Extraction process cross-flow

A single-stage extraction using the same total volume of solvent achieves only 92% extraction, and the extract concentration is only 0.23, vs. nearly 0.25 for the cross-flow extraction. The use of four cross-flow extraction stages is clearly preferable to a single extraction. Equally, of course, the use of more than four extraction stages, each with a proportionately smaller volume, would improve the performance. In the limit, one would seek a differential contacting process similar to the Soxhlet extractor employed for extraction from solid phases, but such a contactor has not found use in solvent extraction. 

A 1000 kg/hr stream of a solution containing 30 wt% acetic acid and 70 wt% water is to be fed to a countercurrent extraction process. The solvent is 99% isopropyl ether and 1% acetic acid, and has an inlet flowrate of 2500 kg/hr. The exiting raflflnate stream should contain 10 wt% acetic acid. The equilibrium data are the same as given in Table 5.1 for the cross-flow Example 5.1. Find the number of equilibrium-limited stages required. 

As these commercial exanples illustrate, the conplete extraction process includes the extraction unit and the solvent recovery process. This is shown schematically in Figure 13-1. In many applications the downstream solvent recovery step (often distillation or a chemical stripping step) is more expensive than the actual extraction step. Woods (1995. Table 4-8) lists a variety of commercial processes and the solvent regeneration step enployed. A variety of extraction cascades including single-stages, countercurrent cascades, and cross-flow cascades can be used we discuss these later. 

Eq. (6-24) may be also applied to differential stagewise extraction operated as a stagewise cross-flow extraction process, with the number of extraction cycles tending to infinity (n oo). The extract phase may be withdrawn continuously and fresh solvent is fed. For TV, - oo. 

Again most of the best solutions were very similar to the industrial flowsheets which include rotary drum filtration, solvent extraction, crystallization, filtration and drying. However when LCA or CWTM environmental criteria are used the solvent extraction process is replaced by cross flow filtration and ion exchange with other potential small changes. This is an expensive option but has clear environmental advantages. The... 

Q Simulate a counter-current extraction of six stages. What is the process behavior and what is the fundamental difference with the single-stage and the cross flow system (dynamically and statically) ... 

---