Pervaporation systems batch

Figure 9.16 Flow diagram and typical performance for a 50-gal cyclic batch pervaporation system. The treatment time for the first 50-gal batch was set at 120 min because the unit was cold thereafter, the cycle time was set at 90 min. The system achieved 99.8 % removal of toluene from the feed water [13]...

Pervaporation can also operate in batch mode, and this is done typically when testing membranes for small plants and for some larger multipurpose plants. Batch pervaporation systems are robust, well proven, and flexible in operation. The pumparound rate on batch systems is normally set high to give a low permeate quantity per pass. Pervaporative cooling effects are small, and such systems can be built with a single preheater and unheated modules (Fig. 3). 

A choice of batch or continuous pervaporation systems, or continuous vapor permeation depending on the duty. 

For a rapid conversion of lab-scale results into an economically viable reaction-pervaporation system, an optimum value can be determined for each parameter. Based on experimental results as well as a model describing the kinetics of the system, it has been found that the temperature has the strongest influence on the performance of the system as it affects both the kinetics of esterification and of pervaporation. The rate of reaction increases with temperature according to an Arrhenius law, whereas the pervaporation is accelerated by an increased temperature also. Consequently, the water content fluctuates much faster at a higher temperature. The second important parameter is the initial molar ratio. It has to be noted, however, that a deviation in the initial molar ratio from the stoichiometric value requires a rather expensive separation step to recover the unreacted component afterwards. The third factor is the ratio of membrane area to reaction volume, at least in the case of a batch reactor. For continuous operation, the flow rate should be considered as the determining factor for the contact time of the mixture with the membrane and subsequently the permeation... 

Schematic systems of (a) once-through pervaporation system design and (b) feed-and-bleed batch system. (Adapted from Baker, 2004.)... 

For treating water containing VOCs with separation factors of more than 500, for which concentration polarization is a serious problem, feed-and-bleed systems similar to those described in the chapter on ultrafiltration can be used. For small feed volumes a batch process as illustrated in Figure 9.16 is more suitable. In a batch system, feed solution is accumulated in a surge tank. A portion of this solution is then transferred to the feed tank and circulated at high velocity through the pervaporation modules until the VOC concentration reaches the desired level. At this time, the treated water is removed from the feed tank, the tank is loaded with a new batch of untreated solution, and the cycle is repeated. 

Similar TS-1 films have been applied for phenol hydroxyl-ation reaction to dihydroxybenzenes (hydroquinone and catechol) [354] and catalytic oxidation of styrene to benzaldehyde and phenylacetaldehyde [355] with hydrogen peroxide as oxidant in batch-type membrane reactors. The dihydroxybenzenes and phenylacetaldehyde selectivity values increased with in-framework Ti content. In order to reduce the TS-1 membrane costs, Chen et al. [356] have successMly synthesized TS-1 on mullite tubes by replacing TPAOH with TPABr/EtjNH system (4% of the initial cost). The catalytic activity was tested in the probe reaction of isopropyl alcohol oxidation with hydrogen peroxide under pervaporation condition at 60°C. In general, future work on TS-1 film catalysts is required to improve mass transfer resistances and reaction conversion without compromising selectivity. 

The interest in w-butanol as a biofuel has increased in recent years owing to its superior fuel qualities compared to ethanol. These include a higher octane number, lower heat of vaporization, higher energy density (energy/volume), and lower vapor pressure. However, in the traditional ABE (acetone-butanol-ethanol) fermentation process, the concentration of n-butanol coming from the fermenter is lower than that achieved in ethanol fermentation. In addition, acetone and ethanol are also produced. Recent studies to improve yield and increase w-butanol concentration have explored fed-batch systems with stripping, adsorption, liquid-liquid extraction, distillation, and/or pervaporation to recover products. 

In the resin manufacturing industry, resin manufacturers lose 30% of the reactants in the wastewater. The process is very similar to esterification. The reaction produces water with the formation of resins. At the end, 30% of the reactant remains unreacted due to the presence of water. Similar to esterification in the later stage, the reaction slows down. This step takes a lot of time to complete the batch. It has been demonstrated in a resin manufacturing application that if an AZEO SEP pervaporation hybrid system is incorporated with the conventional system, it increases the yield. It also reduces the reaction time and the wastewater problem. The savings in recovering the unreacted reactants could be phenomenal. It has... 

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