Effect of biphasic system constituents on liquid-liquid extraction of 5-hydroxymethylfurfural

Abstract

HMF (5-hydroxymethylfurfural) is one of the bio renewable materials that can be used as an important platform chemical to produce biofuel and various chemical products. The main application of HMF in the chemical industry is a platform chemical for the production of plant-based polyethylene terephthalate (PET). HMF is produced through hexose dehydration which fructose or glucose is arranged as a feedstock. Liquid-liquid extraction can be applied in HMF production to enhance the selectivity and yield of HMF. HMF can be extracted from aqueous solution into the organic phase which prevents the degradation of HMF. Furthermore, it has been recognized that ionic liquid (IL) and deep eutectic solvent (DES) can be used as stabilizing agent in HMF production by suppressing the formation of side-products, hence increase the HMF yield as well. However, research on the systematic thermodynamics of HMF extraction is quite limited and needed to be developed. The thermodynamic data, such as phase equilibrium data and partitioning of HMF into organic phase are needed as basis for a rational design and optimal separation of HMF from the aqueous solution.
The objective of this research is systematically study the effect of biphasic system constituents on the liquid-liquid extraction of HMF at 313.15 K and atmospheric pressure (0.1 MPa). The extraction performance was evaluated based on the values of separation factor and HMF distribution coefficient which were determined from liquid-liquid equilibrium (LLE) data. The experimental LLE data of the investigated systems were also correlated well using thermodynamics models. The NRTL and UNIQUAC models were used to correlate the ternary experimental LLE data, whilst the experimental LLE data containing salt, IL, DES, and sugar were correlated using the NRTL model. We used aqueous-organic biphasic systems, and also added IL [EMIM][BF4] (1-ethyl-3-methylimidazolium tetrafluoroborate) or DES ChCl-urea (choline chloride-urea) in the aqueous phase. The effect of the addition of sugar (fructose) and salt in the variety of cation (Na+, K+) and anion (Cl-, SO4 2-) were also studied. Three different extraction solvents, methyl isobutyl ketone (MIBK), 2-pentanol, and tributyl phosphate (TBP), were used for the comparison.
According to the results in this study, it indicated that for 2-pentanol the HMF distribution coefficient is up to 1.4 times higher than MIBK. Besides, MIBK has a 2-3 times higher separation factor than 2-pentanol. While TBP is more selective as extraction solvent than the other two solvents, TBP is also superior in terms of HMF distribution coefficient. The salting-out strength of salts for organic solvent (MIBK or 2-pentanol)-HMF-water-salt systems are in the order NaCl > Na2SO4 > KCl > K2SO4. NaCl was found superior in both separation factor and distribution coefficient of HMF compared to the other salts studied. Furthermore, the separation factor and HMF distribution coefficient decreased with the increase of IL [EMIM][BF4] and DES (ChCl-urea) concentrations. However, DES (ChCl-urea) decreased the extraction performance less than IL [EMIM][BF4]. The addition of salt (NaCl) enhanced the separation factor and the distribution coefficient of HMF, enabling compensation of the IL and DES effects. The presence of salt can enhance both the extraction performance parameters up to 2-4 times for all the investigated systems studied using three different organic
solvents and also in the presence of IL or DES. While, the presence of fructose in the solution had limited effect on the extraction performance. In general, it can be inferred that by taking the advantage of IL/DES as stabilizing agent, aqueous IL/DES with NaCl is a good combination applied in HMF extraction process to achieve good extraction performance.