Method of removing contaminants from used oil

Information

  • Patent Grant
  • 6398948
  • Patent Number
    6,398,948
  • Date Filed
    Monday, September 18, 2000
    24 years ago
  • Date Issued
    Tuesday, June 4, 2002
    22 years ago
Abstract
In a method of removing acidic compounds, color, and polynuclear aromatic hydrocarbons, and for removing or converting hydrocarbons containing heteroatoms from used oil distillate, phase transfer catalysts are employed to facilitate the transfer of inorganic or organic bases to the substrate of the oil distillate. An inorganic or organic base, a phase transfer catalyst selected from the group including quaternary ammonium salts, polyol ethers and crown ethers, and used oil distillate are mixed and heated. Thereafter, contaminants are removed from the used oil distillate through distillation.
Description




TECHNICAL FIELD




This invention relates generally to the removal of contaminants from used oil, and more particularly to a method of removing acidic compounds, color, and polynuclear aromatic hydrocarbons, and removing or converting heteroatoms from used oil distillates.




BACKGROUND AND SUMMARY OF THE INVENTION




It has long been recognized that used motor oils can be recycled by removing the contaminants which accumulate therein during operation of the motor vehicles in which the motor oils are utilized. Recently, the American Society for Testing and Materials (ASTM) has promulgated its Designation: D 6074-99 wherein the ASTM Committee D-2 on Petroleum Products and Lubricants has promulgated standards for re-refined base oils. Included in Designation: D 6074-99 are numerous attributes of base oils, including attributes relating to physical properties, compositional properties, chemical properties, and toxicological properties.




Prior to World War II, used motor oil was re-refined using a process involving the addition of sulphuric acid in order to separate the contaminants from the useful hydrocarbon components of used motor oil. Re-refining processes of the type involving the addition of sulphuric acid to used motor oil are no longer used because they result in the generation of large amounts of highly toxic acidic sludge which cannot be disposed of economically. Additionally, such re-refining techniques do not fulfill the requirements of ASTM Designation: D 6074-99.




More recently, used motor oils have been re-refined utilizing a process known as hydrotreating. In accordance with the hydrotreating process, used motor oils are treated with hydrogen under high pressure. Hydrotreating is successful in removing olefins and alkanes from used motor oils and can also be used in removing heteroatoms therefrom. However, the hydrotreating process is expensive to the point that it cannot be operated profitably.




U.S. Pat. No. 5,814,207 discloses a used motor oil re-refining method and apparatus wherein up to four evaporators are connected one to another in a series. It will therefore be understood that the apparatus of the '207 patent is expensive to install and use. More importantly, the used motor oil re-refining method of the '207 patent cannot meet the requirements of ASTM Designation: D 6074-99 because it cannot remove heteroatoms and because it cannot meet the toxicological requirements of the designation.




Co-pending U.S. application Ser. No. 09/250,741 filed Feb. 16, 1999, and assigned to the assignee hereof discloses a re-refining process wherein used motor oil is treated with an organic or inorganic base in the presence of a phase transfer catalyst. The process is successful in removing acidic compounds, color, and polynuclear aromatic hydrocarbons and in removing or substituting heteroatoms from used motor oil distillates. Co-pending application Ser. No. 09/265,903 filed Mar. 24, 1999, and also assigned to the assignee hereof discloses a re-refining process wherein used motor oil is contacted with a highly polar organic solvent, such as N, N-dimethylformamide. The process is successful in removing polynuclear aromatic hydrocarbons, sulphur-containing substances, nitrogen-containing substances, and other contaminants from used motor oil and distillates.




The present invention comprises a process for re-refining used motor oils which is an improvement over the process of application Ser. No. 09/250,741. The process of the invention is unique in that it is the only known process which safely and economically fulfills all of the requirements of ASTM Designation: D 6074-99.











BRIEF DESCRIPTION OF THE DRAWINGS




A more complete understanding of the invention may be had by reference to the following Detailed Description when taken in conjunction with the accompanying Drawings wherein:





FIG. 1

is a diagrammatic illustration of a continuous flow apparatus catalyzed base treatment of used motor oil to remove contaminants therefrom.











DETAILED DESCRIPTION




The process of the present invention removes acidic compounds and color from used motor oil and other petroleum distillates. Additionally, the process removes or substitutes hydrocarbons containing heteroatoms, namely chlorine, boron, phosphorous, sulfur and nitrogen from the used motor oil. In removing these classes of compounds, the process uses inorganic or organic bases to catalyze various reactions and to neutralize organic acids. Further, the process is capable of removing polynuclear aromatic hydrocarbons from used motor oil. In removing these contaminants, the process makes use of a class of catalysts known as phase transfer catalysts, which are employed in the process to facilitate the transfer of inorganic or organic bases to the substrate in the used oil.




Examples of phase transfer catalysts that may be utilized in the process include: quaternary ammonium salts, polyol ethers, glycols and crown ethers. Through either the base catalysts or the neutralization reactions, undesirable components of the distillate oil are most often converted to forms that are easily removed from the used oil through distillation. Components that are not removed from the distillate are transposed to forms that may remain in the distillate with no adverse effect on the oil quality.




The invention is capable of operating in either a batch mode or a continuous flow mode. When the process is operated in the continuous flow mode, the catalyst and the base are injected into the used oil and passed through a heat exchanger to increase the temperature of the mixture. The mixture is then pumped through one or more static mixers to thoroughly mix the used oil with the catalyst and base. The mixture is then passed directly to the distillation apparatus, where additional mixing occurs and the catalyst and resulting oil are recovered separately. The catalyst is recovered in a form virtually free of hydrocarbon contamination. However, the catalyst contains small quantities of water, typically less than 1%, which is usable directly in the process.




Although other phase transfer catalysts can be used in the process, the use of ethylene glycol is preferred because, when ethylene glycol is used, the source of the catalyst can be used with glycol-based engine coolants. Thus, the catalyst can be acquired in raw form with little, if any, expenditure.




The relative amounts of base and phase transfer catalyst are predicated upon the level of contamination in the used oil. Thus, used oil containing greater than 500 parts-per-million total organic halogen would require a higher concentration of base and phase transfer catalyst to ensure that the dehalogenation reactions occur within a timeframe suitable for a continuous flow process.




A further benefit of the continuous flow mode is the fact that the only wastewater generated by the process is that which is originally present in the used oil and the small amount present in the base. No further water is required for the process. Additionally, all of the wastewater is recovered following distillation of the water and is therefore acceptable for direct discharge. If further treatment of the wastewater is required, the treatment scheme employed is minimal.




Flow Process




A process for removing contaminants from used motor oil


10


comprising a continuous flow process is shown in FIG.


1


. In the process


10


, the used oil from a source


12


is passed through a used oil feed pump


14


to a heater


16


. At the same time, a 50% aqueous solution of sodium or potassium hydroxide from a source


18


is passed through a caustic feed pump


20


and into the used oil after it passes through and is heated to 70 to 100° C. by a heater


16


. The amount of sodium or potassium hydroxide added to the used oil is such that the concentration of base in the oil, on a dry weight basis, is between 0.5 and 5 weight percent. The used oil and the sodium or potassium hydroxide passes through a caustic mixer


22


and a heater


24


, heating the mixture to 110 to 150° C. The used oil mixture is then passed into a water flash drum


26


where water and a small amount of naphtha are removed through flash outlet


28


. The water flash drum is best operated at atmospheric pressure, thus allowing a higher feed temperature to promote the reactions. However, in principle the flash drum could operate under vacuum. The resultant dehydrated used oil mixture is then removed from the water flash drum


26


through a flash oil outlet


30


.




Ethylene glycol from a source


32


is passed through a catalyst feed pump


34


and into the dehydrated used oil mixture. The amount of ethylene glycol that is added to the used oil is such that the concentration of glycol in the resulting mixture ranges from 1 to 10 weight percent of the used oil. The used oil feed pump


14


, the caustic feed pump


20


, and the catalyst feed pump


34


are each engaged at flow rates that provide the desired amounts of each material. The used oil mixture is passed through a catalyst mixer


36


and a heater


38


, where it is heated to between about 275 and 350° C., and proceeds into a stage I evaporator


40


. Heating the mixture beyond 350° C. is not recommended as temperatures above 350° C. result in excessive cracking of the used oil molecules. The stage I evaporator is typically operated under vacuum, with pressures ranging from about 150 to 300 millimeters. The catalyst and light hydrocarbons are removed through flash catalyst outlet


42


and the oil is removed through oil outlet


44


. Part of the oil passes through a recycle pump


46


and back into the dehydrated used oil mixture after the catalyst mixer


36


, but before the heater


38


.




The remainder of the oil passes through a finishing pump


48


and a heater


50


, where it is heated to from about 300 to 350° C., and into a stage II evaporator


52


. The stage II evaporator operates under vacuum with pressures ranging from 5 to 0.05 millimeters. The stage II evaporator may be operated at lower temperatures and pressures, but this will result in a lower yield of the heavier base oil product. The stage II evaporator separates the oil into three fractions, the viscosities of which depend upon the used oil feed. The table below lists products from a typical used oil feed:





















Fraction




Color




Chlorine




Viscosity













light base oil




<0.5




<5 ppm




100 SUS







medium base oil




<1.0




<5 ppm




150 SUS







heavy base oil




<1.5




<5 ppm




300 SUS







still bottoms




n/a




n/a




n/a















The light base oil is recovered through outlet


54


, the medium base oil through outlet


56


, the heavy base oil through outlet


58


, and the still bottoms through outlet


60


.




The still bottoms resulting from the simultaneous combination of the catalyzed base treatment with distillation yields important properties when combined with asphalt. In general, the still bottoms comprise a high value asphalt modifier, capable of extending the useful temperature range of most straight run asphalts. Specifically, the still bottoms impart favorable low temperature characteristics to asphalt, while maintaining the high temperature properties of the asphalt.




Although preferred embodiments of the invention have been illustrated in the accompanying drawings and described in the foregoing detailed description, it will be understood that the invention is not limited to the disclosed embodiments, but is capable of numerous rearrangements, modifications, and substitutions of parts and elements without departing from the spirit of the invention.



Claims
  • 1. A method of removing contaminants from used oil comprising the steps of:causing a continuous flow of used oil; mixing the used oil with a base introduced at such a rate as to maintain the base at about 1 weight % to about 10 weight % of the used oil; mixing the used oil/base mixture with a phase transfer catalyst introduced at such a rate as to maintain the phase transfer catalyst at about 1 weight % to about 10 weight % of the used oil; heating the composition to a temperature between about 200° C. and about 275° C.; separating the resultant mixture using a first distillation at a temperature of from about 200° C. to about 275° C. and a pressure of from about 100 torr to about 200 torr; and purifying the used oil using a second distillation at a temperature of from about 275° C. to about 300° C. and a pressure of from about 0.05 torr to about 0.20 torr.
  • 2. The method as recited in claim 1 additionally comprising the step of:heating the oil composition obtained from the first distillation to a temperature between about 200° C. and about 300° C.; and mixing the composition after the first distillation but before the second distillation.
  • 3. A method of removing contaminants from used oil comprising the steps of:causing a continuous flow of used oil; mixing the used oil with a base selected from the group including sodium hydroxide and potassium hydroxide introduced at such a rate as to maintain the base at about 1 weight % to about 10 weight % of the used oil; mixing the used oil with ethylene glycol introduced at such a rate as to maintain the phase transfer catalyst at about 1 weight % to about 10 weight % of the used oil; heating the composition to a temperature between about 200° C. and about 275° C.; separating the resultant mixture using a first distillation at a temperature of from about 200° C. to about 275° C. and a pressure of from about 100 torr to about 200 torr; and purifying the used oil using a second distillation at a temperature of from about 275° C. to about 350° C. and a pressure of from about 0.05 torr to about 0.20 torr.
CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 09/418,448 filed Oct. 15, 1999, now U.S. Pat. No. 6,179,999, which is a continuation-in-part of application Ser. No. 09/250,741 filed Feb. 16, 1999, now U.S. Pat. No. 6,007,701.

US Referenced Citations (1)
Number Name Date Kind
5814207 Kenton Sep 1998 A
Continuations (1)
Number Date Country
Parent 09/418448 Oct 1999 US
Child 09/664195 US
Continuation in Parts (1)
Number Date Country
Parent 09/250741 Feb 1999 US
Child 09/418448 US