Methane ammonia reactions

Two synthesis processes account for most of the hydrogen cyanide produced. The dominant commercial process for direct production of hydrogen cyanide is based on classic technology (23—32) involving the reaction of ammonia, methane (natural gas), and air over a platinum catalyst it is called the Andmssow process. The second process involves the reaction of ammonia and methane and is called the BlausAure-Methan-Ammoniak (BMA) process (30,33—35) it was developed by Degussa in Germany. Hydrogen cyanide is also obtained as a by-product in the manufacture of acrylonitrile (qv) by the ammoxidation of propjiene (Sohio process). 

The reaction produces additional hydrogen for ammonia synthesis. The shift reactor effluent is cooled and tlie condensed water is separated. The gas is purified by removing carbon dioxide from the synthesis gas by absorption with hot carbonate, Selexol, or methyl ethyl amine (MEA). After purification, the remaining traces of carbon monoxide and carbon dioxide are removed in the methanation reactions. 

Oxygen-containing molecules cannot be tolerated in the ammonia synthesis, primarily because they form iron oxide that blocks the active surface. First the CO2 is removed, through a scrubber, by reaction with a strong base. The remaining CO (and CO2) is then removed by the methanation reaction, converting the CO into methane and water. Finally the water is removed by, for example, molecular sieves. Methane does not present problems because it interacts weakly with the catalyst surface. The gas mixture (Tab. 8.6) is compressed to the roughly 200 bar needed for ammonia synthesis and admitted to the reactor. 

Hydrogen cyanide is generally produced in industrial quantities by high temperature catalytic reaction between ammonia, methane, and air (the Andrussow process). The stoichiometry of the process is ... 

The methanation reaction is primarily used to remove any traces of CO and C02 in the hydrogen feed gas for ammonia synthesis. The reaction has been known for more than a century [141]. This reaction has found renewed interest in connection with the transformation of coal to natural gas. The hydrogen for ammonia synthesis is here normally produced by steam reforming with subsequent water gas... 

The methanation reaction is a highly exothermic process (AH = —49.2 kcal/ mol). The high reaction heat does not cause problems in the purification of hydrogen for ammonia synthesis since only low amounts of residual CO is involved. In methanation of synthesis gas, however, specially designed reactors, cooling systems and highly diluted reactants must be applied. In adiabatic operation less than 3% of CO is allowed in the feed.214 Temperature control is also important to prevent carbon deposition and catalyst sintering. The mechanism of methanation is believed to follow the same pathway as that of Fischer-Tropsch synthesis. 

The gas composition is optimized with DOFs outside the CO2 scrubbing system with regard to inert composition (methane and argon) and hydrogen to nitrogen ratio since the levels of these components affect downstream (ammonia synthesis) reaction kinetics. Improved kinetics at lower inert levels are achieved at the expense of using more fuel or feedstock, since lower inerts can be achieved by firing the primary... 

Ruthenium supported on oxides is a catalyst of various reactions. It is active in methanation reactions [e.g. 1, 2, 3], in Fischer-Tropsch synthesis [e.g. 4, 5, 6], in CO oxidation [7, 8], in the synthesis of methyl alcohol [9], 1" the redu ction of NO to nitrogen CIO] and in hydrogenolysis of ethane [11] and of butane [12]. Ru supported on carbon is supposed to replace the iron in ammonia synthesis [13]. Lately ruthenium supported on oxides is intensively investigated as a potential... 

Description Natural gas or another hydrocarbon feedstock is compressed (if required), desulfurized, mixed with steam and then converted into synthesis gas. The reforming section comprises a prereformer (optional, but gives particular benefits when the feedstock is higher hydrocarbons or naphtha), a fired tubular reformer and a secondary reformer, where process air is added. The amount of air is adjusted to obtain an H2/N2 ratio of 3.0 as required by the ammonia synthesis reaction. The tubular steam reformer is Topsoe s proprietary side-wall-fired design. After the reforming section, the synthesis gas undergoes high- and low-temperature shift conversion, carbon dioxide removal and methanation. 

All steam reforming catalysts in the activated form contain metallic nickel as active component, but the composition and structure of the support and the nickel content differ considerably in the various commercial brands. Thus the theoretical picture is less uniform than for the ammonia synthesis reaction, and the number of scientific publications is much smaller. The literature on steam reforming kinetics published before 1993 is summarized by Rostrup - Nielsen [362], and a more recent review is given by K. Kochloefl [422]. There is a general agreement that the steam reforming reaction is first order with respect to methane, but for the other kinetic parameters the results from experimental investigations differ considerably for various catalysts and reaction conditions studied by a number of researchers. 

Both GC-ECD and GC-MS with El or ECNI maybe used for the final analysis of PBDEs [5]. ECNI-MS is a very sensitive method for many halogenated compounds [1]. Using GC-MS, the type of reaction gas can influence the data. A study of PBDE residues in guillemot eggs showed an increase in levels of 2,2, 4,4 -TeBDE, an unidentified PeBDE, and 2,2, 4,4, 5-PeBDE of respectively 10-35%, 25 -80%, and 0-20% after re-analysis using ammonia as reaction gas instead of methane [1]. 

Potassium is used as a dopant on catalysts for the methanation reaction and ammonia synthesis. Its purpose is to increase the rate of the reaction. Potassium is also used on the steam reforming catalyst, not as a promotor but as a dopant that inhibits catalyst deactivation by coke formation (ref. 1). It is reasonable that the role of potassium as a promotor of reaction rates is to lower some barrier to bond dissociation. Since molecular beam techniques afford a convenient means of measuring changes in barrier heights as well as in shapes of the barrier through measurements of the dissociation probability versus energy, the possible effect of potassium on the dissociation of CH4 is investigated. 

Carbon monoxide still has to be removed since it will react with ammonia to form solid ammonium carbamate. A methanation reaction is used to remove CO this will also remove the residual C02. 

The conventional ammonia production line consists of seven gas-solid catalytic reactors, namely desulfurization unit, primary reformer, secondary reformer, high temperature shift, low temperature shift, methanator and finally the ammonia converter. In addition the production line includes an absorption-stripping unit for the removal of CO2 from the gas stream leaving the low temperature shift converter. The ammonia converter is certainly the heart of the process with all the other units serving to prepare the gases for the ammonia synthesis reaction which takes place over an iron promoted catalyst under conditions of high temperature and pressure. 

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. 

Hydrogen Cyanide from Ammonia and Natural Gas. In the general discussion of the reaction of ammonia with hydrocarbons, reference was made to the s mthesis of HCN from ammonia, methane (natural gas), and air. The over-all reaction CHi + NHj 1.50 —>HCN -t- 3H 0 can be... 

Carbon monoxide and carbon dioxide are poisons for many hydrogenation catalysts used in ammonia synthesis, refinery processes and petrochemical processes. Therefore, in steam reformers designed to produce hydrogen for hydrogenations, carbon oxides are removed to very low levels, typically a maximum of 5 ppm [7]. The conventional method of achieving this specification is to use a nickel or ruthenium catalyst to convert carbon oxides to methane. The conversion proceeds in accordance with the following methanation reactions ... 

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