Methanation side reactions

Then Semina et al. [38] reported the effect of synthesis method on M02C catalysts. According to them the highest catalyst activity in the WGS reaction was found for the M02C/M0 system synthesized via the simultaneous electroreduction of carbonate and molybdate ions. The activity of this catalyst was three orders of magnitude higher than the activity of the commercial Cu/Zn0/Al203 catalyst. The stability tests performed for the catalysts showed that this system remains active for at least 5000 h. In addition, no methanation side reaction is found. 

This reaction is an undesirable side reaction in the manufacture of hydrogen but utilised as a means of removing traces of carbon monoxide left at the end of the second stage reaction. The gases are passed over a nickel catalyst at 450 K when traces of carbon monoxide form methane. (Methane does not poison the catalyst in the Haber process -carbon monoxide Joes.)... 

In practice side reactions intervene to reduce the efficiency of the propagation steps The chain sequence is interrupted whenever two odd electron species combine to give an even electron product Reactions of this type are called chain terminating steps Some commonly observed chain terminating steps m the chlorination of methane are shown m the following equations... 

Methane [74-82-8] reacts with sulfur essentially without side reactions ... 

Side reactions reduce the yield (99). Proposed processes for obtaining carbon disulfide from hydrogen sulfide and methane include a high temperature plasma (100) and low temperature operation with a catalyst and oxygen (101). 

An important side reaction is the formation of diaryl methane derivatives ArCHaAr. Moreover poly substituted products may be obtained as minor products. Aromatic compounds have been treated with formaldehyde and hydrogen bromide or hydrogen iodide instead of hydrogen chloride. The formaldehyde may be replaced by another aldehyde the term Blanc reaction however stands for the chloromethylation only. 

The cyclic kotal (19) was again used as protection and the methane sulphonyl (MeSOg or Ms, mesylate) group was used as the leaving group X (p T2S) (20). The protecting group was left in until the end to avoid any side reactions. 

In the presence of metal catalysts, hydrogen peroxide oxidations proceed in improved yields. The most common catalyst is an iron(II) salt which produces the well-known Fenton system or reagent. Dimethyl sulphoxide is oxidized to the sulphone using this system although a range of unwanted side-products such as methanol and methane are produced Diphenyl sulphoxide does not react using this reagent due to its insolubility and in all cases some iron(III) is formed by other side-reactions. 

Sulfur trioxide is not only much cheaper than hexachloroplatinate, but the sulfur dioxide formed can in principle be converted back to sulfur trioxide by oxidation with air. Methylbisulfate can be hydrolyzed to methanol, and so a complete cycle that converts CH4 and 02 into CH3OH can be envisioned. Overoxidation of methane to C02 - a major side reaction of many procedures - was relatively limited in the... 

The side reaction of hydrogenolysis of the methyl-ruthenium intermediate to methane also may become predominant when the carbonyl insertion-methyl migration step of the process (Scheme 1) proceeds at a low rate. To reduce this drawback some Lewis acid promoters (i.e. metal alkali cations, classical Lewis acids such as AII3, SbCl etc.)... 

To retain consistency throughout this presentation, we will consider a general nonadiabatic, packed bed reactor, as shown in Fig. 1, with a central axial thermal well and countercurrent flow of cooling fluid in an exterior jacket.1 We focus on the methanation reaction since methanation is a reaction of industrial importance and since methanation exhibits many common difficulties such as high exothermicity and undesirable side reactions. 

Methanation is one of a more general class of Fischer-Tropsch processes in which carbon monoxide and carbon dioxide are hydrogenated to form various light hydrocarbons and water. Although the primary reaction using a nickel on alumina catalyst is the methanation of carbon monoxide, appreciable side reactions can occur in the methanation system. The reactions in the methanation system are shown in Table I and include carbon dioxide... 

Most of the side reactions have already been discussed in Section 26.1.3.3. (dediazoniation in organic solvents). Chlorinated aliphatic solvents, such as 1,2-dichloroethane and dichloro-methane, lead to an extensive formation of chloroaromatics, and aromatic solvents, even halogenated examples, can be arylated to some extent by arenediazonium tetrafluoroborates (vide supra). For example, during dediazoniation of benzenediazonium tetrafluoroborate in toluene, chlorobenzene, bromobenzene or anisole, 3-5 % of substituted biphenyls Ph-C6H4-X (X = Me, Cl, Br, OMe) are formed together with 0.5-0.8% of fluorobiphenyls.5 Fluorobiphenyls are formed through an ionic pathway (only 2- and 4-isomers are formed) whereas chlorobiphenyls result from a radical process (X = Cl, 2-/3-/4-isomer 26 47 27).243... 

Superacids were shown to have the ability to effect the protolytic ionization of a bonds to form carbocations even in the presence of benzene.190 The formed car-bocations then alkylate benzene to form alkylbenzenes. The alkylation reaction of benzene with Ci—C5 alkanes (methane, ethane, propane, butane, isobutane, isopentane) are accompanied by the usual acid-catalyzed side reactions (isomerization, disproportionation). Oxidative removal of hydrogen by SbF5 is the driving force of the reaction ... 

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