The amount of purified product made in one cycle is the product of the amount injected and the recovery yield. Thus, the specific production can be written as [43]... 

The analysis must be completed with the minimum solvent consumption. 4/ The maximum mass sensitivity must be realized. 

The optimum mobile phase velocity will also be determined in the above calculations together with the minimum radius to achieve minimum solvent consumption and maximum mass sensitivity. The column specifications and operating conditions are summarized in Table 4. 

The reader will find here a complete mathematical development of the models of chromatography and other physical laws which direct the chemical engineer in the design and scale-up of chromatographic processes. For preparative chromatographic separations, our ultimate purpose is the optimization of the experimental conditions for maximum production rate, minimum solvent consumption, or minimum production cost, with or without constraints on the recovery yield. The considerable amormt of work done on this critical topic is presented in the... 

The maximum and minimum flow rate available from the solvent pump may also, under certain circumstances, determine the minimum or maximum column diameter that can be employed. As a consequence, limits will be placed on the mass sensitivity of the chromatographic system as well as the solvent consumption. Almost all commercially available LC solvent pumps, however, have a flow rate range that will include all optimum flow rates that are likely to be required in analytical chromatography... 

Another critical instrument specification is the total extra-column dispersion. The subject of extra-column dispersion has already been discussed in chapter 9. It has been shown that the extra-column dispersion determines the minimum column radius and, thus, both the solvent consumption per analysis and the mass sensitivity of the overall chromatographic system. The overall extra-column variance, therefore, must be known and quantitatively specified. 

Due to scientific and public concern about environmental pollution, new developments in environmental analysis are focused on the implementation of environmental-friendly practices in the laboratories. Main strategies are addressed to saving energy and to reduce solvent consumption with the minimum sample manipulation by using on-site, online, and direct analysis (e.g., biosensors) [42],... 

A thirty-plate bubble-cap column is to be used to remove n-pentane from a solvent oil by means of steam stripping. The inlet oil contains 6 kmol of n-pentane/100 kmol of pure oil and it is desired to reduce the solute content of 0.1 kmol/100 kmol of solvent. Assuming isothermal operation and an overall plate efficiency of 30 per cent, what is the specific steam consumption, that is kmol of steam required/kmol of solvent oil treated, and the ratio of the specific and minimum steam consumptions. How many plates would be required if this ratio is 2.0 ... 

The analytical specifications must prescribe the ultimate performance of the total chromatographic system, in appropriate numerical values, to demonstrate the performance that has been achieved. The separation of the critical pair would require a minimum column efficiency and the number of theoretical plated produced by the column should be reported. The second most important requisite is that the analysis should be achieved in the minimum time and thus the analysis time should also be given. The analyst will also want to know the maximum volume of charge that can be placed on the column, the solvent consumption per analysis, the mass sensitivity and finally the total peak capacity of the chromatogram. The analytical specifications can be summarized as follows. 

The ROSE process is a solvent deasphalting process with minimum energy consumption using a super-critical solvent recovery system and the process is of value in obtaining oils for further processing. (Gearhart, 1980 Low et al., 1995, Hydrocarbon Processing, 1996 Northrup and Sloan, 1996). 

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