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Reaction Selectivity (reaction + selectivity)
Selected AbstractsSelectivity effects on series reactions by reactant storage and PSA operationAICHE JOURNAL, Issue 11 2000Adriaan J. Kodde This work evaluates adsorptive reactors used to improve the operation of a sequential reaction scheme, , for the total removal of A from a stream with an excess of B. In the adsorptive-reactor concept, the reactor is filled with a physical mixture of catalyst and an adsorbent, the latter being thermodynamically selective toward primary reactant A. In this case, the sorbent is periodically regenerated using the principles of pressure swing adsorption and purged with secondary reactant D. This concept is restricted to low temperatures to have sufficient adsorption capacity. Improved reaction selectivity arises from the accumulation of A in the unit. The reaction of A maximizes the driving force for regeneration and thus accelerates the regeneration half-cycle. The adsorptive reactor is compared to a conventional plug-flow reactor (PFR) and to PSA and PFR units in series. Reaction selectivity improved and pure B recovered over these alternative reactors under realistic conditions. The volume-based productivity is lower than that of PFR, but higher than that of PSA. The purge-gas flow rate can be manipulated to balance the sorption flux and reaction rate, thereby maximizing the conversion of A. The influence of differences in sorption kinetics is discussed and the required sorbent characteristics are identified. [source] Alkyne Hydroarylations with Chelating Dicarbene Palladium(II) Complex Catalysts: Improved and Unexpected Reactivity Patterns Disclosed Upon Additive Screening,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2009Andrea Biffis Abstract Palladium(II) complexes with a ligand set made from a chelating N-heterocyclic dicarbene ligand and two weakly coordinating anions (generally introduced in situ upon addition of 2 equiv. of a suitable silver salt) were found to be very active and selective catalysts for the room-temperature hydroarylation of alkynes at low catalyst loading (0.1 mol-%). Moreover, the screening of various strong acids as reaction promoters revealed that both the strength of the acid and the coordinating ability of its conjugated base influence the catalytic performance. Most remarkably, the use of HBF4 together with a dicarbene Pd complex catalyst provides a dramatic change in the selectivity of the reaction, with the prevalent formation of a product stemming from the insertion of two molecules of alkyne into the aromatic C,H bond. The results presented herein highlight the fact that the dicarbene ligand, apart from stabilising the catalyst, is also able to enhance catalytic activity and, most notably, to steer the reaction selectivity towards novel products. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Alkaline hydrolysis of cinnamaldehyde to benzaldehyde in the presence of ,-cyclodextrinAICHE JOURNAL, Issue 2 2010Hongyan Chen Abstract A facile, novel, and cost-effective alkaline hydrolysis process of cinnamaldehyde to benzaldehyde under rather mild conditions has been investigated systematically in the presence of ,-cyclodextrin (,-CD), with water as the only solvent. ,-CD could form inclusion complex with cinnamaldehyde in water, with molar ratio of 1:1, so as to promote the reaction selectivity. The complex has been investigated experimentally and with computational methods. 1H-NMR, ROESY, UV,Vis, and FTIR have been utilized to analyze the inclusion complex. It shows that the equilibrium constant for inclusion (Ka) is 363 M,1, and the standard Gibbs function for the reaction, ,,G (298 K), is ,14.6 kJ mol,1. In addition, the structures of the proposed inclusion compounds were optimized with hybrid ONIOM theory. Benzaldehyde could be obtained at an yield of 42% under optimum conditions [50°C, 18 h, 2% NaOH (w/v), cinnamaldehyde:,-CD (molar ratio) = 1:1]. To explain the experimental data, NMR, FTIR, and elemental analysis results were used to determine the main reaction by-product 1-naphthalenemethanol. A feasible reaction mechanism including the retro-Aldol condensation of cinnamaldehyde and the Aldol condensation of acetaldehyde and cinnamaldehyde in basic aqueous ,-CD solution has been proposed. The calculated activation energy for the reaction was 45.27 kJ mol,1 by initial concentrations method. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Selectivity effects on series reactions by reactant storage and PSA operationAICHE JOURNAL, Issue 11 2000Adriaan J. Kodde This work evaluates adsorptive reactors used to improve the operation of a sequential reaction scheme, , for the total removal of A from a stream with an excess of B. In the adsorptive-reactor concept, the reactor is filled with a physical mixture of catalyst and an adsorbent, the latter being thermodynamically selective toward primary reactant A. In this case, the sorbent is periodically regenerated using the principles of pressure swing adsorption and purged with secondary reactant D. This concept is restricted to low temperatures to have sufficient adsorption capacity. Improved reaction selectivity arises from the accumulation of A in the unit. The reaction of A maximizes the driving force for regeneration and thus accelerates the regeneration half-cycle. The adsorptive reactor is compared to a conventional plug-flow reactor (PFR) and to PSA and PFR units in series. Reaction selectivity improved and pure B recovered over these alternative reactors under realistic conditions. The volume-based productivity is lower than that of PFR, but higher than that of PSA. The purge-gas flow rate can be manipulated to balance the sorption flux and reaction rate, thereby maximizing the conversion of A. The influence of differences in sorption kinetics is discussed and the required sorbent characteristics are identified. [source] Oxidation of Benzene to Maleic Anhydride in a Fluidized Bed ReactorCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2007C. Uraz Abstract In this project, the selective oxidation of benzene to maleic anhydride (MAN) was studied. Gas phase catalytic oxidation of benzene was carried out in a laboratory scale fluidized bed reactor on six different types of catalysts, which have different compositions. Effects of temperature, flow rates of benzene and air and catalyst type on the reaction selectivity were investigated at atmospheric pressure. The experiments were performed over a temperature range of 325 to 400,°C, a space-time (W/FA0) range from 11.28,×,105 to 31.9,×,105 g,s,mol,1, and benzene/air mole ratio changes between 0.0109 and 0.0477. It was seen that conversion of benzene to MAN increased with increasing temperature for the catalysts supported by silica gel, aluminum oxide and titanium oxide. From the results it was found that conversion increased with increasing flow rate of air. When the comparison of the catalysts were made, it could be said that catalysts supported by silica gel showed higher MAN conversions. So it can be concluded that catalysts supported by silica gel were more suitable catalysts for benzene oxidation to MAN in a fluidized bed reactor. [source] Mechanistic Insights into Selectivity Control for Heterogeneous Olefin Oxidation: Styrene Oxidation on Au(111)CHEMISTRY - AN ASIAN JOURNAL, Issue 1 2010Abstract We demonstrate that intermolecular interactions, controlled by both oxygen and styrene coverage, alter reaction selectivity for styrene oxidation on oxygen-covered Au(111). Several partial oxidation products are formed,styrene oxide, acetophenone, benzoic acid, benzeneacetic acid, and phenylketene,in competition with combustion. The maximum ratio of the yields of styrene oxide to the total CO2 produced is obtained for the maximum styrene coverage for the first two layers (0.28,ML) adsorbed on Au(111) precovered with 0.2,ML of O. Furthermore, our reactivity and infrared studies support a mechanism whereby styrene oxidation proceeds via two oxametallacycle intermediates which, under oxygen-lean conditions, lead to the formation of styrene oxide, acetophenone, and phenylketene. Benzoate, identified on the basis of infrared reflection absorption spectroscopy, is converted into benzoic acid during temperature-programmed reaction. These results demonstrate the ability to tune the epoxidation selectivity using reactant coverages and provide important mechanistic insight into styrene oxidation reactions. [source] | ||||||||||