JP2010053360A - Lubricant formulation and method for lubricating combustion system to achieve improved emission catalyst durability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lubricant composition solving a problem of catalyst poisoning as a result of combustion of phosphorus in a combustion system. <P>SOLUTION: In the lubricant composition comprising (a) base oil and (b) an additive composition including a zinc dialkyldithiophosphate component, a lubricant has a phosphorous content of less than about 800 ppm and a TEOST MHT-4 test yield of less than about 30 mg of deposit; and a TEOST MHT-4 volatile fraction has a phosphorous content of less than 100 ppm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lubricant formulation and a combustion system lubrication method for obtaining improved emissions catalyst durability in an emissions control system associated with the combustion system. In particular, the method relates to using a relatively small amount of a predetermined phosphorus-containing additive in the lubricant to minimize poisoning of the emission control catalyst. The present invention also relates to examining the captured volatiles of TEOST MHT to select specific phosphorus-containing additives that produce the least amount of emission control catalyst poisoning.

  Phosphorus is a known element that is found and incorporated in lubricant compositions for combustion systems. Unfortunately, emissions from combustion systems that contain phosphorus can poison the catalyst components of the emissions control system. In particular, phosphorus emissions from lubricants can poison these catalysts as a result of blow-by volatiles or combustion, thereby reducing the efficiency of the emissions catalyst or reducing or converting harmful combustion system emissions. Reduce. For example, there has been a long-standing concern that phosphorus from engine oil vaporizes, passes through the combustion chamber, and subsequently accumulates on the passenger car catalyst system, reducing the efficiency of the automobile emission control system. Therefore, as new engine oil standards are introduced, there is a continuing trend to demand a reduction in the amount of phosphorus in fresh engine oil.

  Accordingly, an object of the present invention is to help solve the problem of catalyst poisoning as a result of the combustion of phosphorus in a combustion system. Furthermore, it is an object of the present invention to pay particular attention to certain types of ZDDP that can be used as additives in lubricant compositions. In addition, the use of specific ZDDP composition selection methods combined with industry constraints on the phosphorus content in lubricant compositions can be used to control and help minimize catalyst phosphorus poisoning in emissions control systems. It can be.

  It has been found that different zinc dialkyldithiophosphates (ZDDP) exhibit different volatility and have different effects on automobile emission control catalysts. In other words, ZDDP decomposes as a result of normal wear and use in the engine crankcase. Therefore, different ZDDP molecules break down into different fragment molecules. Degraded fragments can have substantially different levels of volatility. ZDDP and their respective decomposition fragments, which have low volatility, have a correspondingly low harmful effect on combustion emissions control simply because fewer phosphorus atoms pass through the combustion system and reach the emission control system. It affects the system. In other words, the lower the volatility of harmful molecules, the fewer molecules pass through the combustion system due to engine blow-by or simple combustion. Conversely, when ZDDP and their respective degradation fragments are highly volatile, the number of these molecules that pass through the combustion system increases, resulting in increased poisoning of the emission control catalyst. Because fewer phosphorus atoms reach the emission control system, they have a corresponding low harmful effect on the combustion emission control system.

  ZDDP is a well-known lubricant additive used by all types of internal combustion engines. ZDDP is included in the additive package for the purpose of at least improved wear resistance and antioxidant properties. However, the term “ZDDP” actually refers to many different alternative molecules. The difference between these molecules is largely due to the relationship in space between the different alkyl components and the alkyl components around the phosphorus molecule. Different ZDDPs can have different performance in the lubricant.

  To simplify, ZDDP is formed by combining an alcohol with a thiophosphate. ZDDP is generally described by the alcohol used in the synthesis process to donate alkyl groups to the ZDDP molecule. For example, “primary” ZDDPs include, but are not limited to, n-decanol, n-octanol, 2-ethyl-1-hexanol, 1-hexanol, 4-methyl-1-pentanol, 2-methyl-1-propanol, Formed from primary alcohols including 1-pentanol, 1-butanol, 1-propanol, and mixtures thereof. Similarly, “secondary” ZDDPs include, but are not limited to, 2-propanol, 2-butanol, 2-pentanol, 4-methyl-2-pentanol, 2-hexanol, 2-octanol, and 2-decanol. Formed from secondary alcohols, including mixtures of these. “Aryl” ZDDPs include those formed from phenol, butylated phenol, 4-dodecylphenol, and 4-nonylphenol and mixtures thereof. In lubricant formulations, different ZDDPs are often mixed to obtain the different benefits of different types of ZDDPs.

  Surprisingly, it has been found that ZDDP formed by a high proportion or 100% of methyl isobutyl carbonol (MIBC or 4-methyl-2-pentanol) exhibits significantly lower volatility than other ZDDPs. It was done. In general, it is known that a ZDDP compound undergoes a rearrangement reaction including esterification and beta-cleavage when heated. Esterification produces new neutral or non-metal containing phosphate triesters. It is envisioned that the neutral phosphate compound is more volatile than the phosphate metal salt. It is believed that the steric bulk around the oxygen portion of ZDDP can reduce the rate of ester formation. It is hypothesized that MIBZ ZDDP exhibits low volatility due to the steric bulk present in the MIBC alcohol moiety.

  It is an important finding that a mixture of ZDDP containing 100% MIBC ZDDP or a high proportion of MIBC ZDDP exhibits a relatively low volatility compared to other ZDDPs. As a result, 100% MIBC ZDDP has a less detrimental effect on the exhaust catalyst than other ZDDPs. This means that the relative assessment of negative effects on emissions is not a direct correlation to phosphorus content. Therefore, after evaluating the actual effect of ZDDP in performance testing, it is necessary to determine the requirements for reducing the phosphorus content in the lubricant.

  In addition to MIBC ZDDP, it is possible that there may be other ZDDPs that have relatively lower volatility than conventional ZDDP. Other low volatility ZDDPs can include those made with high molecular weight secondary alcohols such as 2-ethylhexyl alcohol, or with mixtures of MIBC alcohol and other high molecular weight secondary alcohols.

  Similarly, other lubricant additive components can affect the volatility of the phosphorus-containing compound in the lubricant composition. In one example, a detergent comprising calcium sulfonate can reduce harmful phosphorus poisoning of emission control system catalysts when used with a ZDDP additive in a lubricant composition. While recognizing these benefits, it is believed that the use of detergents does not have any distinguishing effect on phosphorus poisoning. Therefore, identifying low volatility ZDDP has a beneficial effect in addition to or independent of the use of detergents. Similarly, it is possible that other additive chemicals may reduce the deleterious effects of phosphorus poisoning in general, but the idea is that none of these effects treats the various ZDDPs that can be used differentially. It is done. Thus, for example, ZDDP analysis of a lubricant formulation that does not include a detergent additive component may be the most accurate analysis of the beneficial effects of selecting a low volatility ZDDP component.

  Figure 2 shows physical results demonstrating the low volatility of MIBC ZDDP in various tests including phosphorus retention test and TEOST MHT-4 test.

Phosphorus retention test The phosphorus retention test measures the concentration of phosphorus remaining in the used lubricant after a 100 hour Sequence III G test. This test compares the phosphorus concentration in used oil with the concentration of phosphorus in fresh oil. The formula for calculating phosphorus retention is:
PR100 = ([new calcium] / [calcium @ 100 hours] × ([phosphorus @ 100 hours] / [new phosphorus]) × (phosphorus @ 100 hours / new phosphorus)
This equation adjusts the phosphorus concentration against the loss of volatile base material as measured by increasing calcium concentration. This phosphorus retention analysis is important for lubricant testing because all oils are distinguished by the amount of phosphorus released. As mentioned above, the phosphorus released by the oil is finally burned and flows to the catalyst in the emission control system.

  100% MIBC ZDDP exhibits a phosphorus retention average of about 87%. The average phosphorus retention for mixed ZDDP is 81%. The average phosphorus retention for secondary ZDDP is 78%. As is apparent from these results, the amount of phosphorus retained in the lubricant is significantly higher when 100% MIBC ZDDP is used. In one example, the range for phosphorus retention is about 85% or greater.

TEOST MHT-4
The TEOST MHT-4 test is a standard test in the lubricant industry to evaluate engine oil oxidation and carbonaceous deposit formation characteristics. This test is designed to simulate high temperature (285 ° C.) deposits in the piston ring belt region of the engine. The focus of this test is to obtain the weight of the deposit that is formed on the resistance heated deposit tester rod held in the casing when bulk oil is flowed at a rate of 0.25 g / min. The temperature of the rod is controlled by a thermocouple. A 3/2/1 ratio iron, lead, and tin catalyst is used to increase the oxidative stress on the oil. Oxidation in the test is measured in the form of the weight of the deposit formed on the rod.

  The amount of 100% MIBC ZDDP produced is required to be approximately 25 mg. It is desirable to have a test yield of less than about 30 mg. Other ZDDP types consisting of primary, secondary, mixed, and arylzinc produced 35-70 mg in the TEOST MHT-4 test. Volatile sections are collected during standard operation of the TEOST MHT-4 test. This section was analyzed for phosphorus content by ICP.

TEOST MHT-4 Volatile ICP Analysis By examining the captured volatiles of TEOST MHT-4, a selection of ZDDP chemicals that produce a minimum or reduced amount of volatile phosphorus can be made. Volatiles captured in the TEOST test are subjected to inductively coupled plasma (ICP) analysis to quantify the amount of volatile phosphorus compounds that are representative of ZDDP degradation products. The ICP test is described by the test protocol ASTM D5185. Briefly, the sample is dissolved in a suitable solvent matrix and pumped from the nebulizer so that a fine spray is introduced into the highly charged argon plasma. The plasma energy desolvates, atomizes, and ionizes elements in the sample. Atomic and ionic transitions occur due to the excited state of the element, and subsequent decay to low energy states can be observed in the ultraviolet and visible spectra. Each element present in the sample emits light at an individual wavelength. This is separated by an echelle grating and focused on a solid state CID detector. A quantitative value can be obtained by comparing the luminescence intensity of each element with respect to the sample against a standard luminescence containing the element at a known concentration.

A similar lubricant formulation was tested. Volatiles from the TEOST test were analyzed by ICP analysis. For a fully formulated oil containing phosphorus from 500 ppm ZDDP, the results were found as follows.

As is apparent from the above test results, the volatile phosphorus reduction order relative to the crankcase ZDDP is as follows.
Aryl ZDDP> 100% MIBC C6 ZDDP> C8 primary high overbase ZDDP> secondary ZDDP> mixed ZDDP> primary C4 / C5 / C8 ZDDP
Aryl ZDDP exhibited a low volatility phosphorus category, but its MHT-4 deposit value was relatively high. The best results have both a low volatility phosphorus category and a low deposit value. Preferably, the ZDDP should have a volatile fraction with a phosphorus content of less than about 100 ppm and a low MHT-4 test yield of deposit of less than about 30 mg. Thus, it is clear that testing TEOST volatiles using ICP analysis can be a quantitative measure for selecting a ZDDP that has an improved or reduced effect on the exhaust catalyst.

  Lubricants that benefit most from the discovery of low volatility ZDDP are low total phosphorus content lubricants. With historical concentrations of ZDDP greater than 1,000 ppm, the relative volatility of the phosphorus component is due to the presence of large amounts of phosphorus and any volatility level is sufficient to poison the emission control catalyst. The problem becomes suspicious. However, if the lubricant has less than 800 ppm, or in another example less than 700 ppm, or even alternatively less than 600 ppm phosphorus, the reduced volatility is significant with respect to maintaining an emission control catalyst. Durability improvements can be presented.

  The previous examples relate to 100% or substantially 100% MIBZ ZDDP. It is conceivable that ZDDP containing a high ratio or a part of MIBC ZDDP can obtain a merit from a decrease in phosphorus volatility. In the preceding example, MIB ZDDP accounts for 100% or substantially 100% of the ZDDP used. In another example, the ZDDP incorporates at least 90% MIBC ZDDP. In yet a further example, the lubricant may incorporate at least 80%, or even alternatively, at least 70% MIBC ZDDP. Still further, it is conceivable that the lubricant will benefit from incorporating at least 50% MIBC ZDDP when reducing phosphorus volatility. The present invention is subject to considerable variations in this implementation. Therefore, the foregoing description is not intended to limit the invention to the specific illustrations presented above, and should not be considered limiting. Rather, what is intended to be covered is as indicated in the equivalents of the claims and the legal matter that are allowed.

  The patentee does not intend to dedicate any disclosed aspect to the public, and to the extent that any disclosed variant or modification is not literally within the scope of this claim, Is considered part of

Claims (16)

An additive composition comprising (a) a base oil and (b) a zinc dialkyldithiophosphate component;
The lubricant has a phosphorus content of less than about 800 ppm;
A lubricant composition wherein the lubricant has a TEOST MHT-4 test yield of less than about 30 mg of deposit, and the TEOST MHT-4 volatile fraction has a phosphorus content of less than 100 ppm.   The lubricant composition of claim 1, wherein the TEOST MHT-4 test yield is less than about 25 mg.   The lubricant composition of claim 1, further wherein the TEOST MHT-4 volatile fraction has a phosphorus content of less than 65 ppm.   The lubricant composition of claim 3, further comprising a TEOST MHT-4 volatile fraction having a phosphorus content of less than 40 ppm.   The lubricant composition of claim 1, wherein substantially all of the phosphorus in the lubricant originates from a zinc dialkyldithiophosphate additive component.   The lubricant composition of claim 1, wherein the phosphorus retention value of the lubricant composition after oil aging is about 85% or more based on the initial amount of phosphorus in the lubricant composition.   The lubricant composition of claim 6, wherein the phosphorus retention value is about 87% or greater.   The lubricant composition of claim 1, wherein substantially all of the zinc dialkyldithiophosphate comprises methyl isobutylcarbanol zinc dialkyldithiophosphate.   The lubricant composition of claim 1, wherein the zinc dialkyldithiophosphate comprises at least 90% methyl isobutylcarbanol zinc dialkyldithiophosphate.   The lubricant composition of claim 1, wherein the zinc dialkyldithiophosphate comprises at least 80% methyl isobutylcarbanol zinc dialkyldithiophosphate.   The lubricant composition of claim 1, wherein the zinc dialkyldithiophosphate comprises at least 50% methyl isobutylcarbanol zinc dialkyldithiophosphate. Providing a lubricant comprising a zinc dialkyldithiophosphate additive component;
Performing a TEOST MHT-4 test with this lubricant;
Combustion emissions comprising collecting captured volatiles resulting from the TEOST MHT-4 test, and analyzing the captured volatiles to quantify the amount of phosphorus in the captured volatiles. Method for evaluating zinc dialkyldithiophosphate additives for use in engine lubricant formulations having reduced catalyst poisoning effects in product control systems.   The method of claim 12, wherein the step of analyzing comprises analyzing the captured volatiles using ICP analysis.   13. The method of claim 12, further comprising selecting a special zinc dialkyldithiophosphate additive component that provides the least amount of phosphorus in the trapped volatiles. An additive composition comprising (a) a base oil and (b) a zinc dialkyldithiophosphate component;
The lubricant has a phosphorus content of less than about 800 ppm;
A lubricant composition wherein the trapped volatiles resulting from the TEOST MHT-4 test using ICP analysis result in a phosphorus content of about 60 ppm or less.   16. The method of claim 15, wherein ICP analysis results in a phosphorus content of about 40 ppm or less.