Membrane separation processes nanofiltration

To make supercritical extraction processes more economic, separation of solute and solvent can be performed thanks to a membrane system. Sartorelli and Brunner [19] demonstrated that a membrane separation process can be proposed instead of the typical supercritical fluid cycle in the case of supercritical extraction to drastically reduce the energy losses. In fact, a stream of low volatile compounds (LVC) extracted by SC CO2 can be discharged of 80%-90% of LVC using a nanofiltration membrane with a drop of pressure equal to 2 MPa instead of about 20 MPa in the typical supercritical fluid cycle. 

The traditional membrane separation processes (reverse osmosis, micro-, ultra- and nanofiltration, electrodialysis, perva-poration, etc.), already largely used in many different applications, are today combined with new membrane systems such as CMRs and membrane contactors. Membranes are applied not only in traditional separation processes such as seawater desalination but also in medicine, bioengineering, microelectronics, the life in the space, etc. 

The investigation of Dean vortices and their application to membrane separation processes has been the subject of several experimental and theoretical studies concerning the improvement of microfiltration (ME), ultrafiltration (UF), and nanofiltration (NF),... 

Finally, in Chap. 8, attempts are made to correlate the AFM parameters, such as nodule and pore sizes, to the membrane performance data. Membranes used for a variety of membrane processes, including reverse osmosis, nanofiltration, ultrafiltration, microfiltration, gas and vapor separation, pervaporation, and other membrane separation processes, are covered in this chapter. AFM parameters are also correlated to membrane biofouhng. This chapter also includes appUcations of AFM to characterize biomedical materials, including artificial organs cind drug release. 

Nanohybrid materials have been furthermore used for ultra-/nanofiltration applications. Nanofiltration is a pressure-driven membrane separation process and can be used for the production of drinking water as well as for the treatment of process and waste waters. Some apphcations are desalination of brackish water, water softening, removal of micropollutants, and retention of dyes. Ultrafiltration membranes based on polysulfones filled with zirconia nanoparticles are usually prepared via a phase-inversion technique and have been used since 1990 [328]. Various studies were done in order to assess the effect of the addition of Zr02 to polysulfone-based ultrafiltration membranes [329] and the influence of filler loading on the compaction and filtration properties of membranes. The results indicate that the elastic strain of the nanohybrid membranes decreases and the time-dependent strain... 

The membrane separation process was initially conducted in degumming vegetable oil and then was adapted for the recovery of carotenoids. Dense polymeric membranes are employed in this system and are very effective in the separatirm of xanthophylls, phospholipids, and chlorophyll, with retention of 80-100 %, producing an oil rich in carotenes [72,73]. This process, however, requires an additional step of hydrolysis or transesterification. Chiu, Coutinho, and Gruigalves examined the membrane technology as an alternative to concentrate carotenoids from crude palm oil in detriment of ethyl esters. A flat sheet polymeric membrane constituted by polyethersulfone was used and obtained a retention rate of 78.5 % [74]. Damoko and Cheryan obtained similar results using nanofiltration with 2.76 MPa and 40 °C in red palm methyl esters [75]. Whereas Tsui and Cheryan combined ultraiiltration with nanofiltration to separate zein and xanthophylls from ethanolic com extract [76]. 

Membrane separation processes have been applied to many industrial production systems for the purpose of clarification, concentration, desalting, waste treatment, or product recovery. Broadly speaking, membrane filtration can be classified as microfiltration, ultrafiltration, nanofiltration, reverse osmosis, and dialysis or electrodialysis. In this section, the discussion will only cover microfiltration and ultrafiltration, both of which are pressure-driven membrane processes. 

Nanofiltration softening membranes may be an economic alternative to conventional softening. Possible advantages of membrane filtration for softening include smaller space requirements, no lime requirement, superior quality water, and less operator attendance. As for all membrane separation processes, suitability of softening membranes for a given apphcation must be made on a case-by-case analysis. 

Membrane separation processes are not restricted to the mechanical principles discussed in this chapter. Different terminologies (microfiltration, nltrafiltration, nanofiltration, reverse osmosis, etc.) point to the fact that separation mechanisms change as particles become smaller and membranes become denser. The smaller the particles are, the greater the pressures used in membrane separation processes... 

The concept of carbon membrane is not necessarily novel. Ash et al. compressed nonporons graphite carbon into a plug and called it carbon membrane in early seventies. The practical usefulness of carbon membrane was however realized in the begiiming of eighties for the first time by the work of Koresh and Soffer who pyro-lyzed many thermosetting polymers to produce carbon molectrlar sieve membranes. Since then attempts have been made to use carbon membranes for gas separation, nanofiltration and other membrane separation processes. 

The individual membrane filtration processes are defined chiefly by pore size although there is some overlap. The smallest membrane pore size is used in reverse osmosis (0.0005—0.002 microns), followed by nanofiltration (0.001—0.01 microns), ultrafHtration (0.002—0.1 microns), and microfiltration (0.1—1.0 microns). Electro dialysis uses electric current to transport ionic species across a membrane. Micro- and ultrafHtration rely on pore size for material separation, reverse osmosis on pore size and diffusion, and electro dialysis on diffusion. Separation efficiency does not reach 100% for any of these membrane processes. For example, when used to desalinate—soften water for industrial processes, the concentrated salt stream (reject) from reverse osmosis can be 20% of the total flow. These concentrated, yet stiH dilute streams, may require additional treatment or special disposal methods. 

When ionic liquids are used as replacements for organic solvents in processes with nonvolatile products, downstream processing may become complicated. This may apply to many biotransformations in which the better selectivity of the biocatalyst is used to transform more complex molecules. In such cases, product isolation can be achieved by, for example, extraction with supercritical CO2 [50]. Recently, membrane processes such as pervaporation and nanofiltration have been used. The use of pervaporation for less volatile compounds such as phenylethanol has been reported by Crespo and co-workers [51]. We have developed a separation process based on nanofiltration [52, 53] which is especially well suited for isolation of nonvolatile compounds such as carbohydrates or charged compounds. It may also be used for easy recovery and/or purification of ionic liquids. 

Membrane degumming. Membrane separation has also been evaluated as an alternative process to conventional oil refining processing. Ultrafiltration (UF) and nanofiltration (NF) membranes separate phospholipids almost completely, and FFAs, pigments, and other components can also be removed with the phospholipids to a certain extent. Less effort is required in the later processing steps. 

Membrane technology may become essential if zero-discharge mills become a requirement or legislation on water use becomes very restrictive. The type of membrane fractionation required varies according to the use that is to be made of the treated water. This issue is addressed in Chapter 35, which describes the apphcation of membrane processes in the pulp and paper industry for treatment of the effluent generated. Chapter 36 focuses on the apphcation of membrane bioreactors in wastewater treatment. Chapter 37 describes the apphcations of hollow fiber contactors in membrane-assisted solvent extraction for the recovery of metallic pollutants. The apphcations of membrane contactors in the treatment of gaseous waste streams are presented in Chapter 38. Chapter 39 deals with an important development in the strip dispersion technique for actinide recovery/metal separation. Chapter 40 focuses on electrically enhanced membrane separation and catalysis. Chapter 41 contains important case studies on the treatment of effluent in the leather industry. The case studies cover the work carried out at pilot plant level with membrane bioreactors and reverse osmosis. Development in nanofiltration and a case study on the recovery of impurity-free sodium thiocyanate in the acrylic industry are described in Chapter 42. 

Membranes having effective pore sizes between 0.001 and 0.01 pm are used in nanofiltration. NF is placed between reverse osmosis and ultrafiltration, and because of that it is sometimes considered as loose reverse osmosis. Typical operating pressures for NF are 0.3-1.4 MPa. The process allows to separate monovalent ions from multivalent ions, which are retained by NF membrane. The process can be used for separation of organic compounds of moderate molecular weight from the solution of monovalent salts. The very well-known application in nuclear industry is boric acid recovery from contaminated cooling water in nuclear reactor. There are some examples of nanofiltration applications and studies done with the aim of implementation in nuclear centers described in literature. Some of them are listed in the Table 30.4. 

Separation processes as a whole have grown in importance because of increasingly stringent requirements for product purity [1]. Among the different membrane techniques, pressure-driven processes such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) were the first to undergo rapid commercialization [2-A], These processes basically differ in pore size distribution of membranes used and the types of compounds recovered. A typical schematic of the exclusion of various compounds through different membrane processes is illustrated in Figure 42.1. 

Nanofiltration is a rapidly advancing membrane separation technique for concentration/separation of important fine chemicals as well as treatment of effluents in pharmaceutical industry due to its unique charge-based repulsion property [5]. Nanofiltration, also termed as loose reverse osmosis, is capable of solving a wide variety of separation problems associated with bulk drug industry. It is a pressure-driven membrane process and indicates a specific domain of membrane technology that hes between ultrafiltration and reverse osmosis [6]. The process uses a membrane that selectively restricts flow of solutes while permitting flow of the solvent. It is closely related to reverse osmosis and is called loose RO as the pores in NF are more open than those in RO and compounds with molecular weight 150-300 Da are rejected. NF is a kinetic process and not equilibrium driven [7]. 

Nano filtration According to the International Union of Pure and Applied Chemistry (lUPAC) recommendations [16] nanofiltration is a pressure-driven membrane-based separation process in which particles and dissolved molecules smaller than about 2 nm are retained. ... 

Deposition of polyelectrolytes Lajimi et al. [56] explored the surface modification of nanofiltration cellulose acetate (CA) membranes by alternating layer-by-layer deposition of acidic chitosan (CHI) and sodium alginate (AEG) as the cationic and anionic polyelectrolyte, respectively. The supporting CA membranes were obtained by a phase separation process from acetone/formamide. The permeation rate of salted solutions was found to be higher than that of pure water. The rejection of monovalent salt was decreased, while that of divalent salt remained constant so that the retention ratio increased. Increasing the concentration of feed solutions enhanced this selectivity effect. 

The main characteristics of nanofiltration membranes made of oxide ceramics is that they exhibit a microporous structure with charged pore walls depending on pH and ionic strength of feed solutions. Three main cases are distinguished in the discussion of mechanisms involved in permeation and separation processes using microporous ceramic nanofilters ... 

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