Ind. Eng. Chem. Res. 1997, 36, 4763-4767
4763
Hydrocoprocessing of Scrap Automotive Tires and Coal. Analysis of Oils from Autoclave Coprocessing Larry L. Anderson,† Marisol Calle´ n,‡ Weibing Ding,† Jing Liang,† Ana M. Mastral,*,‡ M. Carmen Mayoral,‡ and Ramo´ n Murillo‡ Department of Chemical and Fuels Engineering, 3290 MEB, University of Utah, Salt Lake City, Utah 84112, and Instituto de Carboquı´mica, CSIC C/Poeta Luciano Gracia, No. 5, 50015 Zaragoza, Spain
Hydrocoprocessing of scrap automotive tires and a low-rank coal was carried out in a magnetically stirred autoclave. Reaction temperature (400 °C) and time (30 min) were kept constant in every experiment, while different pressures (10, 5, and 1 MPa of H2 and 0.1 MPa of N2) were studied. An iron-based catalyst was used to improve yields. Derived oils were analyzed by GC-MS and TLC-FID. In terms of yields, it is shown that there is a synergism between these two materials, although it can only be observed working at low hydrogen pressure. The oils obtained in the coprocessing showed a more aromatic nature than those obtained when both materials are processed alone, and higher boiling points, suggesting that radicals from rubber and coal react between each other instead of reacting with hydrogen radicals. Introduction Modern society produces growing amounts of difficult disposal wastes. This is the case of plastics and old tires. Until now the final step of these residues has been mainly dumping or landfilling, but any of these solutions are not environmentally acceptable due to the destruction of natural places and the risk of fires with the following emissions of dangerous products for health. Recycling them for energy has been studied extensively, finding that there are only a limited number of facilities capable of tapping this resource (Lamarre, 1995). It is important to find a way to recycle these residues to reclaim products feasible of reuse, either as raw materials or as an additional source of chemicals. In the scientific literature there are a significant number of works dealing with this target: in recycling of rubber tire, obtaining of activated carbon (Teng et al., 1995), production of coke (Chaala and Roy, 1996), gas production (Conesa et al., 1996), and liquids for further refining (Williams et al., 1990). Tires are mostly composed of 70% of material that has been shown suitable to be transformed into pentane soluble products (Williams et al., 1993). These materials are mainly natural rubber or synthetic polymeric products derived from petroleum-like polybutadiene or styrene-butadiene rubber depending on the brand or purpose. In addition an extender oil is added as filler. The other 30% is mostly carbon black which cannot be transformed into liquid products (Mastral et al., 1996) but could be reused in the manufacturing of new tires or as a fuel to produce energy due to its high calorific value. There are some coals that are not appropriate to be burnt due to their high sulfur content but which have excellent behavior in hydrogenation to produce liquid fuels through coal liquefaction processes (Mastral, 1993). The main problem of these coal liquefaction processes is the need of high pressure of hydrogen. This way the liquid fuels obtained are not economically competitive compared to liquids derived from petroleum. * Author to whom correspondence should be addressed. Telephone: 34-76-73 39 77. Fax: 34-76-73 33 18. E-mail address:
[email protected]. † University of Utah. ‡ Instituto de Carboquı ´mica. S0888-5885(97)00307-2 CCC: $14.00
The two most used approaches to improve coal conversion are the addition of hydrogen donor solvents to enhance hydrogen spillover and mass transport and the use of supported or unsupported (Mo, Fe, Co, or Ni based) catalysts (Derbyshire and Hager, 1994). Another possibility could be to add wastes which are rich in hydrogen, such us plastics (Taighei et al., 1994; Ding et al., 1996; Orr et al., 1996; Harrison and Ross, 1996) or old tires (Farcasiu and Smith, 1992; Liu et al., 1994, 1995; Mastral et al., 1996). This way conversions could be improved due to the interactions between radicals involved in the coal-rubber hydrocoprocessing (Ibrahim and Sheehra, 1995), hydrogen donation, or the simple reduction of heat and mass transport phenomena, and economical costs could be lower. Besides, a cheap ironbased or any other active metal catalyst could be added to improve on the yields obtained in noncatalyzed processes (Mastral et al., 1995). Previous work on coal-rubber tires coprocessing was carried out using tubing bomb reactors (Mastral et al., 1996, 1997a,b), but in this work a more realistic approach was used: using a stirred autoclave which provided a perfect mixture as in commercial reactors, avoiding temperature profiles, and maximizing mass transport. Moreover, standardized analytical methods used in the petrochemical industry were used to characterize derived products such us simulated distillation or thin layer chromatography with an FID detector. Experimental Section Discarded automotive tires supplied by AMSA, grounded and sifted to 1 mm particle size, were used in this work. The steel thread and the textile netting were previously removed. A low-rank subbituminous coal provided by SAMCA was used in the coprocessing experiments. It was grounded and sifted to a particle size between 0.25 and 0.50 mm and stored under nitrogen atmosphere until use. The ultimate and proximate analyses are shown in Table 1, where “daf” means dry and ash free, “mf” means moisture free, “af” means ash free, and “ar” means as received. Red mud (33.6% in Fe2O3) was also used in some of the runs as an iron catalytic precursor in order to improve on the conversion obtained in noncatalyzed experiments. The solid was mixed manually with the coal or tire as powder in a 5% w/w daf coal load. Previous work © 1997 American Chemical Society
4764 Ind. Eng. Chem. Res., Vol. 36, No. 11, 1997 Table 1. Tire and Coal Proximate and Ultimate Analyses C (daf) H (daf) N (daf) S (mf) moisture (af) ash (mf) volatiles (ar) fixed carbon (ar) calorific value (kcal/kg)
tire
coal
88.64 8.26 0.43 1.43 0.94 3.83 67.30 31.14 9159
80.17 6.69 1.01 5.68 22.05 26.93 48.62 28.45 3714
characterized the extent of active phase (FexS) formation in similar environments by SEM-EDX and Mossbauer spectroscopy techniques (Mastral et al., 1995). The coal-tire ratios used were 100% coal (1/0), 100% tire (0/1), and 50% coal-50% tire (1/1) by weight. The cold hydrogen pressures used were 10, 5, and 1 MPa and atmospheric pressure in the case of nitrogen. The experiments were performed in a magnetically stirred autoclave (Autoclave Engineers) with a volume of 150 mL and a marine propeller as a mixer. The stirring velocity was kept constant at 800 rpm. Heating up time was 60 min, and once the process temperature (400 °C in all runs) was reached, it was kept for 30 min; cooling time was 20 min. After reaction, gases were purged, collected at liquid nitrogen temperature, and weighed once room temperature is reached. Gas yield is defined in eq 1. Other liquefaction products were separated into oil (pentane soluble) and asphaltenes + preasphaltenes (THF soluble but pentane insoluble) by Soxhlet extraction. The amount of THF insoluble was used to calculate the conversion obtained using eq 2. Asphaltenes yields were calculated with eq 3 and oil yield was determined by difference using eq 4. Standard deviation for conversion is 2.1% and for oils, asphaltenes, and gases it is lower than 2%.
% gas )
100mgas
(1)
(mcoal + mtire)daf
% conversion ) (mcoal + mtire)mf - THF insolubles (mcoal + mtire)daf % asphaltenes )
masphaltenes (mcoal + mtire)daf
× 100 (2)
× 100
(3)
% oils ) % conversion - % gas - % asphaltenes (4) The analysis performed for derived liquids were as follows: (1) TLC-FID analysis in a Iatroscan chromatograph model MK-5 in order to identify the hydrocarbon type. The elution times were 20 min in n-hexane (saturated fraction), 10 min in toluene (aromatic fraction), and 2 min in dichloromethane/methanol (polar fraction). Standard deviation for the analysis is 2.6%. (2) Simulated distillation in a model 5890 Series II Hewlett-Packard gas chromatograph using a Petrocol column in order to know the percentages of gasoline (bp < 200 °C), kerosene (200 °C < bp < 275 °C), gas oil (275 °C < bp < 325 °C), heavy gas oil (325 °C < bp < 400 °C), vacuum gas oil (400 °C < bp < 538 °C), and vacuum residue (bp > 538 °C) present in the derived oils. (3) GC-MS analyses in a 5890 Series II HewlettPackard gas chromatograph coupled to a Hewlett-
Figure 1. Results obtained in rubber tire hydrogenation at 400 °C as a function of pressure.
Packard 5971A mass spectrometer in order to determine the presence of individual compounds. The peak’s identification was carried out by comparing the mass spectra to those of a library of pure compounds. Results and Discussion 1. Tire Rubber Processing. Noncatalyzed Experiments. Results obtained in tire processing as a function of pressure are shown in Figure 1. Despite total conversion at around 70% and not 100%, it can be considered as complete conversion, because carbon black content for this tire, measured as fixed carbon in the proximate analysis, is about 31%, which is not reactive under these conditions (Mastral et al., 1996). These results are consistent with the data obtained by Liu et al. (1994) where a maximum constant conversion of 67% for tire liquefaction was achieved despite a hydrogen donor solvent being added and the solid residue composed mainly of carbon black. Total conversion remained almost constant and asphaltenes percentage was minimum, while the oil/gas ratio was a function of reaction pressure. The lower the pressure, the higher the percentage of gas produced. The low amount of asphaltenes and the high total conversion obtained indicate that in this stirred autoclave, retrogressive or repolymerization reactions are minimized or even avoided. Actually, previous works with tubing bomb reactors (Mastral et al., 1997a) presented similar results in terms of conversion, but a lower oil/gas ratio occurred at these conditions. The GC-MS analysis of derived oils showed that despite the fact that there are some linear and branched hydrocarbons, most of the compounds present are alkyl benzenes together with some alkyl naphthalenes and some linear long chain hydrocarbons ranging from C8 to C20. The alkyl benzenes are probably formed during styrene-polybutadiene polymer (SBR) depolymerization which is present in the original tires in a high percentage. The most abundant rubber depolymerization product observed in all the samples analyzed was 1-methyl4-isopropylbenzene. It seems to be obvious that this compound could come from SBR pyrolysis, and its presence does not depend on the process pressure or on the nature of the gas used. The linear long chain hydrocarbons could come from polybutadiene depolymerization, another main component of tires, and the alkyl naphthalenes could be produced in cyclization reactions of the alkyl benzenes from rubber depolymerization. Similar compounds have been found by Williams et al. (1990) and by Zmeirczak et al. (1996) in
Ind. Eng. Chem. Res., Vol. 36, No. 11, 1997 4765 Table 2. Hydrocarbon Type Analyses by TLC-FID of Rubber Tire Derived Oils as a Function of Pressure (400 °C, 30 min) blank experiments P (MPa) 10 5 1 0.1
H2 H2 H2 N2
catalyzed experiments
% oils
% saturated
% aromatic
% polar
% oils
% saturated
% aromatic
% polar
67.7 68.5 49.1 39.0
11.9 12.3 12.4 9.0
74.8 73.8 71.6 74.7
13.3 13.9 16.0 16.3
71.1 70.1 69.2
24.0 17.6 14.9
64.0 69.9 74.3
11.9 12.5 10.8
the pyrolysis of scrap automotive tires and in the liquefaction of SBR, respectively. TLC-FID analyses present in Table 2 show that there are not significant differences between oils obtained at different pressures. The only difference found is a slight increase of polar hydrocarbons from aromatic hydrocarbons, but analyses are too close to conclude that significant differences are observed. It is observed that derived oils from rubber are mainly aromatic perhaps due to the high presence of alkyl benzenes previously identified by GC-MS. Catalyzed Experiments. Conversions obtained in catalyzed rubber tire processing are very similar compared to the ones obtained in the absence of a catalyst. The only difference relative to the noncatalyzed experiments is found in the product distribution: gas production is minimized, having oil production of 70% at all the pressures studied. The GC-MS analyses are very similar compared to the liquids produced in noncatalyzed reactions. The main difference is found in the presence of a very high amount of 1-methyl-4-isopropylcyclohexane which could be the result of deeper hydrogenation. The TLC-FID analyses are shown in Table 2. It is observed that the percentage of polar hydrocarbons are lower than those obtained in noncatalyzed experiments, and there is a remarkable increase of saturated hydrocarbons due to a decrease in aromatic hydrocarbons, as a consequence of a better hydrogenation. The higher the pressure, the higher the percentage of saturated hydrocarbons. The catalyst has been able to transform part of the aromatic hydrocarbons into saturated hydrocarbons, and this transformation is a function of hydrogen pressure. 2. Coal Processing. Figure 2a shows the results obtained during coal processing as a function of pressure. In this case the pressure has a relevant influence on conversions. Whereas at 10 MPa the conversion is almost total (97%), at 0.1 MPa of nitrogen it is only 31%. As in the case of the tire, the lower the pressure, the higher the gas yield obtained. The GC-MS analyses show an abundance of phenolic compounds and alkyl aromatic compounds with one and two rings. Therefore a high yield of polar hydrocarbons was expected to be found in TLC-FID analyses. In Table 3 it can be observed that oils’ nature is mainly polar due to the high presence of phenolic compounds detected by GC-MS. It is shown that the lower the pressure, the higher the relative amount of polar hydrocarbons. This suggests that fragments of coal with heteroatoms are more reactive and easier to be converted into soluble products than fragments without them. The effect of the catalyst depends on the hydrogen pressure (see Figure 2b). At 10 MPa the catalyst seems to have no effect over the high pressure of hydrogen, so no change can be observed either on the conversion or on the product distribution. At 5 MPa there is an increase of 8% in total conversion, but the most dramatic increase is produced at 1 MPa where total conversion
Figure 2. Results obtained in coal hydrogenation at 400 °C as a function of pressure: (a) noncatalyzed experiments and (b) catalyzed experiments.
is increased by 27%. This increase is reflected in an increase of oil and asphaltenes formation. In the case of gas formation, a decrease is observed similar to the results for tire rubber processing. The TLC-FID results show an important decrease in polar hydrocarbons with high hydrogen pressures, which mainly was driven by an increase in aromatic hydrocarbons. This is probably due to deoxygenation effects of iron present in the red mud. 3. Coal-Rubber Coprocessing. The coprocessing of tire rubber and coal was carried out using a feed mixture formed by 50% coal and 50% tire by weight (1/1 ratio). One possible way of evaluating any synergetic effect between tires and coal is to compare the theoretical and the experimental yields obtained. The theoretical yield is calculated as the average of coal and tire conversion values. In the case of 10 MPa there is no difference between theoretical and real values (see Table 4). At lower pressures the results indicate a synergism between rubber and coal: conversion percentages increase by 7% at these conditions. This positive effect is reflected in a growth of asphaltenes and oil yield while the gas percentage remains constant. On the other hand, no synergism was observed for experiments using nitrogen. This may suggest that hydrogen is always needed in coal-tires coprocessing if an improvement of coal conversion is desired. Perhaps radicals coming
4766 Ind. Eng. Chem. Res., Vol. 36, No. 11, 1997 Table 3. Hydrocarbon Type Analyses by TLC-FID of Coal-Derived Oils as a Function of Pressure (400 °C, 30 min) blank experiments P (MPa) 10 5 1 0.1
H2 H2 H2 N2
catalyzed experiments
% oils
% saturated
% aromatic
% polar
% oils
% saturated
% aromatic
% polar
67.7 49.4 22.5 8.9
6.1 7.2 4.8 9.0
36.2 32.7 22.6 21.8
57.6 60.2 72.6 69.1
63.2 57.7 55.9
5.0 9.7 6.3
45.2 37.4 32.0
49.8 52.9 61.7
Table 4. Experimental and Theoretical Results Obtained in Coal-Tire Coprocessing (1/1 Ratio) at 400 °C for 30 min and Hydrocarbon Type Analyses quantitative results P (MPa) 10
H2
5
H2
1
H2
0.1
N2
experimental theoretical experimental theoretical experimental theoretical experimental theoretical
hydrocarbon type distribution in oils
% conversion
% asphaltenes
% gases
% oils
% saturated
% aromatic
% polar
82.5 84.3 82.3 75.1 66.6 58.9 49.1 50.0
13.7 15.6 14.0 10.5 6.9 2.1 2.1 0.9
2.7 4.1 8.0 5.7 20.0 21.0 23.6 25.1
66.1 64.5 60.3 59.0 39.7 35.8 23.4 24.0
11.4 9.0 8.9 9.7 10.8 8.6 9.1 9.0
58.5 55.5 58.7 53.2 63.1 47.1 68.8 48.3
30.1 35.5 32.4 37.0 26.2 44.3 22.1 42.7
Table 5. Experimental and Theoretical Results Obtained in Catalytic Coal-Tire Coprocessing (1/1 Ratio) at 400 °C for 30 min and Hydrocarbon Type Analyses quantitative results P (MPa) 10
H2
5
H2
1
H2
experimental theoretical experimental theoretical experimental theoretical
hydrocarbon type distribution in oils
% conversion
% asphaltenes
% gases
% oils
% saturated
% aromatic
% polar
83.3 85.9 82.6 79.6 78.9 73.8
14.1 16.4 14.0 12.7 10.7 6.5
2.9 2.4 3.1 2.9 5.6 4.7
66.3 67.1 65.5 63.9 62.6 62.6
14.5 14.5 12.9 13.7 11.7 10.6
62.0 54.6 61.8 53.6 61.8 53.1
23.5 30.9 25.3 32.7 27.8 36.3
from tire are not able to break down coal structure but can stabilize radicals formed due to a hydrogen reaction. Maybe these radicals have steric hindrance to penetrate inside the coal matrix or they are not reactive enough to break down strong aromatic-aliphatic links. The GC-MS analyses revealed the presence of mainly alkyl benzene compounds with some phenolic compounds. The alkyl benzene compounds may have their origin in rubber depolymerization because high yields of 1-methyl-4-isopropylbenzene were achieved. The phenolic compounds may have their source mainly in the low-rank coal used, since they were not found in tirederived oils but were found in coal-derived oils. Table 4 shows experimental and theoretical results of the analyses performed on the derived oils produced in coal-rubber coprocessing as a function of pressure. Theoretical yields were calculated taking into account the analyses of the derived oils in the processing of both raw materials alone for conversion, asphaltenes, oils, and gas yields. It is shown that at 10 and 5 MPa, there is a trend of lower polar fraction in favor of aromatic percentages, and in the cases of 1 MPa of hydrogen and 0.1 MPa of nitrogen, this effect is remarkable. Therefore, the addition of tire rubber to coal liquefaction not only improves the yields obtained but also improves the amount of aromatic compounds produced, confirming the proposed mechanism of radicals from tire-stabilizing coal fragments, and reducing retrogressive reactions and high molecular weight species for all the pressures studied. Results from catalyzed processes are shown in Table 5. At 10 and 5 MPa conversion reached is the maximum possible, but at 1 MPa the effect of adding a catalyst is essential. Total conversion has been substantially increased. This conversion increase is mostly reflected on oils formation. In noncatalyzed reactions, at 5 and 10 MPa the possible synergism is not observed since the
conversion obtained is very high and positive interactions between coal and rubber may be screened by high hydrogen pressures. At 1 MPa there are some differences between theoretical and experimental values, but they are not as relevant as for noncatalyzed reactions. Table 5 shows the analyses of oils derived in coal/ rubber catalytic hydrocoprocessing. Comparing theoretical and experimental results, it is observed that there is an improvement in the formation of aromatic compounds due to a decrease of polar compounds. This positive effect of rubber was also present in noncatalyzed reactions. In addition, as in the case of processing only coal, iron showed a deoxygenating effect contributing to the decrease of polar compounds. The simulated distillation results showed that oils from coal are heavier than oils from tire; that is, a lower amount of gasoline and higher amount of kerosene and in general heavier oils are produced from coal. While gasoline was the most abundant component of oils from rubber, kerosene is the main fraction of oils from coal. In coal-tire coprocessing heavier fractions, heavy gas oil, vacuum gas oil, and vacuum residue are the main components. According to these results, radicals from both coal and rubber seem to stabilize between themselves and with the hydrogen gas in the reactor. In this way, molecules of higher molecular weight can be formed. Conclusions It can be concluded that a synergism in coal-tires hydrocoprocessing is observed but it is only manifest at low hydrogen pressures. At higher hydrogen pressures high conversions obtained could be screening this effect and the effect of hydrogen gas and rubber cannot be discerned. Synergism was only observed when hydrogen gas was present in the reaction atmosphere,
Ind. Eng. Chem. Res., Vol. 36, No. 11, 1997 4767
probably due to steric hindrance of tire radicals to penetrate the coal matrix, so hydrogen seems to be needed to break down the coal structure. Coal radicals generated would be stabilized by rubber and hydrogen radicals. The addition of red mud as a catalyst was effective in improving yields obtained in the case of coal and modifying the products distribution in experiments with rubber. The use of the catalyst also affected the nature of the oils produced, promoting the formation of saturated and aromatic compounds while decreasing the formation of polar compounds produced. Literature Cited Chaala, A.; Roy, C. Production of coke from scrap tire vacuum pyrolysis oil. Fuel Process. Technol. 1996, 46, 227. Conesa, J. A.; Font, R.; Marcilla, A. Gas from the pyrolysis of scrap tires in a fluidized bed reactor. Energy Fuels 1996, 10, 134. Derbyshire, F.; Hager, T. Coal liquefaction and catalysis. Fuel 1994, 73, 1087. Ding, W. B.; Tuntawiroon, W.; Liang, J.; Anderson, L. L. Depolymerisation of waste plastics with coal over metal-loaded silicaalumina catalysts. Fuel Process. Technol. 1996, 49, 49. Farcasiu, M.; Smith, C. M. Coprocessing of coal and waste rubber. Am. Chem. Soc. Div. Fuel Chem. Prep. Pap. 1992, 37, 472. Harrison, G.; Ross, A. Use of tyre pyrolysis oil for solvent augmentation in two-stage coal liquefaction. Fuel 1996, 75, 1009. Ibrahim, M. M.; Sheehra, M. S. Free radical monitoring of the coprocessing of coal with chemical components of waste tires. Fuel Process. Technol. 1995, 45, 213. Lamarre, L. Tapping the tire pile. EPRI J. 1995, Sept.-Oct., 31. Liu, Z.; Zondlo, J. W; Dadyburjor, D. B. Tire liquefaction and its effect on coal liquefaction. Energy Fuels 1994, 8, 607. Liu, Z.; Zondlo, J. W; Dadyburjor, D. B. Coal/tire coliquefaction using iron sulfide catalyst impregnated in situ in the coal. Energy Fuels 1995, 9, 673. Mastral, A. M. Valorization of coal conversion by swelling measuring. Final Report CSIC to ECSC, Contract 7220/EC/755; Instituto de Carboquı´mica: Zaragoza, Spain, 1993.
Mastral, A. M.; Mayoral, M. C.; Izquierdo, M. T.; Rubio, B. Role of iron in dry coal hydroconversion. Energy Fuels 1995, 9, 753. Mastral, A. M.; Murillo, R.; Pe´rez-Surio, M. J.; Calle´n, M. Coal hydrocoprocessing with tires and tire components. Energy Fuels 1996, 10, 941. Mastral, A. M.; Murillo, R.; Pe´rez-Surio, M. J.; Calle´n, M.; Mayoral, M. C. Assessment of the tire role in coal-tire hydroprocessing. Energy Fuels 1997a, 11, 676. Mastral, A. M.; Murillo, R.; Palacios, J. M.; Mayoral, M. C.; Calle´n, M. Fe catalyzed coal tire coprocessing. Influence of feed composition and hydrogen pressure on conversion products distribution. Energy Fuels 1997b, 11, 815. Orr, E. C.; Shi, Y.; Shao, L.; Liang, J.; Ding, W.; Anderson L. L.; Eyring, E. M.. Waste oils used as solvents for different ranks of coal. Fuel Process. Technol., 1996, 49, 233. Taghiei, M.; Feng, Z.; Huggins, F. E.; Huffman, G. P. Coliquefaction of waste plastics with coal. Energy Fuels 1994, 8, 1228. Teng, H.; Serio, M. A.; Wo´jtowicz, M. A.; Bassilakis, R.; Solomon, P. R. Reprocessing of used tires into activated carbon and other products. Ind. Eng. Chem. Res. 1995, 34, 3102. Williams, P. T.; Besler, S.; Taylor, D. T. The batch pyrolysis of tire waste. Fuel properties of the derived pyrolytic oil and overall plant economics. Fuel 1990, 69, 1474. Williams, P. T.; Besler, S.; Taylor, D. T. The pyrolysis of scrap automotive tires. The influence of temperature and heating rate on products composition. Proc. Inst. Mech. Eng. 1993, 207, 55. Zmierczak, W.; Xiao, X.; Shabtai, J. Depolymerisation-liquefaction of plastics and rubbers. Polystyrene and styrene-butadiene copolymers. Fuel Process. Technol. 1996, 49, 31.
Received for review May 1, 1997 Revised manuscript received July 26, 1997 Accepted August 1, 1997X IE970307F
X Abstract published in Advance ACS Abstracts, October 1, 1997.
