Dynamic Cross-flow Filtration Research Articles

Regression Metamodel-Based Digital Twin for an Industrial Dynamic Crossflow Filtration Process.

Dynamic crossflow filtration (DCF) is the state-of-the-art technology for solid-liquid separation from viscous and sensitive feed streams in the food and biopharma industry. Up to now, the potential of industrial processes is often not fully exploited, because fixed recipes are usually applied to run the processes. In order to take the varying properties of biological feed materials into account, we aim to develop a digital twin of an industrial brownfield DCF plant, allowing to optimize setpoint decisions in almost real time. The core of the digital twin is a mechanistic-empirical process model combining fundamental filtration laws with process expert knowledge. The effect of variation in the selected process and model parameters on plant productivity has been assessed using a model-based design-of-experiments approach, and a regression metamodel has been trained with the data. A cyclic program that bidirectionally communicates with the DCF asset serves as frame of the digital twin. It monitors the process dynamics membrane torque and transmembrane pressure and feeds back the optimum permeate flow rate setpoint to the physical asset in almost real-time during process runs. We considered a total of 24 industrial production batches from the filtration of grape juice from the years 2022 and 2023 in the study. After implementation of the digital twin on site, the campaign mean productivity increased by 15% over the course of the year 2023. The presented digital twin framework is a simple example how an industrial established process can be controlled by a hybrid model-based algorithm. With a digital process dynamics model at hand, the presented metamodel optimization approach can be easily transferred to other (bio)chemical processes.

Polyacrylonitrile and polyethersulfone based co-axial electrospun nanofibers for fluoride removal from contaminated stream

Coaxial electrospun polyacrylonitrile (PAN) and polyethersulfone (PES) based nanofibers were prepared and was used for filtration of fluoride from drinking water for the first time. Well defined fiber geometry was obtained at 1 ml/h of core polymer, i.e., PES flow rate, 1.4 ml/h of shell polymer, i.e., PAN flow rate, voltage of 22 kV, while the distance between the needle tip and the collector was 15–17 cm. Increase in bead like structure in fiber strands was observed with higher PAN concentration, while it decreased for lower PES concentration, thereby giving an optimum composition (6 wt% PAN and 10 wt% PES) for uniform fiber morphology. This nanofiber, abbreviated as N2 acted as an ultrafiltration membrane having permeability in the lower range, i.e., 0.5 × 10−11 m/s Pa and its fluoride removal efficacy was 46%. Fibers were also hydrophilic with considerable porous nature. Uptake of fluoride by this N2 nanofibers were evident from binding energy of 685.2 eV during XPS analysis. It is probable that nitrile and sulfone groups present in the core and shell of the nanofibers played an active in fluoride uptake, which was estimated as 110 mg/g at 298 K. Isoelectric point was in alkaline range which promoted negative fluoride ion uptake on positive nanofiber surface. Lead played higher masking effect in the uptake of fluoride in comparison to arsenic as coexisting ion. Dynamic cross flow filtration was also studied with this nanofiber in both synthetic and real life feed solution.

Experimental Study on the Recovery of Lignin from Black Liquor by Blade Dynamic Cross-Flow Filtration Device

The separation and recovery of lignin in black liquor is a hot topic in current research. Ceramic membrane technology has become the main method of lignin separation in black liquor due to its advantages of green environmental protection, high efficiency and high recovery rate. However, in the separation process, the problem of ceramic membrane fouling has always existed and has become the key to hinder its continuous separation. Aiming at the problem that the existing filtration methods can not meet the continuous separation of lignin in black liquor, this paper proposes to apply the blade dynamic cross-flow filtration device to the separation process of lignin in black liquor, and the influence of blade rotation speed on the separation performance is studied experimentally. The results showed that increasing the rotating speed of the blade could effectively reduce the accumulation of filter cake on the membrane surface and achieve the purpose of improving the filtration flux.

Purification of crosslinked, highly viscous and viscoelastic hyaluronic acid hydrogels by dynamic diafiltration

The current study shows a new possibility to purify crosslinked hydrogels based on hyaluronic acid (HA) to remove the residual crosslinking agent 1,4 - butanediol diglycidyl ether (BDDE) and its byproduct 1,4-butanediol di-(propan-2,3-diolyl) ether (EPD) using a crossflow filtration (CFF) device. Therefore, a dynamic crossflow-filtration (DCF) device with rotating and semipermeable ceramic filter discs (5 nm, 60 nm, 2000 nm) was used. No negative impacts on the thermal stability and rheological characteristics of the biopolymer could be shown. Furthermore, it was discovered, that 7 diafiltration volumes (DV) are sufficient to reduce the residual contaminants to < 0.1 % from the initial concentration and that the hyaluronic acid (HA) rejection coefficient (R) is 0.99 regardless of the chosen membrane pore size, while the permeability of BDDE and EPD remains at almost 100 %. No correlation between the membrane pore size and the flux could be found. For all membranes, the flux is surprisingly dropping after 0.5 DV was processed, which could be linked to the HA swelling and membrane pore blocking effects. The highest flux was determined for the 60 nm membrane with 32 Lm-2h−1 at steady state. The stability of the biopolymer is neither negatively influenced by the applied shear forces due to the rotational membrane velocity, nor by the applied thermal stress conditions for 6 months at 25 °C, 60 % relative humidity (r.h.) and 40 °C, 75 % r.h. The presented results show that a dynamic diafiltration can be regarded as a promising alternative to conventional purification methods.

Isolation of bacterial exopolysaccharides from Streptococcus thermophilus via dynamic cross flow filtration in pilot scale

A variety of exopolysaccharides (EPS) producing bacterial starter cultures are manufactured for their use in food industry, leaving the almost cell free and EPS containing fermentation broth as waste product. The concentration of EPS in the fermentation broth is approximately 1 gL−1, depending on fermentation conditions and bacteria strain. The use of bacterially produced EPS as a food additive is promising because it has a high water binding capacity, which is beneficial for the stability and viscosity of emulsion-based products and enables a sustainable production process. However, concentration and separation of EPS from the complex fermentation broth is cost-intensive and time-consuming. This work presents a simplified EPS-isolation scheme in comparison to the established laboratory process, that can be transferred to pilot scale. The method consists of a microfiltration or ultracentrifugation for removal of the remaining cell, an ultrafiltration to concentrate the EPS and a final diafiltration washing step to remove lower molecular components like salts and sugars. Subsequent to freeze drying, the final product is isolated as EPS-powder. This can easily be integrated in industrial processes to replace herbal food additives like xanthan gum or locust bean gum.

High performance in-situ tuned self-doped polyaniline (PANI) membranes for organic solvent (nano)filtration

Cross-linked polyaniline (PANI) membranes are attractive for organic solvent nanofiltration (OSN). However, inadequate tuneability to cover the full nanofiltration (NF) separation range, prolonged post-treatment cross-linking using hazardous organic chemicals and poor permeance limit their widespread application. This work introduces a new strategy to tune the transport properties of PANI membranes to suit the rejection spectrum of NF membranes without compromising permeance. Incorporating different molecular weight organic acids, metanilic acid (MA) and poly (2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA), facilitated cross-linking during polymer precipitation at different aqueous coagulation bath acidic strength using non-solvent induced phase separation (NIPS). Static ageing tests for PANI membranes immersed in tetrahydrofuran (THF) for 30 days showed no physical or chemical deterioration. All membranes were stable during long-term dynamic crossflow filtration tests over 250 h with sequential feed of methanol, acetonitrile and THF. THF permeance was 2.1–16.4 L m−2 h−1 bar−1 with apparent molecular weight cut off (MWCO) between 250 and 1000 g mol−1. PAMPSA doped membranes were successfully cross-linked but required wet annealing post-treatment to obtain membranes in NF range. The MA doped membranes surpassed the performance of cross-linked PANI membranes with glutaraldehyde (organic cross-linker) showing a 2.5 times higher permeance with better rejection. In comparison to commercial polyimide membranes, PANI membranes prepared in coagulation bath ≥0.5 M HCl(aq) were stable in N,N-dimethylformamide (DMF) whereas the former suffered complete damage. This work represents a simplified technique to in-situ optimise permselective properties of OSN self-doped PANI membranes for various applications in food, pharmaceutical and petrochemical industries.

Application of Dynamic Cross-Flow Filtration for Solving the Technological Problems of Project Breakthrough

The results of experiments on the clarification of solution simulators obtainable by means of dynamic crossflow filtration during the reprocessing of mixed uranium-plutonium nitride spent fuel are presented. The experiments were performed using full-scale, dynamic, cross-fl ow filtration stands at the RT-1 radiochemical plant at the Mayak Production Association. It is shown that this method yields high-quality clarification of solutions without the use of flocculants – the obtained permeates were completely free of the solid phase and silicic acid in the γ-form. In addition, the concentration of the solid phase can reach 100 g/cm3 without loss-of-clarification. It is shown that the method of dynamic cross-fl ow fi ltration is effective for clearing transuranium elements from liquid radwaste. After their co-precipitation with the carrier (trivalent iron) and clarification, the obtained permeates are low-level wastes according to the Basic Sanitary Rules for Radiation Safety (OSPORB-99/2010).

Dynamic crossflow filtration with a rotating tubular membrane: Using centripetal force to decrease fouling by buoyant particles

This paper describes a dynamic membrane filtration system that combines crossflow filtration and centrifugal separation in a rotating tubular membrane. Because of the no-slip boundary condition, membrane rotation leads to higher centripetal force near the lumen wall than introduction of a rotating flow. In this fundamental exploratory study, hollow glass microspheres (5–35μm diameters) serve as model low-density, separate-phase foulants during filtration of aqueous suspensions through a tubular ceramic membrane (nominal 0.14μm pore size). At low crossflow rates, membrane rotation at 1725rpm decreases fouling and shifts the microsphere size distribution in the membrane cake toward smaller diameters. Force balance calculations suggest that centripetal force should move particles with diameters >∼17μm away from the lumen surface. Moreover, azimuthal and longitudinal shear stresses will also selectively remove larger particles from the membrane cake. Computational fluid dynamics (CFD) simulations show that the rotational flow does not fully develop in the membrane lumen and the fluid radial velocity peaks before the membrane wall. Both of these factors will decrease movement of low-density particles away from the lumen wall. Nevertheless, consistent with experimental data, CFD simulations show greatly decreasing encounters of particles with the membrane wall as particle size increases.

Dynamic cross-flow filtration: enhanced continuous small-scale solid-liquid separation

In a previous study, a small-scale dynamic filtration device (SFD) was analyzed and the basic mechanisms governing the filtration process were characterized. The present work aims at improving the device’s performance in terms of actual production. Various operation modes were tested in order to increase permeate flow and concentration factors (CF), while maintaining a fully continuous production mode. Both, a vacuum-enhanced and a pulsating operation mode, proved to be superior to the currently implemented open-operation mode. For example, for lactose, an increase of the CF could be achieved from 1.7 in open mode to 7.6 in pulsating operation mode. The investigated operation strategy enables process control systems to rapidly react to fluctuating feeds that may occur due to changes in upstream manufacturing steps. As a result, not only filtration performance in terms of permeate rate but also process flexibility can be significantly increased. Overall, vacuum-enhanced operation was shown to be most promising for integration into an industrial environment. The option to elevate achievable concentration factors, ease of flow monitoring as well as the ability to react to changes in the feed conditions allow for effective and efficient continuous small-scale filtration.

Continuous Processing of Active Pharmaceutical Ingredients Suspensions via Dynamic Cross-Flow Filtration

Over the last years, continuous manufacturing has created significant interest in the pharmaceutical industry. Continuous filtration at low flow rates and high solid loadings poses, however, a significant challenge. A commercially available, continuously operating, dynamic cross-flow filtration device (CFF) is tested and characterized. It is shown that the CFF is a highly suitable technology for continuous filtration. For all tested model active pharmaceutical ingredients, a material-specific strictly linear relationship between feed and permeate rate is identified. Moreover, for each tested substance, a constant concentration factor is reached. A one-parameter model based on a linear equation is suitable to fully describe the CFF filtration performance. This rather unexpected finding and the concentration polarization layer buildup is analyzed and a basic model to describe the observed filtration behavior is developed.

Mechanical Stress on Lysozyme Crystals during Dynamic Cross‐Flow Filtration

AbstractThe influence of mechanical stress on the crystal size distribution of lysozyme crystal slurries in a dynamic cross‐flow device is discussed. The reduction of crystal size may have an influence on mass and resistance of the fouling layer. A filter test device with a filter area of 130 cm2 is used for thickening. After thickening, a model impurity, namely bovine serum albumin, is washed out of the suspension. A reduction of crystal size due to stirring and a reduced fouling layer with increasing stirrer speed is observed. Furthermore, a higher stirring speed increases the specific filtrate flux. In the presence of the impurity, more crystal aggregates than single isometric crystals are formed and, hence, the decrease of crystal size due to shear forces is more pronounced than without impurity.

Dynamic cross-flow filtration of oilfield produced water by rotating ceramic filter discs

The purpose of this research paper is to assess the effects of the process parameters—membrane rotational speed (1,200, 1,500 and 1,800 rpm), volume concentration factor (VCF) and feed characteristics—in terms of oil and total organic carbon (TOC) separation capability, permeability and permeate quality. For this, a series of membrane filtration experiments were carried out systematically using rotating ceramic filter discs in a fed-batch operating mode. The variation of membrane rotational speed was found to minimize the membrane fouling in a significant amount. High oil (>99%) and TOC rejection (>98%) was achieved with both microfiltration (MF) and ultrafiltration (UF) membranes, independent of the rotational speed and the feed concentration The experimental results are presented for the dynamic cross-flow MF (0.2-μm pores) and UF (7-nm pores) of oilfield produced water as well as oily model solutions (OMS).

Dynamic cross flow filtration with Novoflow's single shaft disk filters

Dynamic cross flow filtration means rotating filter elements for this purpose. Rotating filter elements allow for decoupling of overflow velocity from transmembrane pressure (TMP). Considerable energy savings are realized compared to conventional tubular systems, because there is no need for constant circulation (pumping) of the feed over the membranes in order to generate shear forces. The combination of centrifugal and shear forces in dynamic cross flow modules improves control of cover layer build-up which extends operating life. Novoflow has specialized on compact and modular single shaft designs and has developed a proprietary process of disk manufacturing from almost any flat membranes. Applications in many fields have proven the economic viability of the concept. Dynamic cross flow technology has shown advantages for the application of high performance membranes. These are very thin and hard membranes with absolute pore sizes and open outflow, i.e. no drainage layers and support structure. In the absence of complex support structures (with tortuous channels), flux performances of high performance membranes reach by orders of magnitude higher levels at much lower filtration pressures (TMP) than conventional membranes. On the other hand, this higher performance causes higher concentration polarization and fast cover layer build-up on the concentrate/retentate side. Novoflow's dynamic cross flow filtration design has proven to be an ideal way to remove the accelerated cover layer build-up for high performance membranes.

Numerical Simulation of Dynamic Cross-flow Filtration Processes

Numerical Simulation of Dynamic Cross-flow Filtration Processes

Dynamic cross flow filtration

The dynamic cross flow filtration with the DYNO filter is a very versatile and economic high performance filtration process especially for suspensions with critical separation characteristics. Thickening, washing and clarifying of suspensions but also a classifying sieve filtration can be performed with the DYNO filter in a continuous operation with permanently high throughput rates. The principle of the dynamic high shear filtration ensures almost ideally physical conditions for the separation process. Contrary to classical cross flow filters a repeated recirculation of the suspension is not necessary for attaining the separation target. In the DYNO filter suspensions can be highly concentrated up to the flow limit in only one filtration cycle. In most cases, the concentrate is as dry as a firm filter cake and the filtrate is crystal-clear. Sieve filtration tasks for separating of coarse grain are performed with high concentration factors of up to 1000. Thus, the coarse fraction is obtained highly concentrated.

Concentration of ferric hydroxide suspensions in saline medium by dynamic cross-flow filtration

We have investigated the concentration of ferric hydroxide suspension in saline solution by high shear cross-flow filtration using a prototype unit with a disk rotating parallel to a circular membrane at speeds up to 1500 RPM. Three different membranes were used in the tests: two organic (nylon with 0.2 μm pores, PVDF with 40 kDa cut-off) and a mineral one (zirconium oxide, 0.1 μm pores). The system operates in the laminar boundary layer regime with a core fluid rotating at about 42% of the disk angular speed. The local permeate flux increases with increasing radius and is twice as large in the external ring as in the central part of the membrane within a 3 cm radius. With the nylon membrane at a speed of 1500 RPM, the permeate flux averaged over the total membrane area decays from 520 l/h m 2 at a Fe 3+concentration of 15 g/l to 250 l/h m 2 at 100 g/l, values which are much higher than those obtained with the same suspension in tubular membranes. With the zirconium oxide membrane which has a lower permeability, the permeate flux at a concentration of 9 g/l rises linearly with pressure and reaches 450 l/h m 2at 110 kPa, which is exactly the value given by hydraulic permeability, confirming the absence of fouling. A particular feature of this device is that the permeate flux actually rises when concentration increases up to 30 g/l because transmembrane pressure increases with suspension density and viscosity. This work confirms that dynamic filtration is well suited to the concentration of ferric hydroxide suspensions up to concentrations of 130 g/l.