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Original article
06 2022
:15;
103821
doi:
10.1016/j.arabjc.2022.103821

Experimental analysis and thermodynamic modelling of lenalidomide solubility in supercritical carbon dioxide

Department of Chemical Engineering, Faculty of Engineering, University of Kashan, 87317-53153 Kashan, Iran
South Zagros Oil and Gas Production, National Iranian Oil Company, 7135717991 Shiraz, Iran
Department of Chemical Engineering, Islamic Azad University, Robat Karim Branch, 37616-16461 Robat Karim, Iran
Department of Chemical Engineering, Tarbiat Modares University, P.O. Box: 14115-111, Tehran, Iran
Department of Nanotechnology and Advanced Materials, Materials and Energy Research Center, 14155-4777 Karaj, Iran
Laboratory of Computational Modeling of Drugs, South Ural State University, 76 Lenin Prospekt, 454080 Chelyabinsk, Russia

⁎Corresponding author at: Department of Chemical Engineering, Tarbiat Modares University, P.O. Box: 14115-111, Tehran, Iran. n.saadati@modares.ac.ir (Nedasadat Saadati Ardestani)

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

Abstract

  • Lenalidomide (LND) solubility in supercritical CO2 (sc-CO2) was measured for the first time.

  • Solubility data were correlated by different density-based models.

  • Experimental data was also correlated by Modeified Wilson and SRK models.

  • The accuracy of the models was evaluated by statistical criteria (AARD%), (Radj).

  • Thermodynamic enthalpies of Lenalidomide were estimated.

Abstract

Reduction of the size of pharmaceutical particles to micro/nano scale is an approved strategy to enhance their dissolution rate at decremented side effects. Production of drug micro/nanoparticles via a supercritical carbon dioxide (sc-CO2)- based process requires accurate data on the drug solubility in sc-CO2. In this study, the solubility of Lenalidomide (LND), an anti-cancer, was experimentally determined in sc-CO2 at various temperatures (308–338 K) and pressures (120–300 bar). Furthermore, the obtained solubility data were correlated by different theoretical methods. LND solubility, in terms of mole fraction, was obtained in the range of 0.02 × 10−4–1.08 × 10−4 depending on the conditions. The empirical models with different adjustable parameters, Soave–Redlich–Kwong equation of state (SRK-EoS) with two parameters van der Waals (vdW2) mixing rule, and expanded liquid theory (modified Wilson’s model) were applied for experimental data correlation. According to the results, modified Wilson’s model can correlate LND solubility in sc-CO2 with high accuracy. However, the SRK-EoS did not show acceptable accuracy in the correlation of LND solubility in sc-CO2. Among the empirical models, Alwi and Garlapati, Sung and Shim, Ch and Madras, Hozhabr et al., Garlapati and Madras, Keshmiri et al., Sparks et al., Reddy and Garlapati, Bian et al. (2011) and Belghait et al. showed Radj values higher than 0.99 and produced the best correlation with 3,4, 5, 6 and 8 adjustable parameters, respectively. Moreover, the approximate values of total mixing heat ( Δ H total ) as well as vaporization ( Δ H vap ), and solvation ( Δ H sol ) enthalpies were computed.

Keywords

Lenalidomide
Solubility
Supercritical carbon dioxide
Empirical model
Modified Wilson’s model
Soave-Redlich-Kwong (SRK) equation of state
PubMed

Nomenclature

a 0 - a 10

Adjustable parameters of empirical model

AARD%

Average absolute relative deviation

a ( T )

Energy parameter of the cubic EoS (Nm4 mol−2)

b

Volume parameter for equations of state (m3 mol−1)

f2L

The fugacity of the solid solute in the supercritical phase

f2s

The fugacity of the solute in the solid phase

Hf

Molar heat of fusion(kJ.mol−1)

gE

Excess Gibbs free energy

kij

Binary interaction parameters in the mixing rules

lij

Binary interaction parameters in the mixing rules

MSR

Mean square regression

MSE

Mean square residual

N

Number of data points, dimensionless

Psub

Sublimation pressure (Pa)

Q

Number of independent variables

R2

Correlation coefficient

Radj

Adjusted correlation coefficient

S

Equilibrium solubility

SSE

Error sum of squares

SST

Total sum of squares

SSR

Regression sum of squares

T c

Critical temperature

vs

Solid molar volume

vdW2

Van der Waals mixing rule with two adjustable parameters

y

Mole fraction solubility

Z

Number of adjustable parameters

Greek symbols

α(Tr, ω)

Temperature-dependent function in the attractive parameter of the EoS

φ

Fugacity coefficient

ω

Acentric factor

α

Regressed parameters of Wilson’s model

β

Regressed parameters of Wilson’s model

Λ′

Regressed parameters of Wilson’s model

Λ

Adjustable parameters

γ 2

The activity coefficient of the solid solute at infinite dilution

Superscripts

cal

Calculated

exp

Experimental

i, j

Component

1

1 Introduction

With the commercial name of Revlimid, Lenalidomide (LND) (C13H13N3O3) acts as an angiogenesis inhibitor, an antineoplastic agent as well as an immunomodulatory drug. It is the first FDA-approved oral medication for the treatment of multiple myeloma, since 2004 (Li et al., 2019). In recent years, it was also approved for the treatment of Mantle Cell Lymphoma, Myelodysplastic syndromes (MDS) and deletion 5q Myelodysplastic syndromes (Attal et al., 2012). This drug also exhibited promising therapeutic effects in other hematologic disorders. However, hydrophobicity and poor solubility of LND in water hinder its penetration into tumors; i.e. low bioavailability (less than 33%) (Yang et al., 2019). Therefore, long term usage or high doses of this drug may be accompanied by severe side effects including immune system depletion, metastasis to neighboring organs, cutaneous adverse neutropenia, deep vein thrombosis, infection, and hematological cancer (Patrizi et al., 2014).

Various approaches such as salt formation, co-crystallization, amorphous solid dispersion (ASD), and particle size reduction (micronization/nanonization) have been developed in medicinal chemistry, to enhance aqueous solubility and bioavailability (Liu et al., 2016). Diverse measures have been proposed to improve the aqueous solubility of LND and therapeutic efficacy; including, co-crystallization with various substances such as urea and 3,5-dihydroxybenzoic acid (Song et al., 2014) and gallic acid (GA), formation of different LND salts including methanesulfonate (Rangineni, 2010), sulfate, hydrochloride, and hydrosulphate (Stiegel, 2011), hydrates of benzene sulfonate and p-toluene sulfonate (Eupen, 2011) and acesulfame (Chen et al., 2019), as well as LND conjugation onto polymeric nanoparticles (such as chitosan (Gomathi et al., 2014) and LND complexing with gold ions (Arib and Spadavecchia, 2020).

Among the mentioned methods, micronization/nanonization has attracted a huge deal of attention due to enhancing the surface area of drug particles and incrementing drug solubility, hence lowering drug dosage and side effects. Supercritical fluid (SCF)-based processes are green and clean technologies for micro/nanoparticles formation. Low operational temperature, high quality products with uniform morphology and narrow size distribution, and elimination or significant reduction of used organic solvents are the main advantages of these processes (Ardestani and Amani, 2021). Supercritical carbon dioxide (sc-CO2) is the most commonly used SFC due to its low price, mild critical pressure and temperature, environmental compatibility, non-exclusivity, non-toxicity and chemical stability (Sodeifian et al., 2016; Sodeifian et al., 2018; Sodeifian et al., 2019). The solubility of a drug in sc-CO2 is the essential parameter in producing fine particles. This parameter determines the feasibility of using the sc-CO2 process for the considered drug and also the role of sc-CO2 in the supercritical process (as solvent, anti-solvent or reaction media) (Amani et al., 2021). Generally, RESS-based processes can be utilized for the preparation of nanoparticles and submicron drugs with high solubility in SC–CO2. In contrast, anti-solvent processes are recommended for the preparation of materials with low solubility in SC–CO2. To this end, the solubility of solid pharmaceuticals should be estimated in SCFs to select the proper method (Ardestani and Amani, 2021; Saadati Ardestani et al., 2020). Furthermore, solubility should be determined at a wide range of pressures and temperatures for the industrial development of supercritical processes. Given this necessity, the determination of the solubility of different drugs in sc-CO2 has become one of the most interesting pharmaceutical research topics during the past two decades. In this regard, solubility of various drugs has been assessed since the beginning of 2020, among which; Chloroquine (Pishnamazi, 2021), Capecitabine (Ardestani et al., 2020), Montelukast (Sajadian et al., 2022); Azathioprine (Sodeifian, 2020), Temozolomide (Zabihi, 2021), Lornoxicam (Pelalak, 2021), Aprepitant (Sodeifian et al., 2017); Gliclazide and Captopril (Wang et al., 2021), Glibenclamide (Esfandiari and Sajadian, 2022), Decitabine (Pishnamazi et al., 2021); Tamoxifen (Pishnamazi, 2020), Busulfan (Pishnamazi, 2020), Fenoprofen (Zabihi et al., 2020), Salsalate (Zabihi, 2021), Lornoxicam (Pelalak, 2021), Tolmetin (Pishnamazi et al., 2020), Tenoxicam  (Zabihi et al., 2021); Carbamazepine (Kalikin, 2020); Sodium valproate (Sodeifian et al., 2020); Minoxidil (Sodeifian et al., 2020); Loxoprofen (Zabihi et al., 2020), Favipiravir (Sajadian et al., 2022); ipriflavone (Wang and Su, 2020), and Methylsalicylic Acid Isomers (Wang et al., 2021) can be mentioned.

However, experimental measurement of the sc-CO2 solubility of all the drugs in a wide range of pressure and temperature is costly, time-consuming, and even impossible in some cases. Therefore, several theoretical predictive models such as equation of states (EoSs), expanded liquid models and empirical models have been developed for correlating the sc-CO2 solubility of various substances at different operational conditions. EoS models (cubic and non-cubic) are one of the most popular theoretical models in which sc-CO2 is regarded as a condensed gas and the modeling is performed according to solute fugacity coefficient. Cubic EoSs can be rewritten as a cubic function of molar volume (e.g. Peng-Robinson (PR) and Soave- Redlich-Kowang (SRK)), while non-cubic models are based on statistical associating fluid theory (SAFT) (e.g. Perturbed-Chain Polar Statistical Associating Fluid Theory (PCP-SAFT)). In expanded liquid models (e.g. universal quasi-chemical (UNIQUAC) and modified Wilson's models), sc-CO2 is considered as an expanded liquid and modelling was based on the solute activity coefficient. The necessity of knowledge on the solute physicochemical properties such as acentric factor, critical pressure and temperature, sublimation pressure and its molar volume is the main challenge of EoS and expanded liquid models. These properties are usually unknown, especially for complex pharmaceutical components, and should be computed by various group contribution (GC) methods. In return, the empirical models have been developed according to linear relationship between the logarithm of solute solubility and the sc-CO2 density. These models only need to know pressure, temperature, and sc-CO2 density while their correlation accuracy is comparable to the EoSs method (Zabihi, 2021). Noteworthy, the accuracy of the proposed models could be different for each pharmaceutical component, making it impossible to specify the most accurate model for the proper correlation of the sc-CO2 solubility of all drugs (Zabihi et al., 2020). So, the correct predictive model indicating the best fitting with the experimental results was determined by comparison between the correlation and experimental results.

The sc-CO2 solubility of many drugs has been measured and correlated as a function of pressure and temperature while no report can be found on LND solubility in sc-CO2. Thus, this research is aimed to experimentally measure of LND solubility in sc-CO2 at various temperatures (308–338 K) and pressures (120–300 bar). Afterward, experimental solubility results were correlated by thirty well-known empirical density-based models, EoS model (SRK) and expanded liquid models (modified Wilson's model). The results of these models were validated by computing some statistical criteria including the average absolute relative deviation (AARD%), the adjusted correlation coefficient (Radj), and F-value.

2

2 Materials and methods

2.1

2.1 Materials

Lenalidomide (LND) (CAS No. 191732–72-6) was purchased from Abidi pharmaceutical company, with a minimum purity of 99%. Carbon dioxide (CO2), with a purity of 99.98% was provided from Oxygen Novin Co. (Shiraz, Iran). Analytical-grade methanol was provided by Merck (Darmstadt, Germany). All of these compounds were used with no additional purification.

2.2

2.2 Experimental procedure for solubility determination

The experimental setup for determining the solubility of LND in sc-CO2 is schematically depicted in Fig. 1. All the equipment, piping and connections were made from stainless steel 316 at 1/8″ in size. As can be seen in Fig. 1, after passing the CO2 gas from the molecular sieve filter (1 μm in pore size), it enters the refrigerator with an approximate temperature of −15 °C to be liquefied. The liquid CO2 was guided to the high-pressure reciprocating pump (an air-driven liquid pump, type-M64, Shineeast Co., Shandong, China), at the pressure of 60 bar (the CO2 tank pressure). Using the pressure gauge (Indumart pressure gauges, Canada), and transmitter, measurements were performed at a precision of ±1 bar. Afterward, liquid CO2 and LND (3000 mg) were homogenized with a magnetic stirrer (100 rpm) ((E-8, Alfa, D-500 180), in a cell with a capacity of 300 mL to reach an equilibrium phase. To keep the temperature at the desired level, the cell was placed in an oven equipped with a digital display whose temperature was measured with a precision of ±0.1 K. A porous filter (1 μm) was used on both sides of the cell to keep the LND in the cell and prevent its escape. CO2 was pressurized and transferred to the cell at the appropriate pressure. Based on preliminary experiments, the time required to reach the equilibrium, the static time, was considered as 120 min; after which, saturated sc-CO2 (600 μL) was introduced into the injection loop using a three-port two-position valve. By redirecting the injection valve, the loop was depressurized into the collection vial containing a certain volume of methanol (solvent). In this part, the micrometer valve was used for controlling the flow. In the final step, 1 mL of solvent was injected by an external needle-valve to wash the loop and the solution was collected in the vial. The final volume of the solution was 5 mL.

Experimental apparatus for supercritical solubility measurement.
Fig. 1
Experimental apparatus for supercritical solubility measurement.

Each experiment was carried out in triplicates and the solubility values were determined by the absorbance assays at λmax (250 nm) on a Perkin-Elmer UV–Vis spectrophotometer (LAMBDA 365, PerkinElmer-USA) with 1 cm long quartz cell. Finally, LND solubility was calculated from its concentration using the calibration curve (with a regression coefficient of 0.996) and the UV-absorbance. The values of LND solubility in sc-CO2 in terms of equilibrium mole fraction (y) and solubility (S (g L−1)) were computed at different temperatures and pressures via the equations in the literature (Saadati Ardestani et al., 2020).

The solubility measurement device was validated by evaluating the solubility of naphthalene at 308 K and different pressures and comparing them with the reports by Iwai et al.  (Iwai et al., 1991), Yamini et al. (Yamini et al., 1998) and Sodeifian et al. (Sodeifian et al., 2017), as listed in Table 1.

Table 1 Experimental solubility data of naphthalene in sc-CO2 at 308 K and comparison with the literature data.
Pressure (MPa)a Iwai et al.36 (y × 103) Yamini et al.37 (y × 103) Sodeifian et al.38 (y × 103) This work (y × 103) a
10.7 11.6 11.4 11.7 ± 0.2
13.8 14.1 15.2 14.3 14.8 ± 0.3
16.8 16.5 16.2 16.6 16.1 ± 0.3
20.4 17.6 17.4 17.7 17.9 ± 0.2
24.0 19.9 ± 0.4
Standard uncertainty u are u(P) = 0.1 MPa and relative uncertainty (ur), u (y) = 0.10.

2.3

2.3 Theoretical studies

2.3.1

2.3.1 Empirical models

Numerous empirical models have been proposed for correlating the solubility of a solid solute in sc-CO2. No need to solute properties (unlike the EoSs), simple application, and acceptable accuracy are the most important benefits, and the requirement of experimental solubility data is the only drawback of these models. Following the model proposed by Stahl et al. (Stahl et al., 1978) in 1978, several models have been developed with various adjustable parameters (in the range of 3 to 10) to enhance the correlation of experimental data.

In this research, thirty traditional empirical models are used to correlate the solubility of LND in sc-CO2, whose mathematical formulas are presented in Table 2. According to the solubility functions (Table 2), the proposed models can be classified into five groups; (i) solubility as a function of sc-CO2 density (Stahl et al., 1978), models with solubility dependency to sc-CO2 density and temperature (Chrastil, 1982; Kumar and Johnston, 1988; Andonova and Chandrasekhar, 2016; Alwi and Garlapati, 2021; Del Valle and Aguilera, 1988; Sung et al., 1999; Adachi and Lu, 1983; Garlapati and Madras, 2010; Bian et al., 2016; Sparks et al., 2008; Si-Moussa et al., 2017; Bian et al., 2011; Belghait et al., 2018; Amooey, 2014); (ii) solubility as a function of sc-CO2 density and pressure (Haghbakhsh et al., 2013); (iii) solubility as a function of pressure and temperature (Mitra and Wilson, 1991; Reddy et al., 2018; Gordillo et al., 1999; Yu et al., 1994; Reddy and Garlapati, 2019), and (iv) solubility as a function of sc-CO2 density, pressure and temperature (Bartle et al., 1991; Méndez-Santiago and Teja, 1999; Jafari Nejad et al., 2010; Ch and Madras, 2010; Hozhabr et al., 2014; Keshmiri et al., 2014; Asgarpour Khansary et al., 2015; Sodeifian et al., 2019; Jouyban et al., 2002).

Table 2 Formula of the empirical models used in this work.
Empirical models
Model Formula Reference
Stahl et al. ln y = a 0 + a 1 ln ( ρ ) (Sajadian et al., 2022)
Chrastil ln y = a 0 + a 1 ln ( ρ ) + a 2 T Δ H t = - a 2 . R (Wang and Su, 2020)
Kumar- Johnston (K-J) ln y = a 0 + a 1 ρ + a 2 T Δ H t = - a 2 . R (Wang et al., 2021)
Bartle et al. ln y . P P ref = a 0 + a 1 ( ρ - ρ ref ) + a 2 T Δ H vap = - a 2 . R (Haghbakhsh et al., 2013)
Mendez-Santiago and Teja T ln ( y . P ) = a 0 + a 1 ρ + a 2 T (Mitra and Wilson, 1991)
Andonova and Garlapati y = a 0 ρ r a 1 T r a 2 (Saadati Ardestani et al., 2020)
Alwi and Garlapati y = 1 ( ρ r T r ) exp ( a 0 + a 1 T r + a 2 ρ r ) (Iwai et al., 1991)
del Valle and Aguilera ln y = a 0 + a 1 ln ( ρ ) + a 2 T + a 3 T 2 (Yamini et al., 1998)
Sung and Shim ln y = ( a 0 + a 1 T ) ln ( ρ ) + a 2 T + a 3 (Stahl et al., 1978)
Jafari Nejad et al. ln y = a 0 + a 1 P 2 + a 3 T 2 + a 4 ln ( ρ ) (Reddy and R.S., Chandrasekhar Garlapati, , 2018)
Ch and Madras y = ( P P ref ) ( a 0 - 1 ) exp ( a 1 T + a 2 ρ + a 3 ) (Gordillo et al., 1999)
Hozhabr et al. In y = a 0 + a 1 T + a 2 ρ T - a 3 In P (Yu et al., 1994)
Mitra and Wilson ln S = a 0 ln ( P ) + a 1 T + a 2 T P + a 3 P T + a 4 (Sparks et al., 2008)
Adachi and Lu ln y = a 0 + ( a 1 + a 2 ρ + a 3 ρ 2 ) ln ρ + a 4 T (Chrastil, 1982)
Garlapati and Madras ln y = a 0 + ( a 1 + a 2 ρ ) ln ρ + a 3 T + a 4 ln ( ρ T ) (Kumar and Johnston, 1988)
Keshmiri et al. ln y = a 0 + a 1 T + a 2 P 2 + ( a 3 + a 4 T ) ln ( ρ ) (Reddy and Garlapati, 2019)
Khansary et al. ln y = a 0 T + a 1 P + a 2 P 2 T + ( a 3 + a 4 P ) ln ( ρ ) (Bartle et al., 1991)
Bian et al. (2016) ln y = a 0 + a 1 T + a 2 ρ T + a 3 + a 4 ρ ln ρ (Andonova and Chandrasekhar, 2016)
Reddy et al. y = ( a 0 + a 1 P r ) T r 2 + ( a 2 + a 3 P r ) T r + a 5 (Si-Moussa et al., 2017)
Sodeifian et al. ln y = a 0 + a 1 P 2 T + a 2 ln ( ρ T ) + a 3 ρ ln ( ρ ) + a 4 P ln ( T ) + a 5 ln ( ρ ) T (Méndez-Santiago and Teja, 1999)
Yu et al. y = a 0 + a 1 P + a 2 P 2 + a 3 P T ( 1 - y ) + a 4 T + a 5 T 2 (Belghait et al., 2018)
Gordillo et al. ln y = a 0 + a 1 P + a 2 P 2 + a 3 P T + a 4 T + a 5 T 2 (Bian et al., 2011)
Jouyban et al. ln y = a 0 + a 1 P + a 2 P 2 + a 3 P T + a 4 T P + a 5 ln ( ρ ) (Jafari Nejad et al., 2010)
Sparks et al. S ρ c = ρ r ( a 0 + a 1 ρ r + a 2 ρ r 2 ) exp ( a 3 + a 4 T r + a 5 T r 2 ) (Alwi and Garlapati, 2021)
Si-Moussa et al. ln y = a 0 + a 1 ρ + a 2 ρ 2 + a 3 ρ T + a 4 T ρ + a 5 ln ( ρ ) (Del Valle and Aguilera, 1988)
Reddy and Garlapati y = ( a 0 + a 1 P r + a 2 P r 2 ) T r + ( a 3 + a 4 P r + a 5 P r 2 ) (Amooey, 2014)
Bian et al. (2011) S = ρ a 0 + a 1 ρ + a 2 ln T exp a 3 + a 4 ρ T + a 5 (Sung et al., 1999)
Belghait et al. ln y = a 0 + a 1 ρ + a 2 ρ 2 + a 3 ρ T + a 4 T + a 5 T 2 + a 6 ln ( ρ ) + a 7 T (Adachi and Lu, 1983)
Amooey ln y = ( a 0 + a 1 ρ + a 1 ρ 2 + a 3 ln ( T ) + a 4 ( ln T ) 2 1 + a 5 ρ + a 6 ln T + a 7 ( ln T ) 2 + a 8 ln T ) (Garlapati and Madras, 2010)
Haghbakhsh et al. y = 10 - 5 ( a 0 + a 1 P + a 2 ρ + a 3 P 2 + a 4 ρ 2 + a 5 P ρ + a 6 P 3 + a 7 ρ 3 + a 8 P ρ 2 + a 9 P 2 ρ (Bian et al., 2016)

In these models, y and S represent the equilibrium mole fraction and solubility of the solute (kg m−3), ρ, ρref and ρr (=ρ/ρc) also denote the sc-CO2 density, the reference density (700 kg m−3) and reduced density in which ρc is the sc-CO2 critical density (467.6 kg m−3), respectively. T and Tr (=T/Tc) are temperature (K) and reduced temperature in which Tc is the sc-CO2 critical temperature (304 K), P, Pref, and Pr (=P/Pc) are pressure (bar), reference pressure (1 bar), and reduced pressure in which Pc is the sc-CO2 critical pressure (73.8 bar).

Empirical density-based models rely on simple error minimization and their adjustable parameters can be optimized through the simulated annealing (SA) algorithm in MATLAB software.

2.3.2

2.3.2 Equation of state-based (EOS) model (Soave- Redlich-Kowang (SRK))

Equality of the solute fugacity coefficient in the two phases (solvent (1) - solute (2)) is the vital condition to achieve equilibrium solubility. Equilibrium solute solubility in sc-CO2 (y2) can be expressed by Eq. (1), through considering some assumptions such as the insolubility of sc-CO2 in the solute phase, the purity and incompressibility of the solute, no dependency of the solute molar volume to pressure and very little solute vapor pressure.

(1)
y 2 = P 2 sub ( T ) P φ 2 sat , s ( T ) φ 2 ( T , P , y ) exp ν 2 s ( P - P 2 sub ( T ) ) R T where P, T, and R are pressure (MPa), temperature (K) and gas constant (8.314 J mol−1 K−1), respectively. v 2 s (m3 mol−1) denotes the solute molar volume and P 2 sub T is the solute sublimation pressure, estimated by the Immirzi method (Immirzi and Perini, 1977) and Ambrose-Walton corresponding states method (Poling, 2001), respectively (Table 3). φ 2 sat , s ( T ) also stands for the solute saturation fugacity coefficient which can be assumed as unity for solutes with very small sublimation pressures. ϕ 2 ( T , P , y ) is the solute fugacity coefficient in the sc-CO2 phase was computed by SRK-EoS (Soave, 1972); combined with the van der Waals mixing rule. Using this EoS, ϕ 2 ( T , P , y ) was calculated by the following equation (Amani and Saadati Ardestani, 2021):
(2)
RT ln φ i = - R T ln Z + V P n i T , V , n j n i - RT V d V
where Z (=PV/RT), ni, and V are the compressibility factor, the moles number of species i and the sc-CO2 molar volume, respectively.
Table 3 Molecular weight and chemical structure along with estimated boiling point (Tb), melting point (Tm), critical temperature (Tc), critical pressure (Pc), acentric factor (ω), solute molar volume (vs), and sublimation pressure (Psub) of LND.
Component MWa (kg kmol−1) Tbb (K) Tmb (K) Tcb (K) Pc b (bar) ωc v s d (cm3 mol−1) T (K)
308 318 328 338
Psub × 106(Pa)e
LND 259.25 663.20 560.65 1006.12 36.54 0.64 166.40 1.13 4.31 14.98 43.39
Molecular weight.
Marrero - Gani method (Asgarpour Khansary et al., 2015).
Constantinou - Gani method (Sodeifian et al., 2019).
Immirzi method (Ch and Madras, 2010).
Ambrose–Walton corresponding states method (Hozhabr et al., 2014).

The relations of SRK-EoS is as follows:

(3)
P = RT ν - b - a ( T ) ν ( ν + b )

Here, a(T) and b, can be defined by the following relations for a single component:

(4)
a ( T ) = 0.42747 R 2 T c 2 P c × α ( T r , ω ) & α ( T r , ω ) = [ 1 + m ( 1 - T r 0.5 ) ] 2 & m = 0.480 + 1.574 ω - 0.176 ω 2 b = 0.08664 R T c P c

In this research, critical pressure (Pc), critical temperature (Tc), boiling point (Tb) and melting point (Tm) of LND were computed using Marrero and Gani contribution method (Marrero and Gani, 2001). Also, LND acentric factor (ω) was estimated by Constantinou - Gani method (Constantinou and Gani, 1994). All the mentioned physical and critical properties of LND are reported in Table 3.

For the binary system (LND/sc-CO2), a(T) and b can be defined by the van der Waals (vdW) mixing rule considering two parameters (Van der Waals, 1873):

(5)
a m = j y i y j a i a j ( 1 - k ij )
(6)
b m = j y i y j ( b i + b j ) 2 ( 1 - l ij )
where l ij and k ij are the binary interaction parameters which were optimized by minimizing the AARD% value, using the simulated annealing (SA) algorithm (Sodeifian et al., 2017).

2.3.3

2.3.3 Expanded liquid theory (Wilson’s model)

Due to the relatively high density of supercritical fluids and their proximity to liquids density, they can be considered as an expanded liquid (Higashi et al., 2001). In this case, equality of the fugacity of the solute in the solid phase ( f 2 S ) with the fugacity of the solute in the SCF (liquid) phase ( f 2 L = S C F ) was used for the thermo-dynamical description of the equilibrium state between the solute and sc-CO2. Regarding the negligible solubility of sc-CO2 in the pure solid phase, the term of f 2 S can be considered equal to the fugacity of the pure solid solute ( f 2 0 S ) . The fugacity of the solute in the liquid phase can be expressed based on the solute activity coefficient:

(7)
f 2 L = γ 2 y 2 f 2 0 L which can be rewritten as:
(8)
f 2 0 S = γ 2 y 2 f 2 0 L
where γ 2 , y 2 and f 2 0 L are the solute activity coefficient, the solute mole fraction (solubility) and the fugacity of the pure solid solute in the expanded liquid phase, respectively. Prausnitz et al. (Prausnitz et al., 1998) defined a relationship between the f 2 0 L and f 2 0 S as:
(9)
ln f 2 0 S f 2 0 L = - Δ H 2 f R 1 T - 1 T m - Δ c p RT T - T m T + Δ c p R l n T T m
where Δ H 2 f is the LND heat of fusion which was calculated via the Marrero and Gani group contribution method, as 46.87 kJ mol−1. Also, T m and Δ c p are the melting point and the variation of heat capacity of the solute, respectively. Ignoring Δ c p and considering the condition of infinite dilution due to very poor solubility of the solid solute in sc-CO2 (Nasri et al., 2013), the solute solubility ( y 2 ) can be obtained using a combination of Eqs. (8) and (9), in which γ 2 γ 2 :
(10)
y 2 = 1 γ 2 exp - Δ H 2 f R 1 T - 1 T m

Here, γ 2 is the activity coefficient of the solid solute at the infinite dilution condition, which in this study was determined using the modified Wilson’s model (Nasri, 2018). This model is somewhat based on Flory’s theory (combinatorial contribution) with the following its usual form according to excess Gibbs energy (GE):

(11)
G E RT = - y 1 ln y 1 + y 2 Λ 12 - y 2 ln y 1 Λ 21 + y 2

Here, Λ12 and Λ21 are the adjustable parameters which depend on the molar volume of the pure sc-CO2 ( υ 1 ) and the solid solute ( υ 2 ) and also to characteristic energy differences as:

(12)
Λ 12 υ 2 υ 1 exp - λ 12 - λ 11 RT
(13)
Λ 21 υ 1 υ 2 exp - λ 21 - λ 22 RT

In the above relations, λ is the interaction energy between the specified species in the subscripts (sc-CO2 (1) and solid solute (2)) (Prausnitz et al., 1998). After differentiation of the excess Gibbs energy function (Eq. (11)) and rearrangement of the equation, the solute activity coefficient ( γ 2 ) can be expressed by:

(14)
ln γ 2 = - ln y 2 + y 1 Λ 21 - y 1 Λ 12 y 1 + y 2 Λ 12 - Λ 21 y 2 + y 1 Λ 21

According to Assael et al. (Assael et al., 1996), for infinite dilution, the above relation can be summarized:

(15)
ln γ 2 = 1 - Λ 12 - ln Λ 21

Regardless of the terms of λ11 and λ22 at the infinite dilution condition, (Eq. (12)) and (Eq. (13)) can be written in reduced forms as:

(16)
Λ 12 = υ 2 ρ c 1 ρ r exp - λ 12 T r
(17)
Λ 21 = 1 υ 2 ρ c 1 ρ r exp - λ 21 T r
where ρ r ( = ρ ρ cr ) is the reduced density of the sc-CO2 and ρ cr is its critical density. Additionally, λ ' 12 ( = λ 12 R T cr ) and λ ' 21 = λ R T cr are the dimensionless interaction energies. Nasri (Nasri, 2018) applied a simple correlation for expressing the molar volume υ 2 , as a linear function of the reduced density:
(18)
υ 2 = α ρ r + β

Accordingly, the Eqs.16 and 17 become:

(19)
Λ 12 = α ρ r + β ρ c 1 ρ r exp - λ 12 T r
(20)
Λ 21 = 1 α ρ r + β ρ c 1 ρ r exp - λ 21 T r
where α , β , λ ' 12 and λ ' 21 are the model parameters obtained via regression.

The accuracy and precision of the applied models in correlate the sc-CO2 solubility of solids were assessed by the statistical criteria including the AARD%, Radj and F-value, as follows (Jouyban et al., 2002):

(21)
AARD % = 1 N - Z i = 1 n ( y i , c a l - y i , exp y i , exp ) × 100 % where ycal and yexp stand for computational and experimental solubility values in terms of solute mole fraction and N is the number of data points for each set.
(22)
R adj = R 2 - ( Q ( 1 - R 2 ) / ( N - Q - 1 ) )

Here, Q is the number of independent variables of each model and R2 indicates the correlation coefficient which can be calculated by the following equation:

(23)
R 2 = 1 - S S E S S T

In this relation, SSE and SST are the error and total sum of squares, respectively.

The parameter of F-value indicates the capability of the model in fitting the experimental data:

(24)
F - v a l u e = S S R / Q S S E / ( N - Q - 1 ) = M S R M S E where SSR stands for the regression sum of squares; MSR and MSE represent the mean square regression and the mean square residual, respectively. F-value is distributed as an F statistic function with Q and N-Q-1 degrees of freedom (Montgomery, 2012).

3

3 Results and discussions

3.1

3.1 Experimental solubility determination

The experimental solubility of LND in sc-CO2 was determined in terms of equilibrium mole fraction (y) at different temperatures (308, 318, 328, and 338 K) over a pressure range of 120–300 bar. Each experiment was repeated three times and the mean values with a relative standard deviation of less than 3% were reported in Table 4. Sc-CO2 density was obtained from the NIST chemistry web-book (http://webbook.nist.gov/chemistry). Furthermore, equilibrium solubility, S, of LND in sc-CO2 was also computed as presented in Table 4.

Table 4 Solubility data of LND in sc-CO2 at different temperatures (T) and pressures (P).
T (K) a P (bar) a ρ (kg m—3) b y × 104c Standard deviation of the mean, SD ( y ¯ ) × (1 0 4) Expanded uncertainty × 104 S × 10 (g/l) d
308 120 768.42 0.17 0.0002 0.011 0.7704
150 816.06 0.22 0.0042 0.016 1.0596
180 848.87 0.31 0.0051 0.060 1.5526
210 874.40 0.36 0.0075 0.052 1.8567
240 895.54 0.45 0.0067 0.082 2.3765
270 913.69 0.56 0.0105 0.033 3.0168
300 929.68 0.70 0.0085 0.079 3.8354
318 120 659.73 0.09 0.0009 0.037 0.3506
150 743.17 0.17 0.0021 0.064 0.7458
180 790.18 0.30 0.0048 0.124 1.3987
210 823.71 0.39 0.0052 0.098 1.8949
240 850.10 0.51 0.0091 0.148 2.5567
270 872.04 0.67 0.0086 0.057 3.4449
300 890.92 0.83 0.0107 0.113 4.3582
328 120 506.85 0.04 0.0008 0.029 0.1201
150 654.94 0.14 0.0023 0.017 0.5415
180 724.13 0.31 0.0056 0.123 1.3246
210 768.74 0.44 0.0090 0.129 1.995
240 801.92 0.58 0.0103 0.094 2.7426
270 828.51 0.80 0.0099 0.119 3.9077
300 850.83 0.94 0.0189 0.079 4.7137
338 120 384.17 0.02 0.0032 0.327 0.0456
150 555.23 0.10 0.0019 0.109 0.3285
180 651.18 0.32 0.0063 0.058 1.2302
210 709.69 0.52 0.0096 0.109 2.1768
240 751.17 0.72 0.0136 0.049 3.1888
270 783.29 0.93 0.0153 0.100 4.2939
300 809.58 1.08 0.0129 0.122 5.1532
Standard uncertainty u are u(T) = 0.1 K; u(P) = 1 bar; ur(ρ) = 0.002. Also, standard uncertainties are obtained below 3% for mole fractions and solubilities.
Values of sc-CO2 density (ρ) were obtained from NIST web-book (http://webbook.nist.gov/chemistry).
y is equilibrium mole fraction of LND in sc-CO2.
S is equilibrium solubility of LND in sc-CO2.

Based on Table 4, the maximum solubility of LND in sc-CO2 is 1.08 × 10−4 in terms of equilibrium mole fraction, which was achieved at the highest temperature and pressure (338 K and 300 bar). The influence of temperature and pressure on LND solubility in sc-CO2 can be analyzed in Fig. 2. Increasing the sc-CO2 pressure/density at a constant temperature enhanced the solubility in sc-CO2, which was intensified at higher temperatures. Reducing the intermolecular distance of CO2 molecules and increasing their density at higher pressures led to stronger LND (solute)/sc-CO2 (solvent) interactions, improving the solvation power of sc-CO2 (Dong et al., 2010). However, the effect of temperature on solute solubility in sc-CO2 is more complex, which can be explained according to its inverse effect on two competing parameters of solute vapor pressure (volatility) and sc-CO2 density (solvency power). Temperature elevation had a positive effect on solute solubility while reducing the second one and limiting the solubility. This opposite trend was usually demonstrated by the presence of a crossover point which is around 18 MPa for the LND/sc-CO2 binary system (Fig. 2b). At pressures lower than this point, the effect of sc-CO2 density is dominant and temperature increment declined the solubility. However, at higher pressures, the sensitivity of sc-CO2 density to temperature got lower, and solute volatility was the determinant parameter. Therefore, temperature increment above the crossover pressure enhanced the solubility ( y 338 y 328 y 318 y 308 ). The dual influence of temperature on the solubility of different solutes in sc-CO2 was previously reported as well (Sodeifian et al., 2018; Jin et al., 2014).

LND solubility at various temperatures vs. (a) sc-CO2 density and (b) pressure.
Fig. 2
LND solubility at various temperatures vs. (a) sc-CO2 density and (b) pressure.

3.2

3.2 Correlation of solubility data

Due to the high time and cost required for solubility correlation, many theoretical models have been proposed. As previously mentioned, LND solubility in sc-CO2 was correlated using common empirical models, equation of state (SRK-EoS), and modified Wilson’s model.

3.2.1

3.2.1 Empirical (Density-based) models

In this study, thirty empirical models were applied for correlating the experimental solubility data of LND in sc-CO2 (Table 2). Obtained solubility values of these models were compared with the experimental data and the results were presented in terms of AARD%, Radj and F-value. The adjustable parameters along with AARD%, Radj and F-value of each empirical model are reported in Table 5. These models were compared in terms of Radj value in the range of 0.90 to 1.0, as shown in Fig. 3. Models proposed by Alwi and Garlapati, Sung and Shim, Ch and Madras, Hozhabr et al., Garlapati and Madras, Keshmiri et al., Sparks et al., Reddy and Garlapati, Bian et al. (2011) and Belghait et al. offered Radj value above 0.99. Among these, Keshmiri et al. model with the highest Radj of 0.995 and low AARD% value of 8.535 and the highest F-value of 553.991 showed the smallest deviation from the experimental data. After that, Bian et al. (2011) model (AARD% = 7.781) and Reddy and Garlapati model (AARD% = 10.589) with Radj values of 0.994 represent high correlation accuracy. Unexpectedly, the Haghbakhsh et al. model with the highest number of adjustable parameters did not represent an acceptable performance (AARD% = 17.47, Radj = 0.857). Moreover, the solubility values correlated via the best fitting models with different numbers of adjustable parameters were compared with the experimental findings in Fig. 4.

Table 5 Adjustable parameters, AARD%, Radj and F-value of the (LND/sc-CO2) binary system achieved various empirical models.
Model Adjustable parameters AARD(%) Radj F-value
a 0 a 1 a 2 a 3 a 4 a 5 a 6 a 7 a 8 a 9
Stahl et al. −9.402 4.297 47.730 0.128 1.224
Chrastil 9.283 6.463 −5.747e + 3 15.093 0.983 263.918
Kumar and Johnston 0.594 9.177 −5.801e + 3 9.076 0.990 443.568
Bartle et al. 9.631e + 3 13.744 −8.357e + 3 16.409 0.982 249.423
Mendez-Santiago and Teja
Andonova and Garlapati
−1.158e + 4
1.346e + 13
0.417e + 4
6.480
20.901
17.890

-

-

-

-

-

-

-
11.867
14.620
0.986
0.98
336.071
263.97
Alwi and Garlapati −5.555 −20.589 5.025e3 8.210 0.991 498.26
del Valle and Aguilera 73.310 6.531 −47149.226 6.683e + 6 12.738 0.979 159.949
Sung and Shim 3.089 −3734.650 –23.748 9921.15 11.268 0.993 515.400
Jafari Nedjad et al. −16.307 6.968e-7 6.817e-4 5.247 9.886 0.987 269.413
Ch and Madras 1.314 −5.339 8.255 −1.789 8.525 0.992 408.803
Hozhabr et al. 6.460 −7881.083 2822.879 −0.170 7.998 0.993 513.477
Mitra and Wilson 8.660 2.65e-2 7.19e-5 −51.758 36.237 0.968 102.577
Adachi and Lu 9.804 1.934 11.798 −4.692 −5800.866 7.789 0.988 238.143
Garlapati and Madras
Keshmiri et al.
−231.566
1.366
222.734
−3370.615
7.938
5.486e-6
−5228.331
−18.532
2.953
7787.419

-

-

-

-

-
8.037
8.535
0.991
0.995
306.508
553.991
Khansary et al. −3089.229 −7.56e-4 2.585e + 3 6.343 −0.0156 9.711 0.990 271.296
Bian et al. (2016) 10.248 −5861.46 −36.812 2.975 7.793 8.108 0.988 239.967
Reddy et al. (2018) 0.00145 0.000202 −0.00364 −0.000186 0.00218 12.412 0.985 174.016
Sodeifian et al. −27.75 −0.012 2.414 −3.286 4.57e-3 242.495 11.450 0.990 231.4
Yu et al. 1.393e-5 −3.881e-8 2.474e-10 1.14e-9 4.031e-9 −5.11e-10 19.413 0.926 28.115
Gordillo et al. 3.484 −0.0748 −6.318e-5 3.546e-4 −0.0397 −6.054e-5 19.615 0.961 62.274
Jouyban et al. 0.151 −13.317 −2.37e-5 6.098e-5 −0.0835 11.273 11.836 0.990 238.13
Sparks et al. 2.309 10.820 −1.92e5 23.57 –22.35 1.127 8.330 0.993 330.33
Si-Moussa et al.
Reddy and Garlapati
−15.335
8.766e-5
−8.059
1.16–4
−4.377
6.07e-5
0.0435
6.918e-5
0.0165
1.30e-4
14.814
6.11e-5

-

-

-

-
10.115
10.589
0.984
0.994
146.014
353.960
Bian et al. (2011) −20.634 −2.146 116.745 −9.455e3 4.196e3 16.837 7.781 0.994 430.118
Belghait et al. −25.513 0.264 4.248 1.829ee4 0.0196 6.224e5 1.98 26.506 7.516 0.991 195.48
Amooey −8.75e15 −1.824e15 8.547e14 1.657e14 −3.96e34 −1.920e14 −1.60e14 4.33e13 7.247e12 12.180 0.979 70.317
Haghbakhsh et al. 5.854 −0.238 25.612 7.32e4 −103.85 0.471 6.22e6 15.85 0.694 −5e-3 17.470 0.857 8.48
Comparison the empirical models for correlating the solubility of LND in sc-CO2 in terms of Radj.
Fig. 3
Comparison the empirical models for correlating the solubility of LND in sc-CO2 in terms of Radj.
Comparison of experimental (points) and calculated (line) solubility of LND in the sc-CO2: a) Alwi and Garlapati, b) Hozhabr et al., c) Keshmiri et al., d) Bian et al., e) Belghait et al., models at various conditions.
Fig. 4
Comparison of experimental (points) and calculated (line) solubility of LND in the sc-CO2: a) Alwi and Garlapati, b) Hozhabr et al., c) Keshmiri et al., d) Bian et al., e) Belghait et al., models at various conditions.

The total mixing heat (ΔHt) of the LND/sc-CO2 binary system can be calculated using a2 adjustable parameter of Chrastil and also Kumar- Johnston models ( Δ H t = - a 2 . R ). The vaporization enthalpy (ΔHvap) of this system can be estimated by utilization of the adjustable parameter of the Bartle model ( Δ H vap = - a 2 . R ). Furthermore, solvation enthalpy (ΔHsol) can be obtained by subtraction of vaporization enthalpy from the total reaction heat, based on Hess's rule. The total mixing heat of this binary system is obtained as 47.8 kJ mol−1 and 48.2 kJ mol−1 according to Chrastil and also Kumar- Johnston models, which exhibited good consistency with each other. Similarly, vaporization and solvation enthalpies were computed as 69.5 kJ mol−1 and −21.5 kJ mol−1 (based on the mean value of the obtained ΔHtotal (48 kJ mol−1)), respectively. LND evaporation and solvation were endothermic and exothermic processes, respectively. Also, the resulting solvation energy indicates the presence of remarkable intermolecular interactions between the LND and sc-CO2 molecules in the supercritical fluid phase (Hojjati et al., 2007).

3.2.2

3.2.2 Equation of state (SRK-EoS) based model

Among the available cubic equation of states, SRK-EoS combined with vdW2 mixing rule was selected for correlating of LND solubility in sc-CO2. The SRK-EoS-correlated solubility data are presented in Fig. 5 at different temperatures (308, 318, 328, and 338 K). As can be seen, correlated solubility values by SRK-EoS did not match the experimental data.

(a) Comparison of experimental (points) and calculated (line) solubility of LND in sc-CO2 based on SRK-EoS model. (b) Linear function of lij and kij versus temperature.
Fig. 5
(a) Comparison of experimental (points) and calculated (line) solubility of LND in sc-CO2 based on SRK-EoS model. (b) Linear function of lij and kij versus temperature.

The optimum interaction parameters ( l ij and k ij ) of this model were obtained by minimizing the difference between the experimental LND solubility values and the calculated ones. The optimized values of these binary parameters as well as the statistical parameters (AARD%, Radj and F-value) of the SRK-EoS are reported in Table 6. Generally, the l ij and k ij interaction parameters are linear functions of temperature, in which the slope and intercept values of these linear functions were estimated by linear regression analysis. Obtained functions for LND/sc-CO2 binary system were as follows, as also shown in Fig. 5b:

(25)
l ij = - 0.0054 T + 1.7046
(26)
k ij = - 0.0183 T + 5.9182
Table 6 Correlation results for solubility of LND in sc-CO2 by SRK combined with the vdW2 mixing rule.
Model Parameter T = 308 K T = 318 K T = 328 K T = 338 K
SRK- vdW2 k 12 −0.7859 −0.8057 −0.9995 −1
l 12 0.8194 0.1946 −0.5784 −1.0564
AARD/% 39.17 49.89 45.50 29.27
F value 798.22 630.14 599.74 688.01
Radj 0.983 0.974 0.978 0.990

Accordingly, these equations can be applied for estimating the solubility of LND in sc-CO2 in the temperature range of 308–338 K. It is clear that both interaction parameters were descending functions of temperature.

3.2.3

3.2.3 Modified Wilson’s model

Optimized adjustable parameters (α, β, Λ'12 and Λ'21) and the statistical parameters (AARD%, Radj, and F-value) of the modified Wilson’s model are reported in Table 7 for the LND/sc-CO2 binary system. The correlation results are also represented in Fig. 6. According to the statistical parameters of AARD% (5.926), Radj (0.995) and F-value (1275.581), it can be concluded that Wilson’s model possesses proper accuracy and high precision for correlating the solubility of LND in sc-CO2. Furthermore, the interaction parameters (Λ12 and Λ21 ) were computed (Eqs. (19) and (20)) for each data point of the LND/sc-CO2 system and the obtained ranges for the Λ12 and Λ21 are 3.906 to 10.985 and 0.025 × 10−4 to 0.180 × 10−4, respectively. The parameter of Λ21is significantly smaller than Λ12 which is in accordance with the previously reported data, confirming the higher value of Λ12 , as the interaction parameter of the solvent (1) around the solid solute (2), for complex solute molecules (Sodeifian et al., 2020; Higashi et al., 2001; Nasri, 2018).

Table 7 Correlation results for solubility of LND in sc-CO2 by modified Wilson’s model.
Model α β Λ'12 Λ'21 AARD/% F value Radj
Modified Wilson −7.194 1.788 −1.166 11.803 5.926 1275.581 0.995
Comparison of experimental (points) and calculated (line) solubility of LND in sc-CO2 based on modified Wilson’s model.
Fig. 6
Comparison of experimental (points) and calculated (line) solubility of LND in sc-CO2 based on modified Wilson’s model.

Comparing the statistical criteria of all applied models, it can be concluded that the modified Wilson’s model with the lowest AARD% (5.926) along with the highest Radj (0.995) and F-value, followed by Keshmiri et al. model with the same Radj value and low AARD% (8.535) exhibited the lowest deviation from the experimental data and can be reliably used to correlate the solubility of LND in sc-CO2.

4

4 Conclusion

In the present research, the solubility of Lenalidomide (LND), as an anti-cancer drug, in supercritical CO2 (sc-CO2) was measured at different pressures (120–300 bar) and temperatures (308–338 K) using a statistical method. LND solubility in sc-CO2 was obtained in the range of 0.02 × 10-4 to 1.08 × 10-4 in terms of mole fraction. The maximum solubility was achieved at 338 K and 300 bar.

Furthermore, the experimental data were correlated with well-known empirical density-based models, SRK equation of state (SRK-EoS) with two parameters of van der Waals (vdW2) mixing rule, as well as, expanded liquid theory (modified Wilson’s model). According to the results, modified Wilson’s model exhibited the highest consistency with the experimental data for correlating the solubility of LND in sc-CO2. However, the SRK-EoS did not show acceptable accuracy in the correlation of LND solubility in sc-CO2. Among the empirical models, Alwi and Garlapati (AARD% = 8.210), Sung and Shim (AARD% = 11.268), Ch and Madras (AARD% = 8.525), Hozhabr et al. (AARD% = 7.998), Garlapati and Madras (AARD% = 8.037), Keshmiri et al. (AARD% = 8.535), Sparks et al. (AARD% = 8.330), Reddy and Garlapati (AARD% = 10.589), Bian et al. (2011) (AARD% = 7.781), and Belghait et al. (AARD% = 7.516) possessed Radj value above 0.99 and can be reliably employed to correlate the solubility of LND in sc-CO2. Various critical properties of LND were calculated by different group contribution methods. Also, the approximate values of total mixing heat ( Δ H total = 48 kJ mol−1) as well as vaporization ( Δ H vap  = 69.5 kJ mol−1), and solvation ( Δ H sol  = -21.5 kJ mol−1) enthalpies were computed via the obtained adjustable parameters of empirical models.

As mentioned previously, the appropriate supercritical method for producing LND micro/nanoparticles can be selected based on its solubility in sc-CO2. Due to the poor solubility of LND in sc-CO2, the supercritical gas anti-solvent (GAS) process can be considered a suitable choice. Therefore, producing LND micro/nanoparticles with desired morphology and narrow size distribution via the GAS process can be considered in future investigations.

Acknowledgements

The authors would like to thank the generous financial support provided by the Supercritical fluids development group, Shiraz, Iran.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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