Exercise 04 solution ENG

Pagina 1

Page 1 of 3 Dipartimento di Chimica, Materiali e Ingegneria Chimica “Giulio Natta” POLITECNICO di MILANO Practical class (informatic laboratory) of Chemical Processes and Technologies (Prof. Stefania Moioli) Results Binary distillation Solving the overall and component material balance for the more volatile component (i.e., benzene) F D B F D B Fz Dx Bx =+  =+ considering the two purity specifications (xD = 0.95, xB = 0.04), it is possible to obtain: D/F = 0.2857; B/F = 0.7143. To calculate the relative volatility of benzene with respect to toluene at the thermal conditions of the top of the column, of the bottom of the column and of the feed stream (since the feed stream is at its bubble point), the following three temperatures are determined: • dew point temperature of the distillate product: Td,D = 355. 74 [K]; • bubble point temperature of the bottom product: Tb,B = 381.92 [K]; • bubble point temperature of the feed stream: Tb,F = 371.61 [K]. The corresponding relative volatilities are: • αtop = 2.5770; • αbottom = 2.3613; • αfeed = 2.4397. Thus, the average volatility is 3 top bottom feed    = =   = 2.4577 (this average is used in this case, thus also including αfeed, because the feed is at its bubble point, i.e. q = 1). The minimum reflux ratio is Rmin = 2.0519 (it can be determined using the formula available for q = 1, since, in this problem, the feed stream is at its bubble point). Page 2 of 3 When using the graphical McCabe-Thiele method, it is possible to draw on the x-y diagram: • the equilibrium curve: ( )11 xy x  = +− ; • the operating line of the rectifying (upper) section of the column : 1 11 D nn xRyx RR +=+ ++ → it is a straight line passing through the point (xD,xD) and having a slope related to R = 1.3∙Rmin; • the q-line, having equation…