Since the industrial revolution, modern society has been built by consuming a large amount of fossil fuels, however, the atmospheric concentration of carbon dioxide has correspondingly increased, and this increase is more accelerated by environmental destruction such as deforestation, etc.
Global warming is caused by an increase of greenhouse gases such as carbon dioxide, Freon, and methane in the atmosphere. Thus, it is very important to reduce the atmospheric concentration of carbon dioxide which significantly contributes to global warming, and various researches into emission regulation, immobilization, etc., have been conducted on a global scale.
Among them, a copolymerization reaction of carbon dioxide and epoxide discovered by Inoue et al., has been expected as a reaction to solve the global warming problem, and has been actively researched not only in view of fixation of chemical carbon dioxide but also in view of the use of carbon dioxide as a carbon source.
In particular, in recent years, the polyalkylene carbonate resin obtained by the polymerization of carbon dioxide and epoxide has received much attention as a kind of biodegradable resin.
In the production of the polyalkylene carbonate resin, solution polymerization in which reaction heat and molecular weight are easily controlled is generally used.
However, in the solution polymerization process, viscosity increases rapidly as a solid content included in a solution increases, and thus there is a great restriction in performing subsequent processes.
Further, an amount of loss during filtration and transfer processes of the solution is increased due to the high viscosity of the solution, which reduces a yield of a final resin.
On the other hand, a process of removing the solvent is required in the production of the resin by solution polymerization.
However, in a conventional method (flash separation method) in which a solvent is volatilized by increasing a temperature of a solution, a solution in which a polymer is dispersed in the solvent has remarkably reduced volatilization efficiency of the solvent as compared to that of a pure solvent.
Accordingly, when the resin is produced by the solution polymerization, the process of removing the solvent using the flash separation method has problems in that a processing time is long, and a lot of energy is consumed.
In particular, since the polyalkylene carbonate resin is able to be easily decomposed by heat, there are various restrictions on the process of separating the solvent by heat.
For example, when the temperature of the flash separation process is lowered to prevent the decomposition of the resin, removal efficiency of the solvent is rapidly decreased. When a facility is configured in multi-stages to increase efficiency, a large capacity facility is required.
Further, in order to recover the solvent and monomers gasified in the flash separation process, there are drawbacks in that operation of a freezing condenser, etc., is required, which increases operation cost.
In addition, a pelletizing process by extrusion is required to ensure workability of a resin in the production of the polyalkylene carbonate resin.
However, when the alkylene carbonate produced in the polymerization is included in the resin at a certain level or more, the pelletizing process cannot be performed.
Therefore, it is essential to perform a washing process for removing the alkylene carbonate included in the resin prior to performing the pelletizing process.
However, there is a problem in that a large amount of wastewater occurs in the washing process, and thus the cost of treating wastewater is increased.