Extraction processes are common industrial and laboratory operations in chemistry. Specifically, liquid-liquid extractions are often the go-to operation in undergraduate organic laboratories to isolate target products after reaction procedures. In industry, liquid-liquid extraction applies to the separation of penicillin from broth; and the separation of aromatic hydrocarbons (e.g., toluene, benzene) from paraffin in petroleum processing. However, experimental variables involved in the liquid-liquid extraction are often superficially explained to students. Thus, students develop an attitude that the extraction steps are procedures to follow without inspection of its efficiency and intrinsic characteristics. For example, students might understand that extraction is a process where one or more solutes are removed from a liquid by transfer into a second liquid phase. But fail to realize that: (1) the two liquid phases must be immiscible or partially immiscible; (2) the distribution ratio (Kd, or equilibrium “constant”) depends on the composition of the feed solution (i.e., liquid phase carrying the interest solute) and the amount of extracting solvent added into the mixture; (3) the selection of the extracting solvent is based on its high selectivity with the solute and not with other contaminants, easiness of separation from the solute (often by distillation), toxicity, chemical stability, among other properties. The work presented herein designs laboratory experiences that foster a deeper understanding of the distribution ratio (Kd) during liquid-liquid extractions in systems where the liquid phases are immiscible (e.g., water-acetone-1-octanol) and partially miscible (e.g., water-acetone-chloroform). The variability of the Kd was determined for different mass percent compositions of feed solutions. To complete the laboratory experience, students need to collect data from many mixtures and shared their collective results for all the class to compile and interpret. All laboratory procedures and techniques are planned for introductory level chemistry laboratories. Thus, the proposed experience aligns with desired goals for laboratory education put forth by the National Research Council in 2005: “understanding of the nature of science, and supporting mastery of subject matter.” Examples of procedures, data, and results will be presented and discussed in light of their design and implementation for introductory chemistry laboratory programs.

Design of chemical engineering experiences of liquid-liquid extraction into project-based experimentation for introductory chemistry laboratories

2019 Fall National Meeting

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