Title: Study of Ionic Liquids as "Green" Solvents: Applications in Metal Deposition (Studie van ionische vloeistoffen als groene solventen: toepassingen in metaaldeposities)
Other Titles: Study of Ionic Liquids as "Green" Solvents: Applications in Metal Deposition
Authors: Haerens, Kurt
Issue Date: 3-Oct-2011
Abstract: Ionic liquids and deep eutectic solvents have gained a lot of interest as solvents in a broad range of different applications. Among the most studied is the (electro)deposition of metals and their alloys. While the main interest in the literature goes to the electrodeposition process itself and its possibilities, this work focuses on the main problems that can be expected when using ionic liquids or deep eutectic solvents on a large scale as "green" solvents for the (electro)deposition of metals.Four topics were selected, exemplifying the problems associated with scaling-up of the applications under study. These topics are the production of ionic liquids on a large scale, the bath maintenance through controlling the metal content and the anode reactions, the intrinsic process safety and the recycling of the solvent from rinse water.A key property of the solvent to be selected for (electro)plating is its cost. Currently most ionic liquids are not available on a large scale or still rather expensive. Furthermore, in electroplating the impurity level influences the deposition properties to a large extent. Both of these problems were the driving force to investigate electrodialysis as an alternative ion-exchange process. Electrodialysis offers advantages over other production processes, such as its high yield and its good electrochemical efficiency. The main advantage, however, is the ease of operation and the ability to prepare many combinations of anion and cation in a rather good quality.The longevity of the process bath was investigated through the maintenance of the metal content and the reactions at the electrodes.An existing immersion silver solution for printed circuit boards was used to evaluate the possibility of maintaining the metal content in the deep eutectic solvent. Electrochemical regeneration and regeneration with ion-exchange resins were studied as possible regeneration techniques. The use of ion-exchange resins proved to yield the best results.Both at the cathode and the anode, decomposition of the deep eutectic solvent was observed during electrodeposition. At the cathode the decomposition is small as the main process is the electrodeposition of the metal. At the anode the use of soluble anodes offered the best alternative to prevent decomposition. However, soluble anodes are not always applicable or available. In those cases the addition of sacrificial products was investigated. Unfortunately decomposition of the solvent could not be completely eliminated.The overall process safety was investigated for a deep eutectic solvent based on choline chloride and ethylene glycol. As this solvent is neither harmful, nor (eco)toxic and readily biodegradable, drag-out was determined as the main parameter for the environmental impact of the process. Drag-out is higher compared to aqueous process solutions due to the higher viscosity of the liquids. Classical best available technologies such as ion-exchange can still be applied to remove metals from the rinse water.Recycling of the deep eutectic solvent from the waste water was investigated with membrane technologies. Nanofiltration and reverse osmosis failed for the solvent under study. Furthermore, these pressure driven membrane technologies are limited by the osmotic pressure of the solutions. The deep eutectic solvent could neither be recycled using pervaporation due to the presence of a small uncharged organic molecule. However, for genuine ionic liquids, the use of pervaporation can be applied to remove small amounts of water at the end of the purification.<w:latentstyles deflockedstate="false" defunhidewhenused="true"  <w:lsdexception="" locked="false" priority="0" semihidden="false"  
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Process Engineering for Sustainable Systems Section
Chemical Engineering - miscellaneous
Chemistry - miscellaneous
Sustainable Chemical Process Technology TC, Technology Campuses Ghent and Aalst
Sustainable Chemical Process Technology TC

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