Biochar material evaluation through shock electrodialysis phenomenon for sustainable separation devices

PAULA MONTES; CAMILA ANTUNEZ; MATÍAS TRUJILLO; GABRIELA IGLESIAS; JOSÉ TREJO GONZALEZ; ROSSANA MADRID; ADOLFO ÁVILA

Conferencia; 2018 AIChE Annual Meeting; 2018

The shock electrodialysis phenomenon is associated with the emerging concepts related to shock deionization through porous media developed during the last years [1 ? 6]. Basically, it requires a flowing electrolyte solution through a weakly charged porous media which is located between two interphases with ionic selectivity such as electrodes or ionic membranes. When a growing electric potential is applied between the two electrodes, the current intensity increases steadily up to reaching a plateau zone. In this diffusion-limited current zone, an ion concentration polarization effect appears in the electrode interphase which is enlarged by the presence of the porous media. As a consequence, an ion depleted zone formed in the electrode-porous media interphase and an enriched ion zone in the bulk are able to be separated. New separation applications are thus envisioned for water desalination, waste treatments, microfluidics and nanofiltration. The availability of biomass associated with agroindustry residues provides excellent opportunities for new bioproducts applications for sustainable processes. Biochar is a costeffective carbonaceous material which can serve as raw material to create new separation agents and microdevices for gas purification, water treatment, biomolecule separation, controlled drug delivery, electrochemical reactors, microseparators and many other advanced applications.In this work, we used biochar disks derived from biomass harvest residues as a porous media to study the shock electrodialysis phenomenon. A home-made cell for continuous electrolyte flow including two stainless steel electrodes was used to study this phenomenon. The feed flow to the cell is located in the bulk electrolyte zone while the outlet flow leaves the cell exactly from the interphase region between the electrode and the porous biochar media. Comparative cyclic voltamperometry measurements were performed using the cell in batch mode with 1x10-4 M KCl solution either including or not including the biochar porous media. The difference between both voltamperametry profiles showed how the presence of the porous material modified the extension of theplateau zone related to the diffusion-limited current density. A set of continuous flow runs considering both distilled water (2.0 ? 6.0 µS/cm) and 1x10-4 M KCl solution (~17 µS/cm) were performed under an applied electric potential of 0.7 V previously selected from the voltamperometry measurements. The continuous monitoring of the solution ion conductivity in the cell outlet throughout each run provided important insights.Initially, the system was equilibrated by flowing feed solution at 30ccm (101.3 kPa, 25C) without applying electric potential until the outlet ion conductivity value remains constant. At the same initial flow rate conditions, the applied voltage to the cell essentially did not affect the outlet ion conductivity. A decrease in the outlet ion conductivity was observed when the feed flow rate was reduced while keeping the same applied voltage value. A ~5 to ~20% decrease in the outlet ion conductivity was observed for distilled water when the flow rate was reduced up to 50% of its original value. Only a ~2% decrease of the ion conductivity was observed for the KCl solution when the flow rate was 20% of its original value. The decrease of the outlet ion conductivity when the electric potential was applied to the cell indicated the presence of the ion concentration polarization effect through the biochar porous material. The polarization effect was deepened when flow velocities and electrolyte concentrations were lower. With a proper engineering design (geometry, thickness and morphology) and considering optimized operating conditions (flow rate, applied voltage and ion concentration), this cost-effective carbonaceous material can play an important role in the development of new separation technologies for water treatment.