Solventless Technology Of Preparing Alfa-Alkyl Betaine Zwitterionic Surfactants

Alfa-alkyl betaine zwitterionic surfactant with excellent performance can be prepared by simple two-step route from cheap natural fatty acids. Solventless synthesis technology can avoid the use of additional solvent and obtain solid product directly, so the quality of product was improved significantly. Excess trimethylamine was recovered by distillation to achieve zero emission during the preparation process.The subject mainly studied the new technology of solventless synthesis ofα-capric betaine (α-CB) by the reaction ofα-chlorododecanoic acid (α-CDA) with trimethylamine (TMA). The optimized condition was obtained and was amplified under pressure-thermal condition. The orthogonal experiments were carried out to improve the yield ofα-CB, which can provide basic data for further research.α-dodecyl betaine,α-tetradecyl betaine andα-hexadecyl betaine were synthesized through solventless technology. Gravimetric method of phosphotungstic acid was adopted to establish an analysis method of alfa-alkyl betaine for industrial production. The main conclusions were as follows:Solventless synthesis technology can be implemented when the reaction system was homogenous, which required the molar ratio of TMA andα-CDA greater than 6. The structure ofα-CB prepared by the ammonolysis ofα-CDA with TMA was confirmed by IR, MS, H-NMR, and elemental analysis after purification. A gravimetric method of phosphotungstic acid was developed to accurately determineα-CB in industrial analysis. Compared with the method of high performance liquid chromatography coupled with evaporative light-scattering detection (HPLC-ELSD) and the method of back titration with Hamming of phosphotungstic acid, the gravimetric method of phosphotungstic acid can receive near accuracy with simply operation while requiring no large analysis instrument such as high-performance centrifuge and evaporative light-scattering detection.Since the ammonolysis reaction was nucleophilic substitution reaction, AlCL₃, NaOH, KOH, CH₃CH₂ONa, KI (together with NaOH) were added respectively in order to increase the yield ofα-CB. The results showed that there existed lots of side effects when AlCL₃ was added, so the yield can not be improved; CH₃CH₂ONa can not promote the reaction notably; the yield ofα-CB increased significantly when NaOH or KOH was added in the system, but under the condition of alkaline, the hydrolyze ofα-CDA was easily to happen andα-hydroxyldodecanoic acid (α-HDA) was produced; KI didn't catalyze the ammonolysis ofα-CDA markedly under the condition of alkaline solventless system. The optimum conditions were determined: n(NaOH):n(α-CDA):n(TMA) = 1.1:1:10, the reaction lasted 10 h under 90℃. The yield ofα-CB reached 73.5%.The effect of temperature on the reaction ofα-CDA with TMA was studied under the condition of solventless system in a hermetic reactor. The yield ofα-CB increased remarkably with the increase of temperature in the region of 90-110℃and reached 91.1% at 110℃. Then the yield ofα-CB decreased with the increase of temperature.The solventless synthesis process ofα-CB was amplified in the autoclave. Orthogonal experiments were designed to optimize the conditions of ammonolysis process. The optimum conditions were as follows: n(TMA):n(α-CDA)=10:1, the reaction time 8 h at 110℃. The yield ofα-CB reached 91.0%.α-dodecyl betaine,α-tetradecyl betaine andα-hexadecyl betaine were synthesized as the molar ratio of TMA toα-CDA was 10, and the reaction time was 8 at 110℃. The yield of the products was 90.2%, 89.5%, 88.4% respectively.