Removal of carcinogenic hydrocarbons from used lubricating oil

Abstract: A system for the substantial removal of polynuclear aromatic compounds from lubricating oil used to lubricate the engine of a motor vehicle comprising a sorbent located within the lubricating system and through which the lubricating oil circulates which is capable of removing substantially all of the polynuclear aromatic hydrocarbons from the lubricating oil. The sorbent is preferably activated carbon which may be impregnated with additives typically found in lubricating oils especially antioxidants to prolong the useful life of the oil.

Description: The present invention relates to the removal of polynuclear aromatic compounds from lubricating oil circulating in an internal combustion engine. Polynuclear aromatic compounds especially those containing three or more aromatic nuclei are frequently present in relatively small quantities in used lubricating oil, especially from gasoline engines where the high temperatures during engine operation tend to promote the formation of polynuclear aromatics in the oil leading to concentrations higher than 100 parts per million rendering disposal of the used oil hazardous. The present invention provides a use of a wood-based or peat-based activated carbon sorbent for removing dissolved polynuclear aromatic compounds (PNAs) from lubricating oil circulating in an internal combustion engine and passing in contact with the sorbent. Suitable wood-based activated carbons may have a pore volume distribution, based on pores exceeding 18Å (1.8 nm) radius, in the following range: 0.15 cm 3 /g in pores less than 3.5 nm; 0.23 cm 3 /g in pores of from 3.5 to 10.0 nm; 0.22 cm 3 /g in pores of from 10.0 to 100.0 nm; 0.25 cm 3 /g in pores exceeding 100 nm. Suitable peat-based activated carbons may have a pore volume distribution, based on pores exceeding 18Å (1.8 nm) in one of the following ranges, (a) or (b): (a) 0.08 cm 3 /g in pores less than 3.5 nm; 0.12 cm 3 g in pores of from 3.5 to 10.0 nm; 0.14 cm 3 /g in pores of from 10.0 to 100.0 nm; 0.50 cm 3 /g in pores exceeding 100 nm. (b) 0.05 cm 3 /g in pores less than 3.5 nm; 0.09 cm 3 /g in pores of from 3.5 to 10.0 nm; 0.17 cm 3 /g in pores of from 10.0 to 100.0 nm; 0.37 cm 3 /g in pores exceeding 100 nm. The sorbent may be retained in wire gauze or filter paper through which the oil passes. The sorbent may be located in a container. The sorbent may be located in an engine oil filter unit of the engine. The sorbent may be impregnated with one or more additives of the type generally used in lubricating oil for internal combustion engines. The sorbent may be impregnated with an antioxidant (e.g., zinc dialkyl dithiophosphate and/or alkylphenols and/or alkylphenol sulfides) and/or an antiwear agent and/or a friction modifier and/or a detergent and/or a pour depressant and/or a dispersant. The dissolved PNAs which are removed may have 3 or more aromatic rings, e.g. from 4 to 6 aromatic rings. Thus, the present invention provides that carcinogenic agents such as polynuclear aromatic hydrocarbons (and, incidentally, heavy metals such as lead and chromium) can be significantly removed from lubricating oil used to lubricate the engine of a motor vehicle by the use of a system comprising the said sorbent positioned within the lubricating system and through which the lubricating oil circulates, which sorbent is capable of removing polynuclear aromatic hydrocarbons from the lubricating oil. The invention may be used in the lubricating system of an internal combustion engine of a motor vehicle and is particularly suitable for gasoline engines, but it can be used for diesel engines. It is only necessary to have the sorbent located at a position in the lubricating system through which lubricating oil must be circulated after being used to lubricate the moving parts of the engine. In a preferred embodiment the sorbent is part of the filter system provided for filtering oil, or it may be separate therefrom. The sorbent can be conveniently located on the engine block or near the sump, preferably downstream of the oil as it circulates through the engine, ie after it has been heated. The system of the present invention may be used in automotive engines, railroad, marine and truck engines which may be gasoline, diesel, heavy fuel or gas-fired. This means that polynuclear aromatic hydrocarbons are removed by the sorbent during the normal flow of the lubricating oil through the system and they may therefore be removed and readily disposed of simply by removal of the sorbent. The polynuclear aromatics to be removed generally may contain 3 or more aromatic rings and the present invention is far simpler than the currently required disposal of large volumes of lubricating oil having a high polynuclear aromatic hydrocarbon content. It may be necessary to provide a container to hold the sorbent, such as a circular mass of sorbent supported on wire gauze. Alternatively the filters could comprise the sorbent capable of combining with polynuclear aromatic hydrocarbons held in pockets of filter paper. We use the said active carbon since it is selective for the removal of polynuclear aromatics containing more than 3 aromatic rings. It has the added advantage that polynuclear aromatics are tightly bound to the carbon and cannot be leached out to provide free polynuclear aromatics after disposal. Furthermore the polynuclear aromatics contained will not be redissolved in the used engine oil as it circulates. Activated carbon will also remove heavy metals such as lead and chromium from the lubricating oil. Particular types of activated carbons are advantageous for removal of polynuclear aromatics. Although most activated carbons will remove polynuclear aromatics to some extent we have found particular types are essential, in accordance with the invention, for removal of 3 and 4 ring aromatics. Characteristics such as active surface area and pore structure were found to be less important than the materials from which the activated carbon had been made. Wood and peat based activated carbons are significantly more effective than carbons derived from coal or coconut presumably due to the combination of surface active species and a pore structure allowing large polynuclear aromatics access to the surface active species. The amount of sorbent required, in accordance with the invention, will depend upon the concentration of the polynuclear aromatic compounds in the lubricating oil, but about 50 to 150 grams of the activated carbon can reduce the polynuclear aromatic content of the lubricating oil, eg used engine oil, by up to 90%. Used engine oils usually contain 10 to 10,000, eg 10 to 4,000 ppm. of polynuclear aromatic compounds. In a preferred form of the present invention the sorbent is mixed or coated with additives traditionally present in lubricating oils which may be taken up by the lubricating oil to replenish the additives as they become depleted. Typical examples of such additives are dispersants, antiwear additives, antioxidants, friction modifiers, detergents and pour depressants. This is particularly useful when the additive is a compound included to give antioxidant properties to the oil. We have found that this not only results in removal of polynuclear aromatics from the oil, but also extends the useful life of the lubricating oil. Examples of antioxidants are the zinc dialkyldithiphosphates which can also act as anti-wear additives and the alkyl phenols and alkyl phenol sulphides frequently used as such antioxidants. The ease with which the additive is released into the oil depends upon the nature of the additive, we prefer it to be totally released within 150 hours of operation of the engine. We prefer that the sorbent contain from 50 to 100% by weight based on the weight of activated carbon of the lubricant additive, which generally corresponds to 0.5 to 1.0 wt% of the additive in the lubricant. We have found that the preferred embodiment of the present invention not only results in removal of polynuclear aromatics from the oil, but also extends the useful life of the lubricating oil. We have found that polynuclear aromatic compounds, especially those with three or more rings, can be substantially removed (ie a reduction of 60% to 80%) from the lubricating oils. Examples of trinuclear aromatic compounds which are removed are phenanthrene, anthracene and 9,10-dihydroanthracene. Examples of tetranuclear aromatic compounds which are removed are pyrene, 1,2-benzanthracene, chrysene, tetracene and fluoranthrene whilst examples of pentanuclear aromatic compounds which are removed are dibenzanthracene, benzo(e)pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene and benzo(a)pyrene. Examples of hexanuclear aromatic compounds which are removed are benzo(phi)perylene and coronene. We have found that the practice of the present invention has the added advantage that the sorbent also removes heavy metals such as lead and chromium from the lubricating oil. Example 1 In this Example laboratory apparatus was used for testing the removal of polynuclear aromatics from used motor oils and the apparatus used is illustrated in Figure 1. Referring to Figure 1 the used motor oil 1 was placed in a 250 ml flask 2 provided with a stirrer 3. Tubing 5 provided with a tap 4 connects the bottom of the flask 2 with a Teflon (Trade Mark) filter unit 6. Connected downstream of this filter unit 6 is tubing 7 provided with a pump 8 connecting to a rotameter 9 to measure the rate of flow of oil. Tubing 10 connects the rotameter 9 with the flask 2. The pump 8 is provided by with a bypass 11 having a tap 12 and a gauge 13 can measure the oil pressure in tubing 7. Finally there is a drain tap 14. Several runs were made using various activated carbons in the filter sandwiched between two sheets of commercial oil filter paper. The properties of the activated carbons used are given in Table 1 as is the removal of polynuclear aromatics after treatment for approximately 100 hours. Example 2 The NORIT RO-0.8 activated carbon used in Example 1 was used in engine tests both in an engine laboratory and in field trials with Esso Extra Motor Oil (registered Trade Mark). In these tests the polynuclear aromatic content of the lubricating oil when using a traditional filter was compared with that when the traditional filter was replaced with one also containing the activated carbon and impregnated with about an equal weight based on carbon of a zinc dialkyl dithiophosphate (known as chemical filter). In the first laboratory test, a Fiat (registered Trade Mark) engine was run in the laboratory for 100 hours on a normal filter followed by 51.5 hours using the chemical filter according to the invention. The PNA content of the lubricating oil at various times is shown in Figure 2 and by dividing measured ppm PNA at 151.5 hours by estimated PNA content at 151.5 hours using the normal filter result extrapolated from 100 hours (see Figure 2), we can see that inserting the chemical filter according to the invention resulted in about 62% reduction of 4,5 and 6 ring PNAs. Figure 3 shows the PNA content of the lubricating oil during a 192-hour test using the chemical filter throughout in a similar engine, and includes the predicted PNA content when using a normal filter. It was also found that after a 96 hour test using a normal filter the oil contained 2320 ppm of lead and 3.2 ppm of chromium whilst after a similar 96 hour trial using a chemical filter the lead content was 1410 ppm and the chromium content was below 0.2 ppm. In a car test, the car was driven 3,000 miles (4,828 km) using a normal filter followed by 3,000 miles (4,828 km) using a chemical filter. Data calculated by dividing the 6,000 mile (9,656 km) PNA content by 3/4 of the PNA content at 8,000 mile (12,874 km) from a separate experiment shows about 83% reduction of 4,5 and 6 ring PNAs by use of the chemical filter. The oxidation stability of the oil was determined by measuring the Differential Scanning Calorimeter ('DSC') break temperature. The DSC measures the exothermic reaction inside the oil as its temperature increases, thus when an oil loses its oxidative stability (i.e. the antioxidants are consumed) a large exotherm takes place. A higher DSC temperature thus indicates a more oxidatively stable oil. During the laboratory test with the Fiat engine the oxidative stability was found to be as follows. Filter Hours on Test DSC Break Temp °C Normal 0 246 Normal 48 225 Normal 96 225 Chemical 144 225 Chemical 151.5 236 The DSC break temperature for the oil used in the car trials was also measured and found to be: Thousands of miles on Total Test Thousands of miles using Chemical Filter DSC Break Temp. °C 0 246 4 1 216 5 2 234 6 3 235 The filter was changed to the chemical filter after 3,000 miles (4,828 km).

Claims: Use of a wood-based or peat-based activated carbon sorbent for removing dissolved polynuclear aromatic compounds (PNAs) from lubricating oil circulating in an internal combustion engine and passing in contact with the sorbent. Use as in claim 1 wherein the sorbent is a wood-based activated carbon having a pore volume distribution, based on pores exceeding 18Å (1.8 nm) radius, in the following range : 0.15 cm 3 /g in pores less than 3.5 nm; 0.23 cm 3 /g in pores of from 3.5 to 10.0 nm; 0.22 cm 3 /g in pores of from 10.0 to 100.0 nm; 0.25 cm 3 /g in pores exceeding 100 nm. Use as in claim 1 wherein the sorbent is a peat-based activated carbon having a pore volume distribution, based on pores exceeding 18Å (1.8 nm) in one of the following ranges, (a) or (b) : (a) 0.08 cm 3 /g in pores less than 3.5 nm; 0.12 cm 3 /g in pores of from 3.5 to 10.0 nm; 0.14 cm 3 /g in pores of from 10.0 to 100.0 nm; 0.50 cm 3 /g in pores exceeding 100 nm. (b) 0.05 cm 3 /g in pores less than 3.5 nm; 0.09 cm 3 /g in pores of from 3.5 to 10.0 nm; 0.17 cm 3 /g in pores of from 10.0 to 100.0 nm; 0.37 cm 3 /g in pores exceeding 100 nm. Use as in any one of claims 1 to 3 wherein the sorbent is retained in wire gauze or filter paper through which the oil passes. Use as in any one of claims 1 to 4 wherein the sorbent is located in a container. Use as in any one of claims 1 to 5 wherein the sorbent is located in an engine oil filter unit of the engine. Use as in any one of claims 1 to 6 wherein the sorbent is impregnated with one or more additives of the type generally used in lubricating oil for internal combustion engines. Use as in claim 7 wherein the sorbent is impregnated with an antioxidant (e.g., zinc dialkyl dithiophosphate and/or alkylphenols and/or alkylphenol sulfides) and/or an antiwear agent and/or a friction modifier and/or a detergent and/or a pour depressant and/or a dispersant. Use as in any one of claims 1 to 8 wherein the dissolved PNAs which are removed have 3 or more aromatic rings, e.g. from 4 to 6 aromatic rings.

Inventors: BROWNAWELL DARRELL WILLIAM, NORRIS DONALD JAMES, SHAUB HAROLD, BROWNAWELL, DARRELL WILLIAM, NORRIS, DONALD JAMES, SHAUB, HAROLD
Applicants: EXXON CHEMICAL PATENTS INC, EXXON CHEMICAL PATENTS INC.
Application year: 1988
Main classification: C10M177
IPC codes: C10G25, C10M175, B01D15, C10N40, C10M177, A62D5