Separation of Organic−Water Mixtures by Co-current Vapor−Liquid Pervaporation with Transverse Hollow-Fiber Membranes

Abstract

The advantages of a liquid−vapor feed in a pervaporation unit are presented in comparison to a single-phase feed pervaporation unit that uses interstage heating. The comparison is based on calculations for the dehydration of isopropyl alcohol (IPA) from 13 to 1 wt % in a transverse system with hollow-fiber membranes. Because of the presence of the vapor phase, high mass- and heat-transfer coefficients in combination with low pressure drops are achieved. Vapor also supplies the heat for the evaporation and expansion of the permeating components through the membrane. Mass-transfer coefficients from the liquid to the membrane surface were measured using an electrochemical method. At low liquid superficial velocities, mass transfer increases up to 4-fold as compared to single-phase flow. Both the enhancement in mass and heat transfer to the membrane and the energy supply to the liquid result in a reduction of the required membrane area of 45%. This reduction in membrane area combined with the avoidance of interstage heat exchangers results in a marked reduction of capital costs, thus significantly expanding the application window of pervaporation.

Theoretical and Experimental Evaluation of a Distillation–Pervaporation in a Single Unit Column for the Separation of an Azeotropic Mixture

“…14 As a result, a smaller membrane area is required than a conventional pervaporation. 15 Also, a DPSU column does not required interstage heating for the pervaporation modules. The energy for the pervaporation process is supplied by the vapor phase condensation, and the energy is compensated by the column reboiler.…”

Analysis of a hybrid distillation‐pervaporation column in a single unit: Intermediate membrane section in the rectifying and stripping section

“…[15] The vapour phase induces turbulence on the liquid phase, increasing the mass and energy transfer on the membrane surface. [15,16] In addition, the heat required for the evaporation of the components that permeate is provided by the vapour phase. Thus, an inter-stage heating system is not necessary.…”

“…Thus, the internal vapour and liquid streams behave as the two-phase feed in pervaporation. [16,17] Inside the membrane section (MS), the separation is performed simultaneously by the distillation and pervaporation mechanisms. The energy consumed in the pervaporation process is supplied by vapour condensation on the liquid phase and it is compensated by the column reboiler.…”

Analysis of ethanol dehydration using membrane separation processes

“…For the distillate stream the ethanol recovery and purity were input as design specifications with 99.09% and 92.01% (81.81% mol) purity, based on initial ethanol convenient to combine membrane separation methods with conventional separation processes; several works have addressed this approach through the integration of distillation and membrane separation systems [17][18][19][20][21]. Design methods applied as part of optimization models for hybrid distillation-pervaporation and distillation-vapor permeation systems have also been reported [22][23][24][25]. Other configurations have been recently considered, such as the use of nano-filtration membranes [26], the integration of solar-driven membranes with distillation [27], and the novel development of membrane bioreactors [28][29][30].…”

“…On the order hand, the composition is close to the azeotropic condition; therefore, k i values are close 1.0 and it can be assumed that y i -x i ≈0. Applying this condition to equation (22), one obtains, (23) Equation 23was used to solve the liquid enthalpy change for the PV process.…”