The Nitrogen-Ethane System

When the fit is judged to be excellent the statistically best interaction parameters can be efficiently obtained by performing implicit ML estimation. This was found to be the case with the methane-methanol and the nitrogen-ethane systems presented later in this chapter. 

Figure 14.2 Vapor-liquid equilibrium data and calculated values for the nitrogen-ethane system [reprinted from the Canadian Journal of Chemical Engineering with permission].

Data at two temperatures were obtained from Zeck and Knapp (1986) for the nitrogen-ethane system. The implicit LS estimates of the binary interaction parameters are ka=0, kb=0, kc=0 and kd=0.0460. The standard deviation of kd was found to be equai to 0.0040. The vapor liquid phase equilibrium was computed and the fit was found to be excellent (Englezos et al. 1993). Subsequently, implicit ML calculations were performed and a parameter value of kd=0.0493 with a standard deviation equal to 0.0070 was computed. Figure 14.2 shows the experimental phase diagram as well as the calculated one using the implicit ML parameter estimate. 

Preston et al. (17) studied the effect of temperature on Henry s constant in simple mixtures. They showed that for nitrogen-ethane system, the Henry s constant went through a maximum at about temperature of 190 K. 

Helium and Natural-Gas Systems Separation Helium is produced primarily by separation of hehum-rich natural gas. The hemim content of the natural gas from plants operated by the U.S. Bureau of Mines normally has varied from 1 to 2 percent while the nitrogen content of the natural gas has varied from 12 to 80 percent. The remainder of the natural gas is methane, ethane, and heavier hydrocarbons. 

The gas mixture containing the nitrogen oxides is very important as well. Experiments and modeling carried out for N2/NOx mixtures, or with addition of 02, H20, C02 and hydrocarbons will be discussed. Typical hydrocarbon additives investigated are ethane, propene, propane, 2-propene-l-ol, 2-propanol, etc. As compared to the case without hydrocarbons, NO oxidation occurs much faster when hydrocarbons are present. The reaction paths for NO removal change significantly, in fact the chemical mechanism itself is completely different from that of without hydrocarbon additives. Another additive investigated extensively is ammonia, used especially in corona radical shower systems. 

The 3-morpholinosydnonimine system generates superoxide radicals and nitrogen monoxide, forming peroxynitrite, which releases ethane from KMB (a-keto-y-methiolbutyric acid). This method was used by Lavelli and others (1999) to investigate the radical-scavenging activity of fresh and air-dried tomatoes. 

Figure 14.7 Typical chromatogram obtained by using the refinery analyser system shown in Figure 14.6. Peak identification is as follows 1, hydrogen 2, C6+, 3, propane 4, acetylene 5, propene 6, hydrogen sulfide 6, iso-butane 8, propadiene 9, n-butane, 10. iso-butene 11, 1-butene 12, trans-2-b itene 13, cw-2-butene 14, 1,3-butadiene 15, iso-pentane 16, n-pentane 17,1-pentene 18, fram -pentene 19, cw-2-pentene 20, 2-methyl-2-butene 21, carbon dioxide 22, ethene 23, ethane 24, oxygen + argon, 25, nitrogen, 26, carbon monoxide.

All the simple hydrocarbons are able to suppress the low pressure ignition of the H2 + O2 system. However, there are major differences of behaviour between methane and neopentane on the one hand, and most other hydrocarbons and related materials on the other [329—332]. With formaldehyde [333], ethane [334—336], propane [329, 337], and n- and i-butane [338] the second limit in KCl coated vessels falls more or less linearly with increasing partial pressure of additive. In the experiments of Baldwin et al. [333—338], the mole fractions, x and y, of H2 and O2, respectively, could be varied independently of each other by working with H2 + N2 + O2 mixtures and adjusting the nitrogen content appropriately. The rate of fall of the second limit at constant x was almost inversely proportional to y while at constant y and not too small x, it was almost independent of x. The limit did not change much with vessel size. The observations may be accounted for by adding reactions (1)—(lii)... 

It is known that nitrogenase reduces ethyne (acetylene) to ethene and ethane. This is also the case for Schrauzer s system mentioned above. Schrauzer (1975) tested his process with diazene, which may be an intermediate in the reduction of dinitrogen (see, however, the remark about diazene made earlier). Diazene decomposed, however, to hydrazine, following Scheme 3-28. The experiment neither supports nor contradicts the hypothesis of the intermediacy of diazene in nitrogen fixation, because it is known that hydrazine is reduced to ammonia if added to the natural nitrogenase system. 

The column system is the heart of the separating system. The Danalyzer column system is composed of three basic columns. The first column is the backflush column and is used to separate the heavy components, hexane from the rest of the components. The second column separates the intermediate components, propane, iso-butane, normal butane, neo-pentane, iso-pentane, and normal pentane. The third column is used to separate the light components, nitrogen, methane, carbon dioxide and ethane. 

We consider a system of adsorption of ethane, propane and nitrogen onto activated carbon at 303 K and a total pressure of 1 atm. At this temperature, ethane and propane adsorb onto activated carbon, and their adsorption isotherm can be adequately described by a Langmuir equation. The isotherm parameters for nitrogen, ethane and propane are ... 

Poly(4-hydroxystyrene-co-styrene). A series of well-defined random poly(4-hydroxystyrene-co-styrene) were prepared by the living free radical copolymerization of 4-acetoxystyrene (1) and styrene (2), using the unimolecular initiating system, l-phenyl-l-(2, 2, 6, 6 -tetramethyl-r-piperidinyloxy)ethane (4) at a temperature of 130°C (Scheme 1). All of the copolymerizations were carried out neat under a nitrogen environment. The resulting well-defined poly(4-acetoxystyrene-co-styrene) polymers (5) were then quantitatively converted to poly(4-hydroxystyrene-... 

Figure 5.104 Experimental and predicted LLE data using VTPR for the ternary system nitrogen-ethane-methane at 122K and the binary system ethane-nitrogen [3].

These systems illustrate various elements of the Lewis structure. Ethane, for example, consists of a o-bonded framework only. Ammonia and water have one and two lone pairs in addition to the a-framework. The calculation on benzene shows that extended n systems can be modeled, and cystein shows that all these elements can be present simultaneously. The cystein zwitterion (Figure 4) illustrates how ionized atoms can be accommodated when the Lewis structure for the zwitterion is constructed, the presence of four bonds to the nitrogen implies that the nitrogen atom is ionized as the cation. After all the other Lewis structural elements have been added, one of the oxygen atoms is found to have an unused orbital. This is characteristic of an ionized carboxylic acid group, therefore the oxygen is presumed to be ionized as the anion. 

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