Benzene methane conversion

In this manner, a nearly universal and very nonselective detector is created that is a compromise between widespread response and high selectivity. For example, the photoionization detector (PID) can detect part-per-billion levels of benzene but cannot detect methane. Conversely, the flame ionization detector (FID) can detect part-per-billion levels of methane but does not detect chlorinated compounds like CCl very effectively. By combining the filament and electrochemical sensor, all of these chemicals can be detected but only at part-per-million levels and above. Because most chemical vapors have toxic exposure limits above 1 ppm (a few such as hydrazines have limits below 1 ppm), this sensitivity is adequate for the initial applications. Several cases of electrochemical sensors being used at the sub-part-per-million level have been reported (3, 16). The filament and electrochemical sensor form the basic gas sensor required for detecting a wide variety of chemicals in air, but with little or no selectivity. The next step is to use an array of such sensors in a variety of ways (modes) to obtain the information required to perform the qualitative analysis of an unknown airborne chemical. 

Therefore, in analogy with methane system, in the course of experiments as Cl-atom reacts with chloro or dichloro-methane, there is a potential for formation of HO-radicals. Hence in the initial stages of the reaction at lower rates of methane conversion we expect that HO will primarily attack benzene. As the reaction proceeds, oxidation products of CH4 and benzene increase in concentration and compete for the HO radicals. Thus, we expect to observe a curvature in relative rate plot of benzene at longer irradiation times, as shown in Figure 13.6. In FTIR studies, for the case of experiments in nitrogen diluent, curvature was observed but substantially lower concentrations of benzene were consumed. It is... 

The catalytic formation of benzene from methane was observed on nanostructured molybdenum-containing films in microreactors. The results confirm that M02C/M0O3 is an active catalyst for methane conversion. 

Improvements in the MDA performance of Mo/HZSM-5 catalysts have also been achieved by the addition of promoters, such as Ru [22] and Co or Fe [23], The partial exchange of H" in HZSM-5 with Cu2" ions markedly increased the methane conversion and benzene yield (from 15 to 70 %) by suppressing the dealumination of the zeolite framework upon incorporation of Mo and decreasing the formation of coke on the catalyst [24]. 

Transition metal-incorporated zeolites have been shown to be effident catalysts for direct conversion of methane to benzene and toluene under nonoxidative conditions [45,46]. Bao and co-workers revealed that Mo/ H-MCM-22 catalysts are desirable bifiinctional catalysts for methane dehydroaromatization reaction [47]. In terms of catalytic performances of Mo/H-MCM-22 with varied metal loading, catalyst with a Mo loading of ca. 6 wt% was found to exhibit the optimal benzene selectivity, suppressed naphthalene yield, and prolonged catalyst hfe under a moderate methane conversion. Although both Bronsted and Lewis acid sites are capable of catalysing methane conversion reaction, active sites with higher acidic strengths are anticipated to play the dominant role. 

Recently, it has been reported that highly dispersed molybdenum oxide supported on HZSM-5 exhibits nonoxidative conversion of methane into aromatics (benzene and naphthalene) and other hydrocarbons (126). At around 970 K and atmospheric pressure, benzene selectivities of 60-70% were observed at a methane conversion of 5-12%. These values approach the calculated values of... 

There are several areas of concern for the industrial practice of the reaction at the current stage of development (131). In addition to the equilibrium limitation of the methane-to-benzene conversion, the intrinsic activity of the Mo/ZSM-5 catalyst is rather low, for example, 7% conversion at Gas Hourly Space Velocity (GHSV) = 800 h (107). The promotion of the catalyst with W, Zr, Ru (132), and Fe (133) resulted in only modest success. Catalyst stability or lifetime should also be improved. Coke formation causes a gradual decrease in methane conversion to benzene with time on stream. Catalyst promotion with Fe or the addition of CO/CO2 in the methane feed improves the stability (133). 

Comparison of the Mo-lM-5 and Mo-ZSM-5 catalysts in nonoxidative aromatization of methane [64] showed that the former exhibits a higher methane conversion and higher benzene selectivity. The Mo-lM-5 catalyst was also more stable than Mo-ZSM-5. The catalytic behavior of Mo-lM-5 may be attributed to its unusual two-dimensional 10-memberring channel system with the character of three-dimensional cavity. 

The space velocity was varied from 2539 to 9130 scf/hr ft3 catalyst. Carbon monoxide and ethane were at equilibrium conversion at all space velocities however, some carbon dioxide breakthrough was noticed at the higher space velocities. A bed of activated carbon and zinc oxide at 149 °C reduced the sulfur content of the feed gas from about 2 ppm to less than 0.1 ppm in order to avoid catalyst deactivation by sulfur poisoning. Subsequent tests have indicated that the catalyst is equally effective for feed gases containing up to 1 mole % benzene and 0.5 ppm sulfur (5). These are the maximum concentrations of impurities that can be present in methanation section feed gases. 

The liquid stream can readily be separated into relatively pure components by distillation, the benzene taken off as product, diphenyl as an unwanted byproduct and the toluene recycled. It is possible to recycle the diphenyl to improve selectivity, but it will be assumed that is not done here. The hydrogen feed contains methane as an impurity at a mole fraction of 0.05. The production rate of benzene required is 265 kmol-lr1. Assume initially that a phase split can separate the reactor effluent into a vapor stream containing only hydrogen and methane, and a liquid containing only benzene, toluene and diphenyl, and that it can be separated to produce essentially pure products. For a conversion in the reactor of 0.75,... 

The reaction is to be conducted at 500 K and 10 atm with the starting composition benzene = 100, hydrogen = 400, methane (inert) = 100 and 90% conversion is required. Find the catalyst requirement per unit of benzene feed. 

Hydrogasification. Hydrogasification of coal involves reaction of hydrogen with coal carried out at elevated temperatures under high partial pressure of hydrogen. The objective is to add sufficient hydrogen to coal to produce methane as the major product. It has been found that many types of coal can be hydrogasi-fied if the coal is heated rapidly to reaction temperatures. Even under favorable conditions, however, conversion to methane is not complete and aromatics such as benzene are made as by-products. 

Reaction X. (6) Catalytic Conversion o Simple Hydrocarbons into more Complex Hydrocarbons.—These reactions are usually accomplished at high temperatures in presence of catalysts. Acetylene, propylene and even methane can be converted into benzene. (E.P., 374,422 369,351 366,394.)... 

Beside methanol and formaldehyde, the oxidation of methane may be directed to another route, leading to the formation of its condensation products, for example, ethane, ethylene and benzene. This route may provide an alternative way for the chemical use of natural sources of methane. Here, various catalysts were also tested using both 02 and N20 as the oxidants [22], The general picture observed by most authors was similar to that with methane oxidation to oxygenates. The conversion of methane was always higher with 02 than with N20. However, the selectivity to the coupling products showed an opposite trend. 

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