Ethoxylates, narrow-range

The presence of volatile components in alcohol ethoxylates (e.g., free alcohol) places some restriction on the level and type of alcohol ethoxylate that can be spray-dried. Volatile components cause pluming in spray tower emissions. These emissions can be minimized by using a peaked or narrow range ethoxylate or by postdosing the nonionic onto a previously spray-dried powder [36]. The peaked ethoxylate contains inherently less of the volatile components. 

The polyoxyethylene group is obtained by addition of ethylene oxide to fatty alcohols, mostly with an alkalic catalyst such as NaOH or NaOCH3, giving a broad polyoxyethylene oxide distribution. For special applications the ethoxyl-ation can be catalyzed by Lewis acids [11] to achieve a narrow range distribution. Other narrow range catalysts can also be used to improve certain properties. 

Because alkylphenol has a more acid H atom in the phenolic OH group, the ethoxylation with NaOH or NaOCH3 and other alkaline catalysts gives a narrow range EO distribution. 

For cosmetic compositions an ether carboxylate is used, derived from a fatty acid monoethanolamide [35]. It is known that the ethoxylation takes place on the OH and not on the NH of the ethanolamide group. Due to the acid H atom a narrow range distribution is obtained. The carboxymethylation is carried out with NaOH and SMCA, followed by a washing step with an aqueous solution of a strong acid at high temperatures. The ether carboxylates have the structure... 

Ca, Sr, and Ba salts have been described as catalysts for the making of narrow range alcohol ethoxylates [237]. 

Benson, H.L. Chiu, Y. C. "Relationship of Detergency to Micellar Properties for Narrow Range Alcohol Ethoxylates". Technical Bulletin, SC 443-80, Shell Chemical Co. Houston, Texas, U.S.A., 1980. 

A further development in the 1980s/1990s was the introduction of some newer catalysts. Narrow range or peaked ethoxylates can be made using acid activated metal alkoxides, metal phosphates or activated metal oxides as catalyst. These catalysts are insoluble and therefore heterogeneous in nature and the major process difference is that catalyst slurry is added to the reactor after which the conditions are exactly as with normal alkaline catalysts. The reactions are slightly quicker and need less catalyst but it must be filtered out. Most producers [ 12-20 ] have patents on these systems, the advantages of which are seen in the finished products as ... 

FIG. 8.10 Typical ethoxylate adduct distributions in narrow range and broad range C12-04 alcohol surfactants with similar cloud points. (Reproduced from Dillan, K.W.,. /. Am. Oil Chem. Soc., 62, 1144, 1985. With permission.)... 

One of the modem technological trends consists in the production of ethoxylated alcohols having a rather narrow molecular weight distribution [9, 35-37]. It can be achieved by an intermediate distillation of the initial and low-ethoxylated products or by using more selective ethoxylation catalysts. Narrow-range ethoxylates present a new formulation potential, particularly in modem low-temperature detergents for automatic machines [38]. 

As discussed earlier in this chapter, peaked or narrow-range ethoxylates are available which have peaked or narrow ethoxymer distributions. Peaking the distribution effectively concentrates certain ethoxymers. If these ethoxymers are key to performance, then the latter (soil removal, wetting, etc.) will be enhanced. However, the opposite is also true, which is why utilizing peaked ethoxylates requires optimization of EO content in order to obtain the benefit of peaking. 

The reaction is often catalyzed by alkalis such as potassium or sodium hydroxide. The average number of ethylene oxide groups depends on the reaction conditions. However, commercial ethoxylated alcohols have a broad range of ethylene oxide units along with some amount of unreacted fatty alcohols. Narrow range ethoxylated fatty alcohols can be obtained by using specific catalysts. 

The ultralow interfacial tension can be produced by using a combination of two surfactants, one predominantly water soluble (such as sodium dodecyl sulfate) and the other predominantly oil soluble (such as a medium-chain alcohol, e.g., pentanol or hexanol). In some cases, one surfactant may be sufficient to produce the microemulsion, e.g., Aerosol OT (dioctyl sulfosuccinate), which can produce a W/O microemulsions. Nonionic surfactants, such as alcohol ethoxylates, can also produce O/W microemulsions, within a narrow temperature range. As the temperature of the system increases, the interfacial tension decreases, reaching a very low value near the phase inversion temperature. At such temperatures, an O/W microemulsion may be produced. 

Because of its basic phenomenon, the PIT is however limited to ethoxylated nonionic surfactant systems, and its experimentally attainable range (that tits the liquid water state at atmospheric pressure) is sometimes rather narrow, particularly in dealing with highly ethoxylated detergents and emuisilier,s. 

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