Batch column

Batch distillation, which is the process of separating a specific quantity (the charge) of a liquid mixture into products, is used extensively in the laboratory and in small production units that may have to serve for many mixtures. When there are N components in the feed, one batch column will suffice where N — 1 simple continuous-distillatiou columns would be required. 

For the distillation of a multi-component system in a batch column, the established practice leads to sequential removal of products from lower to higher boiling points. A strategy has been suggested, with a proper analysis, which involves the removal of all the products except the heavies, with subsequent fractionation of the mixture. 

Figure 5.214. The batch column was started with total reflux the reflux was then reduced to 0.25 at t = 75 and then increased (from 1.0 to 5.0 to 50.0) whenever the distillate tank composition XO fell below 0.9. The response of the plate compositions and the fraction distilled, FRAC, are shown.

Activated carbon adsorption may be accomplished by batch, column, or fluid-ized-bed operations. The usual contacting systems are fixed-bed or countercurrent moving beds, as shown in Figure 8.2. The fixed beds may employ downflow or upflow of water. The countercurrent moving beds employ upflow of the water and downflow of the carbon, since the carbon can be moved by the force of gravity. Both fixed beds and moving beds may use gravity or pressure flow. 

In fixed bed columns (batch columns), the fluid and solid phase concentrations are functions of both position and time. Considering a conventional, idealized,... 

Buchacher et al. [43] discussed the continuous separation of protein polymers from monomers by continuous annular size exclusion chromatography. The P-CAC used for the experiments was a laboratory P-CAC type 3 as described in Table 1. The results were compared to conventional batch column chromatography in regard to resolution, recovery, fouling, and productivity. The protein used in the studies was an IgG preparation rich in aggregates. Under the conditions used, the polymers could be separated from the monomers, although no baseline separation could be achieved in either the continuous or the batch mode. The... 

Christensen and Lun [57] developed a speciation procedure using a cation-exchange resin (Chelex 100) in a sequential batch/column/batch system for determining free divalent cadmium and cadmium complexes of various stabilities at the cadmium concentrations typically found in landfill leachates... 

Sorption coefficients also have been determined from the motion of an unconfined sor-bate plume in a simulated aquifer box model. MacIntyre et al. (1991) compared the sorption coefficients for naphthalene on low soil organic carbon (less than 0.1%) aquifer materials determined by the batch, column, and box methods, and found good agreement among the three methods. 

MacIntyre, W.G., T.B. Stauffer, and C.P. Antworth. 1991. A comparison of sorption coefficients determined by batch, column, and box methods on a low organic carbon aquifer material. Ground Water 29(6) 908-913. 

Bierck and Chang (1994) Granular Activated Carbon (GAC) Batch, column... 

In this study, the effects of cosolvent (EtOH) addition on the solubilization and recovery of PCE by a nonionic surfactant (Tween 80) was evaluated using a combination of batch, column and 2-D box studies. Batch results demonstrated that the addition of 5% and 10% EtOH increased the solubilization capacity of Tween 80 from 0.69 g PCE/g surfactant to 1.09 g PCE/g surfactant. For a 4% Tween 80 solution, this translates into a solubility enhancement of more than 50%, from 26,900 mg/L to 42,300. mg/L. When the surfactant formulations were flushed through soil columns containing residual PCE, effluent concentration data clearly showed that PCE solubilization was rate-limited, regardless of the EtOH concentration. Using analytical solutions to the 1-D ADR equation, effective mass transfer coefficients (Ke) were obtained from the effluent concentration data for both steady-state (A e ) and no flow conditions The addition of EtOH had... 

Figure 9 Comparison of previously reported values of kSA for reduction by Fe° with external mass transport coefficients estimated for batch, column, and rotating disk electrode reactors. References for the overall rate coefficients are given in Fig. 1 of Ref. 101. Mass transport coefficients were estimated for the batch and column reactors based on empirical correlations discussed in Refs. 125 and 101. Mass transport coefficients for the RDE were calculated using the Levich equation [178].

For a complete model of a SMBR unit, the model above describing a single-batch column can simply be repeated for each column in the unit, whilst adding the changes along the fluid path due to the inlet and outlet ports as well as the switching procedure [16]. 

In this mode heat input to the reboiler is held constant throughout. In practice it is set to its maximum limit, the value of which depends on the heat exchange system to the reboiler. Domenech and Enjalbert (1974), Greaves et al. (2001), Greaves (2003) used this mode of operation in their laboratory conventional batch column. Cuille and Reklaitis (1986) and Mujtaba (1989) also used this mode of operation in their simulation studies. 

In practice, an empty conventional batch column is started up in the following sequence ... 

Rose et al. (1950) and Rose and O Brien (1952) studied the effect of holdup for binary and ternary mixtures in a laboratory batch column. They qualitatively defined the term sharpness of separation as the sharpness in the break between successive components in the graph of instantaneous distillate composition against percentage distilled. They showed that an increase in column holdup enhanced the sharpness of separation at low reflux ratio but did not have any effect at a very high reflux ratio. 

Unlike continuous distillation, batch distillation is inherently an unsteady state process. Dynamics in continuous distillation are usually in the form of relatively small upsets from steady state operation, whereas in batch distillation individual species can completely disappear from the column, first from the reboiler (in the case of CBD columns) and then from the entire column. Therefore the model describing a batch column is always dynamic in nature and results in a system of Ordinary Differential Equations (ODEs) or a coupled system of Differential and Algebraic Equations (DAEs) (model types III, IV and V). 

The optimal operation of a batch column depends of course on the objectives one wishes to achieve at the end of the process. Depending on the objective function and any associated constraints, a variety of dynamic optimisation problems were defined in the past for conventional batch distillation column. Brief formulations of these optimisation problems are presented in the following subsections. Situations in which each formulation can be applied are discussed. 

For example, if all the reaction products are valuable and have lower boiling temperature than the reactants, then conventional batch distillation would be most suitable. As the reaction proceeds the products will be separated in different main-cuts in sequential order. Conversion and yield can be greatly improved in such cases. If only some of the reaction products have low boiling temperature, then a conventional batch column will only remove those products as distillation proceeds. To separate the rest of the products by conventional distillation would require the removal of unreacted reactants from the column first. 

Table 9.1. Most Suitable Batch Column Configuration for Several Chemical...

Also Mujtaba (1997) considered the separation of binary mixtures into one distillate product of specified purity. The objectives were to find out whether it was possible to replace conventional dynamic operation of batch columns by steady state operation using continuous columns for a comparable recovery, energy consumption, operation time, productivity, etc. and to obtain optimal operating policy in terms of reflux ratio. The following strategy was considered to compare the performances of the two types of operations ... 

In the last few sections, the implications of operating batch distillation in continuous columns have been discussed. It is observed that for a given batch time and recovery of key component and energy consumption, the CBD operation can be replaced by a continuous column operation using low feed flow rate. Compared to batch columns, the modelling and optimisation tasks become easier with the use of continuous columns. For the same number of passes or reflux intervals with any feed flow rate continuous column operation results in a better recovery compared to conventional batch operation. 

Greaves et al. (2003) proposed a framework to optimise the operation of MVC columns with substantial reduction of the computational power needed to carry out the optimisation calculations. The framework relies on the use of NN based process model. The optimisation of a pilot-plant middle-vessel batch column (MVC) was considered to test the viability of the proposed framework. The maximum product problem was considered and solved by optimising the column operating parameters, such as the reflux and reboil ratios and the batch time. The NN based model is found to be capable of reproducing the actual plant dynamics with good accuracy, and that the proposed framework allows a large number of optimisation studies to be carried out with little computational effort. 

Imafuku et al.46 measured the pressure drop caused by the suspended solids in the liquid in a batch-column (i.e., no liquid flow) and used these data to obtain the critical gas velocity needed to suspend all solid particles completely. The value of the critical gas velocity was found to be independent of the bottom shape of the column. 

Preparative chromatography is a proven technology for the separation of specialty chemicals mainly in food and pharmaceutical industries, particularly the enantioseparation of chiral compounds on chiral stationary phases. The potential of preparative chromatographic systems were further increased by the development of continuous chromatographic processes like the simulated moving bed (SMB) process. Compared to the batch column chromatography, the SMB process offers better performance in terms of productivity and solvent consumption [2]. 

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