Stable diesel microemulsion using diammonium ionic liquids and their effects on fuel properties, particle size characteristics and combustion calculations

Ecofriendly and stable Fuel Microemulsions based on renewable components were prepared through solubilizing ethanol in diesel and waste cooking oil blend (4:1). New diquaternary ammonium ionic liquids (3a & 3b) were synthesized through a quaternization reaction of the synthesized dihaloester with diethyl ethanolamine tridecantrioate and triethyl amine tridecantrioate, respectively. The chemical structures were elucidated by NMR spectroscopy. It was observed from DLS analyses that the ethanol particles in all samples have sizes between 4.77 to 11.22 nm. The distribution becomes narrower with the decrease in the ionic liquid concentrations. The fuel properties fall within the ASTM D975 acceptable specifications and are close to the neat diesel properties. The Cetane index were 53 and 53.5, heating values were 38.5 and 38.5 MJ/kg, viscosities were 2.91 and 2.98 mm2/s, densities were 8.26 and 8.29 g/mL and flash points were 49 °C and 48 °C for 3a1 and 3b1 microemulsions, respectively. The particle sizes of samples were examined by DLS for 160 days and they were significantly stable. The amount of ethanol solubilized increases with the increase in the amount of the synthesized ionic liquids and cosurfactant. The combustion calculations pointed out that the microemulsions 3a1 and 3b1 need 13.07 kg air/kg fuel and 12.79 kg air/kg fuel, respectively, which are less than the air required to combust the pure diesel. According to theoretical combustion, using ionic liquids saves the air consumption required for combustion and reduces the quantities of combustion products. The prepared microemulsions were successfully used as a diesel substitute due to their improved combustion properties than pure diesel and low pollution levels.

Structured ternary fluids as nanocrystal incubators for enhanced crystallization control

Crystallization in structured ternary fluids can proceed via higher nucleation rate and slower crystal growth pathways that are impossible to access in normal unstructured solutions. Hence, structured ternary fluids can act as nanocrystal incubators.

Surfactant-Free Microemulsion Based on CO2-Induced Ionic Liquids

A novel surfactant-free microemulsion (SFME) based on CO₂-induced ionic liquids (ILs) was prepared. Among them, dipropylamine (DPA) was directly reacted with CO₂ to form the ILs that were composed of the ammonium salts and the ammonium carbamate salts, which was confirmed by ¹³C NMR, Fourier transform infrared, electrical conductivity, and pH. In addition, the purity of ILs was determined by ¹H NMR. We used water as a polar phase, ILs as an amphi-solvent, and 1-dodecanol as a nonpolar phase to prepare SFME. The multiphase zone and the single-phase zone of the SFME were obtained from the ternary-phase diagram. Then, the microstructure of the studied SFME was determined to be the O/W type by the staining method. The demulsification process of SFME was explored by means of conductivity, pH, dynamic light scattering, and gas chromatography. Under the introduction of N₂, CO₂ could be removed, and the ILs could be reversibly restored to DPA, resulting in a change in polarity, which caused most of DPA to transfer into the oil phase, eventually leading to demulsification.

Conversion of a surfactant-based microemulsion to a surfactant-free microemulsion by CO2

A microemulsion with a CO₂ response was prepared by mixing the surfactant sodium oleate (NaOA), the co-surfactant isopropyl alcohol (IPA), oil phase oleic acid (HOA) and water. This surfactant-based microemulsion (SBME) shows a CO₂ responsive behavior, and the introduction of CO₂ can breakdown the microemulsion. Through the research in this paper, it is found that the content of IPA has a direct impact on the CO₂ response behavior of SBME. It was found that the lower the IPA content (22.73 wt%), the more obvious the CO₂ response behavior of SBME. Conversely, when the concentration of IPA is high (54.05 wt% and 63.83 wt%), the introduction of CO₂ does not directly lead to the demulsification of the microemulsion. NaOA can be converted to HOA under the action of CO₂, which is why SBME shows CO₂ response behavior. By comparing the effects of CO₂ on the (pseudo-)ternary phase diagrams of SBME and surfactant-free microemulsion (SFME), we found evidence that SBME shows different CO₂ response behaviors. When CO₂ was bubbled into the SBME system with a low IPA content, IPA cannot stabilize the excessive HOA and water in the system and eventually break the microemulsion. The situation is different when CO₂ is applied to the SBME system with a high IPA content. IPA as an amphiphilic solvent can stabilize the HOA and water in the system to form SFME. In this process, SBME can be demulsified (low IPA content) or can be converted to SFME (high IPA content) in the presence of CO₂.

CO2-Responsive Surfactant-Free Microemulsion

A surfactant-free microemulsion (SFME) with CO₂ stimuli responsive properties was prepared. The oil and the water phases were N, N-dimethylcyclohexylamine (DMCHA) and deionized water, respectively, and N, N-dimethylethanolamine was used as an amphisolvent. The single-phase and multiphase zones were measured by the ternary-phase diagram, and the microstructure of the SFME was determined by measuring the change trend of the electrical conductivity of the system with increasing DMCHA content. While using methyl orange as a probe, the microstructure of the SFME was further confirmed by an UV-visible spectrometer. The microstructures of water-in-oil (SFME-I) and oil-in-water (SFME-II) microemulsions were obtained by changing the DMCHA content in the system. The SFME-I system has a significant phase separation after the action of CO₂. However, with the continuous introduction of CO₂, the upper phase of DMCHA is gradually protonated and dissolves in the aqueous phase, resulting in a gradual decrease in the volume of the upper phase, and eventually in an aqueous solution of ammonium bicarbonate. For SFME-II, CO₂ does not directly cause phase separation, but eventually it becomes an aqueous solution of ammonium bicarbonate with the addition of CO₂. Both the water-in-oil structure SFME-I and the oil-in-water structure SFME-II have excellent CO₂ stimuli responsive performance.

Surfactant-Free Microemulsions of 1-Butyl-3-methylimidazolium Hexafluorophosphate, Diethylammonium Formate, and Water

Surfactant-free microemulsions (SFMEs) are a unique kind of microemulsion, which form from immiscible fluids (i.e., oil and water phases) in the presence of amphi-solvents rather than traditional surfactants. In comparison with traditional surfactant-based microemulsions (SBMEs), SFMEs have received much less attention, and the current understanding of the unique system is very limited. Herein, we report a SFME consisting of the hydrophobic ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF₆), the protic IL diethylammonium formate (DEAF), and water, in which the bmimPF₆ and DEAF are used as the oil phase and amphi-solvent, respectively. Three kinds of microstructures, namely, water-in-bmimPF₆ (W/IL), bicontinuous (BC), and bmimPF₆-in-water (IL/W), are identified for the SFME, using cyclic voltammetry, cryo-TEM, and DLS techniques. Especially, the volumetric and surface free energy properties of the SFME are investigated by excess molar volume ( V_m^E) and surface tension (γ) measurements, and they are found to be similar to those of SBMEs. Discontinuous changes in V_m^E and γ with the system compositions are observed as the system microstructures change, which can be used to identify the structural transition of SFMEs. We think this study provides a better understanding of SFME features.

A surfactant-free microemulsion composed of isopentyl acetate, n-propanol, and water

It has been demonstrated that in the absence of traditional surfactants, microemulsions can form from a ternary mixture of oil, water, and an amphi-solvent. These microemulsions are called surfactant-free microemulsions (SFMEs). To date, only a small number of SFME systems have been reported, and the current understanding of SFMEs is very limited. Herein, we report an SFME consisting of isopentyl acetate (IA), n-propanol, and water, in which IA (a simple ester compound) and n-propanol are used as the oil phase and amphi-solvent, respectively. The microstructures and structural transition of the SFME were investigated by cyclic voltammetry, fluorescence spectroscopy, and UV-visible spectroscopy techniques. Moreover, three kinds of microstructures, namely, oil-in-water (O/W), bicontinuous (BC), and water-in-oil (W/O), have been identified in the SFME, which are directly verified by cryo-TEM observations. A change in the composition of the SFME may lead to a structural transition from O/W through BC to W/O or vice versa, which is similar to the case of traditional surfactant-based microemulsions (SBMEs). To the best of our knowledge, this is the first time that the microstructures and structural transition of an SFME obtained using a simple ester compound as the oil phase have been identified.

Surfactant-free microemulsions (SFMEs) can form from the mixture of isopentyl acetate (oil phase), n-propanol (amphi-solvent), and water. They may show W/O, bicontinuous (BC), and O/W microstructures depending on the composition of the SFMEs.

Surfactant-free microemulsions of 1-butyl-3-methylimidazolium hexafluorophosphate, propylamine nitrate, and water

Generally, surfactants (or amphiphiles) are believed to be necessary components of microemulsions. However, it has been demonstrated that, in the absence of traditional surfactants, microemulsions can also form from a ternary system of two immiscible fluids (i.e., oil and water phases) and an amphi-solvent, but the current understanding of such surfactant-free microemulsions (SFMEs) is very limited. Herein, we report an SFME consisting of the hydrophobic ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF₆), the protic IL propylamine nitrate (PAN), and water, in which bmimPF₆ and PAN are used as the oil phase and the amphi-solvent, respectively. The microstructures and structural transitions of the SFME were investigated using cyclic voltammetry, fluorescence spectroscopy, and ultraviolet-visible spectroscopy. The SFME exhibited water-in-bmimPF₆ (W/IL), bicontinuous (BC), and bmimPF₆-in-water (IL/W) microstructures, depending on the composition of the ternary system, similar to the case of traditional surfactant-based microemulsions (SBMEs). The three kinds of microstructures were confirmed by cryogenic transmission electron microscopy (cryo-TEM) observations. To the best of our knowledge, this is the first report on SFMEs composed of two ILs as components, especially where one is used as the amphi-solvent.