Aromatic oils oxidative stability

Lube oil extraction plants often use phenol as solvent. Phenol is used because of its solvent power with a wide range of feed stocks and its ease of recovery. Phenol preferentially dissolves aromatic-type hydrocarbons from the feed stock and improves its oxidation stability and to some extent its color. Phenol extraction can be used over the entire viscosity range of lube distillates and deasphalted oils. The phenol solvent extraction separation is primarily by molecular type or composition. In order to accomplish a separation by solvent extraction, it is necessary that two liquid phases be present. In phenol solvent extraction of lubricating oils these two phases are an oil-rich phase and a phenol-rich phase. Tne oil-rich phase or raffinate solution consists of the "treated" oil from which undesirable naphthenic and aromatic components have been removed plus some dissolved phenol. The phenol-rich phase or extract solution consists mainly of the bulk of the phenol plus the undesirable components removed from the oil feed. The oil materials remaining... 

Physical properties of carbon black-filled EPR and EPDM elastomers have been found to be comparable with the suUur-cured analogues [372]. Aromatic oils increase the optimum dose requirement for these compounds due to the reaction of the transient intermediates formed during radiolysis of the polymer with the oil as well as energy transfer which is particularly effective when the oil contains aromatic groups. The performance and oxidative stability of unfilled EPDM as well as its blend with PE [373], and the thermal stabdity and radiation-initiated oxidation of EPR compounds are reported by a number of workers [374,375]. 

Environmental demands and are as follows (a) improved fuel economy (reduced viscosities, reduced friction, special viscosity improvers), (b) reduced oil consumption (unconventional base oils, improved seal compatibility), (c) extended oil life (improved thermo-oxidative stability), (d) extended engine life (improved detergents and antiwear additives), (e) beneficial effects on emission/after treatment hardware (new additives), (f) technological and environmental sensitivity (no halogens, limited metal types/concentrations, new organic compounds), (g) recyclability (limitations the polycyclic aromatic hydrocarbons content and high chlorine levels (Havet et al., 2001 Waara et al., 2001). 

The quality of a refined oil is usually evaluated by traditional quality parameters such as a low residual FFA content, a high oxidative stability, a light color, and a neutral odor and taste. In addition, high-quality food oils should contain low transfatty acid (TEA) levels, high amounts of natural antioxidants and vitamins, low levels of polymeric and oxidized triacylglycerols, and no contaminants (pesticides, polycyclic aromatic hydrocarbons, dioxins and polychlorinated biphenyls, etc.) (Tables 5 and 6). 

Solvent extraction replaced acid treatment as the method for improving oxidative stability and viscosity/temperature characteristics of base oils. The solvent selectively dissolves the undesired aromatic components, the extract, leaving the desirable saturated components, especially alkanes, as a separate phase, the raffinate. Choice of solvent is determined by a number of factors, which are as follows ... 

The above result, that the antioxidant response in two-stage hydroprocessed oils is clearly better than in solvent-refined base stocks, has recently been confirmed [76]. It was demonstrated that phenolic-based formulations, blended into two-stage hydroprocessed oils, gave the greatest oxidative stability when total and polynuclear aromatics were lowest. Most fully formulated turbine oils make use of the synergistic interaction between phenolic and aminic antioxidants, see Reaction (4.70). Thus, depending on the performance requirements and the base oil composition, phenol/amino ratios of 1 1 to 4 1 are used [77],... 

In another example of this technique, D. E. Cranton,36 at Imperial Oil, as part of a study on base stock oxidation stability, separated a midcontinent 150N solvent refined oil by thermal analysis and the ten fractions obtained were then further separated into saturates and aromatics by silica gel chromatography. Mass spectral analyses (Tables 3.11 and 3.12) show the results of the separation obtained in... 

Clay treating has a marked effect on the oxidation stability of oil 7 (Table 5.4), described as a moderately aromatic residual-type base stock of intermediate VI. 

Von Fuchs and Diamond (Shell Oil) pursued these results further by examining the effects of increasing the content of the aromatics on base stock oxidation rates.15 They undertook this study because of the increasing realization that while solvent extraction technology improved lubricant performance, overextraction of the base stock could make it less resistant to oxidation because of removal of the autoretardant components. Since extraction removed aromatics and nitrogen and sulfur compounds, a relationship between these levels and oxidation stability seemed likely. 

Larsen et al.10 concluded that the stability of lubricating oils was due to the presence of natural inhibitors and that these were not hydrocarbons. Denison16 (Standard Oil of California) addressed this issue and deduced that it was the sulfur-containing components of the aromatics fraction that inhibited oxidation. The presence of sulfur compounds in solvent refined base stocks was therefore deemed critical for their performance. In his studies he found that desulfurized lubricating oils behaved like white oils under oxidation conditions (i.e., they were very unstable to oxygen and they oxidized very rapidly in an autocatalytic manner), whereas for the original undesulfurized oils, oxidation rates were slow... 

It was investigated that the viscosity index, pour point, oxidation stability, and other related properties of base oil depended on the composition and chemical nature of the aromatic, paraffinic, and naphthenic carbon contents (Yates et al., 1992). In this study, carbon types between KH150BS and filtrated oils were obtained using some base data of physical properties, and the method was similar to SH/T0729-2004. The results are shown in Table 5. 

Polyurethanes are sensitive to strong acids, strong alkalis, aromatics, alcohols, hot water, hot moist air and saturated steam. The hydrolytic stability of polyurethanes in applications must be considered carefully. However, polyurethanes are resistant to weak acids, weak alkalis, ozone, oxygen, mineral grease, oils and petroleum. There are doubts for the oxidation stability of polytetramethylene ether glycol based polyurethanes. Polycarbonate urethane is a promising substitute with good oxidation stability. 

It was described earlier that the interaction between radical anions and ketones in a partially oxidized, PCB contaminated oil, produces alcohols. It would therefore be expected that the formation of aromatic alcohols in particular would give rise to natural oxidation inhibitors. It is very likely that the effectiveness of the inhibitors formed in this way is small, relative to DBPC but, in any case, the oil should not be deleteriously affected by the treatment provided that the reclaimed oil has DBPC added to it. The oxidation stability of the processed oil should then be as good as, or possibly better than, new oil. Experimental data have shown that the oxidation stability of oils treated by the MOP system are the same as new oil by ASTM D2112. 

The properties of the lube oil that are set by the extraetion process are the viscosity index (VI), oxidation stability and thermal stability. These properties are related to aromatics, aliphatic sulfur, total sulfur and nitrogen levels present in the base stock. 

Almost all premium lubricants are so-called paraffinic oils composed primarily of both paraffinic and aUcycUc stmctures, with only a minor portion of aromatics. When stabilized with an oxidation inhibitor and fortified with other appropriate additives, these paraffinic—aUcycUc compositions provide nonsludging oils that are satisfactory for almost any type of service. 

Larger refineries with a wider product range can justify catalytic hydrogenation facilities. Olefins and aromatics are reduced to their saturated equivalents, paraffins and naphthenes. This method of decolorization decreases the number and extent of conjugated double bonded species and stabilizes the lubricating oil stocks toward oxidation. 

Aromatics have densities and viscosities which are yet still higher. Viscosity/temperature characteristics are in general rather poor but melting points are low. Although they have the best solvency power for additives, their stability to oxidation is poor. As for alicyclics, single-ring aromatics with long side chains, alkylbenzenes, may be very desirable base oil components. 

---