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.     

Mikrostrukturuntersuchungen an porösen Feststoffen durch Physisorptionsmessungen

Studies of the microstructure of porous solids by physisorption measurements . The principal experimental methods for studying the microstructure of porous solids are based on physisorption measurements. The resulting sorption isotherms can yield data such as surface area and pore radius distribution, which are of great importance for development and characterization of porous catalysts. After a brief presentation of available measuring equipment, the main concern of this survey is the evaluation of sorption isotherms. In particular, methods for determining the micropore contribution to the total pore volume and the pore radius distribution in the micropore range are examined critically with regard to their reliability.     

Tensile strength of silicon carbide fibre bundles at elevated temperatures

The mechanical properties of commercially available SiC-based ceramic fibres were measured in the temperature range from 400–1300°C. The measurements were performed in air and in inert gas atmospheres, respectively. The Nicalon and Tyranno fibres were tested as filament bundles and the decrease in strength occurring at temperatures above 600 °C was found in both atmospheres. To obtain a well-defined gauge length at the testing temperature, a furnace with very steep temperature gradients at both ends was built. To eliminate grip-induced damage in the heating zone the fibre bundles were fixed outside the furnace with cold grip units. These grips guaranteed the uniformity of load distribution imposed on to each of the individual filaments in the fibre bundle. A significant shrinkage of the fibres occurring during the creep test performed under low loads indicates a change in the microstructure of the fibres at high temperatures.     

Mutagenicity, genotoxicity and cogenotoxicity of environmentally relevant nitro musk compounds

In the present study a new in vivo/in vitro animal model was used to study the ability and potency of musk ketone and musk xylene to induce liver specific oxygenases (in vivo) which are necessary of toxify different premutagens, pregenotoxicants and/or precarcinogens to the ultimate DNA damaging agents. Therefore, rats were pretreated with 10, 20 and 40 mg/d nitro musk (NMV) for 5 days by intraperitoneal (i.p.) injection. Then the postmitochondrial fractions of the hepatocytes (S9M) were used to examine the metabolic potency for toxification of the pregenotoxicants benzo[a]pyrene (B[a]P) and 2-aminoanthracene (2-AA) using the SOS chromotest (in vitro). Furthermore, musk xylene, musk ketone, musk ambrette, musk moskene and musk tibetene were examined for their mutagenicity in the Salmonella/microsome assay using S. typhimurium TA97, TA98, TA100 and TA102 and for their genotoxicity in the SOS chromotest using Escherichia coli PQ37 (sfiA::lacZ) in the presence and absence of an exogenous metabolizing system (S9 of PCB induced rats = S9A). Both musk ketone and musk xylene were identified als inducers of toxifying enzymes (oxygenases) in rat liver. Using the in vivo/in vitro model these isoenzyme inductions led to a metabolisation (toxification) of the pregenotoxicants benzo[a]pyrene (B[a]P) and/or 2-aminoanthracene (2-AA) (cogenotoxicity). Using S9M fractions of rats which were i.p.-pretreated with 5 x 40 mg musk ketone the induction factor in the SOS chromotest was IFmax = 4.0 by using 1 nmole B[a]P and IFmax > 4.0 by using 20 nmole 2-AA. Thus, musk ketone seems to be a Cytochrome P450 1A1 and 1A2 isoenzyme inducer in mammals. On the other hand the S9M fractions of musk xylene pretreated rats showed only a toxification of 2-AA (IFmax = 3.0). Therefore, a synergistic effect of enzyme inducers, i.e. musk xylene and musk ketone, and pregenotoxicants, i.e. B[a]P and 2-AA, regarding DNS damaging effects was identified. Musk ambrette showed high mutagenicity in S. typhimurium TA100 (500 His(-)-revertants per mumole, +S9A). Unexpectedly, these DNA damaging effects were not caused by bacterial nitroreductases but by rat S9A metabolisation (!). SOS inducing DNA damages in E. coli PQ37 were not produced (IFmax < 1.5). On the basis of the results presented and under consideration of the concentrations of NMV, other cogenotoxicants and pregenotoxicants such as B[a]P and 2-AA in environmental samples and human tissues, a genotoxic risk for humans has to be assumed.     

Heterogeneously catalyzed oxidative dehydrogenation of isobutyric acid to methacrylic acid: A new application of periodic flow reversal

The heterogeneously catalyzed oxidative dehydrogenation of isobutyric acid in a fixed bed reactor using molybdenum (Mo) heteropoly acids as catalysts shows a loss of Mo into the gas phase due to the formation of volatile Mo-complexes under reaction conditions. To avoid this loss of catalyst and to keep the catalytic material in the fixed bed and thus increase the catalyst's lifetime, the process has been performed under periodic flow reversal within the reactor. In this work, periodic flow reversal is tried in a semi-pilot test reactor as a method to fix the Mo-compounds in the catalyst bed. The influence of this mode of operation on the temperature profile in the reactor, on conversion, selectivity and yield of the product methacrylic acid is investigated in comparison with the process without periodic flow reversal.     

Transalkylation of biphenyl over zeolites: Optimizing the reaction conditions and kinetic modeling

The shape-selective transalkylation of biphenyl with pentamethylbenzene over ultrastable Y-faujasites to produce para-methylated biphenyls was studied in the liquid slurry phase. The reaction was carried out in a discontinuously operated stainless steel autoclave using n-heptane as the solvent with a temperature range of 513 to 533 K and a pressure of 3 MPa. As for the progress of the reaction the presence of strong Brønsted acid sites was essential, an ultrastable faujasite treated with aqueous hydrochloric acid having a high content of those sites was used as the catalyst. Thus, a yield of the target product 4,4′-dimethylbiphenyl of above 11% referring to biphenyl could be achieved. The effect of the operating conditions on the formation of the target product was investigated. The decisive influence was acted out by the molar ratio of biphenyl to alkylating agent, in so far as a surplus of pentamethylbenzene of 7:1 referring to biphenyl enhanced the yield of the target product to 14%. The kinetics of the reaction could be successfully descibed with a lumped reaction scheme, introducing pseudo components, summarizing structural isomers, and pseudo reactions, such as the formation of coke.