Solid solutions, propylene oxidation

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. 

The PEO salt complexes are generally prepared by direct interaction in solution for soluble systems or by immersion method, soaking the network cross-linked PEO in the appropriate salt solution [52-57]. Besides PEO, poly(propylene)oxide, poly(ethylene)suceinate, poly(epichlorohydrin), and polyethylene imine) have also been explored as base polymers for solid electrolytes [58]. Polyethylene imine) (PEI) is prepared by the ring-opening polymerization of 2-methyloxazoline. Solid solutions of PEI and Nal are obtained by dissolving both in acetonitrile (80 °C) followed by cooling to room temperature and solvent evaporation in vacuo. Polyethyleneimine-NaCF3S03 complexes have also been explored [59],... 

Al-containing SBA mesoporous solid was prepared as reported 9 mL tetraethyl orthosilicate (TEOS) and the calculated amount of aluminum tri-tert-butoxide, in order to obtain a well defined Si/Al ratio equal to 10, were added to 10 mL of HC1 aqueous solution at pH=1.5 water. This solution was stirred for over 3 h and then added to a second solution containing 4 g triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (EO20PO70EO20 Aldrich) in 150 mL of HC1 aqueous solution at pH=1.5 at 313 K. The mixture was stirred for another 1 h and allowed to react at 373 K for 48 h. The solid product was filtered, dried at 373 K, and finally calcined in air flow (9 L h 1) at 823 K for 4 h with a heating rate of 24 K h"1. The SBA-15 was prepared according to the literature [11]. In what follows, the samples are denoted AlSBA and SBA, respectively. 

A similar lack of clarity pervades other areas concerning the relationship between the catalytic performance and fundamental properties of the catalysts. Wakabayashl et al. (10) reported that the optimized conversion of propylene to acrolein (>7%) over alumina-supported tin-antimony oxide (3 1) was dependent on the sintering temperature of the catalyst and was maximized after heating at 10(X)°C for 3 hr. Further work (22) showed that both electrical conductivity and surface area were maximized in the material containing 3% antimony and a close association between acrolein production and solid solution formation was suggested. 

Christie et al. (53) reported data on the catalytic performance which may also be related to the solid state properties of tin-antimony oxide. A material containing 6% antimony in a batch reactor showed maximized specific activity and low selectivity toward propylene. Above 10% antimony the selectivities exceeded 60% and increased little with increasing antimony content. It is interesting that the " Sn Mossbauer parameters (17) showed similar trends, which were attributed to effects in the solid solution. 

The first real characterization of active phases has been made for the high temperature polymorph of CoMoO (called (a) by us and later (b) by other authors) in the selective oxidation of butane to butadiene (20,21), as well as for (22) and bismuth molybdates (23,24) for oxidation, and ammoxidation of propylene. Additional examples include solid solutions such as (Mo V. )90t (with 0benzene conversion to maleic anhydride (25,26 and the solid solution up to 15% of Sb O in the SnO -Sb O system for propylene oxidation to acrolein (14,2/). 

The Bi2 Ce Mo-O. two phase system has been examined for its activity in the catalytic oxidation of propylene to acrylonitrile. The two phases have been characterized as a solid solution of Bi in cerium in bismuth molybdate. Results of studies have been correlated with... 

Increased propylene ammoxidation activity of each phase upon alterion doping is due to the juxtaposition of all necessary elements for oxidation catalysis in a single phase. The requirements of a good oxidation catalyst are a) activation of the substrate molecule, b) oxidation activity (oxygen inserting) and c) facile redox capabilities to ease electron conduction and site reconstruction. For reasons discussed extensively in the literature (7 ), we assign these roles to Bi, Mo, and Ce ion sites respectively in the catalysts described here. The solid solution formation observed in these materials enables all of these functions to be represented in one phase and on one surface of the catalyst. Analysis of the Multiphase Catalyst... 

Polymers are also essential for the stabilisation of nonaqueous dispersions, since in this case electrostatic stabilisation is not possible (due to the low dielectric constant of the medium). In order to understand the role of nonionic surfactants and polymers in dispersion stability, it is essential to consider the adsorption and conformation of the surfactant and macromolecule at the solid/liquid interface (this point was discussed in detail in Chapters 5 and 6). With nonionic surfactants of the alcohol ethoxylate-type (which may be represented as A-B stmctures), the hydrophobic chain B (the alkyl group) becomes adsorbed onto the hydrophobic particle or droplet surface so as to leave the strongly hydrated poly(ethylene oxide) (PEO) chain A dangling in solution The latter provides not only the steric repulsion but also a hydrodynamic thickness 5 that is determined by the number of ethylene oxide (EO) units present. The polymeric surfactants used for steric stabilisation are mostly of the A-B-A type, with the hydrophobic B chain [e.g., poly (propylene oxide)] forming the anchor as a result of its being strongly adsorbed onto the hydrophobic particle or oil droplet The A chains consist of hydrophilic components (e.g., EO groups), and these provide the effective steric repulsion. 

Nitrogen was bubbled for five minutes through a solution of 2.0 g (8.9 mmol) of 1.1.12a and 5 mL of propylene oxide in 100 mL of aq. acetone (acetone/water, 95 5). The solution was irradiated (Rayonet photoreactor RPR 208, X = 300 nm) for 4 h. After rota-evaporation of the solvent, the residue was dissolved in ether and extracted with 5% sodium bicarbonate solution. The alkali extract was then cooled and acidified with dil. sulfuric acid. Extraction of the separated oil in ether and concentration of the ether layer gave a solid which was crystallized from petroleum ether to yield 1.28 g (70%) of 1.1.12b, mp 76 -77 °C. 

Figure 4. Propylene oxidation with various spinel solid solutions as a function of temperature and space velocity...

Pluronics, also known as poloxamers, are a class of synthetic block copolymers which consist of hydrophilic poly(ethylene oxide) (PEO) and hydrophobic poly(propylene oxide) (PPO), arranged in an A-B-A triblock structure, thus giving PEO-PPO-PEO (Fig. 11.7) (Batrakova and Kabanov 2008). They can be found either as liquids, pastes or solids (Ruel-Gariepy and Leroux 2004). Due to their amphiphilic characteristics (presence of hydrophobic and hydrophilic components), pluronics possess surfactant properties which allow them to interact with hydrophobic surfaces and biological membranes (Batrakova and Kabanov 2008). Being amphiphilic also results in the ability of the individual block copolymers, known as unimers, to combine and form micelles in aqueous solutions. When the concentration of the block copolymers is below that of the critical micelle concentration (CMC), the unimers remain as molecular solutions in water. However, as the block copolymer concentration is increased above the CMC, the unimers will self-assemble and form micelles, which can take on spherical, rod-shaped or lamellar geometries. Their shapes depend on the length and concentration of the block copolymers (i.e. EO and PO), and the temperature (Kabanov et al. 2002). Micelles usually have a hydrophobie eore, in this case the PO chains, and a hydrophilic shell, the EO ehains. 

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