Batch pervaporation process

A batch pervaporation process is applied to remove butanol from a fermentation broth. A volume reduction of 13% is observed when the butanol concentration has been decreased from 6% to 0.6%. Calculate... 

Based on experimental results and 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 Arrhenius law, whereas an increased temperature accelerates the pervaporation process also. Consequently, the water content decreases much faster at a higher temperature. The second important parameter is the initial molar ratio of the reactants involved. 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 opera-... 

Martin, N. Flexible and efficient. Batch pervaporation units for flexible dehydration. Process Eur. 2000, 1, 20-21. 

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. 

This example illustrates the distillation of a binary mixture in an open-batch distillery with flowing sweep gas and pervaporation by having a porous plate floating on top of the liquid hold up, as shown in Fig. 4.20. The porous plate was made from inert sintered metal with various pore sizes between 100 and 1 mfi, and had a thickness of 1 mm. The porosity was 40 % and the tortuosity factor was about 2. This results in an effective liquid phase mass transfer coefficient of about hiq = 2 X 10-7 m s-i, which results in Kiiq = 1.9 X 10 22. Therefore, one would expect the distillation process to be nonselective - that is, Si = xi - xi = 0. 

Offline pervaporation allows the membrane unit to be utilized at full capacity throughout the batch—in fact it can also be used when the reactor is not operating. In addition, such a unit is easily coupled to other reactors. Such units enhance the economy of a batch processing operation, while providing a high degree of flexibility. 

Nemec D and van Gemert R (2005), Performing esterification reactions by combining heterogeneous catalysis and pervaporation in a batch process , Ind Eng Chem Res, 44,9718-9726. 

Eq. VI - 127 can be used to calculate the conversion rate when the water permeability coefficient of the pervaporation membrane is known. Figure VI - 77 shows a conversion curve for a value of B = 0 (traditional equilibrium batch process) and a value of B > 10. 

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. 

For acetone-butanol-ethanol (ABE) fermentation, the broth contains about 25-35 g/1 of mixed solvents. Butanol concentration is usually less than 20 g/1, which makes its recovery by distillation expensive. This low butanol concentration in the fermentation broth is related to the inability of Clostridium species to produce more butanol due to solvent toxicity (Lee et al., 2008). Metabolic engineering and advanced fermentation techniques are ongoing to enhance the organisms abilities to produce and tolerate higher concentrations of butanol and increase productivity. Several integrated fermentation and recovery processes, such as fed-batch fermentation with pervaporation and continuous fermentation with gas stripping, have been reviewed elsewhere (Lee et al., 2008). 

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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