A CFD Model for Fluid Dynamics in a Gas-fluidised Bed

A modified particle bed model derived from the two-fluid momentum balance equations was employed to predict the gas-fluidised bed behaviour. Additional terms are included in both the fluid and the particle mo-mentum balance equations to take into account the effect of the dispersed solid phase. This model has been extended to two-dimensional formulations and has been implemented in the commercial code CFX 4.3. The model correctly simulates the homogeneous fluidisation of Geldart Group A and the bubbling fluidisation of Geldart Group B in gas-solid fluidised beds.     

The influence of cell adsorbent interactions on protein adsorption in expanded beds

Expanded bed adsorption (EBA) is a primary recovery operation allowing the adsorption of proteins directly from unclarified feedstock, e.g. culture suspensions, homogenates or crude extracts. Thus solid-liquid separation is combined with adsorptive purification in a single step. The concept of integration requires that the solid components of the feed solution are regarded as a part of the process, which influences stability, reproducibility, and overall performance. This aspect is investigated here at the example of the influence of presence and concentration of intact yeast cells (S. cerevisiae) on the adsorption of model proteins (hen egg white lysozyme and bovine serum albumin) to various stationary phases (cation and anion-exchange, hydrophobic interaction, immobilised metal affinity). The interaction of the cells with the adsorbents is determined qualitatively and quantitatively by a pulse response method as well as by a finite bath technique under different operating conditions. The consequence of these interactions for the stability of expanded beds in suspensions of varying cell concentration is measured by residence time distributions (RTDs) after tracer pulse injection (NaBr, LiCl). Analysis of the measured RTD by the PDE model allows the calculation of the fraction of perfectly fluidised bed (phi), a parameter which may be regarded as a critical quantity for the estimation of the quality of fluidisation of adsorbents in cell containing suspensions. The correlation between bed stability and performance is made by analysing the breakthrough of model proteins during adsorption from unclarified yeast culture broth. A clear relationship is found between the degree of cell/adsorbent interaction, bed stability in terms of the phi parameter, and the sorption efficiency. Only beds characterised by a phi value larger than 0.8 in the presence of cells will show a conserved performance compared to adsorption from cell free solutions. A drop in phi, which is due to interactions of the fluidised adsorbent particles with cells from the feed, will directly result in a reduced breakthrough efficiency. The data presented highlight the importance of including the potential interaction of solid feedstock components and the expanded adsorbents into the design of EBA processes, as the interrelation found here is a key factor for the overall performance of EBA as a truly integrated operation.     

Expansion and hydrodynamic properties of cellulose-stainless steel powder composite matrix for expanded bed adsorption

For better understanding the influences of solid phase properties on the performance of the expanded bed, the expansion and hydrodynamic properties of cellulose-stainless steel powder composite matrix with a series of densities was investigated and analyzed in an expanded bed. Two kinds of matrix particle diameter fractions, the small one (60-125 microm) and the large (125-300 microm), were used in the present work. In general, the expansion factors decreased obviously with the increase of matrix density. A linear relation between the mean density of matrix and superficial velocity at expansion factor of 2.5 was found for same series of matrices. The Richardson-Zaki equation could correlate the bed expansion and operation fluid velocity for all matrices tested. The theoretical prediction of correlation parameters (the terminal settling velocity U(t) and expansion index n) was improved with the modification of equations in the literature. The residence time distributions were investigated to characterize the hydrodynamic property in expanded bed. Compared with three evaluation factors (the height equivalent of theoretical plate, Bo number and axial distribution coefficient D(ax)), the results indicated that D(ax) is the best parameter to analyze the bed stability of expanded bed under various operation conditions and matrix properties. In addition, it was found that fluid velocity is the most essential factor to influence the hydrodynamic properties in the bed. A linear relation between the D(ax) and superficial fluid velocity for all matrices tested was established.     

Characterization and evaluation of a macroporous adsorbent for possible use in the expanded bed adsorption of flavonoids from Ginkgo biloba L.

The suitability of the use of macroporous adsorbent Amberlite XAD7HP in expanded bed adsorption processes for the isolation of flavonoids from crude extracts of Ginkgo biloba L. has been assessed. The expansion and hydrodynamic properties of expanded beds were investigated and analyzed. The bed expansion as a function of operational fluid velocity was measured and correlated with the Richardson–Zaki equation. Theoretical predictions of the correlation parameters (the terminal settling velocity u_t and exponent n) were improved by modifying equations in the literature. Residence time distributions (RTDs) were studied using acetone as a tracer. Three measures of liquid phase dispersion (the height equivalent of theoretical plate, Bodenstein number and axial distribution coefficient) were investigated and compared to values previously obtained with commercial EBA adsorbents developed for protein purification. A suitable bed expansion ratio was found to be 1.25 times the settled bed height, which occurred at a corresponding flow velocity of 183 cm/h. For an initial settled bed height of 42 cm, the mean residence time of liquid in the expanded bed was around 28 min. Under these flow conditions, the axial mixing coefficient D_ax was 7.54 × 10⁻⁶ m²/s and the Bodenstein number was 28; the number of theoretical plates (N) was 19 and the height equivalent of a theoretical plate (HETP) was 2.77 cm. Rutin trihydrate was used as a model flavonoid for the characterization of the adsorption properties of Amberlite XAD7HP. Adsorption was observed to reach equilibrium within 3 h with 70% of the adsorption capacity being achieved within 30 min. The estimated maximum equilibrium adsorption capacity for rutin was estimated to be 43.0 mg/(g resin) when the results were fitted to Langmuir isotherms. The adsorption performance was not seriously impaired by the physical presence of G. biloba leaf powders. Assessment of the kinetics of the adsorption of rutin revealed that the rate constant for adsorption was only reduced by 15% in the presence of leaf powders at a concentration of 50 mg/mL. The results demonstrated that Amberlite XAD7HP should be suitable for expanded bed adsorption of flavonoids from crude extracts of G. biloba L.     

Expansion and hydrodynamic properties of β-cyclodextrin polymer/tungsten carbide composite matrix in an expanded bed

The expansion and hydrodynamic properties of matrix are significant for expanded bed adsorption (EBA) processes. A series of new composite matrices CroCD-TuC are studied and estimated in an expanded bed. It is found that the heavier matrix is better suited for high operation fluid velocity than the lighters. Although the Richardson–Zaki equation can well correlate the bed voidage with fluid velocity for all CroCD-TuC matrices tested, the modifications are proposed to improve the accuracy of theoretical predictions of correlation parameters, including terminal settling velocity (U_t) and expansion index (n). Residence time distributions (RTDs) are determined, and the Bodenstein number (Bo) and axial dispersion coefficient (D_ax) are employed to analyze the liquid mixing in the expanded bed. It is found for CroCD-TuC matrices, both parameters notably changed with the variation of fluid velocity and viscosity. Furthermore, D_ax is an intuitive parameter estimating the bed stability on various operating conditions, and also a restriction on developing the matrix for high operation fluid velocity. The comparison of the hydrodynamic properties on different matrices reveals that CroCD-TuC 3 and CroCD-TuC 4 seem superior to other matrices in hydrodynamic properties, making them promising matrices for further use. The correlations as the functions of fluid velocity and viscosity have been established which may provide beneficial information for practical applications of CroCD-TuC matrices in EBA processes.     

Particle size and density distributions of two dense matrices in an expanded bed system

The size and density distributions of two commercial media, that is, Streamline particles and 6% agarose coated steel beads (6AS), in an expanded bed system has been studied with a glass column (26 mm I.D.) modified by side ports. The Streamline particles have a broad size distribution but a relatively uniform density, while the 6AS beads have both broad size and density distributions. The effect of liquid-phase flow velocity, liquid viscosity and settled bed height on the particle size and density distributions is investigated. It is found that the radial mean particle size and density of the two matrices are uniform, while axial classifications are obvious in the expanded beds. For the Streamline, the volume-weighted mean particle size decreases linearly with increasing expanded bed height. For the 6AS beads, however, the mean particle size is even in the axial direction, but the particle density decreases exponentially with the increase of bed height. Moreover, the mean particle size of the Streamline or the density of the 6AS beads is well expressed as a function of the normalized bed height (that is, the ratio of the distance from bed bottom to the expanded bed height). The liquid flow-rate, liquid viscosity and settled bed height influence the mean axial size or density distribution by affecting the expanded bed height.     

Adsorption Strategy of Plasmid DNA Nanoparticulate: Preparative Purification by a Simple Custom Expanded Bed Column

This paper summarizes the critical examination of the hydrodynamic performance of the NBG expanded bed contactor operated with streamline-DEAE adsorbent under various operating conditions for expanded bed adsorption of plasmid DNA nanoparticles from alkaline lysate. The purification process is not RNase-free. In this study, a rapid and efficient scaleable purification protocol obtaining, plasmid DNA nanoparticles (average size of 40 nm) with a high purity level for use as therapeutic agent in customized NBG expanded bed columns was developed. This technique allows efficient levels of binding to the column media and vector purification without centrifugation or filtration steps. Residence time distribution (RTD) studies were exploited to achieve the optimal condition of plasmid DNA nanoparticle (pDNA) recovery upon anion exchange adsorbent in this contactor. In addition, the purification experiments were carried out in the expanded bed columns with settle bed height of 6.0 ± 0.2 cm. NaCl gradient elution enabled the isolation of supercoiled plasmid from low-Mr RNA, cDNA and plasmid variants. Subsequently dynamic binding capacity of the adsorbent was calculated while these values decreased with increase in flow velocity. Moreover, the effect of pH upon the performance of this recovery process and the feedstock volume upon the expanded bed anion exchange purification was investigated. The results demonstrated that separation of low-Mr RNA from plasmid DNA isoforms in the range of pH between 5.5 and 7.5 is achievable in this column. The yield of recovery of pDNA in optimal condition was higher than 88.51% which was a superior result in one-pass frontal chromatography. The generic application of simple customized NBG expanded bed column and its potential for the purification and recovery of plasmid DNA as a nanoparticulate bioproduct is strongly discussed.     

Evaluation of new high-density ion exchange adsorbents for expanded bed adsorption chromatography

New adsorbents Q HyperZ and CM HyperZ composed of hydrogel-filled porous zirconium oxide particles were evaluated for expanded bed adsorption applications in the present work. The HyperZ adsorbents have wet density of 3.16 g ml(-1), particle size of 44.5-100.8 microm and average sphere diameter of 67 microm. The bed expansion as the function of flow velocity and fluid viscosity was measured and correlated with Richardson-Zaki equation. The suitable expansion factor was considered less than 2.5, while the corresponding flow velocity was about 450 cmh(-1). Liquid mixing in the bed was determined to evaluate the stability of expanded bed. The Bodenstein numbers tested were higher than 40 and the axial mixing coefficients (D(ax)) were between 0.5 and 9.7x10(-6)m(2)s(-1), which demonstrated that a stable expanded bed could be formed under suitable operation conditions. Bovine serum albumin (BSA) and lysozyme were used as model proteins to estimate the adsorption capacities of Q and CM HyperZ, respectively. The maximum equilibrium adsorption of Q and CM HyperZ could reach 45.7 and 27.2 mg g(-1) drained adsorbents, respectively. It was found that yeast cells had little influence on the adsorption capacities of the two adsorbents tested. The dynamic adsorption capacity of BSA at 10% breakthrough with Q HyperZ was 35.9 mg g(-1) drained adsorbent at flow velocity of 100 cm h(-1) for packed bed adsorption. The values for expanded bed adsorption were 34.4 mg g(-1) drained adsorbent at flow velocity of 200 cm h(-1), 33.6 mg g(-1) drained adsorbent at 300 cm h(-1) and 31.7 mg g(-1) drained adsorbent 400 cm h(-1). The results demonstrated that Q HyperZ and CM HyperZ are suitable for expanded bed adsorption of biomolecules.     

Pellicular expanded bed matrix suitable for high flow rates

A new type of expanded bed matrix with a heavy core of stainless steel covered with an agarose layer was prepared. Two bead size fractions, the smaller one (32-75 microm diameter) having a single particle core and the larger (75-180 microm diameter) with an agglomerate of stainless steel particles constituting the core, were chosen for further characterisation. The dispersion behaviour was determined both in packed bed and expanded bed modes by the retention time distribution method (RTD) and compared with the Streamline matrix (Amersham Pharmacia Biotech). The comparison turned out in favour of the new matrix. Flow rates as high as 3000 cm/h were used with the larger fraction, giving stable expanded beds with good mass transfer properties. The matrices were mechanically stable without any tendency to crack or peal, even after prolonged use.     

Influence of particle diameter distribution on protein recovery in the expanded bed adsorption process

The General Rate model has been developed and solved to describe protein adsorption in an expanded bed. The model takes into account axial and local variation of particle size distribution (PSD), external and intra-particle mass transfer resistances, and dispersion in liquid phase. The influence of PSD on breakthrough profiles has been analysed. The simulation results show that for a significantly high expanded bed the lower part of the breakthrough curve profiles, calculated for local particle size distribution (LPSD) and for axial average particle size distribution (APSD) are very similar. However, the upper part of breakthrough profiles calculated for LPSD approaches inlet concentration much more slowly than those calculated for APSD. The retention times of the lower part of uptake curves calculated with average particle diameter are constantly shorter than those obtained from LPSD. For the calculation of the dynamic capacity (DC), the LPSD can be replaced by APSD for large expanded bed heights. Using breakthrough profiles calculated for average particle size, DC values are constantly underestimated.     

一种球形纤维素/钛白粉扩张床吸附剂的研究--组成对性能的影响

采用反相悬浮再生法 ,以超细钛白粉颗粒作增重剂 ,包埋于纤维素骨架之中 ,经环氧氯丙烷活化后与二乙胺连接 ,制得一种球形扩张床吸附剂 .研究表明 ,吸附剂的密度、机械强度和孔结构可以随钛白粉用量的变化而改变 ;钛白粉颗粒的掺入有利于基质的活化 ,活化后环氧基含量可达 2 2 0 μmol mL .吸附剂具有良好的扩张床性能 ,扩张床中的蛋白质吸附行为与填充床中相似 ,吸附容量为 4 8 9mg牛血清白蛋白 mL吸附剂     

Affinity purification of proteins using expanded beds.

The use of expanded beds of affinity adsorbents for the purification of proteins from feedstocks containing whole or broken cells is described. It is demonstrated that such feedstocks can be applied to the bed without prior removal of particulate material by centrifugation or filtration thus showing considerable potential for this approach in simplifying downstream processing flow-sheets. A stable, expanded bed can be obtained using simple equipment adapted from that used for conventional packed bed adsorption and chromatography processes. Circulation and mixing of the adsorbent particles is minimal and liquid flow through the expanded bed shows characteristics similar to those of plug flow. Frontal analysis performed with the highly selective affinity system involving the adsorption of human polyclonal immunoglobulin G onto Protein A Sepharose Fast Flow indicate that the adsorption performance of the expanded bed is similar to that achieved when the same amount of adsorbent is used in a packed configuration at the same volumetric flow-rate. The adsorption performance of the expanded bed was not diminished when adsorption was carried out in the presence of intact yeast cells. Batch adsorption experiments also indicated that the adsorption characteristics of the affinity system were not greatly altered in the presence of cells in contrast to results from a less selective ion-exchange system. An expanded bed of Cibacron Blue Sepharose Fast Flow was used to purify phosphofructokinase from feedstock of disrupted yeast prepared by high pressure homogenisation without the need for prior removal of particulate material. The potential for the use of expanded beds in large scale purification systems is discussed.     

Expanded Bed Adsorption Chromatography for Recovery of Phycocyanins from the Microalga Spirulina Platensis

We carried out the purification of C-phycocyanin and allophycocyanin from Spirulina platensis taking advantage of the adsorption properties of the expanded beds. Initially, phycobiliproteins were released from the microalga cells by osmotic shock. Next, phycocyanins were recovered by applying the centrifuged cell suspension directly to the anion exchanger Streamline-DEAE using expanded bed columns, equilibrated with 50 mM sodium phosphate buffer, pH 7.0. After adsorption, washing was carried out in the expanded-bed mode. Having removed unbound proteins and cellular debris, the bed was allowed to sediment and phycocyanins rich solution was eluted with a downward flow of 500 mM sodium phosphate buffer, pH 7.0. Finally, we utilized conventional gel filtration and ion exchange chromatography methods for separation and purification of C-phycocyanin and allophycocyanin. The purification steps were monitored using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the purity of recovered phycocyanins was confirmed by absorption and emission spectroscopy. The main advantage of this new method is the high yield achieved in the steps of product extraction and adsorption by expanded bed adsorption, so reducing both processing times and costs.     

Transport properties of graphite/epoxy composites: Thermal, permeability and dielectric characterization

In this study nanocomposites were prepared by dispersing three different grades of graphite particles, expanded graphite, commercial graphene nanoplatelets and natural graphite, in a commercial epoxy matrix. Dielectric properties, thermal conductivity and permeability to oxygen of the composites were studied and compared to those of the unfilled epoxy matrix. An increase of all properties is obtained using expanded graphite, suggesting the presence of a good dispersion of the filler in the matrix and a strong polar interactions of the filler with the matrix, attributed to the partially oxidised surfaces of the expanded graphite. All the measured transport properties were fitted with simple mathematical models obtaining good agreement between the experimental results and theoretical predictions. The model parameters were related to the aspect ratio of the filler, defined as the ratio between the in-plane average dimension and the thickness of the reinforcement. An aspect ratio between 1250 and 1550 indicates that graphite thin platelets (or graphene stacks), characterized by a thickness of the order of a few tens of nanometers, were dispersed in the epoxy matrix.     

Nonlinear optical properties and excited-state dynamics of highly symmetric expanded porphyrins

A strong correlation among calculated Nucleus-Independent Chemical Shift (NICS) values, molecular planarity, and the observed two-photon absorption (TPA) values was found for a series of closely matched expanded porphyrins. The expanded porphyrins in question consisted of [26]hexaphyrin, [28]hexaphyrin, rubyrin, amethyrin, cyclo[6]pyrrole, cyclo[7]pyrrole, and cyclo[8]pyrrole containing 22, 24, 26, 28, and 30 pi-electrons. Two of the systems, [28]hexaphyrin and amethyrin, were considered to be antiaromatic as judged from a simple application of Hückel's [4n + 2] rule. These systems displayed positive NICS(0) values (+43.5 and +17.1 ppm, respectively) and gave rise to TPA values of 2600 and 3100 GM, respectively. By contrast, a set of congeners containing 22, 26, and 30 pi-electrons (cyclo[n]pyrrole, n = 6, 7, and 8, respectively) were characterized by a linear correlation between the NICS and TPA values. In the case of the oligopyrrolic macrocycles containing 26 pi-electron systems, a further correlation between the molecular structure and various markers associated with aromaticity was seen. In particular, a decrease in the excited state lifetimes and an increase in the TPA values were seen as the flexibility of the systems increased. Based on the findings presented here, it is proposed that various readily measurable optical properties, including the two-photon absorption cross-section, can provide a quantitative experimental measure of aromaticity in macrocyclic pi-conjugated systems.     

Macroporous copolymer matrix. IV. Expanded bed adsorption application

Macroporous crosslinked hydroxyethyl methacrylate-ethylene dimethacrylate copolymeric beads (HEG beads) were synthesized by suspension polymerization in the presence of a pore generating agent. These beads were coupled to alpha-cyclodextrin through a urethane spacer. These modified copolymer beads (affinity-HEG beads) so prepared were evaluated for their suitability in expanded bed chromatography. The optimum thickness of the distributor plate for stable expanded bed for use in expanded bed adsorption (EBA) was established. The affinity-HEG beads are comparable in density to Streamline diethyl amino ethane (DEAE) and exhibit better mechanical stability at higher superficial velocity under fluidization. The affinity-BEG beads were used as affinity chromatography matrices for the purification of cyclodextrin glycosyltransferase. Feeding of 5-fold diluted fermented broth to the column containing affinity-HEG beads of settled bed height 7.5 cm (I.D. 26 mm and length 42 cm) at double bed expansion resulted in a sharp breakthrough curve of alpha-cyclodextrin glycosyltransferase (CGTase). The adsorbed enzyme was eluted from the bed in 50 mM Tris-HCl buffer containing 10 mM CaCl2 at 25 degrees C in packed bed configuration.     

Variations of particle size and bed voidage distributions in expanded bed during transient operation processes

Changes in bed expansion are frequently encountered during an expanded bed adsorption, such as during the initial bed expansion, feed loading and washing processes. We have here studied the changes of local particle size distribution and bed voidage of an expanded bed in the initial bed expansion process as well as those during the changes in mobile phase viscosity, which imitated feed loading and column washing processes. Using a glass column modified with three side sampling ports and Streamline AC as the solid phase, experimental measurements on a series of operation moments during the transient processes were carried out by sampling the particles from within the column at different axial positions. In the initial bed expansion process, the gradual formation of an axial classification from a settled bed to a stable expanded bed was first displayed. By changing the mobile phase from water to 10% (w/w) glycerol solution or vice versa, the variations in both the particle size distribution and bed voidage corresponding to the increase or decrease of the bed height caused by the changes of the mobile phase viscosity were examined as well. The transient changes of the local particle size distribution and bed voidage first occurred in the bed bottom and then progressed from bottom to top along the axial direction. However, the changes of bed voidage at different axial positions were not unidirectional. That is, by changing the mobile phase to the high-viscosity glycerol solution, a constant increase of the bed voidage was observed in the bed bottom, while a distinct decrease of the bed voidage before its increase was involved at the middle and top positions. This is ascribed to the compression effect caused by the upward movement of the lower part particles.     

Particle circulation and oxygen mass transfer in an immobilized cell bioreactor

Two important considerations in the design of an aerobic particulate immobilized cell bioreactor are the provision of sufficient oxygen to maintain the desired metabolism of the immobilized organism, and the biomass holdup (which is proportional to the number of immobilized cell particles in the reactor). The Circulating Bed Reactor, a reactor developed for use with those forms of immobilization that result in particles of essentially neutral buoyancy, operates with an expanded bed of circulating particles. The particle number density attainable in such a reactor has been found to be dependent upon the circulation cell aspect ratio, the individual particle properties, the static bed voidage of the particles, and the superficial gas velocity. The oxygen mass transfer characteristics have been found to be dependent upon the circulatory nature of the system, the particle (solids) holdup, the particle porosity, and the superficial gas velocity.     

Evaluation of shock absorption properties of rubber materials regarding footwear applications

A challenge that faces the footwear market is the improvement of casual shoe comfort, being shock absorption one of the most significant properties for comfort. However, the methodologies available for the quantification of the shock absorption properties in materials for footwear applications are limited. With this work, an evaluation methodology of the shock absorption properties of rubber materials is proposed and the relationship between different test methods is established. Eight different commercial compact heeled rubber materials at six different thicknesses were prepared and characterized according to their physical and impact absorption properties. From the experimental values, the following correlations were defined: energy compression/hardness and energy compression/maximum deceleration. Shock absorption prediction curves were also determined from the experimental maximum deceleration values. Results present an excellent tool for industrial applications since they allow correlation of shock absorption properties and heel thickness, and also to predict the contribution of rubber material composition to the final product shock absorption properties.     

Immobilised metal affinity chromatography of beta-galactosidase from unclarified Escherichia coli homogenates using expanded bed adsorption

The development of an expanded bed process for the direct extraction and partial purification of beta-galactosidase from unclarified Escherichia coli homogenates using its natural affinity for metal loaded STREAMLINE Chelating is described. Small packed beds were used to determine the effect of chelated metal ion (Cu2+, Ni2+, Co2+ or Zn2+), loading pH and ionic strength on the selective binding capacity, and recovery of beta-galactosidase from clarified homogenates. An elution protocol was developed using the competitive displacer, imidazole, to recover beta-galactosidase in 87% yield and 3.4-fold purification. These results were then used to develop a separation for the recovery of beta-galactosidase from unclarified homogenates in a 2.5-cm diameter expanded bed. Although Ni2+ loaded STREAMLINE Chelating had a 5% dynamic capacity for beta-galactosidase of just 118 U ml(-1) (0.39 mg ml(-1)), the low capacity was thought to be due to the large size of the target (464,000) relative to the exclusion limit of the macroporous adsorbent. Despite this low capacity, Ni2 STREAMLINE Chelating was used successfully to recover beta-galactosidase from an unclarified homogenate in 86.4% yield and at 5.95-fold purification. The degree of purification relative to a commercial standard, as assessed using the purification factor and sodium dodecyl sulphate-polyacrylamide gel electrophoresis was high suggesting that this pseudo-affinity procedure compared favourably with alternative methods.