Process for regenerating used lubricating oils

Abstract

Used lubricating oils containing soluble metal compounds, particularly those recovered from internal combustion engines, gear-boxes and differentials, are regenerated by circulating them along a first face of a membrane permeable to hydrocarbons, preferably an ultra-filtration membrane, and collecting a purified oil on the other face of the membrane.

Description

The invention concerns a new process for regenerating used oils recovered, for example, from internal combustion engines, gear-boxes and differentials.

Only a small proportion of these used oils is treated for the purpose of separating the mineral oil base from the impurities contained therein.

These impurities consist of suspended solid materials, such as:

COAL-LIKE MATERIALS

METALS RESULTING FROM WEAR (IRON, COPPER, TIN, ALUMINUM)

LEAD DERIVATIVES, FOR EXAMPLE LEAD OXIDES, CHLORIDES, OXYCHLORIDES OR BROMIDES.

They also consist of soluble constituents, such as:

DISPERSANT-DETERGENT ADDITIVES, FOR EXAMPLE CALCIUM, BARIUM, MAGNESIUM, ZINC OR ALUMINUM SALICYLATES, SULFONATES, PHENATES AND THIO-PHOSPHONATES. Ashless additives, such as acrylic copolymers, polyamides and alkyl derivatives of succinimide;

ANTIOXIDANT, ANTIWEAR ADDITIVES, SUCH AS METAL DITHIOPHOSPHATES, FOR EXAMPLE ZINC DITHIOPHOSPHATE, SULFUR ORGANIC COMPOUNDS, CHLORINE COMPOUNDS, PHOSPHATES, PHOSPHITES, PHOSPHONATES OR PHOSPHINATES (THE LATTER BEING CHIEFLY RECOVERED FROM GEAR-BOX OR DIFFERENTIAL OILS, PARTICULARLY THOSE WHOSE METAL IS CALCIUM, BARIUM, MAGNESIUM, ZINC OR ALUMINUM;

ANTI-FOAM ADDITIVES, FOR EXAMPLE SILICONE OILS;

VISCOSITY INDEX ADDITIVES:

POLYOLEFINS: POLYISOBUTENE, ETHYLENE-PROPYLENE COPOLYMERS;

ESTER POLYMERS: POLYACRYLATES, POLYMETHACRYLATES OR POLYFUMARATES.

These impurities also consist of the products resulting from the cracking of these additives or of the oil itself.

The oil may also contain lead compounds, for example lead soaps.

As a rule, the metal content of the used oils, particularly in the form of the hereinbefore described soluble metal compounds, is from 0.1 to 10 % by weight as metal.

The additives for lubricating oils are well known; so that they will not be described in detail.

The major portion of these oils, however, is not purified and constitutes a major source of pollution, particularly of rivers.

As to the conventionally used regeneration processes, which make use of sulfuric acid, they yield sulfuric muds which constitute a by-product which cannot be easily treated or removed without introducing another source of pollution.

We have now found, and this is the object of our invention, that these pollution-yielding chemical treatments can be replaced by a physical process which is sufficiently efficient to provide for the easy and non-polluting regeneration of important amounts of used oil.

Briefly stated, the invention concerns a process for regenerating used lubricating oil containing soluble metal compounds, which comprises circulating such an oil along a first side of a membrane permeable to hydrocarbons and recovering a purified oil on the other side of the membrane.

The preferred membranes to be used according to the invention are ultrafiltration membranes. By membranes having ultra-filtration properties, we mean membranes which can be traversed by elements of small size, for example molecules of solvent, and which can retain elements, for example molecules, of larger size.

Although the use of ultrafiltration membranes for purifying organic liquids such as oils is not new, it could not be expected that good results would be obtained with modern lubricating oils which contain not only mineral oil but also additives of various types, for example oil-soluble metal salts or complexes. It could not be expected that the ultrafiltration membranes would selectively retain these soluble metal additives or the products derived therefrom.

In this process, we preferably use an ultrafiltration membrane having a cut zone of from 5,000 to 300,000, preferably 10,000 to 100,000.

By cut zone of an ultrafiltration membrane we mean the approximate molecular weight constituting the limit between the molecular weights of the proteins retained by the membrane and the molecular weights of the proteins not-retained by the membrane, provided the aqueous solution of these proteins is ultra-filtrated under a pressure of about 2 bars.

As ultrafiltration membranes, we preferably use those formed of the following materials: cellulose, cellulose esters, polytetrafluoroethylene, polypentaerythritol, sulfonated polystyrene, quaternary ammonium salts obtained from dialkylamino polystyrene; ionically cross-linked complex polyelectrolytes manufactured from a polymer having sulfonic group and a polymer having quaternary ammonium groups, these polymers being preferably individually insoluble in water and hydrocarbons; sulfonated polyarylethersulfones; polyethylene, polypropylene, polymers of 2-chlorobutadiene; butadiene-styrene copolymers; vulcanized natural rubber; isoprene-isobutene copolymers; copolymers of acrylonitrile and ionic monomers, specially those subjected to thermal water treatment. In these various polymers, the molecular weight and the content of ionic groups are such as to make the membranes, used according to the invention, insoluble in the treated oils.

Useful membranes are described in the French Pat. Nos. 2,105,306 and 2,105,502 and the Belgian Pat. Nos. 785,741 and 783,835.

Other useful membranes contain the following materials: polyisoprene, polybutadiene, copolymers of butadiene with acrylonitrile having a low content of nitrile groups; butyl rubber, ethylene-propylene copolymers having short molecular chains, such as EPR-EPDM-EPT.

These materials may be used as such or charged with products conventionally used for this operation.

Although, when treating used oils of low viscosity, the ultrafiltration of the oil may be carried out without solvent, we prefer to operate with a solution of the oil in a solvent, so as to reduce its viscosity.

It has been found that the ultrafiltration of used oils in solution could be advantageously carried out with oil-solvent mixtures having an oil content of, for example, 10 to 50 % by volume (v/v), preferably 15 to 35 % by volume (v/v).

The solvent is preferably selected from the light hydrocarbons, so that it may be easily separated from the oil. We shall mention, for example, among the light hydrocarbons: propane, butane, pentane, hexane, heptane, petroleum ether or a light gasoline cut. As other solvents, we can mention lower cyclanic and aromatic hydrocarbons and chlorinated hydrocarbons. The conditions of temperature and pressure must be such as to maintain the oil-solvent mixture in the liquid state.

When using a temperature higher than room-temperature, i.e., higher than 20.degree.C, the viscosity of the feed charge is reduced, its flow through the ultrafiltration modules, becomes easier and the flow rate of the oil through the membrane is increased. In any case, this temperature must be compatible with the membrane resistance, so that temperatures higher than 70.degree. to 80.degree.C should be avoided.

An efficient means for increasing the oil passage rate consists of increasing the difference between the respective pressures on both sides of the membrane. Although, beyond a given pressure difference, the polarization phenomena tend to reduce the so-obtained gain, so that pressure differences in excess of 10 to 15 atmospheres are not advantageous in practice. Pressure differences of from 0.2 to 10 atmospheres are thus preferred.

The oil flow rate is preferably higher than 0.5 m/sec, so as to reduce the polarization effect, and preferably lower than 3 m/sec, so as to avoid too high flow rates. By providing turbulence promoters consisting of a grid or excrescences placed cross-wise with respect to the flow direction, we obtain high oil passage rates while reducing the oil flow rate.

We can also operate by merely agitating the oil or its solution in the vicinity of the ultrafiltration membrane. The oil is preferably circulated in the form of a liquid layer whose thickness ranges from 0.5 to 5 millimeters.

Although we prefer the embodiment which consists of filtering under relative overpressure (ultrafiltration), we can also operate by dialysis, with or without overpressure, by providing, in that case, a solvent of the oil in contact with the second face of the membrane.

The membranes which can be used for ultrafiltration may often be also used for dialysis.

An advantage of the dialysis technique results from the possibility of fractionating the regenerated oils.

FIGS. 1-5 illustrate different systems of apparatus for carrying out the process of the invention.

The apparatus preferably comprises one or more, preferably serially disposed, cells and evaporators for concentrating the collected oil.

A cell consists, for example, of membranes arranged in a parallel direction between plates, so as to constitute enclosures through which the feed charge is circulated. The used oil is fed through line 3 of FIG. No. 1 to the enclosures 1 and the solvent through line 4 to the enclosures 2. A solution of purified oil in the solvent is discharged through line 5 and the residue through line 6.

FIG. 2 illustrates the dialysis embodiment. The feed charge consisting of a mineral oil containing dissolved or suspended impurities is supplied, as such or diluted in the extraction solvent, to the cell I (FIG. 2) through line 11 and is thus contacted with the dialysis membranes. It is discharged through line 12 with a lower content of mineral oil and a higher content of solvent, which solvent has been passed through the membrane in a direction opposite to that of the extracted oil.

The residue is supplied from line 12 to the evaporator 13 (the valves 28 and 29 are closed and the valve 27 open) where it is made free of its solvent; it is discharged through lines 14 and 15 (the valve 30 is closed).

The solvent is supplied to cell I through line 16 (the valves 17 and 18 are closed and the valve 19 is open and is discharged through line 20 with a higher mineral oil content; the oily solution is supplied to evaporator 21 wherefrom the solvent is discharged through line 22 (the valve 23 is closed). The dry dialyzed oil is recovered in line 24. The solvent vapors are circulated through line 22 and supplied to condenser 25, while the recovered liquid solvent accumulates in tank 26 and is recycled to cell I.

The extraction efficiency may be increased by providing two or more serially arranged cells. The solvent-containing residue which is discharged from cell I through line 12 may be fed to cell II where it is re-extracted (valve 27 closed and valves 28 and 29 open); it is then supplied through line 12 to evaporator 13. The collected residue is discharged through purge pipe 15 or partly recycled through line 31 to the main feed pipe (valve 30 is open) when it has a too high content of mineral oil

The solvent is supplied through line 16 (valve 19 is open and valves 17 and 18 are closed) to cell II where it extracts a portion of the mineral oil; the resulting oily solution is fed through line 32 to cell I, where its content of mineral oil increases again. The dialyzate is then fed to evaporator 21 wherefrom mineral oil is discharged through line 24.

Dialyzed oils of various viscosities may be also manufactured from the same charge of used oil. The feed charge is circulated as above from one cell to another cell while pure solvent is supplied to each cell (the valves 17, 19, 23 and 33 are open while the valve 18 is closed); the resulting dialyzates are fed to the evaporators 21 and 35, one through line 20 and the other through line 34, we obtain in line 36 an oil of greater viscosity than the oil of line 24.

The following examples illustrate the invention:

EXAMPLE 1

The experiment is carried out with used oil consisting mainly of used motor oil; this oil is subjected to steamstripping at 160.degree.C for removal of the lightest constituents thereof.

We use an ultrafiltration cell comprising membranes arranged on parallel fritted metal plates, so that compartments are designed, through which the liquid to be treated is passed at a substantially uniform circulation velocity. By maintaining a sufficient circulation velocity, the so-called polarization effects are reduced, said effects consisting in the formation of an impurity rich zone close to the interface, which results in a reduction of the ultrafiltrate flow rate.

The arrangement is shown in FIG. 3. A mixture of oil and hexane is supplied through pipe 51; the solvent to oil ratio is 2:1 by volume. Pump P.sub.1 feeds the ultrafiltration module M I, provided with a membrane having a surface of 500 cm.sup.2, at a rate of 500 cc of mixture per hour. The membrane employed is made of a copolymer of acrylonitrile and sodium methallylsulfonate which has been subjected to a hot water treatment. The recirculation pump P.sub.2 arranged on line 53 maintains a flow rate of the mixture oil/hexane along the membrane of 1 meter per second. The ultrafiltration temperature is 25.degree.C. Two fractions are discharged from the module. The fraction discharged from line 52 consists of an impurity concentrate and a hexane fraction. Valve V I is so regulated as to maintain a pressure difference of 2 atmospheres between the two compartments of the cell. The ultrafiltrate discharged through pipe 54 consists of the treated oil and the solvent fraction which is simultaneously discharged. The oil yield is defined as the ratio (% by weight) of the oil discharged through 54 to the oil charged in 51: it is 80 %. We have observed that the solvent filters at a higher speed than the oil, so that the ratio by volume of the solvent to the oil is only 1.17 in the mixture discharged through pipe 52.

The analysis by emission spectrometry, before and after treatment, shows a substantial reduction of the amount of most additives.

______________________________________ Content before Content after Elements ultrafiltration ultrafiltration (ppm by weight) (ppm by weight) ______________________________________ B <10 <10 Fe 128 <10 Cu 28 25 Mg 52 <10 Si 22 <5 Al 23 <10 Cr <10 <5 Ca 970 100 Ba 1800 <10 Pb >250 250 P 470 450 ______________________________________

In order that the treatment of the used oil by ultrafiltration be economically attractive, it is important to obtain a high oil yield. This yield can be increased by increasing the surface of the membrane, the pressure difference or the solvent ratio, but these methods result in a substantial increase of the cost of the treated oil. An advantageous solution consists of operating according to the method illustrated in Example 2.

EXAMPLE 2

The oil to be treated is the same as in Example 1. 170cc per hour of this oil (pump P.sub.4) and 170 cc per hour of hexane (pump P.sub.5) are supplied and the mixture is fed through pipe 62 to the ultrafiltration module M I which is provided with a membrane of a surface of 430 cm.sup.2. The membrane is the same as in Example 1 and there is applied a difference of pressure of 2 atmospheres between the two compartments separated by the membrane.

The ultrafiltration temperature is 25.degree.C. A circulation velocity of 1 meter per second is applied by means of a recirculation pump not shown on the drawing. 258 cc per hour of mixture is recovered from pipe 59; after separation of the solvent, 118 cc per hour of treated oil is obtained. The mixture with an increased impurity content is recovered from pipe 64 and passed through pump P.sub.8 ; it is admixed with 170 cc per hour of solvent supplied from pump P.sub.7 and pipe 58 and fed through pipe 63 to a second filtering module M II, which is provided with a membrane having a surface of 70 cm.sup.2. The difference of pressure between the two compartments separated by the membrane is 2 atmospheres, the ultrafiltration temperature 25.degree.C and the circulation velocity 1 meter per second. 120 cc per hour of mixture is collected in pipe 60; after separation of the solvent, the flow rate of treated oil is 30 cc per hour. The oil of higher impurity content is discharged through line 61.

By working in this manner, we obtain a higher oil yield for a given total surface of the membrane and the same solvent proportion.

The number of serially arranged stages is not necessarily limited to 2 and the arrangement of FIG. 4 may be used with any number of stages.

When working with several stages, it is possible, with the same total solvent proportion, to obtain a higher proportion of solvent in the cell operated with the product of higher impurity content and to compensate at least partly for the decrease of the oil flow resulting from an increase of the impurity proportion.

A reduction of the solvent proportion is possible provided there is used the ultrafiltrate of high solvent proportion from the module M II as the dilution liquid for the oil charged to the module M I. This method is illustrated by Example 3 (FIG. 5).

EXAMPLE 3

We have treated the same oil as in Example 2. The pump P.sub.10 feeds the pipe 65 with 140 cc of this oil which is admixed with 200 cc per hour of the recycled material supplied through pipe 66. This mixture is supplied through pipe 73 to the ultrafiltration unit M I, which has the same membrane and the same membrane surface as in Example 2.

The difference between the respective pressures applied on each side of the membrane is 2 atmospheres, the ultrafiltration temperature 25.degree.C and the circulation flow rate 1 meter per second. 270 cc per hour of mixture is discharged through pipe 70 and, after solvent separation, 125 cc per hour of treated oil. The mixture of increased impurity content is discharged through pipe 71 and passed through pump P.sub.12, admixed with 200 cc per hour of solvent supplied from pump P.sub.11 and pipe 67 and passed through pipe 72 to the ultrafiltration unit M II, whose membrane surface is 100 cm.sup.2 ; the difference between the respective pressures on each side of the membrane is 2 atmospheres, the ultrafiltration temperature is 25.degree. C and the circulation flow rate 1 meter per second. 200 cc per hour of mixture is discharged through pipe 69, said mixture being recirculated through pump P.sub.13. 70 cc per hour of mixture is discharged through pipe 68 and, after solvent separation, 15 cc per hour of an impurity concentrate. When operating industrially, each stage may consist of several filtration zones serially arranged, each zone being provided with its recirculation device. In this manner, the ultrafiltration rate is higher than that obtained in units arranged in parallel or provided with only one recirculation device since the concentration of impurities increases only stepwise from one unit to another.

EXAMPLE 4

5 cc of used oil are diluted with 45 cc of n-hexane (the specific viscosity of the mixture is 0.3 at 25.degree.C).

This mixture is subjected to ultrafiltration in an ultrafiltration cell having the following characteristics:

no recirculation

nature of the membrane: a complex polyelectrolyte based on a mixture of two copolymers, a copolymer of acrylonitrile and sodium methallylsulfonate, on the one hand, and a copolymer of acrylonitrile and vinylpyridine quaternized with methyl sulfate, on the other hand. Its permeability to water under 2 bars is 20 m.sup.3 /day.m.sup.2 ;

cut zone: 20,000

useful surface of the membrane: 12.5 cm.sup.2

differential pressure between the two sides of the membrane: 2 bars;

stirring of the used oil at the membrane surface by means of a rotative magnetic rod;

temperature: 20.degree.C

We have collected 40 cc of ultrafiltrate at an average rate of 1,900 liters/day.m.sup.2. This ultrafiltrate is evaporated by distillation in a rotative evaporator under a pressure reduced down to 5 cm Hg (absolute pressure).

We have obtained 4 cc of a residue consisting of purified oil. The productivity was 190 liters/day.m.sup.2, with respect to the membrane surface.

Compared properties of the used oil and the purified oil (the content of sulfuric ashes is determined according to the method AFNOR NF 07037 of May 1970):

Content of sulfuric ashes of the used oil: 1.05 %

Content of sulfuric ashes of the purified oil: 0.16 %

EXAMPLE 5

We have repeated example 4, except that we have used a mixture obtained by diluting 10 cc of used oil with 40 cc of n-hexane (specific viscosity of the mixture: 0.8).

We have collected 40 cc of ultrafiltrate (average flow rate: 1273 liters/day.m.sup.2) which has resulted in 8 cc of purified oil (productivity: 255 liters/day.m.sup.2).

EXAMPLE 6

We have repeated Example 4, except that we have used a mixture obtained by diluting 20 cc of the used oil with 30 cc of n-hexane (specific viscosity of the mixture: 2.8).

We have collected 40 cc of ultrafiltrate (average flow rate: 485 liters/day.m.sup.2) which has resulted in 16 cc of purified oil (productivity: 194 liters/day.m.sup.2).

EXAMPLE 7

We have subjected to ultrafiltration a mixture obtained by diluting 300 cc of used oil with 1700 cc of n-hexane.

The used oil was the same as in Examples 4-6.

The ultrafiltration apparatus was provided with a device for recirculating liquid to the membrane inlet, this device permitting the circulation of the mixture to be ultra-filtrated at the membrane surface.

The membrane was the same as in Example 1, and its useful surface was 110 cm.sup.2. The velocity of the mixture to be ultra-filtrated at the membrane surface was 1.1 m/sec. The differential pressure between the two sides of the membrane was 2 bars.

The temperature was 23.degree.C

We have collected 1,500 cc of ultra-filtrate which was evaporated as in Example 1 (average flow rate: 935 liters/day.m.sup.2)

We have obtained 225 cc of a residue consisting of a purified oil (productivity : 141 liters/day.m.sup.2) having a sulfuric ash content of 0.15 %.

EXAMPLE 8

Example 7 was repeated, except that the treated mixture consisted of 500 cc of used oil and 1500 cc of n-hexane (specific viscosity of the mixture: 1).

We have collected 1500 cc of ultrafiltrate (average flow rate: 698 liters/day.m.sup.2) which resulted in 375 cc of a purified oil (productivity: 174 liters/day.m.sup.2) having a sulfuric ash content of 0.16 %.

EXAMPLE 9

Example 7 is repeated, except that the treated mixture consists of 700 cc of used oil and 1300 cc of n-hexane.

1500 cc of ultrafiltrate is recovered (average rate: 458 liters/day.m.sup.2), which yields 525 cc of purified oil (productivity: 160 liters/day.m.sup.2).

EXAMPLE 10

Example 8 is repeated, except that the liquid to be treated is circulated along the membrane surface at a velocity of 2.3 m/s.

1500 cc of ultrafiltrate is collected; its average flow rate is 976 liters/day.m.sup.2. We have obtained 375 cc of purified oil (productivity: 244 liters/day.m.sup.2).

EXAMPLE 11

Example 8 is repeated by providing the ultrafiltration apparatus with a polypropylene grid arranged on the membrane. This grid constitutes a turbulence promoter; it consists of two layers of straight wires all arranged in parallel in both layers (diameter of the wire: 1mm; mesh size: 5mm; angle of the wires: 120.degree.).

1500 cc of ultrafiltrate is collected at an average flow rate of 3195 1/day.m.sup.2, which yields 375 cc of purified oil (productivity: 798 liters/day.m.sup.2); content of sulfuric ash: 0.125 %.

EXAMPLE 12

The experiment is carried out with used oil mainly consisting of used motor oil made free of its lightest constituents by steam-treatment at 160.degree.C. We use a dialysis membrane of polyisoprene arranged in a dialysis cell.

Used oil feedstock: 1,000 Kg

Flow rate of the used oil: 192 liters/hour

Flow rate of the solvent (hexane): 500 liters/hour

Dialysis temperature: 30.degree.C

Membrane surface: 20 m.sup.2

Membrane thickness: 50 microns

Weight of dialyzed oil: 745 Kg

Time: 4.04 hours

Extraction yield: 74.5 %

Viscosity of the dialyzed oil: at 37.8.degree.C:30 centistokes

Viscosity of the dialyzed oil: at 98.9.degree.C:5.25 centistokes

ASTM color: 5

Membrane efficiency (weight of oil/hour/m.sup.2 of the membrane): 9.2 kg/hour/m.sup.2.

The absence of carbonyl bands in the IR spectrum of the dialyzed oil shows that the viscosity index polymers of the polyester type have been removed.

EXAMPLE 13

The used oil of example 12 is employed again, but two cells are used and their dialyzates are separately concentrated.

The feed rates are the same as above, the surface of the polyisoprene membrane being 40 m.sup.2.

Dialyzed oil of cell No. 1

Viscosity at 37.8.degree.C: 27 cst

Viscosity at 98.9.degree.C: 5.05 cst

Dialyzed oil of cell No. 2

Viscosity at 37.8.degree.C: 50.7 cst

Viscosity at 98.9.degree.C: 6.8 cst

These two oils have been admixed for analysis.

The results of emission spectrometry given in the following table show that the detergent and antioxidant additives of organometallic nature are practically completely removed by the treatment, whereas the other impurities are reduced in a large proportion.

______________________________________ Elements Content before dialysis Content after dialysis ppm by weight ppm by weight ______________________________________ B 8 1 Fe 128 <5 Pb >250 230 P 460 260 Sn <5 <5 Cu 28 5 Mg 52 <2 Si 22 22 Al 23 <5 Ni <5 <5 Cr 5 <5 V <5 <5 Ca 970 4 Ba 1800 0 Zn 590 5 ______________________________________

Content of sulfate ashes: <0.1 %

EXAMPLE 14

The same used oil as in Examples No. 12 and 13 is treated with an ultra-filtration membrane of cellulose ester whose pores have a diameter of about 100 Angstroms; the temperature and feed rates are unchanged.

Membrane surface: 20 m.sup.2

Dialyzed oil: 760 kg

Time: 4 hours

Extraction yield: 76 %

Viscosity of the dialyzed oil: 7.47 cst at 98.9.degree.C

ASTM color: 8

Membrane efficiency: 9.5 kg/hour/m.sup.2

The analysis of the dialyzed oil shows an impurity content higher than that observed according to the prior example:

Pb = 300 ppm by weight

Cu = 17 ppm by weight

Mg = 20 ppm by weight

Ba = 300 ppm by weight

Ca = 300 ppm by weight

Zn = 220 ppm by weight

P = 450 ppm by weight

EXAMPLE 15

We have used the same membrane as according to Example No. 1 in order to treat the same oil as according to Examples 12-14; the temperature and feed rates were unchanged.

Membrane surface: 20 m.sup.2

Membrane thickness: 40 microns

Dialyzed oil: 465.5 Kg

Time: 2.5 hours

Extraction yield: 46.55 %

Viscosity of the dialyzed oil: at 37.8.degree.C: 43.1

(in centistokes): at 98.9.degree.C: 6.4

Performance: 9.3 kg/hour/m.sup.2

Sulfate ash content: 0.07 %

Astm color: 5

Analysis of the oil by emission spectrometry:

Elements Content before dialysis Content after dialysis ppm by weight ppm by weight ______________________________________ Ca 460 <50 Pb 620 160 Zn 540 <50 P 520 360 Ba 1150 <50 Fe 200 <5 Mg 85 <5 Cu 35 <5 Si 35 18 Na 35 <5 Cr 10 <5 Al 10 <5 Li 10 <5 Mo 10 <5 Sn 10 <5 B 10 <5 Mn <10 <5 Ni <10 <5 Sr <35 <5 Cl 1700 715 N 910 150 S 10030 9600 ______________________________________

The absence of carbonyl bands in the IR spectrum of the dialyzed oil shows that the V.I. polymers of the polyester type have been removed.

Claims

What we claim is:

1. A process for regenerating a used lubricating oil containing at least one soluble metal compound of lead, calcium, barium, magnesium, zinc or aluminum, which comprises circulating said oil along a first face of a membrane permeable to hydrocarbons and collecting a purified oil on the second face of the membrane, said membrane having a cut zone in the range of from 5,000 to 300,000.

2. A process according to claim 1, wherein the pressure applied to the first face of the membrane is higher than the pressure applied to the second face thereof.

3. A process according to claim 1 wherein an extraction solvent is circulated in contact with the second face of the membrane.

4. A process according to claims 1, wherein the content of soluble metal compound of the oil is 0.1-10 % by weight, expressed as metal.

5. A process according to claim 1, wherein the soluble metal compounds comprise at least one of calcium, barium, magnesium, zinc or aluminum salicylates, sulfonates, phenates, phosphonates or thiophosphonates or the decomposition products thereof.

6. A process according to claim 1, wherein the soluble metal compound comprises a lead compound.

7. A process according to claim 1, wherein the oil contains viscosity index polymeric additives or their decomposition products.

8. A process according to claim 1, wherein the process is that of ultrafiltration and the membrane is an ultrafiltration membrane.

9. A process according to calim 1, wherein the membrane is a membrane whose cut zone is in the range of from 10,000 to 100,000.

10. A process according to claim 1, wherein the ultrafiltration membrane comprises a material selected from the group consisting of cellulose, cellulosic esters, polytetrafluorethylene, polychlorotrifluorethylene, crosslinked or vulcanized organopolysiloxanes, polypentaerythritol, sulfonated polystyrene, quaternary ammonium salts of dialkylamino polystyrene, the ionically cross-linked complex polyelectrolytes obtained from a polymer containing sulfonic groups and a polymer containing quaternary ammonium groups, sulfonated polyarylether sulfones, polyethylene, polypropylene, polymers of 2-chloro butadiene, butadienestyrene copolymers, vulcanized natural rubber, isopreneisobutene copolymers and copolymers of acrylonitrile with ionic monomers.

11. A process according to claim 1, wherein the used lubricating oil is filtered in the form of an oilsolvent mixture having an oil content of from 10 to 50 % by volume.

12. A process according to claim 1, wherein the used lubricating oil is filtered in the form of an oilsolvent mixture having an oil content of from 15 to 35 % by volume.

13. A process according to claim 1, wherein the oil is diluted with a solvent, said solvent being separated from the oil after treatment and recycled.

14. A process according to claim 1, wherein a portion of the oil of higher impurity content, when withdrawn from the filtration zone, is recycled to the inlet of the latter zone.

15. A process according to claim 1, wherein the oil or the mixture of oil and solvent is circulated along the membrane at a velocity of from 0.5 to 3 m/s.

16. A process according to claim 1, wherein the oil is circulated in the form of a layer of a 0.5-5 mm thickness.

17. A process according to claim 1, wherein a turbulence promoting grid is present in the path of the oil.

18. A process according to claim 1, wherein the pressures applied to each side of the membrane differ by 1-15 atmospheres.

19. A process according to claim 13, wherein the solvent is a hydrocarbon or a hydrocarbon mixture.

20. A process according to claim 19, wherein the hydrocarbon is propane, butane, pentane or hexane.

21. A process according to claim 13, wherein the process is operated in a plurality of serially arranged stages, the solvent being introduced fractionwise at the inlet of each stage.

22. A process according to claim 13, wherein the process is operated in a plurality of serially arranged stages, the oil fed at each stage being admixed with the filtration product of at least one following stage, the solvent being fed at the inlet of the last stage and the solution of regenerated oil consisting of the filtrate of the first stage.

23. A process according to claim 13, wherein the process is operated in two serially arranged stages, the charged oil being admixed with the filtration product from the second stage, the solvent being fed at the inlet of the second stage and the solution of regenerated oil consisting of the filtrate of the first stage.

24. A process according to claim 13, wherein the process is operated in a plurality of stages, each stage comprising several serially arranged filtration zones, each of them having its own recirculation circuit.

25. A process according to claim 3, wherein the extraction solvent is circulated in counter-current with respect to the oil.

26. A process according to claim 1 wherein the process is that of dialysis.