Hydrocarbon concentration

Hydrocarbon fumes evolved during anode baking are generally disposed of by burning. Additional fuel is required to support combustion because the hydrocarbon concentration is low. In some plants these products are now absorbed in a fluid bed of alurnina for burning in a concentrated form. This treatment also catches the fluoride evolved during anode baking. 

Fig. 8. isopleth diagram showing the response of concentrations to changes in initial NO and nonmethane hydrocarbon concentrations expressed as parts per million of carbon atoms (ppm C). The response to NO reductions is dependent on the particular initial concentrations. At point A, the graph indicates that decreasing NO would increase formation, and at point C, a decrease in the NO concentration results in a much larger decrease in... 

Typically NO conversion ranges from 80 to 95% and there are corresponding decreases in CO and hydrocarbon concentrations. Potential problems associated with NSCR appHcations include catalyst poisoning by oil additives, such as phosphoms and 2inc, and inadequate control systems (37). 

Some vent streams, such as light hydrocarbons, can be discharged directly to the atmosphere even though they are flammable and explosive. This can be done because the high-velocity discharge entrains sufficient air to lower the hydrocarbon concentration below the lower explosive limit (API RP 521, 1997). Toxic vapors must be sent to a flare or scrubber to render them harmless. Multiphase streams, such as those discharged as a result of a runaway reaction, for example, must first be routed to separation or containment equipment before final discharge to a flare or scrubber. 

The large number of individual hydrocarbons in the atmosphere and the many different hydrocarbon classes make ambient air monitoring a very difficult task. The ambient atmosphere contains an ubiquitous concentration of methane (CH4) at approximately 1.6 ppm worldwide (9). The concentration of all other hydrocarbons in ambient air can range from 100 times less to 10 times greater than the methane concentration for a rural versus an urban location. The terminology of the concentration of hydrocarbon compounds is potentially confusing. Hydrocarbon concentrations are referred to by two units—parts per million by volume (ppmV) and parts per million by carbon (ppmC). Thus, 1 fx of gas in 1 liter of air is 1 ppmV, so the following is true ... 

An estimate is required of the total hydrocarbon concentration 300 meters downwind of an expressway on an overcast day with wind speed 4 m/s. Tlie expressway runs norlli-south and the wind is from tlie west. Tlie measured traffic flow is 8000 vehicles per hour during tlris rush hour, and the average speed of the velucles is 40 mph. At tlris speed tlie average vehicle is expected to... 

The competition between dilution of NMHQ (here [NMHCJq represents the initial hydrocarbon concentration) and its reaction with HO to generate an oxidant molecule enters through the dimensionless parameter S fcd/k25[HO ] that compares the rate of the HO reaction to the rate of dilution. Also important is the relative reactivity of the oxidation product PROD to the parent hydrocarbon as defined by the dimensionless parameter If the oxidation products... 

One notes in Table 1.2 a uniform increase in the adsorption energies of the alkanes when the microspore size decreases (compare 12-ring-channel zeohte MOR with 10-ring-channel TON). However, at the temperature of hydroisomerization the equilibrium constant for adsorption is less in the narrow-pore zeohte than in the wide-pore system. This difference is due to the more limited mobility of the hydrocarbon in the narrow-pore material. This can be used to compute Eq. (1.22b) with the result that the overall hydroisomerization rate in the narrow-pore material is lower than that in the wide-pore material. This entropy-difference-dominated effect is reflected in a substantially decreased hydrocarbon concentration in the narrow-pore material. 

Maleic anhydride is an important industrial fine chemical (see original citations in [43]). The oxidation of C4-hydrocarbons in air is a highly exothermic process, therefore carried out at low hydrocarbon concentration (about 1.5%) and high conversion. The selectivity of 1-butene to maleic anhydride so far is low. The reaction is composed of a series of elementary reactions via intermediates such as furan and can proceed to carbon dioxide with even larger heat release. As a consequence, hot spots form in conventional fixed-bed reactors, decrease selectivity and favor other parallel reactions. 

Bishop CA, Rouse JD. 2000. Chlorinated hydrocarbon concentrations in plasma of Lake Erie water snake Nerodia sipedon insularum) and northern water snake (Nemdia sipedon sipedon) from the Great Lakes Basin in 1998. Arch Environ Contam Toxicol 39 500-505. 

Due to the narrow safe area in the hydrocarbon-lean zone, operation in the n-hexane-rich zone was preferred. In the latter case, however, feed compositions having high hydrocarbon concentration had to be avoided, in order to hmit the contribution of radical-chain reactions, favoured at high temperature under aerobic conditions. Therefore, operation with a diluted feed was preferred the ballast used for the reaction was helium, in order to allow evaluation of the amount of N2 produced by ammonia combustion. 

Experimental temperature determination reveals little difference between the gases at 355 kHz, as is evident in Figs. 14.15a and b, similar to the results of Okitsu et al. The likely explanation for this seemingly contradictory result is that the MRR method, which requires the presence of a significant amount of hydrocarbon within the bubble core, yields a temperature value that is dictated by the hydrocarbon itself. In other words, the probe itself determines the temperature measured. This becomes apparent at higher frequency (1,056 kHz Fig. 14.15c) where it is clear that the temperature that is obtained when one extrapolates to zero hydrocarbon concentration varies depending on the probe molecule. The lower temperature for /(77-butanol is attributed to a greater rate of hydrocarbon product formation. 

While the gases used in stripping are usually air, nitrogen, or helium, electrolytically evolved hydrogen has been used as a collector for hydrocarbons [49]. In this technique, the gas is not passed through a column of adsorbent, but instead collects in the headspace of the container. Since the volume of seawater and of hydrogen are known, the hydrocarbon concentration in the headspace can be used to calculate the partition coefficients and the concentration of hydrocarbon in the seawater. 

A second system, the removal of volatiles by vacuum, can be set up in two ways either as a flow-through or as a batch process. As a flow-through process, the sample is drawn continuously through the system, and the gases taken off by the vacuum pass through a sampling loop. Periodically, the material in the loop is injected into the gas chromatograph. In this manner it is possible to derive almost continuous profiles of volatile hydrocarbon concentrations [19]. 

The border conditions between chain and nonchain mechanisms of oxidation depends not only on temperature but also on the hydrocarbon concentration and the rate of chain initiation. The following equation describes this dependence ... 

It was shown in the previous section that hydrocarbon oxidation catalyzed by cobalt salts occurs under the quasistationary conditions with the rate proportional to the square of the hydrocarbon concentration and independent of the catalyst (Equation [10.9]). This limit with respect to the rate is caused by the fact that at the fast catalytic decomposition of the formed hydroperoxide, the process is limited by the reaction of R02 with RH. The introduction of the bromide ions into the system makes it possible to surmount this limit because these ions create a new additional route of hydrocarbon oxidation. In the reactions with ROOH and R02 the Co2+ ions are oxidized into Co3+, which in the reaction with ROOH are reduced to Co2+ and do not participate in initiation. 

When the hydrocarbon concentration is high enough for the reaction of the sulfonyl-peroxyl radical with hydrocarbon not to limit the chain propagation, the following equation describes the dependence of the initial rate v of initiated (Vj) chain sulfoxidation of alkane [25] ... 

Heit, M., C.S. Klusek, and K.M. Miller. 1980. Trace element, radionuclide, and polynuclear aromatic hydrocarbon concentrations in Unionidae mussels from northern Lake George. Environ Sci. Technol. 14 465A68. 

Glegg, G. A. and Rowland, S. J. (1996). The Braer oil spill hydrocarbon concentrations in intertidal organisms. Marine Pollution Bulletin 32 486 492. 

Significant differences at the 99% confidence level were observed for the extraction technique and for the polyaromatic hydrocarbons concentration in the soil. The average recovery by the Soxhlet technique was 74.5% whereas 62.8% was the average Polytron recovery. A much higher proportion was extracted with polyaromatic hydrocarbons at the 50pg/g level (72.6%) than at the 5pg/g level (64.6%) suggesting that the extraction efficiency is not constant with concentration. 

Soils containing elevated hydrocarbon concentrations such that the soil may be considered a hazardous waste ... 

Figure 4.15a are LNAPL obtained from two adjacent sites with different histories, and representative unaltered regular unleaded and premium unleaded gasoline samples. High BTEX hydrocarbon concentrations in LNAPL and groundwater are often indicative of gasoline presence. A noticeable depletion in benzene and toluene is evident in the LNAPL samples as compared with unaltered dispensed gasoline,... 

FIGURE 10.18 Graphs of total volatile petroleum hydrocarbons concentration with time at... 

Confirmatory soil sampling was subsequently performed. Three soil borings were drilled and samples retrieved from the impacted area. Soil from a depth of 30 ft and below were reported as nondetectable however, samples from a depth of 21 ft still contained significant gasoline components with TPH-gasoline ranging up to 3600 ppm. This zone of elevated hydrocarbons was anticipated due to the presence of clays and silt at this depth. Ventilation of these low-permeability soils was not deemed cost-effective, and significant reduction of the residual hydrocarbon concentrations unlikely. 

Extent of contamination/plume stability Hydrocarbon type Chromatographic evidence Hydrocarbon concentration Soil pH... 

Natural attenuation had reduced overall hydrocarbon concentrations and would be expected to continue, although slowly, in the future. 

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