Applicability of nonthermal plasma (NTP) to chemical reactions such as removal of hazardous air pollutants (HAPs), hydrogen production from small molecules, and hydrocarbon reforming is discussed on the basis of NTP-generating methods, the physicochemical nature of NTP, the reaction behavior of N2, O2, volatile organic compounds, and nitrogen oxides, and synergistic effects of NTP and catalysts/photocatalysts. Plasma-generating methods greatly affect the mean electron temperature and the distribution of active species formed in NTP. Hybridization of NTP with catalysts/photocatalysts is mandatory to increase the energy efficiency of the reaction system. Issues for practical application of NTP is discussed, using HAPs control as an example. The results of the authors' feasibility study indicate that the scale-up merit of the NTP reactor depends on the plasma-generating method.
The catalytic performance of noble metals supported on zeolites and related materials such as Al-pillared clays (Al-PILCs) and mesoporous silica (MCM-41) for the hydrodesulfurization (HDS) of thiophene and benzothiophene as a model HDS reaction were investigated to develop highly active new HDS catalysts. Pt/HZSM-5, Rh/Al-PILM (montmorillonite), sulfided Rh/Al-PILH (hectorite) and Pt/MCM-41 catalysts showed high and stable activities for the HDS of thiophene which were higher than that of commercial CoMo/Al2O3 HDS catalyst. Pt/HZSM-5, Pt/Al-PILH and Pt/MCM-41 catalysts showed higher activity for the HDS of benzothiophene than CoMo/Al2O3 catalyst, indicating that these catalysts have high activity for the HDS of large organic sulfur molecules in petroleum feedstocks. Therefore, noble metals supported on zeolites and related materials might provide promising new catalysts for the HDS of petroleum feedstocks. Furthermore, noble metals supported on zeolites and related materials act as bifunctional catalysts for the HDS reactions, in which the noble metal acts as the active site for the activation of hydrogen to form spillover hydrogen and the acid sites of the support acts as the active site for activation of thiophenes. As the spillover hydrogen formed on the noble metals attacks the activated thiophenes formed on the acid sites of the support, the HDS reaction proceeds smoothly to form hydrogen sulfide and hydrocarbons. Therefore, the hydrogen activation of the noble metal and the acidity of the support must be complementary to develop much more active noble metals HDS catalysts supported on zeolites and related materials.
Reduction of NO was examined over the potassium-doped active carbon modified with Ce and Mn (K, Ce, Mn/C) in the presence and/or absence of O2. NO is reduced at temperatures above 473K even in the absence of O2, while the reduction of NO is enhanced at 473K in the presence of O2. Twenty-five percent of NO was steadily reduced at 473K in the reaction of NO with K, Ce, Mn/C under simulated exhaust gas containing oxygen (2%). The NO conversions on both K, Ce/C and K, Mn/C were less than 10% under the same condition. Therefore, co-existence of Ce and Mn acts attractively for the steady reduction of NO to N2 with carbon.
Hydrothermal visbreaking of bitumen in supercritical water with alkali was investigated to assess the feasibility and reaction conditions for developing a new on-site visbreaking technology combined with the SAGD process. The results can be summarized as follows: (1) Bitumen was easily converted to light oils with a conversion ratio of more than 85%, with simultaneous 50% reduction of sulfur content and coke production of ca. 8%, at 430°C reaction temperature and 15min reaction time with 1mol dm-3 KOH solution at 20% water fill. (2) The oils produced were sufficiently light for pipeline transportation. (3) Fluctuations of flow rate and oil-water ratio in the feed to the reactor had no serious effect. (4) The visbreaking and coking reactions were apparently hindered by the presence of water, compared with pyrolysis. (5) The viscosity of the oil was drastically reduced in the first 5min, which occurred at a higher reaction temperature and/or a lower water fill.
The catalytic activity of alumina for NO reduction by propene was considerably enhanced by mixing mechanically with Ag/SiO2. Based on catalyst characterization, it was concluded that the activity enhancement was due to the formation of Ag/Al2O3 by migration of silver from Ag/SiO2 to alumina under the reaction conditions. The migration of silver was found to occur in oxidizing atmospheres, and accelerated by the presence of H2O. The same performance of mechanically mixed catalysts was also observed for NO reduction by decane.
Direct formation of methacrolein from isobutane was investigated using a combination of the catalyst effective for oxidative dehydrogenation of isobutane, Ni2P2O7, and the catalyst effective for selective oxidation of olefins, Bi1-Mo12-Fe1-Co6-Ni2-Cs0.14-Oxide. Methacrolein was formed with the selectivity as high as 65% in a reactor with two catalyst beds in series. A mixed catalyst consisting of a mixture of the powders of both catalysts was effective for isobutene formation, although the conversion was reduced, whereas a mixture of granules was less effective. Addition of water vapor to the reaction system reduced the formation of oxygenates and promoted the formation of isobutene.
Hydrogenation of CO was investigated over Pt, Ni, and Pd polycrystalline foils. The activity and selectivity of the reaction varied remarkably with repeated hydrogen reduction and reaction temperature. X-Ray diffraction measurement and electron back scattering diffraction analyses revealed that the preferential crystallographic orientation and the crystalline size in the metal foils were changed by the hydrogen reduction treatment and that these changes influenced the catalytic properties. The main products were methane and methanol using Pt foil, and the formation rates increased with higher reduction temperature. In contrast, C1-C4 hydrocarbons were the major products using Ni foil, and the formation rate changed with the thickness of the foils. The main products were methanol and acetaldehyde using Pd foil. The size and crystallographic orientation of the polycrystalline structure is the key factor controlling the activity and selectivity of CO hydrogenation.
The complex variable boundary element method (CVBEM) owes its elegance, the computational accuracy and efficiency, to the Cauchy's integral formula, and it can be interpreted as a semi-analytical scheme. Despite its sound mathematical foundations, the real performance of the CVBEM may be affected by its computational foundations. This study focuses on two of such fundamental aspects: the formulations of the CVBEM and the treatment of sink and source singularities. Here proposed are three types of formulations for the CVBEM, and their performances are assessed. Formulation I using known-variable equivalence may accumulate errors on unprescribed boundaries resulting in severe oscillation in error profiles. Formulation II using unknown-variable equivalence yields error profiles that are smoother and smaller than those of Formulation I. Formulation III using dual-variable equivalence yields the best accuracy among the three. By virtue of the semi-analytic nature of the CVBEM, the singularity programming, which separates singular and non-singular solutions, can be applied to the CVBEM. Non-singular flow behaves smoothly, and the CVBEM yields accurate non-singular solutions. A complete solution is obtained by adding an analytic singular solution to the non-singular solution. With the singularity programming, the CVBEM can handle the sink and source singularities without a loss of accuracy.
Desulfurization reaction of 4, 6-dimethyldibenzothiophene (4, 6-DMDBT), which is the most refractory sulfur species in the light gas oil, was performed at 270°C under hydrogen at 2.5MPa over catalyst consisting of CoMo/Al2O3 mixed with various zeolites. Skeletal isomerization of 4, 6-DMDBT was carried out over various zeolite catalysts using a Curie-point pyrolyzer. The effects of isomerization activity, Si/Al ratios and Ni loadings of zeolite catalysts on the desulfurization activity were investigated. Desulfurization activity increased with increasing isomerization activity of the zeolite catalysts. Zeolite catalysts, with lower Si/Al ratio and mesoporous structure formed by dealumination, were effective for the isomerization of 4, 6-DMDBT. In addition, loading of Ni on the zeolite catalysts improved the desulfurization activity. Desulfurization of 4, 6-DMDBT was ca. 40% over a CoMo/Al2O3 catalyst. The conversion was enhanced to 78% by adding 2wt% Ni-HY zeolite into the CoMo/Al2O3 catalyst.
In order to discuss the possibility of steam reforming of kerosene to produce hydrogen for the on-site fuel cell co-generation system, steam reforming of dodecane, as a model compound of kerosene, was carried out in the presence or absence of oxygen at 773-1073K using a fixed bed flow reactor. The catalytic performance of Ru, Rh, and Ir-loaded catalysts was compared. In the steam reforming of dodecane, Rh/La2O3 and Ru/La2O3 afforded higher dodecane conversions and hydrogen yields than those with Ir/La2O3. Dodecane conversion, however, increased with the addition of a small amount of oxygen together with steam over Ir/La2O3 catalyst, and the conversion of dodecane reached those obtained over Rh and Ru/La2O3 catalysts. Basic support La2O3 exhibited the best performance for the steam reforming in the presence of oxygen using Ir catalyst among the supports tested.
Chemical cleaning is a fouling removal technology based on circulation of chemicals through petroleum refining plant. The method can prolong run length by eliminating the necessity to open the plant, reduce scheduled turnaround period, and allow safe entry for repair of equipment. A chemical application technology was developed to remove fouling in vacuum distillation units. The key points are the addition of aromatic solvent during light gas oil circulation before the cleaning steps, and more effective sludge removal. The technology achieves almost the same cleaning performance as conventional hydro jet cleaning during scheduled turnaround. However, chemical oxygen demand and total nitrogen content of the water-based chem ical cleaning effluent are very high, so cannot be discharged into waterways without purification. Therefore, an effective method for the purification of the water-based chemical cleaning effluent was established using active carbon and ionexchange resin technologies.
Platinum nanosheets between graphite layers were active for hydrogenation of ethynyl group of phenylacetylene but less active for that of aromatic rings of phenylacetylene and benzene due to its structural characteristics.