Vietnam Journal of Chemistry, 2018, 56(2), 156-161 Article DOI: 10.1002/vjch.201800005 156 Wiley Online Library © 2018 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Optimization of the synthesis of amidoamine-based surfactant Bui Duy Hung, Pham Thi Nam Binh * , Vu Thi Thu Ha, Duong Quang Thang National Key Laboratory for Petrochemicals and Refinery Technologies, 02, Pham Ngu Lao Street, Hoan Kiem District, Hanoi Received 9 Oct 2017; Accepted for publication 1 March 2018 Abstract In this study, lauryl amidoamine was synthesized by reaction of methyl laurate with ethylendiamine. The reaction conditions were optimized using Modde 5.0 software. According to the results, the optimum molar ratio of ethylenediamine to methyl laurate, reaction temperature and reaction time were 2,135 o C and 3.8 h, respectively. The actual experimental yield was 96.69 % under the optimum condition, which compared well with the maximum predicted value of 97.22 %. The synthesis of coconut amidoamine from coconut methyl esters had yield 95.73 % under the same conditions. Size of water in diesel oil 0.05S emulsion using coconut amidoamine as an emulsifier of 147 nm was obtained. Keywords. Optimization, lauryl, coconut, amidoamine, emulsion. 1. INTRODUCTION At present, the diesel engine is being widely used all over the world. However, with the large amounts of wastes, such as NO x , SO x , CO, CO 2 , particulate matters and unburned hydrocarbons, diesel engine is also one of the major causes of environmental pollution. One of the ways to increase the burning efficiency and reduce the emission of pollutants is to use the water-in-diesel microemulsion. [1-4] The water-in-diesel microemulsion is prepared by dispersing a small amount of water in diesel oil (DO) using surfactants. To date, for this research topic, the most commonly used surfactants are nonionic ones. [3-5] The fatty amidoamines (FAA) are a group of non- ionic surfactants that are widely applied in industry and life. They are used to produce foaming agents, emulsification agents, fibre softening agents, anti-corrosive agents, anti-gel formation agents, viscosity reducing agents and are groups of important intermediate substances to synthesize other surfactants like imidazoline, ethoxylated amidoamine.... [6-13] FAA can be synthesized from renewable resources via amidation of fatty acids from nature or their esters with polyamine such as ethylenediamine, diethylenetriamine, trimethylenetetramine.… In Vietnam, there are some publications related to the synthesis of surfactants based on alkanolamides and alkanediamides, and their applications for preparation of water in paraffin emulsion. [14,15] However, no study on the synthesis of surfactants and their usages for preparing water in DO microemulsion had been reported. This paper presented the results of synthesis of FAA of biological origin and initial research on its applicability as an emulsifier in the formation of water in DO microemulsion system. 2. EXPERIMENTAL 2.1. Chemicals Chemicals were obtained from Sigma-Aldrich and used without further purification. The coconut methyl esters were synthesized at National Key Laboratory of Petrochemicals and Oil Refinery Technologies. 2.2. Preparation of lauryl amidoamine In a 250-mL three-necked flask, connected with a condenser, an amount of the methyl laurate (or coconut methyl esters) and ethylenediamine were mixed. The mixture was refluxed under continuous stirring for 4 h at 135 o C. The distillation of the excessed ethylenediamine out of the mixture was then carried out by maintaining the reaction mixture at 116 o C. The remained solid after distillation was washed by ethyl acetate several times and dried in the vacuum oven at 70 o C in 6