Method of Removing Soluble Metal Salts in Used Turbine/Circulating Oil

1. Field of the Invention

This invention relates to the reclamation or reconditioning of used lubricating oils, e.g., used turbine and/or circulating oils. More specifically, it relates to a process or method wherein soluble metal salts present in such used oils are removed economically and efficiently as sediments thereby retarding the deterioration and sludge formation of the oils.

2. Description of Prior Art

The oxidation of turbine/circulating oils in the presence of metals can often result in the formation of soluble metal salts. Used turbine/circulating oils therefore usually contain soluble metal salts which act as oxidation catalysts to accelerate oil deterioration. Thus, removal of these catalytically active metal salts retards the deterioration and sludge formation of the oils, thereby providing longer service life. However, it is difficult to remove such salts even with ultrafine filtration or ultracentrifugation. Oil users, accordingly, make little or no attempt to remove them because as stated supra no simple method is available. The novel method that we have developed has demonstrated that removal can be achieved easily and economically. Also, conceptually, this novel method can be utilized in the rerefining of waste lubricating oils and also in removing undesirable metal salts in commercial processes of catalytically cracking hydrocarbon feeds. Nevertheless, the present invention is particularly directed to the reclamation of used turbine and/or circulating oils by eliminating soluble metal salts produced from oil deterioration (oxidation).

In accordance with the present invention there is provided a method for reclaiming used turbine and/or circulating oils.

The process of the present invention comprises mixing the used turbine oil with a soluble triazole or mixture of soluble triazoles under suitable conditions of temperature and thereafter separating the resultant sediments from said used oil.

The hydrocarbyl lubricating oil stock which may be treated in accordance with the present invention includes mineral oils or fractions of mineral oils, synthetic oils and mixtures of mineral and synthetic oils. The synthetic hydrocarbon oils include long chain alkanes such as cetanes and olefin polymers such as trimers and tetramers of octene and decene. The synthetic oils with which these can be mixed include (1) ester oils such as pentaerythritol esters of monocarboxylic acids having 2 to 20 carbon atoms, (2) polyglycol ethers, (3) polyacetals and (4) siloxane fluids. Especially useful among the synthetic esters are those made from polycarboxylic acids and monohydric alcohols. More preferred are the ester fluids made from pentaerythritol, or mixtures thereof with di- and tripentaerythritol, and an aliphatic monocarboxylic acid containing from 1 to 20 carbon atoms, or mixtures of such acids. The mineral oils generally include any high boiling range material, such as those boilng above 600.degree. F.

Any suitable triazole compound may be used in the process of this invention provided it is soluble. Suitable triazole compounds include benzotriazole, alkylbenzotriazoles having from 4 to 36 carbon atoms, tolyl triazole, alkyl derivatives of tolyl triazoles having from 4 to 36 carbon atoms, and dimercapto thiadiazoles.

The operating parameters in the present process are maintained for such time as required to achieve optimum sedimentation thereby providing optimum upgrading or restoration of the quality of the oil stock. The mixing temperature of the oil and the triazoles is generally maintained within the range of about 70.degree. to about 180.degree. F., with a preferred range of from about 120.degree. to about 140.degree. F.

As noted above any suitable mixing time may be used which will give the desired degree of sedimentation.

The soluble triazoles in accordance herewith are used in small or minor amounts of from about 0.001 to about 1.0 wt. % by weight of the oil stock with a preferable range of from about 0.025 to about 0.075 wt. %. Additionally the triazoles in accordance herewith are not detrimental to any additives normally present in the used oil.

The following specific examples which are in no way limiting are presented to more fully illustrate the present invention. The data given in Table 1 was obtained by spectrographic analysis and the data of Table 2 was derived via a B-10 Oxidation Test, which outline is given below.

Example 1 is a used turbine oil sample having the following general description:

which did not contain a triazole compound.

Example 2 was the same turbine oil sample as Example 1 containing 0.05 wt. % of a triazole compound, an isomeric mixture of 1- and 2-(didodecylaminomethyl) benzotriazole.

Example 3 was the same turbine oil sample as Example 1 containing 0.05 wt. % of another triazole compound, a reaction product of a commercially obtained tertiary-alkyl primary amine and tolyl triazole. The exact carbon number of the alkyl substitutent is not revealed but is believed to be a lower alkyl moiety.

Table 1 summarizes the comparative filtration and centrifugation data for the three Examples: used turbine oil without triazole (Example 1) and two used turbine oil with 0.05 percent each of a different triazole (Examples 2 and 3). Table 2 represents metal contents by emission spectrograph analysis, showing the depletion of metals in the used turbine oil. Table 3 gives B-10 oxidation data on reconditioned turbine oils, showing our reconditioning method hinders formation of sludges.

The B-10 oxidation test composition was subjected to a stream of air which bubbled through the composition at a rate of 5 liters per hour at 260.degree. F. for 40 hours. Contrary to normal procedure no metal catalysts were present in the composition. The compositions were rated on the basis of oxidative stability or prevention of oil deterioration as measured by the increase in acid formation or neutralization number (NN) and sludge formation occasioned by oxidation.

It is evident from the data of Tables 1, 2 and 3 that the reclaimed used turbine oil is suitable for reuse for a variety of purposes.

While this invention has been described with reference to preferred compositions and components therefor, it will be understood by those skilled in the art that departure from the preferred embodiments can be effectively made and are within the scope of the specification.