Filtration spectrum

Figure 1.1 "Filtration Spectrum" comparing the rejection capabilities of reverse osmosis with other membrane technologies and with the separation afforded by conventional filtration.

FIG. 22-46 The filtration spectrum. Ctypyright 1996. Reprinted by permission of Osmonics, Minnetonka, MN.)... 

The Filtration Spectrum is shown in Figure 9.6 [8]. A wide variety of materials and particle sizes are placed on the figure to give readers some perspective on the size range and materials separated by the various filtration processes. A detailed description of each process follows. 

As shown on the Filtration Spectrum, microfiltration membranes have pores in the range of 0.05 to 2 pm while ultrafiltration membranes are in the range of 0.003 to 0.1 pm. As the names imply, these processes are used to separate (filter) a solvent (usually water) from suspended solids or colloidal material. The solvent passes through the membrane while the solids are retained on the feed side of the membrane. The choice of membrane is dictated by the particle size of the retained material. 

Nanofiltration is sometimes called loose RO or leaky RO because of its similarity to RO the exception is that NF membranes allow more ions to pass through than an RO membrane. Because of the lower rejection of dissolved solids, the increase in osmotic pressure is not as significant with an NF system as it is with RO. Thus, NF operates at lower pressure than RO, typically 50-150 psi. Nanofiltration falls between RO and UF on the filtration spectrum shown in Figure 1.1. Table 16.5 compares the general differences in rejection of species between NF and RO membranes. 

Among the above categories, the pore size classification is most widely used because it is directly related to the properties of impurities to be removed. In Fig. 13.1 [1], the filtration spectrum presents the relationships among pore size, impurity materials, and filtration technology in varying filter media. In Sect. 13.3.1, a description of those filtration membranes made of electrospun nanofibers is summarized. 

Fig. 13.1 The filtration spectrum [1] (Reprinted with permission from Ref. [1]. Copyright 2007, Elsevier)...

Process Description Microfiltration (MF) separates particles from true solutions, be they liquid or gas phase. Alone among the membrane processes, microfiltration may be accomplished without the use of a membrane. The usual materi s retained by a microfiltra-tion membrane range in size from several [Lm down to 0.2 [Lm. At the low end of this spectrum, very large soluble macromolecules are retained by a microfilter. Bacteria and other microorganisms are a particularly important class of particles retained by MF membranes. Among membrane processes, dead-end filtration is uniquely common to MF, but cross-flow configurations are often used. 

Floor acceleration This is the time history of acceleration of a partictilar floor nr structure caused by a given ground acceleration (Figure 14.16). It may have an amplified narrow band spectrum due to structural filtration, where single frequency excitation and resonance may predominate, depending upon the dynamic characteristics of the structure. A floor response spectrum (FR.S). as shown in Figure 14.18, can be derived from this history. Consideration of GRS or FRS will depend upon the location of the object under test. 

The ethanolie filtrate can be concentrated to 10-15 ml. under reduced pressure to obtain 0.3 g. (7%) of crude product, m.p. 187-202°. Unchanged starting material, if present, is concentrated in this second fraction and may be detected by the furan resonance at 8 5.85 in the proton magnetic resonance spectrum or by a sharp infrared absorption... 

Solid sodium nitrite (0.97 g) was added at room temperature with stirring over a period of one hour to a solution of 2-chloro-9-(2-hydroxyethoxymethyl)adenine (0.5 g) in glacial acetic acid (10 ml). The reaction mixture was stirred for an additional A A hours. The white solid was removed by filtration, washed with cold acetic acid and then well triturated with cold water to remove the sodium acetate present. The solid product was retained. The combined acetic acid filtrate and wash was evaporated at reduced pressure and 40°C bath temperature and the residual oil triturated with cold water. The resulting solid material was combined with the previously isolated solid and the combined solids dried and recrystallized from ethanol to give 2chloro-9-(2-hydroxyethoxymethyl)+iypoxanthine (0.25 g), MP>310°C. Elemental analysis and NMR spectrum were consistent with this structure. 

After concentrating the filtrate to approximately 400 ml, solids started crystallizing out at which time the filtrate was cooled by refrigerating at 5°C for several hours. Filtration gave 1B.7 g of L-Dopa, MP 284° to 286°C (dec.) [oJd 8.81° (1% solution in aqueous 4% HCI). The infrared spectrum and paper chromatography indicated very good L-Dopa according to U.S. Patent 3,253,023. 

N-Acetylation of Kasugamycinic Acid (9a). A solution of kasugamycinic acid (225 mg.) dissolved in 10 ml. of water was treated with acetic anhydride (0.3 ml.) under cooling sodium bicarbonate was used to keep the pH 7.2 and stirring continued for 30 minutes. The reaction product was passed through Dowex 50W-X2 (H form) and the column was washed with water. The combined filtrate was subjected to lyophilization to afford 234 mg. of a crude N-acetyl derivative. Its infrared spectrum showed strong absorptions at 1740 cm-1 characteristic of oxamic acid group. The N-acetyl derivative (178 mg.) was treated with 40 ml. 

The ethereal filtrate and washings are distilled under reduced pressure (Note 9) with the use of a 6-in. Vigreux column, and pure ketene di(2-methoxyethyl) acetal (Note 10) is obtained b.p. 81-84° (2.0 mm.), m25d 1.4411, yield 98-132 g. (56-75%). The infrared spectrum of the product shows a very strong C=C absorption band at 1640 cm.-1. 

The a-plienylcinnamonitrile (Note 4) present in the distillation flask can be recovered. The residue is broken up with 75 ml. of methanol, the mixture stirred and cooled, and the product recovered by filtration. Recrystallization from methanol gives 17-20 g. of crystalline material, m.p. 86-88°. The proton magnetic resonance spectrum (chloroform-d) shows complex multiplets at 5 7.20-8.00. 

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