Separation of Acids from Asphalts Zdravko Ramljak and Aleksandar Sole Civil Engineering Institute of Croatia, Zagreb, Yugoslavia
Patrick Arpiño,* Jean-Marie Schmitter, and Georges Gulochon Ecole Polytechnique, Laboratoire de Chimie Analytique Physique, Route de Saclay, 91128—Palaiseau Cedex, France
A procedure has been devised for the rapid separation of acids from asphalts using a modified soxhlet filled with potassium hydroxide treated silica. Acids from a whole air blown asphalt and from the maltene and asphaltene fractions from this asphalt were extracted by this procedure and characterized by Infrared spectroscopy.
A decade ago separation of asphalts was mainly achieved by difference of solubility in various organic solvents yielding the subsequent oil, resin, and asphaltene fractions (1). Other methods based on chemical properties of the organic substances present in asphalt are now coming into use: an asphalt may be separated into basic, neutral, and acidic fractions; then further separation is achieved by a combination of chromatographic techniques using adsorption, partition, or gel permeation. Claims for positive evidence of some of the oxygencontaining substances found in asphalt have been controversial: Knotnerus (2, 3) has indicated the presence of esters and small amounts of ketones, aldehydes, and carboxylic acids in asphalts. However, Campbell and Wright (4), did not confirm the presence of esters; they attributed the presence of the carbonyl band seen in the infrared (IR) spectrum to the remaining functional groups. Later Petersen (5-10) found dicarboxylic anhydrides but no esters in oxidized asphalts. Evidences of free carboxylic acids were assumed from the shift of the carbonyl band after reaction of asphalt with potassium bicarbonate, or by silylation. Petersen suggested that strong hydrogen bonding forces resulting from the presence of free carboxylic acids as well as structures exhibiting basicity could influence the physical properties of asphalts. The role of carboxylic acids was emphasized although other functional groups such as phenols or enolic forms of 2-quinolones which are also acidic may be encountered in asphalts. Carboxylic acids can be quantitatively determined in geochemical mixtures without separation (6); however, attempts to get complementary information by means of different spectroscopic methods such as fluorescence, mass, or infrared spectrometry are best carried out after selective removal of the acids, so a method was investigated to that end. Standard methods for separation of acidic fractions from low boiling petroleum distillates and crude oils cannot be applied to asphalts. In our experiments, extraction with an ethanolic solution of sodium hydroxide (11, 12) gave precipitation of asphaltic residues; the method developed by the Bureau of Mines (API-Research Project 60) (13, 14) which makes use of macroreticular exchange resins could not be applied to asphalts because the eluting solvent is pentane, a poor solvent for asphalt. We have modified a method originally suggested by McCarthy and Duthie (15) for biolipids, and later adapted to bitumens from oil shales and crude oils (16). In the method described below, a recycling chromatographic column similar to the device described by Jewell et al. (14) is used; the re1222
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ANALYTICAL CHEMISTRY, VOL. 49, NO. 8, JULY 1977
quired amount of solvent is low and most of the separation process can be left unattended. This procedure has been used for the selective removal of acids from an air blown asphalt.
EXPERIMENTAL A 60-70 penetration grade paving asphalt (supplied by INA Petroleum refinery, Rijeka, Yugoslavia) was obtained by vacuum distillation of an Iraq oil followed by air blowing. The asphaltenes and maltenes were separated from the asphalt by standard methods (17). The preparation of the modified silica for column chromatography is as indicated in the original paper (15) except that chloroform, a better solvent for asphalt, was used instead of ether. Forty mL of a saturated solution of potassium hydroxide in isopropanol (50 g/L) is mixed with 20 g of silica (Merck 0. 0063-0.200 mm) and 100 mL of chloroform. After standing for 5 min, the suspension is slurried into the device shown in Figure 1. All the potassium hydroxide is retained on the silica and presumably reacts to form potassium silicate. The adsorbent is washed by cycling chloroform for 10 min. Then about 1 g of the material under investigation is deposited on top of the bed and chloroform is cycled at a flow rate of approximately 5 mL/min. Neutral, basic, and weak acidic materials are eluted during the first 6 h and can then be recovered in the bottom flask. A second fraction containing acidic materials and strongly polar organic substances is eluted after addition through the top of the column of 450 mL of 20% formic acid in chloroform followed by recycling of the solvent for 2 h. Fractions were recovered from the solutions by vacuum distillation of the solvents in a rotatory evaporator. Methyl esters were obtained after reaction of the “acidic fraction” with diazomethane prepared from p-tolylsulfonylmethylnitrosamide (18). Infrared spectra were recorded on a Perkin-Elmer Model 277 using solutions of the material in carbon tetrachloride. Control tests by means of thin layer chromatography (TLC) were performed with potassium hydroxide modified silica H (Merck) deposited on glass plates using a TLC spreader (Desaga) according to a previously described method (19). It was found later than commercial plates (Merck TLC plates of silica 60 F254) could be modified by immersion of 5 min in a saturated solution of potassium hydroxide in isopropanol. Solvents were evaporated from the plates at ambient temperature; no activation of the adsorbent by heating was attempted.
RESULTS AND DISCUSSION Figures 2 and 3 show elution curves obtained from the separation of reference mixtures in the recycling column: 50-mL subfractions were obtained by stopping the device every 10 min to determine the amount of recovered material. A neutral molecule such as naphthalene is eluted immediately by chloroform within 1 bed volume of solvent. Ketones and esters showed similar behavior. On the other hand, a strong acid such as benzoic acid does not elute at all as long as the formic acid solution is not percolated through the silica bed. Significant retention of slightly acidic substances such as phenols (Figure 3) is observed during elution with chloroform. This could be of use if separation between neutral, weakly acidic, and strongly acidic fractions were attempted. In all cases, no loss of material was observed (recovery exceeded 98%).
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Figure 4. TLC of reference substances listed in Table I. Silica H plate modified by immersion in an isopropanol/potassium hydroxide solution, then dried and developed with chloroform. (A, B, C) position of the spots after one, two, three developments by chloroform, (D) position of the spots after a development by a 20% formic acid in chloroform solution
was
Figure 1. Chromatographic column with recycling of the solvent
1800 (ml)
Figure 2. Plot of percentage of sample material recovered vs. volume of solvent percolated through the column. Sample: 1 g of a 9/1 by weight mixture of naphthalene and benzoic acid
Table I. Reference Substances Used for TLC Experiments Substance Spot No. 1 n-Nonadecane 2 Naphthalene 3 Carbazole 4 o-Cresol 5 p-Cresol m-Cresoi 6 Resorcinol 7 8 2-Naphthol
1-Naphthol m-Chlorophenol o-Chlorophenol m-Nitrophenol p-Nitrophenol n-Octadecanoic acid Benzoic acid
(%)
CHCÍ,
55 ! 50
.
45.
P Ka -
-
11 12 13
12.10 10.20 10.17 10.01 9.81 9.51 9.34 8.85 8.49 8.25 7.15
14 15
4.19
9
10
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N
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100
200
300
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practically infinite retention. A similar situation occurs with the recycling column; it was shown that 6 h is a long enough time to elute completely all phenols tested including p-nitrophenol; thus this value was selected for the separation of asphalt in two fractions. As asphalts are complex mixtures of organic substances, we cannot eliminate the possibility that some complex polar molecules with many functional groups but no carboxylic acid could only be eluted from the column by the formic acid/ chloroform solution. However, many of these substances can be separated by column chromatography over silica after methylation of the acidic fraction obtained after this first step. The elution curve obtained during the separation of the whole asphalt in the recycling column (Figure 5) shows that 98% of mixture is recovered after 1 h of elution by chloroform. Table II shows quantitative data obtained from the separation of the whole asphalt, the asphaltenes, and the maltenes: each sample was analyzed four times to find out if the method was reproducible. As expected, the asphaltenes are more acid rich (4%) than the whole asphalt (0.8%) or the maltenes (0.4%). The infrared spectra between 4000 cm"1 and 1000 cm"1 of the “acidic” and the “neutral” fractions separated from the whole asphalt are shown in Figure 6; the spectra between 1800 cm"1 and 1400 cm"1 of the acidic fraction before and after a
APHTHAE ENE
p-500
600
700
1400
1500
(ml)
Figure 3. Plot of percentage of sample material recovered vs. volume of solvent percolated through the column. Sample: 7/2 mixture of naphthalene and a-naphthol
The influence of the acidity of the material on the elution order is shown in Figure 4. Organic substances with decreasing pKa (see Table I) were deposited on the modified TLC plates described above and developed three times by chloroform, the solvent being air-evaporated between two successive runs. The positions of the spots after each stage are reproduced in Figure 4, A, B, and C. A last elution by 20% formic acid in chloroform moves all the spots to the front of the solvent (Figure 4D). Migration speed decreases with decreasing pKa values; but all tested substances, except the two carboxylic acids, can cross the plate if enough development runs are performed; carboxylic acids on the other hand have
ANALYTICAL CHEMISTRY, VOL. 49, NO. 8, JULY 1977
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Quantitative Data from the Separation of
Table II.
an Iraq Asphalt Recovered “acids”
Sample Total asphalt
Asphaltene
Maltene
Total on-column by weight, Run No. load mg 1 1004 8.1 2 1083 9.0 3 970 6.9 4 1062 8.9 1 113 4.9 2 96 4.7 3 123 4.8 4 85 3.2 1 941 4.0 2 926 4.4 3 995 3.2 4 645 2.9
Recovered “neutrals”
% of total
by weight,
0.81 0.83 0.71 0.82 4.34 4.90 3.90 3.76 0.43 0.48 0.36 0.45
993 1087 959 1046 108
mg
Losses
%of total
by weight,
98.9
2.9 7.0
mg
98.5 98.9 98.5 95.5
118 81
935 918 890 641
0.2 0.2 0.1 0.4 2.0 3.6 1.8 1.1
99.4 99.1 99.4 99.4
Figure 5. Plot of percentage of sample material recovered vs. volume of solvent percolated through the column. Sample: ca. 1 g of total air blown asphalt
1800
0.29 0.65 0.42 0.69 0.17 0.20 0.80 0.49 0.21 0.39 0.20 1.17
4.1 7.9
95 96 96
91
1600
% of total
1400
WAVE NUMBER ¡cm'1)
Figure 7. Infrared spectrum of the acidic (—) and of the methylated acidic (---) fractions
agreement with previous results obtained on long chain waxes (20), cholesteryl esters (15), aliphatic and pentacyclic ketones (20) , aliphatic polyols and phenols, unsaturated fatty acids (21) This is consistent with the assumption that the column material is not potassium hydroxide retained on silica, but potassium silicate. Other functional groups such as carboxylic anhydride or lactone groups have not yet been investigated. The method is easily adaptable to larger amounts of starting material: in a recent version of the device shown in Figure 1, using a 10 cm long X 6 cm diameter bed of adsorbent, 150 g of an acidic rich, high boiling crude oil was separated in one run; therefore gram amounts of acidic fractions separated from asphalts, heavy petroleum distillates, or crude oil can be easily prepared and made suitable for further fractionation. .
Figure 6. Infrared spectrum of the neutral (---) and acidic (—) fraction recovered after separation of the air blown asphalt
shown in Figure 7. The difference in the region in Figure 6 could be caused by stretching vibrations of -OH groups from free carboxylic groups although other functional groups such as -NH from pyrrole-type compounds may also show in this region. The acidic fractions show strong bands centered at 1705 cm™1 suggesting possible free carboxylic acid groups; this is confirmed by the clear shift observed after methylation (Figure 6). A similar shift was observed after methylation of the “acidic” fraction extracted from the asphaltenes and the maltenes. The results prove the presence of a large proportion of free carboxylic acids in the so called “acidic fraction” obtained from the asphalts. No evidence of chemical change induced by the column material during the procedure has been found yet, in
methylation 3500-2500
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are
cm™1
ANALYTICAL CHEMISTRY, VOL. 49, NO. 8, JULY 1977
LITERATURE
CITED
(1) R. N. Traxler, “Asphalt, Its Composition Properties and Uses,” Relnhold
Publishing Corp., New York, 1961, pp 7-32. (2) J. Knotnerus, J. Inst. Pet., 42, 355 (1956). (3) J. M. Goppel and J. Knotnerus, Proc. Fourth World Pet. Congr. Sect.
III.G, 399 (1955).
(4) P. G. Campbell and J. R. Wright, J. Res. Natl. Bur. Stand., Sect. C, 68, 115 (1964). (5) J. C. Petersen, F. A. Barbour, and S. M. Dorrence, Anal. Chem., 47, 107 (1975). (6) J. C. Petersen, Anal. Chem., 47, 112 (1975). (7) R. V. Helm and J. C. Petersen, Anal. Chem., 40, 1100 (1968). (8) J. C. Petersen, J. Phys. Chem., 75, 1129 (1971). (9) J. C. Petersen, R. V. Barbour, S. M. Dorrence, F. A. Barbour, and R. V. Helm, Anal. Chem., 43, 1491 (1971). (10) R. V. Barbour and J. C. Petersen, Anal. Chem., 46, 273 (1974). (11) W. K. Seifert and W. G. Howells, Anal. Chem., 41, 554 (1969). (12) R. M. Teeter and W. K. Seifert, Prepr., Dlv. Pet. Chem., Am., Chem. Soc., 16, A-7 (1971). (13) J. F. McKay, T. E. Cogswell, and D. R. Latham, Prepr., Div. Pet. Chem., Am. Chem. Soc., 18, 25 (1974).
(14) D. M. Jewell, J. H. Weber, J. W. Burger, H. Plancher, and D. R. Latham, Anal. Chem., 44, 1391 (1972). (15) R. D. McCarthy and A. H. Duthie, J. Lipid. Res., 3, 117 (1962). (16) W. Van Hoeven, M. Calvin, and J. R. Maxwell, Geochim. Cosmochim. Acta, 33, 877 (1969). (17) “IP Standards for Petroleum and Its Products”, Part. I, Sec. 1, 33th ed., Barking, Essex, 1974, Method IP 143/57, pp 545-548. (18) A. T. Vogel, “Practical Organic Chemistry , Longman, Green and Co. Inc, London, New York, Toronto, 1954, pp 967-972.
(19) A. G. Douglas and T. G. Powell, J. Chromatogr., 43, 241 (1969). (20) P. Arpiño, in “Sciences Geologlques, No. 39, edited by the Geological Institute of Strasbourg, France, 1973. (21) B. Klmland, A. J. Aasen, S. O. Almquist, P. Arpiño, and C. R. Enzell, Phytochemistry, 12, 835 (1973).
Received for review January 5,1977. Accepted April 18,1977.
Separation Method for Coal-Derived Solids and Heavy Liquids Joseph E. Schiller* and Dennis R. Mathiason1 Grand Forks Energy Research Center, Grand Forks, North Dakota 58202
A rapid, simple chromatographic procedure has been developed to fractionate coal-derived solids and liquids for subsequent analysis by mass spectrometry and other spectral methods. The sample is pre-adsorbed on neutral alumina (activity I), and eluted with hexane, toluene, chloroform (2 fractions) and 9:1 tetrahydrofuran-ethanol. The principal compound types eluted in each fraction, respectively, are: saturated hydrocarbons, aromatic hydrocarbons and benzofurans, ethers, nitrogen compounds, and hydroxyl compounds. Mass spectral analysis is enhanced because the toluene eluate contains only aromatic hydrocarbons and ethers, while the second chloroform fraction includes almost all of the nitrogen compounds in the sample.
At the Grand Forks Energy Research Center (GFERC), the liquefaction of low-rank coal by the CO-Steam Process (1) is being studied. Research is under way to determine reaction kinetics, to study reactor design, and to determine product composition for this process. Essential to this work was the development of a simple separation scheme that would allow detailed analysis of samples by mass spectrometry (MS). Changes in product that are measured by MS have been related to reaction parameters (2). Since the batch autoclave used to determine kinetics is capable of hot charging and timed sampling during a run, many samples are generated. The ideal separation method for our purposes would be rapid and routine (i.e., performed by relatively untrained personnel), would not require purification or preparation of adsorbents, eluents, and other materials prior to use, would analyze the whole sample and generate only a few fractions. Previously used methods (3-5) for separating petroleum residues and coal-derived products have yielded satisfactory results in similar applications, but these methods are time consuming and laborious. Most such procedures allow separation of only the pentane-soluble portion of the sample (6), and this is a severe limitation for heavy coal-derived liquids. Too many fractions are produced for subsequent characterization of a large number of samples. In a recently reported separation scheme for solvent refined coal (7), nine fractions are isolated on the basis of chemical functionality. However, oxygen and nitrogen compounds are not resolved. The method developed in our laboratory involves preadsorption (8) of the sample on neutral alumina, elution of fractions with hexane, toluene, chloroform (2 fractions), and 9:1 tetrahydrofuran-ethanol. Vaporization of the solvent leaves the isolated fraction for further analysis.
EXPERIMENTAL Apparatus and Materials. Reagent grade adsorbents
(alumina, activity I, Fisher No. A950; florisil, MCB No. FX 254; and silica, Fisher No. S-150) were used as obtained. Initial work indicated that no significant improvement in results occurred when these adsorbents were activated at the following conditions: florisil and silica, 200 °C for 8 h; alumina, 350 °C for 8 h. Solvents were used as obtained from the supplier (Burdick & Jackson Co., Muskegon, Mich.). Tetrahydrofuran was purchased without inhibitor. An ISCO fraction collector and a Schoeffel Model 770 UV detector were used for studies to determine the efficiency of group separation. Gas chromatography (GC) data were obtained on a Varían Aerograph Model 2740 gas chromatograph equipped with a FID. The majority of the GC work was done with a Vs-inch, 10-foot stainless steel column packed with 5% SE-30 on Chromosorb W. A 10-foot, V s-inch stainless steel column packed with 5% Dexsil on Varaport 30 was also used but did not produce the overall separation found in the SE-30 column. Gas chromatograph-mass spectrometry (GC-MS) was accomplished using a DuPont 21-491B mass spectrometer interfaced with a Varían Aerograph Model 2740 gas chromatograph. High resolution mass spectrometry (HRMS) and low voltage (10 V)-high resolution mass spectrometry (LV-HRMS) were done using an AEI MS-30 equipped with a DS-50 data system. Separation Procedure. An accurately weighed (±0.1 mg) sample of 0.1 to 0.15 g was dissolved, with gentle warming if necessary, in 1 mL of chloroform or tetrahydrofuran. An additional 1 mL of solvent was used to wash down the sides of the container and then 2-3 g of neutral alumina was added while the mixture was stirred with a glass stirring rod. The alumina added was sufficient to adsorb the entire solution so as to produce a material that physically resembled wet sand. The alumina with sample was transferred to a test tube. The test tube was evacuated with a mechanical vacuum pump, and the temperature was maintained at a level (20-30 °C). This caused the alumina to fluidize smoothly without entrainment as the solvent was removed. After fluidization, the last traces of solvent were removed by heating to about 50 °C for 5 min. The alumina with sample was then added to an 11-mm o.d. X 500-mm chromatography column containing 6 g of neutral alumina, activity I. The sample was eluted as follows to give the fractions indicated. Fraction 1, 20 mL hexane added to the column, 15 mL collected. Fraction 2, 50 mL toluene. Fraction 3, Chloroform (to the point just before a large dark band began to come off the column (20-30 mL). Fraction 4, Chloroform (a volume sufficient to elute all of the dark material, 30-40 mL). Fraction 5, 50 mL 9:1 tetrahydrofuranabsolute ethanol. Solvents were removed from the solutions by warming in a gentle stream of air, and the collected fractions were weighed.
RESULTS AND DISCUSSION A large number of solvent combinations and adsorbents were
1
Present address, Moorhead State College, Moorhead, Minn.
surveyed before selecting the combination described here.
Fluorisil and silica gel did not give well-resolved fractions, and ANALYTICAL CHEMISTRY, VOL. 49, NO. 8, JULY 1977
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