Studies On Thermal Polymerization Process Of Typical Conjugated Dienes And Effect Of Inhibitors

With the increasing development of domestic ethene industry, the amount of cracking C4 and C5 fraction has increased significantly, of which the respective representative material is 1,3-butadiene and isoprene. Extractive distillation is presently the main manufacture method of 1,3-butadiene and isoprene due to low cost and mature technology. Most conjugated dienes have higher polymerization activity. During the extractive distillation process it is very easy for them to react due to high temperature or other factors like water, oxygen, and metal ion, which result in the monomer loss and lower product yield. In order to restrain the undesirable products and ensure safe and effective operation it is necessary to add highly efficient inhibitors during the course of storage, purifying and usage. The current understanding of the thermal polymerization process and relevant mechanism of conjugated dienes is still not enough because of varieties of factors in the reaction process and comparatively complex reaction products.In this dissertation thermal polymerization of 1,3-butadiene and isoprene were carried out in the micro high pressure reactor similar to industrial extractive distillation conditions. Effect of different factors was investigated by means of both gas chromatographic analysis and gravimetric method to analyze the conjugated dienes loss mechanism. Different inhibitors were studied to examine the inhibition effect. Finally the dimerization kinetics were researched with addition of enough inhibitor under the oxygen free condition.The study finds that with certain oxygen content in gas phase, the thermal polymerization process of 1,3-butadiene and isoprene can be divided into two types of reaction, namely free radical polymerization and Diels-Alder reaction, and the corresponding products are high polymer and dimer. Reaction time has no influence on the dimer mass fraction in products. High reaction temperature significantly increases the dimer fraction, of which the 1,3-butadiene dimer fraction changes from 59% to 83% while the isoprene dimer fraction from 56% to 80%. The result shows that the main loss in high temperatures is dimer. Polymerization of monomer is significantly reinforced by increasing the oxygen content in gas phase. The main product of 1,3-butadiene and isoprene is dimer under oxygen free condition. Acetonitrile and N,N-dimethylformamide have no oblivious influence on the thermal polymerization process while different dissolved oxygen content can affect the high polymer conversion.With certain oxygen content in gas phase, inhibition effect of several different types of inhibitors was studied. Addition of proper inhibitor can completely suppress the formation of high polymer while the inhibitors have no influence on dimerization. At the same reaction condition, TEMPO>DEHA>TBC. The inhibition effect is reinforced by increased amount of inhibitors, and TEMPO and DEHA show clear enhancement effect while TBC is less oblivious. The inhibition effect observed at 115℃ is the most apparent at investigated temperature range. According to Arrhenius equation, the dimerization kinetics were obtained through experiments with no oxygen in gas phase and addition of enough high efficient inhibitor:1,3-butadiene: K=1.19×105exp(-83.9×103/RT); isoprene: K=3.89×106exp(-95.6×10-3/RT).