Systems and methods for automatic maintenance of lube oil quality include a storage tank for storing fresh lube oil, a lube oil reservoir containing a volume of operational lube oil, and an oil disposal tank. A first controllable flow system transports lube oil from the reservoir to the oil disposal tank, and a second controllable flow system transports fresh lube oil from the storage tank to the reservoir. Provided are a level transmitter to measure a level of lube oil within the reservoir and an antioxidant sensor to measure a concentration of antioxidant level inside the lube oil reservoir. A control system activates and deactivates the first controllable flow system based upon the concentration of antioxidant measured by the antioxidant sensor, and activates and deactivates the second controllable flow system based upon the level of lube oil measured by the level transmitter.

Lubricant compositions comprising a base oil, one or more antioxidants selected from a group consisting of N-α-naphthyl-N-phenylamine antioxidants and diphenylamine antioxidants; and a sulfur-containing additive comprising up to seven carbon atoms exhibit outstanding oxidative stability and non-corrosion properties. The N-α-naphthyl-N-phenylamine antioxidants plus diphenylamine antioxidants in total may be present from about 0.2 wt % to about 0.8 wt %, based on the total weight of the lubricant composition. The sulfur provided by the sulfur-containing additive may be present from about 50 ppm to about 1000 ppm by weight, based on the total weight of the lubricant composition.

A turbine oil used in a turbine of a jet engine, containing: a base oil (A) containing a polyol ester (A1); an antioxidant (B) containing an amine-based antioxidant (B1); a polymethacrylate (C) having a weight average molecular weight of 50,000 to 600,000; and an alkyl aromatic compound (D), having a content of the component (D) of 1,000 parts by mass or less per 100 parts by mass of a total resin content of the component (C), and satisfying the following requirements (1) and (2): requirement (1): a viscosity index of 140 or more; and requirement (2): a coking amount attached to a panel of 80 mg or less after a panel coking test under the prescribed condition. The turbine oil has a high viscosity index to such an extent that an oil film can be retained in the use under a high temperature environment as in a turbine of a jet engine mounted on an aircraft, and is excellent in low temperature viscosity characteristics while retaining excellent heat resistance.

A liquid blend of octylated phenyl-α-naphthylamine, and at least one low molecular weight aromatic ester, wherein the octylated phenyl-α-naphthylamine is present from about 15% to about 35% by weight of the blend, as well as a lubricating composition comprising a lubricant base and an amount of the blend which provides up to 2.0% by weight of the octylated phenyl-α-naphthylamine in the composition.

Disclosed herein are processes for the preparation of compounds of formula (I) from one or more bio-derived reactants, and their use as base oils:

(R.sub.1-A).sub.b-(CH.sub.x).sub.a(CHR.sub.2).sub.m(C(R.sub.4R.sub.5)).sub.n(CHR.sub.3).sub.o(CH.sub.y).sub.c-(A-R.sub.1).sub.d(I)

wherein a and c are independently 0 or 1, b and d are independently 1 or 2, x and y are independently 1 or 2, dependent upon the values of a-d, m and o are independently 0 or 1, n is an integer of 0-6, and each A is independently an unsaturated furan ring, a partially saturated furan ring, a saturated furan ring, or (CH.sub.2).sub.4. Also, R.sub.1, R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are independently selected from the group consisting of H and alkyl groups having 1 to 18 carbon atoms, with a proviso that at least one of R.sub.2, R.sub.3, R.sub.4, and R.sub.5 is not hydrogen, and the total carbon content of the compound of formula (I) is in the range of 20-62.

Lubricant compositions comprising a base oil, one or more antioxidants selected from a group consisting of N--naphthyl-N-phenylamine antioxidants and diphenylamine antioxidants; and a sulfur-containing additive comprising up to seven carbon atoms exhibit outstanding oxidative stability and non-corrosion properties. The N--naphthyl-N-phenylamine antioxidants plus diphenylamine antioxidants in total may be present from about 0.2 wt % to about 0.8 wt %, based on the total weight of the lubricant composition. The sulfur provided by the sulfur-containing additive may be present from about 50 ppm to about 1000 ppm by weight, based on the total weight of the lubricant composition.

A fluid contains a base oil and an antioxidant, the base oil consisting of sulfur-containing polyalkylene glycol where greater than 80 weight-percent of the fluid is a sulfur-containing polyalkylene glycol and less than one weight-percent of the fluid is water, with weight percent based on total fluid weight an wherein the sulfur-containing polyalkylene glycol is free of oxygen bound directly to sulfur.

A turbine oil used in a turbine of a jet engine, containing: a base oil (A) containing a polyol ester (A1); an antioxidant (B) containing an amine-based antioxidant (B1); a polymethacrylate (C) having a weight average molecular weight of 50,000 to 600,000; and an alkyl aromatic compound (D), having a content of the component (D) of 1,000 parts by mass or less per 100 parts by mass of a total resin content of the component (C), and satisfying the following requirements (1) and (2): requirement (1): a viscosity index of 140 or more; and requirement (2): a coking amount attached to a panel of 80 mg or less after a panel coking test under the prescribed condition. The turbine oil has a high viscosity index to such an extent that an oil film can be retained in the use under a high temperature environment as in a turbine of a jet engine mounted on an aircraft, and is excellent in low temperature viscosity characteristics while retaining excellent heat resistance.

One aspect of the present invention relates to a dinaphthyl ether compound represented by formula (1):

##STR00001##

in the formula (1), R.sup.1 and R.sup.2 are the same or different and each represent a linear or branched hydrocarbon group having 6 to 32 carbon atoms; m and n are each a real number of 0 or more and satisfy 1.0?m+n?3.0.

One aspect of the present invention relates to a naphthyl phenyl ether compound represented by formula (1):

##STR00001##

in the formula (1), R.sup.1 and R.sup.2 are the same or different and each represent a linear or branched hydrocarbon group having 6 to 28 carbon atoms; m and n are each a real number of 0 or more and satisfy 1.0?m+n?3.0.