AU6057498A - Method of stabilizing coal liqueified oil - Google Patents

Description

P/00/oil RequlaLioan 3.2

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

We, KOBE STEEL LTD. of 3-18. Wakinoharna-cho I-choine. Chuo-ku, Kobe-shi, H-yogo-ken, Japan, MITSUBISHI CHEMICAL CORPORATION, of 5-2 Marunouchi 2chomie. Chivoda-ku. Tokyo. Japan. ILJENITSU KOSAN CO. L'ID, of 1-1 Marunouchi 3-chorne. Civoca-ku. Thkyu. Japan. COS-11 OIL, COMPANY LTD, of 1-1, Shihaura I1-chome. Mkinato-ku. Tokyo 105-8528. Japan and NISSHO MWAI CORPORATrION. oi Iniabashi 2-choine, Chuo-ku. Osaka 541-0042, Japan TO BE COMPLETED BY APPLICANT Name of Applicant: Actual Inventors: Address for Service: invention Title: NIPPON BRIOWN CO)AL LIQUEFACTION CO., LTD NOBUYUKI KOMATSU, KOUIOHI SATOU, TOSHIAKI OKUI CALLINAN LAWRIE, 711 High Street, Kew, 3101.,.- Victoria, Australia METHOD OF STABILIZING COAL LIQ2UEFIED OIL The following statement is a full description of this invention, including the best method of performing it known to me:- ~Z~i~if~Fi t i.: INVENTION TITLE METHOD OF STABILIZING COAL LIQUEFIED OIL BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method of stabilizing coal liquefied oil, and more specifically, to a technical field relating to a method of stabilizing coal liquefied oil obtained by hydrogenating raw coal.

Description of the Related Arts With a two-times petroleum crisis as a turning point, the technical development concerning fuel in place of petroleum has been eagerly demanded. Particularly, to liquefy coal richly buried underground to obtain fuel oil in place of coal is an important technique.

As a typical example of the process for liquefying coal, there can be mentioned a method of liquefying coal, comprising: mixing a solvent and a catalyst into crushed raw coal to obtain a slurry-like mixture, adding a hydrogen gas to said mixture under high temperature and high pressure, and separating oil from the hydroproduct obtained.

In the stage of the coal liquefied oil obtained directly from the above-described coal liquefying process, when the coal liquefied oil is used as a transporting fuel as it is, since the fuel characteristics such as octane

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1 -lAnumber and cetane number are low, it is necessary to have it subjected to an up-grading process (a hydrorefining process) for further improving the fuel characteristics.

However, it is known that in the case where in the coal liquefying process, the coal liquefied oil is stored in a tank or a drum for feeding the coal liquefied oil obtained by the coal liquefying process to the up-grading process, solid components such as gum or sludge are produced from the coal liquefied oil during the period of storage, or color of the coal liquefied oil is changed into brown or color close to black from transparent color. The occurrence of solid components or discoloration during the storage is not desirable because giving rise to problems such as the blockage of the solid components within a transfer pipe, and the catalyst for up-grading being poisoned by the solid components and in addition, the occurrence of change in quality of the coal liquefied oil when transferring to upgrading equipment in order to improve the fuel characteristics of the coal liquefied oil and during the modifying process in the equipment.

"pi In order to cope with the above-described problems, there have been proposed a method of modifying the coal S- liquefied oil by hydrotreating it in a fixed bed type reactor, and a method of removing substances such as gum, sludge or the like from the coal liquefied oil by adsorption or the like. Particularly, a nitrogen-contained compound in the,coal liquefied oil has been considered to be a material which produces solid components such as gum and sludge from the coal liquefied oil and gives rise to discoloration. There have been proposed some methods of removing the nitrogen-contained compound by modification or adsorption. For example, Japanese Patent Laid-Open No. 40195 proposes a method of removing nitrogen contained hydrocarbons by adsorbing it on titanium oxide and silica, as a method for reducing nitrogen-contained hydrocarbons for the purpose of improving the stability when the hydrocarbons are stored (hereinafter referred to as the storage stability). Further, Japanese Patent Laid-Open No.

60-18579 proposes a method of contacting heavy oil with zeolite having a strong acid strength to remove a basic nitrogen-contained compound.

However, these methods are to remove only the nitrogen-contained compound within the coal liquefied oil o,.

and are not aimed at other substances which worsen the e storage stability of in the coal liquefied oil (stability when the coal liquefied oil is stored). Further, a reference value relating to the reducing amount of the content of the nitrogen-contained compound for indicating Sthe sufficient storage stability by the coal liquefied oil is not definitely mentioned. Therefore, the production of o solid components such as gum and sludge during the period of storage of the coal liquefied oil and discoloration cannot be always prevented positively, and under the existing circumstances, the technique capable of stabilizing the coal liquefied oil so as to be able to prevent the production of solid components and

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discoloration positively and sufficiently is not yet established.

SUMMARY OF THE INVENTION The present invention has been accomplished in view of the foregoing. An object of the present invention is to provide a method of stabilizing coal liquefied oil capable of stabilizing the coal liquefied oil so as to be able to prevent the production of solid components such as gum and sludge during the period of storage of the coal liquefied oil and discoloration positively and sufficiently.

For achieving the aforesaid object, the method of stabilizing coal liquefied oil according to the present invention comprises methods of stabilizing coal liquefied oil according to claims 1 and 2 having the following constitution. That is, claim 1 provides a method of stabilizing coal liquefied oil characterized in that coal liquefied oil obtained by hydrogenating raw coal is modified so that a nitrogen content in the coal liquefied oil is less than 1000 ppm, and an oxygen content is less than 5000 ppm (the first invention).

Claim 2 provides the method of stabilizing coal liquefied oil according to claim i, wherein said raw coal is brown coal (the second invention).

According to the method of stabilizing coal liquefied oil of the present invention, there can stabilize coal liquefied oil so as to be able to prevent the production of solid components such as gum and sludge during the period

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/j r ii j: tin of storage of the coal liquefied oil and discoloration positively and sufficiently.

That is, the coal liquefied oil is stabilized sufficiently and positively, the production of solid components such as gum and sludge from the coal liquefied oil is hard to occur, and even if the solid components are produced, the production amount thereof is at least less than 2 mg/100 ml. Further, the discoloration of the coal liquefied oil is hard to occur, and the color is not changed into brown or color close to black.

Therefore, it is possible to prevent problems such as blockage of the transporting pipe due to the solid components in the transporting process of the coal liquefied oil and the catalyst being poisoned due to the solid components in the up-grading process of the coal liquefied oil, and to prevent the coal liquefied oil from lowering in quality due to the discoloration.

BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a view showing an outline of one example of a method of stabilizing coal liquefied oil according to the r present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a method of stabilizing coal liquefied oil. For example, the invention is embodied as follows: Coal liquefied oil obtained by hydrogenating raw coal is modified so that a nitrogen content in the coal liquefied oil is less than 1000 ppm, and an oxygen content is less than 5000 ppm. The modification herein is carried out by a method of hydrotreating the coal liquefied oil, or a method of flowing the coal liquefied oil into an adsorbent filling layer.

The present invention has been completed on the basis of knowledge obtained as the result of earnest studies on the storage stability of the coal liquefied oil. The invention will be described in detail hereinafter.

The coal liquefied oil obtained by hydrogenating coal contains a nitrogen-contained compound, a sulphur-contained compounded, and an oxygen-contained compound according to quantities of nitrogen, sulphur and oxygen contained in raw coal. Particularly, in the case where brown coal is used as the raw coal, since the oxygen content in raw brown coal is generally high, not less than 20 weight (mass) the oxygen-contained compound corresponding to 3 to 4 weight in quantity of oxygen is contained in the coal liquefied oil obtained.

The present inventors have found, as the result of earnest studies on the storage stability of coal liquefied oil, that the oxygen-contained compound in the coal liquefied oil is participated in as a material which worsens the storage stability of the coal liquefied oil similar to the nitrogen-contained compound, and particularly, an aromatic compound (such as phenol) having a hydroxyl group (-OH group) in the oxygen-contained compound is a material which worsens the storage stability of the coal liquefied oil similar to the nitrogen-contained compound.

That is, when the oxygen-contained compound contained in the coal liquefied oil produced using various brown coals as raw material was analyzed by a GC-MS method (a gas chromatography mass analyzing method) and identification of the compound was carried out, it was made apparent that benzofurans, phenols and phenylethers were contained as the oxygen-contained compound. An m-cresol was selected as a typical example from these oxygen-contained compounds. The m-cresol was mixed into ethanol of a solvent to prepare a testing sample, which was stored for three months at room temperature in air and thereafter, the change thereof was observed. As a result, it was found that the sample was violently colored and solid components were produced.

As described above, it has been found that not only ,the conventional nitrogen-contained compound but also new oxygen-contained compound were anticipated in as the material which worsens the storage stability of the coal liquefied oil. Accordingly, it is contemplated that if these materials are removed by the modifying process such as hydrotreatment, adsorption and the like, the coal liquefied oil is stabilized, and the storage stability of the coal liquefied oil is improved. However, a reference value when these materials are removed and reduced in an attempt of improving the storage stability of the coal liquefied oil was not definite.

Then, experiments were carried out in order to clarify the reference value. It has been found as a result that if the quantity of nitrogen-contained compound in the coal liquefied oil is set less than 1000 ppm in nitrogen quantity and the quantity of oxygen-contained compound is set less than 5000 ppm in oxygen quantity, the coal liquefied oil is stabilized positively and sufficiently, and the storage stability of the coal liquefied oil is improved.

That is, several kinds of brown coal were used as raw coal to produce coal liquefied oil. The coal liquefied oil was subjected to hydrotreatment under various conditions for modification to prepare samples of coal liquefied oil for testing inwhich in the coal liquefied oil, a nitrogen content is 2 to 7500 ppm, and an oxygen content is 500 to I 4000 ppm. With respect to these samples of coal liquefied Soil for testing, a' relationship between the nitrogen content and oxygen content in the sample of the coal liquefied oil and the change of the production quantity of solid components (sludge) after stored for three months at room temperature in air and color was examined. The measurement of the production quantity of the solid components was conducted in accordance with a method for testing fine-amount foreign matter of JIS K 2276, and the I measurement of the color was conducted in accordance witha a i method for testing ASTM color of JIS K 2580. ~m As a result, it has been **ound that a logarithmic value of the nitrogen content and the oxygen content in the coal liquefied oil is substantially proportional to a logarithmic value of the production quantity of solid components, and the production quantity of solid components increases for one which is high in the nitrogen content or the oxygen content in the coal liquefied oil. It has been also found that the color of the coal liquefied oil is also related to the nitrogen content and the oxygen content, and color of the coal liquefied oil after stor-d for three months is brown or color close to black for one which is i high in nitrogen content and oxygen content in the coal liquefied oil.

In the evaluation of the storage stability of the coal liquefied oil, it is said that the production quantity of solid components in the coal liquefied oil in the case where the processing in the up-grading process without trouble such as blockage of the transporting pipe in the transporting process of the coal liquefied oil is carried out without trouble is less than 2 mg/100 ml (2 mg of solid components with respect to 100 ml of coal liquefied oil) as a standard. The nitrogen content and the oxygen content in the coal liquefied oil in the case where -the production quantity of solid components will suffice to be less than 2 mg/100 ml were examined. As a result, it has been found that the coal liquefied oil is subjected to modification so that the nitrogen content in the coal liquefied oil is less .i than 1000 ppm and the oxygen content therein is less than v--i 500 ppm, whereby the production quantity of solid components is less than 2 mg/100 ml. That is, when the nitrogen content in the coal liquefied oil exceeds 1000 ppm and/or the oxygen content therein exceeds 5000 ppm, the stability of the coal liquefied oil is not sufficient, the production quantity of solid components from the coal liquefied oil exceeds 2 mg/100 ml, color of the coal liquefied oil sometimes changes into brown or color close to black, and the storage stability of the coal liquefied oil is insufficient. On the other hand, when the nitrogen content in the coal liquefied oil is less than 1000 ppm and the oxygen content therein is less than 5000 ppm, the coal liquefied oil is stabilized positively and sufficiently, the production quantity of solid components from the coal liquefied oil is less than 2 mg/100 ml, the change in color of the coal liquefied oil rarely occurs, and the storage stability of the coal liquefied oil is improved sufficiently and positively.

Thus, according to the method of stabilizing coal liquefied oil of the present invention, coal liquefied oil obtained by hydrogenating raw coal is modified so that a nitrogen content in the coal liquefied oil is less than 1000 ppm, and an oxygen content is less than 5000 ppm (the first invention). Accordingly, according to the method of stabilizing coal liquefied oil of the present invention, as will be apparent from the knowledge noted above, it is possible to stabilize the coal liquefied oil so as to be able to positively and sufficiently prevent production and idiscoloration of solid components such as gum and sludge during the period of storage of the coal liquefied oil.

That is, the coal liquefied oil is stabilized sufficiently and positively, the production of solid components such as gum and sludge from the coal liquefied oil is hard to occur, and even if the solid components are produced, the production amount thereof is at least less than 2 mg/100 ml. Further, the discoloration of the coal liquefied oil is hard to occur, and the color is not changed into brown or color close to black. Therefore, it is possible to prevent problems such as blockage of the transporting pipe due to the solid components in the transporting process of the coal liquefied oil and the catalyst being poisoned due to the solid components in the up-grading process of the coal liquefied oil, and to prevent the coal liquefied oil from lowering in quality due to the discoloration.

As described above, since the oxygen content in brown coal is high, 20 weight (mass) when the brown coal is used as raw coal, the coal liquefied oil obtained is large in content of the oxygen-contained compound. The oxygencontained compound is one of materials which worsen the stability of the coal liquefied oil. Accordingly, the method of stabilizing coal liquefied oil according to the present invention is particularly effective for the stabilization of coal liquefied oil obtained when brown coal is used as raw coal (the second invention).

In the present invention, the modifying method by which the nitrogen content in the coal liquefied oil is -11-

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y_ ijij 71* less than 5000 ppm and the oxygen content therein is less than 500 ppm is not particularly limited, but for example, methods such as hydrotreatment and adsorption can be applied. As the typical example of modifying the coal liquefied oil by way of hydrotreatment, there can be mentioned a method comprising: using a reactor of a fixed bed type continuous flowing system, and flowing coal liquefied oil into a layer filled with a catalyst (such as Ni, Mo, Co, etc.) for modification under the conditions of high temperature and hydrogen pressure to decompose and remove the nitrogen-contained compound and oxygen-contained compound in the coal liquefied oil. The method of modifying coal liquefied oil by way of adsorption is a method of adsorbing the nitrogen-contained compound and oxygencontained compound in the coal liquefied oil on the adsorbent for removal. As the typical example therefor, there can be mentioned a method for flowing coal liquefied oil into a layer filled with an adsorbent such as zeolite, silica, alumina, etc.

The nitrogen-contained compounds in the coal liquefied oil include pyridines, quinolines, anilines, naphthylamines, azaphenanesurenes, etc. The oxygen compounds include benzofuranes, phenols, phenylethers, etc., as mentioned above.

More specifically, the method of stabilizing coal liquefied oil according to the present in. ntion is carried out by the apparatus and process flow shown in FIG. 1, for t-

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r's ;1 example, details of which will be described in the following.

Dried and crushed raw coal and a circulating solvent are supplied to a coal slurry preparation tank to mix them to obtain a slurry mixture. A hydrogen gas is added to the slurry mixture, which is fed to a preheater(2) for preheating. The slurry mixture after preheated is fed to a hydrogenetion reactor At this time, a typical hydrogenation reactor is a bubble tower type reactor. In the hydrogenation reactor liquefying reaction is carried out to obtain a hydroproduct. The typical conditions of the hydroliquefying reaction are temperature 450 0 C, pressure 15 MPa, and time 1 hr.

The thus obtained hydroproduct is introduced into a gas-liquid separator to separate a gas-phase component under the high temperature and high pressure, and the gasphase component is fed to a hydrotreater as it is, where hydrotreatment is carried out to obtain a hydrotreated solvent. Here, the gas-phase component is the coal liquefied oil obtained by hydrogenating raw coal, which corresponds to one example of coal liquefied oil subjected to modification. The hydrotreatment corresponds to one example of modification of coal liquefied oil. As a typical hydrotreating apparatus, a flowing system pipe type reactor filled with a hydrotreating catalyst of a fixed bed type is used. The typical conditions of the hydrotreating are temperature 350 0 C, pressure 15 MPa, LHSV (Liquid Space Velocity) 1 hr-!.

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r -13- The thus obtained hydrotreated solvent is introduced into a gas-liquid separator so that the solvent is separated into light oil less than 300'C of boiling point and 300 to 420 0 C of boiling point, and the separated heavy oil is fed as a circulating solvent to the coal slurry preparation tank On the other hand, the light oil is moved out of the process as a coal liquefied oil (product oil). This coal liquefied oil corresponds to one example of the modified coal liquefied oil. Note, the hydrotreated solvent also corresponds to one example of the modified coal liquefied oil.

On the other hand, a liquid phase portion including a catalyst is separated from the gas-liquid separator A part of the liquid phase portion is circulated and supplied directly to the hydrogenation reactor A further part thereof is supplied to the oil separator and separated into an oil and a residue containing a solid component.

The embodiments of the present invention will be described hereinafter, but the present invention is not limited thereto unless they are beyond the subject matter thereof.

Embodiment 1 As raw coal, brown coal A (calorific power 5930 Kcal/Kg dry non-mineral reference, fuel ratio 0.89, nitrogen content 0.43 weight dry non-mineral reference, oxygen content 28.30 weight dry non-mineral reference) i was used, and as a catalyst, 3 weight (mass) of pyrite -14-

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was used. Liquefying reaction was carried out under the conditions of temperature 450°C and hydrogen pressure MPa under the presence of the catalyst to obtain coal liquefied oil. The coal liquefied oil was modified by hydrotreating it under the conditions of temperature 350°C, hydrogen pressure 15 MPa and LHSV 1.0 hr- I using a flowing type fixed bed high pressure reactor filled with a Ni-Mo catalyst. The nitrogen content and oxygen content of the modified coal liquefied oil were obtained by analysis. The nitrogen content was 600 ppm, and the oxygen content was 4500 ppm, as shown in Table 1.

The modified coal liquefied oil was stored for three months at room temperature and under the atmosphere of air.

The coal liquefied oil after storage was filtered using a filter of 0.8 pm. The quantity of the obtained filtered residue (solid component) was 1.8 mg/100 ml (1.8 mg of solid component with respect to 100 ml of coal liquefied oil) as shown in Table 1. The color of the coal liquefied oil after storage for three months was examined by a method in accordance with JIS K 2580. The color was transparent, as shown in Table 1.

Embodiment 2 Coal liquefied oil was obtained by the method similar to that of Embodiment 1. The coal liquefied oil was modified by hydrotreating it under the conditions of temperature 370 0 C, hydrogen pressure 15 MPa and LHSV hr 1 using a flowing type fixed bed high pressure -R ll- ~--r~a~pII c LII-r~o~-ru a reactor filled with a Ni-Mo catalyst. The nitrogen content of the modified coal liquefied oil was 250 ppm, and the oxygen content thereof.was 2860 ppm.

The modified coal liquefied oil was stored for three months by the method similar to that of Embodiment 1. The quantity of the solid component produced from the coal liquefied oil was measured by the method similar to that of Embodiment 1. Its quantity was 0.3 mg/100 ml. The color of the coal liquefied oil after storage for three months was examined by the mettl similar to that of Embodiment 1. The color was L0.5, transparent.

Embodiment 3 ~As raw brown coal, brown coal B (calorific power 6640 Kcal/Kg dry non-mineral reference, fuel ratio 0.94, nitrogen content 1.10 weight dry non-mineral reference, oxygen content 22.05 weight dry non-mineral reference) was used to obtain coal liquefied oil by the method similar to that of Embodiment 1. The coal liquefied oil was modified by hydrotreating it under the conditions of temperature 350 0 C, hydrogen pressure 15 MPa and LHSV hr I using a flowing type fixed bed high pressure i reactor filled with a Ni-Mo catalyst. The nitrogen content of the modified coal liquefied oil was 780 ppm, and the oxygen content thereof was 2600 ppm.

The modified coal liquefied oil was stored for three months by the method similar to that of Embodiment 1. The coal liquefied oil after storage was filtered using a

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filter of 0.8 rm. The quantity of solid components produced from the coal liquefied oil was measured by the method similar to that of Embodiment 1. Its quantity was mg/100 ml. The color of the coal liquefied oil after storage for three months was examined. The color was transparent.

Embodiment 4 The coal liquefied oil was by the method similar to that of Embodiment 3. The coal liquefied oil was modified by hydrotreating it under the conditions of temperature 370 0 C, hydrogen pressure 15 MPa and LHSV 1.0 hr- 1 using a flowing type fixed bed high pressure reactor filled with a Ni-Mo catalyst. The nitrogen content of the modified coal liquefied oil was 550 ppm, and the oxygen content thereof was 1800 ppm.

The modified coal liquefied oil was stored for three months by the method similar to that of Embodiment 1. The quantity of solid components produced from the coal liquefied oil was measured by the method similar to that of Embodiment 1. Its quantity was 0.5 mg/100 ml. The color of the coal liquefied oil after storage for three months was examined. The color was LO.5, transparent.

Comparative Examle 1 The coal liquefied oil was by the method similar to that of Embodiment 1. The coal liquefied oil was modified by hydrotreating it under the conditions of temperature 300 0 C, hydrogen pressure 15 MPa and LHSV 1.0 hr-i using a flowing type fixed bed high pressure reactor filled with a Ni-Mo catalyst. The nitrogen content of the modified coal liquefied oil was 3000 ppm, and the oxygen content thereof was 11000 ppm as shown in Table 1.

The modified coal liquefied oil was stored for three months by the method similar to that of Embodiment 1. The quantity of solid components produced from the coal liquefied oil was measured by the method similar to that of Embodiment i. Its quantity was 110.0 mg/100 ml as shown in Table 1. The color of the coal liquefied oil after storage for three months was examined by the method similar to that of Embodiment 1. The color was L8.0, as shown in Table 1, the color being discolored into that close to black.

Comparative Examle 2 The coal liquefied oil was.by the method Sililar to that of Embodiment 1. The coal liquefied oil was modified by hydrotreating it under the conditions of temperature 350 0 C, hydrogen pressure 10 MPa and LHSV 1.5 hr- 1 using a flowing type fixed bed high pressure reactor filled with a Ni-Mo catalyst. The nitrogen content of the modified coal liquefied oil was 980 ppm, and the oxygen content thereof was 6500 ppm.

The modified coal liquefied oil was stored for three months by the method similar to that of Embodiment 1. The quantity of solid components produced from the coal ,liquefied oil was measured. Its quantity was 8.3 mg/100 ml.

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-18- The color of the coal liquefied oil after storage for three months was examined. The color was L6.5 and the color was close to brown.

Comparative Example 3 The coal liquefied oil was by the method similar to that of Embodiment 3. The coal liquefied oil was modified by hydrotreating it under the conditions of temperature 350 0 C, hydrogen pressure 10 MPa and LHSV 1.5 hr- 1 using a flowing type fixed bed high pressure reactor filled with a Ni-Mo catalyst. The nitrogen content of the modified coal liquefied oil was 1680 ppm, and the oxygen content thereof was 4800 ppm.

The modified coal liquefied oil was stored for three months by the method similar to that of Embodiment 1. The quantity of solid components produced from the coal liquefied oil was measured. Its quantity was 14.6 mg/100 ml. The color of the coal liquefied oil after storage for three months was examined. The color was L5.5 and the color was close to brown.

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Table 1 Results of Ana- Results of Raw lyzing Coal Testing Storage Coal Liquefied Oil Stability 1 Elements Nitrogen Oxygen Sludge Color Content Content Producing 3) Amount 2) LML ppm mg/100 ml ASTM Embodiment 1 Brown 600 4,500 1.8 Coal A Embodiment 2 Brown 250 2,860 0.3 Coal A Embodiment 3 Brown 780 2,600 1.5 Coal B Embodiment 4 Brown 550 1,800 0.5 Coal B Comparative Brown 3,000 11,000 110.0 Example 1 Coal A Comparative Brown 980 6,500 8.3 Example 2 Coal A Comparative Brown 1,680 4,800 14.6 Example 3 Coal B

[NOTE]

1) Results of evaluating storage stability after storage for three months in air at room temperature 2) Calculated from results of measuring weight after filtering by a filter of 0.8 pm, washing filtered residue by a solvent acetone and drying in vacuum 3) In accordance with JIS K 2580

Claims (5)

1. A method of stabilizing coal liquefied oil characterized in that coal liquefied oil obtained by hydrogenating raw coal is modified so that a nitrogen content in the coal liquefied oil is less than 1000 ppm, and an oxygen content is less than 5000 ppm.

2. The method of stabilizing coal liquefied oil according to claim 1, wherein said raw coal is brown coal. DATED this -31st day of March 1998 NIPPON BROWN COAL LIQUEFACTION 66., LTD By their Patent Attorneys CALLINAN LAWRIE We, KOBE STEEL LTD, of 3-18, Wakinohama-cho 1-chomne, Chuo-ku, Kobe-shi, Hyogo-ken, Japan, MITSUBISHI CHEMICAL CORPORATION, of 5-2 Marunouchi 2- chome. Chiyoda-ku. Tokyo, Japan, IDEMITSU KOSAN CO. LTD, ofl1-I Marunouchi

3-chorne. Chiyoda-ku. Tokyo. Japan, COSMO OIL COMPANY LTD. of 1-1, Shibaura 1-inoe.

Minato-ku, Tokyo [05-8528, Japan and NISSHO IWAI CORPORATIOy"

5-8, Imabashi 2-chorne, Chuo-ku, Osaka 541-0042, Japan