Adsorption of fatty acids to layered double hydroxides in aqueous systems

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 CO 3 2-.

Adsorption of oleic acid dissolved in isopropanol–water mixtures on hydrotalcite

“…One problem of the adsorption of long carboxylic acids on hydrotalcite is the accessibility of the interlayer. It can be increased by swelling the adsorbent in components like glycerol (Hansen and Taylor, 1991;Wiesen et al, 2015). LDH materials can also be modified prior to adsorption by calcination (Carlino, 1997;Crepaldi et al, 2002;Ulibarri et al, 2001;Wiesen et al, 2015).…”

“…It can be increased by swelling the adsorbent in components like glycerol (Hansen and Taylor, 1991;Wiesen et al, 2015). LDH materials can also be modified prior to adsorption by calcination (Carlino, 1997;Crepaldi et al, 2002;Ulibarri et al, 2001;Wiesen et al, 2015). The water and carbonate ions are removed from the interlayer by applying high temperature, which leads to a change in the structure of the metal hydroxide layer to a mixed metal oxide (Bergaya et al, 2006;Crepaldi et al, 2002).…”

“…The water and carbonate ions are removed from the interlayer by applying high temperature, which leads to a change in the structure of the metal hydroxide layer to a mixed metal oxide (Bergaya et al, 2006;Crepaldi et al, 2002). Upon adsorption, the interlayer is rebuilt (Carlino, 1997;Ulibarri et al, 2001;Wiesen et al, 2015). Wiesen et al (2015) show that calcinated hydrotalcites are efficient adsorbents for fatty acids.…”

“…Upon adsorption, the interlayer is rebuilt (Carlino, 1997;Ulibarri et al, 2001;Wiesen et al, 2015). Wiesen et al (2015) show that calcinated hydrotalcites are efficient adsorbents for fatty acids. However, the advantage of calcination for the adsorption goes together with an increased effort for desorption and regeneration, which requires calcination.…”

“…Upon adsorption, the interlayer is rebuilt (Carlino, 1997; Ulibarri et al., 2001; Wiesen et al., 2015). Wiesen et al. (2015) show that calcinated hydrotalcites are efficient adsorbents for fatty acids.…”