New correlation for liquid hold-up of sodium citrate buffer solution in a Raschig ring packed column

Dynamic liquid hold-up was measured with an air/aqueous sodium citrate buffer solution at 20–40 °C, and an air/water system at 23 °C, in a 0.1 m diameter/1 m high glass column covered by a heat-isolating vacuum jacket and packed with 0.012 m nominal size ceramic Raschig rings. The superficial gas velocity range was extended to 1.2 m s⁻¹. Experimental results of this work were compared with literature data, with different correlations and with a general equation. All expressions were found to be unacceptable for the air/buffer system and useable for the air/water system. In the case of the air/buffer solution a new correlation is recommended on the basis of our measured data and literature values.     

Liquid holdup determination in packed columns for sulfur dioxide absorption

Total, static and dynamic holdups have been measured for 0.012 m ceramic Raschig rings with air rates from 0 to 700 kg m⁻² h⁻¹ and sodium citrate solution rates from 2000 to 60 000 kg m⁻² h⁻¹ at 40°C using the draining method. Equations presented for estimating holdups are discussed.     

Local solid mixing in gas–solid fluidized beds

Diffusivity of the solid particles in a 152-mm ID gas–solid fluidized bed was determined at different regimes of fluidization. The gas was air at room temperature and atmospheric pressure and the solids were 385 μm sand or 70 μm FCC particles. The experiments were done at superficial gas velocities from 0.5 to 2.8 m/s for sand and 0.44 to 0.9 m/s for FCC (in both bubbling and turbulent regimes). Movement of a tracer was monitored by radioactive particle tracking (RPT) technique. Once the time-position data became available, local axial and radial diffusivity of solids were calculated from these data. Calculated diffusivities are in the range of 3.3×10⁻³ to 5.6×10⁻² m²/s for axial and 2.6×10⁻⁴ to 1.5×10⁻³ m²/s for radial direction. The results show that the diffusivities, both axial and radial, increase with superficial gas velocity and are linearly correlated to the axial solid velocity gradient. Solid diffusivity in a bed of FCC was found to be higher than that of a bed of sand at the same excess superficial gas velocity.     

Preparation of ZnO-glass composite hollow fiber and its application in formation of ZIF-8 membrane

The sintering temperature of ZnO ceramic hollow fibers (HFs) is generally up to 1400°C and presents a major challenge to obtain HFs with high permeability and mechanical strength at lower sintering temperature. This work proposed a glass powder-assisted method to reduce the sintering temperature by using their adhesive property. ZnO-glass composite HFs with longer finger-like channels, high permeability (3.12 × 10⁻⁵–9.1 × 10⁻⁶ mol·m⁻²·s⁻¹·Pa⁻¹) and good mechanical strength (42.12–52.75 MPa) were obtained at sintering temperature of 1150°C. More glass powders can generate stronger bonding effect during the ZnO particles, resulting in a decrease in porosity and an increase in the mechanical strength of ZnO-HF. These ZnO-HFs were further applied for inducing ZIF-8 membranes by one-step solvothermal growth. ZnO not only provides the growth and nucleation centers but also acts as transitional bridge to make the ZIF embed into support to improve the bonding force between membrane and support. Therefore, HF-supported-ZIF-8 membrane exhibited both mechanical and thermal robustness by maintaining their gas separation performance during the 30-min sonication treatment and 50-h operation testing at 25–200°C. Furthermore, this membrane provided good reproducibility. This work opens prospects for preparing ceramic HFs at lower sintering temperature and their functional applications as well as the preparation of MOF membranes.     

Enzyme mass transfer coefficient in aqueous two phase system using a packed extraction column

Fractional dispersed phase hold-up and dispersed side mass transfer coefficients for amyloglucosidase were measured in a 56 mm i.d. packed extraction column using a sodium sulphate-polyethylene glycol 4000 system. Raschig rings (3 to 13.3 mm), Berl saddles (12 mm), Pall rings (12.6 mm), glass spheres (5.2 mm) and structured wire gauze were used as packings. The effect of packing size was investigated in the case of ceramic Raschig rings. The effect of phase composition of the aqueous phase system also was studied. Correlations have been developed for fractional dispersed phase hold-up and volumetric mass transfer coefficient with packing voidage, dry surface area of packings, superficial dispersed phase velocity and the liquid phase physical properties.     

Effect of B-site substitution on the luminescence,thermal stability and temperature sensitivity of Ba2NaNb5O15:Eu3+/Er3+ glass ceramics

Transparent glass ceramic with Ba₂NaNb₅O₁₅ as the main crystal phase was prepared, and the appropriate heat treatment condition was selected as 710 °C/150 min through various characterizations. The luminous intensity and thermal stability were enhanced significantly when the glass ceramic was used as the luminous matrix. After introducing Ti⁴⁺ ions as charge compensators, the luminescence performance and thermal stability were further improved, and the reasons for this were analyzed. At 458 K, the luminous intensity of 0.5%Eu³⁺ doped glass ceramic containing 0.5%Ti⁴⁺ can maintain about 65% of room temperature with a chromaticity shift of 5.16 × 10⁻². The relative and absolute sensitivities of 0.7%Er³⁺ doped glass ceramic were 4.04 × 10⁻³ K⁻¹ and 1.31% K⁻¹. Introducing Ti⁴⁺ ions would weaken the population redistribution ability of ²H_11/2 and ⁴S_3/2 levels and reduce the temperature sensitivity. However, the sample containing Ti⁴⁺ shows good thermal stability, its green emission at 458 K has a small chromaticity shift of 6.45 × 10⁻³. The research shows that the glass ceramic can be used as a good luminescent host material, and Eu³⁺/Er³⁺ doped glass ceramic can be used in the fields of LEDs or temperature sensing.     

Faraday Glasses with a Large Size and High Performance

A kind of Faraday glass with a size of Φ40 mm × 14 mm and Φ100–300 mm × 25 mm, respectively, was prepared by the melting and casting process, which had neither a Pt particulate nor a bubble or striation. The measurement results showed that the surface homogeneity of the samples was up to ± 1 × 10⁻⁶, the laser threshold reached 10 J/cm² (1ω, 3 ns), and the Verdet constants of the glasses were −0.273 min/Oe/cm at 632.8 nm and −0.076 min/Oe/cm at 1064 nm, respectively.     

The ablation behavior and mechanical property of C/C-SiC-ZrB2 composites fabricated by reactive melt infiltration

In order to improve the ablation resistance of carbon/carbon (C/C) composites, SiC-ZrB₂ di-phase ceramic were introduced by reactive melt infiltration. The ablation properties of these composites were evaluated by oxyacetylene torch with a heat flux of 2.38 MW/m² for 60 s. Compared with the pure C/C composites, the C/C-SiC-ZrB₂ composites show a significant improvement in the ablation resistance, and the linear and mass ablation rates decreased from 10.28×10⁻³ mm/s to 6.72×10⁻³ mm/s and from 3.08×10⁻³ g/s to 0.61×10⁻³ g/s, respectively. After ablation test, the flexural strength retentions of the C/C and C/C-SiC-ZrB₂ composites near the ablated center region are 39.7% and 81.6%, respectively. The higher strength retention rate of C/C-SiC-ZrB₂ composites was attributed to the introduction of SiC-ZrB₂ ceramic phases, which have excellent ablation resistant property. During ablation test, an ‘embedding structure’ of Zr-O-Si glass layer was formed, which could act as an effective barrier for oxygen and heat. The oxide ceramic coating could protect the C/C-SiC-ZrB₂ composites from further ablation, and thus contribute to retaining the mechanical property of C/C-SiC-ZrB₂ composites after ablation.     

Interfacial area and liquid side mass transfer coefficient in trickle bed reactors operating with organic liquids

Interfacial area and liquid-side mass transfer coefficients measured in a 5cm diameter trickle-bed reactor operating with organic liquids are presented d_p≤ 2.4 mm and cylindrical catalyst of size 0.9 mm × 5 mm. A few data concern also 5.9 and 6.4 mm Raschig rings. Gas and liquid flowrates a Mass transfer parameters have been determined by the chemical technique using the carbamation of the reactants cyclohexylamine, monoethanolamine or die results obtained at low gas-liquid interaction with low liquid flowrate are reported for the ionic aqueous systems CO₂-NaOH and O₂-Na₂SO₃. The variation of the mass transfer data, the gas pressure drop and the liquid holdup with the gas and liquid flowrates show that there exists a strong connection between these parameters. This has led to correlate the with the liquid-solid friction factor within a $\text{+}$30% accuracy.     

Liquid/Solid Mass Transfer in Fixed Beds

The liquid/solid mass transfer behavior of a fixed bed of cylinders was studied using the diffusion‐controlled dissolution of copper in acidified potassium dichromate. Variables studied were solution velocity and cylinder diameter. For a steady flow, the data were correlated for the conditions 25 < Re < 600 and Sc = 990 by the equation Sh = 2.65 Sc^0.33 Re^0.5. A comparison between the present data and previously obtained data for a fixed bed of Raschig rings has revealed that cylinder packing produces higher rates of mass transfer than Raschig rings.     

Effective interfacial area and liquid and gas side mass transfer coefficients in a packed column

The theory of gas absorption accompanied by fast pseudo-mth order reaction was used to obtain values of effective interfacial area in a packed column, irrigated with aqueous solutions and provided with 1 in. ceramic Raschig rings, 1 in. P.V.C. Raschig rings, 1 in. ceramic Intalox saddles, 1 in. polypropylene Intalox saddles, 1 in. stainless steel Pall rings and 1 in. polypropylene Pall rings. The values of liquid side mass transfer coefficient were obtained by physical absorption of carbon dioxide in water. In addition, the values of gas side mass transfer coefficient for a range of gas and liquid flow rates were obtained.     

HYDRODYNAMICS AND GAS-LIQUID-SOLID INTERFACIAL PARAMETERS OF CO-CURRENT DOWNWARD TWO-PHASE FLOW IN TRICKLE-BED REACTORS†

Design of trickle-fixed bed reactors requires knowledge of the hydrodynamics of two-phase co-current downward flow through fixed porous catalytic media and interfacial parameters. Unfortunately, most of the published papers deal exclusively with the hydrodynamics of an air-water system and the determination of gas-liquid-solid interfacial parameters in highly ionic solutions. In this paper, we present some experimental results on the hydrodynamics, pressure drop, liquid holdup, different flow patterns, gas-liquid interfacial areas and liquid-side mass transfer coefficients for organic non-viscous and viscous liquids and liquid-solid mass transfer coefficients with different packings: glass beads (d_p = 1.16 × 10^?3 m and 4 × 10^?3 m), spherical catalyst (d_p = 2.4 × 10^?3 m) and glass Raschig rings (d_p = 6.48 × 10^?3 m). Comparison between our values and correlations in the literature will be discussed.     

High gas permeability and directional channels of mullite porous ceramics prepared by pectin-based freeze-drying method

New gel system for preparing mullite porous ceramics by gel-casting freeze-drying was proposed, using pectin as gel source and alumina and silica as raw materials. Directional channels were formed due to sublimation of water during freeze-drying and decomposition of pectin during high temperature sintering to prepare porous mullite ceramic membranes. Effects of solid content on the properties of mullite ceramics in terms of phase composition, microstructure, apparent porosity, bulk density, pore size distribution, compressive strength, thermal conductivity, pressure drop, and gas permeability were investigated. It was found that prepared porous mullite possessed high apparent porosity (56.04%–75.34%), low bulk density (.77–1.37 g/cm³), uniform pore size distribution, relatively high compressive strength (.61–3.03 MPa), low thermal conductivity (.224–.329 W/(m·K)), high gas permeability coefficient (1.11 × 10⁻¹⁰–4.73 × 10⁻¹¹ m²), and gas permeance (2.18 × 10⁻²–9.32 × 10⁻³ mol⋅m⁻²⋅s⁻¹⋅Pa⁻¹). These properties make prepared lightweight mullite ceramic membranes promising for application in high temperature flue gas filtration. Proposed gel system is expected to provide a new route to prepare porous ceramics with high porosity and directional channels.     

Dynamic Ring-on-Ring Equibiaxial Flexural Strength of Borosilicate Glass

A novel dynamic ring-on-ring equibiaxial flexural testing technique with single pulse loading capability is established on a modified Kolsky bar. This technique is then utilized to investigate the loading-rate and surface-condition effects on the flexural strength of a borosilicate glass. Quasi-static and dynamic experiments are performed at loading rates ranging from 5 × 10⁻¹ to 5 × 10⁶ MPa/s. It is found that the flexural strength of the borosilicate glass strongly depends on the applied loading rates. HF acid corrosion on the surface promotes the flexural strength to above 1.3 GPa. Fractographic analysis shows that surface modification has changed the type of flaws that govern the flexural strength of glass samples.     

Cytarabine trapping in poly(2-hydroxyethyl methacrylate-co-acrylamide) hydrogels: drug delivery studies

Copolymeric hydrogels of poly(2-hydroxyethyl methacrylate-co-acrylamide) [p(HEMA-co-A)] crosslinked with ethylene glycol dimethacrylate, with a high equilibrium degree of swelling (37–65 wt%) in saline solution (NaCl 0.9 wt%) were synthesized as devices for controlled release of cytarabine (ara-C). Two compositions of the copolymer, each with a different degree of crosslinking have been studied, HEMA80/A20 and HEMA60/A40. The antineoplasic drug was included in the feed mixture of polymerization, and discs 3.7 ± 0.4 mm thick and 11.8 ± 0.2 mm in diameter with 5–40 mg (1.0–8.3 wt%) of ara-C were obtained. The diffusion studies followed Fick's second law. The diffusion coefficients for swelling of the gels were between 3.60 × 10⁻¹¹ and 15.8 × 10⁻¹¹ m² s⁻¹; those for release of ara-C were between 0.31 × 10⁻¹¹ and 7.18 × 10⁻¹¹ m² s⁻¹. The activation energies for swelling were in the range 23.4–31.9 kJ mol⁻¹ and those for ara-C release were 42.2–61.6 kJ mol⁻¹; their values indicate that the drug release process depends on drug–matrix and drug–water interactions that are influenced by the aqueous solution content and the network size of the gels. Total release of the drug takes place between 17 h from H60/A40/E2 at 310 K and 6 days from H80/A20/E10 at 288 K. Ara-C degradation was not observed either during loading of the gels or during drug release. © 1999 Society of Chemical Industry     

Joining of SiC ceramics using CaO-Al2O3-SiO2 (CAS) glass ceramics

CaO-Al₂O₃-SiO₂(CAS) glass ceramics were designed and prepared using a melt-quench approach. The coefficient of the thermal expansion (CTE) of the synthesized CAS (4.12 × 10⁻⁶ K⁻¹) matched perfectly with that of the SiC ceramic (4.01 × 10⁻⁶ K⁻¹). Thermal analysis of the CAS was conducted. Then the joining of the SiC ceramics by the CAS glass ceramics under various process parameters were conducted. The bonding temperature affects the fluidity of the CAS glass and the oxidation of the SiC substrate. The holding duration decides the infiltration of the CAS glass into the SiC substrate. The optimal bonding parameter is 1400 ℃/10 min and the corresponding highest shear strength of the SiC/CAS/SiC bonded joints in average was 56 MPa. Fracture observation was also conducted to help analyze the relationship between the interfacial microstructure and the joint strength. Finally, the formation mechanism of the SiC/CAS/SiC bonded joints was proposed.     

Ablation behaviors and mechanism of ultra-thick anti-oxidation layer coating on carbon-bonded carbon fiber composites

To enhance the oxidation resistance capability of the carbon-bonded carbon fiber composites (CBCFs), a silicide ultra-thick coating as high as 1.6 mm with gradient structure is designed and fabricated via a multi-step rapid sintering method. Compared with other ceramic layers on carbon fiber-based composites, ultra-thick anti-oxidation layer coated-CBCFs have the lowest thermal conductivity. Additionally, ablation behaviors of the ultra-thick ceramics layer coated-CBCFs under the oxyacetylene torch are also investigated. After being exposed to oxyacetylene torch, the ultra-thick ceramics layer coated-CBCFs possess a linear rate range from 0.6 to 1.2 μm/s, while a mass ablation rate ranges from 4.95 × 10⁻⁵ g/m² s to 1.45 × 10⁻³ g/m² s.     

Bio-cellular glass–ceramic composite with embedded calcium phosphate from eggshell for alternative biomaterials in medical and dental applications

Green biomaterial foams with nontoxicity, low weight, low density, and high-compressive strength, which can be easily manufactured at low cost, are urgently sought. When implanted as a scaffold, bio-cellular glass–ceramic composite has potential for bone bonding, connective tissue growth, and reconstruction of lost tissue. The present study investigates the physical-thermo-mechanical properties of bio-cellular glass–ceramic composite supplemented with calcium phosphate from eggshell powder (0, 1, 3, or 5 wt%) and sodium-silicate binder. The composite materials were prepared by hand pressing and fired at 800 or 900°C for 1 h. The composites containing 1 and 3 wt% calcium phosphate from eggshell powder and fired at 800°C achieved suitable porosity (74–79%), pore size (20–800 μm), bulk density (0.57–0.70 g/cm³), true density (0.98–1.06 g/cm³), water absorption (10.31–21.41%), compressive strength (2.71–3.23 MPa), and thermal expansion coefficient ([5.95–5.98] × 10⁻⁶°C⁻¹) for practical applications. The obtained bio-cellular glass–ceramic composite is an alternative biomaterial for biomedical and dental applications.     

气流在板波填料内的径向混合——(Ⅰ)试验与关联

本文在φ200和φ287mm两种塔内,对4.5型和6.3型板波填料进行了气流径向混合试验,试验采用CO_2作为示踪剂.试验结果表明,板波填料具有良好的径向混合性能.4.5型板波填料的Pe_r仅为1.5左右,而φ15mm拉西环的Pe_r约为3.5.影响气流在板波填料中径向混合的因素有:填料的盘高、盘径、波纹倾角以及气速等.在低Re下,板波填料的Pe_r较低,且随Re的增大而增加,当Re>800以后.Pe_r趋于定值.本文提出了Pe_r与诸参数间的经验关联式.     

Permeability behavior of silicon carbide-based membrane and performance study for oily wastewater treatment

Porous SiC ceramic is considered as a suitable material for hot gas filtration, microfiltration, and many others industrial applications. However, full utilizations of porous SiC ceramics have been limited by high-processing costs. In this study, mullite-bonded porous SiC ceramics membranes were prepared using commercial SiC powder, alumina, clay, and different sacrificial pore formers. The effect of different pore formers on the microstructure, mechanical strength, porosity and pore size distribution, air, and water permeability of porous SiC ceramics were investigated. The average pore diameter, porosities, and flexural strength of the final ceramics varied in the range 3.7-6.5 µm, 38-50 vol. %, and 28-38 MPa, respectively, depending on the characteristics of pore former. The Darcian (k₁) and non-Darcian (k₂) permeability evaluated from air permeation behavior at room temperature was found to vary from 1.48 × 10⁻¹³ to 4.64 × 10⁻¹³ m² and 1.46 × 10⁻⁸ to 6.51 × 10⁻⁸ m, respectively. All membranes showed high oil rejection rate (89%-93%) from feed wastewater with oil concentration of 1557 mg/L. The membrane with porosity ~48 vol% and mechanical strength 31.5 MPa showed and highest pure water permeability of 13 298 Lm⁻²h⁻¹bar⁻¹.