Positive Pressure Filtration Research Articles

Small-Scale Solids Production Plant with Cooling Crystallization, Washing, and Drying in a Modular, Continuous Plant

Small-scale continuous apparatuses for solid product manufacturing are receiving increasing interest due to the demand for the fast market availability of specialty chemical products manufactured in integrated and modular processing plants. Relevant unit operations span from crystallization over solid–liquid separation and filter cake washing to drying. For this purpose, the quasi-continuous filter belt crystallizer (QCFBC) was developed and is presented here. The newly integrated unit operations with positive pressure filtration (Δpmax = 0.8 bar), filter cake washing (V˙wash = 55 mL·min−1), and convection drying (Tdry = 60 °C) have been individually characterized and integrated into the filter apparatus that has been modified for continuous operation. They were synchronized with the flexible cooling crystallization, enabling for a seamless production process. Sucrose in water was used as model substance system. Long-term operations of up to 14 h were successfully performed with dry product filter cakes (22.64 g ± 1.64 g·h−1) of constant quality attributes (x50,3 = 216.095 ± 14.766, span = 0.347 ± 0.109, Yrel. = 69.9% ± 5%, XRM = 1.64 mg·g−1 ± 1.38 mg·g−1).

Foaming of oxidized nanocellulose for the preparation of high-flux water filters

Treatment of polluted water is an important task to secure access to clean water also for future generations. Filters are an efficient means to reject various pollutants on a wide range of size scales either by size-exclusion or electrostatic interaction, respectively. Commonly, filters and membranes from various synthetic materials are employed for these applications. Recently, filters based on renewable (nano) cellulose papers and coatings emerged as sustainable alternative to synthetic materials usually utilized. However, fabrication of such paper network structures from aqueous suspension by filtration processes is a time-consuming process caused by the high water holding capacity of highly hydrophilic and negatively charged nanocellulose fibrils. To optimize the preparation of nanocellulose coated filters, substitution of water by air and thus generating nanocellulose foams that are collapsed onto a substrate would be an appealing approach. Here we present the development of foams from negatively charged TEMPO-oxidized nanocellulose by screening various surfactants and concentrations to generate a foam stable enough to be transferred onto a viscose substrate. Foams were collapsed by oven consolidation, positive pressure filtration, or hot-pressing, respectively. Consolidated filters were tested for their water permeance and rejection of heavy metal ions using copper ions as model system. Very high permeances competitive to commercial filters based on synthetic polymers were achieved. Furthermore, adsorption capacities for copper of up to 70 mg/g were found. This is close to adsorption capacities reported for negatively charged TEMPO-oxidized nanocellulose in conventional batch-wise static adsorption. However, in the current process adsorption takes place during filtration of water through filters in a continuous process which constitutes a tremendous advantage.Graphical

Reagent elution combined with positive pressure filtration: A zero-discharge method for cyanide tailings remediation

At present, the cyanide gold extraction process is still the main technology for gold production. Generated cyanide tailings containing highly toxic substances exhibit potential environmental risks. These tailings are in urgent need of purification treatment, especially after being classified as hazardous waste. In this study, the impacts of elution methods, operating time, tailings/water ratios, reagent types on the elution rates of cyanide were investigated. Furthermore, the composite elution method developed in this research was extended for engineering. Results showed that the optimum elution conditions were determined to be: stirring elution, tailings/water ratio (M/V; 1:1) and operating time (10-20 min). Besides, 4 reagents (sodium dodecyl benzene sulfonate, cyclodextrin, sodium silicate and calcium hydroxide) were selected from four categories of 21 reagents for further composite elution. The cyanide elution rate was the highest (90.7%±0.1%) while the molar ratio of these 4 reagents was 5:2:2:1. Moreover, the combination of reagent elution and positive pressure filtration improved the elution efficiency of cyanide (92.6%±0.8%). And the cyanide content in the toxic leaching solution was lower than the standard value (5.0 mg/L). Furthermore, the composite elution method developed in this study was also extended for engineering. The concentration of cyanide in the leachate was < 5.0 mg/L, and was stable during 189 days of detection. Notably, the effluent can be reused directly, or reused after further treatment. The zero discharge of effluents and solid wastes was realized in the processes. The above results provided supports for the engineering treatment of cyanide tailings.

2D foaming of ultrathin MXene sheets with highly conductive silver nanowires for wearable electromagnetic interference shielding applications owing to multiple reflections within created free space

Interest has been growing in electromagnetic interference (EMI) shielding materials in view of soaring EM radiation and its pollution control, which is necessary for public health and normal communication. To realize high EMI shielding effectiveness (SE), two factors of high electrical conductivity and strong multiple reflections are quite important. However, it is still a big challenge to obtain these two characteristics simultaneously in one material system. Here, we present a lightweight composite film integrating silver nanowires (AgNWs) as the skeleton and MXene as the covering decoration (AgNWs/Ti3C2Tx) for foaming structure. The composite film exhibits a low density of about 1 g cm−3 and an electrical conductivity of up to 15 038 S cm−1, which give a superiorly high specific EMI SE per unit thickness of 270 997 dB · cm2 g−1, and an EMI SE of 41.3 dB at a thickness of 1.2 μm (or 96.7 dB at a thickness of 40 μm) in the X-band. A film formation method of positive pressure filtration helps to easily control free space created during foaming for adequate EM wave scattering, yet remaining within the skin depth and strong multiple reflections have been achieved. The superior EMI shielding properties make the lightweight AgNWs/Ti3C2Tx composite film a promising candidate in high-end applications.

Simultaneous enhancement of electrical conductivity and mechanical properties in buckypaper-reinforced polydivinylbenzene(doped polyaniline) composites

The key barrier to design conductive polymer composites with maintained mechanical performance is to increase the content of conductive nanofillers with well-dispersity in the polymer matrix. Here we report new buckypaper (BP) reinforced polydivinylbenzene (PDVB)/doped polyaniline (DPANI) composites with significant improvement in both electrical and mechanical properties. The composites have been fabricated through a positive-pressure filtration method which features high loading of well-dispersed oxidized MWCNTs. The electrical conductivity and the elastic modulus of the BP reinforced composites were found to be 11.56 and 6.88-times improved, respectively, compared to the native PDVB(DPANI). The enhancement mechanism is explained by the formation of electrical transport pathways and an extensive molecular-level interaction between BP and DPANI. The enhancement effect has also been confirmed by comparing the experiment result with theoretical calculations following the Tandon-Weng model. The fabrication strategy and the analysis method presented herein can be used for the design of new functional polymer composites with both high electrical conductivity and high modulus.

Binder-free freestanding flexible Si nanoparticle–multi-walled carbon nanotube composite paper anodes for high energy Li-ion batteries

Abstract

Filtration of washed erythrocytes in atherosclerosis and diabetes mellitus

A positive-pressure filtration technique, using 5 µm pore-size Nuclepore filters, was used to study erythrocyte deformability in 47 atherosclerotic patients (compared with 25 controls) and 55 diabetics (compared with 37 controls). The effects of hyperproteinaemia, which caused significant increases in plasma viscosity and whole-blood viscosity in the atherosclerotic patients, and which can also impair erythrocyte filtration, were eliminated by washing the erythrocytes. The leucocytosis of diabetes mellitus, which can also impair erythrocyte filtration, was corrected for by adjusting the filtration results to a standard leucocyte count of 7.5 × 109/l. After elimination of these extrinsic variables, the filterability of atherosclerotic and diabetic erythrocytes, from out-patients in the steady state, was not significantly different from that of control erythrocytes.

Comparison of initial-flow-rate and positive-pressure filtration methods for the study of erythrocyte deformability

Comparison of initial-flow-rate and positive-pressure filtration methods for the study of erythrocyte deformability

Improving the interlaminar fracture toughness of carbon/epoxy laminates by directly incorporating with porous carbon nanotube buckypaper

In this study, thin carbon nanotube (CNT) buckypapers (BPs) with desired porosity were prepared by using of positive pressure filtration method. The obtained porous BP was then directly incorporated into the middle interface of a composite laminate to improve the interlaminar fracture toughness. Double cantilever beam and end-notch flexure tests were conducted to examine the influence of the obtained BP on mode I and mode II interlaminar fracture toughness ( GIC and GIIC) of the laminates. Results have shown the porous BPs would significantly enhance the GIC and GIIC up to 74% and 82%, respectively. Improved interfacial bonding and increased large fracture surfaces were obtained for the laminate incorporated with thin CNT BPs. Similar enhancement was also detected in acoustic emission energy variation for mode II fracture and auxiliary proved the reinforcing effect of the BP.

Evaluation on the dewatering process of cyanobacteria-containing AlCl3 and PACl drinking water sludge

Most researches focused on the high efficiency removal of cyanobacteria from water phase during drinking water treatment, but did not address the potential danger of cyanobacterial cells being transferred into the sludge, especially during the dewatering process. In this study, the characteristics of cell lysis and microcystin (MC) release in the filtration of cyanobacteria-containing sludge were investigated. By evaluating filtration rates, filtrate microcystins (MCs) and turbidity levels, and SEM micrographs of the sludge in different operating conditions, the influences of mechanical actions and physical/chemical effects on the integrity of cyanobacterial cells were explicated, and the corresponding operation conditions were also optimized. The results showed that the sludge accumulation on unit filter area had significant influence on sludge dewatering characteristics, and with increase in the volume of sludge filtrated, more and more sludge accumulated on the surface of the filter media, resulting in reduced filtration rates and potential cyanobacteria lysis. More hydrophilic filter media with lower porosity should be chosen to enhance filtration efficiency. Compared with positive pressure filtration, vacuum filtration with low-destructibility should be a better choice considering the MC release. Under increased vacuum pressure, cyanobacteria-containing sludge had increasing filtration rate without causing damage of cyanobacterial cells. While the storage time of cyanobacteria-containing sludge should be severely restricted in actual water supply factories (4d for AlCl3 sludge and 2d for PACl sludge) to avoid the adverse influences of cyanobacteria lysis on sludge dewaterability and filtrate quality. This study produced deeper knowledge on the fate of cyanobacterial cells and intracellular MCs in the sludge dewatering process, and the results provided valuable scientific references for volume reduction of cyanobacteria-containing sludge in the actual treatment operations.

Correlation between Porosity and Electrical‐Mechanical Properties of Carbon Nanotube Buckypaper with Various Porosities

Porous carbon nanotube (CNT) buckypapers (BPs) with various porosities were obtained by using a positive pressure filtration method. The porosity of the BPs fell into a wide range of 11.3–39.3%. Electrical conductivities and tensile mechanical properties of the prepared BPs were then measured and correlated with the porosity of the CNT BPs. Results demonstrated that the conductivities, tensile strength, and elastic modulus of the BPs could decrease by increasing their porosity. The elongation at break of the BPs on the other hand did increase significantly, suggesting improved toughness of the BPs. The obtained electrical conductivity and tensile strength of the porous BPs can reach nearly 0.6 S/m and 26 MPa, respectively, which may be potentially useful in composites reinforcement and conductive materials.

Effect of beraprost, a stable prostacyclin analogue, on red blood cell deformability impairment in the presence of hypercholesterolemia in rabbits.

We evaluated the effects of orally administered beraprost, a stable prostacyclin analogue, on the rheological behavior of red blood cells (RBC) in the presence of hypercholesterolemia. Rabbits fed a cholesterolrich diet were administered various doses of beraprost or pravastatin. We evaluated rheological behavior of RBC by assessing RBC deformability, using a positive-pressure filtration method. The maximum pressure generated by passing a suspension of RBC through a membrane filter was used as an index of RBC deformability. After animals were fed cholesterol for 16 weeks, the maximum pressure increased significantly from 172 +/- 15 mm Hg at baseline to 261 +/- 18 mm Hg (p < 0.01, n = 24). The reduction in RBC deformability associated with hypercholesterolemia improved dose dependently during 1-h incubation with various doses of beraprost. In ex vivo study, beraprost markedly restored RBC deformability 3 h after its oral administration to 218 +/- 17 mm Hg (n = 9) at a low dose and to 215 +/- 20 mm Hg (n = 9) at a high dose. The effect persisted for at least 2 h. Pravastatin failed to reduce the increased maximum pressure. Findings suggest that beraprost treatment may improve the microcirculation by restoring RBC deformability in the presence of hypercholesterolemia.

Leucocytes and free radicals in stable angina pectoris.

Bicycle ergometer exercise was used to induce ischemia in 20 patients with stable angina pectoris (SAP). Superoxide dismutase (SOD) blood concentrations, free radical generation (by the SOD-inhibitable reaction of ferricytochrome C), malondialdehyde (MDA) plasma concentrations, the unfractionated leucocyte filterability rate and the filterability rates of the granulocyte and mononuclear sub-fractions (using a positive pressure filtration system and 5 mu diameter Nuclepore filters), were monitored before and after exercise in the patients and in 18 matched controls. At the onset of ischemia a significant increase in the level of MDA plasma concentrations and significant decreases in both SOD blood concentrations and the SOD-inhibitable reduction of ferricytochrome C indicated oxygen free radicals had been released in the SAP patients. These changes were associated with significant impairments of granulocyte and unfractionated leucocyte filterabilities and with morphological evidence of granulocyte activation.

Biological qualities of saliva sterilized by filtration or ethylene oxide treatment

Stimulated whole saliva was centrifuged and sterilized either by filtration in the presence or absence of dithiothreitol (DTT) or by ethylene oxide treatment. Filtration was accomplished by 2 different techniques: conventional positive pressure filtration through prefilters and membranes with decreasing pore sizes and tangential flow microporous filtration. The sterile saliva samples were analyzed for enzyme activities of phosphatases, esterases, glucuronidase, and lysozyme. The samples were also tested by polyacrylamide electrophoresis, isoelectric focusing and for IgA concentration. Moreover, the samples were tested for support of bacterial growth of strains from the genera Actinomyces, Lactobacillus, Neisseria, Rothia and Streptococcus after the addition of glucose at a final concentration of 0.5%. The samples treated with ethylene oxide appeared to be more affected by this treatment than samples treated otherwise, as demonstrated by the electrophoretic analyses and analyses of enzyme activities. Ethylene oxide-treated saliva also was the least favorable saliva sample to support growth of bacteria. The positive pressure technique gave more rapid filtration than the tangential flow technique. DTT treatment of saliva facilitated filtration and, in contrast to ethylene oxide treatment, it affected the qualities of saliva only to a minor extent compared with the original saliva sample.

A simple positive pressure apparatus for the ultrafiltration of soil solution

Abstract A positive pressure filtration apparatus is described which employs compressed gas to provide the differential pressure required to permit the ultrafiltration of soil solution. The apparatus uses low‐cost membrane filter elements and is suitable for use with small volume samples, as there is little retention of solution within the filtration cells. Initial flow rates of‐5 and 25 mL/min were achieved through 0.025 and 0.05 μm pore‐diameter filter elements, respectively. Compressed nitrogen is the preferred gas source as exposure of solutions of pH 6 or higher to compressed air resulted in a lowering of pH levels.

Relative contribution of leukotriene B4 to the neutrophil chemotactic activity produced by the resident human alveolar macrophage.

Human alveolar macrophages release chemotactic activity for neutrophils, providing a role for alveolar macrophages in regulating inflammation in the lung. As alveolar macrophages produce large amounts of leukotriene B4 (LTB4), a chemotactically active lipoxygenase product of arachidonic acid, we investigated the contribution of LTB4 to the total neutrophil chemotactic activity produced by these cells. Normal human alveolar macrophages were recovered by bronchoalveolar lavage from healthy volunteers and incubated either with the calcium ionophore A23187 for 1 h, or with opsonized zymosan particles or latex beads for 3 h. Nordihydroguaretic acid (NDGA), a relatively specific lipoxygenase inhibitor, blocked the release of neutrophil chemotactic activity after all three stimuli in a dose-dependent manner. This correlated with blockade of LTB4 production as measured by high performance liquid chromatography using freshly isolated alveolar macrophages, as well as blockade of [3H]LTB4 production by macrophages prelabeled with [3H]arachidonate. Molecular sieve chromatography using Sephadex G-50 confirmed that essentially all of the chemotactic activity in the stimulated macrophage supernatants co-eluted with authentic [3H]LTB4, and that NDGA completely blocked the chemotactic activity in the eluting fractions. Readdition of authentic LTB4 (1 X 10(-7) M) to the NDGA-blocked macrophage supernatants restored the chemotactic activity in the supernatants. The macrophage supernatants did not contain platelet-activating factor-like activity, as measured by the stimulation of [3H]serotonin release from rabbit platelets, and by high performance liquid chromatography. NDGA did not change the protein-secretion profiles of fresh alveolar macrophages, or of macrophages prelabeled with [35S]methionine. The complement (C) components C5adesarg were not detected in any of the supernatants by radioimmunoassay. Concentration of the supernatants by positive pressure filtration (5,000-D membrane) did not augment chemotactic activity in the stimulated supernatants or uncover chemotactic activity in the NDGA-blocked supernatants. As with the 3-h studies, when alveolar macrophages were incubated overnight with opsonized zymosan, all of the increase in chemotactic activity could also be blocked by NDGA. These data indicate that LTB4 is the predominant neutrophil chemotactic factor secreted by the normal resident human alveolar macrophage in response to two major types of stimuli, calcium fluxes across the cell membrane and the phagocytosis of opsonized particulates.

Filtration deformability of rabbit pulmonary macrophage.

Rabbit PAM deformability was evaluated by positive-pressure filtration through Nucleopore membranes of well-specified pore diameter. The PAM filtration method was standardized and was influenced by apparatus variations (pore size, flow rate, cell concentration), environment (temperature, pH, divalent cations, protein concentration), and differences in PAM cell volume. The influence of phagocyte function on filtration deformability was evaluated by exposing PAMs to pharmacologic and physiologic agents with somewhat exclusive influences on phagocyte physiology. Agents that interact with microfilament contractile protein (N-ethylmaleimide, cytochalasin B) altered deformability profoundly, but no effect was observed with agents interacting with microtubules (vinblastine, colchicine). Agents that cause general PAM activation (phorbol myristate acetate) or stimulate chemotaxis (F-Met-Leu-Phe) increased deformability. On the contrary, PAM deformability was not changed by phagocytosis of Staphylococcus aureus or latex beads. Pharmacologic agents that alter PAM adhesion (aspirin, indomethacin, physiologic dose hydrocortisone) or inhibit glycolysis (2-deoxyglucose) had no influence on filtration deformability. Filtration PAM deformability reflects passive whole cell rigidity, which appears to be determined by the state of polymerization of the actin-myosin microfilament complex.

An Apparatus for Sterilizing Heat-labile Solutions

POSITIVE pressure filtration for the sterilization of fluids avoids the risks of suck-back from the pump and prevents concentration of the fluid by evaporation. It is, however, more difficult to ensure sterile collection of the filtrate. The apparatus shown in Fig. 1 minimizes the risks of infection. The narrow funnel containing the glass sinter fits into an elongated bell-housing, its stem projecting into a Universal container, wedged into the housing with cotton- wool.