- Saved 2 hours per batch - 50% increase in batches per day
- Significant energy savings
- Improved batch to batch consistency
Using plastic waste responsibly is of paramount importance for the development of a circular and sustainable economy, and PET can play a key role. Bottle-to-bottle recycling is often the most referenced PET recycling method, but it can also be upcycled into other products that help to reduce energy consumption and CO2 emissions.
Through a chemical depolymerisation process, PET flakes can be used to produce polyols, a key raw material used in the manufacturing of high-performance insulation.
This conversion involves a glycolysis reaction whereby PET flakes are submerged in a glycol solution, mixed, and heated to high temperatures of 220ºC-240ºC over a period of 6-8 hours. The reaction causes the molecular structure of the polymer to break down into smaller molecules for further processing.
One big challenge in this process is identifying the true reaction endpoint within the two-hour window. This endpoint can also vary with different batches of r-PET. Energy consumption is also a key driver for improvement as there could be up to two hours of wasted energy per batch.
Keeping many process variables within a predefined limit is critical in controlling the reaction, but viscosity is one variable that can determine when the reaction is complete. As depolymerisation occurs, the molecule bonds are broken down, reducing their resistance to flow. This leads to a decrease in viscosity. The reaction endpoint is then determined once the product has stabilised at a target viscosity.
XL7 High Temperature viscometer installed directly in the reactor
An inline viscometer can track the decrease in viscosity in real-time and provide the operators with the insight required to terminate the reaction. The variance often seen between batches of r-PET is also no longer a problem as each batch is terminated accordingly.
This process improvement results in significant energy savings of up to 2 hours per batch, as well as increasing the number of batches that can be produced each day.
About the Sensor
Hydramotion’s XL7-HT viscometer can be used with fluids at up to 450ºC 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.
Like all Hydramotion on-line viscometers, the XL7-HT is unaffected by flow rate and can be tank or pipe 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 316 stainless steel construction with no moving parts to wear out or seize, maintenance is minimal.
The dedicated readout unit can be located up to 1000 metres from the sensor. Outputs include a 420 mA analogue viscosity signal and an RS232 or RS485 serial data link for recording or remote monitoring.