Dataset for the interfacial tension and phase properties of the ternary system water – 2-butoxyethanol – toluene

Two-phase samples containing water, 2-butoxyethanol, and toluene in the different mass ratios were gravimetrically prepared in the jacketed cells at T=293.15 K and p=0.100 MPa and equilibrated for 24 h. The samples were volumetrically titrated until homogeneous. Then new samples were prepared in the two-phase region with compositions in the immediate proximity to the expected separation boundary and titrated until homogeneous. The critical point was located, keeping the phase ratio of 1:1 during the titration. The density of homogeneous samples obtained during titration was measured using the density meter. These data were used to construct an interpolation of the density along the separation boundary. New two-phase samples were prepared; the interfacial tension, density, and viscosity were measured. Thus, interfacial tension isotherm and viscosity isotherm were obtained using density interpolation to determine the composition of the equilibrated phases. The obtained data can be used to prepare the two-phase samples with desired properties, design the oil-water separation processes, and develop new oil spill dispersants containing 2-butoxyethanol. This article is a co-submission with a paper [1].


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Two-phase samples containing water, 2-butoxyethanol, and toluene in the different mass ratios were gravimetrically prepared in the jacketed cells at T = 293.15 K and p = 0.100 MPa and equilibrated for 24 h. The samples were volumetrically titrated until homogeneous. Then new samples were prepared in the two-phase region with compositions in the immediate proximity to the expected separation boundary and titrated until homogeneous. The critical point was located, keeping the phase ratio of 1:1 during the titration. The density of homogeneous samples obtained during titration was measured using the density meter. These data were used to construct an interpolation of the density along the separation boundary. New two-phase samples were prepared; the interfacial tension, density, and viscosity were measured. Thus, interfacial tension isotherm and viscosity isotherm were obtained using density interpolation to determine the composition of the equilibrated phases. The obtained data can be used to prepare the twophase samples with desired properties, design the oil-water

Value of the data
• In this work, we compared behavior of hydrotropes -tertiary butanol (TBA) and 2butoxyethanol (BEG) -at the oil/water interface. It shows a high degree of universality, however, more hydrophobic BEG demonstrates higher adsorption at the oil/water interface and shifts the critical point closer to the water vertex. These results could be used to predict the behavior of the systems with different hydrotropes. • The present data on the phase equilibria can be useful in constructing phase diagrams of ternary systems containing low-molecular-weight amphiphiles. • It has been shown that measuring density along the separation boundary can be used to determine the composition of equilibrium phases in the two-phase region with a high accuracy. • Data on interfacial tension, density, and viscosity could be used to rationally design oil spill dispersants.

Data Description
The data on phase equilibrium and interfacial phenomena of the system water -BEGtoluene is reported in this work in accordance with recent IUPAC recommendations [2] . Compositions of two-phase and one-phase samples along the phase separation boundary are presented in Table 1 . Data in Table 1 include the densities of water -BEG -toluene homogeneous systems obtained during titration, which were further used to construct an interpolation of the density along the separation boundary ( Fig. 1 ). Approximated binodal curves at 293.15 K for ternary water -BEG -toluene and water -TBA -toluene systems and fitting residuals are shown in Fig. 2 (the data for the Fig. 2 construction are in Table 2 ). The ternary phase diagrams of water -BEG -toluene and water -TBA -toluene systems at 293.15 K are shown in Fig. 3 . The comparison of water -BEG -toluene with other ternary systems containing BEG (or MeEG) is presented in Fig. 4 . Compositions of water -BEG -toluene system samples used to construct  Table 1 ( ω Tol is from Column VII; ω BEG is from Column VI; ρ is from Column XIV).    n/a n/a n/a 0.0 0 05 b 0 0.9995 b n/a n/a n/a 0.
3 . Y residuals is difference between experimental and fitted value (9th order polynomial) of mass fraction of hydrotrope. Fig. 3. Phase diagrams at 293.15 K of the systems W-BEG-TOL (this work) and W-TBA-TOL [6] in mole percentage; circles are experimental points (titration), color lines are 9th order polynomial approximations; red filled markers denote critical points; blue-filled area corresponds to the two-phase region in the W-BEG-TOL system. Data on W-BEG-TOL system are from  Data on W-BEG-TOL system are from Table 1 ( ω H2O is from Column V; ω BEG is from Column VI; ω Tol is from Column VII).  Table 3 , Column VIII; ρ is from Table 4 , Column XVI). Table 1 . Table 3 contains the compositions of the two-phase liquid samples, the interfacial tension between the equilibrated phases, and the normalized interfacial tension, which is illustrated by the interfacial tension isotherm shown in Fig. 6 . Compositions, density, viscosity of the equilibrated phases, and density difference of the equilibrated phases are reported in Table 4 . Fig. 5 shows density difference of the equilibrated phases for ternary systems water -BEG -toluene ( Table 4 ) and water -TBA -toluene.    a the maximum error in density measurement is 5 ·10 −5 g/mL, the maximum error is 0.5 % of the measured value for viscosity. b viscosity of pure water [11] and toluene [12] . c literature data on solubility of toluene in water and water in toluene [10] .  Table 3 ( ω BEG in water phase is from Column X; γ / γ 0 is from Column XII).

Experimental Design, Materials and Methods
For the preparation of samples of the ternary system toluene (99.9% purity determined by the manufacturer, Ecos-1, Russia), BEG (99.5% purity determined by the manufacturer, Ecos-1, Russia), and deionized water ( ≥18.1 M ·cm, Simplicity UV, Millipore) were used. The samples were prepared in custom-made jacketed cells with an inverted ground joint using the freshly calibrated balances PA413C (resolution 0.001 g, maximum error ±0.01 g, Ohaus, USA).
The location of the binodal curve and the critical point on the diagram was determined by volumetric titration from a two-phase state (detected visually as turbidity of the sample) to a homogeneous solution at 293.15 ±0.10 K. The position of the critical point was determined by titration with a volumetric phase ratio of 1:1. The samples were titrated in two stages. First, two-component water-toluene samples were titrated with BEG. Then, new two-phase samples with compositions in the immediate proximity to the expected separation boundary were prepared and titrated using small amounts of the titrants. The solubilities of toluene in water and water in toluene were obtained by titrating two-component samples with water or toluene. The combined standard uncertainty ( U c ) was calculated according to JCGM 10 0:20 08, taking into account the purity of the components, maximum errors of weighing, and dosing uncertainty of titrants [3] . The densities of homogeneous titrated samples were measured with density meter DMA 4500 (Anton Paar, Austria) to construct an interpolation of the density along the separation boundary. The maximum error in density measurement is 5 ·10 −5 g/mL.
The two-phase samples for density, viscosity, and interfacial tension measurements were magnetically stirred for at least 12 h at 293.15 ±0.1 K after preparation, and then they were equilibrated without stirring for at least 12 h for complete stratification of phases. The density and dynamic viscosity of equilibrated phases in the two-phase region were measured at 293.15 ±0.03 K using a rolling-ball viscometer Lovis 20 0 0 ME (Anton Paar, Austria) integrated with a density meter DMA 4500. The maximum error is 0.5 % of the measured value for viscosity. The interfacial tension of two-phase samples was measured using a spinning drop tensiometer SDT (Krüss, Hamburg, Germany) equipped with a circulation thermostat, Ministat 230 (Huber, Offenburg, Germany). The interfacial tension between water and toluene was determined with a force tensiometer K20 (Krüss, Hamburg, Germany) equipped with a circulation thermostat, MPC-E (Huber, Offenbur g, Germany), by the Wilhelmy plate method. The compositions of equilibrated phases were obtained through density-interpolation data collected during titration. The interfacial tension data were approximated by a crossover function [4] , combining the Langmuir -von Szyszkowski isotherm and the near-critical behavior predicted by the scaling theory [5] .

Ethics Statements
The studies described in the manuscript were conducted adhering to Ethics in publishing standards ( https://www.elsevier.com/journals/data-in-brief/2352-3409/guide-for-authors ) and did not involve human or animal subjects.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.