Use of an organic solvent for denitrogenationation of light oil by extraction

Abstract: The use is provided of an organic solvent comprising either a heterocyclic compound containing nitrogen or an acid amide compound for denitrogenating a light oil by extraction. The heterocylic compound may be a ketone or a pyridinium salt. Such a heterocyclic ketone may be a pyrrolidone compound, an imidazolidinone or a pyrimidinone. Any of such ketones may be substituted by an alkyl group. The acid amide which may form the organic solvent can be dimethylformamide, dimethylacetamide or N,N-dimethylbenzamide.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention: This invention relates to the denitrogenation of light oil by extraction. 2. Description of Prior Art: The term "light oil" means either an intermediate or a final product obtained from the process of petroleum refining. Light oil as an intermediate product usually contains about 1% by weight of sulfur compounds. Thesulfur compounds not only exert an adverse effect on the quality of petroleum products, but also form as a result of combustion sulfur oxides which cause environmental pollution. Light oil is, therefore, desulfurized to make a wide range of products including a cleanser, a fuel for a diesel engine, or burner, absorption oil, oil gas, and thermally or catalytically cracked gasoline. In addition, light oil contains nitrogen compounds in concentration of from about a hundred to several hundreds ppm. As the nitrogen compounds form as a result of combustion NO x which causes environmental pollution, it is desirable to remove said nitrogen compounds from light oil as much as possible. But the efficient denitrogenation of light oil has not been reported. US-A-3 197 400 discloses a process for refining mineral oil fractions to reduce their sulfur content by contacting the oil with a sweetening solvent of a dialkyl N-substituted aliphatic acid amide such as N,N-dimethylformamide. The use of such a solvent is also indicated to improve the colour of the oil. The use of such solvents is contrasted with the use of pyridine and piperidine in this reference which are indicated to be largely ineffective. SUMMARY OF THE INVENTION Under these circumstances, it is an object of this invention to provide the use of certain organic solvents for denitrogenating light oil by extraction. It is further object of this invention to provide denitrogenated light oil. We, the inventors of this invention, have found that, while light oil contains aliphatic and aromatic sulfur compounds, it is mainly aromatic sulfur compounds that remain unremoved in a hydrodesulfurized product of light oil. We have, therefore, made an extensive scope of research work to explore a method of removing aromatic sulfur compounds from light oil, and found that extraction, which has hitherto not been employed for desulfurizing light oil, can desulfurize light oil easily and effectively, particularly if it is perfomed by using a specific kind of organic solvent and found that extraction with said specific solvent is effective also for denitrogenating light oil. Thus, the above object is essentially attained by the use of an organic solvent comprising either a heterocyclic compound containing nitrogen or an acid amide compound for denitrogenating a light oil by extraction. Preferably the solvent comprises a heterocyclic ketone containing nitrogen or a pyridinium salt. The heterocyclic ketone is preferably a pyrrolidone, an imidazolidinone, or a pyrimidinone any of which may be substituted by alkyl. The acid amide compound is preferably dimethylformamide, dimethylacetamide or N,N-dimethylbenzamide. The use of this invention can remove from light oil nitrogen compounds only by extraction which is a simple process. Therefore said process of this invention can be a drastic measure for reducing NO x originated from light oil. When the use of this invention is carried out using a multistage extraction technique, it can reduce the solvent ratio which is the proportion by weight of the solvent to that of the light oil taken as 1, and raise the rate of denitrogenaticnand the yield of raffinate oil. Other features and advantages of this invention will be apparent from the following description DETAILED DESCRIPTION OF THE INVENTION For the purpose of this invention, light oil is a petroleum fraction having a boiling range between those of kerosine and heavy oil, and containing nitrogen compounds such as carbazoles that have to be removed. It may, or may not be a product of hydrodesulfurization. The use of this invention is carried out by employing a heterocyclic compound containing nitrogen, or an acid-amide compound as the organic solvent containing nitrogen. The solvent is employed for removing carbazoles from light oil. It is possible to use either a single compound or a mixture of compounds, or even a mixture of a compound containing nitrogen and a compound not containing nitrogen. Examples of the heterocyclic compounds containing nitrogen which can be employed are heterocyclic ketones containing nitrogen, such as pyrrolidones, imidazolidinones, pyrimidinones, piperidones, pyrazolidinones and piperazinones. It is possible to use either an unsubstituted or an alkylsubstituted compound. Pyrrolidones such as N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone, imidazolidinones such as 1,3-dimethyl-2-imidazolidinone, 1,3-diethyl-2-imidazolidinone, and pyrimidinones such as 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone, are, among others, preferred. Other examples are pyridinium salts, such as trimethylpyridinium hydrobromide, 1,2,4,6-tetramethylpyridinium iodide and N-ethylpyridinium bromide. If a pyridinium salt is used as the solvent, the use of another solvent having one or more hydroxyl groups, such as methanol, ethanol, ethylene glycol or glycerol with the pyridinium salt is preferred from the standpoint of extraction efficiency. Example of the acid-amide compounds include dimethylformamide, diethylformamide, and dimethylacetamide. Apart from using a specific kind of solvent, the use of this invention is carried out by following any ordinary process for liquid-liquid extraction. Thus, the light oil to be denitrogenated and the solvent are mixed in appropriate proportions, and after a vessel containing their mixture has been shaken for an appropriately long time at room temperature, it is separated into two phases and the solvent phase is removed from the vessel. The oil phase is, then, rinsed with e.g. water, if required. Although the extraction process is usually carried out at room temperature, it is possible to heat the liquid mixture to obtain a higher extraction efficiency. The mixing proportion of light oil and the solvent depends on the nitrogen content of the light oil to be treated and the nature of the solvent, and preferably the weight proportion of light oil and a solvent is 1:0.5-4.0. It is preferable that a solvent is used as little as possible from the standpoint of the process cost. When the multistage extraction is effected according to this invention, good results of denitrogenation are obtained even though the solvent ratio is low. When water is added to the solvent in this invention, the yield of raffinate oil can be increased. The nitrogen content of denitrogenated light oil varies in wide range depending upon the nitrogen content of untreated light oil and the nature of the solvent used. Although it is preferable that the content of treated light oil is as little as possible, the combination of the use of this invention with an ordinary process of hydrodesulfurization yields a desulfurized and denitrogenated product of light oil having sulfur content and nitrogen content not exceeding 0.1% by weight and 100 ppm, in particular not exceeding 0.01% by weight and 20 ppm, respectively. The invention will now be described in further detail with reference to specific examples. It is, however, to be understood that the following description is not intented for limiting the scope of this invention. B. Denitrogenation by Extraction: The examination of denitrogenation of light oil by extraction was carried out. B-1: The Relation between Rate of Denitrogenation and Solvent Ratio In the example, a sample of light oil having sulfur content of 0.198% by weight and nitrogen content of 202 ppm, which is called IGO and is an intermediate product, were employed, and will be referred to as light oil C. A separatory funnel was charged with light oil C and N-methyl-2-pyrrolidone (NMP) as an extraction solvent in a weight proportion of 1:0.5-4.0, and after it had been satisfactorily shaken, it was left to stand to allow the separation of two phases, a raffinate phase and an extracted phase. From both phases each oil phase was collected. The sulfur content and nitrogen content of said each oil phase were determined by the radiation type excite method according to JIS K 2541 and the nitrogen analysis method by chemiluminescence according to JIS K 2609, respectively. Also, these oil phases were subjected to FIA analysis according to JIS K 2536. In addition, the oil phase from the raffinate phase was subjected to the determination of Saybolt color according to JIS K 2580 and the analysis of aromatic components by means of liquid chromatography on silica gel. The results are summarized in TABLE 1. It is obvious from TABLE 1 that the rate of denitrogenation increased with the rise of the solvent ratio, though the yield of raffinate was decreased. In particular, when the solvent ratio is 2.5 and more, the rate of denitrogenation exceeded 90%. In addition, it was recognized that the solvent used in this invention had the significant effect of decolorization. Further, it was proved that the solvent used in this invention tended to extract polycyclic aromatic components more than monocyclic ones. Meanwhile, as polycyclic aromatic components are a principal factor of particulates emitted from diesel engines, the solvent in this invention enables light oil to increase in cetane index. The properties of untreated light oil and each raffinate oil obtained by extraction described above are summarized in TABLE 2. Untreated light oil Light oil C treated with solvent below NMP NMP NMP NMP NMP Solvent ratio - 0.5 1.0 1.5 2.5 4.0 Density (15°C) 0.8465 0.8376 0.8330 0.8302 0.8268 0.8235 Sulfur content (wt. %) 0.198 0.124 0.092 0.073 0.057 0.042 Nitrogen content (ppm) 202 76 51 38 27 19 FIA (vol%) SAT 79.3 83.6 87.1 88.8 93.1 94.3 AROM 20.7 16.4 12.9 11.2 6.9 5.7 OLE 0 0 0 0 0 0 Kinetic viscosity (30°C) Cst 6.058 6.072 6.120 6.131 6.211 6.291 Cetane index JIS 59.6 63.4 65.7 67.2 69.0 70.6 ASTM 60.4 65.0 67.7 69.4 71.9 74.0 Pour point °C 0 0 0 +2.5 +2.5 +5 Cloud point °C +2 +3 +3 +4 +4 +6 CFPP °C -2 -3 0 0 +1 +1 Flash point °C 104 107 105 109 108 110 Shade (ASTM) L1.5 0.5 L0.5 L0.5 L0.5 L0.5 (Footnote) In the column of cetane index, "JIS" means the values obtained according to JIS K 2536, and in the column of cetane index and shade, "ASTM" means the values obtained according to ASTM. B-2: Denitrogenation with various Solvents A separatory funnel was charged with light oil C used in B-1 and 1,3-dimethyl-2-imidazolidinone (DMI), dimethylacetoamide (DMA), dimethylformamide (DMF), ethylsuccinylamide (ESI) or 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone (DTP) which is an extraction solvent in this invention, in the weight proportion of 1:1, and after it had been satisfactorily shaken, it was left to stand to allow the separation of two phases, a raffinate phase and an extracted phase. From both phases each oil phase was collected. The sulfur content and nitrogen content of said each oil phase were determined by the radiation type excite method according to JIS K 2541 and the nitrogen analysis method by chemiluminescence according to JIS K 2609, respectively. Also, these oil phases were subjected to FIA analysis according to JIS K 2536. Further, Saybolt color of the oil phase from the raffinate phase was determined according to JIS K 2580. The results are summarized in TABLE 3. In addition, the extraction with diethylene glycol (DEG), furfral (FURF), sulfuran (SULF) or dimethyl sulfoxide (DMSO) was effected in a similar manner as above. The results are summarized in TABLE 4. Light oil C treated with solvent below NMP DMI DMA DMF ESI DTP Solvent ratio 1.0 1.0 1.0 1.0 1.0 1.0 Yield (wt%) RAFF 82.4 85.2 81.7 88.1 92.1 79.3 EXT 17.6 14.8 18.3 11.9 7.9 20.7 Sulfur content (wt. %) RAFF 0.092 0.095 0.102 0.110 0.131 0.097 EXT 0.731 0.812 0.674 0.895 1.031 0.627 Nitrogen content (ppm) RAFF 51 58 58 63 72 60 EXT 860 780 560 1030 1770 660 Saybolt color +6 -1 -1 -5 - - FIA (vol%) RAFF SAT 87.1 83.9 84.7 84.1 81.0 85.8 AROM 12.9 16.1 15.3 15.9 19.0 14.2 EXT SAT 40.8 36.2 44.8 31.3 - 47.4 AROM 59.2 63.8 55.2 68.7 - 52.6 Selection rate S vs AROM 1.88 2.34 1.96 2.06 - 1.87 N vs AROM 3.99 3.69 2.87 4.15 - 3.18 S vs OIL 7.95 8.55 6.61 8.14 7.87 6.46 N vs OIL 16.86 13.45 9.66 16.35 24.58 11.00 Rate of desulfurization (%) 62.1 59.7 58.1 51.5 40.4 62.6 Rate of denitration (%) 79.4 75.9 76.7 74.5 69.2 77.3 Light oil C treated with solvent below DEG FURF SULF DMSO Solvent ratio 1.0 1.0 1.0 1.0 Yield (wt%) RAFF 98.8 91.8 96.3 96.3 EXT 1.2 8.2 3.7 3.7 Sulfur content (wt. %) RAFF 0.187 0.122 0.163 0.152 EXT 1.515 1.075 1.442 1.549 Nitrogen content (ppm) RAFF 107 62 91 75 EXT 10000 1250 2550 2550 Saybolt color < 16 -13 -16 -15 FIA (vol%) RAFF SAT 78.5 84.4 80.7 80.5 AROM 21.5 15.6 19.3 19.5 EXT SAT - 14.3 12.2 10.6 AROM - 85.7 87.8 88.4 Selection rate S vs AROM - 1.81 2.19 2.51 N vs AROM - 4.14 6.92 8.36 S vs OIL 8.10 8.81 8.85 10.19 N vs OIL 93.46 20.16 28.02 34.00 Rate of desulfurization (%) 9.0 42.1 24.0 27.8 Rate of denitration (%) 49.0 71.2 58.4 65.1 As is obvious from TABLES 3 and 4, the use of this invention enables relatively high yield of raffinate oil, and high rate of denitrogenation, while in comparative test (TABLE 4) the rate of denitrogenation was low. B-3: Denitrogenation with Solvent containing Water In the example a mixture of NMP and water having weight proportion of 1:2.0-20.2 was used as a solvent. A separatory funnel was charged with light oil C used in B-1 and the solvent containing water described above in the weight proportion of 1:1, and after it had been satisfactorily shaken, it was left tostand to allow the separation of two phases, a raffinate phase and an extracted phase. From both phases each oil phase was collected. The sulfur content and nitrogen content of said each oil phase were determined by the radiation type excite method according to JIS K 2541 and the nitrogen analysis method by chemiluminescence according to JIS K 2609, respectively. Also, these oil phases were subjected to FIA analysis according to JIS K 2536. Further, Saybolt color of the oil phase from the raffinate phase was determined according to JIS K 2580. The results are summarized in TABLE 5. Untreated light oil Light oil C treated with solvent below NMP NMP NMP NMP NMP Solvent ratio - 1.0 1.0 1.0 1.0 1.0 Added water content (wt%) 0.0 2.0 5.1 10.0 20.2 Yield (wt%) RAFF - 82.4 87.9 92.2 94.9 97.6 EXT - 17.6 12.1 7.8 5.1 2.4 Sulfur content (wt. %) RAFF 0.198 0.092 0.103 0.116 0.140 0.164 EXT - 0.731 0.939 1.242 1.470 1.779 Nitrogen content (ppm) RAFF 202 51 54 64 74 96 EXT - 860 1120 1570 2100 - Saybolt color < -16 +6 +2 +3 -8 < -16 FIA (vol%) RAFF SAT 79.3 87.1 85.8 82.7 79.9 79.2 AROM 20.7 12.9 14.2 17.3 20.1 20.8 EXT SAT - 40.8 29.7 11.8 8.7 5.5 AROM - 59.2 70.3 88.2 91.3 94.5 Selection rate S vs AROM - 1.88 2.03 2.37 2.61 2.70 N vs AROM - 3.99 4.62 5.79 7.05 - S vs OIL - 7.95 9.12 10.71 10.50 10.85 N vs OIL - 16.86 20.74 26.17 28.38 - Rate of desulfurization (%) - 62.1 54.7 46.8 33.6 20.3 Rate of denitration (%) - 79.4 76.7 73.0 65.6 54.2 As is obvious from TABLE 5, the yield of raffinate oil becomes higher as added water content is more. B-4: Extraction of Fractional Distillates of IGO with Solvent In the example three fractional distillates of light oil C used in B-1 were denitrogenated. These distillates were ones with distillation range between the initial boiling point and 290°C (distillate A), between 290°C and 310°C (distillate B), and between 310°C and the stop point (distillate C). A separatory funnel was charged with each distillate and NMP, the solvent in the weight proportion of 1:1, and after it had been satisfactorily shaken, it was left to stand to allow the separation of two phases, a raffinate phase and an extracted phase. From both phases each oil phase was collected. The sulfur content and nitrogen content of said each oil phase were determined by the radiation type excite method according to JIS K 2541 and the nitrogen analysis method by chemiluminescence according to JIS K 2609, respectively. Also, these oil phases were subjected to FIA analysis according to JIS K 2536. Further, Saybolt color of the oil phase from the raffinate phase was determined according to JIS K 2580. The results are summarized in TABLE 6. Ditillate A Ditillate B Ditillate C a b a b a b Solvent ratio - 1.0 - 1.0 - 1.0 Yield (wt%) RAFF - 78.5 - 83.8 - 85.4 EXT - 21.5 - 16.2 - 14.6 Sulfur content (wt. %) RAFF 0.042 0.029 0.169 0.075 0.358 0.153 EXT - 0.108 - 0.683 - 1.605 Nitrogen content (ppm) RAFF 56 27 128 35 336 87 EXT - 167 - 530 - 1960 Saybolt color +17 +27 -5 +21 < -16 -16 FIA (vol%) RAFF SAT 78.9 86.7 80.5 87.3 79.0 87.8 AROM 21.1 13.3 19.5 12.7 21.1 12.2 EXT SAT - 50.2 - 45.6 - 10.2 AROM - 49.8 - 54.4 - 89.8 Selection rate S vs AROM - 1.06 - 2.29 - 1.63 N vs AROM - 1.76 - 3.80 - 3.38 S vs OIL - 3.72 - 9.11 - 10.49 N vs OIL - 6.19 - 15.14 - 21.79 Rate of desulfurization (%) - 47.3 - 63.9 - 65.2 Rate of denitration (%) - 63.2 - 77.8 - 78.9 (Footnote) The column "a" indicates the values of untreated distillates, and the column "b" indicates the values of treated distillates. As is obvious from TABLE 6, the higher the boiling point of the ditillate is, the higher the rate of denitrogenation is. In addition, since most of the sulfur components and nitrogen components concentrate in the distillate with higher distillation range, one can see that the denitrogenation can be effected with high efficiency, when the extraction is effcted for the distillate of light oil with higher distillation range after light oil was fractionated by distillation. B-5: Extraction of Light Oil of Low Sulfur Content with Solvent A separatory funnel was charged with light oil of low sulfur content (having a sulfur content of 0.064% by weight and a nitrogen content of 186 ppm, reffered to as light oil D) and NMP, the solvent in a weight proportion of 1:1 or 1:2.5, and after it had been satisfactorily shaken, it was left to stand to allow the separation of two phases, a raffinate phase and an extracted phase. From both phases each oil phase was collected. The sulfur content and nitrogen content of said each oil phase were determined by the radiation type excite method according to JIS K 2541 and the nitrogen analysis method by chemiluminescence according to JIS K 2609, respectively. Also these oil phases were subjected to FIA analysis according to JIS K 2536. Further, Saybolt color of the oil phase from the raffinate phase was determined according to JIS K 2580. The results are summarized in TABLE 7. Untreated light oil Light oil D treated with solvent below NMP NMP Solvent ratio - 1.0 2.5 Yield (wt%) RAFF - 82.1 69.0 EXT - 17.9 31.0 Sulfur content (wt. %) RAFF 0.064 0.023 0.014 EXT - 0.225 0.164 Nitrogen content (ppm) RAFF 186 42 21 EXT - 820 510 Saybolt color < -16 -1 +15 FIA (vol%) RAFF SAT 77.7 85.3 90.4 AROM 22.3 14.7 9.6 EXT SAT - 40.0 48.1 AROM - 60.0 51.9 Selection rate S vs AROM - 2.59 2.34 N vs AROM - 5.18 4.84 S vs OIL - 9.78 11.71 N vs OIL - 19.52 24.29 Rate of desulfurization (%) - 71.1 85.2 Rate of denitration (%) - 81.8 92.3 Also in the case of light oil of low sulfur content, the rate of denitrogenation became higher with a rise in the solvent ratio. B-6: Multistage Extraction In the example the multistage extraction was effected utilizing as a solvent light oil C used in B-1 (having a sulfur content of 0.198% by weight) or light oil D used in B-5 (having a sulfur content of 0.064% by weight). The number of stages was 3, and the solvent ratio was 1.0 ultimately. The results are summarized in TABLE 8. Light oil C Light oil D The number of stage 1st 2nd 3rd 1st 2nd 3rd RAFF Yield (wt%) (83.6) (80.6) 76.6 (88.0) (83.9) 74.8 Sulfur content (wt. %) 0.115 0.072 0.040 0.036 0.024 0.015 Nitrogen content (ppm) 60 35 17 50 23 12 Saybolt color -1 +15 +20 -7 +14 +23 FIA (vol%) SAT 83.4 85.0 91.6 79.7 84.6 90.0 AROM 16.6 15.0 8.4 20.3 15.4 10.0 Aromatic component of RAFF (vol%) monocyclic - - 7.4 - - 7.3 polycyclic - - 0.0 - - 0.0 Cetane index JIS - - 67.6 - - 68.5 ASTM - - 69.9 - - 71.0 As is obvious from TABLE 8, when the multistage extraction was effected according to this invention, good results of denitrogenation were obtained even though the solvent ratio was low. It was also recognized that the level of decolorization became higher with an increase in the number of stages. Further, it was proved that the solvent in this invention tended to extract polycyclic aromatic components more than monocyclic ones. B-7: Separation of Extracted Phase into Solvent and Extracted Oil In the example the regeneration of a solvent was attempted. At first an extracted phase was obtained by subjecting light oil to extraction with a solvent, NMP. The extracted phase had an extracted oil content of 12.6% by weight and a solvent content of 87.4% by weight. 20, 50 or 100% by weight of water was added to the extracted phase, and after it had been satisfactorily shaken, it was left to stand to allow the separation of the water phase and oil phase. Each phase was examined for the distribution of components. The results are summarized in TABLE 9. The quantity of added water 0% 20% 50% 100% Separated phases - EXT NMP EXT NMP EXT NMP Weight of phase (wt. %) - 7.6 92.4 7.5 92.5 6.0 94.0 Distribution Extracted oil - 70.1 29.9 87.5 12.5 94.9 5.1 NMP - 0.4 99.6 0.3 99.7 0.1 99.9 Composition Extracted oil 12.6 96.4 3.4 98.0 1.2 99.3 0.3 NMP 87.4 3.6 78.5 2.0 62.8 0.7 46.5 Water - 0.0 18.1 0.0 36.0 0.0 53.2 Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 When water is added to an extracted phase which comprises an solvent and extracted oil, the solvent in most of the cases becomes an aqueous solution if the solvent is NMP. A little extracted oil is contained in the aqueous solution, but most of the extracted oil forms an extracted oil phase. As a mixture of NMP and water is not an azotropic mixture, the NMP can be removed with the aid of the difference of boiling points between NMP and water. In this way, NMP can be removed to be used again as a solvent. In addition, the oil phase is little contaminated by NMP, and the more the quantity of added water is, the less the level of contamination is. Meanwhile, the process described above is more effctive from a standpoint of process cost than the process wherein the extracted phase is directly distilled.

Claims: The use of an organic solvent comprising either a heterocyclic compound containing nitrogen or an acid amide compound for denitrogenating a light oil by extraction. The use according to claim 1, wherein said solvent comprises a heterocyclic ketone containing nitrogen or a pyridinium salt. The use according to claim 2, wherein said heterocyclic ketone is a pyrrolidone, an imidazolidinone, or a pyrimidinone any of which may be substituted by alkyl. The use according to claim 1, wherein said acid amide compound is dimethylformamide, dimethylacetamide or N,N-dimethylbenzamide.

Inventors: DOI SADAAKI, HORII YUJI, MORI TOSHIATSU, ONUKI HITOSHI, OOKURO TSUYOSHI, SATO HIDEAKI, SUGAWARA TORU, TAKATORI TAEKO, DOI, SADAAKI, HORII, YUJI, MORI, TOSHIATSU, ONUKI, HITOSHI, OOKURO, TSUYOSHI, SATO, HIDEAKI, SUGAWARA, TORU, TAKATORI, TAEKO, DOI, SADAAKI, C/O CENTRAL LATORATORY, HORII, YUJI, C/O CENTRAL LATORATORY, MORI, TOSHIATSU, C/O CENTRAL LATORATORY, ONUKI, HITOSHI, C/O CENTRAL LATORATORY, OOKURO, TSUYOSHI, C/O CENTRAL LATORATORY, SATO, HIDEAKI, C/O CENTRAL LATORATORY, SUGAWARA, TORU, C/O KABUSHIKI KAISHA GENETECH, TAKATORI, TAEKO, C/O CENTRAL LATORATORY
Applicants: GEN SEKIYU KABUSHIKI KAISHA, GENERAL SEKIYU KABUSHIKI KAISHA
Application year: 1992
Main classification: C10G21
IPC codes: C10G21