WO1996000273A1

WO1996000273A1 - Process for the reclamation of used lubricating oils

Info

Publication number: WO1996000273A1
Application number: PCT/US1995/007987
Authority: WO
Inventors: Giora HÖNIG
Original assignee: Corex Technologies (1993) Ltd.; Golan, Gadi
Priority date: 1994-06-23
Filing date: 1995-06-23
Publication date: 1996-01-04
Also published as: IL110104A; ZA955135B; AU3124695A; IL110104A0

Abstract

A process for the reclamation of used oils comprises the steps of: subjecting the crude, used oil to centrifugation; contacting the centrifugated oil with diammonium phosphate and/or oxalic acid in aqueous solution; and separating the oil phase and aqueous pohase thus produced.

Description

PROCESS FOR THE RECLAMATION OF USED LUBRICATING

OILS

Field of the Invention

This invention relates to a process for the reclamation of used oils, particularly lubricating oils, viz. for the removal of impurities contained therein as a result of their use and/or of the additives, such as generally used in the lubricating oil art.

Background of the Invention

The disposal of waste oils poses important practical problems, in view of the very large amount in which they are generated in technology and industry. The most desirable way of disposing of these oils is, of course, reclaiming them so that they can be reused, thereby on the one hand recovering valuable products and on the other hand removing environmental contamination.

The art has dealt with the used oil reclamation problem for a number of years, and has developed several processes. Typically such processes involve adding suitable agents that will cause the transportation of the contaminants and separating such contaminants by various physical treatment means. As an example, in a classic, well known process, the contaminants are precipitated by means of an acid treatment, e.g. by the addition of concentrated sulfuric acid. Acid sludge is separated, the remaining product is neutralized by adding lime and clay and a main sludge is produced by sedimentation. The product from which the sludge has been separated is subjected to vacuum distillation and the sludge is disposed of. This process produces a large amount of sludge, about 30% of the volume of the dried oil, thereby creating a serious disposal problem, and causing the loss of a substantial percentage of the useful oil.

In other processes, solvents are used in place of acid to precipitate the contaminants.

British Patent Specification 1598723 discloses an oil reclamation process which comprises compacting the used lubricating oil with an aqueous solution of a treating agent, consisting essentially of an ammonium salt, under conditions of temperature, pressure and time sufficient to disperse the agent in the used lubricating oil and to react the agent with the ash- forming components of the used oil, removing a major portion of water from the resulting mixture by distillation, separating the oil phase from the mixture resulting from the last-mentioned step, and thereafter recovering the resulting oil phase as a product of the process. This process involves operations at high temperature and pressure, long treating times, and a high consumption of energy for water distillation. It does not remove all the additives and no organometallic disconnection occurs. Excess reactants cannot be recycled and must be discarded with the heavy metals. Polymers, usually contained in modern multigrade oils, cause filtration problems. Further, it requires two finishing treatments and cannot be easily integrated into existing plants. Portuguese Patent Specification No. 94502 discloses a process for demetallizing oils which comprises heating the oil to a temperature from about 70°C-130°C, heating an aqueous solution containing 3-6% by weight of ammonium bisulfate (NH₄)HS0 , adding ethoxynonane heated to at least 80°C to the said solution, mixing the oil and the resulting solution, and separating the oily from the aqueous phase while the solution is maintained at a temperature higher than 80°C. This process however does not permit to demetallize the oils to the required degree and does not remove organic compounds (such as succinic acid, sulfonates, esters, and the like) that are usually present and have a negative effect on the conventional after-treatments of the recovered oils. Further, it requires to maintain the oil at a relatively high temperature.

U.S. P. 4,250,021 discloses a treatment of used oils which comprises treating the oil with an aqueous solution containing a surfactant and anions which form an insoluble salt with at least one metal present in the oil. Said treatment has the disadvantage of requiring the use of a surfactant. Metal removal is not fully satisfactory unless multi-step contacting of the oil with the treating solution, preferably followed by washing, is not resorted to. Further, there takes place dilution of the aqueous solution, separated from the oil after treatment, by the water present in the oil, which requires the addition of treating chemicals to maintain the desired concentrations, thereby causing build-up of the treating solution in its repeated use and waste of chemicals. It is a purpose of the invention to provide a process for the reclamation of used oils that is free from the drawbacks of previously known processes.

It is another purpose of the invention to provide such a process which a affords high reclamation yields.

It is a further purpose of this invention to provide such a process which does not require the use of pressure or of excessively high temperatures .

It is a still further purpose of this invention to provide such a process that achieves a highly effective separation of metals and additives from the treated oil.

It is a still further purpose of this invention to provide such a process that is essentially a single-step treatment.

It is a still further purpose of this invention to provide such a process that permits reuse of the recovered treating solution.

It is a still further purpose of the invention to provide such a process in which the required separation operations are extremely simple and efficient.

It is a still further purpose of the invention to provide such a process which requires economical and easily available treating agents. Other purposes and advantages of the process will become apparent as the description proceeds.

Summary of the Invention

The process according to the invention is characterized in that it comprises the steps of:

- subjecting the crude, used oil to centrifugation, particularly to separate water and solid impurities; contacting the centrifugated oil with diammonium phosphate and/or oxalic acid in aqueous solution, preferably at a temperature not substantially lower than 60°C and not substantially higher than 85-90°C: and

- separating the oil phase and aqueous phase thus produced, preferably by centrifugation.

The first, centrifugation step is carried out by two-phase or, preferably, three-phase centrifuges, capable of separating particles of less than 0.5 μ dimensions.

The oxalic acid and diammonium phosphate (hereinafter also "the treating agents") , when both are used in the second step of the process, may be contacted with the used oil by dissolving them in water and adding their solution to the oil, or two solutions, one of oxalic acid and one of diammonium phosphate, may be prepared and successively added to the oil, the two aqueous phases becoming mixed after their addition to the oil. The mixture of the oil with the solution(s) of oxalic acid and diammonium phosphate is carried out at a temperature from 50 to 100°C and preferably at about 80-85°C. The oil and the solution or solutions of treating agents may be previously heated to the desired mixing temperature and successively mixed at said temperature, or at least one of said components may be previously heated to a higher temperature, so that when they are mixed, the temperature will be lowered to the desired mixing temperature.

Oxalic acid and diammonium phosphate are used in amounts, by weight with respect to the oil, from 0.5 to 6%. and preferably from 2.5 to 5% for oxalic acid, and from 0.5 to 6% and preferably from 2.5 to 4.5% for diammonium phosphate. If only one of them is used, it is used in an amount of about 4 to 8%. If oxalic acid and diammonium phosphate are dissolved together in a single aqueous solution, their concentrations in said solution are respectively from 2 to 16% and from 2 to 17%. If separate solutions of oxalic acid and diammonium phosphate are prepared and successively added to the oil, their concentration should be such that if they were previously mixed they would provide a solution having the concentrations of oxalic acid and diammonium phosphate respectively from 4 to 20% and from 4 to 22%.

The separation of the aqueous phase from the oil phase of the mixture of oil and solutions of treating agents, which is the third step of the process, is carried out either by dynamic means, e.g. centrifugation or filtration, e.g. membrane filtration, or by a combination of the addition, to said mixture of oil and solutions of treating agents, of an emulsion-breaking agent (hereinafter also "the third treating agent") and gravitational separation, e.g. decantation. When dynamic means are used, two-phase or preferably three-phase centrifugation is employed, by the same means by which the first, centrifugation steps is carried out. The emulsion- breaking agent, when used, is an alkylphenol, preferably nonylphenol, which may be added to the solution of oxalic acid or of diammonium phosphate or to both, or may be added separately to the oil, the oil and aqueous phase being then separated by decantation. When no emulsion- breaking agent is present, reaction temperatures of 60°C. and occasionally even lower, can be used.

The process can be carried out either continuously or batchwise, as desired. The aqueous solution of treating agents may be reused with a small make-up. The reuse eliminates disposal or reaction with metals from tap water. The small amount of heavy sludge produced can be either used in the lead or nuclear industry, or disposed of in the cement industry. The reclaimed oil may be further distilled in high vacuum distillation and hydrogenated to minimize halogen and sulfur content, and maximize yield.

Description of the Drawings

In the drawings:

- Figs. 1 and 2 are two block diagrams illustrating two alternative ways of carrying out the process of the invention. Detailed Description of Preferred Embodiments

By way of illustration, the treatment of a specific used oil will now be described. The used oil has the properties set forth in the following table.

Table I

Characteristics Test Units Used Treated Light Heavy oil oil oil oil

Color ASTM Black Brown 1.5 L2.0 D1500

Flash point ASTM C 170 180 220 245 D92

Total acid number ASTM mg 2.5 2.5 0.03 0.03

D664 KOH/g

Ash content ASTM g/100g l.4 <0.1 0 0 D482

Oxidation Stability DIN g/100g- - 0.42 0

51352

Sulfur content DIN % 0.85 0.60 0.45 0.45 51400

Metal trace Plasma ppm 6200 <35 <2 <2 elements Emission

Example

The used oil is separated in a centrifuge, of the kind mentioned hereinafter, at ambient or higher temperature, to reduce water content to less than 1% and ash content to less than 2% (centrifuge velocity >4000 rpm). In a 1 liter glass vessel, 500 ml oil is heated to 95°C. In a separate 300 ml glass vessel, 20 mg of oxalic acid (>95%) is dissolved and heated to 85°C in 200 ml of tap water. The solution is added to the oil while continuously stirring. The contents are mixed for five minutes for full contact, always at temperatures from about 80° to about 85°C .

In a separate 300 ml glass vessel, 20 mg diammonium phosphate is dissolved in 100 ml of hot water (85°C). The solution is then added to the previous mixture under stirring for five minutes. The mixture of oil- water-sludge is separated into its several phases through a two- or three- stage centrifuge, followed by oil filtering through a diatomized filter cake.

The oil, containing almost no additives, is charged into a fractional distillation column, or is evaporated in thin film under high vacuum conditions (50-500 MBAR stage I, 2-3 MBAR stage II).

Fig. 1 is a block diagram indicating a first way of carrying out the invention. Solutions of oxalic acid and of diammonium phosphate are separately prepared, and are mixed and heated to the desired temperature. A solution of the emulsion-breaking agent, preferably nonylphenol is prepared and mixed with that of the first two agents - this step being optional, especially if a three-phase centrifugation is used, as shown in the block diagram, and is therefore shown in the diagram in broken lines. The used oil from the storage, after separation therefrom of water and ash by three-phase centrifugation, is mixed with the solution of agents. The mixture is then separated into an oily phase, an aqueous phase and a sludge, by means of a three-phase centrifuge, which may be the same used for the separation of water and ash or a different one. Both centrifuges, as mentioned hereinbefore, must be able to separate particles having dimensions below 0.5 μ. Examples of suitable industrial centrifuges available on the market are Krauss-Maffei AF 2000 SMO, Flottweg Z34-4/053 and Alfa Laval WHPX 413-G.

The aqueous phase can be reused by feeding it back to the mixture phase with a small make-up. The oil phase is subjected to high vacuum distillation, to obtain from it gas oil, light oil and heavy oil, and this latter may be subjected to hydrogenation.

Fig. 2 shows an alternative process flow diagram, which is distinguished from that of Fig. 1 because the three treating agents - oxalic acid, diammonium phosphate and optionally nonylphenol - are added successively to the oil instead of being previously mixed and being added together.

In the example described hereinbefore, the oil and the solutions of oxalic acid and diammonium phosphate are separately heated before mixing to the desired mixing temperature or slightly above it, and the emulsion- breaking additive is not used. As has been mentioned before, the physical conditions at which the mixing is carried out may be varied, and therefore it is possible to heat one of the components of the mixture, particularly the oil, to a higher temperature, and the other component or components to a lower temperature, as long as the appropriate temperature will be obtained when they are mixed together.

The process according to the invention has many advantages over the prior art. It is essentially a one-step process, which does not require multi-step contact or washings, and yet achieves better purification of the oil than prior art processes. It does not require the use of surfactants. It eliminates the build-up of the treating solution, caused by it mixing with the water (that is always present in the crude oil in amounts of 5-10%) which takes place in the prior art processes, and therefore significantly reduces the consumption of chemicals. It removes from the oil, water, metals and additives. It eliminates long term operations, such as hot gravity separation. Because of the said combination of advantages, it is more economical and constitutes a significant improvement over the prior art.

While embodiments of the invention have been described by way of illustration, it will be apparent that the invention may be carried out by persons skilled in the art with many modifications, variations and adaptations, without departing from its spirit and the scope of the claims.

Claims

C L A I M S

1 - Process for the reclamation of used oils, characterized in that it comprises the steps of:

- subjecting the crude, used oil to centrifugation; contacting the centrifugated oil with diammonium phosphate and/or oxalic acid in aqueous solution; and

- separating the oil phase and aqueous phase thus produced.

2 - Process according to claim 1, wherein the centrifugated oil with diammonium phosphate and/or oxalic acid at a temperature not substantially lower than 60°C.

3 - Process according to claim 2, wherein the centrifugated oil with diammonium phosphate and/or oxalic acid at a temperature not substantially lower than 80°C.

4 - Process according to claim 3, wherein the centrifugated oil is contacted with oxalic acid and/or ammonium phosphate at temperatures between 80° and 90°C.

5 - Process according to claim 3, wherein the oil phase is separated from the aqueous phase by centrifugation. 6 - Process according to claim 1 or 5, wherein the centrifugation steps are carried out by three-phase centrifuges capable of separating particles of less than 0.5 μ dimensions.

7 - Process according to claim 1, further comprising reusing the aqueous phase separated from the oil with a small make-up.

8 - Process according to claim 1, wherein the oxalic acid and diammonium phosphate are contacted with the used oil by dissolving them in water and adding their solution to the oil.

9 - Process according to claim 1, wherein two solutions, one of oxalic acid and one of diammonium phosphate, are prepared and successively added to the oil, the two aqueous phases becoming mixed after their addition to the oil.

10 - Process according to claim 1, wherein the mixing of the oil with the solution(s) of oxalic acid and diammonium phosphate is carried out at a temperature from 50 to 100°C.

11 - Process according to claim 1, wherein the mixing of the oil with the solution(s) of oxalic acid and diammonium phosphate is carried out at the temperature at which the oil is to be contacted with said solutions.

12 - Process according to claim 1, wherein oxalic acid is used in amounts, by weight with respect to the oil, from 0.5 to 6% and preferably from 2.5 to 5% and diammonium phosphate is used in amounts, by weight with respect to the oil, from 0.5 to 6% and preferably from 2.5 to 4.5%.

13 - Process according to claim 1, wherein oxalic acid and diammonium phosphate are dissolved together in a single aqueous solution and their concentrations in said solution are respectively from 2 to 16 % and from 2 to 17%.

14 - Process according to claim 1. wherein separate solutions of oxalic acid and diammonium phosphate are prepared and successively added to the oil, and their concentrations are such that, if they were previously mixed, they would provide a solution having the concentrations of oxalic acid and diammonium phosphate respectively from 4 to 20% and from 4 to 22%.

15 - Process according to claim 1, comprising adding to the oil and/or the oxalic acid and/or ammonium phosphate solution an emulsion breaking agent.

16 -Process according to claim 15, wherein the emulsion-breaking agent is an alkylphenol.

17 - Process according to claim 1, carried out continuously.

18 - Process according to claim 1, carried out batchwise. 19 - Process according to claim 1, comprising further distilling the reclaimed oil in high vacuum distillation and hydrogenating the same.

20 - Process for the reclamation of used oils, substantially as described and illustrated.