Research On The Synthesis Of Dimer Acid From Montmorillonite Catalytic Fatty Acid

Dimer acid is a dimer obtained from the polymerization of two C18 unsaturated fatty acid molecules. It is an important and versatile fine chemical material because of its distinctive molecular structure and physicohecmical properties. Low yield and quality of dimer acid for domestic production technology limits the application of dimer acid. Further research to improve the yield and quality of dimer acid is necessary and good for the development of dimer acid industry.The atmosphere, temperature, reaction time, reaction pressure, catalyst and fatty acid composition of raw material have important impact on the generation of dimer acid. Clay substances like montmorillonite are common catalysts for the synthesis of dimer acid. The active ingredient content of montmorillonoid and the type of the interlayer cations could affect the catalytic activity of montmorillonite and the yield of a dimer acid. Moreover, the yield of dimer acid also varies greatly with the fatty acid composition of raw materials. The key to improve reaction selectivity and the yield of dimer acid is to choose suitable catalyst and raw materials. The thesis lays emphasis on the research of the raw materials and catalyst for producing dimer acid.To choose suitable reaction materials and catalyst, three raw materials with different fatty acid composition such as soybean oleic acid, cotton oleic acid and Xipu oleic acid, and three catalysts such as Na-montmorillonite, Ca-montmorillonite and activated clay were chosen and compared. To obtain suitable technological conditions, the influence of the reaction temperature, reaction time, the dosage of catalyst, the dosage of promoter and the stirring rate on the synthesis of dimer acid were explored when Na-montmorillonite was used as the catalyst, and three four-factor-four-level orthogonal experiments were designed to optimize the operating conditions when soybean oleic acid, cotton oleic acid and Xipu oleic acid were used as raw materials respectively. The optimal operating conditions were basically the same for the three raw materials as follows: ordinary pressure, nitrogen protection, and the stirring rate is 550 rpm, the reaction temperature is 260?, the reaction time is 7 h, the dosage of catalyst is 16%?w? of the mass of fatty acid, the dosage of promoter is 2%?w? of the mass of fatty acid. Under the optimized conditions, the yield of dimer acid increases with the increase of the iodine value of the raw material. The yield of dimer acid, for soybean oleic, cotton oleic acid and Xipu oleic acid, was 63.4%, 56.8% and 37.1% respectively. Soybean fatty acid contains 39.93% oleic acid and 52.5% linoleic acid, and is an ideal raw material for the synthesis of dimer acid. The catalytic performance of Na-montmorillonite is the best among the three investigated catalysts.To further enhance the catalytic activity of Na-montmorillonite, three catalyst modification method such as ion exchange modification, organic modification and acid modification were investigated respectively. The modified Na-montmorillonite by ion exchange with Li Cl or cetyl trimethyl ammonium bromide?CTAB? had bigger interlayer spacing and more preferable lipophilicity. The activity of catalytic sites in Na-montmorillonite modified by ion exchange with Li Cl could be strengthened, and the coordination state of the catalytic activity could be improved, thus the catalytic perfourmance could be enhanced. When the exchange capacity of Li Cl was 0.61 g Li Cl/20 g Na-montmorillonite, the interlay spacing could be increased to 1.54 nm and the yield of dimer acid could be increased to 69.0%. When the dosage of CTAB was 0.3g CTAB/20 g Na-montmorillonite, the yield of dimer acid could be increased to 66.5%. Furthermore, 15%?wt? sulfuric acid, 0.5mol/L AlCl₃ and the sucessive combination of 15%?wt? sulfuric acid and 0.5mol/L AlCl₃ respectively were used to modify montmorillonite in order to explore the influence of Lewis acid and Bronsted acid on montmorillonite on the synthesis of dimer acid. Lewis acid could improve the catalytic activity of montmorillonite while Bronsted acid went against the synthesis of dimer acid. The modified montmorillonite need be dried and calcined under a high temperature. The influence of calcination temperature on the catalytic activity of montmorillonite was explored. The catalytic activity will not be affected when the calcination temperature was more than 70?.At last, the dimer acid product with purity of 90% was obtained through the coupling solvent extraction and filtration to remove catalyst granules, and reduced pressure distillation with the operation pressure of 40 Pa and distillation temperature 200? to remove unreacted acid monomer, and molecular distillation with the operation pressure of 0.1Pa and distillation temperature 220? to remove polymer. The dimer acid production was characterized by liquid chromatogram and infrared absorption spectrum.