Decomposition of methane and

This moderately endothermic process results in the formation of 2 moles of hydrogen per mole of methane consumed above a certain threshold reaction temperature. A gradual catalyst deactivation is expected due to the accumulation of carbon on the catalyst. The catalyst can be regenerated by removing the carbon on the catalyst in a separate step. Thus, hydrogen production by this approach involves two distinct steps (a) catalytic decomposition of methane and (b) regeneration of catalyst. 

CH4 may be converted to synthesis gas by steam reforming or by reaction with Oj through secondary reforming and partial oxidation [1]. Steam may also be replaced by COj. As for all processes where hydrocarbons or carbon oxides are exposed to high temperamres, carbon deposition is a possible problem in the production of synthesis gas. In the production of synthesis gas, carbon may be formed by decomposition of methane (and higher hydrocarbons) or by the Boudouard reaction [2] ... 

Steam reforming involves the risk for carbon formation by the decomposition of methane and other hydrocarbons or by the Boudouard reaction (ref. 1). 

The Decomposition of Methane and Methyl Chloride in a Microwave Discharge... 

Figure 4.1 is a flow diagram of the Andrussow process [7], To avoid the decomposition of methane and ammonia, the ratio of reactants must be carefully controlled. The products are cooled where care is taken to avoid the formation of azulmic acids, polymers formed by the reaction between hydrogen cyanide, ammonia, and water. The products go to a scrubbing tower where unconverted ammonia is absorbed in sulfuric acid. The product is then absorbed in water, stripped, and distilled to produce greater than 99% HCN [8]. Yields are 70 and 60% for methane and ammonia, respectively. 

Atmospheric pressure CVD of NbCi-yN, using NbCl, NH3, and CH4 has been employed in three separate approaches toward the optimization of reaction characteristics [69]. These were (i) simultaneous deposition of niobium, carbon, and nitrogen by hydrogen reduction of NbCls with decomposition of methane and ammonia at a temperature of 900-1000°C (ii) deposition of a niobium amide complex derived from NbCl.s/NHi in nitrogen as a carrier gas at 250-350 °C, and subsequent conversion in ammonia/methane at 1 000-1 100 °C (iii) separate deposition of elemental niobium or NbCl.3 by hydrogen reduction at 500-1000°C and subsequent conversion to NbCi yNy in an ammonia/methane atmosphere at 1000-1 100°C. The results of these three approaches are given below. 

The decomposition of methane and sulfate (cf. Chapter 8) occur for both reactants in specific depths at identical rates which were entered into the spreadsheet. The adjustment to the measured profiles was committed only by these (microbial) decomposition rates. The decomposition parameter is set to 0.0 in all other cells, so that a dif-fnsion controlled transport occnrs with a constant concentration gradient. 

Autocatalysis, carbon formation and surface effects The third or autocatalytic stage In the methane pyrolysis. In which the yield of ethane begins to rise sharply again after the steady-state plateau (fig. 1) Is not predicted or explained by the reaction mechanism postulated above. The autocatalysis Is most evident In the yield of ethane, but almost certainly affects the other products as well, although It Is less obvious because their yields are already rising sharply. Autocatalysis has frequently been reported in the decomposition of methane, and under various conditions of pressure, temperature, conversion or surface, may have a variety of causes. It is most commonly associated with the formation of carbon, and attributed to reactions occuring at a carbon surface. 

Since metallic nickel is a catalyst for the formation of carbon due to the decomposition of methane and the disproportionation of CO, these processes can result in catalyst deactivation and the clogging of the proton-exchange membrane of a fuel element by elementary carbon ... 

Carbon Formation. Steam reforming involves the risk of carbon formation by the decomposition of methane and other hydrocarbons or by the Boudouard reaction (reactions (7) -(10)). Reactions (7) - (8) are catalyzed by nickel (Rostrup-Nielsen, 1984a). The carbon grows as a fibre (whisker) with a nickel crystal at the tip. The methane or carbon monoxide is adsorbed dissociatively on the nickel surface (Alstrup, 1988). Carbon atoms not reacting to gaseous molecules are dissolved in the nickel crystal, and solid carbon nucleates at the non-exposed side of the nickel crystal, preferably from Ae dense (111) surface planes. Reaction (10) results in pyrolytic carbon encapsulating the catalyst. 

As discussed previously, pyrolytic carbon obtained from small molecules was investigated as early as the 1950s. In 1953, it was discovered that methane decomposed on the surface of porcelain balls at 1000°C to produce pyrolytic carbon, and pyrolytic carbon was also prepared by decomposition of methane and benzene on the surface of Pt at 900-1000°C. Other metals such as Fe, Co, and Ni could also act as catalysts for the formation of pyrolytic carbons from small molecules [1]. In 1957, it was found that phenylbenzene decomposed at 1200°C into thick carbon film and sponge-like carbon together with the ball-like structure of carbon black. 

Decomposition. Acetaldehyde decomposes at temperatures above 400°C, forming principally methane and carbon monoxide [630-08-0]. The activation energy of the pyrolysis reaction is 97.7 kj/mol (408.8 kcal/mol) (27). There have been many investigations of the photolytic and radical-induced decomposition of acetaldehyde and deuterated acetaldehyde (28—30). 

Chemistry. Coal gasification iavolves the thermal decomposition of coal and the reaction of the carbon ia the coal, and other pyrolysis products with oxygen, water, and hydrogen to produce fuel gases such as methane by internal hydrogen shifts... 

I. Gas movement. In most cases, over 90 percent of the gas volume produced from the decomposition of sohd wastes consists of methane and carbon dioxide. Although most of the methane escapes to the atmosphere, both methane and carbon dioxide have been found in concentrations of up to 40 percent at lateral distances of up to 120 m (400 ft) from the edges of landfills. Methane can accumulate below buildings or in other enclosed spaces on or close to a sanitaiy landfill. With proper venting, methane should not pose a problem. 

SSIMS has also been used to study the adsorption of propene on ruthenium [3.29], the decomposition of ammonia on silicon [3.30], and the decomposition of methane thiol on nickel [3.31]. 

British Foreign Minister Ernest Bevin once said that "The Kingdom of Heaven runs on righteousness, but the Kingdom of Earth tuns on alkanes." Well, actually he said "tuns on oil" not "runs on alkanes," but they re essentially the same. By far, the major sources of alkanes are the world s natural gas and petroleum deposits. Laid down eons ago, these deposits are thought to be derived from the decomposition of plant and animal matter, primarily of marine origin. Natural gas consists chiefly of methane but also contains ethane, propane, and butane. Petroleum is a complex mixture of hydrocarbons that must be separated into fractions and then further refined before it can be used. 

The steam reforming of natural gas process is the most economic near-term process among the conventional processes. On the other hand, the steam reforming natural gas process consists of reacting methane with steam to produce CO and H2. The CO is further reacted or shifted with steam to form additional hydrogen and CO2. The CO2 is then removed from the gas mixture to produce a clean stream of hydrogen. Normally the CO2 is vented into the atmosphere. For decarbonization, the CO2 must be sequestered[l,2]. The alternative method for hydrogen production with sequestration of carbon is the thermal decomposition of methane. 

A thermal plasma system has been developed for the decomposition of methane. A schematic diagram of the experimental apparatus is shown in Fig. 1. The system consists primarily of D.C. plasma torch, plasma reactor and filter assembly. Plasma was discharged between a tungsten cathode and a copper anode using N2 gas. All the experiments were carried out at atmospheric pressure at 6 kW input electric power and N2 flow rate of 10 to 12 1/min. The feed gas (CH4) flow rates were varied from 3 to 15 1/min depending on the operating conditions, shown in Table. 1. 

Direct thermal decomposition of methane was carried out, using a thermal plasma system which is an environmentally favorable process. For comparison, thermodynamic equilibrium compositions were calculated by software program for the steam reforming and thermal decomposition. In case of thermal decomposition, high purity of the hydrogen and solidified carbon can be achieved without any contaminant. 

Screening of metal oxide catalysts for carbon nanotubes and hydrogen production via catalytic decomposition of methane... 

Table 3 shows the performance of the promoted-catalysts for the decomposition of methane to hydrogen at 5, 60, 120 and 180 min of time on stream. The results in Table 3 revealed that the activity of the parent catalyst and MnOx-doped catalyst remained almost constant until 120 min of time on stream. The activity of the other promoted-catalysts, on the other hand, decreased with an increase in the time on stream. The data for the CoO-doped catalyst and 20 mol%NiO/Ti02 could not be recorded at 120 min and 180 min, respectively because of the pressure build-up in the reactor. This finding indicates that adding MnOx enhances the stability and the resistibility of the NiO/Ti02 catalyst towards its deactivation. 

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