Perform a technically feasible design for the following process for removing acetone from water using trichloroethane (TCE). As TCE is valuable and also regulated, it is recycled after distillation. It removes essentially all of the acetone. The bottoms from the distillation (TCE) will be at a temperature of 55 ◦C and will be available for recycle for reuse in the acetone extraction.
a. Process and design specifications: A 1000-L/min water stream at 25 ◦C containing 200 g/L of acetone must be treated to remove the acetone prior to waste discharge into a nearby river. A supply of 1,1,2- trichloreothane (TCE) is available to remove the acetone by liquid–liquid extraction.
b. Mass contactor design: A liquid–liquid mass contactor(s) must be specified. The height, diameter, and the mixer power must be determined to complete your design. In addition, you must also specify exit stream flow rates and acetone concentrations. For this design, you will need to consider the experimental data for this acetone–water–TCE system presented in Figure 4.2.
c. Separator design: The fluid–fluid mixture from the mass contactor must be separated into two streams, a TCE-free water stream, qII, and a water-free TCE stream, qI . This needs to be accomplished in a decanter or separator, which will allow the water droplets to separate from the TCE. The geometry and dimensions of the separator must be specified to complete the design.
d. Heat exchanger design: The TCE stream from the separator is passed to a distillation column (not to be designed) to strip the acetone. The regenerated TCE is recycled to the beginning of the process at a temperature specified by the bottoms of the distillation column. Appropriate thermal management must be designed into the process so that the extraction previously discussed is carried out at 25 ◦C. Chilled water is available at 10 ◦C for heat exchange and can be returned to the utility company at no hotter than 60 ◦C. Any heat exchanger employed in the process will need to be specified in sufficient detail to send for a quote or fabrication.
Provide a process flow diagram (showing all process equipment) with accompanying stream tables, technically feasible designs of the mass contactor(s), separator, and heat exchanger with associated equipment tables and supporting calculations. Comment on the amount of acetone that can be reasonably removed from the water and the suitability of discharging the effluent water into the environment, as well as on alternative strategies for efficiently removing the acetone. DATA: An experiment to determine the transient partitioning of acetone between an aqueous phase and an organic TCE phase has been performed. The experiment was performed in a batch system at 25 ◦C. 2 L of an acetone (A) – water (W) solution was contacted with 2 L of an initially acetone-free TCE phase in a batch mass contactor. This mass contactor consisted of a 5-L cylindrical tank (Dvessel
= 0.172 m). A lab-scale impeller was employed to disperse the aqueous phase in the TCE phase. Relatively large bubbles (average diameter of 1 cm) of the aqueous phase resulted. Small samples of the TCE phase were taken throughout the experiment. The concentration of acetone in the TCE phase (I) was measured through gas chromatography analysis and is reported in the following table.