TUTORIAL FST 359 CHAPTER 4: SOLVENT EXTRACTION QUESTION 1 Groundnuts containing 26% (w/w) oil was extracted through a single stage operation under atmospheric pressure with n-hexane as solvent. The clear liquid containing 20% (w/w) oil (solute) was discharged from the top layer and the precipitate leaving from the bottom contained 72% (w/w) solids. If the flow rate of feed was 350 kg/h (F) and the stage operation was ideal, calculate the flow rate of solvent (S) and flow rate of overflow product (V). (10 marks) ANSWER: Step 1: Extract information from question Feed contain 26% oil = 0.26 Clear liquid contain 20% solute = 0.2 Underflow (L)= 100% - 72% = 28% = 0.28 Feed flow (F) = 350 kg/h Step 2: Design a graph Step 3: From graph, we know that: SM = 5.1cm FM = 5.2cm LM = 3.0cm VM = 3.0cm Step 4: To get amount of solvent (S) apply this formula
S FM F SM FM S F SM 5.2 S 350 5.1 kg S 356.87 h
S FM F SM
Step 5: To get quantities of extract overflow (V), apply these formulas
F S V L L VM V LM VM L V LM 3.0 L V 3.0 L 1V F S V L 350 356.87 V 1V 706.87 2V kg V 353.43 h
HOW TO DRAW A GRAPH STEP 1
L VM and V LM
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