Downstream processing

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.

More information

Ion-exchange resin on Wikipedia
Activated carbon on Wikipedia

 

Application examples

Application 1035

A performance comparison between a column (fixed bed reactor) and rotating bed reactor (RBR) for de-ionizing 1000 L of tap water. Using best-in-class standard protocols for both technologies, we tested which technology could de-ionize to a desired endpoint conductivity value the quickest. The result show that the RBR is significantly faster, reaching 3.7 times faster a conductivity level of 0.15 µS/cm compared to the column.

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    Details

    4L of Lewatit NM 60 mixed bed resin were packed in a Siliex 1C column and RBR S5, respectively. The output of the column was used as the desired endpoint conductivity value, as it is the less flexible output compared to the RBR. 1000 L of tap water (conducitivity starting point was ca 112 µS/cm, temperature 6-10C) was pumped through the column at a flow rate of 1.8 L/min and after 556 minutes all 1000 L had passed the column. The treated water had an average conductivity value of about 0.15 µS/cm. The same water conditions was used for the RBR where it spun at 300 RPM and reached the same conductivity (0.15 µS/cm) after only 150 minutes.

Application 1034

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.

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    Details

    Deionized tap water (7000 L) was filled in a rectangular vessel where the rotating bed reactor (RBR) S100 was lowered off center. Activated carbon (Epibon Y 12/40, 79 L) was filled in nylon bags (24 pcs, 75 μm mesh size) and the bags were placed evenly distributed in the RBR. 15g of methylene blue was added to the water (2 mg/L) and the RBR S100 was run at 180 rpm and stopped at 71 minutes. The absorbance was measured using an UV-VIS spectrophotometer and after 38 minutes, the measured absorbance was below 5% of the initial value.

Application 9004

Blue dye was removed from a highly viscous liquid using a SpinChem® RBR S2 in an EasyMax™ 102 Advanced Synthesis Workstation. Monitoring of the reaction was easily recorded as no freely suspended ion exchange resin beads or resin debris interfered with the readings. This demonstrates that the RBR technology is extremely well suited for in-line monitoring. The viscosity of the solution was determined to ca 230 cP at 25°C, showing that it is possible to absorb dye even from a highly viscous solution.

Application 1008

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.

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    Details

    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.

Application 1003

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.

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    Details

    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.

Application 1006

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.

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    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.

Application 1009

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.

Products: SpinChem® RBR S2
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    Details

    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.

Application 1031

The SpinChem® RBR S5 was used to remove methylene blue in an IBC tank using the ProRBR IBC add-on, operating at 150 rpm. The image shows the normalized absorbance over time, where 95% of the initial concentration of methylene blue was adsorbed by Purolite® NRW1160 in 138 minutes.

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    Conditions: 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.