Salt removal

Chemical Neutralization. Spray-type air washers are used extensively for removal or neutrali2ation of noxious components from large volumes of air, particularly exhaust air streams. Appropriate reagents are sprayed into the washer to purify the air by neutrali2ation, eg, sodium hydroxide solution is used if the air contains acidic gases. The solution must be continuously reconcentrated and any precipitated salts removed. The contact efficiency of such washers is high, and the simple constmction provides easy maintenance and constant efficiency (see AiRPOLLUTlON CONTROL METHODS). 

Laminates. Laminate manufacture involves the impregnation of a web with a Hquid phenoHc resin in a dip-coating operation. Solvent type, resin concentration, and viscosity determine the degree of fiber penetration. The treated web is dried in an oven and the resin cures, sometimes to the B-stage (semicured). Final resin content is between 30 and 70%. The dry sheet is cut and stacked, ready for lamination. In the curing step, multilayers of laminate are stacked or laid up in a press and cured at 150—175°C for several hours. The resins are generally low molecular weight resoles, which have been neutralized with the salt removed. Common carrier solvents for the varnish include acetone, alcohol, and toluene. Alkylated phenols such as cresols improve flexibiUty and moisture resistance in the fused products. 

PhenoHc and furfuryl alcohol resins have a high char strength and penetrate into the fibrous core of the fiber stmcture. The phenoHc resins are low viscosity resoles some have been neutralized and have the salt removed. An autoclave is used to apply the vacuum and pressure required for good impregnation and sufficient heat for a resin cure, eg, at 180°C. The slow pyrolysis of the part foUows temperatures of 730—1000°C are recommended for the best properties. On occasion, temperatures up to 1260°C are used and constant weight is possible even up to 2760°C (93). 

Many other polymerization processes have been patented, but only some of them appear to be developed or under development ia 1996. One large-scale process uses an acid montmorrillonite clay and acetic anhydride (209) another process uses strong perfiuorosulfonic acid reski catalysts (170,210). The polymerization product ia these processes is a poly(tetramethylene ether) with acetate end groups, which have to be removed by alkaline hydrolysis (211) or hydrogenolysis (212). If necessary, the product is then neutralized, eg, with phosphoric acid (213), and the salts removed by filtration. Instead of montmorrillonite clay, other acidic catalysts can be used, such as EuUer s earth or zeoHtes (214—216). 

When heat stable salt buildup becomes a problem a variety of options may manage it. These include partial or total solution replacement, heat stable salt removal, or adding caustic to neutralize the heat stable salts. Many operators choose caustic addition because it is perceived to be a more economical way to stop corrosion and subsequent foaming and loss problems. 

Efficiency The effectiveness of the operational performance of an ion ex- changer. Efficiency in the adsorption of ions is expressed as the quantity of regenerant required to effect the removal of a specified unit weight of adsorbed material, for example, pounds of acid per kilogram of salt removed. 

To ensure maximum pigment retention, the acidic eluates should be checked for their pH values and if required, aqueous ammonia has been proven viable for pH adjustment to reach 5 to 7 pH values. While Sephadex G types were used in earlier studies for purification and desalting, Sephadex LH-20 is the material of choice today. Since the betalains will elute with water, it is doubtful whether effective salt removal is possible. However, Sephadex LH-20 has proven excellent for removing... 

As will be discussed in detail in the next section, when the reduction of the parent compound 6 was conducted at low temperature (—20 °C) with 2 equiv. of Na in tetrahydrofuran (THF) saturated with ethylene, complete salt removal was achieved, and the r 2-ethylene complex 20 was isolated.22 Upon irradiation, the latter released ethylene, behaving as a source of the d2 [W / -Bu -calix[4]-(0)4 ] carbenoid, which coupled to give a new W=W dimer [W=W, 2.582(1) A], isolated as the bis-Bu NC adduct 21. In H NMR, 21 exhibits a C5-symmetric pattern of signals for the calix[4]arene moiety. 

A better method has been described by Schwarz (S6). Washed red blood cells are lysed, precipitated with trichloroacetic acid below 0°C and the supernatant quickly neutralized. Speed and low temperatures are necessary to prevent hydrolysis of galactose-l-phosphate which is very sensitive to acid. Barium acetate and ethanol are added, and the precipitated barium salt of galactose-l-phosphate washed with 80% ethanol. The barium salt is then hydrolyzed by heating with dilute hydrochloric acid, acid and salts removed with mixed ion-exchange resins, and the galactose estimated by paper chromatography as described above. It is probably better to avoid the Amberlite MB-1 resin used by Schwarz and, instead, to use a weak base resin mixture, such as Amberlite MB-4. Recovery of added galactose-l-phosphate should be determined simultaneously. 

Why does adding salt remove a blood stain ... 

Another aspect that may be taken into account is that of membrane electrolysers having a lower power consumption (Fig. 15.4). Not only does the new technology save power but it also requires less steam to evaporate the cell caustic product to 50%. Additionally, salt removal equipment required in diaphragm plants uses power. This benefit can also be turned around so that for the same power consumed by a diaphragm cell room extra volumes of rayon-grade caustic soda can be produced from the membrane electrolysers. 

---