Extrusion International 5-2022

89 Extrusion International 5/2022 RECYCLING High monomer purity The processes named above produce monomers of the same quality as their petroleum-based counterparts. These are present in the process liquids in a dis- solved state and must be sepa- rated. In other words, once de- polymerization is complete, the monomers are precipitated from the solution and the suspension is fed to a filter. This is where the separation of solvents, catalysts and other components takes place. The quality of the virgin PET to be produced depends to a large extent on the purity of the monomer, since impurities significantly impair the con - version to polymers and the reactions take a different course. This product purity, which is necessary for a suc- cessful recycling process, is mainly achieved by solid-liquid separation with effective cake washing. Several international companies that apply one of the recycling processes de- scribed rely on the proven process en- gineering solutions of BHS-Sonthofen for this step. Multi-stage counterflow washing with low resource consumption BHS-Sonthofen supplied two in- dexing belt filters of type BF to one of these customers. Both machines operate in parallel in the production line with a throughput rate of 2 t/h. The indexing belt filter of type BF is a continuously operating, horizontal vacuum filter used for the efficient and gentle separation of sediment- ing solids from suspensions. The application involves multi- stage counterflow washing with washing filtrates, which is a highly efficient method of cake washing. In this process, fresh, application-specif- ic washing liquid is used in the final washing zone, which is then reused in the preceding zones. This operat- ing mode is particularly suitable for producing a high level of purity de- spite low washing liquid and energy consumption. This is a particularly important feature of cake washing, especially in view of the fact that process effi - ciency is one of the factors that will determine how chemical plastics re- cycling develops on the market in the future. And, as an added benefit, the fresh liquid is used to wash the filter cloth before it is used again for fil - tration and then cake washing. The solid material washed off the cloth is returned to the cycle and reused as a product. This significantly increases the product yield. BHS-Sonthofen has adapted its fil - tration process to the requirements of chemical recycling. This means that monomers can be efficiently recov - ered at high purity levels, allowing it to be used for the synthesis of new PET without requiring any further process steps. Here, the company was also able to draw on its experi - ence from the use of its filters in nu - merous plastics applications. Alternative pressure filtration Another technology suitable for use in the chemical recycling of PET is the BHS rotary pressure filter of type RPF. This is a continuously operating device for pressure filtration, cake washing and drying of suspensions. BHS-Sont- hofen has proven through empirical data and extensive trials that both technologies can be successfully used for the chemical recycling of PET. Cus- tomers also benefit from the compa - ny’s many years of experience in the production of virgin PET. Outlook: Product quality and process efficiency are decisive In summary, chemical plastic recy- cling offers several advantages: The new processes avoid so-called “ther - mal recycling,” which is nothing more than the incineration of plastics, and they also help to reduce the use of fos- sil rawmaterials. Even heavily contam- inated plastic waste can be recycled, and waste streams that were previ- ously ineligible for recycling can be used. However, there are challenges of an ecological and economic nature to be overcome. In terms of energy and resource consumption, the pro- cesses must be designed in such a way that they have a positive eco-balance and are also viable from an economic perspective. Therefore, in addition to the quality of the recovered monomers, process efficiency is the most decisive factor when it comes to the industrial use of the processes described. This calls for new, innovative process solutions that ensure product quality and efficiency in equal measure. With the use of efficient machines, high yields of monomers are achieved in addition to reduced energy and re- source consumption. A tailor-made solution for solid-liquid separation for the respective customer application thus contributes decisively to mak- ing the chemical recycling of plastics feasible on a large scale. If technically functional and commercially viable solutions can be established on the market, the industry will have made a decisive breakthrough in the sustain- able production of plastics. BHS-Sonthofen GmbH An der Eisenschmelze 47, 87527 Sonthofen, Germany www.bhs-sonthofen.de Pressure filtration is also suitable for use in chemical PET recycling The BHS rotary pressure filter of type RPF is a continuously operating system for pressure filtration, cake washing and drying of suspensions