Diesel fuel containing ester to reduce emissions

Details Diesel fuel containing ester to reduce emissions Diesel fuel containing ester to reduce emissions

2000-07-13

2002-10-22

Toomer, Cephia D. (Department: 1714)

Fuel and related compositions

Liquid fuels

Containing organic -c

C044S389000, C044S398000

Reexamination Certificate

active

06468319

ABSTRACT:

This invention relates to fuel compositions of low sulphur content which contain at least one component capable of reducing particulate emissions from the exhausts of engines which generate power by combustion of such fuels.
Of particular interest are fuels such as diesel which are used rather widely in automotive transport and for providing power for heavy duty equipment such as, e.g., those used in underground mines due to their high fuel economy and low carbon monoxide emissions. However, one of the problems with such fuels is the pollutants in the exhaust gases of diesel powered engines and equipment. For instance, some of the most common pollutants in diesel exhausts are nitric oxide and nitrogen dioxide (hereafter abbreviated as “NOx”), hydrocarbons and sulphur dioxide, and to a lesser extent carbon monoxide and carbon dioxide. In addition, diesel powered engines also generate a significant amount of particulate emission which include inter alia soot, adsorbed hydrocarbons and sulphates, which are usually formed due to the incomplete combustion of the fuel and are hence the cause of dense black smoke emitted by such engines through the exhaust. The oxides of sulphur have recently been reduced considerably by refining the fuel, e.g., by hydrodesulphurisation thereby reducing the sulphur levels in the fuel itself and hence in the exhaust emissions. However, the presence of particulate matter in such exhaust emissions has been a more complex problem. It is known that the cause of the particulate matter emission is incomplete combustion of the fuel and to this end attempts have been made to introduce into the fuel organic compounds which have oxygen value therein (hereafter referred to as “oxygenates”) to facilitate combustion. Oxygenates are known to facilitate the combustion of fuel to reduce the particulate matter. Examples of such compounds include some of the lower aliphatic esters such as eg the ortho esters of formic and acetic acid, ethers, glycols, polyoxyalkylene glycols, ethers and esters of glycerol, and carbonic acid esters. The following list of references by way of example describe the use of these compounds for reducing particulate emissions and smoke suppression:
a. Society of Automotive Engineers (SAE) Technical Paper Series No. 950400, 1995 by McDonald, J F et al entitled, “Emissions Characteristics of Soy Methyl Ester Fuels in an IDI Compression Ignition Engine”.
b. Society of Automotive Engineers (SAE) Technical Paper Series No. 932734, 1993 by Liotta Jr, F J et al entitled, “The Effect of Oxygenated Fuels on Emissions from a Modern Heavy-Duty Diesel Engine”.
c. Society of Automotive Engineers (SAE) Technical Paper Series No. 962115, 1996 by Noboru Miyamoto et al entitled, “Improvement of Diesel Combustion and Emissions with Addition of Various Oxygenated Agents to Diesel Fuels”.
d. EP-A-0 861 882 A1
e. U.S. Pat. No. 5,425,790
f. WO-98 28383
g. WO 98 21293
h. U.S. Pat. No. 5,308,365
i. JP-A-09194859
j. JP-A-07331262
k. U.S. Pat. No. 5,268,008
l. JP-A-62007791
m. JP-A-50058104
Some of the problems with these and other oxygenated compounds are that either
i) they are deficient in other required attributes, eg, boiling point range, cetane number, flash point, toxicity etc. leading to product quality issues; or
ii) they have too much oxygen in them and are hence too polar thereby making them immiscible or incompatible with the fuel; or
iii) they have too little oxygen and hence need to be added in large quantities to achieve the desired improvement in combustion and are hence incompatible with the fuel when used in such large quantities.
It has now been found that these problems can be mitigated by the use of a complex mixture of esters readily generated from commercially available carboxylic acids and hydroxy compounds and which mixture achieves the desired reduction in particulate matter in the exhausts from diesel powered engines.
Accordingly, the present invention is a fuel composition comprising in addition to the fuel at least 3% w/w of an ester additive mixture derivable by reacting together either
(a) (i) a saturated, aliphatic polyhydric alcohol having three or more primary alcohol groups, (ii) a C2-C15 saturated, aliphatic branched chain monohydric alcohol and (iii) a saturated, aliphatic C4-C10 dicarboxylic acid, or
(b) a saturated aliphatic polyhydric alcohol having three or more primary alcohol groups with a C6-C15 saturated, aliphatic straight chain or branched chain monocarboxylic acid, or
(c) a C2-C15 branched chain saturated aliphatic alcohol with a saturated, aliphatic dicarboxylic acid having 6-10 carbon atoms said ester additive mixture having a boiling point of at least 150° C. and an oxygen content of at least 13% by weight of said ester additive mixture, the oxygen content being calculated based on atomic weight and molecular structure.
The fuels that may be used in and benefit by the compositions of the present invention comprise inter alia distillate fuels, and typically comprise a major amount of diesel fuel, jet fuel, kerosene or mixtures thereof. The distillate fuel itself may be a conventional petroleum distillate, or may be synthesized, e.g., by the Fischer-Tropsch method or the like. The invention is particularly applicable to diesel fuels.
The ester additive is suitably derived by reacting together either
(a) (i) a saturated, aliphatic polyhydric alcohol having three or more primary alcohol groups, (ii) a C2-C15 saturated, aliphatic, straight or branched chain monohydric alcohol and (iii) a saturated, aliphatic C4-C10 dicarboxylic acid, or
(b) a saturated aliphatic polyhydric alcohol having three or more primary alcohol groups with one or more C6-C15 saturated, aliphatic straight chain or branched chain monocarboxylic acids, or
(c) a C2-C15 branched chain saturated, aliphatic monohydric alcohol with a saturated, aliphatic dicarboxylic acid having 6-10 carbon atoms under esterification conditions.
More specifically, component (i) in ester (a) is suitably selected from one or more of trimethylol ethane, trimethylol propane, monopenta-erythritol, di-pentaerythritol and tri-pentaerythritol. Technical grades of pentaerythritol generally contain a mixture of mono- (88%), di- (10-12%) and the remainder tri-pentaerythritols. Of these, trimethylol propane is preferred.
Component (ii) in ester (a) is suitably selected from one or more of 2-ethyl hexanol, n-octanol, iso-octanol, nonanol, iso-nonanol, decanol, isodecanol, undecanol, dodecanol and isotridecanol. Of these isodecanol is preferred.
Component (iii) in ester (a) is suitably a dicarboxylic acid selected from succinic acid, glutaric acid, adipic acid, sebacic acid, azelaic acid and suberic acid. Of these, adipic acid is preferred.
The esterification of an admixture of components (i), (ii) and (iii) is suitably carried optionally in the presence of an acid catalyst at a temperature in the range from 140° C. to about 250° C., and a pressure in the range from subatmospheric to atmospheric eg from about 4 KPa to about 105 KPa, over a duration of about 0.1-12 hours, preferably about 2 to 8 hours. The stoichiometry in the reactor is variable, and is capable of vacuum stripping excess reactants, especially acids, to generate a crude ester product which may be further refined by well known methods of contact with compounds capable of removing residual acidity or colour from the product to generate the desired ester mixture. Examples of such compounds capable of removing residual acidity include, activated carbon, alumina, Fuller's earth, clay, zeolites and the like.
Similarly, in ester (b) the polyhydric alcohol component may be the same as that used for making ester (a). The saturated aliphatic monocarboxylic acid component for ester (b) is suitably a monocarboxylic acid which may be produced by the so called “oxo” process by hydroformylation of commercial branched C5-C14 olefin fractions to a corresponding branched C6-C15 aldehyde-containing oxonation product. In the process for forming oxo acids, it is desirable to recover the crude oxo-aldehyde intermediate from the oxonation p

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