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.
Rotating bed reactors
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.
Accelerated video showing the enhanced adsorption rates of methylene blue onto activated carbon using a rotating bed reactor (RBR) compared to a stirred tank reactor (STR). The RBR decolourized the solution almost twice as fast, did not create any visible fines and required no filtration.
Conditions: Adsorption of methylene blue (100 mg) onto activated carbon (40 mL, 12-40 mesh) placed either in a SpinChem® S311 rotating bed reactor (RBR) or stirred free in solution agitated by a 5 cm impeller, both operated at 800 rpm within a SpinChem® V311 flower-baffled reaction vessel containing 1000 mL water at room temperature. The video is shown at 12x the normal speed. The solution was decolourized after 5 minutes with the RBR, versus close to 10 minutes with the stirred tank reactor (STR). Samples from the RBR set-up required no filtration, but from the STR all samples required filtration through a 45 µm syringe filter for analysis.
Illustrative video showing how a phenolic colourant is deprotonated and extracted from an organic to an aqueous solvent. Using SpinChem® RBR in a flower-baffled reaction vessel created fine emulsion droplets resulting in effective phase-transfer between the two liquids and the solid phase.
Conditions: Red 2,6-dichloroindophenol (about 3 mg) in dichloromethane (70 mL) with water (70 mL) converted to its blue phenolate anion using Purolite A500P (25 mL) in OH form (created by treating Cl form with NaOH) packed into a SpinChem® RBR S221 rotating at 500 rpm in a SpinChem® V211 flower-baffled reaction vessel.
Video revealing the efficient mass transfer and resulting shorter reaction time with a rotating bed reactor (RBR) during ion-exchange neutralization of a base. The reaction with the RBR finished 30% faster and left a completely clear solution without any particles.
Conditions: Neutralization of sodium hydroxide (1 M, 200 µL) by cation exchanger Amberlite IRN99 (20 mL) placed either in a SpinChem® S311 rotating bed reactor (RBR) or distributed in solution agitated by a 5 cm impeller, both operated at 800 rpm within a SpinChem® V311 flower-baffled reaction vessel containing 800 mL water with phenolphthalein (20 mg/L). The reaction with RBR finished after 23 s versus 33s for the stirred tank reactor with impeller.
Video illustrating how a mixture of red and blue dyes with different chemical properties can be selectively extracted onto different adsorbents within the same run using a rotating bed reactor (RBR). The dyes were separated based on ionic and hydrophobic interactions, respectively.
Conditions: Allura red (40 µM) and methylene blue (13 µM) in deionized water (about 160 mL) were adsorbed onto Amberlite IRA900 Cl (13 mL, 650-820 µm) and Amberlite XAD1600N (13 mL, 400±50 µm), respectively. Each adsorbent was filled into two of the four compartments in a SpinChem® S221 rotating bed reactor (RBR) operated at 800 rpm within a SpinChem® V221 flower-baffled reaction vessel. The total extraction time for one run was nine minutes and the video contains photos of the adsorbents before and after two repeated extractions.