A misture containing 500 wt% acetone and 50.0 wt% water is to be separated into two streams?one
Question:
A misture containing 500 wt% acetone and 50.0 wt% water is to be separated into two streams?one enriched in acetone. the other in water. The separation process consists of extraction of the acetone from the water into methyl isobutyl ketone (MIBK). which dissolves acetone but is nearly immiscible with water. The description that follows introduces some of the terms commonly used in reference to liquid extraction processes The process is shown schematically below.
The acetone (winte)-water (diluent) mixture is first contacted with the MIRK (solvent) in a mixer that provides good contact between the two liquid phases. A portion of the acetone in the feed transfers from the aqueous (water) phase to the organic (MIRK) phase in this step. The mixture passes into a settling tank. where the phases separate and are separately withdrawn. The phase rich in the diluent (water. in this process) is referred to as the raflinate. and the phase rich in the solvent (MIRK) is the extract. The mixer-settler combination is the first stage of this separation process. The raffinate passes to a second extraction stage vs here it is contacted with a second stream of pure MIRK. leading to the transfer of more acetone. The two phases are allowed to separate in a second settler. and the raflinate from this stage is discarded. The extracts from the two mixer-settler stages are combined and fed to a distillation column. The overhead effluent is rich in acetone and is the
process product. The bottom effluent is rich in MIBK and in a real process would he treated further and regrled hack to the first extraction stage. but we will not consider recycle in this example. In a pilot-plant study, for every WO kg of acetone-water fed to the first extraction stage. Its) kg of MIBK is fed to the first stage and 75 kg is fed to the second stage. The extract from the first stage is found to contain 27.5 wt% acetone. (All percentages in the remainder of this P3r"PaPh arc weight percents.) The second-stage raflinate has a mass of 43.1 kg and contains )1% acetone, 1.6% MIRK. and 93.1% water, and the second-stage extract contains 9.0% ace-T0oe: . MP% MIRK, and 3.0% water. The overhead prduct from the distillation column contains % 1.0% water, and the balance acetone.
Taking a basis of calculation of 100 kg acetone-water feed, calculate the masses and composi-cornbirkd exuactrit weight Percentages) of the Stage I raflinate and extract, the Stage 2 extract, the. and the distillation overhead and bottoms products.
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