Article pubs.acs.org/jced
Equilibrium Solubilities of Diisooctyl Sebacate in Supercritical Carbon Dioxide Xin Yang,† Ligong Chen,*,† Wen Zhou,‡ Li Liu,† and Shuo Xiang† †
Department of Oil Application & Management Engineering, Logistical Engineering University, Chongqing 401311, China Construction Engineering Research Institute of the General Logistics Department, Xi’an 710032, China
‡
ABSTRACT: The extraction of base oil from waste lubricating oil is becoming the preferred way of handling used oil to protect the environment and conserve petroleum resources. Supercritical carbon dioxide extraction has become a potential technology for the regeneration of waste lubricant oil because carbon dioxide has high dissolving power, is nontoxic, nonflammable, and inexpensive. Since the equilibrium solubility data are important for supercritical extraction processes, in this study the equilibrium solubilities for one of the synthetic ester lubricant oils, diisooctyl sebacate [bis (2ethylhexyl) sebacate], in supercritical carbon dioxide (sc-CO2) were obtained at 313.2 K, 328.2 K, 343.2 K, 358.2 K and in a pressure range from 7.24 MPa up to 15.96 MPa. Oil solubility increased with pressure but decreased with temperature, providing sc-CO2 with the highest oil solubility (82.1959 g/L) at 313.2 K and 13.96 MPa, which showed that the solubility is strongly dependent on the density of CO2. The experimental solubility results were correlated with three density-based models: Chrastil model, del Valle and Aguilera model, and the Adachi and Lu model. While all of the three models correlated the experimental data very well, the nonlinear equation of Adachi and Lu model showed the best fit.
1. INTRODUCTION Lubricant oil keeps our cars as well as many other machines running smoothly; however, once oil is deteriorated, it can pollute the environment if it is not disposed of properly because used oils are hardly biodegradable. Impurities such as asphaltic impurities, metal scrapings, water and additives, can get mixed in with the oil; their disposal in the environment is therefore hazardous for soil and water.1−3 Accordingly, regeneration of waste lubricating oil is becoming the preferred way of handling used oil to protect the environment and conserve petroleum resources. Several technologies have been proposed to regenerate base oil from waste lubricating oils, but some problems have been presented about the technological processes that were industrially tested. The conventional process of recycling the waste lubricant oil requires the use of concentrated sulfuric acid, which does not easily remove asphaltic impurities and produces contaminating byproducts: acid sludge and acid water.4,5 The combination process of vacuum distillation and hydrofinishing not only removes most of the contaminants but also produces high quality standard recovered oil with a yield of approximately 82% and minimized polluting byproducts.6 Despite the above-mentioned advantages, this method has a high investment cost. In recent years supercritical fluid extraction (SFE) has been seen as a very potential and environmentally friendly technology over other conventional methods for recovering waste lubricant oil. Carbon dioxide © XXXX American Chemical Society
(CO2) is one of the most attractive solvents, mainly because of its relatively moderate critical temperature and critical pressure (Tc = 304.15 K, Pc = 7.38 MPa) as well as other advantageous properties such as its high density, nontoxicity, nonflammability, and low cost.7,8 Since supercritical extraction processes require a cost evaluation for laboratory scale up to the industrial scale, both the equilibrium solubility data and solubility models are important for the process design as well as the most adequate operating conditions.9−13 The solubility data of rice bran oil in supercritical CO2 (sc-CO2) was investigated, then the experimental extraction behavior was explained using the Chrastil model, which showed a good agreement with the values by the correlation of the Chrastil model.9 Supercritical CO2 was used to extract the remaining fat from rendered poultry meal, and the solubility data was correlated successfully by solubility model as a function of density and temperature.10 The experimental measurement the solubility of Irgacure 2959 in sc-CO2 at 308.2 K, 318.2 K, and 328.2 K in a pressure range from 10.0 MPa up to 26.0 MPa, the solubility data were correlated with three density-based models (Chrastil, Bartle, and Mendez-Santiago-Teja models) and with an equation-ofstate (EOS) model. Accordingly, it is necessary to acquire a precise knowledge of the solubility data and solubility model for Received: June 2, 2015 Accepted: October 1, 2015
A
DOI: 10.1021/acs.jced.5b00457 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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the sc-CO2 extraction of the involved compounds under different conditions of temperature and pressure.7 In developing the application of using supercritical CO2 to extract fresh base oil from waste lubricant oil, the equilibrium solubility data are very valuable. The equilibrium solubility of the lubricant oil fraction (hydrocarbons) in supercritical CO2 can be diagnosed, being useful for practical operation. In particular, for a better design of separation processes, the operating conditions, such as pressure and temperature should be considered in order to minimize the energy losses and optimize the overall process. Note that the type and composition of the lubricant oil are many and complex; in this research a single fraction was chosen to be analyzed first. Diisooctyl sebacate, an important and widely used synthetic ester base oil was studied by the static method. The equilibrium solubility data of the diisooctyl sebacate in sc-CO2 was measured in the pressure range from 7.24 MPa to 15.96 MPa and at temperatures of 313.2 K, 328.2 K, 343.2 K, 358.2 K. The experimental solubility data were analyzed by the Chrastil model, del Valle and Aguilera model, and Adachi and Lu model to correlate the solubility data, respectively.
Figure 1. Schematic diagram of the experimental apparatus for measured equilibrium solubility. (1) CO2 storage tank, (2) cryogenic liquid storage, (3) piston vessel, (4) hand compressed booster pump, (5) high pressure variable volume cell, (6) temperature recorder, (7) pressure recorder, (8) liquid sampling valve, (9) gas sampling valve, (10) bumper, (11) desiccators, (12) vacuum pump.
2. EXPERIMENTAL PROCEDURES 2.1. Materials. The experimental sample in this research is given in Table 1.
maintained at a certain isothermal condition. To reach the desired pressure, on the one hand, carbon dioxide was fed to the cell using a hand compressed booster pump if the pressure waslower than the desired pressure; on the other hand, the needle-type valve on the top of the high-pressure variable volume cell was opened to release excess carbon dioxide if the pressure was higher than the desired pressure. Furthermore, accurate pressure can be controlled by pulling up or pressing down the movable piston in the variable volume cell. The equilibrium solubility was measured when the phase interface could be observed by visual window as well as the pressure and temperature remaining constant. It usually takes 90−120 min to reach equilibrium. The equilibrium solubility sample of supercritical and oil phase was taken by a 10 mL sampler (small sampling steel vessel, Hai’an Petroleum Scientific Research Apparatus Inc., Jiangsu, China), which weighed with standard uncertainty of 0.0001 g. The oil or supercritical phase sample was obtained by a 10 mL sampling vessel with needle-type valve, then the sampler was quickly immersed in an ice−water vessel. After the sample was cooled, the 10 mL vessel connected to a buffer tank of known volume (100 mL) with a pressure gauge; meanwhile, the buffer tank’s temperature was measured with a thermometer. In addition, the air in the sampler was removed by vacuum pump before samples were taken and the air in the buffer tank was removed by vacuum pump before a cooled sampler was connected to it. As a result of the pressure in the bumper tank being almost equal to or slightly below the atmosphere pressure, the CO2 mole fraction in sc-CO2 phase (y1) could be calculated by the equation of state of ideal gas.15 The reliability of the designed experimental setup in this study was tested by a representative binary system such as CO2−ethanol, and three values of vapor−liquid equilibrium data were chosen and measured.16 It was found that the apparatus could measure new solubility data of the CO2− diisooctyl sebacate system after being tested with the CO2− ethanol equilibrium data. The mole fraction of CO2 in the liquid phase (x1) and gas phase (y1) is given in Table 2.
Table 1. Experimental Sample Table chemical name
CAS No.
source
carbon dioxide
124-38-9
diisooctyl sebacate
122-62-3
ethanol
64-17-5
Shenfeng Gas Co. Ltd., Chongqing, China Bangcheng Chemical Co. Ltd., Shanghai, China Chuandong Chemical Co. Ltd., Chongqing, China
initial weight fraction purity
purification method
99.9 %
none
98.0 %
none
99.8 %
none
2.2. Experimental Methods. The high-pressure equilibrium solubility data was measured using an experimental apparatus shown in Figure 1. It was utilized in our previous report which is based in the static-analytic method.14 The apparatus mainly included a CO2 storage tank (Shenfeng Gas Co. Ltd., Chongqing, China), cryogenic liquid storage, piston vessel, hand compressed booster pump, and high-pressure variable volume cell [Hai’an Petroleum Research Instrument Plant, Nantong, Jiangsu], temperature/pressure recorder [Shengke Instrument Co. Ltd., Jiangsu, China], sampling vessel [Hai’an Petroleum Research Instrument Plant, Nantong, Jiangsu], vacuum pump [Lingzhi pump Co. Ltd., Sichuan, China]. First, the residual air in the setup was removed by the carbon dioxide flush out at low pressure. Then, approximately 30 g to 45 g of diisooctyl sebacate sample was loaded into the bottom of the high-pressure variable volume cell using a vacuum pump. After the carbon dioxide was cooled by cryogenic liquid storage, the cell was fed with the liquid carbon dioxide by means of the hand compressed booster pump. The heating rods placed in the cell were increased up to the desired condition of maintaining the operating temperature ((313.2, 328.2, 343.2, and 358.2) K). Finally, the pressure was varied under the temperature B
DOI: 10.1021/acs.jced.5b00457 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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in Table 4. Furthermore, in order to pictorial understand the extraction behavior, Figure 2 shows the CO2 mole fraction in the sc-CO2 phase, Figure 3 shows the solubility trends of diisooctyl sebacate at various temperatures and pressures obtained from experimental data. From Figure 2 and Figure 3, it can be seen that increasing pressure at a constant temperature will increase the solubility, while increasing temperature at a constant pressure will decrease the solubility. The results might be used in the effect of oil solubility in CO2 being related to the density of CO2 and the dissolving capacity of sc-CO2. At a constant temperature, CO2 density can be significantly increased by increasing pressure and lead to an increase in the dissolving capacity of sc-CO2, which results in a positive effect on the extraction process. On the contrary, at a constant pressure, the decreasing CO2 density with the increasing temperature leads to a decrease in the dissolving capacity of sc-CO2. As the result, the solubility of oil in CO2 decreases at this state. With regard to the temperature, because the density of scCO2 is closely related to the relative low pressure of 7.26 MPa, the solubility is slightly decreased under the investigated four temperatures. However, at relatively high pressure (exceed 11 MPa), the solubility is sharply decreased with an increasing temperature from 313.2 K to 358.2 K. It can be observed in Figure 3 that for the same solubility, the pressure needed increased much more when the temperature was at 358.2 K than when the temperature is at 343.2 K, 328.2 K, and 313.2 K. This result might be explained as follows: on the one hand, the mole fraction of diisooctyl sebacate in sc-CO2 phase (1 − y1) decreased with the increasing temperature at each constant pressure, which caused a decrease in solvent density and leads to reduce the dissolving capacity of sc-CO2. One the other hand, the solute’s volatility and diffusibility was increased as itemperature increased, which helps the extraction of the diisooctyl sebacate by sc-CO2. In addition, under these conditions the change of solvent density is more effective
Table 2. Comparison of Measured Values with Literature Vapor−Liquid Equilibrium Data for Temperature T, Pressure p, Liquid-Phase Mole Fraction x, and Gas-Phase Mole Fraction y, for the System CO2 (1) + Ethanol (2)a
a
T/K
p/MPa
x1
SD (%)
y1
SD (%)
333.4 333.4 333.4 333.4 333.4 333.4
9.02 9.95 10.66 9.024 9.949 10.654
0.4934 0.6111 0.8164 0.49416 0.61016 0.81716
0.50 0.51 0.46
0.9725 0.9532 0.9085 0.97216 0.95416 0.90816
0.47 0.44 0.56
Standard uncertainties u are u(T) = 0.24 K, u(p) = 0.02 MPa.
1 n−1
SD(x) =
SD(y) =
n
∑ (xi − x ̅)2 i
1 n−1
n
∑ (yi − y ̅ )2 i
3. RESULTS AND DISCUSSION 3.1. Phase Equilibrium Solubility Experimental Results. The phase equilibrium solubility of the experimental data at (313.2, 328.2, 343.2, and 358.2) K in the pressure ranges 7.24 MPa to 15.96 MPa is reported in Table 3 providing the CO2 mole fraction (y1) in the supercritical phase. According to Cheng et al.,17 the solubility of solute in the sc-CO2 in terms of CO2 mole fraction in the supercritical fluid phase is given by eq 1: S=
Mi × (1 − yCO ) 2
MCO2 × yCO /ρ
(1)
2
Accordingly, the solubility of diisooctyl sebacate in sc-CO2 was determined from the above eq 1 in this work, which was shown
Table 3. Equilibrium data for Temperature T, Pressure p, Liquid-Phase Mole Fraction x1, Supercritical-Phase Mole Fraction y1, for the System CO2 (1) + Diisooctyl Sebacate (2)a
a
T/K
P/MPa
x1
SD/%
y1
SD/%
T/K
P/MPa
x1
SD/%
y1
SD/%
313.2 313.2 313.2 313.2 313.2 313.2 313.2 343.2 343.2 343.2 343.2 343.2 343.2 343.2
7.26 8.18 9.00 10.66 12.00 13.08 13.96 7.26 8.38 9.68 11.58 13.00 14.62 15.82
0.4415 0.4724 0.4988 0.5616 0.6292 0.6808 0.7351 0.4029 0.4261 0.4543 0.5141 0.5613 0.6243 0.6902
0.51 0.56 0.49 0.47 0.56 0.42 0.44 0.50 0.53 0.50 0.39 0.46 0.57 0.61
0.9973 0.9961 0.9950 0.9935 0.9922 0.9908 0.9890 0.9981 0.9972 0.9960 0.9946 0.9933 0.9917 0.9901
0.53 0.51 0.55 0.50 0.50 0.56 0.56 0.47 0.46 0.56 0.50 0.39 0.42 0.56
328.2 328.2 328.2 328.2 328.2 328.2 328.2 358.2 358.2 358.2 358.2 358.2 358.2 358.2
7.24 9.18 10.02 11.24 12.22 14.08 15.42 7.28 8.62 9.98 11.08 12.98 14.24 15.96
0.4228 0.4623 0.4943 0.5372 0.5814 0.6605 0.7436 0.3942 0.4157 0.4432 0.4671 0.5095 0.5524 0.6263
0.57 0.46 0.47 0.56 0.42 0.61 0.47 0.55 0.50 0.50 0.44 0.49 0.46 0.57
0.9976 0.9959 0.9951 0.9939 0.9928 0.9910 0.9892 0.9986 0.9975 0.9966 0.9956 0.9943 0.9931 0.9914
0.42 0.46 0.50 0.51 0.44 0.50 0.49 0.50 0.61 0.49 0.44 0.57 0.47 0.50
Standard uncertainties u are u(T) = 0.24 K, u(p) = 0.02 MPa.
SD(x) =
SD(y) =
1 n−1
n
∑ (xi − x ̅)2 i
1 n−1
n
∑ (yi − y ̅ )2 i
C
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Table 4. Equilibrium Solubility Data for the System sc-CO2 (1) + Diisooctyl Sebacate (2) at 313.2K, 328.2K, 343.2 K, and 358.2 K. y1: Experimental Data Are Reported as CO2 mole fraction in sc-CO2 phase.Solubility of diisooctyl sebacate in the sc-CO2 phase (S: grams of diisooctyl sebacate per liter of sc-CO2)
b
T/K
P/MPa
y1
ρ(CO2)b/g/L
S/g/L
T/K
P/MPa
y1
ρ(CO2)b/g/L
S/g/L
313.2 313.2 313.2 313.2 313.2 313.2 313.2 343.2 343.2 343.2 343.2 343.2 343.2 343.2
7.26 8.18 9.00 10.66 12.00 13.08 13.96 7.26 8.38 9.68 11.58 13.00 14.62 15.82
0.9973 0.9961 0.9950 0.9935 0.9922 0.9908 0.9890 0.9981 0.9972 0.9960 0.9946 0.9933 0.9917 0.9901
214.11 299.59 483.10 667.52 717.22 744.36 762.12 150.91 186.05 234.27 323.01 401.35 487.54 540.31
5.6209 11.3741 23.5404 42.3486 54.6735 67.0215 82.1959 2.7857 5.0656 9.1232 17.0055 26.2511 39.5638 52.3876
328.2 328.2 328.2 328.2 328.2 328.2 328.2 358.2 358.2 358.2 358.2 358.2 358.2 358.2
7.24 9.18 10.02 11.24 12.22 14.08 15.42 7.28 8.62 9.98 11.08 12.98 14.24 15.96
0.9976 0.9959 0.9951 0.9939 0.9928 0.9910 0.9892 0.9986 0.9975 0.9966 0.9956 0.9943 0.9931 0.9914
171.91 266.29 326.25 436.98 520.55 621.07 665.37 136.71 171.27 210.88 246.66 316.28 366.26 434.07
4.0104 10.6305 15.5779 26.0063 36.6069 54.6939 70.4421 1.8585 4.1623 6.9763 10.5705 17.5816 24.6760 36.5122
Reference18; http://webbook.nist.gov/chemistry/fluid.
isothermal conditions while the effect of temperature showed different trends depending on the pressures. An undegraded triglycerides fraction was recovered from the waste frying oil by supercritical CO2 extraction; the maximum extraction yields obtained about 70 % under investigated pressure and temperature, indicating supercritical carbon dioxide extraction technology is feasible for the recycle of waste frying oil.20 3.2. Solubility Models. On the one hand, the resulting semiempirical density-based models use only available variables such as temperature, pressure, and density of pure supercritical fluids instead of solute thermophysical data such as critical properties, acentric factor, solute molar volume, and sublimation pressure.21 On the other hand, regarding the calculation process, the density-based models are much easier than the equations of state models. Therefore, in this research, three density-based models (Chrastil, del Valle and Aguilera, Adachi and Lu models) were employed to correlate the solubility behavior of diisooctyl sebacate in sc-CO2. The Chrastil equation22 is the classical density-based model for correlating the solubility behavior of oils and considers a linear correlation between the solute solubility, solvent density, and the extraction temperature, as expressed in eq 2: a ln S = k ln ρ + +b (2) T
Figure 2. CO2 mole fraction in sc-CO2 phase.
where S is the solubility of diisooctyl sebacate (g/L), is the density of sc-CO2 (g/L) at the operating condition and T is the temperature (K), constants a represent the thermal effects involved in the solubilization process, while constant b relates to the solute and the solvent molecular weights. The association number k is the slope of the linear correlation which represents the average number of CO2 molecules in the solvated complex. The del Valle and Aguilera equation23 is a modification of the Chrastil’s equation that was considered the change of the enthalpy of vaporisation with temperature, as shown in the eq 3:
Figure 3. Solubility of diisooctyl sebacate in sc-CO2.
than the solute’s volatility and diffusibility.19,20 The maximum solubility of 82.1959g/L was obtained under the measured condition: T = 313.2 K, P = 13.96 MPa under the research conditions in this work. The solubility behavior of this work showed the same trends with previous researches; for example, according to Kitchens et al.,10 supercritical CO2 was used to extract the remaining fat from rendered poultrymeal, and fat solubility increased with pressure but decreased with temperature. According to Rincón et al.20 and Zhao et al.,21 the solubility of a solute in supercritical CO2 increased with increasing pressure under
ln S = k ln ρ +
a b + 2 +c T T
(3)
where S is the solubility of diisooctyl sebacate (g/L), ρ is the density of sc-CO2 (g/L) at the operating condition, and T is the temperature (K); constants a and b represent the thermal D
DOI: 10.1021/acs.jced.5b00457 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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effects involved in the solubilization process, while constant c relates to the solute and the solvent molecular weights, and k represents the same parameter proposed by Chrastil. To improve the results over the Chrastil model, the Adachi and Lu model24 was proposed with an association number to a second-order polynomial of the supercritical fluid density. Adachi and Lu have changed the association number to a second-order polynomial of the supercritical fluid density; therefore, they proposed another equation as expressed below eq 4, (5): a ln S = (e0 + e1ρ + e 2ρ2 ) ln ρ + +b (4) T k = e0 + e1ρ + e 2ρ2
(5)
Figure 5. Logarithmic relationship between diisooctyl sebacate solubility in sc-CO2 and the density of pure sc-CO2 with the del Valle and Aguilera model.
where S is the solubility of diisooctyl sebacate (g/L), ρ is the density of sc-CO2 (g/L) at the operating condition, and T is the temperature (K), while the association number K is the exponent of the density (referred to as k in the original Chrastil equation). The constant a is dependent on the heats of solvation and vaporization of solute, and the constant b is dependent on the molecular weights of carbon dioxide and solute. To provide a reliable accuracy criterion to compare the accuracy of the models, the average absolute relative deviation (AARD) was calculated using eq 6: AARD% =
1 n
∑
Scal − Sexp Sexp
100 (6)
Figure 4, Figure 5, and Figure 6 compare the calculated solubility results of diisooctyl sebacate in sc-CO2 using the
Figure 6. Logarithmic relationship between diisooctyl sebacate solubility in sc-CO2 and the density of pure sc-CO2 with Adachi and Lu model.
Table 5. Fitting Constants and the Average Absolute Relative Deviations Obtained for Chrastil Model T/K
k
a
b
AARD%
313.2 328.2 343.2 358.2
1.9506 2.0358 2.2173 2.4950
−1527.9390 −1651.1820 −2180.6600 −2395.0252
−3.8817 −4.0341 −3.6453 −4.8030
10.67 4.68 5.12 7.94
According to Li et al.,25 the AARD value of the Chrastil equation for the solubilities of jatropha oil in sc-CO2 under the experimental conditions is 10.1 %, which indicates that all of the three solubility models in this research can correlate the experimental data well. In addition, a comparison of the simulating effect of the selected three solubility models for measured data showed that Adachi and Lu model > del Valle and Aguilera model > Chrastil model. Accordingly, the solubility of the lubricant oil (diisooctyl sebacate) in sc-CO2 can be most perfectly fit as the nonlinear function, Adachi and Lu model. Despite these semiempirical density based models being considered to have less physical significance than the equation of state model, these models are concise methods to correlate solubility behavior of a solute in supercritical fluid. In addition, the critical or thermophysical properties of the solute and the supercritical fluid do not need to be estimated or calculated by these semiempirical density-based models.19,21
Figure 4. Logarithmic relationship between diisooctyl sebacate solubility in sc-CO2 and the density of pure sc-CO2 with the Chrastil model.
Chrastil, del Valle and Aguilera, and Adachi and Lu equations against the experimentally measured values, respectively. It can be graphically displayed that the solubility curves of the three investigated density-based correlations are in almost satisfactorily agreement with the experimental values. The constants for the Chrastil, del Valle and Aguilera, and Adachi and Lu models are given in Table 5, Table 6, Table 7 with their AARD for the pressures under the isothermal state. As shown in these Tables, the AARD values for the Chrastil model range from 4.68% to 10.67%, the values for the del Valle and Aguilera model range from 4.53% to 9.04%, and the values for the Adachi and Lu model range from 0.72% to 3.31%, respectively. E
DOI: 10.1021/acs.jced.5b00457 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 6. Fitting Constants and the Average Absolute Relative Deviations Obtained for del Valle and Aguilera Model T/K
k
a
b
c
AARD%
313.2 328.2 343.2 358.2
1.9506 2.0358 2.2173 2.4950
−1161.3057 −1207.6073 −1106.0420 −1399.4043
−394840.9542 −398221.3176 −516871.5933 −358286.6128
−1.0272 −1.6886 −2.3882 −4.7901
9.04 4.53 5.03 7.95
Table 7. Fitting Constants and the Average Absolute Relative Deviations Obtained for Adachi and Lu Model T/K
e0
e1
e2
a
b
AARD%
313.2 328.2 343.2 358.2
6.6273 3.9869 5.0904 6.2835
−0.0039 −0.0018 −0.0029 −0.0043
2.5653·10−6 1.3717·10−6 2.3623·10−6 3.9350·10−6
−3711.5014 −36037.7595 −5870.6465 −4925.4072
18.2137 92.0786 −5.4913 −13.9927
3.31 0.91 0.72 1.81
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4. CONCLUSIONS We have studied the equilibrium solubility of diisooctyl sebacate, one of the synthetic ester lubricant oils, in supercritical carbon dioxide at temperatures of 313.2 K, 328.2 K, 343.2 K, and 358.2 K under pressures ranging from 7.24 MPa to 15.96 MPa. The solubility of the lubricating oil decreased with increasing temperature at the constant pressure while increasing with increasing pressure under isothermal conditions. The equilibrium solubilities data were correlated with the three selected density-based equations (Chrastil model, del Valle and Aguilera model, Adachi and Lu model). All of the three equations give satisfactory results. Furthermore, it was shown that the Adachi and Lu model can be best applied for modeling the sc-CO2 extraction of diisooctyl sebacate. The highest oil solubility in sc-CO2 was reached at 82.1959 g/L at 313.2 K and 13.96 MPa under research conditions. The supercritical CO2 extraction technology is highly efficient, green, and economical, and seems to be a potential way to separate fresh lubricant oil from waste lubricant oil.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Funding
The authors gratefully acknowledge the financial and other support provided by the Natural Science Foundation of Chongqing (CSTC2014jcyjA90013). Notes
The authors declare no competing financial interest.
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DOI: 10.1021/acs.jced.5b00457 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.jced.5b00457 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
