WASTE MOTOR OIL TO DIESEL FUEL BACKGROUND OF THE INVENTION

This invention is directed towards the art of converting used motor oil to a useable fuel source. Currently, the market for used motor oil has stymied many recycling and reclamation efforts. The market for used motor oil has largely been geared to limited processing steps which convert the used motor oil into a low quality fuel such as bunker oil (#6 fuel oil) . Alternatively, a limited amount of used motor oil is reclaimed and converted into a recycled motor oil product.

Used motor oil retains a high energy potential. However, hazards and cost associated with collecting, storing, transporting, and general handling of used motor oil has limited the efforts to collect used motor oil for disposal or recycling. Although the prior art provides limited processing of used motor oil for other petroleum products, there remains a need for improvement within the art of converting used motor oil to a high quality energy source. SUMMARY OF THE INVENTION

It is thus an object of this invention to provide a process for converting used motor oil into a diesel fuel product.

It is a further object of this invention to provide an apparatus and process for the low temperature, ambient pressure cracking of used motor oil into a diesel product.

It is yet another object of this invention to provide for mobile processing for the conversion of used motor oil to a diesel fuel product. These, as well as other objects of this invention, are provided by a process including providing a cracking apparatus, the apparatus comprising a cracking vessel, the vessel in

communication with a heating means for heating the used oil, a distillation column in communication with the vessel, and a condenser in communication with the distillation column; supplying the cracking vessel with a source of used motor oil; heating the used motor oil to a cracking temperature; cracking the used motor oil to a mixture of lighter molecular weight compounds; separating the lighter molecular weight compounds into a first mixture of a small fraction of volatile light ends and a second mixture of diesel fuel; collecting the second mixture of diesel fuel.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow chart of the process of converting used motor oil into diesel fuel.

Figure 2 is a graph of distillation curves of used motor oil.

DETAILED DESCRIPTION In accordance with this invention, it has been found that waste oil from internal combustion engines can be cracked under low temperature, low severity conditions to yield a number two grade diesel fuel. This process occurs at much lower temperatures than conventionally held to be possible and permits the continuous flow processing of waste oil to a number two grade diesel fuel without coking or fouling of the cracking apparatus. As best seen in reference to figure 1, waste oil collected from gas and diesel internal combustion engines is fed into a cracking unit which also serves as a reboiler. While a variety of designs can be employed, the cracking unit/reboiler presently employed is a direct fired unit which burns diesel fuel and air as the heating means for boiler tubes located within the cracking vessel. Heat from the boiler tubes is used to convectively heat waste oil via heat exchange with the boiler tubes.

Attached to the cracking/reboiler unit is an overhead distillation column which may be either a packed column or a plate column, both of which are well known in the art of refining petroleum. The distillation column enables the collection of vaporized lighter molecular weight compounds from the top of the column. The vaporized fraction from the top of the column can be collected in an adjacent condenser. A portion of the condensed vapors are returned to the distillation column and provide reflux for the distillation system. The reflux permits the return of material which is heavier than diesel fuel to the cracking vessel for cracking into lighter materials. The amount of the reflux can be varied according to the type of equipment used, the quality of the initial column separation and variations in the feed stock starting material.

The starting hydrocarbon material, used motor oil, is characterized by a mixture of parafins, napthenes, aromatics, and olefins. As seen in figure 2, a comparison of an ASTM D-86 distillation curve of a typical waste oil feed stock is provided in conjunction with an ASTM D-1160 distillation curve of the same feed stock run under low pressure and at temperatures too low for cracking to occur. The D-1160 curve has been corrected as described in ASTM D-1160-87 to normal atmospheric pressure and at the indicated temperatures. A comparison of the two curves indicates that above thirty percent distilled, cracking becomes vigorous between 60 and

650°F. The condensation temperature of the distilled material never exceeds the maximum boiling point temperature for #2 two diesel fuel. Therefore, in terms of boiling points, the cracked material meets the specifications for #2 diesel fuel.

Further comparison of the D-86 curve with the D-1160 curve indicates that a low level of cracking activity begins at approximately 520°F. D-86 distillation runs from a variety of

waste oil feed stocks from around the United States indicates that the data in figure 2 is representative of waste oil in general.

The condensed primary product from the cracking process is characterized by a mixture of light ends, paraffins, napthenes, olefins, and aromatics. To ensure a sufficiently high flashpoint, it is desirable to remove some of the light ends from the primary collected product. These light ends can be vaporized with an electric band heater prior to being collected in the condenser, or, alternatively, the primary product can be reheated and passed through a flash pot or a vapor separator where the more volatile light ends are separated and collected. These separated light ends can then be condensed and used to fuel the heat source for the cracking unit. Under steady state operating conditions, the removal of the light ends described above, yields a diesel fuel product which will meet federal specifications for number two diesel fuel. As indicated in table 1, the diesel product has a sufficiently high flash point, cetane rating, and distillation profile to meet federal standards for #2 diesel fuel.

Sample A of Table #1 is a composite of the diesel product collected over a several hour-long run on September 23, 1992. The feed stock of waste oil was collected from a service station in the vicinity of Charleston, South Carolina. Sample B is a product sample collected from a run on September 26, 1992. It is from the same feed stock as described in sample A.

Sample C is a product sample from a run conducted

September 27, 1992, from the feed stock described in sample A. Sample D is a composite sample of the test run as described in sample C and combined with an additional separate run conducted on September 27, 1992.

Sample E is a composite of five different samples withdrawn over the course of a run conducted on November 7, 1992. The feed stock for sample E is a mixture of the feed stock used in sample A combined with a feed stock from a diesel truck fleet which operates in the vicinity of Charleston, South Carolina.

While the data provided in Table #1 indicates the diesel products meets federal standards for #2 diesel fuel, it has proven beneficial to routinely perform additional steps to maintain continuous production of a high quality diesel fuel. Initially, the collected diesel product is of a light tea color which will meet stringent pipe' line color standards. However, the diesel fuel product will often darken over time due to the presence of reactive olefins within the fuel. To prevent the discoloration, well known fuel stabilizers can be added to the product which will stabilize the olefins.

As an alternative, the diesel fuel product can be hydrotreated. The hydrotreat ent saturates the double bonds of olefins, thereby preventing the discoloration of the product. Further, hydrotreatment has the additional advantage of removing sulfur compounds from the diesel product.

While hydrotreating is not necessary to meet the specifications for number two diesel fuel, hydrotreating will permit a much wider range of feed stock to be used in the process. Highly uniform feed stock sources, such as those from an oil recovery system for fleet vehicles, is ideal for processing. However, there is a vast supply of used motor oil which varies as to content and source. Specialty lube shops and service stations represent a feed stock source of extreme variation in oil types in terms of viscosity, gas/diesel ratings, anti-oxidant content, detergent additives and the presence of synthetic oils. Further, community collection

sites for used oil often contained other petroleum products such as greases, gear oils and other types of lubricating oils. Some of these heavier, more diverse feed stocks will include sulfur compounds which are added to prevent metal to metal contact. By incorporating a hydro-treatment step in the refining process, a more diverse range of feed stocks can be efficiently processed by removing sulfur compounds as well as reducing the level of reactive olefins.

It is believed that the above low temperature cracking process is facilitated by the presence of metal particles which are present in the waste oil. Metal particles and shavings from engine wear are suspended in the waste oil. These particles are typically in the micron and submicron range and represent particles sufficiently small such that they pass through standard oil filters. These metal shavings are believed to promote the efficiency of the cracking process in several ways. The large number of the metal particles vastly increases the surface area of metal to hydrocarbon contact within the cracking vessel. Further, the metal particles are thought to operate as a catalyst for the cracking process.

While it is difficult to analyze the cracking reactions, it is believed that the majority of the cracking is occurring within the interior portions of the hydrocarbon molecule. Only a small percentage of light ends are being produced relative to diesel product. Therefore, it is inferred that cracking under the mild conditions employed is minimized along the end portions of the parent hydrocarbon chains.

Coke formation, a common problem in petroleum cracking, is not occurring on the cracking equipment used in the present process. While coke formation is a poorly understood phenomena, it is believed that the low temperatures employed to crack the waste oil are sufficiently mild such that coking is avoided.

It may also be that any coke formation which may be occurring, is being selectively deposited upon the suspended metal particles. If so, then the metal/coke particles are removed as part of a continuous slurry withdrawal process. This slurry can be used directly as a bunker fuel oil source. Alternatively, the slurry sediments, namely metal ash and high molecular weight hydrocarbons, can be further condensed with the liquid portions being returned to the feed stock for reentry into the cracking process. The process permits the operator to choose between these two approaches.

It is thus seen that the present process provides for a method of converting used motor oil to a diesel fuel product. As many variations and modifications of the above process will be apparent to those having skill in the art from a reading of the above specification, and, therefore, such variation are within the spirit and scope of the following appended claims.