Membrane module transmembrane pressure

The sensitivity of productivity or flux to transmembrane pressure (TMP) is referred to as the permeability L = flux/transmembrane pressure. TMP refers to a module average. Pure-component permeability (e.g., water permeability) refers to membrane properties while the more industrially relevant process permeability includes fouling and polarization effects. 

The factors to consider in the selection of crossflow filtration include the flow configuration, tangential linear velocity, transmembrane pressure drop (driving force), separation characteristics of the membrane (permeability and pore size), size of particulates relative to the membrane pore dimensions, low protein-binding ability, and hydrodynamic conditions within the flow module. Again, since particle-particle and particle-membrane interactions are key, broth conditioning (ionic strength, pH, etc.) may be necessary to optimize performance. 

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. 

Polymer-Assisted Ultrafiltration of Boric Acid. The Quickstand (AGT, Needham, MA) filtration apparatus is pictured schematically in Figure 3. The hollow fiber membrane module contained approximately 30 fibers with 0.5 mm internal diameter and had a nominal molecular weight cut-off of 10,000 and a surface area of 0.015 m2. A pinch clamp in the retentate recycle line was used to supply back pressure to the system. In a typical run, the transmembrane pressure was maintained at 25 psig and the retentate and permeate flow rates were 25 ml/min and 3 ml/min, respectively. Permeate flux remained constant throughout the experiments. 

It is interesting to note that the problem of operation with large pressure differences between the feed/retentate side and the permeate compartment of membrane filtration modules was identified long ago. The concept of operation under low uniform transmembrane pressure (UTMP) was pioneered and first... 

Dynamic filtration modules present a relative movement between the membrane and the module, or between the membrane and a rotor. Thus, it is possible to adjust the shear stress independently of the feed flow rate and of the transmembrane pressure drop. 

The term membrane element refers to the basic form in which a membrane is prepared. There are three types of membrane elements flat sheets, hollow hbers, and tubular membranes. The device within which the membrane element is housed is referred to as the membrane module. The design of the membrane module largely depends on the type of membrane element, as well as on additional requirements such as the need for cleaning and disassembling, the required transmembrane pressure (TMP), and the required hydrodynamic conditions. Some of the different modules types are (see Figures 18.3 through 18.7) ... 

The viscosity of the mixture was adjusted by the addition of approximately 50 % of toluene. The pilot plant consist of oxo-reactor and the membrane unit, which was directly connected to the reactor. Standard plate modules from Dow (Type DDS 30-4.5) were used. The conditions of the membrane separation were overflow 200 1/h, separation temperature 40 °C, transmembrane pressure 1 MPa. The unit was continuously operated over a period of 12 weeks. No decrease of activity of the catalyst was observed. In order to obtain a dialdehyde selectivity > 90 %, the Rh concentration must be increased to 100 ppm. Most of the loss of ligand was due to traces of oxygen, which could not excluded totally on pilot scale. 

The DMF module (PaU Corp., New York) which consists of several disks mounted on the same shaft [2, 135]. The reported studies of the apphcation of the rotating disk dynamic membrane indicate that high shear-induced filtration is much less sensitive to the solids concentration. Advantage of the rotational system is that it permits operation at both very low transmembrane pressure-drop, and low upstream mass velocity, without loss in depolarization efficiency. It is thus possible with this system to achieve cleaner separation of solute components, than is achievable with conventional systems. Equipment for this process is, unfortunately, significandy more costly, and maintenance costs much higher also, than those for conventional membrane systems. 

Fortunately, hollow fibers may be cleaned by back-washing which tends to compensate for their propensity to foul. Manufacturers of tubes, plate and frame units, and spiral wound modules do not recommend back-washing due to problems with membrane delamination and glue line seal rupture. Because hollow fibers are self-supporting and hold up well under the compression force of a reverse transmembrane pressure drop, they can easily withstand back-wash pressures of 15 to 20 psi. However, the back-wash fluid should be filtered to remove any particles which would tend to lodge in the porous wall of the fiber. 

A cross-flow nanofillration module (SEPA CFII, GE Osmonics, Miime lis, MN) was used for this process with a maximum operating pressure of 7.0 MPa. The sur ce area of the membrane is 140 cm. The holdup volume of the membrane unit is 70 mL. The fermentation broth was placed in a 5-L fermentation vessel to control the temperature, agitation, and pH. A bench-top pump (M03-S, Hydra cell, MinneapoUs, MN) was used to pump the fermentation broth through the cross-flow membrane separation unit and recycle back to the fermentor (Fig. 2). The permeate was collected on a digital balance attached to a laptop computer with a RS-COM version 2.40 system (A D, Milpitas, CA) that recorded the amount of permeate collected every 0.5 min. The fermentation brofli was kept at constant temperature (37 °C), pH (5.5), and agitation (200 rpm). Transmembrane pressures of 1.4, 2.1, and 2.8 MPa were used in the nanofiltration tests. Each condition was tested twice, and each test lasted for 2 h. Samples of the original broth (before separation), permeate, and letentate were collected for analysis. 

Dynamic filtration processes counteract the formation of a covering layer over the active surface of the membrane This is defined as gelpolarization of fouling In modules with tubular and capillary membranes, transmembrane pressure can be calculated as follows ... 

In a general way, most of ceramic membrane modules operate in a cross-flow filtration mode [37] as shown in Figure 9.18. However, as discussed hereafter, a dead-end filtration mode may be used in some specific applications. Membrane modules constitute basic units from which all sorts of filtration plants can be designed not only for current liquid applications but also for gas and vapor separation, membrane reactors, and contactors, which represent the future applications of ceramic membranes. In liquid filtration, hydrodynamics in each module can be described as one incoming flow on the feed side Qp which results in two outgoing flows related to retentate Q, and permeate gp sides, respectively. The permeation flux J per membrane surface unit is directly calculated from Q. Two important parameters account for hydrodynamic working conditions of a module, one is the flow velocity, v, in the module calculated as the ratio of the incoming flow <2/ (mVs) by the hydraulic section of the module Q (m ), the other is the transmembrane pressure, P. ... 

Porous membrane modules were therefore effectively used in bioreactors as an alternative to direct two-liquid contact systems, as long as phase breakthrough was avoided. This required a careful control of the transmembrane pressure, particularly if surface-active material was produced during bioconversions [126,184, 187]. Fouling problems also developed in membrane-assisted multi-phase separation systems. This was observed by Conrad and Lee in the recovery of an aqueous bioconversion product from a broth containing 20% soybean oil by using ceramic membranes fouling was caused mainly by soluble proteins and surfactants [188]. 

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