12
Aug 2022
Crystallization of a Monomer from a Waste Depolymerization Process
Recycling of polymer products (“plastics”) is an important contribution to reduce the amount of waste that can turn into microplastic and pollute the environment for decades, and for an improved carbon dioxide balance in production of new polymers. The latter can be achieved by depolymerization of polymers by either thermal pyrolysis or in case of polyesters by interesterification in a suitable medium. However, the recovered monomer usually must meet strict quality requirements. Therefore, besides yield, the purity achieved is an essential criterion for the economy of the overall process. Depending on the properties of the monomer, different separation processes are available for this purpose. In addition to distillation methods, crystallization is one possibility for achieving high quality products. Using crystallization, it is also possible to not only have a strict control of purity but also on the crystal morphology and size distribution. In addition, customers are looking for continuous processes rather than batchwise operation. This is where the Technoforce Plug Flow Crystallizer (TPFC) comes into play.
The Technoforce Plug Flow Crystallizer consists of a horizontal cylinder fitted with one or more separate double jackets. This allows the crystallizer to be individually tempered in different sections to create a graduated temperature profile. In cooling crystallization, for example, an 80°C solution could be cooled to 60°C, then to 40°C and further to 20°C to control crystallization. A specially designed rotor ensures good mixing within a section, however from section to section (i.e., from temperature level to subsequent temperature level) the system forces a plug flow without significant back-mixing. The rotor design also minimizes mechanical energy transfer into the crystal slurry to avoid breaking of mature crystals into fines. By this, unwanted secondary nucleation and uncontrolled crystal growth can be reduced considerably.
Technoforce Plug Flow Crystallizer with cross section
By optimizing the crystallization process with our pilot size Technoforce Plug Flow Crystallizer, we were able to maximize yield with a narrow crystal size distribution for the monomer. The solution was directly coming from the upstream depolymerization at elevated temperature and was gradually cooled down at two different cooling media temperatures in one single TPFC. Thus, in one step we achieved the desired separation, while for demands of even higher purity it is always possible to repeat the crystallization by using either the same or a different solvent, a process known as re-crystallization.
In our laboratories in Nashik/India or Geleen/The Netherlands we can offer our customers bench scale and pilot scale crystallization trials in our continuous Plug Flow Crystallizers. Choice of suitable solvent as well as some pre-investigations regarding solubility curves should be performed by the customer beforehand to speed-up the project.
Technoforce has already designed and built several hundred skids of process intensification technology for oils and fats applications, fine chemistry, polymers, food and pharma products and other industrial sectors. We also offer other evaporation technologies like Short Path Distillation, Agitated Thin Film Evaporation and Drying, Falling Film, Rising Film and Forced Circulation Evaporation, as well as Liquid-Liquid Extraction in columns or centrifugal systems.