It’s one of the most pressing environmental issues: Massive, multiplying amounts of small plastic particles pollute the world’s oceans and coasts. Plastic waste has become a major global concern. Under public pressure, plastic manufacturers are searching for effective recycling methods. In addition, the European Union has set a target for PET bottles to consist of at least 25 percent recycled plastic by 2025 and by 2030, all plastic beverage bottles must be recyclable. According to consulting company McKinsey, the reuse and recycling of plastic could lead to revenue opportunities of up to 60 billion dollars for the plastic and petrochemical industry.
However, conventional recycling processes have limitations: Thermomechanical technology reuses plastic by melting it and then reforming it into recycled plastics. It is a downward spiral of waste and degraded materials because quality is lost in each cycle. This makes it impossible to obtain new products from 100 percent recycled PET. But there are alternatives. Currently, three variants of chemical recycling stand out that allow infinite recycling of all types of PET waste. These methods are used to generate virgin plastic material allowing for the production of 100 percent recycled and recyclable PET products. Glycolysis, methanolysis, and hydrolysis (partly with enzymatic enhancement) are recycling techniques suitable to the circular economy. Some companies have been focusing on each of these methods. The selection depends on the quality of the reclaimed input material.
High purity of monomers for fresh PET
All three methods break down any kind of PET. These depolymerization processes enable the regeneration of monomers while maintaining the same quality as their petroleum-based counterparts. Monomers such as terephthalic acid and ethylene glycol are recovered by treating PET through one of these techniques. After separation and purification, the monomers extracted from the process can be used for the synthesis of fresh PET. In any case, the key factor is the purity of the products from which the fresh PET is then produced.
Purity is achieved by the means of solid-liquid separation and effective cake washing – an essential feature offered by BHS belt filters and rotary pressure filters. For this reason, several customers have already opted for BHS-Sonthofen and commissioned the company to deliver equipment for PET recycling plants.
Multi-stage counter-current washing – with low consumption of resources
Once depolymerization is completed, the monomers are precipitated from the solution and the suspension is fed to the filter. This is where the separation from solvents, catalysts and other components takes place. For one project, BHS-Sonthofen supplied two indexing belt filter of type BF, which is very well suited to produce high purity with its multi-stage counter-current washing system – with low washing liquid and energy consumption. Uninterrupted continuous operation is another requirement the machine meets. The filters are operating in parallel for the production line with a throughput capacity of 2 t/h.
The BHS indexing belt filter of type BF is a continuously operating, horizontal vacuum filter used for the efficient and gentle separation of sedimenting solids from suspensions. In these applications, a multi-stage counter-current washing with washing filtrates takes place, which is a particularly efficient form of cake washing. In the countercurrent washing process, fresh, application-specific washing liquid is used in the final wash zone, which is then reused in the previous zones.
The fresh liquid is used to wash the cloth before it is employed for cake washing. The solid that is washed off the cloth recirculates and becomes usable as product. This increases the product yield.
While BHS-Sonthofen’s effective cake washing has already proven itself in numerous plastic applications, BHS further optimized the process for the chemical recycling of plastic. This process is crucial for ensuring that the recycled monomers are recovered from the suspension in the required purity, meeting the highest requirements in product quality.
Comprehensive know-how in plastics production
Another technology that is suited for chemical recycling of PET is the BHS rotary pressure filter of type RPF. This is a continuously operating unit for pressure filtration, cake washing, and drying of slurries. BHS-Sonthofen has shown that both technologies can successfully be applied to the chemical recycling of PET. Customers also benefit from the company’s extensive experience and know-how in the production of PET virgin material. With filtration tailored to each customer's application, the stage is set for the circular economy in the field of chemical plastic recycling.