Energy & Fuels 2005, 19, 1995-2000
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Characterization of Feeds, Intermediates, and Products from Heavy Oil Processes by High-Temperature Simulated Distillation and Thin-Layer Chromatography with Flame Ionization Detection Bhajendra N. Barman* Texaco FLTD, 4545 Savannah Avenue, Port Arthur, Texas 77640 Received January 7, 2005. Revised Manuscript Received May 16, 2005
High-temperature simulated distillation (HTSD) and thin-layer chromatography with flame ionization detection (TLC-FID) have been applied for the characterization of an atmospheric resid and its gas oil fractions that belong to several viscosity grades and vacuum resid obtained by vacuum distillation. TLC-FID has provided the hydrocarbon type data. The boiling range distribution results for various samples have been derived from HTSD chromatograms. Raffinates, aromatic extracts, waxes, and base oils obtained from solvent refining and dewaxing of vacuum gas oils have also been analyzed. These two techniques are shown to be equally applicable to the feed and product samples from catalytic dewaxing. The results from these methods reveal differences caused by processing schemes as exemplified with three bright stocks derived from the same deasphalted oil. When combined, the boiling range distributions by HTSD and compositional analyses by TLC-FID provide quantitative data not only for comparison of the results between samples or sample types, but also for assessing the efficiency of heavy oil refining processes.
Introduction Many petroleum-based heavy oils are derived from the leftover materials from the atmospheric distillation of crude oil. The upgrading of a high-boiling atmospheric resid (normally, 343 °C+ material) or other crude oil fractions to obtain high-value products, such as lubricant base stocks, represents a class of heavy oil processes of growing commercial and economic interest. Such processes include vacuum distillation, deasphalting, solvent extraction, solvent or catalytic dewaxing, and hydrotreatment.1 For these processes, there is an increasing need for better analytical methods to optimize process variables, as well as to monitor the quality of feedstock, and to ensure consistency of the end products. Ideally, any such methods should provide information that clearly shows meaningful compositional differences among the feeds, intermediates, and products. If the process involves catalysts, their evaluation also is dependent on the quality of these analytical results. In this context, boiling range distributions and compositional analyses should be considered critical to heavy oil processing and the quality of the associated products. This study involves the production and analysis of gas oil fractions, deasphalted oil (DAO), and a vacuum resid * Author to whom correspondence should be addressed. Telephone: (908) 659-2557. E-mail address:
[email protected]. † Current address: Alpharma/Purepac, 200 Elmora Avenue, Elizabeth, NJ 07207. (Note: The Texaco FTLD facility is no longer in operation.) (1) Sequeira, A., Jr. Lubricant Base Oil and Wax Processing; Chemical Industries, Vol. 60; Marcel Dekker: New York, 1994.
derived from an atmospheric resid by vacuum distillation. The propane deasphalting of vacuum tower bottom has provided DAO. As shown in Figure 1, the three vacuum gas oils (VGOs) and DAO represent neutral boiling range cuts that differ in viscosity measured as Seybolt Universal Seconds (SUS) at 37.8 °C by the ASTM D88-81 method. Also shown in this figure is an extraction step with N-methyl pyrrolidone (NMP), which is applied to remove undesired aromatics and polars from each of these cuts. Each raffinate (solventextracted lube fraction) from NMP extraction contains both base oil and wax. Solvent dewaxing, often coupled with hydrotreatment (to improve color and stability), then provides the base oil. The wax can also be processed further to obtain high-viscosity-index (HVI) base stock. High-temperature simulated distillation (HTSD) and thin-layer chromatography with flame ionization detection (TLC-FID) are shown to be very appropriate for the characterization of the feed, distillation cuts, intermediates (such as extracts, raffinates, and wax), and base oil products that relate to vacuum distillation. Samples from other heavy oil processes have also been analyzed. HTSD provides elution features and boiling range distributions that show similarities as well as differences, as appropriate, from these samples. Quantitative hydrocarbon type data for saturates, aromatics, and polars are obtained using TLC-FID.2-6 (2) Barman, B. N. J. Chromatogr. Sci. 1996, 34, 219-25. (3) Barman, B. N. Tribol. Int. 2002, 35, 15-26. (4) Kaminski, M.; Gudebska, J.; Gorecki, T.; Kartanowicz, R. J. Chromatogr. A 2003, 991, 255-266.
10.1021/ef0580016 CCC: $30.25 © 2005 American Chemical Society Published on Web 07/29/2005
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Figure 1. Heavy oil processing using vacuum distillation, extraction, and dewaxing schemes providing four viscosity-grade base oils and waxes from an atmospheric resid.
Experimental Section Samples. Atmospheric resid was derived from an Arabian light crude. All distillation cut samples were obtained from a pilot-plant study. Extracts, raffinates, oils, and waxes were obtained from small-scale NMP extraction and dewaxing processes. All these fractions were collected and normalized to 100% of the atmospheric resid, ignoring minor loss of samples in various processing steps. Hydrotreated and catalytic dewaxed bright stock samples were also obtained from pilot-unit studies using commercial catalysts. High-Temperature Simulated Distillation. The details of an in-house HTSD method can be found in ref 3. A HP 5890 Series II gas chromatograph that was equipped with a flame ionization detector from Hewlett-Packard (Avondale, PA) was used. Hydrocarbon standards and polywax sample were used for boiling range calibration covering carbon numbers from C14 to C100.3 Following an approach similar to ASTM method D5307-97, the retention time was transformed to the temperature and the response to sample mass. All samples were diluted with carbon disulfide (1:100, m/v) before they were injected on a 4-m HT50 capillary column from SGE (Austin, TX). The flow rate of the nitrogen carrier gas was maintained at 38 mL/min with an electronic pressure controller. The column temperature was programmed from 40 °C for 1 min to 430 °C at a rate of 11 °C/min with a 17.5 min hold at the end. The injection port temperature was also programmed from 100 °C for 1 min to 440 °C at a rate of 20 °C/min. The aforementioned conditions are somewhat different from those used in the ASTM D6352-98 method, where the column temperature was in the range of 50-400 °C to cover a boiling range from 174 °C to 700 °C. In this work, the final column temperature is 430 °C, compared to 400 °C in the ASTM D6352-98 method. The higher column temperature is more appropriate for some of the heavy samples with final boiling points close to or above 700 °C (see later). Thin-Layer Chromatography-Flame Ionization Detection. The details of the TLC-FID procedure have been highlighted elsewhere.2,3,6 A model MK-5 Iatroscan instrument (5) Cebolla, V. L.; Membrado, L.; Domingo, M. P.; Henrion, P.; Garriga, R.; Gonzalez, P.; Cossio, F. P.; Arrieta, A.; Vela, J. J. Chromatogr. Sci. 1999, 37, 219-226. (6) Barman, B. N. J. Sep. Sci. 2004, 27, 311-315.
(Iatron Labs, Tokyo, Japan) was used. Hydrocarbon type separation was achieved on Silica SIII Chromarods. For FID, the hydrogen and air flow rates were maintained at 160 and 2000 mL/min, respectively. All samples were diluted to a concentration of 10 mg/mL with toluene. A rack of ten Chromarods, each spotted with ∼1 µL of diluted sample at the bottom, was first developed with toluene for 5 min. After drying the Chromarods at 70 °C for 2 min, a second development was conducted with n-heptane for 30 min. Following another drying, the Chromarods were scanned lengthwise under oxy-hydrogen flame with a scan rate of 30 s per Chromarod. TLC-FID hydrocarbon type data are reported in terms of weight percentage, assuming identical response factors for saturates, aromatics, and polars.2,7
Results and Discussion AtmosphericResid,VacuumGasOils,andVacuum Resid. Typical volume percentages of different fractions (and subfractions) of the atmospheric resid are as follows: 12% 60 N VGO, which is comprised of 9% raffinate (8% from oil and 1% from wax) and 3% extract; 12% 150 N VGO, which is comprised of 8% raffinate (7% from oil and 1% from wax) and 4% extract; 22% 500 N VGO, which is comprised of 12% raffinate (10% from oil and 2% from wax) and 10% extract; 17% DAO, which is comprised of 15% oil and 2% wax; and 37% vacuum resid. The aforementioned data indicate that the atmospheric resid contains high-value products, such as oil and wax, totaling 40% and 6%, respectively. High-temperature gas chromatograms of the atmospheric resid (as feed) and three vacuum distillates (defined as 60, 150, and 500 N fractions) are shown in Figure 2. Also included in this figure is a DAO chromatogram. It is observed that there is an incremental shift to higher boiling-range distributions as the VGO or DAO viscosity grade increases. Simulated distillation data for atmospheric resid, three VGOs, DAO, and (7) Vela, J.; Cebolla, V. L.; Membrado, L.; Andre´s, J. M. J. Chromatogr. Sci. 1995, 33, 417-425.
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Figure 2. High-temperature gas chromatograms of atmospheric resid; 60 N, 150 N, and 500 N vacuum gas oils (VGOs); and deasphalted oil. Table 1. High-Temperature Simulated Distillation Data of Atmospheric Resid and Its Fractions Cut Point (°C)a sample
IBP
5%
20% 50% 80% 95%
FBP
atmospheric resid 60 N vacuum gas oil 150 N vacuum gas oil 500 N vacuum gas oil deasphalted oil vacuum resid
287 253 294 314 389 402
349 300 348 398 487 495
419 336 387 438 523 541
(793) 507 580 682 (767) (799)
501 371 424 475 566 591
604 409 461 513 615 657
693 451 502 568 663 734
a IBP and FBP are equivalent to 0.5% and 99.5% cut points. Numbers in parentheses are values that lie >20 °C above the highest calibration temperature of 720 °C, which is the boiling point of C100 hydrocarbon.
vacuum resid are given in Table 1. The 50% cut points for the atmospheric resid and vacuum resid correspond to carbon numbers of C37 and C54, respectively. For various fractions, 50% cut points for 60 N VGO, 150 N VGO, 500 N VGO, and DAO correspond to carbon numbers C22, C27, C33, and C48, respectively. As is typical for a refinery, the two resids and all fractions display broad boiling-range distributions. TLC-FID chromatograms a-e in Figure 3 represent the atmospheric resid and its four fractions (the VGOs and the DAO) belonging to different viscosity grades. Chromatogram f in Figure 3 is for the vacuum resid. The quantitative hydrocarbon type data derived from these chromatograms are given in Table 2. The three VGOs and the DAO vary in hydrocarbon type results. Typically, more polars and aromatics are observed when the viscosity of the fraction is higher. In Figure 3, aromatics with increasingly higher ring numbers are found in samples in the following order: 60 N VGO < 150 N VGO < 500 N VGO < DAO. Very high amounts of polars are observed in both atmospheric resid and vacuum resid. The consistency of TLC-FID data is checked by comparing hydrocarbon type data of the atmospheric resid with that of a composite sample using volume fractions of gas oils, DAO, and vacuum resid, as well
Figure 3. Thin-layer chromatography-flame ionization detection (TLC-FID) chromatograms of (a) atmospheric resid (chromatogram a), 60 N VGO (chromatogram b), 150 N VGO (chromatogram c), 500 N VGO (chromatogram d), deasphalted oil (DAO) (chromatogram e), and vacuum resid (chromatogram f). Table 2. Hydrocarbon Type and Composition of Atmospheric Resid and Its Fraction by TLC-FID Composition (% m/m)
sample
sample type
saturates
aromatics
polars
atmospheric resid 60 N vacuum gas oil 150 N vacuum gas oil 500 N vacuum gas oil deasphalted oil vacuum resid
feed fraction fraction fraction fraction residuum
28.6 52.5 47.5 35.6 38.4 9.0
56.8 46.6 49.8 61.4 56.4 58.5
14.6 0.9 2.7 3.0 5.2 32.5
as hydrocarbon type data given in Table 2. The absolute differences between hydrocarbon type data are determined to be 1.1%, 0.5%, and 0.6% for the saturates, aromatics, and polars, respectively. 500 N Vacuum Gas Oil, Intermediates, and Base Oil. Both HTSD and TLC-FID can be applied to evaluate VGO, intermediates, and base oil that belong to a specific viscosity grade. This is demonstrated with 500 N VGO, extract, raffinate, wax, and base oil. Figure 4 shows their gas chromatograms that display distinct elution profiles primarily because of their compositional differences. The chromatogram for wax, displayed as chromatogram d in Figure 4, with large amounts of longchain normal saturated hydrocarbons shows numerous peaks. On the other hand, the extract shows an almost smooth and broad distribution of compounds (chromatograph b in Figure 4). The remaining chromatograms fall in between. However, from the elution ranges in Figure 4, it is apparent that the boiling-point distributions of these samples are very similar, as listed in Table 3. The 50% cut points of all these samples fall between the C32 (466 °C) and C34 (481 °C) carbon number range. The
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Figure 4. High-temperature gas chromatograms of 500 N VGO and its various fractions: VGO (chromatogram a), extract (chromatogram b), raffinate (chromatogram c), wax (chromatogram d), and base oil (chromatogram e). Table 3. High-Temperature Simulated Distillation Data of 500 N Vacuum Gas Oil Feed, Intermediates, and Base Oil Product Cut Point (°C) sample
IBP
5%
20% 50% 80% 95% FBP
500 N vacuum gas oil aromatic extract raffinate wax 500 N base oil
314 261 271 345 312
398 385 402 411 392
438 431 443 447 439
475 469 479 482 477
513 506 518 517 514
568 555 571 564 561
682 669 682 696 672
sharp peaks near the origin of chromatograms b and c in Figure 4 represent residual solvent from the extraction process. A set of TLC-FID chromatograms for the 500 N samples and their hydrocarbon type data are given in Figure 5 and Table 4, respectively. Table 4 also contains hydrocarbon type data for a 150 N VGO, its intermediates, and the base oil. Figure 5 shows that hydrocarbon type compositions of the VGO feed, intermediates, and oil product for a specific viscosity-grade sample can vary significantly from each other, thus providing a clear differentiation among samples. As listed in Table 4, the aromatic extract from the NMP extraction of VGO is heavily loaded with aromatics and polars. In contrast, wax has the least amount of aromatics plus polars. For both 150 and 500 N samples, the amounts of aromatics vary in the following order: extract > base oil > raffinate > wax. The extraction efficiency can be determined from the net change, for an example, in the aromatics plus polars from the feed to the base oil. Catalytic Dewaxing. A slack wax from the solvent dewaxing process or other sources can be hydroisomerized with a zeolyte catalyst to produce HVI base oil. During hydroisomerization, long-chain paraffin wax is transformed to isoparaffinic oil with some light fuels as byproducts. As a result, the oil content is enhanced from a typical value of 20% in the feed to 80% in the product. The residual wax is again removed from the hydroisomerized product by solvent dewaxing. Figure 6 shows gas chromatograms of a slack wax feed, its hydroisomerized product, and the separated
Figure 5. TLC-FID chromatograms of 500 N VGO and its various fractions: VGO (chromatogram a), extract (chromatogram b), raffinate (chromatogram c), wax (chromatogram d), and base oil (chromatogram e). Table 4. Hydrocarbon Type Data for 150 N and 500 N Materials by TLC-FID Composition (% m/m) sample
sample type
saturates
aromatics
polars
150 N Vacuum Gas Oil, Intermediates, and Base Oil vacuum gas oil feed 47.5 49.8 aromatic extract fraction 12.2 84.4 raffinate fraction 79.8 19.8 wax fraction 96.2 3.3 base oil product 77.8 21.3
2.7 3.4 0.4 0.5 0.9
500 N Vacuum Gas Oil, Intermediates, and Base Oil vacuum gas oil feed 35.6 61.4 aromatic extract fraction 14.0 80.1 raffinate fraction 64.5 33.9 wax fraction 93.7 4.7 base oil product 58.7 39.7
3.0 5.9 1.6 1.6 1.6
wax and oil by solvent dewaxing. It is apparent from Figure 6 that there is a downward shift in the boilingrange distribution, because of some cracking during hydroisomerization process. The 50% cut points obtained by HTSD for the slack wax is 471 °C (C33), compared to 429 °C (C28), 462° (C32), and 421 °C (C27) for the hydroisomerized product (oil plus wax), wax, and base oil, respectively. TLC-FID chromatograms of the aforementioned samples are shown in Figure 7. The hydrocarbon type results are as follows: for slack wax (chromatogram a in Figure 7): 93.4% (m/m) saturates, 6.3% aromatics, and 0.3% polars; for the hydroisomerized product (chromatogram b in Figure 7): 93.1% saturates, 6.9% aromatics, and 0.0% polars; for the separated wax (chromatogram c in Figure 7): 96.4% saturates, 3.5% aromatics, and 0.1% polars; and for the base oil (chromatogram d in Figure 7): 89.6% saturates, 10.3%
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Figure 6. High-temperature gas chromatograms of the slack wax feed (chromatogram a) and the product from catalytic dewaxing (chromatogram b), as well as that of wax (chromatogram c) and the base oil (chromatogram d) obtained by the final solvent dewaxing.
Figure 8. TLC-FID chromatograms of bright stocks obtained by three processing options: (a) NMP refining, solvent dewaxing, and hydrotreatment; (b) NMP refining and catalytic dewaxing; and (c) NMP refining and solvent dewaxing.
Variation of Bright Stocks due to Processing Options. A solvent-refined DAO provides base oil commonly known as “bright stock”. As shown in Figure 1, to obtain bright stock, the DAO raffinate can be further processed using schemes such as (i) solvent dewaxing and hydrogen finishing, (ii) catalytic dewaxing, and (iii) solvent dewaxing. Although TLC-FID is expected to reveal compositional differences in the hydrocarbon type data caused by processing options, the HTSD would show minimal differences in their boilingrange distributions. For example, although the greatest difference is expected between the products from schemes (ii) and (iii), they show 50% cut points at 586 °C (C52) and 574 °C (C50), respectively.
Figure 7. TLC-FID chromatograms of the slack wax feed (chromatogram a) and the product from catalytic dewaxing (chromatogram b), as well as that of wax (chromatogram c), and the base oil (chromatogram d) obtained subsequently by solvent dewaxing.
aromatics, and 0.1% polars. It is apparent that the hydroisomerization process provides base oils with lower aromatics than the solvent extraction process, as exemplified in Table 4 with 150 N base oil, which contains 21% aromatics, and 500 N base oil, which has 40% aromatics.
In Figure 8, TLC-FID chromatograms reflect the lowest aromatics and polars contents in the product from catalytic dewaxing (chromatogram b in Figure 8). Solvent dewaxing (chromatogram c in Figure 8) yields product with the highest aromatics plus polars. The product from scheme (i) will have reduced aromatics plus polars content, because of the hydrotreatment after solvent dewaxing. The hydrocarbon type results for the solvent dewaxed bright stock are as follows: 41.4% (m/ m) saturates, 55.6% aromatics, and 3.0% polars. The solvent-dewaxed and hydrogen-finished sample is observed to have 43.1% saturates, 55.4% aromatics, and 1.5% polars. Finally, the catalytic dewaxed bright stock contains 52.3% saturates, 46.4% aromatics, and 1.3% polars.
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Conclusions Thin-layer chromatography-flame ionization detection is unique for its universal applications to the feed, products, and residuum involved in heavy oil processes, because sample components are separated by their displacement on Chromarods and are subsequently detected and measured by burning the Chromarods with an oxy-hydrogen flame. In a method such as normal liquid-phase chromatography,8,9 where sample elution and backflusing through a polar column are needed, there are issues such as (i) resolution between hydrocarbon types; (ii) irreversible adsorption of some heavy aromatics and polar compounds; and (iii) loss of sample integrity, because of prefiltration of the sample to remove materials such as asphaltenes and polar aro(8) Pasadakis, N.; Varotsis, N. Energy Fuels 2000, 14, 1184-1187. (9) Barman, B. N.; Cebolla, V. L.; Membrado, L. Crit. Rev. Anal. Chem. 2000, 30, 75-120.
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matics, because of their low solubility in the mobile phase. In this context, TLC-FID is a much better choice than normal liquid-phase chromatography for quantitative hydrocarbon type analyses of atmospheric resid, vacuum distillates, solvent-refined streams, and vacuum resid. Similarly, high-temperature simulated distillation (HTSD) is shown to provide boiling-range distributions of all these samples. The results from these two techniques provide useful information for the feed and products that can be used to adjust the operating parameters in the heavy oil processes. These adjustments are necessary to improve the efficiency of the operation and to monitor the quality of the end products. Acknowledgment. The author appreciates John B. Holland for providing all the samples and much helpful data and information on heavy oil processes. EF0580016
