# Optimization of Oil Recovery from Japonica Luna Rice Bran by Supercritical Carbon Dioxide Applying Design of Experiments: Characterization of the Oil and Mass Transfer Modeling

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

_{2}), based on design of experiments (DoE). Initially, a 2

^{4−1}two level fractional factorial design (FFD) was used, and pressure, temperature, and scCO

_{2}flow rate were determined as the significant variables; while the yield, total flavonoids content (TFC), and total polyphenols content (TPC) were the response functions used to analyze the quality of the extracts recovered. Subsequently, central composite design (CCD) was applied to examine the effects of the significant variables on the responses and create quadratic surfaces that optimize the latter. The following values of pressure = 34.35 MPa, temperature = 339.5 K, and scCO

_{2}flow rate = 1.8 × 10

^{−3}kg/min were found to simultaneously optimize the yield (6.83%), TPC (61.28 μmol GAE/g ext), and TFC (1696.8 μmol EC/g ext). The fatty acid profile of the oils was characterized by GC-FID. It was demonstrated that the acids in largest quantities are C16:0 (15–16%), C18:1 (41%), and C18:2 (38–39%). Finally, three mass transfer models were applied to determine the mass transfer coefficients and assess the cumulative extraction curves, with an AAD% of 4.16, for the best model.

## 1. Introduction

_{2}(scCO

_{2}) extraction. It was demonstrated that rice varieties had a greater effect on the concentration of phytochemicals in the RBO than the extraction methods applied [9]. Still, for a given rice variety—black rice samples in the particular case—the RBO recovered by applying scCO

_{2}showed the best physicochemical and antioxidant properties [8].

_{2}extraction parameters (pressure, temperature, scCO

_{2}flow rate, co-solvent presence) on the quality of the RBO and its composition are numerous, see for example [2,3,10,11,12,13,14,15,16]. The oils were evaluated in terms of antioxidant activity, fatty acid profile, and composition of bioactives and phytochemicals—such as phytosterols, tocopherols, and γ-oryzanol among others.

_{2}extraction of RBO—with or without a co-solvent—not only achieves yield comparable to that of conventional n-hexane extraction, but the extracts obtained have lower levels of phosphate and wax and present an improved color.

_{2}applying Chrastil equation and used two models—a thermodynamic and a simple kinetic one—to explain the experimental extraction behavior.

_{2}are even fewer in number and provide limited data. For example, Wang et al. [13] carried out a more exhaustive work on the application of DoE, but did not perform any modeling of the results obtained. They used a two-factor central composite scheme composed of response surface methodology to verify the optimum values of temperature and pressure of the RBO scCO

_{2}extraction that will lead to an increase in the concentration of oryzanols in the removed oil. Simultaneously, the authors examined the influence of the supercritical solvent flow—either down-flow or up-flow—on the recovery of the RBO, and concluded that the latter is more advantageous.

_{2}will have many advantages since, as discussed extensively in the literature, experimental design is a useful method of optimizing the operational parameters for any technique to maximize the extent of suitable information acquired with the minimum number of experiments. It delivers a more effective and complete optimization compared to the approach “Vary one factor at a time while allocating fixed values to the other factors” [17].

_{2}extraction of RBO obtained from Japonica Luna variety, applying DoE. To achieve that goal, firstly, unlike other similar studies, two different DoE methods—namely a fractional factorial design (FFD) and, subsequently, a central composite design (CCD)—were combined and applied to determine the optimum values of the scCO

_{2}process operating parameters. The influence of the latter on the yield and total phenolic and flavonoid content of the RBOs recovered was examined, with the details of the methodology applied outlined in the sections to follow.

## 2. Materials and Methods

#### 2.1. Raw Material

#### 2.2. Reagents

_{2}), 99.995%, supplied by Air Liquide (Lisbon, Portugal) was employed for supercritical fluid extractions. Hexane (Analar NORMAPUR 98%) from VWR, PROLABO (Barcelona, Spain). Methanol (HPLC grade, 99.99%), boron trifluoride-methanol solution, BF

_{3}/MeOH (10%, w/w), and ethanol (99%+, absolute, extra pure) were from Fisher Chemical (Madrid, Spain); AlCl

_{3}(98%) was obtained from Merck and ultra-pure water (Mili-Q system, Milipore Corporation, Darmstadt, Germany).

_{2}CO

_{3}; 99.5%), catechin (98%), and Folin–Ciocalteu reagent, 2 N, were purchased from Sigma Aldrich (Darmstadt, Germany).

#### 2.3. Methods and Equipments

^{3}internal capacity extractor. The equipment allows operating at pressures and temperatures up to 60.0 MPa and 120 °C, respectively, its comprehensive description is given in [2,18,19], hence no further details will be given herewith.

^{2}= 0.997. The sensitivity was determined according to the limit of detection (LOD = 10.24 µg/mL) and limit of quantification (LOQ = 34.13 µg/mL), where A

_{S}is the measured absorbance of the sample and C

_{S}is the concentration of the sample in µg/mL.

_{3}/MeOH (10%, w/w) [2].

#### 2.4. Design of Experiments

^{4−1}two-level fractional factorial design (FFD) with three factors was applied to our system, which means that each experimental factor has only two levels, and the experimental runs include all combinations of these factors. While two-level factorial designs are unable to fully search a wide region in the factor space, they still provide useful information for relatively few runs per factor.

_{0}—the constant coefficient, a

_{i}—linear coefficients, a

_{ii}—quadratic coefficients, a

_{ij}—interaction coefficients, and X

_{i}and X

_{j}are the coded values of the independent parameters in the experience.

#### 2.5. Mathematical Modeling of scCO_{2} Kinetics Extractions

_{2}extraction kinetics, see for example [23,24,25,26,27].

^{−1}); C is the solute (oil) concentration in the scCO

_{2}(kg·kg

^{−1}); q—the solute concentration in the solid phase (kg·kg

^{−1}); u—the superficial velocity of supercritical fluid (m·s

^{−1}); ε is the void fraction of the bed; h—the axial coordinate (m), t—time (s); ρ

_{f}—the fluid density (kg·m

^{−3}); ρ

_{s}—solid density (kg·m

^{−3}); Q-fluid flow rate (kg·s

^{−}

^{1}); H—height of the extraction bed (m); q

_{0}—solute concentration in the solid phase at t = 0 (kg·kg

^{−1}); and C

_{0}is the initial concentration of the oil in the scCO

_{2}, which is assumed to be equal to the oil solubility in the solvent.

_{0}is introduced because of the complexity of the raw materials and the uncertainty of the interactions among the compounds comprising them. Hence, the calculations can be simplified either by representing the oil as a single compound or by considering one specific solute as the unique compound to be dissolved in the scCO

_{2.}In addition, solubility of the oils is approximated using data from the first period of the process, namely the slope of the cumulative extraction curves.

_{d}is the desorption constant, q*—the interfacial concentration of the solute (kg·kg

^{−1}). Further details of the model solution and applications can be found in [23,25,29].

_{f}external mass transfer coefficient, (m·s

^{−1}), a—the surface of a unit volume of particles and q

_{k}—the initial content of the difficult accessible solute in the solid (kg·kg

^{−1}), and

_{s}is the internal mass transfer coefficient (m·s

^{−1}). Again, the analytical solution of Equations (8) and (9) is well documented [23,24,25,29].

_{s}, and the initial fraction of solute in broken cells r = 1 − q

_{k}/q

_{o}. Further details and explanations can be found in [24,29].

## 3. Results and Discussion

#### 3.1. Design of Experiments

#### 3.1.1. Fractional Factorial Design

_{2}flow rate—and their influence on the three response functions used to analyze the quality of the extracts was studied. The response functions chosen were yield (%), TPC, and TFC.

^{4−1}FFD, eight experimental runs were required. Each experiment was carried out until a maximum of the yield was achieved. The experimental kinetic curves obtained were simulated applying the mass transfer models, presented in Section 2.4.

_{2}extraction performed at the corresponding experimental conditions (Table 1).

^{2}= 0.921, 0.996, and 0.938, respectively.

_{2}flow rate (kg·min

^{−1}) are represented by Equations (11)–(13), respectively.

_{2}flow rate was identified as the variable without significance to the model.

#### 3.1.2. Central Composite Design

_{2}flowrate was fixed at 1.8 × 10

^{−3}kg/min, since the FFD design indicated its unsubstantial influence on the three responses.

#### 3.2. Extract Compositions—Fatty Acid Methyl Esters (FAMEs) Analysis

_{2}flow rate on the rice bran oils recovered in terms of their fatty acid compositions was analyzed, and the results are presented in Table 5. It should be noted that Table 5 displays the results for just some of the oils obtained since they did not differ significantly for the rest.

#### 3.3. Mathematical Models Based on Differential Mass Balances

_{2}extraction was performed using the methods outlined briefly in Section 2.4. All experimental results obtained from FFD and CCD design were analyzed.

_{p}= 3.0 × 10

^{−3}m; solid density, ρ

_{s}= 580.0 kg·m

^{−3}; solute concentration in the solid phase at t = 0, q

_{0}= 8.2 × 10

^{−2}kg·kg

^{−1}, which corresponds to the maximum yield obtained by the Soxhlet hexane extraction (Table 1); the surface of a unit volume of particles, a = 6/d

_{p}; the initial content of the difficult accessible solute in the solid, q

_{k}= 2.60 × 10

^{−2}(kg·kg

^{−1}), the initial fraction of solute in broken cells r = 0.45 and the fluid density, ρ

_{f}, was taken from the NIST chemistry book (https://webbook.nist.gov/chemistry/) accessed on 11 April 2022.

_{12}, applying the equation of Wilke–Chang [36], and the theorical external mass transfer, k

_{f}, by the correlation of Wakao and Kaguei [37], it is assumed that triolein is the representative compound in the oil. This assumption is validated and based on the results of the GC-FID analyses which show that the principal fatty acid identified in the oils is C18:1. In addition, the properties of this triacylglycerol are well documented [35].

_{2}flow rate, at 313.2 K, on the extraction yield of RBO. Regarding Tan and Liou 1984 model, only one curve is presented in order just to demonstrate the actual considerable deviations from the experimental data due to the fact that: (i) oil extraction rate predictions in the first part of the process are quite high; (ii) the decrease in the amount of solute available in the solid phase is not accounted for given the correlation of solute concentration in the fluid and solid phases in the matrix.

_{2}flow rate on the yield as a function of time.

## 4. Conclusions

_{2}to the recovery of oil from Japonica Luna rice bran not only eliminates the use of organic solvents in the process but achieves yields similar to that reported by n-hexane extraction.

_{2}extraction process, and the influence of the factors of principal significance; pressure and temperature on the extraction process responses yield, TPC, TFC, and fatty acid composition of RBOs, analyzed by GC-FID, was discussed. The reliability of the models was demonstrated by performing two experimental tests applying the best operating conditions leading to the optimum values of the three responses.

_{2}recovery of RBO applying DoE, followed by modeling of the process kinetics and identification and quantification of free fatty acids in the oils recovered. The results obtained can be used in the design and scale-up of environmentally safe and sustainable scCO

_{2}processes targeting efficient valorization of wastes generated from rice milling.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

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**Figure 1.**Estimated (represented by the straight line), and experimental values for the rice bran oil yield (%) recovered by scCO

_{2}extraction, and at the FFD design tests conditions shown in Table 1.

**Figure 2.**Estimated (represented by the straight line), and experimental values for the rice bran oil recovered by scCO

_{2}extraction at the FFD design tests conditions shown in Table 1: (

**a**) TPC (μmol CE/g ext) and (

**b**) TFC (μmol GAE/g ext).

**Figure 3.**Response surface plot showing the effects of the temperature and pressure on the rice oil bran extraction yield.

**Figure 4.**Extraction yield curves representing the influence of pressure (MPa) and CO

_{2}flow rates (kg/min) at 313.15 K, on RBO yield, as a function of time. The symbols are the experimental data, and line-model predictions.

**Figure 5.**Extraction yield curves representing the influence of pressure (MPa) at temperature (338.15 K) and CO

_{2}flow rates (1.8×10

^{−3}kg/min), on bran rice oil yield, as a function of time. The symbols are the experimental data, and line-model predictions.

Run | Pressure (MPa) | Temperature (K) | Flow Rate (kg/min) | Yield (%) | TPC (μmol GAE/g ext) | Flavonoids (μmol CE/g ext) |
---|---|---|---|---|---|---|

HE | - | - | - | 8.20 | 60.24 ± 3.91 | 2092.19 ± 78.97 |

A1 | 25.0 | 313.15 | 2.7 × 10^{−3} | 6.48 | 58.76 ± 2.67 | 1538.99 ± 97.96 |

A2 | 40.0 | 353.15 | 0.9 × 10^{−3} | 6.91 | 58.67 ± 0.52 | 1547.83 ± 78.21 |

A3 | 25.0 | 313.15 | 0.9 × 10^{−3} | 6.26 | 58.14 ± 3.31 | 1765.87 ± 29.90 |

A4 | 40.0 | 313.15 | 0.9 × 10^{−3} | 6.43 | 73.41 ± 1.55 | 1863.10 ± 124.90 |

A5 | 40.0 | 313.15 | 2.7 × 10^{−3} | 5.97 | 66.99 ± 3.55 | 1902.88 ± 105.60 |

A6 | 25.0 | 353.15 | 0.9 × 10^{−3} | 5.07 | 55.35 ± 1.12 | 1314.32 ± 79.87 |

A7 | 25.0 | 353.15 | 2.7 × 10^{−3} | 6.45 | 62.79 ± 3.70 | 1536.78 ± 174.03 |

A8 | 40.0 | 353.15 | 2.7 × 10^{−3} | 6.46 | 56.02 ± 3.50 | 1670.11 ± 81.74 |

Run | Pressure (MPa) | Temperature (K) | Yield (%) | TPC (μmol GAE/g ext) | Flavonoids (μmol CE/g ext) |
---|---|---|---|---|---|

A9 | 30.0 | 323.15 | 5.72 | 59.98 ± 1.99 | 1537.24 ± 129.38 |

A10 | 40.0 | 323.15 | 6.50 | 62.21 ± 2.58 | 1565.42 ± 73.94 |

A11 | 30.0 | 353.15 | 6.57 | 53.38 ± 3.03 | 1636.68 ± 77.85 |

A12 | 42.0 | 338.15 | 6.67 | 60.04 ± 2.12 | 1707.95 ± 24.58 |

A13 | 35.0 | 338.15 | 6.81 | 68.58 ± 0.84 | 1641.84 ± 194.11 |

A14 | 35.0 | 338.15 | 6.67 | 65.89 ± 1.95 | 1631.53 ± 116.81 |

A15 | 35.0 | 317.15 | 6.32 | 63.27 ± 1.99 | 1907.39 ± 4.52 |

A16 | 35.0 | 338.15 | 7.12 | 60.78 ± 0.96 | 1831.15 ± 254.14 |

A17 | 40.0 | 353.15 | 6.91 | 54.98 ± 2.37 | 1683.09 ± 155.90 |

A18 | 35.0 | 359.15 | 6.87 | 63.01 ± 1.71 | 1751.05 ± 121.03 |

A19 | 27.9 | 338.15 | 5.93 | 61.97 ± 2.04 | 1771.49 ± 128.09 |

**Table 3.**ANOVA results on the CCD models selected. Estimated regression model of the relationship between a response variable and the independent variables.

Yield (%) | ||||
---|---|---|---|---|

Source | SS ^{a} | MS ^{b} | F-Value | p-Value |

Model | 1.6000 | 0.3206 | 15.32 | 0.0047 |

X_{1}-Pressure (MPa) | 0.5867 | 0.5867 | 28.04 | 0.0032 |

X_{2}-Temperature(K) | 0.5191 | 0.5191 | 24.81 | 0.0042 |

X_{1}X_{2} | 0.0484 | 0.0484 | 2.31 | 0.1888 |

X_{1}^{2} | 0.4342 | 0.4342 | 20.75 | 0.0061 |

X_{2}^{2} | 0.0951 | 0.0951 | 4.55 | 0.0862 |

Residual | 0.1046 | 0.0209 | ||

Lack of Fit | 0.0307 | 0.0102 | 0.2775 | 0.8406 |

Pure Error | 0.0739 | 0.0369 | ||

Cor Total | 1.71 |

**Sums of squares.**

^{a}^{b}Mean square.

**Table 4.**Predicted and experimental values of the responses were obtained at the optimum conditions of the independent variables. The experimental data are given as the mean ± SD (n = 2).

Pressure (MPa) | Temperature (K) | Yields (%) | TPC (μmol GAE/g ext) | Flavonoids (μmol CE/g ext) | |
---|---|---|---|---|---|

Predicted values | 34.3587 | 339.493 | 6.82706 | 61.2809 | 1696.8 |

Experimental values | 34.5 | 339.5 | 6.79 ± 0.06 | 64.20 ± 5.42 | 1739.1 ± 75.4 |

FFD | CCD | ||||||
---|---|---|---|---|---|---|---|

Run A2 | Run A3 | Run A4 | Run A12 | Run A16 | Run A17 | Run A10 | |

Fatty Acid | 40/353.15 | 25/313.15 | 40/313.15 | 42/338.15 | 35/338.15 | 40/353.15 | 27.9/338.15 |

C14:0—Myristic | 0.06 ± 0.02 | 0.08 ± 0.03 | 0.05 ± 0.01 | 0.06 ± 0.02 | 0.06 ± 0.02 | 0.06 ± 0.02 | 0.07 ± 0.03 |

C16:0—Palmitic | 15.32 ± 0.59 | 15.95 ± 0.61 | 15.35 ± 0.49 | 15.22 ± 0.55 | 15.38 ± 0.63 | 15.12 ± 0.65 | 15.87 ± 0.53 |

C18:0—Stearic | 1.58 ± 0.08 | 1.84 ± 0.07 | 1.43 ± 0.06 | 1.45 ± 0.07 | 1.41 ± 0.07 | 1.43 ± 0.08 | 1.63 ± 0.07 |

C18:1—Oleic | 41.37 ± 1.00 | 41.78 ± 0.95 | 41.53 ± 0.89 | 41.65 ± 1.01 | 41.47 ± 1.00 | 41.58 ± 0.96 | 41.31 ± 0.98 |

C18:2—Linoleic | 39.03 ± 0.97 | 38.69 ± 1.00 | 39.42 ± 1.05 | 39.27 ± 0.94 | 39.65 ± 1.06 | 39.61 ± 1.05 | 39.45 ± 1.01 |

C18:3—Linolenic | 1.54 ± 0.06 | 1.02 ± 0.07 | 1.34 ± 0.08 | 1.48 ± 0.07 | 1.36 ± 0.06 | 1.46 ± 0.07 | 1.32 ± 0.06 |

C20:0—Arachidic | 0.25 ± 0.02 | 0.18 ± 0.02 | 0.27± 0.03 | 0.24 ± 0.02 | 0.26 ± 0.02 | 0.12 ± 0.02 | 0.10 ± 0.02 |

C20:1—Gadoleic | 0.53 ± 0.03 | 0.24 ± 0.02 | 0.38 ± 0.02 | 0.41 ± 0.03 | 0.19 ± 0.02 | 0.34 ± 0.02 | 0.13 ± 0.02 |

C22:0 —Behenic | 0.11 ± 0.02 | 0.08 ± 0.03 | 0.12 ± 0.02 | 0.09 ± 0.02 | 0.12 ± 0.02 | 0.14 ± 0.02 | 0.07 ± 0.03 |

C22:1—Erucic | 0.15 ± 0.03 | 0.06 ± 0.02 | 0.07 ± 0.02 | 0.08 ± 0.03 | 0.05 ± 0.02 | 0.12 ± 0.02 | 0.05 ± 0.02 |

C24:0—Lignoceric | 0.06 ± 0.03 | ----- | 0.07 ± 0.03 | 0.06 ± 0.03 | 0.05 ± 0.04 | 0.07 ± 0.03 | ----- |

DUFA | 39.03 | 38.69 | 39.42 | 39.27 | 39.65 | 39.61 | 39.45 |

MUFA | 42.05 | 42.08 | 41.98 | 42.14 | 41.71 | 42.04 | 41.49 |

SFA | 17.38 | 18.13 | 17.29 | 17.12 | 17.28 | 16.94 | 17.74 |

UI | 1.201 | 1.195 | 1.208 | 1.207 | 1.210 | 1.213 | 1.204 |

**Table 6.**Experimental conditions, principal parameters, and mass transfer coefficients for the rice bran oil extraction by SC-CO

_{2}.

Run | P (MPa) | T (K) | Flow Rate f (kg/s) × 10 ^{5} | Superficial Velocity u (m·s^{−1}) × 10^{4} | C_{o}(kg/kg) × 10 ^{2} | Tan and Liou [28] k _{d} × 10^{4} (s^{−1}) | Sovová [30] k _{s} × 10^{8} (m·s^{−1})/k _{f} × 10^{6} (m·s^{−1}) | Sovová [31] k _{s} × 10^{8} (m·s^{−1}) | ^{a} D_{12} × 10^{9}(m ^{2}·s^{−1}) | ^{b}k_{f} × 10^{6}(m·s ^{−1}) |
---|---|---|---|---|---|---|---|---|---|---|

A1 (FFD) | 25.0 | 313.15 | 4.49 | 3.32 | 1.30 | 5.056 (8.98%) | 0.609/0.201 (3.42%) | 1.87 (3.86%) | 2.872 | 7.971 |

A3 (FFD) | 25.0 | 313.15 | 1.62 | 1.19 | 1.30 | 1.431 (10.7%) | 0.0432/0.0876 (5.52%) | 0.444 (3.26%) | 2.872 | 3.401 |

A6 (FFD) | 25.0 | 353.15 | 1.58 | 1.49 | 0.60 | 0.739 (6.76%) | 0.0376/0.0924 (10.5%) | 0.444 (3.24%) | 5.008 | 6.534 |

A7 (FFD) | 25.0 | 353.15 | 4.57 | 4.32 | 0.60 | 1.998 (7.97%) | 0.0942/0.230 (7.82%) | 0.790 (4.41%) | 5.008 | 1.581 |

A19 (CCD) | 27.9 | 338.15 | 3.08 | 2.53 | 1.10 | 3.300 (4.77%) | 0.492/0.188 (4.40%) | 2.85 (2.21%) | 3.826 | 8.120 |

A9 (CCD) | 30.0 | 323.15 | 3.12 | 2.33 | 1.60 | 4.514 (8.97%) | 0.304/0.155(1.56%) | 1.49 (4.59%) | 3.029 | 6.193 |

A11 (CCD) | 30.0 | 353.15 | 3.08 | 2.69 | 1.20 | 3.956(6.00%) | 1.099/0.196 (4.87%) | 3.94 (1.24%) | 4.397 | 9.551 |

A13 (CCD) | 35.0 | 338.15 | 3.12 | 2.40 | 2.20 | 5.872 (5.12%) | 1.572/0.137 (2.87%) | 4.66 (2.63%) | 3.370 | 6.920 |

A14 (CCD) | 35.0 | 338.15 | 3.09 | 2.38 | 2.20 | 5.884 (7.62%) | 1.627/0.126 (3.13%) | 4.60 (3.69%) | 3.368 | 6.870 |

A16 (CCD) | 35.0 | 338.15 | 3.11 | 2.40 | 2.20 | 6.337 (6.27%) | 1.711/0.134 (3.77%) | 4.48 (4.77%) | 3.368 | 6.918 |

A15 (CCD) | 35.0 | 317.15 | 3.15 | 2.22 | 2.00 | 4.964 (8.30%) | 0.948/0.117 (1.90%) | 2.40 (4.13%) | 2.609 | 5.185 |

A18 (CCD) | 35.0 | 359.15 | 3.10 | 2.62 | 2.10 | 5.663 (4.80%) | 1.769/0.135 (2.13%) | 4.71 (2.81%) | 4.251 | 9.034 |

A4 (FFD) | 40.0 | 313.15 | 1.61 | 1.09 | 2.10 | 2.335 (8.71%) | 0.148/0.0521 (1.13%) | 0.867 (4.29%) | 2.337 | 2.590 |

A5 (FFD) | 40.0 | 313.15 | 4.64 | 3.15 | 2.10 | 6.624 (16.3%) | 0.424/0.181 (4.13%) | 1.65 (5.11%) | 2.337 | 6.250 |

A10 (CCD) | 40.0 | 323.15 | 3.11 | 2.19 | 2.30 | 6.654 (12.7%) | 0.821/3.126 (1.80%) | 3.98 (7.99%) | 2.639 | 5.156 |

A17 (CCD) | 40.0 | 353.15 | 3.13 | 2.47 | 2.30 | 7.445 (9.22%) | 1.412/1.361 (3.19%) | 7.74 (5.47%) | 3.683 | 7.599 |

A8 (FFD) | 40.0 | 353.15 | 4.59 | 3.62 | 2.90 | 10.12 (10.0%) | 1.677/0.217 (2.21%) | 7.00 (4.37%) | 3.683 | 1.044 |

A2 (FFD) | 40.0 | 353.15 | 1.60 | 1.26 | 2.90 | 3.445 (9.91%) | 0.310/0.0691 (1.48%) | 1.97 (4.98%) | 3.683 | 4.346 |

A12(CCD) | 42.0 | 338.15 | 3.06 | 2.25 | 2.60 | 7.110 (12.6%) | 1.063/2.357 (2.52%) | 8.51 (6.02%) | 3.057 | 5.987 |

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**MDPI and ACS Style**

Coelho, J.P.; Robalo, M.P.; Fernandes, I.S.; Stateva, R.P.
Optimization of Oil Recovery from *Japonica* Luna Rice Bran by Supercritical Carbon Dioxide Applying Design of Experiments: Characterization of the Oil and Mass Transfer Modeling. *ChemEngineering* **2022**, *6*, 63.
https://doi.org/10.3390/chemengineering6040063

**AMA Style**

Coelho JP, Robalo MP, Fernandes IS, Stateva RP.
Optimization of Oil Recovery from *Japonica* Luna Rice Bran by Supercritical Carbon Dioxide Applying Design of Experiments: Characterization of the Oil and Mass Transfer Modeling. *ChemEngineering*. 2022; 6(4):63.
https://doi.org/10.3390/chemengineering6040063

**Chicago/Turabian Style**

Coelho, José P., Maria Paula Robalo, Inês S. Fernandes, and Roumiana P. Stateva.
2022. "Optimization of Oil Recovery from *Japonica* Luna Rice Bran by Supercritical Carbon Dioxide Applying Design of Experiments: Characterization of the Oil and Mass Transfer Modeling" *ChemEngineering* 6, no. 4: 63.
https://doi.org/10.3390/chemengineering6040063