Salt filtration

Also, nylon-6 waste may be hydrolyzed in the presence of an aqueous alkali metal hydroxide or acid5 to produce an alkali metal or acid salt of 6-aminocaproic acid (ACA). The reaction of nylon-6 waste with dilute hydrochloric acid is rapid at 90- 100°C. The reaction mixture is poured into water to form a dilute aqueous solution of the ACA salt. Filtration is used to remove undissolved impurities such as pigments, additives, and fillers followed by treatment of the acid solution with a strong cation exchange resin. A sulfonic acid cationic exchanger absorbs ACA salt and pure ACA is eluted with ammonium hydroxide to form a dilute aqueous solution. Pure ACA is obtained by crystallization of die solution. 

Generally, the AQUATECH approach to recycling involves the precipitation of the heavy metal from the waste acid. The subsequent filtration via ultrafiltration and plate and frame filtration of the slurry usually results in a clear salt filtrate suitable for feed to the AQUATECH stack. The metal hydroxide cake can be dried or recycled as is (or after a drying step) to upstream metal smelting process. 

On account of the Donnan exclusion, the concentration of absorbed salt in the membrane — also called diffusible salt — is very low. Therefore it is explicable that if a salt solution is pressed through an ion exchange membrane, under certain conditions salt filtration occurs. 

If a salt solution is pressed through an ion-exchange membrane, salt filtration can take place caused by the Donnan exclusion. 

Lefebvre X, Palmeri J, Sandeaux J, Sandeaux R, David P, Maleyre B, Guizard C, Amblard P, Diaz J-F, and Lamaze B. Nanofiltration modelling A comparative study of the salt filtration performance of a charged ceramic membrane and an organic nanofilter using the computer simulation program NANOFLUX. Sep. Purif. Technol. 2003 32(1-3) 117-126. 

Table 10-3 Effect of Initial MSA Charge on MSA Salt Filtration...

Condom, S. et al.. Behaviour of cobalt spinel ultrali Ill ation membrane during salt filtration with different ionic strengths, J. Membr. Sci., 268, 175, 2006. 

The separations feasible by filtration have expanded enormously over the last generation. The developments this symposium has commemorated, and the individuals it has honored, have been largely responsible. The removal of dissolved solutes or other low-molecular-weight substances from water by hyperfiltration or reverse osmosis, which the Loeb-Sourlrljan membrane made technically and economically feasible, has become an industrial-scale operation. Ultrafiltration of colloids and filtration of coarser materials from liquids have become much more efficient with the use of cross flow of liquid to slow the buildup of flltercake appreciation of the benefits from shear at the Interface has become much more general from the necessity of controlling concentration polarization and fouling in salt filtration. 

Preparation of m-nitrophenol from m-nitroaniline 557 A cold mixture of water (450 ml and concentrated sulfuric acid (330 ml) is poured, with stirring, over finely powdered ra-nitro-aniline (210 g), and ice (800 g) is added. When the mixture has become homogeneous, a solution of sodium nitrite (105 g) in water (250 ml) is run in during 8-10 min from a dropping funnel until the starch-iodine reaction remains positive. The temperature is kept between 0° and 5° and the mixture is stirred for a further 5-10 min. Then the m-nitrobenzenediazonium sulfate is allowed to settle, the supernatant liquid is poured off and the solid washed, if necessary, with water by decantation in order to purify the salt filtration is necessary only when gross impurity is present. 

Hie above three isolation procedures can usually be conducted in such a way as to effect simultaneous purification from undesired by-product isomers. Thus, with the first method (dilution with water) the pure para isomer of tohienesulfonie acid is obtained since the ortho isomer is soluble likewise, the 1,5- and l, isulfonates (d anthraquinone are separated by taking advantage of different solubilities in sulfuric acid. When the second procedure is applied to the isolation of anthraquinone-l-sulfonate as the potassium salt, filtration at 85°C ensures removal of the 1,5-disulfonate in the aqueous filtrate. Metallic sulfonates are frequently purified further by recrystallization from water, often with the addition of brine to ensure a good yield by salting-out. 

Overall, the flux ratios (J/Jwo, solution flux after filtration of 120 mL of solution relative to the pure water flux before the experiment) correspond well to the salt rejection. This indicates a concentration polarisation and osmotic pressure effect due to the accumulation of ions at the membrane surface and an increase in cell concentration. This flux decline was fully reversible. The flux of the CA-UF membrane consistently increases after salt filtration, probably due to an increased hydrophilicity after ion adsorption in the membrane. Rejection of calcium is stable and generally does not increase with the concentration in the feed cell. 

To NiClj SHjO (4.7 g, 20 mmol), methyl acrylate (5.0 ml, 55 mmol), and p5Tidine (5.0 ml, 61 mmol) in THF (50 ml) was added Zn powder (5.0 g, 76 mmol). The suspension was heated to 60 °C, and the oil bath was removed. After 2 h the mixture was filtered, and the solid residue was washed with THF (3x15 ml). After removal of the solvent in vacuo, extraction with Et20 (50 mL) left behind the insoluble zinc salts. Filtration and evaporation of the extract in vacuo gave a red oil which was treated with hexane to dissolve the excess pyridine and methyl acrylate. The hexane layer was discarded, and the residual oil was dissolved in EtaO (50 mL). Cooling to -18 °C afforded 69 as a pale orange powder yield 4.3 g (70%) mp 80 °C (dec). 

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