Oxygen reaction time

The hydrolysis products of the hydrolyzable tannins are not dissimilar to some of the novel oxygen scavengers developed to replace hydrazine. Oxygen reaction rates and application rates are also similar. The oxygen reaction time for tannin blends varies with pH levels and temperature but at 45 °C (113 °F) is on the order of 75% complete within 5 seconds and 90% complete within 10 seconds. 

Effect of Pressure of Reacting Gas on the Apparent Leak Rale for Oxygen (Reaction time 10 minutes, 900°C. mullite double-walled tube, 30-minute test)... 

Figure 1. Effect of gamma irradiation on the oxygencarrying capacity of different concentrations of oxygenated hemocyanins in phosphate buffer at pH 7.0. The oxygenation reaction time was 10 minutes and the deoxygenation reaction time was 30 minutes...

Direct hydrohquefaction of biomass or wastes can be achieved by direct hydrogenation of wood chips on treatment at 10,132 kPa and 340 to 350°C with water and Raney nickel catalyst (45). The wood is completely converted to an oily Hquid, methane, and other hydrocarbon gases. Batch reaction times of 4 hours give oil yields of about 35 wt % of the feed the oil contains about 12 wt % oxygen and has a heating value of about 37.2 MJ /kg (16,000 Btu/lb). Distillation yields a significant fraction that boils in the same range as diesel fuel and is completely miscible with it. 

Burning a portion of a combustible reactant with a small additive of air or oxygen. Such oxidative pyrolysis of light hydrocarbons to acetylene is done in a special burner, at 0.001 to 0.01 s reaction time, peak at 1,400°C (2,552°F), followed by rapid quenching with oil or water. 

The method described here gives higher yields of the macrocyclic tetraethers and allows the product from furan and cyclohexanone to be formed directly in 5-10% yield, whereas this product was previously obtained only by an indirect route. The added lithium perchlorate undoubtedly accelerates the reaction, since after short reaction times the product was isolated in 20% yield when the salt was present and in only 5% yield when the salt was absent. The lithium cation is presumably acting as a template which coordinates with the oxygen atoms of... 

The sodium derivative of ethyl 4,4,4-trifluoroacetoacetate is usually alkylated at the oxygen atom [39], However, in the presence of HMPA, the ratio of O alkylation to C alkylation depends on reaction time. This observation is explained by a reversible O-alkylation process [40] (equations 35 and 36). 

Together with a shift of the proton from the a-carbon to the alkoxide oxygen, the tertiary amine is eliminated from the addition product to yield the unsaturated product 3. Early examples of the Baylis-Hillman reaction posed the problem of low conversions and slow reaction kinetics, which could not be improved with the use of simple tertiary amines. The search for catalytically active substances led to more properly adjusted, often highly specific compounds, with shorter reaction times." Suitable catalysts are, for example, the nucleophilic, sterically less hindered bases diazabicyclo[2.2.2]octane (DABCO) 6, quinuclidin-3-one 7 and quinuclidin-3-ol (3-QDL) 8. The latter compound can stabilize the zwitterionic intermediate through hydrogen bonding. ... 

Because hydride ion is a base as well as a nucleophile, the actual nucleophilic acyl substitution step takes place on the carboxylate ion rather than on the free carboxylic acid and gives a high-energy dianion intermediate. In this intermediate, the two oxygens are undoubtedly complexed to a Lewis acidic aluminum species. Thus, the reaction is relatively difficult, and acid reductions require higher temperatures and extended reaction times. 

Oxidative Heck arylation of enamides with arylboronic acids, using oxygen gas as a reoxidant for Pd(0) and 2,9-dimethyl-1,10-phenanthroline as a chelating regiocontrolling ligand, yielded a (= internally) arylated reaction product as the major compound with a very good a//3 selectivity [92]. Microwave irradiation with prepressurized sealed vials proved useful in reducing the reaction time (Scheme 82). 

The oxygen evolution rate was measured by using the photosynthetic activity measurement system (Fig. 1). When light was illuminated to the reaction vessel, algal cells began to evolve oxygen and the linearity between dissolved oxygen and time was observed just after a few... 

Figure 2.27. Mixing, mass transfer and oxygen consumption in a bubble column bioreactor (Oosterhuis, 1984). Tj - reaction time constant, Xmt - ass transfer time constant, tmix -mixing time constant. ro2 - oxygen consumption rate, Vs - superficial gas velocity.

Correct experimental conditions are vital. In particular, it is essential to irradiate only the benzophenone chromophore, which can be achieved by employing an appropriate u.v. laser, for direct excitation of the azo compound produces a singlet diradical that collapses to bicyclopentane. Oxygen pressure (150 psi) and reaction time (60-70 h) must be carefully regulated to obtain optimum yields (ca. 20%) of 9. 

Measuring the relative oxidative stability of polymers is important. Measurements can be used to determine dependencies on structural and molecular weight/weight distribution or the effectiveness of an antioxidant, or to perhaps assess the amount present in a polymer sample, etc. The preferred and commonest method consists in raising the sample temperature to a predetermined level, while in an inert atmosphere, then switching the atmosphere to air or oxygen. The time to the onset of exothermic reaction is measured. 

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