Methane to Aromatics

After commercial success with the propane/butane to aromatics processes, attempts were made to extend these catalysts to convert methane to aromatics. In 1993, Wang et al. [97] discovered that Mo/MFl is capable of catalyzing the difficult reaction. Almost all successful catalysts for this transformation are based on this bifunctional basis. Both strong acid sites and Mo are necessary to convert CH4 

Zeolite S1O2/ AI2O3 ratio Catalyst/ oil ratio Feed Temperature Pressure 

Bao s recent discovery of a Mo loaded MWW zeolite is starting to push the field forward [99] (Table 12.17). 

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Carbon black, also classed as an inorganic petrochemical, is made predominandy by the partial combustion of carbonaceous (organic) material in a limited supply of air. Carbonaceous sources vary from methane to aromatic petroleum oils to coal tar by-products. Carbon black is used primarily for the production of synthetic mbber (see Carbon, carbon black). 

Wan et al. [61] also reported the highly effective conversion of methane to aromatic hydrocarbons over Cu, Ni, Fe, and Al catalysts. The effects of the type of catalyst, its configuration, and the microwave irradiation conditions on reaction path and product selectivity were examined under both batch and continuous-flow conditions. 

Reactions of halogen-stabilized carbenoids with imines have been carried out using prefoimed lithium species (e.g. equation 36), or via a carbenoid generated from diiodomethane utilizing zinc-copper couple (Simmons-Smith conditions). A stereospecific ring closure is observed after the addition of lithiodichloromethane to a benzaldimine (equation 37).The addition of lithiochloro(phenylsulfon-yl)methane to aromatic imines affords 2-phenylsulfonyl-substituted aziridines, which can be deproton-ated and alkylated in excellent yield (Scheme 20). 

Dependence of 4,4 -(l-Methylethylidene)bisphenol Novolac Molecular Weight on the mole ratio of Methanal to Aromatic monomer (data from ref [33])... 

Steady-state conversion of methane to aromatics in high yields using an integrated recycle reaction system. Catal Lett, 48,11-15. 

Claridge JB, Green MLH, Tsang SC, York APE. Oxidative oligomerisation of methane to aromatics. Appl Catal... 

The competitive method employed for determining relative rates of substitution in homolytic phenylation cannot be applied for methylation because of the high reactivity of the primary reaction products toward free methyl radicals. Szwarc and his co-workers, however, developed a technique for measuring the relative rates of addition of methyl radicals to aromatic and heteroaromatic systems. - In the decomposition of acetyl peroxide in isooctane the most important reaction is the formation of methane by the abstraction of hydrogen atoms from the solvent by methyl radicals. When an aromatic compound is added to this system it competes with the solvent for methyl radicals, Eqs, (28) and (29). Reaction (28) results in a decrease in the amount... 

MoZSM-5 Methane dehydroaromatization Higher activity and selectivity to aromatics Higher tolerance to coking [75]... 

For each case we will also present catalytic analogues, namely (1) the activation of methane to form methanol with platinum, the reaction of certain aromatics with palladium to give alkene-substituted aromatics, and (2) the alkylation of aromatics with ruthenium catalysts, and the borylation of alkanes and arenes with a variety of metal complexes. 

Methane to Benzene Both oxidative and nonoxidative routes have been reported. Most attention has been directed at nonoxidative aromatization. In particular, Chinese workers are active in this field. Recently, attractive results have been reported for Mo-loaded HZSM-5 catalysts. 

The dehydroaromatization of light alkane feeds (methane to butanes) into aromatics has come into prominence as a method of converting the unreactive light paraffins into useful chemical precursors. In many of the world s markets, light alkanes are very undesired off-gasses which can not be used other than as fuel. To accomplish this difficult transformation, catalysts typically are bifunctional, containing a dehydrogenating component such as Pt, Ga, Zn or Mo with an acidic zeolite. 

The paraffins and 1-alcohols are relatively low-risk compounds. When we make a comparison of their TLV values versus the number of carbon atoms Ac, we find that paraffins from methane to propane are not considered toxic, but the paraffins from butane to nonane are increasingly more toxic with Ac, which is shown in figure 10.4. The 1-alcohols make a curious volcanic curve, starting from the toxic methanol to the relatively harmless ethanol, and the trend is downwards from propanol to butanol. The aromatics are much more toxic, but the lower molecular weight benzene is more toxic than toluene, which is more toxic than the higher molecular weight ethyl benzene. 

One of the most important challenges in the modern chemical industry is represented by the development of new processes aimed at the exploitation of alternative raw materials, in replacement of technologies that make use of building blocks derived from oil (olefins and aromatics). This has led to a scientific activity devoted to the valorization of natural gas components, through catalytic, environmentally benign processes of transformation (1). Examples include the direct exoenthalpic transformation of methane to methanol, DME or formaldehyde, the oxidation of ethane to acetic acid or its oxychlorination to vinyl chloride, the oxidation of propane to acrylic acid or its ammoxidation to acrylonitrile, the oxidation of isobutane to... 

The direct catalytic conversion of methane has been actively pursued for many years. Much of the emphasis has been on the direct production of methanol via selective partial oxidation (8), coupling of methane to ethylene (9), or methane aromatization (10). At this time none of these technologies has been demonstrated commercially due to low yields of desired products due to combustion by-products or low equilibrium conversion at reasonable process temperatures and pressures. The potential benefits of a hypothetical process for the direct partial oxidation of methane to methanol (11) are presented as an example. 

The exchange of a considerable number of linear, branched-chain, and cyclic alkanes have been studied (5i). The exchange rate increases with increase in the carbon chain length forn-alkanes (methane to hexane). It is found that there is a linear correlation between the logarithm of the exchange rate and the ionization potential of the alkane (Fig. 5 n-alkanes are plotted as circles). This correlation extends to aromatic compounds (Fig. 5 aromatic compounds are plotted as squares) and is evidence that alkanes and aromatic compounds react by a common mechanism. Indeed, the least reactive aromatic, benzene, is only about... 

The first polymerizations reported by Kops and Schuerch147 were those of l,4-anhydro-2,3,6-tri-0-methyl-/3-D-galactopyranose and 1,4-anhydro-2,3-di-0-methyl-a -L-arabinopyranose. The latter compound was slightly contaminated with l,4-anhydro-2,3-di-0-methyl-a-D-xy-lopyranose, but the course of the polymerization could nevertheless be monitored reasonably accurately. For the most part, the polymerizations were conducted at 10% concentration (g/mL) in dichloro-methane, or aromatic hydrocarbons, with 1-5 mol% of phosphorus pentafluoride, or boron trifluoride etherate. At low temperature (—78 to —97°), the d.p. of both polymers produced was —90 at increasing temperatures of polymerization, termination processes became more severe, and the d.p. lower. Usually, the reaction times were long (perhaps unnecessarily so), and the conversions were 50 to 90%. The specific rotations of the D-galactans prepared at —28 and —90° differ by only —10° ( — 85 to — 95°), but those of the L-arabinans varied from + 6... 

It should be noted that fluorodiazonium hexafluoroantimonate (4) also reacts with aromatic compounds, forming fluorobenzenes, in low yield.193 A more recent report concerns the electrophilic fluorination of methane to fluoromethane using fluorodiazonium and tetrafluoroammonium salts.198... 

Hydrocarbons are ubiquitously in the environment. Natural hydrocarbons range widely in size from methane to /3-carotene (Fig. 2.12) many other branched, ole-finic, cyclic, and aromatic hydrocarbons are found in fossil fuels, or tend to derive... 

Hydrocarbon formation from methyl chloride can be catalyzed by ZSM-5482 483 or bifunctional acid-base catalysts such as W03 on alumina.420,447 The reaction on ZSM-5 gives a product distribution (43.1% aliphatics and 57.1% aromatics at 369°C) that is very similar to that in the transformation of methanol, suggesting a similar reaction pathway in both reactions.483 W03 on A1203 gives 42.8% C2-C5 hydrocarbons at 327°C at 36% conversion.447 When using methyl bromide as the feed, conversions are comparable. However, in this case, HBr can be very readily air-oxidized to Br2 allowing a catalytic cycle to be operated. Since bromine is the oxidant, the reaction is economical. The one step oxidative condensation of methane to higher hydrocarbons was also achieved in the presence of chlorine or bromine over superacidic catalysts.357... 

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