Volume 42, Issue 6

Labeled surfactants have impurities in the form of un-reacted molecules or distributed products which is a constraint in evaluating its performance. This short review deals with the purity issue of surfactants and is divided into two parts. The first part deals with the methods of purification employed for obtaining a surface chemically pure surfactant for evaluation. In the second part the use of surface chemically impure surfactant in application areas of formulations is presented to highlight the impending impact on reproducibility of results.

The new European Detergents Regulation will enter into force 8 October 2005, dealing with the aerobic biodegradation of surfactants so far. An expansion of the regulation regarding all main organic detergent ingredients and anaerobic biodegradation aspects shall be reviewed until April 2009. Within the scope of this expansion also bleach activators will be affected, whereat in our opinion thought should been given to a specific characteristic of this ingredients category: whereas other detergent ingredients as surfactants, builders or solvents act in the washing process due to physical effects and therefore arrive at the environment in a chemical unchanged way, bleach activators react with per-oxo compounds during the washing process and hence change their chemical structure. So, regarding bleach activators, the environmental relevant compound differs from the compound being existent in the washing agent. This issue shall be pointed out considering various bleach activators as example.

In this work, drilling fluids with 135 400 mg kg −1 of total petroleum hydrocarbons (TPH) were washed with six different surfactants (the non-ionic Emulgin 600, Emulgin 1000, Brij 35 and Tween 80, ionic SDS, and zwitterionic Polafix CAPB) and their mixtures. Due to the high Ca content in the samples, three different approaches were employed when washing with SDS, because of its ionic character: a) using mixtures of surfactants, b) addition of NaCl, and c) addition of a Ca sequestrant, i. e., sodium metasilicate. Drilling fluids were washed; TPH, electric conductivity (EC, as an indirect measurement of salinity), and pH values were measured before and after the washing process. Surface tension of the clean and spent washing solutions (surfactant or surfactants mixture, with or without salts) was measured. TPH removals as high as 75% were achieved using SDS + sodium metasilicate. EC values diminished 75% with the washing process, but for the experiments in which salts were added, increments in electric conductivity of up to 367% were observed. Regarding the pH changes, initial sample pH value was 7.77, and in most cases this value was reduced, except for some of the cases where salt was added. Surfactant solution's surface tension changes (before and after the washing process) correlated fairly with TPH removals.

The solubility of polyoxyethylated nonionic surfactants (POSs) in water is limited by an upper and a lower critical temperature. The former, called cloud point (CP), is the temperature at which POSs precipitate from solution on heating because of excessive dehydration of their polyoxyethylene (POE) moieties. The latter, called Krafft point (KP), is the temperature at which POSs crystallize from solution on cooling because of increased alignment and attraction between their hydrocarbon chains. It occurs less frequently: Even if the POSs were capable of crystallizing, ice often crystallizes first. Aqueous solutions of over 100 POSs were examined by obtaining their CPs and ascertaining whether they exhibit KPs. KPs were found in polyoxyethylated primary alcohols and fatty acid amides and in polyethylene glycol esters of fatty acids. Only surfactants with strictly linear hydrocarbon chains crystallize, exhibiting KPs. Any branching, including that in polyoxyethylated linear secondary alcohols, prevents crystallization. Crystallization only occurs when the number m of carbon atoms in the hydrocarbon chains equals or exceeds 12. The KPs are then proportional to m . In homologous series, the surfactants most prone to crystallizing are those with borderline solubility, which possess just enough oxyethylene groups to promote solubility in cold water. Large POE moieties depress or eliminate KPs.

Kinetic study for the heterogeneous decomposition of hydrogen peroxide over different non-soluble metal oxides (CuO, Fe 2 O 3 and PbO 2 ) was taken as a model reaction, mainly in normal micellar, inverse micellar microemulsion of sodium dodecyl sulfate (SDS). Other micellar phases of different surfactants [sodium dioctylsulfosuccinate (AOT), cetyle trimethyl ammonium bromide (CTAB) and triton X100] have been studied. Different organic solvents have been investigated. A promotional effect was generally observed. The reaction rate determining step was estimated. Reaction rate constants and thermodynamic parameters (ΔG * , ΔH * and ΔS * ) were calculated. It was found that the highest promotional influence was observed in the case of (SDS/Fe 3 O 4 ) in micellar and inverse micellar micro-emulsion media.

The wetting power of anionic surfactant: sodium dodecyl sulfate (SDS), and nonionic surfactants: polyoxyethelene(14)monolaurate [La(EO) 14 ] and polyoxyethelene(14)monooleate [Ol(EO) 14 ] has been studied to determine their performance as wetting agents. The study reveals that the nonionic compound with a long hydrophobic chain exhibits higher wettability than the shorter one when used at very low concentrations (below CMC), and the reverse is shown with high concentrations (above CMC). The wetting power of the investigated surfactants increases as the CMC values increases. In case of the nonionic compounds and at surfactant concentrations equal their CMC values, Ol(EO) 14 shows a higher wetting power than La(EO) 14 while it possesses a lower HLB value. The anionic surfactant shows an optimum wetting in comparison with the tested nonionic ones. The wettability of all the investigated samples increases as the surface tension of their solutions increases to the allowed limit that can be reached in the presence of surfactant.