Recent remarkable progress in understanding and engineering enzymes and whole cells as highly selective and environment-friendly catalysts enabling novel routes for the production of pharmaceuticals, fine and platform chemicals, and biofuels has spurred the quest for fast biocatalyst screening and development of efficient processes with long-term biocatalyst use. Besides this, current efforts towards more sustainable production systems and bio-based products have triggered an intense research on chemo-enzymatic cascades and establishment of continuous end-to-end processing. Microreaction technology, which has in the last two decades changed the paradigm in the laboratory and production scale organic synthesis, is recently gaining attention also in the field of applied biocatalysis. Based on the trends highlighted within this article, microfluidic systems linked with appropriate monitoring and feedback control can greatly contribute to successful implementation of biocatalysis in industrial production. Microflow-based droplets facilitate ultrahigh-throughput biocatalyst engineering, screening at various operational conditions, and very fast collection of data on reaction kinetics using minute amounts of time and reagents. Harnessing the benefits of microflow devices results in faster and cheaper selection of substrate(s) and media, and development of suitable immobilization methods for continuous biocatalyst use. Furthermore, the use of highly efficient reactor designs integrated with downstream processing enabling also faster and more reliable scale-up can bridge the gap between the academic research and industrial use of biocatalysts.
A Mangelsdorf's approach to modeling the epoxy-amine cure kinetics has been developed. Analysis of the data by means of Mangelsdorf's
approach makes it possible not only to determine the reaction rate constant and the heat of epoxy ring opening, but also to
elucidate the reaction mechanism. However, to model the kinetic curves obtained by the calorimetric method for the complicated
reaction should be derived an equation expressing the rate of change of the heat with time, as a function of the reaction
rate and the extent of conversion. In a detailed examination the thermokinetic data, we found that glassy state transition
is kinetically feasible. Using data available in literature, the kinetic model for epoxy-amine cure reaction was developed.
Our treatment of glass formation is based on the picture of the reaction system as a miscible mixture of two structurally
different liquids. This approach is similar to that presented by Bendler and Shlesinger as a Two-Fluid model. In the application
of this model to reaction kinetics, we believe the explanation of glass structure formation lies in the splitting of the homogeneous
mixture into two liquid phases.
Authors:F. Langmaier, P. Mokrejs, K. Kolomazník, M. Mládek, and R. Karnas
Differential scanning calorimetry was employed to investigate the reaction of diglycidyl ethers of bisphenol A (DGEBA) of
mean molecular mass 348–480 Da, with collagen hydrolysate of chrome-tanned leather waste in a solvent-free environment. The
reaction leads to biodegradable polymers that might facilitate recycling of plastic parts in products of the automotive and/or
aeronautics industry provided with protective films on this basis. The reaction proceeds in a temperature interval of 205–220°C,
at temperatures approx. 30–40°C below temperature of thermal degradation of collagen hydrolysate. The found value of reaction
enthalpy, 519.19 J g−1 (= 101.24 kJ mol−1 of epoxide groups) corresponds with currently found enthalpy values of the reaction of oxirane ring with amino groups. Reaction
heat depends on the composition of reaction mixture (or on mass fraction of diglycidyl ethers in the reaction mixture); proving
the dependence of kinetic parameters of the reaction (Arrhenius pre-exponential factor A (min−1) and activation energy Ea (kJ mol−1)) did not succeed. Obtained values of kinetic parameters are on a level corresponding to the assumption that reaction kinetics
is determined by diffusion.
The reaction between copper(I) sulphide and excess copper(II) sulphate in the temperature range 600–750 K was investigated by methods of thermal analysis as well as by measuring the phase composition as a function of the fractional conversions. The reaction proceeds in four stages. The transient products are Cu2S, a Cu2SO2 phase and CU2SO4, and the final product is CU2O with the non-defect structure. The initial composition of the substrate mixture strongly influence the reaction kinetics.
Authors:Jian-Zhong Guo, Zhao-Yin Hou, and Xiao-Ming Zheng
in the journal last year ( ReactionKinetics, Mechanisms and Catalysis , 2010 , 101, 129–140; DOI 10.1007/s11144-010-0210-2 ).
After the publication of the paper, the following facts became obvious to the editors.
Awareness of the environmental aspects of the quality of crop production has increased in recent decades, leading to renewed interest in organics such as crop residues, green manures and organic manures. The effect of organics on urea transformation was investigated by conducting a laboratory incubation experiment in alluvial clay loam soil (Typic Ustifluvents) at 33±1°C with two moisture levels (1:1 soil:water ratio and field capacity). The rate of urea hydrolysis decreased as the time of incubation increased and the disappearance of urea N was associated with a corresponding increase in the (NH
)-N content in soils treated with crop residues (rice straw and wheat straw), organic manures (poultry manure and farmyard manure) and green manures (cowpea and sesbania). In untreated soil, the time taken for the complete hydrolysis of the applied urea (200 μg urea N g
soil) was more than 96 h at both the moisture levels, whereas in amended soils it was completed in 48 h. The rate of urea hydrolysis was more rapid at field capacity than at the 1:1 soil:water ratio. Urea hydrolysis was higher in sesbaniatreated soils, followed by cowpea, poultry manure, farmyard manure, rice straw and wheat straw at both the moisture levels. At field capacity, 85.5% urea was hydrolysed in sesbania-treated soil as compared to 32% in untreated soil after 24 hours of incubation, while at the 1:1 soil:water ratio the corresponding values were 81.5 and 27.5%. Urea hydrolysis followed first order reaction kinetics at both the moisture levels.
Authors:Christine Fräulin, Günter Rinke, and Roland Dittmeyer
, 4593 – 4605 ;
(g) Schäfer, R. Bubble Interactions, Bubble Size Distributions and ReactionKinetics for the Autocatalytic Oxidation of Cyclohexane in a Bubble Column Reactor . PhD Thesis, University of Stuttgart , 2005 ;
Authors:M. Reading, D. Dollimore, J. Rouquerol, and F. Rouquerol
The uncertainty surrounding the significance of the measured kinetic parameters of solid state decomposition reactions is discussed briefly. Some suggestions are made about what precautions should be taken in order to favour the measurement of undistorted results. Some criteria are proposed for deciding whether a measuredE value can be considered to have its usual meaning. The results of a series of experiments aimed at measuring the activation energy of the decomposition of calcium carbonate using a variety of methods, sample sizes and experimental conditions are presented. These results are compared with results found in the literature and it is concluded that it is possible to measure a reproducible value forE and it is tentatively proposed that this value is meaningful in terms of the energy barrier model of chemical reaction kinetics.
These data can be used to calculate the reactionkinetics for isothermal treatments by varying the soaking temperature, by the relationship ( 8 ). The obtained results are shown in Fig. 7