Assuming you have a mixture of ethanol and water, design a distillation column that can achieve a 95% purity of ethanol in the distillate using the minimum number of plates possible. The feed to the column contains 40% ethanol and 60% water, and the distillate and bottoms products need to be at least 95% pure. The column operates at atmospheric pressure and the feed rate is 100 kg/hr. Also, determine the reflux ratio required to achieve this separation.

Question

Assuming you have a mixture of ethanol and water, design a distillation column that can achieve a 95% purity of ethanol in the distillate using the minimum number of plates possible. The feed to the column contains 40% ethanol and 60% water, and the distillate and bottoms products need to be at least 95% pure. The column operates at atmospheric pressure a

Answer 1

To design a distillation column for this separation, we will use the McCabe-Thiele method. First, we need to determine the equilibrium data for the ethanol-water system at atmospheric pressure. The vapor-liquid equilibrium data can be obtained from literature or experimental data. For simplicity, we will use the following approximate VLE data for ethanol-water at atmospheric pressure:x  mole fraction of ethanol in liquid phase  : 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0y  mole fraction of ethanol in vapor phase  : 0.0, 0.2, 0.4, 0.5, 0.6, 0.7, 0.8, 0.85, 0.9, 0.95, 1.01. Determine the feed composition and the desired product compositions in mole fractions.Feed: 40% ethanol and 60% water  by mass . Assuming the molecular weights of ethanol and water are 46 g/mol and 18 g/mol, respectively, we can convert the mass fractions to mole fractions:xF =  0.4 * 100 kg/hr  /  0.4 * 100 kg/hr + 0.6 * 100 kg/hr  = 0.342xD = 0.95  desired purity of ethanol in distillate xB = 0.05  desired purity of ethanol in bottoms, since it's 95% water 2. Determine the q-line.Since the feed is a liquid at its boiling point, q = 1. The q-line equation is:y = x +  1 - q  xF - x  / qy = x +  xF - x 3. Determine the number of equilibrium stages using the McCabe-Thiele graphical method.Plot the equilibrium curve  y vs. x , the q-line, and the rectifying line  y = R/ R+1 x + xD/ R+1   on the same graph. The intersection of the q-line and the rectifying line gives the feed plate location. Start from the xD point on the equilibrium curve and step off the stages using the rectifying line and the equilibrium curve. Repeat this process until you reach the xB point.4. Determine the minimum reflux ratio  Rmin  and the actual reflux ratio  R .Find the point where the rectifying line is tangent to the equilibrium curve. The slope of the tangent line at this point is the minimum reflux ratio  Rmin . To ensure a good separation, it is common to use a reflux ratio of 1.2 to 1.5 times the minimum reflux ratio  R = 1.2 * Rmin to 1.5 * Rmin .After performing the McCabe-Thiele graphical method, you will obtain the minimum number of equilibrium stages required, the feed plate location, and the reflux ratio needed to achieve the desired separation of 95% pure ethanol in the distillate and 95% pure water in the bottoms product.