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Oxidation of petroleum fractions
Letters to the Editor
Oxidation of petroleum fractions Speros E. Moschopedis and James G. Speight Fuel Sciences Division, Research Council of Alberta, 113l5-87th (Received 20 October 1972)
In previous
communications to this journal’32 we have described the effects of a variety of oxidizing agents on a petroleum asphaltene. In general, the asphaltene reacted slowly with all but the strongest reagent, i.e. nitric acid. This prompted further investigation into the effects of aerial oxygen on petroleum fractions in an attempt to throw some light on, in this case, the oxidation and weathering of Athabasca bitumen. In this respect, the bitumen as located in the formation under ~100 ft* of overburden has a viscosity of 7.3” API whilst that in various outcrops frequently contacted by air, wind, etc. has a viscosity of ~5’ API (J. G. Speight, unpublished observations). For the purposes of these investigations, the bitumen was separated into several constituent fractions, viz light oils, dark oils, resins, and asphaltenes, first by precipitation of the asphaltenes and subsequently by elution of the deasphalted oil from fuller’s earth using solvents of increasing polarity. Thus, treatment of the separate fractions with oxygen or air at 150-250°C produced interesting results. The light oils which are mostly paraffinic materials (H/C = 1.90) showed relatively little reactivity to oxygen in the temperature range studied whilst the dark oils (H/C m 1.55) and resins (H/C x 1.45) were significantly more reactive; the asphaltenes (H/C = 1.20) showed some reactivity to oxygen. Condensation appeared to proceed in preference to molecular degradation but prolonged reaction times and higher temperatures afforded some lowermolecular-weight products. The comparative inactivity of the light oils to oxygen or air is not surprising since paraffin waxes which could conceivably contain the same type of constituents as those in the light oils are oxidized efficiently at temperatures in, and above, this range only in the presence of a catalyst3. For the present, we note that colour changes occurred (from light yellow to red-brown) and infra-red and n.m.r. spectra indicated the onset of aromatization. Treatment for prolonged periods (up to 50 h instead of the usual l-4 h) produced higher-molecular-weight aromatic material as well as the usual water-soluble and alkali-soluble material. The dark oils and the resins oxidized comparatively easily over the temperature range studied at treatment periods varying from 1 to 4 h. Presumably this is due to branches in the aliphatic moieties of the molecules and also condensation between aromatic ring systems. In this respect, we note that pentane-insoluble organic material (i.e. ‘asphaltenes’) was produced from both fractions as well as the usual water-soluble and alkali-soluble material. * 1 ft = 0.305 m
Avenue, Edmonton 7, Alberta, Canada
Over more prolonged periods, the complexity of the synthetic ‘asphaltenes’ increased. Oxidation of the asphaltenes was, as previously noted’**, slow but nevertheless some (<5% w/w) alkali-soluble material was produced together with higher-molecular-weight However, we now note that lower-molecularorganics. weight asphaltenes, as defined in a previous communication4, are more reactive than their more complex highermolecular-weight counterparts. Particularly worthy of note is the oxidation of the bitumen itself. After 4 h at 200°C, oxidation of the bitumen yielded an oil containing suspended organic matter which proved to be asphaltenes; very little of these materials remains in the oil. The proportions of resins and dark oils were significantly reduced during this procedure whilst the proportion of the light oils remained relatively unchanged thereby suggesting that the resins, and possibly the dark oils, are responsible for the ‘solubility’ of the asphaltenes. This aspect of the work will be discussed in more detail in a later communication. In all cases increases in oxygen contents of the products were noted - high oxygen contents were typical of waterand alkali-soluble materials whilst but little additional Similar oxygen appeared in the hydrophobic materials. results were also recorded using a variety of oxidizing agents with each fraction. From these, and other, results obtained in our laboratories, we are inclined to believe that the predominant trend in these reactions is the formation of highermolecular-weight more complex materials and that the water-soluble organics are by-products arising from oxidative fission of aliphatic side-chains. Indeed, this is particularly evident when exposed bitumen (~5’ API) is fractionated and shown to contain significantly more of the highermolecular-weight fractions than unexposed material. However, as more prolonged reaction times are employed, oxidative degradation of the aromatic systems will ensue giving rise to the hydrophilic organic systems. Nevertheless, we are of the opinion that these latter stages are not dominant and that weathering of the bitumen involves the more dominant oxidative coupling and dehydrogenation processes.
REFERENCES 1 Moschopedis, S. E. and Speight, J. G. Fuel, Land. 1971, SO, 34 2 Moschopedis, S. E. and Speight, J. G. Fuel, Lond. 1971, 50, 211 3 Asinger, F. ‘Paraffins - Chemistry and Technology’, Pergamon Press, London, 1968, p 626 et seq. 4 Speight, J. G.Fuel, Lond. 1971,50, 102
FUEL, 1973, Vol. 52, January
83
Oxidation of petroleum fractions Speros E. Moschopedis and James G. Speight Fuel Sciences Division, Research Council of Alberta, 113l5-87th (Received 20 October 1972)
In previous
communications to this journal’32 we have described the effects of a variety of oxidizing agents on a petroleum asphaltene. In general, the asphaltene reacted slowly with all but the strongest reagent, i.e. nitric acid. This prompted further investigation into the effects of aerial oxygen on petroleum fractions in an attempt to throw some light on, in this case, the oxidation and weathering of Athabasca bitumen. In this respect, the bitumen as located in the formation under ~100 ft* of overburden has a viscosity of 7.3” API whilst that in various outcrops frequently contacted by air, wind, etc. has a viscosity of ~5’ API (J. G. Speight, unpublished observations). For the purposes of these investigations, the bitumen was separated into several constituent fractions, viz light oils, dark oils, resins, and asphaltenes, first by precipitation of the asphaltenes and subsequently by elution of the deasphalted oil from fuller’s earth using solvents of increasing polarity. Thus, treatment of the separate fractions with oxygen or air at 150-250°C produced interesting results. The light oils which are mostly paraffinic materials (H/C = 1.90) showed relatively little reactivity to oxygen in the temperature range studied whilst the dark oils (H/C m 1.55) and resins (H/C x 1.45) were significantly more reactive; the asphaltenes (H/C = 1.20) showed some reactivity to oxygen. Condensation appeared to proceed in preference to molecular degradation but prolonged reaction times and higher temperatures afforded some lowermolecular-weight products. The comparative inactivity of the light oils to oxygen or air is not surprising since paraffin waxes which could conceivably contain the same type of constituents as those in the light oils are oxidized efficiently at temperatures in, and above, this range only in the presence of a catalyst3. For the present, we note that colour changes occurred (from light yellow to red-brown) and infra-red and n.m.r. spectra indicated the onset of aromatization. Treatment for prolonged periods (up to 50 h instead of the usual l-4 h) produced higher-molecular-weight aromatic material as well as the usual water-soluble and alkali-soluble material. The dark oils and the resins oxidized comparatively easily over the temperature range studied at treatment periods varying from 1 to 4 h. Presumably this is due to branches in the aliphatic moieties of the molecules and also condensation between aromatic ring systems. In this respect, we note that pentane-insoluble organic material (i.e. ‘asphaltenes’) was produced from both fractions as well as the usual water-soluble and alkali-soluble material. * 1 ft = 0.305 m
Avenue, Edmonton 7, Alberta, Canada
Over more prolonged periods, the complexity of the synthetic ‘asphaltenes’ increased. Oxidation of the asphaltenes was, as previously noted’**, slow but nevertheless some (<5% w/w) alkali-soluble material was produced together with higher-molecular-weight However, we now note that lower-molecularorganics. weight asphaltenes, as defined in a previous communication4, are more reactive than their more complex highermolecular-weight counterparts. Particularly worthy of note is the oxidation of the bitumen itself. After 4 h at 200°C, oxidation of the bitumen yielded an oil containing suspended organic matter which proved to be asphaltenes; very little of these materials remains in the oil. The proportions of resins and dark oils were significantly reduced during this procedure whilst the proportion of the light oils remained relatively unchanged thereby suggesting that the resins, and possibly the dark oils, are responsible for the ‘solubility’ of the asphaltenes. This aspect of the work will be discussed in more detail in a later communication. In all cases increases in oxygen contents of the products were noted - high oxygen contents were typical of waterand alkali-soluble materials whilst but little additional Similar oxygen appeared in the hydrophobic materials. results were also recorded using a variety of oxidizing agents with each fraction. From these, and other, results obtained in our laboratories, we are inclined to believe that the predominant trend in these reactions is the formation of highermolecular-weight more complex materials and that the water-soluble organics are by-products arising from oxidative fission of aliphatic side-chains. Indeed, this is particularly evident when exposed bitumen (~5’ API) is fractionated and shown to contain significantly more of the highermolecular-weight fractions than unexposed material. However, as more prolonged reaction times are employed, oxidative degradation of the aromatic systems will ensue giving rise to the hydrophilic organic systems. Nevertheless, we are of the opinion that these latter stages are not dominant and that weathering of the bitumen involves the more dominant oxidative coupling and dehydrogenation processes.
REFERENCES 1 Moschopedis, S. E. and Speight, J. G. Fuel, Land. 1971, SO, 34 2 Moschopedis, S. E. and Speight, J. G. Fuel, Lond. 1971, 50, 211 3 Asinger, F. ‘Paraffins - Chemistry and Technology’, Pergamon Press, London, 1968, p 626 et seq. 4 Speight, J. G.Fuel, Lond. 1971,50, 102
FUEL, 1973, Vol. 52, January
83