Ionic Liquid Structure Impact On Catalytic Esterification Synthesis Of Tributyl Citrate Esters And Thermodynamic Analysis

The plasticizer in the world today is almost phthalate acid esters. The use have been restricted because of their carcinogenicity, affect the development period of reproductive system. So we need to develop a new type of environmental, protection and non-toxic plasticize. As tributyl citrate ester is non-toxic; small volatile; good compatibility; cold resistant, water resistant, high light resistance and advantages of excellent plasticizing efficiency, it has become gradually replacement of non-toxic plasticizer. According to the need of catalytic,ionic liquid can appropriately control itself anion and cation. It will improve the reaction yield 、selectivity and the reaction rate obviously.The purpose of this paper is to explore the influence rule of different ionic liquid structure to synthesis of tributyl citrate esters. At the same time explore the influence rule about technological factors on the synthesis of tributyl citrate esters. After that,we analysis the possibility tributyl citrate ester synthesis based on the thermodynamics. The main research content and the results are as follows:1.The preparation and characterization of ionic liquidsSynthesis 5 kinds of pyridine ionic liquid, 6 kinds of imidazoles ionic liquids, 6 kinds of quaternary ammonium salt ionic liquid by using one-step and two-step. Ionic liquids are as follows: [（C₅H₅）NH][HSO₄]、[（C₅H₅）NH][C₇H₇O₃S]、[（C₅H₅）N（CH₂）₃SO₃H][HSO₄] 、[（C₅H₅）N（CH₂）₃SO₃H][C₇H₇O₃S] 、[（C₅H₅）N（CH₂）₃SO₃H] [CH₃O₃S]; [CH₃（C₃H₃N）NH][HSO₄]、 [(CH₃（C₃H₃N）NH][C₇H₇O₃S]、[(CH₃（C₃H₃ N）NH][CH₃O₃S]、[(CH₃（C₃H₃N）N（CH₂）₃SO₃H][HSO₄]、[(CH₃（C₃H₃N）N（CH2_）3SO₃H][C₇H₇O₃S] 、[(CH₃（C₃H₃N）N（CH₂）₃SO₃H][CH₃O₃S];（CH₃CH₂）₃NH][C₇H₇O₃S]、[（CH₃（CH₂）₃）₃NH][C₇H₇O₃S]、（CH₃CH₂）₃N（CH₂）₃SO₃H][HSO₄]、[（CH₃CH₂）₃N（CH₂）₃SO₃H][C₇H₇O₃S] 、[（CH₃CH₂）₃N（CH₂）₃SO₃H][CH₃O₃S] 、[（CH₃（CH₂）₃）₃N（CH₂）₃SO₃H][C₇H₇O₃S]. Their structure are analyzed by IR and NMR. It shows their are the target ionic liquids.2. The study of ionic liquid acid, solubility and stabilityIonic liquids aqueous acidic are measured by pH meter, When the anion is consistent, the same type of the functionalized ionic liquid acid is stronger than the unfunctionalized ionic liquids; The same kind of ionic liquid, the more concentration in the aqueous solution, the acid stronger; Imidazoles ionic liquids and anion HSO₄^- have a stronger acid. Ionic liquids dissolved in water, n-butyl alcohol and citric acid, citric acid butyl ester standard ability research results show that, the shorter the liquid carbon chain quaternary ammonium salt ions, dissolved well before reaction and effect layered after reaction. An analysis of the thermal stability of ionic liquids, except for [(CH₃（C₃H₃N）NH][CH₃O₃S]（Mim-MSA） shows, ionic liquids decomposition temperature are all above the required TBC synthesis temperature. So they can be used in catalytic synthesis of TBC. Imidazoles ionic liquids thermal stability are worse than the quaternary amine salts of ionic liquids and pyridine type of ionic liquids.3.The influence law of synthesis of TBC by the structure of the ionic liquidWhen we use the unfunctionalized ionic liquid as catalyst in synthesis of TBC reaction,the reaction time is long; Production rate is low; High acid value; And the catalyst is hard to separate. Functional ionic liquids’ anion is [HSO₄]- will get the highest TBC yield, but anion is[C₇H₇O₃S]- can be separate much well. Cation is Py-PS has the highest yield, but unable to layered after reaction, the yield of [（C₅H₅）N（CH₂）₃SO₃H]⁺ take second place and lowest product acid value, thus considering the TEA-PS-H₂SO₄ and TEA-PS-p TSA used as catalyst for the synthesis of TBC.4.The influence law of process factors on the catalytic synthesis of TBCUsing T3 and T4 ionic liquids as the catalyst for catalytic synthesis of TBC, by single factor variable method to find the best reaction condition, the experimental results show that: T3 as catalyst, dosage of system total quality accounted is about 3.61 %, alcohol acid molar ratio is 4.0:1, the reaction temperature is 130 ℃, reaction time is 2.5 h, the yield can reach more than 98 %; T4 as catalyst, the amount of total quality is about 3.88 %, alcohol acid mole ratio is 4.0:1, the reaction temperature is 130 ℃, reaction time is 3 h, the yield can reach more than 97 %. T3 and T4 ionic liquids are not processed, directly using to catalytic synthesis of TBC cycle three times, TBC yield is no less than 90 %. The product mixed with 5 % aqueous solution Na2CO3 according to 1:1, let stand points, three times as long as after a simple washing,the acid value can reach to the standard quality of plasticizer（1 mg KOH/g）. So the ionic liquid catalytic synthesis of TBC is feasible in industrial application, the synthesis has a certain potential.5.Thermodynamic analysis of tributyl citrate ester synthesis reactionClearly analysis of the thermodynamic process of esterification reaction citric about citric acid and n-butyl alcohol in synthesis of tributyl citrate esters, can be used to judge the direction of the reaction and limit, at the same time,it can provide theoretical guidance to reaction adjust and control condition in the process reaction. The theoretical calculation results show that the reaction under the condition of no water diversion is impossible to occur spontaneously. Under the condition of water diversion, increase the mole ratio of alcohol acid or reaction temperature can improve the conversion rate of citric acid. However, high temperature will cause poor color products, low temperature will waste reaction time, mole ratio of alcohol acid will increase the dosage of catalyst. So temperature should be around 410 K, alkyd mole ratio selection is 4.5:1 advisable, citric acid conversion rate can reach more than 99 %. Theoretical calculation match well with the actual measured value of conversion, the theoretical calculation and experimental results are basic to be trusted.