Ethylene selectivity

This leads to a limiting ethylene selectivity of 6/7 or 85.7%, which has been exceeded, as reported in several patents (104—106). 

Interestingly, the ethylene selectivity can increase with increasing methane conversion. This is because of the predominantly consecutive nature of the OCM reaction network ... 

The ethylene selectivity (Fig. 5) and thus the ethylene yield depend strongly on the adsorbent mass (Fig. 5). For fixed catalyst mass, oxygen supply I/2F and methane conversion there is an optimal amount of adsorbent for maximizing ethylene selectivity and yield (Fig. 5). Excessive amounts of adsorbent cause quantitative trapping of ethane and thus a decrease in ethylene yield according to the above reaction network. This shows the important synergy between the catalytic and adsorbent units which significantly affects the product distribution and yield. 

Figure 6a shows the effect of F02 on the C2 selectivity and yield. The C2 yield is up to 53%. Figure 6b refers to the same experiments and shows the corresponding elBfect of CH4 conversion on the selectivity and yield of ethylene and ethane. The ethylene yield is up to 50% (65% ethylene selectivity at 76% methane conversion). To the best of our knowledge this is the maximum ethylene yield obtained for the OCM reaction under continuous-flow steady-state conditions. 

The Zr-FI catalyst selectively forms PE even in the presence of ethylene and 1-octene, while the Hf complex affords amorphous copolymers, resulting in the catalytic generation of PE- and poly(ethylene-c6>-l-octene)-based multiblock copolymers through a reversible chain transfer reaction mediated by R2Zn. The development of an FI catalyst with extremely high ethylene selectivity as well as a reversible chain transfer nature has made it possible to produce these unique polymers. Therefore, both Ti- and Zr-FI catalysts are at the forefront of the commercial production of polyolefinic block copolymers. 

Methane to Ethylene One target is to achieve an ethylene selectively of 90% at a methane conversion level of 50% in a single pass. Additionally, design of novel recycle reactors or membrane systems (to remove the ethylene produced) remain part of the active research. 

ZSM-5 propylene and higher alkene selectivities are typically higher and ethylene selectivity is typically lower compared to SAPO-34 [97]. Over Beta light alkene breakdown is closer to thermodynamic equilibrium compared with ZSM-5 and SAPO-34 [97]. While the SAPO-34 pore opening is not large enough to let aromatics and branched alkanes out, di- and trimethylbenzenes and even some tetra-methylbenzenes are observed over ZSM-5 as products in the effluent and hexamethylbenzenes are observed over Beta as products in the effluent [98, 99]. 

The ideal feed for ethylene production is ethane, which can give the highest ultimate yield via dehydrogenation. Ethylene selectivities of 85-90% can be achieved at temperatures above 800°C and a steam ethane ratio of about 0.3. 

A new catalyst formulation containing alkali metals and W on a silica support gives more promising results.549 Alkali metals are able to lower the phase transition temperature from amorphous silica to a-crystoballite, shown to be critically important for an effective catalyst, while incorporation of W enhances catalytic activity to ensure high methane conversion and excellent ethylene selectivity. An alkali-stabilized tungsten oxo species is thought to be the active site. 

Practical Applications. IFP s Alphabutol process is used to dimerize ethylene selectively to 1-butene.43,85 The significance of this technology is the use of 1-butene as a comonomer in the polymerization of ethylene to produce linear low-density polyethylene (see Section 13.2.6). Under the reaction conditions applied in industry (50-60°C, 22-27 atm), the selectivity of 1-butene formation is higher than 90% at the conversion of 80-85%. Since no metal hydride is involved in this system, isomerization does not take place and only a small amount of higher-molecular-weight terminal alkenes is formed. 

The different degrees of water inhibition on the ether and olefin formation from ethanol on alumina, and the agreement of ether/ethylene selectivity ratios found experimentally with those calculated by the Monte Carlo simulation of the hydrated surface of alumina [144],... 

Institute for Industrial Research of Oslo, Norway. A unique metallo-organic catalyst system has been discovered which enables the selective trimerization of ethylene to 3-methyl-2-pentene. High temperature de-methanation of this compound results in the formation of isoprene in good yields. Similarly, since 1-butene and 2-butene are dimers of ethylene, they react with ethylene selectively in the liquid phase to produce 3-methyl-2-pentene. 

Catalyst composition Ethane conversion (%) Ethylene selectivity (5)... 

Fig. 3.15 Comparison of (a) ethane conversion and (b) ethylene selectivity between Nio.63Nbo.37O, and Mo0.72V0.26Nb0.02Oj, as a function of temperature.

The library, on a quartz substrate, consisted of almost 50 catalysts (ca. 200 pg). Each catalyst was heated by C02-laser irradiation to between 300 and 400 °C before reaction. Then, a gas mixture of N2, C2H6 and 02 (molar ratio 5 4 1) was blown to each catalysts. A library consisting of Mo-V-Nb with 10% compositional increments per matrix element was prepared and screened. The binary catalysts of Mo-V-O show low conversion and ethylene selectivity. The presence of Nb increases both activity and selectivity dramatically. The superior catalysts found by the screening were scaled up and showed similar catalysis. 

Volpe, A. F., Weinberg, W. H., Woo, L., Zysk, J., Combinatorial heterogeneous catalysis oxidative dehydrogenation of ethane to ethylene, selective oxidation of ethane to acetic acid, and selective ammonoxidation of propane to acrylonitrile, Top. Catal. 2003, 23, 65-79. 

Angelescu, E., Che, M., Andruh, M., Zavoianu, R., Costentin, G., Mirica, C. and Dumitru Pavel, O. Ethylene selective dimerization on polymer complex catalyst of Ni(4,4 -bipyridine)Cl2 coactivated with A1C1(C2H5)2. J. Mol. Catal., A, 219, 2004, 13-19. 

The center section of Fig. 12.17 indicates the expected and observed increases of ethylene selectivity in the membrane reactor. This increase is related to the sequence of reaction orders with respect to oxygen, as was discussed above. 

It is interesting to note also that the mixed oxide supported catalysts increase their activity with reduction temperature, although the impregnated sample performs better. In all cases ethylene selectivity was lower for alumina-supported sample and higher for titania-supported catalyst, and after an initial period the selectivity remained constant. 

Methane-based commercial production of ethylene via oxidative coupling has been investigated, but to date the lower per pass conversions required for acceptable ethylene selectivities combined with purified oxygen costs make this process noncompetitive with thermal cracking of ethane from natural gas liquids. 

Encouraging re ul) have aJ o been obtained by A. L. Dem with cobalt manganese and tron manganese systems (138]. Ethylene selectivities of 45% could be observed with the Co/Mn system. 

CuPt clusters have been found to have high ethylene selectivity in the hydrogen assisted dechlorination of 1,2-dichloroethane. Avdeev et al. have used DFT to investigate the adsorption of ethylene on Cui2Pt2 clusters to help explain these... 

Recently, Pereira et al. have reported data on a low tonperature catalysts (ternary mixture of Ca, Ni, and K oxides), with unusually high selectivities toward C2 hydrocarbons. The authors have reported ethane and ethylene selectivities of nearly 100% at temperatures lower than 600 °C. However, recent report by Dooley and Ross indicate that carbonate fcxmation is responsible for the lack of CO products. 

Figure 5. Influence of the reduction temperature on ethylene selectivity.

The effect of the partial pressure of carbon dioxide on the ethane dehydrogenation over oxidized diamond-supported Cr203 catalyst was examined. The results are shown in Fig. 4. Ethane conversion and ethylene yield markedly increased at a low partial pressure of CO2, and increased with increasing partial pressure. However, the ethylene selectivity slightly decreased with increasing partial pressure. The following reaction with CO2, in the dehydrogenation of ethane, would be possible ... 

Ethylene production by steam cracking of ethane Eonr cases with two or three objectives from (1) maximization of ethane conversion, (2) maximization of ethylene selectivity, and (3) maximization of ethylene flow rate. NSGA-n Reactor inlet temperatnre and length were observed to be the most important decision variables. Tarafder et al. (2005b)... 

A complete analysis of the products reported in Fig. 1 requires some more comments on cyclopentadiene and benzene. Both are typical secondary products, and are mainly the result of successive addition and condensation reactions of alkenes and unsaturated radicals. Once a significant amount of ethylene and propylene is formed, vinyl and allyl radicals are present in the reacting system and form butadiene, via butenyl radicals. Successive addition reactions of vinyl and allyl-like radicals on alkenes and dialkenes sequentially explain the formation of cyclopentadiene and benzene. These reactions are discussed in-depth in the literature and will be also analysed in the coming paragraphs (Dente et al., 1979). It seems worthwhile mentioning that these successive reactions and interactions of small unsaturated radicals and species constitute the critical sub-mechanism for the correct evaluation of ethylene selectivity. In fact, once the primary decomposition of the hydrocarbon feed has largely completed, the primary products and mainly small alkenes can be... 

Ethylene selectivity increases with carbon number due to the importance of the -decomposition of large intermediate radicals. 

Due to the regular branched structure of this isomer, linear 1-alkenes heavier than 1-heptene are not present and the relative amount of propyl and butyl radicals is significantly different too. In other words, the lumped H-abstraction reaction of a single model component loses the variety of primary products obtained from the previous lumped A0C15. It seems relevant to observe that to improve ethylene selectivity prediction, alkene components heavier than hexenes can be conveniently described with two different species, respectively corresponding to the true component 1-C H2 and to a lumped mixture of the remaining normal and branched isomers. 

Ethylene selectivity among C,-compounds is plotted as a function of specific... 

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