Column configurations of continuous heterogeneous extractive distillation

Abstract

in Wiley InterScience (www.interscience.wiley.com).Increasing regulations and constraints have renewed interest for more efficient distillation process in separating azeotropic mixtures and close boiling components. We investigate the feasibility of heterogeneous extractive distillation process in a continuous column considering several feed point strategies for the entrainer recycle stream and for the main azeotropic feed. Depending on these choices, the heterogeneous distillation column is composed of one, two, or three column sections. A differential mass balance model enables to compute continuous liquid composition profiles of the rectifying, extractive, and stripping sections. Unlike homogeneous extractive distillation, reflux policy composed by a single or both decanted liquid phases is considered as well as the external feeding influence on the composition of the top column liquid stream. Limiting operating conditions of key parameters like the entrainer/feed flowrate ratio and reflux ratio required to obtain a target top and bottom product compositions are obtained. For illustration, separation of acetonitrile-water mixture using butyl acetate as a heavy heterogeneous entrainer is selected. In this case, withdrawal of a saddle binary heteroazeotrope is the main difference of this process compared with the well-known heterogeneous azeotropic distillation process where the top vapor product is the lower boiling point of the ternary system.

Reducing energy consumption and CO2 emissions in extractive distillation: Part II. Dynamic behavior

“…(Rodriguez- Donis et al, 2007;Kossack et al, 2008). Extractive distillation is widely used in several different processes: recovery of aromas or fragrances (Pollien et al, 1998;Chaintreau, 2001), separation of aqueous alcohol solutions (Pinto et al, 2000;Zhigang et al, 2002;Llano-Restrepo and Aguilar-Arias, 2003), mixtures which exhibit an azeotrope (Wu et al, 2007;Gil et al, 2009) and separation of hydrocarbons with close boiling points (Wentink et al, 2007;Abushwireb et al, 2007).…”

Heterogeneous extractive batch distillation of chloroform–methanol–water: Feasibility and experiments

“…Whatever the reflux policy, x R and y T are located on the same liquid-liquid tie line. However, the additional mixing of the entrainer to the liquid reflux coming from the decanter sets a new x 0 line between the selected liquid -liquid tie line and the entrainer vertex (Rodriguez-Donis et al 2007). The x 0 line has to be computed for a fixed With the column configuration defined (Fig.…”

Extractive distillation: recent advances in operation strategies

“…A solvent recovery column comes next, where the purified raffinate, B, is obtained as distillate and the solvent is recovered from the bottom and recycled to the extractive distillation column. Unlike the homogeneous distillation process, heterogeneous entrainers provide a simple technique to cross a basic distillation boundary, and the overall mass balance line Brought to you by | Carleton University OCUL Authenticated Download Date | 6/15/15 4:00 AM can connect two streams located in different distillation regions (Rodriguez-Donis et al 2007). …”

“…An entrainer recovery column and a preconcentrator are commonly associated with the heteroazeotropic column. Rodriguez-Donis et al (2007) investigated the feasibility of heterogeneous extractive distillation processes in a continuous column considering several feed point strategies for the entrainer recycle stream and for the main azeotropic feed (Figure 4). Depending on these choices, the heterogeneous distillation column is composed of one, two, or three column sections.…”