Jiří Cakl

Effects of backflushing conditions on permeate flux in membrane crossflow microfiltration of oil emulsion

The paper reports results of experiments with oil-in-water emulsion, which were carried out in a laboratory crossflow microfiltration unit equipped with backflushed zirconia ceramic membranes. The results demonstrate that the membrane backflushing can maintain the permeate flux at a level which is nearly three-fold over the long-term flux in the absence of membrane backflushing. It was observed that the effect of backflushing was the more pronounced when the backpulse duration was shorter, the transmembrane pressure difference was higher, and the retentate velocity was lower in forward filtration. An optimum backflushing frequency which maximized the average permeate flux was found to be in the range of 1 to 50 s depending on the operating conditions. The magnitude of the transmembrane pressure difference in the reverse flow had a relatively small effect. Attempt has also been made to explain the results in terms of a simple semiempirical model of the process. Parameters evaluated from dynamic and steady state experiments without membrane backflushing were shown to be useful in estimating the performance of the process with membrane backflushing. The influence of backflushing duration and frequency, transmembrane pressure difference, and retentate velocity on average permeate flux were well predicted using this model.

Permeate flow in hexagonal 19-channel inorganic membrane under filtration and backflush operating modes

Numerical simulations and experimental study of incompressible Newtonian permeate flow in porous support of hexagonal 19-channel inorganic membrane are presented both for filtration and backflush operating modes. Under several simplifying assumptions the problem could be treated as two-dimensional potential flow. The mathematical model was solved using finite element method. The results of numerical simulations show that the contributions of particular channels to the total permeate flux are not equal and depend on the ratio of skin layer to porous support permeability as well as on the distance of a channel from the membrane outer surface. For membranes with high permeability of skin layer there is an area of nearly constant pressure around inner channels and their contribution to total flux is negligible. This effect will probably be more pronounced in backflush operating mode while in filtration mode possible dynamic membrane adds a resistance to that of skin layer which leads to more uniform permeate flux distribution. Qualitative trends of the numerical simulations were verified by experiments with ceramic 19-channel membranes of Membralox® type in backflush operating mode.

Flux and fouling in the crossflow ceramic membrane microfiltration of polymer colloids

Abstract The results of an experimental study of ceramic membrane microfiltration of synthetic polymer colloids differing greatly in average particle size and distribution broadness are presented. The effects of the polymer nature, pressure difference, feed velocity, and particle to membrane pore diameter ratio on the permeate flux and membrane fouling are discussed. Attempts have also been made to explain the results in terms of simple models of the operative mechanisms.

Gas-liquid two-phase flow in microfiltration mineral tubular membranes: relationship between flux enhancement and hydrodynamic parameters

Abstract An application of the gas—liquid two-phase flow for the flux enhancement during the microfiltration of aqueous titanium dioxide dispersions on an aluminium oxide tubular membrane has been studied. The results of experiments showed a positive effect of the constant gas—liquid two-phase flow on the flux. It might be concluded from the analysis of experimental results based on the dead-end filtration model that a two-phase flow seemed to expand the particle cake as it increased both the cake porosity and thickness, thus allowing higher fluxes. A mathematical model for the flux prediction during two-phase gas—liquid microfiltration has been developed. The results showed a good agreement between experimental data and model prediction.

Removal of industrial latex dispersions from waste waters using microporous alumina membranes

Abstract A study has been made on the utilization of alumina membranes for the microfiltration of dilute latex dispersions in latex production. In this operation tubular microfiltration membranes were used with the mean pore diameter equal to 0.1 μm. Feed circulation velocities ranging from 0.4–3.6 m/s (Reynolds number, Re=2,200–20,000) were investigated. It has been shown that the ceramic membranes used are acceptable for microfiltration of industrial waste water containing poly(vinyl acetate) and acrylic copolymer latex dispersions. A limiting flux was observed which depended on the species of the latexes and on the flow velocity of the feed. The decrease in the flux of permeate was attributed to the resistance of the cake (gel) layer formed on the membrane or blocking of the pores in the membrane. Several technical parameters of interest such as flux characteristics, membrane fouling, and latex stability are discussed.

Recovery of H2SO4 and NaOH from Na2SO4 by electrodialysis with heterogeneous bipolar membrane

AbstractElectrodialysis (ED) with heterogeneous bipolar membranes (BPMs) was studied experimentally on a laboratory scale in order to examine the recovery of the sodium sulfate solution into sulfuric acid and sodium hydroxide. The capacity of the system was evaluated in terms of its dependence on membrane configuration, product concentration, temperature, and circulation flow rate. A preliminary economic evaluation of ED with a heterogeneous BPM in a uranium ore mining wastewater treatment plant was also carried out. This process is primarily used in cases where the purity of the sulfuric acid and sodium hydroxide recycled does not play a significant role and the high costs of the homogeneous BPMs negatively affect the economy.