Reaction product selectivity

Nuclear Reaction Spectroscopy Light element, isotope analysis H+D+He3+ 0.2-2MeV Reaction products Selected elements isotopes 1-10"4... 

Enhancement in conversion by the usage of a membrane reactor has been demonstrated for many dehydrogenation reactions. Product selectivity of some hydrogenation and other reactions arc found to improve with a permselective membrane as part of the reactor. Several dense metal as well as solid elecu olyte membranes and porous metal as well as various oxide membranes have been discovered to be effective for the reaction performance. 

Ethylene oxide is produced by the catalytic oxidation of ethylene with oxygen, C2H4 + 5O2 -> (C2H2)20. The feed to the catalyst bed is a 10 1 (volume) ratio of air to ethylene, and conversion of ethylene is 23% per pass. The ethylene oxide is removed Irom the reaction products selectively. The unreacted ethylene must be recycled. 

A second type of reaction was studied in which sohd reaction products selectively deposited on the crystal. For example, when nickel or iron crystals, cut in the form of a sphere to expose all possible faces, were heated in carbon monoxide or a carbon monoxide-hydrogen mixture, carbon formed rapidly on certain faces while the rate was very slow or negligible on others (6). 

At relatively low temperatures, it is thermodynamically possible to produce many organic compounds from CO and hydrogen. This situation leads to the major problem area in CO/H2 synthesis reactions— product selectivity. One of the major research objectives today in this area is the development of new catalyst systems which maximize the more desirable products such as low molecular weight olefins and alco-... 

Fig. 4 (a) Oxygen reduction reaction pathways in the absence Qeft) and in the presence (right) of a contaminant. The presence of a contaminant affects the surface coverage G, oxygen reduction reaction product selectivity (j), and faradaic efficiency 0. (b) Platinum dissolution rate in the absence (top) and in the presence (bottom) of sulfur contamination either from the air intake or from the carbon support. The increased platinum dissolution rate favors a decrease in ionomer ionic conductivity. 

Reaction time, h Yieid of desirabie reaction product, % Selectivity to desirable reaction product, % Conversion degree of triethoxysilane, % Conversion degree of hexadecene,y ... 

Ramamurthy, V. and Sanderson, D. R., Relative size of the host and the guest determine the reaction-product selectivity Norrish type II reaction of alkanones within zeolites. Tetrahedron Lett., 33, 2757, 1992. 

Recently, the state-selective detection of reaction products tluough infrared absorption on vibrational transitions has been achieved and applied to the study of HF products from the F + H2 reaction by Nesbitt and co-workers (Chapman et al [7]). The relatively low sensitivity for direct absorption has been circumvented by the use of a multi-pass absorption arrangement with a narrow-band tunable infrared laser and dual beam differential detection of the incident and transmission beams on matched detectors. A particular advantage of probing the products tluough absorption is that the absolute concentration of the product molecules in a given vibration-rotation state can be detenuined. 

Final state analysis is where dynamical methods of evolving states meet the concepts of stationary states. By their definition, final states are relatively long lived. Therefore experiment often selects a single stationary state or a statistical mixture of stationary states. Since END evolution includes the possibility of electronic excitations, we analyze reaction products in terms of rovibronic states. 

Potcntiomctric Titrations In Chapter 9 we noted that one method for determining the equivalence point of an acid-base titration is to follow the change in pH with a pH electrode. The potentiometric determination of equivalence points is feasible for acid-base, complexation, redox, and precipitation titrations, as well as for titrations in aqueous and nonaqueous solvents. Acid-base, complexation, and precipitation potentiometric titrations are usually monitored with an ion-selective electrode that is selective for the analyte, although an electrode that is selective for the titrant or a reaction product also can be used. A redox electrode, such as a Pt wire, and a reference electrode are used for potentiometric redox titrations. More details about potentiometric titrations are found in Chapter 9. 

Boron trifluoride catalyst may be recovered by distillation, chemical reactions, or a combination of these methods. Ammonia or amines are frequently added to the spent catalyst to form stable coordination compounds that can be separated from the reaction products. Subsequent treatment with sulfuric acid releases boron trifluoride. An organic compound may be added that forms an adduct more stable than that formed by the desired product and boron trifluoride. In another procedure, a fluoride is added to the reaction products to precipitate the boron trifluoride which is then released by heating. Selective solvents may also be employed in recovery procedures (see Catalysts,regeneration). 

The reaction product of salicylaldehyde and a secondary aniline is the benzyUc alcohol, with total para-selectivity (57). The yield is 93%... 

Fresh butane mixed with recycled gas encounters freshly oxidized catalyst at the bottom of the transport-bed reactor and is oxidized to maleic anhydride and CO during its passage up the reactor. Catalyst densities (80 160 kg/m ) in the transport-bed reactor are substantially lower than the catalyst density in a typical fluidized-bed reactor (480 640 kg/m ) (109). The gas flow pattern in the riser is nearly plug flow which avoids the negative effect of backmixing on reaction selectivity. Reduced catalyst is separated from the reaction products by cyclones and is further stripped of products and reactants in a separate stripping vessel. The reduced catalyst is reoxidized in a separate fluidized-bed oxidizer where the exothermic heat of reaction is removed by steam cods. The rate of reoxidation of the VPO catalyst is slower than the rate of oxidation of butane, and consequently residence times are longer in the oxidizer than in the transport-bed reactor. 

Reduction processes are characterized either by the reducing agent selected or by the physical state of the metallic product. The separation of reaction products determines the choice and design of the furnace. Reduction processes are classified according to the physical state of the reduced metal. 

Catalytic Properties. In zeoHtes, catalysis takes place preferentially within the intracrystaUine voids. Catalytic reactions are affected by aperture size and type of channel system, through which reactants and products must diffuse. Modification techniques include ion exchange, variation of Si/A1 ratio, hydrothermal dealumination or stabilization, which produces Lewis acidity, introduction of acidic groups such as bridging Si(OH)Al, which impart Briimsted acidity, and introducing dispersed metal phases such as noble metals. In addition, the zeoHte framework stmcture determines shape-selective effects. Several types have been demonstrated including reactant selectivity, product selectivity, and restricted transition-state selectivity (28). Nonshape-selective surface activity is observed on very small crystals, and it may be desirable to poison these sites selectively, eg, with bulky heterocycHc compounds unable to penetrate the channel apertures, or by surface sdation. 

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