Refining Of Used Lubricating Oils

Abstract

Used lubricating oils, particularly those containing additives such as V. I. improvers, dispersants and the like, are reclaimed by a preliminary treat with a C.sub.4 to C.sub.5 aliphatic alcohol, which causes the separation of a layer of sludge which contains polar additives and oxidation products. The desludged oil is then subjected to conventional lubricating oil refining steps such as treatment with fuming sulfuric acid followed by neutralizing, washing, and clay treating steps. Alternatively, the desludged oil is subjected to a hydrogenation treatment rather than the sulfuric acid treatment. Extraction with phenol, furfural, etc. can also be included, as well as redistillation or fractionation. Advantages over prior art oil reclaiming processes include higher yields of finished reclaimed oil, the formation of appreciably less byproduct sludge, and the obtaining of a more oxidation-resistant reclaimed oil. BACKGROUND OF THE INVENTION It is well known in the prior art to reclaim used lubricating oils by various methods, all of which employ some means for removing undesirable constituents such as oxidation products. A typical process will include the steps of heating the oil and allowing separated matter to settle out, subjecting the supernatant oil to an acid treating step and removing from the oil the resultant acid sludge, then neutralizing the oil with a basic material, followed by some form of clay treating and filtration. Some reclaiming processes omit the acid treating step and substitute a more severe clay treatment, which may or may not be preceded by heating, fractionation or distillation steps. In all of the prior art oil reclaiming processes there is a serious problem in disposing of sulfuric acid sludge and/or sludgy clay from the clay treating steps. In recent years, with the realization that pollution problems are increasing, there has been a demand for a more efficient oil reclaiming process in which there will be a minimum of sludge, contaminated clay, and the like to be disposed of. Furthermore, with the more extended use of dispersants in lubricating oils the cost of reclaiming used oil has increased. Rising costs of oil reclaiming have discouraged a number of rerefiners from continuing in the oil reclaiming business. However, because of the increased emphasis on reduction of pollution, the disposal of used oil in sewers and rivers or by dumping on open ground has been at least discouraged if not legally barred. Thus, there is now a need for new reclaiming processes which will allow the production of reclaimed lubricating oils at reduced cost and increased yields.

Description

DESCRIPTION OF THE INVENTION

In accordance with the present invention, it has been found that the reclaiming of used lubricating oils can be greatly improved if the used oil is first subjected to a precipitation step wherein an oxygenated polar liquid is used to bring about the precipitation of sludge, polymeric materials and the like. The precipitated material contains useful components as will hereinafter be explained. The oxygenated material used in this invention is an aliphatic monohydric alcohol of from 4 to 5 carbon atoms. Alcohols of from 1 to 3 carbon atoms are not miscible with the oil and do not bring about precipitation of polymers and sludge. Likewise diols including 1,3-ethanediol, 1,4 -butane diol, and 1,5-pentane diol are partly miscible with used oil and do not induce precipitation of polymers and sludge. The preferred precipitation agent is normal butanol. Other effective alcohols include secondary butyl alcohol, isobutyl alcohol, and isoamyl alcohol, and mixtures of such alcohols.

In conducting the precipitation step of the process of this invention the used oil is mixed with from about one-third to twice its volume of the precipitating alcohol; preferably about equal volumes of used oil and alcohol are employed. The precipitation is normally carried out at ambient temperatures, e.g., from about about 60.degree. to 100.degree. F. Precipitation does not occur immediately and will usually require from about 12 to 24 hours to complete. Separation can be improved by centrifuging the mixture of oil and alcohol, as for example, from 10 to 30 minutes at 700 -800 g's. Precipitation can be facilitated by employing a small quantity of a C.sub.4 to C.sub. 6 aliphatic hydrocarbon, along with the alcohol. This will usually be about 5 to 30 volumes of hydrocarbon per 100 volumes of the alcohol, e.g., from about 10 to 25 parts of pentane for each 100 parts of the alcohol. The pentane can be normal pentane or mixed pentanes. Hexane could also be used as well as mixed pentanes and hexanes. While butane is normally too volatile its use can be made possible with pressure equipment. In most instances pentane will be preferred.

Depending on the starting used oil, the precipitate obtained after settling and/or centrifuging will amount to about 3 to 8 percent of the used oil. The oil separated from the precipitated sludge can then be subjected to acid and clay treatment or to a hydrogenation treatment as shown in the examples. The separated oil can additionally, or alternatively, be subjected to other conventional lubricating oil refining steps, including solvent refining, e.g., extraction with phenol or furfural or the like, redistillation, etc. Another alternative, if the oil reclaiming plant is part of a conventional petroleum refinery, involves blending the separated oil, obtained in the sludge precipitation steps of this invention, with the usual lubricating oil fraction obtained in the distillation of a crude oil, to be subsequently handled as part of the freed stream sent to the lubricating oil section of the refinery.

In some cases, when the used oil is subjected to the precipitation step with C.sub. 4 to C.sub. 5 aliphatic alcohol, three layers are formed, the bottom layer being sludge, the middle layer being a viscous material which contains viscosity index improvers, and a top oily layer containing recoverable lubricating oil. It is feasible to reclaim and reuse the viscosity index improver that is present the the middle layer. In other instances there will be only two layers, in which case the viscosity index improver of the used oil will come out with the sludge layer. The three-layer separation appears to occur most often if the viscosity index improver is of the polyisobutylene type. In the case of two layer separation wherein the viscosity index improver tends to come out with the sludge, and recovery of viscosity index improver therefrom is not economically feasible, the viscous sludge layer could find use as a rubber extender oil or as a component of newspaper printing ink.

The nature of this invention and the manner in which it can be practiced will be more fully understood from the following examples, which include a preferred embodiment.

EXAMPLE 1

One hundred volumes of a sample of used crankcase oil containing conventional additives, including V.I. improvers, was heated at 190.degree. C. to remove gasoline components and water, giving 97 volumes of stripped used oil. To this were added 78 volumes of normal butyl alcohol and 19 volumes of pentane. After settling and centrifuging, three distinct layers were formed, the bottom layer being sludge, the middle layer being a viscous layer and the top layer being an oily layer. The oily layer contained 92 volumes of oil, 73 volumes of butanol and 18 volumes of pentane.

The oily layer was subjected to a distillation to recover the pentane and normal butanol for recycle to the process, leaving 92 volumes of oil as bottoms. The 92 volumes of oil were then treated with 14 volumes of fuming sulfuric acid (containing 20 weight percent SO.sub. 3 ) causing the formation of 25 volumes of sludge and 70 volumes of acid treated oil. The acid treated oil was separated from the sludge and neutralized with 50 volumes of an aqueous solution containing 10 percent (by weight) of sodium carbonate. After the pH of the water layer reached a value of between 7 and 8, eight volumes of isopropyl alcohol were added to the blend. The purpose of this step was to neutralize the residual acidity in the oil resulting from the sulfuric acid treat and to extract the sodium sulfonates resulting from this neutralization.

The mixture of oil, isopropyl alcohol and sodium carbonate solution was allowed to settle, giving three layers. The bottom layer contained the inorganic salts e.g., sodium carbonate and sodium sulfate, dissolved in water diluted with some isopropyl alcohol. The second layer contained the sodium sulfonates dissolved in isopropyl alcohol diluted with some water. The top layer was the neutralized oil diluted with some isopropyl alcohol and water.

Then the oil was stripped at 140.degree. C. and 15 millimeters mercury pressure and yielded 61 weight percent of reclaimed oil based on the amount of oil at the beginning of the process. The ASTM color of this reclaimed oil was 3.5. Further improvement in color was obtained by subjecting the oil to a clay treatment in which 100 parts of oil were percolated for 45 minutes at 130.degree. C. with 5 parts by weight of Attapulgus clay. The operation was followed by a filtration to separate the oil from the clay.

The above steps of the reclaiming process and the products of each of the steps are outlined in table I which follows: ##SPC1##

EXAMPLE 2

Another portion of the used oil described in example 1 was subjected to the stripping and normal butanol precipitating steps therein described. Portions of the thus treated oil were then subjected to a hydrogenation treatment at various temperatures and pressures using a nickel hydrogenation catalyst (Harshaw Ni-0104T). In each case, 136 grams of the treated used oil and 34 grams of catalyst were placed in a 300 milliliter high pressure cell and the cell was then purged with nitrogen before the hydrogenation treatment began. In each run hydrogenation was conducted for 18 hours. The total hydrogen absorbed was computed from a record of the hydrogen that had been added to the high pressure cell. The results obtained are shown in table II which follows: ##SPC2##

COMPARATIVE EXAMPLE

A portion of the used oil described in example 1 was stripped of water and gasoline in the same manner as described in example 1. Then the oil was treated with 15 vol. percent of fuming sulfuric acid (20 percent SO.sub. 3 ), the temperature being maintained below 110.degree. F. Resulting acid sludge was separated from the product and the acid treated oil was then neutralized with a mixture of isopropyl alcohol and 10 percent aqueous sodium carbonate solution, the amount of alcohol being about 7 weight percent based on the amount of used oil before stripping, and the amount of sodium carbonate solution being approximately 50 weight percent of the amount of starting oil. Three layers were formed, one containing inorganic salts dissolved in a water-rich phase, one containing sulfonates and the remaining one consisting of neutralized oil. The oil then was stripped at 140.degree. C. and 15 millimeters mercury pressure and yielded 58 weight percent of reclaimed oil based on the amount of oil at the beginning of the process. In this example the amount of sulfuric acid sludge formed was about 32 weight percent based on the starting oil, whereas in example 1, using the process of the present invention, the amount of sulfuric acid sludge formed was only 23 weight percent based on the starting oil.

Inspection data of the reclaimed oil obtained in this comparative example are compared with those of the reclaimed oil obtained in example 1, in the following table III. ##SPC3##

The table also gives inspection data for typical refined lubricating oil base stocks of about 150 and 200 SUS viscosity, respectively, at 100.degree. F. These data show that the rerefined oil obtained in accordance with the present invention had properties that were comparable with those of a conventionally refined lubricating oil and that were somewhat superior to those of the oil reclaimed by conventional treatment with sulfuric acid alone.

The foregoing examples demonstrate that the present invention provides an improvement in the art of reclaiming used lubricating oil wherein high quality lubricating oil can be obtained along with useful byproducts heretofore discarded in the prior art reclaiming processes. At the same time there is less acid sludge to be disposed of.

It is, of course, not intended that this invention be limited in any way by the specific examples, as numerous modifications thereof are possible without departing from the scope of the invention as defined by the appended claims.

Claims

What is claimed is:

1. In a process for reclaiming a used lubricating oil wherein the used oil is stripped of water and volatile constituents and subsequently subjected to a conventional lubricating oil refining step, the improvement which comprises removal of sludge components of the used oil by treating the oil with from 30 to 200 volumes of a C.sub. 4 or C.sub. 5 aliphatic alcohol per 100 volumes of used oil following the stripping step and prior to the conventional refining step.

2. Improvement as defined by claim 1 wherein said alcohol is normal butanol.

3. Improvement as defined by claim 1 wherein said alcohol is mixed with a minor proportion of a C.sub. 4 to C.sub. 6 aliphatic hydrocarbon to facilitate precipitation of sludge.

4. Improvements as defined by claim 3 wherein said hydrocarbon is pentane.

5. Improvement as defined by claim 1 wherein said subsequent refining step includes acid treating.

6. Improvement as defined by claim 1 wherein said subsequent refining step includes treatment with hydrogen.

7. Improvement as defined by claim 1 wherein said subsequent refining step includes solvent extraction with phenol.

8. An improved process for reclaiming a used hydrocarbon lubricating oil containing additives including V.I. improvers and dispersants which includes the steps of distilling volatile substituents from said oil, mixing 1 volume of the resulting stripped oil with from one-third to 2 volumes of a mixture of normal butanol and normal pentane whereby a sludge layer is caused to precipitate from said oil, separating said sludge from said oil, and thereafter subjecting said oil to a treatment with fuming sulfuric acid followed by neutralizing the acid treated oil.

9. Process as defined by claim 8 which includes a final clay treating step.

10. An improved process for reclaiming a used hydrocarbon oil containing additives including V.I. improvers and dispersants which includes the steps of distilling volatile constituents from the oil, treating the stripped oil with a mixture of normal butanol and normal pentane whereby a sludge layer is formed, separating said sludge from said oil, and subjecting the sludge-free oil to a hydrogenation step.