Cosolvent Effect and Solubility Measurement for Butyl (Meth)acrylate

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Ind. Eng. Chem. Res. 2006, 45, 3354-3365

Cosolvent Effect and Solubility Measurement for Butyl (Meth)acrylate Polymers in Benign Environmental Supercritical Solvents Hun-Soo Byun* and Dong-Hyun Lee Department of Chemical Engineering, Yosu National UniVersity, Yosu, Chonnam 550-749, South Korea

Cloud-point phase behavior curves to 190 °C and 2570 bar are measured for binary and ternary mixtures of poly(isobutyl acrylate)-CO2-isobutyl acrylate, poly(tert-butyl acrylate)-CO2-tert-butyl acrylate, poly(isobutyl methacrylate)-CO2-isobutyl methacrylate, and poly(tert-butyl methacrylate)-CO2-tert-butyl methacrylate systems. The phase behavior for the poly(isobutyl acrylate)-CO2-isobutyl acrylate system with cosolvent concentrations of 0, 3.2, 8.8, 18.1, 31.9, and 40.7 wt % are measured in the changes of the pressure-temperature slope. With 58.7 wt % isobutyl acrylate to the poly(isobutyl acrylate)-CO2 solution significantly changing, the phase behavior curves takes on the appearance of a typical LCST boundary. The cloud-point curves for the poly(tert-butyl acrylate)-CO2-0, 8.5, 14.9, 34.7, 56.0, and 57.7 wt % tert-butyl acrylate system changes the P-T curve from the UCST region to the LCST region as the tert-butyl acrylate concentration increases. The cloud-point curves for the poly(isobutyl methacrylate)-CO2-isobutyl methacrylate system show the slope changes of the pressure-temperature diagram and cosolvent concentrations of 0, 6.5, 12.6, 21.7, and 32.3 wt %. With 49.8 wt % isobutyl methacrylate added to the poly(isobutyl methacrylate)-CO2 solution, the phase behavior curves show a typical LCST boundary. And also, the cloud-point curves for the poly(tert-butyl methacrylate)-CO2-0, 10.2, 20.5, 31.3, and 46.4 wt % tert-butyl methacrylate system change the P-T curve from the UCST region to the LCST region as the tert-butyl acrylate concentration increases. High-pressure vapor-liquid equilibria are obtained for the CO2-isobutyl acrylate, CO2-tert-butyl acrylate, CO2-isobutyl methacrylate, and CO2-tert-butyl methacrylate systems at the range of temperature of 40120 °C and pressure up to 160 bar. The CO2-isobutyl acrylate, CO2-tert-butyl acrylate, CO2-isobutyl methacrylate, and CO2-tert-butyl methacrylate systems exhibit type-I phase behavior with a continuous mixture-critical curve. Three-phase, liquid-liquid-vapor equilibrium was not observed at these conditions. The experimental results for CO2-isobutyl acrylate, CO2-tert-butyl acrylate, CO2-isobutyl methacrylate, and CO2-tert-butyl methacrylate mixtures are modeled using the Peng-Robinson equation of state. Introduction The thermodynamic information of polymers in the supercritical fluids is an important role in most polymerization processes, fractionation, processing technologies, material development, and industrial application.1-3 Phase behavior data for polymer-supercritical fluids systems are required for efficient operation and plant design of supercritical fluid polymer processes. Also, the design and operation of the separation process for a hydrocarbon in supercritical fluid solvents requires knowledge of high-pressure experimental data. In particular, high-pressure phase equilibrium data for binary mixtures containing supercritical carbon dioxide will be needed for plant designs, industrial application, and supercritical fluid extraction.4 Recently we have demonstrated that it is possible to dissolve polar butyl methacrylate polymer in supercritical fluid solvents over a wide range of temperature at high pressure if the methacrylate monomer is used.5 The solubility curve data with the cosolvent effect of butyl acrylate on the phase behavior of poly(butyl acrylate)-supercritical CO2 mixtures were reported by McHugh et al.6 Also, Byun and McHugh5 have demonstrated that poly(butyl methacrylate)-CO2 phase behavior curves present the upper critical solution temperature (UCST) curve at 1400-2000 bar at below 240 °C. The high-pressure, polymer-supercritical fluid solvent-cosolvent studies reported in the literature show that cloud points * To whom correspondence should be addressed. Tel: +82-61-6593296. Fax: +82-61-653-3659. E-mail: [email protected].

monotonically decrease in pressure and temperature with the addition of a polar cosolvent as long as the cosolvent does not form a complex with the polar repeat units in the polymer.7-9 In these cases, the cosolvent effect is directly related to the polar forces of attraction contributing to the cosolvent and to the increase in solvent density resulting from the addition of a liquid cosolvent to a supercritical fluid solvent. The location of the cloud-point curve is a reflection of the free volume difference between the dense polymer and the expanded CO2 rather than the balance of intermolecular interactions.5,6 The primary purpose of this work is to present the determination of the impact of isobutyl acrylate, tert-butyl acrylate, isobutyl methacrylate, and tert-butyl methacrylate cosolvent on the phase behavior of the poly(isobutyl acrylate)-CO2, poly(tert-butyl acrylate)-CO2, poly(isobutyl methacrylate)-CO2, and poly(tert-butyl methacrylate)-CO2 systems. Considering that CO2 has been a desirable reaction medium for free radical polymerizations,10 the phase behavior for these ternary poly(isobutyl acrylate)-supercritical CO2-isobutyl acrylate, poly(tert-butyl acrylate)-supercritical CO2-tert-butyl acrylate, poly(isobutyl methacrylate)-supercritical CO2-isobutyl methacrylate, and poly(tert-butyl methacrylate)-supercritical CO2-tert-butyl methacrylate mixtures provides the information needed on the regions where homogeneous polymerization may occur in the presence of excess monomer. McHugh et al.6 have demonstrated that the poly(butyl acrylate)-CO2 curves are almost vertical at ∼1100 to 2700 bar at high temperatures. Byun and McHugh5 have demonstrated that poly(butyl methacrylate)-CO2 phase behavior curves present the UCST curve at ∼1400 to 2000 bar at below 240 °C. The difference in phase behaviors is attributed

10.1021/ie050705f CCC: $33.50 © 2006 American Chemical Society Published on Web 11/16/2005

Ind. Eng. Chem. Res., Vol. 45, No. 10, 2006 3355

Figure 1. Schematic diagram of the high pressures experimental apparatus used in this study.

to the different degree of chain flexibility for these four polymers which implies a more unfavorable conformational entropy of mixing for poly(hexyl acrylate)11 and poly(cyclohexyl acrylate).12 The key issue is how to account for the intra- and intersegmental interactions of many segments of the polymer relative to the small number of segments in a solvent molecule. Experimental data for binary CO2-isobutyl acrylate, CO2tert-butyl acrylate, CO2-isobutyl methacrylate, and CO2-tertbutyl methacrylate systems are obtained to complement the poly(isobutyl acrylate)-CO2-isobutyl acrylate, poly(tert-butyl acrylate)-CO2-tert-butyl acrylate, poly(isobutyl methacrylate)-CO2-isobutyl methacrylate, and poly(tert-butyl methacrylate)-CO2-tert-butyl methacrylate studies presented here since there are no literature phase behavior data available on this mixture. The second purpose for obtaining CO2-isobutyl acrylate, CO2-tert-butyl acrylate, CO2-isobutyl methacrylate, and CO2-tert-butyl methacrylate systems is to determine whether CO2 and isobutyl acrylate, tert-butyl acrylate, isobutyl methacrylate, or tert-butyl methacrylate form multiple phases in the pressure-temperature-composition regions explored in the poly(isobutyl acrylate)-CO2-isobutyl acrylate, poly(tertbutyl acrylate)-CO2-tert-butyl acrylate, poly(isobutyl methacrylate)-CO2-isobutyl methacrylate, and poly(tert-butyl methacrylate)-CO2-tert-butyl methacrylate studies. The experimental data of CO2-isobutyl acrylate, CO2-tertbutyl acrylate, CO2-isobutyl methacrylate, and CO2-tert-butyl methacrylate systems are fitted to the Peng-Robinson equation of state,16 and the phase behavior for this binary solvent mixture is calculated at elevated operating temperatures and pressure. Experimental Section Figure 1 shows a schematic diagram of the experimental apparatus used for pressure-composition isotherms for the CO2-isobutyl acrylate, CO2-tert-butyl acrylate, CO2-isobutyl methacrylate, and CO2-tert-butyl methacrylate mixtures13,14 obtained from cloud-point curves for poly(isobutyl acrylate)CO2-isobutyl acrylate, poly(tert-butyl acrylate)-CO2-tertbutyl acrylate, poly(isobutyl methacrylate)-CO2-isobutyl methacrylate, and poly(tert-butyl methacrylate)-CO2-tert-butyl methacrylate ternary mixtures.15,16 The bubble-point, dew-point, and cloud-point curves are obtained with a high-pressure, variable-volume cell described in detail elsewhere.13-16 Cloud points are measured for the polymer solutions at a fixed poly(isobutyl acrylate), poly(tert-butyl acrylate), poly(isobutyl methacrylate), and poly(tert-butyl methacrylate) concentration of 5.0 ( 0.5 wt %, which is a typical of the concentrations, used for

polymer-supercritical fluid solvent studies.21 The polymer is loaded into the cell to within (0.002 g, and then the cell is purged with nitrogen followed by CO2 to ensure that all of the air is removed. The liquid monomer is injected into the cell to within (0.002 g using a syringe, and CO2 is transferred into the cell gravimetrically to within (0.004 g using a high-pressure bomb. The mixture is compressed to the desired pressure with an internal piston displaced with water in a high-pressure generator (HIP Inc., Model 37-5.75-60). The pressure of the mixture is measured with a Heise gauge (Dresser Ind., Model CM-108952, 0-3450 bar, accurate to within ( 3.5 bar). The temperature in the cell is measured using a platinum-resistance thermometer (Thermometrics Corp., Class A) connected to a digital multimeter (Yokogawa, Model 7563, accurate to within (0.005%). The system temperature is typically maintained to within (0.2 °C below 200 °C and within (0.4 °C above 200 °C. The mixture inside the cell is viewed on a video monitor using a camera coupled to a borescope (Olympus Corp., Model F100-038-00050) placed against the outside of the sapphire window. Light is transmitted into the cell with a fiber optic cable connected at one end to a high-density illuminator (Olympus Optical Co., Model ILK-5) and at the other end to a borescope. The polymer-supercritical solvent-monomer mixture in the cell is heated to the desired temperature and pressurized until a single phase is achieved. The mixtures (polymer-solventmonomer system) are maintained in the one-phase region at the designed temperature for at least 1 h so that the cell can reach thermal equilibrium. The pressure is then slowly decreased until the solution becomes cloudy. In binary CO2-monomers, the mole fractions are accurate to within (0.0025. Cloud points are measured and reproduced at least twice to within (2.8 bar and (0.3 °C. Bubble-, dew-, and critical-point transitions for the CO2-isobutyl acrylate, CO2-tert-butyl acrylate, CO2-isobutyl methacrylate, and CO2tert-butyl methacrylate mixtures are measured and reproduced at least twice to within (0.3 bar and (0.2 °C. Materials Carbon dioxide (99.9% minimum purity) was obtained from Daesung Industrial Gases Co., and poly(isobutyl acrylate) (Mw ) 120 000 Mw/Mn ) 5.45), poly(tert-butyl acrylate) (Mw ) 250 000 Mw/Mn ) 3.47), poly(isobutyl methacrylate) (Mw ) 200 000 Mw/Mn )1.75), and poly(tert-butyl methacrylate) (Mw ) 180 000 Mw/Mn ) 2.58) are obtained from Polysciences, Inc. and used as received. Isobutyl acrylate (99.0% purity), tertbutyl acryale (98.0% purity), isobutyl methacrylate (97.0% purity), and tert-butyl methacrylate (98.0% purity) used in this worik were obtained from Aldrich Co. and Polysciences Inc., respectively. To prevent isobutyl acrylate, tert-butyl acrylate, isobutyl methacrylate, and tert-butyl methacrylate polymerization, 2,6-di-tert-butyl-4-methylphenol (Aldrich, 99% purity) was used as an inhibitor at a concentration of 0.005 times the amount of isobutyl acrylate, tert-butyl acrylate, isobutyl methacrylate, and tert-butyl methacrylate. Since poly(isobutyl acrylate) and poly(tert-butyl acrylate) were supplied in a toluene solution, the polymer solution was placed under vacuum for at least 10 h by the Rotary Evaporator (Tamato Scientific Co., Model RE-47) for toluene removal. Results and Discussion Phase Behavior for Poly(iso, tert-butyl acrylate) and Poly(iso, tert-butyl methacrylate) in Supercritical CO2. Figure 2

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Ind. Eng. Chem. Res., Vol. 45, No. 10, 2006 Table 1. Experimental Cloud-Point Data for the Poly(isobutyl acrylate)-CO2-Isobutyl Acrylate System Measured in This Study T (°C)

P (bar)

5.5 wt % P(iso-BA) + 0.0 wt % iso-BA 50.8 1822.4 52.9 1384.5 65.8 1044.8 73.4 970.7 90.1 925.9 105.8 915.5 119.8 915.5 134.9 919.0 150.0 925.5

Figure 2. Experimental cloud-point curves for the poly(isobutyl acrylate), poly(n-butyl acrylate),6 and poly(tert-butyl acrylate) in supercritical CO2. The concentration of polymers in solution is ∼5 wt %.

5.2 wt % P(iso-BA) + 3.2 wt % iso-BA 42.6 917.2 50.6 839.0 60.2 792.1 74.2 790.3 90.2 800.0 105.0 811.7 120.9 824.8 134.0 834.8 148.6 843.1 5.4 wt % P(iso-BA) + 8.8 wt % iso-BA 45.5 590.3 60.1 611.4 74.5 644.0 90.1 670.7 105.9 699.3 120.6 722.4 135.3 736.9 149.0 746.2

Figure 3. Experimental cloud-point curves for the poly(isobutyl methacrylate), poly(n-butyl methacrylate),5 and poly(tert-butyl methacrylate) in supercritical CO2. The concentration of polymers in solution is ∼5 wt %.

shows the experimental cloud-point curves for the poly(isobutyl acrylate), poly(n-butyl acrylate),6 and poly(tert-butyl acrylate) in supercritical CO2. The cloud-point behavior for poly(isobutyl acrylate)-CO2, poly(n-butyl acrylate)-CO2, and poly(tert-butyl acrylate)-CO2 system exhibits upper critical solution temperature (UCST) curves with a negative slope. The 5.5 wt % poly(isobutyl acrylate)-CO2 system is presented at the temperature range of 50-150 °C and pressure to 1822 bar. The 4.8 wt % poly(tert-butyl acrylate)-CO2 system is shown at the temperature range of 122-185 °C and pressure range of 1215-2064 bar. Figure 3 shows the impact of the phase behavior of poly(isobutyl methacrylate), poly(n-butyl methacrylate),5 and poly(tert-butyl methacrylate) in supercritical CO2. Experimental cloud-point behavior of the poly(isobutyl methacrylate)-CO2 system shows at pressures up to ∼2050 bar and in the range of temperature from 82 to 162 °C. The cloud-point curve for the poly(tert-butyl methacrylate)-CO2 mixture increases rapidly as the temperature decreases. Phase Behavior of Poly(iso, tert-butyl acrylate)-CO2-Iso, tert-Butyl Acrylate System. Table 1 and Figure 4 show the cloud-point behavior of the poly(isobutyl acrylate)-CO2isobutyl acrylate mixture obtained in this study. The phase behavior of the 5.5 wt % poly(isobutyl acrylate)-CO2-0.0 wt % isobutyl acrylate mixture exhibits a negative slope dissolving at a temperature of 150 °C and a pressure of 1822 bar. With 3.2 wt % isobutyl acrylate added to the solution, the cloudpoint curve exhibits upper/lower critical solution temperature (U-LCST) region phase behavior with a positive/negative slope.

4.7 wt % P(iso-BA) + 18.1 wt % iso-BA 46.2 361.0 60.2 432.8 75.0 472.1 90.5 516.9 105.7 555.9 121.5 581.0 135.4 599.0 148.2 603.1 4.8 wt % P(iso-BA) + 31.9 wt % iso-BA 44.8 337.9 59.0 392.8 73.6 434.5 88.8 474.8 104.1 521.0 119.7 550.0 134.3 571.7 148.0 579.3 4.7 wt % P(iso-BA) + 40.7 wt % iso-BA 45.6 277.6 59.0 332.1 73.6 381.4 89.6 455.2 105.2 482.8 119.8 511.4 135.0 534.5 149.4 553.8

With 8.8 wt % isobutyl acrylate in solution, the cloud-point pressure decreases the lower critical solution temperature (LCST) region behavior at the temperature range from 42 to 148 °C. The phase behavior of the poly(isobutyl acrylate)CO2-18.1 wt % isobutyl acrylate mixture exhibits the LCSTtype phase behavior from positive slope at low pressures. When 31.9 and 40.7 wt % isobutyl acrylate is added to the solution, the cloud-point curve exhibits LCST-type phase behavior of positive slope at 45-150 °C. The phase behavior of the poly(isobutyl acrylate)-CO2-31.9 and 40.7 wt % isobutyl acrylate system shows 2.3 bar/°C and 2.7 bar/°C in positive slope, respectively. The effect of the butyl acrylate cosolvent on the phase behavior is similar to that observed in the poly(butyl acrylate)-CO2-butyl acrylate6 mixture. When 58.7 wt % isobutyl acrylate is added to the poly(isobutyl acrylate)-CO2 solution, the cloud-point curve shown


Figure 4. Effect of isobutyl acrylate on the phase behavior of the poly(isobutyl acrylate)-CO2-x wt % isobutyl acrylate system, where x equals 0 (open circles), 3.2 (open squares), 8.8 (open triangles), 18.1 (closed circles), 31.9 (closed squares), 40.7 (closed triangle), and the lines mean only bridge between symbols. The concentration of polymers in solution is ∼5 wt %.

Figure 5. Phase behavior of the poly(isobutyl acrylate)-CO2-58.7 wt % isobutyl acrylate system obtained in this study. Open circles represent fluidfliquid + liquid transitions, closed squares represent fluidfliquid + vapor transitions, and closed circles represent liquid + liquid + vapor (LLV) data. The concentration of polymers in solution is ∼5 wt %. Table 2. Experimental Cloud-Point, Bubble-Point, and Liquid-Liquid-Vapor Data for the Poly(isobutyl acrylate)-CO2-Isobutyl Acrylate System Measured in This Study T (°C)

P (bar)

transition

5.3 wt % P(iso-BA) + 58.7 wt % iso-BA 54.5 64.8 82.9 97.5 113.2 127.0 141.2 155.5

Cloud-Point Transition 125.9 155.2 208.6 250.0 286.9 312.1 332.8 341.7

CP CP CP CP CP CP CP CP

30.7 36.1 44.4

Bubble-Point Transition 70.2 81.0 91.4

BP BP BP

54.5 64.0

Liquid-Liquid-Vapor Transition 104.0 117.5

LLV LLV

in Figure 5 and Table 2 is obtained on the typical appearance of a lower critical solution temperature (LCST) boundary. At 120 °C, the phase boundary has shifted from 400 to 300 bar as the concentration of isobutyl acrylate is increased from 40.7 to 58.7 wt %. The poly(isobutyl acrylate)-CO2-58.7 wt % isobutyl acrylate phase behavior curve intersects a fluidf liquid + vapor (LV) curve at ∼44 °C and ∼91 bar. A liquid and vapor

Figure 6. Effect of tert-butyl acrylate on the phase behavior of the poly(tert-butyl acrylate)-CO2-x wt % tert-butyl acrylate system, where x equals 0 (open circles), 8.5 (open squares), 14.9 (open triangles) 34.7 (closed circles), 56.0 (closed triangles), and the lines mean only bridge between symbols. The concentration of polymers in solution is ∼5 wt %.

phase coexists at pressures below this curve, and the LV curve switches to a liquid1 + liquid2 + vapor (LLV) curve at temperatures higher than about 44 °C. The positive slope of the poly(isobutyl acrylate)-CO2-58.7 wt % isobutyl acrylate LCST curve at the lowest pressures is ∼2.4 bar/°C. The results obtained in this study demonstrate clearly that it is possible to obtain a single phase that extends over the modest pressures when operating with supercritical CO2 as long as sufficient amounts of free isobutyl acrylate monomer are presented in the solution. Figure 6 and Table 3 show the impact of phase behavior of the poly(tert-butyl acrylate)-CO2-x wt % tert-butyl acrylate mixture obtained in this study. The poly(tert-butyl acrylate) does dissolve in pure CO2 at the temperature of 185 °C and at the pressure of 2064 bar. With 8.5 wt % tert-butyl acrylate added to the solution, the phase behavior exhibits UCST-type behavior with a negative slope. The cloud-point curve is presented almost virtually flat at the temperature range from 85 °C to 150 °C, and the phase behavior pressure increases rapidly at below 85 °C. With 14.9 wt % tert-butyl acrylate in solution, the cloudpoint pressure curve is shown at the range of pressure from ∼890 bar to 1760 bar and of the temperature from 62 to 152 °C, and the phase behavior pressure increases rapidly at below 70 °C. When 34.7 wt % tert-butyl acrylate is added to the solution, the cloud-point curve exhibits LCST-type phase behavior to the positive slope at low pressures. The cloud-point curve for the poly(tert-butyl acrylate)-CO2-56.0 wt % tertbutyl acrylate system exhibits LCST region phase behavior with a positive slope, and it is a continuous curve down to 47 °C and ∼180 bar. When 57.5 wt % tert-butyl acrylate is added to the poly(tert-butyl acrylate)-CO2 solution, the cloud-point curve shown in Figure 7 and Table 4 is obtained on the typical appearance of a lower critical solution temperature (LCST) boundary. At 140 °C, the phase boundary has shifted from 400 to 445 bar as the concentration of tert-butyl acrylate increases from 56.0 to 57.7 wt %. The poly(tert-butyl acrylate)-CO2-57.7 wt % tertbutyl acrylate phase behavior curve intersects a fluidf liquid + vapor (LV) curve at ∼63 °C and ∼230 bar. A liquid and vapor phase coexist at pressures below this curve, and the LV curve switches to a liquid1 + liquid2 + vapor (LLV) curve at temperatures greater than ∼63 °C. The effect of tert-butyl acrylate cosolvent on the phase behavior is similar to that observed for the poly(butyl acrylate)-CO2-butyl acrylate.6 The slope of the 57.7 wt % tert-butyl acrylate curve is ∼2.2 bar/°C,

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Ind. Eng. Chem. Res., Vol. 45, No. 10, 2006

Table 3. Experimental Cloud-Point Data for the Poly(tert-butyl acrylate)-CO2-tert-Butyl Acrylate System Measured in This Study T (°C)

P (bar)

4.8 wt % P(t-BA) + 0.0 wt % t-BA 122.4 2063.8 128.7 1711.4 138.2 1427.2 154.3 1294.5 169.4 1240.7 184.5 1215.2 5.2 wt % P(t-BA) + 8.5 wt % t-BA 83.2 1791.4 84.5 1408.6 90.4 1215.9 105.3 1114.8 119.9 1071.7 134.0 1030.3 150.3 1001.7 4.8 wt % P(t-BA) + 14.9 wt % t-BA 62.0 1760.3 63.4 1390.3 74.0 1080.3 90.2 975.5 106.0 928.6 118.9 912.8 133.4 900.7 152.0 891.0 4.6 wt % P(t-BA) + 34.7 wt % t-BA 46.7 560.3 59.0 557.9 73.0 569.3 90.6 598.3 107.0 620.7 121.5 639.7 134.9 650.0 150.8 657.9 5.0 wt % P(t-BA) + 56.0 wt % t-BA 46.7 182.4 59.2 227.2 73.6 266.2 89.9 321.4 103.9 353.5 118.6 381.0 133.6 406.2 148.7 425.9

which is very close to that of the poly(butyl acrylate)-CO232 wt % butyl acrylate curve.6 Phase Behavior of Poly(iso, tert-butyl methacrylate)CO2-Iso, tert-Butyl Methacrylate System. Table 5 and Figure 8 show the cloud-point curve of the poly(isobutyl methacrylate)-CO2-x wt % isobutyl methacrylate system data obtained in this study. The poly(isobutyl methacrylate) does dissolve in pure CO2 to temperature of 162 °C and the pressure of 2046

Table 4. Experimental Cloud-Point, Bubble-Point, and Liquid-Liquid-Vapor Data for the Poly(tert-butyl acrylate)-CO2-tert-Butyl Acrylate System Measured in This Study T (°C)

P (bar)

transition

4.7 wt % P(t-BA) + 57.7 wt % t-BA 73.2 88.3 104.6 118.7 133.8 150.2

Cloud-Point Transition 284.9 327.9 373.5 403.8 432.1 454.5

CP CP CP CP CP CP

46.7 59.2

Bubble-Point Transition 202.4 227.2

BP BP

73.0

Liquid-Liquid-Vapor Transition 255.0

LLV

Table 5. Experimental Cloud-Point Data for the Poly(isobutyl methacrylate)-CO2-Isobutyl Methacrylate System Measured in This Study T (°C)

P (bar)

5.3 wt % P(i-BMA) + 0.0 wt % i-BMA 82.8 2046.6 86.4 1784.5 95.3 1493.1 107.6 1374.5 119.9 1302.1 134.5 1246.6 149.2 1226.9 162.5 1221.4 5.5 wt % P(i-BMA) + 6.5 wt % i-BMA 57.3 1722.4 63.6 1517.6 72.5 1259.7 87.0 1112.8 102.7 1051.0 114.7 1030.0 132.5 1021.0 145.8 1019.0 162.6 1017.2 5.3 wt % P(i-BMA) + 12.6 wt % i-BMA 43.3 1039.7 60.1 885.2 78.4 838.3 98.1 841.7 120.2 853.5 139.4 862.4 160.9 874.5 5.3 wt % P(i-BMA) + 21.7 wt % i-BMA 47.4 643.1 63.9 652.8 82.7 677.6 97.0 692.1 119.6 724.5 137.1 744.1 161.1 778.6 5.1 wt % P(i-BMA) + 32.3 wt % i-BMA 47.9 420.0 58.9 449.3 82.2 502.8 102.5 552.1 122.2 593.5 142.0 631.0 162.0 640.4

Figure 7. Phase behavior of the poly(tert-butyl acrylate)-CO2-57.7 wt % tert-butyl acrylate system obtained in this study. Open squares represent fluidfliquid + liquid transitions, closed circles represent fluidfliquid + vapor transitions, and closed squares represent liquid + liquid + vapor (LLV) data. The concentration of polymers in solution is ∼5 wt %.

bar. When 6.5 wt % isobutyl methacrylate is added to the poly(isobutyl methacrylate)-CO2-isobutyl methacrylate solution, the cloud-point curve exhibits UCST-type phase behavior of the negative slope at the range of temperature from 57 to 162 °C, and the phase behavior pressure increases rapidly at below 70 °C. With 12.6 wt % isobutyl methacrylate added to the solution, the cloud-point curve exhibits UCST-type phase of the negative slope. The cloud-point behavior shows virtually flat at ∼850 bar and at the temperature range from 60 to 160 °C.


Figure 8. Effect of isobutyl methacrylate on the phase behavior of the poly(isobutyl methacrylate)-CO2-x wt % isobutyl methacrylate system, where x equals 0 (open circles), 6.5 (open squares), 12.6 (open triangles), 21.7 (closed circles), 32.3 (closed squares), and the lines mean only bridge between symbols. The concentration of polymers in solution is ∼5 wt %.

Figure 9. Phase behavior of the poly(isobutyl methacrylate)-CO2-49.8 wt % isobutyl methacrylate system obtained in this study. Open circles represent fluidfliquid + liquid transitions, squares closed circles represent fluidfliquid + vapor transitions, and closed squares represent liquid + liquid + vapor (LLV) data. The concentration of polymers in solution is ∼5 wt %. Table 6. Experimental Cloud-Point, Bubble-Point, and Liquid-Liquid-Vapor Data for the Poly(isobutyl methacrylate)-CO2-Isobutyl Methacrylate System Measured in This Study T (°C)

P (bar)

transition

5.1 wt % P(i-BMA) + 49.8 wt % i-BMA 57.4 78.2 101.5 120.2 138.2 160.1


CP CP CP CP CP CP

45.7 50.0

Bubble-Point Transition 234.8 246.6

BP BP

66.0 71.0


LLV LLV

With 21.7 and 32.3 wt % isobutyl methacrylate is added to the poly(isobutyl methacrylate)-CO2-isobutyl methacrylate solution, the cloud-point curve exhibits LCST-type phase behavior of the positive slope at the temperature range from 47 to 162 °C and at a pressure below 778 bar. Also at 100 °C, the cloud-point pressure of the poly(isobutyl methacrylate)-CO2isobutyl methacrylate system decreases by ∼400 bar with the first 6.5 wt % isobutyl methacrylate added to the solution, and

Figure 10. Effect of tert-butyl methacrylate on the phase behavior of the poly(tert-butyl methacrylate)-CO2- x wt % tert-butyl methacrylate system, where x equals 0 (open squares), 10.2 (open triangles), 20.5 (closed circles), 31.3 (closed squares), and the lines mean only bridge between symbols. The concentration of polymers in solution is ∼5 wt %.

it decreases by another ∼200, ∼100, and ∼100 bar with the addition of the next 6.1, 9.1, and 10.6 wt %. Similarities are apparent between the phase behavior of the poly(isobutyl methacrylate)-CO2-49.8 wt % isobutyl methacrylate mixtures shown in Figure 9 (Table 6) and that of the poly(isobutyl acrylate)-CO2-58.7 wt % isobutyl acrylate mixture shown in Figure 5. When 49.8 wt % isobutyl methacrylate is added to the solution, the phase behavior curve exhibits LCST-type cloud-point behavior with a positive slope. The poly(isobutyl methacrylate)-CO2-isobutyl methacrylate cloud-point (LCST) curve intersects the LV curve at 53 °C and 250 bar with 49.8 wt % isobutyl methacrylate. A liquid and vapor phase coexists at pressures below this curve. Note that the LV behavior curve is switched to a liquid + liquid + vapor (LLV) curve at greater than 53 °C, the slope of the poly(isobutyl methacrylate)-CO2-isobutyl methacrylate LCST curve, ∼2.2 bar/°C. Figure 10 and Table 7 show the solubility behavior on the impact of the cosolvent effect for the poly(tert-butyl methacrylate)-CO2-x wt % tert-butyl methacrylate mixture. The phase behavior of the poly(tert-butyl methacrylate)-CO2-0.0 wt % tert-butyl methacrylate mixture presents a negative slope with dissolve at a temperature of 190 °C and a pressure of 2575 bar. When 10.2 wt % tert-butyl methacrylate is added to the poly(tert-butyl methacrylate)-CO2-tert-butyl methacrylate mixture, the cloud-point behavior exhibits UCST region behavior with a negative slope. With 20.5 wt % tert-butyl methacrylate in solution, the cloud-point pressure remains virtually constant at ∼810 bar over the temperature range from 50 to 163 °C. The phase behavior of the poly(tert-butyl methacrylate)-CO2-20.5 wt % tert-butyl methacrylate mixture exhibits the UCST-type phase behavior which shows a slightly negative slope at low pressures. If 31.3 wt % tert-butyl methacrylate is added to the solution, the cloud-point curve exhibits LCST-type phase behavior of positive slope at 44-159 °C. The phase behavior of poly(tert-butyl methacrylate)-CO2-31.3 wt % tert-butyl methacrylate system shows 1.4 bar/°C in positive slope. When 46.4 wt % tert-butyl methacrylate is added to the poly(tert-butyl methacrylate)-CO2 solution, the cloud-point curve shown in Figure 11 and Table 8 is obtained on the typical appearance of a LCST boundary. The poly(tert-butyl methacrylate)-CO2-46.4 wt % tert-butyl methacrylate phase behavior curve intersects a fluidf liquid + vapor (LV) curve at ∼70 °C and ∼90 bar. A liquid and vapor phase coexists at pressures

3360


Table 7. Experimental Cloud-Point Data for the Poly(tert-butyl methacrylate)-CO2-tert-Butyl Methacrylate System Measured in This Study T (°C)

P (bar)

4.6 wt % P(t-BMA) + 0.0 wt % t-BMA 161.8 2575.5 164.6 2377.6 171.6 2186.6 183.0 1933.8 190.8 1913.1 5.2 wt % P(t-BMA) + 10.2 wt % t-BMA 86.3 2172.8 86.7 1998.3 96.8 1600.0 102.6 1482.8 113.6 1348.3 121.1 1311.4 131.2 1261.4 141.0 1202.4 149.0 1200.3 158.6 1165.5 160.7 1193.1 5.7 wt % P(t-BMA) + 20.5 wt % t-BMA 49.9 882.1 59.0 844.8 79.4 815.5 98.5 813.1 122.2 811.0 139.3 806.9 163.0 801.7 5.2 wt % P(t-BMA) +31.3 wt % t-BMA 44.0 485.9 58.5 516.6 83.2 568.6 100.5 599.3 118.5 620.0 140.4 633.8 158.5 649.3

below this curve, and the LV curve is switched to a liquid1 + liquid2 + vapor (LLV) curve at temperatures greater than about 70 °C. Phase Behavior of CO2-Iso, tert-Butyl Acrylate and CO2-Iso, tert-Butyl Methacrylate Mixture. Bubble-, dew-, and critical-point data for the CO2-isobutyl acrylate, CO2tert-butyl acrylate, CO2-isobutyl methacrylate, and CO2-tertbutyl methacrylate systems are measured and reproduced at least twice to within (0.3 bar and (0.2 °C for a loading of the cell. The mole fractions are accurate to (0.002. The CO2-isobutyl acrylate, CO2-tert-butyl acrylate, CO2-isobutyl methacrylate, and CO2-tert-butyl methacrylate mole fraction for the solubility

Figure 11. Phase behavior of the poly(tert-butyl methacrylate)-CO246.4 wt % tert-butyl methacrylate system obtained in this study. Open squares represent fluidfliquid + liquid (L+L) transitions, closed circles represent fluidfliquid + vapor transitions, and closed squares represent liquid + liquid + vapor (LLV) data. The concentration of polymers in solution is ∼5 wt %.

Table 8. Experimental Cloud-Point, Bubble-Point, and Liquid-Liquid-Vapor Data for the Poly(tert-butyl methacrylate)-CO2-tert-Butyl Methacrylate System Measured in This Study T (°C)

P (bar)

transition

5.4 wt % P(t-BMA) + 46.4 wt % t-BMA 70.7 81.5 102.3 119.6 141.6 159.9


CP CP CP CP CP CP

41.6 51.3 59.8

Bubble-Point Transition 62.4 75.2 82.4

BP BP BP

81.0 92.0


LLV LLV

isotherms at 40-120 °C have an estimated and accumulated error of less than (1.0%. Figure 12 and Table 9 show the experimental pressurecomposition (P-x) isotherms for the carbon dioxide-isobutyl acrylate system at 40, 60, 80, 100, and 120 °C and the range of pressures of 24-148 bar. As shown in Figure 12, three phases were not observed at any of the five temperatures studied. Figure 13 and Table 10 present the phase behavior data for the CO2-tert-butyl acrylate system at 40, 60, 80, 100, and 120 °C and pressure up to 140 bar. As shown in Figure 13, the mixture-critical pressure shows 119.7 bar (at 80 °C), 129.3 bar (at 100 °C), and 139.7 bar (at 120 °C). The pressure of each mixture-critical point continually increases as the temperature increases. Figure 14 and Table 11 show the experimental data for the CO2-isobutyl methacrylate mixture at the range of temperature from 40 to 120 °C and the range of pressure of 33-159 bar. Three phases were not observed at any of the five temperatures. The P-x isotherms shown in Figure 14 are consistent with those expected for a type-I24 system where a maximum occurs in the critical mixture curve. Figure 15 and Table 12 present the experimental P-x isotherms at 40, 60, 80, 100, and 120 °C, and the range of pressure of 32-147 bar for the CO2-tert-butyl methacrylate system. Also, for the CO2-tert-butyl methacrylate system is observed a type-I phase behavior.24 In Figure 15, the mixture critical pressures show 103.0 bar (at 60 °C), 121.0 bar (at 80 °C), 136.8 bar (at 100 °C), and 147.2 bar (at 120 °C), respectively.

Figure 12. A comparison of experimental data (symbol) for the carbon dioxide-isobutyl acrylate system with calculations (solid line) obtained with the Peng-Robinson equation of state with kij equal to 0.0125 and ηij equal to -0.0223.

Ind. Eng. Chem. Res., Vol. 45, No. 10, 2006 3361 Table 9. Experimental Isotherms Data for CO2-Isobutyl Acrylate System Obtained in This Study isobutyl acrylate mole fraction

a

P (bar)

transitiona

0.054 0.092 0.148 0.211 0.296 0.390 0.444 0.549 0.701

T ) 40 °C 74.5 73.6 69.3 61.4 56.2 47.9 45.4 37.6 24.1

BP BP BP BP BP BP BP BP BP

0.054 0.092 0.148 0.211 0.296 0.390 0.444 0.549 0.701

T ) 60 °C 100.0 98.5 91.0 84.5 72.6 63.6 56.4 46.9 28.1

BP BP BP BP BP BP BP BP BP

0.054 0.092 0.148 0.211 0.296 0.390 0.444 0.549 0.701

T ) 80 °C 120.6 121.1 115.5 107.1 92.8 79.3 70.3 58.3 33.5

DP CP BP BP BP BP BP BP BP

0.054 0.092 0.148 0.211 0.296 0.390 0.444 0.549 0.701

T ) 100 °C 132.1 136.9 137.2 125.9 111.7 93.8 82.8 66.6 36.4

DP DP CP BP BP BP BP BP BP

0.054 0.092 0.148 0.211 0.296 0.390 0.444 0.549 0.701

T ) 120 °C 132.1 144.3 147.9 142.2 127.6 107.6 95.2 75.5 42.4

DP DP CP BP BP BP BP BP BP

BP is a bubble point, CP is a critical point, and DP is a dew point.

The behavior shown in the CO2-isobutyl acrylate, CO2tert-butyl acrylate, CO2-isobutyl methacrylate, and CO2-tertbutyl methacrylate systems is consistent with that of the CO2butyl acrylate,6 CO2-butyl methacrylate,5 CO2-hexyl acrylate,11 CO2-hexyl methacrylate,11 and CO2-octadecyl acrylate18 systems. Note that the bubble-point portion of the P-x isotherms for the CO2-isobutyl acrylate, CO2-tert-butyl acrylate, CO2isobutyl methacrylate, and CO2-tert-butyl methacrylate systems is convex toward lower pressures which mean that CO2 is very miscible in the isobutyl acrylate, tert-butyl acrylate, isobutyl methacrylate, and tert-butyl methacrylate-rich liquid phase. The lower solubility of CO2 in the isobutyl acrylate and tert-butyl acrylate is likely due to the steric hindrance of the isobutyl and tert-butyl chain that prevents facile complex formation between CO2 and the acrylate carbonyl oxygen. Moreover, the strength of a CO2-isobutyl acrylate and CO2-tert-butyl acrylate complex is expected to be lower than that of a CO2-isobutyl methacrylate and CO2-tert-butyl methacrylate complex since the electron donating character of isobutyl acrylate and tert-

Figure 13. A comparison of experimental data (symbol) for the carbon dioxide-tert-butyl acrylate system with calculations (solid line) obtained with the Peng-Robinson equation of state with kij equal to -0.0255 and ηij equal to -0.0636.

butyl acrylate is less than that of isobutyl methacrylate and tertbutyl methacrylate due to its larger molar volume. The phase behavior experimental data obtained in this work are modeled using the Peng-Robinson equation of state. The equation of state is briefly described here. The Peng-Robinson equation of state19 is used with the following mixing rules.

P)

R(T) RT (V - b) V(V + b) + b(V - b) R2Tc2 R(T) ) 0.45724 Pc

(2)

RTc Pc

(3)

∑i ∑j xixjaij

(4)

b ) 0.07780 amix )

aij ) (aiiajj)1/2(1 - kij) bmix )

(1)

(5)

∑i ∑j xixjbij

(6)

bij ) 0.5[(bii + bjj)](1 - ηij)

(7)

These two binary interaction parameters were determined by regression experimental data with the Peng-Robinson equation of state. Objection function (OBF) and root-mean-squared relative deviation (RMSD) percent of this calculation were defined as follows. N

OBF )

∑i

(

RMSD(%) )

)

Pexp - Pcal Pexp

2

× 100 xOBF ND

(8)

(9)

ND in eq 9 means the number of data points. We used Marquardt20 to optimize objection function. All isotherms were included for calculation. The expression for the fugacity coefficient using these mixing rules is given by Peng and Robinson19 and is not reproduced here. Table 13 lists the pure component critical temperatures, critical pressures, and the acentric factors for CO2, isobutyl

3362


Table 10. Experimental Isotherms Data for CO2-tert-Butyl Acrylate System Obtained in This Study tert-butyl acrylate mole fraction

a

P (bar)

transitiona

0.090 0.122 0.167 0.233 0.235 0.319 0.358 0.441 0.496 0.564 0.664

T ) 40 °C 76.6 71.7 68.3 56.2 59.7 52.5 49.5 43.5 36.7 30.2 23.8

BP BP BP BP BP BP BP BP BP BP BP

0.090 0.122 0.167 0.233 0.235 0.319 0.358 0.441 0.496 0.564 0.664

T ) 60 °C 99.4 93.5 86.9 79.7 80.3 69.3 65.4 56.7 49.1 42.5 33.6

BP BP BP BP BP BP BP BP BP BP BP

0.090 0.122 0.167 0.233 0.235 0.319 0.358 0.441 0.496 0.564 0.664

T ) 80 °C 119.7 116.6 110.4 99.8 100.3 85.5 80.2 71.2 62.2 53.1 42.2

CP BP BP BP BP BP BP BP BP BP BP

0.090 0.122 0.167 0.233 0.235 0.319 0.358 0.441 0.496 0.564 0.664

T ) 100 °C 128.6 129.3 127.7 116.7 119.0 102.4 95.7 82.4 72.9 63.8 47.6

DP CP BP BP BP BP BP BP BP BP BP

0.090 0.122 0.167 0.233 0.235 0.319 0.358 0.441 0.496 0.564 0.664

T ) 120 °C 131.0 138.3 139.7 131.0 131.4 116.2 108.4 92.8 83.6 71.0 53.9

DP DP CP BP BP BP BP BP BP BP BP


acrylate, tert-butyl acrylate, isobutyl methacrylate, and tert-butyl methacrylate used with the Peng-Robinson equation of state. The critical properties of isobutyl acrylate, tert-butyl acrylate, isobutyl methacrylate, and tert-butyl methacrylate were obtained by Lydersen’s method in group contribution.21 The vapor pressures were calculated by the Lee-Kesler method.21 Figure 16 presents the comparison of the CO2-isobutyl acrylate experimental results with the calculated data obtained using the Peng-Robinson equation of state at a temperature of 80 °C. The values of the optimized parameters (bubble-point data ) 7, RMSD ) 3.51%) of the Peng-Robinson equation of

Figure 14. A comparison of experimental data (symbol) for the carbon dioxide-isobutyl methacrylate system with calculations (solid line) obtained with the Peng-Robinson equation of state with kij equal to 0.0256 and ηij equal to -0.0294.

state for the CO2-isobutyl acrylate system are kij ) 0.0125 and ηij ) -0.0223. A reasonable fit of the data is obtained over most of the composition range even if no binary interaction parameters are used. But if two mixture parameters (kij ) 0.0125 and ηij ) -0.0223) are used the fit of the experimental results is significantly better. We compared the experimental results with calculated P-x isotherms at temperatures of 40, 60, 100, and 120 °C for the CO2-isobutyl acrylate system using the optimized values of kij and ηij determined at 80 °C. Therefore, Figure 12 shows the comparison of experimental results with calculated P-x isotherms at temperatures of 40, 60, 100, and 120 °C for the CO2-isobutyl acrylate system using the adjusted values of kij and ηij determined at 80 °C. A good fit of the data are obtained with the Peng-Robinson equation using two adjustable mixture parameters for the CO2-isobutyl acrylate system. The RMSD at five temperatures for the CO2-isobutyl acrylate system was 5.14% of the bubble-point number 37. Figure 13 shows the comparison of experimental data with calculated results at 40, 60, 80, 100, and 120 °C for the CO2tert-butyl acrylate system. These isotherms are calculated using the optimized values (bubble-point data ) 10, RMSD ) 1.22%) of kij equal to -0.0255 and ηij equal to -0.0636 determined at 80 °C in the same way as above (Figure 12). The RMSD at five temperatures for the CO2-tert-butyl acrylate system was 3.60% of the bubble-point number 39. The calculated mixture critical curve is type-I, in agreement with the experimental results. Figure 14 shows the comparison of experimental data with calculated result using the Peng-Robinson equation of state at 40, 60, 80, 100, and 120 °C for the CO2-isobutyl methacrylate system. These P-x isotherms are calculated using the optimized values (bubble-point data ) 9, RMSD ) 2.21%) of kij ) 0.0256 and ηij ) -0.0294 determined at 80 °C. The values of the optimized parameters (bubble-point data ) 34, RMSD ) 4.68%) of the Peng-Robinson equation of state for the CO2-isobutyl methacrylate system are kij ) -0.0435 and ηij ) -0.0175. A good fit of the data is obtained from Peng-Robinson equation of state using two adjustable mixture parameters for the CO2isoisobutyl methacrylate system. Figure 15 shows predicted P-x isotherms for the CO2-tertbutyl methacrylate mixture at 40, 60, 80, 100, and 120 °C using the Peng-Robinson equation of state with kij equal to -0.0150 and ηij equal to -0.0675. These optimized values of the mixture parameters (bubble-point data ) 13, RMSD ) 0.85%) are obtained by fitting the 353.2 K isotherms between the experi-

Ind. Eng. Chem. Res., Vol. 45, No. 10, 2006 3363 Table 11. Phase Behavior of the CO2-Isobutyl Methacrylate System Obtained in This Study isobutyl methacrylate mole fraction

a

P (bar)

transitiona

0.067 0.101 0.134 0.176 0.241 0.297 0.366 0.467 0.524 0.620

T ) 40 °C 73.1 69.3 69.0 65.5 62.4 59.5 53.5 44.5 40.2 33.1

BP BP BP BP BP BP BP BP BP BP

0.067 0.101 0.134 0.176 0.241 0.297 0.366 0.467 0.524 0.620

T ) 60 °C 103.5 101.4 97.9 90.7 86.2 80.0 69.3 57.6 51.8 39.6

BP BP BP BP BP BP BP BP BP BP

0.067 0.101 0.134 0.176 0.241 0.297 0.366 0.467 0.524 0.620

T ) 80 °C 127.8 125.9 125.5 117.6 108.6 99.7 86.6 69.7 63.5 45.8

CP BP BP BP BP BP BP BP BP BP

0.067 0.101 0.134 0.176 0.241 0.297 0.366 0.467 0.524 0.620

T ) 100 °C 144.1 145.2 145.2 137.2 127.2 116.6 102.4 82.1 72.8 51.6

DP CP BP BP BP BP BP BP BP BP

0.067 0.101 0.134 0.176 0.241 0.297 0.366 0.467 0.524 0.620

T ) 120 °C 154.1 156.9 159.3 152.8 144.1 131.0 115.2 93.1 82.1 57.8

DP DP CP BP BP BP BP BP BP BP

Figure 15. A comparison of experimental data (symbol) for the carbon dioxide-tert-butyl methacrylate system with calculations (solid line) obtained with the Peng-Robinson equation of state with kij equal to -0.0150 and ηij equal to -0.0675. Table 12. Phase Behavior of the CO2-tert-Butyl Methacrylate System Obtained in This Study t-BMA mole fraction

P (bar)

transitiona

0.039 0.096 0.124 0.141 0.180 0.217 0.235 0.272

76.9 71.2 69.7 69.3 67.3 63.5 63.4 40.5

BP BP BP BP BP BP BP BP

0.039 0.096 0.124 0.141 0.180 0.217 0.235 0.272

103.0 99.0 95.5 94.1 87.2 87.2 83.1 77.1

CP BP BP BP BP BP BP BP

0.039 0.096 0.124 0.141 0.180 0.217 0.235 0.272

P (bar)

transitiona

0.335 0.345 0.385 0.409 0.462 0.543 0.606

55.7 54.8 50.1 47.4 42.5 36.3 32.5

BP BP BP BP BP BP BP

0.335 0.345 0.385 0.409 0.462 0.543 0.606

69.3 68.1 65.3 61.3 55.2 47.0 41.0


112.4 121.0 119.3 117.6 112.1 106.6 102.1 94.8

T ) 80 °C DP 0.335 CP 0.345 BP 0.385 BP 0.409 BP 0.462 BP 0.543 BP 0.606 BP

84.8 82.9 79.4 75.9 69.0 58.0 51.0


0.039 0.096 0.124 0.141 0.180 0.217 0.235 0.272

118.3 134.8 136.8 135.9 132.1 124.5 122.8 113.3

T ) 100 °C DP 0.335 DP 0.345 CP 0.385 BP 0.409 BP 0.462 BP 0.543 BP 0.606 BP

102.4 99.2 93.1 88.2 81.3 66.9 58.2


0.039 0.096 0.124 0.141 0.180 0.217 0.235 0.272

106.9 143.5 146.5 147.2 145.2 138.6 137.8 128.0

T ) 120 °C DP 0.335 DP 0.345 DP 0.385 CP 0.409 BP 0.462 BP 0.543 BP 0.606 BP

116.2 113.8 105.9 99.3 91.2 77.4 66.4


T ) 40 °C

T ) 60 °C


mental and calculated results. RMSD at five temperatures for the CO2-tert-butyl methacrylate system was 2.41% of the bubble-point number 65. Figure 17 shows the mixture-critical curve for the CO2isobutyl acrylate system predicted by the Peng-Robinson equation of state. The calculated mixture-critical curve is typeI, which shows an agreement with experimental observations. As shown Figure 17, the solid lines represent the vapor pressure for pure CO222 and isobutyl acrylate,21 and the solid circles do the critical point for pure CO221,23 and isobutyl acrylate.21 The dash lines represent the calculated value obtained using the Peng-Robinson equation of state. The upper part of the dash line is one phase (fluid), the lower part of it is two phase (vapor-liquid). The open squares mean the mixture-critical points determined from isotherms measured in this experiment.

t-BMA mole fraction

a


The binary mixture parameters are then obtained of the PengRobinson equation, with kij equal to 0.0125 and ηij equal to -0.0223. Figure 18 shows the mixture-critical curve for the CO2-tertbutyl acrylate system predicted by the Peng-Robinson equation

3364


Table 13. Pure Component Critical Properties with the Peng-Robinson Equation of State21-23 component carbon dioxide isobutyl acrylate tert-butyl acrylate isobutyl methacrylate tert-butyl methacrylate

Tb (°C)

Tc (°C)

Pc (bar)

acentric factor

132.65 145.05 154.05 160.05

31.1 309.45 336.05 333.85 349.65

73.9 29.7 30.1 27.0 27.3

0.225 0.449 0.386 0.468 0.405

of state. The calculated mixture-critical curve is type-I, which shows an agreement with experimental observations. As shown in Figure 18, the solid lines represent the vapor pressure for pure CO222 and tert-butyl acrylate,21 and the dash lines do the calculated value obtained using the Peng-Robinson equation of state. The binary mixture parameters are then obtained from the Peng-Robinson equation of state, with kij equal to -0.0255 and ηij equal to -0.0636. The process of obtaining optimum binary interaction parameters is identified with the method in the CO2-tert-butyl acrylate system. Figures 19 and 20 show the mixture-critical curve for the CO2-isobutyl methacrylate and CO2-tert-butyl methacrylate system predicted by the Peng-Robinson equation of state. The calculated mixture-critical curve is type-I, in agreement with experimental observations. As shown in Figures 19 and 20, the solid lines represent the vapor pressure for pure CO2,22 isobutyl methacrylate,21 and tert-butyl methacrylate,21 and the solid circles do the critical point for pure carbon dioxide, isobutyl methacrylate, and tert-butyl methacrylate. The upper part of the dash line is single phase (fluid), the lower part is two phase

Figure 18. Pressure-temperature diagram for the CO2-isobutyl methacrylate system. The solid lines and the solid circles represent the vaporliquid lines and the critical points for pure CO2 and isobutyl methacrylate. The open squares are critical points determined from isotherms measured in this work. The dashed lines represent calculations obtained using PengRobinson equation of state with kij equal to 0.0256 and ηij equal to -0.0294.

Figure 19.

Figure 16. Comparison of the best fit of Peng-Robinson equation of state to the CO2-isobutyl acrylate system at 80 °C.

Figure 20.

(vapor-liquid). The solid squares mean the mixture-critical points determined from isotherms measured in this experiment. The dash lines represent the calculated value obtained using the Peng-Robinson equation of state. Conclusions Figure 17. Pressure-temperature diagram for the CO2-isobutyl acrylate system. The solid lines and the solid circles represent the vapor-liquid lines and the critical points for pure CO2 and isobutyl acrylate. The open squares are critical points determined from isotherms measured in this work. The dashed lines represent calculations obtained using Peng-Robinson equation of state with kij equal to 0.0125 and ηij equal to -0.0223.

The cloud-point data for the system poly(isobutyl acrylate)CO2-isobutyl acrylate are measured with isobutyl acrylate concentrations of 0.0, 3.2, 8.8, 18.1, 31.9, 40.7, and 58.7 wt %. This system changes the pressure-temperature slope of the phase behavior curves from UCST region to LCST region as the isobutyl acrylate concentration increases. The experimental


phase behavior data are presented for the poly(tert-butyl acrylate)-CO2-0, 8.5, 14.9, 34.7, and 56.0 wt % tert-butyl acrylate mixture. When 57.5 wt % tert-butyl acrylate is added to the poly(tert-butyl acrylate)-CO2 solution, the cloud-point curve shown on the typical appearance of a lower critical solution temperature (LCST) boundary. Cloud-point data are obtained for poly(isobutyl methacrylate)-CO2-isobutyl methacrylate mixtures with isobutyl methacrylate concentration of 0.0, 6.5, 12.6, 21.7, 32.3, and 49.8 wt %. The phase behavior curves shows from positive slope to negative slope in the pressure-temperature diagram. The phase behavior experimental curves shows the from the UCST region to the LCST region as the tert-butyl methacrylate concentration for the poly(tert-butyl methacrylate)-CO2-0.0, 10.2, 20.5, 31.3, 46.4 wt % tert-butyl methacrylate system. High-pressure phase behavior for the CO2-isobutyl acrylate, CO2-tert-butyl acrylate, CO2-isobutyl methacrylate and CO2tert-butyl methacrylate systems show at the range of temperature of 40-120 °C and pressure of 24-160 bar. The P-x bubblepoint curves are convex which indicates that CO2 exhibits a high solubility in isobutyl acrylate, tert-butyl acrylate, isobutyl methacrylate, and tert-butyl methacrylate probably due to the formation of a weak complex between the carboxylic oxygen in isobutyl acrylate, tert-butyl acrylate, isobutyl methacrylate, tert-butyl methacrylate, and the carbon in CO2. The PengRobinson equation of state can be used with two adjustable parameters to calculate a reasonable representation of the phase behavior of the CO2-isobutyl acrylate, CO2-tert-butyl acrylate, CO2-isobutyl methacrylate, and CO2-tert-butyl methacrylate systems. The temperature-independent interaction parameter quantitative agreement can be obtained between experimental data and calculated phase behavior. Acknowledgment This work was supported by the Korea Research Foundation Grant (KRF-2004-041-D00153). Note Added after ASAP Publication. The E-mail address of the corresponding author has been changed from that in the version published on the Web 11/16/2005. The correct version was posted 4/5/2006. Literature Cited (1) Kirby, C. F.; McHugh, M. A. Phase Behavior of Polymers in Supercritical Fluid Solvents. Chem. ReV. 1999, 99, 565. (2) DeSimone, J. M.; Maury, E. E.; Menceloglu, Y. Z.; McClain, J. B.; Romack, T. J.; Combes, J. R. Dispersion Polymerization in Supercritical Carbon Dioxide. Science 1994, 265, 356. (3) Poliakoff, M.; Darr, J. A. New Directions in Inorganic and MetalOrganic Coordination Chemistry in Supercritical Fluids. Chem. ReV. 1999, 99, 495 (4) McHugh, M. A.; Krukonis, V. J. Supercritical Fluid Extraction: Principles and Practice, 2nd ed.; Stoneham: Butterworth: MA, 1994.

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ReceiVed for reView June 15, 2005 ReVised manuscript receiVed September 23, 2005 Accepted October 17, 2005 IE050705F

Cosolvent Effect and Solubility Measurement for Butyl (Meth)acrylate

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