Foam Fractionation Column Research Articles

Theoretical analysis of the performance of a foam fractionation column.

A model system for theory and experiment which is relevant to foam fractionation consists of a column of foam moving through an inverted U-tube between two pools of surfactant solution. The foam drainage equation is used for a detailed theoretical analysis of this process. In a previous paper, we focused on the case where the lengths of the two legs are large. In this work, we examine the approach to the limiting case (i.e. the effects of finite leg lengths) and how it affects the performance of the fractionation column. We also briefly discuss some alternative set-ups that are of interest in industry and experiment, with numerical and analytical results to support them. Our analysis is shown to be generally applicable to a range of fractionation columns.

Study on Potato Protien Recovery by Batch Foam Separation

The feasibility of foam separation as a technique was assessed for the recovery of potato protein from the simulated potato processing waste effluent (SPWE). The effects of initial protein concentration, pH, air flow rate ,liquid loading volume on separation performance were examined by using a foam fractionation column with partial horizontally flowing foam phase. Based on the comprehensive consideration of effect on the enrichment ratio and the recovery percentage, the optimal conditions were initial protein concentration 0.5 g/L, initial pH 4.0, air flow rate 62.5 L/h ,liquid loading volume 200mL, Under the conditions, a greater enrichment ratio of the protein of 9.1 was obtained with a recovery percentage of the protein of 84.3%.The research are aimed at laying a foundation for the industrialization of recovering potato protein from the wastewater by foam separation.

Surfactant transport onto a foam lamella

A modelling study of surfactant evolution on a film surface coupled to lamellar film drainage has been carried out. This study simulates the surfactant transport onto a lamella in a foam fractionation column with reflux: such columns offer greater control over enrichment and recovery of the surface active material. Insoluble surfactant is assumed during the simulation as such surfactants potentially derive more benefit from a reflux system. There are two terms involved in the equation for surfactant flux which are the Marangoni flow – from the Plateau border to the centre of the lamella – and the film drainage – which is directed from the centre of the lamella to the Plateau border. The extent of film drainage is bounded using two extremal assumptions of mobile or rigid interfaces. On a mobile interface, the film drainage dominates the Marangoni effect, while on a rigid interface, the Marangoni effect is dominant. The numerical simulation was carried out using a material point method followed by a bookkeeping operation to regrid the film. Analytical solutions for the case of no drainage and for a (quasi) steady state in which Marangoni flows and drainage are balanced were used to verify the numerical simulation. From the simulations, it can be concluded that the film drainage obtained using surfactant with a mobile interface is much faster than that determined using surfactant with a rigid interface, meaning that surfactant tends to be washed out of the film in the mobile case. The desirable condition in a foam fractionation column is however where the Marangoni flow dominates the liquid drainage which can be achieved when using surfactant that gives a rigid interface. The (quasi) steady state solution verifies the simulation result at later time for the case of film with a rigid interface. An asymptotic solution in the case of film with a mobile interface gives a prediction of the surface concentration of surfactant at the centre of the film, but also predicts growing surfactant concentration gradients and growing Marangoni stresses near the film's edge, which may then invalidate model assumptions.

Kinetics of Chromium Ion Removal from Wastewater with Internal Circulation Foam Flotation

A new type of foam fractionation column with spiral internal had been designed for enhancing the foam drainage and thus for the removal of minute hazardous materials. Chromium was separated from wastewater using the continuous foam separation method. According to the similar physical behavior of foam separation and chemical reaction processes, the equivalent chemical reaction constant was introduced, Establishment concentrate distributed mathematical model of the whole tower under the condition of continuous foam separation with SDS as active agent. The model has been tested by experiments. The result indicated that foam separation process could be regarded as a first order reaction, and diffusion coefficient was 4.86cm2/s.

Recovery of Surfactant from an Aqueous Solution Using Continuous Multistage Foam Fractionation: Mixed Surfactant System

A continuous multistage foam fractionation column with bubble caps was used for surfactant recovery from mixed surfactant solutions containing polyethylene glycol tert-octylphenyl (OPEO10) and cetylpyridinium chloride (CPC) and the effects of air flow rate, foam height, and feed flow rate were investigated under a steady state of conditions. For the mixed surfactant system, the effect of synergism in the surfactant adsorption density was found. For separation efficiency, the total residual factor remained unchanged with an increasing feed molar fraction of OPEO10 (α), suggesting that the addition of OPEO10 does not increase the total separation efficiency. The residual factor of CPC increased with an increasing molar fraction of OPEO10 (α), while the residual factor of OPEO10 was lower for the mixed surfactant systems. A competitive removal was found in that the OPEO10 can compete with CPC for the bubble surface. The total separation factors and enrichment ratio of mixed surfactant systems were in-between the two single surfactant systems at a long foam residence time and, in contrast, showed antagonism at short foam residence. This is due to the difference in liquid entrainment in foam at long and short foam residence times.

Recovery of surfactant from an aqueous solution using continuous multistage foam fractionation: Influence of design parameters

A multistage foam fractionation column with bubble cap trays was used to recover a surfactant from water at low concentrations. The effects of design parameters—including the number of bubble caps, foam height, and tray spacing—were first investigated under steady state conditions using cetylpyridinium chloride (CPC) as the model surfactant. An increase in bubble caps per tray significantly increased the separation efficiency, both in terms of the enrichment ratio and recovery of the CPC and of the separation factor (ratio of foamate concentration to effluent concentration). The increase in bubble caps per tray also increased the foam production rate, leading to increasing the adsorptive transport. An increase in tray spacing increased both the enrichment ratio and the residual factor of the CPC, whereas the CPC recovery and liquid entrainment in foam were reduced. An increase in foam height produces drier foams, leading to decreasing bulk liquid transport.

Enhancing foam drainage using foam fractionation column with spiral internal for separation of sodium dodecyl sulfate

A new type of foam fractionation column with spiral internal had been designed for enhancing the foam drainage and thus for the removal of minute hazardous materials. The column without spiral internal was served as the comparison column, and an anionic surfactant sodium dodecyl sulfate (SDS) was used as the foaming solution. Effects of liquid loading volume, initial SDS concentration and superficial gas velocity on enrichment ratio and recovery percentage of SDS were investigated. The experimental results showed that the spiral column successfully enhanced the enrichment ratio of SDS by reducing countercurrent resistance between the rising bubbles and the entrained liquid of reflux. Enrichment ratio of SDS obtained by using the spiral column was 15.7, which was 2.5 times of that obtained by using the comparison column under the suitable operating conditions of liquid loading volume 0.4 L, initial SDS concentration 0.2 g/L and superficial gas velocity 1.7 mm/s.

Removal of trace Cd 2+ using continuous multistage ion foam fractionation. Part III—Effect of salt addition

In this study, a multistage foam fractionation column with 5 bubble-cap trays was used to remove cadmium (Cd) at a low concentration (mg/L) with sodium dodecyl sulfate (SDS) used to generate foam. The effects of anions (NO 3 −, Cl −, and SO 4 2−) and cations (Na +, K +, Mg 2+, and Ca 2+) were investigated by addition of sodium salts and nitrate salts, respectively. The addition of each studied cation was found to increase the residual factor of Cd (Cd concentration in effluent/Cd concentration in feed) due to the effect of the competitive adsorption of added counterions with Cd 2+ at the air–water interface of foam at a relatively high concentration of cation whereas, for all studied sodium salts, the residual factor of Cd decreased slightly with increasing counterion concentration at low concentrations. However, the added anions had a little effect. The effect of added cations and anions on the reduction of Cd removal are in the following order: Ca 2+ > Mg 2+ ≫K + > Na + and SO 4 2− ≈ Cl − > NO 3 −, respectively. The SDS recovery was found to increase significantly with increasing added salt concentration because the repulsion force among the head groups of SDS is greatly reduced by the co-adsorption of the counterions from added salt, leading to increasing SDS adsorption at the air–water interface of foam. The added salts of divalent cations were found to affect both Cd and SDS separation performance more than those of monovalent cations.

Removal of Trace Cd2+ Using Continuous Multistage Ion Foam Fractionation: Part II—The Effects of Operational Parameters

A multistage ion foam fractionation column with bubble-cap trays was employed to study the removal of cadmium ions from simulated wastewater having low Cd concentrations (10–30 mg/L), examining the effects of foam height, air flow rate, feed flow rate, and feed Cd concentration. Sodium dodecyl sulfate (SDS) was used to generate foam in this study. An increase in foam height, which reduces liquid hold-up in the generated foam, resulted in the enhancement of the enrichment ratios of both SDS and Cd while the removal and residual factor of Cd showed insignificant change. An increase in air flow rate increased the foam generation rate, foamate volumetric ratio, and the removal efficiency of Cd but decreased the enrichment ratios of both Cd and SDS. The separation factors of both Cd and SDS decreased with increasing feed flow rate, which is mainly attributable to both the effects of the enhancement of foamate volumetric ratio and the increases in both SDS and Cd input rates. An increase in feed Cd concentration was found to increase Cd effluent concentration and SDS removal but to decrease the enrichment ratios of both Cd and SDS because of the increasing liquid entrainment in the produced foam.

Comments on ‘Intensified Effect of Reduced Pressure on the Foam Fractionation Process of Bovine Serum Albumin’ of Wang et al.

A recent publication of a method for the intensification of the foam fractionation of a protein by reducing the pressure in the column is examined. It is demonstrated by invoking the original experimental results and by a theoretical analysis that the proposed method has no inherent advantage over a conventional foam fractionation column operated under normal conditions. Possible methods for valid process intensification are also discussed.

Process intensification of foam fractionation by successive contraction and expansion

Enrichment in foam fractionation is enhanced by reducing the liquid flux while maintaining the flux of bubble surfaces. We show that it is possible to do so in a continuous foam fractionation column by inserting a plate into the foam layer and forcing the foam through a narrower tube (foam riser) mounted at the centre of the plate. A 35% reduction in liquid flux was observed by using a single plate-foam riser assembly in a foam stabilised by 0.52 g/L sodium dodecyl sulphate solution, and the liquid rejected from the foam due to the presence of the foam riser had the same concentration as the feed solution. However, due to the nature of the adsorption isotherm of SDS, the enrichment enhancement measured in the experiments hererin was modest. The mechanism of the foam riser plate was explained by invoking recent theoretical studies on pneumatic foam. It was demonstrated that the reduction in liquid flux was affected by sudden expansion of the flow area causing a rejection of interstitial liquid to the top of the plate and extracted, whence it was recycled back to the feed. Preliminary experiments on the effect of liquid pool depth and foam height on interfacial adsorption were also carried out to demonstrate that the insertion of the plate does not affect the adsorption of the target substance to the bubble surface in the current system. It was found that equilibrium could be achieved within 0.2 m of liquid pool depth or foam height, however the equilibrium surface excess on a rising bubble in the liquid pool is roughly 51% of the equilibrium value on a quiescent interface, while that in the foam layer is roughly 73% of the equilibrium value on a quiescent interface.

Removal of trace Cd 2+ using continuous multistage ion foam fractionation: Part I—The effect of feed SDS/Cd molar ratio

In this research, a continuous multistage ion foam fractionation column with bubble-cap trays was employed to remove cadmium ions from simulated wastewater having cadmium ions at a low level (10 mg/L). In this study, sodium dodecyl sulfate (SDS) was used to generate the foam. An increase in feed SDS/Cd molar ratio enhanced the removal of Cd. However, the SDS concentration above a certain level resulted in wetter foams, leading to having a high volume of generated foam that lowered both the enrichment ratio and separation factor of the Cd. The SDS recovery tended to increase with increasing feed SDS/Cd molar ratio. The molar ratio of SDS/Cd in foamate was found to be close to the theoretical adsorption molar ratio of 2/1 on the air–water interface of foam when the system was operated at a feed SDS/Cd molar ratio in the range of 2/1–7/1. Ion foam fractionation has been demonstrated in this study to be a promising technique for high heavy metal removal (more than 99%) for a feed having a low heavy metal concentration in the ppm (mg/L) level.

Polarized light based scheme to monitor column performance in a continuous foam fractionation column

BackgroundA polarized light scattering technique was used to monitor the performance of a continuously operated foam fractionation process. The S11 and S12 parameters, elements of the light scattering matrix, combined together (S11+S12) have been correlated with the bubble size and liquid content for the case of a freely draining foam. The performance of a foam fractionation column is known to have a strong dependence on the bubble size distribution and liquid hold up in foam. In this study the enrichment is used as a metric, representative of foam properties and column performance, and correlated to the S11+S12 parameter.ResultsThree different superficial gas velocities (6.9, 7.5, and 10.6 cm/min) and four different pH values (4.8, 5.5, 6.5, and 7.5) are tested for the foam fractionation of a dilute solution of bovine serum albumin (0.1 mg/ml). As a result, at scattering angle of 125° the magnitude of S11+S12 is higher as the pH increases. When the bubble sizes are small with a larger liquid content, the foam is strongly back scattering resulting in lower values of S11+S12 (at 125°) at pH = 4.8. The light scattering data and the enrichment values are measured over a period of 90 minutes and correlated using a linear model. The predictive power of the model was found to be statistically significant.ConclusionThe time average S11+S12 shows a direct proportionality with the enrichment value, indicating that polarized light should be a valuable technique for monitoring foam fractionation columns. Additional knowledge of the nature of dependence between foam properties and S11+S12 combined with models relating the enrichment to the bubble size and liquid hold up is needed to develop an accurate diagnostics tool for monitoring enrichment utilizing S11+S12 measurements.

Enhanced foam drainage using parallel inclined channels in a single-stage foam fractionation column

A single-stage vertical foam fractionation column was investigated under continuous steady-state experimental conditions. Using a simple power-law expression to describe the drainage velocity through the foam, and in conjunction with continuity arguments, a theoretical framework was developed to analyse the performance of the vertical column. A reduction in the degrees of freedom in the analysis was achieved by using a fixed feed to gas flux ratio to promote a reasonably constant surfactant recovery. It was then possible to measure the process performance by determining the change in the level of enrichment produced from a change in the gas flux, and corresponding change in the feed flux. For a constant recovery, the enrichment is directly proportional to the volume reduction (defined as the ratio of the feed volume processed to foamate volume produced in a given time). The analysis was found to be consistent with experimental data and demonstrated the need to limit the gas flux, and hence the feed flux, to relatively low values in order to produce satisfactory volume reductions, and in turn achieve high enrichment. To overcome this processing constraint, three parallel inclined channels1 (PIC) were used to provide an effective increase in the vessel area, and hence facilitate the release of the entrained liquid within the foam. A significant increase in the volume reduction was obtained using the inclined channel arrangement. For the same processing rate, the PIC column achieved up to a 4 fold increase in enrichment compared to the vertical column. A slight decrease in recovery, however, was observed using the PIC column.

Determination of the liquid pool surfactant and protein concentration for semi-batch foam fractionation columns

Abstract - A model is derived for the change with time of the concentration of a surface-active component in the liquid pool of a semi-batch foam fractionation process. The transport of surface-active material to the gas-liquid interface was assumed to be limited by the mass transfer rates, and the concentration of the adsorbed material at the interface was assumed to be in equilibrium with the concentration of liquid adjacent to the bubble gas surface. This model was compared to experimental data obtained for semi-batch foam fractionation of aqueous solutions of bovine serum albumin and cetyltrimetylammonium bromide. Keywords : Foam fractionation; Proteins; Surfactant; Bubble column. INTRODUCTION Foam fractionation processes are based on the adsorption of a surface-active material at the gas-liquid interface originating in the introduction of a gas phase at the bottom of the liquid that contains the surfactant. The swarm of bubbles ascends in the liquid pool and produces a foam column on the top of the liquid. The foam that leaves the column, after transformed in liquid, will yield a solution with a higher surfactant concentration than the liquid pool due to the drainage of some of the liquid in the foam and the enrichment of solute at the gas-liquid interface. Since drainage is faster in a more unstable foam column, process efficiency increases with a decrease in surfactant concentration, provided that there is enough surfactant in the liquid to form foam. This factor enables use of the process to separate very dilute solutions of surface-active species where other processes are, in general, economically impractical (Brown et al., 1990). Proteins are surface-active materials that are found downstream of many processes in the dilute concentration regime therefore, foam fractionation techniques can be used either to recover the material or to reduce the amount of nitrogen in the wastewater before release. Some examples of this are the concentration of bovine serum albumin (Ahmad, 1975; Lalchev and Exerowa, 1981; Gehle and Schurgerl, 1984). For instance, lactoferrin is a protein found in human and bovine milk, tears, blood, and other secretory fluids that has been used to prevent infection with potential microbial pathogens by its ability to bind with iron

Modelling continuous foam fractionation with reflux

An equilibrium stage approach is taken to modelling the performance of a continuous foam fractionation column with reflux. Such an approach has been facilitated by recent developments in the understanding of pneumatic columns of foam that allow liquid rates within the rising column of foam to be predicted with confidence. It is shown that the recovery of surfactant into the product stream increases monotonically with increasing reflux ratio but this is at the expense of reduced product rate.

Batch production of biosurfactant with foam fractionation

AbstractMethods of producing the biosurfactant surfactin from cultures of Bacillus subtilis (BBK006) have been investigated. A reactor with integrated foam fractionation was designed and used in batch mode, and the performance compared with that of the same culture in shaken flasks. In the batch reactor, significant foaming occurred between 12.5 h and 14.5 h of culture time. During this period, the foam was routed through the foam fractionation column to a mechanical foam breaker, and a biosurfactant‐enriched foamate was collected. Concentration of surfactin in the foamate product was around 50 times greater than that in the culture medium. Using the integrated reactor, 136 mg L−1 of surfactin was produced, significantly more than was achieved in shaken flasks (92 mg L−1). The foam fractionation method allowed a real‐time measurement of the rate of surfactin production during growth. This showed that the maximum rate of production occurred at the interphase between log and stationary modes of growth, in contrast to previous work showing that surfactin is exclusively a secondary metabolite. The high value of surfactin yield in relation to biomass (YP/x = 0.262) indicated that surfactin was produced very efficiently by Bacillus subtilis (BBK006) in this integrated bioreactor. Copyright © 2006 Society of Chemical Industry

Removing Proteins from an Aerated Yeast Fermentation by Pulsing Carbon Dioxide: Replacing Salting-Out as a Method of Protein Precipitation

Salting-out is a common technique used for precipitating proteins and other materials from fermentation and tissue culture processes. It leaves a salt residue in the system. Foam fractionation can also be used to remove proteins by protein precipitation from a dilute solution. In doing so, there is usually a trade-off between enrichment and recovery. An increase in the airflow rate will increase the recovery, but only at the expense of the enrichment. A new method for increasing the recovery in foam fractionations and in yeast fermentations is to add a burst of CO2 to the process and then restore the air. This CO2 acts like a temporary salt, but it does not leave behind a residue. The recovery increases as a result of the joint use of these gases, perhaps by more than 10-fold, without sacrificing the enrichment. Chicken egg albumin in a foam fractionation column can serve as a simple, experimental model for the proposed recovery process in lieu of the fermentation process.

Development of a multistaged foam fractionation column

Surface active materials stabilise foam by adsorption at the gas/liquid interface. In foam fractionation, the foam is condensed to give a “foamate” liquid rich in surfactant. We have developed equipment and a process able to supply a number of stages of separation, working with an inert stripping gas. We have tested this with aqueous surfactant, and also with a surfactant which extracts and concentrates an organic solute. The measured liquid compositions are in good agreement with a model which describes the equilibrium using an adsorption isotherm, and which makes a mass balance for each stage in the column. The effect of liquid reflux is shown to be important. Possible applications of this process are in the fields of water purification and the recovery of components such as proteins from solution.

Variation of bubble size distribution in a protein foam fractionation column measured using a capillary probe with photoelectric sensors

Bubble size is used to characterize not only bubble-specific interfacial area but also bubble coalescence in a foam column. The bubble size distributions were obtained in a continuous foam fractionation process for concentrating ovalbumin using a developed photoelectric probe. When the continuous process reached steady state, the bubble size distribution pattern remained stable. Bubble size distribution data above (+1 cm) or below (−1 cm) the bulk liquid–foam interface showed symmetry along the diameter of the column (14 cm ID). The bubble size distribution was affected by the column wall. The nearly constant protein concentration distribution across the column cross-section indicated that the bubble flow distribution approached a flat profile across the column. A log-normal bubble distribution pattern best fit the weighted range of bubbles in the column at column lengths above and below the liquid–foam interface. These observations may prove to be useful in understanding the mechanisms underlying the foam fractionation of proteins.