Mineral oils: processes and products – Refining – Purifying used oil
Reexamination Certificate
1999-05-26
2001-01-16
Yildirim, Bekir L. (Department: 1764)
Mineral oils: processes and products
Refining
Purifying used oil
C208S045000, C208S180000, C208S181000, C208S182000
Reexamination Certificate
active
06174431
ABSTRACT:
I. BACKGROUND OF THE INVENTION
A. Field of the Invention
The present invention relates generally to the recovery and regeneration of used lubricant and industrial oils. More specifically, the present invention relates to the treatment and refinement of used lubricants and industrial oils to produce re-refined base oil and to remove additives and impurities from used oils and lubricants.
B. Description of Related Art
Commercial, residential and industrial machinery generate large amounts of used oils. In particular, the maintenance of mechanical devices with active components generates a considerable amount of used oil. In this context, used oil refers to used lubricants and industrial oils, whether they are used for lubricating, hydraulic, or other purposes, in mechanical, electrical electrical or other types of equipment. Used oil also includes synthetic oils and mineral oils that are obtained from natural sources.
Used oil does not retain the characteristics that made the original base oil suitable for its intended purpose, and it must be disposed of or re-refined. Burning used oil is one way of disposing of it. Although this causes significant pollution and releases many hazardous metals into the air, burning of used oil is accepted as a used oil disposal method. Whereas burning used oil dramatically reduces the amount of solid and liquid material that must eventually be disposed of, the volatile products that are emitted during incineration are found to be unacceptable under some environmental risk assessment and management schemes. In addition, incineration of used oil leads to calcination products and dissipated thermal energy. Incineration products may give rise to environmental pollutants, depending on the substances that are present in the incinerated products. Thermal energy that is dissipated in the environment may be an unacceptable source of thermal pollution. Finally, incineration of used oil products may also cause environmental pollution through the emission of gases and particulate matter that increase air pollution or contribute to detrimental greenhouse effects. Due to the problems associated with the burning of used oil, reprocessing (or re-refining) is an alternative that should be considered on environmental and economic grounds. In addition, some countries have banned the burning of used oil.
Used oil can be reprocessed into useful base oil. To be economically efficient, the oil must be regenerated by a process that preserves the useful characteristics of the oil, but removes additives and impurities. This recovery and regeneration goal faces the challenge imposed by the complex chemical composition of used oil. For most applications, oil is a mixture of a base oil and a number of additives; the additives enhance the useful characteristics of oil. For example, engine oil typically contains rust inhibitors, antioxidants, antiwear agents, detergent-dispersants, antifoaming agents and viscosity index improvers. When oil is used, however, the constituents of the base oil and the additives break down through a series of chemical and thermal reactions. These reactions create a complex mixture of chemical species.
For example, in addition to degraded and broken down additives, used engine oil contains metals and metal compounds that include lead, iron, calcium, zinc, sodium and magnesium, and phosphorous, sulfur and nitrogen containing compounds. This complexity is the main challenge faced by any used oil re-re-refining method. For example, some of the chemical species present in used oil directly interfere with re-refining operations. Other chemical species react during re-refining and form products that interfere with subsequent re-refining steps. Finally, some chemical species are not removed by the re-refining process and interfere with intended uses of the re-refined base oil. As used herein, re-refining and its related terms refer to the series of recovery and regeneration operations that transform used oil into a useful base oil by removing additives, asphaltic material, and other impurities. A base oil is a re-refined oil that can be used in industrial applications in general and as a lubricant in particular. Base oil that is substantially free of impurities can also be used as a feed stock to petroleum refinery process units including the fluid catalytic cracking unit. Additives can be incorporated into the re-refined base oil when the specific application so requires. Asphaltic material and impurities consist of a heavy fraction, or high molar mass fraction, and breakdown products of the oil and its additives. The asphaltic material and other impurities can form a residuum (often simply called resid) which is useful as a asphalt extender.
The impurities that must be removed from used oil during re-refining include acids, water, suspended solids, light hydrocarbons, glycols, sulfur compounds, metals and organometallic compounds, and mixtures of a variety of polymers. In particular, the removal of organometallic compounds and polymers from used oil is difficult because they are hydrophillic, and most of them vaporize at a temperature that is very similar to that at which the base oil vaporizes. In addition, used oil has a high viscosity which is detrimental to the distillation step in the re-refining process.
Polymers and metals, including zinc, calcium, and phosphorous compounds, are among the impurities that must be eliminated during re-refining to obtain a good quality base oil and to avoid fouling of re-refining equipment. In particular, the elimination or reduction of zinc compounds in used oil to a non-interfering level is very important for avoiding downstream re-refining equipment fouling. Zinc is an active species in polymerization reactions and it is present as a zinc dialkyldithiophosphate (ZdP), among other forms. ZdPs and related compounds are added to oils because they act as antioxidant agents. They also reduce the oil's wear as a lubricant, and they protect metals against corrosion. Nevertheless, ZdPs undergo hydrolysis and thermal decomposition. ZdP decomposition has been studied by, for example, J. J. Dickert and C. N. Rowe,
Journal of Organic Chemistry,
Vol. U32 (1967), pp. 647 et seq. This reference is incorporated by reference herein. ZdP is a source of acidic compounds, and it eventually forms insoluble zinc phosphate that causes fouling of re-refining equipment. Thermal decomposition of ZdP usually produces a glassy insoluble polymeric solid that is one of the major causes of re-refining equipment fouling. This fouling includes the plating out of the polymers in heat exchangers and distillation columns.
One method of processing and re-refining used oil uses propane as a solvent to extract oil. For example, U.S. Pat. No. 2,070,626 describes a process for mixing used oil with liquid propane to remove asphaltic materials and other oxidation products. This patent is incorporated by reference herein. Similarly, U.S. Pat. No. 2,196,989 describes a process for separating asphaltic compounds from crude oil to produce a lubricating oil. This patent is incorporated by reference herein. In this process, the oil is mixed with a light hydrocarbon solvent such as liquid propane or butane. A substantially inert gas precipitates impurities from the oil-propane mixture. U.S. Pat. No. 3,870,625 describes another process for de-asphalting residues from the vacuum distillation of petroleum or from used mineral oils. This patent is incorporated by reference herein. The oil or distillation residue is injected under pressure into liquid propane in a pulsed manner to facilitate dispersion of the oil material in the solvent as fine droplets. Improvements to this process are disclosed in U.S. Pat. No. 4,265,734, which is also incorporated by reference herein. Finally, U.S. Pat. Nos. 5,286,380 and 5,556,548 disclose an apparatus and method for removing contaminants from used motor oil by means of extraction with a liquid hydrocarbon and a gas. These patents are incorporated by reference herein.
A major disadvantage of these prior methods is that the
Krzykawski Jan
Williams Michael R.
Interline Hydrocarbon Inc.
McCarthy Daniel
Yildirim Bekir L.
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