DECHEMA

About: DECHEMA is a nonprofit organization based out in Frankfurt am Main, Germany. It is known for research contribution in the topics: Corrosion & Oxide. The organization has 756 authors who have published 1307 publications receiving 25693 citations.

Heterologous expression of 2-methylisoborneol / 2 methylenebornane biosynthesis genes in Escherichia coli yields novel C11-terpenes.

Abstract: The structural diversity of terpenoids is limited by the isoprene rule which states that all primary terpene synthase products derive from methyl-branched building blocks with five carbon atoms. With this study we discover a broad spectrum of novel terpenoids with eleven carbon atoms as byproducts of bacterial 2-methylisoborneol or 2-methylenebornane synthases. Both enzymes use 2-methyl-GPP as substrate, which is synthesized from GPP by the action of a methyltransferase. We used E. coli strains that heterologously produce different C11-terpene synthases together with the GPP methyltransferase and the mevalonate pathway enzymes. With this de novo approach, 35 different C11-terpenes could be produced. In addition to eleven known compounds, it was possible to detect 24 novel C11-terpenes which have not yet been described as terpene synthase products. Four of them, 3,4-dimethylcumene, 2-methylborneol and the two diastereomers of 2-methylcitronellol could be identified. Furthermore, we showed that an E. coli strain expressing the GPP-methyltransferase can produce the C16-terpene 6-methylfarnesol which indicates the condensation of 2-methyl-GPP and IPP to 6-methyl-FPP by the E. coli FPP-synthase. Our study demonstrates the broad range of unusual terpenes accessible by expression of GPP-methyltransferases and C11-terpene synthases in E. coli and provides an extended mechanism for C11-terpene synthases.

Catalytic Membrane Reactors

Abstract: The sections in this article are Introduction Types of Membrane Reactor Catalytic Reactors with Hydrogen-Selective Membranes Membrane Types Organic Polymers Solid Polymer Electrolytes Metals Microporous Membranes Ceramic Proton Conductors and Cermets Final Remarks Selective Removal of Hydrogen Dehydrogenation Hydrocarbons Alcohols Water Gas Shift Reaction Reforming Packed-Bed Membrane Reformers Fluidized-Bed Membrane Reformers Microstructured Membrane Reformers Techno-Economic Evaluation Selective Supply of Hydrogen Hydrogenation Hydroxylation by In-Situ H2O2 Formation Perspectives Reactors with Oxygen-Selective Membranes Membrane Types Mixed Oxygen-Ion- and Electron-Conducting Membranes Solid Electrolytes for Electrochemical Operation Membranes for Selective Removal of Oxygenates Pore Membranes for Non-Selective Oxygen Feeding Selective Supply of Oxygen Production of Pure Oxygen and of Oxygen-Enriched Air Partial Oxidation of Methane to Synthesis Gas Oxidative Dehydrogenation of Light Alkanes to Olefins Oxidative Coupling of Methane to C2-Hydrocarbons Solid Electrolyte Membrane Reactors Perspectives Catalytic Reactors with Non-Selective Membranes Distributed Feeding through Membranes Catalytic Membrane Contactors Gas–Liquid Applications Liquid–Liquid Applications Gas–Gas Applications Perspectives Design of Catalytic Membrane Modules Novel Inorganic Membrane Supports High-Temperature Membrane Reactor Design Concluding Remarks Keywords: membrane reactors; hydrogen-selective membranes; microporous membranes; dehydrogenation; water gas shift reaction; reforming; catalytic membrane modules

Gaseous corrosion of alloys and novel coatings in simulated environments for coal, waste and biomass boilers

Abstract: The reduction of emissions from power generation plants is a key part of the Kyoto Protocol Reduced emissions per unit of power produced can be achieved via increased thermal efficiency and this can be achieved by increasing steam parameters (ie temperature and pressure) Increased steam parameters in turn leads to accelerated corrosion of boiler components Biomass and solid waste fuels introduce a number of aggressive species into process environments that result in enhanced rates of boiler degradation This paper reports on studies, both theoretical and experimental, of the corrosion behaviour of high-alloy steels and Ni-base alloys as well as coatings for use in high efficiency coal and/or biomass- and waste-fired power plants Coatings produced within the SUNASPO project have been laboratory tested in gaseous atmospheres representative of coal combustion, biomass combustion and waste incineration Laboratory tests were carried out mainly in the temperature range 500 °C to 800 °C Initial results showed the poor performance of traditional uncoated low-alloy boiler steels P91 (9% Cr) and HCM12A (12% Cr), as well as the higher alloy steel, 17Cr/13Ni Results show the beneficial effects of coatings containing Al, Si, Al + Si, Al + Ti and Al + B in reducing the rate of corrosive attack In a combustion product gas containing 100 ppm HCl and 1000 ppm SO2, aluminizing affords corrosion resistance of low-alloy steels such as HCM12A and P91 similar to that of Alloy 800 over 1000 h of test The presence of Al inhibits internal, sometimes localized corrosion by promoting the formation of a protective surface oxide layer even at relatively low temperatures The results of experiments in simulated coal; biomass and waste atmospheres are presented and discussed in terms of both corrosion kinetics and mechanisms of degradation

Temperature dependence of a diffusion-limited immobilized enzyme reaction.

Abstract: The apparent activation energy of N-alpha-benzoyl-L-arginine-ethyl ester (BAEE) hydrolysis by immobilized trypsin varies with the bulk substrate concentration from its maximum value, comparable to that of the free enzyme, to considerably lower values. Thus, with a concentration change from 3 x 10(-2) to 10(-4) M the apparent activation energy diminishes from 9.5 to 4.5 kcal/mol. This experimental finding is interpreted to be due to Michaelis-type kinetics in a heterogeneous system, in one case reflecting the temperature dependence of the maximal enzyme reaction rate, in another case illustrating the diffusion limited overall reaction at low substrate concentrations. As a consequence it may not be feasible to operate a reaction at elevated temperatures in a high conversion range, since diffusion limitation may restrict the enhancement of the overall reaction rate. Some further data are given concerning the buffer effect on the reaction rate, which should occur due to its limitation by proton transfer in the buffer-free system.