Kinetics Analysis of Wheat Straw Pulping Process

This paper analyzes the delignification mechanism of wheat straw pulping process. The lignin removal of pulping process is left in black liquor. The higher the black liquor lignin content is, the bigger the lignin of paper pulp is removed. The relations of black liquor lignin content and alkali concentration to pulping time are described in detail. The results show that delignification process is divided into two stages: quick and slow stage. The lignin removal rate in the first stage is much higher than the second, that is, lignin has been removed more sufficiently after quick stage. In first stage, reaction order of delignification is 1.0, and 0.7 with respect to OH-, the activation energy is 38.62 kJ • mol-1. The latter delignification also belongs to the first-order reaction and 4.4 with respect to OH-, the activation energy is 75.56 kJ • mol-1. Apparently, slow stage needs to consume large amounts of energy to removal lignin.

Preparation and Luminescence Properties of Rare Earth Magnesium Strontium Silicate Luminescent Fiber

The polypropylene luminescent fiber containing Sr2MgSi2O7: Eu2+, Dy3+ phosphors was prepared by melt-spinning method. Crystal phase structure, spectral features and afterglow properties of the luminescent fiber were tested and analyzed. The results show that the fiber has independent superposition phase features of both Sr2MgSi2O7: Eu2+, Dy3+ and polypropylene; the range of its excitation light wavelength locates among 250~450 nm; it can emit blue light of 460 nm wavelength; its initial luminescent intensity is more than 600 mcd/m2, and afterglow time lasts 7 h; the process of afterglow decay consists of fast stage and slow stage.

Kinetics and mechanism of the plutonium catalysed nitric acid oxidation of U(IV) ions in 30% tributyl phosphate solution

The oxidation of U(IV) ions in the diluted solvent phase, 30% TBP/U2PuPu2NO + HNOThe overall reaction stoichiometry is the same as for the oxidation of U(IV) by HNOU(NOThe rate equations of both these rate limiting steps have been determined, with that for the U(IV)-Pu(IV) reaction (5) being given by the equation below, whereThe rate of the second slow stage, the Pu(III)-HNOMechanistically, it was shown that the U(IV)-Pu(IV) reaction may proceed

End-group interchain exchange reaction in polymer blends: evolution of the block weight distribution

The kinetics of interchain exchange reactions proceeding via end-group mechanism in homogeneous polymer blends is studied theoretically. A set of kinetic equations describing the evolution of the block weight distribution is derived. It is demonstrated that the process may be divided into a fast and a slow stage. The fast stage is characterized by alteration in the fractions of end sequences of different type. At the same time most of the homopolymer chains transform into copolymer with block weight distribution close to the Flory distribution. In the course of the subsequent slow stage, the distribution shape is preserved, with average block lengths gradually decreasing to the values typical of the completely random copolymer. The copolymer composition is found to change mostly in the course of the fast stage of the process. The possibilities of using kinetic data for the discrimination between end-group and direct interchange mechanisms are discussed.

Direct interchain exchange reaction in a polymer blend: evolution of the block weight distribution

The kinetics of an interchain exchange reaction in homogeneous polymer blends is studied theoretically. A set of kinetic equations describing the evolution of the block weight distribution is derived. It is demonstrated that the process may be divided into a fast and a slow stage. The former results in the almost full disappearance of homopolymer chains. Simultaneously, the block weight distribution becomes close to the Flory distribution. In the course of the slow stage, the average block lengths decrease to values typical of a completely random copolymer. It is explicitly shown that for an initial blend of homopolymers characterized by the Flory distribution, the transient block weight distribution takes the Flory form starting from the onset of the reaction. The copolymer composition is proved to change in the course of the fast stage of the process. Previous attempts to address the problem are discussed.