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Lower Conversion (lower + conversion)
Selected AbstractsPerformance study of modified ZSM-5 as support for bimetallic chromium,copper catalysts for VOC combustionJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2004Ahmad Zuhairi Abdullah Abstract The catalytic performance of bimetallic chromium,copper supported over untreated ZSM-5 (CrCu/Z), ZSM-5 treated with silicon tetrachloride (Cr,Cu/SiCl4 -Z) and ZSM-5 treated with steam (Cr,Cu/H2O-Z) is reported. The activity is based on the combustion of ethyl ethanoate and benzene at a feed concentration of 2000 ppm and a gas hourly space velocity (GHSV) of 32 000 h,1. Due to higher reactivity and larger molecular size compared with that of water molecules, SiCl4 reacted at the external surface of ZSM-5 crystals. Cr,Cu/SiCl4 -Z and Cr,Cu/H2O-Z both gave slightly lower conversion and carbon dioxide yield compared with Cr,Cu/Z. This was attributed to larger active metal crystallites formed in the mesopores and narrowing pore mouth and pore intersection by extraframework species. Cr,Cu/SiCl4 -Z and Cr,Cu/H2O-Z both had reduced concentration and strength of acid sites, thus making them less susceptible to deactivation by coking. The coke accumulated by these two catalysts was relatively softer and more easily decomposed in oxygen during catalyst regeneration. Copyright © 2004 Society of Chemical Industry [source] Modeling of partial oxidation in gas,solids downer reactorsAICHE JOURNAL, Issue 8 2010S. Vaishali Abstract Selective partial oxidations represent an important class of reactions in the process industry. Of particular interest is the partial oxidation of n-butane to maleic anhydride (MAN), which is arguably the largest commercialized alkane partial oxidation process. Partial oxidation of n-butane, which uses vanadium phosphorous oxide (VPO) as a heterogeneous catalyst, is believed to operate through a unique mechanism in which lattice oxygen oxidizes n-butane selectively to MAN. Past work has shown that performing partial oxidation reactions in gas,solids riser configuration is realizable and commercially viable, which has lead to commercialization of this technology in the last decade. Though the riser configuration allows optimal and independent control of the oxidation and reduction steps, the riser unit suffers from solid backmixing at walls, which in turn result into lower conversion, nonoptimal selectivity and diminished overall yield of desired product. In recent years, there has been growing interest in downers involving cocurrent downflow of both solids and gas phases, hence offering relatively uniform flow characteristics. In this contribution, we explore through modeling the implications of effecting partial oxidation reactions in a downer (gas,solids cocurrent downflow) compared to that in a conventional riser reactor (gas,solids cocurrent up flow) operated under equivalent operating conditions. Further, we explore the operational space of downers for these reactions, suggesting ways for improving the productivity of downer for partial oxidation applications. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Gelation and Hollow Particle Formation in Nitroxide-Mediated Radical Copolymerization of Styrene and Divinylbenzene in MiniemulsionMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 2 2009Per B. Zetterlund Abstract Network formation in the nitroxide-mediated cross-linking copolymerization of styrene and divinylbenzene (3 or 8.2 mol-% relative to total monomer) using the nitroxide 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) at 125,°C can proceed markedly differently in aqueous miniemulsion compared to the corresponding solution polymerization depending on the organic-phase composition. When the organic phase comprises 54 vol-% of the hydrophobe tetradecane, gelation occurs at much lower conversion in miniemulsion than in solution, and at significantly lower conversion than predicted by Flory,Stockmayer gelation theory. This is proposed to be a result of an effect of the oil,water interface, whereby the concentration of polymer with pendant unsaturations is higher near the interface than in the particle interior. [source] Co-current and Countercurrent Configurations for a Membrane Dual Type Methanol ReactorCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 1 2008R. Rahimpour Abstract A dynamic model for a membrane dual-type methanol reactor was developed in the presence of catalyst deactivation. This reactor is a shell and tube type where the first reactor is cooled with cooling water and the second one with feed synthesis gas. In this reactor system, the wall of the tubes in the gas-cooled reactor is covered with a palladium-silver membrane which is only permeable to hydrogen. Hydrogen can penetrate from the feed synthesis gas side into the reaction side due to the hydrogen partial pressure driving force. Hydrogen permeation through the membrane shifts the reaction towards the product side according to the thermodynamic equilibrium. Moreover, the performance of the reactor was investigated when the reaction gas side and feed gas side streams are continuously either co-current or countercurrent. Comparison between co-current and countercurrent mode in terms of temperature, activity, methanol production rate as well as permeation rate of hydrogen through the membrane shows that the reactor in co-current configuration operates with lower conversion and also lower permeation rate of hydrogen but with longer catalyst life than does the reactor in countercurrent configuration. [source] Lipase-catalyzed production of biodiesel from rice bran oilJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2005Chao-Chin Lai Abstract Biodiesel has attracted considerable attention as an alternative fuel during the past decades. The main hurdle to the commercialization of biodiesel is the cost of the raw material. Use of an inexpensive raw material such as rice bran oil is an attractive option to lower the cost of biodiesel. Two commercially available immobilized lipases, Novozym 435 and IM 60, were employed as catalyst for the reaction of rice bran oil and methanol. Novozym 435 was found to be more effective in catalyzing the methanolysis of rice bran oil. Methanolysis of refined rice bran oil and fatty acids (derived from rice bran oil) catalyzed by Novozym 435 (5% based on oil weight) can reach a conversion of over 98% in 6 h and 1 h, respectively. Methanolysis of rice bran oil with a free fatty acid content higher than 18% resulted in lower conversions (<68%). A two-step lipase-catalyzed methanolysis of rice bran oil was developed for the efficient conversion of both free fatty acid and acylglycerides into fatty acid methyl ester. More than 98% conversion can be obtained in 4,6 h depending on the relative proportion of free fatty acid and acylglycerides in the rice bran oil. Inactivation of lipase by phospholipids and other minor components was observed during the methanolysis of crude rice bran oil. Simultaneous dewaxing/degumming proved to be efficient in removing phospholipids and other minor components that inhibit lipase activity from crude rice bran oil. Copyright © 2005 Society of Chemical Industry [source] Kinetic Modeling of Thiol-Ene Reactions with Both Step and Chain Growth AspectsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 4 2005Oguz Okay Abstract Summary: A kinetic model is presented for thiol-ene cross-linking photopolymerizations including the allowance for chain growth reaction of the ene, i.e., homopolymerization. The kinetic model is based on a description of the average chain lengths derived from differential equations of the type of Smoluchowski coagulation equations. The method of moments was applied to obtain average properties of thiol-ene reaction systems. The model predicts the molecular weight distribution of active and inactive species in the pre-gel regime of thiol-enes, as well as the gel points depending on the synthesis parameters. It is shown that, when no homopolymerization is allowed, the average molecular weights and the gel point conversion are given by the typical equations valid for the step-growth polymerization. Increasing the extent of homopolymerization also increases the average molecular weights and shifts the gel point toward lower conversions and shorter reaction times. It is also shown that the ratio of thiyl radical propagation to the chain transfer kinetic parameter (kp1/ktr) affects the gelation time, tcr. Gelation occurs earlier as the kp1/ktr ratio is increased due to the predominant attack of thiyl radicals on the vinyl groups and formation of more stable carbon radicals. The gel point in thiol-ene reactions is also found to be very sensitive to the extent of cyclization, particularly, if the monomer functionalities are low. Number-average chain length of carbon radicals (solid curves) and thiyl radicals (dashed curves) plotted against the vinyl group conversion, xM, during thiol-ene polymerization. Calculations were for six different kp/ktr ratios. [source] | |||||||||||||