C2 hydrocarbons

These processes use expensive C2 hydrocarbons as feedstocks and thus have higher overall acrylonitrile production costs compared to the propylene-based process technology. The last commercial plants using these process technologies were shut down by 1970. 

The dephlegmator process recovers a substantially higher purity C2+ hydrocarbon product with 50—75% lower methane content than the conventional partial condensation process. The C2+ product from the cryogenic separation process can be compressed and further separated in a de-ethanizer column to provide a high purity C3+ (LPG) product and a mixed ethylene—ethane product with 10—15% methane. Additional refrigeration for the deethanization process can be provided by a package Freon, propane or propylene refrigeration system. 

This process uses propylene carbonate as a physical solvent to remove CO2 and H2S. Propylene carbonate also removes C2+ hydrocarbons, COS, SO2, CS2, and H2O from the natural gas stream. Thus, in one step the natural gas can be sweetened and dehydrated to pipeline quality. In general, this process is used for bulk removal of CO2 and is not used to treat to less than 3% CO2, as may be required for pipeline quality gas. The system requires special design features, larger absorbers, and higher circulation rates to obtain pipeline quality and usually is not economically applicable for these outlet requirements. 

In a parallel study Eng and Stoukides30 also reported A values up to five for this reaction and also detected the presence of trace C2 hydrocarbons in the effluent stream. Since YSZ is known to promote catalytically the oxidative coupling of CH4,32 the extent to which C2 hydrocarbons can be found in the products is dictated by the ratio of YSZ and Pt surfaces present in the reactor. 

The oxidative coupling of CH4 (OCM) in solid oxide fuel cells has attracted considerable attention in recent years because of the strong interest in the production of C2 hydrocarbons from natural gas. Work in this area utilizing solid electrolytes prior to 1999 has been reviewed.53... 

It is known32 reported that the solid electrolyte itself, i.e. Y203-doped-Zr02, is a reasonably selective catalyst for CH4 conversion to C2 hydrocarbons, i.e., ethane and ethylene32 and this should be taken into account in studies employing stabilized Zr02 cells. At the same time it was found54 that the use of Ag catalyst films leads to C2 selectivities above 0.6 for low methane conversions. 

Figure 8,49. Effect of Ag/YSZ catalyst potential on CH4 conversion and on selectivity to C2 hydrocarbons. T=800°C, pO2=0.25 kPa, pCH4=lO.I3 kPa, U R=-0.45 V.2,54 Open symbols correspond to open-circuit. Reprinted from ref. 2 with permission from Elsevier Science.

Similar studies utilizing Au electrodes on YSZ showed again that the selectivity and yield of C2 hydrocarbons can be significantly affected by applying currents or potentials to the cell.40,41,53 The behaviour with Au appears to be qualitatively similar with that obtained with Ag electrodes although electrophilic behaviour is also reported.40,41... 

Direct conversion of methane to ethane and ethylene (C2 hydrocarbons) has a large implication towards the utilization of natural gas in the gas-based petrochemical and liquid fuels industries [ 1 ]. CO2 OCM process provides an alternative route to produce useful chemicals and materials where the process utilizes CO2 as the feedstock in an environmentally-benefiting chemical process. Carbon dioxide rather than oxygen seems to be an alternative oxidant as methyl radicals are induced in the presence of oxygen. Basicity, reducibility, and ability of catalyst to form oxygen vacancies are some of the physico-chemical criteria that are essential in designing a suitable catalyst for the CO2 OCM process [2]. The synergism between catalyst reducibility and basicity was reported to play an important role in the activation of the carbon dioxide and methane reaction [2]. 

In this paper, the selective conversion of methane to C2 hydrocarbons over ternary Ca0-Mn0/Ce02 catalysts in the CO2 OCM process are presented. The synergistic effect between catalyst reducibility and distribution of basic sites are highlighted. The most promising catalyst was then tested towards its stability. 

Next, we investigated the effect of input power on ps formation rates and on carbon-selectivity. As shown in Fig. 3, the amount of product inerrased as the input powear increased. The selectivity to carbon monoxide and C2 hydrocarbons was constant despite the change of the input power. These results showed m identical trend to that of the gas phase... 

Pearson CR, McConnell G. 1975. Chlorinated Cl and C2 hydrocarbons in the marine environment. Proc R Soc Lond [Biol] 189 305-332. 

Keller and Bhasin were first to report in 1982 [1] on the catalytic one-step oxidative dimerization or coupling of methane (OCM) to C2 hydrocarbons, ethane and ethylene. Numerous investigations have followed this seminal work and a large number of catalysts have been found which give total selectivity to C2 hydrocarbons higher than 90% at low (<2%) methane conversion [2-6]. 

However, it was generally found that the total C2 hydrocarbon selectivity decreases drastically with increasing conversion of methane, so that Yc2 (the total C2 hydrocarbon yield) was always found, until very recently, to be less than 30% [1-9]. Achieving C2 hydrocarbon yield in excess of 50% is a necessary requirement for the development of an economically viable industrial process. 

Figure 2. Effect of methane conversion and applied current on the C2 hydrocarbon (a) and on the ethylene (b) selectivity (filled sjnmbols) and yield (open symbols). (Reprinted with permission from the AAAS, ref. 12).

Two conqiletely different behaviors of oxidative transformation of methane, namely the Oxidative Coupling of Methane to C2 Hydrocarbons(OCM) and the Partial Oxidation of Methane to Syngas(POM), were performed and related over the nickel-based catalysts due to different modification and different supports. It is concluded that the acidic property favors keeping the reduced nickel and the reduced nickel is necessary for POM reaction, and the bade property frvors keeping the oxidized nickel and the oxidized mckel is necessary for OCM reaction. POM and OCM reactions proceed at different active sites caused by different... 

The oxidative coupling of methane has been studied by several authors. The most elusive transformation has been the oxidative coupling of methane into C2 hydrocarbons (ethene, ethane), because the reaction is more endothermic than other transformations [2]. The application of fast and efficient microwave heating to endothermic reactions is particular interest. 

Similarly, Bond et al. [4] confirmed that the microwave stimulation of methane transformation reactions in the presence of a number of rare earth basic oxides to form C2 hydrocarbons (ethene, ethane) was achieved at a lower temperature and with the increased selectivity. Microwave irradiation resulted in an increase of the ethene/ethane ratio, which was desirable. The results obtained were explained by the formation of hot spots (Sect. 10.3.3) of higher temperature than the bulk catalyst. This means that methane is activated at these hot spots. 

Suib et al. [77] used microwaves to generate plasma in an atmosphere containing methane and oxygen. The plasma passing over a metal or metal oxide catalyst led to formation of C2 hydrocarbons and some oxygenates. 

The l-alkene/2-alkene ratio for the C4 hydrocarbon fraction is presented in Figure 7.13e, while the alkene/(alkene + alkane) fractions for the C2 hydrocarbon products from FTS for unpromoted a-I c203 and promoted catalysts are... 

Oxygenates were recovered from the Fischer-Tropsch aqueous product, employing a separation strategy similar to that in the Sasol 1 refinery. The main difference was in volume, and this made further separation of the different alcohols and carbonyl compounds worthwhile. Some of the ethanol served as a blending component in motor gasoline, with the final blend containing around 10% ethanol.38 Most of the alcohols and carbonyl compounds were sold as chemicals. In addition to the oxygenates, the C2 hydrocarbons were also recovered and sold. 

Ethane or ethylene (C2 hydrocarbons) have been observed in a few cases. -Z"i... 

Hexachloroethane is not currently produced for commercial distribution in the United States. It is a by-product in the industrial chlorination of saturated and unsaturated C2 hydrocarbons by several U.S. companies, including Dow Chemical, PPG Industries, and Occidental Petroleum Corporation. The product may be used captively in-house or recycled in feedstock to produce tetrachloroethylene or carbon tetrachloride. Estimates of current production volumes were not located (Gordon et al. 1991 Santodonato et al. 1985 TRI93 1995). 

Class T, Ballschmiter K. 1986. Chemistry of organic traces in ajr. V. Determinati i-C2-hydrocarbons in clean marine air and ambient continental air and rain by hig... 

Figures 12.3 and 12.3c show mean velocity (Fig. 12.36) and mean temperature (Fig. 12.3c) fields under bluff-body stabilized combustion of stoichiometric methane-air mixture at inlet velocity 10 m/s, and ABC of Eq. (12.19) at the combustor outlet. Functions Wj, Wij, and W2j in Eq. (12.1) were obtained by solving the problem of laminar flame propagation with the detailed reaction mechanism [31] of Ci-C2-hydrocarbon oxidation (35 species, 280 reactions) including CH4 oxidation chemistry. The PDF of Eq. (12.4) was used in this calculation.

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