Research On The Thermal Hazard Of The Synthesis Process Of Low Molecular Weight Polyacrylic Acid

Low molecular weight polyacrylic acid and its salts have been used in many industries due to their various excellent physical and chemical properties.However,there is a certain degree of danger due to the production of reactive substances such as the polymerized monomer acrylic acid,the initiator ammonium persulfate,and the large amount of heat released during the reaction.Therefore,studying the thermal hazard of the synthesis process of low molecular weight polyacrylic acid is essential to understand and reduce the objective hazards,which has certain guiding significance for safe production.In order to better simulate the actual production process of low molecular weight polyacrylic acid,this article chooses the commonly used industrial production aqueous solution polymerization as the acrylic acid polymerization method,chooses ammonium persulfate as the initiator,and sodium bisulfite as the chain transfer agent.Then the thermal hazard of materials and the thermal hazard of reaction in the synthesis process of low molecular weight polyacrylic acid were studied.1.Differential scanning calorimeter（DSC）,AKTS kinetic software,and adiabatic acceleration calorimeter（ARC）were used as tools to study the thermal stability of acrylic monomer without polymerization inhibitor,ammonium persulfate and sodium bisulfite.The results show that:（1）Acrylic acid has a flash point of 48.5℃,steam and air form an explosive mixture,and the self-polymerization heat can produce an adiabatic temperature rise of 28.7℃.Once impurities are mixed in or local overheating,explosion accidents are likely to occur.The self-polymerization product begins to decarboxylate and decompose at250.7℃and produce CO₂ gas.After evaluation,the product decom-position has a greater potential for explosion hazard.However,it is predicted by T_D24 that the heat released by the self-polymerization reaction is difficult to cause decomposition of the product.（2）The initial decomposition temperature of ammonium persulfate is 125.4℃.After the induction period,it can reach the maximum heat release rate within10 minutes,and decompose to produce NH₃,SO₃ and other gases.It is estimated that the potential explosion hazard is greater.（3）The possibility of decomposition of sodium bisulfite stored at room temperature is very small.It is estimated that the exothermic process is less dangerous,but it can release toxic SO₂ gas after decomposition.2.ARC was used to investigate the effect of three polymerization inhibitors（4-methoxyphenol,hydroquinone,phenothiazine）on the self-polymerization of acrylic acid,and the influence of impurities（water,acrylic acid,sodium bisulfite）on the heat risk of ammonium persulfate.The results show that:（1）Hydroquinone and phenothiazine have equivalent inhibitory effects,which are significantly better than4-methoxyphenol.（2）The initial decomposition temperature of ammonium persulfate mixed with water and acrylic acid impurities decreased from 125.4℃to 66.0℃and 86.7℃respectively.The induction period was shortened from 7 h to 2.5 h and 25 min,respectively.Decomposition can reach the maximum temperature rise rate of 171.9℃/min and 193.8℃/min,respectively.The explosion hazard is significantly increased.3.Reaction calorimeter（RC1e）was used to study the influence of different reaction temperature,stirring rate,and feed rate on the exothermic characteristics of the reaction process.At the same time,the monomer conversion rate and molecular weight were analyzed.The results show that under the selected process conditions,the molecular weight of the product polyacrylic acid is in the low molecular weight range,and this reaction is a slow reaction.There is heat accumulation in the feeding process,and the reaction cannot be quickly terminated by stopping the feeding when a danger occurs.However,the degree of heat accumulation can be reduced by appropriately increasing the reaction temperature and extending the feeding time.The suitable process conditions are:reaction temperature 60℃,rotating speed 200 r/min,dropping rate 2.53 g/min.4.The risk matrix method and the process risk assessment method are used when evaluating the selected different process conditions.The results show that the“one-pot method”is adopted for production,and the risk level is level 3,which is high in risk.By equipping the automatic control system,the feed can be stopped in time after abnormal conditions occur,and the risk level can be reduced to level 1,which is acceptable.