Iranian Journal of Chemical Engineering (IJChE)

Abstract The quantity of by-products and polymeric compounds produced in the ethylene dimerization reaction is a critical factor from the industrial viewpoint. It may lead to the shutting down of 1-butene reactors. It is, therefore, highly desirable to identify the factors that are responsible for the formation of polymeric materials and how the formation of these heavy compounds can be minimized or prevented. A significant way to overcome this drawback is by judicious choice of the catalyst and reaction conditions. In this regard, a systematic study has been carried out on a titanium-based catalyst using tetrahydropyran (THP) and tetrahydrofuran (THF) as modifiers, and bromoethane as a new efficient accelerator in combination with triethylaluminum (Et3Al) activator. The addition of bromoethane led to dramatic increases in the rate of reaction and yield, and remarkable decreases in the amounts of heavy and polymeric compounds. It is proposed that specific weak coordination of the halide to the dimeric Et3Al may result in breakage of the Et3Al dimer and the release of monomeric Et3Al. The latter is more reactive than Et3Al dimer and leads to the facile generation of an increased number of the active metal sites that are responsible for the dimerization reaction. Finally, the catalytic performance of the novel homogeneous system [titanium tetrabutoxide Ti(OC 4H 9)4)/THP/Et3Al/bromoethane] has been examined under various
operating conditions.

Abstract Lanthanum in the A-site of LaMn 0.8Cu 0.2O 3±δ perovskite was partially substituted by silver. La 1–x Ag x Mn 0.8Cu 0.2O 3 samples (x=0, 0.1, 0.2, 0.3) were prepared by the two Pechini and sol–gel methods and their catalytic activity was evaluated for CH4 combustion and CO oxidation reactions. FT-IR analysis of different samples before calcination confirmed the formation of different complexes between the elements. Calcined samples were characterized using XRD, TPR, BET, SEM and XRF techniques. XRD results revealed that the Pechini method led to perovskite structures with higher
purity and that segregation of Ag in samples prepared by the sol–gel method was higher. SEM images and EDS results for samples before and after catalytic tests showed that the Pechini samples had a lower particle size and better distribution of the elements. The catalytic results indicate that the oxidation activity increased with the amount of Ag in the oxide, but the stability of the structure decreased.

Abstract In this study, we examined a scale-up to production of nickel perovskite catalyst, used in the conversion of natural gas to synthesis gas, using the sol-gel method in the laboratory and a bench-scale reactor. The required volume of solvent and catalyst activity in the methane-reforming reaction was determined from the optimum catalyst production conditions at the laboratory scale. This information was then used to design the bench-scale unit. We used heat-transfer models in a non-continuous bench reactor and scale-up fundamentals to achieve the same physical and chemical properties of the catalyst as that in the laboratory sample. A correlation coefficient corresponding to the experiment conditions, including the stirrer geometry, is presented based on the heat transfer equations in stirred tanks. This correlation can be used to estimate the heattransfer coefficient at larger scales, such as in a pilot reactor.

Abstract In this study we developed LaNixAl1-xO3 perovskite systems using a sol-gelmethod (with propionic acid as solvent) to use in methane-reforming reactions for producing synthesis gas. To understand the roles of the nature of the precursor and calcination conditions on the formation of LaNixAl1-xO3, we carried out identifications using NMR, FT-IR, XRD, SEM, and TEM. The precursor structure is a function of raw materials and calcination conditions. Nitrate salts of nickel, aluminium, and lanthanum, and calcinations at 750ºC for 4 h gave pure LaNixAl1-xO3 perovskite with good homogeneity, even at nanoscopic scales. These systems are highly efficient catalysts in steam and the dry reforming of methane. Various ratios of hydrogen to carbon monoxide in synthesis gas can be achieved by changing the feed type. We also investigated stabilization of these systems by studying the perovskite structure after reactivity tests. The optimum mixed perovskite for steam and dry reforming of methane is LaNi0.3Al0.7O3. The total conversion of CH4 is rapidly obtained at 750°C in steam reforming with a H2O/CH4 ratio = 3, the selectivity of CO is lower (55%) and the yield of hydrogen (98%) is higher compared to the ratio H2O/CH4 = 1. After 170 h of reaction, no deactivation had occurred, methane conversion remained higher than 90% at 750°C and in dry reforming, methane conversion and CO yield are about 98% and 95% respectively.