Ethane and Propane

When combined with acid gas mixtures, ethane and carbon dioxide exhibit azeotropy, as do propane and hydrogen sulfide. Although the azeotrope does not have a significant effect on the acid gas injection process, it tells a tale about the phase equilibrium in these mixtures. 

To demonstrate the effect of ethane and propane on the phase envelopes of acid gas mixtures, consider figures 3.7 and 3.8, which 

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The structural features of methane ethane and propane are summarrzed rn Ergure 2 7 All of the carbon atoms have four bonds all of the bonds are srngle bonds and the bond angles are close to tetrahedral In the next sectron we 11 see how to adapt the valence bond model to accommodate the observed structures... 

FIGURE 2 7 Structures of methane ethane and propane showing bond distances and bond angles... 

Bonding m n butane and isobutane continues the theme begun with methane ethane and propane All of the carbon atoms are sp hybridized all of the bonds are ct bonds and the bond angles at carbon are close to tetrahedral This generalization holds for all alkanes regardless of the number of carbons they have... 

Natural gas is an abundant source of methane ethane and propane Petro leum IS a liquid mixture of many hydrocarbons including alkanes A1 kanes also occur naturally m the waxy coating of leaves and fruits... 

Athene formation requires that X and Y be substituents on adjacent carbon atoms By mak mg X the reference atom and identifying the carbon attached to it as the a carbon we see that atom Y is a substituent on the p carbon Carbons succeedmgly more remote from the reference atom are designated 7 8 and so on Only p elimination reactions will be dis cussed m this chapter [Beta (p) elimination reactions are also known as i 2 eliminations ] You are already familiar with one type of p elimination having seen m Section 5 1 that ethylene and propene are prepared on an industrial scale by the high temperature dehydrogenation of ethane and propane Both reactions involve (3 elimination of H2... 

Since the early 1980s olefin plants in the United States were designed to have substantial flexibiHty to consume a wide range of feedstocks. Most of the flexibiHty to use various feedstocks is found in plants with associated refineries, where integrated olefins plants can optimize feedstocks using either gas Hquids or heavier refinery streams. Companies whose primary business is the production of ethylene derivatives, such as thermoplastics, tend to use ethane and propane feedstocks which minimize by-product streams and maximize ethylene production for their derivative plants. 

Natural gas Hquids represent a significant source of feedstocks for the production of important chemical building blocks that form the basis for many commercial and iadustrial products. Ethyleae (qv) is produced by steam-crackiag the ethane and propane fractions obtained from natural gas, and the butane fraction can be catalyticaHy dehydrogenated to yield 1,3-butadiene, a compound used ia the preparatioa of many polymers (see Butadiene). The / -butane fractioa can also be used as a feedstock ia the manufacture of MTBE. 

Methane, ethane, and propane are the first three members of the alkane hydrocarbon series having the composition, Selected properties of these... 

Table 1. Selected Properties of Methane, Ethane, and Propane ...

The main commercial source of methane, ethane, and propane is natural gas, which is found ia many areas of the world ia porous reservoirs they are associated either with cmde oil (associated gas) or ia gas reservoirs ia which no oil is present (nonassociated gas). These gases are basic raw materials for the organic chemical industry as well as sources of energy. The composition of natural gas varies widely but the principal hydrocarbon usually is methane (see Gas, natural). Compositions of typical natural gases are Hsted ia Table 2. 

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. 

Other. Ethylene can be produced by steam cocracking of propylene with ethane and propane. Ethylene and butenes can also be produced by catalytic disproportionation of propylene (108). 

When a mixture is cracked, one or more components in the feed may also be formed as products. Eor example, in the cocracking of ethane and propane, ethane is formed as a product of propane cracking and propane is formed as a product of ethane cracking. Therefore, the "out" term in the above equation contains the contribution or formation from other feed components and hence does not represent tme conversion. Eor simple mixtures, the product formation can be accounted for, and approximate tme conversions can be calculated (29). Eor Hquid feeds like naphtha, it is impractical if not impossible to calculate the tme conversion. Based on measured feed components, one can calculate a weighted average conversion (A) (30) ... 

FeedSa.tura.tlon, When gas feeds like ethane and propane are cracked, dilution steam can be added via direct humidification in towers known as feed saturators. This design reduces the load on the dilution steam system and/or medium pressure (MP) steam level. 

The liquid collected at the bottom of the demethanizer tower is a mixture of ethane, propane, butane, and condensate (EPBC), which is taken off in a stream and pumped—as a liquid, at 1,000 psig—to a customer facility. Another part of the EPBC is introduced into a deethanizer tower. The stream of EPBC liquid entering the deethanizer tower is further separated into PBC liquid and pumped to the El Paso Natural Gas facility in Gallup, New Mexico. EP (ethane and propane)... 

For a molecule as simple as Fl2, it is hard to see much difference between the valence bond and molecular orbital methods. The most important differences appear- in molecules with more than two atoms. In those cases, the valence bond method continues to view a molecule as a collection of bonds between connected atoms. The molecular- orbital method, however, leads to a picture in which the sane electron can be associated with many, or even all, of the atoms in a molecule. We ll have more to say about the similarities and differences in valence bond and molecular- orbital theory as we continue to develop their principles, beginning with the simplest alkanes methane, ethane, and propane. 

Mehra has developed a valuable series of working charts for the common industrial refrigerants along with application examples for ethylene, propylene, ethane, and propane. 

In mechanical refrigeration, a multicomponent refrigerant consisting of nitrogen, methane, ethane, and propane is used through a cascade cycle. When these liquids evaporate, the heat required is obtained from... 

Butane is primarily used as a fuel gas within the LPG mixture. Like ethane and propane, the main chemical use of butane is as feedstock for steam cracking units for olefin production. Dehydrogenation of n-butane to butenes and to butadiene is an important route for the production of synthetic rubber. n-Butane is also a starting material for acetic acid and maleic anhydride production (Chapter 6). 

Cracking n-hutane is also similar to ethane and propane, hut the yield of ethylene is even lower. It has been noted that cracking either propane or butanes at nearly similar severity produced approximately equal liquid yields. Mixtures of propane and butane LPG are becoming important steam cracker feedstocks for C2-C4 olefin production. It has been forecasted that world LPG markets will grow from 114.7 million metric tons/day in 1988 to 136.9 MMtpd in the year 2000, and the largest portion of growth will be in the chemicals field. 

Figure 3-13. The influence of conversion severity on the theoretical product yield for the cracking of propane. Acetylene, methyl acetylene, and propadiene are hydrogenated and both ethane and propane are recycled to extinction (wt%)." ...

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