Preparation Of Dimer Acids By Mechanical Activation

Dimer acid is a di-polymer produced by the polymerization of two unsaturated C₁₈ fatty acids.Dimer acid is widely used in the synthesis of various chemical products because of its special physicochemical properties.The synthesis process of dimer acid mainly includes thermal polymerization and catalytic polymerization.Industrial production of dimer acid is mostly catalyzed by clays and carried out in a stirred tanks.The catalytic performance of clay is related to its ore source.Traditional stirred tanks have problems such as weak mixing strength,huge dead space volume in reactors,and poor scaling effects.The thesis studied the relationship between clays’composition and its catalytic performance,and designed and made a ball milled-tank reactor and a ball milled-rotary drum reactor,and studied the polymerization process in the two reactors.X-ray fluorescence spectroscopy was used to analyze the composition of six types of clays from different ore sources.The six clays were used to catalyze the synthesis of dimer acids in a flask,and their catalytic performances were determined and compared by the yield of dimer acids.Furthermore,the effects of the composition and structure of clays on its catalytic properties were investigated.The results show that there are differences in the composition and structure of the clays from different sources,and the catalytic performance is quite different.Various factors such as the acidity of clay,the contained metal ions,and interlayer spacing affect the catalytic performance of clays.In general,acidic clays have better catalytic performance than alkaline clays.According to the results,the clays were pretreated by acidification and metal ion exchange in order to improve the catalytic performance.The results showed that the acidification was beneficial to improve the catalytic performance of clays,the catalytic performance of clays increases with the decrease of pH for acidification.The suitable pH value of clays is between 2.4 and 6.2.The concentration of sulfuric acid used in acidification has little effect on the catalytic performance of clays.Ball milling intensification technology was applied to the synthesis of dimer acid.A ball milled-tank reactor was constructed,and synthesis of dimer acid in the reactor was investigated.By introducing the effect of mechanical chemistry,such as grinding,shearing and extrusion,the active site of the clay catalyst can be better exposed and the mass transfer between the materials can be strengthened.Compared with the traditional mechanical stirred reactor,the ball milled reactor has low stirring intensity,good solid-liquid mixing and reaction effect.When reacting in a steam atmosphere,the content of dimer acid can be increased to 69.6%from 38.7%in the conventional stirred reactor.Through the process optimization,the suitable reaction conditions for preparing dimer acid in the ball milled reactor are:reaction temperature 260°C,catalyst dosage 24%,co-catalyst dosage 0.5%,ball milling media dosage 1500g,stirring speed 173rpm,steam atmosphere,reaction time 6 hours.Under these conditions,a crude product with a dimer acid content of 79%,an acid value of 196 mg KOH/g,and a viscosity of 1640 mPa·s was obtained,and the dimer acid yield was58.7%.A rotary-drum reactor with the ball milling intensification was further constructed to realize the continuous production of dimer acid.In the reactor,the structure and size of the internal components,the reactor wall temperature,the rotation speed of the reactor,the residence time of the material in the reactor,and the material of the reactor,internal components and ball milling medium have impacts on the content of dimer acid in the product.The suitable reaction conditions are wall temperature 300°C,rotation speed 20rpm,residence time 2.1h,the baffle width 3cm.Under this condition,the dimer acid content can reach 50%.The dissolution of metal ions from reactor and other components,especially nickel ions,inhibits the synthesis of dimer acids.The inner wall of the reactor and the surface of internal components are required to be coated,and zirconia beads are required as the ball grinding media.