Continuous stirred-tank extractor

Following the approach of Hatton, Reed and coworkers (107) have analyzed continuous stirred tank extractors when reaction reversibility contributes. They have developed a simple way to extend the simpler pseudo steady state advancing front model to predict extractor performance even when reaction reversibility may be significant. 

Recently, Bunge and Noble (39) have extended the approach of Ho et al. ( ) to Include reversibility of reaction 1. Batch extractions and calculations from this reversible reaction model demonstrate that reaction reversibility significantly affects extraction performance in some cases (39,40). In this paper, we extend these batch extraction calculations to a continuous stirred-tank extractor. We show that a single, dimensionless parameter can be used to assess the likely contribution of reversibility for a given set of conditions. 

Figure 1 diagrams a continuous stirred-tank extractor and indicates the pertinent design parameters. In a well-stirred, steady-state extractor, the bulk phase concentration of solute is uniform throughout the tank and equal to the constant outlet concentration, C b bulk phase feed enters the extractor at a concentration... 

Laboratory studies of the rearrangement process began with semi-continuous operation in a single, 200-mL, glass reactor, feeding 1 as a liquid and simultaneous distillation of 2,5-DHF, crotonaldehyde and unreacted 1. Catalyst recovery was performed as needed in a separatory funnel with n-octane as the extraction solvent. Further laboratory development was performed with one or more 1000-mL continuous reactors in series and catalyst recovery used a laboratory-scale, reciprocating-plate, counter-current, continuous extractor (Karr extractor). Final scale-up was to a semiworks plant (capacity ca. 4500 kg/day) using three, stainless steel, continuous stirred tank reactors (CSTR). 

The Eastman process has operated in Texas (USA) with three continuous, stirred-tank reactors, a wiped-film evaporator, a distillation train and a continuous, counter-current, liquid-liquid extractor for recovery of the catalysts since 1996 (1400 metric tons per year capacity, e.g., semiworks facility), but full commercial capacity has not yet been reached. The main problem is still the formation of oligomers. Another answer to the problem of IL loss to the organic phase consists in the extraction of the products from the IL using a supercritical fluid [101], but operational costs are high. 

If fiuid streams with or without solid particles are entering and other streams are exiting the well-stirred separator continuously, we have a continuous stirred tank separator (CSTS), provided that its properties are uniform throughout the separator. Figure 6.4.1(a) illustrates a CSTS which is a crystallizer. The conditions in such a separator are time- and space-invariant However, the intensity of mixing conditions in the separator is such that the fresh feed introduced into the separator is mixed in a time interval which is very short compared to the mean residence time of the fluid elements (and solid particles) in the separator. Figure 6.4.1(b) illustrates a continuous well-stirred extractor... 

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