Oxidation reactor conditions

Only the surface layers of the catalyst soHd ate generaHy thought to participate in the reaction (125,133). This implies that while the bulk of the catalyst may have an oxidation state of 4+ under reactor conditions, the oxidation state of the surface vanadium may be very different. It has been postulated that both V" " and V " oxidation states exist on the surface of the catalyst, the latter arising from oxygen chemisorption (133). Phosphoms enrichment is also observed at the surface of the catalyst (125,126). The exact role of this excess surface phosphoms is not weH understood, but it may play a role in active site isolation and consequently, the oxidation state of the surface vanadium. 

The U.S. Department of Energy has funded a research program to develop the Hquid-phase methanol process (LPMEOH) (33). This process utilizes a catalyst such as copper—zinc oxide suspended in a hydrocarbon oil. The Hquid phase is used as a heat-transfer medium and allows the reaction to be conducted at higher conversions than conventional reactor designs. In addition, the use of the LPMEOH process allows the use of a coal-derived, CO-rich synthesis gas. Typical reactor conditions for this process are 3.5—6.3 MPa (35—60 atm) and 473—563 K (see Methanol). 

Under polymerisation conditions, the active center of the transition-metal haHde is reduced to a lower valence state, ultimately to which is unable to polymerise monomers other than ethylene. The ratio /V +, in particular, under reactor conditions is the determining factor for catalyst activity to produce EPM and EPDM species. This ratio /V + can be upgraded by adding to the reaction mixture a promoter, which causes oxidation of to Examples of promoters in the eadier Hterature were carbon tetrachloride, hexachlorocyclopentadiene, trichloroacetic ester, and hensotrichloride (8). Later, butyl perchlorocrotonate and other proprietary compounds were introduced (9,10). 

If the catalytic HBr oxidation reactor is required to serve as a central facility for recycling a variety of waste HBr streams and conditions that combust all of the organic contaminants cannot be discovered, then further bromine purification operations are probably required. The simplest operation is distillation of the bromine. Due to the high bromine vapor pressure, bromine distillation can be accomplished using relatively small equipment. This is expected to be a highly effective method of purification, particularly where the boiling points of any contaminants are greater than 10°C different from that of bromine. In other applications, absorption or extraction may be needed. 

A peculiarity of the processes described in the patents is that all of them use isobutane-rich conditions, with isobutane-to-dioxygen molar ratios between 2 (for processes that include a relatively low concentration of inert components) and 0.8, and so closer to the stoichiometric value 0.5 (for those processes where a large amount of inert components is present). This is shown in Figure 14.1, which reports in a triangular diagram the feed composition claimed by the various companies, with reference to the flammability area at room temperature. Low isobutane conversions are achieved in all cases, and recirculation of unconverted isobutane becomes a compulsory choice. For this reason, Sumitomo claimed the oxidation of CO to CO2 (contained in the effluents from the oxidation reactor) in... 

Under some in-reactor conditions, other oxide phases, including perovskite phases (ideally AB03), may form. These are known to contain Ru, Zr, Ba, U, and Pu (Kleykamp 1985 Thomas et al. 1992)... 

Of the technological modifications, Fischer-Tropsch synthesis in the liquid phase (slurry process) may be used to produce either gasoline or light alkenes under appropriate conditions249,251 in a very efficient and economical way.267 The slurry reactor conditions appear to establish appropriate redox (reduction-oxidation) conditions throughout the catalyst sample. The favorable surface composition of the catalyst (oxide and carbide phases) suppresses secondary transformations (alkene hydrogenation, isomerization), thus ensuring selective a-olefin formation.268... 

Fig. 14.1 Flow diagram for the oxidation of CH4 under moderately fuel-rich to lean conditions in atmospheric pressure flames and under flow reactor conditions.

Enzymes are biocatalysts constructed of a folded chain of amino acids. They may be used under mild conditions for specific and selective reactions. While many enzymes have been found to be catalytically active in both aqueous and organic solutions, it was not until quite recently that enzymes were used to catalyze reactions in carbon dioxide when Randolph et al. (1985) performed the enzyme-catalyzed hydrolysis of disodium p-nitrophenol using alkaline phosphatase and Hammond et al. (1985) used polyphenol oxidase to catalyze the oxidation of p-cresol and p-chlorophenol. Since that time, more than 80 papers have been published concerning reactions in this medium. Enzymes can be 10-15 times more active in carbon dioxide than in organic solvents (Mori and Okahata, 1998). Reactions include hydrolysis, esterification, transesterification, and oxidation. Reactor configurations for these reactions were batch, semibatch, and continuous. 

The presence of the intermediate methane in the ethane and propane oxidation experiments, coupled with failure to detect ethane or ethene intermediates in the propane experiments constitutes indirect evidence that the reaction rate constants are in the order k >k >k, This order is confirmed by comparing Tablls°5fnlo tVlan t s rate constants calculated on the assumption of first order kinetics, decrease with percent reaction. This is presumably the consequence of the closed reactor conditions and for this reason, rate constants are not given in the tables. However, on average, the assumption of first order kinetics with respect to... 

Operating conditions in partial oxidation reactors and steam reformers vary considerably - depending on the feedstock that is being used. An operating temperature of 1400°C (i.e., the temperature of the inner surface of the lining) is not critical for many refractory materials. However factors other than temperature determine the refractory selection and the refractory design. 

The Fischer-Tropsch Synthesis (FTS) converts synthesis gas (a mixture of CO and H,) to hydrocarbons. Iron-based catalysts lose activity with time on stream (TOS). The rate of deactivation is dependent on the presence/absence of promoters such as potassium and/or binders such as silica [1.2]. Several possible causes of catalyst deactivation have been postulated [3] (i) Sintering, (ii) Carbon deposition, and, (iii) Phase transformations. With respect to phase transformations, there is considerable disagreement whether the active phase for the FTS is iron oxide or carbide [4,5]. In addition, certain reactor conditions, such as a high partial pressure of water, are known to cause a decline in activity [6]. 

The feed to the partial oxidation reactor is a mixture of hydrocarbons, steam, and air or oxygen (or mixtures thereof). The reactor is in general adiabatic or auto-thermal and the exit gas is in many cases close to equilibrium at the exit temperature and pressure at chemical equilibrium. The exit composition can be determined based on the inlet temperature and composition, and on the assumption that all oxygen has reacted. In Fig. 9, product gas compositions are given at various conditions with oxygen as oxidant, assuming that chemical equilibrium is obtained. 

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