吸交法提取柠檬酸主要工艺参数的优化

通过单因素试验研究了柠檬酸流速、硫酸流速、硫酸浓度对吸交法提取柠檬酸的影响，并采用正交试验对提取工艺进行优化。结果表明，柠檬酸收率的主要影响因素及其顺序为：硫酸浓度〉柠檬酸流速〉硫酸流速；最佳工艺参数为：柠檬酸流速3．5mL／min，硫酸流速2．5mL／min，硫酸浓度20％，此条件下柠檬酸收率达85％。

吸交法提取柠檬酸新工艺简介

天津轻工业学院食品工程系有机酸研究组从1990年开始试验“吸交法”提取柠檬酸新工艺,在四川万县飞亚公司,连云港发酵厂等许多厂家的大力支持与协助下,经过无数次试验,攻克了一道道难题,取得了小试的初步结果,于1996年在连云港发酵厂进行了中试。充分证明该工艺的特点:比“钙盐法”

减少CO_2排放的柠檬酸生产新工艺

从柠檬酸发酵液中提取柠檬酸的提取工艺直接影响到产品的产量与质量,本文简单叙述了一种新的柠檬酸提取方法,与传统"钙盐法"比较,它具有回收率高、环境污染少、经济效益显著等特点。这项新技术将成为从发酵液中分离提取柠檬酸的清洁生产工艺。

Determination of Exchangeable Ca and Mg Contents in Tobacco Growing Area by Atomic Absorption Spectrometry

[Objective] A method for the determination of exchangeable Ca and Mg contents in tobacco growing area by atomic absorption spectrometry was established. [Method] Factors in the extraction process, sample weight, ammonium acetate volume, extraction time and strontium chloride volume were tested, and the stability, precision and accuracy of the method were also investigated. Meanwhile, samples at different pH values were determined by this method. [Result] The results showed that this method operation has simple operation with good stability and high precision. [Conclusion] This method could be applied to determine exchangeable Ca and Mg contents in tobacco growing area.

Wave field forward modeling and theoretical analysis of weakness in discrete media

The elasticity, viscosity, and the relationships derived from rheology weakness properties are taken into account in mechanics. Comparing with the corresponding relationships derived from damage mechanics, we find the weakness factor has the same significance as the damage factor. We simulate the wave field using a staggered-grid pseudospectral method to show the influence of the weakness factor qualitatively. Applying the analytical solution of plane waves, we give the velocity and attenuation coefficient of three body waves, which are affected by the wave frequency and the weakness factor of saturated discrete media. Our results show that velocity decreases with increasing weakness factor, the attenuation coefficient increases with an increase in the weakness factor, and that the influence of weakness depends on the mode of the body waves.

Three Measurement Methods of Two-photon Absorption Cross-section

Through the experimental design and theoretical analysis, three technologies used for characterizing the two-photon absorption(TPA) properties, such as nonlinear transmission experiment and theory, Z-scan technology and two-photon induced fluorescence method, are introduced. The properties of the three experiments to be utilizable and realizable under desirable limitation are simply analyzed. The advantages of the measurements for TPA characterization are also analyzed.

Arsenic Removal from Pinctada martensii Enzymatic Hydrolysate by Using Zr(Ⅳ)-Loaded Chelating Resin

The present study investigated the removal of inorganic arsenic from Pinctada martensii enzymatic hydrolysate through unmodified resin （D296） and Zr（IV）-loaded chelating resin （Zr-D401）. By loading Zr to macroporous chelating resin D401, the as exchange adsorption active sites are generated. This transforms D401 from a material that does not have the arsenic adsorption capacity into a material that has excellent arsenic exchange adsorption capacity. The static adsorption experiments were conducted to investigate the optimal removal condition for D296 and Zr-D401. The experimental results show that： the optimum condition for D296 is that T= 25℃, pH= 5, resin additive amount= 1 g （50 mL）-1, and contact time = 10 h, the corresponding arsenic removal rate being 65.7%, and protein loss being 2.33%; the optimum condition for Zr-D401 is that T=25 ℃, pH = 8, resin additive amount= 1 g （50 mL）-1, and contact time=10 h, the corresponding arsenic removal rate being 70.3%, and protein loss being 4.65%. These results show that both of the two resins are effective in arsenic removal for preserving useful substance. Our research provides scientific evidence and advances in the processing technology for heavy metal removal in shellfish.

ISOLATION AND PURIFICATION OF ALKALOIDS FROM PLUMULA NELUMBINIS BY DOUBLE-COLUMN ADSORPTION CHROMOTOGRAPHY

The performance of adsorption and separation for liensinine, isoliensinine and neferine was studied by double-column adsorption chromatography using macroporous adsorption and cation exchange resins. The alkaloid extract with 49.2% total contents by mass representing 10.6% liensinine, 10.6% isoliensinine and 28.0% neferine respectively was prepared by D72 cation exchange resins, in which most of the impurities were water-soluble alkaloids. Furthermore,the alkaloid extract with 82.6% total contents by mass containing 33.1%, 15.0% and 34.5% of the three adsorbates respectively was prepared by double-column adsorption chromatography using AKS-W macroporous adsorption and D72 cation exchange resins. As a result, the content of single and total alkaloids has been greatly increased by the double-column adsorption chromatography.

Understanding the Effect of the Exchange-Correlation Functionals on Methane and Ethane Formation over Ruthenium Catalysts

Density functional theory(DFT)has been established as a powerful research tool for heterogeneous catalysis research in obtaining key thermodynamic and/or kinetic parameters like adsorption energies,enthalpies of reaction,activation barriers,and rate constants.Understanding of density functional exchangecorrelation approximations is essential to reveal the mechanism and performance of a catalyst.In the present work,we reported the influence of six exchange-correlation density functionals,including PBE,RPBE,BEEF+vdW,optB86b+vdW,SCAN,and SCAN+rVV10,on the adsorption energies,reaction energies and activation barriers of carbon hydrogenation and carbon-carbon couplings during the formation of methane and ethane over Ru(0001)and Ru(1011)surfaces.We found the calculated reaction energies are strongly dependent on exchange-correlation density functionals due to the difference in coordination number between reactants and products on surfaces.The deviation of the calculated elementary reaction energies can be accumulated to a large value for chemical reaction involving multiple steps and vary considerably with different exchange-correlation density functionals calculations.The different exchange-correlation density functionals are found to influence considerably the selectivity of Ru(0001)surface for methane,ethylene,and ethane formation determined by the adsorption energies of intermediates involved.However,the influence on the barriers of the elementary surface reactions and the structural sensitivity of Ru(0001)and Ru(1011)are modest.Our work highlights the limitation of exchange-correlation density functionals on computational catalysis and the importance of choosing a proper exchange-correlation density functional in correctly evaluating the activity and selectivity of a catalyst.

Modeling seismic wave propagation in a coal-bearing porous medium by a staggered-grid finite difference method

A staggered-grid finite difference method is used to model seismic wave records in a coal bearing, porous medium. The variables analyzed include the order of the difference calculations, the use of a perfect match layer to provide absorbing boundary conditions, the source location, the stability conditions, and dispersion in the medium. The results show that the location of the first derivative of the dynamic variable with respect to space is coincident with the location of the first derivative of the kinematic varable with respect to time. Outgoing waves are effectively absorbed and reflection at the boundary is very weak when more than 20 perfect match layer cells are used. Blot theory considers the liquid phase to be homogeneous so the ratio of liquid to solid exposure of the seismic source depends upon the medium porosity. Numerical dispersion and generation of false frequencies is reduced by increasing the accuracy of the difference calculations and by reducing the grid size and time step. Temporal second order accuracy, a tenth order spatial accuracy, and a wavelength over more than ten grid points gave acceptable numerical results. Larger grid step sizes in the lateral direction and smaller grid sizes in the vertical direction allow control of dispersion when the medium is a low speed body. This provides a useful way to simulate seismic waves in a porous coal bearing medium.

Compact Thermosyphon Heat Exchanger for Power Electronics Cooling

The heat losses density in power electronics products follows an ever increasing trend. Nowadays they reach 200 W/cmz at chip level and 50 W/cm2 at heatsink base level. Water cooling is the most effective cooling method but unfortunately water is often undesired due to high voltages or costumer requirements. Two-phase cooling is a promising technology for electronics cooling. It allows using dielectric fluids in passive systems and still benefits from very high heat transfer coefficients. Thermosyphons are a particularly interesting technology in the field of power electronics because it is entirely passive and a simple equipment. ABB has developed a compact thermosyphon heat exchanger based on automotive technology, which uses numerous multi-port extruded tubes with capillary sized channels disposed in parallel and brazed to a heated base plate in order to achieve the desired compactness. The experimental performances of this novel power electronics cooling system are presented with R134a as a working fluid. The influence of several parameters on the performances was studied experimentally： coolant flow rate, coolant temperature, heat load and fluid filling.

Contamination,Fractionation and Availability of Metals in Urban Soils in the Vicinity of Former Lead and Zinc Smelters,France

Soil contamination by metals from anthropogenic activities （e.g., mining and smelting） is a major concern for the environment and human health. Environmental availability of cadmium （Cd）, lead （Pb）, zinc （Zn）, copper （Cu）, and indium （In） in 27 urban soils located around two former Pb and Zn smelters in Northern France were studied by analysing the chemical forms of these metals and evaluating their phytoavailability. These metals were determined using flame or electrothermal absorption atomic spectrometry （FAAS or ETAAS）, depending on their concentration levels. After optimisation of the ETAAS method, characteristic mass of In in water and aqua regia were 9.9 and 18 pg, respectively, showing the high sensitivity of the analytical procedure. Metal partitioning was conducted using a four-step sequential extraction procedure. The results showed that Cd and Zn were mainly in the acid-extractable and reducible forms in the urban soils studied. In contrast, Pb and In were largely in the reducible fraction. However, in some samples, the amount of In extracted in the residual or exchangeable fraction was higher than that in the reducible fraction. Copper was mainly found in the reducible and residual fractions. A pot experiment was conducted in a glasshouse with seven soils （six contaminated and one uncontaminated） and two plant species, ryegrass and lettuce. The results showed transfer of metals from the contaminated soils to the shoots of ryegrass and the edible part of lettuce. The metal bioconcentration factor was in the order of Cd 〉〉 Cu 〉 In 〉 Zn 〉〉 Pb for lettuce leaves, whereas for ryegrass shoots, three orders were found, Cd 〉 Zn 〉 Cu 〉〉 In 〉 Pb, Cd 〉〉 In 〉 Zn 〉 Cu 〉〉Pb, and Zn 〉 Cd 〉 Cu 〉 In 〉〉 Pb, depending on the physico-chemical properties of the soils, such as pH, cation exchange capacity, carbonates, and organic matter. It was established that the metal toxicity was related to the contamination levels and the physico-chemical properties, including pH, organic matter, and in a lesser extent, Ca, Mg, and phosphorus contents, of the soils. However, it was shown that lettuce could grow on soils having high Cd and CaCO3 contents. Cadmium was one of the most available metals while Pb was always the least available in the soils studied.