The manufacturing of pharmaceuticals, cosmetics and food items consists largely of altering the structure or function of chemicals and chemical compounds. To reach a satisfactory quality of the end-products, there is often also a need for downstream processing, including purification, extraction and polishing. Two solid materials commonly used for such heterogeneous procedures are activated carbon and ion exchangers.
Activated carbon is produced by exposing carbon-rich material to high temperatures under certain conditions; the source material is either pre-treated with chemicals, or exposed to hot gases to achieve a porous structure. The resulting material has a vast surface area (>3000 m²/g) due to the tiny pores having been created between the carbon atoms. The excessive porosity makes activated carbon a suitable material for adsorption, where molecules adhere to a surface by van der Waals forces. Due to this, activated carbon is commonly used in the chemical industry to remove organic impurities in the production of pharmaceuticals and fine chemicals. Other areas of usage include metal extraction, mercury scrubbing, and the purification of various liquids and gases, including polluted water and air.
Ion-exchangers are used to purify, separate, decontaminate and catalyse a wide variety of chemical compounds and processes. These polymeric matrices are typically cross-linked into porous microbeads in the size range of 200-500 µm. The properties of ion-exchange resins are determined by the functional groups attached to the internal and external surfaces of the beads. The two most common types of ion exchange resins are anion and cation exchangers, which attract negatively and positively charged ions, respectively. During an ion exchange process, the resin beads acts as a medium to which charged compounds bind, as the loosely bound ions originally attached to the resin are released into the solution. Ion exchangers are not physically altered by the process, and are, by definition, insoluble acids or bases with equally insoluble salts.
In downstream processing, the soluble compound of interest must come in contact and interact with the solid particles conducting the purification, extraction or polishing. The mass transfer in these cases can be mediated by packed columns, also known as fixed bed reactors (FBR), or by stirred tank reactors (STR). However, these methods have their drawbacks, such as low flow rate, high back pressure, limited mass transfer and mechanical stress on the solid phase particles.
With the SpinChem® rotating bed reactor (RBR), the solid phase is kept inside a rotating stainless-steel cylinder. As the cylinder spins, solution is pushed through the filters of the cylinder and through the packed bed within by centrifugal forces. Simultaneously, new solution enters the cylinder through the centre hole to subsequently be pushed through the bed, thus repeating the process. This allows every liquid parcel to do multiple passages through the bed, optimizing the resin utilization. By increasing the rotational speed of the RBR, the process can be sped up without risking degradation of the solid phase, which is kept well-protected from mechanical forces. The SpinChem® RBR works perfect with ion-exchange resins and granular activated carbon in downstream processing applications. Due to the enhanced mass transfer, the SpinChem® RBR allows for the use of larger, more manageable solid phase particles, without suffering from reduced reaction speed or inferior efficiency.
Time lapse video demonstrating a prototype vehicle capable of processing two cubic metres of coloured water within five minutes. The raft was carrying two rotating bed reactors that neutralized the basic surface water in a square pond by ion exchange.
Activated carbon is a common choice for removing impurities or capturing compounds from a product batch. However, the carbon may itself foul the product and be difficult to separate. The rotating bed reactor offers a clean way to deploy activated carbon that removes the need for time-consuming filtration and extends the lifetime of the solid phase.
Soudabeh Saeid, Pasi Tolvanen, Narendra Kumar, Kari Eränen, Janne Peltonen, Markus Peurla, Jyri-Pekka Mikkola, Andreas Franz, and Tapio Salmi Appl. Catal. B, 2018, 230, pp. 77-90.
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.
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.
Roger A. Sheldon and Pedro C. Pereira Chem. Soc. Rev., 2017, 46(10), pp. 2678-2691.
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.
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.
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.
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.
Adsorption of methylene blue (3 g, 5 mg/L) onto Purolite® NRW1160 (4.2 L) placed in a SpinChem® S5 RBR operated at 147 rpm. The SpinChem® S5 RBR was placed within a 600 L IBC tank, using the ProRBR IBC add-on, where the tank was filled with water. The data was acquired using a UV-VIS spectrophotometer.
Decolorization, pesticide remediation, catalysis, and many other applications involve dealing with viscous liquid that needs to be modified in some way. The rotating bed reactor presents an efficient way to treat viscous liquids, without the challenges of conventional reactors.
A large scale decolourization experiment using the SpinChem® rotating bed reactor (RBR) S100, packed with 79 L of activated carbon. The vessel contained 7000 L of water with added methylene blue dye. In under 40 minutes, 95% of the initial concentration of methylene blue was removed from the water, which shows that the RBR S100 can achieve fast reaction times in large scale processes.
The rotating bed reactor (RBR) is a clean way to use activated carbon for purification, which eliminates the need for time-consuming filtration and extends the lifetime of the solid phase. It is available on scales ranging from milliliters to hundreds of cubic meters and offers faster decolorization, elimination of filtration, and extended adsorbent lifetime.
The SpinChem® rotating bed reactor (RBR) S100, with a solid phase capacity of 100 L, was used to deionize 7000 L of tap water. The RBR S100 was operating at 160 rpm and filled with 36.5 L of mixed bed ion exchange resin. The results show that the RBR S100 can efficiently process large liquid volumes. As shown by the successful deionization, the performance of the RBR remains high even when it is partially filled, which proves the extreme robustness of the RBR technology.
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.
Hendrik Mallin, Jan Muschiol, Emil Byström, and Uwe T. Bornscheuer ChemCatChem, 2013, 5, pp. 3529-3532.
Whole cell biocatalysis is powerful, but not straightforward. One way of utilizing whole cells is to encapsulate them in a matrix such as alginate to make them easier to separate from a reaction mixture. However, alginate beads are not mechanically stable enough to be packed into columns and are easily destroyed in stirred tank reactors (STR). This makes enzyme recycling ineffective, at the same time as mass transfer limitations may prevail.
Carl-Johan Aurell, Staffan Karlsson, Fritiof Pontén, and Søren M. Andersen Org. Process Res. Dev., 2014, 18(9), pp. 1116-1119.
Jochen Wachtmeister and Dörte Rother Curr. Opin. Biotechnol., 2016, 42, pp. 169-177.
This case study presents a lipase-mediated stereoselective acetylation of a racemic amine 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.
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.
Contaminations in liquids can often be removed using an adsorbent, such as granular activated carbon (GAC). The best choice of adsorbent is unique for each contaminant, and the effectiveness depends on many parameters. Failing to investigate these can lead to unnecessarily high material costs and long processing times.
Hydrogenation reactions using hydrogen gas are usually efficient and clean. Drawbacks are the safety issues of handling hydrogen gas, need for reactors made for pressurized reactions, and the necessity of vigorous stirring to make these solid-liquid-gaseous reactions work well.
Heterogeneous reactions involving viscous solutions put high demands on equipment and materials. Columns face high pressure drops and require powerful pumps and durable solid phase particles. Stirred tank reactors do not face the same problem, but the high liquid viscosity and low particle density will have a negative impact on reaction kinetics and require tedious filtration to separate the solids afterwards.
Catalyst recovery is an important step in downstream processing. Using an appropriate scavenger resin and a rotating bed reactor to deploy it, the recovery is straightforward and effective.
Scavenging of soluble undesirable compounds and substances onto solid phase is used in a wide range of applications. In this example, a rotating bed reactor (RBR) is used to capture low concentrations of a phenol onto readily available Strong Anion Exchange (SAX) resin as a scavenger.
Soudabeh Saeid, Matilda Kråkström, Pasi Tolvanen, Narendra Kumar, Kari Eränen, Jyri-Pekka Mikkola, Leif Kronberg, Patrik Eklund, Markus Peurla, Atte Aho, Andrey Shchukarev and Tapio Salmi Catalysts, 2020, 10(1), 90.
Roger A. Sheldon and Dean Brady ACS Sustainable Chem. Eng., 2021, 9(24), pp. 8032–8052.
Soudabeh Saeid, Matilda Kråkström, Pasi Tolvanen, Narendra Kumar, Kari Eränen, Markus Peurla, Jyri-Pekka Mikkola, Laurent Maël, Leif Kronberg, Patrik Eklund, and Tapio Salmi Catalysts, 2020, 10(7), 786.
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