(601i) Multi-Stage Thermal Simulated Moving Bed Concentrator: An Adsorptive Process for Wastewater Treatment and Solute Recovery

Wastewater generated from the effluent of various industrial activities is one of the main sources for water pollution. Many industries recycle and/or reuse this wastewater to both reduce water pollution and supply water for the plant. Many technologies have been developed and used for wastewater treatment. Adsorption provides an interesting and attractive alternative for wastewater treatment because of its ability to purify wastewater while concentrating the solutes contained in wastewater. Conventional adsorption systems often have major disadvantages. For example, regenerating the carbon in a kiln does not recover the solutes and eventually destroys the carbon. More gentle thermal adsorption processes and solvent regeneration of the adsorbent are typically operated as batch processes and have low efficiency of adsorbent use. Chromatography is very useful for separation of closely related compounds, but it has several limitations, such as low throughput, low efficiency (because the adsorbent packed in a column is not fully utilized), and solute dilution.  The need for large amounts of a chemical desorbent can pose additional waste issues or high energy consumption for desorbent recovery. Although chromatography would not normally be used for water treatment, chromatography in a simulated moving bed (SMB) can be adapted to wastewater. The isothermal simulated moving bed (SMB) overcomes the throughput and efficiency limitations. However, solute dilution and high desorbent consumption still persist. The integration of SMB process with temperature swing adsorption (TSA), or thermal SMB, has been shown to overcome the inherent limitations of isothermal SMB^1-3. In addition, a single 4-zone thermal SMB unit can simultaneously separate and concentrate binary dilute solutes as well as recover desorbent/solvent⁴. A different thermal SMB configuration with potential for water purification and concentration of one or more dilute solutes (thermal SMB concentrator) has been shown to have thermal energy consumption that is as low as 3% of an equivalent single-stage evaporator⁵. In the thermal SMB processes, adsorbent is regenerated at high temperature and solutes are adsorbed at cold temperature to regenerate the desorbent. This results in an extended ability of thermal SMB to separate solute and recover desorbent. In dilute systems separation is achieved without the use of additional desorbent. In this study, the application of two-zone, thermal SMB concentrator is extended to a multi-stage cascade of two-zone, thermal SMB concentrators for use in concentrating very dilute solutes and simultaneously producing purified water.  The optimum operating conditions are determined by extending the standing wave design (SWD) method⁴ to the two zone system and to a cascade of two zone, thermal SMB concentrators. The separation achieved at the optimum conditions is checked with detailed simulations using Aspen Chromatography.

References

1. Migliorini C, Wendlinger M, Mazzotti M. Temperature gradient operation of a simulated moving bed unit. Ind Eng Chem Res. 2001;40:2606–17.
2. Kim JK, Abunasser N, Wankat PC. Thermally Assisted Simulated Moving Bed Systems. Adsorption. 2005;11:579–584.
3. Jin W, Wankat PC. Thermal Operation of Four-Zone Simulated Moving Beds. Ind Eng Chem Res. 2007;46:7208–7220.
4. Soepriatna N, Wang NHL, Wankat PC. Standing Wave Design of a Four-Zone Thermal SMB Fractionator and Concentrator (4-zone TSMB-FC) for Linear Systems. Adsorption. 2013:In Press.
5. Lee JW, Wankat PC. Thermal Simulated Moving Bed Concentrator. Chem Eng J. 2011;166:511-522.