Continuous and selective separation of EGCG from tea polyphenols by fractional extraction: Experiment and simulation

A new and efficient method was explored to continuously separate (−)-epigallocatechin-3-gallate (EGCG) from tea polyphenols (TPs) by fractional extraction in centrifugal contactor separators (CCSs). The effects of different organic solvents on distribution behavior of monomers of TPs were studied, and two green extraction systems were established without reactive extractant. Based on phase equilibrium and the law of conservation of mass, a fractional extraction model was developed to investigate the influence of the process parameters such as phase ratio and the number of stages on extraction efficiency. By simulation and optimization, optimal parameters can be obtained for the separation of EGCG. EGCG can be separated by batch and continuous separation. Excellent results can be achieved by the two methods with high purity, high yield, and large output. Compared to the batch method, the continuous separation is more suitable for production in an industrial scale due to low-cost and continuous separation. © 2018 American Institute of Chemical Engineers AIChE J, 65: 259–269, 2019     

茶叶茶多酚、咖啡碱提取及超滤-吸附综合分离纯化过程研究

介绍了采用三级错流提取茶叶有效成分茶多酚、咖啡碱的优化提取工艺。该工艺提取率高达９０％ 以上,其提取液经醋酸纤维素复合钛微孔体超滤膜初步纯化,可得到茶多酚含量大于４０％ 的部标三级品。并建立了茶叶水提取液超滤过程修正凝胶极化模型。超滤透过液经聚酰胺树脂吸附、８５％ 乙醇洗脱,得到茶多酚含量大于９０％ ,咖啡碱含量低于４％ 的部标茶多酚一级品。该工艺具有不另外添加物质、不使用有毒溶剂、工艺简单等特点。     

Separation of epigallocatechin-3-gallate from crude tea polyphenols by using Cellulose diacetate graft BoldItalic-cyclodextrin copolymer asymmetric membrane

This study demonstrates a new Cellulose diacetate graft β-cyclodextrin (CDA-β-CD) copolymer asymmetric membrane prepared by a phase inversion technique for the separation of (-)-epigallocatechin-3-gallate (EGCG) from other polyphenols in crude tea. The graft copolymer, CDA-β-CD, was synthesized by prepolymerization of cellulose diacetate (CDA) and 1,6-hexamethylene-diisocyanate (HDI), which was then grafted with β-cyclodextrin (β-CD). Surface and cross-section morphologies of the CDA-β-CD membranes were analyzed by using scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FT-IR) indicated that the β-CD was grafted onto the CDA by chemical bonding. The influences of the HDI/CDA mass ratio and the catalyst mass fraction on the β-CD graft yield were investigated. The optimum conditions of a HDI/CDA mass ratio of 0.35 g·g^-1 and a catalyst mass fraction of 0.18 wt-% produced a β-CD graft yield of 26.51 wt-%. The effects of the β-CD graft yield and the concentration of the polymer cast solution on the separation of EGCG were also investigated. Under optimum conditions of a β-CD graft yield of 24.21 wt-% and a polymer concentration of 13 wt-%, the purity of EGCG increased from 26.51 to 86.91 wt-%.     

膜法提纯浓缩茶皂素

采用陶瓷膜、有机膜进行了茶皂素提纯浓缩的小试和中试研究。结果表明:0.5μm的陶瓷膜预处理加PW超滤膜浓缩提纯的工艺适宜用于茶皂素的提纯浓缩。最终浓缩液为46%,浓缩液茶皂素纯度为93%,茶皂素最终得率为72%。在pH=4的条件下,用乙二胺四乙酸溶液作为清洗剂,膜通量恢复率达到93%。     

Improvement in antifouling and separation performance of PVDF hybrid membrane by incorporation of room‐temperature ionic liquids grafted halloysite nanotubes for oil–water separation

Novel hybrid poly(vinylidene fluoride) ultrafiltration membranes were fabricated via immersion precipitation method through the incorporation of the halloysite nanotubes functionalized with 1‐methyl‐3–(3‐triethoxysilypropyl) imidazolium chloride. The modified halloysite nanotubes were confirmed by Fourier transform infrared spectrometer, thermogravimetric analysis, and transmission electron microscopy. The morphologies of hybrid membranes were characterized by atomic force microscopy and energy dispersive spectrometer, while the filtration and antifouling performance were investigated by means of porosity, mean pore radius, pure water permeability, rejection ratio, and flux recovery ratio. The addition of the modified halloysite nanotubes obviously improved the membrane hydrophilicity. Besides, the flux recovery ratios were as high as 96% for humic acid and 94% for bovine serum albumin after two filtration cycles. Finally, the modified membranes were used to separate diesel oil–water emulsions. The rejection ratio and flux recovery ratio were as high as 99% and 94%, respectively. The poly(vinylidene fluoride) membranes incorporated by the novel halloysite nanotubes provided a promising alternative for oil–water emulsions separation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46278.     

Fabrication and characterization of robust hydrophobic lotus leaf-like surface on Si3N4 porous membrane via polymer-derived SiNCO inorganic nanoparticle modification

Robust hydrophobic surface was produced by modifying the surface of porous Si₃N₄ membrane, via aminolysis and pyrolysis process, with organosilane-derived inorganic SiNCO nanoparticles, which are tightly adhered to the Si₃N₄ grains. The resultant material had a high water contact angle of 142°, attributed to -Si-CH₃ surface terminal groups and a lotus leaf-like hierarchical structure of the nanoparticles, which had a frame structure with Si-N and Si-O covalent bonds in their bulk. The hydrophobic behavior remained practically unchanged after exposure of the produced membranes to aqueous solutions of humic acid, HCl and NaOH, to benzene, as well as to stirring abrasive slurry with SiC particles, and after exposure at high temperatures, up to 500?°C, to air. The inorganic membrane can be considered for use in a broad range of applications which require robust hydrophobic surfaces.     

Complex membrane of cellulose and chitin nanocrystals with cationic guar gum for oil/water separation

In an effort to develop a membrane system with low cost and easy fabrication process for oil/water separation, cellulose nanocrystals (CNC), chitin nanocrystals (ChiNC), and cationic guar gum (CGG) are used to prepare a complex membrane on top of a poly(ethylene terephthalate) (PET) nonwoven fabric via a vacuum filtration method. The interactions among CNC, ChiNC, and CGG complexation are discussed, and the functionalization of the PET nonwoven fabric with these polysaccharide derivatives provides a high rate of water absorption and permeability on applying pressure. The morphology and wettability studies demonstrate that the as-prepared membrane has a porous structure and exhibits hydrophilic and underwater superoleophobic properties. The results of separation experiments show that the membrane can effectively separate oil/water emulsions with a relatively high flux and rejection ratio. This low-cost process can easily be scaled up to fabricate complex membranes for oil/water separation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47947.     

Determination of mass transfer resistance during absorption of carbon dioxide by mixed absorbents in PVDF and PP membrane contactor

In this study, the absorption of carbon dioxide by the absorbent which was composed of 2-amino-2-methyl-l-propanol (AMP) + piperazine (PZ) or methyldiethanolamine (MDEA) + piperazine (PZ) in polyvinylidinefluoride (PVDF) and polypropylene (PP) membrane contactors werewas examined. Three resistances were considered in each hollow fiber, i.e., liquid-film diffusion, membrane diffusion, and gas-film diffusion. The mass transfer resistance of membrane k_m was influenced by the wetting ratio using an absorbent with higher reaction rate. The wetting ratio was affected by contact angle between the membrane and absorbent and the viscosity of absorbent. The calculated absorption rates considering wetting ratio of membrane and using the modified correlation equation of gas-phase mass transfer coefficient were reasonably agreeable to those of measured ones (standard deviation, 4%). The fractional resistance of each transport step during the experiments was then determined. The rate-controlling step was dominated by the resistance of gas-film diffusion with mixed absorbents. The absorption rates of CO₂ increase with the increasing of gas flow rates in the most experimental cases. The resistance of liquid-film diffusion was only important using an absorbent with lower reaction rate. The rate-controlling step was the membrane diffusion only at higher gas flow rate with the absorbent composed of AMP and PZ in PVDF hollow fiber membrane contactor.     

Highly active and robust biomimetic ceramic catalyst for oxygen reduction reaction: Inspired by plant leaves

Structural instability under working conditions is critical issue that restricts applications of perovskite O₂ catalysts in the field of solid oxide fuel cells. Inspired by plant leaves, a biomimetic ceramic catalyst with PrBaCo₂O_5+δ ‘mesophyll’ and Gd_0.1Ce_0.9O_1.95 ‘epidermis’ and ‘vein’ was successfully engineered in this work. The ‘epidermis’ reduces the polarization resistance of O₂ reduction reaction on catalyst surface by ∼24%, and the ‘vein’ reduces resistance of O²⁻ transport through cathode layer by ∼65%. Moreover, this biomimetic catalyst increases output power density of the cell by 79% and reverses rapid decay trend of the cell with a 23% increase in power density during first 20 h followed by stabilization at 0.91 W cm⁻² (at 750 °C and 0.7 V). This discovery provides new avenue for the development of high-performance O₂ catalysts with practical applications and enriches the scientific understanding of catalysis.     

Comparison between supported gas membrane process and supported liquid membrane process for the separation of NH3 from aqueous media containing NH3 and CO2

A comparison between the hollow fibre supported gas membrane (SGM) process and the hollow fibre supported liquid membrane (SLM) process for the separation of NH₃ from aqueous solutions containing NH₃ and CO₂ was performed. The experimental data as well as the model simulation demonstrate that the SLM process can remove NH₃ from aqueous solutions of NH₃ and CO₂ at a higher rate than the SGM process when the NH₃ loading is low or the ratio of NH₃ to CO₂ is low. This study suggests that the proper combination of the SGM process and the SLM process can strip NH₃ more effectively from aqueous solutions containing NH₃ and CO₂.     

Polymer composites with enhanced thermal conductivity via oriented boron nitride and alumina hybrid fillers assisted by 3-D printing

Herein, oriented boron nitride (BN)/alumina (Al₂O₃)/polydimethylsiloxane (PDMS) composites were obtained by filler orientation due to the shear-inducing effect via 3-D printing. The oriented BN platelets acted as a rapid highway for heat transfer in the matrix and resulted in a significant increase in the thermal conductivity along the orientation direction. Extra addition of spherical Al₂O₃ enhanced the fillers networks and resulted in the dramatic growth of slurry viscosity. This, together with filler orientation induced the synergism and provided large increases in the thermal conductivity. A high orientation degree of 90.65% and in-plane thermal conductivity of 3.64 W/(m∙K) were realized in the composites with oriented 35 wt% BN and 30 wt% Al₂O₃ hybrid fillers. We attributed the influence of filler orientation and hybrid fillers on the thermal conductivity to the decrease of thermal interface resistance of composites and proposed possible theoretical models for the thermal conductivity enhancement mechanisms.     

Ultrahigh molecular weight polyethylene with improved crosslink density,oxidation stability,and microbial inhibition by chemical crosslinking and tea polyphenols for total joint replacements

Highly crosslinked ultrahigh molecular weight polyethylene (UHMWPE) stabilized by vitamin E (VE) is widely applied in artificial joints as the bearings. Despite the approval, there is a discord that VE lowers the crosslinking efficiency, limiting its use at high concentration. In this work, we aim to obtain highly crosslinked and oxidation resistant UHMWPE through the conjunction of tea polyphenol and chemical crosslinking. We hypothesized that highly incorporated tea polyphenol with multiple reactive sites can ameliorate crosslinking efficiency of chemical crosslinked UHMWPE in comparison to VE. Epigallocatechin gallate (EGCG) as representative tea polyphenol was incorporated into UHMWPE at high concentration (2–8 wt%), followed by chemical crosslinking with 2 wt% organic peroxide. Unlike VE/UHMWPE blends as the control, chemical crosslinking achieved an increasing trend in crosslink density of EGCG/UHMWPE blends with increasing antioxidant concentration. High concentration of EGCG also enhanced the oxidation stability of UHMWPE. Intriguingly, EGCG endowed UHMWPE with an excellent antimicrobial property, which was inefficient in VE/UHMWPE. Cell viability was hardly affected by the high loaded antioxidant and peroxide. The chemically crosslinked UHMWPE blended with EGCG is proved to be a reasonable, cost effective and realistic alternative for use in artificial joints.     

Synthesis and characterization of poly(γ‐methacryloxypropyltrimethoxysilane)‐grafted silica hybrid nanoparticles prepared by surface‐initiated atom transfer radical polymerization

Poly(γ‐methacryloxypropyltrimethoxysilane) (PMPTS)‐grafted silica hybrid nanoparticles were prepared by surface‐initiated atom transfer radical polymerization (SI‐ATRP). The resulting PMPTS‐grafted silica hybrid nanoparticles were characterized using Fourier transform infrared spectroscopy (FTIRS), nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), X‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), static water contact angle (WCA) measurement, and thermogravimetric analysis (TGA). Combined FTIRS, NMR, XPS, SEM, and TGA studies confirmed that these hybrid nanoparticles were successfully prepared by surface‐initiated ATRP. SEM and AFM studies revealed that the surfaces of the nanoparticles were rough at the nanoscale. In addition, the results of the static WCA measurements showed that the nanoparticles are of low surface energy and their surface energy reaches as low as 6.10 mN m^?1. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Carbon dioxide separation and dry reforming of methane for synthesis of syngas by a dual‐phase membrane reactor

High‐temperature CO₂ selective membranes offer potential for use to separate flue gas and produce a warm, pure CO₂ stream as a chemical feedstock. The coupling of separation of CO₂ by a ceramic–carbonate dual‐phase membrane with dry reforming of CH₄ to produce syngas is reported. CO₂ permeation and the dry reforming reaction performance of the membrane reactor were experimentally studied with a CO₂–N₂ mixture as the feed and CH₄ as the sweep gas passing through either an empty permeation chamber or one that was packed with a solid catalyst. CO₂ permeation flux through the membrane matches the rate of dry reforming of methane using a 10% Ni/γ‐alumina catalyst at temperatures above 750°C. At 850°C under the reaction conditions, the membrane reactor gives a CO₂ permeation flux of 0.17 mL min^?1 cm^?2, hydrogen production rate of 0.3 mL min^?1 cm^?2 with a H₂ to CO formation ratio of about 1, and conversion of CO₂ and CH₄, respectively, of 88.5 and 8.1%. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2207–2218, 2013     

Magnetite/poly(D,L-lactide-co-glycolide) and hydroxyapatite/poly(D,L-lactide-co-glycolide) prepared by W/O/W emulsion technique for drug carrier: Evaluation of in vitro release of dexamethasone from composite nanoparticles

Biocompatible polymeric carriers containing inorganic materials for delivering therapeutic agents to a targeted site are promising candidate for drug delivery. Two nanocomposite nanoparticles, magnetite/poly(D,L-lactide-co-glycolide) and hydroxyapatite/poly(D,L-lactide-co-glycolide) (Fe₃O₄/PLGA and HAp/PLGA, respectively), with different weight ratios of inorganics to polymer and different polymer molecular weights were prepared by water-in-oil-in-water (W/O/W) emulsion technique to determine incorporation and in vitro release profile of the small molecule drugs water-insoluble dexamethasone acetate (DEX-Ac) and water-soluble dexamethasone phosphate (DEX-P). The in vitro release for DEX-Ac nanoparticles showed an initial burst release followed by a continuous slower release, whereas DEX-P nanoparticles showed only rapid initial release behavior.     

A novel ternary mixed-matrix membrane comprising Pebax-1657, [HMIM][NTf2] IL,and Al2O3 nanoparticles for efficient CO2 separation

An innovative technique to efficiently remove CO₂ involves introducing a third component with a positive affinity with CO₂ into a binary mixed-matrix membrane (MMM) and eliminating interfacial defects in its structure. In this research, novel ternary MMMs (TMMMs) were synthesized by embedding 1–Hexyl–3–methylimidazolium bis(trifluoromethylsulfonyl)imide ([HMIM][NTf₂]) ionic liquid (IL) and aluminum oxide (γ–Al₂O₃) nanoparticles into poly (ether-block-amide) (Pebax-1657) matrix for enhancing CO₂ removal from light gases. FESEM, DSC, ATR-FTIR, and XRD analyses were used to evaluate the fabricated MMMs structurally. The permeation tests of gases (CH₄, N₂, and CO₂) through prepared membranes were conducted at 25°C and 4, 6, 8, and 10 bar pressures. In accordance with the permeation outcomes, the ternary MMMs exhibited enhanced CO₂ separation performances compared to the unloaded polymeric membrane. Also, the optimized MMM comprising 10 wt.% of the IL and 6 wt.% of the nanoparticles obtained a CO₂ permeability of 173.90 Barrer, as well as CO₂/N₂ and CO₂/CH₄ selectivities of 77.98 and 24.29 at 10 bar and 25°C, which are higher by about 51%, 23%, and 22%, respectively than those of the pristine polymeric membrane. Based on these results, the prepared membrane appears to be a promising choice for separating CO₂ from light gases.     

Magnetic-field-induced Fe3O4@CNTs/PES/SPSf composite membrane for efficient removal of methylene blue by adsorption and catalytic degradation

Novel composite membranes are successfully developed for adsorption and catalytic degradation of methylene blue (MB) by blending Fe₃O₄-coated CNTs (Fe₃O₄@CNTs) nanoparticles in polyethersulfone (PES) and sulfonated polysulfone (SPSf) matrix via nonsolvent-induced phase separation (NIPS) method assisted by magnetic field. Fe₃O₄@CNTs nanoparticles migrate to the separation layer under the induction of magnetic field, thus Fe₃O₄@CNTs/PES/SPSf composite membranes prepared under magnetic field exhibit a better dye removal ability compared with that without magnetic field. The MB removal ratio by Fe₃O₄@CNTs/PES/SPSf composite membrane containing 8 wt% Fe₃O₄@CNTs (M2−M) can reach up to 99% in 30 min under the conditions of 0.25 g composite membrane, 20 mg/L MB, 0.1 mol/L H₂O₂, pH = 3 and 80°C. Furthermore, the composite membranes show excellent recycling performance, as the MB removal capacity remains at 99% even after four cycles.     

Optimization of electrochemically synthesized Cu3(BTC)2 by Taguchi method for CO2/N2 separation and data validation through artificial neural network modeling

Cu₃(BTC)₂, a common type of metal organic framework (MOF), was synthesized through electrochemical route for CO₂ capture and its separation from N₂. Taguchi method was employed for optimization of key parameters affecting the synthesis of Cu₃(BTC)₂. The results indicated that the optimum synthesis conditions with the highest CO₂ selectivity can be obtained using 1 g of ligand, applied voltage of 25 V, synthesis time of 2 h, and electrode length of 3 cm. The single gas sorption capacity of the synthetized microstructure Cu₃(BTC)₂ for CO₂ (at 298 K and 1 bar) was a considerable value of 4.40 mmol·g⁻¹. The isosteric heat of adsorption of both gases was calculated by inserting temperature-dependent form of Langmuir isotherm model in the Clausius-Clapeyron equation. The adsorption of CO₂/N₂ binary mixture with a concentration ratio of 15/85 vol-% was also studied experimentally and the result was in a good agreement with the predicted value of IAST method. Moreover, Cu₃(BTC)₂ showed no considerable loss in CO₂ adsorption after six sequential cycles. In addition, artificial neural networks (ANNs) were also applied to predict the separation behavior of CO₂/N₂ mixture by MOFs and the results revealed that ANNs could serve as an appropriate tool to predict the adsorptive selectivity of the binary gas mixture in the absence of experimental data.