Electrically enhanced crossflow membrane filtration of oily waste water using the membrane as a cathode

The effect of an external electric field on the flux in crossflow membrane filtration of a model oily waste water was studied using a carbon fibre – carbon composite membrane as a cathode. Limiting fluxes for low flow rate increased significantly under the conditions studied, from 75 l/m² h without an electric field to more than 350 l/m² h using an electric field. The experimentally determined increase in the limiting flux showed good agreement with the theoretical value of 430 l/m² h calculated using a simple model. The limiting flux increase was affected by the electrophoretic mobility of the oil droplets and the applied electric field strength. When there were no cakes without an electric field due to the high flow rate, the flux increase when using an electric field under at the same conditions was minor. The critical electric field strength was determined, and experimentally obtained values were corresponded with calculated values. Decreasing the crossflow velocity above the critical electric field strength increased the flux, or had no effect, depending on the size of the particles. Permeate quality was also improved to some extent when using the electric field, and a membrane with a large pore size could be used when an electric field was applied. The main disadvantage in using the membrane as a cathode was foaming at the membrane surface causing decrease in the flux enhancement as the conductivity of the feed increased. It was not possible to restore the flux to the original value by applying an electric field after filtration of the oil emulsion without an electric field. An intermittent electric field was thus not efficient enough for keeping the flux at high level.     

Economic aspects of critical flux operability in star shaped microfiltration membranes: Influence of some operating conditions

The economic feasibility of operating at the achievable critical flux under different operating parameters (feed concentration, crossflow velocities and pH) using non-circular channelled membranes has been investigated. The increase in critical fluxes with increasing crossflow velocities is accompanied by increasing axial pressure loss. This leads to substantial increase in the specific energy consumption, reducing the energy-saving potential. Minimum specific energy consumption occurs at the crossflow velocity of 0.9 m s⁻¹ where the trade-off between axial pressure loss and the achievable critical flux occurs. Increasing the feed concentrations and pH led to declining and increasing critical fluxes, respectively. Axial pressure loss remains consistent at feed concentrations <10 g l⁻¹ and increases at feed concentrations >10 g l⁻¹. This is attributed to the change in the viscosity of the suspension which affects the specific energy consumption. The influence of pH on critical flux is attributed to the changes in the titanium dioxide particle charges and coincides with the changes in the viscosity of the suspension. The optimum energy-saving potential was found at pH 9.0. Solution chemistry (particle charges and rheology) and hydrodynamics influence the achievable critical flux and axial pressure loss within these channels which ultimately determine the economics of operation.     

A new reflector structure for facility thermalizing D–T neutrons

A facility for thermalization of fast neutrons (14.2 MeV) emitted by compact deuterium–tritium (D–T) neutron generators (NGs) for thermal neutron activation analysis is proposed. Its final design is based on Monte Carlo calculations (MCNP5). To maximize the ratio between the thermal neutron flux and the total neutron flux and simultaneously to ensure the highest possible value of the thermal neutron flux at the output surface, the facility should consist of a two-layer reflector [tungsten (W)—the inner part, molybdenum—the outer part], a two-layer multiplier (W followed by lead), a moderator (polyethylene followed by magnesium fluoride) and a collimator (molybdenum and nickel near the output surface). For the D–T NG producing the maximum available neutron yield 10¹⁵ n s^?1, the facility provides the thermal neutron flux 2.0 × 10¹¹ n cm^?2 s ^?1 and a slightly higher fast neutron flux 2.3 × 10¹¹ n cm^?2 s^?1. To improve the ratio of the thermal neutron flux to the fast neutron flux (above 2.7) an addition of a silicon layer to the moderator and especially a proper adjustment and a threefold increase of the multiplier thickness is necessary.     

Flux decline in crossflow microfiltration and ultrafiltration: experimental verification of fouling dynamics

The theory of fouling dynamics in crossflow membrane filtration is compared with ultrafiltration experiments with suspensions of 0.12 μm silica colloids. It has been experimentally verified that colloidal fouling in crossflow filtration is a dynamics process from non-equilibrium to equilibrium and that the steady state flux is the limiting flux. With the cake concentration c_g identified from an independent experiment and the specific cake resistance calculated by Carman–Kozeny equation, the time-dependent flux and the time to reach steady state in the experiments of this study are correctly predicted with the theory of fouling dynamics.     

Pilot plant studies of novel membranes and devices for direct contact membrane distillation-based desalination

A small pilot plant for direct contact membrane distillation (DCMD) based desalination was built and operated successfully on a daily basis for 3 months. The operation employed hot brine at 64–93 °C and distillate at 20–54 °C. The hot brine was either city water, city water containing salt at the level of 3.5, 6 or 10%, or sea water trucked in from Long Island Sound, CT. One to ten horizontal crossflow hollow fiber membrane modules each having either 2448 or 2652 hollow fibers and 0.61 or 0.66 m² surface area were combined in various configurations to study the plant performance. The highest water vapor flux of 55 kg/(m² h) was achieved with two modules in series; the flux varied between 15 and 33 kg/(m² h) for configurations employing 6–10 modules. The highest distillate production rate achieved was 0.62 gallons per minute (gpm). The membrane modules never showed any sign of distillate contamination by salt. The plant operated successfully with a very limited flux reduction at salt concentrations up to 19.5% from sea water. A mathematical model was successfully developed to describe the performance of the pilot plant with multiple crossflow modules in different test configurations.     

Experimental evaluation of a uniform transmembrane pressure crossflow microfiltration unit for the concentration of micellar casein from skim milk

A uniform transmembrane pressure (UTMP) crossflow microfiltration (CFMF) system maintains a low but uniform transmembrane pressure (ΔP_TM) with high crossflow velocity (CFV), which reduces fouling and cake build-up, and improves the utilization of available filtration area. A CFMF system, with a 0.2 μm nominal pore size ceramic filter, filtration area 0.184 m², was operated in both UTMP and non-UTMP modes. The two modes were compared for their effectiveness in maintaining a steady flux during the separation of casein micelles from skim milk up to a concentration factor (CF) 10 at 50°C. Experiments were performed at an average CFV of 7.2 m s⁻¹ and ΔP_TM from 89 to 380 kPa. Up to CF 4 the non-UTMP mode maintained a slightly better flux and process time than the UTMP mode, but reached the minimally acceptable flux (below 0.005 kg m⁻² s⁻¹) at CF 6. Depending upon the ΔP_TM maintained, the UTMP mode approached the minimal flux at CF 7 or 10 depending upon the combination of ΔP_TM and CFV used. Cake resistance (R_cm) was modified to include the effect of an increase in retentate viscosity with concentration. R_cm increased for the non-UTMP mode and decreased for the UTMP mode with a decrease in the ratio of permeation flux/wall shear stress (J_p/τ_w) (which occurred as the retentate gets concentrated). This indicated that the cake formed during the non-UTMP mode of operation was more compact and durable (harder to erode) than in the UTMP mode. A central composite rotatable design estimated the optimal operating region at a CFV of 7.1 m s⁻¹ and ΔP_TM of 241±10 kPa to achieve maximum flux and a high concentration.     

Use of alternating electrical fields as anti-fouling strategy in ultrafiltration of biological suspensions – Introduction of a new experimental procedure for crossflow filtration

Results of a parameter study concerning the electro-ultrafiltration with alternating electric fields of aqueous solutions of bovine serum albumin are presented. The alternating electric field diminishes membrane fouling and hence yields a higher specific filtrate flux. The effect of the electric field depends on frequency (0.5–50 Hz), field strength (0–80 V cm⁻¹), conductivity (1–10 mS cm⁻¹), protein concentration (0.1–5 w%), and membrane material (values in brackets are the range of each parameter examined in this work). Low frequency and high field strength yield the best result for electro-ultrafiltration with alternating fields. The effectiveness of the electric field increases with rising conductivity up to the point where a limiting electrolytic current is reached. Increasing protein concentration diminishes the effect of the electric field. A new procedure to perform crossflow filtration experiments, the so-called step-change experiment, is proposed. The results of the new procedure are compared to results of conventional experiments. The step-change experiments yielded reproducible results in good agreement with conventional experiments.     

Influence of inorganic scalants and natural organic matter on nanofiltration membrane fouling

The influence of inorganic scalants and NOM on nanofiltration (NF) membrane fouling was investigated by a crossflow bench-scale test cell. Mathematical fouling models were used to determine kinetics and fouling mechanisms of NF membrane. It was observed that, with natural organic matter (NOM) at a concentration of 10 mg L⁻¹, divalent cation, i.e. calcium (Ca²⁺), exhibited greater flux decline than monovalent cation, i.e. sodium (Na⁺), while solution flux curves dominated cake formation model, especially at high ionic strength. For inorganic scalants of polyanions, i.e. carbonate (CO₃²⁻), sulphate (SO₄²⁻), and phosphate (PO₄³⁻), solution flux curves were relatively fitted well with pore blocking model, possibly due to precipitated species formed and blocked on membrane surface and/or pores. For different divalent cations (i.e. calcium and magnesium (Mg²⁺)), calcium showed greater flux decline than magnesium, possibly due to higher concentration of precipitated calcium species than that of precipitated magnesium species based on the pC (−log concentration) and pH diagram.     

Determination of neutron flux parameters in PUSPATI TRIGA Mark II Research Reactor, Malaysia

In standardization NAA, it is necessary to characterize the neutron spectrum parameters such as epithermal neutron flux shape factor (α), thermal to epithermal neutron flux ratio (f), thermal neutron flux (φ _th) and epithermal neutron flux (φ _epi) in the irradiation facility to determine the concentration of an element in the sample using absolute and k ₀ standardization methods. The α and f were determined using Cd-ratio multi monitor method using experimental data obtained in PUSPATI TRIGA Mark II research reactor at four irradiation positions (10, 20, 30 and 40) of the rotary rack. The calculated values of α and f ranged from 0.006 to 0.0281 and 18.56 to 19.12 respectively. The average values of φ _th and φ _epi were found as 2.33 × 10¹² and 1.23 × 10¹¹ n cm^?2 s^?1 respectively. Moreover, a comparison of the neutron flux parameters in the present study shows an acceptable level of consistency with those of previous studies.     

Aktivierungsanalytische Bestimmung von Thallium in gesteinen

In a series of rock samples—including some USGS standard rocks—thallium was determined by thermal neutron activation analysis. After complete radiochemical purification the radioactivity of the samples was measured with conventional methane flow counters using the 97.9% β-decay and by evaluating the Hg-X-rays from 2.1% electron capture of²⁰⁴T (T=3.8y). Whith a Ge(Li) detector concentrations of 1 ppb (after 3 days irradiation at a thermal neutron flux of 6·10¹³ n·cm^?2·sec^?1) could be detected after a very simple radiochemical procedure based on ion exchange.     

Removal of suspended clay from water using transmembrane pressure pulsed microfiltration

Transmembrane pressure pulsing (TPP) uses the frequent and periodic reversal of the transmembrane pressure to reduce flux resistances due to membrane fouling. This study examined the effect of TPP on the microfiltration of simulated drinking water (hydrated aluminum silicate solution). Solutions of kaolin clay (0.1–4.0 μm particles, at an approximate concentration of 500 mg l⁻¹ and a turbidity of 402±17 NTU, 0.5 mM CaCl, 2.0 mM NaHCO₃, pH 7.5–7.8) were microfiltered with polyethersulfone (PES) 0.16 μm microfiltration membranes at an operating pressure of 30 kPa. Crossflow shear rates were varied between 165 and 1490 s⁻¹. Pulse frequency was varied between 0.3×10⁻² and 2 Hz, and pulse amplitude was varied between −3 and −16.5 kPa. It was found that the crossflow shear rates did not significantly effect the non-pulsed permeate flux. An optimum pulse amplitude of about 10 kPa was necessary to maximize the permeate flux for pulse frequencies between 0.3×10⁻² and 2.0 Hz. To insure a reduced solute flux, pulse frequencies less than 0.1 Hz were required. These results indicate that TPP can significantly reduce membrane fouling by inorganic particulate materials that are potentially important constituents of natural waters without negatively impacting the rejection of sub-micron particles due to interactions with material accumulated on the membrane.     

High conduction neutron absorber to simulate fast reactor environment in an existing test reactor

A new metal matrix composite material has been developed to serve as a thermal neutron absorber for testing fast reactor fuels and materials in an existing pressurized water reactor. The performance of this material was evaluated by placing neutron fluence monitors within shrouded and unshrouded holders and irradiating for up to four cycles. The monitor wires were analyzed by gamma and X-ray spectrometry to determine the activities of the activation products. Adjusted neutron fluences were calculated and grouped into three bins—thermal, epithermal, and fast—to evaluate the spectral shift created by the new material. A comparison of shrouded and unshrouded fluence monitors shows a thermal fluence decrease of ~11 % for the shielded monitors. Radioisotope activity and mass for each of the major activation products is given to provide insight into the evolution of thermal absorption cross-section during irradiation. The thermal neutron absorption capability of the composite material appears to diminish at total neutron fluence levels of ~8 × 10²⁵ n/m². Calculated values for dpa in excess of 2.0 were obtained for two common structural materials (iron and nickel) of interest for future fast flux experiments.     

The Rules Governing the Formation of Silver Azide Photolysis Products

Irradiation of silver azide at λ = 365 nm (I > 1 × 10¹⁵ quantum cm^?2 s^?1) in a vacuum (1 × 10^?5 Pa) leads to an increase in the rate of photolysis and photoinduced current and the appearance of a new long-wave region of spectral sensitivity. The photolysis products, silver metal and gaseous nitrogen, are formed in a stoichiometric ratio on the surface of silver azide. The rate constants for silver azide photolysis were determined. Measurements of contact potential difference, current—voltage characteristics, photoelectromotive force, and photocurrent showed that AgN₃(A₁)—Ag (photolysis product) microheterogeneous systems were formed in silver azide photolysis. The limiting stage of silver azide photolysis is the diffusion of interstitial silver cations to the (T_nAg_m)⁰ neutral center.     

Kinetics of the reactions of OH radicals with n-alkanes at 299 ± 2 K

Relative rate constants for the reaction of OH radicals with a series of n-alkanes have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with n-butane of 2.58 × 10^?12 cm³ molecule^?1s^?1, the rate constants obtained are (X10¹² cm³ molecule^?1 s^?1): propane 1.22 ± 0.05, n-pentane 4.13 ± 0.08, n-heptane 7.30 ± 0.17, n-octane 9.01 ± 0.19, n-nonane 10.7 ± 0.4, and n-decane 11.4 ± 0.6. The data for propane, n-pentane, and n-octane are in good agreement with literature values, while those for n-heptane, n-nonane, and n-decane are reported for the first time. These data show that the rate constant per secondary C—H bond is ∽40% higher for —CH₂— groups bonded to two other —CH₂— groups than for those bonded to a —CH₂— group and a —CH₃ group.     

Modeling of concentration polarization and depolarization with high-frequency backpulsing

Rapid backpulsing to reduce membrane fouling during crossflow microfiltration and ultrafiltration is studied by solving the convection-diffusion equation for concentration polarization and depolarization during cyclic operation with transmembrane pressure reversal. For a fixed duration of reverse filtration, there is a critical duration of forward filtration which must not be exceeded if the formation of a cake or gel layer on the membrane surface is to be avoided. The theory also predicts an optimum duration of forward filtration which maximizes the net flux, since backpulsing at too high of frequency does not allow for adequate permeate collection during forward filtration relative to that lost during reverse filtration, whereas backpulsing at too low of frequency results in significant flux decline due to cake or gel buildup during each period of forward filtration. In general, short backpulse durations, low feed concentrations, high shear rates, and high forward transmembrane pressures give the highest net fluxes, whereas the magnitude of the reverse transmembrane pressure has a relatively small effect.Rapid backpulsing experiments with yeast suspended in deionized water performed with a flat-sheet crossflow microfiltration module and cellulose acetate membranes with 0.07 μm average pore diameter. The optimum forward filtration times were found to be 1.5, 3, and 5 s, respectively, for backpulse durations of 0.1, 0.2, and 0.3 s. Both theory and experiment gave net fluxes with backpulsing of about 85% of the clean membrane flux (0.022 cm/s = 790 l/m² h), whereas the long-term flux in the absence of backpulsing is an order-of-magnitude lower (0.0026 cm/s = 94 l/m² h).     

The New Cesium Praseodymium Thiophosphate Cs3Pr5[PS4]6

Transparent platelet‐shaped green single crystals of the title compound were obtained by the reaction of cesium bromide, praseodymium, sulfur, and red phosphorus in the molar ratio 1:2:8:2 with an excess of CsBr as flux in evacuated silica ampoules at 950 °C for fourteen days. Cs₃Pr₅[PS₄]₆ crystallizes monoclinically in the space group C2/c (a = 1627.78(7), b = 1315.09(6), c = 2110.45(9) pm, β = 103.276(5)°; Z = 4). Its crystal structure is different from all the other alkali‐metal containing ortho‐thiophosphates of the lanthanides, since it is not possible to formulate a layer containing the praseodymium centered sulfur polyhedra ([PrS₈]^13—, d(Pr—S) = 286 — 307 pm) and the isolated [PS₄]^3— tetrahedra (d(P—S) = 202 — 207 pm, ?(S—P—S) = 104 — 106°). All these tetrahedra are edge‐sharing with the metal polyhedra to build up a framework instead. The coordination sphere of the half occupied (Cs2)⁺ cations (CN = 10 + 2) can be described as two six‐membered sulfur rings in chair conformation containing a “cesium‐pair” in the middle. In contrast the (Cs1)⁺ cations are surrounded in the not unusual configuration of tetracapped trigonal prisms (CN = 10, better 10 + 2 as well).     

IONIC CONDUCTIVITIES OF SEGMENTED POLYETHER POLYURETHANEUREA COMPLEXES WITH LiClO4

Ionic conductivity values for segmented polyether polyurethaneurea (PEUU) complexes with LiClO_4 were determined and values as high as～1.1×10~(-4) S·cm~(-1) at 353K and～1.0×10~(-5)S·cm~(-1) at 306K were achieved. The ionic conductivity data were analyzed using the VTF (Vogel-Tamman-Fulcher) equation and WLF (Williams-Landel-Ferry) type equation. Values have been estimated for the "apparent" activation energies of ion transport from VTF equation and they lie in the range 2.70—5.53 kJ·mol~(-1).     

Ultrasonic Solution Degradations of Poly(Alkyl Methacrylates)

Ultrasonic (70 W, 20 kHz) solution (2%) degradations of poly(alkyl methacrylates) have been carried out in toluene at 27°C and in tetrahydrofuran (THF) at -20°C. M_w and M_n of all polymers (before and after sonification) were computed from GPC. Irrespective of the alkyl substituent, M_w decreased rapidly at first and then slowly approached limiting values. All M_w/M_n ratios were in the vicinity of 1.5 at the limiting chain lengths. For identical M_n, the rate constants k were (4.2 ± 2.0) × 10^?6 min^?1 in toluene at 27°C and (5.4 ± 2.0) × 10^?6 min^?1 in THF at -20°C. For poly(isopropyl methacrylate) and poly(octadecyl methacrylate) with higher, but identical, M_n,0, k values were higher ((9.0 ± 1.0) × 10^?6 min^?1 at 27°C and (18.0 ± 1.5) × 10^?6 min^?1 at -20°C). This suggests that M_n,0 and not the bulk size of the alkyl substituents is the factor that determines the rate of degradation. Lowering of the temperature accelerates degradation due primarily to lower chain mobility of poly-(alkyl methacrylates) and enhanced cavitation. The average number of chain scissions ([(M_n)₀/(M_n)_t] - 1) calculated from component degradation data are much higher than those obtained with overall M_n,t values.     

Evaluation of metal hydride thermograms by a differential-correction technique

A least-squares linear-Taylor differential-correction technique has been used for the rapid evaluation of thermogravimetric curves obtained during the decomposition of magnesium hydride, iron—titanium hydride and lanthanum—nickel hydride. For magnesium hydride and iron—titanium hydride the Avrami—Erofe'ev equation fits the experimental data, thus indicating that nucleation is the rate-determining step under thermogravimetric conditions. For lanthanum—nickel hydride a combination of the Avrami—Erofe'ev equation and the phase boundary movement equation fits the data up to a fractional decomposition of 0.8. For magnesium hydride decomposition the activation energy E and the pre-exponential factor Z are dependent on the hydrogen pressure (E = 101.2 kJ mole^?1 and Z = 8.96 × 10⁷ at 0.30 MPa, while E = 66.3 kJ mole^?1 and Z = 4.77 × 10⁷ at 0.11 MPa). For iron—titanium hydride (E = 28.4 kJ mole^?1) and lanthanum—nickel hydride (E = 13.4 kJ mole^?1) the values are independent of pressure.     

Self-forming dynamic membrane for ultrafiltration of pineapple juice

The formation of self-forming dynamic membrane on a porous ceramic support was studied. Pineapple juice of 12° Brix concentration was used in the experiments which were carried out at 25°C by circulating the pineapple juice at the applied pressure of 100, 200, and 300 kPa and at cross-flow velocities of 1.30–2.95 m s⁻¹ through the ceramic membrane module for 1 h. The experimental data of flux and rejections showed that the dynamic membrane was well-formed after 30 min of circulation under the applied pressure of 300 kPa and at a cross-flow velocity of 2.0 m s⁻¹ in which the steady values of flux and rejections of macromolecules and sugars obtained from the filtration mode were 6.0×10⁻³ m³/m² h, 84–87% and 6%, respectively. The corresponding values for ultrafiltration by alumina membrane of MW cut-off 50,000, using equivalent conditions, were 15.8×10⁻³ m³/m² h, 91% and 10.5%. Ultrafiltration was found to be more promising. The stability of the self-forming dynamic membrane was acceptable when subjected to change of filtration conditions. The permeation flux increased with cross-flow velocity and decreased when the applied pressure was reduced. The resistances for filtration by dynamic membrane and by ultrafiltration were calculated. For a porous support of large pore sizes, an in-pore blockage of solutes which were smaller than the membrane pores reduced the pore volume and induced fouling. Internal fouling resistance (R_f) was, therefore significant and responsible for the values of flux and rejection and was approximately 70% of total resistance. While in ultrafiltration, in which membrane with a smaller pore diameter was used, R_f was only 20% but R_p, the polarized layer resistance, was as high as 60% of total resistance.