Trioctylamine is abbreviated as "TOA". It is an important tertiary amine extractant. Molecular formula C24H51N. molecular weight 353.6. colorless viscous oily liquid. It has a pungent odor. Specific gravity 0.8110. boiling point 180-202℃(400Pa). Refractive index 1.4449. insoluble in water, easily soluble in organic solvents. Trioctylamine is one of the excellent extractants commonly used in analytical chemistry and radiochemistry. It is used in metallurgy to extract and separate precious metals such as cobalt, nickel, actinium, lanthanum, etc. It is widely used for the separation and determination of neptunium and plutonium in nuclear fuel and fission products. Trioctylamine can also be used to extract organic acids, or to treat organic acids, phenols, alcohols, organic amines, etc. contained in wastewater. In addition, trioctylamine can also be used for the synthesis of quaternary ammonium surfactants.
In recent years, as the complex extraction process is widely used in chemical production, more research on trioctylamine in the extraction process has been carried out. This also reflects the increasing productivity and environmental requirements of chemical production. In this paper, we have collected and organized the research progress of trioctylamine in extraction process in recent years by reviewing the reference literature and make a brief introduction.
1, Trioctylamine for the treatment of organic wastewater from epoxy resin production
Epoxy resin has been widely used in various fields of national economy because of its excellent electrical insulation properties, good processing properties, strong corrosion resistance and high bonding strength. However, a large amount of wastewater is discharged during the production of epoxy resin, which is composed of complex components, mainly unreacted monomer epichlorohydrin, NaCl, lye, glycerol and isopropanol. Due to the stable structure of halogenated organic compounds and high toxicity to organisms, there is no real effective method to treat low and medium concentration epoxy resin wastewater in China, while incineration method is used for high concentration organic halides at home and abroad.
Wei Fengyu et al. from the School of Chemical Engineering of Hefei University of Technology used trioctylamine as extractant and white kerosene as diluent for complex extraction of epoxy resin wastewater. The results showed that at pH= 1.0, oil-water volume ratio of 0.35 and extractant-to-diluent volume ratio of 2, the removal rates of COD and Cl- by three-stage staggered flow extraction reached 97.6% and 92.0%, respectively; the extraction phase could be used repeatedly after 10 min of reverse extraction with 5% NaO H and oil-base volume ratio of 2; the infrared spectroscopy results proved that the extraction of epichlorohydrin with trioctylamine was mainly based on the ion-conjugation mechanism. The reaction mechanism was mainly ion-conjugation reaction. The complexation extraction method was used to treat epoxy resin production wastewater, and good results were achieved.
2、The study of trioctylamine for the separation of organic acids
Biological fermentation liquid, fine chemical primary products and industrial discharge liquid are mostly polar organic dilute solutions. Compared with the physical extraction method based on the rule of "similar solubility", the chemical extraction method has high efficiency and high selectivity for the separation of polar organic dilute solutions [1]. Due to the multiple functional groups or self-polymerization of organic solutes, the extractants often show various extraction ratios with the concentration of the extractant and the extracted solute, so the extraction mechanism is very complex, and there is a lack of relevant research reports. Binary organic carboxylic acids and bases can form mono- and dibasic salts. It is useful to explore the basic rules of the extraction ratio and establish empirical rules by using the characteristics of their two carboxyl groups.
Wang Min, Qin Wei, Li Zhenyu and Dai Youyuan from the Department of Chemical Engineering, Tsinghua University have experimentally determined the equilibrium and loading solvent infrared spectral properties of trioctylamine (TOA) in three diluents of n-octanol, methyl isobutyl ketone (MIBK) and chloroform for the extraction of malic acid using malic acid, a binary organic acid, as the isolated solute. The results showed that the effects of TOA concentration and diluent type on the extraction equilibrium were related to the concentration of malic acid; the extractant could provide a larger extraction capacity when the concentration of acid in the equilibrium aqueous phase was low, and there was an "overload" phenomenon after the stoichiometric saturation of TOA, and the overload amount was MIBK > n-octanol > chloroform. The extracts of TOA are mainly in the form of (2:1), (1:1) and (1:2) acid-amine ratios, in which the combination of malic acid and TOA in the (1:2) extract is one ion-to-salt and one hydrogen bonding.
3, Process study of trioctylamine for the separation of chloroethanol and hydrogen chloride
Chloroethanol is an important organic solvent and raw material for organic synthesis. At present, the preparation process of chloroethanol in China mainly adopts ethylene hypochlorination method, and there are several disadvantages in the production process. It is difficult to recover the generated hydrogen chloride, and it can only be neutralized by lime milk, which wastes useful hydrogen chloride and lime, and generates a large amount of low concentration calcium chloride wastewater, and the amount of lime milk added is not properly controlled, which will also react with chloroethanol to generate by-products. The low concentration of chloroethanol in the reaction solution leads to high energy consumption in the subsequent product separation process.
Gao Fei of Qingdao University of Science and Technology adopted the extraction method of "one extractant for two extraction reactions at the same time", i.e., using trioctylamine as the extractant, the by-products of hydrogen chloride in the reaction were extracted chemically, and the resulting trioctylamine hydrochloride was a good solvent for chloroethanol, and the chloroethanol was well separated from water by physical extraction. The physical extraction can be used to separate the chloroethanol from water. Extraction at room temperature can achieve a more satisfactory effect, the process conditions are suitable. The extractant can be regenerated easily by simple distillation and adding alkali to regenerate trioctylamine. The process can achieve the purpose of reducing energy consumption, but also improve the purity of the product (its purity can reach 98.3 %), and without complete extraction, to avoid the subsequent separation system with salt, scarring. In the whole process, no three waste emissions.
