Study On Synthesis Of Unsaturated Wax Esters By Chemical Method

Wax esters are the main components of natural waxes,which are composed of long-chain（>12 carbon atoms）fatty acids and alcohols.Wax esters are classified as saturated wax esters or unsaturated wax esters depending on their degree of unsaturation.Unsaturated wax esters（liquid wax esters）are derived from jojoba oil and spermaceti oil.After the global ban on whaling,the jojoba oil has been the primary natural source for wax esters production.However,the main limitations to the use of jojoba oil are its cost and availability.Therefore,it is highly desirable to synthesize wax esters for various industry applications.The purpose of this project is to synthesize the substitutes of natural unsaturated wax esters with low-cost natural fatty acids（oleic acid）and fatty alcohols by chemical method.Catalysis-free synthesis of unsaturated wax ester from oleic acid and long carbon chain fatty alcohol（C12-C18）has been studied.Taking the esterification reaction of oleic acid and cetyl alcohol as the model reaction,the effects of various factors on the esterification reaction were studied.Under the conditions of reaction temperature of 190 ^oC,molar ratio of oleic acid to cetyl alcohol of 1.5:1 and reaction time of 4 h,the conversion of cetyl alcohol reached 97.2%and the yield of wax ester was 95.4%.Under the optimal conditions,the yield of oleic acid-wax esters（lauryl oleate,myristyl oleate,cetyl oleate,stearyl oleate）were more than 94%.The kinetic model was also studied.The kinetic results showed that the reaction order was 2and the reaction activation energy was 48.76 k J mol^-1.The auto-catalytic process,omitting the separation step for catalysts and solvents,could be considered as a promising process to synthesize unsaturated wax esters.In order to green and efficient synthesis of unsaturated wax esters under mild reaction conditions,the acidic deep eutectic solvent（P-DES）composed of choline chloride and p-toluenesulfonic acid（1:4,mol/mol）was used as an efficient recyclable catalyst in the esterification reaction of oleic acid and long carbon chain fatty alcohol to synthesize oleic acid liquid wax esters.Taking the esterification of oleic acid with cetyl alcohol as the model reaction,the esterification conversion of cetyl alcohol could reach 99.1%under optimum reaction conditions（5%DES as catalyst,molar ratio of fatty acid to alcohol of 1.3:1 and reaction temperature of 70 ^oC for 3 h）.Importantly,the catalyst recovery experiments showed that this low-price acidic DES catalyst could be reused for five times with loss of activity.Moreover,DES-catalyzed solvent-free esterification could be applied in the preparation of other oleic acid-based wax esters and excellent conversions（>96%）could be obtained under such mild conditions.In order to improve the efficiency of acid catalyst,we studied the synthesis of oleic acid-based wax esters by esterification of oleic acid with long-chain fatty alcohol using 4-dodecylbenzene sulfonic acid（DBSA）as catalyst.The DBSA catalytic esterification mechanism showed that DBSA catalyzed esterification reaction in water could form O/W type emulsion,thus removing the water produced in the reaction system.A 93.6%conversion of cetyl alcohol was obtained under the optimal condition:reaction temperature 40 ^oC,reaction time 4 h,DBSA amount 10 mol%and molar ratio of fatty acid/alcohol 1.3:1.And this DBSA-catalyzed esterification reaction could be applied in the preparation of various oleic acid-based wax esters and excellent conversions（>90%）into esters were obtained under such mild conditions.This DBSA-catalyzed esterification reaction will provide a simple and efficient method for the preparation of liquid wax esters.Finally,the unsaturated wax esters were purified.Five methods of purification（acid-base neutralization,washing,column chromatography,solvent extraction and distillation）were compared.The results showed that solvent extraction was more suitable.The process conditions for the purification of unsaturated wax esters by solvent extraction were optimized.The final separation process parameters were as follows:extraction using methanol as solvent,extraction temperature of 20 ^oC,methanol dosage of 4 m L/g,extraction time of 0.5 h,methanol extraction for 5 times.Under these conditions,the yield of wax ester was 92.0%,and the acid value was 2.7 mg/g.Other oleic acid-wax esters were purified.The yield of wax esters was above 90%,and the acid value was below 3 mg/g.The physicochemical preparties of the purified unsaturated wax esters were determined.