Adsorption of fatty acids to layered double hydroxides in aqueous systems
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Adsorption of fatty acids to layered double hydroxides in aqueous systems Sebastian Wiesen1 • Nils Tippko¨tter1 • Kai Muffler1 • Kirstin Suck2 Ulrich Sohling2 • Friedrich Ruf2 • Roland Ulber1
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Received: 8 August 2014 / Revised: 30 June 2015 / Accepted: 1 July 2015 Ó Springer Science+Business Media New York 2015
Abstract Due to their anion exchange characteristics, layered double hydroxides (LDHs) are suitable for the detoxification of aqueous, fatty acid containing fermentation substrates. The aim of this study is to examine the adsorption mechanism, using crude glycerol from plant oil esterification as a model system. Changes in the intercalation structure in relation to the amount of fatty acids adsorbed are monitored by X-ray diffraction and infra-red spectroscopy. Additionally, calcination of LDH is investigated in order to increase the binding capacity for fatty acids. Our data propose that, at ambient temperature, fatty acids can be bound to the hydrotalcite by adsorption or in addition by intercalation, depending on fatty acid concentration. The adsorption of fatty acids from crude glycerol shows a BET-like behavior. Above a fatty acid concentration of 3.5 g L-1, intercalation of fatty acids can be shown by the appearance of an increased interlayer spacing. This observation suggests a two phase adsorption process. Calcination of LDHs allows increasing the binding capacity for fatty acids by more than six times, mainly by reduction of structural CO32-. Keywords Fatty acids Hydrotalcite Layered double hydroxides Adsorption Glycerol
& Sebastian Wiesen [email protected] 1
Bioprocess Engineering, University of Kaiserslautern, Gottlieb-Daimler-Str. 49, 67655 Kaiserslautern, Germany
2
Clariant-Produkte (Deutschland) GmbH, Ostenrieder Str. 15, 85368 Moosburg, Germany
1 Introduction Layered double hydroxides (LDHs), also called hydrotalcite-like materials, are known as anion exchanging clays. They are made up of layers containing metal cations, leading to an overall positive charge. The charge is neutralized by intercalation of exchangeable anions (Auerbach et al. 2004). Structurally, hydrotalcite is derived from the mineral brucite (Mg(OH)2), in which some of the Mg2? cations in the layer structure were replaced by Al3? in octahedral sites. The Mg2? ions are coordinated six-fold to hydroxyl groups. Electroneutrality is maintained by carbonate ions intercalated between the layers. The chemical formula of hydrotalcite is Mg0.75Al0.25(OH)2(CO3)0.50.5H2O (Bergaya et al. 2006). The thickness of the interlayer between the Al3? and Mg2? containing sheets is dependent on the number, size, and strength of the bonds between the anions and hydroxyl groups (Cavani et al. 1991). LDHs are used for a wide variety of applications in catalysis and polymer, pharmaceutical and medical industries. Some of the classical applications of LDHs are listed in the following. Because of the wide variety of its chemical compositions and large specific surface area, LDHs are common in the field of catalysis. Reactions cata
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