Pulse-injection technique

Yang J, Kondoh T, Kozawa T, Yoshida H, Tagawa S. (2006) Pulse radiolysis based on a femtosecond electron beam and a femtosecond laser light with double-pulse injection technique. Rad Phys Chem 75 1034-1040. 

Masuda T, Mukai SR, Hashimoto K, The liquid pulse injection technique—a. new method to obtain long vapor-grown carbon-fibers at high growth-rates. Carbon, 31(5), 783-787, 1993. 

The particle velocity is a very difficult parameter to determine experimentally. Pulse-injection techniques have been suggested for its measurement, as well as isolation of a section of the flow system by selenoid valves. The laser Doppler velocimeter system can be employed on dilute systems to measure the solids velocity. Table 4-3 gives a hsting of expressions for the determination of Up. 

A promising technique is cavity ringdown laser absorption spectroscopy (307), in which the rate of decay of laser pulses injected into an optical cavity containing the sample is measured. Absorption sensitivities of 5 x 10 have been measured on a ]ls time scale. AppHcations from the uv to the ir... 

The prevacuum technique, as its name implies, eliminates air by creating a vacuum. This procedure faciUtates steam penetration and permits more rapid steam penetration. Consequendy this results in shorter cycle times. Prevacuum cycles employ either a vacuum pump/steam (or air) ejector combination to reduce air residuals in the chamber or rely on the pulse-vacuum technique of alternating steam injection and evacuation until the air residuals have been removed. Pulse-vacuum techniques are generally more economical vacuum pumps or vacuum-pump—condenser combinations may be employed. The vacuum pumps used in these systems are water-seal or water-ring types, because of the problems created by mixing oil and steam. Prevacuum cycles are used for fabric loads and wrapped or unwrapped instmments (see Vacuum technology). 

The characterization is performed by means of residence time distribution (RTD) investigation [23]. Typically, holdup is low, and therefore the mean residence time is expected to be relatively short Consequently, it is required to shorten the distance between the pulse injection and the reactor inlet. Besides, it is necessary to use specific experimental techniques with fast time response. Since it is rather difficult, in practice, to perfectly perform a Dirac pulse, a signal deconvolution between inlet and outlet signals is always required. 

The second part of this work will be dedicated to the start of the game what are the pieces motions How can the adsorbed molecules react on the surface and among all the playground, where does the real action take place This is the so-called in situ approach for which techniques such as temperature-programmed surface reaction (TPSR) or transient analysis by pulse injection have been developed. 

Ideally, a sample is introduced into a chromatograph as a perfect plug. In practice, this is not the case, and diffusion occurs because of the injector. For narrow-bore and microbore applications, injectors capable of introducing the required sample volumes are commercially available and optimized to reduce dispersion. This is not the case for capillary LC, and homemade injection systems include the sample tube technique, in-column injection, stopped-flow injection, pressure pulse-driven stopped-flow injection (PSI), groove injection, split injection, heart-cut injection, and the moving injection technique (MIT). Of the injection techniques, only the split injector, MIT and PSI approaches can introduce subnanoliter sample volumes accu-... 

Dogu and Smith [22,23] have given the theoretical basis for the dynamic pulse response technique. If the experimental conditions are identical to those described for the step injection and the injection time is much lower than the diffusion time L2/Z), the theoretical first moment is... 

More recent studies preferred injector temperatures of below 200°C to avoid decomposition in the splitless injector [146]. However, low injector temperatures increase the risk of an incomplete transfer of the sample onto the GC column. To overcome this problem, a pressure-pulsed injection has been suggested [125, 157-159]. Detailed investigations with single toxaphene components have shown that the response factors of less volatile components can be increased fourfold by this technique using an injector temperature of 230°C (see Fig. 9 for an example) [158,159],... 

For mono-methyl paraffm separation, two pulse test techniques, one with and one without iso-octane pre-pulse, were developed (2,3). In each test the feed was a mixture containing equal volumes of 3,3,S-trimethyl heptane, 2,6-dimethyl octane, 2-methyl nonane, n-decane, and I,3,S-trimethyl benzene. The pulse test column had a volume of 70 cc and was held at a temperature of 120 C in the experiments shown. The flow rate through the column was 1.2 ml/min. The adsorbent was silicalite and the desorbent was a 30/30 volume % mixture of n-hexane/cyclohexane. Test I was run without a pre-pulse and test 2 was run with a pre-pulse of 40 ml of iso-octane injected into the test loop immediately before the feed mixture was injected. Iso-octane pre-pulse diluted the n-hexane concentration at the adsorption zone and increased the adsorbent selectivity for mono-methyl paraffin. 

The 10-membered ring zeolites (ZSM-22 and ZSM-23) were kindly provided by Prof. Martens (COK, KULeuven). Both of the zeolites have unidimensional pore structures without any intersection. The crystals are needle-like shaped for both materials. Zeolite ZSM-22 (belonging to the TON fhmily) has free pore dimensions of 0.44 X 0.55 nm and zeolite ZSM-23 (MTT fiimily) has free pore diameters of 0.45 X 0.42 nm. The framework structures are sketched in Figure 2. The low coverage adsorption properties were determined with the pulse chromatographic technique. The details of the experimental method are discussed elsewhere. The Henry constant was determined from the first moment of the response curve on the TCD detector alter injection of an alkane trace. Adsorption enthalpy and entropy were obtained by fitting the temperature dependence of the Henry constant to the van t Hoff equation. 

The system was based on a microreactor to which the feed was injected by pulses. The technique (25,26) is similar to but more perfected than that used by Corella ei al. (13) and by Larocca ct al, (18). A number of runs with 6-7 pulses each were made. Temperature ranged from 495 to 595 C. 

A pulse reaction technique was used to study (1) the behavior of the catalysts in the first step of the reaction, (2) the initial carbon deposition and, (3) the effects of carbon deposition on conversion and selectivity. Experiments were carried out at 853 K by injecting pulses of pure propane (pulse volume 0.50 cm 8TP) to the catalytic bed, which was maintained under flowing He (30 ml min ) between two successive pulses. The samples were previously reduced for 3h at 853 K under flowing H2. The reaction products were analyzed in a FID chromatographic system with a packed column (Porapack Q). 

Fig, 10.24. Simplified schematics illustrating some deposition techniques (a) thermal evaporation (b) stamping (c) liquid-solid interface (d) electro-chemistry set-up (e) Langmuir-Blodgett technique (f) electro-spray deposition (g) pulse injection method (h) solution casting (i) spin-coating. 

Among the methods that have considerable promise but that are yet to be significantly exploited are pulse electrochemical techniques, impedance methods, flow-injection analysis, the use of nonaqueous solvents in the sensor, the combined use of chemometrics and multi-electrode measurements for analysis of complex mixtures, the use of ultramicroelectrodes in applications outside the clinical and biological areas, and rapid deaeration of flow systems. 

A. Herbelin, J. Ruzicka, Pulse modulation. A novel approach to gradient-based flow injection techniques, Collect. Czech. Chem. Commun. 66 (2001) 1219. 

A flow reactor tends to be easy to automate and high precision measurements of conditions are easily achieved by measuring before and after a variable change. High precision is important when trends are being determined that can have fairly subtle impacts on the chemistry. One method for liquid phase reactions that will be described in Chapter 13 by Hickman and Sobeck is the use of a pulse reactant injection technique. This approach uses very small amounts of reagents and has... 

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