Ethylene-Based Active Control

Similarly, the ethylene-based control system was used to actively control the spark timing of the NFS predetonator tube. When ethylene is detected at the tail-end, a signal is sent to actuate the ignitor ensuring full tube fills and minimizing wasted fuel. As shown in Fig. 10.9, the missing peaks in the equivalence ratio histories are due to detonation failure due to pulse-to-pulse interference. The actively controlled spark is able to reduce this performance-degrading behavior. 

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Progress is reported on the development of a wavelength-agile temperature and pressure sensor, a propane concentration sensor, an ethylene-based active control scheme, and a two-phase flow diagnostic. In the area of shock-tube kinetics studies, progress is reported on JP-10 ignition times and decomposition products to aid in the development of reduced chemical mechanisms. 

Figure 10.7 Schematic of ethylene-based active control scheme applied to the Stanford PDE.

Further evidence of the living polymerization nature was obtained by the fact that the GPC peaks of the PE produced shift to higher molecular mass on increasing the polymerization time. The monomodal shape is retained, and no shoulders or low molecular mass tails are detected.1134 The stability of the living polymer chain was investigated utilizing the MAO-activated complex 137 at 25 °C.1134 First, the activated complex is treated with ethylene-saturated toluene for 65 min. The values of Mn versus time clearly indicate that after 3 min all the ethylene is consumed. After 65 min under an N2 atmosphere, ethylene gas was fed to the system for 2 additional min. The Mw/Mn value resulting after the additional 2 min ethylene feed is 1.14, which indicates that no termination reaction occurred for at least 60 min in the absence of ethylene. This remarkable result opens the route to the controlled synthesis of ethylene-based block co-polymers. 

Although numbers of Ni-based catalysts for olefin polymerization have been reported over the past 50 years, examples of structurally characterized Ni/Al heterometaUic complexes resulting from the reaction of a Ni-based precatalyst and an organoaluminum cocatalyst were only recently reported [182, 183] (Fig. 13). Complex 115 oligomerizes ethylene with a moderate activity in the absence of any cocatalyst to selectively form 1-butene, while species 116 and 117 polymerizes ethylene in a controlled manner. 

Most chromium-based catalysts are activated in the beginning of a polymerization reaction through exposure to ethylene at high temperature. The activation step can be accelerated with carbon monoxide. Phillips catalysts operate at 85—110°C (38,40), and exhibit very high activity, from 3 to 10 kg HDPE per g of catalyst (300—1000 kg HDPE/g Cr). Molecular weights and MWDs of the resins are controlled primarily by two factors, the reaction temperature and the composition and preparation procedure of the catalyst (38,39). Phillips catalysts produce HDPE with a MJM ratio of about 6—12 and MFR values of 90—120. 

The rate of peroxide decomposition and the resultant rate of oxidation are markedly increased by the presence of ions of metals such as iron, copper, manganese, and cobalt [13]. This catalytic decomposition is based on a redox mechanism, as in Figure 15.2. Consequently, it is important to control and limit the amounts of metal impurities in raw rubber. The influence of antioxidants against these rubber poisons depends at least partially on a complex formation (chelation) of the damaging ion. In favor of this theory is the fact that simple chelating agents that have no aging-protective activity, like ethylene diamine tetracetic acid (EDTA), act as copper protectors. 

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 ... 

At 252 °C based on kg/ks = 0.15 reaction (9) accounts for only 34 % of the ethane and 11 % of the ethylene. Reactions (6) and (7) are required to explain the concordance of results based on gas analysis and with those based on tetramethyl lead analysis. All observed orders and activation energies are consistent with this mechanism. If reaction (1) is the rate-controlling step in the initiation, the rate of this reaction can be calculated from... 

Five-coordinate aluminum alkyls are useful as oxirane-polymerization catalysts. Controlled polymerization of lactones102 and lactides103 has been achieved with Schiff base aluminum alkyl complexes. Ketiminate-based five-coordinate aluminum alkyl (OCMeCHCMeNAr)AlEt2 were found to be active catalyst for the ring-opening polymerization of -caprolactone.88 Salen aluminum alkyls have also been found to be active catalysts for the preparation of ethylene carbonate from sc C02 and ethylene oxide.1 4 Their catalytic activity is markedly enhanced in the presence of a Lewis base or a quaternary salt. 

Deng et al. (1997) studied the reaction of metallic iron powder (5 g 40 mesh) and vinyl chloride (15.0 mL) under anaerobic conditions at various temperatures. In the experiments, the vials containing the iron and vinyl chloride were placed on a roller drum set at 8 rpm. Separate reactions were performed at 4, 20, 32, and 45 °C. The major degradate produced was ethylene. Degradation followed pseudo-first-order kinetics. The rate of degradation increased as the temperature increased. Based on the estimated activation energy for vinyl chloride reduction of 40 kilojoules/mol, the investigators concluded that the overall rate of reaction was controlled at the surface rather than the solution. 

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