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Experimental solubility of carbon dioxide and hydrogen sulfide in 2,2′-thiodiglycol
J. Chem. Thermodynamics 133 (2019) 202–207
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Experimental solubility of carbon dioxide and hydrogen sulfide in 2,20 -thiodiglycol Mehdi Vahidi ⇑, Mohammad Shokouhi Gas Research Division, Research Institute of Petroleum Industry (R.I.P.I.), Tehran 14665-137, Iran
a r t i c l e
i n f o
Article history: Received 23 December 2018 Received in revised form 20 February 2019 Accepted 20 February 2019 Available online 21 February 2019 Keywords: Gas absorption Physical solvent Density Carbon dioxide Hydrogen sulfide 2,20 -Thiodiglycol
a b s t r a c t The solubility of acid gases such as CO2 and H2S in 2,2-thiodiglycol (TDG) were measured by static method so called isochoric saturation within the temperature range (303.15–353.15) K by steps of 10 K and pressure up to 1.2 MPa. To calculate the absorption behaviour of gases, density of 2,2thiodiglycol at the related temperature range was measured with Anton Paar SVM 3000, as well. The outcome solubility data were modelled using Stryjek-Vera modification of Peng-Robinson cubic equation of state (PRSV EoS), and thermodynamic solubility quantities at infinitely diluted solution in 2,2thiodiglycol were reported. Ó 2019 Published by Elsevier Ltd.
1. Introduction Molecular structures of mercaptans are in such a way that are not chemically absorbed in amine solution and their physical absorption capacity in aqueous amine solution is not adequate to satisfy mercaptan specifications, thus there was an essential demand to omit these compounds other than H2S and CO2 via the use of hybrid solvents. 2,20 -Thiodiglycol has newly been employed in commercial solvent formulation in sour gas treating as a hybrid solvents so-called HySWEET [1,2] technology with two types of processes, HySWEET@ DEA and HySWEET@ MDEA, in which by changing the solvent composition (TDG, H2O and Amine), it is possible to reach an optimal composition of solvent to remove all acid gases simultaneously (mercaptan along with other acid gases) and also not co-absorb hydrocarbon in the course of sweetening process and thereby additional treatment such as merox process would be deleted. Furthermore, 2,20 -thiodiglycol as a radical/O2 scavenger has been studied to decrease the MEA oxidative degradation in CO2 capture processes [3–6]. Some other application of 2,20 -thiodiglycol in chemical synthesis, manufacture of polymers and the like have been summarized in literature [7]. In continuing studies on acid gases absorption in physical solvents, in present paper, 1) density of 2,20 -thiodiglycol at temperatures of interest was measured and then, 2) solubility measurement of CO2 and H2S in 2,20 -thiodiglycol were studied. All ⇑ Corresponding author. E-mail address: [email protected] (M. Vahidi). https://doi.org/10.1016/j.jct.2019.02.024 0021-9614/Ó 2019 Published by Elsevier Ltd.
solubility tests were performed via the static technique within the temperature range (303.15–353.15) K by step 10 K and pressure up to 1.2 MPa. The solubility data are modelled using Stryjek-Vera modification of Peng-Robinson cubic equation of state (PRSV EoS) [8,9]. Some partial molar thermodynamic quantities such as partial molar volume, Gibbs energy, enthalpy and entropy of dissolution of CO2 and H2S at infinitely diluted 2,20 -thiodiglycol were calculated. 2. Experimental 2.1. Materials Carbon dioxide and hydrogen sulfide (mass fraction purity c.p. grade 0.9995 min) were obtained from Roham Gas Company. The 2,20 -thiodiglycol was purchased from ALDRICH company and was used without further purification. The characteristic and suppliers of the chemicals used in present work are listed in Table 1. Solvent was prepared by mass on a calibrated balance (SARTORIUS AG GERMANY CA200D) with an uncertainty ±0.001 g and measuring the volume of the solution by a standard volumetric flask up to 100 mL. 2.2. Apparatus and procedure 2.2.1. Solubility measurement The experimental method and gas solubility set-up used in this work is the same as that rendered in our previous papers [10–14] and only a little description would be presented here.
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M. Vahidi, M. Shokouhi / J. Chem. Thermodynamics 133 (2019) 202–207 Table 1 Specifications and sources of chemicals used in this work. Chemical name
Molecular formula molar mass /g∙ mol1
CAS registry number
Mass fraction purity
Source
Hydrogen sulfide Carbon dioxide 2,20 -thiodiglycol
H2S/34.08 CO2/44.01 C4H10O2S/122.19
[7783-06-4] [124-38-9] [111-48-8]
99.95% 99.5% 99%
Roham Gas Company Roham Gas Company ALDRICH
The amount of solute gas dissolved in liquid 2,20 -thiodiglycol is obtained as follows [2,3,15–17]:
nlag ¼
ðqi - qf Þ V gc ðV EC V S Þ qag 1 V1 ag qag
Table 2 Critical properties of 2,20 -thiodiglycol, H2S and CO2, and also Antoine constants for vapour pressure of 2,20 -thiodiglycol.
ð1Þ
and solubility on the base of molality and mole fraction of the solute gas is defined as:
mag
nlag ðmoleÞ ¼ wS ðkgÞ
xag ¼
nlag ðmoleÞ wS ðkgÞ nlag þ M S ðkgÞ
ð2Þ
¼
nlag l nag þ ns
a
ð3Þ
Here Vgc indicates the volume of the gas container, qi and qf are mole density related to the initial and final states of acid gas in gas container. The VEC, Vg and VS are respectively the volume of equilibrium cell, gas phase volume in equilibrium cell and gas free solvent volume with mass of ws and V 1 ag is partial molar volume of acid gas at infinitely diluted solution. The qag represents the density of acid
b c
2.2.2. Density measurement Measurement of the density of fresh 2,20 -thiodiglycol at operational temperature was carried out with Anton Paar SVM 3000 which is equipped with an automatic temperature compensation for fast concentration measurements. 3. Results and discussion Several reports of the vapour pressure of 2,20 -thiodiglycol may be found in the literature which have been correlated with the Antoine equation by Brozena et al. [20]. Critical pressure and temperature of 2,20 -thiodiglycol were obtained with Joback Method [21,22] and summarized in Table 2. The molar volume of gas free solvent, VS was calculated from experimental density, d. The experimental densities measured in this work were listed in Table 3 and correlated with linear equation with temperature, Eq. (5) (with determination coefficient, R2 = 0.9996),
d= g cm3 ¼ 7:3600 104 T=K þ 1:3976
ð5Þ
As shown in Table 3, except for the density value at T = 298.15 K reported by Budavari et al. [23] which deviate 3.21% from our
Tc/(K)
w
9.0a 7.377a 5.09476b
373.1a 304.13a 719.76b
0.1a 0.22394a 1.334c
2,20 -thiodiglycol
Temperature range (K) 298.15–521.15
Antoine equation ln(Ps/Pa) = 24.3482 6224.0/ (67.9546 + (T/K))
Ref. [18]. Ref. [21] (Joback Method). Obtained from w = log(Pr)Tr=0.7–1.
Density/(gcm3) T ± 0.01/K d ± 0.0010 273.15 293.15 298.15 298.15 298.15 303.15 313.15 313.15 323.15 333.15 333.15 343.15 353.15
ð4Þ
where PT and PVP refer to the total pressure and vapour pressure of solvent, respectively. All information about experimental mole density of acid gases (qi , qf and qag ) were obtained from the National Institute of Standards and Technology (NIST) [18]. The uncertainties of reported solubility data were estimated using the error propagation theory [19] which has been explained in detail in previous work [13].
Pc/MPa
H2S CO2 TDG
Table 3 Atmospheric density, d, values of 2,20 -thiodiglycol that experimentally obtained in present work compared with other reported values in literature and correlation data from Eq. (5).
gas at the equilibrium temperature and pressure, P eag , in the gas phase in the equilibrium cell. MS and ns refer to the molar mass of solvent in kg per mole and the number of mole of solvent, respectively. The partial pressure of acid gases at equilibrium condition was obtained as follows:
Peag ¼ P T PVP
Chemical name
a b c d
Ref. Ref. Ref. Ref.
1.1824
Reported in literature
Data from Eq. (5)
1.1973a 1.221b 1.177c 1.1793a 1.1805d
1.1966 1.1818 1.1782
1.1740 1.1670
1.1745 1.1671 d
1.1688 1.1600 1.1520
1.1598 1.1524 1.1529d
1.1450 1.1380
1.1450 1.1377
[25]. [23]. [24]. [26].
reported value, the other calculated density using Eq. (5) over the temperature range (298.15–333.15) K agree within 0.11% of the experimental values reported in literature [24–26]. Initially, by ignoring V 1 ag in Eq. (5), the solubility values were estimated and modelled using PRSV EoS, thereby molar volumes at infinite dilution of acid gas, V 1 ag were obtained and solubility values were recalculated as experimental data. Experimental solubility values of H2S and CO2 in 2,20 -thiodiglycol are summarized in Tables 4 and 5 and curve of PT-x at isothermals (303.15–353.15) K are shown in Figs. 1 and 2, as well. The Henry’s constant for either the molality or mole fraction ð0Þ
ð0Þ
base,hH;m or hH;x , were obtained as follows, ð0Þ
hH;m ðTÞ ¼ lim
m=m0 !0
ð0Þ
hH;x ðTÞ ¼ lim
x!0
f ðT; p; fyi gÞ m=m0
f ðT; p; fyi gÞ x
ð6Þ
ð7Þ
where m refers the molality of solute in liquid 2,20 -thiodiglycol, m0 = 1 molkg1 2,20 -thiodiglycol and f is the fugacity of acid gases
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Table 4 Experimental solubility of CO2 in 2,20 -thiodiglycol. (T is temperature, Pt is total pressure, xCO2 and DxCO2 are mole fraction and uncertainty of mole fraction of CO2).a T ± 0.01/K
Pt ± 0.003/MPa
xCO2
±DxCO2
m/molkg1
T ± 0.01/K
Pt ± 0.003/MPa
xCO2
±DxCO2
m/molkg1
303.15
0.2070 0.4341 0.6419 0.8713 1.0360 1.1375
0.0080 0.0172 0.0244 0.0332 0.0398 0.0443
0.0012 0.0015 0.0020 0.0025 0.0030 0.0040
0.066 0.144 0.205 0.281 0.340 0.379
333.15
0.2325 0.4910 0.7250 0.9856 1.1740
0.0071 0.0149 0.0215 0.0294 0.0353
0.0012 0.0014 0.0025 0.0028 0.0033
0.059 0.124 0.180 0.248 0.300
343.15 313.15
0.2150 0.4540 0.6700 0.9110 1.0840 1.1668
0.0078 0.0162 0.0233 0.0314 0.0377 0.0405
0.0012 0.0016 0.0022 0.0023 0.0029 0.0040
0.064 0.134 0.195 0.265 0.321 0.345
0.2405 0.5085 0.7503 1.0200 1.2163
0.0070 0.0145 0.0212 0.0291 0.0348
0.0011 0.0015 0.0022 0.0026 0.0033
0.058 0.121 0.177 0.245 0.296
353.15
0.2240 0.4728 0.6980 0.9490 1.1300
0.0074 0.0154 0.0223 0.0302 0.0362
0.0013 0.0015 0.0022 0.0024 0.0031
0.061 0.128 0.186 0.255 0.308
0.2480 0.5250 0.7750 1.0840 1.2967
0.0070 0.0144 0.0211 0.0289 0.0348
0.0012 0.0015 0.002 0.0028 0.0035
0.057 0.120 0.176 0.244 0.295
323.15
a
Standard uncertainty (u) are u(T) = ±0.01 K and u(Pt) = ±0.003 MPa (standard uncertainties in table are reported with 0.68 level of confidence).
Table 5 Experimental solubility of H2S in 2,20 -thiodiglycol. (T is temperature, Pt is total pressure, xH2S and DxH2S are mole fraction and uncertainty of mole fraction of H2S).a T ± 0.01/K
Pt ± 0.003/MPa
xH2S
±DxH2S
m/molkg1
T ± 0.01/K
Pt ± 0.003/MPa
xH2S
±DxH2S
m/molkg1
303.15
0.0900 0.2210 0.3700 0.5250 0.6550 0.8330 0.1010 0.2490 0.4170 0.5910 0.7380 0.9360 0.1120 0.2750 0.4610 0.6530 0.8160 1.0400
0.0270 0.0622 0.1007 0.1385 0.1698 0.2097 0.0254 0.0581 0.0944 0.1302 0.1599 0.1984 0.0239 0.0548 0.0890 0.1231 0.1514 0.1876
0.0037 0.0059 0.0077 0.0094 0.0109 0.0114 0.0038 0.0059 0.0079 0.0096 0.0112 0.0118 0.0038 0.0060 0.0080 0.0098 0.0114 0.0121
0.2274 0.5427 0.9168 1.3158 1.6737 2.1719 0.2130 0.5047 0.8533 1.2253 1.5579 2.0250 0.2004 0.4745 0.7994 1.1487 1.4601 1.8897
333.15
0.1220 0.2980 0.5010 0.7110 0.8900 1.1380 0.1320 0.3240 0.5450 0.7730 0.9680 1.2500 0.1440 0.3430 0.5850 0.8290 1.0400 1.3640
0.0226 0.0520 0.0844 0.1169 0.1439 0.1782 0.0213 0.0491 0.0796 0.1105 0.1362 0.1670 0.0203 0.0474 0.0756 0.1053 0.1298 0.1559
0.0038 0.0060 0.0081 0.0100 0.0116 0.0125 0.0038 0.0061 0.0082 0.0101 0.0119 0.0129 0.0038 0.0061 0.0083 0.0103 0.0121 0.0133
0.1890 0.4487 0.7544 1.0834 1.3761 1.7742 0.1785 0.4223 0.7082 1.0167 1.2902 1.6405 0.1697 0.4071 0.6697 0.9634 1.2208 1.5111
313.15
323.15
a
343.15
353.15
Standard uncertainty (u) are u(T) = ±0.01 K and u(Pt) = ±0.003 MPa (standard uncertainties in table are reported with 0.68 level of confidence).
Fig. 1. Experimental data for CO2 – 2,20 -thiodiglycol system at different temperatures and pressure (points) compared with PRSV EoS (lines).
Fig. 2. Experimental data for H2S – 2,20 -thiodiglycol system at different temperatures and pressure (points) compared with PRSV EoS (solid lines).
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Table 6 ð0Þ Thermodynamic properties of H2S and CO2 solubility in 2,20 -thiodiglycol: T, temperature; hH;x , Henry’s law constant at the zero pressure in mole fraction base; V 1 ag , partial molar 1 1 volume at infinite dilution obtained from PRSV; Dsol G1 m;x , Gibbs free energy of solution; Dsol H m;x , enthalpy of solution; Dsol Sm;x , entropy of solution at infinite dilution. hH;x /MPa
1 Dsol G1 m /kJ∙mole
1 Dsol H1 m /kJ∙mole
1 Dsol S1 mol1 m /J∙K
3 1 V1 ag /cm ∙mole
H2S in 2,20 -thiodiglycol 303.15 313.15 323.15 333.15 343.15 353.15
3.55 ± 0.04 4.26 ± 0.15 4.99 ± 0.17 5.72 ± 0.20 6.57 ± 0.24 7.38 ± 0.10
3.29 3.77 4.28 4.82 5.37 5.95
11.05 11.79 12.55 13.34 14.15 14.99
47.29 49.69 52.09 54.50 56.90 59.31
33.44 33.63 33.81 33.99 34.13 34.26
CO2 in 2,20 -thiodiglycol 303.15 313.15 323.15 333.15 343.15 353.15
25.15 ± 0.27 27.72 ± 0.52 30.3 ± 0.52 32.59 ± 0.51 34.39 ± 0.47 35.82 ± 0.52
8.19 8.65 9.12 9.60 10.09 10.60
5.49 5.86 6.24 6.63 7.03 7.45
45.12 46.32 47.51 48.71 49.90 51.10
27.35 27.00 26.62 26.18 25.83 25.42
T ± 0.01/K
ð0Þ
Table 7 ð0Þ Numerical values of the parameters of Eq. (8), hH;x =MPa (Henry’s law constant on mole fraction base). H2S in 2,20 -thiodiglycol Ah;x 0.014456
Bh;x 3.07731
CO2 in 2,20 -thiodiglycol C h;x 0.13562
Ah;x 0.007181
in gas phase in equilibrium cell at temperature T, pressure p and compositionfyi g. The fugacity and composition of CO2 and H2S in gas phase was estimated using bubble pressure algorithm with the PRSV EoS. Henry’s constant accompanied with V 1 ag for each solute were reported in Table 6. Temperature dependency of Henry’s law constant on the base of mole fraction was described by: ð0Þ
lnðhH;x =MPaÞ ¼ Ah;x :ðT=KÞ þ Bh;x þ C h;x =ðT=KÞ
ð8Þ
Bh;x 1.073847
C h;x 0.114927
reported in literature and schematically been depicted in Figs. 3 and 4. Results show the solubility of CO2 in different solvents as follows; DMF [11] > PC [27] SFL [28] > DMSO [11] > DEG [27] > 2,20 -thiodiglycol > PG [30] and for the case of H2S; SFL [28] DMF [11] TEG [31] >PC [27] > DEG [29] > 2,20 -thiodiglycol > PG [12] > EG [12]. 3.1. Modelling
Ah;x , Bh;x and C h;x are tuneable factors estimated via regression procedure and reported in Table 7. The partial molar Gibbs energy 1 Dsol G1 m;x , the partial molar enthalpy Dsol Hm;x , and the partial molar entropy Dsol S1 of gas dissolution via thermodynamic relations m;x were calculated and reported in Table 6, as well. A comparison of CO2 and H2S absorption capacity has been made among 2,20 -thiodiglycol and some typical organic solvents
In 1986, Sterejik and Vera [8,9] modified the Peng & Robinson [32] equation of state in order to be applicable for polar systems and rendered a new version so-called PRSV EoS in which by introducing of an adjustable pure compound parameter, j1i , made it more appropriate for the greater range of compound with different functional group. The EoS was extended to mixtures by applying the following classical mixing rules,
Fig. 3. Comparison of solubility of CO2 in 2,20 -thiodiglycol (this work), sulfolane (SFL) (Jalili et al. [28]), dimethylsufoxide (DMSO) and dimethylformamide (DMF) (Shokouhi et al. [11]), propylene carbonate (PC) (Murrieta-Guevara [27]), diethyleneglycol (DEG) (Jou et al. 2000 [29]) and propyleneglycol (PG) (Galvao et al. [30]) reported in literature at given temperatures.
Fig. 4. Comparison of solubility of H2S in 2,20 -thiodiglycol (this work), sulfolane (SFL) (Jalili et al. [28]), propylene carbonate (PC) (Murrieta-Guevara [27]), dimethylformamide (DMF) (Shokouhi et al. [11]), diethyleneglycol (DEG) (Jou et al. 2000 [29]), ethyleneglycol and propyleneglycol (PG) (Shokouhi et al. [12]) and triethyleneglycol (TEG) (Jou et al. 1987 [31]) reported in literature at T = 323.15 K.
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M. Vahidi, M. Shokouhi / J. Chem. Thermodynamics 133 (2019) 202–207 Table 8 Parameters of PRSV EoS for pure compounds and optimal binary interaction parameters in PRSV, and also ARD %, MRD%.
2,2-Thiodiglycol CO2 H2S
k12 k21 ARD% (PRSV) MRD% (PRSV)
a¼
XX i
b¼
j1i
138.15–378.77 218–304
0.99 0.04285 0.032574
optimal binary interaction parameters CO2/2,20 -thiodiglycol
H2S/2,20 -thiodiglycol
0.25188 0.0005986 T/K 0.15386 0.01451 T/K 0.92% 3.85%
0.0044512 0.6976816 1.01% 3.64%
xi xj aij
ð9Þ
xi xj bij
ð10Þ
j
XX i
DT/K
j
wherein cross term, aij is obtained from Pangiotopoulos-Reid expression [33],
aðT Þij ¼
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi aðT Þi :aðT Þj 1 xi kij xj kji
ð11Þ
In Eq. (11) kij and kji are binary interaction parameters, and that for parameter b is obtained with Eq. (12),
bij ¼ bji ¼
bi þ bj 1 lij 2
ð12Þ
in which lij is zero for the systems studied in present work. The optimum binary interaction parameters along with the average relative deviation, ARD %, and the maximum relative deviation, MRD % were summarized in Table 8 and also quality of correlation was graphically shown in Figs. 1 and 2 and compared with experimental values. 4. Conclusions The solubility of H2S and CO2 in 2,20 -thiodiglycol was measured within the temperature range (303.15–353.15) K and pressure up to about 1.2 MPa. The results were modelled using Stryjek-Vera modification of Peng-Robinson cubic equation of state (PRSV EoS). As shown in Figs. 1 and 2 and reported in Table 7, this model has sound capability in correlation of mTp data. In addition as can be seen in Figs. 3 and 4, solubility of H2S and CO2 in 2,20 thiodiglycol is lower than that of DEG. This means that in the DEG structure, replacement of oxygen with sulfur would lessen solubility of both CO2 and H2S. Acknowledgement We would like to express our appreciation to Research Council of the Research Institute of Petroleum Industry (RIPI) for financial support of this work. References [1] S. Capdeville, J.L. Peytavy, G. Fremy, D. Anglerot, Process for purifying gaseous mixtures containing mercaptans and other acidic gases, French Patent 0600448, International Publication Number WO 2007/083012 A1, January 18, 2006. [2] R. Cadours, V. Shah, C. Weiss, HySWEET process for improved mercaptan removal, presented at International Petroleum Technology Conference held in Doha, Qatar, 7-9 December 2009.
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JCT 2018-1072
Contents lists available at ScienceDirect
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Experimental solubility of carbon dioxide and hydrogen sulfide in 2,20 -thiodiglycol Mehdi Vahidi ⇑, Mohammad Shokouhi Gas Research Division, Research Institute of Petroleum Industry (R.I.P.I.), Tehran 14665-137, Iran
a r t i c l e
i n f o
Article history: Received 23 December 2018 Received in revised form 20 February 2019 Accepted 20 February 2019 Available online 21 February 2019 Keywords: Gas absorption Physical solvent Density Carbon dioxide Hydrogen sulfide 2,20 -Thiodiglycol
a b s t r a c t The solubility of acid gases such as CO2 and H2S in 2,2-thiodiglycol (TDG) were measured by static method so called isochoric saturation within the temperature range (303.15–353.15) K by steps of 10 K and pressure up to 1.2 MPa. To calculate the absorption behaviour of gases, density of 2,2thiodiglycol at the related temperature range was measured with Anton Paar SVM 3000, as well. The outcome solubility data were modelled using Stryjek-Vera modification of Peng-Robinson cubic equation of state (PRSV EoS), and thermodynamic solubility quantities at infinitely diluted solution in 2,2thiodiglycol were reported. Ó 2019 Published by Elsevier Ltd.
1. Introduction Molecular structures of mercaptans are in such a way that are not chemically absorbed in amine solution and their physical absorption capacity in aqueous amine solution is not adequate to satisfy mercaptan specifications, thus there was an essential demand to omit these compounds other than H2S and CO2 via the use of hybrid solvents. 2,20 -Thiodiglycol has newly been employed in commercial solvent formulation in sour gas treating as a hybrid solvents so-called HySWEET [1,2] technology with two types of processes, HySWEET@ DEA and HySWEET@ MDEA, in which by changing the solvent composition (TDG, H2O and Amine), it is possible to reach an optimal composition of solvent to remove all acid gases simultaneously (mercaptan along with other acid gases) and also not co-absorb hydrocarbon in the course of sweetening process and thereby additional treatment such as merox process would be deleted. Furthermore, 2,20 -thiodiglycol as a radical/O2 scavenger has been studied to decrease the MEA oxidative degradation in CO2 capture processes [3–6]. Some other application of 2,20 -thiodiglycol in chemical synthesis, manufacture of polymers and the like have been summarized in literature [7]. In continuing studies on acid gases absorption in physical solvents, in present paper, 1) density of 2,20 -thiodiglycol at temperatures of interest was measured and then, 2) solubility measurement of CO2 and H2S in 2,20 -thiodiglycol were studied. All ⇑ Corresponding author. E-mail address: [email protected] (M. Vahidi). https://doi.org/10.1016/j.jct.2019.02.024 0021-9614/Ó 2019 Published by Elsevier Ltd.
solubility tests were performed via the static technique within the temperature range (303.15–353.15) K by step 10 K and pressure up to 1.2 MPa. The solubility data are modelled using Stryjek-Vera modification of Peng-Robinson cubic equation of state (PRSV EoS) [8,9]. Some partial molar thermodynamic quantities such as partial molar volume, Gibbs energy, enthalpy and entropy of dissolution of CO2 and H2S at infinitely diluted 2,20 -thiodiglycol were calculated. 2. Experimental 2.1. Materials Carbon dioxide and hydrogen sulfide (mass fraction purity c.p. grade 0.9995 min) were obtained from Roham Gas Company. The 2,20 -thiodiglycol was purchased from ALDRICH company and was used without further purification. The characteristic and suppliers of the chemicals used in present work are listed in Table 1. Solvent was prepared by mass on a calibrated balance (SARTORIUS AG GERMANY CA200D) with an uncertainty ±0.001 g and measuring the volume of the solution by a standard volumetric flask up to 100 mL. 2.2. Apparatus and procedure 2.2.1. Solubility measurement The experimental method and gas solubility set-up used in this work is the same as that rendered in our previous papers [10–14] and only a little description would be presented here.
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M. Vahidi, M. Shokouhi / J. Chem. Thermodynamics 133 (2019) 202–207 Table 1 Specifications and sources of chemicals used in this work. Chemical name
Molecular formula molar mass /g∙ mol1
CAS registry number
Mass fraction purity
Source
Hydrogen sulfide Carbon dioxide 2,20 -thiodiglycol
H2S/34.08 CO2/44.01 C4H10O2S/122.19
[7783-06-4] [124-38-9] [111-48-8]
99.95% 99.5% 99%
Roham Gas Company Roham Gas Company ALDRICH
The amount of solute gas dissolved in liquid 2,20 -thiodiglycol is obtained as follows [2,3,15–17]:
nlag ¼
ðqi - qf Þ V gc ðV EC V S Þ qag 1 V1 ag qag
Table 2 Critical properties of 2,20 -thiodiglycol, H2S and CO2, and also Antoine constants for vapour pressure of 2,20 -thiodiglycol.
ð1Þ
and solubility on the base of molality and mole fraction of the solute gas is defined as:
mag
nlag ðmoleÞ ¼ wS ðkgÞ
xag ¼
nlag ðmoleÞ wS ðkgÞ nlag þ M S ðkgÞ
ð2Þ
¼
nlag l nag þ ns
a
ð3Þ
Here Vgc indicates the volume of the gas container, qi and qf are mole density related to the initial and final states of acid gas in gas container. The VEC, Vg and VS are respectively the volume of equilibrium cell, gas phase volume in equilibrium cell and gas free solvent volume with mass of ws and V 1 ag is partial molar volume of acid gas at infinitely diluted solution. The qag represents the density of acid
b c
2.2.2. Density measurement Measurement of the density of fresh 2,20 -thiodiglycol at operational temperature was carried out with Anton Paar SVM 3000 which is equipped with an automatic temperature compensation for fast concentration measurements. 3. Results and discussion Several reports of the vapour pressure of 2,20 -thiodiglycol may be found in the literature which have been correlated with the Antoine equation by Brozena et al. [20]. Critical pressure and temperature of 2,20 -thiodiglycol were obtained with Joback Method [21,22] and summarized in Table 2. The molar volume of gas free solvent, VS was calculated from experimental density, d. The experimental densities measured in this work were listed in Table 3 and correlated with linear equation with temperature, Eq. (5) (with determination coefficient, R2 = 0.9996),
d= g cm3 ¼ 7:3600 104 T=K þ 1:3976
ð5Þ
As shown in Table 3, except for the density value at T = 298.15 K reported by Budavari et al. [23] which deviate 3.21% from our
Tc/(K)
w
9.0a 7.377a 5.09476b
373.1a 304.13a 719.76b
0.1a 0.22394a 1.334c
2,20 -thiodiglycol
Temperature range (K) 298.15–521.15
Antoine equation ln(Ps/Pa) = 24.3482 6224.0/ (67.9546 + (T/K))
Ref. [18]. Ref. [21] (Joback Method). Obtained from w = log(Pr)Tr=0.7–1.
Density/(gcm3) T ± 0.01/K d ± 0.0010 273.15 293.15 298.15 298.15 298.15 303.15 313.15 313.15 323.15 333.15 333.15 343.15 353.15
ð4Þ
where PT and PVP refer to the total pressure and vapour pressure of solvent, respectively. All information about experimental mole density of acid gases (qi , qf and qag ) were obtained from the National Institute of Standards and Technology (NIST) [18]. The uncertainties of reported solubility data were estimated using the error propagation theory [19] which has been explained in detail in previous work [13].
Pc/MPa
H2S CO2 TDG
Table 3 Atmospheric density, d, values of 2,20 -thiodiglycol that experimentally obtained in present work compared with other reported values in literature and correlation data from Eq. (5).
gas at the equilibrium temperature and pressure, P eag , in the gas phase in the equilibrium cell. MS and ns refer to the molar mass of solvent in kg per mole and the number of mole of solvent, respectively. The partial pressure of acid gases at equilibrium condition was obtained as follows:
Peag ¼ P T PVP
Chemical name
a b c d
Ref. Ref. Ref. Ref.
1.1824
Reported in literature
Data from Eq. (5)
1.1973a 1.221b 1.177c 1.1793a 1.1805d
1.1966 1.1818 1.1782
1.1740 1.1670
1.1745 1.1671 d
1.1688 1.1600 1.1520
1.1598 1.1524 1.1529d
1.1450 1.1380
1.1450 1.1377
[25]. [23]. [24]. [26].
reported value, the other calculated density using Eq. (5) over the temperature range (298.15–333.15) K agree within 0.11% of the experimental values reported in literature [24–26]. Initially, by ignoring V 1 ag in Eq. (5), the solubility values were estimated and modelled using PRSV EoS, thereby molar volumes at infinite dilution of acid gas, V 1 ag were obtained and solubility values were recalculated as experimental data. Experimental solubility values of H2S and CO2 in 2,20 -thiodiglycol are summarized in Tables 4 and 5 and curve of PT-x at isothermals (303.15–353.15) K are shown in Figs. 1 and 2, as well. The Henry’s constant for either the molality or mole fraction ð0Þ
ð0Þ
base,hH;m or hH;x , were obtained as follows, ð0Þ
hH;m ðTÞ ¼ lim
m=m0 !0
ð0Þ
hH;x ðTÞ ¼ lim
x!0
f ðT; p; fyi gÞ m=m0
f ðT; p; fyi gÞ x
ð6Þ
ð7Þ
where m refers the molality of solute in liquid 2,20 -thiodiglycol, m0 = 1 molkg1 2,20 -thiodiglycol and f is the fugacity of acid gases
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Table 4 Experimental solubility of CO2 in 2,20 -thiodiglycol. (T is temperature, Pt is total pressure, xCO2 and DxCO2 are mole fraction and uncertainty of mole fraction of CO2).a T ± 0.01/K
Pt ± 0.003/MPa
xCO2
±DxCO2
m/molkg1
T ± 0.01/K
Pt ± 0.003/MPa
xCO2
±DxCO2
m/molkg1
303.15
0.2070 0.4341 0.6419 0.8713 1.0360 1.1375
0.0080 0.0172 0.0244 0.0332 0.0398 0.0443
0.0012 0.0015 0.0020 0.0025 0.0030 0.0040
0.066 0.144 0.205 0.281 0.340 0.379
333.15
0.2325 0.4910 0.7250 0.9856 1.1740
0.0071 0.0149 0.0215 0.0294 0.0353
0.0012 0.0014 0.0025 0.0028 0.0033
0.059 0.124 0.180 0.248 0.300
343.15 313.15
0.2150 0.4540 0.6700 0.9110 1.0840 1.1668
0.0078 0.0162 0.0233 0.0314 0.0377 0.0405
0.0012 0.0016 0.0022 0.0023 0.0029 0.0040
0.064 0.134 0.195 0.265 0.321 0.345
0.2405 0.5085 0.7503 1.0200 1.2163
0.0070 0.0145 0.0212 0.0291 0.0348
0.0011 0.0015 0.0022 0.0026 0.0033
0.058 0.121 0.177 0.245 0.296
353.15
0.2240 0.4728 0.6980 0.9490 1.1300
0.0074 0.0154 0.0223 0.0302 0.0362
0.0013 0.0015 0.0022 0.0024 0.0031
0.061 0.128 0.186 0.255 0.308
0.2480 0.5250 0.7750 1.0840 1.2967
0.0070 0.0144 0.0211 0.0289 0.0348
0.0012 0.0015 0.002 0.0028 0.0035
0.057 0.120 0.176 0.244 0.295
323.15
a
Standard uncertainty (u) are u(T) = ±0.01 K and u(Pt) = ±0.003 MPa (standard uncertainties in table are reported with 0.68 level of confidence).
Table 5 Experimental solubility of H2S in 2,20 -thiodiglycol. (T is temperature, Pt is total pressure, xH2S and DxH2S are mole fraction and uncertainty of mole fraction of H2S).a T ± 0.01/K
Pt ± 0.003/MPa
xH2S
±DxH2S
m/molkg1
T ± 0.01/K
Pt ± 0.003/MPa
xH2S
±DxH2S
m/molkg1
303.15
0.0900 0.2210 0.3700 0.5250 0.6550 0.8330 0.1010 0.2490 0.4170 0.5910 0.7380 0.9360 0.1120 0.2750 0.4610 0.6530 0.8160 1.0400
0.0270 0.0622 0.1007 0.1385 0.1698 0.2097 0.0254 0.0581 0.0944 0.1302 0.1599 0.1984 0.0239 0.0548 0.0890 0.1231 0.1514 0.1876
0.0037 0.0059 0.0077 0.0094 0.0109 0.0114 0.0038 0.0059 0.0079 0.0096 0.0112 0.0118 0.0038 0.0060 0.0080 0.0098 0.0114 0.0121
0.2274 0.5427 0.9168 1.3158 1.6737 2.1719 0.2130 0.5047 0.8533 1.2253 1.5579 2.0250 0.2004 0.4745 0.7994 1.1487 1.4601 1.8897
333.15
0.1220 0.2980 0.5010 0.7110 0.8900 1.1380 0.1320 0.3240 0.5450 0.7730 0.9680 1.2500 0.1440 0.3430 0.5850 0.8290 1.0400 1.3640
0.0226 0.0520 0.0844 0.1169 0.1439 0.1782 0.0213 0.0491 0.0796 0.1105 0.1362 0.1670 0.0203 0.0474 0.0756 0.1053 0.1298 0.1559
0.0038 0.0060 0.0081 0.0100 0.0116 0.0125 0.0038 0.0061 0.0082 0.0101 0.0119 0.0129 0.0038 0.0061 0.0083 0.0103 0.0121 0.0133
0.1890 0.4487 0.7544 1.0834 1.3761 1.7742 0.1785 0.4223 0.7082 1.0167 1.2902 1.6405 0.1697 0.4071 0.6697 0.9634 1.2208 1.5111
313.15
323.15
a
343.15
353.15
Standard uncertainty (u) are u(T) = ±0.01 K and u(Pt) = ±0.003 MPa (standard uncertainties in table are reported with 0.68 level of confidence).
Fig. 1. Experimental data for CO2 – 2,20 -thiodiglycol system at different temperatures and pressure (points) compared with PRSV EoS (lines).
Fig. 2. Experimental data for H2S – 2,20 -thiodiglycol system at different temperatures and pressure (points) compared with PRSV EoS (solid lines).
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Table 6 ð0Þ Thermodynamic properties of H2S and CO2 solubility in 2,20 -thiodiglycol: T, temperature; hH;x , Henry’s law constant at the zero pressure in mole fraction base; V 1 ag , partial molar 1 1 volume at infinite dilution obtained from PRSV; Dsol G1 m;x , Gibbs free energy of solution; Dsol H m;x , enthalpy of solution; Dsol Sm;x , entropy of solution at infinite dilution. hH;x /MPa
1 Dsol G1 m /kJ∙mole
1 Dsol H1 m /kJ∙mole
1 Dsol S1 mol1 m /J∙K
3 1 V1 ag /cm ∙mole
H2S in 2,20 -thiodiglycol 303.15 313.15 323.15 333.15 343.15 353.15
3.55 ± 0.04 4.26 ± 0.15 4.99 ± 0.17 5.72 ± 0.20 6.57 ± 0.24 7.38 ± 0.10
3.29 3.77 4.28 4.82 5.37 5.95
11.05 11.79 12.55 13.34 14.15 14.99
47.29 49.69 52.09 54.50 56.90 59.31
33.44 33.63 33.81 33.99 34.13 34.26
CO2 in 2,20 -thiodiglycol 303.15 313.15 323.15 333.15 343.15 353.15
25.15 ± 0.27 27.72 ± 0.52 30.3 ± 0.52 32.59 ± 0.51 34.39 ± 0.47 35.82 ± 0.52
8.19 8.65 9.12 9.60 10.09 10.60
5.49 5.86 6.24 6.63 7.03 7.45
45.12 46.32 47.51 48.71 49.90 51.10
27.35 27.00 26.62 26.18 25.83 25.42
T ± 0.01/K
ð0Þ
Table 7 ð0Þ Numerical values of the parameters of Eq. (8), hH;x =MPa (Henry’s law constant on mole fraction base). H2S in 2,20 -thiodiglycol Ah;x 0.014456
Bh;x 3.07731
CO2 in 2,20 -thiodiglycol C h;x 0.13562
Ah;x 0.007181
in gas phase in equilibrium cell at temperature T, pressure p and compositionfyi g. The fugacity and composition of CO2 and H2S in gas phase was estimated using bubble pressure algorithm with the PRSV EoS. Henry’s constant accompanied with V 1 ag for each solute were reported in Table 6. Temperature dependency of Henry’s law constant on the base of mole fraction was described by: ð0Þ
lnðhH;x =MPaÞ ¼ Ah;x :ðT=KÞ þ Bh;x þ C h;x =ðT=KÞ
ð8Þ
Bh;x 1.073847
C h;x 0.114927
reported in literature and schematically been depicted in Figs. 3 and 4. Results show the solubility of CO2 in different solvents as follows; DMF [11] > PC [27] SFL [28] > DMSO [11] > DEG [27] > 2,20 -thiodiglycol > PG [30] and for the case of H2S; SFL [28] DMF [11] TEG [31] >PC [27] > DEG [29] > 2,20 -thiodiglycol > PG [12] > EG [12]. 3.1. Modelling
Ah;x , Bh;x and C h;x are tuneable factors estimated via regression procedure and reported in Table 7. The partial molar Gibbs energy 1 Dsol G1 m;x , the partial molar enthalpy Dsol Hm;x , and the partial molar entropy Dsol S1 of gas dissolution via thermodynamic relations m;x were calculated and reported in Table 6, as well. A comparison of CO2 and H2S absorption capacity has been made among 2,20 -thiodiglycol and some typical organic solvents
In 1986, Sterejik and Vera [8,9] modified the Peng & Robinson [32] equation of state in order to be applicable for polar systems and rendered a new version so-called PRSV EoS in which by introducing of an adjustable pure compound parameter, j1i , made it more appropriate for the greater range of compound with different functional group. The EoS was extended to mixtures by applying the following classical mixing rules,
Fig. 3. Comparison of solubility of CO2 in 2,20 -thiodiglycol (this work), sulfolane (SFL) (Jalili et al. [28]), dimethylsufoxide (DMSO) and dimethylformamide (DMF) (Shokouhi et al. [11]), propylene carbonate (PC) (Murrieta-Guevara [27]), diethyleneglycol (DEG) (Jou et al. 2000 [29]) and propyleneglycol (PG) (Galvao et al. [30]) reported in literature at given temperatures.
Fig. 4. Comparison of solubility of H2S in 2,20 -thiodiglycol (this work), sulfolane (SFL) (Jalili et al. [28]), propylene carbonate (PC) (Murrieta-Guevara [27]), dimethylformamide (DMF) (Shokouhi et al. [11]), diethyleneglycol (DEG) (Jou et al. 2000 [29]), ethyleneglycol and propyleneglycol (PG) (Shokouhi et al. [12]) and triethyleneglycol (TEG) (Jou et al. 1987 [31]) reported in literature at T = 323.15 K.
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M. Vahidi, M. Shokouhi / J. Chem. Thermodynamics 133 (2019) 202–207 Table 8 Parameters of PRSV EoS for pure compounds and optimal binary interaction parameters in PRSV, and also ARD %, MRD%.
2,2-Thiodiglycol CO2 H2S
k12 k21 ARD% (PRSV) MRD% (PRSV)
a¼
XX i
b¼
j1i
138.15–378.77 218–304
0.99 0.04285 0.032574
optimal binary interaction parameters CO2/2,20 -thiodiglycol
H2S/2,20 -thiodiglycol
0.25188 0.0005986 T/K 0.15386 0.01451 T/K 0.92% 3.85%
0.0044512 0.6976816 1.01% 3.64%
xi xj aij
ð9Þ
xi xj bij
ð10Þ
j
XX i
DT/K
j
wherein cross term, aij is obtained from Pangiotopoulos-Reid expression [33],
aðT Þij ¼
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi aðT Þi :aðT Þj 1 xi kij xj kji
ð11Þ
In Eq. (11) kij and kji are binary interaction parameters, and that for parameter b is obtained with Eq. (12),
bij ¼ bji ¼
bi þ bj 1 lij 2
ð12Þ
in which lij is zero for the systems studied in present work. The optimum binary interaction parameters along with the average relative deviation, ARD %, and the maximum relative deviation, MRD % were summarized in Table 8 and also quality of correlation was graphically shown in Figs. 1 and 2 and compared with experimental values. 4. Conclusions The solubility of H2S and CO2 in 2,20 -thiodiglycol was measured within the temperature range (303.15–353.15) K and pressure up to about 1.2 MPa. The results were modelled using Stryjek-Vera modification of Peng-Robinson cubic equation of state (PRSV EoS). As shown in Figs. 1 and 2 and reported in Table 7, this model has sound capability in correlation of mTp data. In addition as can be seen in Figs. 3 and 4, solubility of H2S and CO2 in 2,20 thiodiglycol is lower than that of DEG. This means that in the DEG structure, replacement of oxygen with sulfur would lessen solubility of both CO2 and H2S. Acknowledgement We would like to express our appreciation to Research Council of the Research Institute of Petroleum Industry (RIPI) for financial support of this work. References [1] S. Capdeville, J.L. Peytavy, G. Fremy, D. Anglerot, Process for purifying gaseous mixtures containing mercaptans and other acidic gases, French Patent 0600448, International Publication Number WO 2007/083012 A1, January 18, 2006. [2] R. Cadours, V. Shah, C. Weiss, HySWEET process for improved mercaptan removal, presented at International Petroleum Technology Conference held in Doha, Qatar, 7-9 December 2009.
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JCT 2018-1072