Resins weak base

Weak Base. Weak base anion-exchange resins may have primary, secondary, or tertiary amines as the functional group. The tertiary amine -N(CH2)2 is most common. Weak base resins are frequentiy preferred over strong base resins for removal of strong acids in order to take advantage of the greater ease in regeneration. 

Weak base resins when in the free base (hydroxyl) form are not capable of splitting neutral salts such as sodium chloride. Salt forms of weak base resins release anions to the Hquid phase if other ions for which the resin has a greater selectivity are present. 

The standard cation—anion process has been modified in many systems to reduce the use of cosdy regenerants and the production of waste. Modifications include the use of decarbonators, weak acid and weak base resins. Several different approaches to demineralization using these processes are shown in Figure 1. 

Ion-exchange resins swell in water to an extent which depends on the amount of crosslinking in the polymer, so that columns should be prepared from the wet material by adding it as a suspension in water to a tube already partially filled with water. (This also avoids trapping air bubbles.) The exchange capacity of a resin is commonly expressed as mg equiv./mL of wet resin. This quantity is pH-dependent for weak-acid or weak-base resins but is constant at about 0.6-2 for most strong-acid or strong-base types. 

Weak base resins are like weak acid resins, in that the degree of ionization is strongly influenced by pH. Consequently, weak base resins exhibit minimum exchange capacity above a pH of 7.0. These resins merely sorb strong acids they caimot split salts. 

In an ion exchange wastewater deionization unit, the wastewater would pass first through a bed of strong acid resin. Replacement of the metal cations (Ni. Cu ) With hydrogen ions would lower the solution pH. The anions (S04. Cl ) can then be removed with a weak base resin because the entering wastewater will normally be acidic and weak base resins sorb acids. Weak base resins are preferred over strong base resins because they require less regenerant chemical. A reaction between the resin in the free base form and HCl would proceed as follows ... 

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. 

Acrylic tow, 11 212 Acrylic weak base resins, 14 389 Acrylonitrile (AN), 1 397—414 10 665-666 11 5 17 228 24 272 acetylene-derived, 1 229 Alfrey-Price parameters, 7 617t azeotropes, l 399t... 

The absolute order depends on the individual ion exchanger, but deviations from the above order are usually only slight for different cation and anion exchangers. For weak-acid resins, H+ is preferred over any common cation, while weak-base resins prefer OH over any of the common anions. 

The use of the anion-exchange resin Duolite A-7 for concentrating organic acids was reported as early as 1965 by Abrams and Breslin (7) and more recently by Leenheer (8). A-7 is a high-surface-area, macro-porous, phenol-formaldehyde, weak-base resin. This resin combines weak-base, secondary-amine functional groups with the relatively hydrophilic phenol-formaldehyde matrix to effectively sorb and elute organic acids. 

Strong- and weak-base resins exchange anions with their aqueous environment and therefore extract only metals that form anionic complexes in solution. Strong- and weak-base resins display a similar affinity for anionic species, which increases with the charge and the polarizability of the anion. Strong-base resins have quaternary amine functional groups that possess a permanent... 

Weak-base resins have primary, secondary or tertiary amine functional groups and, in neutral or alkaline solution, the amines are in the free-base (un-ionized) form and have no ion-exchange properties. In acidic solution, the amine groups are protonated and extract anions according to the following equations ... 

Anion-exchange resins are eluted either by reversal of the equilibria shown in equations (94) to (96) or, in some cases, by chemical destruction of the anionic complex ML/-. The elution of strong-base resins requires a large excess of the co-ion, X-, whereas the elution of weak-base resins can be achieved most effectively by treatment of the resin with a stoichiometric amount of hydroxide ions, which restores the resin to the free-base form ... 

Weak-base resins have been tested from time to time but have not found wide acceptance in the uranium industry, The main reason for this is that the major advantage of weak- over strong-base resins, viz. elution by neutralization, cannot be utilized in uranium processing since it is not possible for the weak-base resin to be converted to the free-base form without diuranate precipitating within the pores of the resin (unless a complexing agent such as carbonate is added to the eluate). In the presence of carbonate, uranium remains in solution as the uranyl carbonate anion, even in very alkaline solution, so is readily eluted from a weak-base resin in the free-base form. This eluate would then be treated as depicted in equations (105) and (106) for the recovery of uranium. Alternatively, weak-base resins can be eluted by ion-exchange mass action. 

The elution of aurocyanide and other anions from a weak-base resin is achieved by neutralization of the amine functional groups (equation 96). The method is cheap and very effective 366 this is a major factor favouring the use of weak-base resins, particularly since recent research has shown that modem weak-base resins extract "aurocyanide efficiently from cyanide leach liquors that have undergone minimal adjustment of pH.358 368... 

Polyamines, such as diethylenetriamine [111-40-0] are used at times in the synthesis of microporous weak base resins to achieve significantly higher capacity. However, these resins generally have lower physical and chemical stability than resins prepared from primary or secondary amines. 

The acrylic weak base resins are synthesized from copolymers similar to those used for the manufacture of weak acid cation-exchange resins. For example, under appropriate temperature and pressure conditions, a weak acid resin reacts with a polyfunctional amine, such as dimethylaminopropylamine [109-55-7] (7) to give a weak base resin with a tertiary amine functionality. 

Both the styrenic and the acrylic weak base resins are used in industrial applications for the same purposes, primarily the removal of acidic components in... 

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