Volume 54, Issue 2

Microbial surfactants are produced by various sources (terrestrial and marine environments, sludges, etc.) of microorganisms. The production of biosurfactants in a culture medium is determined by the secretion of the surface active molecules, which supports both the reduction of the surface tension and the lowering of the critical micelle concentration (CMC). Biosurfactant molecules consisting of lipophilic and hydrophilic moieties have been described for various applications (physiochemical, biological, commercial and nanotechnological) due to their structural properties and their molecular weight, which is generally between 500 Da – 1 500 Da. Although, biosurfactants have normally better application properties than conventional surfactants, the production of them in higher scale is limited due to certain constraints. These constrains are addressed in different studies: Kinetics, statistical design (Taguchi, factorial design, RSM etc.) and computational tool (ANN-GA) have been performed to improve the yields. Along with that, few studies also described the batch and fed batch fermentation for the better commercial level production. However, no defined commercial method is available for the purification of the biosurfactants. Few studies demonstrated the purification by gel exclusion chromatography (SEC, gel filtration chromatography) and ultrafiltration/diafiltration that have been partially established. This review article outlines the detailed reports on these.

The pulp of the fruit of Sapindus saponaria (soapnut tree) consists mainly of saponin. Surface-active characteristics of this raw saponin such as critical micelle concentration, area per molecule and, hydrophilic-lipophilic balance were investigated; this information is valuable to assess its implementation in different applications of industrial interest. By using surface tension measures and dynamic light scattering studies, the value of critical micelle concentration was found in the range of 0.03 – 0.046 g mL −1 . Further increase in the concentration of crude saponin leads to a constant value of surface tension (44 mN m −1 ). These results were analyzed using the Gibbs adsorption isotherm yielding an estimated value of the area occupied per molecule at the air/water interface of 57.2 Å 2 . Besides, Griffin method was used to determine the hydrophilic-lipophilic balance value (14.3). Sapindus saponaria extract properties are comparable to that of commercial surfactants, hence it could be used as an economical biosurfactant.

Foxtail millet is a short life cycle plant and known as a drought tolerant crop. Nowadays, contaminated wastewater with laundry detergent is used for irrigation. A pot experiment was conducted to evaluate the effect of contaminated water with laundry detergent on foxtail millet root and physiological traits. Contaminated water (concentration of 0, 0.1, 1 and 10 g l −1 of laundry detergent) and irrigation interval (1, 2 and 3 days) made the factors. Results showed that drought and contamination decreased chlorophyll, root number, root dry weight, root volume and root surface area. High concentrations of laundry detergent decreased the leaf relative water content. The sodium content of root was increased under drought and moderate concentration of laundry detergent, but the root potassium content was decreased by drought and detergent.

Washing machines use different technologies to enhance their washing performance. Despite different names, some of these technologies use additional circulation pumps. These pumps allow spraying of suds into the inner drum and circulation of suds in the gap between the inner and the outer drum. A washing machine without circulation pump was used as a reference. Experiments were carried out similar to typical household conditions using a 40 °C program for cotton. A set of 20 stains was used to evaluate the primary washing effect for different stain groups and of individual stains. The results showed that generally, the circulation pumps did not change the performance. However, for two stains significant advantages could be found only in the case of a system with two circulation pumps for two single stains, CS32 sebum and CS06 salad dressing. It is concluded that the differences between machines from different manufacturers are mainly influenced by variations of the parameters according to Sinner's Circle.

Response surface methodology (RSM) and artificial neural networks (ANNs) architectures to predict the density, speed of sound, kinematic viscosity, and surface tension of aqueous solutions were developed. All models implemented using the root mean square error (RMSE) for training and validation phase were evaluated. The ANN models implemented show good values of R 2 (upper than 0.974) and low errors in terms of average percentage deviation (APD) (lower than 2.92 %). Nevertheless, RSM models present low APD values for density and speed of sound prediction (lower than 0.31 %) and higher APD values around 5.18 % for kinematic viscosity and 14.73 % for surface tension. The results show that the different individual artificial neural networks implemented are a useful tool to predict the density, speed of sound, kinematic viscosity, and surface tension with reasonably accuracy.

The effect of amino acids (L-glycine, L-alanine, L-phenylalanine, L-serine, L-leucine, L-aspartic acid, L-lysine, L-methionine) on the micellization, surface activity, volumetric and viscometric properties of the cationic surfactant cetylpyridinium bromide in aqueous solution was studied. The critical micelle concentration and free energy of micellization were evaluated and discussed. The surface excess concentration, the minimum area per molecule, the surface pressure at the critical micelle concentration and the standard free energy of adsorption were obtained from the surface activity studies. The behavior of standard partial molar volume is discussed. The viscosity data were analyzed by Jones-Dole semi-empirical equation for both the premicellar and postmicellar regions.

Effects of various additives including inorganic salts, nonionic and ionic surfactants on the cloud point of the linear nonionic surfactant, Tergitol 15-S-7 were investigated. The cloud point of this surfactant is a function of its concentration, as well as the additive concentration. The cloud points of nonionic surfactant mixtures lay in between the cloud points of individual surfactant. The presence of two ionic surfactants, sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) in the system leads to a substantial increase in the cloud point of a 1 wt% Tergitol 15-S-7 micellar solution. The inorganic salts (< 0.1 M) decrease the cloud point only slightly. However, when inorganic salts are added to the Tergitol 15-S-7 solution in the presence of SDS or CTAB, the cloud point decreases drastically. For SDS-Tergitol 15-S-7 mixed micellar solutions, the polyvalent cations of the added inorganic salts are more active than the univalent cation, the order of decreasing effect is LaCl 3 > MgCl 2 > KCl; while for CTAB-Tergitol 15-S-7 mixed micellar solutions, the polyvalent anions of the added inorganic salts are more effective than the univalent anion, the order of decreasing effect is Na 3 PO 4 > Na 2 SO 4 > NaNO 3 .

Series of bi-component nonylphenol alkyl sulfonate surfactants (C 12 /C n -NPAS, n = 8, 10, 14, 16) were synthesized through sulfonation-alkylation-neutralization using a mixture of linear alpha olefin (C 12 -olefin and C n -olefin, n = 8, 10, 14, 16), SO 3 and nonylphenol as raw materials. The effect of the raw materials composition on the properties, such as surface tension, interfacial tension, wettability, foam properties of the prepared C 12 /C n -NPAS ( n = 8, 10, 14, 16) surfactants was systematically investigated. The critical micelle concentrations (CMC) of C 12 /C 8 -NPAS, C 12 /C 10 -NPAS, C 12 /C 14 -NPAS and C 12 /C 16 -NPAS are 0.42, 0.26, 0.22 and 0.40 mmol · L −1 , and surface tensions at CMC (γ CMC ) are 34.7, 27.9, 31.8 and 33.3 mN · m −1 , respectively. Compared with SDBS and HABS, the surface properties of the prepared C 12 /C n -NPAS are superior to traditional surfactants. Interfacial tension between Daqing crude oil and weakly alkaline ASP oil flooding system containing 0.1 wt% of C 12 /C 14 -NPAS could reach an ultralow level of 9.78 × 10 −3 mN · m −1 , which is lower than that for C 12 -NPAS and HABS. C 12 /C 10 -NPAS shows better wetting performance and foamability and foam stability than other synthesized surfactants.

A new group of cleavable di-anionic surfactants aliphatic glycerol acetal di-sodium sulfosuccinates has been successfully synthesized starting from esterification reaction of aliphatic glycerol acetals with maleic anhydride, followed by sulfonation with sodium sulfite. The prepared surfactants were characterized by Fourier transform infrared spectroscopy (FT-IR), mass spectroscopy (MS) and elemental analysis. The surface active properties of the new surfactants, such as surface tension, critical micelle concentration (CMC), foaming property, and emulsifying power were determined.

Cloud point extraction (CPE) experiments were carried out for separation of copper(II) from aqueous saline sulphate medium with the Schiff's base chelating extractant, N,N′-bis(salicylidene)ethylenediamine (H 2 SALEN), using the polyethoxylated alcohol Tergitol 15-S-7 as a biodegradable non-ionic surfactant. The obtained results were compared with those previously obtained in presence of Triton X-100. The effects of the main experimental parameters such as pH , extractant concentration, and non-ionic surfactant concentration on the cloud point extraction behavior of copper(II) with H 2 SALEN were studied and discussed. The use of both systems namely, Triton X-100/H 2 SALEN/Na 2 SO 4 and Tergitol 15-S-7/H 2 SALEN/Na 2 SO 4 , led to very good extraction efficiency and concentrating ability for Cu(II) pollutant. Indeed, nearly 100 % extraction efficiency with a minimal volume fraction of the surfactant-rich phase, ϕ s , was achieved at pH 7.25 and 8 in the systems Tergitol 15-S-7/H 2 SALEN/Na 2 SO 4 and Triton X-100/H 2 SALEN/Na 2 SO 4 , respectively. The Tergitol 15-S-7/H 2 SALEN/Na 2 SO 4 extraction system was found to be more efficient for Cu(II) removal compared to Triton X-100/H 2 SALEN/Na 2 SO 4 system, providing higher concentration factor, C f , and a lesser separation temperature, T s . The analysis of the extraction data revealed that the cloud point process of copper proceeds via a cation exchange mechanism. The stoichiometry of the extracted complexes was ascertained by the Yoe-Jones mole ratio method having a composition of 1 : 1 [Cu: H 2 SALEN].