Polycarbonate resin powder production via steam precipitation process: Experiment and CFD simulation

Polycarbonate (PC) is a widely used thermoplastic material with excellent transparency and physical toughness. Steam precipitation is a common method for converting PC in dichloromethane (DCM) solution into PC powder. To solve the problem of uneven droplet size and distribution in the steam precipitation atomization process, this paper constructs a simulation model of the atomization process of a steam precipitation jet, combines CFD theoretical analysis and experimental numerical analysis, and investigates the effects of ejector structure and operating conditions on the droplet size and distribution, including the diameter (D) of the feed hole, the steam flow rate, and the feed pressure. The results show that when the steam flow rate is at a high position, the average size of droplets is the smallest, and the number of droplets with a diameter less than 0.07 mm is the largest, accounting for about 57 % of the total number of droplets. Under the liquid flow rate kept constant, the smaller nozzle diameter of the ejector leads to smaller droplet size and wilder distribution. The number of droplets whose diameter is less than 0.07 mm accounts for almost about 50 %，70 %, and 80 % of the total when the nozzle diameter is 3.30 mm, 2.50 mm, and 2.0 mm, respectively. it is recommended to use D = 2.50 mm to improve the atomization dispersion effect, reduce energy consumption, and obtain a larger average particle size and a smaller distribution coefficient, which can avoid the accumulation of PC particles and thermal change caused by the presence of the retention zone and improve the efficiency of the atomization process. This study further optimizes the process conditions of the steam precipitation process, provides an essential reference for the improvement of the ejector, improves the efficiency and product quality of the PC powder production process, and promotes the promotion and development of the technology in the practical application of PC.