Effect of hydrotropes on solubility and mass transfer coefficient of lauric acid

A comprehensive investigation on the solubility and mass transfer coefficient enhancement of lauric acid through hydrotropy has been undertaken. The solubility and mass transfer studies were carried out using hydrotropes such as sodium cumene sulfonate, sodium p-xylene sulfonate and sodium p-toluene sulfonate under a wide range of hydrotrope concentrations (0 to 3.0 mol/L) and different system temperatures (303 to 333 K). The effectiveness of hydrotropes was measured in terms of Setschnew constant K _s and reported for all hydrotropes used in this study. The solubility data are also fitted in a polynomial equation as the function of hydrotrope concentration.     

Partitioning of o/p-Nitrophenols in the Presence of Hydrotropes in Aqueous Solutions

Abstract

Partitioning of o/p-nitrophenols between organic solvents and water in the presence of hydrotropes such as sodium toluene sulfonate, sodium xylene sulfonate, and sodium cumene sulfonate, has been experimentally investigated and modelled in terms of co-aggregation of the hydrotrope and nitrophenols in aqueous solutions. The phenol-hydrotrope and hydrotrope-hydrotrope interactions are characterized by an aggregation model. The experimental data for a series of hydrotropes are further used to predict the partitioning behavior of p-nitrophenol in the presence of sodium butyl benzene sulfonate (Na-NBBS). The aggregation number of NaNBBS, (～30) obtained from the partitioning data, matches well with that obtained by small angle neutron scattering.     

Effect of hydrotropes on the aqueous solution behavior of surfactants

Aqueous solutions of surfactants—cationic: tetradecyltrimethylammonium bromide (C₁₄TABr); anionic: sodium dodecyl sulfate (SDS); and nonionic: polyoxyethylene t-octylphenol (trade name Triton X-102, also called OPE-8)— in the presence of three hydrotropes, viz., sodium xylene sulfonate, sodium p-toluene sulfonate, and sodium chlorobenzene sulfonate, were examined by measuring surface tension, viscosity, and cloud points for the nonionic surfactant. The results show a marked decrease in the critical micelle concentration with increase in hydrotrope concentration for C₁₄TABr, a marginal decrease for SDS, and very little change for OPE-8 up to 0.1 M hydrotrope. The viscosity of cationic surfactant solutions showed a remarkable increase in the presence of trace amounts of hydrotropes (up to 15 mM). In contrast, the SDS solution showed only a slight increase in viscosity at high hydrotrope concentration (150 mM), and the viscosity of the OPE-8 solution remained constant. The cloud point of OPE-8 increased in the presence of hydrotropes, unlike its behavior with the simple salt NaCl. The strong dependence of the solution behavior of cationic surfactants on the presence of hydrotropes is discussed in terms of electrostatic interaction.     

Hydrotropic properties of a novel alkylnaphthalene sulfonate

Alkylbenzenesulfonates based on toluene, xylene, as well as cumene, and alkylnaphthalenesulfonates, act as hydrotropes in surfactant systems. A novel sodium diisopropyl-naphthalene sulfonate (SDIPNS) has been devepoped that contains about 92% diisopropylnaphthalene sulfonate, compared to other diisopropylnaphthalene sulfonate preparations that contain less than 50% diisopropylnaphthalene sulfonate. This material is both a hydrotrope and a surfactant. The color of a 35% solution is light yellow, Gardner 3, significantly lighter than comparable materials. Draves wetting time for a 0.5% solution is about 30 s. The Ross-Miles foam test (1% solution) indicates a significant level of initial foam, but the foam is unstable. The solubilites of toluene and limonene in SDIPNS are much higher than in other hydrotropes tested. Hydrotropes raise the cloud point of nonionic surfactants; SDIPNS is the most efficient hydrotrope found for this application. Another measure of hydrotropicity is the amount of hydrotrope required to clear a cloudy detergent formulation; this hydrotrope is quite effective. Another measure is the modification of surfactant formulation viscosity; SDIPNS is quite effective. Additionally, SDIPNS changes the solubility of nonionic surfactants in water. SDIPNS is a surfactant as well as a hydrotrope, demonstrating a critical micelle concentration at about 1%. Presented as a poster session at the American Oil Chemists' Society Annual Meeting & Expo, May 11–13, 1998, Chicago, IL.     

Hydrotropic Extraction of Reserpine from Rauwolfia vomitoria Roots

Aqueous solutions of sodium cumene sulfonate give quantitative and faster extraction of reserpine from Rauwolfia vomitoria as compared to the extraction using methanol. The extraction rate is influenced by intraparticle diffusion and increases with increasing temperature and hydrotrope concentration. The dynamic extraction data were fitted in a mass transfer model to evaluate diffusion coefficient of reserpine in the solid plant matrix. Amongst all hydrotropes, sodium cumene sulfonate, gave the best extraction and extraction rates of reserpine. The reserpine crystals recovered from aqueous hydrotrope solutions were much smaller in size and showed different morphology than those from methanol.     

ENHANCEMENT OF SOLUBILITY AND MASS-TRANSFER COEFFICIENT OF 1,2-DIHYDROXY-9,10-ANTHRAQUINONE (ALIZARIN) THROUGH HYDROTROPY

The effect of hydrotropes potassium p-toluene sulfonate (KPTS), citric acid, and nicotinamide on the solubility and mass-transfer coefficient of 1,2-dihydroxy-9,10-anthraquinone (alizarin) was studied. Solubility studies were carried out under a wide range of hydrotrope concentrations (0 to 3.0 mol·L^?1) and different system temperatures (303 to 333 K). It was observed that the solubility and mass-transfer coefficient of alizarin increases with an increase in hydrotrope concentration and system temperature. The maximum enhancement factor, the ratio of the value of solubility in the presence and absence of a hydrotrope, was determined for all experiments under study. The effectivity of hydrotropes was measured by the determination of the Setschenow constant, K_s. The order of effectiveness of various hydrotropes based on K_s values is potassium p-toluene sulfonate > citric acid > nicotinamide.     

Effective Separation of Petro Products through Hydrotropy

This paper presents a comprehensive study on the effect of hydrotropes such as sodium salicylate, sodium benzoate, and nicotinamide on the separation of a near boiling mixture, o‐/p‐xylene. The influence of a wide range of hydrotrope concentrations (0 to 3.0 mol/L) and different system temperatures (303 to 333 K) on the separation of o‐/p‐xylene were studied. All hydrotropes used in this work showed an enhancement in the percentage extraction of p‐xylene to different degrees. The percentage extraction of p‐xylene from the o‐/p‐xylene mixture increases with an increase in hydrotrope concentration and also with system temperature. A minimum hydrotrope concentration (MHC) was found essential to initiate significant extraction of p‐xylene from the o‐/p‐xylene mixture. The maximum enhancement factor, which is the ratio of the value in the presence and absence of a hydrotrope, was determined for both cases. The Setschenow constant, k_s, a measure of the effectiveness of a hydrotrope, was determined for each case.     

Hydrotropic properties of some short-chain alkylbenzene- and alkylnaphthalene sulfonates

Alkylbenzene sulfonates based on toluene, xylene and cumene, and alkylnaphthalene sulfonates act as hydrotropes in surfactant systems. One measure of hydrotropicity is the amount of hydrotrope required to clear a cloudy detergent formulation; some hydrotropes are more effective than others, depending on the surfactant formulation. Another measure is the modification of the viscosity of surfactant formulations; the change in the viscosity depends on the amount and type of hydrotrope used and on the specific formulation involved. Additionally, alkylnaphthalene sulfonate hydrotropes change the solubility of nonionic surfactants in water, and both types of hydrotrope raise the cloud point of nonionic surfactant solutions; however, the naphthalene-based hydrotropes are more efficient. Ross-Miles foam test data are used to compare the foam characteristics of different alkylnaphthalene sulfonates. A critical micelle concentration (CMC) was determined for the alkylnaphthalene sulfonates, but although alkylbenzene sulfonates do show some surface activity, a CMC could not be found for these materials. Presented as a poster session at the AOCS Annual Meeting & Expo, May 1997, Seattle, Washington, and at Soaps, Detergents, and Oleochemicals: An AOCS International Conference, October 1997, Fort Lauderdale, Florida.     

Aqueous Hydrotropic Solution as an Efficient Solubilizing Agent for Andrographolide from Andrographis paniculata Leaves

Abstract

An aqueous solution based extraction process for andrographolide from Andrographis paniculata leaves has been developed using alkyl benzene sulfonates and carboxylates as hydrotropes. The plant cells are permeabilized by the hydrotrope solutions followed by solubilization of andrographolide into the solutions. The extraction and solubilization of andrographolide is affected by structure and concentration of hydrotrope, temperature and particle size. Sodium cumene sulfonate (Na‐CS) shows the most efficient solubilization of andrographolide amongst the hydrotropes studied. The solubility of andrographolide increased by two orders of magnitude in Na‐CS aqueous solutions and ～96% andrographolide extraction was achieved in just 20 min.     

Selective Extraction of Embelin from Embelia ribes by Hydrotropes

Abstract

The research work proposes an alternate strategy of the extraction of embelin (2,5‐dihydroxy‐3‐undecyl‐p‐benzoquinone) from Embelia ribes. The aromatic hydrotropes such as sodium n butyl benzene sulfonate (NaNBBS), and sodium cumene sulfonate (NaCS) were found to be effective for the selective extraction of embelin with a recovery of 95% embelin from the aqueous solution of hydrotropes with high purity. The process was further optimized with respect to concentration of hydrotropes and temperature of extraction.     

Hydrotropic and surfactant properties of novel diisopropyl naphthalene sulfonates

A novel surfactant and hydrotrope, sodium diisopropylnaphthalene sulfonate (SDIPNS) has been developed. It contains about 92% diisopropylnaphthalene sulfonate, compared to other materials which are less than 50% diisopropylnaphthalene sulfonate. Aqueous solutions of 34–36% active SDIPNS have dual functionality. They have excellent surface properties and are compatible with conventional anionic, nonionic, and amphoteric surfactants. They demonstrate good laundering detergency in combination with sodium lauryl ethoxy sulfate, with or without builder. They maintain surface activity in 150 ppm hard water (Ca²⁺/Mg²⁺=2∶1), 5% NaCl, pH 2, and pH 12. They are effective hydrotropes. They enhance surfactant solubility, raise the cloud point of nonionic surfactants, and modify the viscosity of surfactant formulations. They are light in color and are low-foaming. Presented as a Poster Session at the American Oil Chemists' Society Annual Meeting, May 9–12, 1999, Orlando, Florida.     

Claisen–Schmidt reaction in a hydrotropic medium

The Claisen–Schmidt condensation of benzaldehydes with acetophenones was carried out in an aqueous medium using sodium butylmonoglycolsulfate (NaBMGS) and sodium salts of aromatic sulfonic acids as hydrotropes. Substantial enhancement in the rate of the reaction was obtained, along with the easy recovery of the product. Recycling of the hydrotrope solutions has been tested without any loss in the rate of the reaction.     

酸性助水溶剂脱除木质素机理分析

系统探讨了酸性助水溶剂对甲苯磺酸(p-toluenesulfonic acid,TSA)和马来酸(maleic acid,MA)分离桉木各组分的工艺过程,并对其中木质素脱除机理进行了研究。通过分析对比两种优化后的工艺发现：(1)两种酸性助水溶剂都可以高效脱除木质素,TSA木质素脱除率为67.94%,MA为65.14%;(2)在相同质量分数下,TSA的木质素脱除率比MA更高;(3)在温和条件下,TSA木质素的β-芳醚键含量比MA的高,随着反应条件的加剧,TSA和MA处理后木质素产品中β-芳醚键含量逐渐减少;(4)两种酸性助水溶剂处理后,纤维素保留率都较高,可保持90%以上;但是半纤维素的降解程度随着反应条件的加剧而增加;(5)酸性助水溶剂质量分数越高,在疏水表面的接触角越小,对木质素的助溶作用越明显,脱除木质素效率越高,溶液中木质素聚集体的粒径越小。综上所述,酸性助水溶剂对木质素的脱除基于润湿溶解、木质素芳醚键断裂、半纤维素降解等的综合作用。相关研究可为后续实现温和条件脱木质素工艺优化及机理提供参考。     

Extraction of Piperine from Piper Nigrum (Black Pepper) by Aqueous Solutions of Surfactant and Surfactant + Hydrotrope Mixtures

Abstract

The effect of combining butyl benzene sulfonate as hydrotrope with a surfactant in aqueous solutions is investigated for isolation of piperine, an alkaloid, from black pepper. The standard free energy change associated with piperine solubilization in the aqueous solutions of surfactant and hydrotrope individually and in their mixtures is determined from the solubility of piperine in these solutions. A combination of sodium dodecyl sulfate (SDS) and the hydrotrope gives increased percentage extraction of piperine as compared to the hydrotrope alone. The piperine purity recovered from aqueous solutions was higher as compared to the purity of piperine recovered using organic solvents. The piperine crystallized from aqueous solutions of surfactants and hydrotrope also showed cleaner surfaces and uniform structures with sharp edges, unlike the particles crystallized from organic solvents.     

Additive-induced association in unconventional systems: A case of the hydrotrope

It is well known that hydrotropes have a very high minimum hydrotrope concentration (MHC), posing a question on their applications. We have found that MHC (obtained by conductivity and surface tension measurements) can be reduced by the addition of foreign materials. The association tendency can be improved by the addition of salts, n-alkanols, and ureas. Urea decreases or increases the MHC depending on whether the urea content is lower or higher (e.g., the increased solubility of sparingly soluble riboflavin corroborates the increase in the hydrotropic properties of the system). In the present work, the association tendencies of sodium salicylate (a well-known hydrotrope), sodium dodecyl sulfate, and sodium bromide were compared. The results have direct implications in the mechanism of protein denaturation and may provide insight into the role of urea in supramolecular assemblies.     

Performance of New Biodegradable Di‐Sulfonate Surfactants as Hydrotropes in High‐Temperature and Salinity Environments

Propyl alkyl ether sulfonate (PAES) surfactants, recently developed by The Dow Chemical Company, show excellent electrolyte, hard water and caustic solubility, with attractive ECOTOX profile and biodegradability. Due to their unique structure and properties, they are good candidates for use as hydrotropes in formulations containing nonionic surfactants. The goal of these studies was to evaluate hydrotropic efficiency of PAES materials via cloud point analysis. The effects of PAES alkyl tail length, concentration, and mono‐ and di‐sulfonate components on the cloud point of TERGITOL? 15‐S‐9 in solutions of varying electrolyte strength were investigated. In the presence of high electrolyte levels, PAES 12C had the highest hydrotropic efficiency of all materials tested, including commonly used commercial hydrotropes. Di‐sulfonate components of the PAES materials were found to be more efficient hydrotropes than mono‐sulfonate in high electrolyte environments for all tail lengths tested. The di/mono ratio and tail length were found to be critical parameters.     

Anionic hydrotropes for industrial and institutional rinse aids

The effectiveness of eight commercial hydrotropes having differing structures (sodium xylenesulfonate, sodium-2-ethyl hexysulfate, phosphate ester of oxyethylated phenol, amine alkylaryl sulfonate, linear alkyl naphthalene sulfonate, TEA salt of DDBS, sodium dihexyl sulfosuccinate, and sodium dodecylbenzene sulfonate) was evaluated with seven commercial rinse aid surfactants of the following structural types: block copolymers and alcohol oxyalkylates with high and low levels of ethylene oxide. Two hydrotrope levels (3 and 6 wt %) were evaluated at two surfactant levels (20 and 40 wt %). Dispersibility, compatibility index, and blender foam heights were measured; the test methods are described.     

Rheological Investigation of Wormlike Micelles Based on Gemini Surfactant in EG–Water Solution

The self‐assembly behavior of gemini surfactants in ethylene glycol (EG)‐water (5/95, v/v) mixed solvent was investigated by rheological measurements at 10 °C. The influence of molecular structure of the gemini surfactant and added hydrotrope on the solution properties was studied. Sodium salicylate (NaSal) showed stronger ability to induce 2‐hydroxyl‐propanediyl‐α,ω‐bis‐(dimethyldodecylammonium bromide), referred to as 12‐3(OH)‐12, to form wormlike micelles than sodium benzoate. Less NaSal is required to promote a sphere to rod transition and to reach the peak viscosity. Moreover, the concentrations of hydrotrope and gemini surfactant are both lower than conventional single‐chain surfactant systems to reach a comparable viscosity. The strong hydrophobicity of gemini surfactants and hydrotropes is responsible for the high efficiency in forming wormlike micelles in EG/water systems. The geometric structure of gemini surfactants also plays a vital role in self‐assembly into wormlike micelles. Dimethylene‐1,2‐bis‐(dodecyl dimethylammonium bromide), referred to as 12‐2‐12, shows absolute superiority over 12‐3(OH)‐12 in constructing wormlike micelles. The present study will be helpful for developing de‐icing fluids and anti‐freezing solutions, which need rheology control in EG‐aqueous medium at low temperature.     

Hydrotrope-Induced Enhancement of Room Temperature Surface Activity for High Krafft Point Fluorinated Surfactants

Potassium perfluorooctane sulfonate (KPFOS) and sodium perfluorooctane sulfonate (NaPFOS) exhibit poor surface activities in aqueous solution at room temperature because of their high Krafft points. In this work, we attempted to increase the solubility of KPFOS and NaPFOS and consequently improve their surface activities at room temperature with sodium p‐methylbenzene sulfonate (BS) and urea, which are typical hydrotropes in industrial applications. The effects of BS and urea on the surface tension of the aqueous solutions of KPFOS and NaPFOS were investigated at 25 °C. When the hydrotropes were added, the effectiveness of KPFOS and NaPFOS in surface tension reduction was greatly enhanced and KPFOS showed higher efficiency in surface tension reduction than NaPFOS. On the other hand, BS had much stronger ability than urea to reduce the surface tension of KPFOS and NaPFOS in water. In particular, with the assistance of BS the minimum surface tension of KPFOS approached 19 mN/m at 25 °C. It was worth noting that in the presence of BS, the surface tension of an apparently “saturated” solution (i.e., with coexisting surfactant solid) continuously decreased with increasing surfactant concentration. This behavior was ascribed to enrichment of branched PFOS isomers in aqueous phase with the assistance of BS, as evidenced by high‐resolution ¹⁹F NMR. Hydrotropes were able to recover the inherent character of KPFOS and NaPFOS as highly surface‐active fluorinated surfactants by increasing the solubility of branched isomers. This is an easy way to enhance the effectiveness in surface tension reduction at room temperature for fluorinated surfactants with high Krafft points.     

Solubilizing and Hydrotropic Properties of Isosorbide Monoalkyl- and Dimethyl-Ethers

Isosorbide is a diol readily obtained from starch that can be used as a polar building block for the synthesis of derivatives ranging from solvents to surfactants: dimethyl isosorbide (DMI) is a “sustainable solvent” already on the market, used notably in cosmetic and pharmaceutical formulations; monoalkyl derivatives of isosorbide are non-ionic hydrotropes that could be potential substitutes to short-chain glycol ethers. The use of these isosorbide derivatives as bio-sourced alternatives to petroleum-derived products for applications such as compatibilizers in liquid detergent formulations or solubilizing agents in aqueous hard-surface cleaning is discussed in this paper. DMI reveals to have interesting coupling properties for the former applications, whereas the monopentyl ether of isosorbide (C₅Iso) is a particularly efficient hydrotrope for the latter.