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Study of lignite catalytic depolymerization products. Chemical reduction of asphaltenes and toluene extract
Fuel Processing Technology, 17 (1988) 277-284
277
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Study of Lignite Catalytic Depolymerization Products Chemical Reduction of Asphaltenes and Toluene Extract B. RUBIO and A.M. MASTRAL
Instituto de Carboquimica ( CSIC ), Plaza Pardiso 1, 50004 Zaragoza (Spain) (Received February 5th, 1987; accepted June 3rd, 1987)
ABSTRACT
Chemical reduction of bitumen and asphaltenes derived from a Spanish lignite depolymerized with BF:~ in phenol has been achieved by lithium in ethylamine. The extent of the reduction has been evaluated by means of elemental analysis and 'H NMR spectroscopy, and some structural features have been established for the reduced products. After eight hours of reaction, the aromatic hydrogen content showed a large decrease, which was greater for asphaltenes than for bitumen. Structural parameters indicated for the treated samples that a half of the aromatic nuclei have been hydrogenated. 'H NMR and IR spectroscopic data show a similar behaviour of asphaltenes and bitumen in the reduction process.
INTRODUCTION
Several types of reducing systems that imply the use of alkali metals in amines have been applied to the reduction of coals and related products. Natrium in NH3 was applied by Lazarov and Angelova [ 1 ] to the reduction of subbituminous coals. Lithium in ethylenediamine and ethylamine was used by Reggel et al. [ 2 ], and Duffy and Given [ 3 ] for reducing vitrinites, and by Brooks and Silberman [4 ] for reducing cokes and tars. In these cases, a greater extent of reduction was found for coal and coal derived products with a carbon content near 90%. A noticeable increase of chloroform or pyridine solubility was also found [ 1,2,5 ]. In the reaction conditions, the breaking of C-C, C-S and C-O bonds is produced, and solvent and water molecules are added, besides of hydrogen. SH groups are removed and some OH groups tautomerize to ketones. Breaking of some C-C bonds can reduce the molecular weight increasing the solubility 0378-3820/88/$03.50
© 1988 Elsevier Science Publishers B.V.
278 TABLE 1 Elemental analysis of lignite derived bitumen (BD 1 ) and asphaltenes (AD 1 )
BD1 AD1
%C
%H
%N
78.81 76.90
6.76 5.65
0.17 0.51
of the product. In a first step of the reduction, the equilibrium between metal and solvent is reached, the amount of metal depending on the coal rank. Generally, low rank coal consumes larger amounts of reducing agent, since the acidic and easily extractable protons of these coals react with the metal, decreasing the concentration of its active form. The lithium-ethylamine system has been applied in the present work to bitumen and asphaltenes derived by depolymerization of a Spanish low rank coal. The bitumen contained a 36% of oils and 64% of asphaltenes, the latter showing 77% of polar compounds [6,7]. Asphaltenes as welt as bitumen contained a variety of functional groups, mainly aromatic ether and hydroxyl groups. The carbon contents of both samples (77 and 79%, respectively) was situated below the rank found by Reggel et al. [8] as the most adequate in adding hydrogen. However, the great solubility of asphaltenes and bitumen in ethylamine allows to expect and extensive reduction. EXPERIMENTAL
The elemental and ultimate analysis of the Utrillas lignite as well as the depolymerization procedure are described elsewhere [ 9 ]. Boron trifluoride and phenol were used as catalyst and solvent, respectively, in the depolymerization reaction. The bitumen and asphaltenes derived from the depolymerized lignite were reduced as described below (their elemental analyses are shown in Table 1 ).
Reduction with lithium in etylamine About 50 cm 3 of ethylamine was condensed in a three necked flask provided with a gas inlet, a glass stirrer and a reflux condenser through which an ethanol-water mixture at - 25 ° C was circulated. The bitumen or asphaltenes (2.00 g) and the lithium (5.00 g) cut in small pieces under nitrogen were cautiously added. A deep blue or red colour developed in 5-10 min. The mixture was allowed to react for eight hours at the reflux temperature of ethylamine under a small flow of nitrogen. The hydrolysis was carried out in two ways for each sample: (a) adding cautiously and slowly 50 cm 3 of deionized water in the presence of the remain-
279 ing unreacted lithium, and (b) by addition of 50 cm 3 of deionized water after removing the unreacted lithium. In both cases, the solution was maintained under nitrogen and was then acidified with HC1. The bitumen was recovered from the aqueous solution by extraction with three 50 cm 3 portions of chloroform. The solvent was then removed at reduced pressure. The asphaltenes precipitated after the acidification and were filtered, washed with deionized water and dried under vacuum. Elemental analysis were performed in a LECO CHN 600. Molecular weights were determined isopiestically in tetrahydrofuran solutions in a Hitachi-Perkin Elmer 115 apparatus. FTIR spectra were recorded in a Nicolet MX 10 in KBr pellets for asphaltenes and as a thin film on KBr windows for bitumen. RESULTS AND DISCUSSION The elemental analysis (dry basis) of reduced bitumen (BR1, BR2) and asphaltenes (ASFR1, ASFR2) is shown in Table 2. The observed decrease in the carbon content, more evident for bitumen was also observed by other authors [2] and attributed to a dilution effect produced by the material added during the reduction (ethylamine, water and lithium compounds). In Table 3 the d.a.f, elemental analysis, atomic H/C ratio and average molecular weight of the original and reduced samples are given. The nitrogen and hydrogen increases are higher for the bitumen as well as the decrease of the oxygen content. The atomic H/C ratio shows a remarkable increase in all cases. In order to correct the hydrogen content for the presence of the added ethylamine, it has been supposed that all nitrogen present in the starting material remains and the increase is due to the nitrogen of ethylamine. The amount of incorporated ethylamine and the number of atoms added per 100 carbon atoms are given in Table 4. Though it is possible that some of the oxygen has been lost by reaction with the amine giving Schiff's bases, other mechanisms may be implicated, since the number of lost oxygen atoms is an all cases higher than that of added nitrogen. It is not unlikely that breaking of C-O bonds has taken place.The highest acidity determined by potentiometric titration in dimethyl-formamide, 7.85 meq. g-1 for ASFRI and 2.3 meq. g-1 for BR2) [10] found for the samples which added highest amount of hydrogen, would confirm that point if it is considered the breaking of C-O bonds as source of hydroxyl groups. The amount of added ethylamine was higher in the case of the bitumen and the same occurred for the number of hydrogen atoms added (57 for BR1) even corrected for the presence of the incorporated amine. There is no clear relationship between the extent of the reduction and the type of hydrolysis carried out. ASFR1 and BR1 were hydrolized in presence of
280 TABLE 2 Elemental analysis (dry basis) of reduced bitumen (BR1, BR2) and asphaltenes (ASFR1, ASFR2)
ASFR1 ASFR2 BR1 BR2
%C
%H
%N
% ash
77.50 71.90 53.20 52.85
7.22 7.00 7.28 7,18
1.11 1.16 2.45 3.09
0.35 5.73 36.93 36.88
TABLE 3 Elemental analysis (d.a.f.), atomic H / C ratio a n d average molecular weight of original and reduced samples
C (%) H (%) N (% ) Diff. ( % ) Ha H/C H/C a MW
ASFD1
ASFR1
ASFR2
BD1
BR1
BR2
77.05 5.45 0.59 16.91 0.84 314
77.95 7.26 1.11 13.65 7.07 1.11 1.10 469
77.05 7.50 1.24 14.21 7.44 1.16 1.15 692
78.60 6.60 0.51 14.29 1.00 205
84.43 11.55 3.88 0.54 10.33 1.64 1.57 310
84.00 11.30 4.70 9.67 1.61 1.47 347
aCorrected for the added ethylamine. TABLE 4 E x t e n t of the reduction in asphaltenes a n d b i t u m e n Atoms added/100 C
ASFR1 ASFR2 BR1 BR2
g added ethylamine/100 g
C
H
N
Ha
0.4 0.4 2.8 5.6
27 37 64 61
0.2 0.2 1.4 2.8
26 31 57 47
1.61 0.49 10.42 14.00
~Corrected for the added ethylamine.
the remaining unreacted lithium and ASFR2, BR2 after removing the unreacted lithium. The differences are related with their structural features. According to Benkesser et al. [ 11 ], in the case of phenol, the slow hydrolysis in presence of an excess of lithium gives a mixture of cyclohexanone and cyclohexanol, while in the absence of an excess of lithium, ketones are the main product. The F T I R spectra of the reduced bitumen and asphaltenes show a marked increase of the aliphatic C - H absorption at 2950 c m - 1 (Fig. 1 ). In the spectra
281
4000
3200
2000
1400
800
cm-1
Fig. 1. FTIR spectra of lithium-ethylamine treated bitumen (a,b) and asphaltenes (c,d).
of BR2 the aliphatic absorptions appearing at 2950 c m - 1 and 1350 c m - 1 [ 12 ] have also increased. A strong band appears at 1100 cm -1, assignable to secondary aliphatic alcohol [ 13 ] probably originated in the reduction of phenols. The OH absorption appearing in the 2300-3500 c m - 1 region shows, in turn, a decrease. The ~H N M R spectroscopy (Figs. 2 and 3) shows a large decrease of the aromatic hydrogen for asphaltenes and bitmen after the lithium treatment. The simultaneous increase of alphatic hydrogen is due mainly to the hydrogen situated in fl position to the aromatic ring (Table 5 ). Also noteworthy is the decrease, in the case of asphaltenes, of hydrogen in OH groups after the reduction. Aliphatic hydrogen in a position markedly increases after the reduction of asphaltenes and bitumen. The increase of Hp, however, is much more important for asphaltenes (from 8.7 to 4.4% ) than for bitumen (from 31.7 to 49% ). Hy does not show significant variations.
282
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1
9
8
7
6
5
4
3
2
1
0
10
9
8
7
6
5
4
3
2
1
o
ppm
ppm
Fig. 2. ~H NMR spectra of original (a) and lithium-ethylamine treated asphaltenes (b,c). Fig. 3.1H N MR spectra of original (a) and lithium-ethylamine treated bitumen (b,c).
Some structural parameters calculated for the original and reduced samples are show in Table 6. The method used to calculate them was the structural analysis scheme proposed by Bartle et al. [ 14 ]. The calculated values of these parameters, show a trend of saturation of aromatic rings expressed as the decrease of RA from 4 to 2 for asphaltenes and from 2.4 to 1 for bitumen. There is also a large increase of the number of alkyl and naphthenic carbons, which is more important for asphaltenes. The degree of alkyl substitution increases in both cases from a 10% of available sites on the aromatic units occupied before the reduction to a 30% after the process.
283 TABLE 5 Hydrogen distribution in original (ASFD1, BD1) and reduced asphaltenes (ASFR1, ASFR2) and bitumen (BR1, BR2) Type of hydrogen
ASFD1
ASFR1
ASFR2
BD1
BR1
BR2
H,r HoH H~. H,~ Hz H~
46.4 16.4 7.3 15.2 8.5 6.0
22.1 5.4 6.3 26.3 34.7 5.2
18.5 4.1 2.6 22.5 44.1 8.0
36.4 -13.2 9.3 31.7 9.3
18.2 -10.9 23.6 41.0 6.1
23.7 -22.3 48.9 4.9
H,r=aromatic hydrogen; HOH =hydrogen in phenolic OH; H~.=hydrogen in ring-joining methylene; H,~=hydrogen in CH:~, CH~and CH groups a to an aromatic ring; H/j=hydrogen in CH:~, CH2 and CH groups fl to an aromatic ring and CH2, CH y or further from an aromatic ring; H~= hydrogen in CH:~y or further from an aromatic ring. TABLE6 Some structural parameters calculated according to Bartle et al. [14] for original and reduced asphaltenes and bitumen Symbol
C' H' C'~, AG C'l~ RAM R~, % C~r
Asphaltenes
Bitumen
ASFD1
ASFR1
ASFR2
BD1
BR1
BR2
29.2 26.0 3.34 1.8 24.8 1.0 3.8 83.9 0.1
30.3 33.8 13.5 5.4 15.2 1.6 1.9 60.2 0.3
41.4 49.3 18.8 5.9 21.9 0.6 3.1 53.0 0.3
13.4 13.7 3.2 0.6 9.3 0.9 2.4 69.1 0.1
13.7 22.6 6.8 2.3 5.7 1.2 1.0 41.6 0.4
15.9 24.5 7.5 2.2 8.4 1.1 52.7 0.3
Definition of symbols: C' =number of carbon atoms in the average molecule; H' =number of hydrogen atoms in the average molecule; C'~=alkyl and naphthenic carbon in the average molecule; AG=number of alkyl and naphthenic groups; C'R=aromatic and ring-joining carbon; RAM = ring-joining methylene; Ra = number of aromatic rings; % C~r= aromatic carbon; 5 = degree of alkyl substitution. CONCLUSIONS Toluene soluble products (asphaltenes and bitumen) obtained from a Spanish low r a n k coal b y a m i l d p r o c e s s as c a t a l y t i c d e p o l y m e r i z a t i o n c a n b e e x t e n sively reduced increasing their hydrogen content by lithium in ethylamine. A s p h a l t e n e s show a m o r e e x t e n s i v e increase of t h e i r a l i p h a t i c h y d r o g e n cont e n t f r o m 36.5 t o 87.4%. I n t h e c a s e o f b i t u m e n t h e i n c r e a s e o f H J H a r r a t i o is
284 lower. If the t o t a l n u m b e r of h y d r o g e n a t o m s a d d e d / 1 0 0 C is considered, asp h a l t e n e s add less h y d r o g e n t h a n b i t u m e n . S i m u l t a n e o u s l y with an increase in t h e aliphatic h y d r o g e n c o n t e n t , the degree of alkyl s u b s t i t u t i o n of the a r o m a t i c u n i t s increases for b o t h samples from 10 to 30% of the available sites occupied.
REFERENCES 1 Lazarov, L. and Angelova, G., 1968. Treatment of coals with sodium in liquid ammonia solution. Fuel, 47: 333. 2 Reggel, L., Raymond, R., Frieman, S., Friedel, R.A. and Wender, W., 1958. Reduction of coal by lithium-ethylenediamine. Fuel, 37: 126. 3 Duffy, L.S. and Given, P.H., 1985. Reduction of vitrinites with lithium in ethylamine and the chemistry of the products. Fuel, 64: 212. 4 Brooks, J.D. and Silberman, H., 1962. The chemical reduction of some cokes and chars. Fuel, 41: 67. 5 Given, P.H., Peover, M.E. and Wiss, W.F., 1960. Chemical properties of coal macerals I. Introductory survey, and some properties of exinites. Fuel, 39: 323. 6 Mastral, A.M. and Cebolla, V.L., 1985. Characterization of lignite low-severity depolymerization products. Fuel Processing Technol. 11: 87. 7 Mastral, A.M., Membrado, L., Rubio, G., Cebolla, U.L. and Nicolas, C., 1985. Catalyzed chemistry depolymerization of a lignite: Nature of the degradation products. In: Proc. International Conference on Coal Science, Sydney, Australia. Pergamon, Chap. 11, p. 742. 8 Reggel,L., Raymond, R., Steiner, W.A., Friedel, R.A. and Wender, J., 1961. Reduction of coal by lithium-ethylenediamine. Studies on a series of vitrains. Fuel, 40: 339. 9 Mastral, A.M. and Rubio, B., 1984. Recovery, fractionation and study of oils from lignite depolymerization. Fuel, 63: 355. 10 Rubio, B., 1986. Oils from lignite. Recovery and study. Ph. D. Thesis, University of Zaragoza. 11 Benkesser, R,A., Arnold, C1, Lambert, R.F. and Thomas, O.H., 1955. Reduction of organic compounds by lithium in low molecular weight amines. III. Reduction of aromatic compounds containing functional groups. J.Amer. Chem. Soc., 80: 6042. 12 Bartle, K.D., Jones, D.W. and Pakdel, H., 1978. Separation and spectroscopy of paraffinic hydrocarbons from coal. In: C. Karr (Ed.), Analytical Methods for Coal and Coal Products, Vol. II. Academic Press, New York, Chap. 25, p. 209. 13 Pretsch, E., Clerc, T., Seibl, J. and Simon, W., 1980. IR Spectroscopy. In: Alhambra (Ed.) Structural Elucidation of Organic Compounds by Spectroscopic Methods, p.178. 14 Bartle, K.D., Ladner, W.R. Martin, T.G., Snape, C.E. and Williams, D.K., 1979. Structural analysis of supercritical-gas extracts of coals. Fuel, 58: 413.
277
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Study of Lignite Catalytic Depolymerization Products Chemical Reduction of Asphaltenes and Toluene Extract B. RUBIO and A.M. MASTRAL
Instituto de Carboquimica ( CSIC ), Plaza Pardiso 1, 50004 Zaragoza (Spain) (Received February 5th, 1987; accepted June 3rd, 1987)
ABSTRACT
Chemical reduction of bitumen and asphaltenes derived from a Spanish lignite depolymerized with BF:~ in phenol has been achieved by lithium in ethylamine. The extent of the reduction has been evaluated by means of elemental analysis and 'H NMR spectroscopy, and some structural features have been established for the reduced products. After eight hours of reaction, the aromatic hydrogen content showed a large decrease, which was greater for asphaltenes than for bitumen. Structural parameters indicated for the treated samples that a half of the aromatic nuclei have been hydrogenated. 'H NMR and IR spectroscopic data show a similar behaviour of asphaltenes and bitumen in the reduction process.
INTRODUCTION
Several types of reducing systems that imply the use of alkali metals in amines have been applied to the reduction of coals and related products. Natrium in NH3 was applied by Lazarov and Angelova [ 1 ] to the reduction of subbituminous coals. Lithium in ethylenediamine and ethylamine was used by Reggel et al. [ 2 ], and Duffy and Given [ 3 ] for reducing vitrinites, and by Brooks and Silberman [4 ] for reducing cokes and tars. In these cases, a greater extent of reduction was found for coal and coal derived products with a carbon content near 90%. A noticeable increase of chloroform or pyridine solubility was also found [ 1,2,5 ]. In the reaction conditions, the breaking of C-C, C-S and C-O bonds is produced, and solvent and water molecules are added, besides of hydrogen. SH groups are removed and some OH groups tautomerize to ketones. Breaking of some C-C bonds can reduce the molecular weight increasing the solubility 0378-3820/88/$03.50
© 1988 Elsevier Science Publishers B.V.
278 TABLE 1 Elemental analysis of lignite derived bitumen (BD 1 ) and asphaltenes (AD 1 )
BD1 AD1
%C
%H
%N
78.81 76.90
6.76 5.65
0.17 0.51
of the product. In a first step of the reduction, the equilibrium between metal and solvent is reached, the amount of metal depending on the coal rank. Generally, low rank coal consumes larger amounts of reducing agent, since the acidic and easily extractable protons of these coals react with the metal, decreasing the concentration of its active form. The lithium-ethylamine system has been applied in the present work to bitumen and asphaltenes derived by depolymerization of a Spanish low rank coal. The bitumen contained a 36% of oils and 64% of asphaltenes, the latter showing 77% of polar compounds [6,7]. Asphaltenes as welt as bitumen contained a variety of functional groups, mainly aromatic ether and hydroxyl groups. The carbon contents of both samples (77 and 79%, respectively) was situated below the rank found by Reggel et al. [8] as the most adequate in adding hydrogen. However, the great solubility of asphaltenes and bitumen in ethylamine allows to expect and extensive reduction. EXPERIMENTAL
The elemental and ultimate analysis of the Utrillas lignite as well as the depolymerization procedure are described elsewhere [ 9 ]. Boron trifluoride and phenol were used as catalyst and solvent, respectively, in the depolymerization reaction. The bitumen and asphaltenes derived from the depolymerized lignite were reduced as described below (their elemental analyses are shown in Table 1 ).
Reduction with lithium in etylamine About 50 cm 3 of ethylamine was condensed in a three necked flask provided with a gas inlet, a glass stirrer and a reflux condenser through which an ethanol-water mixture at - 25 ° C was circulated. The bitumen or asphaltenes (2.00 g) and the lithium (5.00 g) cut in small pieces under nitrogen were cautiously added. A deep blue or red colour developed in 5-10 min. The mixture was allowed to react for eight hours at the reflux temperature of ethylamine under a small flow of nitrogen. The hydrolysis was carried out in two ways for each sample: (a) adding cautiously and slowly 50 cm 3 of deionized water in the presence of the remain-
279 ing unreacted lithium, and (b) by addition of 50 cm 3 of deionized water after removing the unreacted lithium. In both cases, the solution was maintained under nitrogen and was then acidified with HC1. The bitumen was recovered from the aqueous solution by extraction with three 50 cm 3 portions of chloroform. The solvent was then removed at reduced pressure. The asphaltenes precipitated after the acidification and were filtered, washed with deionized water and dried under vacuum. Elemental analysis were performed in a LECO CHN 600. Molecular weights were determined isopiestically in tetrahydrofuran solutions in a Hitachi-Perkin Elmer 115 apparatus. FTIR spectra were recorded in a Nicolet MX 10 in KBr pellets for asphaltenes and as a thin film on KBr windows for bitumen. RESULTS AND DISCUSSION The elemental analysis (dry basis) of reduced bitumen (BR1, BR2) and asphaltenes (ASFR1, ASFR2) is shown in Table 2. The observed decrease in the carbon content, more evident for bitumen was also observed by other authors [2] and attributed to a dilution effect produced by the material added during the reduction (ethylamine, water and lithium compounds). In Table 3 the d.a.f, elemental analysis, atomic H/C ratio and average molecular weight of the original and reduced samples are given. The nitrogen and hydrogen increases are higher for the bitumen as well as the decrease of the oxygen content. The atomic H/C ratio shows a remarkable increase in all cases. In order to correct the hydrogen content for the presence of the added ethylamine, it has been supposed that all nitrogen present in the starting material remains and the increase is due to the nitrogen of ethylamine. The amount of incorporated ethylamine and the number of atoms added per 100 carbon atoms are given in Table 4. Though it is possible that some of the oxygen has been lost by reaction with the amine giving Schiff's bases, other mechanisms may be implicated, since the number of lost oxygen atoms is an all cases higher than that of added nitrogen. It is not unlikely that breaking of C-O bonds has taken place.The highest acidity determined by potentiometric titration in dimethyl-formamide, 7.85 meq. g-1 for ASFRI and 2.3 meq. g-1 for BR2) [10] found for the samples which added highest amount of hydrogen, would confirm that point if it is considered the breaking of C-O bonds as source of hydroxyl groups. The amount of added ethylamine was higher in the case of the bitumen and the same occurred for the number of hydrogen atoms added (57 for BR1) even corrected for the presence of the incorporated amine. There is no clear relationship between the extent of the reduction and the type of hydrolysis carried out. ASFR1 and BR1 were hydrolized in presence of
280 TABLE 2 Elemental analysis (dry basis) of reduced bitumen (BR1, BR2) and asphaltenes (ASFR1, ASFR2)
ASFR1 ASFR2 BR1 BR2
%C
%H
%N
% ash
77.50 71.90 53.20 52.85
7.22 7.00 7.28 7,18
1.11 1.16 2.45 3.09
0.35 5.73 36.93 36.88
TABLE 3 Elemental analysis (d.a.f.), atomic H / C ratio a n d average molecular weight of original and reduced samples
C (%) H (%) N (% ) Diff. ( % ) Ha H/C H/C a MW
ASFD1
ASFR1
ASFR2
BD1
BR1
BR2
77.05 5.45 0.59 16.91 0.84 314
77.95 7.26 1.11 13.65 7.07 1.11 1.10 469
77.05 7.50 1.24 14.21 7.44 1.16 1.15 692
78.60 6.60 0.51 14.29 1.00 205
84.43 11.55 3.88 0.54 10.33 1.64 1.57 310
84.00 11.30 4.70 9.67 1.61 1.47 347
aCorrected for the added ethylamine. TABLE 4 E x t e n t of the reduction in asphaltenes a n d b i t u m e n Atoms added/100 C
ASFR1 ASFR2 BR1 BR2
g added ethylamine/100 g
C
H
N
Ha
0.4 0.4 2.8 5.6
27 37 64 61
0.2 0.2 1.4 2.8
26 31 57 47
1.61 0.49 10.42 14.00
~Corrected for the added ethylamine.
the remaining unreacted lithium and ASFR2, BR2 after removing the unreacted lithium. The differences are related with their structural features. According to Benkesser et al. [ 11 ], in the case of phenol, the slow hydrolysis in presence of an excess of lithium gives a mixture of cyclohexanone and cyclohexanol, while in the absence of an excess of lithium, ketones are the main product. The F T I R spectra of the reduced bitumen and asphaltenes show a marked increase of the aliphatic C - H absorption at 2950 c m - 1 (Fig. 1 ). In the spectra
281
4000
3200
2000
1400
800
cm-1
Fig. 1. FTIR spectra of lithium-ethylamine treated bitumen (a,b) and asphaltenes (c,d).
of BR2 the aliphatic absorptions appearing at 2950 c m - 1 and 1350 c m - 1 [ 12 ] have also increased. A strong band appears at 1100 cm -1, assignable to secondary aliphatic alcohol [ 13 ] probably originated in the reduction of phenols. The OH absorption appearing in the 2300-3500 c m - 1 region shows, in turn, a decrease. The ~H N M R spectroscopy (Figs. 2 and 3) shows a large decrease of the aromatic hydrogen for asphaltenes and bitmen after the lithium treatment. The simultaneous increase of alphatic hydrogen is due mainly to the hydrogen situated in fl position to the aromatic ring (Table 5 ). Also noteworthy is the decrease, in the case of asphaltenes, of hydrogen in OH groups after the reduction. Aliphatic hydrogen in a position markedly increases after the reduction of asphaltenes and bitumen. The increase of Hp, however, is much more important for asphaltenes (from 8.7 to 4.4% ) than for bitumen (from 31.7 to 49% ). Hy does not show significant variations.
282
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1
1
9
8
7
6
5
4
3
2
1
0
10
9
8
7
6
5
4
3
2
1
o
ppm
ppm
Fig. 2. ~H NMR spectra of original (a) and lithium-ethylamine treated asphaltenes (b,c). Fig. 3.1H N MR spectra of original (a) and lithium-ethylamine treated bitumen (b,c).
Some structural parameters calculated for the original and reduced samples are show in Table 6. The method used to calculate them was the structural analysis scheme proposed by Bartle et al. [ 14 ]. The calculated values of these parameters, show a trend of saturation of aromatic rings expressed as the decrease of RA from 4 to 2 for asphaltenes and from 2.4 to 1 for bitumen. There is also a large increase of the number of alkyl and naphthenic carbons, which is more important for asphaltenes. The degree of alkyl substitution increases in both cases from a 10% of available sites on the aromatic units occupied before the reduction to a 30% after the process.
283 TABLE 5 Hydrogen distribution in original (ASFD1, BD1) and reduced asphaltenes (ASFR1, ASFR2) and bitumen (BR1, BR2) Type of hydrogen
ASFD1
ASFR1
ASFR2
BD1
BR1
BR2
H,r HoH H~. H,~ Hz H~
46.4 16.4 7.3 15.2 8.5 6.0
22.1 5.4 6.3 26.3 34.7 5.2
18.5 4.1 2.6 22.5 44.1 8.0
36.4 -13.2 9.3 31.7 9.3
18.2 -10.9 23.6 41.0 6.1
23.7 -22.3 48.9 4.9
H,r=aromatic hydrogen; HOH =hydrogen in phenolic OH; H~.=hydrogen in ring-joining methylene; H,~=hydrogen in CH:~, CH~and CH groups a to an aromatic ring; H/j=hydrogen in CH:~, CH2 and CH groups fl to an aromatic ring and CH2, CH y or further from an aromatic ring; H~= hydrogen in CH:~y or further from an aromatic ring. TABLE6 Some structural parameters calculated according to Bartle et al. [14] for original and reduced asphaltenes and bitumen Symbol
C' H' C'~, AG C'l~ RAM R~, % C~r
Asphaltenes
Bitumen
ASFD1
ASFR1
ASFR2
BD1
BR1
BR2
29.2 26.0 3.34 1.8 24.8 1.0 3.8 83.9 0.1
30.3 33.8 13.5 5.4 15.2 1.6 1.9 60.2 0.3
41.4 49.3 18.8 5.9 21.9 0.6 3.1 53.0 0.3
13.4 13.7 3.2 0.6 9.3 0.9 2.4 69.1 0.1
13.7 22.6 6.8 2.3 5.7 1.2 1.0 41.6 0.4
15.9 24.5 7.5 2.2 8.4 1.1 52.7 0.3
Definition of symbols: C' =number of carbon atoms in the average molecule; H' =number of hydrogen atoms in the average molecule; C'~=alkyl and naphthenic carbon in the average molecule; AG=number of alkyl and naphthenic groups; C'R=aromatic and ring-joining carbon; RAM = ring-joining methylene; Ra = number of aromatic rings; % C~r= aromatic carbon; 5 = degree of alkyl substitution. CONCLUSIONS Toluene soluble products (asphaltenes and bitumen) obtained from a Spanish low r a n k coal b y a m i l d p r o c e s s as c a t a l y t i c d e p o l y m e r i z a t i o n c a n b e e x t e n sively reduced increasing their hydrogen content by lithium in ethylamine. A s p h a l t e n e s show a m o r e e x t e n s i v e increase of t h e i r a l i p h a t i c h y d r o g e n cont e n t f r o m 36.5 t o 87.4%. I n t h e c a s e o f b i t u m e n t h e i n c r e a s e o f H J H a r r a t i o is
284 lower. If the t o t a l n u m b e r of h y d r o g e n a t o m s a d d e d / 1 0 0 C is considered, asp h a l t e n e s add less h y d r o g e n t h a n b i t u m e n . S i m u l t a n e o u s l y with an increase in t h e aliphatic h y d r o g e n c o n t e n t , the degree of alkyl s u b s t i t u t i o n of the a r o m a t i c u n i t s increases for b o t h samples from 10 to 30% of the available sites occupied.
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