Peaked ethoxylates

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. 

There are technologies available that produce the so-called peaked ethoxylates , which increase the amount of the desired adduct and minimise the formation of lighter and heavier adducts. 

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 ... 

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 general relationship described above between hydrophobe structure and EO chain length of alcohol ethoxylates also applies to MEEs. However, since the catalysts used to prepare MEEs are often the same catalysts used to produce peaked ethoxylates, the ethoxymer distributions for MEEs are in fact already peaked . The degree of peaking, however, varies significantly depending on the catalyst used. 

Surface tension methods measure either static or dynamic surface tension. Static methods measure surface tension at equilibrium, if sufficient time is allowed for the measurement, and characterize the system. Dynamic surface tension methods provide information on adsorption kinetics of surfactants at the air-liquid interface or at a liquid-liquid interface. Dynamic surface tension can be measured in a timescale ranging from a few milliseconds to several minutes [315]. However, a demarkation line between static and dynamic methods is not very sharp because surfactant adsorption kinetics can also affect the results obtained by static methods. It has been argued [316] that in many industrial processes, sufficient time is not available for the surfactant molecules to attain equilibrium. In such situations, dynamic surface tension, dependent on the rate of interface formation, is more meaningful than the equilibrium surface tension. For example, peaked alcohol ethoxylates, because they are more water soluble, do not lower surface tension under static conditions as much as the conventional alcohol ethoxylates. Under dynamic conditions, however, peaked ethoxylates are equally or more effective than conventional ethoxylates in lowering surface tension [317]. 

Recently, patented ethoxylation catalysts have become available that can significantly narrow the ethylene oxide distribution of the alcohol ethoxylates used to obtain alcohol ether sulfates. These products are termed peaked alcohol ether sulfates whereas all others are termed conventional alcohol ether sulfates. Peaked alcohol ether sulfate solutions thicken more than those with a conventional ethylene oxide distribution [78]. Peaked alcohol ether sulfate solutions also exhibit behaviors different from those of conventional sulfates [79]. Smith [78] studied the viscosities of 15% sodium dodecyl ether sulfate solutions of both families with NaCl content between 2% and 10% at 25°C using a Brookfield model DVII viscometer at a shear rate of 2 s 1. The results are shown in Fig. 5 where the very different viscosities achieved are clearly observed. 

We have studied demulsifier association by the electron spin resonance (ESR) technique. The spin label is covalently attached (Figure 5a) to the demulsifier. Normally, the ESR spectrum of a freely tumbling nitroxyl radical consists of three sharp peaks (Figure 5b). However, the spectrum for a tagged ethoxylated nonyl phenol resin (Figure 6a or 6b) shows only a single broad peak. 

In one study, however, atmospheric pressure chemical ionisation (APCI)-MS was applied for the simultaneous determination of LAS and octylphenol ethoxylates (OPEO) in surface waters after preconcentration by solid-phase extraction (SPE) on Cis cartridges [1]. In the chromatogram from a Ci-reversed phase (RP) column, peaks arising from both the anionic LAS and the non-ionic OPEO were detected after positive ionisation, while in negative ionisation mode, OPEO were discriminated and only the anionic surfactant was observed. Surprisingly, the relative sensitivity for detection of LAS was approximately five times higher in positive ion mode, which led the authors to the conclusion that this ionisation mode was desirable for quantitative work. 

Quantitative analysis of AP/APEO by HPLC-FL can be performed with external standard solutions of mixtures of AP or APEO. Initially quantification of oligomeric mixtures was based on the elaborate procedure of normal-phase analysis with subsequent quantification of all oligomeric peaks [27]. Kiewiet et al. [28] have described the general principle of quantification of ethoxymers in reversed-phase LC with spectroscopic detection in detail using the example of derivatised alcohol ethoxylates. Based on this method the quantitative analysis of... 

Fig. 1.5. Separation of non-sulphated (first group of peaks) and sulphated anionie (second group) oligomers in a partially sulphated Serdox NNP 4 sample of ethoxylated nonylphenol on a Silasorb SPH Amine, 7.5 pm. column (3()0.v4.2 mm i.d.) using elution wilh a linear gradient from ().(X)5 mol/l to 0.0.3 mol/l CTAB in 2-propanoI-/i-heptane I I in 90 min at I ml/min. Detection L V. 230 nm.

Nonionic surfactants of the ethoxylate type are not so efficiently separated compared to ionic surfactants. The complexity of the surfactant mixtures and the lack of charge leads to insufficient peak resolution and high detection limits. 

Figure 1. Equilibrium diagrams for the exchange on silicon (v = 4) of the following groups A methoxyl vs. ethoxyl at 150°C, B methoxyl vs. chloro at 120°C, and C dimethylaraino vs. chloro at 25°C. The dotted lines correspond to the random situation, and each curve exhibits a peak value at the value of the parameter R corresponding to the composition of the compound it represents.

The substitution position of ethoxyl groups was located based on the correlation peaks of methylene proton on ethoxyl groups and ring carbons. For example, the gray HMBC peaks labeled S3CH2-C3 indicates the three bond coupling between the sidechain methylene protons and the glycosidic carbon at position C3. 

Relative positional DS at C2, C3 and C6 could be obtained from the integration of cross peaks on HOHAHA (Figure 3). The adjacent proton coupling constants for the three ethoxyl groups were found to be similar ( 15Hz) as measured from DQF-COSY. The three HOHAHA cross peak... 

Figure 13.13. Distribution of ethoxymers for the preparation of 60% EO ethoxylates by using sodium hydroxide (NaOH) and a proprietary peaked distribution catalyst...

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