Runaway Characteristics And Damage Control Technology Of Polymerization Of Vinyl Acetate

Vinyl acetate (VAC) play an important role as raw material for organic synthesis. The polymerization reaction of VAC is exothermic strongly. Once the reaction is out of control, it will cause great damage to the personnel and the environment. In order to control damage, many scholars have conducted a lot of research on two controlling means of venting and adding inhibitor. DIERS (the Design Institute of for Emergency Relief Systems) has invested a lot of money and manpower for the study of the venting method. A set of relatively complete venting design method has been obtained and the corresponding experimental device has been designed. On the basis, many scholars have verified the reliability of the DIERS method by different reaction objects which have relatively mild runaway behavior. Polymerization reaction has more violent runaway behavior where the applicability of the DIERS method requires further research. In addition, the addition of inhibitor to control runaway has been studied, but it often affects the quality of the reactants. The diluent is the raw material in the reaction, and will not contaminate the reactants. So the method of adding diluent halfway to control runaway was considered.Based on this, this paper took the polymerization of vinyl acetate as the research object, and studied the runaway characteristics and damage control technology. The main contents and conclusions are as follows.(1) The runaway behavior of vinyl acetate polymerization was studied based on VSP2 calorimeter. The reaction runaway is very violent, and "burst polymerization" phenomenon happen. The maximum temperature rise rate (dT/dt)max is more than 1000?·min-1. The calculation method of the maximum temperature rise ?T and the maximum pressure Pmax after the runaway reaction was established under the adiabatic condition. The calculated results are in good agreement with the experimental results. The concentration of initiator and diluent influence the violent degree of the reaction runaway. With the increase of initiator concentration, (dT/dt)max and (dP/dt)max increase. With the increase of diluent concentration, (dT/dt)max and (dP/dt)max decrease. Filling rate affects thermal inertia factor, but has little effect on the violent degree of the reaction runaway. Two criteria method is established where Runaway reaction is determined when T?75? and dT/dt?3?·min-1. The interval between the critical point and the maximum temperature rise is about 120 s. Based on the Visual Basic, Software for simulation of runaway process of polymerization reaction was prepared. The results of simulation and experiment were compared. It is found that the simulation results are accurate to a certain extent.(2) The VSP2 experimental device was modified to make it suitable for adding diluent halfway. The influence of different adding amount of diluent, different adding temperature, different adiabatic condition and different filling rate on the inhibiting effect of runaway were studied. Adding diluent can result in two kinds of results of delaying runaway and completely inhibiting runaway. When the filling ratio is 75%, the reaction runaway can't be completely inhibited only by adding diluent. If the system temperature is above 60? and the reaction system is in the adiabatic state after addition of diluent, the phenomenon of runaway reaction will occur again after a period of time. In addition, the diluent mixed with inhibitor will improve the inhibitory effect, completely inhibiting the reaction runaway. The conditions of second runaway are given as the following. After the diluent is added, the lower the temperature is, the longer time is needed for the second runaway phenomenon. But when the temperature is below a certain value (below 60?), the second runaway will no longer happen.(3) According to the experimental data, the safety relief design of vinyl acetate polymerization was carried out. The venting of vinyl acetate is steam venting, for which safety relief design can be carried out by DIERS method. In the case of the reactor's volume of 8 m3, the filling rate of 40%, initiator concentration of 0.1%, diluent concentration of 5%, the required venting area is 0.04424 m2. The venting experiments were carried out using VSP2 experimental device at relief pressure of 0.2 MPa and 0.4MPa respectively. In the case of 0.4 MPa relief pressure, non-equilibrium venting happens. The venting area calculated by DIERS method is not conservative at 0.4 MPa relief pressure. Increasing the relief pressure will reduce the venting capacity of the venting device, so the relief pressure should not exceed 0.4 MPa. Increasing initiator concentration and reactor's filling rate will increase the venting area of the reactor, while increasing diluent concentrations will decrease the venting area of the reactor. With other conditions being the same, increasing reactor'size will increase the venting area proportionally. Finally, the effect of adding diluent halfway on venting was analyzed, and it was found that the required venting area is smaller after addition of the diluent halfway, which will not pose a threat to the safety relief.