A computational method for determination of the mass-transfer coefficient in packed-bed immobilized enzyme reactors

A computational method was developed that determined the mass-transfer coefficient k_L or the volumetric mass-transfer coefficient k_La in packed-bed immobilized enzyme (IME) reactors. To study the performance of this method, two experimental systems were considered where an enzyme was immobilized on a non-porous support surface (surface-IME system) or within a porous support (pore-IME system). The values of k_L and k_La determined in these packed-bed IME reactor systems were successfully expressed in terms of the substrate concentration at the reactor inlet and the liquid flow rate. Furthermore, the correlations obtained for k_L and k_La were used to calculate the unconverted fractions of substrate at the reactor outlet. Comparison showed that the calculated results were in satisfactory agreement with the experimental values.     

Structure and composition of surface depletion layers in poled aluminosilicate glasses

Thermal poling processes can be used to form modified surface layers on glass that, under ion-blocking electrode conditions, are depleted of virtually all network-modifying cations relative to the network-forming species. During this process, many outstanding questions remain as to the structure of these layers and how it may vary between glasses of different “parent” composition, with important implications for resultant surface properties and industrial applications of this technology. This phenomenon of depleting modifiers is particularly difficult to rationalize in aluminosilicate glass compositions, where—in the parent glass—aluminum ions are predominantly present as cation-charge-compensated [AlO4]⁻ tetrahedra prior to poling. Here, we present results of a detailed investigation into the surface depletion layers formed across a wide range of ternary sodium aluminosilicate (NAS) glasses, applying a host of surface-sensitive spectroscopy methods to directly interrogate the resulting composition and structure within the Na-depleted, anode-side surface layers. The desired depletion layers were successfully formed on all of the NAS glasses attempted, all showing (a) near-complete depletion of alkali within 300-500 nm-thick layers on the anode-side surfaces, (b) thin zones of Al depletion with the Na-depleted layer, and (c) the absence of injected H⁺ ions that could serve as an alternative charge-compensation mechanism. These data essentially confirmed a true binary Al₂O₃–SiO₂ composition inside the depletion layers. However, no significant structural dependence was found as a function of parent glass, where initial compositions ranged from peralkaline to charge-balanced. Importantly, TEM imaging showed the depletion layers to be fully amorphous and homogeneous (not phase-separated) at the nanoscale, despite final compositions in the range of 5-33 mol% Al₂O₃—a composition space notoriously prone to phase-separation if prepared by conventional melting. Within the depletion layers, ELNES and TEY-XANES evidence is shown for retention of Al in a 4-coordinated state, along with XPS data indicating elimination of non-bridging oxygen. Taken as a whole, our results indicate a highly-connected aluminosilicate network, most likely with a relatively high concentration of 3-coordinated oxygen—or O “triclusters”—as a plausible means of charge-compensating 4-coordinated Al in the absence of Na⁺ or H⁺. The combined results of this work provide convincing new evidence for unique glass structures within the depletion layers not achievable through analogous melt pathways, with important implications for surface properties.     

Tubes with coated and sintered porous surface for highly efficient heat exchangers

Surface modification is a direct and effective way to enhance the efficiency of heat exchangers. Surface modification by forming a microporous coated layer can greatly enhance the boiling heat transfer and thus achieve a high performance. In this paper, we systematically investigate the boiling behavior on a plain surface with/without sintered microporous coatings of copper powder. The results demonstrated that the sintered surface has a better performance in nucleate boiling due to the increased nucleation sites. The superheat degree is lower and the bubble departure diameter is larger for the sintered surface than for the plain surface, so the heat can be carried away more efficiently on the sintered surface. In addition, the heat transfer capacity on the sintered surface depends on both the powder size and the coating thickness for a high flux tube. The optimum heat transfer capacity can be obtained when the thickness of the microporous coating layer is 3–5 times of the sintered powder diameter. As a result, the heat transfer coefficient tube can be up to 3 times higher for the tube with a sintered surface than that with a plain surface, showing a pronounced enhancement in heat transfer and a high potential in chemical engineering industry application.

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Factors influencing the stability of a novel enzyme immobilisation support – colloidal liquid aphrons (CLAs)

A key factor in the immobilisation of enzymes is the stability of the support. An investigation was carried out on the stability of colloidal liquid aphrons (CLAs) in dilute dispersion, looking particularly at the effects of process parameters and CLA composition. CLAs were formulated from a Softanol 30/decane solvent phase and sodium dodecyl sulfate (SDS)/β‐galactosidase aqueous phase. The aim of this work was to gain an understanding of the mechanisms stabilising CLAs, and to characterise the effects of process parameters on stability such that the knowledge gained could be used in the design of a membrane bioreactor. CLA stability was measured using a light scattering technique (defined by a first order CLA half‐life). It was proposed that CLA break‐up occurred by the collision of CLAs with sufficient energy to overcome the forces stabilising the CLAs. Stability was found not to be dependent on the bulk aqueous phase ionic strength, but increasing the concentration of the ionic surfactant increased stability, indicating that stability was influenced by charge repulsion. Stability was also found to increase for increasing enzyme (β‐galactosidase) concentration, indicating steric interactions and elastic effects were also important. Finally, the effect of process parameters (reactor temperature, CLA concentration and circulation velocity) were assessed, and their effect was explained in terms of their influence on collision energy and the activation energy necessary for CLA break‐up; increasing CLA concentration was found to improve stability considerably. © 2000 Society of Chemical Industry     

Optimisation of polyacrylamide gel composition as support for enzyme immobilisation by covalent linking

A methodology based on experimental design to optimise a polyacrylamide gel as the support for enzyme immobilisation by covalent linking is described. A proper selection of the variables responsible for the gel structure, the amount of the linking agent, the support enzyme and suitable synthesis conditions lead to an increase in the activity retained by the gel. The maximum retained activity is chosen with the response surface methodology in terms of gel composition. © 2000 Society of Chemical Industry     

Structure,biocompatibility and corrosion resistance of the ceramic-metal surface of porous nitinol

One of the key aspects of the biochemical compatibility of medical alloys is the surface corrosion resistance in living organisms. This study discusses the structure of the ceramic-metal surface layer of a porous nickel-titanium alloy (nitinol) and the corrosion resistance in simulated physiological liquids. The structure of the protective layer and glass-ceramic non-metallic inclusions in the surface of the porous alloy have been studied. The formation of the surface ceramic-metal layer and crystallization of various glass-metal-ceramic phases as a result of chemisorption from reaction gases and epitaxial growth from the gas phase during the self-propagating high-temperature synthesis are observed.     

浅谈钢结构表面处理处理的粗糙度

对钢结构防腐技术的研究表明：涂装前表面处理质量对涂层寿命（即防腐蚀效果）的影响最大。文章介绍了表面处理中对清洁度和粗糙度的要求,尤其就粗糙度的概念、作用、控制、评定等若干问题提出看法,供同行参考。     

Preparation of porous polymeric structures for enzyme immobilization

Porous polymethacrylic acid‐co‐triethylene glycol dimethacrylate (MAA‐co‐3G) and polyacrylic acid‐co‐triethylene glycol dimethacrylate (AA‐co‐3G) were prepared by four different polymerization techniques, namely, suspension, dispersion, seed, and microemulsion polymerization using an inert diluent (n‐hexane and polystyrene). The morphology and porosity of the obtained polymers were examined by means of a scanning electron microscope. The surface areas of the obtained polymers were determined colorimetrically. The copolymers were modified by hydroximation and chlorination using hydroxyl amine and thionyl chloride, respectively. The effect of polymerization type, surface area, modification, and pH on the protease enzyme immobilization over poly(MAA‐co‐3G) and poly(AA‐co‐3G) was examined. The enzyme activity was measured by means of a spectrophotometer. The reactivity ratios of the two monomers MAA and 3G were determined by means of the elemental analysis method. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 594–601, 2000     

钢结构表面处理标准和质量评定

论述了钢结构表面缺陷评定和处理等级、钢结构表面油脂清理,清洁度和粗糙度的评定标准以及可溶性盐分的测试标准.     

Tuning of strain and surface roughness of porous silicon layers for higher-quality seeds for epitaxial growth

Sintered porous silicon is a well-known seed for homo-epitaxy that enables fabricating transferrable monocrystalline foils. The crystalline quality of these foils depends on the surface roughness and the strain of this porous seed, which should both be minimized. In order to provide guidelines for an optimum foil growth, we present a systematic investigation of the impact of the thickness of this seed and of its sintering time prior to epitaxial growth on strain and surface roughness. Strain and surface roughness were monitored in monolayers and double layers with different porosities as a function of seed thickness and of sintering time by high-resolution X-ray diffraction and profilometry, respectively. Unexpectedly, we found that strain in double and monolayers evolves in opposite ways with respect to layer thickness. This suggests that an interaction between layers in multiple stacks is to be considered. We also found that if higher seed thickness and longer annealing time are to be preferred to minimize the strain in double layers, the opposite is required to achieve smoother layers. The impact of these two parameters may be explained by considering the morphological evolution of the pores upon sintering and, in particular, the disappearance of interconnections between the porous seed and the bulk as well as the enlargement of pores near the surface. An optimum epitaxial growth hence calls for a trade-off in seed thickness and annealing time, between minimum-strained layers and rougher surfaces.

PACS codes

81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties; 81.05.Rm Porous materials; granular materials; 82.80.Ej X-ray, Mössbauer and other γ-ray spectroscopic analysis methods     

Investigation of the surface area and polarity of porous copolymers of maleic anhydride and divinylbezene

Porous copolymers of maleic anhydride (MA) and divinylbezene (DVB) in the form of regular microspheres were prepared by suspension polymerization. During copolymerization the mixture of 1,4-dioxane and n-dodecane as a pore-forming diluent was used. It was found that specific surface area of the obtained beads is strongly dependent on the diluent system and polymerization medium and achieves a value from 4 to 535 m²/g. To determine the influence of polymerization medium on the selectivity and polarity of the copolymers, inverse gas chromatography (IGC) was applied. To determine these parameters, three procedures were applied: overall polarity, the selectivity triangle, and the ΔC method. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

A novel method for continuous production of cyclodextrins using an immobilized enzyme system

Selected specific α-amylase and glucoamylase enzymes were immobilized and combined with immobilized cyclodextrin glycosyltransferase to continuously produce cyclodextrin (CD). The liquefied starch was cyclized to CD by ICGTase and then treated by immobilized α-amylase and glucoamylase to contain CD and glucose only. β-CD and soluble CD (α- and γ-CD) in the final CD solution could be easily separated. The pH-activity curve, temperature-activity curve, batch re-usability and continuous operation stability of immobilized enzymes were discussed. The continuous production of CD by an immobilized enzyme system was also reported. The optimal conditions for using immobilized α-amylase and glucoamylase simultaneously were 40°C and pH 4.5 adjusted by 1 mol dm^?3 HCl/NaOH. A 70% yield of CD could be obtained from 1% (w/v) of liquefied starch under continuous operation at 0.055 h^?1 space velocity, and almost all the oligosaccharides (β 98%) were converted to glucose. In this study, the separation of α-CD, γ-CD and glucose, using organic solvent from the final product after precipitating β-CD, was also investigated.     

Simulations of the surfaces of soda lime aluminoborosilicate glasses exposed to water

Molecular dynamics simulations of 7 compositionally different sodium calcium alumino‐borosilicate glasses showed formation of ⁴B and ⁵Al more consistent with experimental data without compromising the other structural features that match experimental results observed in recent simulations of these glasses. Analysis of the dry surfaces of these glasses show a lack of ⁴B in the top 5‐6 Å of the surface in comparison to the bulk concentration for all glasses and no ⁵Al. Upon exposure to water, the simulations show that the ³B in the top 5‐6 Å of the glasses are preferentially attacked, decreasing the number of B bonds to O originally from the glass, indicating a change in the glass network. Inclusion of all B–O bonds in the top 5‐6 Å (i.e., including O from water) shows a decrease in ³B but an increase in ⁴B that is consistent with NEXAFS analysis, which the simulations show are hydroxylated. There is an increase in the concentration of ³Al in the dry surface in comparison to the bulk, but exposure to water converts almost all of these ³Al to ⁴Al. Hydroxyl concentrations vary from 2.6/nm² to 4.1/nm², with SiOH and BOH dominating these surface hydroxyls. Upon exposure to water, network linkages to B are preferentially ruptured. This, and the preferential loss of the nonbridging oxygen sites attached to Na, provide atomistic evidence of the initial stages of removal of B and Na from glass surfaces exposed to water.     

An online acquisition method for monitoring the surface growth of flame retardant protective layers

This paper describes the development of a video acquisition system aimed at monitoring the surface growth of flame‐retarded polymers during flammability and combustion tests. The system minimizes the disturbances of the flames on the image sensors, thus gathering a video of the material surface. The device continuously records and quantitatively measures the carbonization front growth rate. The apparatus consists of a camera with customized lighting and dedicated software acquiring images of the burning specimen. The UL94 test procedure has been used during the development of the device and as test bed for the apparatus. Copyright © 2015 John Wiley & Sons, Ltd.     

等离子体优化修饰技术在固定化酶载体材料中的应用进展

运用等离子体聚合或表面处理技术改变载体材料的表面性质,进而固定酶蛋白的方法主要有4类:等离子体表面处理、等离子体聚合、等离子体接枝共聚和等离子体化学气相沉积。综述了近年来用等离子体优化修饰技术处理载体材料进行固定化酶研究的新进展,指出今后应加强等离子体体系表面改性规律及机理、等离子体单体气体种类、放电条件及底衬材料等方面的研究。     

具有多级孔道结构的高比表面多孔炭活化策略及VOCs吸附性能

以废弃榛壳为前体,采用不同活化策略制备多孔炭,探究活化策略和活化温度对多孔炭挥发性有机化合物（VOCs）吸附性能的影响,以及多孔炭的结构、表面性质与VOCs吸附性能的构效关系。结果表明,H₃PO₄法制备的多孔炭介孔体积大,且炭结构缺陷较少,吸附位点较少; KOH法获得的微孔体积较大,孔径集中在0.5~0.7nm的微孔,不利于VOCs分子吸附位点的有效利用。H₃PO₄-KOH分步法在850℃下制备具有高比表面积,孔径集中在0.5~1nm的宽微介孔分布,且炭结构高度无序并含有丰富缺陷位的多孔炭,为VOCs吸附提供了充足的吸附位点并提高了吸附位点了利用率,相比于H₃PO₄与KOH活化法制备的多孔炭的VOCs饱和吸附量显著提升,特别是对于弱极性VOCs。另外,H₃PO₄-KOH分步法制备的多孔炭表面官能团含量较低,极性较低,对非极性VOCs的吸附量远大于极性VOCs。因此,H₃PO₄-KOH分步活化策略是制备具有高比表面积、高VOCs吸附性能多孔炭的最优策略与方案。     

镁合金激光表面处理技术

镁合金激光表面处理能改变表面合金成分,细化表面晶粒,从而提高合金的耐腐蚀和耐磨擦性能.本文介绍了镁合金激光熔融、镁合金激光表面合金化和激光熔覆技术,总结了镁合金激光表面处理技术的基本原则,指出了激光表面处理技术的发展前景.     

Optimization of growth medium for the production of α‐amylase from Bacillus amyloliquefaciens using response surface methodology

The optimization of nutrient levels for the production of α‐amylase by Bacillus amyloliquefaciens was carried out using response surface methodology (RSM) based on the 2³ factorial central composite design (CCD). This procedure limited the number of actual experiments performed while allowing for possible interactions between three components. RSM was adopted to derive a statistical model for the effect of starch, peptone and yeast extract (YE) on α‐amylase production. The P‐value of the coefficient for linear effects of starch and YE concentration was <0.0001, suggesting that this was the principal experimental variable, having the greatest effect on the production of α‐amylase. The optimal combinations of media constituents for maximum α‐amylase production were determined as 12.61 g L^?1 starch, 2.83 g L^?1 peptone and 1.25 g L^?1 YE. The optimization of the medium resulted not only in a 34% higher enzyme activity than unoptimized medium but also in a reduced amount of the required medium constituents. Copyright © 2006 Society of Chemical Industry     

大豆粕加压酸解工艺及其产物表面活性的研究

实验研究了加压酸解下大豆粕新溶解工艺,其较佳反应条件为:硫酸质量分数为20%,反应时间为20 min,温度(压强)为110℃(0.104 5 MPa),液料质量比为10。通过对大豆粕溶解液表面活性的测试可知其表面活性较好。