Elimination of Tar in Biomass Gasification Process: LiquidâLiquid

Article pubs.acs.org/jced

Elimination of Tar in Biomass Gasification Process: Liquid−Liquid Equilibrium of Ternary Systems {Water + Solvent (p‑Xylene and Methyl Hexadecanoate) + Model Molecules of Tar (Thiophene, Pyridine, Naphthalene, Phenathrene, and Anthracene)} Georgio Bassil,*,† Ilham Mokbel,‡ Joseph Saab,§ Ramy Abou Naccoul,∥ Jacques Jose,‡ and Christelle Goutaudier‡ †

Faculty of Engineering, Université Libano-Canadienne, LCU, 32 Zouk Mikael, Aintoura-Kesrouan, Lebanon LMI UMR 5615. Bât. Berthollet 2ème étage, Université Claude Bernard Lyon 1, 43 bd du 11 Novembre 1918, 69622 Villeurbanne Cedex, France § Faculty of Sciences, Deptartment of Chemistry Biochemistry, Group ThEA-Thermodynamic Phase Equilibria and Analysis, Holy Spirit University of Kaslik, B.P. 446 Jounieh, Lebanon ∥ Shimadzu Scientific Instruments, Analytical and Measuring Instruments, Le Luzard II−Bat. A Bd Salvador Allende, Noisiel 77448 Marne la Vallée, France ‡

ABSTRACT: Nowadays attention is focused on biomass as a renewable energy source, but still one of the remaining drawbacks to be solved is the elimination of the high level of tar present in the syngas from the gasification process of the biomass. The objective of this work is to perform experimental measurements of liquid−liquid equilibria that will be used for the operation of tar removal from the gasification process. With this aim, the liquid−liquid equilibrium of water + solvent (p-xylene or methyl hexadecanoate) + model molecules of tar (thiophene, or pyridine, or naphthalene, or phenanthrene, or anthracene) were studied at 303.2, 323.2, and 343.2 K. The obtained data were correlated with the nonrandom twoliquid and universal quasi-chemical models.

1. INTRODUCTION Biomass is well-known as an important primary and renewable energy source.1−3 The gasification process of biomass, which is regarded as one of the most promising techniques for utilizing biomass, produces syngas.1,4,5 One of the major problems that has not been yet solved is the high amount of the organic impurities (tar) in the product gas4,5 either inside or outside the gasifier.3 Tars consist of a mixture of hydrocarbons which includes compounds with one or more aromatic cycles that can contain heteroatoms.6 The latter are undesirable and can cause various problems associated with condensation, formation of tar aerosols, and polymerization to more complex structures that leads to operational difficulties in a downstream process by blocking filter elements and gas coolers, and plugging the coldest parts of the plant.3−5 Nowadays, the most advanced method to eliminate tar is by using a suitable extracting solvent. The focus of the work is to eliminate tars, which are represented in our case by these model molecules (thiophene, pyridine, naphthalene, phenanthrene, and anthracene), from the aqueous phase downstream of the gasifier using biodiesel solvents represented by methyl hexadecanoate (or methyl palmitate) and a fossil solvent (p-xylene); the latter solvent was chosen as a reference solvent for comparison with the biosolvent, it has also an elevated © 2017 American Chemical Society

dissolving power and a low vapor pressure at room temperature. With this aim, the liquid−liquid equilibrium of water + p-xylene (or methyl hexadecanoate) + the model molecule of tar (thiophene, or pyridine, or naphthalene, or phenanthrene, or anthracene) was performed at three different temperatures Table 1. Details of the Chemicals Used in This Study chemical name thiophene pyridine naphthalene phenanthrene anthracene p-xylene methyl hexadecanoate(methyl palmitate) octane hexadecane

source Sigma-Aldrich Sigma-Aldrich Prolabo Sigma-Aldrich Carlo ERBA Sigma-Aldrich Sigma-Aldrich Acros Organics Janssen Chimica

mole fraction purity

CAS

>0.99 0.998 0.99 >0.995 0.99 0.99 0.97

110-02-1 110-86-1 91-20-3 85-01-8 120-12-7 106-42-3 112-39-0

0.99 0.99

111-65-9 544-76-3

Received: October 3, 2016 Accepted: February 1, 2017 Published: February 10, 2017 1028

DOI: 10.1021/acs.jced.6b00857 J. Chem. Eng. Data 2017, 62, 1028−1035

Journal of Chemical & Engineering Data

Article

(303.2 K or 308.2 K and 323.2 K and 343.2 K) and at atmospheric pressure. The experimental results were then correlated using the nonrandom two-liquid (NRTL) model and the universal quasi-chemical (UNIQUAC) model in order to verify our experimental database.

Table 2. Analytical Conditions Used for the Organic and Aqueous Phase GC analyses thiophene and pyridine type column type column length column i.d. column film thickness injector type injection volume detector type carrier gas

naphthalene, phenanthrene, and anthracene

Agilent Technologies 7890A Restek Rtx-35 amine 30 m 0.32 mm 1 μm

Agilent Technologies 6890 Varian DB-35 MS 30 m 0.25 mm 0.25 μm

split (organic phase), splitless (aqueous phase) 1 μL

split (aqueous phase)

FID He (flow: 2.09 mL/min)

MS He (flow: 1 mL/min)

2. EXPERIMENTAL SECTION 2.1. Materials. Materials that are used for this work are represented by distilled and deionized water by Milli-Q system from Millipore. As for chemicals, we used them as received from the supplier without any further purification (Table 1). GC analysis did not detect any appreciable peaks of impurities which can alter the experimental measurements. 2.2. Device and Procedure. Liquid−liquid equilibrium was carried out in a glass cell of about 300 mL. The equilibrium cell is equipped with a magnetic stirrer and a double jacketed membrane in

1 μL

Table 3. Experimental Liquid−Liquid Equilibrium Data for the Ternary System Expressed in Molar Fractions (xi) at T = 303.2 K, 323.2 K, 343.2 K, and Pressure p = 0.1 MPa.a K Represents the Partition Coefficient of the Solute and S Is the Selectivity of the Solvent p-xylene (1) + thiophene (2) + water (3) aqueous phase 5

hydrocarbon-rich phase 5

10 x1

10 x2

3.28 (±0.11) 3.28 (±0.11) 3.28 (±0.11)

5.02 (±0.12) 1.92 (±0.07) 0.50 (±0.04)

3.87 (±0.15) 3.87 (±0.15) 3.87 (±0.15)

5.91 (±0.02) 2.36 (±0.02) 0.61 (±0.004)

5.07 (±0.17) 5.07 (±0.17) 5.07 (±0.17)

7.32 (±0.34) 2.82 (±0.14) 0.77 (±0.05)

x1

303.2 K 0.933 6.40 (±0.20) 0.971 2.55 (±0.004) 0.990 0.68 (±0.007) 323.2 K 0.932 6.38 (±0.08) 0.970 2.55 (±0.02) 0.989 0.68 (±0.02) 343.2 K 0.929 6.34 (±0.04) 0.967 2.53 (±0.01) 0.986 0.68 (±0.005) p-xylene (1) + pyridine (2) + water (3)

aqueous phase 105x1

103x3

K

S

3.01 (±0.02) 3.01 (±0.02) 3.01 (±0.02)

1275 1328 1353

4.24 × 105 4.41 × 105 4.45 × 105

4.68 (±0.03) 4.68 (±0.03) 4.68 (±0.03)

1080 1081 1111

2.31 × 105 2.31 × 105 2.37 × 105

7.30 (±0.32) 7.30 (±0.32) 7.30 (±0.32)

866 897 882

1.19 × 105 1.23 × 105 1.21 × 105

103x3

K

S

(±0.02) (±0.02) (±0.02)

9.56 9.59 9.41

3.18 × 103 3.19 × 103 3.13 × 103

(±0.03) (±0.03) (±0.03)

12.10 11.82 12.03

2.58 × 103 2.53 × 103 2.57 × 103

(±0.32) (±0.32) (±0.32)

13.97 14.00 14.08

1.91 × 103 1.92 × 103 1.93 × 103

103x3

K

S

3.01 (±0.02) 3.01 (±0.02) 3.01 (±0.02)

72977 73584 75009

2.42 × 107 2.44 × 107 2.49 × 107

4.68 (±0.03) 4.68 (±0.03)

53286 52627

1.14 × 107 1.12 × 107

hydrocarbon-rich phase 103x2

3.28 (±0.11) 3.28 (±0.11) 3.28 (±0.11)

4.09 (±0.06) 1.70 (±0.02) 0.50 (±0.03)

3.87 (±0.15) 3.87 (±0.15) 3.87 (±0.15)

3.48 (±0.04) 1.48 (±0.007) 0.41 (±0.01)

5.07 (±0.17) 5.07 (±0.17) 5.07 (±0.17)

3.15 (±0.13) 1.30 (±0.06) 0.37 (±0.01)

x1

102x2

303.2 K 0.958 3.91 (±0.08) 3.01 0.981 1.63 (±0.01) 3.01 0.992 0.46 (±0.008) 3.01 323.2 K 0.953 4.21 (±0.06) 4.68 0.978 1.75 (±0.01) 4.68 0.990 0.50 (±0.01) 4.68 343.2 K 0.949 4.40 (±0.03) 7.30 0.975 1.82 (±0.007) 7.30 0.988 0.52 (±0.006) 7.30 p-xylene (1) + naphthalene (2) + water (3)

aqueous phase 105x1

102x2


x1

3.28 (±0.11) 3.28 (±0.11) 3.28 (±0.11)

5.71(±0.13) 2.26(±0.03) 0.56 (±0.01)

0.955 0.980 0.993

3.87 (±0.15) 3.87 (±0.15)

7.82 (±0.09) 3.16 (±0.08)

0.954 0.979

102x2 303.2 K 4.17 (±0.07) 1.66 (±0.05) 0.42 (±0.009) 323.2 K 4.17 (±0.07) 1.66 (±0.05) 1029



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Table 3. continued p-xylene (1) + naphthalene (2) + water (3) aqueous phase 105x1


3.87 (±0.15)

0.79 (±0.02)

5.07 (±0.17) 5.07 (±0.17) 5.07 (±0.17)

11.8 (±0.75) 4.89 (±0.13) 1.22 (±0.06)

323.2 K 0.991 0.42 (±0.009) 343.2 K 0.951 4.17 (±0.07) 0.976 1.66 (±0.05) 0.989 0.42 (±0.009) p-xylene (1) + phenanthrene (2) + water

aqueous phase 5

10 x2

3.28 (±0.11) 3.28 (±0.11) 3.28 (±0.11)

5.26 (±0.28) 2.48 (±0.11) 0.82 (±0.07)

3.87 (±0.15) 3.87 (±0.15) 3.87 (±0.15)

7.39 (±0.29) 3.78 (±0.21) 0.13 (±0.07)

5.07 (±0.17) 5.07 (±0.17) 5.07 (±0.17)

14.4 (±0.39) 6.88 (±0.29) 2.17 (±0.05)

10 x1

K

S

4.68 (±0.03)

52886

1.13 × 107

7.30 (±0.32) 7.30 (±0.32) 7.30 (±0.32) (3)

35314 34008 34246

4.84 × 106 4.66 × 106 4.69 × 106

103x3

K

S

(±0.02) (±0.02) (±0.02)

576806 485484 362015

1.92 × 108 1.61 × 108 1.20 × 108

(±0.03) (±0.03) (±0.03)

410555 318519 225985

8.77 × 107 6.81 × 107 4.83 × 107

(±0.32) (±0.32) (±0.32)

210694 175000 137465

2.89 × 107 2.40 × 107 1.88 × 107

103x3

K

S

3.01 (±0.02) 3.01 (±0.02) 3.01 (±0.02)

462039 427907 318568

1.54 × 108 1.42 × 108 1.06 × 108

4.68 (±0.03) 4.68 (±0.03) 4.68 (±0.03)

211511 209825 164071

4.52 × 107 4.48 × 107 3.51 × 107

7.30 (±0.32) 7.30 (±0.32) 7.30 (±0.32)

105055 109725 102650

1.44 × 107 1.50 × 107 1.41 × 107

102x2

x1

303.2 K 0.967 3.02 (±0.05) 3.01 0.985 1.20 (±0.02) 3.01 0.994 0.30 (±0.007) 3.01 323.2 K 0.965 3.02 (±0.05) 4.68 0.983 1.20 (±0.02) 4.68 0.992 0.30 (±0.007) 4.68 343.2 K 0.963 3.02 (±0.05) 7.30 0.981 1.20 (±0.02) 7.30 0.990 0.30 (±0.007) 7.30 p-xylene (1) + anthracene (2) + water (3)

aqueous phase 5

103x3


10 x1

102x2

x1


10 x2

103x2

x1

3.28 (±0.11) 3.28 (±0.11) 3.28 (±0.11)

1.03 (±0.08) 0.56 (±0.02) 0.38 (±0.02)

0.992 0.995 0.996

3.87 (±0.15) 3.87 (±0.15) 3.87 (±0.15)

2.25 (±0.05) 1.14 (±0.05) 0.73 (±0.03)

0.991 0.993 0.994

5.07 (±0.17) 5.07 (±0.17) 5.07 (±0.17)

4.53 (±0.07) 2.18 (±0.09) 1.17 (±0.04)

0.988 0.990 0.992

303.2 K 4.76 (±0.06) 2.39 (±0.05) 1.20 (±0.05) 323.2 K 4.76 (±0.06) 2.39 (±0.05) 1.20 (±0.05) 343.2 K 4.76 (±0.06) 2.39 (±0.05) 1.20 (±0.05)

a

Standard uncertainties u are u(T) = 0.1 K and u(p) = 10 kPa. Standard uncertainties in mole fractions u(x) are presented in parentheses with a 95% confidence interval.

which a fluid circulates to maintain the temperature of the liquid mixture constant. The temperature was controlled to within 0.1 K. The water mixture is added first to the equilibrium cell by weighing, then the solvent in which we have dissolved our model molecule of tar at different mass concentration (0.5%, 2%, and 5%) is added to the aqueous phase. These mixtures were vigorously agitated for 8 h and then the two phases were settled for 8 h to obtain equilibrium. Once equilibrium is set, we begin withdrawing samples from lower and upper phases from the cell by means of two preheated sampling lines (one destined for the organic phase and the other one for the aqueous phase). As for some model molecules of tars (naphthalene, phenanthrene, and anthracene) only the aqueous phase has been withdrawn. The samples were collected in an auxiliary solvent (ethanol which water content is about 20 mg/L for thiophene and pyridine) and in another auxiliary solvent (dichloromethane for naphthalene, phenanthrene, and anthracene) in order to maintain their homogeneity. The analytical conditions used are described in Table 2. To obtain quantitative

results, the internal standard method was applied (internal standard, octane for thiophene and pyridine; hexadecane for naphthalene, phenanthrene, and anthracene). The calibration is prepared so as to cover the range of mass concentrations for each compound already selected for the same conditions. Before performing any equilibrium data, calibration curves were established by analyzing five to six different standard solutions containing known quantities of the thiophene, pyridine, naphthalene, phenanthrene, and anthracene, and the internal standard was diluted with p-xylene (or methyl hexadecanoate) and analyzed by GC-FID or GC−MS. The content of water in the organic phase was analyzed by coulometric Karl Fischer titration. Prior to measurements of water in the studied solvents, the KF determination of water was controlled by analyzing certified water standards “Hydranal-coulomat E” from Fluka (relative standard deviation RSD certified as 1%), where RSD(%) = 100 1030

S X̅i DOI: 10.1021/acs.jced.6b00857 J. Chem. Eng. Data 2017, 62, 1028−1035


Article

Table 4. Experimental Liquid−Liquid Equilibrium Data for the Ternary System Expressed in Molar Fractions (xi) at T = 308.2 K, 323.2 K, 343.2 K and Pressure P = 0.1 Mpa.a K Represents the Partition Coefficient of the Solute and S Is the Selectivity of the Solvent methyl hexadecanoate (1) + thiophene (2) + water (3) aqueous phase

hydrocarbon-rich phase

7

5

10 x1

10 x2

9.42 (±0.24) 9.42 (±0.24) 9.42 (±0.24)

10.6 (±0.32) 4.11 (±0.13) 1.34 (±0.02)

13.40 (±0.53) 13.40 (±0.53) 13.40 (±0.53)

11.4 (±0.56) 4.74 (±0.36) 1.40 (±0.09)

21.8 (±0.77) 21.8 (±0.77) 21.8 (±0.77)

14.6 (±0.07) 5.38 (±0.23) 1.61 (±0.15)

102x2

x1

303.2 K 0.820 14.4 (±0.21) 3.64 0.899 6.45 (±0.02) 3.64 0.945 1.90 (±0.008) 3.64 323.2 K 0.822 13.9 (±0.03) 3.93 0.899 6.20 (±0.02) 3.93 0.943 1.78 (±0.007) 3.93 343.2 K 0.817 13.7 (±0.03) 4.58 0.893 6.17 (±0.04) 4.58 0.937 1.72 (±0.005) 4.58 methyl hexadecanoate (1) + pyridine (2) + water (3)

aqueous phase

K

S

(±0.08) (±0.08) (±0.08)

1358 1569 1418

3.73 × 104 4.31 × 104 3.90 × 104

(±0.09) (±0.09) (±0.09)

1219 1308 1271

3.10 × 104 3.33 × 104 3.24 × 104

(±0.25) (±0.25) (±0.25)

938 1147 1068

2.05 × 104 2.50 × 104 2.33 × 104

K

S

16.18 19.32 19.60

4.44 × 102 5.31 × 102 5.38 × 102

17.91 20.35 21.39

4.56 × 102 5.18 × 102 5.44 × 102

19.63 22.07 23.15

4.29 × 102 4.82 × 102 5.05 × 102


107x1

103x2

9.42 (±0.24) 9.42 (±0.24) 9.42 (±0.24)

5.31 (±0.17) 2.07 (±0.08) 0.60 (±0.01)

13.40 (±0.53) 13.40 (±0.53) 13.40 (±0.53)

4.88 (±0.24) 1.98 (±0.07) 0.55 (±0.03)

21.8 (±0.77) 21.8 (±0.77) 21.8 (±0.77)

4.57 (±0.02) 1.88 (±0.04) 0.51 (±0.05)

102x2

x1

102x3

303.2 K 8.59 (±0.13) 3.64 (±0.08) 4.00 (±0.02) 3.64 (±0.08) 1.17 (±0.006) 3.64 (±0.08) 323.2 K 0.873 8.74 (±0.03) 3.93 (±0.09) 0.920 4.03 (±0.01) 3.93 (±0.09) 0.949 1.17 (±0.005) 3.93 (±0.09) 343.2 K 0.865 8.97 (±0.08) 4.58 (±0.25) 0.913 4.15 (±0.03) 4.58 (±0.25) 0.942 1.19 (±0.005) 4.58 (±0.25) methyl hexadecanoate (1) + naphthalene (2) + water (3) 0.878 0.924 0.952

aqueous phase


107x1

107x2

9.42 (±0.24) 9.42 (±0.24) 9.42 (±0.24)

7.18 (±0.03) 2.96 (±0.09) 0.82 (±0.03)

13.40 (±0.53) 13.40 (±0.53) 13.40 (±0.53)

9.94 (±0.06) 4.39 (±0.11) 1.13 (±0.04)

21.8 (±0.77) 21.8 (±0.77) 21.8 (±0.77)

15.0 (±0.28) 6.56 (±0.22) 1.74 (±0.03)

x1

102x2

102x3

303.2 K 9.89 (±0.08) 3.64 (±0.08) 4.12 (±0.06) 3.64 (±0.08) 1.05 (±0.04) 3.64 (±0.08) 323.2 K 0.862 9.89 (±0.08) 3.93 (±0.09) 0.920 4.12 (±0.06) 3.93 (±0.09) 0.950 1.05 (±0.04) 3.93 (±0.09) 343.2 K 0.855 9.89 (±0.08) 4.58 (±0.25) 0.913 4.12 (±0.06) 4.58 (±0.25) 0.944 1.05 (±0.04) 4.58 (±0.25) methyl hexadecanoate (1) + phenanthrene (2) + water (3) 0.865 0.922 0.953

aqueous phase 107x1

102x3

K

S

137716 139020 128922

3.78 3.82 3.54

99477 93736 93097

2.53 2.39 2.37

65920 62729 60460

1.44 1.37 1.32


x1

9.42 (±0.24) 9.42 (±0.24) 9.42 (±0.24)

3.17 (±0.05) 1.68 (±0.09) 0.82 (±0.03)

0.890 0.934 0.956

13.40 (±0.53) 13.40 (±0.53) 13.40 (±0.53)

5.41 (±0.12) 2.64 (±0.12) 0.99 (±0.04)

0.887 0.931 0.953

102x2 303.2 K 7.33 (±0.07) 3.01 (±0.04) 0.78 (±0.02) 323.2 K 7.33 (±0.07) 3.01 (±0.04) 0.78 (±0.02) 1031

102x3

K

S

3.64 (±0.08) 3.64 (±0.08) 3.64 (±0.08)

231230 179167 122433

6.35 × 106 4.92 × 106 3.36 × 106

3.93 (±0.09) 3.93 (±0.09) 3.93 (±0.09)

135490 114015 78680

3.45 × 106 2.90 × 106 2.00 × 106



Article

Table 4. continued methyl hexadecanoate (1) + phenanthrene (2) + water (3) aqueous phase 107x1


21.8 (±0.77) 21.8 (±0.77) 21.8 (±0.77)

11.6 (±0.43) 6.51 (±0.07) 1.93 (±0.09)

102x2

x1

102x3

343.2 K 0.881 7.33 (±0.07) 0.924 3.01 (±0.04) 0.946 0.78 (±0.02) methyl hexadecanoate (1) + anthracene (2) +

aqueous phase

K

S

63190 46237 40155

1.38 × 106 1.01 × 106 8.77 × 105

102x3

K

S

3.64 (±0.08) 3.64 (±0.08) 3.64 (±0.08)

220401 168975 117857

6.05 × 106 4.64 × 106 3.24 × 106

3.93 (±0.09) 3.93 (±0.09) 3.93 (±0.09)

115238 96063 58696

2.93 × 106 2.44 × 106 1.49 × 106

4.58 (±0.25) 4.58 (±0.25) 4.58 (±0.25)

47082 39355 27248

1.03 × 106 8.59 × 105 5.95 × 105

4.58 (±0.25) 4.58 (±0.25) 4.58 (±0.25) water (3)


107x1

108x2

x1

9.42 (±0.24) 9.42 (±0.24) 9.42 (±0.24)

5.49 (±0.17) 3.61 (±0.10) 2.52 (±0.14)

0.952 0.958 0.961

13.40 (±0.53) 13.40 (±0.53) 13.40 (±0.53)

10.5 (±0.29) 6.35 (±0.17) 5.06 (±0.28)

0.949 0.955 0.958

21.8 (±0.77) 21.8 (±0.77) 21.8 (±0.77)

25.7 (±1.04) 15.5 (±0.23) 10.9 (±0.12)

0.942 0.948 0.951

103x2 303.2 K 12.1 (±0.21) 6.10 (±0.15) 2.97 (±0.09) 323.2 K 12.1 (±0.21) 6.10 (±0.15) 2.97 (±0.09) 343.2 K 12.1 (±0.21) 6.10 (±0.15) 2.97 (±0.09)

a Standard uncertainties u are u(T) = 0.1 K and u(p) = 10 kPa. Standard uncertainties in mole fractions u(x) are presented in parentheses with a 95% confidence interval.

Table 5. Hand’s Constants and Regression Coefficients p-xylene + thiophene + water T/K 303.15 323.15 343.15 T/K 303.15 323.15 343.15 T/K 303.15 323.15 343.15

Figure 1. Hand’s correlation for the mixture naphthalene + water + p-xylene.

T/K

3. RESULTS AND DISCUSSION 3.1. Binary Systems. The binary systems were described and studied in our previous work.7 In the previous publication the mutual solubility data expressed in terms of mole fraction of the binary systems water + p-xylene (or methyl hexadecanoate) are represented. Each measurement was replicated at least five to six times and the maximum relative standard deviation (RSD) is less than 3%. These mutual solubility measurements relative to the binary system (water/p-xylene) are in a good agreement with the literature data. Those measurements relative to the binary system (water/methyl hexadecanoate) are original and were not found in the literature. 3.2. Ternary Systems. Tables 3 and 4 report the experimental study of the liquid−liquid equilibrium data for the ternary

303.15 323.15 343.15

A

B

0.9999 7.2194 1.0125 7.1704 1.0190 7.0226 p-xylene + pyridine + water A

B

1.0318 2.4751 1.0171 2.6224 1.0132 2.7583 p-xylene + naphthalene + water A

B

1.0039 11.294 1.0188 11.187 1.0281 10.981 p-xylene + phenanthrene + water A

B

1.2760 17.777 1.3604 18.867 1.2384 16.042 p-xylene + anthracene + water

R2 1 0.9999 1 R2 1 0.9998 1 R2 1 0.9999 0.9997 R2 1 0.9998 0.9998

T/K

A

B

R2

303.15 323.15 343.15

1.3510 1.2114 1.0176

19.544 16.032 11.888

0.9849 0.9854 0.9978

systems p-xylene−water + thiophene, + pyridine, + naphthalene, + phenanthrene, + anthracene, and methyl hexadecanoate− water + thiophene, + pyridine, + naphthalene, + phenanthrene, + anthracene. Standard uncertainties with a 95% confidence interval are written in parentheses for the molar fraction 1032



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presents the smallest partition coefficient due to its polarity, whereas phenanthrene and the anthracene are the compounds that represent the highest partition coefficient. The partition coefficient values of the ternary systems decrease as the temperature increases (except the extracting solvent−water + pyridine systems). Hence, the lowest temperature is recommended to extract tar from aqueous medium due to their highest partition coefficient. We have also used the effectiveness of a solvent which is expressed by the selectivity “S”, of the solvent. The selectivity of the two solvents (p-xylene and methyl palmitate), which measures the ability of a solvent to separate the solutes (thiophene, pyridine, naphthalene, phenanthrene, and anthracene), from water is given by

(Tables 3 and 4). For these mixtures and systems, no literature data, for comparison, were found. For that and in order to check the coherence of our experimental data we have correlated these data by Hand’s equation:8,9 ln

φ org Xsolute φ org Xorganicsolvent

= A + B ln

φ aq Xsolute φ aq X water

(1)

org where Xϕsolute is the molar fraction of the solute in the organic ϕ org phase, Xorganic solvent is the molar fraction of the organic solvent in Aq the organic phase, Xϕsolute is the molar fraction of the solute in the Aq aqueous phase, and Xϕwater is the molar fraction of water in the aqueous phase. The linearity of the Hand’s equation plots indicates the coherence of the data for all systems excepting the extracting solvent−water + anthracene system, where the regression coefficient is a little bit far from 1, indicating that the systems with anthracene as a model molecule of tar is not ideal; an example is shown in Figure 1. Tables 5 and 6 show the fitting parameters and the regression coefficient R2 of the Hand equation.

S=

methyl hexadecanoate + thiophene + water 308.15 323.15 343.15 T/K 308.15 323.15 343.15 T/K 308.15 323.15 343.15 T/K 308.15 323.15 343.15

A

B

1.0505 7.9102 1.0467 7.7339 0.9955 7.0446 methyl hexadecanoate + pyridine + water A

B

0.9506 2.6806 0.9569 2.8015 0.9639 2.9361 methyl hexadecanoate + naphthalene + water A

B

1.0694 12.962 1.0727 12.636 1.0828 12.344 methyl hexadecanoate + phenanthrene + water A

B

1.4584 19.322 1.3835 17.491 1.2883 15.043 methyl hexadecanoate + anthracene + water

R2

R2 0.9980 0.9996 0.9997

N

OF =

k

1 0.9991 0.9996

j

rmsd =

R2

308.15 323.15 343.15

1.8126 1.8423 1.6306

25.961 25.299 20.427

0.9966 0.9492 0.9876

(4)

i

2

3

∑∑∑ k

1 0.9993 0.9926 R2

3

The root-mean-square deviation (rmsd) describes the quality of a correlation and is calculated as follows: N

B

j

i

exptl calcd 2 (xijk − xijk )

6N

(5)

where N is defined as the number of tie lines; xexptl is the experimental mole fraction; xcalcd is the calculated mole fraction; the subscript i indexes the components, j indexes the phases, and k represents the tie lines. In Table 7 are listed the regressed parameters of the two equations with the root mean-square deviation (rmsd) values. With respect to the rmsd, both NRTL and UNIQUAC models give a good representation of the liquid−liquid-equilibrium (LLE) data of all the systems studied here. In addition, when comparing the rmsd between p-xylene and methyl palmitate systems, the modelization is more accurate for the p-xylene systems than the methyl palmitate systems.

In this study, the partition coefficient is used to evaluate the solubility of the model molecules of tars in each phase which is given by the following equation: xorg xaq

2

∑ ∑ ∑ (xijkexptl − xijkcalcd)2

R2

A

(3)

4. DATA CORRELATION We have utilized the NRTL10 and the UNIQUAC11 models in order to fit the experimental data of the ternary systems. We set the nonrandomness parameter (αij) for NRTL equation to 0.2 for the majority of the ternary systems. By minimizing the objective function, OF, we obtain the other parameters for both equations. The OF is given by eq 4:

0.9974 0.9999 0.9970

T/K

K=

(x 2/x3)water

where the subscript 2 represents the solute and 3 represents water. We can find in Table 3 and Table 4, the list of the experimental values of the selectivity, “S”. As seen, “S” is almost constant when going through the tie lines from high to low concentration of solute (except the extracting solvent−water + phenanthrene and anthracene systems). For a given system: the higher is the temperature, the lower is the selectivity; however, the order of magnitude of “S” is respected.

Table 6. Hand’s Constants and Regression Coefficients T/K

(x 2/x3)extractingsolvent

5. CONCLUSION Liquid−liquid equilibrium data for ternary systems constituted by p-xylene−water + thiophene (or + pyridine or + naphthalene or + phenanthrene or + anthracene) and methyl hexadecanoate− water + thiophene (or + pyridine or + naphthalene or + phenanthrene or + anthracene) were measured at 303.2 or 308.2 K, and 323.2 and 343.2 K and atmospheric pressure, 0.1 MPa. The experimental data were then correlated with Hand’s equation;

(2)

xorg = molar fraction of the solute in the organic phase; xaq = molar fraction of the solute in the aqueous phase We have reported the partition coefficient of the solutes (thiophene, pyridine, naphthalene, phenanthrene, and anthracene) at three different temperatures: 303.2 or 308.2, 323.2, and 343.2 K in Tables 3 and 4. Pyridine is the compound which by far 1033



Article

Table 7. UNIQUAC and NRTL Parameters for the Ternary Systems component i−j

UNIQUAC Aij (J·mol−1)

1−2 1−3 2−3

−391.62 7826.17 11752.86

1−2 1−3 2−3

−849.41 7826.17 −5547.98

1−2 1−3 2−3

51.71 7826.17 7514.46

1−2 1−3 2−3

1754.98 7826.17 7575.13

1−2 1−3 2−3

1869.83 7826.17 7576.89

1−2 1−3 2−3

165.71 4386.92 11752.86

1−2 1−3 2−3

483.67 4386.92 −5547.98

1−2 1−3 2−3

−461.50 4386.92 7514.46

1−2 1−3 2−3

1202.90 4386.92 7575.13

1−2 1−3 2−3

1167.34 4386.92 7575.13

Aji (J·mol−1)

NRTL Aij (J·mol−1)

rmsd

p-Xylene (1) + Thiophene (2) + Water (3) 447.48 −1788.31 2988.81 3159.55 0.0021 11280.66 23873.25 3054.32 10270.40 14983.56 p-Xylene (1) + Pyridine (2) + Water (3) 638.41 −1335.21 1867.77 3159.55 0.0019 13378.39 23397.77 3972.71 1823.91 6534.86 p-Xylene (1) + Naphthalene (2) + Water (3) 285.56 642.32 −559.55 3159.55 0.0024 13425.77 23387.17 3012.48 11560.20 25882.73 p-Xylene (1) + Phenanthrene(2) + Water (3) −162.34 7353.20 873.52 3159.55 0.0023 13425.77 23387.17 3094.07 12699.80 36296.33 p-Xylene (1) + Anthracene (2) + Water (3) −147.28 7297.92 854.95 3159.55 0.0021 13425.77 23387.17 3092.06 12700.72 36296.93 Methyl Hexadecanoate (1) + Thiophene (2) + Water (3) 622.10 12949.84 −6486.41 2095.43 0.022 14423.73 49784.43 3054.32 10875.91 14685.40 Methyl Hexadecanoate (1) + Pyridine (2) + Water (3) −976.45 −2892.78 3858.15 2095.43 0.010 7679.58 42817.25 3972.71 1567.57 6512.59 Methyl Hexadecanoate (1) + Naphthalene (2) + Water (3) 602.54 −3926.05 6706.77 2095.43 0.0046 7233.76 42867.05 3012.48 11553.33 25883.50 Methyl Hexadecanoate (1) + Phenanthrene (2) + Water (3) 1004.16 5964.20 6599.22 2095.43 0.0051 7594.05 42827.72 3094.07 12699.26 36296.48 Methyl Hexadecanoate (1) + Anthracene (2) + Water (3) 1004.16 5963.97 6597.82 2095.43 0.0059 7212.20 42872.79 3092.06 12698.74 36297.53

α

rmsd

0.20 0.20 0.20

0.00080

0.20 0.20 0.693

0.0028

0.20 0.20 0.20

0.0024

0.20 0.20 0.20

0.0023

0.20 0.20 0.20

0.0021

0.20 0.20 0.20

0.021

0.20 0.20 0.693

0.0095

0.20 0.20 0.20

0.0083

0.20 0.20 0.20

0.0037

0.20 0.20 0.20

0.012

Funding

the linearity of the plots for the different systems indicates the coherence of our data. The partition coefficient values of the ternary systems decrease as the temperature increases, and the selectivity also decreases when the temperature increases. Hence, the lowest temperature is recommended to extract tar from aqueous medium. On the other hand, the descriptions of the systems using NRTL and UNIQUAC models have shown good agreement with the experimental measurements. As mentioned previously, the purpose of this study was to constitute a database which will be used to extract tars from the biomass conversion process.

■

Aji (J·mol−1)

This project, VeGaz, was funded by a grant from the Agence Nationale pour la Recherche within the scope of the Bioenergy program titled “Green natural gas production from syngas through biomass gasification”. Acknowledgements are also expressed to MIRA program (Mobilité Internationale RegionsAlpes). Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Han, J.; Kim, H. The reduction and control technology of tar during biomass gasification/pyrolysis: An overview. Renewable Sustainable Energy Rev. 2008, 12, 397−416. (2) Guehenneux, G.; Baussand, P.; Brothier, M.; Poletiko, C.; Boissonne, G. Energy production from biomass pyrolysis. Fuel 2005, 84, 733−739.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Georgio Bassil: 0000-0001-9170-7631 1034



Article

(3) Devi, L.; Ptasinski, K. J.; Janssen, F. J. J. G. A review of the primary measures for tar elimination in biomass gasification processes. Biomass Bioenergy 2003, 24, 125−140. (4) Devi, L.; Ptasinski, K. J.; Janssen, J. J. G. F.; Paasen, V. B. S.; Bergman, C. A. P.; Kiel, H. A. J. Catalytic decomposition of biomass tars: use of dolomite and untreated olivine. Renewable Energy 2005, 30, 565− 587. (5) Pfeifer, C.; Hofbauer, H. Development of catalytic tar decomposition downstream from a dual fluidized bed biomass steam gasifier. Powder Technol. 2008, 180, 9−16. (6) Milne, T. A.; Abatzaglou, N.; Evans, R. J. Biomass gasifier “Tars”: Their nature, formation and conversion. NREL/TP-570-25357; National Renewable Energy Laboratory, 1998, DOI:10.2172/3726. (7) Bassil, G.; Mokbel, I.; Abou Naccoul, R.; Stephan, J.; Jose, J.; Goutaudier, C. Tar removal from biosyngas in the biomass gasification process. (Liquid + liquid) equilibrium {water + solvent (p-xylene and methyl hexadecanoate) + model molecules of tar (benzene, toluene, phenol)}. J. Chem. Thermodyn. 2012, 48, 123−128. (8) Carniti, P.; Cori, L.; Ragaini, V. A critical analysis of the hand and Othmer-Tobias correlations. Fluid Phase Equilib. 1978, 2, 39−47. (9) Abrams, D. S.; Prausnitz, J. M. Statistical thermodynamics of liquid mixtures: a new expression for the excess Gibbs energy of partly or completely miscible systems. AIChE J. 1975, 21, 116−128. (10) Bohon, R. L.; Claussen, W. F. The Solubility of Aromatic Hydrocarbons in Water. J. Am. Chem. Soc. 1951, 73, 1571−1578. (11) Andrews, L. J.; Keefer, R. M. Cation Complexes of compounds containing Carbon-Carbon double bonds. IV. The argentation of aromatic hydrocarbons. J. Am. Chem. Soc. 1949, 71, 3644−3647.

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Elimination of Tar in Biomass Gasification Process: LiquidâLiquid

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