Catalytic propylene oxidation reaction rate

Freeder, B. G. et al., J. Loss Prev. Process Ind., 1988, 1, 164-168 Accidental contamination of a 90 kg cylinder of ethylene oxide with a little sodium hydroxide solution led to explosive failure of the cylinder over 8 hours later [1], Based on later studies of the kinetics and heat release of the poly condensation reaction, it was estimated that after 8 hours and 1 min, some 12.7% of the oxide had condensed with an increase in temperature from 20 to 100°C. At this point the heat release rate was calculated to be 2.1 MJ/min, and 100 s later the temperature and heat release rate would be 160° and 1.67 MJ/s respectively, with 28% condensation. Complete reaction would have been attained some 16 s later at a temperature of 700°C [2], Precautions designed to prevent explosive polymerisation of ethylene oxide are discussed, including rigid exclusion of acids covalent halides, such as aluminium chloride, iron(III) chloride, tin(IV) chloride basic materials like alkali hydroxides, ammonia, amines, metallic potassium and catalytically active solids such as aluminium oxide, iron oxide, or rust [1] A comparative study of the runaway exothermic polymerisation of ethylene oxide and of propylene oxide by 10 wt% of solutions of sodium hydroxide of various concentrations has been done using ARC. Results below show onset temperatures/corrected adiabatic exotherm/maximum pressure attained and heat of polymerisation for the least (0.125 M) and most (1 M) concentrated alkali solutions used as catalysts. 

In most cases the catalytically active metal complex moiety is attached to a polymer carrying tertiary phosphine units. Such phosphinated polymers can be prepared from well-known water soluble polymers such as poly(ethyleneimine), poly(acryhc acid) [90,91] or polyethers [92] (see also Chapter 2). The solubility of these catalysts is often pH-dependent [90,91,93] so they can be separated from the reaction mixture by proper manipulation of the pH. Some polymers, such as the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers, have inverse temperature dependent solubihty in water and retain this property after functionahzation with PPh2 and subsequent complexation with rhodium(I). The effect of temperature was demonstrated in the hydrogenation of aqueous allyl alcohol, which proceeded rapidly at 0 °C but stopped completely at 40 °C at which temperature the catalyst precipitated hydrogenation resumed by coohng the solution to 0 °C [92]. Such smart catalysts may have special value in regulating the rate of strongly exothermic catalytic reactions. 

Cu " Pd " -, Cu " -, and Pd -TSMs are completely different from each other in catalytic activity. Cu - and Pd " -TSMs catalyze no reaction and the total oxidation of propylene, respectively, whereas Cu Pd " -TSM catalyzes the oxidation to form acetone selectively, suggesting that the Wacker type oxidation takes place over the catalyst (41). The results are shown in Fig. 6. The higher initial activity is observed for Cu Pd -TSM with the lower Cu Pd ratio, namely the higher Pd " loading. This might be explainable by the second order dependency of the reaction rate on Pd " concentration, observed for the homogeneous system by Vargaftik et al. in the... 

Alkyl transfer steps in the catalytic alkylation of benzene, toluene, and cyclohexane have been investigated over supported Pt, Ir, Ru, and Au. The influence of hydrocarbon partial pressure ratios, temperature, catalyst support, catalyst acidity and basicity, and method of catalyst preparation have been examined. The results are discussed in terms of competitive chemisorption of hydrocarbons. H2 transfer between benzene and C6-hydrocarbons, " and O2 transfer between CO and C02, ethylene and ethylene oxide, and propylene and propylene oxide have also been studied in an attempt to correlate catalyst and reaction variables with resultant rates of reaction. 

Complex reactions with consecutive or parallel steps are commonly encountered in catalytic slurry reactors, e.g. in hydration of propylene oxide, ethynylation of formaldehyde to bu-tinediol or hydrogenation of unsatturated oils [35, 36, 37, 38, 39]. If one can assume in a simplified analysis of these reactions that the concentrations of the liquid reactants are in excess, compared to the gaseous one (Aj ) the rate of reaction of the gaseous reactant (in the absence of intraparticle diffusion) can be expressed as... 

In this catalytic system, as schematically shown in Fig. 10.9 [48], a most probable pathway is that over the Au surfaces O2 and H2 react with each other to form H2O2, which then move to isolated sites of Ti cations to form Ti-OOH species [49]. This oxidic species react with propylene adsorbed on the support surfaces to form PO. It has recently been verified that Ti-OOH species is a true reaction intermediate and that a bidentate propoxy species is probably a spectator on the surface [50]. The coverage, 6, of the Ti-hydroperoxo species was determined from the area of the pre-edge peak in the Ti K-edge XANES spectra at reaction conditions. Measurement of the changes in Ti-hydroperoxo coverage, dO/dt, under transient experiments at reaction conditions with H2/02/Ar and C3H6/H2/O2 gas mixtures, allowed the estimation of initial net rate of propylene epoxidation (3.4 x 10 s ), which closely matched the TOP (2.5 x 10 s ) obtained for the same catalyst at steady-state conditions. 

Surface Reaction Mechanism. The mechanism of catalytic alkene ammoxidation is invariably linked to allylic oxidation chemistry. Allylic oxidation is the selective oxidation of an alkene at the allylic carbon position. Selective allylic oxidation and ammoxidation proceed by abstraction of the hydrogen from the carbon positioned a to the carbon-carbon double bond. This produces an allylic intermediate in the rate-determining step. In the case where propylene is the hydrocarbon, the reaction is as follows ... 

A polystyrylnickel complex prepared by oxidative addition [490] of bromi-nated polystyrene to Ni(PPh3)4 and activated with BF3-OEt2 and a catalytic amount of water acts as an efficient catalyst for the dimerization of propylene at room temperature and atmospheric pressure. Solvents like n-hexane, toluene, benzene, methylene chloride, and chlorobenzene increase the rate of reaction. One role of the solvent is to swell the matrix pol)mier to allow access of the substrate olefin to the interior of the polymer gel. Some dipole—dipole interaction between the nickel site, the olefin, and the solvent molecule may be prevailing, so that competitive coordination of the olefin and the solvent to the nickel site may be possible. The effect of temperature shows that the rate of the dimerization reaction decreases with an increase in temperature, while selective formation of methyl-pentanes increases up to 90% at 40°C. 2-Methyl-2-pentane is the major Cg olefinic product. 

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