Duration reaction

Gasification systems typically involve partial oxidation of the coal with oxygen and steam in a high-temperature and elevated-pressure reactor. The short-duration reaction proceeds in a highly reducing atmosphere that creates a synthesis gas, a mix of predominantly CO and II2 with some steam and C02. This syngas can be further shifted to increase H2 yield. The gas can be cleaned in conventional ways to recover elemental sulfur (or make sulfuric acid), and a high-concentration C02 stream can be easily isolated and sent for... 

While the majority of wheals in physical urticaria develop rapidly and are of short duration, reactions can also appear with a delay of 2 h or even 4-8 h after stimulation. The most frequent representative of this group is delayed pressure urticaria, with lesions persisting for up to 3 days. 

One of the most important teclmiques for the study of gas-phase reactions is flash photolysis [8, ]. A reaction is initiated by absorption of an intense light pulse, originally generated from flash lamps (duration a=lp.s). Nowadays these have frequently been replaced by pulsed laser sources, with the shortest pulses of the order of a few femtoseconds [22, 64]. 

All hydrocarbons prepared by th -. Wurtz reaction contain small quantities of unsaturated hydrocarbons. These may be removed by shaking repeatedly with 10 pier cent, of the volume of concentrated sulphuric acid until the acid is no longer coloured (or is at most extremely pale yellow) each shaking should be of about 5 minutes duration. The hydrocarbon is washed with water, 10 pier cent sodium carbonate solution, water (twice), and dried with anhydrous magnesium or calcium sulphate. It is then distilled from sodium two distillations are usually necessary... 

The reaction is again most successful with phenol and indole derivatives. Reaction con-litions are also quite mild. Phosphorus oxychloride may be used in refluxing chloroform or ligher boiling hydrocarbons. Duration of the reaction is usually less than 6 hours (T. Kameta-li, 1977 A E.E. van Tamelen, 1969). 

The assumption that k values are constant over the entire duration of the reaction breaks down for termination reactions in bulk polymerizations. Here, as in Sec. 5.2, we can consider the termination process—whether by combination or disproportionation to depend on the rates at which polymer molecules can diffuse into (characterized by kj) or out of (characterized by k ) the same solvent cage and the rate at which chemical reaction between them (characterized by kj.) occurs in that cage. In Chap. 5 we saw that two limiting cases of Eq. (5.8) could be readily identified ... 

We saw in the last chapter that the stationary-state approximation is apphc-able to free-radical homopolymerizations, and the same is true of copolymerizations. Of course, it takes a brief time for the stationary-state radical concentration to be reached, but this period is insignificant compared to the total duration of a polymerization reaction. If the total concentration of radicals is constant, this means that the rate of crossover between the different types of terminal units is also equal, or that R... 

Initiators, usually from 0.02 to 2.0 wt % of the monomer of organic peroxides or azo compounds, are dissolved in the reaction solvents and fed separately to the kettie. Since oxygen is often an inhibitor of acryUc polymerizations, its presence is undesirable. When the polymerization is carried out below reflux temperatures, low oxygen levels are obtained by an initial purge with an inert gas such as carbon dioxide or nitrogen. A blanket of the inert gas is then maintained over the polymerization mixture. The duration of the polymerization is usually 24 h (95). 

Another variation is the mode-locked dye laser, often referred to as an ultrafast laser. Such lasers offer pulses having durations as short as a few hundred femtoseconds (10 s). These have been used to study the dynamics of chemical reactions with very high temporal resolution (see Kinetic LffiASURELffiNTS). 

The availability of lasers having pulse durations in the picosecond or femtosecond range offers many possibiUties for investigation of chemical kinetics. Spectroscopy can be performed on an extremely short time scale, and transient events can be monitored. For example, the growth and decay of intermediate products in a fast chemical reaction can be followed (see Kinetic measurements). 

This reaction has been carried out with a carbon dioxide laser line tuned to the wavelength of 10.61 p.m, which corresponds to the spacing of the lowest few states of the SF ladder. The laser is a high power TEA laser with pulse duration around 100 ns, so that there is no time for energy transfer by coUisions. This example shows the potential for breakup of individual molecules by a tuned laser. As with other laser chemistry, there is interest in driving the dissociation reaction in selected directions, to produce breakup in specific controllable reaction channels. 

Systemic reactions are less severe than with diethylcarbama2ine. The most commonly seen reactions are fever, rash, and lymph-node pain or swelling. Suppressive ivermectin therapy consists of a single oral dose every 6—18 months. The required duration of suppressive therapy is unknown, probably at least three years (36). Ivermectin is available from the CDC Dmg Service on request. It is manufactured by Merck Sharp and Dohme in the United States and England. 

Thermal Decomposition of GIO2. Chloiine dioxide decomposition in the gas phase is chaiacteiized by a slow induction period followed by a rapid autocatalytic phase that may be explosive if the initial concentration is above a partial pressure of 10.1 kPa (76 mm Hg) (27). Mechanistic investigations indicate that the intermediates formed include the unstable chlorine oxide, CI2O2. The presence of water vapor tends to extend the duration of the induction period, presumably by reaction with this intermediate. When water vapor concentration and temperature are both high, the decomposition of chlorine dioxide can proceed smoothly rather than explosively. Apparently under these conditions, all decomposition takes place in the induction period, and water vapor inhibits the autocatalytic phase altogether. The products of chlorine dioxide decomposition in the gas phase include chlorine, oxygen, HCl, HCIO, and HCIO. The ratios of products formed during decomposition depend on the concentration of water vapor and temperature (27). 

Alginate impression materials are chemically reactive mixtures. AH factors that influence reaction rates are, therefore, important in the use of these materials, ie, correct proportioning temperature of the water, powder, and mixing equipment and spatulation rate and duration. 

Batch reaclors are tanks, usually provided with agitation and some mode of heat transfer to maintain temperature within a desirable range. They are primarily employed for relatively slow reactions of several hours duration, since the downtime for filling and emptying large equipment may be an hour or so. Agitation maintains uniformity and improves heat transfer. Modes of heat transfer are illustrated in Figs. 23-1 and 23-2. 

Anions of another group were derivatized with formation of gaseous chemiluminescing species. Chemical reaction - gas extraction has been used with chemiluminescence detection in the stream of canier gas in on-line mode. Rate of a number of reactions has been studied as well as kinetic curves of extraction of gaseous products. Highly sensitive and rapid hybrid procedures have been developed for the determination of lO, BrO, CIO, CIO, NO,, N03, CrO, CIO, Br, T, S, 803 with detection limits at the level of pg/L, duration of analysis 3 min. 

On Figure 6.3.1 the first line tells the date and duration of the experiment. In the third line the number of cycles is five. This indicates that feed and product streams were analyzed five times before an evaluation was made. The concentrations, and all other numbers are the average of the five repeated analyses with the standard deviation given for each average value. The RATE as 1/M means for each component the reaction rate in lb-moles per 1000 lbs of catalyst. 

The condensation reaction and the increase of the molar mass can also be monitored by GPC [25], With longer duration of the acid condensation step, oligomers of higher molar masses are progressively formed. 

At t = 0, Cg = 0, but after a short time, relative to the duration of the reaction, the difference - e 2t reaches the value of unity. The concentration of B is then C gk/kj, which is much less than C, g. After this short induction period, the concentration of B remains almost... 

The chromatogram is freed from mobile phase and evenly sprayed with the spray solution or immersed for 1 s in the dipping solution. After drying the TLC plate is heated to 85 —120°C normally for 10 to 15 min but in exceptional cases for 60 min. It is advisable to observe the chromatogram during the reaction period, because the temperature and duration of heating strongly affect color development. 

An ignidon source must have sufficient energy and duration to initiate a reaction... 

The pressure behind the nonreactive shock is much higher than the CJ detonation pressure, which is not attained until the reaction is complete. The duration of the... 

Nonyl aldehyde (32.66 g, 0.23 mol) and furan (200 mL, 187.2 g, 2.75 mol) were mixed in a 250-mL photolysis flask equipped with a quartz immersion well containing a Vycor filter and a 450-W Hanovia Lamp. The system was kept at -20° C with an isopropyl alcohol bath cooled by a Cryocool Immersion Cooler (CClOO). Nitrogen was bubbled throughout the duration of the reaction, and the solution was stirred vigorously. Additional furan (150 mL, 140.4 g, 2.06 mol) was added during the course of the reaction. TLC analysis indicated completion of the reaction after 20 h. After evaporation of excess furan and NMR analysis of the resultant oil (48.70 g, ca. 100%) indicated the desired photoadduct had been formed, without contamination from unreacted nonyl aldehyde. 

The duration of these reactions appears to be extremely important as longer reaction times resulted in deoxygenation of the thiophene derivative. 

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