Thermodynamic Data for Processing Naphthol with Supercritical

Article pubs.acs.org/jced

Thermodynamic Data for Processing Naphthol with Supercritical Carbon Dioxide Nina Trupej, Mojca Škerget, Otilija Petek, Darija Cör, and Ž eljko Knez* Faculty of Chemistry and Chemical Engineering, University of Maribor, Smetanova 17, SI-2000 Maribor, Slovenia ABSTRACT: The solubilities of 1-naphthol and 2-naphthol in CO2 have been investigated at the temperatures 313, 333, and 353 K in the pressure range from 10 to 60 MPa. The melting points in the presence of CO2 have been determined at pressures from 10 to 60 MPa. The densities of the systems 1-naphthol/CO2 and 2naphthol/CO2 were determined at temperatures of 313, 333, and 353 K and at pressures up to 40 MPa by a densitometer. The solubility decreases with increasing temperature above the pressure of 20 MPa and has a maximum. The melting points of naphthols decrease with increasing pressure to a melting point minimal temperature at pressure 20 MPa. The density of the naphthols/CO2 solution can differ from the density of the pure CO2 (below the critical point also by 100% or more).

1. INTRODUCTION 60% of all products sold by chemical companies are crystalline, polymeric, or amorphous solids, which need to have a defined physical shape and size;1 therefore, the investigation of solid compounds and their properties are of major interest. An alternative to material processing with organic compounds is the promising high-pressure technology with use of sub- and supercritical fluids, like homogenization, micronization, crystallization, impregnation, encapsulation, and so forth.1 With such high-pressure micronization processes small particles with a defined shape and size can be produced, with nonhazardous impact on the substance or environment. For designing supercritical processes, the knowledge of thermodynamic properties of the system is crucial.2 These properties should be determined experimentally if possible, due to some drawbacks (especially for multicomponent systems) of the models that predict the thermodynamic data of solids in supercritical fluids.3 For the determination of the solubility of solids in dense gases several experimental methods are used.1 The applied method depends on the physicochemical properties of the system solid substance/dense gas.1 Naphthol as a solid compound has been interesting for experimental and theoretical studies for many years.4−15 Even if solubility models of different compounds in supercritical fluids exist, the experimental data are the most valuable information for designing processes of producing naphthol with a defined size and shape with supercritical fluids. Therefore, solubility measurements of 1-naphthol16,17 and derivates of 1-naphthol18 in CO2 were performed. The solubility data of 2-naphthol19 and of different mixtures with 2-naphthol8,10,17,20,21 were found in literature and were used for testing different models and their performance of solubilities in supercritical CO2 with or without cosolvents.14,22−25 Naphthols are mainly used for pesticide industries and for dye producing, and it is used for biomarkers in livestock and © XXXX American Chemical Society

humans. Due to the hydroxyl group of naphtalene at position 1 or 2 (1-naphthol and 2-naphthol), it is considered more toxic than naphthalene and other poylcyclic aromatic hydrocarbons, and it is more soluble and portable in aquifers.4 Naphthols are fluorescent organic solid compounds, soluble in alcohols, ethers, and chloroform,26 and due to the importance of naphthols as a component in synthesis of azo dyes and other products,27−35 the research was focused on the thermodynamic data of the system naphthols/CO2. In the present work, solubility data for the naphthols (1naphthol and 2-naphthol) in CO2 are presented at pressures that have not been investigated yet: pressure up to 60 MPa and at temperatures of 313, 333, and 353 K. Due to the possible formation of liquid phase of naphthol in CO2 the static analytic method was applied. These data are a contribution to the already existing thermodynamic data of naphthols/CO2 solution with the extension of the solubility data for a wider pressure range. The melting points of naphthols were determined in the pressure range from 10 to 60 MPa, and densities of the naphthols/CO2 solution were investigated at temperatures of 313, 333, and 353 K at pressures up to 40 MPa with a densitometer. Both the melting points and the densities of the binary systems of 1-naphthol/CO2 and of 2-naphthol/CO2 were not reported before.

2. EXPERIMENTAL SECTION 2.1. Materials. For the solubility measurements carbon dioxide of purity 99.5 wt % was obtained from Messer, Slovenia and 1-naphthol (106223) and 2-naphthol (822290) from producer Merck. The substances were used without further Received: September 4, 2016 Accepted: March 7, 2017

A

DOI: 10.1021/acs.jced.6b00781 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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contains a blade turbine stirrer for mixing and two 60 mm electric heaters inserted in the stainless steel coat of the cell. The procedure for determination melting points was based on the capillary method. The substance was introduced into the glass capillary fixed on the thermocouple and placed in the high-pressure cell. Afterward the gas was introduced into the cell and heated. The melting of the substance in the capillary was observed and pressure were registered at the melting. The cell was loaded with adequate (approximately 2 g) of material (1-naphthol or 2-naphthol). Afterward CO2 was introduced into the view cell using a high-pressure pump, and the system was heated up to the desired temperature. The content of the cell was mixed (1 h). After reaching equilibrium, the gas rich phase was sampled into a glass trap (at atmospheric conditions). The amount of sample in the trap was determined gravimetrically (accurate ±0.1 mg). The volume of CO2 released during sampling was measured with disposal of water. The pressure change observed during sampling was between 0.05 and 0.5 MPa. No temperature change was detected.36,37 For each system of solute/dense gas, the times to achieve equilibrium solubility and to determine the sedimentation time were experimentally verified. The determined solubilities were correlated with the Chrastil model,38 which can be represented with the function ln c = f(ln ρ), where c is the solubility of naphthol in carbon dioxide and ρ the density of carbon dioxide (obtained from NIST39). 2.2.2. Density of the Binary System 1-Naphthol/Carbon Dioxide. The equipment and the method is described in literature,40 but due to the pressure drop and in order to ensure saturation of CO2 with naphthol, a modification of the apparatus and measuring procedure was made as described below. The apparatus is presented on Figure 1. A vibrating tube densitometer was used for the density determination. The main part of the densitometer is the Anton Paar DMA 512 unit. The DMA 60 unit represents the vibration period. The U tube inside the DMA 512 unit was thermostatted with a circulating water bath with an accuracy of ±5 ×

purification. Information of each chemical sample is presented in Table 1. The physical properties of substances are presented in Table 2. Table 1. Sample Table chemical name 1-naphtol 2-naphtol a

source Merck (106223) Merck (822290)

final mode fraction purity

initial mole fraction purity

purification method

0.99

none

GCa

0.99

none

GCa

analysis method

Gas chromatography.

Table 2. Physical Properties of Chemicals Used39 1-naphthol −1

Mw (g mol ) Tmelt (°C) at 0.1 MPa Tboling (°C) at 0.1 MPa appearance

2-naphthol

CO2

144.17 367.15−369.15

144.17 393.15−395.15

44.01 −56.6

278−280

285−286

colorless

colorless to light yellow

−78.5 (sublimation) colorless gas

2.2. Apparatuses and Methods. 2.2.1. Melting Point Determination and Solubility Measurements. The equipment and methods used for the determination of the melting points and solubility measurements are described in our previous research.36,37 Briefly the solubility and melting points was measured by using a high-pressure, variable volume cell (NWA GMBh, Lorrach, Germany). The cell is made of stainless steel (AISI 316). The apparatus can be used at pressures up to 75 MPa and 473 K and has a variable volume between 30 and 60 cm3. The cell is provided with two sapphire windows for visual observation of the interior, a thermocouple for temperature monitoring (accurate ±0.5 K), and with two additional openings for introducing and emptying the gas. The cell

Figure 1. Apparatus for the determination of solubilities and densities of supercritical fluid/solid mixtures; (a) equilibrium establishment, (b) sampling: TI temperature indicator, PI pressure indicator, V valves, A autoclave, CP chromatographic pump, SP syrine pump, H heating, DMA 512 apparatus with the vibrating tube, DMA 60 measuring unit, T1 and T2 thermostats. B



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10−3 K, and the temperature inside the U tube was measured with a GTH 1150 digital thermometer NiCr-Ni with an accuracy of 1%. The autoclave and the U tube were equipped with a manometer Nuova Fima EN837-1 with an accuracy of 0.25% for pressures lower than 60 MPa. For determination of the vibration period the autoclave was filled with a sufficient amount of naphthol (approximately 10 g) and connected to the densitometer (Figure 1). After connecting the components, the whole system was heated by the thermostatic baths and electric wires. After opening the valves, the hand pump was set to the minimum volume, and the whole system was depressurized with a vacuum pump. Then CO2 was introduced into the system to reach the desired pressure. Mixing was performed by a magnetic stirrer. Equilibrium was established after 1 h of mixing, and subsequently the stirring was stopped, and the system was allowed to stand for an additional hour for the sedimentation of undissolved naphthol flakes. Valve V2 was then closed, and the hand pump (Nova Swiss piston pump) was turned to the direction of its maximal volume, which enabled the transport of the saturated carbon dioxide with naphthol to the densitometer. Then valve V1 was closed, and valve V2 was opened; the hand pump was turned back to the beginning position to its minimal volume, and the fluid with saturated naphthol was returned back into the autoclave to the starting conditions (Figure 1). Then the stirring started again; the equilibrium was established, and the circulation of the mixture was repeated. After the third equilibrium establishment and fluid circulation the vibration period of the fluid saturated with naphthol was measured with the DMA 60 unit. Fluid density is calculated from the vibration period. Density determinations were performed with a vibrating tube densitometer which is basically a spring-mass system in which the frequency of vibration of the tubing is measured (vibration period) and related to the fluid density. Equation 1 was applied for calculating the density (ρ/kg·m−3) ρ = K(τ 2 − τ12) + ρ1

Table 3. Melting Point (Melting Pressure Pm, Melting Temperature Tm) of 1-Naphthol under Pressure of CO2a Tm (K)

0.10b 2.40 5.04 10.21 15.07 20.25 30.04 40.84 50.80 60.84

370.54 368.95 365.45 362.65 359.90 358.90 359.15 360.15 360.80 362.95

a Standard deviation u: u(T) = 0.5 K, u(P) = 0.02 MPa. bThis value was measured by DSC.

Table 4. Melting Point (Melting Pressure Pm, Melting Temperature Tm) of 2-Naphthol under Pressure of CO2a Pm (MPa)

Tm (K)

0.10b 2.51 4.98 10.06 14.79 20.48 30.48 39.99 51.12 60.57

396.98 397.40 394.40 390.10 386.05 383.45 384.10 385.05 386.10 387.35

a Standard deviation u: u(T) = 0.8 K, u(P) = 0.03 MPa. bThis value was measured by DSC.

(1)

−1

where K (kg·s ·m ) is the characteristic parameter of the U tube, τ (s−1) is the vibration period of the U tube (of the densitometer) when filled with a fluid of an unknown density, ρ1 (kg·m−3) is the density of reference fluid, and τ1 (s−1) is the vibration period of the U tube filled with the reference fluid. Previously, the characteristic parameter K has to be determined by eq 2.2 at each temperature and pressure by measuring the vibration period of two reference fluids of known densities. ρ − ρ2 K = 21 τ1 − τ22 (2) 2

Pm (MPa)

Figure 2. Melting points (Tm, melting temperature, Pm, melting pressure) of 1-naphthol (○) and 2-naphthol (△) under pressure of CO2 (P).

In the present research, the reference fluids were Milli-Q water and nitrogen. The density data at different temperatures and pressures for calibration fluids are well-known and were obtained from literature.40

of 1-naphthol is at temperature of 358.90 K and pressure of 20.25 MPa while for 2-naphthol it is at temperature of 383.45 K and pressure 20.48 MPa. The difference between the melting point at 0.1 MPa and the minimum melting point is approximately 11 K for 1-naphthol and 13 K for 2-naphthol. Despite the fact that 1-naphthol and 2-naphthol have the same molecular mass, the position of the hydroxyl functional group has a major effect on the melting point of the substance. The position of the hydroxyl group in 2-naphthol causes stronger hydrogen bonds between the molecules due to the lower spherical hindering compared with the molecules at position “1” in 1-naphthol. The melting point difference between 1-

3. RESULTS AND DISCUSSION 3.1. Melting Point Investigation. The melting points of 1-naphthol and 2-naphthol under pressure of carbon dioxide were determined at pressures up to 60 MPa and are presented in Table 3 and Table 4. The melting point curves for 1naphthol and 2-naphthol have a minimum at pressure approximately 20 MPa (Figure 2). The melting point minimum C



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naphthol and 2-naphthol at 0.1 MPa is 27 K, and at melting point the minimum (under pressure of CO2) is 24 K. 3.2. Solubility Determinations. The mole fractions of naphthols in CO2 are presented in Tables 5 to Table 10 and in Figures 3a and 4a.

Table 9. Mole Fraction of 2-Naphthol in CO2 (y2) at a Temperature of 353 Ka

Table 5. Mole Fraction of 1-Naphthol in CO2 (y2) at a Temperature of 313 Ka T (K)

P (MPa)

y2 (mol·mol−1)

313.05 313.05 313.35 313.10 313.33 313.25 313.40

10.04 20.39 29.55 40.23 49.63 57.94 59.53

0.0833 0.0940 0.1096 0.1112 0.1194 0.1057 0.1036

y2 (mol·mol−1)

332.95 333.15 333.25 333.30 333.15 333.35 333.15

10.45 20.80 30.59 41.27 49.47 51.60 58.84

0.0593 0.0840 0.1078 0.1113 0.1084 0.1030 0.0992

y2 (mol·mol−1)

353.25 353.40 353.20 353.30 353.45

9.97 20.02 30.05 39.89 49.95

0.0740 0.0781 0.0765 0.0765 0.0788

Table 10. Mole Fraction of 2-Naphthol in CO2 (y2) at a Temperature of 333 Ka

Table 6. Mole Fraction of 1-Naphthol in CO2 (y2) at a Temperature of 333 Ka P (MPa)

P (MPa)

a Standard deviation u: u(T) = 0.4 K, u(P) = 1.59 MPa, u(y2) = 0.0015 mol·mol−1.


T (K)

T (K)

T (K)

P (MPa)

y2 (mol·mol−1)

333.45 333.30 332.58 333.02 333.45 332.85

9.95 19.84 29.88 40.72 50.06 60.00

0.0736 0.0760 0.0731 0.0727 0.0803 0.0761

a

Standard deviation u: u(T) = 0.6 K, u(P) = 3.11 MPa, u(y2) = 0.0027 mol·mol−1.

a



P (MPa)

y2 (mol·mol−1)

353.35 352.80 353.05 353.30 353.30 353.10

10.49 19.57 30.52 40.58 50.11 59.13

0.0772 0.0834 0.0834 0.0792 0.0784 0.0697

a



P (MPa)

y2 (mol·mol−1)

313.25 313.35 313.20 313.30 313.25 313.05

10.00 20.03 29.85 39.94 49.47 59.64

0.0784 0.0879 0.0903 0.0789 0.0825 0.0851


Figure 3. (a) Mole fraction of 1-naphthol in CO2 (y2) at temperatures 313 K (◊), 333 K (□), and 353 K (△) versus CO2 pressure (P) and comparison to literature Trabelsi et al. 1999:11 318 K (−), 338 K (I); Tan, Weng 1987:17 308 K (○), 318 K (+), 328 K (−). b) Chrastil correlation model. Natural logarithm of 1-naphthol solubility in carbon dioxide (g·m−3) as a function of natural logarithm of carbon dioxide density (kg·m−3) at temperatures 313 K (◊), 333 K (□), and 353 K (△).

The solubility of 1-naphthol in CO2 is the highest at temperature 313 K and in the pressure range between 30 and

60 MPa, followed by the solubilities at temperature 333 K and the lowest at temperature 353 K. The solubility of naphthol in CO2 at constant pressure decreases with increasing temperature, due to the lower density D



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naphthol in the gas phase ( V 2g ) which is at its maximal solubility equal to the molar volume of the pure naphthol * ).46,47 (V2,m Figure 4a represents the mole fraction of 2-naphthol in CO2 at temperatures 313, 333, and 353 K. Solubilities are the highest at temperature 313 K; the solubilities at temperature 333 and 353 K are very similar (difference between 0.5% and 5%). The solubilities’ differences at all investigated temperatures and at pressure 10 MPa and in pressure range 40−60 MPa are maximally 5%. Bigger deviations are at pressure 20 and 30 MPa, with a solubility difference of 20% at 313 and 333 K compared to 353 K. The solubility of 1-napthol in CO2 is higher than the solubility of 2-naphthol, except at low pressures, where the solubilities are similar (313 K) or are even somewhat lower for 1-napthol (333 K). The maximal differences in the solubility of both naphthols in CO2 are at 313 and 333 K observed at 50 MPa, where the solubility of 1-naphthol is by approximately 30% higher as that of 2-naphthol. The solubility of 1-naphthol at temperature 353 K is generally higher for approximately 5% compared to solubility of 2-naphthol in CO2. The reason for the higher solubility of 1-naphthol in CO2 could be a lower dipole moment of 1-naphthol compared to 2napthol molecules. The naphthol solubility in CO2 was compared to the data from literature. Much higher solubility data were determined for the 1-naphthol/CO2 solution compared to literature,17,47 where the mole fractions are for factor 10 or 100 smaller (Figure 3a). Similar conclusions were made for the system 2naphthol/CO2, with a factor of 100 lower than literature data.22,48 One order of magnitude difference (or more) between researches was reported before49,50 and is a consequence of different methods of equilibrium establishment, sampling, and analyzing. The reason for lower solubility found in the previous research could be the crystallization of naphthol from saturated CO2 solution. The determined solubilities were correlated with the Chrastil model38 (eq 3), which represent the function ln c = f(ln ρ), where c is the solubility of naphthol in carbon dioxide and ρ the density of carbon dioxide, and as could be seen from Figures 3b and Figure 4b it can be seen that the determined solubility data corresponds well to the Chrastil model. A linear relationship between solute’s solubility and SC CO2 density were established what ensure that the equilibrium solubility was reached. The equation proposed by Chrastil is:38

Figure 4. a) Mole fraction of 2-naphthol in CO2 (y2) at temperatures 313 K (◊), 333 K (□), and 353 K (△) versus CO2 pressure (P) and comparison to literature Dobbs et al. 1987:20 308 K (×); Schmitt, Reid 1986:48 308 K (X), 318 K (+), 328 K (-), 343 K (_); Tan, Weng 1987:17 308 K (○), 318 K (□), 328 K (▲). b) Chrastil correlation model. Natural logarithm of 2-naphthol solubility in carbon dioxide (g· m−3) as a function of natural logarithm of carbon dioxide density (kg· m−3) at temperatures 313 K (◊), 333 K (□), and 353 K (△).

of the solvent and its decreasing power of dissolving. In the pressure range between 30 and 60 MPa at temperature 333 K the increasing vapor pressure could have dominated over the decreasing solvent density; therefore, the solubility of 1naphthol increased and is similar to solubility at 313 K.41 The 1-naphthol/CO2 solution has a crossover region at approximately 20 MPa. This phenomena was observed before for other binary systems with supercritical fluids found in literature.42−45 The solubilities at temperature 313 and 333 K are similar in pressure range between 30 and 60 MPa (maximum difference is 4%). The solubility difference at pressures 10, 20, and 50 MPa is higher (between 10% and 40%), represented in Figure 3a. The solubilities of 1-naphthol in CO2 at a temperature of 353 K are much lower compared to solubility data at 313 and 333 K. The difference is between 30% and 50% in the pressure range 30−60 MPa. The difference at pressures 10 and 20 MPa is lower for approximately 10%. An exception is at temperature 333 K and 10 MPa, with approximately 20% lower solubility at 313 K compared to the solubility at temperature 353 K. The solubility at pressure 20 MPa and 333 K is for only 0.7% higher compared to the solubility at 353 K. 1-Naphthol is at pressure 20 MPa and temperature 353 K near its melting point; therefore, this could have had an effect on the solubility behavior of 1-naphthol in CO2 at temperature 353 K. Further on, the density of the binary system (1-naphthol and CO2 solution) is lower compared to the density of pure CO2. Solubility lines of 1-naphthol in CO2 at temperatures 313 and 333 K have a similar trend and have a maximum in the pressure range between 40 and 60 MPa. The explanation of this maximum appearance could be in the partial molar volume of

ln c = k ln ρ + a /T + b

(3)

Parameters a and b are defined as

a=−

ΔH R

⎛ [1000M ]k ⎞ B ⎟⎟ + q b = −ln⎜⎜ [ M + kM ⎝ A B] ⎠

(4)

(5)

Parameter k was obtained from the slope of the plot ln(c) = f(ln(ρ)) at a constant temperature. The logarithm of concentration varies linearly with the reciprocal temperature at a constant gas density, and the slope of the line gives the parameter a. The value of b was determined such as to minimize the sum of the deviation of experimental E



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data from the values calculated by eq 3.10 The determined k, a, and b values are presented in Table 11.

Table 12. Density of 1-Naphthol/CO2 Saturated Solution (ρS) and Density of Pure CO2 (ρCO2) (NIST39) at a Temperature of 313 Ka

Table 11. Chrastil Parameters for 1-Naphtol and 2-Naphtol 1-naphtol 2-naphtol

k

a

b

4.411 3.25

−375 −882

−26.78 −20.19

The Chrastil equations are given by 1-napthol: 375 ln c = 4.411 ln ρ − − 26.78 T

(6)

2-napthol: 882 − 20.19 (7) T The obtained absolute relative deviations (%AARD) were between 10.7 and 25.3%. 3.3. Density of the Naphthol/Carbon Dioxide Solution. The density of carbon dioxide with the disolved naphthol was investigated at temperatures 313, 333, and 353 K at pressures up to 40 MPa with a vibrating U tube densitometer. The data are presented in Figure 5 and Tables ln c = 3.25 ln ρ −

P (MPa)

ρS (kg·m−3)

ρCO2 (kg·m−3)

1.16 3.14 5.24 6.33 7.22 8.17 9.97 10.64 12.12 13.98 15.66 18.13 21.59 25.71 29.81 34.29

47.04 83.35 143.14 192.59 237.08 320.90 651.56 704.02 763.20 809.51 831.36 833.74 864.24 892.42 912.78 934.49

20.651 62.163 120.98 163.51 211.68 298.93 626.32 667.32 721.16 762.90 790.13 820.94 853.83 884.24 908.85 931.53

a

Standard deviation u: u(T) = 0.14 K, u(P) = 0.40 MPa, and u(ρS) = 0.09 kg·m−3.


Figure 5. Density of 1-naphthol in CO2 at temperature 313 K (■), 333 K (●), and 353 K (▲), 2-naphthol/CO2 saturated solution at 313 K (□), 333 K (○), and 353 K (△) and pure CO2 (NIST39) at temperature 313 K (×), 333 K (+) and 353 K (horizontal open rectangle) versus pressure (P).

P (MPa)

ρS (kg·m−3)

ρCO2 (kg·m−3)

0.69 3.44 5.54 7.57 9.22 12.22 13.95 16.63 19.29 22.77 26.57 29.2 33.73 39.39

16.18 74.31 137.24 237.62 477.38 712.57 754.37 799.16 830.24 861.64 889.50 906.02 929.35 954.14

12.02 69.39 131.50 237.04 535.98 723.90 762.34 803.24 832.99 863.30 889.79 905.46 928.88 953.64

a


12 to 17. It can be seen that at temperatures 313 K and at pressures lower that 15 MPa the densities of the 1-naphthol/ carbon dioxide system are higher compared to the densities of pure CO2. Above the pressure of 15 MPa the densities of the binary system 1-naphthol/carbon dioxide are higher from 0.3% at pressure 34.29 MPa to 1.6% at pressure 18.13 MPa compared to the density of the pure carbon dioxide. The density of the binary system 2-naphthol/CO2 is higher than the density of the pure CO2 between 34.6% at pressure 0.69 MPa and 0.3% at pressure 7.57 MPa. Above the pressure of 9.22 MPa, the density of the binary system 2-naphthol/CO2 is lower compared to the density of the pure CO2 (between 10.9% and 0.03%). At 333 K the densities of the binary system 1-naphthol/CO2 are higher than the densities of the pure CO2, but above the pressure of 12 MPa the densities of the binary system decrease and have lower values (from 0.3% at pressure 39.48 MPa to 2.5% at pressure 12.28 MPa) compared to the density of pure

CO2. The density of the binary system 2-naphthol/CO2 at temperature 333 K is lower compared to the density of the pure CO2 in the entire investigated pressure range (difference between 0.6% and 3.0%). At temperature 353 K the densities of the binary system 1naphthol/carbon dioxide are lower (from 1.29% at pressure 37.78 MPa up to 10.3% at pressure 1.12 MPa) in the entire pressure range compared to the density of pure carbon dioxide. The densities of the binary system 2-naphthol/carbon dioxide at pressure 353 K are lower compared to the densities of pure CO2 from 7.8% at pressure 1.97 MPa and 0.4% at pressure 39.91 MPa. We assume that at temperature 353 K the 1-naphthol could have melted under a high pressure (according to the melting point determination under a high pressureFigure 2 and Table 2), which could also have an effect on the density. F



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P (MPa)

ρS (kg·m−3)

ρCO2 (kg·m−3)

P (MPa)

ρS (kg·m−3)

ρCO2 (kg·m−3)

1.50 3.1 5.45 6.27 7.03 7.95 9.52 11.32 13.28 15.13 16.12 19.82 25.18 31.15 34.47 39.48

52.02 76.21 142.3 168.46 198.25 229.84 296.29 408.60 509.67 605.61 628.76 749.40 781.03 835.42 855.78 884.589

25.17 55.59 109.85 132.73 155.53 189.66 262.20 381.92 522.59 605.60 638.89 720.78 788.36 838.04 859.75 887.53

1.97 5.04 13.54 19.82 25.88 30.15 35.06 38.91

29.02 85.27 352.64 576.64 686.94 743.88 792.18 820.40

31.31 89.08 362.97 589.51 698.36 747.09 789.42 816.31

a


consequence of the repulsive forces between the molecules of carbon dioxide and naphthol.

4. CONCLUSIONS The melting point of 1-naphthol under pressure of CO2 was measured, and a minimal melting point temperature of 358.90 K was found at pressure 20.25 MPa, while for 2-naphthol under the CO2 minimal melting point temperature was 383.45 K at a pressure of 20.48 MPa. The solubilities of 1-naphthol in CO2 are the lowest at the highest temperature and incresses with increasing pressure to a maximum which depends on the investigated temperature. For the solubility of 2-naphthol in CO2 it was found that pressure has nearly no influence, while the temperature has a high influence on equilibrium solubilities. The solubility of 1napthol in CO2 is higher than the solubility of 2-naphthol, except at low pressures, where the solubilities are similar at temperature of 313 K or are even somewhat lower for 1napthol at temperature of 333 K. The densities of 1-naphthol/CO2 solution were determined at 313, 333, and 353 K. Compared to the densities of pure CO2, the main difference between the densities is at pressures below pressure of 15 MPa at temperature of 313 K and below pressure of 10 MPa at temperature of 333 K where the densities of the binary system are higher compared to the density of pure CO2. The densities of 2-naphthol/CO2 solution are lower compared to the densities of the 1-naphthol/CO2 solution at temperatures 333 and 353 K or even lower compared to the density of the pure carbon dioxide. The density of the 2naphthol/CO2 solution is higher compared to the density of pure CO2 up to the pressure of 7.6 MPa at temperature 313 K. The density of the 2-naphthol/CO2 solution is lower compared to the density of the pure CO2 above the pressure 7.6 MPa. The determined experimental properties are crucial for phase equilibrium studies, due to the lack of experimental data. The determined thermodynamic properties densities of the systems 1-naphthol/CO2 and 2-naphthol/CO2 can be used for further research on density based models or equations of state.

a


Table 15. Density of 2-Naphthol/CO2 Saturated Solution (ρS) and Density of Pure CO2 (ρCO2) (NIST39) at a Temperature of 333 Ka P (MPa)

ρS (kg·m−3)

ρCO2 (kg·m−3)

1.30 3.43 5.66 9.16 13.91 17.00 20.12 25.46 29.39 34.53 39.85

21.31 60.92 112.53 237.55 540.68 651.37 715.08 783.89 818.98 855.16 874.76

21.64 62.38 115.47 243.31 556.93 664.59 725.59 791.12 825.09 860.11 889.39

a


Table 16. Density of 1-Naphthol/CO2 Saturated Solution (ρS) and Density of Pure CO2 (ρCO2) (NIST39) at a Temperature of 353 Ka P (MPa)

ρS (kg·m−3)

ρCO2 (kg·m−3)

1.12 3.09 6.36 9.22 11.95 16.10 19.90 23.30 28.10 31.14 37.78

15.55 48.47 114.62 189.61 289.19 458.82 583.64 649.01 714.82 747.07 798.40

17.34 50.92 118.51 196.18 294.69 472.37 591.47 659.95 725.50 756.57 808.85

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AUTHOR INFORMATION

Corresponding Author

*Phone: +386 2 2294431, fax: +38622527774; e-mail: zeljko. [email protected].

a


ORCID

Mojca Škerget: 0000-0001-5619-3487 Ž eljko Knez: 0000-0003-4213-7614

The lower density of the binary system naphthol/CO2 compared to the density of pure CO2 is probably the G



Article

Notes

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The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Special thanks to Janko Trupej for the grammatical corrections of this article, to Marko Krainer and Gasper Zajc for the technical support, to the Slovenian Research Agency (ARRS) for financial support in programme “junior researcher” and support of research programme group P2-0046: Separation processes and production design, contract no. 1000-15-0552.

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Thermodynamic Data for Processing Naphthol with Supercritical

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