Chitosan-catalyzed n-butyraldehyde self-condensation reaction mechanism and kinetics

The chitosan was found to possess an excellent catalytic performance in n-butyraldehyde selfcondensation to 2E2H. Under suitable conditions, the conversion of n-butyraldehyde, the yield and selectivity of 2E2H separately attained 96.0%, 86.0% and 89.6%. The chitosan catalyst could be recovered and used for 5 times without a significant deactivation after being treated with ammonium hydroxide. In order to elucidate the reaction mechanism, the adsorption and desorption of n-butyraldehyde on the surface of chitosan were studied using in situ FT-IR spectroscopy analysis. The result showed that n-butyraldehyde interacts with-NH₂ group of chitosan to form an intermediate species with an enamine structure. Then the reaction process of n-butyraldehyde self-condensation was monitored by React-IR technique and it was found that n-butyraldehyde self-condensation to 2-ethyl-3-hydroxyhexanal followed by a dehydration reaction to 2-ethyl-2-hexenal. On this basis, chitosan-catalyzed n-butyraldehyde self-condensation reaction mechanism was speculated and its reaction kinetics was investigated. The self-condensation reaction follows auto-catalytic reaction characteristics and then the corresponding kinetic model was established.     

Kinetics of polycyclotrimerization of aromatic dicyanates

Polycyclotrimerization of 4,4′-thiodiphenylcyanate (TDPC) and bisphenol-A dicyanate (BADC) were studied and compared by means of differential scanning calorimetry. Samples of different impurity levels (most likely residual moisture) or different catalyst loadings (n-nonylphenol) were studied. Moisture absorbed may indeed function as a catalyst. In the absence of residual phenols or added catalyst, the polycyclotrimerization of identical species shared the same apparent activation energy and all followed an autocatalyzed first-order rate expression. The autocatalytic effect was justified by the cure behavior of partially cured monofunctional cyanate (p-diphenyl cyanate). The rate expression obtained by the dynamic method is still available for the isothermal method. In the presence of an externally added catalyst (n-nonylphenol, NP), the polycyclotrimerization proceeded at obviously lower temperature as compared with the uncatalyzed case. In addition to the expected lowering of activation energy (independent of the catalyst concentration), the cure reaction exhibited an autocatalyzed higher order kinetics (second order for TDPC system and 1.7-th power for BADC system). These kinetic observations were explained in terms of proposed mechanistic scheme in which the competition between hydroxyl-catalyzed and autocatalytic paths is considered. In particular, formation of NP aggregates ((NP)_m, where m = 7 for TDPC system and m = 5 for BADC system, respectively) is proposed to explain the less-than-additive catalytic capacity with increasing added NP level.     

Measured kinetics of the acid-catalysed hydrolysis of sugar cane bagasse to produce xylose

Experimental trials of the water hydrolysis of bagasse to produce xylose, arabinose and glucose were conducted using a temperature-controlled microwave digester. The experimental variables were temperature, ratio of water mass to bagasse mass, type of bagasse material and reaction time. The pH of the liquid and concentration of dissolved xylose, arabinose and glucose were measured at the completion of each trial. Kinetic modelling of the global rates of formation of monosaccharide products was performed using schemes based on earlier researchers’ models of acid hydrolysis using mineral acids. For the most plentiful product, xylose, the most accurate kinetic model of the global reactions was determined to be two parallel pathways for hydrolysis of xylan to xylose followed by a single pathway for xylose decomposition. The calculated activation energies of the reactions were within the range reported by other researchers for the hydrolysis of a range of lignocellulosic materials using mineral acids.     

Self-organization based on nonlinear nonequilibrium. Dynamics of autonomous agents

This paper discusses a study on the mechanism of self-organization. A global order is organized by the simple and locally coordinated actions of autonomous agents using only local information, so complex or globally coordinated actions which use global communication and high-level strategies are not necessary. The fundamental factors for establishing a global order using self-organization are a “dissipative structure,” an “autocatalysis mechanism,” and “intentional fluctuations.” If an environment where there are agents has a dissipative structure and those agents have some sort of autocatalysis and intentional fluctuation mechanisms within themselves, it is possible to form a global order for them using only their simple and locally coordinated actions. “The blind-hunger dilemma” is used as an example to simulate the self-organization and coordinated actions of agents. In this simulation environment, there are many ant-like agents which must get energy. However, there is only one small energy supply base, so either an efficient method or the coordinated actions of agents is needed. As a result, the agents using our approach could move and get energy more efficiently than agents using conventional coordination mechanisms involving global communication and high-level strategies. Real World Computing Partnership This work was presented, in part, at the Second International Symposium on Artificial Life and Robotics, Oita, Japan, February 18–20, 1997     

Kinetic Analysis of Nonisothermal Reduction of Silica-Supported Nickel Catalyst Precursors in a Hydrogen Atmosphere

A series of silica-supported nickel catalyst precursors was synthesized with different SiO₂/Ni molar ratios. Reduction of Ni catalyst precursors with different SiO₂/Ni molar ratios under a hydrogen atmosphere was investigated at different heating rates. Kinetic parameters were determined using Kissinger–Akahira–Sunose isoconversional and invariant kinetic parameter methods. It was found that for all molar ratios, the apparent activation energy (E_a) is practically constant in the conversion range of 0.20 ≤ α ≤ 0.80. In the considered conversion range, following values of E_a were found: 134.5 kJ mol^?1 (SiO₂/Ni = 0.20), 139.6 kJ mol^?1 (SiO₂/Ni = 0.80), and 128.3 kJ mol^?1 (SiO₂/Ni = 1.15). It was established that the reduction of Ni catalyst precursors with different SiO₂/Ni molar ratios is a complex process and can be described by the ?esták–Berggren autocatalytic model. It was found that the reaction is more Langmuir–Hinshelwood type, as hydrogen dissociates rapidly on surface nuclei and the dissociated hydrogen reacts with the Ni–O active system. It was concluded that the reduction process proceeds through bulk nucleation, which is a dominant mechanism, where three-dimensional growth of crystals with polyhedron-like morphology exists. It was found that the Ni/Si ratio decreases after the reduction process. This has been explained by low Ni and higher Si surface concentrations. It has been disclosed that Ni dispersion decreases.     

Reaction kinetics for the heterogeneously resin-catalyzed and homogeneously self-catalyzed esterification of thioglycolic acid with 2-ethyl-1-hexanol

Producing 2-ethyl-1-hexyl thioglycolate (ETE) via esterification reaction with thioglycolic acid (TGA)aqueous solution as raw material by reactive-separation coupling technology is a promising process inten-sification method.To choose suitable reactive-separation coupling strategy,the kinetic studies of the esterification of TGA with 2-ethyl-1-hexanol (EHL) were carried out in a batch system.The commercial ion exchange resin was employed as an eco-friendly catalyst.The effects of temperature,catalyst concen-tration and molar ratio were determined.It was interesting to observe that the equilibrium conversion of TGA increased with the increase of catalyst mass fraction due to the adsorption of product water onto resin surface.The activity-based pseudo-homogeneous (PH),Eley-Rideal (ER) and Langmuir-Hinshelwood-Ho ugen-Watson (LHHW) models were used to fit the kinetics data of the resin-catalyzed reaction.The models of ER and LHHW performed better than the PH model.The kinetics of the TGA-self-catalyzed reaction was also determined.An activity-based homogeneous kinetics model could well describe this self-catalyzed reaction.These results would be meaningful to the selection and design of an appropriate reaction-separation strategy for the production of ETE,to realize the process intensification.     

General description of martensite transformation curves – a case for bainite

This work describes the results of validation trials of a formal model for the martensite transformation curve in steels. The model is based on microstructural evolution and accepted aspects of athermal, isothermal, mechanical-induced as well as magnetic-assisted martensite transformation modes. The model is operational for martensite and applicable to other intragrain transformations. The paper also explores the extension of the formalism to bainite.     

硝酸在惰性电极上还原机理的研究

用恒电位电解法研究了室温下隋性Ｐｔ电极上硝酸的阴极过程。实验测定了阴极极化曲线和产生的阴极产物。根据所得结果，解释了电解产物与阴极电位的依赖关系和室温下各电位区间内电极过程的自催化性质。根据ＨＮＯ２和ＨＮＯ３的可见和紫外光谱研究，阐明了ＨＮＯ２的催化作用和适当浓度的硝酸可以在惰性电极上直接还原的机理。     

Kinetic model analysis and mechanistic correlation of ammonia borane thermolysis under dynamic heating conditions

Solid state decomposition of ammonia borane has been extensively reported to follow the Avrami-Erofe'ev equation. In this work, thermal analysis of ammonia borane is carried out under dynamic heating conditions under heating rate of 1–5 °C/min. The experimentally derived kinetic data is fitted against various solid state decomposition and autocatalytic kinetic models. It has been observed that the two steps of ammonia borane decomposition reactions follow different kinetics. The first step is more likely to be associated with the homogeneous autocatalytic reactions where the second part demonstrates the traditional nucleation growth kinetics.     

Engineering materials for artificial cells

The grand challenge of engineering a minimal artificial cell provides a controllable framework for studying the biochemical principles of life. Artificial cells contribute to an increased understanding of complex synthetic systems with life-like properties and provide opportunities to create autonomous cell-like materials. Recent efforts to develop life-like artificial cells by bottom-up approaches involve mimicking the behavior of lipid membranes to recapitulate fundamental cellular processes. This review describes the recent progress in engineering biomimetic artificial minimal cells and recently developed chemical strategies to drive de novo membrane formation from simple synthetic precursors. In the end, we briefly point out the challenges and possible future directions in the development of artificial cells.