Mineral oils: processes and products – Paraffin wax; treatment or recovery
Reexamination Certificate
1998-12-15
2002-04-02
Myers, Helane (Department: 1764)
Mineral oils: processes and products
Paraffin wax; treatment or recovery
26, 26
Reexamination Certificate
active
06365037
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for producing a lubricating base oil or insulating oil from a mineral oil, a mixture of a mineral oil and a long-chain alkylbenzene or the like. In particular, the present invention relates to a process for producing a markedly low pour point oil by separating a lighter fraction by distillation after hydrodewaxing treatment.
BACKGROUND OF THE INVENTION
The insulating oil, lubricating oil and the like are required to have fluidity at low temperatures, because they are sometimes used in a cold district. For example, the pour point of the insulating oil is specified at not higher than −27.5° C. as the first-class No. 2 of JIS C2320 and not higher than −45° C. as Class II of IEC 296.
To secure a low-temperature fluidity, it is necessary to use a wax-free oil, because the wax precipitates at low temperatures. Conventionally, the base oil was produced using as a raw material a naphthene crude oil having a small wax content. The naphthene crude oil is available only from a limited district and is therefore exhausted so that the use of it is disadvantageous in cost. Under such situations, a paraffin crude oil is replaced for the naphthene crude oil, but it requires a wax removal step, that is, dewaxing in advance. For dewaxing, adopted is a solvent dewaxing method wherein the wax precipitated by diluting the paraffin crude oil with a solvent such as methyl ethyl ketone/toluene or the like and then cooling is removed by filtration or a hydrodewaxing method wherein the wax is decomposed and removed by a form-selective zeolite catalyst.
The solvent dewaxing method needs much energy for cooling and removal of the solvent. Particularly when an oil having a pour point not higher than −20° C. is desired, it is necessary to lower the cooling temperature correspondingly. The solvent dewaxing treatment tends to be accompanied with the coloring of an insulating oil so that activated clay treatment for the removal of the color is necessary. Owing to the difficulty in the regeneration of the activated clay after the treatment, it must be disposed as an industrial waste. Under such circumstances, a simple hydrodewaxing method which permits dewaxing at a low cost has attracted attentions.
With regards to the production of an insulating oil by hydrodewaxing, a method which comprises obtaining a raffinate by subjecting a fraction of 232 to 566° C. to solvent extraction, hydrodewaxing the raffinate at 260 to 358° C. and hydro-refining the resulting raffinate at 218 to 316° C. is described in U.S. Pat. No. 4,137,148 which corresponds to JP-A54-22413 (the term “JP-A” as used herein means an “unexamined published Japanese patent application). It says that by this method, a base oil having a pour point not higher than −34.4° C. can be manufactured.
Although the hydrodewaxing treatment is suited for the production of a low pour point oil at a low cost, severer conditions are necessary for producing an oil having a pour point not higher than −35° C. Particularly, the production of an oil having a pour point not higher than −40° C. requires markedly severe treatment conditions and in addition, is accompanied with such a problem of a reduction in the yield of the oil.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process for producing a low pour point oil which is free of the above-described problems. Specifically, an object of the present invention is to provide a process which permits the production of a low pour point oil without severer hydrodewaxing treatment conditions.
The present inventors have proceeded with various investigations with a view to overcoming the above-described problems. As a result, it has been found that a lighter fraction of the hydrodewaxed mineral oil has a pour point lower than the heavy fraction. As a result of a further investigation, it has also been found that a lower pour point oil can be produced easily by using a fraction up to the point of 80% distillation, leading to the completion of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The process for producing the oil according to the present invention principally comprises a step of separating from a crude oil a fraction having a boiling point ranging from 250 to 600° C. by distillation; a step of hydrodewaxing the resulting fraction at a temperature range of from 250 to 500° C. in the presence of a zeolite catalyst; a step of removing a fraction having a boiling point not lower than 230° C. but not higher than 250° C.; and a step of separating a lighter fraction up to the point of 80% distillation by distillation.
Since the oil available by the above-described process only is sometimes accompanied with the coloring problem, a hue improving treatment is carried out as needed. For the improvement of the hue, there are two methods; one is the treatment with a solid adsorbent by using, for example, activated clay and the other one is hydrogenating treatment in the presence of a hydro-refining catalyst. The hydro-refining treatment is preferred because the use of activated clay or the like is accompanied with such a problem as the treatment of the adsorbent after use. In the present invention, the hydrodewaxing treatment step is essential so that when a hydro-refining treatment is carried out, the dewaxed mineral oil can be fed continuously to the hydro-refining treatment step as is or after separated by distillation. In this respect, the hydro-refining treatment is preferred.
The production process which has the hydro-refining treatment step added thereto comprises hydrodewaxing a mineral oil fraction, which has been separated from a crude oil by distillation and has a boiling point ranging from 250 to 600° C., at a temperature range of from 250° C. to 500° C. in the presence of a zeolite catalyst; hydrogenating the hydrodewaxed fraction at 320 to 380° C. in the presence of a hydro-refining catalyst; and separating a lighter fraction by distillation. The hydrodewaxed oil may be fed to the hydro-refining treatment step as is or after separated by distillation. This method is suited for the case where the hydro-refining of a heavy fraction is not necessary.
If a nitrogen content in the raw material oil is high and the activity of the zeolite catalyst shows a marked deterioration or if long-term continuous use of the zeolite catalyst is desired, the hydrodewaxing treatment may follow the hydro-refining treatment. Described specifically, such a method comprises hydrogenating a mineral oil fraction, which has been separated from a crude oil by distillation and has a boiling point ranging from 250 to 600° C., at a temperature range of from 320° C. to 380° C. in the presence of a hydro-refining catalyst; hydrodewaxing the resulting fraction at a temperature range of from 250° C. to 500° C. in the presence of a zeolite catalyst; subjecting the hydrodewaxed fraction to hue improving treatment at a temperature range of from 250 to 350° C. in the presence of a hydro-refining catalyst; and separating a lighter fraction by distillation. After the hydrodewaxing treatment, the hydro-refining treatment is carried out at a temperature of 250 to 350° C. for the improvement of the hue. As described above, the hydrodewaxed oil may be fed to the hydro-refining treatment step as is or after separated by distillation.
The process for producing the insulating oil of the present invention will next be described more specifically.
Starting material
As a starting material, a mineral oil which is a fraction separated from a crude oil by distillation and having a boiling point ranging from 250 to 600° C. (in terms of normal pressure) and a viscosity of about 5 to 20 mm
2
/s (40° C.) is preferably employed. The mineral oil subjected to solvent extraction as needed and having a viscosity of 50 to 300 mm
2
/s (40° C.) can also be employed.
Preparation of a refined mineral oil
The above-described mineral oil fraction is hydrodewaxed at 250 to 500° C. in the presence of a zeolite catalyst. As the hydrodewaxing cataly
Fujihara Kazumitu
Morishima Yoshiyuki
Japan Energy Corporation
Myers Helane
Sughrue Mion Zinn Macpeak & Seas, PLLC
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