Chemical production on a deforming substrate

The interplay between chemical reaction and substrate deformation is discussed by adapting Ranz's formulation for scalar mixing to the case of a reactive mixture between segregated reactants, initially separated by an interface whose thickness may not be vanishingly small. Experiments in a simple shear flow demonstrate the existence of three regimes depending on the Damköhler number $Da=t_s/t_c$ where $t_s$ is the mixing time of the interface width and $t_c$ is the chemical time. Instead of treating explicitly the chemical cross-term, we rationalize these different regimes by globalizing it as a production term involving a flux which depends on the rate at which the reaction zone is fed by the reactants, a formulation valid for $Da>1$ . For $Da<1$ , the reactants interpenetrate before they react, giving rise to a ‘diffusio-chemical’ regime where chemical production occurs within a substrate whose width is controlled by molecular diffusion.

Simulation of combustion of methane-air mixture in two-dimensional approximation

The paper presents a mathematical model and the results of a numerical study of the flame propagation of a methane-air mixture. The physical and mathematical formulation of the problem takes into account the thermal expansion of the gas and its subsequent movement. The problem was solved numerically using the Van Leer method to determine the fluxes at the boundaries of the computational cells. A study of flame propagation in a methane-air mixture with a methane content less than or equal to stoichiometric has been carried out. The conditions for focal ignition of a reactive mixture are determined. The influence of the channel walls on the features of flame propagation is shown. The necessity of taking into account the non-isobaricity of the combustion process at the initial stage is demonstrated.

Phosphorylation of Cellulose in the Presence of Urea. Mechanism of Reaction and Reagent Impact.

A mechanism of cellulose phosphorylation in presence of urea is proposed. This model is correlated with the thermal stability of phosphorylating reactive mixture and the yield of phosphorylation for two different reagents: phosphoric acid and lauryl phosphate monoester. Three main successive reactions are involved in the formation of cellulose phosphate: (1) generation of ammonia by urea decomposition, (2) formation of phosphoramidate as intermediate reactive due to the reaction of ammonia with phosphate species, and (3) grafting the phosphate moiety to substrate due to the transfer of phosphate from phosphoramidate to cellulose. The proposed in vitro mechanism is supported by similar phosphorylation processes observed in some biochemical reactions. The limiting factor in the phosphorylation of cellulose is the formation of phosphoramidate intermediate.

Saturation Point and Phase Envelope Calculation for Reactive Systems Based on the RAND Formulation

Analysis of multicomponent reactive systems requires reliable and accurate equilibrium calculation. There are many stoichiometric or non-stoichiometric methods to solve the flash-type calculations of a mixture in chemical and phase equilibrium. In contrast, there is a lack of robust and efficient methods for another important type of equilibrium calculation, the saturation point calculation or the calculation under the phase fraction specification (β-specification), for a reactive mixture. In this work, we developed RAND-based algorithms for calculating the saturation points and phase envelope of a reactive mixture. The RAND formulation is a non-stoichiometric approach recently extended to non-ideal mixtures for different flash specifications. We showed here how to modify the RAND-based flash formulation to solve the β-specification problems. We distinguished between two types of phase fractions, the one based on components and the one based on elements. They led to different constraint equations in the formulation. Furthermore, we introduced element-based partition coefficients, similar to the equilibrium ratios or K-factors used for non-reactive mixtures. Use of these new variables is essential to cross the critical point of a reactive mixture in the phase envelope construction. Since the formulation developed for reactive mixtures is general, it can also be reduced and used for the simpler non-reactive mixtures. We showed how the reduction could be made and how the reduced algorithm served as an alternative approach to the prevailing phase envelope algorithm of Michelsen. We illustrated the robustness and efficiency of the proposed algorithm using four examples: Pxy diagrams for CO2-NaCl brine, a solid-liquid T xy diagram for MgCl2-water, a PT phase envelope for a reactive mixture with the alkene hydration reaction, and a PT phase envelope for a non-reactive hydrocarbon mixture.

Cyclic carbonates of rapeseed methyl esters as monomers for urethane composites

The two-stage synthesis of cyclic carbonates based on methyl esters of fatty acids from rapeseed oil is characterized. The first stage involves the synthesis of epoxides by the reaction of unsaturated methyl esters of rapeseed fatty acids with hydrogen peroxide, orthophosphoric and acetic acids. The second step is a carbonization reaction, which was carried out by passing carbon dioxide through the reactive mixture in the presence of tetrabutylammonium bromide as a catalyst. A reactive oligourethane based on cyclocarbonates cyclic carbonates of rapeseed fatty acids and piperazine was synthesized by the non-isocyanate method via the interaction of cyclocarbonate group with the amino group of piperazine. Polymer composites based on synthesized cyclocarbonates, epoxides and amines of different chemical nature were prepared and studied. Thus, there is a possibility of regulating the physical and mechanical properties of epoxyurethane composites.

RANKING OF FUEL-AIR MIXTURES IN TERMS OF THEIR PROPENSITYTO DEFLAGRATION-TO-DETONATION TRANSITION

The term "detonability" with respect to fuel-air mixtures (FAMs) implies the ability of a reactive mixture of a given composition to support the propagation of a stationary detonation wave in various thermodynamic and gasdynamic conditions. The detonability of FAMs, on the one hand, determines their explosion hazards during storage, transportation, and use in various sectors of the economy and, on the other hand, the possibility of their practical application in advanced energy-converting devices operating on detonative pressure gain combustion.