Ultrasonically Intensified Fixed Bed Reactor(초음파 강화 고정층 반응기)

Sonication can improve catalytic reactions in fixed-bed reactors mainly by intensifying mass transfer around and inside the packed catalyst bed. Additionally, sonication removes passivation and fouling layers from the catalyst surface thereby continuously regenerating the catalyst.

How Sonication Improves Fixed-Bed Catalysis

In a fixed-bed reactor, the catalyst particles remain stationary while liquid, gas, or multiphase reactants flow through the bed. Reaction performance is often limited by external mass transfer, pore diffusion, channeling, fouling, and heat-transfer gradients. Ultrasound can reduce several of these limitations by generating acoustic cavitation, microstreaming, shear forces, and pressure oscillations.

Key Effects of Ultrasonically-Intensified Fixed Bed Reactions

• Improved external mass transfer: Ultrasonic microstreaming reduces the stagnant boundary layer around catalyst particles, allowing reactants to reach active sites more efficiently.
• Enhanced pore accessibility: Cavitation-induced pressure fluctuations and liquid movement can improve penetration of reactants into catalyst pores and removal of products from pores.
• Reduction of fouling and passivation: Sonication can help remove deposits, polymer films, coke precursors, or other passivating layers from catalyst surfaces, maintaining catalytic activity for longer.

Improved liquid-solid contact: Ultrasound promotes better wetting of catalyst particles, which is especially useful in trickle-bed, slurry-fed, or liquid-phase fixed-bed systems.

• Reduced channeling in packed beds: In micropacked-bed studies, ultrasound has been shown to modify flow behavior and reduce dispersion, helping the reactor approach more ideal plug-flow behavior.
• 향상된 열 전달: Acoustic streaming and turbulence improve local heat dissipation, reducing hot spots or cold zones in the catalyst bed.
• Higher conversion and yield: By improving mass transfer and catalyst accessibility, sonication can increase reaction rate, conversion, and product yield, especially when the reaction is transport-limited rather than purely kinetically limited.

How does Sonication Improve Fixed Bed Catalysis?

The main mechanism is acoustic cavitation: ultrasonic waves create microscopic bubbles that grow and collapse violently. Their collapse generates local shear, microjets, shockwaves, and intense mixing. Near catalyst surfaces, these effects can clean, activate, and refresh the solid-liquid interface. Reviews of sonocatalysis describe this as a synergy between ultrasound and solid catalysts, involving improved heat transfer, mass transfer, and localized effects at catalytic surfaces.

Sonication is most beneficial when the fixed-bed reaction suffers from:

• slow diffusion into catalyst pores,
• poor wetting of catalyst particles,
• product accumulation inside pores,
• fouling or surface passivation,
• mass-transfer-limited kinetics,
• multiphase flow maldistribution,
• channeling through the packed bed.

고정층 촉매

고정 베드(때로는 포장 베드라고도 함)에는 일반적으로 촉매 펠릿이 적재되어 있으며, 이는 일반적으로 직경이 1-5mm인 과립입니다. 그들은 단일 베드, 별도의 쉘 또는 튜브 형태로 반응기에 적재 할 수 있습니다. 촉매는 주로 니켈, 구리, 오스뮴, 백금 및 로듐과 같은 금속을 기반으로 합니다.
The effects of power ultrasound on heterogeneous chemical reactions are well known and widely used for industrial catalytic processes. Catalytic reactions in a fixed bed reactor benefit from sonication treatment, too. Ultrasonic irradiation of the fixed bed catalyst generates highly reactive surfaces, increases the mass transport between liquid phase (reactants) and catalyst, and removes passivating coatings (e.g. oxide layers) from the surface.

촉매 반응의 초음파 강화

초음파 혼합 및 교반은 반응물과 촉매 입자 사이의 접촉을 개선하고 반응성이 높은 표면을 생성하며 화학 반응을 시작 및/또는 향상시킵니다.
초음파 촉매 제조는 결정화 거동, 분산/응집 해제 및 표면 특성의 변화를 일으킬 수 있습니다. 또한, 미리 형성된 촉매의 특성은 부동태화 표면층을 제거하고, 분산을 개선하고, 물질 전달을 증가시킴으로써 영향을 받을 수 있습니다.

Examples of Ultrasonically-Improved Reactions

• 수소화 반응을 위한 Ni 촉매의 초음파 전처리
• 주석산이 있는 초음파 처리된 Raney Ni 촉매는 매우 높은 거울상 선택성을 제공합니다.
• Ultrasonic synthesized Fischer-Tropsch catalysts
• 반응성 증가를 위해 Sonochemically 처리된 비정질 분말 촉매
• 비정질 금속 분말의 Sono 합성

초음파 촉매 회수

Solid catalysts in fixed-bed reactors are commonly used in the form of spherical beads, pellets, extrudates, or cylindrical particles. During chemical reactions, the catalyst surface can become passivated by a fouling layer, resulting in a gradual loss of catalytic activity and/or selectivity over time.
The timescale of catalyst deactivation varies considerably. For example, the deactivation of a cracking catalyst may occur within seconds, whereas an iron catalyst used in ammonia synthesis may remain active for 5–10 years. Nevertheless, catalyst deactivation is observed in virtually all catalytic processes. Although different deactivation mechanisms can occur – including chemical, mechanical, and thermal degradation – fouling is one of the most common causes of catalyst decay.
Fouling refers to the physical deposition of species from the fluid phase onto the catalyst surface and within its pores. These deposits block reactive sites, restrict pore accessibility, and reduce contact between reactants and the active catalyst surface. Catalyst fouling by coke or carbonaceous deposits is often a rapid process; however, in many cases it can be partially or fully reversed by ultrasonic regeneration.

Ultrasonic cavitation is an effective method for removing passivating fouling layers from catalyst surfaces. During sonication, high-intensity ultrasound generates cavitation bubbles in a liquid medium. Their collapse produces localized shear forces, microjets, shock waves, and intense micro-mixing. These effects help detach fouling residues from the catalyst surface, reopen blocked pores, and restore access to active sites.
Ultrasonic catalyst recovery is typically carried out by dispersing the catalyst particles in a liquid, such as deionized water or a suitable solvent, and exposing the suspension to controlled ultrasonic treatment. This process can remove fouling residues from various catalyst materials, including platinum/silica fibre catalysts, nickel catalysts, and other supported metal catalysts. As a result, sonication can contribute to catalyst regeneration, extended catalyst lifetime, and improved process sustainability.

Click here to learn more about the ultrasonic regeneration of spent catalysts!

Sonicators for the Integration into Chemical Reactors

Hielscher 초음파는 전력 초음파를 고정층 반응기에 통합하기위한 다양한 초음파 프로세서와 변형을 제공합니다. 다양한 초음파 시스템을 고정층 반응기에 설치할 수 있습니다. 더 복잡한 반응기 유형의 경우 다음을 제공합니다. 맞춤형 초음파 솔루션.
Learn how sonication improves chemical reactions in various reactor designs!
To test the effects of sonication on your chemical reaction, you are welcome to visit our ultrasonic process lab and technical center in Teltow!
오늘 저희에게 연락하십시오! 우리는 당신과 함께 화학 공정의 초음파 강화에 대해 논의하게되어 기쁩니다!
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