Ethane, products from

Fig. ii. Selectivity for ethane production from n-butane hydrogenolysis on iridium as a function of effective particle size. (From R s. HI. 112.) Also shown are data for n-butane hydrogenolysis on supported Ir catalysts The temperature is 47S K in all cases. 

The ligands to be eliminated must be cis to one another for reductive elimination to occur. This is because the process is concerted. Two examples from palladium chemistry make this point clear. Warming in DMSO causes ethane production from the first palladium complex because the two methyl groups are cis in the square planar complex. The more elaborate second bisphosphine forces the two methyl groups to be trans and reductive elimination does not occur under the same conditions. Reductive elimination is one of the most important methods for the removal of a transition... 

Relatively small amounts of methane, ethane, and propane also are produced as by-products from petroleum processes, but these usually are consumed as process or chemical feedstock fuel within the refineries. Some propane is recovered and marketed as LPG. 

The most important commercial use of ethane and propane is in the production of ethylene (qv) by way of high temperature (ca 1000 K) thermal cracking. In the United States, ca 60% of the ethylene is produced by thermal cracking of ethane or ethane/propane mixtures. Large ethylene plants have been built in Saudi Arabia, Iran, and England based on ethane recovery from natural gas in these locations. Ethane cracking units have been installed in AustraHa, Qatar, Romania, and Erance, among others. 

Recoveries of 90—95% ethane have been achieved usiag the expander processes. The Hquid product from the demethanizer may contain 50 Hquid vol % ethane and usually is deHvered by a pipeline to a central fractionation faciHty for separation iato LPG products, chemical feedstocks, and gasoline-blending stocks. 

Aliphatics. Methane, obtained from cmde oil or natural gas, or as a product from various conversion (cracking) processes, is an important source of raw materials for aliphatic petrochemicals (Fig. 10) (see Hydrocarbons). Ethane, also available from natural gas and cracking processes, is an important source of ethylene, which, in turn, provides more valuable routes to petrochemical products (Fig. 11). 

Steam Cracking. Steam cracking is a nonselective process that produces many products from a variety of feedstocks by free-radical reactions. An excellent treatise on the fundamentals of manufacturing ethylene has been given (44). Eeedstocks range from ethane on the light end to heavy vacuum gas oil on the heavy end. All produce the same product slate but in different amounts depending on the feedstock. 

Significant products from a typical steam cracker are ethylene, propylene, butadiene, and pyrolysis gasoline. Typical wt % yields for butylenes from a steam cracker for different feedstocks are ethane, 0.3 propane, 1.2 50% ethane/50% propane mixture, 0.8 butane, 2.8 hill-range naphtha, 7.3 light gas oil, 4.3. A typical steam cracking plant cracks a mixture of feedstocks that results in butylenes yields of about 1% to 4%. These yields can be increased by almost 50% if cracking severity is lowered to maximize propylene production instead of ethylene. 

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. 

The Cj plus bottoms from the demethanizer then go to the deethanizer. A propylene-propane bottoms product containing 90-92% propylene is obtained which may either be sold, used directly as propylene- 90, or further purified. The ethylene-ethane overhead from the deethanizer is separated in the splitter tower yielding a 99.8% overhead ethylene product at -25°F. The ethane bottoms at -l-18°F may either be sent to fuel gas or used as feed to an ethane cracking furnace. Overall ethylene recovery in these facilities is about 98%. The product is of very high purity with less than 50 parts per million of non-hydrocarbon contaminants and a methane plus ethane level below 250 ppm. 

Note that in a high purity condition as is represented in this example, the system is quite sensitive to the overhead withdrawal rate (product from the system). This system is for the purification of propylene from a feed high in propyl lene, with lessor amounts of propane, butane, and ethane. 

Although olefins are intermediates in this reaction, the final product contains a very low olefin concentration. The overall reaction is endothermic due to the predominance of dehydrogenation and cracking. Methane and ethane are by-products from the cracking reaction. Table 6-1 shows the product yields obtained from the Cyclar process developed jointly by British Petroleum and UOP. ° A simplified flow scheme for the Cyclar process is shown in Figure 6-6. 

Fig. 2. Pressure fall —AP (Torr) against time t (arbitrary units) in hydrogenation of acetylene on Pt/AhOa catalyst at 110°C and Pst/Pctnt 2. In the initial slow period of the reaction the main product is ethylene, and after the acceleration, further hydrogenation of ethylene to ethane predominates. From G. C. Bond and P. B. Wells, J. CaM. 4, 211 (1965).

Using a polymer electrolyte membrane cell in which flowed through the anode chamber. The major intermediate chlorinated products from tetrachloroethene or tet-rachloromethane were trichloroethene or trichloromethane, and these were finally reduced to a mixture of ethane and ethene, or methane (Liu et al. 2001). 

Examples for necessary process improvements through catalyst research are the development of one-step processes for a number of bulk products like acetaldehyde and acetic acid (from ethane), phenol (from benzene), acrolein (from propane), or allyl alcohol (from acrolein). For example, allyl alcohol, a chemical which is used in the production of plasticizers, flame resistors and fungicides, can be manufactured via gas-phase acetoxylation of propene in the Hoechst [1] or Bayer process [2], isomerization of propene oxide (BASF-Wyandotte), or by technologies involving the alkaline hydrolysis of allyl chloride (Dow and Shell) thereby producing stoichiometric amounts of unavoidable by-products. However, if there is a catalyst... 

Returning to reaction 6, Schemes I and II and Figure 7 suggest that the loss of hydrogen and ethane result from a common intermediate and that a distinct intermediate is responsible for the elimination of methane. A comparison of the product distributions measured using the ion beam instrument with the relative metastable yields recorded with the reverse sector instrument supports this conjecture (Table HI) in that the ratio of hydrogen to ethane loss is approximately the same and methane elimination is diminished in importance in the metastable data (38). From... 

First structurally known iodine derivatives of this kind were products from the iodination of l,3-dimethyl-4-imidazoline-2-selone,44 of 1,2-6z s-(3-methyl-4-imidazoline-2-selone)ethane,44 and of l,3-diisopropyl-4,5-dimethyl-4-imidazoline-2-selone.42 The fragments for the three compounds... 

The reaction appears to be general and the additions are regiospecific and stereoselective. The product from the reaction with 2-propanol has been used for the synthesis of cis-chrysanthemic acid,8 and the product with methanol has been used for the construction of novel 2, 3 -dideoxy-3 -hydroxymethylnucleosides.9 In addition, ethane-1,2-diol provides the expected photoadduct as a 1 1 mixture of the two possible diastereoisomers, and these can be easily separated as their acetonides, to provide compounds with three contiguous chiral centers emanating from furan-ones with only one chiral center.9 More recently, we have shown that photoinduced-... 

Studies in deuterated water have shown that the hydroxyl proton does not end up in the ethanal formed. The decomposition of the 2-hydroxyethyl is not a simple P-elimination to palladium hydride and vinyl alcohol, which then isomerises to ethanal. Instead, the four protons stemming from ethene are all present in the initial ethanal product [6] (measured at 5 °C in order to suppress deuterium/hydrogen exchange in the product) and most authors have therefore accepted an intramolecular hydride shift as the key-step of the mechanism (see Figure 15.2). There remains some doubt as to how the hydride shift takes place. 

Fig. 10. Methane production from ethane hydro-genolysis over Ni(100) and Ni(l 11) catalysts at total reactant pressures of 100 torr. H2/C2H -100. (From R. 107.)...

Oxidative methane coupling. MngCa r OjK catalyst placed in the pores of the tube. Ethylene and ethane synthesis from methane. Li/MgO (3 wt. % Li) catalyst placed in the pores of the tube. T 850 C. Conversion 30%. Selectivity to Cj products 60% T 700-750°C. Conversion 40%. Selectivity to Cj products 55%. ... 

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