New Reaction Engineering Concepts for Selective Oxidation Reactions

In order to enhance product yields in selective oxidation reactions, numerous reaction engineering concepts are being studied worldwide. Periodic operation has been investigated for decades, yet its application is limited to a few examples, such as the butane oxidation after DuPont or reverse-flow reactors for VOC removal. The use of microchannel reactors is a younger field, but it has already yielded promising results for process optimization. Catalytic wall reactors have proved to be a helpful tool for kinetic studies. On the laboratory scale, membrane reactors have displayed favorable behavior in selective oxidation. The Na vapor-catalyzed dehydrogenation of methanol to formaldehyde is a final example of an unusual new concept for selective oxidation.     

MAGNESIUM HYDROXIDE FILLED EVA: THE EFFECTS OF FILLER SURFACE MODIFICATION ON THE STRENGTH OF FILLER/MATRIX ADHESION AND THE CONSEQUENCES FOR COMPOSITE STRUCTURE AND PROPERTIES

The interaction of ammonium stearate (AS) and γ-aminopropyltriethoxysilane (APS) treatments with a magnesium hydroxide flame retardant filler and their effects on its use in an ethylene vinyl acetate copolymer compound have been investigated. The work has shown clear evidence of changes in the structure of the surface layers formed on the filler as the amount of additive is increased and the levels at which these occur can be correlated with theoretical monolayer quantities. Infrared (IR) spectroscopy data suggest that the stearate coating changes from a half salt to a full salt as the coating level is increased and that the APS coating on the filler initially has a significant bicarbonate content, presumably due to reaction with atmospheric carbon dioxide. The effect of coating level on the melt flow rate, insoluble matrix content, crystallisation behaviour, tensile properties, limiting oxygen index, and ageing of the filled compound has been studied. Distinct trends have been observed, many of which can be correlated with the structure of the filler surface layers. Of particular importance is the observation that, unlike APS, excess stearate appears to promote detrimental ageing effects.     

Physiological phosphorylation of protein kinase A at Thr-197 is by a protein kinase A kinase

Phosphorylation of the catalytic subunit of cyclic AMP-dependent protein kinase, or protein kinase A, on Thr-197 is required for optimal enzyme activity, and enzyme isolated from either animal sources or bacterial expression strains is found phosphorylated at this site. Autophosphorylation of Thr-197 occurs in Escherichia coli and in vitro but is an inefficient intermolecular reaction catalyzed primarily by active, previously phosphorylated molecules. In contrast, the Thr-197 phosphorylation of newly synthesized protein kinase A in intact S49 mouse lymphoma cells is both efficient and insensitive to activators or inhibitors of intracellular protein kinase A. Using [35S]methionine-labeled, nonphosphorylated, recombinant catalytic subunit as the substrate in a gel mobility shift assay, we have identified an activity in extracts of protein kinase A-deficient S49 cells that phosphorylates catalytic subunit on Thr-197. The protein kinase A kinase activity partially purified by anion-exchange and hydroxylapatite chromatography is an efficient catalyst of protein kinase A phosphorylation in terms of both a low Km for ATP and a rapid time course. Phosphorylation of wild-type catalytic subunit by the kinase kinase activates the subunit for binding to a pseudosubstrate peptide inhibitor of protein kinase A. By both the gel shift assay and a [gamma-32P]ATP incorporation assay, the enzyme is active on wild-type catalytic subunit and on an inactive mutant with Met substituted for Lys-72 but inactive on a mutant with Ala substituted for Thr-197. Combined with the results from mutant subunits, phosphoamino acid analysis suggests that the enzyme is specific for phosphorylation of Thr-197.     

Effect of polymerization catalyst technology on the melt processing stability of polyethylenes,Part 3: Additives blends performance

This article considers the interaction between additives that occur during the stabilization process. The simultaneous effects of the additives and associated interactions on melt processing stability and processing discoloration were of particular interest. Melt stability is an important factor to consider because physical changes in the processed polymer can occur during the compounding and fabrication steps. Furthermore, discoloration is one of the most important problems affecting commercial polymers. Most discoloration manifests itself as yellowing, especially in the case of polyolefins. Although yellowing can often be associated with degradation processes caused by various agents, such as light or heat, this is not always the case; yellowing can also be due to the interaction of additives in the stabilizer packages. Blends of primary antioxidants (AOs), secondary AOs, and hindered amine light stabilizers have been studied with the intention of further improving stabilization performance together with cost reduction of the stabilized polymer. Although synergism between AOs and a stabilizer is fairly common, antagonism was also observed in terms of melt flow protection and in color stability in some of the AOs tested. The effects of a range of thermal and light stabilizers on the melt stability (investigated via multiple pass extrusion) and color stability of three different polyethylenes (PEs) were examined. The PEs varied in terms of the catalyst system used to synthesize the polymers and included a high‐density polyethylene (HDPE) produced by using a chromium‐based Phillips catalyst and two linear low‐density polyethylenes (LLDPEs) produced via chromium‐based metallocene and titanium‐based Ziegler‐Natta catalysts. The apparent lack of influence of polymerization catalyst system on the mode of stabilizer interaction should lead to the reassessment of stabilizer formulation strategies in relation to PE type/catalyst system and associated commercial/economic considerations. J. VINYL ADDIT. TECHNOL., 22:117–127, 2016. © 2014 Society of Plastics Engineers     

Computerized ultimate strength analysis of reinforced concrete sections subjected to axial compression and biaxial bending

This article presents a method of evaluating the ultimate strength capacities of reinforced concrete sections of arbitrary shapes and with or without voids subjected to axial compression and biaxial bending. The concept of load fraction is introduced so as to provide a quantitative measure of structural adequacy. An iterative procedure to determine the load fractions is proposed. Necessary integration over arbitrary domains is dealt with by boundary integration method. This procedure can be computerized readily to high automation. A wide range of reinforced concrete sections are analysed, as examples, using a desk-top computer.     

The effect of resin/crosslinker ratio on the mechanical properties and fungal deterioration of a maxillofacial silicone elastomer

Variation of the crosslinker/resin ratio of a room temperature condensation cure maxillofacial silicone elastomer has caused considerable changes in the mechanical properties and deterioration by Candida albicans. Increasing the crosslinker/resin ratio caused a decrease in the tensile strength and stiffness of the elastomer. However, tear strength appeared to show an optimum value at the recommended crosslinker/resin ratio. These effects were due to the low molar mass silicone polymer that acts as a carrier for the actual crosslinking additive. The general decrease in mechanical properties was accompanied by an increase in the hexane extractables content and an increase in the Si–H content of the elastomer. The unbound polymer (extractable material) content of the elastomer was found to influence the colonization of the material by C. albicans. An increase in the unbound polymer content corresponded to an increasing number of hyphae and blastospores observed penetrating into the elastomer. The data obtained in this study have significant implications concerning the degree of control of elastomer formulation and the deterioration of maxillofacial appliances.     

The retention of heterocyclics by siliceous frameworks Part I The role of the heterocyclic

Flow microcalorimetry has been used to probe acid-base interactions between five-membered-ring heterocyclics and thermally pre-treated, porous silica. The adsorbates (1-methylpyrrolidin-2-one, pyridine, pyrrolidine, pyrrole, 2-methylthiophene, 2-octyl-4-isothiazolin-3-one, 4,5-dichloro-2-octyl-4-isothiazolin-3-one and 2-cyclopentenone,) varied in basicity, polarity and -character. The amounts of the adsorbates retained by the silica were determined, along with enthalpy of adsorption (ranging from –5.5 kJ mol^–1 to –57.8 kJ mol^–1) and enthalpy of desorption (ranging from 5.6 kJ mol^–1 to 26.1 kJ mol^–1). For the majority of the adsorbates the enthalpy of adsorption is consistent with hydrogen bonding to isolated silanols. Although increasing basicity enhanced the adsorption enthalpy and hence the strength of associations, desorption was inhibited when a carbonyl, or unsaturated carbonyl, group was adjacent to the active basic centre. Bulky electron-withdrawing agents (chlorine atoms) substituted at the double bond of the unsaturated carbonyl reduced the adsorption considerably. This was attributed to steric hinderance restricting the proximity of the basic groups with the active silanol sites.     

Use of microwave dielectric loss for characterisation of natural rubber/carbon black composites

Summary Microwave dielectric loss spectroscopy (MDS) has shown remarkable potential as a tool for the observation of changes in elastomer network structure within the interphase region of natural rubber/ carbon black composites. During crosslinking (non elemental sulphur system) the dielectric loss progressively increased. However, during ageing at high temperature the dielectric loss decreased. Parallel studies on the unfilled matrix yielded no such variation in dielectric loss. It was therefore concluded that the changes in microwave responses were related to the development of the interphase during curing and its subsequent destruction during ageing. The microwave response was related to the composite mechanical properties as a function of ageing time. The effect of stabiliser was also investigated. Received: 13 September 1999/Revised version: 7 February 2000/Accepted: 10 February 2000     

Factors affecting the adsorption of stabilisers on to carbon black (flow micro-calorimetry studies) Part II Hindered amine light stabilisers (HALS)

The interaction of hindered piperidine light stabilisers (HALS) with carbon black has been examined using flow micro-calorimetry (FMC) and Fourier transform infrared spectroscopy (FTIR). Significant differences in both the overall adsorption activity and molar heats of probe adsorption are observed. Differences in adsorption behaviour between different types of carbon black were clearly evident and, as with a previous paper (see reference 1, in the latter paper, surface chemistry of the carbon blacks investigated is extensively analysed by XPS, FTIR, N₂ BET adsorption and Karl–Fischer analysis), were mainly to be due to differences in carbon black surface chemistry. The specific surface area merely physically affected the level and heat of adsorption (per unit mass of carbon black). Variation in the degree of substitution of the piperidine amine is an important factor that is found to influence the adsorption activity of HALS, as well as the number of adsorption active and sterically accessible functional groups per HALS molecule. In some cases the adsorbed HALS could be detected by FTIR; shifts in absorption frequencies associated with both the adsorbate and the substrate yielded significant insight into the mode of adsorption of several of the HALS investigated.     

PdZn catalysts prepared by washcoating microstructured reactors

Methanol steam reforming is an option for dynamic hydrogen generation in automotive fuel cell systems. Microstructured reactors with small channels (100 μm×100 μm) are being studied. A washcoating procedure applying dispersed ZnO nanoparticles to the microchannel walls was adapted to the PdZn catalyst system. The catalyst layer showed no significant differences during X-ray diffraction and temperature-programmed oxidation and reduction experiments for examination of oxidation state and alloy formation compared with other PdZn systems reported in the literature. Chemisorption with different adsorbates and X-ray backscattering were used for gathering detailed information on PdZn dispersion, diameter and shape with respect to the preparation parameters. Catalytic experiments yielded a relationship between the catalyst properties and the catalytic activity, degradation and secondary reactions.