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Titlelmprovement of Lifetime of Ni/MordeniteCatalysts for CO2 Reforming of Methane bySupport Modification with Alumina and Co-KLoadingAuthor(s)MURATA, Satoru, HATANAKA, Nobuyuki, KIDENA, Koh,NOMURA, MasakatsuCitationJournal of the Japan Petroleum Institute, 49(5):240-245Issue Date 2006Type ArticleText version publisherURL http://hdl.handle.net/10110/93Rights

Catalytic performance of nickel-loaded zeolite-based supports for CO2 reforming of methane was investigated. Among the three zeolites (H-Y, H-mordenite, and Na-mordenite), H-mordenite was the best support for the reaction, probably due to its thermal stability. The initial activity of Ni/H-mordenite (Ni/HM) was higher than that of conventional Ni/alumina catalyst (Ni/Al2O3), whereas deactivation of the former was slightly faster. A physical mixture of alumina and zeolite was a more effective support than zeolite. The resulting Ni/H-mordenite-alumina catalyst (Ni/HM-Al2O3) showed the highest performance among the catalysts tested. Under the conditions of atmospheric pressure of CO2/CH4/He stream (20/20/40ml/min)at 750°C, the initial CO2 conversion was 95% and this value was maintained for more than 20h. The catalytic performance of Ni/HM-Al2O3 was higher than that of Ni/Al2O3.

Thermolytic behavior of asphaltene fractions derived from both vacuum residue of Arabian crude oil and Indonesian natural asphalt was investigated. At first, the asphaltenes were analyzed by 1H- and 13C-NMR spectroscopy to obtain structural information. Structural differences between the two asphaltenes were found in the amount of naphthenic carbon and in the size of polycyclic aromatic units. The asphaltene obtained from Indonesian natural asphalt contains much larger amount of naphthenic carbon but smaller size of polycyclic aromatic units compared those from Arabian crude. Thermal treatments of the asphaltene were conducted in a glass tube at 420°C for 5min in the presence or in the absence of aromatic solvents. The molecular weight distribution of the samples and the products was evaluated by using a gel permeation chromatography. Among the solvents used, partially hydrogenated aromatic compounds such as 9, 10-dihydroanthracene (DHA) showed a slight effect on thermolysis of asphaltene, while polycyclic aromatic compounds such as anthracene (Ant) or acridine (Acr) were more effective. These results could be explained by referring to the radical acceptability of these aromatic solvents.

Three coal tar-derived isotropic pitches obtained by air blowing reaction and two parent pitches obtained by vacuum distillation were extracted with benzene and carbon disulfide respectively. The hydrogen distribution of the soluble fractions was assessed by infrared spectroscopy (IR) and 1H-NMR. Between the respective results of soluble fractions by two analytical techniques, reasonable agreement and good correlation were obtained. A method developed by the authors for the determination of the aromaticity index based on IR spectroscopy was found more reliable than 13C-NMR method to differentiate the aromatic portion from the aliphatic portion in the pitches. Average structural parameters of CS2 solubles of the three air blown pitches indicated the substantial differences in molecular size and shape. The 002-band of X-ray diffraction (XRD) clearly indicated the existence of stacking of aromatic planes in the three air blown pitches at room temperature. Analyses of IR and XRD profiles on the whole pitches suggested that three air blown pitches are different in aromaticity and crystallinity, although their softening points, H/C ratios, and solubilities are almost the same.

The structural properties of the n-C5 insoluble asphaltene isolated from the vacuum residue of Arabian crude mixture have been investigated by referring to the data obtained from pyrolysis gas chromatography/mass spectrometry (Py-GC/MS), 1H/13C NMR, gel permeation chromatography (GPC), and matrix assisted laser desorption/ionization time-of-flight (MALDI TOF) mass spectrometry methods. Assignments of NMR signals have been discussed in detail. The average size of aromatic fused ring systems within the asphaltene has been determined to be 4-5. Pyrolysis experiments implied that the asphaltene sample is constructed with relatively large polycyclic units connected by relatively strong bonds. Our results also support the view that asphaltene is a mixture of complex polydispersed molecules with large variation in molecular sizes.

Hydrocracking of petroleum heavy oils using transition metal-loaded zeolite catalyst was examined. Deasphalted oil (DAO) derived from vacuum residue of a mixture of Arabian light and medium crudes was successfully converted to gasoline fraction, attaining yield of more than 70%, using palladium and nickel co-loaded Y-type zeolite catalyst, at 350°C for 1h, in H2 pressurized to 4.9MPa. The mechanism of this hydrocracking process is discussed briefly. The authors also tried hydrocracking of fraction heavier than DAO, i.e. maltene, this affording gaseous products (C2-C4) and gasoline fraction, 35% and 52%, respectively, under the following conditions: 400°C, for 3h, in H2 pressurized to 6.9MPa, over the same catalyst.

Two kinds of mesocarbon microbeads (indicated MCMB-A and -B), prepared from different coal tar pitch, as well as their derivatives obtained by butylation and solvent extraction subjected to ultrasonic irradiation, were investigated by infrared (IR) spectroscopy, scanning electron microscopy (SEM) and Raman spectroscopy. For IR spectroscopic analysis of these samples, MCMB-B and its derivatives both showed electron transition absorptions at near-IR region and aromaticities at C-H stretching region, stronger than those of MCMB-A and its derivatives. SEM observation suggested that MCMB-B seemed to be rich in free carbon, more than MCMB-A. These results indicated the difference in structural characteristics between two MCMB samples: it could be presumed that MCMB-B would have degree of condensation and graphitization higher than those of MCMB-A. This could account for the experimental results previously reported that MCMB-B is inferior to MCMB-A regarding catalytic reactivity in butylation and solvent extraction. SEM images also indicated that MCMB had a surface layer of about 1-1.5μm. Raman spectra of the MCMB, before and after solvent extraction, suggested that MCMB had a graphitized carbon layer on the surface, higher than the inner carbon.

Hydrodesulfurization of a series of benzothiophene derivatives using hydrogen storage alloys as stoichiometric reagents, typically LaNi 5 , was investigated. It was found that the reactions of benzothiophene and dibenzothiophene with the pre-hydrogenated alloys in nitrogen selectively produced ethylbenzene and biphenyl, respectively, along with extremely minor amounts of aromatic ring-hydrogenated compounds in appropriate conditions. Even with a sterically hindered compound, 4,6-dimethyldibenzothiophene, hydrogenation of which, using conventional Co-Mo or Ni-Mo catalysts, tends to produce ring-saturated products, 3,3'-dimethylbiphenyl, was obtained as the predominant product. The alloys, thus, appear to be useful reagents for selective of elimination sulfur from sulfur-containing aromatic compounds.