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HNCO hydrolysis performance in urea-water solution thermohydrolysis process with and without catalysts
Zhen-chao Chen, Wei-juan Yang, Jun-hu Zhou, Hong-kun Lv, Jian-zhong Liu, Ke-fa Cen
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2010, 11(11): 849-856.
https://doi.org/10.1631/jzus.A0900798
The thermolysis of urea-water solution and its product, HNCO hydrolysis is investigated in a dual-reactor system. For the thermal decomposition below about 1073 K, the main products are ammonia (NH3) and isocyanic acid (HNCO) whereas at higher temperatures the oxidation processes take effect and the products include a low concentration of nitric oxide (NO) and nitrous oxide (N2O). The gas HNCO is quite stable and a high yield of HNCO is observed. The ratio of NH3 to HNCO increases from approximately 1.2 to 1.7 with the temperature. The chemical analysis shows that H radical is in favor of HNCO hydrolysis by instigating the reaction HNCO+H·→·NH2+CO and high temperature has positive effect on H radical. The hydrolysis of HNCO over an alumina catalyst made using a sol-gel process (designated as γ-Al2O3) is investigated. The conversion of HNCO is high even at the high space velocities (6×105 h−1) and low temperatures (393–673 K) in the tests with catalysts, which enhances HNCO hydrolysis and raises the ratio of NH3 to HNCO to approximately 100. The pure γ-Al2O3 shows a better catalytic performance than CuO/γ-Al2O3. The addition of CuO not only reduces the surface area but also decreases the Lewis acid sites which are recognized to have a positive effect on the catalytic activity. The apparent activation energy of the hydrolysis reaction amounts to about 25 kJ/mol in 393–473 K while 13 kJ/mol over 473 K. The overall hydrolysis reaction rate on catalysts is mainly determined by external and internal mass-transfer limitations.
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Application of land use regression for estimating concentrations of major outdoor air pollutants in Jinan, China
Li Chen, Shi-yong Du, Zhi-peng Bai, Shao-fei Kong, Yan You, Bin Han, Dao-wen Han, Zhi-yong Li
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2010, 11(11): 857-867.
https://doi.org/10.1631/jzus.A1000092
SO2, NO2, and PM10 are the major outdoor air pollutants in China, and most of the cities in China have regulatory monitoring sites for these three air pollutants. In this study, we developed a land use regression (LUR) model using regulatory monitoring data to predict the spatial distribution of air pollutant concentrations in Jinan, China. Traffic, land use and census data, and meteorological and physical conditions were included as candidate independent variables, and were tabulated for buffers of varying radii. SO2, NO2, and PM10 concentrations were most highly correlated with the area of industrial land within a buffer of 0.5 km (R2=0.34), the distance from an expressway (R2=0.45), and the area of residential land within a buffer of 1.5 km (R2=0.25), respectively. Three multiple linear regression (MLR) equations were established based on the most significant variables (p<0.05) for SO2, NO2, and PM10, and R2 values obtained were 0.617, 0.640, and 0.600, respectively. An LUR model can be applied to an area with complex terrain. The buffer radii of independent variables for SO2, NO2, and PM10 were chosen to be 0.5, 2, and 1.5 km, respectively based on univariate models. Intercepts of MLR equations can reflect the background concentrations in a certain area, but in this study the intercept values seemed to be higher than background concentrations. Most of the cities in China have a network of regulatory monitoring sites. However, the number of sites has been limited by the level of financial support available. The results of this study could be helpful in promoting the application of LUR models for monitoring pollutants in Chinese cities.
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Removal of sulfamethoxazole by nanofiltration membrane
Su-hua Wu, Hua-qiang Chu, Bing-zhi Dong, Jun-ru Zhou, Yu Huang
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2010, 11(11): 868-878.
https://doi.org/10.1631/jzus.A0900606
The retention of sulfamethoxazole (SMZ) by nanofiltration (NF) membranes is strongly influenced by the pH value of the solution. The retention of SMZ reaches its peak value when the solution pH rises above its pKa2 value as the compound transforms into a negatively charged species. Charge repulsion is the main mechanism involved in SMZ removal by NF membranes. In this study, the removal of SMZ by NF membranes, as a function of solution chemistry, was examined at pH 8.9 to investigate the effect of solution conditions on charge repulsion. The results show that the retention of negatively charged SMZ is relatively independent of SMZ concentration, and an increase in the ionic strength of the solution causes a relatively small reduction in retention. A small effect of humic acid (HA) on SMZ retention was noticed at pH 8.9, which can be explained by a small but insignificant improvement in the zeta potential of the membrane caused by HA at high pH values. However, it was found that SMZ concentration in the feed decreased significantly in solutions containing tannic acid (TA). The Adams-Bohart model was applied to our experimental data and was found to be suitable for describing the initial part of the breakthrough curves. The adsorptive parameters of the membrane were determined.
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Using fracture grouting to lift structures in clayey sand
James C. Ni, Wen-chieh Cheng
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2010, 11(11): 879-886.
https://doi.org/10.1631/jzus.A0900748
An inclined seven-story reinforced concrete building was leveled by a fracture grouting technique with quick-setting grout on a differential thickness of a clayey sand layer. The permeability and strength of clayey sand were controlled by clay content, although sand was the primary component of the foundation soil. The elevations of the building columns at basement level were closely monitored to record both the heaved volume of mat foundation after grouting and the settled volume during pore pressure dissipation. During the stabilizing stage of grouting, the foundation soil was densified by the repetitive fracturing process, which resulted in the lateral movement of the foundation soil. When the grout is less able to push soil laterally than upwards, the building starts to lift, the so-called lifting stage of grouting. The grouting efficiency is influenced by soil type, soil stress history, and foundation pressure. A final grouting efficiency of 27% and a linear relationship between grout use and percentage of elevation were obtained when this building was successfully and permanently leveled.
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Numerical analysis of pipeline in J-lay problem
Li-zhong Wang, Feng Yuan, Zhen Guo, Ling-ling Li
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2010, 11(11): 908-920.
https://doi.org/10.1631/jzus.A0900773
The pipe configuration and internal loads along the pipeline during the pipeline laying process have long been the focus of engineers. Most researchers simplify the seabed to be rigid and the water to be calm, ignoring the pipe embedment into the seabed and the influence of ocean currents. In this paper, a novel numerical approach is proposed for the laying of pipelines in the so-called J-lay method, taking into account the importance of both pipe embedment and ocean currents. The pipeline is divided into two parts, one part suspended in water, and the other laid on the seabed. The continuity of the two parts at the touch down point (TDP) is guaranteed to make a whole. The feasibility of the model is proved by the comparison between the present model and an analytical model, which shows good agreement in both pipeline configuration and bending moment distribution. Finally, parametric study was performed to consider the influence of current velocity, water depth, top inclination angle, and seabed stiffness, and conclusions are drawn.
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8 articles
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