Design of Equilibrium Cells for Phase Equilibria and PVT

Article pubs.acs.org/jced

Design of Equilibrium Cells for Phase Equilibria and PVT Measurements in Large Ranges of Temperatures and Pressures. I. Vapor−Liquid−Liquid Equilibria Petri Uusi-Kyyny,*,† Simona Ionita,† Muhammad Saad Qureshi,† Ville Alopaeus,† and Dominique Richon†,‡ †

School of Chemical Technology, Department of Biotechnology and Chemical Technology, Aalto Univsity, Aalto 00076, Finland Thermodynamics Research Unit, School of Chemical Engineering, Howard College Campus, University of KwaZulu-Natal, King George V Avenue, 4041 Durban, South Africa

‡

S Supporting Information *

ABSTRACT: Acquiring accurate experimental thermodynamic data is very useful for the development of models and chemical processes. Although there are plenty of data in the scientific literature, there are still many missing. In fact, many of the easier measurements have been made, and far more of the remaining ones deal with either complex systems or extreme conditions. Clearly new adequate equipment for acquiring such data are welcome. For these purposes, advice coming from several decades of equipment design experience are exposed herein. After defining the aim pursued and consequently the type of desired thermodynamic quantity, it is necessary to take into account all physical and chemical constraints: viscosity, density, corrosive power of studied chemical systems, temperature, pressure together with other important points such as miniaturization, efficient stirring, avoiding both dead volume and polymer sealing. The other aim of this paper is to present a high temperature and high pressure apparatus capable of measuring the phase equilibria of systems exhibiting vapor−liquid−liquid behavior. The apparatus designed and built consists mainly of an equilibrium cell (70 cm3), novel high temperature, and high pressure samplers and a gas chromatograph. A detailed description of the apparatus is presented. Preliminary measurements are presented for propane in water, cyclohexane in water, and water in cyclohexane up to 498.8 K. In addition the solubility of 2methylfuran in water up to 413 K and 1548 kPa was measured.

1. INTRODUCTION New process technology is needed to meet the great challenges of humanity. It will be a necessity to explore and study many new ways, new possibilities, new systems, new processes, and then new compounds and new mixtures for which experimental data will have to be measured before expecting to find the necessary new ideas to develop accurate enough predictive models. Richon and de Loos1 have presented various existing experimental methods to measure phase equilibria and PVT properties. Existing experimental methods have many advantages but also drawbacks. Further improvements in equipment development can be expected by taking into account the following 10 points: 1. Equilibrium cells must have simple internal shapes; i.e., cylindrical shapes. 2. Stirring devices must be sufficiently powerful and have adequate speed of rotation that is consistent with the rheology of the chemical mixtures under study. 3. Thermal gradients must be minimized for solid and liquid phases. 4. Dead volumes should be completely removed. 5. Sampling systems should be reliable and must not affect reaching and keeping the equilibrium. The sample size must be negligible with respect to sampled phase volume. © XXXX American Chemical Society

Complete analysis of the whole sample must be carried out without discrimination. 6. Cold points must be avoided along sample transfer lines. 7. Component adsorption issues must be reduced by limiting the use of polymers for sealing purposes. 8. Chemical corrosion issues must be taken into account by selecting the most suitable materials (for example titanium alloys, which, apart from their high chemical resistance, have high mechanical resistance and are very light compared to stainless steels). 9. Dynamic sealing with polymer materials at high temperatures and pressures must be avoided. 10. It is advantageous to have the possibility to view the inside of the equilibrium cell. This is the first paper of a series where new static−synthetic methods with variable volume cells (medium and high temperatures) for cloud points, bubble points, and PVT property measurements, and new dynamic−synthetic methods for critical property measurements will be presented. Special Issue: In Honor of Kenneth R. Hall Received: February 14, 2016 Accepted: June 16, 2016

A

DOI: 10.1021/acs.jced.6b00126 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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Figure 1. Schematic diagram of the equipment: 1, Flow regulator; 2, injector; 3, gas chromatograph; 4, oven holding rack; 5, oven axis; 6, timer for solenoid valve control; 7, compressed air source; 8, solenoid valve for sampler actuation; 9, pneumatic liquid sampler; 10, pneumatic vapor sampler; 11, pressure transducer electronic box; 12, pressure transducer; 13, platinum probe; 14, platinum probe electronic box; 15, nonrotating stem valves; 16, syringe pump; 17, nitrogen cylinder; 18, vacuum pump; 19, propane cylinder; 20, oven holding rack; 21, valves; 22, nitrogen cylinder for flushing the oven; 23, mechanism for oven rotation along axis; 24, motor; 25, motor speed regulator; 26, ball bearing; 27, equilibrium cell body; 28, chain; 29, gear wheel; 30, roller ball bearing; 31, external rotating magnetic holder; 32, magnetic stirrer; 33, oven.

ment is suitable by terms of sample quality, it requires longer handling times for producing an analysis result for a sample. In 1985, Guillevic et al.5 designed a cell with manual capillary sampling valves but with limited ranges of temperatures and pressures. One year later, Laugier and Richon6 published a paper presenting a new sampling system which was the starting point of the ROLSI series development.7 Details can be found in trhe ROLSI Success Story.8,9 (The ROLSI is a trademark of ARMINES, France.) Capillary samplers have been used in the field of low temperature phase equilibria down to 70 K13,14 for studies related but not limited to the solids cosolubility in liquid oxygen,15 solubility measurements in potentially hazardous binary mixture such as hydrocarbon−oxygen systems16 and also for the phase equilibria in the presence of gas hydrates.17 The materials used for the construction of the equipment in this work, allow working with hydrogen mixtures. This is particularly suitable for thermodynamic investigations in the petro-bio fields. For modeling purposes it is worthwhile to produce complete isothermal data (P, T, x I , x II , y). Consequently, static−analytic methods are often preferred. For the said method we have accordingly, designed a new capillary sampler which is an advanced tool with respect to the ROLSI samplers described in several patents: (PCT patent 2004/090508, PCT patent 2000/011462, EPO patent EP 1105722). Among other improvements, we now have the possibility of taking samples up to more than 400 °C even with

Herein we have focused on preliminary LLE measurements at reduced pressures and temperatures while sizing and material choices have been done to be able to work up to 400 °C and 40 MPa. The corresponding new equipment design come from continuous developments and continuous improvements along decades2−17 where the static−analytic method has been shown to be a reliable method over a temperature range from 70 to 673 K and a pressure range from 0.3 to 100 MPa. A device2 to measure VLE up to 400 °C and 40 MPa was developed for hydrogen−hydrocarbons mixtures, and it was presented in 1980. The sampling valves (for liquid and vapor phases) are composed of stems that are refrigerated where sealing polymer O-rings are situated. To avoid disturbing the thermal equilibria of mixtures, a heating resistance is used at the upper part of the stems to avoid a thermal gradient in the bottom part of the mixtures. This cell is convenient only if the boiling point of each component of the mixture is lower than the equilibrium temperature. To work with high boiling point compounds, a modification in the experimental analyses procedure was proposed.3 The same laboratory designed a new cell with detachable samplings valves4 for dealing with measurement needs at temperatures encountered in tertiary oil recovery. Samples could be withdrawn at low equilibrium temperatures and placed inside a special gas chromatograph injector for vaporizing all the liquid components at sufficiently high temperature. This method offers no disturbance of thermal equilibrium inside the equilibrium cell. Although this equipB



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water as a component. Three degrees of freedom allow fine adjustment of samples in a wide pressure range. There are no capillary restriction at its extremity as for the ROLSI IV sampler. The new capillary sampler, normally closed, is activated through compressed air and not through an electromagnet mechanism as for the ROLSI IV. The compressed air actuation makes it considerably safer in potentially explosive atmospheres. The new VLLE cell is described herein together with the experimental method. New LLE data are presented and modeled. Details about the sampler are given and various sampler test results are presented. The readers will find the detailed complementary sampler drawings for their own use in the Supporting Information available. As a matter of fact the readers will be able to reproduce the sampler at their convenience. Furthermore, they are highly encouraged to contact the corresponding author to take the benefit of the most recent modifications and improvements.

Figure 3. VLLE cell (cross sectional view): 1, Hastelloy C-276 window holder; 2, sapphire bearing; 3, holder of sapphire bearing; 4, high temperature magnet; 5, Propeller; 6, Hastelloy C-276 cell body; 7, antifriction gasket; 8, Belleville’s gaskets; 9, sapphire window; 10, screw; 11, agitation axis.

2. EQUIPMENT AND MATERIALS The main parts of equipment presented in the flow diagram of the equipment (Figure 1) are the following:

Figure 4. Nonrotating stem valve. (a) Cut view, (b) full view. 1, 1/16 in. tubing location; 2, nut; 3, axial hole; 4, antifriction gasket; 5, piston displacement screw; 6, stem; 7, screw; 8, antifriction gasket; 9, spacer; 10, graphite gasket; 11, radial hole.

Figure 2. VLLE cell: 1, pneumatic capillary sampler; 2, roller ball bearing; 3, window assembly; 4, gear wheel; 5, external rotating magnets holder; 6, modified nonrotating stem valve; 7, connection to pressure sensor; 8, blind well; 9, equilibrium cell body.

carrier gas circuit connected to the pneumatic capillary samplers, a pressure sensor with its readout device, a temperature meter equipped with a platinum probe, a stirrer motor and its speed regulator, a control box with temperature regulators and sampler timer control and finally feeding and evacuating circuits. 2.1. VLLE Cell. The body of the cell (see no. 9 in Figure 2 and no. 6 in Figure 3) is made of Hastelloy C-276 to withstand high pressures at high temperatures in the presence of

The equilibrium cell (see Figures 2 and 3) is fitted with two sapphire windows, two pneumatic capillary samplers, an efficient magnetically driven stirring device, three nonrotating stem valves, and a connection to a pressure transducer. A blind well is managed through the body of the cell to receive one thermal sensor. An oven mounted on a rack allows rotational movement. Several peripherals are connected to the equilibrium cell assembly: a gas chromatograph with its external C



Article

Figure 6. Photo of the equipment. 1, Oven holding rack; 2, pressure transducer; 3, thermally traced carrier gas circuit; 4, gas chromatograph; 5, equilibrium cell; 6, oven; 7, oven rotation axis; 8, pneumatic capillary sampler; 9, motor speed regulator; 10, motor; 11, mechanism for oven tilting by rotation along axis (no. 7) to change phase to be sampled. Figure 5. Sapphire window assembly: (a) half cut view; (b): threequarter cut view. 1, Location of sealing screw; 2, window holder; 3, squeezing screw; 4, antifriction gasket; 5, Belleville’s gaskets; 6, sapphire window; 7, gold O-ring; 8, location of metallic gasket.

sides of the cell body. They are strongly maintained against cell body thanks to eight screws in each holder. The sealing is achieved using a metallic gasket placed in the groove (8) of Figure 3. Window assembly is shown in Figure 5 (half and three-quarter cuts). The Hastelloy C-276 holder (2) receives, in a small groove, a gold O-ring (7) which allows perfect sealing with the sapphire window (6) from Le Rubis Synthetic des Alpes, France. The window is pressed against its holder using two antifriction gaskets (4), two Bellevillés gaskets (5), and a squeezing screw (3). Squeezing screw and Bellevillés gaskets are useful at low pressures and for taking into account thermal expansion. At higher pressures from 2 to 40 MPa internal pressure is enough to ensure perfect sealing. The tubing (7) of Figure 2 is connected to a pressure transducer from Dynisco, model MDT 420F, 0−35 MPa, maximum overload can be 2 times full scale pressure. 2.2. Oven and Rack. The oven and rack are shown in Figure 6. The oven (6) is suspended to the rack (1) with an axis (7) that allows rotation as displayed by the two blue arrows. The mechanism (11) is activated through a crank to rotate the oven and maintain it in the given position requested to have the extremity of the bent capillary of the pneumatic capillary sampler used for liquids samplings in the right phase. On Figure 7 we see that rotating the oven counter clockwise allows sampling liquid 1 (capillary extremity (1) is in the bottom of the cell, Figure 7a) while rotating the oven clockwise allows sampling liquid 2, (capillary extremity (1) is in the medium phase, see Figure 7b). In both positions, the capillary extremity

hydrogen. This alloy was selected to avoid any embrittlement issues. Three nonrotating stem valves (see no. 15) in Figure 1) are used for degassing and feeding purposes. They are commercially available products from Top Industrie, France. The external body of valves are not used as their internal part is directly screwed into the equilibrium cell body (see no. 6 in Figure 2). These valves are however sold with rotating stems but they have been modified to allow nonrotation. Furthermore, the stem has been drilled along its long axis up to its sealing cone where it is also radially drilled to make a flow path for fluids as shown in Figure 4. A cavity was machined into the body of the cell, see no. 8 on Figure 2, to receive a platinum probe with the diameter of 3 mm from Tempcontrol, Netherlands. The two pneumatic capillary samplers in Figure 2 will be described later. The internal stirring device (see Figure 3) is composed of the following: 1an axis (11) ending on both sides with tungsten pivots rotating inside sapphire bearings (2) contained inside two holders (3), two propellers (5), three one-magnet holder with two cylindrical magnets (4). To drive the internal stirrer, we use a rotating assembly (see Figure 2) composed of a rotating gear wheel fixed to a rotating part, containing four ball bearings (2), and supporting two magnet holders (5). The internal and external magnets are Sm2Co17 ultra high temperature magnets from Electron Energy Corporation, USA. Window assemblies (3) are found on both D



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Figure 7. Front view of the VLLE cell. (a) cell is shown rotated counter clockwise along its long horizontal axis to have extremity (1) of bent capillary (connected to liquid sampler and opening inside the cell), immersed in liquid 1; (b) cell is shown rotated clockwise along its long horizontal axis to have the extremity of bent capillary immersed inside liquid 2. In both positions, (a) and (b), the extremity (2) of the linear capillary, connected to the vapor sampler and opening inside the cell, is immersed inside vapor phase.

(2) opens inside the vapor phase. Figure 8 is a picture of a three-phase system composed of water and 2-methylfuran. 2.3. Gas Chromatography. The gas chromatograph (3) in Figure 1 was an Agilent 6890N equipped with two detectors: a thermal conductivity detector (TCD) for water analysis and a flame ionization detector (FID) for propane and 2-methylfuran. Selection of the detectors is enabled with the use of a Deans switch flow modulator. The column used for these measurements was an Agilent J&W PoraPLOT Q with 25 m length, 0.53 mm diameter, and 20 μm film thickness. The carrier gas chosen was helium with a flow rate of 7.4 mL·min−1. The calibrations for water cyclohexane and 2-methylfuran were made by manual injections of components through the GC-inlet. 2-Methylfuran was diluted with methanol to obtain injectable low enough quantities. Cyclohexane was diluted with 2-propanol to obtain injectable low quantities. The propane calibration was carried out by injecting nitrogen + propane mixtures of known composition. The propane + nitrogen mixtures were prepared into a Schott-bottle of measured volume equipped with a screw cap septum. The Schott bottle was purged with nitrogen at atmospheric pressure and capped.

Known volumes of propane were injected to the Schott bottle and mixed carefully. 2.4. Temperature and Pressure Measurement. The temperature was measured with an ASL F200 precision thermometer (14) and a platinum probe calibrated against a thermometer equipped with a Pt100 sensor probe at Finnish National Standards Laboratory (MIKES). The estimated uncertainty of the digital thermometer with fitted probe was ±0.02 K based on calibration report of MIKES. An Agilent 34410A 6 1/2 digital multimeter (11) and a pressure transducer (12) were used for pressure measurements. The pressure transducer was calibrated at all experimental temperatures used. The calibrator used for these purposes was maintained at room temperature; it consists of a Beamex MC2PE electronic readout equipped with two external pressure modules: EXT60 (0.005% of full scale + 0.0125% of reading) or EXT600 (0.007% of full scale + 0.01% of reading). The calibrator is periodically calibrated at the Finnish National Standards Laboratory (MIKES). The estimated uncertainty of the pressure measurement is 10 kPa. 2.5. Pneumatic Capillary Sampler. 2.5.1. Mechanical Structure and Mode of Operation. The sampler that appears in Figure 2 was specially designed to work up to both high E



Article

Figure 10. Pneumatic capillary sampler (partial cut view). 1, Pinholder; 2, titanium pin; 3, carrier gas inlet; 4, carrier gas outlet; 5, capillary.

adjustment of the pin-holder stroke and consequently of the sample sizes. The movable piston is composed of two parts: a piston rear part (6) and a piston front part (9). Sealing between piston front part (9) and sampler rear part (5) is obtained with a silicon gasket (11). Sealing between pin-holder (15), sampler rear part (5), and sampler front part (19) is achieved using a high temperature resistant polymer O-ring (14). Owing to the shape of part (19), the radiator (12) is efficient enough not to exceed 100 °C in the sampler rear part when its front part is heated up to 450 °C. For the heating of the front part a 1/8 in. heating resistance is located inside a hole drilled through the sampler front part beside the screw (20). The heated part of the sampler is insulated with a ceramic insulator (18). The drilled hole (10) is a connection for compressed air which is used to move the piston assembly backward to withdraw samples. By adjusting the pressure of compressed air, the speed of the piston translation is accordingly adjusted, thus making a second independent degree of freedom for sample size adjustments. The pressure of the compressed air is recommended not to exceed 0.3 MPa. For higher compressed air pressures, it is recommended to introduce, between parts (3) and (6), a thin polymer gasket playing the role of a shock absorber (limiting piston rebound). The third and most convenient degree of freedom to use independently, especially at given sampling pressures, is the duration of applied compressed air through a digital timer. On Figure 10, note that the front part of the titanium pin (0.12 mm diameter) is inside the internal part of the capillary (0.15 mm diameter). The smaller is the length of the titanium pin front part inside the capillary, the smaller the pressure drop is, resulting in a higher sample flow rate. The carrier gas that will carry samples when sealing between the titanium pin and capillary is released and enters from the inlet (3). It sweeps the space between the titanium pin and sampler body and exits through no. 4. When fixing the capillary (5) with cone and screw, it is important to ensure the extremity of the capillary is just in front of the hole (4) as shown in Figure 10. 2.5.2. Testing of Pneumatic Capillary Sampler. The repeatability of the sampler was tested by injecting nitrogen at 10 MPa from the cell with the sampler (Figures 11 and 12). The sampler repeatability improved as the aperture time increased. This is most likely resulting from small changes in the actuation air pressure. Additionally the sampler was further

Figure 8. Photo of the front of the cell with a liquid−liquid−vapor mixture.

Figure 9. Cross section of the pneumatic capillary sampler. 1, Force adjusting screw; 2, differential screw; 3, stroke adjustment screw; 4, pin-screw; 5, sampler rear part; 6, piston rear part; 7, force transmitter; 8, helicoidal spring; 9, piston front part; 10, compressed air inlet; 11, silicone gasket; 12, radiator; 13, antifriction gasket; 14, polymer Oring; 15, pin-holder; 16, titanium pin; 17, cone; 18, insulator; 19, sampler front part containing a 1/8 in. heating resistance; 20, screw; 21, capillary.

temperatures and high pressures. Three other constraints were also taken into account: (1) it must be normally closed, (2) it must respect ATEX regulation; (3) it must be corrosion resistant and allow water sampling. The timer for the sampler is used to control the solenoid valve which actuates the sampler with compressed air (Figure 1). Additionally the gas chromatographic run is triggered by the timer. Either the liquid sampler or the vapor sampler can be selected for operation by changing the position of a switch. The different parts of the sampler are displayed in the axial cross sectional view presented in Figure 9. The screw (1) allows adjustment of the force of the spring (8) acting on the pinholder (15), by moving the force transmitter part (7), to achieve perfect sealing between the titanium pin (16) and capillary (21) whatever the sampling pressure. A differential screw (2) and a stroke adjustment screw (3) permits fine F



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Figure 11. Sampler repeatability test with nitrogen. Pressure 10 MPa with various aperture times.

270D). The water + 2-methylfuran system was further pressurized with helium when working at the lowest experimental temperatures. The pressure in the cell has to be higher than the carrier gas pressure to enable sample transfer to the carrier gas line. Helium was used both for pressurizing the cell and as a carrier gas since it is not detectable by the TCD. Thus, the GC analysis is not affected by the pressurizing gas peak. The cell content was efficiently mixed for a minimum of 2 h at the experimental temperature. Stirring was switched off after assuming that the equilibrium state was reached (pressure remaining stable within ±1.27 kPa for at least 30 min). The system was allowed to settle for approximately 1 h prior to sample analysis. The injected sample volume corresponded at least to the total volume of the capillary. The control was achieved by adjustment of the sampling time and stroke length of the sampler.

4. RESULTS AND DISCUSSION 4.1. Solubility of propane in water. The solubility of propane in water was measured at one temperature and for

Figure 12. Effect of aperture time on the GC area response. Error bars are obtained from the standard deviation.

Table 2. Solubility (VLE) of Propane (1) in Water (2)a

tested with nitrogen in a pressure range from 15 to 30.5 MPa with a aperture time of 0.25 s. The operation of the sampler was flawless even at these high pressures. 2.6. Materials. The materials used are presented in Table 1 with their purities.

3. EXPERIMENTAL PROCEDURE For safety reasons in case of cell or line leakage, a small constant flow of nitrogen is continuously added into the oven for displacing air with nitrogen. The evacuated cell was first charged, to the desired level by suction, with water which was subsequently degassed inside the cell. Then either propane, cyclohexane, or 2-methylfuran was added. The propane recipient was heated to reach the desired vapor pressure and then it was fed directly to the equilibrium cell for obtaining the requested thickness of the organic phase. A necessary volume of cyclohexane and 2-methylfuran was injected to the equilibrium cell using an Isco pump (model,

u(x1)

Δx(1)

K

p

x1exp

T

kPa

×10−4

n

×10−6

%

323.13 323.26 323.19 323.41

1548 1208 806 475

1.82 1.52 1.11 0.72

7 6 8 9

7.2 7.5 6.7 25

2.2 1.3 1.7 7.5

a T is temperature, p is system pressure, x1exp is the experimental solubility in mole fraction, n is number of GC-analysis, u(x1) is the 2· standard deviation based on all samples, Δx % is the relative deviation in percent of the measured values compared to the polynomial regression presented in Figure 13 Δx % = (100·(x(1)measured − x(1)regression)/x(1)measured) u(T) = 0.02 K, u(p) = 10 kPa.

pressures to validate and demonstrate the capability of the equipment for solubility measurements. The results are presented in Table 2 and Figure 13. The measurements in

Table 1. List of Chemicals with Their Purities component

cas number

supplier

purity stated by the supplier

comments

water propane cyclohexane 2-methylfuran helium

7732-18-5 74-98-6 110-82-7 534-22-5 7440-59-7

Aalto AGA, Linde Sigma-Aldrich Sigma-Aldrich AGA

99.995 mass % 99.95 mol % 99.9 mass % 99.5 mass % 99.996 mol %

type 2 water, purified in laboratory by Millipore Elix 20 water purification system used without further purification used without further purification, no inpurities detected in GC-analysis used without further purification, see section 4 used without further purification G



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Table 4. Solubility (LLE) of Water(2) in Cyclohexane(1)a T

p

x2exp

u(x2)

Δx(2)

K

kPa

×10−2

n

×10−3

%

423.14 449.05 473.31 498.75

1069 1906 3080 4815

1.86 3.99 7.19 12.6

7 3 5 9

1.6 2.5 0.7 0.6

−16.3 −7.3 −8.5 −11.7

a T is temperature, p is system pressure, x1exp is the experimental solubility in mole fraction, n is number of GC-analysis, u(x1) is the 2· standard deviation based on all samples, Δx % is the relative deviation in percent of the measured values compared to the literature correlation20 Δx % = (100·(x(2)measured − x(2)correlation)/x(2)measured) u(T) = 0.02 K, u(p) = 10 kPa.

Figure 13. Solubility of propane in water at approximately 323.15 K. ●, this work; ○, Chapoy et al.;13 ◊, Kobayashi and Katz;16 , second order polynomial fitted to the data from Chapoy et al.13

Table 3. Solubility (LLE) of Cyclohexane (1) in Water (2)a K

p

x1exp

u(x1)

Δx(1)

T

kPa

×10−4

n

×10−6

%

422.57 498.57 473.98 447.85 397.90

1069 4800 3097 1861 590

1.21 8.34 4.03 2.09 0.617

3 11 6 4 4

3 68 20 7.6 9

7.0 7.3 −1.1 0.2 −2.8

a

T is temperature, p is system pressure, x1exp is the experimental solubility in mole fraction, n is number of GC analyses, u(x1) is the 2· standard deviation based on all samples, Δx % is the relative deviation in percent of the measured values compared to the literature correlation20 Δx % = (100·(x(1)measured − x(1)correlation)/x(1)measured) u(T) = 0.02 K, u(p) = 10 kPa.

Figure 15. Solubility of water in cyclohexane. ●, this work; ○, Tsonopoulos and Wilson;20 ◊, Marche et al.;23 ×, Plenkina et al;24 ----, model.20

Table 5. Solubility (LLE) of 2-Methylfuran (1) in Water (2)a T

p

x1

K

kPa

×10−4

n

×10−5

u(x1)

298.84 312.83 333.41 353.36 374.65 393.65 413.35

589 633 578 704 408 647 1099

7.37 7.18 7.93 10.1 12.2 19.1 24.7

18 5 4 4 11 5 3

12 2.3 6.0 9.1 4.9 5.8 13

a

T is temperature, p is system pressure, n is number of GC analyses, u(x1) is the 2·standard deviation based on all samples, u(T) = 0.02 K, u(p) = 10 kPa. Figure 14. Solubility of cyclohexane in water: ●, this work; ○, Tsonopoulos and Wilson;20 ◊, Marche et al.;21 △, Guseva and Parnot;22 gray circle, three phase critical point;20 ----, model.20

4.2. Solubility of Cyclohexane in Water and Water in Cyclohexane. The solubility of cyclohexane in water is presented in Table 3 and Figure 14. The measurements are very well in line with the literature correlation.20 The relative absolute average deviation between the correlation20 and measurements in this work have a low value of 3.7% in terms of cyclohexane mole fraction. By visual inspection of Figure 14 it seems that the measurements presented by Tsonopoulus and Wilson20 and Marche et al.21 are well in-line in comparison to the values measured in this work. A higher discrepancy was observed for the values presented by Guseva and Parnov22 The solubility of water in cyclohexane is presented in Table 4 and Figure 15. The measurements show a somewhat lower

this work are satisfactory as in-line with the measurements by Chapoy et al.18 and Kobayashi and Katz.19 A second-order polynomial was regressed to describe Chapoy et al.18 measurements. The absolute average deviation between the second order polynomial, fitted to the literature values, and our measurements is only 7·10−6 in propane mole fraction corresponding to a low relative absolute average deviation of 3.2%. H



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GC−MS analysis the following three impurities were detected: tetrahydrofuran, tetrahydro-2-methylfuran, and 2-(2-furanylmethyl)-5-methylfuran, both in the unused sample and the used sample. The main impurity according to the GC-analysis (FID) was tetrahydro-2-methylfuran and its amount increased from 0.3 to 1.2% in mass during the experiment carried out at 413.35 K which was the highest experimental temperature. The aqueous phase in equilibrium with the organic phase at 413.35 K has been analyzed also, and it did not contain detectable amounts of impurities.

5. MODELING The phase equilibria were modeled for the 2-methylfuran + water system using the (γ−φ) approach in Aspen plus V 8.6.

Figure 16. Solubility of 2-methylfuran in water: ●, measured this work; ◊, Smith and Labonte;25 gray circle, Wieland et al.;26 □, Aneja;27 △, Karmilchik and Efimova;28 ···, NRTL, 4-parameters; , NRTL, 6-parameters.

Table 6. Physical Properties Parameters Used in Data Modeling solubility when comparing them with the literature correlation20 for water solubility into cyclohexane. The relative absolute average deviation has a value of 11% in terms of water mole fraction. These results seems to be within the experimental uncertainty by observing the literature values presented at 423.15 K in Figure 15.20,21 4.3. Solubility of 2-Methylfuran in Water. The solubility of 2-methylfuran in water is presented in Table 5 and Figure 16. The measurements ranged from 298 to 413.35 K. The measurement had the highest uncertainty for the measurements taken at 298.84 K. The amount of analysis for this point was increased (18 samples) to reduce the uncertainty of the solubility values. Results show a solubility minimum at approximately 313 K and x(2-methylfuran) = 0.0007. Only one solubility point was found in the literature for the measured system, it is at 298.15 K (Smith and LaBonte25). The Henry’s law constants for 2-methylfuran in water are presented in Wieland et al.26 The solubility values calculated from the results of Wieland et al.26 agree with the measurements presented in this work at 323.15 and 298.15 K. These values are in agreement, within experimental uncertainties, with this work and that from Smith and LaBonte’s (1952).25 For the two higher temperature points there is a discrepancy between our measurements and the results of Wieland et al.26 The solubility value reported by Aneja (1993)27 at 298.15 K is obtained from octanol−water coefficient determinations and shows a deviation which is larger than the experimental uncertainty in this work. Additionally, two solubility points have been reported by Karmilchik and Yefimova.28 The value reported at 293.15 K is very close to other reported literature values, whereas the value measured at 323.15 K is quite different from this work and that based on the work of Wieland et al.26 The literature results show substantial scatter for the solubility measurements of 2methylfuran in water. The solubility of 2-methylfuran in water was challenging to measure. 2-methylfuran reacts in a small extent to a colorful product as can be seen from Figure 8. Extensively long equilibration times for example leaving the sample overnight (16 h) for reaching equilibration cannot be recommended. The same procedure of mixing for 2 h and settling for 0.5 h was used for this system as for the water + hydrocarbon systems. For the highest temperatures a new batch is needed for each solubility point. Both the initial unused 2-methylfuran sample and the organic phase of the sample taken out from the cell after the experiments were analyzed with GC−MS. According to the

parameters ω PC TC Ria Qi a

units MPa K

water

2-methylfuran

DIPPR

NIST

0.344 22.064 647.10 1.4 0.92

0.256 4.780 528.0 3.133 2.62

a

Pure component parameters R and Q for 2-methylfuran were calculated in Aspen plus v. 8.6 using Bondi method.32

Table 7. Parameters for the Vapor Pressure Correlation Used in the Data Modeling component equation type temperature units source property units element 1 element 2 element 3 element 4 element 5 element 6 element 7 element 8 element 9 a

water

2-methylfuran

extended Antoine equationa K DIPPR Pa C1i 73.649 −7258.2 C2i C3i 0 C4i 0 C5i −7.3037 C6i 4.17 × 10−06 2 C7i Tlower 273.16 Tupper 647.1

Wagner 25b

C1i C2i C3i C4i ln Pci Tci Tlower Tupper

K NIST-TRC Pa −7.0533 1.04823 −1.45374 −3.78689 15.3801 528.022 200 528.022

Extended Antoine equation:

ln(Pi) = C1i +

C 2i + C4iT + C5i ln T + C6iT c7i T + C 3i

for C8i ≤ C9i . bWagner 25 equation: ln(Pi) = ln(Pci) + (C1i(1 − Tri) + C 2i(1 − Tri)15 + C3i(1 − Tri)25 + C4i(1 − Tri)5 )/Tri for Tlower ≤ T ≤ Tupper where Tri = T /Tci

The assumption of a binary system was made, since decomposition products were not detected in the aqueous phase. The liquid activity coefficients were regressed using nonrandom two-liquid (NRTL)29 and universal quasichemical (UNIQUAC)30 activity coefficient models, while the vapor I



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Table 8. NRTL Parameters for the Binary Mixturea component i component j temperature units parameters and temperature limits aij aji bij/K−1 bji/K−1 αij dij/K eij/K eji/K f ij/K f ji/K Tmin/K Tmax/K

case 1

case 2

2-methylfuran water K


−14.617 2.912 6291.575 1031.634 0.3 0 0 0 0 0 298 415

−1031.76 101.254 52274.1 −3813.97 0.3 0 151.337 −14.4282 0 0 298 415

Figure 17. VLLE of 2-methylfuran + water: ◇, vapor, Smith and LaBonte;25 ◆, liquid, Smith and LaBonte;25 , NRTL, six parameters.

a

Components i and j represent the order of the compounds in the NRTL model. The coefficients a−f represent the NRTL model parameters. Tmin and Tmax represent the temperature boundaries in which the model parameters are valid. A constant value of αij = 0.3 was used. The formulation of temperature dependence in the NRTL model is given by Gij = exp(− αijτij), where

τij = aij +

bij T

parameters required for the liquid activity coefficient and equation of state models are given in Table 6. Pure component parameters were taken from the Aspen plus database (Pure 32 and NIST-TRC), and the source of data is stated therein. The parameters required for the vapor pressure correlations are given in Table 7. The binary interaction parameters in Tables 8 and 9 of the activity coefficient models were regressed against experimental LLE from this work and VLLE data.25 The ability of our regression using these two activity coefficient models to describe the measurements were examined with two scenarios. In case 1 four parameters of each model (NRTL and UNIQUAC) were regressed while in case 2 six parameters were regressed. It was observed, as can be seen from Figure 16 that the description of the data is improved by using six parameter models. Additionally, both models using six parameters were able to describe the observed solubility minimum at approximately 309 K. There was barely a noticeable difference between the performances of UNIQUAC or NRTL models. However, the average absolute deviation of the liquid mole fraction of 2methylfuran was slightly lower with NRTL (AAD, x = 3.7%) compared to the UNIQUAC (AAD, x = 4.3%). The description of the VLLE data was unaffected by the addition of an extra parameter and only the NRTL-model with six parameters is presented together with the points from the literature25 in Figure 17.

+ eij ln T + fij T

and αij = cij + dij(T − 273.15)

Table 9. UNIQUAC Parameters for the Binary Mixturea case 1 component i component j temperature units parameters and temperature limits aij aji bij/K−1 bji/K−1 cij/K cji/K dij/K dji/K Tmin/K Tmax/K eij/K−1 eji/K−1


−1.34614 8.42568 63.175 −3705.451 0 0 0 0 298 415 0 0

case 2 2-methylfuran water K

−105.484 357.595 4855.41 −17626.5 15.4536 −52.9401 0 0 298 415 0 0

6. CONCLUSIONS A new device for VLLE measurements to work in the presence of hydrogen is presented. Its equilibrium cell is fitted with new pneumatic capillary samplers allowing withdrawal of small samples at temperatures up to 400 °C. Even higher temperatures can be used with this sampler. The sample size is controlled using directly up to four independent parameters, but just one capillary. In comparison the ROLSI IV sampler has only one direct adjustment parameter, and unfortunately capillary changes are necessary to cover the full range of pressures. The new sampler enables extraction of samples with sizes being of the order of the microliter or even much less. The sample amount taken is thus very small in comparison to the typical volumes of mixtures in the range of tens of milliliters in the equilibrium cell. The sampling now leaves the studied mixtures practically in their initial equilibrium conditions after

a Components i and j represent the order of the compounds in the UNIQUAC model. The coefficients a−e represent the UNIQUAC model parameters. Tmin and Tmax represent the temperature boundaries in which the model parameters are valid. The temperature dependency in the model is formulated in Aspen as

⎛ bij eij ⎞ τij = exp⎜aij + + Cij ln T + dijT + 2 ⎟ T T ⎠ ⎝

phase nonidealities were taken into account by using the Peng− Robinson equation of state (EoS).31 The pure component J



Article

(10) Galicia-Luna, L. A.; Ortega-Rodriguez, A.; Richon, D. New apparatus for the fast determination of high-pressure vapor−liquid equilibria of mixtures and of accurate critical pressures. J. Chem. Eng. Data 2000, 45, 265−271. (11) Frost, M.; von Solms, N.; Richon, D.; Kontogeorgis, G. M. Measurement of vapor−liquid−liquid phase equilibriumEquipment and results. Fluid Phase Equilib. 2015, 405, 88−95. (12) Garcia-Sanchez, F.; Laugier, S.; Richon, D. Vapor-Liquid Equilibrium Data for the Methane-Dimethyl Ether and MethaneDiethyl Ether Systems between 282 and 344 K. J. Chem. Eng. Data 1987, 32, 211−215. (13) Baba-Ahmed, A.; Guilbot, P.; Richon, D. New equipment using a static analytic method for the study of vapour-liquid equilibria at temperatures down to 77 K. Fluid Phase Equilib. 1999, 166, 225−236. (14) de Stefani, V.; Baba-Ahmed, A.; Valtz, A.; Meneses, D.; Richon, D. Solubility measurements for carbon dioxide and nitrous oxide in liquid oxygen at temperatures down to 90 K. Fluid Phase Equilib. 2002, 200, 19−30. (15) de Stefani, V.; Baba-Ahmed, A.; Richon, D. Experimental determination of carbon dioxide and nitrous oxide co-solubility in liquid oxygen. Fluid Phase Equilib. 2003, 207, 131−142. (16) Houssin-Agbomson, D.; Coquelet, C.; Richon, D.; Arpentinier, P. Equipment using a ″static-analytic″ method for solubility measurements in potentially hazardous binary mixtures under cryogenic temperatures. Cryogenics 2010, 50, 248−256. (17) Belandria, V.; Eslamimanesh, A.; Mohammadi, A. H.; Richon, D. Study of Gas Hydrate Formation in the Carbon Dioxide plus Hydrogen plus Water Systems: Compositional Analysis of the Gas Phase. Ind. Eng. Chem. Res. 2011, 50, 6455−6459. (18) Chapoy, A.; Mokraoui, S.; Valtz, A.; Richon, D.; Mohammadi, A. H.; Tohidi, B. Solubility measurement and modeling for the system propane−water from 277.62 to 368.16 K. Fluid Phase Equilib. 2004, 226, 213−220. (19) Kobayashi, R.; Katz, D. L. Vapor-Liquid Equilibria for Binary Hydrocarbon-Water Systems. Ind. Eng. Chem. 1953, 45, 440−446. (20) Tsonopoulos, C.; Wilson, G. M. High-temperature mutual solubilities of hydrocarbons and water. Part I: Benzene, cyclohexane and n-hexane. AIChE J. 1983, 29, 990−999. (21) Marche, C.; Delepine, H.; Ferronato, C.; Jose, J. Apparatus for the on-line GC determination of hydrocarbon solubility in water: benzene and cyclohexane from 70 to 150 °C. J. Chem. Eng. Data 2003, 48, 398−401. (22) Guseva, A. N.; Parnov, E. I. The solubility of cyclohexane in water. Zh. Fiz. Khim. 1963, 37, 1494−1494. Extracted from Shaw, D. G. Ed. IUPAC NIST solubility data series 37. Hydrocarbons in Water and Seawater Part I: Hydrocarbons C5 to C7; Pergamon Press: Oxford, 1989. (23) Marche, C.; Ferronato, C.; de Hemptinne, J. C.; Jose, J. Apparatus for the Determination of Water Solubility in Hydrocarbon: Toluene and Alkylcyclohexanes (C6 to C8) from 30 to 180 °C. J. Chem. Eng. Data 2006, 51, 355−359. (24) Plenkina, R. M.; Pryanikova, R. O.; Efremova, G. D. Phase equilibrium and volume ratios in a cyclohexane-water system. Zh. Fiz. Khim. 1971, 45, 2389−2389. (25) Smith, A. S.; LaBonte, J. F. Dehydration of Aqueous Methyl Ethyl Ketone with 2-Methyl Furan. Ind. Eng. Chem. 1952, 44, 2740− 2743. (26) Wieland, F.; Neff, A.; Gloess, A. N.; Poisson, L.; Atlan, S.; Larrain, D.; Prêtre, D.; Blank, I.; Yeretzian, C. Temperature dependence of Henry’s law constants: An automated high-throughput gas stripping cell design coupled to PTR-ToF-MS. Int. J. Mass Spectrom. 2015, 387, 69−77. (27) Aneja, V. P. Organic Compounds in Cloud Water and their Deposition at a Remote Continental Site. Air Waste 1993, 43, 1239− 1244. (28) Karmilchik, A.; Yefimova, L. A study of mutual solubility in a three-component system 5-methylfurfural-silvane-water, Latv. PSR Zinat. Akad. Vestis, Kim. Ser. 1970, 3, 282−286.

the sampling procedure. The sampler is fully described and corresponding execution drawings are provided as Supporting Information. The equipment has been tested with two binary systems: water + propane and water + cyclohexane. The results of water + propane compared satisfactory to literature data.18,19 The results for the water + cyclohexane system compared well with the literature correlation.20 New aqueous solubility data for 2methylfuran in water are presented and correlated. In future papers we shall present data at higher temperatures and higher pressures as the equipment has been carefully designed, based on previous developments where parts were successfully tested independently.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.6b00126. High-temperature−high-pressure pneumatic capillary sampler, execution drawings (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: petri.uusi-kyyny@aalto.fi. Tel.: +358 50 4347365. Funding

Tekes−the Finnish Funding Agency for Innovation, FiDiPro − Program (http://www.fidipro.fi/pages/home.php) is acknowledged for funding the FiDiPro position of D. Richon. Many thanks to Neste Oil, (www.nesteoil.com), Neste Jacobs, (www. nestejacobs.com), UPM, (www.upm.com/en/), Borealis, (www.borealis.com/) for funding, fruitful collaboration, and discussions. The University of KwaZulu Natal (Durban, South Africa) and Aalto University (Finland) are acknowledged for their financial supports. Petri Uusi-Kyyny acknowledges the Academy of Finland for the financial support. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Richon, D.; de Loos, Th.W. Vapour−Liquid Equilibrium at High Pressure. In Measurement of the Thermodynamic Properties of Multiple Phases; Experimental Thermodynamics Vol. VI; Weir, R. D., de Loos, Th.W, Eds.; Elsevier: Amsterdam, 2005; Chapter 6. (2) Figuiere, P.; Hom, J. F.; Laugier, S.; Renon, H.; Richon, D.; Szwarc, H. Vapor-liquid-equilibria up to 40 000 kPa and 400 °C - a new static method. AIChE J. 1980, 26, 872−875. (3) Laugier, S.; Richon, D.; Renon, H. Vapor-liquid-equilibria hydrogen-white oil up to 625.1K and 35 MPa. Fuel 1983, 62, 842− 844. (4) Legret, D.; Richon, D.; Renon, H. Vapor liquid equilibria up to 100 MPa - a new apparatus. AIChE J. 1980, 27, 203−207. (5) Guillevic, J. L.; Richon, D.; Renon, H. Vapor-liquid equilibrium data for the binary system water-ammonia at 403.1 K, 453.1 K, and 503.1 K up to 7.0 MPa. J. Chem. Eng. Data 1985, 30, 332−335. (6) Laugier, S.; Richon, D. New apparatus to perform fast determinations of mixture vapor-liquid-equilibria up to 10 MPa and 423 K. Rev. Sci. Instrum. 1986, 57, 469−472. (7) Guilbot, P.; Valtz, A.; Legendre, H.; Richon, D. Rapid on-line sampler-injector: a reliable tool for HT-HP sampling and on-line GC analysis. Analusis 2000, 28, 426−431. (8) Richon, D. High Temperature−High Pressure Pneumatic Capillary Sampler. DOI: 10.13140/RG.2.1.1067.7204 (accessed 06.16.2016). (9) www.researchgate.net/publication/283319479_Rolsi_Success_ Story (accessed 06.16.2016). K



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(29) Renon, H.; Prausnitz, J. M. Local compositions in thermodynamic excess functions for liquid mixtures. AIChE J. 1968, 14, 135−144. (30) Abrams, D. S.; Prausnitz, J. M. Statistical thermodynamics of liquid mixtures. New expression for the excess Gibbs energy of partly or completely miscible systems. AIChE J. 1975, 21, 116−128. (31) Peng, D. Y.; Robinson, D. B. A New Two-Constant Equation of State. Ind. Eng. Chem. Fundam. 1976, 15, 59−64. (32) Bondi, A. Physical Properties of Molecular Crystals, Liquids and Gases; Wiley: New York, 1968.

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