13 March, 2015

The project REC POLYOLEFIN was carried out for the period between September 2011 and August 2014. The results obtained during that time were satisfactory, achieving optimal outcomes that have given rise to the design and development of a demonstrative plant for recycling and separation of polyolefins.

At the start of the project a full study was carried out about the plastic waste collected by different waste management centres in Comunidad Foral de Navarra and in the Netherlands (taking into account the geographical location of the project’s partners).

Plastic waste

Further to the study conducted in Navarra, it may be said that the percentage of polyolefins in the plastic waste are between 0 and 20 %, according to the origin area. On the other hand, in the Netherlands there is a collection network in charge of the waste management where the plastic waste is sold in batches.

Subsequently, many studies and tests were developed to define the requirements that are favourable for the polyolefins. After this study, it was established that the mixture of polyolefins should have a similar size and need long residence time and high temperature, because better results were obtained.

To carry out the tests, batches of simulated samples were used with the following composition: HDPE (red): 18%; PP (yellow): 12%; LDPE (transparent): 70%.

After defining the requirements, an in-depth study, analysis and evaluation was carried out in order to know the existing techniques for plastic waste treatment and conditioning to obtain a homogenous and suitable input material for the demonstrative line. As a result, the following treatment scheme was designed:

An analysis of the different types of plastic wastes was carried. Furthermore, these wastes were also processed in the conditioning system obtaining interesting results. It was concluded that the most suitable fractions to be used in the project were both the industrial solid waste and the agricultural plastic waste as they were the most homogenous.

Once the waste to be treated and treatment steps were selected, the heat treatment prototype was designed (rotating drum). This prototype is part of the 1st stage of the separation process.

The prototype equipment is able to treat up to 1000 kg/h in order to achieve the optimal thermal contraction of the post-consume polyolefins.

When all the elements and devices of the prototype were bought or built, they were assembled. The following figure shows a picture of the heat treatment prototype:

When the prototype construction was completed, some tests were carried out with simulated samples in order to optimize the system parameters.

During the tests, the system parameters and the materials (temperature, film size, residence time, etc.) were optimized.

After the heat treatment, two fractions are obtained, both containing a mixture of all three types of olefins. For this reason, a later separation stage is needed to achieve the objectives pursued in this project.

For this purpose, in this second stage, two types of separation were raised: electrostatic separation and pneumatic separation.

For the electrostatic separation an in-depth and detailed study was carried out, as well as small-scale tests that showed that the separation of the films by this technique was not suitable.

To design and define the pneumatic system, tests were conducted in separation equipment (owned by the partners) with the simulated samples obtained after the rotating drum. After doing these tests, the pneumatic system was designed on the basis of the defined parameters and technical requirements (supply, surface, etc.). Subsequently, it was built. Once tuned up, some tests were carried out to define the working conditions of the process and to verify the correct functioning of the equipment.

The two fractions obtained after thermal processing (deformed and non-deformed) were used for the tests. Further tests were carried out to optimize parameters.

Once the working conditions were optimized, it was concluded that the pneumatic separation system was optimal and very effective, having high separation performances using different batches.

After the optimization of the equipment, further tests were carried out to start up this demonstrative plant.

Mixtures of post-consumer polyolefins were collected from different sources. They were grinded and then, treated in the 1st stage (heat treatment) and the 2nd stage (pneumatic separation system).

At the 1st stage, the mixture of polyolefins got contracted, obtaining two fractions: deformed polyolefins (low content in PP) and non-deformed polyolefins (high content in PP).

Obtained samples

At the 2nd stage (pneumatic separation system), the PEBD was separated from the other materials with no contraction (PP/PEAD). 

 

 

Heat treatment and obtained samples

After the tests, different fractions were obtained: fractions containing 95.5 % of PEBD and fractions containing 19 % of PEBD with a mixture of PEAD and PP.

After the tests, it was concluded that the successful separation depends mainly on their size, obtaining satisfactory results after the parameters optimization.

Once the separation process for the recycling of PEBD and mixtures of PEAD/PP was developed, the obtained samples were verified by two methods; on the one hand film extrusion and, on the other hand, profile extrusion.

For this purpose, the following tests were carried out:

– Profile extrusion for mixtures of recycled PEAD/PP.

– Film Extrusion-Blowing for recycled PEBD.

 After the tests were done, post-consumer PEBD and PEAD/PP were found to be optimal for end-use applications such as films and profiles, respectively. Furthermore, the developed technology proved to be viable for the separation of waste coming from either simulated samples or mixtures of post-consumer polyolefins. Technical and economically feasible applications for the separated polyolefins would be: