Search

In this work controlled release devices for transdermal administration of metoprolol were developed. Poly(vinyl alcohol) and poly(vinyl pyrrolidone) were used for producing membranes by solvent-casting technique. The release kinetic of the drug from the membranes was evaluated by ex-vivo experimental studies. All the prepared membranes exhibited a linear release profile in the investigated time. The enhancer Tween 80 was added into the polymeric matrices for improving their performance. Different mathematical models were used for fitting the experimental release data. The model that well described the release mechanism was the zero order, indicating a constant drug release in the time. [ABSTRACT FROM AUTHOR]

A theophylline-binding polymer was synthesized utilizing the bulk polymerization technique. Methacrylic acid, ethylene glycol dimethacrylate, 2,2′-azoisobutyronitrile and chloroform were used to synthesize the imprinted polymer. Theophylline was employed as template. The obtained polymer powder were dispersed in the modified poly(ether ether ketone) (PEEK-WC) polymer solution for preparing hybrid imprinted membranes via the phase inversion technique. Membranes containing the non-imprinted polymer were also prepared and used as reference. For evaluating the recognition properties of polymers and membranes re-binding experiments, with the template and its structural homologue caffeine, were carried out. The binding capacity of MIP towards the template was 1.18 µmol/g p and the theophylline/caffeine selectivity factor was 3.2. All the imprinted membranes exhibited good recognition properties compared with blank membranes, which only showed a poor non-specific binding. The membrane containing 30 wt% of the imprinted polymer exhibited the highest binding capacity (10.97 µmol/g memb. ), and a theophylline/caffeine selectivity factor of 71.42. [ABSTRACT FROM AUTHOR]

Hybrid imprinted membranes exhibiting specific recognition properties towards the quercetin (the template) were developed. In this perspective, an imprinted copolymer of acrylonitrile, using acrylamide as functional co-monomer was synthesized. For comparison, a non-imprinted polymer was also prepared. Various membranes were produced by dispersing different copolymer amounts in a poly(ether ether ketone) (PEEK-WC) matrix. Scanning Electron Microscopy, and Fourier Transform Infrared analysis confirmed the presence of the polymer into the hybrid system. Membrane permeability was in the ultrafiltration range (70–180 l/h m 2 bar). The addition of polymer to the support membrane determined a slight decrease of the membrane hydrophobicity. The solvent uptake degree was very low (between 1.2% and 1.32%), suggesting a weak interaction between the polymer and the binding solvent. No significant change in the mechanical properties were observed. The membranes recognized the quercetin in different extend. The highest imprinting factor (3.6) and binding capacity (12.0 mol/g memb .) was exhibited by the membranes containing the 25 wt.% of the imprinted polymer (PEEK-WC/25% MIP). This membrane was also selective v s chrysin and naringin, (structural homologs of quercetin). The selectivity factor quercetin/naringin was 4.5 and that one of the couple quercetin/chrysin was 1.8. The Langmuir adsorption model was suitable for correlation of equilibrium data. The kinetic of quercetin adsorption of PEEK-WC 25% MIP membrane was efficiently predicted by the second-order model. [ABSTRACT FROM AUTHOR]

Abstract: Kinetic properties of tyrosinase immobilized on a polymeric membrane for the production of l-3,4-dihydroxyphenylalanine (l-DOPA) were investigated. A comparison with the properties shown by the free enzyme used in a stirred tank reactor was also carried out. The values of the Michaelis–Menten constant indicated that the immobilized tyrosinase exhibited better affinity for the substrate (K m=1.56mM and 2.10mM for the immobilized and free enzyme, respectively). The stability (pH, thermal, storage and operational) of both free and immobilized tyrosinase was also evaluated. Results showed that the immobilization enhanced the enzyme stability. The optimum pH and temperature for the activity of both free and immobilized enzyme were found at pH 7.0 and 35°C, respectively. However, the immobilized tyrosinase was more stable in the whole range of pH and temperature. These advantages of the immobilized enzyme make it a good candidate for its use in different industrial processes. [Copyright &y& Elsevier]

Abstract: The production of l-3,4-dihydroxyphenylalanine (l-DOPA) from l-tyrosine catalysed from mushroom tyrosinase immobilised in a continuous membrane reactor was studied and compared with free enzyme used in a stirred tank reactor. The enzyme was immobilised by cross-flow filtration in asymmetric tubular membranes made of polyamide having nominal molecular weight cut off of 20kDa. Results showed that the immobilization procedure did not alter the catalytic properties of the enzyme. The immobilised tyrosinase showed high stability over 30h. In a continuous bioreactor the specific activity of tyrosinase is higher than that obtained with the free enzyme and those reported in the literature. The continuous operation minimizes the oxidation of the l-DOPA and for this reason the productivity (22.54mgL−1 h−1) is 95% higher than that obtained with the total recycle reactor. Results obtained in the present study are promising for the development of the bioreactor at larger scale. [Copyright &y& Elsevier]

Abstract: A good seeding is a mandatory step to have defect-free zeolitic membranes prepared by means of a secondary growth method. The transport properties of the zeolitic membranes depend strongly on the seeding procedure of zeolite crystals during which the whole support surface has to be covered uniformly and sufficiently. A new seeding procedure, involving cross-flow filtration of a water suspension combined with rotation and tilting of the membrane support, was developed and utilized for the first time. Porous α-alumina tubes were seeded using a water suspension of 0.2 wt.% in zeolite crystals, at a pH of ca. 9.2 and room temperature. Cumulative stage-cut of the seeding phase was used as design parameter in order to tailor the permeation properties (e.g., permeance) of the resulting NaY zeolite membranes. The secondary growth was accomplished by a hydrothermal treatment. SEM, EDX and XRD analyses show dense intergrown FAU layers with Si/Al ratios of 1.8–2.0 typical of the NaY zeolite. The measured permeance was 5–10% of that showed by the bare support. Another evidence of the membrane quality can be found considering their application in CO selective oxidation reaction [P. Bernardo, C. Algieri, G. Barbieri, E. Drioli, Catal. Today 118(1–2) (2006) 90]: a complete conversion of carbon monoxide which falls down 1000 times from 10,000 to ca. 10ppm indicates very few defects in the zeolite layer. [Copyright &y& Elsevier]

Abstract: Mixed matrix membranes (MMMs) have been prepared by using different protocols in order to improve the affinity between NaA (LTA) zeolite and a modified polyetheretherketone (PEEK-WC). A terpenic resin has been added to the polymer–zeolite slurry for enhancing the polymer chain flexibility and, consequently, its adhesion with the crystals. Coupling agents such as γ-aminopropyl-diethoxymethyl silane (APDEMS) and diethanolamine (DEA) have been used to modify the zeolite surface. The instrumental analyses showed a relative efficiency of these treatments with respect to the simple dispersion of the inorganic fillers within the polymer matrix. At high zeolite concentration (30wt%), MMMs are characterised by gas transport properties lower than neat polymer-based membrane. DEA-based treatment seems the more encouraging approach also taking into account that as the filler concentration decreases, the occurrence of defects at the interface becomes less significant. [Copyright &y& Elsevier]

Abstract: The focus of the present work is on the analysis of CO selective oxidation using catalytic zeolite (Pt/Na-Y) membranes in a continuous flow membrane reactor. A series of membranes with different permeation properties, prepared by secondary growth, Pt-loaded by ion exchange and reduced was used for this study. Catalytic tests were carried out with a simulated dry reformate shifted gas mixture with an operative O2/CO stoichiometric equivalent feed ratio of two, at a temperature of 200–220°C and reaction pressure up to 600kPa. The best performance was achieved by the lowest permeance membrane considered in this work that showed also stable catalytic activity over many hours of testing. The catalytic membranes effectively reduced the CO content from 10,000ppm down to 10–50ppm, depending on the operating conditions. [Copyright &y& Elsevier]

Abstract: CO selective oxidation (Selox) for the purification of hydrogen-rich streams was studied in membrane reactors (MRs) using Pt-loaded catalytic membranes. The catalytic membranes were prepared by the ion-exchange of FAU (Na-Y) zeolitic membranes that were synthesized on tubular α-Al2O3 supports by a secondary growth method. The catalytic MR tests were performed analysing the CO conversion, O2 selectivity and yield of the desired reaction. Different feed compositions (CO, O2, H2 and N2 content and O2/CO ratio), temperatures and pressures were considered with space-time values in the range 0.27–1.2mgPt min/cm3(STP). The CO content in preliminary tests was 10%, 1% in the other experiments. A simulated reformate shifted gas mixture (H2 =60%) was also used. A comparison with other literature data for MRs utilizing different membrane types and packed bed traditional reactors with Pt-based catalysts is also provided. The identified ranges of operating conditions (temperature, pressure, feed molar O2/CO ratio and feed concentration) suggest a profitable use of the catalytic MR (Pt-Y zeolite membranes) for CO Selox after the low-temperature water gas shift unit of a fuel processor converting hydrocarbons into hydrogen-rich gas, operating at similar temperature conditions. [Copyright &y& Elsevier]

Polydimethylsiloxane (PDMS) has been used as host matrix to prepare hybrid membranes, by a dry phase inversion process, where fillers with different surface and molecular sieving properties have been dispersed. The hybrid membranes have been characterised morphologically by scanning electron microscopy (SEM) and their gas transport properties have been measured at different temperatures.The influence of the temperature and different fillers on the gas separation performance of hybrid membranes has been analysed. These membranes showed higher selectivity values for some gas pairs combined to lower permeabilities with respect to pure PDMS films, as consequence of the contribution of the filler to the transport. A proper filler choice could be used to meet some specific requirements in industrial gas separations. [Copyright &y& Elsevier]

A thin MFI zeolite membrane was synthesised on a porous α-Al2O3 tubular support by in situ nucleation and secondary growth. Single gas permeances (CH4, H2, N2, CO, CO2) were measured through the MFI membrane according to the pressure drop method, from room temperature to 280 °C, with pressure differences between 0.1 and 0.4 bar. The membrane combines high permeances (1.6–8.0 μmol m−2 s−1 Pa−1) and also good separation properties (the H2/SF6 permselectivity value is equal to 24 at room temperature). The membrane has been tested also in the pervaporation of an ethanol/water mixture, showing high fluxes (2.1 kg m−2 h−1) and low selectivity. [Copyright &y& Elsevier]

Synthetic dyes, represent a serious hazard for the aquatic environments and groundwater system. The removal of dyes by the adsorption process avoids the production of sludge and secondary toxic compounds and offers high efficiency and very short operational times. In the present work, cationic Methylene Blue (MB) dye was used as a model pollutant to investigate the adsorption properties of a foamed geopolymer. The adsorbent has an apparent density of 0,75 g/cm3. It is characterized by a complex system of spherical and interconnected macro-pores with a mesopore volume of 0.143 cm³ /g that favors the mass transport and a pH pzc equal to 8.2. Batch and fixed granular bed column tests were carried out. The maximum MB uptake, in batch experiments, was 40.0 mg/g. Removal efficiency was around 95% up to a MB concentration of 25 mg/L. The pseudo second order kinetic model and Langmuir isotherm model better describe MB adsorption onto geopolymer. Fixed granular bed column tests were carried out by varying the initial dye concentration at a constant flow rate and bed height. Results are better fitted by Yoon and Nelson model. The obtained results demonstrate that foamed geopolymers are good candidates for the removing MB from aqueous solutions. [Display omitted] • Foamed geopolymer has been tested as adsorbent of Methylene Blue. • The pseudo second order model better describes MB adsorption onto geopolymer. • Langmuir isotherm models shows higher accuracy in fitting experimental data. • The mechanism of MB adsorption onto geopolymer is chemisorption. • Yoon and Nelson model better fits fixed granular bed column experimental data. [ABSTRACT FROM AUTHOR]

Traces of CO in hydrogen rich gas streams poison the anode of proton exchange membrane fuel cells reducing their power output and decreasing the cell life. This paper investigates the CO selective oxidation in simulated reformate gas by using catalytic zeolite membranes. In particular, the CO removal efficiency was explored using catalytic membranes characterized by different permeation properties (prepared using different protocols) and loaded with the catalyst by means of cationic exchange and reduction process. The most promising experimental results are obtained with membranes prepared with small crystals and low concentration of zeolite suspension (during the seeding step) and with a hydrothermal treatment of 90 °C for 24 h. These membranes are characterized by lower permeance and showed interesting catalytic performance in terms of CO reduction and selectivity. [ABSTRACT FROM AUTHOR]

Zeolite membranes represent a potential alternative to the polymeric ones for water desalination because of their high chemical stability and their peculiar ability to reject ions. In this work, supported zeolite membranes having Mordenite Framework Inverted (MFI) topology were scaled-up and membranes 30 cm long were prepared using the secondary growth method coupled with the cross flow seeding procedure. In particular, the influence of rotation time during the seeding procedure was evaluated. The prepared membranes were characterized by scanning electron microscope (SEM), X-ray diffractometry (XRD), Energy Dispersive X-ray (EDX) analysis and single gas permeation, and then underwent to Vacuum Membrane Distillation (VMD) tests using both deionized water and NaCl solutions at different concentrations. The experimental work allowed to identify the membrane able to provide interesting trans-membrane flux and salt rejection values. Specifically, permeate fluxes of 13.8kg m − 2 h − 1 and 8.2 kg m − 2 h − 1 , together with rejections of 99.8% and 99.6%, were achieved for the 0.2 M and 0.9 M feeds, respectively. No changes in the membrane structure after the exposure to salty solutions were detected by SEM and XRD analyses and its original performance was restored by means of an identified cleaning procedure. [ABSTRACT FROM AUTHOR]

This work focuses on the preparation of porous mixed matrix membranes (MMMs) by non-solvent induced phase separation (NIPS) using poly(vinylidenefluoride) (PVDF) as polymer and nano-sized silicalite-1 (S-1) and Ti-silicalite-1 (TS-1) seeds of MFI zeolite structure as inorganic fillers. These MMMs have been used as VOCs adsorbers. Different zeolite seed concentrations (up to 22 wt.%) were homogeneously dispersed into the polymeric matrix to evaluate the influence of the amount of zeolites on the membrane characteristics. In all cases, asymmetric porous membranes, made up of two layers were obtained: the bottom side exhibited spherulitic structure; whereas, at the top side, a smooth layer was observed. With respect to the neat PVDF membranes, the hydrophobic character was found to be improved by the zeolite addition; in particular S-1 nano-seeds. The mechanical properties of the membranes were reduced by the addition of the filler, although the mechanical resistance of the MMMs was still sufficiently preserved. Experiments of hexane adsorption were carried out in order to evaluate the performance of the adsorbers in Volatile Organic Compounds (VOCs) removal. The as-prepared composite porous membranes revealed high adsorption capacity, confirming their potential as adsorbers for removing VOCs traces from waste air environment. [ABSTRACT FROM AUTHOR]

In the last years, intense research efforts were dedicated to the development of zeolite membranes in different separation processes. In this work, zeolite membranes were prepared and characterized by means of single gas and pure water permeation test. Moreover, the membranes performance in vacuum membrane distillation was also studied to determine their potentiality for desalination. Uncalcined defect free MFI (silicalite) membranes on different tubular supports were synthesized by using the secondary growth method coupled with the cross flow seeding procedure. Gas permeation tests showed that, using a support with pore size of 70 nm and a zeolite slurry concentration of 0.032 wt.%, uncalcined defect free MFI membranes were synthesized. To seal the defects formed after the calcination, two different curing treatments, new cross flow filtration with small crystals and dip coating with PDMS, were carried out. Very low defects concentration for the membranes cured with small crystals was evidenced in pure water permeation tests. In fact, permeance values in the nanofiltration range were obtained. Furthermore, these zeolite membranes were used in vacuum membrane distillation tests with promising results in terms of fluxes and salt rejections. [ABSTRACT FROM AUTHOR]

The article reports the preparation of novel composites with hierarchical porosity and their evaluation as CO 2 adsorbents. An activator solution and metakaolin were used as starting mix. Activated carbon, characterized by a surface area of 528 m2/g and a bimodal porosity centered at 4.2 Å and 10 Å, was added to the starting mix to produce hybrid composites. It was in-house produced by thermo-chemical activation of olive pomace waste. H 2 O 2 and egg protein were added to the mix as a facile method to produce foamed composites. Multiphase reaction–crystallization processes, characterized by one or two thermal steps, were designed to favor geopolymerization and in-situ NaX zeolite gel conversion of metakaolin. Both the thermal procedures produce composites in forms of monoliths, as needed for application in real processes. The two thermal steps process, of which the latter is hydrothermal, increases the amount of NaX crystalline phase produced. The foaming process decreases the density and the mechanical properties of the monoliths but it does not affect the geopolymerization and crystallization reactions or the topology of the produced zeolite. The combination of raw materials and thermal treatments affect the textural properties of the adsorbents, mainly in terms of different contribution of ultramicroporosity (<7 Å) and super microporosity (7–20 Å). Several CO 2 adsorption/desorption measurements at room temperature (298 K) up to 15 bar were carried out on all the prepared adsorbents. The information about the textural properties was promptly used to explain the different CO 2 storage capacities, the different behaviours in the reversibility of the single adsorption/desorption process and the different decrease of the maximum storage capacity of the composites with cycling. Notably, all the adsorbents store, already at 1 bar, almost 60% of the CO 2 uptake at the maximum analyzed pressure. The strength of solid-gas interaction was also assessed by the calculating the values of Toth equation fitting parameter K. The proposed robust and facile preparation processes are aimed to obtain adsorbents able to overcome the shortcomings of conventional packed beds by exploiting the binding properties of geopolymer, the adsorption properties of zeolite NaX, the tailored pore structure, the electrical conductibility and the high stability of activated biochar and the macroporosity introduced by the foaming agent. [Display omitted] • Olive pomace was used to produce activated carbon with mixed pore size distribution. • Monoliths were obtained via geopolymerization followed by in situ NaX gel conversion. • H 2 O 2 , egg protein and activated carbon were used to produce foamed/hybrid monoliths. • High CO 2 capacity was measured in foamed/unfoamed multiphase hybrid monoliths. • High adsorbent/CO 2 strength of interaction was found using Toth/Langmuir model. [ABSTRACT FROM AUTHOR]

The 129Xe-NMR method was used for evaluation of the sizes of free volume elements in amorphous glassy materials—random copolymers of tetrafluoroethylene and perfluorodioxoles of different structures. 129Xe chemical shifts were measured at different pressures up to 1060 Torr. The zero pressure chemical shifts obtained by extrapolation were used for calculation of the diameters of microcavities having spherical and cylindrical shapes. The sizes of microcavities are consistent with those found by means of positron annihilation lifetimes and inverse gas chromatography methods. [Copyright &y& Elsevier]

• Faster calcination procedure. • Optimization of the vacuum membrane distillation performance. • Reduced cleaning time between membrane distillation tests. A supported Mordenite Framework Inverted (MFI) zeolite membrane with a length of 30 cm was synthesized by the secondary growth method using a fast heating profile for the template removal (calcination) step. The presence of defects into the zeolite layer (before and after calcination) was assessed by means of single gas permeation tests. Afterwards, the membrane performance was evaluated in Vacuum Membrane Distillation (VMD) for desalination. Two cleaning procedures were applied between consecutive experiments on salty solutions and their efficiency compared. NaCl rejections of 99.9% were achieved for feeds ranging from 0.2 M to 0.9 M, dropping down to 97% for the 1.2 M feed. The highest trans-membrane flux (20.6 kg m−2 h−1) was measured for 0.2 M feed, by working at 70 °C and 120 L/h. [ABSTRACT FROM AUTHOR]