1. Results and Discussion
Pervaporation Separation of n-Butanol from Binary Aqueous Solutions Using Silicon Composite Membranes
Hoda Azimi*, Amit Ubhi, Niloofar Abdehagh, Jules Thibault, F. Handan Tezel, Dipak Rana, Takeshi Matsuura
Department of Chemical and Biological Engineering, University of Ottawa, Ottawa, ON Canada
Abstract
Project Objective
Results and Discussion
Membrane Characterization
To study the morphology of the composite PDMS-AC membranes with different percentages of activated carbon, scanning electron microscope (Vega-II XMU VPSEM and Anatech Hummer VII) has been used.
Nano-activated carbon particles have been used in the matrix of Polydimethylsiloxane (PDMS) membranes to improve the performance of pervaporation separation of biobutanol from butanol aqueous solutions. Results showed that the permeation flux and separation factor increase when an appropriate percentage of particles was added.
The main objective of this study is to improve the membrane performance for butanol separation by pervaporation. Polydimethylsiloxane (PDMS) membranes have shown to be a good option for this purpose. PDMS and PDMS/Nano-activated carbon composite membranes prepared in our laboratory have been studied for the separation of n-butanol from dilute aqueous solutions of 0.5% butanol at 37 °C.
Results showed that, the addition of 6 wt% nano-activated carbons embedded in the membrane matrix increased the the flux and separation factor by 42.6% and 51.9%, respectively in comparison with neat PDMS membranes. a)
Introduction
Pervaporation Experimental Setup
Biobutanol fuel produced from Acetone-Butanol-Ethanol (ABE) fermentation is considered to be an excellent candidate for the partial replacement of fossil fuels. However, some of the main challenges of this production process are the reduction of product inhibition via in-situ recovery and finding an efficient method for solvent recovery and water recycle.
Figure 1. Biofuel life- Cycle
Among the separation techniques considered by various researchers, pervaporation, a membrane based-process, has the greatest potential due to its high selectivity, low energy requirement and high efficiency. Moreover, it has no harmful effects on the microorganism [1]. b) c)
Figure 3. Effect of different percentages of Nano Ac on the pervaporation separation of biobutanol by PDMS membranes.
Proposed Mechanism
Figure 5. a) The cross section image of 6% AC-PDMS, b) free volume as a result of agglomeration, c) AC nanoparticles at the surface of membrane
It is hypothesized that the increase in selectivity is due to the dual mode of sorption: one in the polymer matrix and the other in the activated carbon particles, which enhances preferential butanol permeation. Moreover, the larger surface area (due to increased roughness) and the free volume inside the membrane could increase the flux and separation factor.
Results of SEM pictures confirm our hypothesis the existence of free volume near agglomeration sections as well as the presence of AC particles at the surface of AC-PDMS membranes.
Conclusion
Figure 2. Schematic diagram of pervaporation system
To characterise the membrane separation performance with different percentage of activated carbon (AC), the flux (J) and the separation factor (α) were measured. These parameters are defined in Equations (1)-(2).
The addition of butanol absorbents such as activated carbons within the matrix of the PDMS membrane:
Improves the performance of membrane
Increases the life time of membrane
All together decrease the cost of biobutanol production
PDMS-AC mixed matrix membrane
(1)
References
(2)
[1]. Abdehagh, N et al., Biomass & Bioenergy. 60, (2014).
[2]. Liu, G. et al., ACS Sustainable Chemistry & Engineering. 2, (2014)
where mi is the mass of species i in the permeate stream, A is the effective area of the membrane, t is the time of permeation, yi and xi are the mass fraction of species i in the permeate and feed streams, respectively [2].
Figure 4. Effect of nano Activated- carbon (AC) particles at the performance of PDMS membrane