Light oil composition

The present invention relates to gas oil compositions.

Conventionally known gas oil stocks include those manufactured by hydrorefining treatment or hydrodesulfurization treatment of straight-run gas oil obtained from atmospheric distillation of crude oil and straight-run kerosene obtained from atmospheric distillation of crude oil. Such gas oil stocks contain additives such as cetane number improvers and detergents, which are used as necessary.

Incidentally, purification of diesel engine exhaust gas has been a goal in recent years from the viewpoint of improving the atmospheric environment and reducing environmental load. It has been attempted to achieve this goal by developing gas oil stocks that can reduce contaminants in diesel exhaust gas. For example, Patent document 1 teaches that diesel particulate emission can be reduced by using a compression ignition engine fuel wherein the sulfur and aromatic compound contents and the ratio of isoparaffins and normal paraffins satisfy specific conditions.

[Patent document 1] Japanese Patent Application Laid-Open No. 2005-529213

Even such conventional gas oils, however, cannot be considered to have sufficiently practical characteristics.

In terms of fuel efficiency performance, for example, the ignitability tends to be reduced especially during winter season or in cold districts. In the case of conventional gas oils, the cold flow properties tend to be inadequate, and the aforementioned low ignitability is often accompanied by reduction in the running performance including the cold startability.

Methods for improving the ignition point and cold flow properties may result in a lighter gas oil. Lightening of gas oil is also effective from the standpoint of improving the durability of rubber members. However, simple lightening of a gas oil can impair the essential quality of the oil as a diesel fuel, including the fuel efficiency and output for engine performance.

It is an object of the present invention, which has been accomplished in light of the circumstances described above, to provide a gas oil composition with excellent ignitability and cold flow properties, which can be suitably used during winter season and in cold districts. It is another object of the invention to provide a gas oil composition which maintains adequate essential quality as a diesel fuel while exhibiting improved ignitability and cold flow properties.

With the aim of achieving the objects stated above, the present inventors first analyzed gas oil compositions using Gas Chromatography with Time of Flight Mass Spectrometry (hereinafter abbreviated as GC-TOFMS), and examined the effects of the compositions on ignitability and cold flow properties. As a result it was found that the ignitability and cold flow properties of a gas oil composition can be drastically improved by establishing a specific condition for the molar ratio of isoparaffins with two or more branches to isoparaffins with only one branch, within specified ranges of carbon numbers, and the invention has been completed upon this finding.

Specifically, the invention provides a gas oil composition characterized in that the molar ratio of isoparaffins with carbon number of m and two or more branches to isoparaffins with carbon number of m and one branch within the range of C10-21 is 0.05-3.5, wherein m is an integer of 10-21, and the molar ratio of isoparaffins with carbon number of n and two or more branches to isoparaffins with carbon number of n and one branch within the range of C22-25 is 0.1-10.0, wherein n is an integer of 22-25 (hereinafter referred to as “first gas oil composition”).

By thus ensuring that the aforementioned specific conditions are satisfied for the molar ratio of isoparaffins with two or more branches to isoparaffins with only one branch that have the same carbon number within the respective ranges of C10-21 and C22-25, it is possible to drastically improve both the ignitability and cold flow properties, as a result producing a gas oil composition that can be satisfactorily used during winter season and in cold districts.

The molar ratio of isoparaffins with two or more branches to isoparaffins with only one branch for each range of carbon numbers can be determined using GC-TOFMS, as mentioned above. In GC-TOFMS, first the constituent components of the sample are separated by gas chromatography, and the separated components are ionized. Next, mass separation of the ions is accomplished, utilizing the fact that the flight speed when applying a fixed acceleration voltage to an ion differs depending on the ion mass, and mass spectra are obtained based on the differences in arrival times to the ion detector. The ionization method in GC-TOFMS is preferably FI ionization, since this can inhibit production of fragment ions and further improve measurement precision for the molar ratio of isoparaffins with two or more branches to isoparaffins with only one branch. The measuring apparatus and measuring conditions according to the invention are as follows.

(GC zone)

Column: Agilent HP-5 (30 mB 0.32 mmφ, 0.25 μm-film)
Carrier gas: He, 1.4 mL/min (constant flow rate)


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