Adsorption Neutralization Model and Floc Growth Kinetics Properties of Aluminum Coagulants Based on Sips and Boltzmann Equations.

Single-molecule aluminum salt AlCl3, medium polymerized polyaluminum chloride (PAC), and high polymerized polyaluminum chloride (HPAC) were prepared in a laboratory. The characteristics and coagulation properties of these prepared aluminum salts were investigated. The Langmuir, Freundlich, and Sips adsorption isotherms were first used to describe the adsorption neutralization process in coagulation, and the Boltzmann equation was used to fit the reaction kinetics of floc growth in flocculation. It was novel to find that the experimental data fitted well with the Sips and Boltzmann equation, and the significance of parameters in the equations was discussed simultaneously. Through the Sips equation, the adsorption neutralization reaction was proved to be spontaneous and the adsorption neutralization capacity was HPAC > PAC > AlCl3. Sips equation also indicated that the zeta potential of water samples would reach a limit with the increase of coagulant dosage, and the equilibrium zeta potential values were 30.25, 30.23, and 27.25 mV for AlCl3, PAC, and HPAC, respectively. The lower equilibrium zeta potential value of HPAC might be the reason why the water sample was not easy to achieve restabilization at a high coagulant dosage. Through the Boltzmann equation modeling, the maximum average floc size formed by AlCl3, PAC, and HPAC were 196.0, 188.0, and 203.6 µm, respectively, and the halfway time of reactions were 31.23, 17.08, and 9.55 min, respectively. The HPAC showed the strongest floc formation ability and the fastest floc growth rate in the flocculation process, which might be caused by the stronger adsorption and bridging functions of Alb and Alc contained in HPAC.

Theoretical study on the reactions of the cyclic trinitrogen radical toward oxygen and water.

Recently, the detection of the neutral simplest all-nitrogen ring, cyclic-N(3) radical, has been realized via various techniques, which has led to numerous studies on its structures, energetics, and spectroscopy. In particular, it has been postulated as a possible building block of high energy density materials. Yet, its intermolecular reactivity is poorly understood. In this paper, we for the first time studied the reactions of cyclic-N(3) with the widespread oxygen and water at the CCSD(T)/aug-cc-pVTZ //B3LYP/6-311++G(d,p)+ZPVE and G3B3//B3LYP/6-311++G(d,p) (italics) levels. An addition-elimination mechanism was revealed for the cyclic-N(3) + O(2) reaction that results in the elementary product N(2) + NO + (3)O with an overall barrier as high as 11.8 (11.0) kcal/mol. The calculated low rate constants (even at high temperatures) show that the cyclic-N(3) radical is stable against oxygen. The cyclic-N(3) + H(2)O reaction is associated with a quasi H-abstraction mechanism forming the product cyclic-N(3)H + OH with the rather high barrier of 35.7 (36.2) kcal/mol. This indicates that cyclic-N(3) is chemically inert toward H(2)O. Chemical implications of the present work are discussed.

Gaseous reaction mechanism between two H(2)CN radicals.

The self-recombination of the methylene amidogen radical (H(2)CN) is known to be fast and should play an important role in determining the concentration of H(2)CN radicals in both combustion and astrophysical processes. The rate constants of H(2)CN + H(2)CN have been determined by previous experiments, whereas its detailed evolution process and product distribution are still unclear. In this work, by means of quantum chemical and master equation calculations, we for the first time explored theoretically the potential energy surface and kinetics of the H(2)CN + H(2)CN reaction. At the CCSD(T)/6-311++G(2df,p), CCSD(T)/aug-cc-pVTZ and Gaussian-3 single-point levels based on the B3LYP/6-31++G(d,p) structures, the dominant channel was found to be () H(2)CN + H(2)CN --> H(2)CNNCH(2) () --> r-CH(2)NNCH(2) () --> N(2) + C(2)H(4) () with a zero overall barrier. The calculated rate constants are in agreement with available experiments. Of particular interest, since the formed product involves molecular nitrogen, the H(2)CN + H(2)CN reaction might have important contribution to the nitrogen-recycling in a number of conflagrant and astrophysical processes.

Theoretical study on reaction mechanism of fulminic acid HCNO with CN radical.

The HCNO + CN reaction is one potentially important process during the NO-reburning process for the reduction of NOx pollutants from fossil fuel combustion emissions. To compare with the recent experimental study, we performed the first theoretical potential energy surface investigation on the mechanism of HCNO + CN at the G3B3 and CCSD(T)/aug-cc-pVTZ levels based on the B3LYP/6-311++G(d,p) structures, covering various entrance, isomerization, and decomposition channels. The results indicate that the most favorable channel is to barrierlessly form the entrance isomer L1c NCCHNO followed by successive ring closure and concerted CC and NO bond rupture to generate the product P1 HCN + NCO. However, the formation of P4 (3)HCCN + NO, predicted as the only major product in the recent experiment, is kinetically much less competitive. This conclusion is further supported by the master equation rate constant calculation. Future experimental reinvestigations are strongly desired to test the newly predicted mechanism for the CN + HCNO reaction. Implications of the present results are discussed.