Prediction of mass transfer coefficients in an asymmetric rotating disk contactor using effective diffusivity

Mass transfer characteristics have been investigated in a 113 mm diameter asymmetric rotating disk contactor of the pilot plant scale for two different liquid–liquid systems. The effects of operating parameters including rotor speed and continuous and dispersed phase velocities on the volumetric overall mass transfer coefficients are investigated. The results show that the mass transfer performance is strongly dependent on agitation rate and interfacial tension, but only slightly dependent on phase flow rates. In this study, effective diffusivity is used instead of molecular diffusivity in the Gr?ber equation for estimation of dispersed phase overall mass transfer coefficient.The enhancement factor is determined experimentally and there from an empirical expression is derived for prediction of the enhancement factor as a function of Reynolds number. The predicted results compared to the experimental data show that the proposed correlation can efficiently predict the overall mass transfer coefficients in asymmetric rotating disk contactors.     

非泡沫气泡分离法回收青霉素生产废水中的乙酸丁酯

Two nonfoaming bubble separation techniques, air stripping and solvent sublation, are presented and discussed in order to recover butyl acetate (BA) from discharged wastewater after solvent extraction of penicillin. Results show air stripping is not suitable for the recovery of BA from the wastewater. Axial concentration of BA had a noted maximum point along the column. In contrast, solvent sublation is very effective to recover BA from the wastewater. In solvent sublation experiments, axial concentration of BA along the column first increased and then decreased from the bottom to the top because of two primary mass transport processes. One is the transport by adsorption or attachment to ascending bubbles, and the other is by dispersion at water-solvent interface and by water film in organic solvent layer. In order to elucidate the high removal efficiency in solvent sublation, the microstructure of the wastewater was studied with optic microscope, which was showed to be an emulsion of BA in water at large concentration of BA. Solvent sublation can be successfully used in the removal of BA from its emulsion in the wastewater. The surface tension of simulated solution composed of lysozyme and BA was studied to understand mutual effect of biological materials and BA. Results show that lysozyme affects the adsorption of BA at air-water interface and they may form a complex between BA and lysozyme molecules.     

蒸发鼓泡塔反应器的轴向分散模型

Evaporating bubble column reactor (EBCR) is a kind of aerated reactor in which the reaction heat is removed by the evaporation of volatile reaction mixture. In this paper, a mathematical model that accounts for the gas-liquid exothermic reaction and axial dispersions of both gas and liquid phase is employed to study the performance of EBCR for the process of p-xylene(PX) oxidation. The computational results show that there are remarkable concentration and temperature gradients in EBCR for high ratio of height to diameter (H/DT). The temperature is lower at the bottom of column and higher at the top, due to rapid evaporation induced by the feed gas near the bottom. The concentration profiles in the gas phase are more nonuniform than those (except PX) in the liquid phase, which causes more solvent burning consumption at high H/DT ratio. For p-xylene oxidation, theo ptimal H/DT is around 5.     

空气在二甲基硅油和液压油中扩散系数的测量

A piston-cylinder apparatus was established to measure the solubility and diffusivity of air in dimethyl silicone oils and in hydraulic oils based on the PVT state equation of air and the solution of unsteady one-dimensional diffusion equation. The measured diffusivity-temperature relation can be well fitted by the Arrhenius equation for engineering applications. The correlation between the solute diffusivity D and solvent viscosity  is examined. In terms of Eyring’s activation theory, the activation in the air-silicone-oil diffusion process is quite different from that in the momentum transport of the silicone oil: the activation entropy of the former is positive while that of latter is negative. However, the activation enthalpies of the two processes are in the same order of magnitude, which leads to the observation that D/T is roughly constant.     

表面活性剂双水相分离茶多酚生产废液中的茶氨酸(英文)

Extraction of theanine from waste liquid of tea polyphenol production was studied in aqueous surfactant two-phase system (ASTP) with cationic surfactant (CTAB) and anionic surfactant (SDS). Results indicate that the region of ASTP is narrow and there is only a two-phase region of cationic surfactant. The increase in concentrations of NaBr and Na2SO4 are beneficial to the formation of ASTP. Theanine concentration in the bottom phase increases with increasing concentration of theanine, whereas the partition coefficient and extraction rate only change a little when the concentration of theanine is above 0.2 g·L-1 . With the increase of SDS concentration, the phase ratio and the partition coefficient decrease, while the extraction efficiency of theanine increases and the concentration of theanine changes a little in the range from 2.4/7.5 to 2.8/7.2 for SDS/CTAB ratio. The temperature has a notable effect on the concentration of theanine in the bottom phase, partition coefficient and extraction rate of theanine. The increase of waste liquid decreases the phase ratio, increases the concentration and extraction rate of theanine in the bottom phase, since the protein and the saccharide enter the bottom phase with theanine.     

Spray coating of polysulfone/poly(ethylene glycol) block polymer on macroporous substrates followed by selective swelling for composite ultrafiltration membranes

Polysulfone(PSF) is extensively used for the production of ultrafiltration(UF) membranes thanks to its high strength,chemical stability,and good processibility.However,PSF is intrinsically hydrophobic,and hydrophilic modification is always required to PSF-based membranes if they are intended to be used in aqueous systems.Facile strategies to prepare hydrophilic PSF membranes are thus highly demanded.Herein we spray coat a PSF-based amphiphilic block polymer onto macroporous substrates followed by selective swelling to prepare flat-sheet PSF UF membranes.The polymer is a triblock polymer containing PSF as the majority middle block tethered with shorter block of polyethylene glycol(PEG) on both ends,that is,PEG-b-PSF-b-PEG.We use the technique of spray coa ting to homogeneously dispense diluted triblock polymer solutions on the top of macroporous supports,instantly resulting in uniform,defect-free polymer coating layers with the thickness down to ～1.2 μm.The bi-layered composite structures are then immerged in ethanol/acetone mixture to generate mesoscale pores in the coating layers following the mechanism of selective swelling-induced pore generation,thus producing composite membranes with the mesoporous triblock polymer coating as the selective layers.This facile strategy is free from additional hydrophilic modification and much smaller dosages of polymers are used compared to conventional casting methods.The pore sizes,porositie s,hydrophilicity,and consequently the separation properties of the membranes can be flexibly tuned by changing the swelling duration and the composition of the swelling bath.This strategy combining spray coating and selective swelling is upscalable for the production of highperformance PSF UF membranes.     

丁酸在含氯化钙双水相体系中的有效分离(英文)

One of the bottlenecks for bioproduction of butyric acid as bulk chemical is the difficulty in separating butyric acid from the fermentation broth,compared with the petroleum-based chemical synthesis method.In the present work,a novel separation methodology was developed based on an aqueous two-phase system with inor-ganic salts.Calcium chloride was screened out for effective separation of butyric acid from butyric acid-water-salt systems.Within appropriate concentration range of butyric acid and salt,butyric acid was enriched in the upper phase and most of calcium ions remained in the lower phase.This"salting out"effect is very efficient to separate butyric acid from the simulated butyrate fermentation broth,which consists of butyric acid and acetic acid with concentration ratio of 4︰1,so that the final ratio of butyric acid/acetic acid in the upper phase is improved to 9.87. The aqueous two-phase system was used to separate butyric acid from the actual fermentation broth with satisfac-tory result.     

Preparation and Properties of Sintered Corundum at Low Temperatures with Nano-η-Al_2O_3 Powder

In order to reduce the sintering temperature and improve the properties of sintered corundum, corundum specimens were prepared by granulation and sintering with nano-η-Al_2O_3 as the raw material and polyvinyl alcohol as the binder. The effects of different sintering temperatures(1 550, 1 600, 1 650 and 1 700 ℃) and holding time(2, 4 and 6 h) on the properties and microstructures of the specimens were studied, and the transformation mechanism of η-Al_2O_3 was analyzed. The results show that dense sintered corundum with bulk density of 3.74 g/cm~3 and apparent porosity of 1.77% is obtained by calcinating at 1 650 ℃ for 6 h; the phase transition from η-Al_2O_3 to α-Al_2O_3 occurs first on the surface of alumina particles and then diffuses rapidly to the interior; at lower sintering temperatures there is no abnormal growth of crystals, the bonding between the grains is tight, transgranular fracture is the main fracture mode, there are fewer intergranular pores, and the grain size is in the range of 3.5-7.5 μm.     

APPLICATION OF “VAPOR-PHASE RESISTANCE METHOD” TO THE STUDY ON CONDENSATION IN HORIZONTAL TUBES

A physical model and a mathematical model were established in order to describe and improve the“vapor-phase resistance method” of Bell and Ghaly.Considering the effect of ripples at the interface onvapor-phase resistance,a correction factor v_ι was proposed.Another factor (θ/π)β which correctsthe influence of the liquid pool along the bottom of the horizontal tube on the liquid-phase heat transfercoefficient was derived and the relationship of θ and β was correlated.The heat transfer coefficient pre-dicted by Bell's method are approximately 10—15% lower than the experimental values if the effect ofripples on vapor-phase resistance has not been taken into account.The comparison of the predicted valuesof h_c from the modified vapor-phase resistance method with the experimental data showed a deviation of±10%.     

Optimization of Compressed Ceramics Fiber Insulating Layers

Compressed thin layers of ceramic fiber insulation are used as high temperature insulating layers as well as mechanical support for catalyst coated ceramic monoliths in automotive emission control devices.Minimization of energy losses,choice of material and thickness of compressed insulating layer are based on knowledge of their thermal physical properties.Currently,consistent measurements of materials in a compressed state, as they would be in emission control applications,are absent due to the absence of suitable methods for such tests.A test method was developed for measurement of the thermal conductivity of compressed thin fiber layers.This paper summarizes the results of thermal conductivity and diffusivity measurements of 27 compressed fiber alumina- silica- vermiculite materials in the range of 200- 950 ℃.Thermal physical properties as a function of temperature,density / mechanical pressure,thickness and composition of insulating layers are presented.The whole set of experimental data is generalized on 3D surface plots and described by polynomial functions.The possible heat transfer mechanisms governing apparent thermal conductivity of pressed insulation layers are discussed.     

Investigation and Modeling of Growth,Structure and Oxygen Penetration in Particle Supported Biofilms

Particle supported biofilms have been investigated with respect to biofilm formation, substrate transport and utilization. The investigated autotrophic and heterotrophic biofilms were cultivated in airlift suspension reactors. CLSM was used to describe the biofilm structure by recording volumes of bacteria and EPS glycoconjugates. Additionally, the microelectrode technique was used to measure transport and substrate utilization in the biofilm system. The experimental results on the microscopic scale were used to improve a mathematical model for biofilm growth. The oxygen profiles measured in the particle supported biofilms and the data from CLSM were used to optimize the model parameters.     

Effect of Unfired Tape Porosity on Surface Film Formation by Dip Coating

Thin ceramic layers have been fabricated by dipping green tapes of alumina, formed by the doctor-blade casting method, into aqueous slurries containing mixtures of alumina and either unstabilized zirconia (MZ–ZrO₂) or mullite. It was observed that the formation of a thin layer on the surface of the tape is governed by both liquid entrainment and slip-casting mechanisms, and was accelerated by increasing the withdrawal rate, immersion time, or volume fraction of solids in the slurry used for dip coating. By modifying these parameters, layers as thin as 2 μm and as thick as 108 μm were easily formed. Layer formation was found to be strongly influenced by the structure of the tape surface. Layers formed on the top surface of the tape were found to be as much as 48% thicker than those formed on the bottom surface. This difference appears to be related to the smaller amount of porosity on the bottom surface of the tape. Evidence suggests that the polymer binder, used for doctor-blade casting, concentrated on the bottom of the tape as evaporation occurred from the top surface. The lower porosity on the bottom reduced the casting rate during dip coating and produced significantly thinner layers, relative to the top surface.     

Modeling mass transport and microbial activity in stratified biofilms

The most recent mathematical models of microbial activity in heterogeneous biofilms are based on cellular automata. The main weakness of these models is that to obtain numerical solutions the operator must specify the rules governing microbial cell behaviour in the biofilm, and these rules are difficult to establish experimentally. To avoid this difficulty, we have used an alternative approach, discretizing biofilms into layers, to include the effects of biofilm heterogeneity on biofilm activity. This procedure conceptually converts heterogeneous biofilms into a stack of stratified layers of various densities, activities, and diffusivities, and can include some effects of biofilm heterogeneity, e.g vertical distribution of biofilm density, activity, and effective diffusivity. We present this model and selected examples of computational procedures illustrating it. We found that the activity of homogeneous biofilms can be lower, higher, or equal to the activity of stratified biofilms; since homogeneous biofilms do not exist, their properties have to be assumed. As expected, the model predicts that the growth-limiting nutrient penetrates deeper into stratified biofilms than it does into homogeneous biofilms.     

Biofilm Structure and Extracellular Polymeric Substances in Low and High Dissolved Oxygen Membrane Bioreactors

Abstract

This paper discusses the effect of dissolved oxygen (DO) on the biofilm structure in membrane bioreactor (MBR) and their consequence on membrane permeability and EPS. Two MBRs under high DO (6.0 mg/L, HDO) and low DO (<0.1 mg/L, LDO) were operated in parallel under same hydrodynamic conditions. The microbiological aspects in MBR systems were explored through a series of analysis techniques including PCR‐DGGE, gel filtration chromatography (GFC), confocal laser scanning microscope (CLSM), and image analysis.

The rate of membrane fouling for the LDO MBR was 5 times faster than that for the HDO MBR. The microbial communities between HDO and LDO MBR were quite different, which is likely to be the reason for different structures and permeabilities of the biofilms. The specific biofilm resistance in HDO MBR was lower to that in LDO MBR. This is attributed to relatively lower porosity and higher amount of EPS for the biofilm in LDO MBR. The distributions of cell and EPS were not uniform in the biofilms in both HDO and LDO MBR. The biofilm in LDO MBR contained larger amount of EPS than that in HDO MBR. The ratio of protein to polysaccharide was also higher for biofilm in HDO MBR than in LDO MBR.     

SEBS三嵌段共聚物膜的形态研究

Surface morphologies of the films of poly [styrene-b-（ethylene-co-butene）-b-styrene] （SEBS） have been studied by using tapping-mode atomic force microscopy （TM-AFM）. The films of block copolymer were prepared both by spin-coating on mica and by solvent-casting on different solution surfaces. For spin-coating samples, the effect of solution concentration, solvent, and annealing temperature are investigated. It is shown that changing the concentration of the solution makes no difference on the morphology of the film of the block copolymer. The microstructures are quite stable during thermal annealing; only the size of the domains changes toward the equilibrium configuration. However, solvent annealing can notably change the microstructures. When different selective solvents are used for film spin-coating, different morphologies can be obtained and explained by the different solubility parameters of the solvents. As expected, significant different morphologies in the top and the bottom surfaces of the casting films were observed. The images of the top surfaces reveal cylinder microdomains, while those of the bottom surfaces were spherical morphologies.     

Effect of zirconia tape porosity on fluorapatite surface film formation by dip coating

Thin fluorapatite (FA) layers on porous 3 mol% yttria-partially stabilized zirconia (Y-PSZ) substrates have been fabricated by dipping porous zirconia tapes into aqueous 27.4 vol% fluorapatite slurries. Two porous Y-PSZ tapes with different volume fraction of porosity were developed using an acrylic latex binder: tapes with 31.4 vol% porosity were prepared using 16.6 vol% starch as fugitive additive and those with 12.7 vol% porosity were fabricated without starch. The influence of the porous structure of the tape surfaces, top and bottom, on the casting rate and consequently on the layer thickness formed on each surface was studied. Layers formed on the top and bottom surfaces of the tapes with 12.7 and 31.4 vol% porosity were compared. The formation of a thin layer on the surface of the tape was governed by both liquid entrainment and slip casting mechanisms. The data for the FA layer formation were in good agreement with the slip casting model for immersion times>0. The casting rate at the top surface of both tapes was greater than that at the bottom surface. This difference was attributed to a greater porosity of the top surface with respect to that of the bottom one and was more pronounced for the tapes prepared with starch. Layers formed on the top surface were found to be about 55 and 32% thicker than those formed on the bottom surface for the tapes fabricated with and without starch, respectively. For the tapes prepared with starch, the greater porosity and number of smaller pores in the matrix of the top surface increased the casting rate and produced the thickest dip coated layers     

Influence of extracellular polymeric substances on microbial activity and cell hydrophobicity in biofilms

BACKGROUND: Over the last few decades, the emphasis in studies on extracellular polymeric substances (EPS) has been on the extraction and quantitative analysis methods relating to activated sludge. However, little is currently known about the relationship between EPS and microbial activity and cell hydrophobicity in heterogeneous biofilms. This paper aims to reveal the relationship between them. RESULTS: Experimental results indicated that EPS content and components varied with depth in the aerobic biofilter. Protein was the main component of EPS at all depths within the biofilter, and the ratio of protein to polysaccharide was higher in the upper media than that in the lower media. Most active biomass was present in the bottom 25% of the biofilter near the inlet. By means of repeatedly washing intact cells, a sharp decline of EPS content of washed cells was obtained, while active biomass rarely decreased. Microbial activity as well as cell hydrophobicity at different filter depths decreased with the decline of EPS. CONCLUSION: Results indicated that EPS on cell surfaces are essential for microbial metabolism as well as for the formation and stability of biofilm, and it is possible to take EPS into consideration for biofilter control and microbial activity assessment. Copyright © 2007 Society of Chemical Industry     

自养、异养和混合营养污泥沉降性能差异原因探讨

本研究建立了3个有效容积为4.2L的有机玻璃材料反应器,培养驯化自养、异养和混合营养3种不同营养类型的活性污泥.通过分析3种不同营养类型污泥沉降性能的差异,旨在找出造成3种污泥沉降性能差异的微观原因,为改善污泥的沉降性能提供新的途径和理论依据.研究结果表明,自养污泥沉降性能最好,混合营养污泥次之,异养污泥最差;污泥的粒径对沉降性能无明显影响;Zeta电位和相对疏水性是造成3种污泥沉降性能差异的重要表面理化性质,Zeta电位值越接近于0,相对疏水性越强,污泥沉降性能越好;污泥胞外聚合物(EPS)中腐殖酸和多糖含量对污泥表面Zeta电位、相对疏水性和污泥沉降性能无明显影响;EPS中蛋白质含量直接影响Zeta电位值,进而造成3种污泥污泥沉降性能差异;而EPS总量和3种污泥沉降性能没有明显相关性.     

A vibrating membrane bioreactor (VMBR): Macromolecular transmission—influence of extracellular polymeric substances

The vibrating membrane bioreactor (VMBR) system facilitates the possibility of conducting a separation of macromolecules (BSA) from larger biological components (yeast cells) with a relatively high and stable macromolecular transmission at sub-critical flux. This is not possible to achieve for a static non-vibrating membrane module. A BSA transmission of 74% has been measured in the separation of 4 g/L BSA from 8 g/L dry weight yeast cells in suspension at sub-critical flux . However, this transmission is lower than the 85% BSA transmission measured for at pure 4 g/L BSA solution. This can be ascribed to the presence of extracellular polymeric substances (EPS) from the yeast cells. The initial fouling rate for constant sub-critical flux filtration of unwashed yeast cells is 3-4 times larger than for washed yeast cells . At sub-critical flux, an EPS transmission of around 32% is measured for a pure yeast cell suspension. Thus, EPS and BSA are “competing” in being transmitted which might explain the lowered BSA transmission in the presence of yeast cells. Additionally, EPS heavily foul the membranes, leading to a 86% permeability drop and a fouling resistance 6 times larger than the membrane resistance after 5  h of constant sub-critical flux filtration of pure 8 g/L dry weight yeast cell suspensions. Thus, the addition of hydraulic resistance caused by EPS might also explain the lowered BSA transmission, in the presence of yeast cells, since the membrane pores might be narrowed or partly blocked. EPS is, furthermore, able to cause a relatively large permeability drop even on a membrane module pre-fouled by EPS.     

6.25m捣固焦炉分层捣固技术的应用

将传统的捣固方式设计为7层捣固,使煤饼的堆密度成塔形分布,并根据每层捣固功和下煤量的不同进行调试,使每层煤饼的堆密度和捣固功由下而上逐层递减,每层煤间成叠压交汇,使单炉捣固时间达到420s,提高操作效率20%,塌饼率从10%～20%降至0,入炉煤水分从14%降至12%,提高了煤饼的抗剪力强度,同时改善了焦饼的高向加热。