Ozone Bleaching
Ozone is a toxic gas generated by applying a high voltage to oxygen. The first commercial use of ozone for bleaching was in 1992, so ozone is relatively new for pulp bleaching. However, ozone provides several economic and environmental benefits over other chemical options for elemental chlorine free (ECF) and totally chlorine free (TCF) bleaching. This course discusses the benefits of ozone bleaching, its chemistry, how it is generated, and the process and equipment involved in ozone bleaching.
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Learning Objectives
• State the benefits of ozone bleaching (compared to other chemistries)
• Describe ozone bleaching chemistry
• Explain how ozone is generated
• Explain how ozone bleaches pulp
• Identify important ozone bleaching variables
• Identify and describe ozone bleaching processes and equipment
• Identify and describe safety hazards and safe work practices associated with ozone bleaching
Specs
| Course Level | Intermediate |
| Languages | English, Portuguese |
| Compatibility | Audio, Video |
| Based on: | Industry Standards and Best Practices |
Key Questions
How is ozone generated?
Ozone is created by applying high voltage to a gas that contains oxygen.
What are the advantages of ozone bleaching?
Ozone provides several economical and environmental benefits over chlorine dioxide and other bleaching chemicals. It can be formed from oxygen, it is a strong oxidizer, and reacts quickly with pulp.
Does ozone bleaching require special equipment?
Yes, the equipment depends on the pulp consistency. High consistency is most popular today. A special horizontal reactor is used instead of a large conventional tower because the reaction is fast. A wash press, or similar equipment, is needed to achieve high consistency.
What process variables are important for ozone bleaching?
Temperature, pH, consistency, and mixing all impact the efficiency and selectivity of ozone bleaching.
Is ozone hazardous?
Ozone is toxic even at low concentrations and at high concentrations it can explode. The concentration of ozone gas in air must be continuously monitored.
Sample Video Transcript
Because ozone gas is unstable and cannot be stored, it is manufactured-on-demand. Ozone is created by applying high voltage to a gas that contains oxygen. For pulp bleaching, pure oxygen is used so a high concentration, 10 to 12% of ozone can be generated. Electrons travel across a gap between electrodes. When oxygen molecules collide with the electrons, they break apart into individual oxygen atoms. The individual atoms attach to molecular oxygen and form ozone.
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