Fluid Phase Equilibria 520 (2020) 112660 Contents lists available at ScienceDirect Fluid Phase Equilibria j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / fl u i d Elemental mercury partitioning in high pressure fluids part 1: Literature review and measurements in single components Antonin Chapoy a, *, Pezhman Ahmadi a, Richard Szczepanski b, Xiaohong Zhang b, Alessandro Speranza b, Junya Yamada c, Atsushi Kobayashi c a b c Hydrates, Flow Assurance & Phase Equilibria Research Group, Institute of Petroleum Engineering, Heriot-Watt University, UK KBC (A Yokogawa Company), 42-50 Hersham Road, Walton on Thames, KT12 1RZ, UK Technical Research Center, INPEX Corporation, 9-23-30 Kitakarasuyama, Setagaya-ku, Tokyo, 157-0061, Japan a r t i c l e i n f o a b s t r a c t Article history: Received 22 April 2020 Received in revised form 19 May 2020 Accepted 19 May 2020 Available online 30 May 2020 Mercury in its elemental form is naturally present in most reservoir fluids. The presence of mercury can lead to serious operational and safety/health problems. Knowledge of the maximum solubility of elemental mercury with temperature and pressure in reservoir fluids is important to avoid mercury dropping out during processing operations, as mercury is naturally present in hydrocarbon deposits. In this work, a new experimental approach is presented to determine the mercury content in high pressure gas and liquid systems. Mercury solubility in methane, ethane, propane, nitrogen and carbon dioxide over a wide range of temperature and pressure (243.15e323.15K and up to 20 MPa) have been measured. An extensive literature review has been conducted on the solubilities of mercury in gases and liquid hydrocarbons. A critical evaluation of the literature data has been conducted to identify any inconsistencies in the reported data. The new experimental data generated in this work along with the literature data have been used to tune the binary interaction parameters of the Peng-Robinson and the Soave-Redlich-Kwong equations of state between mercury and the mentioned compounds. © 2020 Elsevier B.V. All rights reserved. Keywords: Mercury Methane Ethane Propane Carbon dioxide Nitrogen Phase behaviour Thermodynamic modelling 1. Introduction Although not present in every gas or oil field, mercury contamination has been reported in several locations worldwide. Hotspots of mercury contamination appear to be spread globally, with higher concentrations in Southeast Asia, North Europe (Germany/Netherlands) and the Middle East [1]. Mercury contamination represents a big risk for the oil and gas industry. Although normally present in small amounts, its effects may be very damaging for the industry. It is an obvious Health, Safety and Environmental (HSE) hazard for the staff and the environment. If not detected promptly and removed from the fluid, mercury can easily be dispersed in the immediate environment, with tragic consequences for the health of the workers on the plant and major risks of contamination of the wider environment. Moreover, mercury is highly corrosive and its accumulation in pipelines or operating units, like heat exchangers or separators, may compromise * Corresponding author. E-mail address: a.chapoy@hw.ac.uk (A. Chapoy). https://doi.org/10.1016/j.fluid.2020.112660 0378-3812/© 2020 Elsevier B.V. All rights reserved. the integrity of the steel walls and cause leaks with associated risk of fire and further risks of contamination from the dispersion of hydrocarbons in the environment [2,3]. The strategies adopted to mitigate risks associated with mercury are obviously very costly. While a conservative approach in design and construction of the facilities is clearly necessary, the adoption of excessive design margins may lead to excessive CAPEX and OPEX or reduced operating capacity. For instance, the correct sizing and positioning of a mercury removal unit may have a major impact on the economics of the project. The ability to determine with improved accuracy the risk of accumulation of mercury across the plant and assess within safety margins, the correct sizing and operating conditions of the mercury removal units would therefore provide great benefit to the industry overall. With increased modelling and simulations capabilities, engineers would be able to assess more effectively the risks associated with mercury contamination, maximize the effectiveness of capital and operational expenditure, and improve their general capability to operate the plant within its actual productive limits, without compromising the safety of the staff and the environment. In this communication, we present experimental techniques, 2 A. Chapoy et al. / Fluid Phase Equilibria 520 (2020) 112660 equipment and thermodynamic modelling for investigating the phase behaviour of systems in presence of mercury. Mercury contents in methane, ethane, propane, carbon dioxide and nitrogen were measured at (243.15, 258.15, 273.15, 298.15 and 323.15) K and pressures up to 20 MPa. Finally, the PR78-EoS [4] and the SRK72-EoS [5] were used to calculate the phase behaviour and the mercury distribution in fluid phases. Binary interaction parameters were adjusted using obtained experimental data and the literature data. In this manuscript, all mercury content data from the literature and from this work are reported in mole fraction (ppm: part per million, i.e. 106 mol fraction/ppb: part per billion, i.e. 10-9 mol fraction). 2. Literature review Experimental data for solubility of mercury in various substances are scarce and limited to a few research groups. Among the published works focusing on solubility data of mercury, the review carried out by Clever [6] is one of the main references for experimental data measured before 1987. An updated literature review for solubility of mercury in various alkanes, carbon dioxide and nitrogen is described in this section. Furthermore, for all the data points found in open literature, details including pressure, temperature and solubility of mercury have been tabulated in the appendix. 2.1. Mercury e alkanes 2.1.1. Methane The most recent data in the literature reported for this system have been measured by Yamada et al. [7]. They have measured the solubility of mercury in methane between (268.15e303.15) K and pressures up to 6 MPa. In addition, Butala et al. [8] measured the solubility of mercury in methane at nine isotherms between (253.15e293.15) K and pressure up to 6.9 MPa. The range of mercury content varies between 1.3 and 77 ppb M in the methane-rich phase. The system has also been studied by McFarlane [9] at Texas A&M University in the solid-liquid equilibrium (SLE). Later in 2016, McFarlane published the results reported in his MSc thesis, with additional experimental results in a journal paper by Marsh et al. Fig. 1. Literature data for solubility of mercury in nC6. ( ): Okouchi & Sasaki [15], ( ): Spencer & Voigt [18], ( ): Reichardt & Bonhoeffer [19], ( ): Kuntz & Mains [17], ( ): Gallup & Bloom [16]. [10]. This article (Marsh et al. [10]) is used as the main reference of the results published by McFarlane in this manuscript. 2.1.2. Ethane The data set measured by Yamada et al. [7] is the most recent reported measurements in the literature. Like the measured data for methane, their measurements cover 8 isotherms between (268.15e303.15) K and pressures up to 3.5 MPa. In addition, Koulocheris et al. [11] reported measurements for the solubility of mercury in ethane at five isotherms of (273, 278, 283, 288 and 293) K and pressures up to 8.2 MPa. 2.1.3. Propane Three sources are available for the phase equilibrium data of mercury-propane binary mixtures. Jepson et al. [12] reported experimental vapour-liquid equilibrium (VLE) of the mercurypropane system. The VLE measurements were conducted at (457.15, 491.15 and 529.15) K and pressures up to 3.3 MPa. The solubility measurements were in a range of (800e10231) ppm. One SLE measurement and few liquid-liquid equilibrium (LLE) data for this binary mixture have been reported by Marsh et al. [10]. LLE measurements were conducted at temperatures between (233.15e343.15) K and pressures up to 2.6 MPa. The mercury concentration in their mixtures was in the range of 0.4e3369 ppb. In addition, the single SLE measurement was carried out at 177.15 K and 0.004 MPa. Finally, five solubility data points obtained at (273.15, 278.15, 283.15, 288.15 and 293.15) K were reported by Mentzelos [13] in 2015. 2.1.4. Butanes For n-butane, 23 data points were found in the literature from the works performed by Jepson et al. [12] and Richardson et al. [14]. Jepson et al. [12] measured VLE at (457.15e529.15) K and pressures up to 3.1 MPa, with a range of mercury content between (614e10448) ppm. The VLE measurements conducted by Richardson et al. focused on binary mixtures with mercury contents between (454e3860) ppm, at P-T ranges of (7e38) MPa and (486e573) K, respectively. For iso-butane, the only available data set in the literature is the work reported by Butala et al. [8], where they obtained Fig. 2. Reported data in the literature for the solubility of mercury in nC7. ( ): Okouchi & Sasaki [15], ( ): Spencer & Voigt [18]. A. Chapoy et al. / Fluid Phase Equilibria 520 (2020) 112660 3 Table 1 Composition of the chemical used in this work (used without further purification). Fig. 3. Literature data for solubility of mercury in nC8. ( ): Okouchi & Sasaki [15], ( ): Spencer & Voigt [18], ( ): Marsh et al. [10], ( ): Vogel et al. [20], ( ): Gallup & Bloom [16], ( ): Miedaner et al. [22], ( ): Migdisov et al. [21]. experimental mercury content data in the isobutane rich phase in VLE and LLE conditions at (263.15, 268.15, 273.15, 278.15 and 283.15) K and pressures up to 8.3 MPa. In these measurements, the mercury contents of the samples were in the range of (50e269) ppb. 2.1.5. Pentanes The available experimental data for solubility of mercury in normal pentane were reported by Marsh et al. [10], Okouchi and Sasaki [15], Butala et al. [8], Gallup and Bloom [16], and Kuntz and Mains [17]. Marsh et al. reported mercury solubility in n-pentane for six isotherms between 233 and 383 K. The obtained mercury content in their experiments was in a range of (9e16161) ppb. Okouchi and Sasaki [15] measured mercury concentration in HgeC5 mixtures at Fig. 4. Mercury content in equilibrium with CO2 at different isotherms. Butala et al. [8]; ( ): T ¼ 293.15, ( ):T ¼ 288.15, ( ):T ¼ 283.15, ( ): T ¼ 278.15, ( ): T ¼ 273.15. Yamada et al. [7]; ( ): data at three isobars (~0.5, 1.5, and 2 MPa). Chemical Symbol CASRN Purity Supplier Mercury Methane Ethane Propane Carbon dioxide Nitrogen Hg CH4 C2H6 C3H8 CO2 N2 7439-97-6 74-82-8 74-84-0 74-98-6 124-38-9 7727-37-9 99.9995 wt% 99.995 vol% 99.99 vol% 99.95 vol% 99.995 vol% 99.9992 vol% Sigma-Aldrich BOC BOC BOC Air Product Air Product six isotherms of (278.15, 283.15, 293.15, 298.15, 303.15 and 313.15) K. The minimum and maximum mercury concentration for these binary mixtures were found to be 190 and 1600 ppb, respectively. The other set of literature data generated by Butala et al. [8] covered a temperature range of (258.15e293.15) K. In their measurements, the mercury contents of the mixtures were found to be between 44 and 464 ppb. Comparison of the measured data from these three works shows a reasonable agreement between their results. In addition, the solubility of mercury in n-pentane at 298.15 K was investigated in two different works performed by Gallup and Bloom [16], and Kuntz and Mains [17]. The mercury contents were found to be 793 ppb by Gallup and Bloom [16], and 674 ppb by Kuntz and Mains [17]. In comparison to the data available for solubility of mercury in nC5 mixtures, for iC5 experimental data is scarce, and only one single point has been reported in the literature by Kuntz and Mains [17] at 298.15 K. The mercury content for this point was found to be 645 ppb, which is less than the value reported for the solubility of mercury in nC5. 2.1.6. Hexanes The solubility of mercury in normal hexane has been measured at temperatures between 273.15 and 336.15 K. Most experimental results were reported by Okouchi and Sasaki [15], and Spencer and Voigt [18]. Experiments conducted by Okouchi and Sasaki were performed at six isotherms between 278.15 and 313.15 K. The obtained mercury contents were found to be between 240 and 1900 ppb. Also, Spencer and Voigt, reported solubility measurements at five isotherms between 273.15 and 308.15 K. A close agreement is seen by comparing the experimental results obtained from these works at similar isotherms (303.15 and 293.15 K). Measurements conducted by Reichardt and Bonhoeffer [19] at 313.15 and 336.15 K, and two single-point measurements at 298.15 K conducted by Gallup and Bloom [16] and Kuntz and Mains [17], are other available data in the open literature as shown in Fig. 1. For the different isomers of hexane, four sets of experimental results were found in the literature. Kuntz and Mains reported solubility measurements at 298.15 K for 3-methylpentane, 2,2dimethylbutane and 2,3-dimethylbutane. Also, Spencer and Voigt performed similar measurements for 2,2-dimethylbutane at different temperatures between 273.15 and 308.15 K, where the measured mercury contents were found to be between 167 and 984 ppb. 2.1.7. Heptanes Two data sets have been reported in the literature for LLE of binary mixtures of Hg-nC7. The first set was reported by Spencer and Voigt [18] and covers six isotherms between 273.15 and 308.15 K, with mercury content in the range of (200e1628) ppb. The second set is the measurements conducted by Okouchi and Sasaki [15] at six isotherms between 278.15 and 313.15 K. In their work, the measured solubility of mercury in normal heptane varied from (290e2200) ppb. The obtained results from the literature are 4 A. Chapoy et al. / Fluid Phase Equilibria 520 (2020) 112660 depicted in Fig. 2. As shown in this figure, except for the points measured at 303.15 K, a similar trend can be seen from both sets of measurements. For the different isomers of heptane, no data were found in the open literature. 2.1.8. Octanes In comparison to other alkanes, experimental results for n-octane are available over a wider temperature range. Spencer and Voigt [18] obtained mercury solubility in equilibrium with nC8 at six isotherms between (273.15e313.15) K. Okouchi and Sasaki [15] conducted a similar study at temperatures between (278.15e313.15) K. Among the measurements carried out in both these works, three isotherms of (298.15, 303.15, 313.15) K are similar. A deviation of up to 10% is seen by comparing the obtained results of these works. Gallup and Bloom [16] and Vogel et al. [20] have also reported measurements at 298.15 K. Comparison of their results with those obtained by Okouchi and Sasaki [15], Spencer and Voigt [18], and Marsh et al. [10] show discrepancies of the experimental results obtained at this temperature. In the experiments conducted by Marsh et al. [10], five other isotherms between (233.15e413.15) K were tested. In these measurements, the concentrations of mercury were in a range of (14e41794) ppb. For higher temperatures, two data sets were found in the literature. In the first one, Migdisove et al. [21] measured the mercury content at (382e483) K, where the mercury contents were found to be in a range of (17,267e314,026) ppb. In this work, the authors have checked the reproducibility of results by repeating the measurements for three temperatures. Based on the available experimental results in the open literature, significant deviations (between 32% and 46%) are observed between the repeated measurements. This can raise questions about the validity of the method used for these measurements. In the second set, Miedaner et al. [22] reported three data points measured at temperatures between (373.15e473.15) K, with obtained solubilities from 54,000 to 821,000 ppb. Fig. 3 summarises the reported literature data for normal octane. In this figure, the Y-axis (mercury content) is in a Logarithmic scale to show all the reported data points. To the best of our knowledge, among the different isomers of octane, 2,2,4-trimethylpentane is the only one with available records in the literature. Vogel et al. [20] and Klehr and Voigt [23] measured the mercury content at 298.15 K. Also, Spencer and Voigt [18] conducted the measurements for seven temperatures in a range of (273.15e308.15) K. The measured mercury contents in their work were in a range of (164e1121) ppb. 2.1.11. Pentadecane/hexadecane For the solubility of mercury in other alkanes with carbon numbers more than 12, only two data points measured by Gallup and Bloom [16] for n-pentadecane and n-hexadecane were found in the literature. The solubility of mercury in C15 at 294.15 K, and in C16 at 294.85 K were reported to be 1371 and 1955 ppb, respectively. 2.2. Mercuryecarbon dioxide The most recent published data in the literature were measured by Yamada et al. [7]. Solubilities of mercury in CO2 were measured at 8 isotherms between (268.15e303.15) K and pressures up to 2 MPa. Also, Butala et al. [8] measured mercury solubility at three different pressures for five isotherms. Fig. 4 summarises all the literature data. 2.3. Mercuryenitrogen The only available data set in the literature are those reported by Mentzelos [13], which includes six data points at 273.15 K. Similar to other data points from this reference, due to the confidentiality of the measured data, exact values of the results were not directly available. 3. Experimental setup and procedures 3.1. Materials The source and purity of gases used in this study are listed in Table 1. Mercury purchased from Sigma-Aldrich used in all tests was 99.9995 wt% pure. No further purification or analysis of the composition of these substances was conducted. 3.2. Setup The equipment in principle is similar to the setup used by Butala et al. [8]. The equipment is comprised of two saturation cells, coiled tubing and a set-up for measuring the mercury content of the equilibrated fluids flowing out of the cell. The two saturation cells are made of stainless steel 316 with inner volume of 50 cm3. The maximum working pressure of these cell is 30 MPa. A schematic of the set-up is shown in Fig. 5. Initially, the test fluid enters the system through a needle valve and passes through coiled tubing (15 m of 1/1600 stainless steel pipe) into the first saturation cell (presaturation), the temperature of the bath (bath 1) in which this cell is immersed is set 5 K higher than the temperature of the bath (bath 2) of the main saturation cell. The test fluid passes then through 2.1.9. Decane Klehr and Voigt [23] measured LLE of Hg-nC10 binary mixtures between (273.15e318.15) K. In their measurements, the concentration of mercury in equilibrium with normal decane was found to be in a range of (401e1077) ppb. Kuntz and Mains [17] measured the solubility of mercury in decane at 298.15 K. In their work, the mercury content was found to be 1077 ppb, 300 ppb less than the value obtained by Klehr and Voigt at this temperature. 2.1.10. Dodecane For binary mixtures of HgeC12, two sets of data points were found in the literature. First, the measurements performed by Gallup and Bloom [16] at 294.65 K and 298.15 K, with reported mercury contents of 1341 and 1600 ppb, respectively. Second, the measured data points reported by Miedaner et al. [22] at five isotherms between (383.15e498.15) K with mercury contents ranging between (76e1049) ppm. Fig. 5. Schematic illustration of the Dynamic Mercury Content Equilibrium Cell. A. Chapoy et al. / Fluid Phase Equilibria 520 (2020) 112660 another coiled tubing (15 m of 1/16” stainless steel pipe) into the second saturation cell. It is therefore assumed that the fluid is therefore supersaturated when it enters the second cell and excess mercury will drop out and the fluid will be saturated at the temperature of the main saturation cell. Both bath temperatures are measured using a PRT (Platinum Resistance Thermometer). The pressure of the setup is measured using a Quartzdyne pressure transducer mounted on the main saturation cell. The outlet from the setup is connected to a temperature (T ¼ 363.15 K) control choke valve and then connected to the gas inlet of an atomic absorption spectroscopy (AAS) setup from Mercury Instruments (VM-3000 - UV absorption is measured at a wavelength of 253.7 nm). For each P/T point around 10 1-L samples are analyzed until the readings are stable and repeatable. The temperatures in the two baths are measured by platinum probe (100 U). The temperature probes were calibrated against a Prema 3040 precision calibrator. Temperature calibration uncertainty is estimated to be 0.05 K, in the temperature range 243.15e323.15 K. A precise pressure transducer (Quartzdyne QS10KeB, pressure range 0e69 MPa) is used to measure system pressure during the measurements. This transducer calibrated regularly using a Budenberg deadweight tester. Pressure calibration uncertainty is estimated to be 0.01 MPa. The mercury analyzer was calibrated against a MC-3000 Mercury calibrator using nitrogen. The mercury content uncertainty is Ucal(yHg) ¼ 2%. 5 Fig. 6. Calculated vapour pressure, Psat, of mercury using the PR-EoS with the MathiasCopeman alpha function [24] e Comparison with Huber et al. [20]. PR=SRK bi ¼ Ub RTC with Ub ¼ 0:08664ðSRKÞ or 0:077796ðPRÞ PC (2) The temperature dependency of the attractive term (1), a, is defined using a Soave type temperature dependency: 4. Thermodynamic modelling In this work, the PR78-EoS [4] and SRK72-EoS [5] were chosen to calculate the phase behaviour and the mercury distribution in all fluid phases. These equations are given below: P¼ 8 RT aSRK ðTÞ i > ðSRKÞ > > SRK > > v v þ bSRK < v bi i > > > > > : (1) aPR ðTÞ i ðPRÞ PR PR v bi þ bPR v bPR v v þ bi i i RT a ¼ a0 aðTÞ (3) h 8 pffiffiffiffiffi i2 > a ðTÞ ¼ 1 þ m 1 Tr > < Where 2 2 > > : a ¼ Ua R Tc with U ¼ 0:42748ðSRKÞ or 0:457240 ðPRÞ a 0 Pc (4) where m is directly related to the acentric factor of the components 8 < SRK : 0:480 þ 1:574u 0:176u2 mðuÞ ¼ aa 0:37464 þ 1:54226u 0:26992u2 if u 0:491 : PR : 0:379642 þ 1:48503u 0:164423u2 þ 0:016666u3 if u > 0:491 The co-volume b for the SRK and PR EoS is given below: (5) To improve the calculation of the vapour pressure of mercury, the Mathias-Copeman (MC) alpha function [24] with three adjustable parameters was also used for this compound: Table 2 Critical parameters, acentric factor and Mathias-Copeman [24] adjusted parameters for mercury and other compounds. Compound Mercury c Methane Ethane Propane Nitrogen CO2 a b Tc/Ka Pc/MPaa ua c1b c2b c3b EoS 1735 160.803 0.16445 190.56 305.32 369.89 126.19 304.13 4.5592 4.8722 4.2512 3.3958 7.3773 0.01142 0.0995 0.1521 0.0372 0.22394 0.23606 0.14738 e e e e e 0.2293 0.1564 e e e e e 0.16092 0.133982 e e e e e SRK72 PR78 e e e e e DIPPR801. Adjusted Mathias-Copeman parameters between 234.3 and 573.15 K (Eq. (6)). 6 A. Chapoy et al. / Fluid Phase Equilibria 520 (2020) 112660 Table 3 Adjusted kij and temperature range of regression for the PR78-EoS. Compound k0 k1 k2 Tmin/K Tmax/K Phase CO2 Nitrogen Methane Ethane Propane n-pentane n-hexane n-heptane n-octane n-nonane n-decane n-dodecane n-pentadecane n-hexadecane i-butane i-pentane n-butane* 1.2406 0.2218 0.1150 0.0428 0.1121 0.0461 0.0115 0.00881 0.02667 0.05516 0.07711 0.10537 0.15205 0.21116 0.04318 0.03560 0.1093 1.253E-02 e e 4.965E-04 6.272E-04 e e e e e e e e e e e 2.429E-05 e e e e e e e e e e e e e e e 243.15 243.15 243.15 253.15 233.15 233.15 273.15 273.15 233.15 273.15 273.15 273.15 294 294 263.15 298.15 258.15 323.15 323.15 323.15 323.15 343.15 383.15 336.15 313.15 413.15 336.15 318.15 473.15 294 294 283.15 298.15 293.15 L&SC SC SC L&SC L L L L L L L L L L L L L *Adjusted using n-butane þ n-pentane þ n-hexane ternary system from Butala et al. [8]. 8 > > > > > ifT < TC; > > < 2 aðTÞ ¼ 41 þ c1 sffiffiffiffiffi ! sffiffiffiffiffi !2 sffiffiffiffiffi !3 32 T T T 5 þ c2 1 þ c3 1 1 TC TC TC > sffiffiffiffiffi !#2 " > > > > T > > : otherwise aðTÞ ¼ 1 þ c1 1 TC where c1, c2 and c3 are the three adjustable parameters. These parameters are listed in Table 2. These parameters were adjusted using the correlation developed by Huber et al. [25]. They estimated that their correlation has an uncertainty (k ¼ 2) of 1% between 273.15 and 400 K, 0.15% from 400 K to the boiling point (629.77K) and 3% above the triple point (TT ¼ 234.3156 K [26]). Their correlation has the following form: h i p T ln ¼ a1 t þ a2 t1:89 þ a3 t2 þ a4 t8 þ a5 t8:5 þ a6 t9 pc Tc (7) where pc ¼ 167MPa; Tc ¼ 1764K; a1 ¼ 4:57618368; a2 ¼ 1:40726277; a3 ¼ 2:36263541; a4 ¼ 31:0889985; a5 ¼ 58:0183959; a6 ¼ 27:6304546. The average deviation between 234.3 and 573.15 K is 0.4% (for both EoS). The comparison between the correlation and the model calculations is shown in Fig. 6. For multicomponent systems, the classical van der Waals mixing rules were used: pffiffiffiffiffiffiffiffi aij ¼ 1 kij ai aj bij ¼ bi þ bj 2 (8) (9) where kij is the binary interaction parameters, in this work the kij is symmetrical, i.e. kij ¼ kji and equal to zero when j ¼ i. For some systems the following temperature dependency was assumed for the binary interaction parameters: kij ¼ k0 þ k1 T þ k2 T 2 (10) (6) It is also assumed that the solubility of components in elemental mercury is negligible and the mercury phase is therefore considered pure (Helium solubility in mercury was measured to have an upper limit (most likely lower) of 1.108 mol fraction at 101.3 kPa and near ambient temperature [27]). 5. Results and discussions The binary interaction parameters between mercury and gases, liquid hydrocarbons and carbon dioxide (Equation (10)) were adjusted using the gathered solubility data through a Simplex algorithm using the objective function, OF, displayed in equation (11): OF ¼ Nexp 1 X xexp xcal N 1 xexp (11) where x is the solubility of mercury, N is the number of data points. The adjusted parameters are reported in Table 3 and Table 4 for the PR78-EoS and the SRK72-EoS, respectively. 5.1. Methane As reported in the literature review, only three sources are available for methane, and the data are limited to pressure lower than 7 MPa. Our new data expand the range both in term of temperature and pressure. The new data are reported in Table 5. The model can reproduce the mercury solubility in the vapour phase with a single binary interaction parameter, as seen in Fig. 7. The optimised kijs are 0.115 and 0.069 for the PR-EoS and SRK-EoS, respectively. The OF (defined in equation (11)) is equal to 5.8% and 5.7% for the PR-EoS and SRK-EoS, respectively. At low pressure A. Chapoy et al. / Fluid Phase Equilibria 520 (2020) 112660 7 Table 4 Adjusted kij and temperature range of regression for the SRK72-EoS. Compound k0 k1 k2 Tmin/K Tmax/K Phase CO2 Nitrogen Methane Ethane Propane n-pentane n-hexane n-heptane n-octane n-nonane n-decane n-dodecane n-pentadecane n-hexadecane i-butane i-pentane n-butane* 1.4174 0.1105 0.0690 0.0436 0.1092 0.0527 0.0251 0.0076 0.0082 0.0344 0.0554 0.10537 0.12721 0.1856 0.04963 0.03560 0.1142 1.390E-02 e e 4.866E-04 6.272E-04 e e e e e e e 2.6899-05 e e e e e e e e e e e e e e e 243.15 243.15 253.15 253.15 233.15 233.15 273.15 273.15 233.15 273.15 273.15 273.15 294 294 263.15 298.15 258.15 323.15 323.15 293.15 293.15 343.15 383.15 336.15 313.15 413.15 336.15 318.15 473.15 294 294 283.15 298.15 293.15 L&SC SC SC L&SC L L L L L L L L L L L L L *Adjusted using the n-butane þ n-pentane þ n-hexane ternary system from Butala et al. [8]. Table 5 Mercury solubility in methane. Npts T/K P/MPa yHg/ppb stdev uc(y) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 244.35 244.55 244.55 245.15 246.15 258.15 258.15 258.15 258.15 258.15 273.15 273.15 273.15 273.15 278.15 283.15 288.15 293.15 298.15 298.15 298.15 298.15 298.15 323.15 323.15 323.15 1.03 2.07 3.45 6.89 10.34 15.51 10.55 5.27 2.59 1.34 2.50 5.09 8.41 18.62 1.03 0.93 1.05 0.80 8.79 2.56 4.90 4.83 1.03 5.17 8.69 2.76 1.43 1.01 0.59 0.51 0.81 2.14 1.95 2.12 2.99 5.42 14.64 9.06 7.87 8.25 45.93 84.24 113.89 226.93 60.66 125.29 77.04 79.94 285.54 491.48 406.58 758.14 0.080 0.020 0.010 0.016 0.034 0.024 0.028 0.018 0.090 0.065 0.056 0.599 0.130 0.080 0.663 0.056 1.156 0.230 0.203 0.401 0.598 0.693 0.373 3.212 0.725 1.072 0.260 0.248 0.246 0.247 0.249 0.251 0.251 0.251 0.270 0.281 0.394 0.674 0.321 0.316 1.116 1.541 2.309 3.688 1.050 2.120 1.426 1.510 4.616 7.713 5.886 10.683 Standard uncertainites are u(T) ¼ 0.005K and u(P) ¼ 0.01 MPa. Stdev is the standard deviation. uc(y) q isffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi the combined standard uncertainty and defined as uc ðyÞ ¼ usys 2 þ uca 2 þ urepeat 2 where usys, uca, and urepeat stand for standard uncertainties of the system (device), the calibration procedure and reproducibility of the results, respectively. for both systems, the mercury content is directly reducing following a Raoult's law (Psat/P). The model is predicting the mercury content at higher pressure (~6 MPa) to slightly increase with pressure similar to what is observed for the methanol or ethanol content in the methane system [28]. 5.2. Ethane The data for the solubility of mercury in ethane are reported in Table 6 and plotted in Fig. 8. The measurements were carried out with ethane below its critical temperature and below the vapour- Fig. 7. Experimental and calculated mercury solubilities in methane at 243.15, 258.15, 263.15, 268.15, 273.15, 278.15, 283.15, 288.15, 293.15, 298.15, 303.15 and 323.15 K; experimental data from Butala et al. [8]: ( ); Yamada et al. [7]: ( ); this work: ( ): 243.15 K; ( ): 258.15 K; ( ): 273.15 K; ( ): 298.15 K; ( ): 323.15 K; Black lines: PR78 with kij reported in Table 3. liquid (ethane)eliquid (Hg) locus, in the liquid region and for isotherms above ethane critical temperature. Two data sets are available for the solubility of mercury in ethane, however only 5 points were reported in the liquid region. At low pressure (P < 2 MPa) in the vapour phase, predictions of the model are hardly affected by the value of the binary interaction parameters as seen in Fig. 9. Predictions using parameters between 0.1 and 0.3 yield close predictions in the vapour region but large difference in the liquid region. It is therefore recommended to tune the model using mercury data in the liquid region. For this reason, only our data were used to optimise the binary interaction parameters. The kijs were found to have a slight temperature dependence as highlighted in Tables 3 and 4. The absolute average deviations (AAD) between the model and the experimental are 5.3% for both EoS (3.8%(SRK)/4.16%(PR) for this work/7.1%/5.9% for [13] and 6.4%/6.4% for [7]) see Fig. 8. Below saturation, the expected trend is observed for this system, the mercury content is decreasing with pressure and the temperature dependency is closely related to the vapour pressure of mercury, however in the liquid region, different trends are observed, an increase in the solubility of mercury in the liquid region is observed. 8 A. Chapoy et al. / Fluid Phase Equilibria 520 (2020) 112660 Table 6 Mercury solubility in ethane. Table 7 Mercury solubility in propane. Npts T/K P/MPa yHg/ppb stdev uc(y) Phases Npts T/K P/MPa yHg/ppb stdev uc(y) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 244.10 243.99 244.10 258.15 258.15 258.15 258.15 258.15 258.15 258.15 258.15 273.15 273.15 273.15 273.15 273.15 273.15 273.15 298.15 298.15 298.15 298.15 298.15 323.15 323.15 323.15 0.83 3.86 6.55 0.76 1.21 1.44 2.31 3.59 4.48 6.95 9.23 0.7 1.38 2.04 3.31 4.00 7.27 9.93 1.72 3.59 5.52 7.38 10.69 3.45 8.96 11.38 1.60 6.31 6.36 7.86 5.68 4.62 16.14 17.75 16.97 17.67 19.20 37.24 21.13 18.02 43.45 45.26 47.94 48.54 178.52 112.00 190.49 213.24 230.81 629.11 734.81 783.54 0.105 0.164 0.060 0.107 0.110 0.143 0.098 0.273 0.150 0.204 0.392 0.41 0.14 0.057 0.972 0.855 0.685 0.706 2.758 0.797 0.000 0.299 1.861 1.081 1.302 0.833 0.269 0.324 0.277 0.320 0.297 0.303 0.445 0.539 0.445 0.476 0.601 0.885 0.492 0.44 1.327 1.269 1.204 1.225 4.518 1.514 3.818 4.282 4.983 12.631 14.756 15.695 V-LHg L-LHg L-LHg V-LHg V-LHg V-LHg L-LHg L-LHg L-LHg L-LHg L-LHg V-LHg V-LHg V-LHg L-LHg L-LHg L-LHg L-LHg V-LHg V-LHg L-LHg L-LHg L-LHg V-LHg V-LHg V-LHg 1 2 3 4 5 6 7 246.65 252.94 263.02 272.89 282.78 297.40 307.69 1.03 1.03 1.03 1.03 1.72 3.45 3.45 14.46 24.86 51.08 88.25 180.40 396.52 624.95 0.455 0.82 0.719 0.098 0.204 3.12 1.16 0.609 1.01 1.501 1.977 4.212 8.52 12.56 Standard uncertainites are u(T) ¼ 0.005K and u(P) ¼ 0.01 MPa; V: vapour; L: Liquid; LHg: liquid mercury. Standard uncertainites are u(T) ¼ 0.005K and u(P) ¼ 0.01 MPa. Table 8 Mercury solubility in CO2. Npts T/K P/MPa yHg/ppb stdev uc(y) Phases 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 243.15 243.15 243.15 243.15 243.15 243.15 258.15 258.15 258.15 258.15 258.15 258.15 273.15 273.15 273.15 273.15 298.15 298.15 298.15 298.15 298.19 323.15 323.15 323.15 0.39 0.68 1.05 1.69 2.45 7.24 0.74 1.39 2.07 2.30 3.45 8.69 1.41 2.11 3.46 7.93 2.77 4.34 7.24 11.72 1.77 5.39 9.51 13.79 2.40 1.29 0.94 1.04 1.06 1.08 7.23 4.55 3.08 3.75 3.83 3.92 22.28 15.97 9.77 12.67 111.90 76.35 85.76 88.89 176.89 429.47 371.43 437.93 0.054 0.049 0.006 0.012 0.006 0.006 0.211 0.079 0.094 0.060 0.060 0.060 0.131 0.150 0.072 0.177 0.717 1.401 1.41 0.12 1.813 1.005 3.720 2.637 0.252 0.251 0.246 0.246 0.246 0.246 0.362 0.277 0.272 0.28 0.282 0.283 0.568 0.457 0.336 0.303 0.758 1.422 1.43 0.27 1.829 1.034 3.720 2.648 V-LHg V-LHg V-LHg L-LHg L-LHg L-LHg V-LHg V-LHg V-LHg L-LHg L-LHg L-LHg V-LHg V-LHg V-LHg L-LHg V-LHg V-LHg L-LHg L-LHg L-LHg V-LHg V-LHg V-LHg Standard uncertainites are u(T) ¼ 0.005K and u(P) ¼ 0.01 MPa. 5.3. Propane Fig. 8. Experimental and calculated mercury solubilities in ethane; experimental data from Mentzelos [13] also discussed/reported in Ref. [11] ( ); Yamada et al. [7]: ( ); this work: ( ): 244.15 K; ($$$): 258.15 K; ( ) 273.15 K; ( ): 298.15 K; ( ): 323.15 K; Black lines: PR-78 with kij reported in Table 3. The mercury content in propane measured in this work are listed in Table 7 and shown in Fig. 10. Four independent data sets (including ours) are available for the solubility of mercury in liquid propane. Like for ethane, the kijs were also found to have a slight temperature dependence (Table 3 & Table 4). The deviations between the model and the experimental are 2.9% for both EoSs. Fig. 9. Impact of Interaction Parameters - Experimental and calculated mercury solubilities in ethane at 273.15 K; experimental data from Mentzelos [13] also discussed/reported in Ref. [11] ( ); Yamada et al. [7]: ( ); this work: ( ); Dashed and solid lines: PR-78. A. Chapoy et al. / Fluid Phase Equilibria 520 (2020) 112660 9 Table 9 Mercury solubility in nitrogen. Fig. 10. Experimental and calculated mercury solubilities in liquid propane; experimental data from Butala et al. [8] ( ); Marsh et al. [10] ( ); Mentzelos [13] also discussed/reported in Refs. [11] ( ) and this work ( ). Dashed grey lines PR-78 (kij ¼ 0)/ Black lines: PR-78 with kij reported in Table 3. 5.4. Carbon dioxide Three data sets (including these new data) are available for the solubility of mercury in carbon dioxide (Fig. 11). The new data are listed in Table 8. As for ethane and propane, only the data in the liquid region and data above the critical points of carbon dioxide were used to optimise the parameters. The kijs were also found to have a slight temperature dependence as reported in Tables 3 and 4. The behaviour is very similar to ethane: (i) in the CO2 vapour region, the mercury content is decreasing with pressure and the temperature dependency is closely related to the vapour pressure of mercury, (ii) in the liquid region, different trends are observed, an increase in the solubility of mercury in the liquid region is observed, however the differences in mercury content between the vapour and liquid region are not as pronounced as for ethane. 5.5. Nitrogen Mercury content in nitrogen has been measured from 243.15 to 423.15 K and up to 19 MPa. The new data are listed in Table 9. Only one source is available for nitrogen, and the data are limited to 273.15 K and pressure lower than 6.9 MPa. Our new data expand the range both in term of temperature and pressure. The model can reproduce the mercury solubility in the vapour phase with a single Figure 11. Experimental and calculated mercury solubilities in Carbon Dioxide at 243.15, 258.15, 268.15, 273.15, 278.15, 283.15, 288.15, 293.15, 298.15, 303.15 and 323.15 K; experimental data from Butala et al. [8]: ( ); Yamada et al. [7]: ( ); this work: ( ): 243.15 K; ( ): 258.15 K; ( ): 273.15 K; ( ): 298.15 K; ): 323.15 K; Black lines: PR-78 with kij reported in Table 3. Npts T/K P/MPa yHg/ppb stdev uc(y) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 244.35 244.35 244.35 244.35 258.15 258.15 258.15 258.15 258.15 273.15 273.15 273.15 273.15 273.15 298.26 298.26 298.28 298.26 298.28 298.15 323.18 323.18 323.18 323.18 0.74 1.42 3.81 5.99 1.23 2.68 5.26 10.41 16.48 1.07 2.62 5.01 8.79 14.34 0.70 1.23 2.49 5.08 9.69 17.25 2.90 5.29 10.20 17.28 1.75 1.04 0.56 0.46 5.22 2.81 1.81 1.27 0.94 25.02 12.43 7.45 5.47 4.58 383.96 231.28 125.40 74.49 51.15 38.57 670.31 416.19 258.06 186.13 0.022 0.047 0.008 0.006 0.275 0.020 0.027 0.015 0.037 0.060 0.360 0.052 0.021 0.051 0.353 1.098 0.373 0.332 0.488 0.353 0.247 1.152 1.721 4.840 0.250 0.251 0.246 0.246 0.387 0.254 0.251 0.248 0.249 0.610 0.516 0.301 0.275 0.271 6.350 3.978 2.117 1.297 1.005 0.768 9.391 5.944 4.009 5.502 Standard uncertainites are u(T) ¼ 0.005K and u(P) ¼ 0.01 MPa. binary interaction parameter as seen in Fig. 12. The optimised kijs are 0.222 and 0.111 for the PR-EoS and SRK-EoS, respectively. The OF (defined in equation (10)) is equal to 13.1% and 12.8% for the PR-EoS and SRK-EoS, respectively. It is worth noting that the experimental uncertainties for the 243.15 K isotherm are greater than the actual measurements hence the relatively high objective function. 5.6. Comparison As seen in Fig. 13, the mercury solubility at the same pressure and temperature conditions is higher in liquid hydrocarbons than in vapour hydrocarbon and non-hydrocarbon gases. The following ranking in term of solubility can be established C3H8>C2H6>CH4>N2 and with the solubility in CO2 very close to N2 in the vapour region and higher in the liquid region but significantly lower than in ethane. In general, for liquid hydrocarbons, it can be observed that the mercury content is increasing with the carbon number. Fig. 12. Experimental and calculated mercury solubilities in nitrogen at 243.15, 258.15, 273.15, 298.15 and 323.15 K; experimental data from Mentzelos [13] also discussed/ reported in Ref. [11]: ( ); this work: ( ): 243.15 K; ( ): 258.15 K; ( ): 273.15 K; ( ): 298.15 K; ( ): 323.15 K; Black lines: PR-78 with kij reported in Table 3. 10 A. Chapoy et al. / Fluid Phase Equilibria 520 (2020) 112660 References Fig. 13. Experimental and calculated mercury solubilities at 273.15 in methane, ethane, propane, N2, and CO2 e Lines were calculated using the PR-EoS (ideal model ¼ PsatHg/ P). 6. Conclusion In this work, the mercury contents in single component fluids have been measured over a wide range of pressure and temperature. From this work, it can be concluded that at intermediate pressure (P < 7 MPa) and in the vapour region, the solubility of mercury is decreasing with pressure. The measurements also show that the mercury solubility in the liquid region is higher than in the gas region, and is higher in liquid hydrocarbons than liquid carbon dioxide. Using the adjusted parameters, the models can provide accurate predictions of mercury partitionning, across a wide range of pressure and temperature. Further measurements for multicomponent mixtures are nevertheless required to validate the model. 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. CRediT authorship contribution statement Antonin Chapoy: Investigation, Data curation, Software, Writing - review & editing. Pezhman Ahmadi: Investigation, Visualization. Richard Szczepanski: Supervision, Visualization, Writing - review & editing. Xiaohong Zhang: Writing - review & editing. Alessandro Speranza: Project administration, Writing - review & editing. Junya Yamada: Project administration, Supervision, Writing - review & editing. Atsushi Kobayashi: Writing - review & editing. Acknowledgments This work was part of a OGIC (Oil & Gas Innovation Centre) project (https://www.ogic.co.uk/mercury-related-risk/) conducted at the Institute of Petroleum Engineering, Heriot Watt University. The project was supported by KBC (A Yokogawa Company), INPEX Corporation and OGIC, which is gratefully acknowledged. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.fluid.2020.112660. [1] A. Chalkidis, D. Jampaiah, P.G. Hartley, Y.M. Sabri, S.K. Bhargava, Mercury in natural gas streams: a review of materials and processes for abatement and remediation, J. Hazard Mater. 382 (2020) 121036, https://doi.org/10.1016/ j.jhazmat.2019.121036. [2] M.D. Bingham, Field detection and implications of mercury in natural gas, SPE Prod. Eng. 5 (1990) 120e124, https://doi.org/10.2118/19357-PA. [3] J.H. 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