Article pubs.acs.org/EF
Separation and Characterization of Olefin/Paraffin in Coal Tar and Petroleum Coker Oil Hongxing Ni,† Chang Samuel Hsu,*,†,‡,§ Chao Ma,† Quan Shi,*,† and Chunming Xu† †
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, People’s Republic of China Petro Bio Oil Consulting, Tallahassee, Florida 32312, United States § Department of Chemical and Biomedical Engineering, Florida State University, Tallahassee, Florida 32310, United States ‡
ABSTRACT: We have investigated and established a preparative method of using a solid-phase extraction cartridge containing Ag+-exchange resin (Ag+-SPE) for separating olefins and paraffins in the saturate fractions of coal tar and petroleum coker oil. The successful separation of paraffins and olefins was confirmed by gas chromatography coupled with mass spectrometry (GC− MS). Proton nuclear magnetic resonance (1H NMR) spectroscopy was applied to determine the olefin structures for olefin-type distributions. None or negligible amounts of iso-α-olefins were detected by 1H NMR in the coal tar but were found significant in the coker oil. Gas chromatography coupled field ionization time-of-flight mass spectrometry (GC−FI-TOF MS) was employed to determine the molecular distribution of paraffins and olefins. With separate paraffin and olefin fractions, the differentiation between isomers, such as monocycloparaffins versus monoolefins, can be made. huge energy and operates under difficult conditions.6,17 To meet the demand for light olefins in the chemical industry and simultaneously achieve the goal of decreasing the energy consumption, many new separation methods have been developed, especially for olefin/paraffin separations, which include adsorption, solvent extraction, and membrane separation. The mechanism of the adsorption method is dispersing AgI or CuI ions on a specific matrix to separate C2−C4 olefins/paraffins. The matrix includes alumina, silica gel,9,14 ion-exchange resin,16 13X/Y molecular sieve,13,18 inert polymer,19 pillared clay,20 etc. The separation effect is acceptable,9 although not as good as solvent extraction and membrane separation. The solvent extraction method uses the higher solubility of olefin in the solvent that contains AgI or CuI to isolate the olefins from a paraffin/olefin mixture.17,21 Olefins can be separated from paraffins by complexing with silver salt incorporated with non-volatile ionic liquid and then recovered after the removal of non-complexing paraffins by distillation.22 The membrane separation method is most widely studied, particularly for the advantages of facilitating transport membrane technology.5 Ag+-exchanged membranes,16 solid polymer electrolyte composite membranes,23 and hollow fiber facilitated transport membrane modules6 are critical elements in membrane separation equipment; the latter two can achieve a good selectivity for ethylene/ethane separation. All of the methods have their own merits on the isolation of light olefin/paraffin; however, none of them has been applied to the separation of heavy olefin/paraffin. Olefins and paraffins in shale oil were separated by highperformance liquid chromatography (HPLC) equipped with an activated silica column.24,25 To enhance the separation efficiency, activated silica columns were replaced by silver-nitrate-impregnated silica columns.26 However, the columns were unstable in which the silver nitrate could be easily eluted.27 Hence, a
1. INTRODUCTION Olefins are widely distributed in petroleum products, which have great influence on the oxidation and thermal stabilities of the products. A high olefin content can lead to plugging the injection nozzles and valves,1 as well as deactivation of the catalysts. The polarity and volatility of olefins are fairly similar to paraffins of the same carbon number; thus, the effective separation between them is difficult to accomplish by conventional methods.2 Because of the enormous demand of ethylene and propylene in the polymer industry, research has mainly focused on the separation of light olefins and paraffins.3−6 Meanwhile, heavy olefins are important raw materials for the synthesis of some specialty chemicals. Copolymers of cyclic olefins show properties of high glass-transition temperature, optical clarity, low birefringence, etc.7 The products from high-temperature Fischer−Tropsch (FT) processes contain considerable amounts of cyclic olefin, dienes, and cyclic dienes;8 therefore, the isolation of heavy olefins and paraffins has extraordinary meaning for the chemical industry. Some metal ions, such as CuI and AgI, have vacant orbitals that form bonds with unsaturated hydrocarbons in a nonclassical manner,9 which is so-called π-complexation. Because of the presence of unsaturated bonds that are absent in paraffins and cycloparaffins, olefins and aromatics can be separated by π-complexation.6 Although the strength of aromatics complexating with AgI is much weaker than that of olefins,10 it has been demonstrated that the π-complexation is strong enough to separate aromatics from paraffins11,12 because it is greater than van der Waals force.13,14 Meanwhile, the π-complexation is reversible and prone to breakdown through altering the operating conditions.14−16 It is much easier for olefins to form π-complexation compared to the aromatics.17 However, both olefins and aromatics can be complexated with metal ions. Hence, the separation of saturates that contain olefins from aromatics prior to separating olefins from paraffins by π-complexation is desirable. The dominant technology used for light olefin/paraffin separations in industry is cryogenic distillation, which consumes © XXXX American Chemical Society
Received: March 17, 2013 Revised: April 26, 2013
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Figure 1. (a) GC−FID results of the 1-C12=/n-C13 standard solution and its two elution fractions, 4 and 12. (b) Elution curve of the mixture (n-C5 as the solvent before fraction 7 and CH2Cl2 after fraction 8).
AgI-modified ion-exchanged silica column is developed to guarantee the separation efficiency and increase the stability under the use of HPLC. However, the lifetime of such columns was less than 2 or 3 months.28 Similar columns were also used in supercritical fluid chromatography (SFC) to separate olefins in gasoline, diesel,28 and jet fuel,1 as well as triacylglycerol from vegetable oils.29 Comprehensive two-dimensional gas chromatography (GC × GC) comprising a polar primary column and a nonpolar secondary column to couple with a time-of-flight mass spectrometer (TOF MS) has clearly separated and distinguished olefins from paraffins and cyclic compounds in FT products.8 These high-efficient separation instruments can do some work in the separation of olefins and paraffins, but the special column used is expensive and not reliable. In addition, a highly skilled operator is needed to accomplish the operations. No quick and easy method has been developed to separate heavy paraffins and olefins. In this paper, we developed a separating method using solidphase extraction cartridges containing Ag+-exchange resin (Ag+SPE) to separate olefins and paraffins. The method was verified by standard compounds and the saturate fractions of coal tar and petroleum coker oil.
held for 10 min, followed by rinsing the cartridge slowly with 10 mL of isopropanol. Thereafter, a total of 15 mL of n-pentane was used to replace isopropanol and balance the cartridge for 15 min to submerge the cartridge matrix in a nonpolar environment. After the above preparation, three cartridges were installed in series. A 15 mg standard mixture containing 47.5 wt % 1-C12= and 52.5 wt % n-C13 was dissolved in 100 μL of n-pentane. The standard solution was loaded onto the cartridges, which were subsequently eluted with 3.5 mL of n-pentane (before fraction 7) and 4 mL of dichloromethane (after fraction 8) at 0.5 mL elution intervals for each fraction, which was analyzed by gas chromatography coupled with a flame ionization detector (GC−FID). For coal tar and coker oil, a 15 mg saturate fraction of each sample was dissolved in 100 μL of n-pentane and loaded onto the cartridges. Normal pentane and dichloromethane were used to elute the cartridges in sequence. In this case, 3.5 mL of n-pentane was collected as the paraffin fraction and, subsequently, 4.0 mL of dichloromethane was collected as the olefin fraction, for each sample. The two fractions of coal tar and coker oil were analyzed by gas chromatography coupled with mass spectrometry (GC−MS) and proton nuclear magnetic resonance (1H NMR) spectroscopy. 2.3. Instrumental Conditions. 2.3.1. GC−MS Analysis. In the GC−MS analysis, both electron-impact ionization (EI) and field ionization (FI) were used for characteristic fragment ions and molecular ions, respectively. For EI, a Thermo-Finnigan Trace DSQ GC−MS was employed to analyze the paraffin and olefin fractions of coal tar and coker oil. A HP-5 MS column (30 m × 0.25 mm inner diameter × 0.25 μm film thickness) was used, which was held at 50 °C for 5 min, ramped to 300 °C at 8 °C/min, and then held at the final temperature for 5 min. The injector and transfer line temperatures were held at 300 and 250 °C, respectively. Helium was used as the carrier gas with a flow rate of 1 mL/min. The ion source temperature of MS was maintained at 250 °C, with an ionizing energy at 70 eV. For FI, a Waters GCT Premier GC−FI TOF was used for the analysis of paraffins and olefins in the two samples. A 0.2 μL sample was injected onto a 30 m × 0.32 mm inner diameter uncoated fused silica capillary GC column, which was held at 60 °C for 2 min, ramped to 330 °C at 15 °C/min, and then held at a final temperature for 20 min. The GC−MS interface temperature was at 350 °C. The field ionization emitter was at 12 kV voltage, with 6 mA emitter current on a 5 μm emitter. 2.3.2. 1H NMR. A Varian Unity Inova 500 MHz NMR spectrometer equipped with a 5 mm double-resonance broadband probe was used to analyze the olefins in coal tar and coker oil. The experimental
2. EXPERIMENTAL SECTION 2.1. Materials. Normal pentane (n-pentane), dichloromethane, and isopropanol were purchased from Beijing Reagent, Ltd. (Daxing District, Beijing, China) and further purified by evaporation. The Ag+SPE (Ag-IC 10, packing 500 mg) was purchased from Agela Technologies. 1-Dodecene (1-C12=) was purchased from Shanghai Jingchun Reagent, Ltd., and normal tridecane (n-C13) was purchased from Green Special Chemical, Ltd., as standard materials. The “saturate” fraction (containing both paraffins and olefins) of coal tar was obtained by saturates, aromatics, resins, and asphaltenes (SARA) fractionation previously described by Long el al.30 The petroleum coker oil was obtained from Liaohe refinery. Its saturate fraction of the coker oil was obtained from a homemade alumina SPE cartridge (3 g of alumina heated for 6 h at 500 °C, followed by deactivation with 1 wt % deionized water) by eluting with n-pentane. The fraction was recovered by evaporating n-pentane. 2.2. Methods. The separation process was carried out in SPE cartridges. First, isopropanol was used to replace methanol that existed in the SPE cartridge. The cartridge was filled with isopropanol and B
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Figure 2. GC−MS chromatogram of the saturated fraction of coal tar (a) and its paraffin fraction (b) and olefin fraction (c) with the expansion of figures within the boxes displayed on the left and right sides of the main figure.
Figure 3. GC−MS chromatogram of the coker oil saturate fraction (a) and its paraffin fraction (b) and olefin fraction (c) with the expansion of figure within the box displayed on the right. parameters included a test temperature (T) of 21.5 °C, a pulse width (pw) of 1.0 μs, a spectrometer width (sw) of 1000 Hz, a NMR frequency of 499.644 MHz, a chemical shift scaling δTMS of 0, and a recycle delay of 3 s. Deuterated chloroform was used as the solvent.
2.3.3. GC−FID. An Agilent 7890A GC−FID was used for the examination of the standard sample. A HP-5 fused silica capillary column (30 m × 0.25 mm inner diameter × 0.25 μm film thickness) was held at 50 °C for 5 min, then programmed to 300 °C at 10 °C/min, C
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Figure 4. Paraffin and olefin distributions in coal tar and coker oil. and held at the final temperature for 5 min. The injector and detector temperatures were held at 300 °C. Nitrogen was used as the carrier gas with a flow rate of 1 mL/min.
Figure 2 displays GC−MS results of the saturate fraction of coal tar before and after paraffin/olefin separation. The total saturate fraction is shown on the top chromatogram (a), while the paraffin and olefin fractions from the saturate fraction are shown in the middle (b) and bottom (c) chromatograms. Figure 3 shows the corresponding GC−MS chromatograms of the saturate fraction of coker oil (a) and its paraffin (b) and olefin (c) fractions. In each figure, enlargements of selected retention regions are shown as insets on the left or right side of the main figure. In Figures 2a and 3a, the strongest peaks are n-paraffin peaks, with smaller linear 1-olefin peaks adjacent to the corresponding n-paraffin peaks of the same carbon numbers, confirmed by GC−MS. The resolution between the n-paraffin and linear 1-olefin decreases with the carbon number, resulting in overlaps of the peaks at higher carbon numbers. The paraffin peaks in the paraffin fractions (Figures 2b and 3b) match the paraffin peaks in the total saturate fractions, while the olefin peaks in olefin fractions (Figures 2c and 3c) agree with the olefin peaks in the total saturate fractions. The separation of paraffins and olefins can be clearly seen in the inset with enlarged views. The paraffin peaks in paraffin fractions appear in the olefin fractions with small carryovers. On the other hand, the olefin peaks are absent in the paraffin fractions. Because of severe overlaps between paraffins and olefins in GC at higher carbon numbers, it is desirable to separate them by the Ag+-SPE cartridges beforehand for more accurate quantitation and distribution of paraffins and olefins. In the olefin fractions, other isomeric olefins adjacent to linear 1-olefins (normal α-olefins) are clearly shown. The separation of paraffins and olefins by this method is especially useful for heavy petroleum and coal tar fractions at high carbon numbers. The individual GC−MS chromatograms from paraffin and olefin fractions clearly display the distinct distribution patterns, including smaller isomers for identification and quantitation.
3. RESULTS AND DISCUSSION 3.1. Method Establishment Using Standard Compounds. The standard solution and its two fractions (4 and 12) were analyzed by GC−FID, with the results shown in Figure 1a for clear separation between 1-C12= and n-C13. The recovery percentage of the analytes, i.e., 1-C12= and n-C13, is plotted against the elution fraction number, as shown in Figure 1b. Neither 1-C12= nor n-C13 came out of the cartridges in the first three fractions. In the following three fractions, dramatic increases in n-paraffin appeared, with no olefin. The 7th and 8th fractions represent a transition period between paraffin and olefin. In the 7th fraction, paraffin accounted for 1.48% of the paraffin loaded and olefin accounted for 0.69% of the olefin loaded. In the 8th fraction, paraffin and olefin accounted for 0.22 and 1.6% of the paraffin and olefin loaded, respectively. No more paraffin appeared after the 9th fraction. Olefin eluted off the cartridges rapidly at the 11−13th fractions. The total recoveries are 99.00% for 1-C12= and 102.19% for n-C13. The olefin/paraffin ratio is 46.6:53.4, close to the initial ratio of 47.5:52.5. The elution curves show that the paraffin (n-C13) eluted by n-pentane rapidly and thoroughly. In contrast, the elution pattern of olefin seems more complicated. The olefin (1-C12=) in 7−11th fractions increased slowly where solvent change (from n-pentane to dichloromethane) occurred. It may be due to the remaining n-pentane in the dead volume (1.5 mL), which affects the efficiency of dichloromethane to break complexation of olefin with Ag+. On the basis of the above results, a good recovery and separation of olefins and paraffins can be obtained using this method. 3.2. Method Validation by Representative Samples. The saturate fractions of a coal tar from lignite and a coker oil from petroleum were used to validate the method established. D
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of molecules in a mixture. The coupling of FIMS with GC can provide isomer distribution based on molecular ions and retention times.32 For nonpolar paraffins and olefins, FI is the most suitable ionization method to obtain molecular profiles (the distribution of molecules in a mixture). The compound distributions in coal tar and coker oil can be displayed as double bond equivalence (DBE) versus carbon number derived from molecular formula, shown in Figure 4.33 The paraffins in coal tar are mostly acyclic (DBE = 0) and monocyclic (DBE = 1). The most dominate monocyclic paraffin is C19, similar to the situation in acyclic alkanes. The carbon number distribution of monocyclics is broader than that of dicyclics, which, in turn, is much broader than tricyclics. This indicates that long side chains are dominant in monocyclics, while polycyclics have more short side chains. In the coal tar olefin fraction, olefins are primarily monoolefins (DBE = 1), with some diolefins and/or cycloolefins. Note that the DBE of both monocyclic paraffins and monoolefins is 1, but they can be differentiated by the presence in either the paraffin or the olefin fraction separated by Ag+-SPE. The compounds with DBE ≥ 4 in the figure correspond to aromatics as carryovers from SARA separation. Similar to coal tar, paraffins in coker oil are predominantly acyclic (DBE = 0) and monocyclic (DBE = 1), while olefins are concentrated at DBE = 1. Again, aromatics are present in the olefin fraction. Unlike coal tar, the distributions of paraffins and olefins in coker oil do not match with the GC−EIMS results shown in Figure 3, because of the difference in ionization method and volatility loss of the sample prior to GC−FI TOF MS analysis. 3.4. Olefin Structure Types by 1H NMR. With a separated olefin fraction, the signals observed in 1H NMR are all from olefinic hydrogen structures. The chemical shift from 4.6 to 5.9 ppm corresponds to H atoms on different structures (types) of double bonds, with the integral of the peak area proportional to the quantity.34
The carbon number distribution of paraffins in coal tar is shown in Figure 2 ranging from C12 to C33. The abundance increases from C12 to C15 steadily, highest at a wide range from C15 to C25, and then decreases rapidly from C26 to the end (∼C35). Without the overlaps of paraffins at a high carbon number, the carbon number distribution of olefins can be determined. The abundance of olefins increases from C12 to C15, highest at C18, and then decreases slowly from C18 to C30. The abundance of C18 olefin is exceptionally high because of some contribution from the C18 olefin contaminant in the SPE cartridge (which was found in the blank run). The recovery was found to be 99%, including the C18 olefin contaminant. The true recovery should be slightly lower than this value. The paraffin/olefin ratio is 73:26. The carbon number distribution of paraffins in coker oil shown in Figure 3 is from C9 to C26, and that of olefins shown in the olefin fraction (Figure 3c) is from C9 to C24. The abundance of paraffins increases slowly from C9 to C20 and then decreases dramatically from C23. For olefins, the most abundant component is C10 1-olefin, with the abundance of higher carbon numbers decreasing slowly to the end (∼C25). The recovery of coker oil was determined to be 95 wt %. The paraffin/olefin ratio is 63:32. 3.3. Molecular Distribution by FI. FI generates only molecular ions without fragmentations.31 Hence, the distribution of molecular ions can be used as a surrogate of the distribution Table 1. Chemical Shifts of Different Olefin Structures and the Contents in Coal Tar and Coker Oil number
from (ppm)
to (ppm)
structure type
content in coal tar/coker oil (mol %)
1 2 3 4 5
5.9 5.6 5.3 5.05 4.8
5.6 5.3 5.05 4.8 4.6
normal α-olefin normal internal olefin iso-internal olefin normal α-olefin iso-α-olefin
65.2/53.4 24.2/19.2 9.4/14.8 65.2/53.4 1.2/12.5
It = I5.3 − 5.6/2 + I5.05 − 5.30 + (I4.8 − 5.05 + I5.6 − 5.9)/3 + I4.6 − 4.8/2
Figure 5. 1H NMR spectrograms of coker oil and coal tar olefin fractions [0.0 ppm corresponds to tetramethylsilane (TMS) and 7.25 ppm corresponds to deuterated chloroform solvent]. E
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normal internal olefin = I5.3 − 5.6/2It
(4) Kang, S. W.; Char, K.; Kang, Y. S. Novel application of partially positively charged silver nanoparticles for facilitated transport in olefin/paraffin separation membranes. Chem. Mater. 2008, 20 (4), 1308−1311. (5) Azhin, M.; Kaghazchi, T.; Rahmani, M. A review on olefin/ paraffin separation using reversible chemical complexation technology. J. Ind. Eng. Chem. 2008, 14 (5), 622−638. (6) Teramoto, M.; Shimizu, S.; Matsuyama, H.; Matsumiya, N. Ethylene/ethane separation and concentration by hollow fiber facilitated transport membrane module with permeation of silver nitrate solution. Sep. Purif. Technol. 2005, 44 (1), 19−29. (7) Shin, J. Y.; Park, J. Y.; Liu, C.; He, J.; Kim, S. C. Chemical structure and physical properties of cyclic olefin copolymers. Pure Appl. Chem. 2005, 77 (5), 801−814. (8) Van der Westhuizen, R.; Crouch, A.; Sandra, P. The use of GC × GC with time-of-flight mass spectrometry to investigate dienes and diels−alder polymerisation products in high-temperature Fischer− Tropsch-based fuels. J. Sep. Sci. 2008, 31 (19), 3423−3428. (9) Yang, R.; Kikkinides, E. New sorbents for olefin/paraffin separations by adsorption via π-complexation. AIChE J. 1995, 41 (3), 509−517. (10) Muhs, M.; Weiss, F. Determination of equilibrium constants of silver−olefin complexes using gas chromatography. J. Am. Chem. Soc. 1962, 84 (24), 4697−4705. (11) Takahashi, A.; Yang, F. H.; Yang, R. T. Aromatics/aliphatics separation by adsorption: New sorbents for selective aromatics adsorption by π-complexation. Ind. Eng. Chem. Res. 2000, 39 (10), 3856−3867. (12) Jones, D.; West, C. E.; Scarlett, A. G.; Frank, R. A.; Rowland, S. J. Isolation and estimation of the ‘aromatic’ naphthenic acid content of an oil sands process-affected water extract. J. Chromatogr., A 2012, 1247, 171−175. (13) Padin, J.; Yang, R. T.; Munson, C. L. New sorbents for olefin/ paraffin separations and olefin purification for C4 hydrocarbons. Ind. Eng. Chem. Res. 1999, 38 (10), 3614−3621. (14) Padin, J.; Yang, R. T. New sorbents for olefin/paraffin separations by adsorption via π-complexation: Synthesis and effects of substrates. Chem. Eng. Sci. 2000, 55 (14), 2607−2616. (15) Wu, Z.; Han, S. S.; Cho, S. H.; Kim, J. N.; Chue, K. T.; Yang, R. T. Modification of resin-type adsorbents for ethane/ethylene separation. Ind. Eng. Chem. Res. 1997, 36 (7), 2749−2756. (16) Yamaguchi, T.; Baertsch, C.; Koval, C. A.; Noble, R. D.; Bowman, C. N. Olefin separation using silver impregnated ionexchange membranes and silver salt/polymer blend membranes. J. Membr. Sci. 1996, 117 (1), 151−161. (17) Safarik, D. J.; Eldridge, R. B. Olefin/paraffin separations by reactive absorption: A review. Ind. Eng. Chem. Res. 1998, 37 (7), 2571−2581. (18) Faiz, R.; Li, K. Polymeric membranes for light olefin/paraffin separation. Desalination 2012, 287, 82−97. (19) Kim, J. H.; Won, J.; Kang, Y. S. Olefin-induced dissolution of silver salts physically dispersed in inert polymers and their application to olefin/paraffin separation. J. Membr. Sci. 2004, 241 (2), 403−407. (20) Cheng, L. S.; Yang, R. T. Monolayer cuprous chloride dispersed on pillared clays for olefin−paraffin separations by π-complexation. Adsorption 1995, 1 (1), 61−75. (21) Bessarabov, D.; Theron, J.; Sanderson, R. Novel application of membrane contactors: Solubility measurements of 1-hexene in solvents containing silver ions for liquid olefin/paraffin separations. Desalination 1998, 115 (3), 279−284. (22) Munson, C. L.; Boudreau, L. C.; Driver, M. S.; Schinski, W. L. Separation of olefins from paraffins using ionic liquid solutions. U.S. Patent 6,623,659 B2, 2003. (23) Pinnau, I.; Toy, L. G. Solid polymer electrolyte composite membranes for olefin/paraffin separation. J. Membr. Sci. 2001, 184 (1), 39−48. (24) Suatoni, J.; Swab, R. HPLC preparative group-type separation of olefins from synfuels. J. Chromatogr. Sci. 1980, 18 (8), 375−378.
iso‐internal olefin = I5.05 − 5.30/It normal α‐olefin = (I4.8 − 5.05 + I5.6 − 5.9)/3It iso‐α ‐olefin = I4.6 − 4.8/2It
where It is the total peak intensity and Ix−y is the peak intensity between x and y ppm. The chemical shifts and the contents of different olefin structure types in coal tar and coker oil are listed in Table 1. The two peaks at 4.6−4.8 ppm in Figure 5 correspond to H atoms on the double bond of iso-α-olefins, which are present significantly in coker oil but negligible in coal tar. In both coal tar and coker oil, the contents are normal α-olefin > normal internal olefin > iso-internal olefin > iso-α-olefin. The later three types have close contents in coker oil but vary considerably in coal tar. The olefins in coal tar and coker oil are mainly normal α-olefins, consistent with the GC−MS results. Although the π-complexation of normal internal olefins is weaker than that of normal α-olefins,10 they are well-separated from paraffins and enriched in the olefin fraction by the Ag+-SPE method.
4. CONCLUSION A method of physically separating olefins from paraffins in a saturate fraction using Ag+-SPE has been developed. When the method was applied to coal tar and coker oil, high-purity paraffin and olefin fractions were obtained. The presence of small amounts of olefin components can only be observed in the chromatogram of the olefin fraction, which cannot be seen in that of the saturate fraction containing both paraffins and olefins. The structures of olefins were determined by 1H NMR for the distribution of olefin types. None or negligible amounts of iso-α-olefins were found in coal tar but were found in significant amounts in coker oil. The separation also facilitates the differentiation of isomers of the same molecular formula, such as monocycloparaffins and monoolefins, in complex mixtures.
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AUTHOR INFORMATION
Corresponding Author
*Telephone: +1-850-410-6684 (C.S.H.); +86-10-8973-3738 (Q.S.). E-mail:
[email protected] (C.S.H.);
[email protected] (Q.S.). Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the National High Technology Research and Development Program of China (2011AA05A202) and the National Natural Science Foundation of China (21236009).
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REFERENCES
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