Synthesis And Rinsability Evaluation Of Sodium N-lauroyl Amino Acid Surfactants

N-acyl amino acid surfactants are kinds of important biosurfactants derived from sustainable biomass materials fatty acid and amino acid.Due to their low irritation,low toxicity,good antibacterial property,biodegradability and biocompatibility,there is a wide application prospect in food industry,drug delivery,cosmetics and personal care products.At present,their industrial synthetic method is mainly via traditional Schotten-Baumann reaction with fatty acyl chloride and amino acids as the starting materials in mixed solvent or direct water solution under the action of alkaline catalyst.This method is efficient to be carried out and is low requirement for equipment.However,there also exist many disadvantages.For example,fatty acyl chloride is not an eco-friendly material,whose synthesis usually pollutes the environment seriously,and it is easy to hydrolyze during the reaction process due to the present of water in the aqueous solution;the by-product NaCl is unavoidable and it does harm to the viscosity control of the reaction system,which leads to a higher soap percent in products.In recent years,researchers concerned more about the synthesis process of N-acyl amino acid surfactants by fatty acid esters due to their shorter reaction route,higher atomic economy and greener process.Our laboratory also developed a method using methyl laurate?ML?and excess sodium glycinate?SG?to synthesis sodium N-lauroyl glycinate?SLG?in methanol.The results showed that a high quality SLG with low soap percent and no NaCl could be obtained after removing the excess SG and solvent.In this paper,firstly,measures will be taken to optimize this reaction,and we find it that it's a great convenience to do this reaction in a pseudo packed-bed reactor?PPBR?.In brief,the SG consists of the packed bed,and then,the raw material ML goes through the packed bed and takes an action with SG.At last,a high quality SLG can be obtained after evaporating the solvent.Secondly,sodium alaninate?SA?and disodium glutamate?DG?will be chosen to represent the other amino salts,in order to determine the feasibility of this PPBR reactor in synthesizing other N-acyl amino acid surfactants,the relationship between this reaction and amino salt solubility in solvent will be further investigated.Lastly,the rinsability of N-acyl amino acid surfactants will be researched,as they have been considered as kinds of easy-rinse surfactants and widely used in water-saving detergent formulations.The main experimental procedures,results and conclusions of this paper are as follows:?1?A lower reaction temperature?30-80??was confirmed based on the solubility of SG in methanol.Relatively,some measures had been taken to optimize this reaction in a batch reactor.Results showed that the yield of SLG reached 89.0%and the by-product sodium laurate?SL?fell to 10.6%under the molar ratios of SG:ML:SM being 50:1:0.1 and catalyzed by SM for 24 h at 60? in methanol,and ML had been transformed completely.Then,we took this reaction in a PPBR reactor,it showed that a higher yield of SLG?92.3%?and lower yield of by-product SL?7.7%?were obtained while the space velocity of this reactor is 0.15h^-1 at 60? under the conditions?0.5 wt%ML,0.1wt%SM?.Therefore,the superiority of this reaction process was preliminarily confirmed.?2?In order to examine the possibility of synthesizing other acyl amino acid surfactants in this way,SA and DG were chosen as the representative of other amino salts.On the one hand,SA has high solubility in methanol.The condensation reaction of ML and SA was optimized by single factor experiments and orthogonal experiments,but the maximum yield of SLA was only 48.5%when conversion rate of ML researched 96.9%.The results showed that the reason for low yield was due to the self-condensation reaction of SA.The by-product H₂O promoted the hydrolysis of ML.On the other hand,DG has low solubility in methanol.Thus,some measures had been taken such as changing the reaction temperatures,increasing SM dosages and using phase transfer catalysts to promote the reaction of DG and ML,however,no SLD could be found in the crude products.After using different organic solvents,SLD could only be found in DMSO solvent.However,the yield of SLD was only 8.6%under the conditions?n?SA?:n?ML?:n?SM?was 4.5:1:0.03 at 130? for 24 h?,and the ML conversion rate is 47.0%relatively.Results show that an important reason for inhibiting the reaction between ML and DG is that the solubility of DG in solvent is too low.?3?The evaluation method for rinsability of surfactants is proposed.A comparative study was run between several used N-acyl amino acid surfactants,sodium soap?SL?,sodium dodecyl benzene sulfonate?LAS?and alkyl ether sulfates?AES?.In this paper,SLG,SLA,SLS and SLD were chosen as the representative of N-acyl amino acid surfactants and their basic physical and chemical properties were investigated.Compared with SL,N-lauroyl amino acid surfactants have better calcium ion stability,foam ability,emulsifying properties,lower wetting time and T_K value.Among them,SLD has best calcium ion stability,SLA has best foam ability in hard water,SLS has best wetting ability and emulsifying property.Based on the simulation of the washing/rinsing process,the primary/residual adsorption quantities of surfactants on cloth and the foaming abilities of the rinsing liquor corresponding to rinse times were investigated.It is shown that N-lauroyl amino acid surfactants are easy-rinse surfactants in reality,the easy-rinse abilities are originated from their moderate calcium ion stabilities in molecular structures.