Study On C₂₂-Tricarboxylic Acids Prepared From Unsaturated Fatty Acids And Their Derivatives

Using natural renewable resources to replace petrochemical resources,preparing high-value fine chemicals and reducing environmental pollution are receiving increasing attention.Palm oil,cottonseed oil,rapeseed oil and other natural plant oils contain a large amount of unsaturated fatty acids such as oleic acid and linoleic acid.By introducing carboxyl groups into these unsaturated fatty acids,biological polyacids can be obtained.Among them,C₂₂-Tricarboxylic Acid can be used to prepare rust inhibitors,lubricants,plasticizers,coatings,inks,fabric softeners and household detergents,etc.,which is a kind of bio-based intermediates with great potential.At present,C₂₂-Tricarboxylic Acid is mostly obtained from linoleic acid through continuous isomerization/addition reaction catalyzed by I₂.In addition,Diels-Alder reaction between maleic anhydride and conjugated linoleic acid（CLA）obtained by base catalysis is also a common way.However,extensive use of strong alkalis can cause environmental pollution,the residue of I₂ makes the product difficult to decolorize,coupled with the non-recyclability of catalysts,it is difficult to industrialize the production of C₂₂-Tricarboxylic Acid.Therefore,the development of heterogeneous catalysts for the preparation of C₂₂-Tricarboxylic Acid is conducive to reducing process costs and three waste emissions,has significant economic and environmental benefits.In this paper,a rare earth doped Ru-based composite oxide catalyst was developed for the maleinization of linoleic acid to prepare C₂₂-Cyclic Tricarboxylic Acid（CTA）;meanwhile,Fe PO₄ was used as Lewis Acid to produce C₂₂-Branched Tricarboxylic Acid（BTA-OA）with oleic Acid and maleic anhydride,and feasibility of preparing C₂₂-Branched Tricarboxylic Acid with linoleic acid was also explored;finally,the surface chemical properties of the prepared C₂₂-Tricarboxylic Acid were studied.The specific research contents are as follows:（1）A series of Ru O_x-REE-LDO composite catalysts were prepared by doping rare earth elements（REE）such as La,Y and Ce to Ru O₂-LDO,and used for maleinization of linoleic acid to prepare CTA.The results showed that:Ru O_X-Y-LDO showed the best catalytic activity,and the yield of 95%CTA could be achieved under the conditions of MA/LA=3,Ru O_x-Y-LDO/linoleic acid=8%（W/W）,reaction temperature 180℃,reaction time 10 h.Combined with the characterization,the doping of Y could significantly improve the alkaline strength and density of the catalyst,as well as the metal-carrier strong interaction between Ru and the support（SMSI effect）,and the doping of Y increased the structural disorder,so as to obtain a larger specific surface area.All the above changes were conducive to the isomerization of linoleic acid into CLA.At the same time,Y₂O₃ in the catalyst also promotes the Diels-Alder reaction between CLA and maleic anhydride.Finally,CTA was synthesized by one-step series reaction.（2）Using Fe PO₄ as a Lewis acid catalyst to catalyze the Alder-Ene reaction between oleic acid and maleic anhydride to synthesize BTA-OA.Response surface analysis was performed to determine the optimal conditions for the synthesize BTA-OA:Fe PO₄/oleic acid=4%（mol/mol）,MA/OA=3.74,reaction time 10.53 h,reaction temperature 200℃,the yield of BTA-OA was83.5%at this time;and the reaction is also suitable for the preparation of BTA-LA from linoleic acid,and the acid value of the crude product is 419 mg KOH·g^-1,which is close to pure C₂₂-Tricarboxylic Acid.The difference in BTA yields can be attributed to the difference in double bonds reactivity.（3）The surface chemical parameters and surface properties of three potassium C₂₂-Tricarboxylic Acids were tested.The results show that the Krafft points of the potassium C₂₂-Tricarboxylic Acids are lower than 0℃,and they have good water solubility at low temperature;although the critical surface tension of potassium C₂₂-Tricarboxylic Acids are slightly higher than potassium oleate,they have lower critical micelle concentration,provide higher surface activity than potassium oleate at lower concentration;the wetting and emulsifying properties of the all potassium C₂₂-Tricarboxylic Acids are slightly weaker than potassium oleate due to the presence of branched chains;compared with potassium oleate,potassium C₂₂-Tricarboxylic Acids have poor foam performance,which is beneficial to the application in detergents.