Residence time methane yield

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%... 

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. 

Fig. 14.11 Influence of residence time on methane conversion and product yield [63]. Reaction conditions Temperature 703 K, pressure 34 bar, CH4/02 ratio 16/1.

Figure 2 shows the results of the pyrolysis experiments conducted with the Spanish lignite at 750-960°C at residence times of 0.52-0.72 sec. It is seen that under the pyrolysis conditions used, 60 - 70% of the sulfur in this coal appears in the gaseous products as H2S, COS, and CS2. As in the previous sulfur study (1), the principal sulfur gaseous product at all temperatures is H2S, with some CS2 formed at T >840°C. The CS2 is apparently formed at the expense of the H2S, by any of several reactions H2S may react with the carbon of the coal and/or the methane evolved in the pyrolysis of the coal to form CS2- A small amount of COS is detected at all temperatures trace amounts of SO2 are also detected. Moreover, the total sulfur yield appears to reach a maximum about 900°C. The decrease in sulfur volatilization as pyrolysis temperature is increased above 900°C is attributed to sulfur retention in the char due to the reaction of H2S with coke or char to form more stable thiophenic structures (2). GC/MS analysis of the tars (diluted to 10 ml) from the pyrolysis at 750 and 850°C did not reveal any sulfur-containing structures. Tars from the pyrolysis at 900 and 950°C, however, contain dibenzothiophene. 

In general, the yields of the products follow the same trend as that of the methane conversion. The selectivities of the respective products did not vary much with either reactor size or residence time. Figure 3 shows that the selectivity of hydrogen has little variance between the different reactor sizes and residence times. The largest variance is 10% with experimental uncertainty accounting for at least 2-3% of this. 

Figures 7-9 show the effect of residence time on the selectivity and yield of the two different feed compositions. The yield basis for hydrogen includes only the net hydrogen produced from the reacted methane. The selectivity towards hydrogen, shown in Figure 7, is lower for the system that contains hydrogen in the feed. However, the conversion is higher in that system resulting in a hydrogen yield that is essentially the same in both systems at each residence time.

The reference test was conducted in a stainless steel reactor assembly which was sized to duplicate the Kureha reactor geometry. The experimental operating conditions compared favorably with the actual plant conditions. In particular, the steam temperature, S F ratio, residence time, oil feed rate, and heat input were matched very closely. However, the reactor exit temperature was somewhat lower than that of the operating plant. The experimental gas yields for ethylene, ethane, propylene, and propadiene agreed very well with the plant. There were slightly lower experimental values for hydrogen, methane, acetylene, and total gas, which indicated a less severe crack. 

Equation 1 shows that the MCP is more strongly influenced by the HCPP than by the residence time. The MCP is a measure of the number of collisions between hydrocarbon molecules and is independent of coil geometry. Figures 3a-3d show methane, ethylene, butadiene, and PFO yields from naphtha as a function of MCP. For decreasing MCP, methane decreases, ethylene increases, butadiene increases, and PFO decreases at constant P/E. 

The influence of residence time on the gasification efficiency was tested in the miniature plant for both glucose and pyrocatechol at 30, 60 and 120 sec. (feed 0.2 M 600°C, 250 bar, KOH). At these conditions the residual TOC content of the effluent solution of pyrocatechol gasification decreases from 2% to less than 0.1 % and the methane yield increases with reaction time (Figure 4). No tar or coke are formed and the effluent is colourless and odourless clear aqueous solution. 

The production of synthesis gas (CO, H2) from methane by partial oxidation is investigated over commercial steam reforming catalyst at several flow rates, temperatures, and at different methane/oxygen ratios (R). Optimum synthesis gas selectivity and yield achieved are 70% and 60%, respectively at methane/oxygen ratio close to 2 and at flow rates of500 cm /min. An initial temperature (665 °C) is necessary to initiate the reaction and then the reaction is stabilized at 883 °C. Tbe effect of methane/oxygen ratios and residence time are effective in determining the synthesis gas selectivity and yield. 

Three sets of experiments have been conducted. The first set is examining the influence of methane/oxygen ratios on the performance of the catalyst the second set is studying the effect of temperature on the synthesis gas formation and the third set is investigating the influence of residence time on synthesis gas selectivity and yield. The experimental data are shown in tables 1 and 2. Selectivity, yield and conversion are defined according to the following ... 

Finally, Crabtree has reported the gas-phase mercury photosensitized reaction of methane with ammonia to yield methylene imine as the ultimate product [41]. Higher imines are also produced if the gas-phase residence time of methylene imine is prolonged. 

H2) where a complex network, involving secondary reactions of CO2 and H2O with CH4, enhance the yield of H2 and CO so that thermodynamic equilibrium can be reached easily [27]. It can be inferred that, like the oxidation of methane to syngas, the partial oxidation of methanol with a CH3OH/O2 ratio near to the stoichiometric value (ca. 2/1) operating with an optimum residence time and temperature can reach very high yields also approaching thermodynamic equilibrium. 

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