超音波増感固定床リアクター

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.
• 熱伝達の強化： 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.

固定床触媒

固定床（充填床と呼ばれることもある）には、通常、直径1～5mmの顆粒状の触媒ペレットが装填される。触媒ペレットは、シングルベッド、セパレートシェル、チューブの形でリアクターに充填される。触媒は主に、ニッケル、銅、オスミウム、白金、ロジウムなどの金属をベースにしている。
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.

超音波による触媒反応の促進

超音波による混合と撹拌は、反応物と触媒粒子の接触を改善し、反応性の高い表面を作り、化学反応を開始および／または促進する。
超音波による触媒調製は、結晶化挙動、分散／脱凝集、表面特性の変化を引き起こす可能性がある。さらに、不動態化表面層の除去、分散性の向上、物質移動の増加などにより、予備成形触媒の特性に影響を与えることができる。

Examples of Ultrasonically-Improved Reactions

• 水素化反応用Ni触媒の超音波前処理
• 酒石酸でソニック処理したRaney Ni触媒は、非常に高いエナンチオ選択性を示す。
• Ultrasonic synthesized Fischer-Tropsch catalysts
• 反応性を高めるソノケミカル処理アモルファス粉末触媒
• アモルファス金属粉末のソノ合成

超音波触媒回収

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 Ultrasonics社は、固定床反応器にパワー超音波を組み込むための様々な超音波プロセッサーとバリエーションを提供しています。固定床反応器に設置するための様々な超音波システムが利用可能です。より複雑なリアクタータイプには カスタマイズ超音波 ソリューションを提供する。
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!
今すぐご連絡ください！お客様の化学プロセスの超音波増強について、喜んでご相談させていただきます！
下の表は、Hielscher社製ソニケーターの処理能力の目安です：