Synthesis Of Chlorinated Polyvinyl Chloride Resin By Gas-solid Phase UV Method

CPVC is a new material widely adopted in recent years. The need for CPVC is becoming more and more and the yield of it can not meet the industrial and commercial demand for its wide application range and long service life. There are many problems for solvent process and aqueous suspension process which are widely used at present, such as high environmental pollution, complicated product post processing, poor performance and so on. However, gas-solid UV process is a promising method, for it could overcome the shortcomings of the former two processes. Unfortunafely, researchings on this process is still at beginning stage, and some drawbacks, such as lower chlorine content in product, easier degradation of raw material, and poor uniformity of chlorination, still exist during the preparation procedure.In order to understand the UV process thoroughly, the process was studied in detail. The structure of PVC particles directly affected the uniformity and chlorine content of the product. The particle size of PVC, plasticizer absorption and particle morphology were investigated firstly and appropriate PVC was selected as raw material. Then, the heat model fluidized bed reactor was designed and the thermal-state small scale experiments were carried out. Three initiation ways including thermal initiation, UV irradiation and double initiation (UV and initiator) were compared. The results show that the way of UV irradiation is more suitable for preparation of CPVC in gas-solid. The single-factor experiments were conducted. The influence of reaction time, reaction temperature, chlorine concentration and UV light intensity on chlorie content of CPVC was investigated. The optimal reaction conditions were as follows:the reaction time 1.5h, reaction temperature 110℃, concentration of chlorine gas 30%, UV light intensity 211μW/cm2. The conception of segmental-intermittent chlorination process was proposed according to the feature of chlorination, that is, the relationship is positive correlation between the chlorine content and softening temperature. The conception was validated by the method of programmed temperature and intermittent initiating UV, and the results show that the method of segmental-intermittent chlorination is feasible, and the content of chlorine about CPVC reached 70%.Based on the experimental data of heat model fluidized bed, the kinetic model of preparing CPVC by the gas-solid UV process was derived and proved to be reasonable for describing the process of PVC chlorination. On the basis of the experiment of heat model fluidized bed and the kinetic model, the circulating fluidized bed was designed and the scale-up experiment of PVC chloriation was carried out. Through the research of the influence of reaction time, reaction temperature on chlorination for two materials, it is proved that the product with higher and even chlorine content can also obtained in a larger scale fluidized bed.The CPVC products were characterized by scanning electron microscopy, infrared spectroscopy, thermogravimetric-differerntial thermal analyzer and mechanical properties test, and the results show that the performance index of CPVC products is similar to the performance index of industrial productions which are produced with the aqueous suspension process.If the engineering problems could be solved, the title new process will be expected to replace the aqueous suspension process.