Hydrocarbon Analyzers

Historically, measurements have classified ambient hydrocarbons in two classes methane (CH4) and all other nonmethane volatile organic compounds (NMVOCs). Analyzing hydrocarbons in the atmosphere involves a three-step process collection, separation, and quantification. Collection involves obtaining an aliquot of air, e.g., with an evacuated canister. The principal separation process is gas chromatography (GC), and the principal quantification technique is wdth a calibrated flame ionization detector (FID). Mass spectroscopy (MS) is used along with GC to identify individual hydrocarbon compounds. 

E.S. Wagner, G.F. Froment, "Steam Reforming Analyzed," Hydrocarbon Processing, July 1992, pp. 69 -77. 

Wagner, E.S., Froment, G.F. 1992. Steam reforming analyzed. Hydrocarbon Proc July 69-77. 

Sampling Studies. To obtain a better understanding of the chemistry of preknock reactions, a number of investigators have sampled and analyzed hydrocarbon-air mixtures undergoing preflame oxidation in engines. The types and concentrations of some of the more stable intermediates taking part in these reactions have been determined. While... 

Total combustibles analyzers (hydrocarbons and carbon monoxide analyzers)... 

By coupling the Chromarod separation technique described in Section 11.4 with the reliable and robust NDIR (nondispersive infrared) technique for detecting the CO2 formed in the combustion, completely new ways of analyzing hydrocarbons are opened up. This principle of detection has the advantage that it is specific for CO2, i.e. cross-sensitivities are largely avoided. 

Concern over oil pollution has led to considerable interest in measuring amounts of hydrocarbons in the marine environment (1,2). A number of researchers have developed specialized procedures for analyzing hydrocarbons in marine sediments (3-14). Unfortunately, because... 

Process GC has developed into one of the most widely used online monitoring techniques in the petrochemical industry. Its popularity is due to the abiUty of GC to quickly analyze hydrocarbon streams for process control. As is the case for aU on-line analyzers, process chromatographs are capable of safe, continuous, unattended, in-plant operation. Because of the need for fast and specific analyses to provide feedback for process control, these chromatographs are usually designed for each specific application. The ideal process gas chromatograph (PGC) has the following characteristics ... 

Froment, G. F. Wagner, E. S., Steam Refoiming Analyzed, Hydrocarbon Process., July, 1992. 

This type of analysis requires several chromatographic columns and detectors. Hydrocarbons are measured with the aid of a flame ionization detector FID, while the other gases are analyzed using a katharometer. A large number of combinations of columns is possible considering the commutations between columns and, potentially, backflushing of the carrier gas. As an example, the hydrocarbons can be separated by a column packed with silicone or alumina while O2, N2 and CO will require a molecular sieve column. H2S is a special case because this gas is fixed irreversibly on a number of chromatographic supports. Its separation can be achieved on certain kinds of supports such as Porapak which are styrene-divinylbenzene copolymers. This type of phase is also used to analyze CO2 and water. 

The hydrocarbons are separated in another column and analyzed by a flame ionization detector, FID. As an example, Figure 3.13 shows the separation obtained for a propane analyzed according to the ISO 7941 standard. Note that certain separations are incomplete as in the case of ethane-ethylene. A better separation could be obtained using an alumina capillary column, for instance. 

Because of the existence of numerous isomers, hydrocarbon mixtures having a large number of carbon atoms can not be easily analyzed in detail. It is common practice either to group the constituents around key components that have large concentrations and whose properties are representative, or to use the concept of petroleum fractions. It is obvious that the grouping around a component or in a fraction can only be done if their chemical natures are similar. It should be kept in mind that the accuracy will be diminished when estimating certain properties particularly sensitive to molecular structure such as octane number or crystallization point. 

As seen in Chapter 2, mixtures of hydrocarbons and petroleum fractions are analyzed in the laboratory using precise standards published by ASTM (American Society for Testing and Materials) and incorporated for the most part into international (ISO), European (EN) and national (NF) collections. We wiil recall below the methods utilizing a classification by boiling point ... 

The desorptive process may be analyzed before boiling. The key assumption is that the vapor and adsorbed phases are ia equiUbrium ia the bulk of the bed. This assumption eliminates iatraparticle resistances from further consideration and is reasonable for rotary kiln appHcations. The two remaining resistances are associated with hydrocarbon diffusion out of the bed and with convection from the bed surface to the bulk gases. The flux of species Fi from the desorbiag bed becomes... 

Aromatic Radical Anions. Many aromatic hydrocarbons react with alkaU metals in polar aprotic solvents to form stable solutions of the corresponding radical anions as shown in equation 8 (3,20). These solutions can be analyzed by uv-visible spectroscopy and stored for further use. The unpaired electron is added to the lowest unoccupied molecular orbital of the aromatic hydrocarbon and a... 

A flame-ionization, total hydrocarbon analyzer determines the THC, and the total carbon content is calculated as methane. Other methods include catalytic combustion to carbon dioxide, which may be deterrnined by a sensitive infrared detector of the nondispersive type. Hydrocarbons other than methane and acetylene are present only in minute quantities and generally are inert in most appHcations. 

EPA Method 25A is the instrumental analyzer method for determination of total gaseous organic concentration using a flame ionization analyzer. The method apphes to the measurement of total gaseous organic concentration of vapors consisting primarily of alkanes, alkenes, and/or arenes (aromatic hydrocarbons). The concentration is expressed in terms of propane (or other appropriate organic calibration gas) or in terms or carrion. 

Air emissions should be monitored regularly for particulate matter and fluorides. Hydrocarbon emissions should be monitored annually on the anode plant and baking furnaces. Liquid effluents should be monitored weekly for pH, total suspended solids, fluoride, and aluminum and at least monthly for other parameters. Monitoring data should be analyzed and reviewed at regular intervals and compared with the operating standards so that any necessary corrective actions can be taken. 

J H Marsh and McLendon (M M, 1997), every five years, reviews and analyzes the 100 largest properly damage losses in the hydrocarbon- chemical industries that occurred over the previous 30 years. Most of the losses involved fires or explosions, flood, windstorm, and pressure rupture losses. 

In a hydrocarbon analyzer using flame ionization, the sample gas is conducted along a heated sampling line to the detector, in the hydrogen flame of which the hydrocarbons are ionized into electrons and positive ions,... 

The flame ionization detector is capable of measuring only gaseous hydrocarbons, in other words, hydrocarbons that have a low boiling point. Emission gases can, however, also contain hydrocarbons in liquid form at ambient temperature and pressure. Therefore, analyzers based on flame ionization detection are generally equipped with heating elements to keep rhe sampling line and the detector at about 200 °C. 

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