Caffeine is often added to headache medications because it affects the flow of b
ID: 889063 • 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 water/g is fed to a mixer at a rate of 595.0 g/min. Na2CO3 is added to the mixer such that the mass ratio of Na2CO3 to coffee slurry is 0.0500. This aqueous solution proceeds to an extractor where CH2Cl2 is added such that the mass ratio of CH2Cl2 to coffee slurry is 0.440. 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 BLANK. What is m7, the mass flow rate of crystallized caffeine? What is m4, the mass flow rate of fresh CH2Cl2 to the process? What is the ratio of the flow rates of recycled CH2Cl2 to fresh CH2Cl2?Explanation / Answer
m1= 595g/min, x1 = 0.01g caffeine/g , x2 =0.08g other solid /g, x3=0.91g water / g
m2=29.7 gNa2CO3/min, m4=261.8g CH2Cl2/min , m5= 267.036g CH2Cl2, m6= 5.236g CH2Cl2/min
m7=5.712g caffeine/min, m3=880.78g aq solution/min,x4=0.00027g caffiene/ g,x5 = 0.055g other solid /g
x6=0.0337g Na2CO3/g , x7 =0.61g water/g,
m7=5.712g caffeine/min
m4=261.8g CH2Cl2/min
Ratio = recycled CH2Cl2 (m6) / fresh CH2Cl2(m4) =5.236/ 261.8 = 0.02