Evaluation of styrene-acrylonitrile copolymerization thermal stability and runaway behavior

Probing into Styrene Polymerization Runaway Hazards: Effects of the Monomer Mass Fraction

Polymerization reactions have caused a number of serious incidents in the past; they are prone to reaction runaways because of their exothermic and autoaccelerating nature. To minimalize the risk, the reaction is commonly performed in a solvent as empirical industrial practice. In this work, the thermal runaway hazards of the ethylbenzene-styrene system with different monomer mass fractions were calorimetrically investigated up to temperatures where decomposition products are unlikely to be produced. Experiments showed that the polymerization runaway "onset" temperature inversely increased with the monomer mass fraction. Experiment and thermodynamic calculations showed that volatile diluent increased system vapor pressure even at a lower adiabatic temperature rise and verified that moderation of the risks could be achieved if the monomer mass fraction is below ca. 85%. A lumped kinetic model developed by Hui and Hamielec was used to predict the runaway profile of this reaction under different dilutions, and the agreement was excellent.

Studies on the runaway reaction of ABS polymerization process

Taiwan has the largest acrylonitrile-butadiene-styrene (ABS) copolymer production in the world. Preventing on unexpected exothermic reactions and related emergency relief hazard is essential in the safety control of ABS emulsion polymerization. A VSP2 (Vent Sizing Package 2) apparatus is capable of studying both normal and abnormal conditions (e.g., cooling failure, mischarge, etc.) of industrial process. In this study, the scenarios were verified from the following abnormal conditions: loss of cooling, double charge of initiator, overcharge of monomer, without charge of solvent, and external fire. An external fire with constant heating will promote higher self-heat rate and this is recommended as the worst case scenario of emulsion polymerization on butadiene. Cooling failure coupled with bulk system of reactant was determined to be the credible worst case in ABS emulsion polymerization. Finally, the emergency vent sizing based on thermokinetics from VSP associated with DIERS methodology were used for evaluating the vent sizing and compared to that of the industrial plants.