Mixing time is defined as the time required for achieving a certain degree of homogeneity of injected tracer in a unit operation vessel. It has been used as a key parameter for assessing the performance of amixing system. From an experimental standpoint, several techniques have been developed for measuring the mixing time. Based on the disturbances to flow, they can be classified into two groups: non-intrusive and intrusive. However, depending on the type of data generated, they can be also classified into direct measurements and indirect measurements (Eulerian and Lagrangian). Since the techniques available for measuring mixing times in an agitated tank do not provide the same information, its choice depends on several factors, namely: accuracy, reproducibility, suitability, cost, sampling speed, type of data, and processing time. A review of the experimental techniques reported in the literature in the last 50 years for themeasurement of mixing time in stirred vessels under single and gas-liquid flowconditions with Newtonian and non-Newtonian fluids in the laminar and turbulent regimeis made, and a comparison between these techniques is also presented.

Solid concentration and particle velocity distributions in the transition section of a ? 200mm turbulent fluidized bed (TFB) and a ? 200mm annulus turbulent fluidized bed (A-TFB)with a ? 50mm central standpipewere measured using a PV6D optical probe. It is concluded that in turbulent regime, the axial distribution of solid concentration in A-TFB was similar to that in TFB, but the former had a shorter transition section. The axial solid concentration distribution, probability density, and power spectral distributions revealed that the standpipe hindered the turbulence of gas-solid two-phase flowat a lowsuperficial gas velocity. Consequently, the bottomflow of A-TFB approached the bubbling fluidization pattern. By contrast, the standpipe facilitated the turbulence at a high superficial gas velocity, thus making the bottom flow of A-TFB approach the fast fluidization pattern. Both the particle velocity and solid concentration distribution presented a unimodal distribution in A-TFB and TFB. However, the standpipe at a high gas velocity and in the transition or dilute phase section significantly affected the radial distribution of flow parameters, presenting a bimodal distribution with particle concentration higher near the internal and external walls and in downward flow. Conversely, particle concentration in the middle annulus area was lower, and particles flowed upward. This result indicated that the standpipe destroyed the coreannular structure of TFB in the transition and dilute phase sections at a high gas velocity and also improved the particle distribution of TFB. In conclusion, the standpipe improved the fluidization quality and flow homogeneity at high gas velocity and in the transition or dilute phase section, but caused opposite phenomena at low gas velocity and in the dense-phase section.

Separation process undertaken in packed columns often displays anisotropic turbulentmass diffusion. The anisotropic turbulent mass diffusion can be characterized rigorously by using the Reynolds mass flux (RMF) model. With the RMF model, the concentration and temperature as well as the velocity distributions can be simulated numerically. Themodeled Reynolds mass flux equation is adopted to close the turbulent mass transfer equation, while themodeled Reynolds heat flux and Reynolds stress equations are used to close the turbulent heat and momentum transfer equations, so that the Boussinesq postulate and the isotropic assumption are abandoned. To validate the presented RMF model, simulation is carried out for CO₂ absorption into aqueous NaOH solutions in a packed column (0.1 m id, packed with 12.7 mm Berl saddles up to a height of 6.55 m). The simulated results are comparedwith the experimental data and satisfactory agreement is found both in concentration and temperature distributions. The sequel Part II extends the model application to the simulation of an unsteady state adsorption process in a packed column.

In order to evaluate the effects of the short blade locations on the anti-cavitation performance of the splitterbladed inducer and the pump, 5 inducerswith different short blade locations are designed. Cavitation simulations and experimental tests of the pumpswith these inducers are carried out. The algebraic slip mixture model in the CFX software is adopted for cavitation simulation. The results showthat there is a vortex at the inlet of the inducer. Asymmetric cavitation on the inducer and on the impeller is observed. The analysis shows that the short blade locations have a minor effect on the internal flow field in the inducer and on the external performance of the pump, but have a significant effect on the anti-cavitation performance. It is suggested that the inducer should be designed appropriately. The present simulations found an optimal inducer with better anti-cavitation performance.

As a newkind of 2D nanomaterials, graphene oxide (GO)with 2-4 layerswas fabricated viaamodified Hummers method and used for the preparation of pervaporation (PV) membranes. Such GO membranes were prepared via a facile vacuum-assisted method on anodic aluminiumoxide disks and applied for the dehydration of butanol. To obtain GO membranes with high performance, effects of pre-treatments, including high-speed centrifugal treatment of GO dispersion and thermal treatment of GO membranes, were investigated. In addition, effects of operation conditions on the performance of GO membranes in the PV process and the stability of GO membranes were also studied. It is of benefit to improve the selectivity of GO membrane by pre-treatment that centrifuges the GO dispersion with 10000 r·min^-1 for 40 min, which could purify the GO dispersion by removing the large size GO sheets. As prepared GO membrane showed high separation performance for the butanol/water system. The separation factor was 230, and the permeability was as high as 3.1 kg·m^-2·h^-1 when the PV temperature was 50 ℃ and the water content in feed was 10% (by mass). Meanwhile, the membrane still showed good stability for the dehydration of butanol after running for 1800 min in the PV process. GO membranes are suitable candidates for butanol dehydration via PV process.

4-Tert-butyl-2-(α-methylbenzyl) phenol (t-BAMBP)was used in cyclohexane in the extraction of rubidiumfrom brine sources containing lithium. The effect of t-BAMBP concentration and aqueous phase pH on the rubidium and lithium extraction equilibrium was studied. t-BAMBP/cyclohexane was efficient and selective for rubidium extraction with optimal operating conditions being pH of 13.0 and initial t-BAMBP concentration of 1.0 mol·L^-1. The stoichiometry of the complex of t-BAMBP with rubidium is 4:1. The apparent extraction equilibrium constant of rubidium was calculated by fitting the experimental data.

NaA zeolite membranes were prepared by secondary growth method on the outer surface of α-Al₂O₃ hollow fiber supports. Vacuum seeding method was used for planting zeolite seeds on the support surfaces. Hydrothermal crystallization was then carried out in a synthesis solution with molar ratio of Al₂O₃:SiO₂:Na₂O:H₂O = 1:2:2:120 at 100 ℃ for 4 h. Effects of seeding conditions on preparation of hollow fiber NaA zeolite membranes were extensively investigated. Moreover, hollow fiber membrane modules with packing membrane areas of ca. 0.1 and 0.2 m² were fabricated to separate ethanol/water mixture. It is found that the thickness of seed layer is obviously affected by seed suspension concentration, coating time and vacuum degree. Close-packing seed layer is required to obtain high-quality membranes. The optimized seeding conditions (seed suspension mass concentration of 0.5%-0.7%, coating time of 5 s and vacuum degree of 10 kPa) lead to dense NaA zeolite layer with a thickness of 6-8 μm. Typically, an as-synthesized hollow fiber NaA zeolite membrane exhibits good pervaporation performance with a permeation flux of 7.02 kg·m^-2·h^-1 and separation factor >10000 for separation of 90% (by mass) ethanol/water mixture at 75 ℃. High reproducibility has been achieved for batch-scale production of hollow fiber NaA zeolite membranes by the hydrothermal synthesis approach.

Synthesizing epichlorohydrin (ECH) from dichloropropanol (DCP) is a complicated reaction due to the partial decomposition of ECH under harsh conditions. A microchemical system can provide a feasible platform for improving this process by conducting a separation once full conversion has been achieved. In thiswork, referring to a common DCP feed used in industry, the reaction performance of mixed DCP isomers with NaOH in the microchemical systemon various time scaleswas investigated. The operating windowfor achieving high conversion and selectivity was on a time scale of seconds, while the side reactions normally occurred on a time scale of minutes. Plenty of Cl^- ions togetherwith a high temperaturewere proved to be critical factors for ECHhydrolysis. A kinetic study of alkaline mediated ECH hydrolysis was performed and the requirements for an improved ECH synthesis were proposed by combining quantitative analysis using a simplified reaction model with experimental results on the time scale of minutes. Comparedwith the conventional distillation process, this new strategy for ECH synthesis exploited microchemical system and decoupled the reaction and separation with potentials of higher productivity and better reliability in scaling up.

Silver modified HZSM-5 (AgHZ) zeolite catalysts were prepared by ion exchange method and their catalytic properties in the 1-butene cracking reaction were measured. The catalysts were characterized by infrared spectroscopy with pyridine adsorption (Py-IR), N₂ adsorption and X-ray diffraction (XRD). The effects of Ag loading and steaming treatment on catalytic performances were studied. It is found that the activity of HZSM-5 (HZ) catalyst significantly decreases with the steaming time,whereas AgHZ catalysts show stable activity in the steaming time of 24-48 h and their activities increase with the Ag loading.When the steaming time is 24-48 h, the yield of propylene over HZ catalyst significantly decreases, whereas it is stable over AgHZ catalysts. The AgHZ catalysts with Ag loadings of 0.28%-0.43% (by mass) show similar propylene yields (~30%), which are higher than that over the AgHZ catalyst with a Ag loading of 0.55% (by mass). These results indicate that the steam-treated AgHZ catalysts with optimum Ag loadings have higher yield of propylene and are more stable than the steamtreated HZ catalyst. The regeneration stability measurement in butene cracking also shows that the AgHZ catalyst steam-treated under a suitable condition has better stability than the HZ catalyst.

Gas-phase dehydration of glycerol to produce acrolein was investigated over commercial catalysts based on γ-Al₂O₃, viz. A-64, A-56, I-62, AP-10, AP-56, AP-64 and KR-104. To understand the effect of Cl^- anions, HCl-impregnated supports have been investigated in the dehydration reaction of glycerol at 375 ℃. For comparison, various H-zeolites were also examined. It was found that the glycerol conversion over the solid acid catalysts was strongly dependent on their acidity and surface area. And the relationship between the catalytic activity and the acidity of the catalysts was discussed. The outstanding properties of Pt/γ-Al₂O₃ catalyst systems for the dehydration of glycerol were revealed. Pt/γ-Al₂O₃ catalyst (AP-64) showed the highest catalytic activity after 50 h of reaction with an acrolein selectivity of 65% at a conversion of glycerol of 90%. Based on these results, catalysts based on γ-Al₂O₃ appear to be most promising for gas phase dehydration of glycerol.

A reaction coupling system of transesterification and methoxycarbonylation with methyl phenyl carbonate (MPC) as intermediate was established to efficiently prepare 1,6-hexamethylene diurethane (HDU) from 1,6-hexamethylene diamine (HDA). The feasibility of the system was explored using the thermodynamics analysis, the reaction mechanism and the experiment results. The optimal reaction was carried out to get higher HDU yield. The thermodynamic analysis showed that the methoxycarbonylation of HDA with MPC, the Gibbs free energy of which was negative, was a spontaneous process. Furthermore, the equilibrium constant of the methoxycarbonylation of HDA with MPC was much greater than that of the transesterification of dimethyl carbonate (DMC) with phenol, so the reaction coupling could be realized under mild conditions. The reaction mechanismanalysis indicated that phenoxy anion was the key species for reaction coupling. HigherMPC concentration was detected when sodium phenoxide was used as transesterification reactant with DMC, since the phenoxy anion of sodium phenoxide could be dissociated more easily. Sodium phenoxide was more suitable to prepare HDU through reaction coupling. A yield of HDU as high as 98.3% could be reached under the optimal conditions of m_PhONa/m_DMC = 0.027 and n_DMC/n_HDA = 8/1 at 90 ℃ in 2 h.

Multi-period heat exchanger network (HEN) retrofit is usually performed by targeting and matching heat transfer areas. In this paper, based on the reverse order matching method we proposed previously, three strategies of matching heat transfer areas are proposed to minimize the investment cost for the retrofit of HEN in multiperiod, in which replacement of heat exchangers, addition of heat exchangers and addition of heat transfer areas are performed. We demonstrate the procedures through three scenarios, including maximum number of substituted heat exchangers after retrofit, minimum additional heat transfer areas in the retrofitted HEN, and minimum investment cost for retrofit. The strategies are extended to a single period HEN retrofit problem. The results of multi-period and single period HEN retrofit problems indicate the effectiveness of the strategies. Moreover, these results are better than those reported in literature. The strategies are simple and easy to implement, which are of great benefit to large-scale HEN retrofit in practice.

A conduction heat transfer process is enhanced by filling prescribed quantity and optimized-shaped high thermal conductivity materials to the substrate. Numerical simulations and analyses are performed on a volume to point conduction problem based on the principle of minimum entropy generation. In the optimization, the arrangement of high thermal conductivity materials is variable, the quantity of high thermal-conductivity material is constrained, and the objective is to obtain the maximum heat conduction rate as the entropy is the minimum. A novel algorithm of thermal conductivity discretization is proposed based on large quantity of calculations. Compared with other algorithms in literature, the average temperature in the substrate by the new algorithm is lower, while the highest temperature in the substrate is in a reasonable range. Thus the new algorithm is feasible. The optimization of volume to point heat conduction is carried out in a rectangular model with radiation boundary condition and constant surface temperature boundary condition. The results demonstrate that the algorithm of thermal conductivity discretization is applicable for volume to point heat conduction problems.

A rigorous approach is proposed to model the mean ion activity coefficient for strong electrolyte systems using the Poisson-Boltzmann equation. An effective screening radius similar to the Debye decay length is introduced to define the local composition and new boundary conditions for the central ion. The crystallographic ion size is also considered in the activity coefficient expressions derived and non-electrostatic contributions are neglected. Themodel is presented for aqueous strong electrolytes and compared with the classical Debye-Hückel (DH) limiting lawfor dilute solutions. The radial distribution function is compared with the DH andMonte Carlo studies. Themean ion activity coefficients are calculated for 1:1 aqueous solutions containing strong electrolytes composed of alkali halides. The individual ion activity coefficients andmean ion activity coefficients in mixed solvents are predicted with the new equations.

Foaming reduces the working volume and limits the biosynthesis of macrolide immunosuppressant ascomycin (FK520) in the batch fermentation process of Streptomyces hygroscopicus FS-35 in a 7.5 L bioreactor. To find the relation between FK520 production and foaming, effects of 10 fermentation parameters including organic acids and membrane permeability were investigated. The results suggest that acetate accumulation caused by short period oxygen deficiency and fast consumption of glucose is the reason for increased foaming and declined FK520 production. Therefore, a fed-batch fermentation strategywas developed to reduce the accumulation of acetate. After optimization, the maximum acetate concentration dropped from 320 mg·L^-1 to 157 mg·L^-1, decreased by 50.8%, and the maximum foam height reduced from 5.32 cm to 3.74 cm, decreased by 29.7%, while the maximum FK520 production increased from 375 mg·L^-1 to 421 mg·L^-1, improved by 12%.

Mortierella alpina has been considered as the most effective producer of arachidonic acid (ARA)-rich oil. It was found that several methods could improve the percentage of ARA in total lipids successfully, as they activated the desaturation system on the endoplasmic reticulum. Additionally, in M. alpina the ARA exists in several forms, such as triacylglycerol (TAG), and diacylglycerol (DAG). These forms are caused by different acyltransferases and they determine the nutrient value of the microbial oil. However, few works revealed detailed fatty acid distribution among lipid classes, which to some extent impeded the accurate regulation in ARA accumulation. Herein, this paper gives information on the accumulation process of main lipid classes and the changes of fatty acid composition in these lipids during ARA accumulation period inM. alpina. The result demonstrates that TAG was the dominant component of the total lipids, and it is the main form for ARA storage. The ARA enrichment stage occurred during 168-192 h when the amount of total lipids maintained steady. Further analysis indicated that the newly formed ARA-TAG might come from the incorporation and modification of saturated and monounsaturated fatty acids in other lipid classes. This work could be helpful for further optimization of ARA-rich TAG production.

Five elephant grass cultivars, Pennisetum purpureum. cv. Huanan (Huanan), P. purpureum. cv. N51 (N51), P. purpureum. cv. Sumu No. 2 (Sumu-2), (Pennisetum americanum × P. purpureum) × P. purpureum cv. Guimu No. 1 (Guimu-1) and P. americanumcv. Tift23A × P. purpureum cv. Tift N51 (Hybrid Pennisetum), at three harvest stages were studied. With dilute sulfuric acid pretreatment followed by enzymatic hydrolysis, it is found that cellulose conversion of the five elephant grass cultivars harvested in August and September is higher than that harvested in October. The cellulose conversion for elephant grass cultivars harvested in August and September follows an order of Hybrid Pennisetum> Sumu-2> Huanan> Guimu-1> N51. This may be explained by the fact that lignification is gradually strengthened with time, inhibiting degradation of cellulose and hemicellulose. Moreover, cellulose conversions of Hybrid Pennisetum, Sumu-2 and Huanan harvested in August and September are higher based on hierarchical clustering results.

In order to enhance the biodecolorization rate and avoid the wash-out problems of redox mediators in continuous systems such as a fluidized bed reactor, polyvinyl alcohol (PVA) beads modified with Ncontaining function groups were investigated and employed as a new sodium anthraquinone-2-sulfonate (AQS) carrier material. Elementary and XPS analyses confirmthe existence of AQS on modified PVA bead. The modified PVA beads suit with immobilizing AQS better in adsorption capability and stability. AQS supported on modified PVA beads shows high catalytic activity for biodecolorization of reactive blue 13 in a long process (> 10 runs).

Superhydrophilic surfaces were fabricated on copper substrates by an electrochemical deposition and sintering process. Superhydrophobic surfaces were prepared by constructing micro/nano-structure on copper substrates through an electrochemical deposition method. Conversion fromsuperhydrophobic to superhydrophilic was obtained via a suitable sintering process. After reduction sintering, the contact angle of the superhydrophilic surfaces changed from 155° to 0°. The scanning electron microscope (SEM) images show that the morphology of superhydrophobic and superhydrophilic surfaces looks like corals and cells respectively. The chemical composition and crystal structure of these surfaceswere examined using energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The results show that the main components on superhydrophobic surfaces are Cu, Cu₂O and CuO, while the superhydrophilic surfaces are composed of Cu merely. The crystal structure is more inerratic and the grain size becomes bigger after the sintering. The interfacial strength of the superhydrophilic surfaces was investigated, showing that the interfacial strength between superhydrophilic layer and copper substrate is considerably high.

Pt-Ru, Pt and Ru catalysts supported on zirconia were prepared by impregnation method and were tested in selective oxidation of methylamine (MA) in aqueous media. Among three catalysts, Ru/ZrO₂ wasmore active than Pt/ZrO₂ while Pt-Ru/ZrO₂ demonstrated the best catalytic activity due to the fact that Pt addition efficiently promoted the dispersion of active species in bimetallic catalyst. Therefore, the ~100% TOC conversion and N₂ selectivity were achieved over Pt-Ru/ZrO₂, Pt/ZrO₂ and Ru/ZrO₂ catalysts at 190, 220 and 250 ℃, respectively.

The steam-gasification reaction characteristics of coal and petroleumcoke (PC)were studied in the drop tube furnace (DTF). The effects of various factors such as types of carbonaceous material, gasification temperature (1100-1400 ℃) and mass ratio of steam to char (0.4:1, 0.6:1 and 1:1 separately) on gasification gas or solid products were investigated. The results showed that for all carbonaceous materials studied, H₂ content exhibited the largest part of gasification gaseous products and CH₄ had the smallest part. For the two petroleum cokes, CO₂ content was higher than CO, which was similar to Zun-yi char.When the steam/char ratio was constant, the carbon conversion of both Shen-fu and PC chars increased with increasing temperature. When the gasification temperature was constant, the carbon conversions of all char samples increased with increasing steam/char ratio. For all the steam/char ratios, compared to water gas shift reaction, char-H₂O and char-CO₂ reaction were further from the thermodynamic equilibrium due to a much lower char gasification rate than that of water gas shift reaction rate. Therefore, kinetic effects may play a more important role in a char gasification step than thermodynamic effects when the gasification reaction of char was held in DTF. The calculating method for the equilibrium shift in this studywill be aworth reference for analysis of the gaseous components in industrial gasifier. The reactivity of residual cokes decreased and the crystal layer (L₀₀₂/d₀₀₂) numbers of residual cokes increased with increasing gasification temperature. Therefore, L₀₀₂/d₀₀₂, the carbon crystallite structure parameter, can be used to evaluate the reactivity of residual cokes.

A system consisting of a two-stage up-flow anaerobic sludge blanket (UASB) reactor and an anoxic/aerobic (A/O) reactor was used to treat municipal landfill leachate. Denitrification took place in the first stage of the UASB reactor (UASB1). The chemical oxygen demand of the UASB1 effluent was further decreased in the second stage (UASB2). Nitrification was accomplished in the A/O reactor. When diluted with tap water at a ratio of 1:1, the ammonia nitrogen concentration of the influent leachate was approximately 1200 mg·L^-1, whereas that of the system effluent was approximately 8-11 mg·L^-1, and the corresponding removal efficiency is about 99.08%. Stable partial nitrification was achieved in the A/O reactor with 88.61%-91.58% of the nitrite accumulation ratio, even at comparatively low temperature (16 ℃). The results demonstrate that free ammonia (FA) concentrations within a suitable range exhibit a positive effect on partial nitrification. In this experiment when FA was within the 1-30 mg·L^-1 range, partial nitrification could be achieved, whereas when FA exceeded 280 mg·L^-1, the nitrification process was entirely inhibited. Temperature was not the key factor leading to partial nitrificationwithin the 16-29 ℃ range. The inhibitory influence of free nitrous acid (FNA) on nitrification was also minimal when pH was greater than 8.5. Thus, FA concentration was a major factor in achieving partial nitrification.

Ni-Fe/Cu/Co/Cu multilayered nanowire arrays were electrodeposited into anodic aluminum oxide template by using dual-bath method at room temperature. Scanning electron microscopy and transmission electron microscopy were used to characterize the morphology and structure of the multilayered nanowire arrays. Vibrating sample magnetometer and physical property measurement system were used to measure their magnetic and giant magnetoresistance (GMR) properties. The effect of sub-layer thickness on the magnetic and GMR properties was investigated. The results indicate that magnetic properties of electrodeposited nanowires are not affected obviously by Cu layer thickness, while magnetic layers (Ni-Fe and Co layers) have significant influence. In addition, GMR ratio presents an oscillatory behavior as Cu layer thickness changes. The magnetic and GMR properties of the multilayered nanowire arrays are optimum at room temperature for the material structure of Ni-Fe (25 nm)/Cu (15 nm)/Co (25 nm)/Cu (15 nm) with 30 deposition cycles.

In this work, we evaluate the properties of solution casted polysulfone (PSf)/sulfonated polyethersulfone (SPES) blend membranes prepared by non-solvent induced phase inversion technique. The morphologies of these blend membranes, observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM) imaging, indicated a smoother skin layer and an increased number of highly interconnected pores in the sub layer. The efficacy of the prepared membranes was evaluated in terms of porosity, ultrafiltration rate (UFR), molecular weight cut-off (MWCO) and mean pore size. The hydrophilicity of these membranes was in consonance with contact angle values. It was observed that the selectivity and the UFR of the blend membranes were higher when compared to pristine membranes. Furthermore, these blend membranes demonstrated an increase in biocompatibility—prolonged blood clotting time, suppressed platelet adhesion, reduced protein adsorption and lower complement activation. These membranes were also investigated for uremic solute removal. Diffusive permeability of middle molecular weight cytochrome-c revealed an increase from 8 × 10^-4 cm·s^-1 to 18 × 10^-4 cm·s^-1 and illustrates the possibility that these sulfonated PES/PSf blend membranes can be used to prepare membrane modules for hemodialysis applications.