Ultrasound dewatering
removing water using ultrasound
Did you know that the Pulp and Paper Sector has the potential to be more energy efficient? A recent report by the U.S. Energy Department (2015) revealed that drying operations offer the biggest opportunity for saving energy in this industry.
We focus on a special class of paper materials called cellulose nanofibrils or CNFs.
CNFs are tiny particles made of cellulose that have a unique set of characteristics such as being renewable, sustainable, biodegradable, and having high mechanical strength.
They can be used in many different applications such as composites, coatings, biomedical devices, and more. However, one challenge in their use is that they are processed in water, which makes them costly to ship.
To make them more economical, they need to be dried or dewatered, but traditional drying methods can damage their nano-size structure and make them clump together.
We decided to tackle this grand challenge and came up with an idea to use ultrasound, instead of heat, to remove water.
This project has been Recognized internationally.
The International Council of Forest and Paper Associations (ICFPA) and the American Forest and Paper Association (AF&PA) presented the lead graduate student, Udita Ringania, with the 2021 Blue Sky Young Researchers and Innovation Award.
Images of CNF using Scanning Electron Microscopy at various magnifications showing the wide range of fibril dimensions present.
Major question
Can we develop a low-cost, scalable and energy-efficient method for dewatering cellulose nanomaterials?
What we’ve discovered
Ultrasound as a Low-Cost and Scalable Dewatering Alternative
We demonstrated ultrasound as a potentially low-cost and scalable alternative to traditional heat-based drying methods for cellulose nanofibril suspensions. We used a direct-contact mode ultrasonic dewatering platform using vibrating mesh transducers.
Modulated Dewatering with Vibrating Mesh Transducers
The degree of dewatering achieved was modulated by the number of transducers, their spatial configuration, and the flow rate of the suspension. We achieved water removal of up to 72 wt.% in 30 minutes, corresponding to a final concentration of 11 wt.% of cellulose nanofibrils.
Energy-Efficient and Redispersible CNFs
We found that the ultrasound dewatering technique is energy-efficient, consuming up to 36% less energy than the enthalpy of evaporation per kilogram of water. More importantly, redispersion of the dewatered cellulose nanofibrils showed no significant difference in morphology compared to the original samples.
Effect of Fines Content
By comparing CNF samples with 60% and 90% fines, we found that higher fines content leads to longer drying times which can be attributed to higher availability to hydrogen bonding sites.
Biphasic Pattern
The water removal follows a biphasic pattern with phase two commencing when 50 % water is removed from the system. Interestingly, in phase two, the systems demonstrate similar dewatering rates irrespective of the fines percentage.
Redispersion Time
Post-dewatering redispersion revealed minimal agglomeration, maintaining quality across samples. However, higher redispersion time is recommended for higher fines content.
Read the papers
Dewatering of cellulose nanofibrils using ultrasound. Cellulose (2022).
Effect of fines percentage on ultrasonic dewatering of cellulose nanofibrils. Cellulose (2023).