Systematic Study On The Crystallization Process Of 11-Cyanoundecanoic Acid And Its Impurities

11-cyanoundecanoic acid(11-CUA)is a key chemical material in industrial production,which is used to synthesize various important chemical products such as nylon-12.Thus,the separation and preparation of high-purity 11-cyanoundecanoic acid is critically important to help to achieve the localization of nylon-12 and break the technical barriers abroad.In addition,the raw materials of 11-CUA commonly mix dodecanedioic acid(DDDA),which also has great values in application.However,DDDA has the similar chemical structure and properties with 11-CUA,which brings about a great influence on the separation process.Thus,this dissertation systematically researched the separation and purification process of 11-cyanoundecanoic acid by crystallization and completed two parts of work as follows.11-CUA has different dissociation constant with DDDA,so reactive crystallization is generally used to purify 11-cyanoundecanoic acid.But explosive nucleation of 11-CUA is extremely easy to occur when pure water is used as the crystallization solvent.Therefore,in this section,we use ethanol-water mixed solvent instead of pure water as the crystallization solvent,and systematically optimize the process parameters through a single factor experiment.When choosing the parameters of 10 ml ethanol/150 ml solvent(crystallization solvent),6.0-6.2(p H at the end),30-32°C(crystallization temperature),aging after the acid being added,and the unidirectional flow,the purity of 11-cyanoundecanoic acid can be increased from 75% of the raw materials to about94.5%,with the fluffy appearance,light color,and good fluidity.After the same process recrystallization,the product purity can reach 98.5% or more.The crystallization processes of DDDA exist some problems more or less at present.Its crystallization process is more complicated,and the crystal properties needs to be better.In this section,we propose a novel crystallization method,the anti-solvent crystallization of ethanol-water system,based on solubility phase diagram of DDDA in ethanol-water mixed solvent,and investigate the crystal properties of DDDA.The optimal process conditions are 30-35℃(crystallization temperature),1.0ml/min(rate of addition of the anti-solvent),300 r/min(stirring rate),and 10:1(volume fraction of ethanol in the anti-solvent,V water: V ethanol).It is found that the fluidity of the product after modification is greatly enhanced,with an average particle size of about300μm and a narrow distribution.X-ray diffraction results show that the crystal form of the improved product has not changed compared with the raw material.Combining optical and scanning electron microscope photographs,it is found that DDDA crystals are mainly needle-shaped or flake-shaped.In summary,this dissertation systematically researched the separation and purification process of 11-CUA raw materials mixed with the impurities of dodecanedioic acid.Firstly,the reactive crystallization method is used to achieve the effective separation of 11-CUA,with the advantages of simple technology and high purity product,which consequently met the needs of industrial production.In addition,we simplified the crystallization process of DDDA based on anti-solvent crystallization and obtained crystals with large size and fine flowability,which had great significance in recycling of DDDA.