Methane residence time

Basile, F., Basini, L., Damore, M., Fornasari, G., Guarinoni, A., Matteuzzi, D., DelPiero, G, Trifiro, F. and Vaccari, A. (1998). Ni/Mg/Al anionic clay derived catalysts for the catalytic partial oxidation of methane - residence time dependence of the reactivity features. J. Catal. 173, 247. 

Table 16.4 Experimentally observed effects of catalyst particle size and promotion on CO and methane residence times, conversion, and a, together with the explanation according to our model [46].

The conversion takes place at high temperature (820-850°C) and very short residence time (hundredth of seconds) in the presence of steam. The by-products are hydrogen, methane and a highly aromatic residual fuel-oil. 

Another hydrogenation process utilizes internally generated hydrogen for hydroconversion in a single-stage, noncatalytic, fluidized-bed reactor (41). Biomass is converted in the reactor, which is operated at about 2.1 kPa, 800°C, and residence times of a few minutes with steam-oxygen injection. About 95% carbon conversion is anticipated to produce a medium heat value (MHV) gas which is subjected to the shift reaction, scmbbing, and methanation to form SNG. The cold gas thermal efficiencies are estimated to be about 60%. 

NMe is now commercially available and is prepd by the vapor phase nitration of methane at a ratio of 9 moles of methane to I mole of nitric acid at 475° and a residence time of 0.18sec (Ref 12) or by the similar nitration of aliphatic hydrocarbons (Ref 8). Other prepns are from Me sulfate and Na nitrite (Ref 26) by the oxidn of Me amine with dinitrogen trioxide in the gas phase or in methylene chloride, yield 27%... 

GP 2] ]R 3a] Studies were performed at constant ethylene content and residence time and by varying the oxygen content by exchange versus methane. An increase... 

Partial methane oxidation comprises very high rates so that high space-time yields can be achieved (see original citations in [3]). Residence times are in the range of a few milliseconds. Based on this and other information, it is believed that syngas facilities can be far smaller and less costly in investment than reforming plants. Industrial partial oxidation plants are on the market, as e.g. provided by the Syntroleum Corporation (Tulsa, OK, USA). Requirements for such processes are operation at elevated pressure, to meet the downstream process requirements, and autothermal operation. 

OS 81] [R 7] [P 61] An increase in residence time by a factor of about 3 was accomplished by changing the flow rate from 3.0 to 0.9-1.1 pi min [19[. By far the main reaction product detected was methane otherwise only traces of methanol were present. Instead, at the shorter residence hme a mixtrue containing 68% ethene, 16% ethane and 15% methane was obtained [19,138[. Hence the presence of methane demonstrates that complete cracking occurred as a consecutive reaction to dehydration. 

Dunker, A., Kumar, S., and Mulawa, P., Production of hydrogen by thermal decomposition of methane in a fluidized bed reactor—effect of catalyst, temperature and residence time, Int.. Hydrogen Energ., 31, 473, 2006. 

To minimize coking, the reactor may be operated at short residence times, or hydrogen may be added to the process stream to convert gas-phase carbon into methane. It is also advantageous to minimize the temperature upstream of the catalyst bed, since gas-phase carbon is less readily formed at low temperatures. 

Figure 4.2 presents a simplified flow diagram of the ENCOAL Liquid from Coal (LFC) process. The process upgrades low-rank coals to two fuels, Process-Derived Coal (PDF ) and Coal-Derived Liquid (CDL ). Coal is first crushed and screened to about 50 mm by 3 mm and conveyed to a rotary grate dryer, where it is heated and dried by a hot gas stream under controlled conditions. The gas temperature and solids residence time are controlled so that the moisture content of the coal is reduced but pyrolysis reactions are not initiated. Under the drier operating conditions most of the coal moisture content is released however, releases of methane, carbon dioxide, and monoxide are minimal. The dried coal is then transferred to a pyrolysis reactor, where hot recycled gas heats the coal to about 540°C. The solids residence time... 

Consequently, in the early 1990s, interest in the direct processes decreased markedly, and the emphasis in research on CH4 conversion returned to the indirect processes giving synthesis gas (13). In 1990, Ashcroft et al. (13) reported some effective noble metal catalysts for the reaction about 90% conversion of methane and more than 90% selectivity to CO and H2 were achieved with a lanthanide ruthenium oxide catalyst (L2Ru207, where L = Pr, Eu, Gd, Dy, Yb or Lu) at a temperature of about 1048 K, atmospheric pressure, and a GHSV of 4 X 104 mL (mL catalyst)-1 h-1. This space velocity is much higher than that employed by Prettre et al. (3). Schmidt et al. (14-16) and Choudhary et al. (17) used even higher space velocities (with reactor residence times close to 10-3 s). 

Recently, such a temperature oscillation was also observed by Zhang et al (27,28) with nickel foils. Furthermore, Basile et al (29) used IR thermography to monitor the surface temperature of the nickel foil during the methane partial oxidation reaction by following its changes with the residence time and reactant concentration. Their results demonstrate that the surface temperature profile was strongly dependent on the catalyst composition and the tendency of nickel to be oxidized. Simulations of the kinetics (30) indicated that the effective thermal conductivity of the catalyst bed influences the hot-spot temperature. 

The pyrolytic reforming reactor was a packed bed in a quartz tube reactor. Quartz was selected to reduce the effect of the reactor construction material on the hydrocarbon decomposition rate. ° The reactor was packed with 5.0 0.1 g of AC (Darco KB-B) or CB (BP2000) carbon-based catalyst. The reactor was heated electrically and operated at 850—950 °C, and the reactants had a residence time of 20—50 s, depending on the fuel. The reactor was tested with propane, natural gas, and gasoline as the fuels. Experiments showed that a flow of 80% hydrogen, with the remainder being methane, was produced for over 180 min of continuous operation.The carbon produced was fine particles that could be blown out... 

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