Thermodynamic analysis of fatty acid harvesting by novel carbon-based adsorbent

Abstract

In this study, separation and concentration of fatty acids (FA) from the synthetic food processing wastewater containing low concentration of FA (250 mg/L) were investigated using expanded graphite (EG) as a novel adsorbent at different temperatures (298~318 K). The adsorption results were further analyzed to verify adsorption mechanisms and thermodynamics of FA onto EG. Results show that the adsorption of FA onto EG was explained well by the Langmuir model with the maximum adsorption capacity up to 8.01 g FA/g EG at 298 K, and considerably affected by temperature. The adsorption kinetics fitted with pseudo-second-order kinetic model and the adsorption mechanism analysis showed that the intraparticle diffusion was not the rate-limiting step, but the coalescence of FA droplets played the significant role for novel adsorption of FA onto EG. The calculated activation energy and thermodynamic parameters such as Gibbs free energy change (ΔG(0)), enthalpy change (ΔH(0)), and entropy change (ΔS(0)) indicated that the adsorption of FA onto EG was very feasible, was highly spontaneous, occurred physically, was exothermic in nature, and was stable in aquatic environmental changes. Overall, FA can be effectively harvested and concentrated from the food processing wastewater by EG even at low concentration.

Adsorption of Lead and Nickel on to Expanded Graphite Decorated with Manganese Oxide Nanoparticles

“…The experimental equilibrium data of Pb 2+ and Ni 2+ adsorption onto the prepared MONPs-EG in single and binary metals systems were characterized using Langmuir and Freundlich isotherms [28][29][30]; their mathematical expressions are given by the following Equations (2) and 3, respectively.…”

“…The higher magnitude of ∆S 0 obtained in the Pb 2+ system signified that it had a better affinity toward and was more stable on the MONPs-EG compared to Ni 2+ . Furthermore, negative values of ∆G 0 at all investigated temperatures indicated that the adsorptions of both metal ions onto the prepared MONPs-EG were thermodynamically favorable and spontaneous in nature [28,50]. Humic acids (HA) are the major components of dissolved organic matter in natural surface water.…”

“…Sci. 2019, 9, x FOR PEER REVIEW 10 of 15values of ΔG 0 at all investigated temperatures indicated that the adsorptions of both metal ions onto the prepared MONPs-EG were thermodynamically favorable and spontaneous in nature[28,50]. Effect of temperature on adsorption behaviors of prepared MONPs-EG for: (a) Pb 2+ ; (b) Ni 2+ in single metal solutions.…”