Ethylene concentration

The ethylene feedstock used in most plants is of high purity and contains 200—2000 ppm of ethane as the only significant impurity. Ethane is inert in the reactor and is rejected from the plant in the vent gas for use as fuel. Dilute gas streams, such as treated fluid-catalytic cracking (FCC) off-gas from refineries with ethylene concentrations as low as 10%, have also been used as the ethylene feedstock. The refinery FCC off-gas, which is otherwise used as fuel, can be an attractive source of ethylene even with the added costs of the treatments needed to remove undesirable impurities such as acetylene and higher olefins. Its use for ethylbenzene production, however, is limited by the quantity available. Only large refineries are capable of deUvering sufficient FCC off-gas to support an ethylbenzene—styrene plant of an economical scale. 

FIG. 26-30 Siipp ression of explosions, Pressures in an ethylene explosion and a sodium bicarbonate suppressed ethylene explosion, Tests conducted by Fike Corp, in a 1-m vessel. Ethylene concentration = 1,2 times stoichiometric concentration for combustion, (dp/dt)e = 169 bar/s (2451 psi/s), = reduced explosion pressure = 0,4 bar gauge (5,8 psig), (F/om Chatrathi, Explosion Testing, Safety and Technology News, vol. 3, issue 1, Pike Cotp., 1.98.9, hy permission. )... 

Fig. 15-4. Ethylene concentrations measured by the DIAL system along a 5-km path length near Menlo Park, California. The open circles are ethylene concentrations of samples taken at three ground-level locations near the line of sight and analyzed by gas chromatography. Source Murray, E. A., and Van der Laan, ). E., Appl. Opt. 17, 814-817 (1978).

Here Ceq is the ethylene concentration equilibrium to the concentration in a gaseous phase, Kp the propagation rate constant, N the concentration of the propagation centers on the catalyst surface, Dpe the diffusion coefficient of ethylene through the polymer film, G the yield of polymer weight unit per unit of the catalyst and y0at, ype are the specific gravity of the catalyst and polyethylene. 

In polymerization by one-component catalysts [chromium oxide catalyst (75), titanium dichloride 159) at ethylene concentrations higher than 1 mole/liter and temperatures below 90°C the transfer with the monomer is a prevailing process. The spontaneous transfer, having a higher activation energy, plays an essential role at higher temperatures and lower concentrations of the monomer. 

Equations of the same form hold for the other pairs C4H8+/C6Hi2+ etc. Figure 8 shows a plot of (C2H4)n i+/(C2H4)n+ vs. the reciprocal ethylene concentration. The data cover an ethylene pressure range from 0.04-1 torr. To obtain the plot, we have replaced the ionic concentration ratio... 

BMO = inlet monomer (ethylene) concentration, mole/l PP = reactor pressure, psia BM = monomer (ethylene) molecular weight CP = heat capacity at constant pressure of the reaction fluid, cal/mole- C... 

We have developed a compact photocatalytic reactor [1], which enables efficient decomposition of organic carbons in a gas or a liquid phase, incorporating a flexible and light-dispersive wire-net coated with titanium dioxide. Ethylene was selected as a model compound which would rot plants in sealed space when emitted. Effects of the titanium dioxide loading, the ethylene concentration, and the humidity were examined in batches. Kinetic analysis elucidated that the surface reaction of adsorbed ethylene could be regarded as a controlling step under the experimental conditions studied, assuming the competitive adsorption of ethylene and water molecules on the same active site. 

Kinetic analysis based on the Langmuir-Hinshelwood model was performed on the assumption that ethylene and water vapor molecules were adsorbed on the same active site competitively [2]. We assumed then that overall photocatalytic decomposition rate was controlled by the surface reaction of adsorbed ethylene. Under the water vapor concentration from 10,200 to 28,300ppm, and the ethylene concentration from 30 to 100 ppm, the reaction rate equation can be represented by Eq.(l), based on the fitting procedure of 1/r vs. 1/ Ccm ... 

As reported, a common Ti-FT catalyst combined with MAO possesses some characteristics of living ethylene polymerization under limited conditions (e.g., short polymerization time and/or controlled ethylene concentration in a polymerization medium). 

It is entirely possible that isomerization may proceed much faster with this catalyst than with the model system considered by Tolman. To test this possibility, reactions were run at reduced ethylene concentrations. This should slow down the insertion reaction (d ) relative to the isomerization reaction (c). No effect on the trans/cis ratio of the product was observed, while the rate of hexadiene formation was reduced over 200-fold (39). So, unlike the Rh systems, the syn-to-anti isomerization appeared too slow to be a controlling factor for the stereoselectivity. 

A kinetic analysis of the data gave k22/k22 = 1.7 x 10-3, k22/k14. = 7.9 x 10 4 and k22/kA6 = 7.9 x 10-3. The dependence of G(H2) on the solute concentrations is shown in Fig. 6, where the chlorine and ethylene concentrations have been normalised by multiplying them by the values of k23fkl4t and k46/k1A respectively. These were calculated from the experimental ratios given above. They are summarised in Table 8. 

As noted earlier, previous theoretical studies (7-8) have shown that the selectivity to ethylene oxide is maximized, when the active material is located at the external surface of the pellet. This behavior results primarily from the fact that the main undesired reaction 2 has a higher activation energy than the desired one. Therefore, intraphase temperature gradients are detrimental to the selectivity. Indeed, in Figure 2, where results for Type 1 pellets are presented, it is shown that for all the temperatures studied, selectivity decreases when the active layer is located deeper inside the pellet. This behavior was observed for all the inlet ethylene concentrations investigated. 

Figure 2. Selectivity as a function of location of the active layer, for various bulk fluid temperatures inlet ethylene concentration = 7.2%.

Figure 5. Yield as a function of reaction temperature for various active layer loadings inlet ethylene concentration = 2.7%.

The kinetic dependence on Cl " is a little uncertain, presumably because we are working in a region where varying Cl also varies the composition of the species present. But the dependence on the ethylene concentration and on the formic acid agrees precisely with this mechanism, and I think it unequivocally demonstrates... 

Thus, the glass transition temperature does no longer systematically decrease proportionally to the ethylene concentration. If the ethylene moieties are short, amorphous domains are favored. Under these circumstances, the glass transition temperature decreases even more strongly. Detailed descriptions concerning the procedure of polymerization are given in the literature (2). 

Several processes based on air or oxygen have been developed.890-895 Oxidation with air (260-280°C) or oxygen (230°C) is carried out at about 15-25 atm at a limited conversion (about 10-15%) to achieve the highest selectivity.896-898 High-purity, sulfur-free ethylene is required to avoid poisoning of the catalyst. Ethylene concentration is about 20-30 vol% or 5 vol% when oxygen or air, respectively, is used as oxidants. The main byproducts are C02 and H20, and a very small amount of acetaldehyde is formed via isomerization of ethylene oxide. Selectivity to ethylene oxide is 65-75% (air process) or 70-80% (02 process).867... 

Fto. 7. The polymerization activity of Cr/silica exhibits almost first-order dependence on ethylene concentration, while the termination rate is less affected. The result, as ethylene pressure increases, is longer chains. 

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