Process Investigation On Aqueous Synthesis Of Sodium N-lauroyl Glutamate

Sodium N-lauroyl glutamate（SLG）is a kind of biomass-derived surfactant.Its raw material lauric acid and sodium glutamate is abundant and has low prices.The product has excellent surface activity,low toxicity,and low irritation and good biodegradable,which is increasingly used in daily chemical products in recent years.Small scale of SLG was synthesized in the early days by the Schotten–Baumann condensation reaction of lauroyl chloride and sodium glutamate in mixed organic solvent/water.The homogeneous system made the reaction speed fast,with high mass and heat transfer efficiency,and low by-products of the hydrolysis reaction,sodium laurate（SLA）.However,the using of organic solvents would result in high levels of volatile organic compounds（VOC）,poor safety,and high solvent recovery costs.Recently,in order to meet the requirements of environmental and green chemistry,the aqueous Schotten–Baumann condensation process is often used in the large scale production of SLG,which makes the production process green and reduces production costs.But the heterogeneity of lauroyl chloride with the aqueous phase Schotten–Baumann condensation process slows down the reaction rate,reduces the mass and heat transfer efficiency,and increases the SLA content in the product,regrettably.These problems greatly limit the development of the aqueous phaseIn this paper,how to overcome the aforementioned problems in the aqueous Schotten–Baumann condensation process caused by the heterogeneity of raw materials is investigated by enhancing the mass and heat transfer in the process.Firstly,a all–in–one quantitative analysis method for various active substances in SLG products was established to quickly analyze product components.It can determine the product technical specification,and find other possible by-products except SLG,which can provide an evaluation method for the optimization of the aqueous synthesis process of SLG.Secondly,the process parameters are optimized in a batch reactor,and the inherent laws and influence factors of the aqueous synthesis process are investigated,which can provide opetical technical parameters for the following process investigation of the aqueous synthesis of SLG.Subsequently,a set of pump reaction–tank aging reactor series device was built for process enhancement research,in order to adapt to the long-term mass transfer characteristics of the aqueous process.At the same time,the mass transfer process improved by high-speed shearing,adjusting the micro-and macro-mixing of the reaction materials,and the heat transfer measures enhanced by adjusting the feed and reflux ratio,pre-cooling the aqueous phase materials,etc.Finally,the application performance of the SLG product obtained under the optimized process conditions was measured,compared with the current commercial.The results and conclusions obtained within the research scope are as follows:（1）For the first time,it was reported that the SLG product synthesized by the aqueous phase Schotten–Baumann condensation process contained the surface active substance N-lauroyl glutamyl glutamate（SLGG）,and by UPLC-MS,FT-IR and ¹H-NMR identified its structure.This discovery has important theoretical significance and practical value for the process research,product quality control and product application performance research of synthesizing fatty acyl amino acid surfactants in the aqueous phase.（2）Established a high performance liquid chromatography coupled with a refractive index detector method,which can simultaneously and quickly quantitatively analyze SLG, SLGG and SLA.The results show that using WondaCract ODS-2 C₁₈ chromatographic column,the mobile phase of methanol,water and formic acid can achieve baseline separation of SLG,SLGG and SLA,and the linear correlation coefficients are all up to 0.9999,and the average recovery rates of standard addition are 99.82%,99.56%and 98.91%,respectively.And the relative standard deviations were 0.84%,1.65%and 1.22%, respectively.This method can realize the simultaneous and accurate quantitative analysis of various active substances in products,and can also be used for process monitoring.（3）In the tank reactor,we based on the mass and heat transfer effects and the characteristics of the raw materials,the process parameters such as the stirring rate,the material concentration,the feeding rate,the feeding ratio,the reaction temperature and the pH are optimized to study the Schotten–Bauman in aqueous phase.The results show that the high material concentration,the pH of the system corresponding to the disodium glutamate solution and the appropriate stirring rate,feeding rate are conducive to the synthesis of SLG.Under the conditions of stirring rate 400～600 r·min^-1,the initial concentration of sodium glutamate 50 wt.%,lye concentration 30 wt.%,acid chloride feed rate is 1.5 g·min^-1,the feed ratio of sodium glutamate to acid chloride is 1.2,reaction temperature is 15℃and pH 12.0,The yields of SLG,SLGG and SLA were 68.01%,10.92%and 21.07%,respectively.（4）In the pump-reaction–tank-aging reactor,the high-shear force of the pump-type reactor is coupled with macroscopic stirring to improve the mass transfer,and the heat transfer is improved by adjusting the material ratio and the material on-line cooling method.Through the research on the enhancement of mass and heat transfer of the device,the final yields of SLG,SLGG and SLA are 74.14%,7.54%and 18.32%,respectively.Compared with the tank reactor and the commercial product,the yield of SLG was increased by 6.13%and 12.10%,the yield of SLGG was decreased by 3.38%and 3.61%,and the yield of SLA was decreased by 2.75%and 8.48%,respectively.It shows that enhanced mass transfer and heat transfer are beneficial to promote the formation of SLG and inhibit the occurrence of side reactions.It has the potential to improve the quality of products synthesized by the aqueous phase Schotten–Baumann condensation process,and it can also greatly improve the efficiency of the aqueous phase process.The product with a solid content of 40%has stable properties,which is more convenient for application.（5）The properties of SLG were measured,the application performance of SLG,optimized product and commercial product were compared.The results show that the dicarboxyl structure of SLG is pH-dependent due to its properties and application performance.At pH 6.0,the foamability,emulsifying ability,wettability and detergency of optimized product are better than those of commercial product.