Filtering and Sieving

Materials used for membranes are cellulose acetate, cellulose triacetate, polytetrafluoroethylene, polyvinylchloride, nitrocellulose, polypropylene, nylon, Fiberglas, and paper. 

Paper Drainage Classifications. The most common way to classify how fast a paper will drain is, slow, medium and fast. 

This is usually accomplished by changing the pore size or increasing the thickness of the paper. The goal is to remove all of the particles desired in the shortest time. There are two standards for determining flow rate the Association for Standard Testing Methods (ASTM) and the Herzberg method. 

Ashless. This type of filter paper has been treated with a dilute solution of HF to volatilize any silica particles. The residue upon ashing is less than 0.1 mg for an 11 cm circle, which is less than the detection limit of a common analytical balance. 

Phase Separation Paper. This paper (Whatman IPS) has been treated with a silicone to make it hydrophobic yet let organic materials pass through. This is a convenient way to separate water from organic mixtures, particularly emulsions. 

---

The processes described in Scheme 2 are also at the core of the investigation of solid-state sensors, reservoirs, filters and sieves for detecting or trapping small... 

Eijkel JCT, and van den Ber A, Nanotechnology for membranes, filters and sieves. A series of mini-reviews covering new trends in fundamental and applied research, and potential applications of miniaturised technologies. Lab. Chip, 2006 6 19—23. 

Direct interception refers to a sieve-type mechanism in which contaminants larger than the filter pore size are directly trapped by the filter. This sieve retention mechanism of particle arrest is the mechanism of choice and occurs owing to geometric or spatial restraint. This type of particle arrest is considered to be absolute, that is, it is independent of filtration conditions. 

Rapid purification Stand over freshly activated alumina, BaO or CaS04 overnight. Filter and distil over CaH2 under reduced pressure ( 12 mm Hg). Store over 4A molecular sieves. 

Conveying and sieving enclose potential dust sources, and filter evacuated gases. 

The second method used to reduce exliaust emissions incorporates postcombustion devices in the form of soot and/or ceramic catalytic converters. Some catalysts currently employ zeolite-based hydrocarbon-trapping materials acting as molecular sieves that can adsorb hydrocarbons at low temperatures and release them at high temperatures, when the catalyst operates with higher efficiency. Advances have been made in soot reduction through adoption of soot filters that chemically convert CO and unburned hydrocarbons into harmless CO, and water vapor, while trapping carbon particles in their ceramic honeycomb walls. Both soot filters and diesel catalysts remove more than 80 percent of carbon particulates from the exliatist, and reduce by more than 90 percent emissions of CO and hydrocarbons. 

Forty-seven grams (0.5 mol) of phenol, 80 mL of 37 wt % aqueous formaldehyde (1.0 mol), and 100 mol of 4 A NaOH were charged to a flask equipped with a reflux condenser and mechanical stirrer. The reaction mixture was stirred at room temperature for 16 h, then heated on a steam bath for 1 h. The mixture was cooled and the pH adjusted to 7.0. The aqueous layer was decanted from the viscous brown liquid product, the wet organic phase was taken up in 500 mL of acetone and dried over anhydrous MgSCL, then over molecular sieves. The dried acetone product solution was filtered and evaporated to yield a water-free light brown syrup. 

Ultrasonication was reported for the extraction of triazines from soil, previously sieved to 2 mm and stored at -18 °C, prior to analysis using CC/NPD and CC/lTD. A 5-g soil sample was placed in a polypropylene column and extracted for 15 min with 4 mL of ethyl acetate in an ultrasonic bath at room temperature. Subsequently, the solvent was filtered and collected in a graduated tube, and the extraction was repeated for another 15-min period using a second 4-mL portion of ethyl acetate. The two extracts... 

Preparation of Grafted Amine-Functionalized Silica. Silica was pressed, cmshed, and sieved to 40-60 mesh particles and calcined at 550°C overnight. To anhydrous toluene (40 mL), silica (1.0 g) was added under N2 and stirred for an hour. Aminopropyltriethoxysilane (APS 1.0 g, 5.58 mmol) was syringed into mixture and stirred for 24 hours at room temperature under nitrogen. The functionalized silica was then filtered, washed with toluene three times, and dried under vacuum at 50°C. 

To a solution of the titanocene(II) reagent 29 in THF (42 mL) in a 300-mL round-bottomed flask, prepared from titanocene dichloride (6.54 g, 26.3 mmol), magnesium turnings (0.766 g, 31.5 mmol), triethyl phosphite (8.96 mL, 52.5 mmol), and finely powdered 4 A molecular sieves (1.31 g) according to the procedure described above, was added a solution of l,l-bis(phenylthio)cyclobutane (63 2.29 g, 8.40 mmol) in THF (14 mL). The reaction mixture was stirred for 15 min. and then a solution of (S)-isopropyl 3-phenylpro-panethioate (91 1.46 g, 7.00 mmol) in THF (21 mL) was injected dropwise over a period of 10 min. The reaction mixture was refluxed for 1 h, then cooled, whereupon 1 m aq. NaOH solution (150 mL) was added. The insoluble materials produced were removed by filtration through Celite and washed with diethyl ether. The aqueous layer was separated and extracted with diethyl ether. The combined ethereal extracts were dried (Na2S04), filtered, and concentrated. The residual liquid was purified by column chromatography (silica gel, hexane) to afford 1.33 g (77%) of (l-isopropylthio-3-phenylpropan-1 -ylidene) cyclobutane (92). 

---