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Reactor engineering

Heterogeneous manufacturing processes based on chemical reactions, biochemical transformations and adsorption, which inherently involve both a solid and a liquid phase, are associated with several technical challenges. One of the most difficult issues is achieving contact between the reagents in the two phases – a phenomenon known as mass transfer limitation. The reagents in the liquid phase must be brought to an active site on the solid phase through transport of the liquid medium relative to the solid particle. In absence of any stirring to create convective flow, this transport only takes the form of diffusion, which is a very slow process. The mass transport is therefore increased in laboratories and production facilities by means of a suitably designed reactor.

Reactor types

The traditional and perhaps most common way to deal with mass transport limitations is a stirred tank reactor (STR). In the STR a two-phase slurry of particles in suspension is stirred using an agitator. This generates a convective flow in the reactor which increases the relative transport of the liquid phase and solid particles, bringing reactants together at a higher rate than if left only to diffusion. The agitator also improves the mixing time of the reactor, being the time taken to disperse any concentration gradients in the liquid bulk that arise due to the local generation or removal of chemical species at the reaction sites. However, the STR may cause physical damage to the solid phase as the particles collide with the agitator and each other. These collisions often lead to grinding of the particles, producing fines that are hard to remove and limit the ability to reuse the solid material. For most applications, the STR thus introduces a need for filtration after the reaction is completed.

A gentler treatment takes place in a packed column, also known as a fixed bed reactor (FBR). Here the solid phase is packed in a stationary bed through which the liquid phase is then pumped. Grinding is then eliminated as there is no relative motion between any solid bodies. Still, associated with the FBR is a back pressure that increases with liquid viscosity and flow rate among other parameters. To avoid slow percolation of viscous liquids through the packed bed, powerful pumps and strong particles that can withstand immense pressures are required for operation of FBR.

Rotating bed reactors

A rotating bed reactor (RBR) is a modern alternative to the traditional reactor types. The solid phase is loaded into the RBR and kept in place by filters that allow the liquid medium to pass through. The RBR is rotated within the reaction vessel containing the liquid which then passes through the RBR due to inertial forces. By keeping the solid phase fixed within the RBR it is protected from grinding. The flow rate, controlled by the rotational speed, can also become many times greater than in a typical column of corresponding volume. This leads to significantly greater reaction rates in mass transport limited cases. Moreover, each fluid parcel will have many passages through the RBR, providing the reagents with plenty of time to react with the solid phase in applications limited by chemical kinetics. Since the solid phase is contained within the RBR it may also be regenerated or reused in-situ for another reaction step without any time-consuming filtration in between.

Flexible deployment with the plug-in rotating bed reactor

The rotating bed reactor (RBR) is a combined tool for chemical transformations and liquid transfer operations, reducing or eliminating the need for external pumps. Filled with a catalyst or adsorbent, and rotated by a motor, the RBR brings the liquid to be processed in contact with the solid-phase at high flow rates. Due to the high flow rate generated, the RBR can not only treat the liquid in the reaction vessel, but also transfer it into the vessel for processing.

Automatic processes for efficient production

Automation of large-scale processes is often a requirement for economically viable chemical processes. The benefits of scale are best harvested at high throughputs and 24/7 operation. This leads to the demand for process automation, and the elimination of hands-on work.

Palladium catalyzed Suzuki couplings in a Mettler-Toledo EasyMax™ 102

Heterogeneous catalysis can be an effective tool for chemical synthesis, particularly in the discovery and development of pharmaceutical ingredients. The handling of these solid catalysts is sometimes challenging as it leads to more unit operations in the factory scale, as well as introduces additional work-up in the laboratory.

Dramatically improved deionization with a rotating bed reactor

Removing ions from liquids is common in industry and society. Ions are remediated in applications ranging from the production of pharmaceuticals to the treatment of communal waste streams. Likewise, the nuclear energy sector deals with the removal of ionic radioactive substances from water on a daily basis.

Decolourization more efficient in rotating bed reactor than in fixed bed reactor

A fixed bed reactor (FBR), also known as a packed bed reactor or column, is a traditional technology for processes such as adsorption or heterogeneous catalysis. Achieving the required level of purification or conversion means running the liquid through the reactor at a sufficiently low flow rate, and the throughput of a fixed bed reactor is therefore often limited.

Rotating bed reactor faster than stirred tank reactor for a mass transfer limited reaction

Mass transfer limited reactions can create problems for applications like the synthesis of chemical products or the manufacture of active pharmaceutical ingredients. Poor yields, high side-product formation or impractically long reactions are potential issues. Efficient reactor design can greatly improve the mass transfer and remove the limitation to a minimum.

High-viscosity applications made faster

Liquids with high viscosity create problems for heterogeneous applications in traditional reactors. Packed bed reactors (columns) suffer from huge back pressures, and stirred tank reactors (STR) exhibit reduced reaction rates due to poor mixing. Both issues lead to longer processing times and expensive operations.

Deployment of Rotating Bed Reactors at Industrial Scale Person in PPE inspecting a rotating bed reactor.

Ion removal in 7000 L of water using the SpinChem® RBR S100

Water with elevated ion concentrations is a common challenge in industries such as the nuclear energy sector. Whether it’s ordinary heavy metals, radionuclides, or any other ions, these can normally be captured by a properly selected ion-exchange resin. The deployment of the resin can however be a challenge, especially at large scale.

Automatic loading and unloading of a production scale rotating bed reactor

The separation of a heterogeneous catalyst, an adsorbent, or an ion-exchange resin from a liquid product is a time-consuming unit operation that often makes the use of these materials impractical. The rotating bed reactor is a more efficient technology for deploying catalysts for manufacturing or adsorbents for purification.

Improving reactions in emulsions using a rotating bed reactor

When working with an emulsion (and particularly with a heterogeneous catalyst) the mass transfer between the phases is critical. Insufficient mixing leads to lower interfacial area per volume, and in turn to poor mass transfer across the phases.

Channelling effects common in columns removed with rotating bed reactors

Fixed bed reactors (FBRs), also known as packed bed reactors (PBRs), are frequently used for purification, ion-exchange processes, or heterogeneous catalysis. Though relatively easy to construct, they are tedious to charge with solids in an effective way. A poorly packed FBR is subject to channelling, where passages are formed in the bed. These passages offer less resistance to the liquid, which will preferentially travel through those regions. In this work, the robustness with respect to channelling of a packed bed reactor was compared to a rotating bed reactor (RBR) using computational fluid dynamics (CFD).

In situ filling and emptying of rotating bed reactors

Video showing how a SpinChem® rotating bed reactor (RBR) was charged with solid particles, followed by draining and replacing the reaction liquid without escape of solids. Lastly, the solid phase was removed without opening the RBR. This procedure illustrates a concept for automatic handling of solid phases in production scale equipment without opening the reaction vessel.

In-tank deployment of large scale rotating bed reactor

How can this process be scaled up? This is perhaps the most important question to consider when developing a chemical process. If it cannot be done on large scale, all the time and resources invested in laboratory work will be unrewarded. Pumping liquids through massive columns or separating solids from a large batch can be unsurmountable challenges that bring a halt to a new project before it has even left the starting blocks.

Mass transfer revolutionized

The SpinChem rotating bed reactor (RBR) can eliminate poor mass transfer in heterogeneous reactions during chemical syntheses and biotransformations, preserve catalyst activity, and facilitate recycling of solid phases. This brochure presents our technology and its applications.

Remediation of wastewater stored in High-Integrity Container (HIC)

Liquid waste is generated by many sources at a nuclear energy plant, during both operation and decommissioning. The waste is sometimes stored in high-integrity containers (HICs) or similar vessels, where it occupies valuable space and poses a liability that eventually needs to be dealt with.

Rotating bed reactor for immobilized enzymatic reactions

In pharmaceutical manufacturing and other industries, traditional methods are burdened by unsustainable use of solvents and transition metal catalysts. The use of enzymes is pursued as an alternative, offering greener synthetic routes and better results due to improved specificity. However, enzymes are costly and reusing them for many cycles is practically a requirement for process economy. This essentially means that the enzymes must be immobilized on a solid support so that they can be separated from the product.

Soft alginate beads used in a rotating bed reactor

Stirred vessels tend to damage soft heterogeneous catalysts, like enzymes immobilized in agarose or alginate beads, with activity loss and tedious workup as consequence. In a fixed bed reactor, these materials are easily compressed by the pressure gradient, leading to a loss of flow rate. Overcoming these challenges opens up the possibility to use biocatalysis as a tool for greener processes and more sustainable manufacturing.

Rotating bed reactors completely avoid grinding of molecular sieves

When using of solid-phase catalysts or adsorbents in reactors, the physical degradation of the materials is a common problem. The traditional stirred tank reactor inflicts mechanical damage to the particles, which causes attrition, fines that are difficult to separate, and loss of the functionality of the solid-phase.

Simple scale-up using flexible reactors

Research and development quickly takes new directions, and the requirements on a laboratory may vary with every new project. Limiting yourself to equipment with a narrow scope of conditions and applications may become expensive, since new equipment must be acquired for anything out of scope. With budgets quickly consumed by other projects, the need for new equipment may mean significant delays and a reduced capability to take on emerging opportunities.

Decolorization at 7,500 L using a mobile reactor

Any producer might need to modify their process because of variations in the available materials or changing demands on the product. However, installing new equipment in a production plant is a costly, time-consuming, and disruptive process. Modifying existing infrastructure often requires extensive downtime, regulatory approvals, and significant capital investment.

Using a rotating bed reactor in different liquid volumes

Research and development quickly takes new directions, and the requirements on a laboratory may vary with every new project. Limiting yourself to equipment with a narrow scope of conditions and applications may become expensive in the long run. The need for new equipment may inflict delays and affect your capability to take on emerging opportunities.

Lipase-catalyzed hydrolysis in 750 L using a rotating bed reactor

Biocatalysis offers many benefits in the production of chemicals and active pharmaceutical ingredients. One major challenge has been the deployment of immobilized enzymes in an efficient way on large scale. The rotating bed reactor offers a convenient way to scale a biocatalytic process.

How the loading of solids influences reaction speed

Sometimes you don’t want to pack the entire rotating bed reactor full with your solid-phase material. Fully loading might simply be wasteful, or you may want to experiment with your reaction conditions. But how does the amount of solids in the rotating bed reactor influence the reaction performance? Can you use only 10% of the full capacity?