Trash to Treasure: Microwave-Assisted Conversion of Polyethylene to Functional Chemicals

Abstract

An effective microwave-assisted process for recycling low-density polyethylene (LDPE) waste into value-added chemicals was developed. To achieve fast and effective oxidative degradation aimed at production of dicarboxylic acids, nitric acid was utilized as an oxidizing agent. Different conditions were evaluated, where recycling time and concentration of oxidizing agent were varied and the end products were characterized by FTIR, NMR, and HPLC. After just 1 h of microwave irradiation at 180 °C in relatively dilute nitric acid solution (0.1 g/mL), LDPE powder was totally degraded. This transformation led to few well-defined water-soluble products, mainly succinic, glutaric, and adipic acids, as well as smaller amounts of longer dicarboxylic acids, acetic acid, and propionic acid. The length of the obtained dicarboxylic acids could to some extent be tuned by adjusting the reaction time, temperature, and amount of oxidizing agent. Finally, the developed process was verified by recycling LDPE freezer bags as model LDPE waste. The freezer bags were converted mainly into dicarboxylic acids with a yield of 71%, and the carbon efficiency of the process was 37%. The developed method can, thus, contribute to a circular economy and offers new possibilities to increase the value of plastic waste.

Marine Environmental Plastic Pollution: Mitigation by Microorganism Degradation and Recycling Valorization

“…Polyethylene is inert to many chemicals, and it is available in multiple types (HDPE, LDPE), which complicates the recycling processes. In fact, PE is the most challenging polymer for recycling and therefore is a waste stream (Bäckström et al, 2017). Its backbone is extremely stable, connected by strong single C-C and C-H bonds containing mainly secondary and primary carbons, both robust to oxidation by exposure to heat or ultraviolet radiation (Jia et al, 2016).…”

“…In an attempt to depolymerize polyethylene (LDPE) by microwave-assisted and oxidative process (1 h of microwave irradiation at 180 • C in nitric acid solution 0.1 g/mL), the LDPE was totally degraded. Different kinds of products were obtained, such as succinic, glutaric, and adipic acids, as well as longer dicarboxylic acids, acetic acid, and propionic acid (Bäckström et al, 2017;Jehanno et al, 2019). In addition to the mentioned alternatives, some studies have explored the use of PE as a precursor in the production of carbon fiber through carbonization (Laycock et al, 2020).…”

Organocatalysis for depolymerisation

“…Despite this fact, Bäckström et al undertook an original initiative to recycle low density PE (LDPE) into value-added functional chemicals via a microwave-assisted fast and effective oxidative process. 72 Through this approach, LDPE powder was totally degraded after just 1 h of microwave irradiation at 180°C in relatively dilute nitric acid solution, which led to well-defined watersoluble products, such as succinic, glutaric, and adipic acids, as well as longer dicarboxylic acids, acetic acid, and propionic acid. Noteably, the length of the dicarboxylic acids could be adjusted by varying the reaction conditions (i.e.…”

Current approaches to waste polymer utilization and minimization: a review

“…Other chemical recycling methods involves photodegradation, ultrasound degradation, degradation in microwave reactor, etc. Despite all its advantages, unfortunately, chemical recycling is not a widespread method, mainly because of energy costs .…”

“…Recycling of condensation polymers such as PET and Nylon by these methods yields monomer units (de-polymerization or monomer recycling) in a relatively short time. 32 Other chemical recycling methods involves photodegradation, [45][46][47] ultrasound degradation, [48][49][50][51][52][53] degradation in microwave reactor, [54][55][56][57][58][59] etc. Despite all its advantages, unfortunately, chemical recycling is not a widespread method, mainly because of energy costs.…”