Article pubs.acs.org/IECR
An in Situ Raman Spectroscopic Study of Benzothiophene and Its Desulfurization under Alkaline Hydrothermal Conditions Zhibao Huo,† Fangming Jin,*,† Guodong Yao,† Heiji Enomoto,‡ and Atsushi Kishita*,‡ †
School of Environmental Science and Engineering, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China ‡ Graduate School of Environmental Studies, Tohoku University, Aoba-ku, Sendai 980-8579, Japan ABSTRACT: In this paper, an in situ Raman spectroscopic study of benzothiophene (BT) and its desulfurization under alkaline hydrothermal conditions is reported. The Raman spectrum of BT was obtained. Based on results of Raman in situ observations combined with GC/MS analyses, the mechanism of desulfurization was investigated. Benzothiophene was desulfurized via a twostep process involving (1) the hydrogenation of benzothiophene at the C2 and C3 positions to produce 2,3dihydrobenzothiophene and (2) the cleavage of the benzene ring−S bond and the C2−S bond to form aromatic products, i.e., ethylbenzene and toluene. The present study provides deep insights into the pathway of BT desulfurization, which is of great significance for developing new methods for the desulfurization of BT using hydrothermal reactions, and will also contribute to the Raman spectroscopic database.
1. INTRODUCTION As the worldwide supply of light crude oil decreases, more attention will be paid to the use of heavy oils and residues. However, these heavy oils and residues often contain significant amounts of asphaltenes (bitumen), i.e., sulfur- and metalcontaining organic compounds, which are sources of air pollution during combustion. Thus, refining heavy oils to lighter and more valuable liquid products and removing impurities is necessary.1,2 Currently, the most frequently used method for sulfur removal is hydrodesulfurization (HDS), which involves the treatment of the oils with hydrogen at high temperatures (>300 °C) and high pressures (>100 atm) in the presence of a metal catalyst.3−7 However, these methods are high in cost (mainly due to the use of metal catalysts and reductants during the reaction), time-consuming, and complex. Therefore, the development of suitable methods for the desulfurization of benzothiophene (BT) is highly desired. It is well-known that the properties of high-temperature water (HTW) are very different from those of liquid water at ambient temperature: HTW has a lower dielectric constant, fewer and weaker hydrogen bonds, and a higher isothermal compressibility.8 Moreover, the constant ionization (kw) of HTW is maximum at near 300 °C at saturated vapor pressure, and the kw is approximately 1000 times larger than that of water at normal temperature and pressure. Thus, HTW can support ionic, polar nonionic, and free-radical reactions, resulting in growing interest in this solvent as a medium for chemical reactions.8 In our previous studies, we reported on the alkaline hydrothermal desulfurization for the upgrading of bitumen in HTW,9−11 and we found that hydrothermal desulfurization was very effective for bitumen with alkali. However, the sulfur content could not be reduced to below 3% in upgraded bitumen, possibly because BT was formed which is more difficult to desulfurize. An understanding of the desulfurization mechanism under hydrothermal conditions is necessary for further decreasing the © 2015 American Chemical Society
sulfur content. However, the desulfurization mechanism of BT needed still to be investigated in detail to date. Thus, it is urgently necessary to fill this gap to utilize hydrothermal methods for further upgrading bitumen or for the desulfurization of BT. In situ Raman spectroscopy is well-known to have the ability to monitor intermediate species, providing real-time information on structural and chemical changes.12−14 Klots and Collier13 and Frank et al.14 have described Raman spectroscopy of BT in detail previously. However, although they reported the Raman spectroscopic study of BT, both of them did not give Raman spectroscopy of BT in supercritical water, and also did not give a desulfurization pathway of BT. In addition, this spectroscopic method gives an intrinsically weak water signal.15 Thus, it is ideally suited for studying the desulfurization pathway during HTW reactions. However, to date, few examples for the in situ Raman spectroscopic analysis of heavy oil have been reported. The purpose of this research was to investigate an in situ Raman spectroscopic analysis of benzothiophene under alkaline hydrothermal conditions and to study the mechanism of desulfurization of BT.
2. EXPERIMENTAL METHODS 2.1. Materials. BT was supplied by Aldrich Chemical Co. Since this material is not soluble in water at room temperature, it was dissolved in ethanol at a concentration of 3.5 mol/L during the reaction. In addition, a KOH aqueous solution of a concentration of 2.0 mol/L was used as an alkaline catalyst. 2.2. Experiments. The reaction system comprised two pumps, which were used for pumping a KOH aqueous solution and BT−ethanol solution. The scheme of the reaction system is Received: Revised: Accepted: Published: 1397
August 13, 2014 January 5, 2015 January 9, 2015 January 9, 2015 DOI: 10.1021/ie503167q Ind. Eng. Chem. Res. 2015, 54, 1397−1406
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Industrial & Engineering Chemistry Research
samples were analyzed with a GC-TCD (HP 5890 Series II Plus) equipped with a thermal conductivity detector and TDX01 column (1 m × 1/8 in.) for the quantification of H2, CO, CO2, and H2S. The carbon balance was determined using a total organic carbon analyzer (TOC, Shimadzu, V-CPN). Identification was achieved via total and selected ion chromatograms with the help of a computer library and by comparison of the GC retention times of the products with those of authentic compounds. A laser Raman spectroscopic device (T64000, Jobin Yvon) was used. The excitation wavelength of 632.8 nm was supplied by a 35 mW He−Ne laser (Showa Optronics), and the excitation wavelength of 488.0 nm was supplied by a 10 mW Ar laser (LEXEL). Vibrational spectra of BT in the liquid states were examined in the region from 100 to 3500 cm−1.
shown in Figure 1. The reactor was made of a Hastelloy C276 (HC-276) tube 200 mm in length and 2 mm thick. Two types
3. RESULTS AND DISCUSSION 3.1. Peak Assignments for the Raman Spectrum of Benzothiophene at Room Temperature. The Raman spectroscopic analysis of BT at room temperature was performed. The obtained Raman spectrum of BT is shown in Figure 2. The peaks were identified based on the characteristic
Figure 1. Scheme of the reaction system. 1, KOH aqueous solution; 2, BT dissolved in ethanol; 3, pump; 4, valve; 5, Raman equipment; 6, preheater; 7, heat insulator; 8, cooling tank; 9, back-pressure valve.
of tubes were used to investigate the effect of the retention time. One tube had a 7.5 mm i.d., providing a volume of 8.9 cm3, which was used when the retention time was 1.8, 3.6, or 5.2 min. The other tube was used for the retention time of 11.1 min and had a 4.4 mm i.d. and a 3.0 cm3 volume. In addition, a coil heater was twisted out of the reactor tube to control the temperature. The preheater was composed of a 15-m-long, 6mm-i.d., and 2-mm-thick SUS316L tube. The optically accessible cell was constructed from HC-276 with a 1.8 mm i.d. and a 1.4-mm-thick diamond, providing the monitoring window for Raman spectroscopy. The internal volume of the cell was 0.20 cm3, and the maximum operating temperature and pressure for the cell were 400 °C and 50 MPa, respectively. During hydrothermal experiment, water was first pumped at a flow rate of 1 mL/min, and then the system pressure was increased by adjusting with a back-pressure regulator (BPR). When the pressure was steady, the system was heated. After reaching the desired temperature and pressure, the solutions (i.e., the BT ethanol solution and KOH aqueous solution) were pumped into the system, and the Raman scattering was measured. During the reaction, the sample was collected at the exit of the back-pressure regulator and then analyzed by gas chromatography (GC)/mass spectrometry (MS). The hydrothermal desulfurization experiments were conducted at 350 °C and 22 MPa. In addition, Raman spectroscopic analysis of related compounds used and benzothiophene were also conducted at room temperature with the same cell. 2.3. Analysis. BT products was extracted from the water sample (obtained from the HTW reaction) with hexane, which was termed the hexane sample. After the extraction, the hexane sample and water sample were both analyzed by GC/MS to identify the intermediate products. The liquid samples were analyzed by a GC/MS (Agilent GC7890A-MS5975C) equipped with an HP Innowax polyethylene glycol capillary column with dimensions of 30 m × 250 μm × 0.25 μm. The gas
Figure 2. Raman spectra of BT at room temperature.
Raman shifts of the related functional groups (see Table 1)16−18 and by referring to the Raman spectra of structurally related compounds (e.g., benzene, toluene, styrene, ethylbenzene, benzofuran, thiophene, thiophenol, and methylthiophenol). 3.1.1. Assignments of Peaks at 4000−2500 cm−1. The expanded Raman spectrum of BT at 2500−4000 cm−1 is shown in Figure 3a. Three peaks at 3106, 3074, and 3061 cm−1 were observed, respectively. From Table 1, C−H stretching vibration of the C−H generally appeared at approximately 3000−3100 cm−1; thus, the three peaks at 3106, 3074, and 3061 cm−1 may be attributed to the stretching vibration of C−H of C−H. For BT, there are three types of stretching vibrations, corresponding to the C2−H, C3−H, and C−H of the benzene ring. To confirm these, Raman spectra of structurally related compounds, such as benzofuran, benzene, and thiophene, were examined, as shown in Figure 3b−d. According to the stretching vibration of the C−H of the benzene ring at 3061 cm−1 in Figure 3c, the peak at 3061 cm−1 for BT was assigned to the C−H of the benzene ring. Because the peak at 3073 cm−1 for benzofuran in Figure 3b was observed, the assignment of the stretching vibration of the C−H of the benzene ring is not affected by the attached groups. 1398
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Industrial & Engineering Chemistry Research Table 1. Peak Assignments of Benzothiophene (BT) Raman Spectra Raman shift (cm−1)
intensity (AU)
3106 3074 3061
59 64 117
1594
201
1558
355
1498
1835
1457 1347 1317 1209
88 177 650 338
1157 1133 1094 1058 1015
57 270 147 148 973
797 710
773 799
666 527 493
108 581 1579
assignment C3−H bond stretch C2−H bond stretch benzene ring C−H stretch benzene ring CC stretch benzene ring CC stretch C2C3 double bond stretch C−H bond bend
referred compds13,14,16−18 benzofuran, thiophene benzene
toluene, ethylbenzene benzene, toluene, ethylbenzene, furan, benzofuran benzofuran
benzene ring−C3 bond stretch pentatomic ring stretch
styrene, methylthiophenol, thiophenol furan, benzofuran, thiophenol, toluene
benzene ring stretch
toluene, ethylbenzene, benzene, etc.
C2−S bond stretch benzene ring−S bond stretch
thiophenol, thiophene, 2methylthiophene, 3methylthiophene
lattice bend
vibration of characteristic groups
The Raman spectrum of thiophene at 2500−4000 cm−1 is shown in Figure 3d; peaks can be observed at 3115 and 3090 cm−1. These two peaks could be attributed to the stretching vibrations of C2H or C5H in thiophene. According to the frequency equation of diatomic molecules as shown in eqs 1 and 2, lower atomic mass will produce high frequency of vibration. Considering the atomic mass of the C or H atom is smaller than the atomic mass of the S atom, the peaks at 3115 and 3090 cm−1 in thiophene were identified as C−H stretching vibration of C2H or C3H. Thus, the peaks at 3106 and 3074 cm−1 in BT were identified as C−H stretching vibration of C2H and C3−H.
ν=
μ=
1 2π
k μ
m1m2 m1 + m2
(1) (2)
where k represents force constants of chemical bonds, μ is a quality of reduced molecules, and m1 and m2 are atomic mass. 3.1.2. Assignments of Peaks at 1900−1450 cm−1. The expanded Raman spectrum of BT in the 200−1800 cm−1 region is shown in Figure 4a. The peak at 1498 cm−1 for BT was assigned as follows: first, the intense peaks between 1500 and 1700 cm−1 were known to be a consequence of CC stretching vibration modes. Thus, the peak at 1498 cm−1could be attributed to the CC stretching mode in the benzene ring or to the C2C3 double bond stretching mode. To determine which CC stretching mode was responsible for the Raman shift at 1498 cm−1, the Raman spectra of structurally related compounds, such as benzene and toluene, were examined. In
Figure 3. Raman spectra of (a) BT (30 s), (b) benzofuran (30 s), (c) benzene (5 s), and (d) thiophene (10 s) in the range 2500−3400 cm−1.
the Raman spectra of benzene and toluene in parts b and c, respectively, of Figure 4 the CC stretching mode was observed close to 1600 cm−1, and no peak appeared at 1500 cm−1. Thus, the peak at 1498 cm−1 for BT was due to the C2 1399
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Figure 4. Raman spectra of (a) BT (30 s), (b) benzene (5 s), (c) toluene (10 s), (d) furan (30 s), and (e) benzofuran (30 s), in the range 0−1900 cm−1.
Figure 5. Raman spectra of (a) BT and (b) benzofuran in the range 900−1500 cm−1 (10 s).
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Figure 6. Raman spectra of (a) styrene, (b) thiophenol, (c) methylthiophenol, (d) 2-methylthiophene, (e) 3-methylthiophene, (f) thiophene, and (g) dibenzothiophene in the range 0−1900 cm−1 (10 s).
1498 cm−1 was a characteristic Raman peak for the intense C2C3 stretching vibration of BT. The successful assignment of the BT peak made it possible to monitor the desulfurization pathway. 3.1.3. Assignments of Peaks at 1500−900 cm−1. The Raman spectrum of BT at selected Raman shifts between 900 and 1500 cm−1 upon compression was analyzed in Figure 5a. An intense peak was observed in the spectral region of 1015 cm−1 and was most likely a consequence of the CC
C3 in the thiophene ring. Furthermore, we investigated the Raman spectrum of furan in Figure 4d and that of benzofuran in Figure 4e and found that the intensities and widths of the peaks at 1484 cm−1 (for furan) and 1537 cm−1 (for benzofuran) were both very similar to those of the BT peak at 1498 cm−1. Additionally, it was coincidental that, for both benzofuran and benzothiophene (Figure 5), the intensity of the C2C3 peak was 3−9-fold higher than that of the CC peak in the benzene ring. Hence, it could be concluded that the peak observed at 1401
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Industrial & Engineering Chemistry Research stretching vibration modes in the benzene ring. To investigate which CC stretching mode was responsible for the Raman shift at 1015 cm−1, a comparative study between the Raman band at 1015 cm−1 and the Raman spectra of structurally related compounds was conducted. We found that the Raman spectra of several structurally related compounds, such as benzene in Figure 4b, toluene in Figure 4c, styrene in Figure 6a and thiophenol in Figure 6b, displayed peaks at approximately 1000 cm−1, and the Raman peak of the disubstituted benzene ring containing methyl and SH groups at the ortho position, i.e., 2-methylthiophenol in Figure 6c, was shifted to approximately 1040 cm−1. Additionally, two similar compounds, BT and benzofuran in Figure 5, gave similar Raman shifts at approximately 1015 cm−1. These results indicate that the intensities and widths of the CC stretching mode peaks observed were very similar to those of the BT peak at 1015 cm−1. Based on this observation, the Raman shift at 1015 cm−1 was determined to be a characteristic Raman peak for the intense CC benzene ring stretching vibration of BT. 3.1.4. Assignments of Peaks at 900−0 cm−1. The Raman spectrum of BT in the range 0−900 cm−1 was analyzed in Figure 4a. As can be observed, Raman bands at 710 and 797 cm−1 were presented; these peaks were assigned to C2−S bond stretching and the C(benzene ring)−S bond. The Raman spectra of structurally related compounds, such as methylthiophenol, 2-methylthiophene, 3-methylthiophene, thiophene, and dibenzothiophene in parts c, d, e, f, and g, respectively, of Figure 6 were collected to verify that the C2−S and C(benzene ring)−S stretching modes were responsible for the Raman shifts at 797 and 710 cm−1. Raman signals were observed at 750 cm−1 in Figure 6f, at 740 cm−1 in Figure 6d, at 680 cm−1 in Figure 6e, and at 800 cm−1 in Figure 6c. It can be observed that the intensities and widths of the peaks were very similar to those of the BT peaks at 710 and 797 cm−1. Additionally, the Raman spectrum of the structurally related compound dibenzothiophene, in Figure 6g, was very similar to that of BT. However, the Raman shift of the C2−S bond stretching was larger than that of the C(benzene ring)−S stretching vibration of BT, respectively. Thus, it is evident from the Raman data that the peaks observed at 710 and 797 cm−1 were characteristic Raman peaks for the intense C2−S and C(benzene ring)−S stretching vibrations of BT, respectively. 3.2. Raman Spectra of BT during Hydrothermal Reactions. Figures 7 and 8 show the Raman spectra of BT at different reaction times in the wavenumber ranges of 500− 1200 and 1400−1800 cm−1, respectively. The spectra are plotted with the same y-axis scale in Figures 7 and 8. Because the Raman signature of the diamond cell was within 1200− 1400 cm−1 and because its intensity was about 2 orders of magnitude larger than that of the sample peak, the peak within 1200−1400 cm−1 was ignored and is not shown herein. Moreover, changes in the Raman spectra in the range 2500− 2700 cm−1 are also not shown because no obvious peaks were observed in this range. According to the Raman assignments described above, the peaks in Figures 7 and 8 were identified, where the peaks at 797, 710, and 1498 cm−1 were assigned to C2−S bond stretching, the C(benzene ring)−S bond, and the C2C3 bond, respectively. It was found that the peak intensities of these three peaks decreased with increasing retention time, providing evidence that BT was decomposed during the hydrothermal reaction. However, the benzene ring stretching peak at 1015 cm−1 was nearly unchanged as the
Figure 7. Change of Raman spectra of BT during alkaline hydrothermal reaction in the range 500−1200 cm−1. (a) Reaction time (RT) = 1.8 min; (b) RT = 3.6 min; (c) RT = 5.2 min; (d) RT = 11.1 min.
Figure 8. Change of Raman spectra of BT during alkaline hydrothermal reaction in the range 1400−1800 cm−1. (a) RT = 1.8 min; (b) RT = 3.6 min; (c) RT = 5.2 min.
reaction time increased, which indicated that the benzene ring was not destroyed during the reaction. In Figure 7, of particular interest is a Raman peak that was not observed in the raw BT material appeared at 885 cm−1. 1402
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Figure 9. Comparison of Raman spectra of (a) BT and ethanol (alkaline hydrothermal reaction), (b) ethanol (alkaline hydrothermal reaction), (c) 5% acetic acid aqueous solution (normal temperature and pressure), and (d) 5% ethanol aqueous solution (normal temperature and pressure).
Figure 10. GC/MS chromatograms of intermediate products in the hexane phase and in the water phase at 11.1 min of reaction time.
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Industrial & Engineering Chemistry Research Table 2. Carbon Balance after Hydrothermal Reaction of BT reaction time (min) 1.8
3.6
5.2
11.1
BT ethanol
58 42
58 42
58 42
58 42
BT 2,3-dihydrobenzothiophenes toluene ethylbenzene acetic acid residual of BT conversion of BT
55.5 1.0 0.2 0.5 3.3 95.0 4.3
55.8 2.6 0.5 0.6 5.5 95.5 3.8
46.4 2.1 0.3 0.6 13.1 78.5 20
25.5 1.8 0.3 0.6 15.1 44.0 56
in (C wt %)
out (C wt %)
C wt % C wt %
the intermediate products. The changes in the BT amount and the appearance of the intermediates as a function of the retention time are listed in Table 2. It can be observed from Table 2 that the residual BT decreased greatly with increasing reaction time. However, no significant change in 2,3dihydrobenzothiophene was observed. This is most likely because 2,3-dihydrobenzothiophene is both formed from BT and decomposed as an intermediate. As shown in Table 2, a carbon balance was performed at 11.1 min. The main products for this transformation were 2,3dihydrobenzothiophenes, toluene, ethylbenzene, and acetic acid. In addition, the recovery of BT was also detected after the reaction. The conversion rate of BT was approximately 56% at 11.1 min. The total yields of main liquid products and recoveried BT were 43.3%, and other liquid products were unknown compounds. Gas products, such as CO, H2, H2S and CO2, were detected during the reaction. 3.4. Desulfurization Pathways of BT in Hydrothermal Reactions. Based on the Raman findings for the structural changes in BT and on the intermediate products analyzed by GC/MS, a possible pathway for the desulfurization of BT is proposed (see Scheme 1). First, the structural changes in BT
This peak was relatively intense at the shorter retention times but became weak after the retention times increased and was hardly detectable after ca. 11 min of reaction time. In addition, during the hydrothermal reaction, two new peaks at 596 and 916 cm−1 were also found. The intensities of these peaks increased as a function of the retention time, which indicated that there were new functional groups formed during the reaction. The assignments for these peaks are described later. Furthermore, because acetic acid was detected in the sample after BT decomposition by GC/MS (see Figure 10b), these two new peaks may correspond to acetic acid. As expected, the Raman spectrum of acetic acid under ambient conditions (see spectrum (d) in Figure 9) showed two characteristic peaks at 933 and 626 cm−1, which implies that the ethanol was transformed to acetic acid during the hydrothermal reactions. This explains why the peak at 885 cm−1 decreased and the peaks at 916 and 596 cm−1 increased during the reactions in Figure 7. Because ethanol was used as a solvent to dissolve BT, it was necessary to investigate the changes in ethanol during the hydrothermal reaction. Figure 9 shows the Raman spectrum of 5 vol % aqueous ethanol in the presence of 2.0 mol/L BT at a reaction time of 5.2 min. For comparison, a spectrum of a 5 vol % aqueous ethanol solution under ambient conditions and of an ethanolic BT solution at a reaction time of 5.2 min are also shown in Figure 9. It can be observed that ethanol of ethanolic BT solution has a characteristic peak at 890 cm−1 at room temperature (Figure 9a), which was slightly blue-shifted to 885 cm−1 due to the increase in reaction temperature (Figure 9b). In spectrum (b), the peak intensity of ethanol at 885 cm−1 was much smaller than that in spectrum (a). This suggested that the ethanol in the hydrothermal reaction may be partly transferred to other compounds, as two new peaks were observed at 916 and 596 cm−1 in spectrum (b). 3.3. Identification of Intermediate Products by GC/MS and Gas Chromatography with Atomic Emission Detection (GC/AED). After investigating the Raman spectra of BT under alkaline hydrothermal conditions, to confirm the conjecture of the Raman spectroscopic analyses of the intermediate products, the hexane and water samples were also analyzed by GC/MS and GC/AED. It was found that in the hexane samples, in addition to the remaining BT, 2,3dihydrobenzothiophene, toluene, ethylbenzene, and styrene were presented, as shown in Figure 10a. In the water samples, not only BT but also benzyl alcohol, thiobenzyl alcohol, and acetic acid were presented, as shown in Figure 10b. This result confirms the conjecture of the Raman spectroscopic analyses of
Scheme 1. Proposed Pathway for the Desulfurization of BT
were clarified based on the intensities of the three Raman peaks (1498, 797, 710 cm−1). Figure 11 shows the changes in the relative intensities of these three peaks at various retention times. As shown in eq 3 and Scheme 1, first, the hydrogenation of the C2C3 bond of BT A took place under hydrothermal conditions, and 2,3-dihydrobenzothiophene B as an intermediate product was obtained. Then, the C(benzene ring)−S bond of intermediate B and the C2−S bond of intermediate C were cleaved in sequence to produce the ethylbenzene D. 1404
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because, in batch experiments in the absence of ethanol, the desulfurization of BT readily occurs.21 It has been reported that HTW can supply hydrogen for some organic reactions or can be split to produce hydrogen.22−25
4. CONCLUSIONS We conducted an in situ Raman spectroscopic study of BT and proposed a desulfurization mechanism under alkaline hydrothermal conditions. The results showed that in situ Raman spectroscopy is an effective way to monitor structural changes during desulfurization reactions. The intermediate products after desulfurization, such as dihydrobenzothiophene, toluene, and ethylbenzene, were identified by GC/MS and Raman spectroscopic analysis. A desulfurization pathway was proposed based on the Raman spectra and the identified intermediate products. Desulfurization of BT via a two-step process involves (1) the hydrogenation of BT at the C2 and C3 positions to produce 2,3-dihydrobenzothiophene, and (2) the cleavage of the benzene ring−S bond and the C2−S bond to form aromatic products, i.e., ethylbenzene and toluene. The present study provides deeper insight into the desulfurization pathway of BT, which is of great significance for developing new methods for the desulfurization of BT by hydrothermal reactions, and will also contribute to the Raman spectroscopic database.
Figure 11. Change of peak intensity with retention time.
Regarding the source of hydrogen for the hydrogenation of BT, as mentioned before, acetic acid was formed after the reaction of BT in the presence of ethanol. The formation of acetic acid may have been caused by the oxidation of ethanol in the hydrothermal reaction. Compared with ambient water, HTW has unusual properties. At 250 °C, the ion product constant (Kw) of HTW is approximately 3 orders of magnitude higher than that at room temperature, as mentioned above. Thus, the concentration of H+ in HTW is very high. Moreover, ethanol has reducing potential because of the presence of −OH groups, which can reduce water during the hydrothermal reaction to produce H2.19 The full process is described in eq 4.
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Corresponding Author
*F.J.: Tel.: +86-21-54742283. Fax: +86-21-54742283. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (No. 21277091), the State Key Program of National Natural Science Foundation of China (No. 21436007), Key Basic Research Projects of Science and Technology Commission of Shanghai (14JC1403100), the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning (ZXDF160002), and the project sponsored by SRF for ROCS, SEM (BG1600002). We thank all the reviewers and editors for reviewing the manuscript and providing valuable comments.
C2H5OH + H 2O → CH3COOH + 2H 2 ° = −5.39 kJ/mol ΔG623
(4)
As shown in Table 3, the presence of BT could enhance the conversion of ethanol into acetic acid. This conversion is likely Table 3. Formation of Acetic Acid from Ethanol in the Absence and Presence of BT experimental condition temperature (°C) pressure (MPa) retention time (min) KOH aqueous solution acetic acid (C wt %)
in absence of BT
in presence of BT
350 22 5.2 1:7 22.6
350 22 5.2 1:6.8 31.2
AUTHOR INFORMATION
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REFERENCES
(1) Scott, D. S.; Radlein, D.; Piskorz, J.; Majerski, P.; deBruijn, T. J. W. Upgrading of bitumen in supercritical fluids. Fuel 2001, 80, 1087. (2) Kim, J. W.; Longstaff, D. C.; Hanson, F. V. Upgrading of bitumen-derived heavy oils over a commercial HDN catalyst. Fuel 1997, 76, 1143. (3) Torres-Mancera, P.; Ramirez, J.; Cuevas, R.; Gutierrez-Alejandre, A.; Murrieta, F.; Luna, R. Hydrodesulfurization of 4,6-DMDBT on NiMo and CoMo catalysts supported on B2O3-Al2O3. Catal. Today 2005, 107−108, 551. (4) Haji, S.; Zhang, Y.; Kang, D. F.; Aindow, M.; Erkey, C. Hydrodesulfurization of model diesel using Pt/Al2O3 catalysts prepared by supercritical deposition. Catal. Today 2005, 99, 365. (5) Cho, A.; Lee, J. J.; Koh, J. H.; Wang, A.; Moon, S. H. Performance of NiMoS/Al2O3 prepared by sonochemical and chemical vapor deposition methods in the hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene. Green Chem. 2007, 9, 620.
because BT acts as a reductant, leading to the efficient oxidation of ethanol to acetic acid. Although the mechanism of BT as a reductant is unknown, one possible mechanism can be proposed as follows. Sulfur from the desulfurization of BT is dissolved into water to form H2S, which then reduces water into hydrogen and oxygen.20 Then, the formed oxygen oxidizes ethanol into acetic acid. In addition to coming from ethanol, the hydrogen for the hydrogenation of BT could also come directly from HTW 1405
DOI: 10.1021/ie503167q Ind. Eng. Chem. Res. 2015, 54, 1397−1406
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DOI: 10.1021/ie503167q Ind. Eng. Chem. Res. 2015, 54, 1397−1406
