Membrane separation unit

Figure 11.1 Schematic representation of a membrane separation unit...

Fig. 13.3 Schematic diagram of two different membrane units, (a) Membrane separator unit composed of two machined blocks of PTFE or Ti (A), and PTFE membrane (B), impregnated with stationary liquid, (b) Membrane unit. The PTFE membrane is placed between the two blocks made of titanium. The two channels (donar and acceptor) that are formed have a nominal volume of 12 pL.

Membrane bioreactors have been reviewed previously in every detail [3,4,7,8,18], There are two main types of membrane bioreactors (i) the system consists of a traditional stirred-tank reactor combined with a membrane separation unit (Figure 14.1) (ii) the membrane contains the immobilized biocatalysts such as enzymes, micro-organisms and antibodies and thus, acts as a support and a separation unit (Figure 14.2). The biocatalyst can be immobilized in or on the membrane by entrapment, gelification, physical adsorption, ionic binding, covalent binding or crosslinking [3, 7, 18]. Our attention will be primarily focused on the second case where the membrane acts as a support for biocatalyst and as a separation unit, in this study. The momentum and mass-transport process, in principle, are the same in both cases, namely when there is... 

In recent years, membrane bioreactors, bioreactors combined with membrane separation unit have established themselves as an alternative configuration for traditional bioreactors. The important advantages offered by membrane bioreactors are the several different types of membrane modules, membrane structures, materials commercially available. Membrane bioreactors seem particularly suited to carry out complex enzymatic/microbial reactions and/or to separate, in situ, the product in order to increase the reaction efficiency. The membrane bioreactor is a new generation of the biochemical/chemical reactors that offer a wide variety of applications for producing new chemical compounds, for treatment of wastewater, and so on. 

An adiabatic membrane separation unit is used to dry (remove water vapor from) a gas mixture containing 10.0 mole% H20(v), 10.0 mole% CO, and the balance CO2. The gas enters the unit at 30 C and flows past a semipermeable membrane. Water vapor permeates through the membrane into an air stream. The dried gas leaves the separator at 30°C containing 2.0 mole% H20(v) and the balance CO and CO2. Air enters the separator at 50 C with an absolute humidity of 0.002 kg H20/kg dry air and leaves at 48 C. Negligible quantities of CO, CO2, O2, and N2 permeate through the membrane. All gas streams are at approximately 1 atm. 

Depending on the type of materials to be used for membrane separation, the module may have different configurations. The footprint of the membrane separation unit may be an important issue where it is going to be placed, and packing density of the module (m /m ) will then have to be considered. Some modules may be suitable for large-volume applications, some for smaller. In most cases investment cost and lifetime of the membrane will decide which one should be chosen. If specific process conditions are necessary for optimum performance of the membrane (pressure, temperature, filtering, and drying of gas), required utilities must be included in cost estimation. 

Permeable gas separation membranes utilize differences in solubility and diffusion of different gas components in polymer materials. In recent years membrane-based technologies have gained increasing importance in gas processing. Typical applications are CO2 removal from natural gas or hydrogen recovery from synthesis gas. The degree of selectivity between different gas components depends on the membrane used so that it is necessary to contact the manufacturers for a concrete project. Membrane separation units are usually supplied skid mounted. 

The best strategy for acceptance in high-temperature gas/vapour separation (T > 200°C) and catalytic membrane reactors is probably its introduction in small-scale processes and/or hybrid installations which exist in two types (a) a combination of a membrane separation unit with a conventional process [4,7,12] and (b) interstage removal of component(s) by a membrane unit in between two reactors in series [15]. 

Both Catofin and Oleflex use an adiabatic reactor concept. The Oleflex process uses four reactor beds in series, which as such is more suitable for addition of a ceramic membrane separation unit than the Catofin process which uses a parallel reactor system. A comparison between the Oleflex process as a base case and an Oleflex process equipped with ceramic membranes is made for the following cases ... 

A cost analysis and comparison between two anaerobic processes for the treatment of wastewater was also carried out by Pillay et al. [6.23]. The first configuration consisted of a conventional system coupling a digester with a sedimentation unit. In the second configuration the sedimentation step was replaced by a membrane separation unit treating a side stream. Pillay et al [6.23] report that for a 60 Ml d plant the MBR process results in capital savings of about 27 % when compared with the classical configuration. 

In 1970, Porter and Michaels84 first suggested the use of membranes to enhance fermentor productivity traditional fermentors could in fact be coupled to a membrane separation unit in a configuration called a "membrane fermentor" where flux through the membrane was pressure driven. Since then a number... 

Cell recycle fermentors consist of two main units a vessel where the biomass is allowed to grow, and a membrane separation unit (as in Figure 7.40). Vessels are usually designed to insure a uniform concentration of nutrients and pH throughout the whole volume. Due to complete mixing, process control and stability of the microbial slurry are not difficult to achieve.88 After anaerobic stabilization, when the biomass is well developed, the reactor biomass is pumped to the UF unit where solid-liquid separation occurs. The sludge is flushed back to the reactor. In most cases, the flow rate of nutrient feed is kept equal to the permeate flow rate thus keeping a constant liquid level in the anaerobic reactor. 

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. 

Chicken extract was obtained from whole chicken carcasses by heating the carcasses with water (Figure 22.3). Then, the extract was treated with ion exchange resin to remove acidic and neutral amino acids and proteins. The chicken extract after the treatment with the ion exchange resin contained 6.79 g/L of anserine and carnosine, and their purity was 60%-70%. Impurities contained in the extract after the treatment with the ion exchange resin were creatinine and sodium chloride. Concentrations of these impurities were 2.30 g/L and 0.85 g/L, respectively. The extract after the treatment with the ion exchange resin was used as material for membrane separation experiments. A bench-scale membrane separation unit supplied by DSS (Danish Separation System) was used in this study. 

Separation of IPA and Water by Pervaporation. In the PV membrane separation unit, the water permselective membrane is used for dehydration. Water in the feed... 

Distillation Unit and Filtration Unit. In this system, purification and recycling of IPA is performed by the combination of the PV membrane dehydration unit, the distillation unit, and the microfiltration unit. In the distillation unit, impurities, which are difficult to separate in the PV membrane separation unit such as dissolved metal ions and high-boiling impurities, are completely eliminated. 

Abemative 2, Eliminate operation of the toluene column and recycle the biphenyl (with the toluene) to extinction. This should increase the yield of benzene. Also, install a membrane separation unit to reduce hydrogen consumption. 

In this chapter some fundamental equations are given that allow a first design of a one-stage membrane separation unit. Questions to be answered are what is the maximum enrichment that can be achieved with a membrane of a given selectivity How is the separation performance influenced by feed and permeate pressure It will be explained why for some applications a high selective membrane will be outperformed by a membrane with, a lower selectivity. 

A SMR is a series of modules (RMM) each composed of a traditional reactor followed by a membrane separation unit. The stream flowing out of the reactor, rich of reaction products, enters into the separation unit where the selective membrane removes one of the products. The retentate of the membrane unit is then fed to the subsequent module. A system of heat exchangers can be present between each unit and the following one. A system composed of two modules is shown in Fig. 1.3. 

---