Quaternary solubility of acetic acid, diacetin and triacetin in supercritical carbon dioxide
Introduction
Over the past decade, it has been imperious to find new applications for glycerol (the major by-product of biodiesel) or convert it to the more applicable or expensive chemicals, due to the introduction of large amounts of it. Esterification of glycerol with acetic acid using catalyst to get mono, di and tri esters of glycerol acetates is one of the proposed solutions for conversion of relatively low-priced glycerol to valuable products. Glycerol acetates named monoacetin (MA), diacetin (DA) and triacetin (TA) have great industrial applications. They can be used as food additive, in the manufacturing of explosives and smokeless powder, as a cocoa butter blooming, as an intermediate in the synthesis of structural lipids, for plasticizer coating and foodstuffs, in cryogenics and biodegradable polyesters, chemical products in the food and cosmetic industries, in cigarette filters, as gelatinizing agent, as fuel additive, solvents for printing inks and dyestuffs, and softening agents [1].
These derivatives of glycerol are synthesized via esterification of glycerol with acetic acid or acetic anhydride with or without a homogeneous or heterogeneous catalyst using an organic solvent in both batch and continuous processes [2]. The three consecutive reversible steps of glycerol esterification with acetic acid is shown in Fig. 1. As it can be seen, all three-glycerol acetates are synthesized simultaneously through the reaction process. Whereas the reaction products is usually accompanied with some by-products that cause a change in the color or the odor. To this end, a purification process is needed that would be difficult and costly. As a result, selective synthesis of esters with high purity has been a great challenge for some researchers [3], [4], [5], [6], [7], [8], [9].
It should be noted that the boiling points of MA (282 °C), DA (260 °C) and TA (259 °C) are close to each other [10]. Especially the close boiling points of DA and TA, make their separation very difficult and costly, using conventional separation methods [11]. Also excess acetic acid remains in the mixture of the products. Therefore, separation of acetic acid for reusing and making the process economical is necessary. Supercritical fluid extraction, compared to conventional extraction methods, has a great potential as an efficient and clean alternative. Supercritical carbon dioxide (scCO2) is known as the most intensively used solvent due to its low critical point (Pc = 73 bar, Tc = 304 K), non-toxicity, inertness, and non-flammability, while remaining an inexpensive and environmentally acceptable substance [12]. The solubility information for the chemicals can provide data applicable for possible tailoring of the abovementioned reaction toward a specific product or higher efficiency including possible separation of mixture components of the products during the continuous synthesis, in scCO2 [13]. Most of the experimental solubility measurements in scCO2 deal with binary systems [14], [15], [16]. However, to the best of our knowledge, quaternary solubility measurements for acetic acid/DA/TA mixture in scCO2 is not reported yet. The main goal of this study was to find proper pressure and temperature in which scCO2 dissolves acetic acid selectively and extract it from the mixture of acetic acid/DA/TA. In this way, it is possible to develop a new process for selective extraction of excess acetic acid during the continuous synthesis of the products.
Section snippets
Materials
CO2 (purity > 99.95%) and ethanol (purity > 99%) were obtained from Zamzam Co. Ltd. (Isfahan, Iran) and Temad Co. (Tehran, Iran), respectively. Acetic acid (purity > 99%) and Pyrex wool were purchased from Merck Co. (Germany), DA (purity = 50% verified by GC-FID), TA (purity > 99%) were from Fluka Co. (Germany), 1-hexanol (purity > 98%) and 1-decanol (purity > 99%) were from Riedel-deHaën Co. (Germany). It must be noted that all the substances was used without further purification.
Procedure
The solubility measurements
Quaternary solubility of acetic acid/DA/TA versus sample weight
The quaternary solubility of acetic acid, DA and TA in scCO2 were measured for the four sample weights of 0.8, 1.5, 3.0 and 6.0 g at 313 K and 100 bar. In each experiment, after passing 1 L of CO2 gas through the trap at constant flow rate, at average laboratory temperature (300 K) and pressure (0.89 bar), samples were taken to measure the amount of extracted out of the cell. The results are shown in Fig. 3, Fig. 4, Fig. 5 . The trend of the solubility versus expanded CO2 volume for the four samples
Conclusions
By using a continuous-flow apparatus, the quaternary solubility of acetic acid, DA and TA in scCO2 were experimentally determined at temperatures of 313, 333 and 348 K from 70 to 180 bar at a constant expanded gas flow rate of 180 mL min−1. Acetic acid solubility increased by increasing density via increasing pressure. In the range of studied temperatures and pressures, in four points, scCO2 can extract acetic acid selectively from the mixture of acetic acid, DA and TA (313 K and 70 bar, 333 K and 70
Acknowledgement
The partial financial support by Isfahan University of Technology is acknowledged.
References (21)
- et al.
From glycerol as the byproduct of biodiesel production to value added monoacetin by continuous and selective esterification in acetic acid
J. Ind. Eng. Chem.
(2015) - et al.
Acetylation of glycerol catalyzed by different solid acids
Catal. Today
(2008) - et al.
Bioadditive synthesis from H3PW12O40-catalyzed glycerol esterification with HOA under mild reaction conditions
Fuel Process. Technol.
(2012) - et al.
Acetylation of glycerol over heteropolyacids supported on activated carbon
Catal. Commun.
(2011) - et al.
Producing triacetylglycerol with glycerol by two steps: esterification and acetylation
Fuel Process. Technol.
(2009) - et al.
Continuous extraction of glycerol acetates from their mixture using scCO2
J. Supercrit. Fluids
(2011) - et al.
Ternary solubility of mono- and di-tert-butyl ethers of glycerol in supercritical carbon dioxide
J. Supercrit. Fluid
(2010) - et al.
The co-solubility of 2-ethylhexanoic acid and some alcohols in scCO2
Fluid Phase Equilib.
(2005) - et al.
High-pressure fluid-phase equilibria: experimental methods and systems investigated (2005–2008)
Fluid Phase Equilib.
(2011) - et al.
High pressure vapour–liquid equilibria of the binary and some of the ternary and multicomponent mixtures of the carbon dioxide + acetic anhydride + α-methylbenzyl alcohol + acetic acid + α-methylbenzyl acetate system experimental and modelling results
Fluid Phase Equilib.
(2006)
Cited by (11)
Application and prospect of organic acid pretreatment in lignocellulosic biomass separation: A review
2022, International Journal of Biological MacromoleculesCitation Excerpt :In particular, the pretreatment of acetic acid and formic acid had good separation effect on lignin. This is attributed to the solubility of lignin, acetic acid and formic acid at 11.0, 10.1 and 12.1, respectively [36,37]. The main organic acids include formic, acetic [38], oxalic [39], levulinic [40], maleic [41], glycolic [42], lactic [43], citric acid [44], and p-toluenesulfonic acids (p-TsOH) [45].
Solubility of aspirin, ketoprofen and R-(-)-carvone in supercritical CO<inf>2</inf> in binary, ternary and quaternary systems: Effect of co-solutes
2022, Journal of Supercritical FluidsCitation Excerpt :Finally, no experimental data at 333.2 and 353.2 K have been reported in the literature, thus the present set of data is new. The higher solubility of carvone compared to those of ketoprofen and aspirin can be explained by its higher vapor pressure and lower molecular weight (Table 1) [22,27]. The RSD% (relative standard deviation) on the compound concentration of about 0.05 using our setup and data processing, reflecting the good repeatability of the experimental data.
Experimental measurement and correlation of solubility of ethosuximide in supercritical carbon dioxide
2019, Journal of Chemical ThermodynamicsCitation Excerpt :A lot of studies measured and correlated the solubility of various substances in SC-CO2 at broad ranges of pressure and temperature [14–19]. There have been several methods for the experimental measurement of solubility data of solids in SC-CO2 [20–24]. Among them, the cloud point method has been applied by a lot of researchers as a typical method to determine the solubility of SC-CO2 systems [25–30].
A review on recent developments and progress in the kinetics and deactivation of catalytic acetylation of glycerol—A byproduct of biodiesel
2017, Renewable and Sustainable Energy ReviewsCitation Excerpt :Glycerol is a highly functional material that requires defunctionalization to synthesize more than a thousand fine chemicals. Pathways such as etherification [23], oligomerization [24], dehydration [25], dehydrogenation [26,27], glycerol oxidation [28,29], transesterification [30], glycerol reforming [31–33], ketalization [34,35] and esterification [36–40] have been used to synthesize fine chemicals from glycerol. Some of fine chemicals synthesized from glycerol are summarized in our previous study [41].
Rigorous Modeling of Solubility of Acid in Supercritical Carbon Dioxide Using Connectionist approach: Comparison between ANN and density based modeling
2021, Energy Sources, Part A: Recovery, Utilization and Environmental Effects