Ethoxylation reactions

The solubility of alkylene oxides in the reaction mass is another important parameter, because the reaction takes place in the liquid phase and the gaseous monomer is transferred from the gas phase to the liquid phase. Because all the propoxylation and ethoxylation reactions are strongly diffusion dependent, the surface of the gas-liquid interface is a very important parameter for the mass transfer from the gas to liquid, and the real consumption of alkylene oxides depends strongly on this parameter. Between the alkoxylation of fatty alcohols and the alkoxylation of glycerol, there are many similarities if we use the Santacesaria kinetic model. Thus if RXH are considered to be the hydroxyl groups of the starter, the reaction rate of alkylene oxides addition is ... 

Practical experience of many ethoxylation reactions proved that in two different reactors, with different hydrodynamic conditions, at the same EO concentration different primary hydroxyl percentages are obtained. 

If the reaction conditions are maintained at constant, the distribution constant K is an important characteristic of the ethoxylation process. If for a given ethoxylation reaction the distribution constant K is determined at any moment, it is possible to appreciate the quantity of EO necessary to obtain the desired primary hydroxyl content for the synthesised EO capped polyether polyol. 

An important aspect of the ethoxylation reaction is that the primary hydroxyl content depends strongly on the hydroxyl number of the intermediate propoxylated polyether polyol. If a polyol is ethoxylated, an intermediate propoxylated polyether with an high hydroxyl number is obtained if the ethoxylation is done with a lower primary hydroxyl content with the same quantity of EO, an intermediate propoxylated polyether with a lower hydroxyl number is obtained (see Table 4.9). 

It is very interesting that by using alkaline-earth catalysts in the ethoxylation reaction (Ca, Sr or Ba alcoholates or carboxylates), a narrower distribution of EO sequences per hydroxyl group resulted, compared to use of alkaline catalysts. For example, with barium alcoholate as catalyst around 80-85% primary hydroxyl, at 15% EO as terminal block, are obtained with polyether triols (MW of 5000 daltons), compared to 65-75% primary hydroxyl obtained in the presence of KOH. The explanation of this behaviour... 

Excellent papers on the propoxylation and ethoxylation reactions of hydroxyl compounds, considering both the mass transfer and the PO consumption by chemical reaction, which proves the fundamental effect of the mass transfer in these diffusion dependent reactions, were published by Santacesaria and co-workers [62-67, 92] and Cramers and co-workers [117-119] and others [114-116]. 

Details regarding the mathematical model of propoxylation or ethoxylation reactions are presented in the work of Santacesaria and co-workers [45-50]. 

Phenol acts as the initiator of the ethoxylation reaction, and shall be regarded as an other reactant since it cannot react with itself or an opened epoxide. The molecule depicted in Figure 2.3 would therefore qualify for the definition of polymer molecule whenever n>3. 

Longer reaction times are usually required for propoxylation reactions due to the preference for lower reaction temperatures necessary to maintain product color and avoid troublesome side reactions such as elimination of a terminal alcohol to generate allyl ethers. Propoxylation reactions can be selectively accelerated at lower temperatures with the use of a double metal cyanide catalyst. The catalyst is extremely sensitive and easily deactivated by moisture and conventional groups I and II catalysts, and will not effectively catalyze ethoxylation reactions. 

However, it has been shown that normally the chain length dependence of the propagation rate coefficient is not important, with the exception of the first unit [200, 201]. Both distributions can be used to describe ethoxylation reactions [202]. 

These proprietary catalysts are more expensive because they must be manufactured rather than simply purchased. Certain catalysts must also be removed from the finished ethoxylate via filtration in order to obtain a clear, transparent ethoxylate. On the other hand, complex catalysts can be significantly more reactive than hydroxide catalysts so that the ethoxylation reaction proceeds in less time, with less catalyst, and at lower temperatures. Ethoxylation with complex catalysts is accomplished via conventional ethoxylation equipment and procedures. 

Variations in methyl ester purity or composition (unsaturation, carbon chain length distribution, etc.) do not appear to influence the ethoxylation reaction or overall ethoxylate quality. The purity of the methyl ester, however, does appear to impact color. A yellow-tinted methyl ester logically yields a yellow-tinted ethoxylate. 

Linked to the nature of the ethoxylation reaction, there is generally a rather broad distribution in the number of EO units per molecule (or ethoxylation degree) also, for lower ethoxylates, a significant amount of unreacted fatty alcohol remains in the surfactant. The proportions of individual homologs depend on various process parameters (degree of polymerization, alkaline or acidic nature of the catalyst, etc.). 

Alcohols, coco, ethoxylated, reaction products with glucose (4 mol EO average molar ratio). See Coceth-4 glucoside... 

Ethoxylation reactions are normally initiated with sodium or potassium hydroxide as catalyst. When the reaction is complete, the catalyst may be removed by filtration or liquid-liquid extraction, or may simply be neutralized and left in the product. The presence of neutralized catalyst may cause problems in certain applications, or may sometimes be detectable as turbidity or even crystals in the product. Normally, if the catalyst is removed, inorganic residues are reduced to the low parts per million level. If the catalyst is simply neutralized, the resulting salt is present in the 0.5-1.0% range. 

Anyone seeking to characterize ethoxylated acids should study the specifications and descriptions of the fatty acid starting materials, for which excellent brochures are available from major suppliers. For example, the oleic acid of commerce is a mixture of carboxyhc acids but also contains other materials, which can total several percent. The purchaser has a choice of several grades of this so-called oleic acid, with the pharmaceutical grades not necessarily being the purest. Consider the fate of the impurities during the ethoxylation reaction to predict what might be likely impurities in the final product. 

Acid hydrolysis to form alcohol ethoxylates reaction with HI to form alkyl iodides Reaction with HI to form alkyl iodides... 

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