High permeate flux

The objective of the present study is to develop a cross-flow filtration module operated under low transmembrane pressure drop that can result in high permeate flux, and also to demonstrate the efficient use of such a module to continuously separate wax from ultrafine iron catalyst particles from simulated FTS catalyst/ wax slurry products from an SBCR pilot plant unit. An important goal of this research was to monitor and record cross-flow flux measurements over a longterm time-on-stream (TOS) period (500+ h). Two types (active and passive) of permeate flux maintenance procedures were developed and tested during this study. Depending on the efficiency of different flux maintenance or filter media cleaning procedures employed over the long-term test to stabilize the flux over time, the most efficient procedure can be selected for further development and cost optimization. The effect of mono-olefins and aliphatic alcohols on permeate flux and on the efficiency of the filter membrane for catalyst/wax separation was also studied. 

The chemical structure of ABS suggests that ABS would allow to reach high permeation fluxes because of its rubbery regions and high separation factors due to the glassy matrix. 

It has been proven over the years that the effect of fouling can be lessened to some extent for the application of whey concentration by pretreating the feed streams for the ultrafilters. Whey contains many insoluble solids such as casein fines, lipoprotein complex, mineral precipitates, free fats and microorganisms. Clarification of these debris helps reduce fouling potential during ultrafiltration. In addition, it is quite evident that calcium phosphate minerals in whey are not stable and their precipitation in the membrane pores often results in flux decline. Demineralization of whey before ultrafiltration helps maintain high permeate flux considerably [Muir and Banks, 1985]. 

Permselectivity is crucial to the utility of any types of membranes. If the permselectivity toward a particular reaction species is high, the separation is quite clean and the need for further separation processing downstream of the membrane reactor is reduced. When a permeate of very high purity is required in some cases, dense membranes are preferred. While a high permselectivity is generally desirable, there may be situations where a high permeate flux in combination with a moderate permselectivity is a better alternative to a high permselectivity with a low permeability, particularly when recycle streams are used. 

Review on current scientific and technological factors governing separation of organic mixtures High selectivity and high permeate fluxes were obtained... 

The first awaited advantage of the process is to be able to work with a high permeate flux because of the low viscosity of SC CO2 (10 times lower than for water). Indeed the membrane used in the process is a hybrid nanofiltration element, constituted from an inorganic substrate (Ti02 with a mean pore diameter of about 10 run) on which a nation layer had been deposited, the prevailing mass transfer mechanism of which is convection. This fact could be checked through experiments conducted successively with water and SC CO2, flows obtained being in the opposite ratio of fluid viscosities within less than 10%. 

On the assumption that permeate flow does not strongly modify hydrodynamics at walls, k is ordinarily estimated using classical dimensionless correlation for non-porous walls, such as the Leveque equation for laminar flow or the Deissler equation for turbulent flow. More recently, in order to account for specific disturbances that take place at pore entrance when high permeate fluxes prevail, new specific equations have been proposed [3]. 

Effects of feed flow rate on permeate flux value and rejection value during the total circulation experiments are shown in Figure 22.7. Feed flow rate showed almost no effect on rejection value. In the case of membranes that showed low permeate flux value, feed flow rate had almost no effect on permeate flux value. However, in the case of membranes with high permeate flux value such as NFT-50, permeate flux increased with feed flow rate up to 10 F/min as shown in Figure 22.7. Therefore, 10 L/min was chosen as a suitable feed flow rate for separation of anserine and carnosine with the nanoliltration membranes. 

High permeation fluxes were obtained with microemulsion. Confocal laser [103]... 

Barona, G. N. B., Choi, M., and Jung, B. 2012. High permeate flux of PVA/PSf thin film composite nanofiltration membrane with aluminosilicate single-waUed nanotubes. Journal of Colloid and Interface Science 386 189-197. 

Currently, PV with zeolite membranes is the most advanced technology at an industrial scale [189]. The growing interest for zeolite-based PV process lies not only in the excellent chemical resistance of these membranes bnt also in the high separation selectivity and high permeate fluxes compared to organopolymeric membranes. The current... 

Among the publications related to this subject, Jafar et al. [268] used a tubular NaA zeolite membrane prepared on a carbon-zirconia support in the vapor space of an esterification reactor to remove the product, water, formed in the reaction of lactic acid with ethanol catalyzed by p-toluenesulfonic acid. This protected the sensitive zeolite A membrane from acid attack and still allowed high permeation fluxes responsible for the enhanced yields of ethyl lactate. The same group [269] applied a... 

The cross-flow filtration is often used in combination with the procedure known as backflushing, whereby the filtration flow is reversed for a short period of time so that particles or molecules very attached are removed from the membrane surface. The speed of cross-flow filtration, transmanbrane pressure, and the frequency of backflushing are important process parameters, which are optimized to obtain low fouling, high permeate flux, and low energy costs. In many such... 

The authors concluded that although pretreatments have caused the changes in the structure and morphology of the membranes as described earlier, it was possible to obtain stable and reproducible performance in terms of permeate flux of isooctane and the formation of anulsions of oil in water, which were stable for at least 3 months. Then the methodology of pretreatment allowed obtains high permeate flux (up to 70 L h m in the membrane of 50 kDa) and low transmembrane pressure (0.5 bar). 

Lai et al. [58], in a combined process of permeation of soybean oil with reverse osmosis NF membranes in combination with extraction by subcritical liquid pressurized carbon dioxide, obtained a preferential permeation of oleic acid in relation to triglycerides. From a system model of 40% of oleic acid and 60% of triglycerides (soybean oil), the permeation through the reverse osmosis membrane (BW 30) resulted in a permeate above 80% w/w of oleic acid, while the permeation through the membrane for NF (NF 90, MWCO = 200 Da) resulted in a permeate with approximately 50% w/w of oleic acid. However, the last membrane showed a significantly high permeate flux compared with that obtained with the BW 30. 

High permeation flux is the key determinant for future commercial application. As aforementioned, thin, few pm thickness, Pd or Pd alloy-based films supported on porous substrates are the right answer, providing the needed mechanical strength for process application, decreasing the cost and sometimes increasing the hydrogen flux. 

On the other hand, with ultra-thin (high permeation flux) membranes, which have recently become available, it has been experimentally shown that the extent of bed-to-wall mass transfer limitations in case of hydrogen purification/ production become prominent, which greatly influences the reactor performance. When these limitations prevail, the hypotheses behind the ID model are no longer valid and more sophisticated 2D models need to be used. 

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