Fabrication Of Switchable Solvents And Emulsions Based On Fatty Acids

Chemical production processes often involve multiple reaction or separation approach,and the optimum solvent for a particular step is different.Therefore the solvent was usually removed after each step and then added a new solvent.Switchable solvents,which can be reversibly switched from one form to another,could eliminat to replace solvents in multiple reaction.Up to now,most of the switchable solvents are based on organic molecules of amidine or amine groups,which are usually toxic and easily adsorbed on solids to generate secondary waste.There is a strong interest in designing a green solvent with low toxicity and negligible adsorption on solid surfaces.Emulsions are metastable colloidal dispersion systems,which can be prepared by surfactants or nanoparticles.Emulsions prepared by nanoparticles are called Pickering emulsions.Emulsions are widely used in a variety of applications including heavy oil transportation,oil recovery and emulsion polymerization.However,in some cases,only temporary emulsion stability is desired.Switchable emulsions with on and off property can solve the above questions.The switchable solvents and switchable emulsions undergo reversible interconversions by specific external stimuli,such as pH,temperature,light irradiation,redox and so on.Compared to other triggers,CO2 is mild,inexpensive and readily removable.CO2-responsive ion pairs can be formed by fatty acid and amine.In this paper,fatty acids with different chain length were used to fabricate switchable solvents and emulsions.The ion pairs formed by middle-chain fatty acids have low interface activity,hence emulsification does not occur.Bubbling and removing CO2 causes the dissociation and association of the ion pairs.The reversible ion pair interactions lead to the switchable hydrophobicity of middle-chain fatty acid.Then,a fatty acid switchable solvents with low toxicity and low adsorption can be designed.The ion pairs formed by long-chain fatty acids have high interface activity,which can be used for the emulsification of extra-heavy oil.In addition,the particles prepared by long-chain fatty acids and amino-functionalized nanoparticles have switchable wettability when bubbling and removing CO2.Therefore,it can be used to prepare switchable Pickering emulsions.In addition,CO2-responsive ion pairs also can be formed by naphthenic acid and amine.This unique character can be used to extract naphthenic acid from crude oil.The whole paper contains four sections:1.A fatty acid solvent with switchable miscibilityIon pair interactions are explored to design a fatty acid solvent of switchable miscibility with water.Fatty acids of medium length chains are immiscible with water but become miscible with water when ion pairs are formed with amines.The ion pairs become phase separated after bubbling CO2 into the solution due to the dissociation of the fatty acid-amine complexes.Ion pairs of caprylic acid(C8)and low toxic poly(oxypropylene)diamine(Jeffamine D 230)were characterized by FTIR and 1H NMR.Log Kow values and surface activity were used to understand the switchable solvent mechanism in removing and recovering oily contaminants.More importantly,the ion pairs show a negligible adsorption on solid surfaces.Furthermore,both C8 and D 230 were recycled during the washing process.Thus the fatty acid as switchable solvent could be applied for oily contaminant removal from oily solid wastes.2.Viscosity reduction of extra-heavy oil using toluene in water emulsionsSurfactants are widely used to reduce the viscosity of heavy oil by emulsifcation,but emulsifcation of an extra-heavy oil is difficult and does not even occur in some cases.A diluent is effective in reducing the viscosity of extra-heavy oil,but substantial volumes are required.In this work,we combined the advantages of a surfactant solution and a diluent in the form of emulsions to emulsify extra-heavy oil.The toluene/water(T/W)emulsion was prepared with mixed surfactants(DOA-AES)formed from a gemini-like surfactant(DOA,prepared by mixing oleic acid(HOA)and Jeffamine D 230)and an anionic surfactant(AES,alkyl polyoxyethylene ether sodium sulfate).Compared with using toluene or DOA-AES surfactant solution alone to achieve the desired extra-heavy oil viscosity(30± 10 mPa·s),the T/W emulsion decreased toluene and surfactant dosage from 56 to 3 wt%and from 12 to 2 mmol/L,respectively.The effect of toluene and DOA-AES mixed surfactant on emulsifcation was analyzed by measuring the viscosity of the resultant extra-heavy oil emulsions.The results suggest that the addition of toluene reduced the viscosity of extra-heavy oil(dispersed phase)and accordingly contributed to emulsify extra-heavy oil.The synergistic effect of the DOA-AES mixed surfactants was evaluated by measuring the interfacial tension and calculating interaction parameters(βm)of the mixed surfactants formed at different AES mole fractions.When the mole fraction of AES was 0.6 in the mixture,the mixed surfactant possessed the highest interfacial activity and the largest negative βm,confirming the strongest synergistic effect.As a result,the best emulsifcation efficiency was achieved at this mole fraction.Increasing toluene content and DOA-AES mixed surfactant concentration was found to increase the emulsion stability against coalescence.The results from this study demonstrate that T/W emulsions prepared using the DOA-AES mixed surfactants can overcome the difficulties in emulsifying the highly viscous extra-heavy oil.3.CO2/magnetic dual responsive Pickering emulsionsCO2/magnetic dual responsive nanoparticles(Fe3O4@SiO2-NH3+OA-)were prepared by Fe3O4@SiO2-NH2 and oleic acid(HOA).Pickering emulsions prepared by Fe3O4@SiO2-NH3+OA-can be rapidly demulsified with CO2 bubbling,resulting in complete oil/water phase separations.Bubbling nitrogen can efficiently re-emulsify the oil phase.By an external magnetic field,the drops of Pickering emulsion can be driven close to each other.The structure and composition of Fe3O4@SiO2-NH3+OA-nanoparticles were analyzed by TEM,FTIR and TGA.The TGA experiment demonstrates bilayer adsorption of HOA.The primary HOA layer is formed through electrostatic interaction with Fe3O4@SiO2-NH2,a secondary HOA layer over the primary layer is formed through hydrophobic interactions.The contact angle and oil-water interfacial tension were measured to understand the emulsification and demulsification mechanisms of Pickering emulsion.The Fe3O4@SiO2-NH3+OA-nanoparticles with suitable wettability and high interface activity can be used to stable Pickering emulsions.Bubbling CO2 to the emulsion,the Fe3O4@SiO2-NH3 OA-was decomposed into Fe3O4@SiO2-NH2 and HOA.The hydrophilic Fe3O4@SiO2-NH2 is anticipated to desorb from oil-water interface and migrate into the aqueous phase.Therefore,Pickering emulsion became readily demulsified.Bubbling N2 to remove CO2,the Fe3O4@SiO2-NH2 reacts with HOA to reform Fe3O4@SiO2-NH3+OA-,leading to the reformation of Pickering emulsions.4.Naphthenic acid removal from model crude oilThe amine(N,N dimethylcyclohexylamine,DMCHA)and amino-functionalized silica nanoparticles(SiO2-NH2)were employed for the naphthenic acid(NA)removal from model crude oil.The water-soluble ion pair(NA-D)with low interface activity is formed by NA and DMCHA.Then NA can be transferred from oil phase to water phase without emulsification.Bubbling CO2 into NA-D aqueous solution,NA-D becomes dissociated to NA and protonated amine(DM+).Bubbling N2 to remove CO2,DM+ is deprotonated to regenerate DMCHA.During the deacidification process,both NA and DMCHA can be recycled.The efficiency of NA removal by using SiO2-NH2 nanoparticles was greater than 92%.The NH2 sites on the silica surface can form pH sensitive ion pairs with NA.Hence,NA can be regenerated by adding acid,and SiO2-NH2 can be recycled by adding alkali.Compared to the traditional adsorption methods,using SiO2-NH2 nanoparticles avoids the use of large amounts of organic solvents,and the adsorption of NA only takes a few minutes.