| Polyurethane composite material is a class of novel polymer compound,which have considerable application in various field.In recent years,with the rapid development of our national economy,the productivity of polyurethane industry increases rapidly and the products quality improve obviously,due to independent research and technology innovation.Isocyanate compounds are important class of raw materials for synthesis of polyurethane,and especially diisocyanate possesses highly value of industrial application.Hexamethylene diisocyanate(HDI),as one of the aliphatic diisocyanates,has excellent chemical stability,mechanical properties,chemical stability,light resistance,weather resistance and yellow resistance because of its saturated molecular structure and smaller space steric hindrance.Along with the extremely increasing application of HDI in various fields in recent years,HDI presents a promising profound in huge market.However,due to special structure nature of HDI compound,the production technology as well as operating procedures in our country have been restricted so far,which falls below that of western developed countries or regions.Furthermore,the research,production and application of ADI(containing HDI,IPDI and H12MDI)and other special isocyanate compounds are relatively backward,relative to developed countries or regions,since the efficient development of the synthetic routes of HDI is an great challenge nowdays.Although phosgene method is considerable applied as the industrial production method of HDI,this method occurs increasing drawbacks with the accumulation of experimental experience.Therefore,more and more researchers focus on the synthetic route about the cracking of carbamate to isocyanate.This route is mainly divided into pyrolysis gas phase and liquid phase cracking,in which the require temperature of liquid phase pyrolysis is lower than that of gas phase pyrolysis.In this paper,some problems about the liquid phase pyrolysis of HDU to HDI by are studied systematically.The main results are as follows:1,High purity hexamethylene diaminodicarboxylate(HDU)was synthesized from the reaction of HDI with methanol,depending on its high chemical activity of isocyanate and alcohol.On the basis of the characterization of FT-IR and melting point,The results showed that the synthesized product was HDU compound,which can be used as the raw materials relating to the thermal cracking HDU to HDI and the the standard sample involving quantitative analysis of HDU.2,The four quantitative analysis methods of HDI,containing toluene di-n-butylamine titration,acetone-di-n-butylamine titration,infrared spectroscopy and high performance liquid chromatography quantitative method,were screened,according to addition reaction principle of-NCO and di-n-butylamine.The results confirmed that the high performance liquid chromatography possessed the best repeatability,highest accuracy and most economical.3,The dioctyl phthalate was determined as the preferred solvent,via screening the heat carrier employing to the HDU liquid phase cracking reaction system and considering the solvent solubility as well as boiling point.4,In the reaction of HDI cracking to HDI,in order to improve the separation efficiency of HDI from products,the reactor reaction device was designed and improved.In order to improve the yield of HDI,a tubular reaction device for circulating feed was designed and analyzed by HDI recovery.The blank experiment verified that the improved experiment device has certain feasibility and prospect.5,HDI can also generate in the absence of catalyst from the reaction of liquid phase cracking of HDU.However,when the zinc powder as a catalyst and dioctylphthalate as both heat carrier and solvent,the yield of HDI is 35.3%,under the optimized reaction condition,e.g.reaction temperature = 240 ?,desreaction time =30 min;HDU concentration = 2.5%;catalyst/HDU molar ratio = 7.5%. |
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