PET can be chemically recycled through glycolysis, a depolymerisation process that breaks the plastic back into valuable intermediates. Hydramotion inline sensors monitor viscosity in real time, enabling manufacturers to control the reaction with increased precision, cutting energy use whilst increasing throughput.
Glycolysis as a Chemical Recycling Route for PET
PET recycling is one of the most mature areas in plastics reprocessing, with bottle-to-bottle reuse being one of the most widespread. But beyond mechanical routes, PET can also be chemically recycled through depolymerisation processes such as glycolysis. This enables the material to be upcycled into intermediates like polyols, which are essential feedstocks for producing products such as high-performance insulation.
During glycolysis PET flakes are suspended in a glycol solution, agitated, and subjected to reaction temperatures of 220ºC-240ºC for a duration of 6-8 hours. Under these reaction conditions, polymer chains undergo transesterification, breaking down the molecules until suitable for further processing.
The Challenge: Identifying True Reaction Endpoint
Depending on batch variability and the intrinsic quality of the rPET flakes, the required reaction time can deviate considerably batch-to-batch. Relying on fixed cycle times often means over compensating by extending reaction time, which results in unnecessary heating, wasted energy, and lower reactor availability.
As depolymerisation proceeds, molecular chains are broken down, reducing their resistance to flow. This leads to a measurable decrease in viscosity - providing a direct indication of reaction progress. The endpoint is then determined once the product has stabilised at a target viscosity.
Traditionally viscosity is measured using offline equipment, but this is error prone and time-sensitive, often taking upwards of 15 minutes per sample. The lack of information availability during the critical completion window means the endpoint is often missed, resulting in inefficient reaction cycles.
Solution: Inline Viscometer for Real-Time Reaction Tracking
Hydramotion inline viscometers can track the decrease in viscosity in real-time - as the reaction proceeds - providing critical data needed to terminate the reaction within the narrow completion window.
This capability allows tighter control and optimisation over the reaction cycle time and energy consumption, whilst also providing the ability to compensate for batch-to-batch variability found with r-PET feedstocks.
This production improvement makes PET chemical recycling more resource-efficient, cutting up to two hours of energy use per batch and increasing daily throughput.
About the Sensor
Hydramotion’s XL7-HT viscometer can be used with fluids at up to 400ºC with no need for special cooling. The sensor always operates at the fluid temperature, thus eliminating potential errors from localised cooling of the fluid. The XL7-HT can also be configured to display viscosity corrected to a standard reference temperature if required.
The dedicated readout unit can be located up to 1000 metres from the sensor and include 4-20mA viscosity and temperature outputs along with an RS232 or RS485 serial data link for recording or remote monitoring.
Like all Hydramotion inline viscometers, the XL7-HT is unaffected by flow rate and can be tank mounted in any orientation using any process fitting. The unique resonant technology of the XL7 naturally rejects ordinary plant noise and vibration, delivering high sensitivity and excellent repeatability even in the most aggressive process environment. As the sensor is an all-welded construction with no moving parts to wear out or seize, maintenance requirements are minimal.
Typical dimensions can be seen above for an indicative XL7 sensor. Hydramotion also offers a bespoke design service - Special Ops - where a sensor of virtually any size or geometry can be designed to fulfil the requirements of the application.
Ready to learn more?
Contact Hydramotion to discuss your depolymerisation application requirements. Or visit the following link to learn more about Hydramotion viscosity sensors.