Ultrasonically Promoted Enzymatic Plastic Recycling

Polyethylene terephthalate (PET) is a huge waste source coming mostly from used water and beverage bottles. Until recently, recycling of PET resulted in low quality plastics. A new mutant enzyme promises the degradation of PET into pristine raw material, which can be used for new high-quality plastics. Ultrasonically promoted enzymes show a higher efficiency, accelerating the enzymatic recycling of plastics and increasing process capacities.

Ultrasonication for Enzymatic Plastic Recycling

Used plastic bottles produce large amounts of plastic waste. Ultrasonic-enzymatic processing is an efficient method of plastic recycling.High-intensity, low-frequency ultrasonication is well known for its effects on enzymatic reactions. Sonication can be used for both, the activation and inactivation of enzymes. Controlled sonication at low to medium amplitudes activates enzymes and promotes the mass transfer between enzymes and substrate, which results in increased catalytic activity of enzymes.
Sonication changes enzyme characteristics thereby promoting enzyme activity. Ultrasonic substrate pretreatment accelerates enzymatic reactions.
Ultrasonic mixing promoted the mass transfer between enzymes and plastic substrate, so that the enzyme can penetrate and degrade the melt of highly crystalline PET. As an energy-efficient and easy-to-operate technology, sonication helps to recycle PET cost-effectively and environmentally-friendly.

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Ultrasound treatment, known as sonication, can promote enzymatic reactions, e.g. enzymatic plastic degradation for recycling applications

Sonicator system for the intensification of enzymatic reactions

Ultrasonic Dispersion of Enzyme and Substrate

Ultrasonically generated shear and micro-turbulences are well known for their high efficiency when it comes to dispersing applications. The ultrasonically induced dispersion of enzyme aggregates as well as of substrate agglomerates improves enzymatic catalytic activity since the breakdown of molecular aggregates and agglomerates increases the active surface area between enzymes and substrate for reaction.

Ultrasonically Promoted Cutinase Enzyme

Sonication has shown good results in the activation of the enzyme utinase Thc_Cut1 in regards to its PET hydrolysis activity. The ultrasonically enhanced enzymatic degradation of PET resulted in a 6.6-fold increase of the released degradation products compared to the untreated PET. An increase of crystalline percentage (28%) in PET powder and films resulted in lower hydrolysis yields, which could be related to the lowered surface avaialbility. (cf. Nikolaivits et al. 2018)

Ultrasonic Effects on Enzymatic Reactions:

  • enhances enzyme activity
  • accelerates enzyme reactions
  • results in more complete reactions

About Enzymatic Plastic Recycling

The hydrolyse enzyme leaf-branch compost cutinase (LLC) occurs in nature and cuts the bonds between the two building blocks of polyethylene terephthalate (PET), terephthalate and ethylene glycol. However, the enzyme’s overall effectiveness and its heat-sensitivity are reaction limiting factors, which reduce the process efficiency significantly. The leaf-branch compost cutinase enzyme begins to degrade at 65°C, whilst PET degradation processes require temperatures of 72°C or higher, the temperature at which PET begins to melt. Molten PET is important process factor since the melt offers a higher surface area where the enzyme can work on.
Reasearchers have re-engineered the naturally occurring leaf-branch compost cutinase enzyme and changed amino acids at its binding sites. This resulted in a mutant enzyme which shows an increased activity by 10,000 times in breaking PET bonds (compared to the native LLC enzyme) and a significantly improved heat-stability. This means the new mutant enzyme does not break down at 72°C, the temperature at which PET starts to melt.
Ultrasonic dispersing and surface activation promotes enzymatically driven catalytic reaction. Specific sonication parameters such as ultrasonic amplitude, time, temperature and pressure can be exactly tuned to the enzyme type to increase its catalytic activity. Ultrasonic processing parameters and their effects on enzymes depend on the specific enzyme type, its amino acid composition and the conformational structure. Thereby, each enzyme type has optimum process conditions under which optimal enzyme activation is achieved.

Benefits of Ultrasonication

  • Increased mass transfer
  • Increased the rate constant
  • Increased catalytic efficiency
  • Precisely controllable to meet the enzymes’ sweet spot
  • Riskfree testing
  • Linearly scalable
  • Cost-effective
  • Safe and simple to operate
  • Low maintenance
  • Fast RoI
  • Environmental-friendly
Agitated ultrasonic tank for batch processing

Tank with 8kW ultrasonicators (4x UIP2000hdT) and agitator

High- Performance Ultrasonic Processors for Enzymatic Reactions

Hielscher Ultrasonics is long-time experienced in designing, manufacturing and distributing high-performance ultrasonicators for power applications in lab and industry. Our knowledge and experience in sophisticated ultrasonic processing is part of the offering we provide our customers.
We guide our customers from first consultation over feasibility testing and process optimisation to the final installation and operation of your ultrasonic system.
Our precisely controllable ultrasonic devices allow to influence enzyme activity, kinetics, thermodynamic properties as well as processing temperature.
Our portfolio of powerful and reliable ultrasonic processors covers the full range from the compact hand-held lab device to bench-top and fully industrial processors. From 200 watts upwards, all ultrasonic devices are equipped with a digital touch-display, intelligent software, remote browser control and automatic data protocolling on an integrated SD-card. The individually adjustable sonication cycle mode (puls mode) allows to set and control the enzyme exposure (time and rest periods) to the ultrasonic treatment. The robustness of Hielscher’s ultrasonic equipment allows for 24/7 operation at heavy duty and in demanding environments.
The table below gives you an indication of the approximate processing capacity of our ultrasonicators:

Batch Volume Flow Rate Recommended Devices
1 to 500mL 10 to 200mL/min UP100H
10 to 2000mL 20 to 400mL/min UP200Ht, UP400St
0.1 to 20L 0.2 to 4L/min UIP2000hdT
10 to 100L 2 to 10L/min UIP4000hdT
n.a. 10 to 100L/min UIP16000
n.a. larger cluster of UIP16000

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Hielscher Ultrasonics manufactures high-performance ultrasonic homogenizers for dispersion, emulsification and cell extraction.

High-power ultrasonic homogenizers from lab to pilot and industrial scale.

Literature / References

Facts Worth Knowing

Acoustic Cavitation Forces

Low-frequency, high-intensity ultrasonication (approx. 20 – 50kHz) causes acoustic / ultrasonic cavitation which produces physical, mechanical and chemical effects. The effects of acoustic cavitation can be observed as the formation, growth and subsequent violent collapse of minute vacuum bubbles, which occur due to pressure fluctuations of the ultrasound waves coupled into a liquid. During the implosion of cavitation bubbles, so-called hot spots occur, which are confined to small space and short duration. Those locally occurring hot-spots are characterised by intense heating of at least 5000 K, pressures up to 1200 bar, and high temperature and pressure differentials occurring within milliseconds. Droplets and particles of the liquid are accelerated into liquid jets with velocities of up to 208m/s.

Ultrasonic / acoustic cavitation creates highly intense forces which activates the surface of enzymes and promotes the mass transfer between enzymes and substrate (Click to enlarge!)

Ultrasonic treatment of enzymes is based on acoustic cavitation and its hydrodynamic shear forces

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