Kinetic-Thermodynamic Analysis of the Reactive Distillation Process of the Cyclohexene Hydration Using the Zeolite Catalyst

Reactive distillation could be utilized to produce cyclohexanol through the cyclohexene hydration. By means of highly active zeolite catalyst HZSM-5, the kinetic-thermodynamic analysis of this reactive distillation has been carried out to get the characteristics of the reactive distillation. Results from kinetic and thermodynamic analysis indicate that the optimal pressure of this reactive distillation process should be set to higher pressure such as 0.3 or 0.4 MPa. To avoid the recovery of cyclohexanol at the top of the column, an unreactive section should be allocated at the upper column. In addition, the inert component benzene is more unfavorable to the reactive distillation process in comparison with the inert cyclohexane.

模糊逻辑控制理论在农业智能温室系统中的应用

现有的农业智能温室系统,由于没有考虑到温室墙体的传热系数和水分自然蒸发等因素,导致不能准确描述温室动态环境。针对农业温室环境中温度和湿度的精确建模与控制问题,提出一种基于模糊逻辑控制(FLC)的控制系统。根据热力—动力学中的热量平衡和质量平衡理论,精确构建温室温度和湿度的动态模型。以温度和湿度的实际值与设定值的差作为输入,通过模糊规则获得加热器、通风器、加湿器和除湿器的控制输出。仿真结果表明,该控制系统能够快速且稳定的跟踪温湿度设定值,对外部环境变化具有较强的鲁棒性。

NUMERICAL PREDICTION OF AIRCRAFT HYDRAULIC SYSTEM BASED ON THERMAL DYNAMIC ANALYSIS

A mathematical model of principal elements of the aircraft hydraulic system is presented based on the heat transfer theory. The dynamic heat transfer process of the hydraulic oil and the pump shells within an aircraft hydraulic system are analyzed by the difference method. A kind of means for the prediction to variational trends of the aircraft hydraulic system temperature is provided during operation. The numerical prediction and simulation under the operational conditions are presented for ground trial running and the decelerated operation in flight. Computational results show that there is a good coincidence between the experimental data and the numerical predictions.

Thermodynamic analysis and dynamics simulation on reaction of Al_2O and AlCl_2 with carbon under vacuum

The feasibility study of the AlCl(g) generated by Al_2O-AlCl_2-C system under vacuum was carried out by thermodynamic analysis and CASTEP package of the Material Studio program which was based on density functional theory(DFT) formalism. Thermodynamic calculations indicate that Al Cl and CO molecules can be formed under conditions of temperature 1760 K and the pressure of 60 Pa. The interaction of Al_2O and AlCl_2 with C shows that the chemical adsorption of Al_2O and AlCl_2 does take place on C(001) crystal plane, and at the same time, new chemical bond is formed between Al atom in Al_2O and Cl atoms from one of the Al—Cl bonds in AlCl_2. The results, after 1.25 ps dynamics simulation, indicate that adsorbed Al Cl molecules are generated and CO molecule will be formed in this system, and they will escape from C(001) surface after a longer period of dynamic simulation time. It means that the reaction of Al_2O and AlCl_2 with C can be carried out under given constraint condition.

Theoretical studies on the complexation of uranyl with typical carboxylate and amidoximate ligands

Understanding of the bonding nature of uranyl and various ligands is the key for designing robust sequestering agents for uranium extraction from seawater. In this paper thermodynamic properties related to the complexation reaction of uranyl（VI） in aqueous solution （i.e. existing in the form of UO2（H20）52＋） by several typical ligands （L） including acetate （CH3CO2）, bicar- bonate （HOCO2-）, carbonate （CO32-）, CH3（NH2）CNO- （acetamidoximate, AO-） and glutarimidedioximate （denoted as GDO2-） have been investigated by using relativistic density functional theory （DFT）. The geometries, vibrational frequencies, natural net charges, and bond orders of the formed uranyl-L complexes in aqueous solution are studied. Based on the DFT analysis we show that the binding interaction between uranyl and amidoximate ligand is the strongest among the selected complexes. The thermodynamics of the complexation reaction are examined, and the calculated results show that complexation of uranyl with amidoximate ligands is most preferred thermodynamically. Besides, reaction paths of the substitution complexation of solvated uranyl by acetate and AO have been studied, respectively. We have obtained two minima along the reaction path of solvated uranyl with acetate, the monodentate-acetate complex and the bidentate-acetate one, while only one minimum involving monodentate-AO complex has been located for AO- ligand. Comparing the energy barriers of the two reaction paths, we find that complexation of uranyl with AO is more difficult in kinetics, though it is more preferable in thermodynamics. These results show that theoretical studies can help to select efficient ligands with fine-tuned thermodynamic and kinetic properties for binding uranyl in seawater.

Chemical vapor infiltration of pyrocarbon from methane pyrolysis: kinetic modeling with texture formation

A complete mechanism of methane pyrolysis is proposed for chemical vapor infiltration of pyrocarbon with different textures, which contains a detailed homogeneous mechanism for gas reactions and a lumped heterogeneous mechanism for pyrocarbon deposition. This model is easily applied to simulate gas compositions and pyrocarbon deposition in a vertical hot-wall flow reactor in the temperature range of 1,323–1,398 K without any adjusting parameters and presents better results than previous mechanisms. Results have shown that the consumption of methane and the production of hydrogen are well enhanced due to pyrocarbon deposition. Pyrocarbon deposition prevents the continuously increasing of acetylene composition and leads to the reduction in the mole fraction of benzene at long residence times in the gas phase. The carbon growth with active sites on the surface is the controlling mechanism of pyrocarbon deposition. C1 species is the precursor of pyrocarbon deposition at 1,323 K,and the primary source over the whole temperature range. As temperature increases, gas phase becomes more mature and depositions from acetylene, benzene and polyaromatic hydrocarbons become more prevalent. A general pyrocarbon formation mechanism is derived with the specific precursors and illustrates that the maturation of gas compositions is beneficial to forming planar structures with hexagonal rings or pentagon-heptagon pairs, namely, high textured pyrocarbon. The results are in well agreement with experiments.