Caffeine is often added to headache medications because it affects the flow of b
ID: 532082 • Letter: C
Question
Caffeine is often added to headache medications because it affects the flow of blood in vessels and may enhance the pain relieving qualities of the medication. You have been tasked with evaluating one process that extracts caffeine from a coffee slurry, and you decide to study a small scale version of the process. A coffee slurry containing a mass fraction of 0.01 g caffeine/g, 0.08 g other solids/g, and 0.91 g waterlg is fed to a mixer at a rate of 745.0 g/min. Na2CO3 is added to the mixer such that the mass ratio of Na2CO3 to coffee slurry is 0.0400. This aqueous solution proceeds to an extractor where CH2Cl2 is added such that the mass ratio of CH2Cl2 to coffee slurry entering the extractor is 0.360. Two streams leave the extractor. The first is a mostly aqueous stream that leaves the process containing some caffeine, all of the other solids in the original slurry, all of the Na2CO3, all of the water and 2% of the mass of CH2Cl2 entering the extractor. The second stream contains the remaining caffeine and CH2Cl2, and enters an evaporator that completely vaporizes the CH2Cl2. The vaporized CH2Cl2 is condensed and is merged with the fresh CH2Cl2 on the way to the extractor. The dried caffeine crystals exit the evaporator and leave the process. Of the caffeine entering the process a fraction of 0.960 leaves the process in this product stream. Label the process flow diagram below. Label any quantities as "unknown" if you have to perform a calculation to obtain the numeric value. DO NOT LEAVE ANY ANSWER SPACE BLANKExplanation / Answer
Flow rate of coffee slurry, m1= 745 g/min. It contains 0.01caffeine/g.
Caffeine entering = 745*0.01 =7.45 gm
Product stream contains 0.96 fraction of Caffeine. Caffeine in the product= 0.96*7.45 =7.152
Caffeine remaining = 7.45-7.152 = 0.298 gm. This leaves along with m3, the aqueous solution.
It is given that mass flow rate of Na2CO3/ mass flow rate of coffee slurry= 0.04
Mass flow rate of Na2CO3= 0.04* 745 =29.8 g/min. Hence m2=29.8 g/min
It is also given mass flow rate of CH2Cl2/mass flow rate of Coffee slurry= 0.360
Mass flow rate of CH2Cl2 to the extractor= 0.36*745 =268.2 g/min. This is m5.
Solids in the slurry = 745*0.08=59.6 g/min. Water in the slurry= 745*0.91= 677.95 g/min
Na2CO3 entering the slurry is leaving along with m3. Hence Na2CO3 in m3= 29.8 g/min
CH2Cl2 in m3= 0.02*268.2= 5.364 g/min
Flow rate of streams in m3: Water= 677.95 g/min, Caffeine= 0.298g/min, solids= 59.6 g/min,Na2CO3=29.8g/min and CH2Cl2= 5.364 g/min.
The sum of all the stream gives m3. Hence m3= 677.95+0.298+59.6+29.8+5.364 =773.012 g/min
Composition of streams in m3 : water= 677.95/773.012 =0.877, caffeine= 0.298/773.012= 0.000385, solids= 59.6/773.012= 0.077, Na2CO3= 29.8/773.012 =0.0385 and CH2Cl2= 5.364/773.012 =0.0069
Wrting overall balance of the plant
Sum of entering streams = sum of leaving streams
Hence m1+m2+m4= m3+m7
745+29.8+m4= 7.152+773.012, m4= 5.364 g/min. This is flow rate of fresh CH2Cl2.
Since m4+m6=m5, m6= recycle CH2Cl2= m5-m4= 268.2-5.364 =262.836 g/min
Ratio of recycled CH2Cl2/ fresh CH2Cl2= 262.836/5.364=49 g of recycled CH2Cl2/fresh CH2C