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Ind. Eng. Chem. Res. 2010, 49, 9462–9468
Liquid-Liquid Equilibrium Data in Ionic Liquid + 4-Methyldibenzothiophene + n-Dodecane Systems Leonardo Hadlich de Oliveira and Martı´n Aznar* School of Chemical Engineering, UniVersity of Campinas, AV. Albert Einstein 500, 13083-852 Campinas, SP, Brazil
In this work, liquid-liquid equilibrium data for 1-ethyl-3-methylimidazolium diethylphosphate ([emim][DEtPO4]) or 1-ethyl-3-methylimidazolium ethylsulfate ([emim][EtSO4]) + 4-methyl-dibenzothiophene (4MDBT) + n-dodecane systems at 25 and 40 °C and atmospheric pressure (≈95 kPa) were determined by refractometry. 4-MDBT is a DBT derivative and it is one of the most difficult diesel sulfur pollutants to remove by the conventional process of hydrodesulfurization. The liquid-liquid equilibrium data were used to study the 4-MDBT extraction from n-dodecane as model diesel oil. 4-MDBT distribution coefficients, solvent selectivities, and extraction data also indicate that [emim][DEtPO4] is a better solvent for extractive desulfurization of n-dodecane than [emim][EtSO4]. For a solvent/n-dodecane mass ratio of 0.6, the sulfur content in n-dodecane decreases 17-24% and 5-15% for [emim][DEtPO4] and [emim][EtSO4], respectively. The quality of the data was ascertained by the Hand and Othmer-Tobias correlations, which presented R2 > 0.97 for all systems. The NRTL model was used to correlate the data and showed root-mean-square deviations of 300 °C, pressure > 30 bar, large amounts of H2, and expensive catalysts.1 Moreover, some sulfur compounds derived from dibenzothiophene (DBT), such as the sterically hindered 4-methyldibenzotiophene (4-MDBT),2-8 are refractory to HDS, making it more difficult to achieve the strict restrictions for S content in the fuel adopted by the United States, the European Union, Japan, and Brazil, which is e50 ppm.9 To remove 4-MDBT from diesel oil in mild operation conditions, alternative processes such oxidative desulfurization (ODS),10-12 biodesulfurization, (BDS)13-15 and extractive desulfurization (EDS) are reported in the literature. The EDS process is the separation of DBT derivatives from diesel by extraction with a liquid solvent that, preferably, does not solubilize in the fuel. As liquid extracting agents, ionic liquids have received attention in recent years because these compounds and n-alkanes present low mutual solubility.1,16 Extraction of DBT1,17-21 and 4-MDBT1 from fuel using ionic liquids and liquid-liquid equilibrium data for alkane + thiophene + ionic liquid systems22-25 are reported in the literature. This work is part of a study of diesel EDS with the focus on removal of DBT, 4-MDBT, and 4,6-dimethyldibenzothiophene (4,6-DMDBT). Liquid-liquid equilibrium data for the systems 1-ethyl-3-methylimidazolium diethylphosphate ([emim][DEtPO4]) or 1-ethyl-3-methylimidazolium ethylsulfate ([emim][EtSO4]) + 4-MDBT + n-dodecane, using n-dodecane as model diesel oil, at 25 and 40 °C and atmospheric pressure (≈95 kPa), were determined. There are no liquid-liquid equilibrium data reported for ionic liquid + sterically hindered sulfur compound + model diesel oil systems as studied here. 2. Experimental Section 2.1. Chemicals. The chemicals used and their properties are listed in Table 1. * To whom correspondence should be addressed. Tel.: +55 19 3521 3962. E-mail:
[email protected].
The ionic liquids were purified under vacuum (8 kPa) and magnetic stirring at 50 °C for 24 h and stored under nitrogen atmosphere. Water content below 500 ppm was achieved. Other chemicals were used as received. 2.2. Procedure. All experiments were carried out in equilibrium glass cells of 23 mL, similar to those suggested by Sandler27 and described elsewhere.28 The cell temperature was regulated by a Tecnal TE-184 thermostatic bath, accurate to (0.1 °C. A cloud point method based on that of Letcher and Siswana29 was utilized for determination of binodal curves for ionic liquidrich phase. By titrating known binary mixtures of 4-MDBT + ionic liquid with n-dodecane until constant turbidity and measuring the refractive index (nD) of each point in triplicate with a Mettler-Toledo RE 40D refractometer, calibration curves were obtained for quantification of the ionic liquid phase. Because the ionic liquids do not solubilize in the alkane-rich phase, the refractive index of known composition of binary mixtures of (n-dodecane + 4-MDBT) binodal curves was measured as well in triplicate. In liquid-liquid equilibrium experiments, ternary mixtures with composition within the immiscibility region were prepared directly inside the cells. Each component was weighed using a Shimadzu AX200 analytical balance, accurate to (0.0001 g. The mixtures were vigorously agitated at approximately 1300 rpm with a Fisatom 752 magnetic stirrer for 12 h to allow good contact between the phases and were left to settle for 24 h until complete separation in two clean liquid phases. An ionic liquid/ n-dodecane feed mass ratio equal to 0.6 was used in all experiments to compare the removal percent of 4-MDBT from n-dodecane obtained for each ionic liquid (see section 3.3). In solid-liquid equilibrium experiments, a binary mixture of 4-MDBT + n-dodecane with 4-MDBT mass fraction equal to 0.4 was stirred for 12 h and allowed to settle for 24 h at 25 °C. One phase (pure 4-MDBT) precipitates in equilibrium with a second phase (saturated liquid mixture of 4-MDBT + n-dodecane). For each unknown composition liquid phase obtained from LLE or SLE experiments, the refractive index was measured
10.1021/ie1009876 2010 American Chemical Society Published on Web 09/07/2010
Ind. Eng. Chem. Res., Vol. 49, No. 19, 2010
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Table 1. Properties of Pure Components refractive index 25 °C
40 °C
chemical
molar mass (g/mol)
exptl
lit.
exptl
[emim][DEtPO4] [emim][EtSO4] 4-MDBT n-dodecane
264.26 236.29 198.28 170.33
1.4733 1.4789
NAa 1.47903b
1.4691 1.4745
NA NA
1.4196
1.42011b
1.4131
1.4129c
a
b
lit.
purity (% mass)
supplier
g98 95 96 99.6
Aldrich Fluka Aldrich Fluka
c
NA, not available. Reference 25. Reference 26.
Table 2. Mass Fraction (w), Refractive Index (nD), and Standard Deviation (σ) of Data Points on the Binodal Curve for Ionic Liquid (1) + 4-MDBT (2) + n-Dodecane (3) Systems at 25 and 40 °C [emim][DEtPO4]
[emim][EtSO4] 4
temperature (°C)
w1
w2
nD
10 σ
w1
w2
nD
104σ
25
0.9967 0.9736 0.9522 0.9312 0.9096
0.0000 0.0225 0.0434 0.0627 0.0808
1.4724 1.4770 1.4812 1.4852 1.4905
0.00 1.15 0.00 1.73 0.00
0.9983 0.9852 0.9795 0.9755 0.9494
0.0000 0.0067 0.0137 0.0177 0.0452
1.4788 1.4799 1.4813 1.4821 1.4878
0.00 1.00 0.58 0.71 1.73
40
0.9951 0.9731 0.9486 0.9269 0.9022
0.0000 0.0226 0.0446 0.0663 0.0888
1.4685 1.4728 1.4775 1.4819 1.4866
0.58 1.15 0.50 0.00 1.00
0.9986 0.9851 0.9711 0.9635 0.9555
0.0000 0.0088 0.0214 0.0293 0.0387
1.4749 1.4770 1.4793 1.4810 1.4828
0.58 0.58 0.58 0.58 0.58
Table 3. Mass Fraction (w), Refractive Index (nD), and Standard Deviation (σ) for Binary Mixtures of n-Dodecane (1) + 4-MDBT (2)a 25 °C
40 °C
w2
nD
10 σ
w2
nD
104σ
0.0000 0.0072 0.0139 0.0209 0.0280 0.0349 0.0607 0.0991 0.1515 0.2313
1.4196 1.4208 1.4219 1.4231 1.4243 1.4255 1.4300 1.4368 1.4464 1.4592
0.00 0.58 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
0.0000 0.0072 0.0139 0.0209 0.0280 0.0349 0.0607 0.0991 0.1515 0.2994
1.4131 1.4143 1.4155 1.4166 1.4178 1.4190 1.4234 1.4302 1.4388 1.4691
0.00 0.00 0.00 0.58 0.58 0.00 0.00 0.00 0.00 0.58
a
4
SLE in bold: solid phase ) pure 4-MDBT.
in triplicate and the average used for the composition determination using the previously prepared calibration curve. 2.3. Thermodynamic Modeling. The nonrandom two-liquid model (NRTL),30 based on the local composition concept, was used to correlate the experimental data. The NRTL equations are given by:
ln γi )
∑
τjiGjixj
j
∑
+
∑G x
j
ki k
k
xjGij
∑G x
kj k
k
τij )
[
τij -
∑
xkτkjGki
k
∑G x
kj k
k
∆gij Bij ) Aij + (τij * τji) RT T
Gij ) exp(-Rijτij)(Rij ) Rji)
]
(1)
F)
M
N-1
k
j
i
∑ ∑ ∑ {(x
I,exptl ijk
δx ) 100
M
N
∑ ∑ (x
I,exptl ij
i
- xI,calcd )2 + (xII,exptl - xII,calcd )2 ij ij ij
j
2MN
(5)
3. Results and Discussion 3.1. Cloud Points and Calibration Curves. The cloud points determined are shown in Table 2. Applying linear or quadratic regression to these data, the equations for the calibration curves obtained for [emim][DEtPO4] (1) + 4-MDBT (2) + n-dodecane (3) system are nD25 ) 1.6741 - 0.2023w1
(6a)
nD25 ) 1.4723 + 0.2163w2
(6b)
nD40 ) 1.6629 - 0.1953w1
(7a)
nD40 ) 1.4684 + 0.2046w2
(7b)
and for [emim][EtSO4] (1) + 4-MDBT (2) + n-dodecane (3) are
(2) (3)
New energy interaction parameters were estimated by using the Fortran code TML-LLE 2.0;31 the procedure is based on the modified Simplex method32 and consists of the minimization of a concentration-based objective function, F.33 D
Calculated compositions can be compared with the experimental ones through the percent root-mean-square deviation (rmsd), given by
- xI,calcd )2 + (xII,exptl - xII,calcd )2} ijk ijk ijk
(4)
nD25 ) 3.3470 - 3.6426w1 + 1.7741w21
(8a)
nD25 ) 1.4786 + 0.2013w2
(8b)
nD40 ) 1.6559 - 0.1815w1
(9a)
nD40 ) 1.4750 + 0.2020w2
(9b)
The binary n-dodecane + 4-MDBT calibration curve points are in Table 3. Applying linear regression, the equations obtained are
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Table 4. Liquid-Liquid Equilibrium Data for [emim][DEtPO4] (1) + 4-MDBT (2) + n-Dodecane (3) System at 25 and 40 °C liquid-liquid equilibrium data feed
alkane phase
ionic liquid phase 4
temperature (°C)
x1
x2
x1
x2
nD
10 σ
x1
x2
nD
104σ
K
S
25
0.2336 0.2665 0.2433 0.2353 0.2487
0.0143 0.0199 0.0432 0.0800 0.1269
0.0000 0.0000 0.0000 0.0000 0.0000
0.0145 0.0209 0.0434 0.0826 0.1375
1.4224 1.4237 1.4283 1.4362 1.4471
0.00 0.00 0.00 0.00 0.58
0.9810 0.9774 0.9556 0.9277 0.8871
0.0141 0.0174 0.0375 0.0635 0.1011
1.4746 1.4751 1.4785 1.4828 1.4892
0.00 0.58 1.53 0.00 1.00
0.9714 0.8316 0.8642 0.7681 0.7350
193.4 156.3 121.3 79.4 53.4
40
0.2731 0.2635 0.2569 0.2412
0.0317 0.0597 0.1025 0.1343
0.0000 0.0000 0.0000 0.0000
0.0331 0.0624 0.1086 0.1425
1.4196 1.4258 1.4355 1.4425
0.58 0.00 0.58 0.00
0.9638 0.9450 0.9151 0.8858
0.0284 0.0462 0.0745 0.1024
1.4728 1.4756 1.4801 1.4846
0.58 0.00 0.58 0.00
0.8566 0.7411 0.6859 0.7186
105.3 78.8 59.1 52.0
Table 5. Liquid-Liquid Equilibrium Data for [emim][EtSO4] (1) + 4-MDBT (2) + n-Dodecane (3) System at 25 and 40 °C liquid-liquid equilibrium data feed
alkane phase
ionic liquid phase
temperature (°C)
x1
x2
x1
x2
nD
10 σ
x1
x2
nD
104σ
K
S
25
0.2945 0.2919 0.2912 0.2818 0.2657
0.0097 0.0194 0.0476 0.0948 0.1440
0.0000 0.0000 0.0000 0.0000 0.0000
0.0121 0.0235 0.0578 0.1183 0.1849
1.4219 1.4242 1.4312 1.4433 1.4564
0.00 0.58 0.00 0.00 0.58
0.9925 0.9846 0.9679 0.9504 0.9399
0.0030 0.0077 0.0206 0.0393 0.0533
1.4791 1.4799 1.4821 1.4853 1.4877
1.73 1.53 0.58 1.15 1.53
0.2448 0.3267 0.3563 0.3323 0.2882
53.7 41.0 29.3 28.4 34.5
40
0.2907 0.2868 0.2825 0.2779 0.2429
0.0187 0.0379 0.0578 0.0764 0.1929
0.0000 0.0000 0.0000 0.0000 0.0000
0.0233 0.0454 0.0685 0.0923 0.2392
1.4175 1.4222 1.4271 1.4321 1.4621
0.00 0.58 0.58 0.58 1.00
0.9881 0.9788 0.9676 0.9610 0.9231
0.0065 0.0147 0.0246 0.0305 0.0640
1.4761 1.4775 1.4792 1.4802 1.4860
0.58 0.58 1.15 1.15 1.00
0.2779 0.3238 0.3594 0.3298 0.2675
50.0 47.6 42.9 35.0 15.7
nD40 ) 1.4194 + 0.1768w2
(10a)
nD40 ) 1.4125 + 0.1851w2
(10b)
In Table 3, the values in bold represent solid-liquid equilibrium, obtained by saturation of 4-MDBT in n-dodecane at 25 °C. The saturation at 40 °C was not determined. 3.2. Experimental Equilibrium Data. Liquid-liquid equilibrium data (mole fractions) for ternary systems [emim][DEtPO4] + 4-MDBT + n-dodecane and [emim][EtSO4] + 4-MDBT + n-dodecane, at 25 and 40 °C and atmospheric pressure (≈95 kPa), are reported in Tables 4 and 5. Also, in these tables are the distribution coefficient and selectivity of the solvent given by eqs 11 and 12, respectively. K)
xilp 2 xap 2
4
to the feed composition, indicating low experimental error by loss of mass or analysis; (b) the LLE data were tested with correlations given by Hand34
()
log
xilp 2
xilp 1
()
) kH log
xap 2
xap 3
+ constH
(13)
and Othmer-Tobias:35
( )
log
1 - xilp 1 xilp 1
( )
) kOT log
1 - xap 3 xap 3
+ constOT
(14)
(11)
xilp 2 S)
xap 2 xilp 3
(12)
xap 3 The symbols “ilp” and “ap” refer to ionic liquid-rich phase and alkane-rich phase, respectively. The LLE data obtained are shown in Figures 1-4, and SLE data are shown in Figures 1 and 3. The distribution of 4-MDBT in both phases (Figure 5) and selectivity values above 50 (Figure 6) lead to the conclusion that [emim][DEtPO4] is a better solvent than [emim][EtSO4] for extraction of 4-MDBT from n-dodecane at the two temperatures studied. The slopes of tie-lines, as well as the values of K, show that 4-MDBT solubilizes preferably in n-dodecane rather than ionic liquid. The quality of the LLE data is pointed out by two factors: (a) tie lines agree very well with the cloud points and are very close
Figure 1. Experimental and calculated phase equilibrium data for the system [emim][DEtPO4] + 4-MDBT + n-dodecane at 25 °C: cloud points (9); feed points (b); tie-lines (2, solid line); 4-MDBT saturation in n-dodecane (]); NRTL correlation (O, dotted line).
Ind. Eng. Chem. Res., Vol. 49, No. 19, 2010
Figure 2. Experimental and calculated phase equilibrium data for the system [emim][DEtPO4] + 4-MDBT + n-dodecane at 40 °C: cloud points (9); feed points (b); tie-lines (2, solid line); NRTL correlation (O, dotted line).
Figure 3. Experimental and calculated phase equilibrium data for the system [emim][EtSO4] + 4-MDBT + n-dodecane at 25 °C: cloud points (9); feed points (b); tie-lines (2, solid line); 4-MDBT saturation in n-dodecane (]); NRTL correlation (O, dotted line).
A regression coefficient R2 > 0.97 was obtained for all systems, as shown in Figures 7 and 8. 3.3. Removal of 4-MDBT. The percent removed of 4-MDBT from n-dodecane is quantified by eq 15 using liquid-liquid equilibrium data presented in Tables 4 and 5. The results of 4-MDBT removal are shown in Table 6 and Figure 9. C0 - Cf % removal ) 100 × ) C0 w2 w2 w2 + w3 feed w2 + w3 alkane phase 100 × (15) w2 w2 + w3 feed
(
) ( ) ( )
C0 is the mass fraction of 4-MDBT in the feed ternary misture with ionic liquid-free basis, that is, the initial
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Figure 4. Experimental and calculated phase equilibrium data for the system [emim][EtSO4] + 4-MDBT + n-dodecane at 40 °C: cloud points (9); feed points (b); tie-lines (2, solid line); NRTL correlation (O, dotted line).
Figure 5. Distribution of 4-MDBT between ionic liquid and n-dodecane phase: [emim][DEtPO4] at 25 °C (b, solid line) and 40 °C (O, dashed lined); [emim][EtSO4] at 25 °C (9, dash-dotted line) and 40 °C (0, dotted line). Lines are calculated by NRTL.
composition of 4-MDBT in the binary mixture (4-MDBT + n-dodecane); Cf is the composition of 4-MDBT in the alkane phase after equilibrium. Figure 9 shows that, for [emim][DEtPO4], the percent of 4-MDBT removal was between 17 and 24% and that for [emim][EtSO4] was between 5 and 15%; that is, [emim][DEtPO4] extracts more 4-MDBT from ndodecane than [emim][EtSO4]. An increase in temperature from 25 to 40 °C did not change significantly the removal percent for both ionic liquids. 3.4. NRTL Parameters. The estimated NTRL parameters are shown in Table 7, and the calculated tie-lines are in Figures 1-4. The calculated distribution and selectivities are in Figures 5 and 6. In Figure 6, the NRTL model gave good approximations for systems with [emim][DEtPO4] for values of selectivity below 125. However, for [emim][EtSO4], NRTL gave poor correlation at 25 °C.
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Ind. Eng. Chem. Res., Vol. 49, No. 19, 2010 Table 6. Removal of 4-MDBT from n-Dodecane by Ionic Liquids at 25 and 40 °C [emim][DEtPO4]
Figure 6. Selectivity of ionic liquids studied here: [emim][DEtPO4] at 25 °C (b, solid line) and 40 °C (O, dashed lined); [emim][EtSO4] at 25 °C (9, dash-dotted line) and 40 °C (0, dotted line). Lines are calculated by NRTL.
[emim][EtSO4]
temperature (°C)
C0
% removal
C0
% removal
25
0.0216 0.0315 0.0658 0.1198 0.1914
22.0 23.2 23.7 20.8 18.2
0.0160 0.0317 0.0773 0.1503
12.4 14.2 13.8 10.2
40
0.0504 0.0931 0.1569 0.2003
23.9 22.8 20.8 19.1
0.0305 0.0613 0.0926 0.1211 0.2847
11.5 14.5 14.8 12.5 5.9
or [emim][EtSO4] + 4-MDBT + n-dodecane systems at 25 and 40 °C and ≈95 kPa. It was concluded that [emim][DEtPO4] is a better solvent than [emim][EtSO4] for extraction of 4-MDBT from n-dodecane, as shown by solvent selectivity, solute distribution in both phases, and removal percent of 4-MDBT from n-dodecane. The removal percent of 4-MDBT was between 17 and 24% for [emim][DEtPO4] and between 5 and 15% for [emim][EtSO4]. It was also verified that n-dodecane is present as small amounts in ionic liquid-rich phase, but the ionic liquids did not dissolve in n-dodecane. The quality of the data was ascertained by the Hand and Othmer-Tobias correlations, with R2 > 0.97. The NRTL model correlates well the data, but gave a poor representation of selectivity for systems with [emim][EtSO4] at 25 °C. The deviations between experimental and calculated compositions were always below 0.14%.
Figure 7. Hand correlation for LLE data determined: [emim][DEtPO4] at 25 °C (b, solid line) and 40 °C (O, dashed lined); [emim][EtSO4] at 25 °C (9, dash-dotted line) and 40 °C (0, dotted line).
Figure 9. Percent of 4-MDBT removal from model oil: [emim][DEtPO4] at 25 °C (b) and 40 °C (O); [emim][EtSO4] at 25 °C (9) and 40 °C (0). Table 7. Estimated NRTL Parameters and rms Deviations i
j
Bij/K
Bji/K
Aij
Aji
Rij
[emim][DEtPO4] (1) + 4-MDBT (2) + n-Dodecane (3), δx ) 0.10%; F ) 13.03
Figure 8. Othmer-Tobias correlation for LLE data determined: [emim][DEtPO4] at 25 °C (b, solid line) and 40 °C (O, dashed lined); [emim][EtSO4] at 25 °C (9, dash-dotted line) and 40 °C (0, dotted line).
1 1 2
2 3 3
9731.6 2302.4 392.7
1.6 -0.7 1.0
-27.0 1.9 -0.5
0.20 0.20 0.24
[emim][EtSO4] (1) + 4-MDBT (2) + n-Dodecane (3), δx ) 0.14%; F ) 30.64
4. Conclusion Phase diagrams showing experimental liquid-liquid and solid-liquid equilibrium data were obtained for [emim][DEtPO4]
-860.1 1397.7 -433.7
1 1 2
2 3 3
35.2 -147.7 -287.0
2637.6 -1797.2 1754.7
0.02 4.3 -0.1
-5.3 15.3 -3.5
0.20 0.20 0.20
Ind. Eng. Chem. Res., Vol. 49, No. 19, 2010
Nomenclature Aij ) NRTL binary parameter Bij ) NRTL temperature dependent binary parameter C0 ) initial concentration of 4-MDBT in model diesel oil Cf ) final concentration of 4-MDBT in model diesel oil constH ) linear coefficient in Hand correlation constOT ) linear coefficient in Othmer-Tobias correlation D ) number of data sets F ) objective function G ) NRTL term K ) distribution coefficient kH ) angular coefficient in Hand correlation kOT ) angular coefficient in Othmer-Tobias correlation M ) number of tie lines N ) number of components nD ) refractive index R2 ) correlation coefficient R ) universal gas constant S ) selectivity w ) mass fraction x ) mole fraction Greek Letters γ ) activity coefficient τ ) NRTL energy parameter ∆g ) energy difference Rij ) NRTL non randomicity parameter δx ) root-mean-square deviation σ ) standard deviation Superscripts/Subscripts exptl ) experimental calcd ) calculated I, II ) phases ap ) alkane phase ilp ) ionic liquid phase i, j, k ) component AbbreViations BDS ) biodesulfurization DBT ) dibenzothiophene DEtPO4 ) diethyl phosphate EDS ) extractive desulfurization emim ) 1-ethyl-3methylimidazolium EtSO4 ) ethyl sulfate HDS ) hydrodesulfurization ODS ) oxidesulfurization 4-MDBT ) 4-methyldibenzothiophene 4,6-DMDBT ) 4,6-dimethyldibenzothiophene
Acknowledgment Financial support from FAPESP (Grants 07/53024-3 and 07/ 52032-2) is gratefully acknowledged. M.A. is the recipient of a CNPq fellowship. Literature Cited (1) Eβer, J.; Wasserscheid, P.; Jess, A. Deep Desulfurization of Oil Refinery Streams by Extraction with Ionic Liquids. Green Chem. 2004, 6, 316–322. (2) Kwak, C.; Lee, J. J.; Bae, J. S.; Choi, K.; Moon, S. H. Hydrodesulfurization of DBT, 4-MDBT, and 4,6-DMDBT on Fluorinated CoMoS/ Al2O3 Catalysts. Appl. Catal., A 2000, 200, 233–242. (3) Kabe, T.; Ishihara, A.; Tajima, H. Hydrodesulfurization of SulfurContaining Polyaromatic Compounds in Light Oil. Ind. Eng. Chem. Res. 1992, 31 (6), 1577–1580.
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ReceiVed for reView April 29, 2010 ReVised manuscript receiVed August 10, 2010 Accepted August 19, 2010 IE1009876
