Research On The Crystallization Process Of Dimethyl 2,2'-azobis(2-methylpropionate)

Dimethyl 2,2'-azobis?2-methylpropionate??AIBME?is an initiator with very promising application in the industry of polymer polyol?POP?.The commercially available crystal product is easily formed into a mass during storage,seriously affecting its follow-up use.After analysis,it was found that the product has a low melting point,a wide particle size distribution,and a lot of fine crystals,so that the formation of crystal bridges between crystal grains is the main reason for agglomeration.Crystallization is the key production step to obtain its solid form from its synthetic mother liquor.No literature reported the crystallization process of AIBME.Therefore,the process of crystallization of this crystal was studied in detail in this paper.The particle size and particle size distribution of AIBME crystal were optimized,and the problem of agglomeration of the crystal during storage was solved.The specific research content is as follows:The thermodynamic data necessary to study the process of crystallization was measured.On the one hand,the solubility of AIBME in five pure solvents such as methanol,ethanol,acetone,toluene,and ethyl acetate were measured by gravimetrical method.After comparing the results of Apelblat and van't Hoff's formula for the solubility data,the former was used to correlate and predict the solubility of AIBME in these five solvents.Methanol was selected as the solvent for the crystallization in consideration of the solubility,economy,and other factors.On the other hand,the metastable zone of AIBME-methanol solution was measured by turbidimetric method and its influencing factors were discussed.The data of metastable zone width was fitted by four nucleation theories.The results showed that Nyvlt method,Kubota method,self-consistent Nyvlt equation had better effect,and it was deduced that the apparent nucleation order of the solution was in the range of 4.03-7.30.An on-line concentration prediction model for AIBME-methanol solution was established based on ATR-FTIR and partial least squares?PLS?.It was applied to the actual concentration monitoring of cooling crystallization.The established model can well indicate the key points and trends of the process of crystallization such as the crystallized point and the decrease of the concentration in solution.On the basis of the measured real-time concentration in solution,the curve of supersaturation derived from the predicted curve of solubility can also accurately reflect the crystallized process.The operating parameters that may affect the size of AIBME were initially studied in a150ml crystallizer.The process analytical technique?PAT?was used in a 2L crystallizer in conjunction with the particle size distribution of the final crystals to analyze the nucleation and growth of crystals during the operation of the process of AIBME cooling crystallization.The goal is to obtain a crystal product with a big particle size and a narrow particle size distribution.The final optimum process conditions are:initial concentration 1.0g/g,cooling rate 0.1°C/min,stirring rate 150rpm,and the addition of seed 3%,the size of seed 200-125?m.D₅₀ of the optimized crystal reaches 1170?m,and the product particle size distribution is very narrow.The anti-caking performance of the optimized crystal product was compared with that of a commercial product.After three months of storage under the same conditions,it was found that the commercially available product was all formed into one piece,and the optimized product still had good fluidity and did not affect its follow-up use.