Hydrocarbons measurement

A different kind of shape selectivity is restricted transition state shape selectivity. It is related not to transport restrictions but instead to size restrictions of the catalyst pores, which hinder the fonnation of transition states that are too large to fit thus reactions proceeding tiirough smaller transition states are favoured. The catalytic activities for the cracking of hexanes to give smaller hydrocarbons, measured as first-order rate constants at 811 K and atmospheric pressure, were found to be the following for the reactions catalysed by crystallites of HZSM-5 14 n-... 

In Equation 1, Iq is the fluorescence intensity of the hydrocarbon measured without DNA, and I is the intensity measured with DNA. 

Infrared diode laser spectroscopy has been used for the measurement of hydrocarbon and CO concentrations in exhaust (13, 14, 15). The adsorption path length, and thus the absorption cell volume, required for hydrocarbon measurement is rather large, limiting the time-resolution of the measurement. The absorption path length required for CO measurement, however, is relatively short and approximately equal to the diameter of a standard exhaust pipe. This allows CO to be measured with high time-resolution by an infrared laser beam passed through an... 

Bottenheim JW, Shepherd MF. 1995. C2-C6 Hydrocarbon measurements at four rural locations across Canada. Atmospheric Environment 29(6) 647-664. 

The relationship between the log A and the van der Waals volumes of alkanes, alkylbenzenes, and polycyclic aromatic hydrocarbons measured in 70% aqueous acetonitrile on octadecyl-bonded silica gels31 is shown in Figure 6.4. 

Thus, as often occurs in petroleum science (Speight, 1999), the definition of total petroleum hydrocarbons depends on the analytical method used because the total petroleum hydrocarbons measurement is the total concentration of the hydrocarbons extracted and measured by a particular method. The same sample analyzed by different methods may produce different values. For this reason, it is important to know exactly how each determination is made since interpretation of the results depends on understanding the capabilities and limitations of the method. If used indiscriminately, measurement of the total petroleum hydrocarbons in a sample can be misleading, leading to an inaccurate assessment of risk. 

Gas chromatographic methods are currently the preferred laboratory methods for measurement of total petroleum hydrocarbon measurement because they detect a broad range of hydrocarbons and provide both sensitivity and selectivity. In addition, identification and quantification of individual constituents of the total petroleum hydrocarbon mix is possible. 

The amount of the total petroleum hydrocarbons measured by this method depends on the ability of the solvent used to extract the hydrocarbon from the environmental media and the absorption of IR light by the hydrocarbons in the solvent extract. In addition, the method (EPA 418.1) is not specific to hydrocarbons and does not always indicate petroleum contamination (e.g., humic acid, a nonpetroleum hydrocarbon, may be detected by this method). 

Another complication with total petroleum hydrocarbons values is that petroleum-derived inputs vary considerably in composition it is essential to bear this in mind when quantifying them in general terms such as an oil or the total petroleum hydrocarbons measurement. Petroleum is complex, containing many thousands of compounds, ranging from gases to residues boiling at about 400°C. 

Methanol was converted to hydrocarbons on HZSM5 and HUSY in the low temperature range 250 - 280 °C and the yield of hydrocarbons measured as a function of duration of experiment (Fig. 2). The reaction is seen to be highly autocatalytic. E. g. with the HZSM5 and 260 °C only after 30 minutes a small hydrocarbon yield of about 2 % is observed. Within the next 30 minutes the yield increases approximately exponentially and after 50 minutes duration of experiment a 100 % conversion of methanol to hydrocarbons and coke is obtained. Autocatalysis is very sensitive against temperature. At an only 10 °C lower reaction temperature the increase of hydrocarbon yield from about 5 to 50 % occurs, from 50 to 100 minutes after start of reaction. At 280 °C increase of hydrocarbon yield from zero to 100 Z occurs already in the period from 5 to 20 minutes and at 300 °C no autocatalysis is observable the degree of conversion... 

Apel, E. C., J. G. Calvert, R. Zika, M. O. Rodgers, V. P. Aneja, J. F. Meagher, and W. A. Lonneman, Hydrocarbon Measurements during the 1992 Southern Oxidants Study Atlanta Intensive Protocol and Quality Assurance, J. Air Waste Manage. Assoc., 45, 521-528(1995). 

Bottenheim, J. W and M. F. Shepherd, C2-C() Hydrocarbon Measurements at Four Rural Locations across Canada, Atmos. Environ., 29, 647-664 (1995). 

Gaffney, J. S., N. A. Marley, and P. V. Doskey, Peroxyacetyl Nitrate and Hydrocarbon Measurements in Mexico City, Invited Paper, Special Session on Mexico City Air Quality, Spring Meeting of the American Geophysical Union (AGU), Boston, Massachusetts, May 25-28, 1998, Atmos. Environ., in press (1999). 

Stephens, R. D P. A. Mulawa, M. T. Giles, K. G. Kennedy, P. J. Groblicki, S. H. Cadle, and K. T. Knapp, An Experimental Evaluation of Remote Sensing-Based Hydrocarbon Measurements A Comparison to FID Measurements, J. Air Waste Manage. Assoc., 46, 148-158 (1996b). 

Figure 4. Relationship between ratios of alkyl nitrates to parent hydrocarbons measured in a field study in rural Pennsylvania.

Here, the uncertainty cr HOj introduced by the relative uncertainty a)X /[T] applies to a single hydrocarbon measurement, and the presence of this uncertainty in both [T] and [T]0 introduces the factor 1.4. If [T](), other reagents, or illumination of the reactor are not constant, [HO](t) can be obtained from the time derivative of equation 25 ... 

Gaseous Hydrocarbons measured as Methane (ppm) 1 1 Federal Specification BB-H-11686, Type I, Grade C... 

Multi-component hydrocarbon standards to provide accurate calibration of instruments (generally gas chromatographs) used to monitor the concentrations of a wide range of volatile organic hydrocarbon compounds (VOCs) in ambient air. These standards currently contain 30 different hydrocarbon species that are important to photochemical ozone formation, with concentrations ranging down to a few parts per billion by molar value. They are disseminated widely in the United Kingdom and the rest of Europe as calibration standards, and as test mixtures for assessment of the quality of international ambient hydrocarbon measurements (often under the auspices of the European Commission - EC). 

A hydrocarbon dew point meter uses a chilled-mirror instrument by which almost invisible films, having sensitivities on the order of 1 ppm, become detectable. Optical fibers are used to detect the reduction of light intensity, and miniature thermocouples measure the surface temperature of the mirror. For total hydrocarbon measurement, the flame ionization analyzer is reliable and accurate, but it requires the attention of operators and also consumes compressed gases. 

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