The Effect Of Modified Hydrotalcite On The Glycerolysis Reaction Of Oils

Monoacylglycerol（MAG）and diacylglycerol（DAG）,oil-based surfactants with good emulsification and dispersion characteristics,are commonly used as nonionic surfactant alternatives to traditional petroleum-based surfactants.Homogenous inorganic bases（like Na OH or KOH）are commonly used to catalyze the glycerolysis reaction of oils in the present industrial preparation of mono-and diacylglycerol（MAG and DAG）.However,the catalyst cannot be recycled after the reaction.As a result of the high reaction temperature（220°C）,product quality would be adversely affected.And using edible vegetable oil as a substrate will not be able to alleviate domestic edible vegetable oil supply pressure.In view of hydrotalcite’s advantages of being green,non-toxic,reusable,low production cost,and environmentally friendly,it was investigated as a new heterocatalysis for the glycerolysis of oils in order to prepare mono-and diacylglycerol.As a result of this process,mono-and diacylglycerol can be produced efficiently and at a low cost simultaneously with advancing oleochemical technology towards green and sustainable development.The catalytic activity of hydrotalcite can be improved by third-party cation modification and organic anion modification.A hydrotalcite-based heterogeneous glycerolysis catalyst can be developed that is environmentally friendly,reusable,and widely applicable.Firstly,ternary hydotalcite-like compounds（La-Mg Al-LDH,Fe-Mg Al-LDH and Co-Mg Al-LDH）,composed of La³⁺,Fe³⁺and Co²⁺as third party metal ions respectively,were prepared by co-precipitation methodology.The corresponding ternary metal composite oxides（Layered double oxides,LDOs）were obtained by calcination.The morphology and structure of the 6 modified hydrotalcite-like compounds LDHs were characterized by X-ray diffractions（XRD）,scanning electron（SEM）,Fourier transform infrared spectroscopy（FT-IR）,BET method,temperature-programmed desorption of CO₂（CO₂-TPD）,etc.According to the proposed results,the hydrotalcite-like layered structure is present in the 3 LDHs.While in the3 LDOs,the formation of metal composite oxides is accompanied by the collapse of the layered structure.Among them,more strongly basic sites are present in La-Mg Al-LDO.Six modified LDHs were used as catalysts for the glycerolysis of castor oil in order to investigate the catalytic performance of ternary LDHs.A certain amount of catalytic activity was demonstrated by all of these catalysts,and La-Mg Al-LDO showed the best catalysis performance among the tested catalysts.The reaction conditions were optimized as follows:reaction temperature 180^oC,catalyst La-Mg Al-LDO dosage 10%（w/w based on the substrates）,castor oil:glycerol,molar ratio 1:2 and 2 h.Under these conditions,TAG（triacylglycerol）conversion and MAG（monoacylglycerol）,DAG（diacylglycerol）yield were93.86±0.76%,49.53±0.31%and 44.33±0.45%,respectively.Under the optimal conditions,the catalytic activity of La-Mg Al-LDO was retained 70%（TAG conversion）after recycling 5times.Secondly,the compound was further organically modified to reduce the reaction temperature and shorten the reaction time in order to enhance the catalytic capacity of La-Mg Al-LDO.The modification was carried out by reduction method of roasting using imidazolium-based ionic liquids（ILs）,including 1-butyl-3-methylimidazolium imidazolide（[Bmim]Im）,1-butyl-3-methylimidazolium hydroxide（[Bmim]OH）,1-ethyl-3-methylimidazolium imidazolide（[Emim]Im）and 1-ethyl-3-methylimidazolium hexafluorophosphate（[Emim]PF₆）.Four ILs modified hydrotalcites（[Bmim]OH-La-LDO,[Bmim]Im-La-LDO,[Emim]Im-La-LDO,[Emim]PF₆-La-LDO）were obtained as new heterogeneous glycerolysis catalysts.The structural composition characteristics of four ILs modified hydrotalcites were examined by XRD,SEM,FT-IR,BET,etc.The results demonstrate that the hydrotalcite-like layered structure of La-Mg Al-LDO is restored after modification by ILs,and ILs are successfully bound in its structure.All IL-La-LDOs were used as catalysts for the preparation of mono-and diacylglycerol by the glycerolysis of castor oil,among which[Bmim]OH-La-LDO showed the best catalytic effect.Effects of reaction variables（the kind of IL-La-LDO,catalyst dosage,temperature,substrate ratio and time）on the glycerolysis of castor oil catalyzed by IL-La-LDOs were investigated.High TAG conversion（92.51±1.73%）and the maximum products yields（59.81±1.83%MAG and32.70±0.10%DAG）were achieved under the following conditions:[Bmim]OH-La-LDO dosage 10%（w/w,based on the total substrates mass）,castor oil:glycerol molar ratio 1:2,160^oC and 1.5 h.Under these conditions,the catalytic activity of[Bmim]OH-La-LDO was retained above 60%（TAG conversion）after recycling 6 times.Finally,the catalytic properties of[Bmim]OH-La-LDO in high free fatty acid（FFA）oils were also investigated in order to expand it’s application.Effects of reaction variables on the glycerolysis of castor oil catalyzed by[Bmim]OH-La-LDO were investigated.The maximum TAG conversion（82.88±1.20%）,MAG yield（29.90±2.26%）and DAG yield（52.98±1.34%）were obtained under the optimized conditions:180℃,2 h,[Bmim]OH-La-LDO load 10%,and substrate molar ratio 1:2.In this circumstance,the anticipated catalytic activity was demonstrated by[Bmim]OH-La-LDO when it was used to catalyze the glycerolysis of high free fatty acid soybean oil.High TAG conversions were obtained using[Bmim]OH-La-LDO as catalyst for the glycerolysis of soybean oil with different acid values（10–50 mg KOH/g）in all cases.Under these conditions,the catalytic activity of[Bmim]OH-La-LDO was retained at70%（TAG conversion）after recycling five times.