Surface adsorption and the effect of column diameter in the continuous foam separation process

Foam separation has been investigated as a technique for removing ethylhexadecyldimethylammonium bromide, a cationic surfactant, from dilute solutions. An ideal foam model has been used to determine the surface excess accumulated at the solution-air interface and to predict the foam and drain concentration in a continuous foam separation process. It was found that the model was valid only under conditions of good drainage and perfect foam stability. An increase in column diameter for a feed of constant composition and supplied at a constant rate increased the concentration of the surfactant in the overhead stream. This highly desirable effect was accompanied by an increase in the drain rate. The results indicate that an increase in column diameter had an entirely beneficial effect on the efficiency of the separation.     

Heat transfer in a continuous bubble column

The effective thermal conductivity k_e was measured for a continuous bubble column operating within the bubbly flow regime. k_e was found to be independent of liquid flow rate but strongly dependent on gas flow rate and physical properties of the liquid phase over the ranges 0.1>u_G>4 cm/s, 0>u_L>3.4 cm/s, 0.00096> μ >0.0028 kg/m μ s and 0.047 >σ>0.072 N/m.     

Development of bubble column for foam separation

The foam separation of metal in model wastewater is performed by using two different bubble columns in a continuous operation mode. The equipment and operation conditions are changed, and the foam flow rate and metal concentration in foam flow are measured. The foam flow ratio (the ratio of foam flow rate to the inlet one) increases with increasing gas velocity, with decreasing liquid velocity, with decreasing foam layer height and with decreasing metal concentration in model wastewater. Metal enrichment (the ratio of metal concentration in foam flow to that in inlet flow) shows the reverse tendencies. When a draft tube is inserted in the bubbling layer, the foam flow rate decreases. The enrichment is strongly governed by the foam flow ratio. Since the foam flow ratio is adjusted by means of the equipment and operation conditions, the metal concentration in foam flow is controlled to be a desired value. This paper was presented at The 5th International Symposium on Separation Technology-Korea and Japan held at Seoul between August 19 and 21, 1999.     

Cell and surfactant separation by column flotation

The separation of rehydrated Saccharomyces cerevisiae and an alkyl polyglycoside surfactant by column flotation was studied as a function of wash water flow and cation concentration. Separation of cells and surfactant was measured under steady-state conditions. Surfactant recovery in the foam concentrate was in the range of 86–95%. Yeast cells were enriched in the foam concentration by a factor of up to 11, but the recovery only reached 55%. The use of wash water was very effective for removing the cells from the foam, giving a good separation between the cells and the surfactant. Addition of chloride salts of Na, K, Ca, and Mg at concentrations in the range of 0.05-0.1 mol/L increased both the enrichment and the recovery of yeast in the foam. The most effective salt levels for cell flotation, less than 0.1 mol/L, were in the same range of concentration as the minimum electrophoretic mobility of the cells.     

The foam separation of colloidal ferric oxide with an anionic and a cationic surfactant

An experimental investigation is presented of the foam separation of colloidal ferric oxide over the pH range 3 to 12 by using an anionic and a cationic surfactant. A sol containing 1.67 mmole/ liter (93 mg/liter) of trivalent iron can be reduced in concentration to 0.09 mmole/liter by 0.17 mmole/liter dodecyl sodium sulfate (anionic) over pH 4.5 to 8; and to 0.18 mmole/liter by 0.17 mmole/liter ethylhexadecyldimethylammonium bromide (cationic) over pH 10 to 12. Soluble iron species produce poorer separations. Between pH 8 and pH 10 the charge of the colloid is reversed from positive to negative, and for an efficient separation a two-step process should be used, first with an anionic surfactant and then with a cationic. The charge of the particulates has little effect on the foam separation of the surfactants although the presence of the particulates has a significant effect, as evidenced by residual surfactant concentrations and collapsed foam volumes.     

Foam separation and precipitate flotation. The problem of surfactant recovery and reuse

An experimental investigation is presented on the recovery of cationic [dimethyl-benzyldodecylammonium bromide (DMBDA-Br)] and anionic [sodium dodecyl-benzylsulphonate (Na-DBS)] surfactants from foam separation and precipitate flotation concentrates. DMBDA-Br was recovered and reused fr m the concentrate of foam separation of perrhenates with recovery of over 90% by applying coacervation by potassium thiocyanate. Na-DBS was recovered and reused from the concentrate of precipitate flotation of copper hydroxide with recovery over 90% by applying precipitation with dodecylbenzylsulphonic acid from solution of concentrate dissolved in sulphuric acid at pH range from 1.0 to 2.5. Recovered surfactants were found efficient for subsequent flotation processes.     

Hydrostatic equilibrium in a foam column

Theoretical investigation into the hydrostatic equilibrium in a foam column revealed that the gravity syneresis of a foam, which causes the redistribution of the liquid along the column height, determines the tendency for the system to pass into the hydrostatic equilibrium state, in which the well-known relation between the pressures in the phases of the system and the capillary pressure is valid. The distribution of the liquid-to-foam density ratio along the foam column height was obtained, and factors affecting the limiting value of the equilibrium foam-column height were considered. The dependences of the column height on the liquid-to-foam density ratio and foam dispersity were derived. The condition was formulated under which the liquid will not drain from a hydrostatically equilibrated foam.     

Mathematical modeling of penicillin G Extraction by a bifunctional surfactant in a continuous extraction column

A bifunctional surfactant was used as a carrier of penicillin G for its continuous extraction by an emulsion liquid membrane without an extradant in a countercurrent extraction column of Oldshue-Rushton type. A permeation model was presented to describe transport mechanism of penicillin G in the continuous extraction system, including an axial dispersion model for the continuous phase and a mass transfer model for the dispersed emulsion phase. The mass transfer model describes the external mass transfer around the emulsion drop, the reaction at the external interface, the diffusion as well as the reaction equilibrium within the w/o emulsion drop, and the pH change of internal aqueous phase. Here, we considered three experimental variables: penicillin G concentration, pH of continuous phase and surfactant concentration. The calculated results from the permeation model fitted the experimental data well. This paper is dedicated to Dr. Youn Yong Lee on the occasion of his retirement from Korea Institute of Science and Technology.     

泡沫相塔壁对泡沫分离牛血清蛋白分离性能的影响

In order to enhance foam drainage, the column with an inner sleeve in the foam phase was designed for studying effect of the column wall of foam phase on foam separation performances using bovine serum albumin(BSA) as the research system. The effects of the wall on the liquid holdup out of the top column, bubble size, enrichment and recovery percentage were investigated. The results indicated that the experimental column with the inner sleeve decreased the liquid holdup, accelerated the coarsening and coalescence of bubbles and increased enrichment of BSA compared the contrasted column without the inner sleeve. Under the conditions of the initial concentration 0.2 g?L-1 of BSA, air flow rate 400 ml?min-1, the experimental column achieved up to a 2.06 fold increase in enrichment compared to the contrasted column. The enrichment of BSA increased with the increase of inner sleeve length. Channel theoretical analysis showed that the ratio of exterior channels to interior channels increased with the increase of bubble diameter. So the experiment column obtained the better performances at the lower concentration and the lower air flow rate. The better performances obtained by experimental column showed that the drainage rate of plateau borders on wall was greater than that of plateau borders between bubbles. So the inner sleeve provided more plateau borders on wall and improved foam drainage.     

胶原多肽基表面活性剂对染料废水的泡沫分离性能

以结晶紫溶液模拟染料废水,研究了胶原多肽基表面活性剂(CBS)对染料废水的泡沫分离性能。通过单因素实验考察了pH、气速、表面活性剂质量浓度、泡沫相与液相高度比(H_F/H_L)、染料初始浓度、乙醇添加量等因素对废水中染料分离的影响。结果表明,CBS适用于碱性条件下染料废水的泡沫分离;随着气速的升高,染料的去除率增加,但富集比降低;随着CBS用量的增加,染料的去除率先增加而后降低,富集比随CBS用量的增加而降低;当泡沫相高度与液相高度比为3左右时,染料去除率较高;添加适量的乙醇对泡沫分离是有利的;在较佳的分离条件下,染料的去除率可达80%,富集比达到16。上述研究结果表明,胶原多肽基表面活性剂可用于染料废水的泡沫分离。     

泡沫分离-Fenton氧化工艺处理表面活性剂废水

采用泡沫分离-Fenton氧化工艺进行处理某炼油公司含SDBS和Brij30废水,研究了气体流速、废水流速、塔内液体高度、pH和Fenton试剂用量对处理效果的影响。得到了优化后的工艺条件为:Fenton试剂用量0.05 mol/L,气体流速0.054~0.072 m3/h,分离塔内液体量为1.8~1.9 L,废水流速2.0~2.2 L/h,Fenton氧化处理pH=3~4。在此最佳工艺基础上进行了工业侧线实验,实验表明,采用泡沫分离-Fenton氧化工艺可将废水中SDBS和Brij30分别降至2 mg/L和5 mg/L以下。     

螺旋构件强化排液的泡沫分离塔用于牛血清蛋白分离

引言 泡沫分离技术又称泡沫吸附分离技术[1],是以气泡作为分离介质,利用被分离组分在气液两相界面吸附性质的差异进行浓缩溶液中表面活性组分.在泡沫分离过程中,通过空气分布器在泡沫塔液相中产生气泡,气泡沿着轴向向上流动,被分离表面活性组分吸附在气泡的气液两相界面上,当吸附接近平衡后,气泡离开液相,在液相上方形成泡沫相.     

Foam separation of complexed cyanide: Studies of rate and of pulsed addition of surfactant

An experimental investigation is presented of the foam separation of cyanide complexed with ferrous iron, using a cationic surfactant, ethylhexadecyldimethylammonium bromide. With a 25 min. foaming time, an initial iron to total cyanide ratio of 0·351:1 and an initial surfactant to complexed cyanide ratio of about 0·34:1 suspensions containing from 1·54 to 3·08 mM total cyanide can be reduced to about 0·11 mM in complexed cyanide and 0·29 mM in non-complexed cyanide. The rate of surfactant removal was satisfied by a first-order relationship, similar to that obtained with colloidal ferric oxide. The rate of complexed cyanide removal was satisfied by a reversible, approximately first-order relationship eliminating the residual surfactant concentration. The pulsed addition of surfactant in three dosages during the course of an experiment, compared with a single dose at the beginning of an experiment, produced lower residual concentrations of complexed cyanide and higher foam volumes. At an iron to total cyanide ratio of 0·351:1,90% of the complexed cyanide concentration could be removed by one fifth less surfactant, using pulsed addition, compared with a single dose.     

Foam fractionation of anions with a cationic surfactant: Orthophosphate

An experimental study has been conducted for the first time of the foam fractionation of orthophosphate using a cationic surfactant. For feed solutions 2.63×10⁻⁴ molar in phosphate and three surfactant concentrations, pH has a pronounced effect on residual concentrations of phosphate. A comparison with the ion flotation of dichromate and with the foam fractionation of phenolate shows dichromate flotation to be the most efficient.     

Efficient simulation of a separation column with axial diffusion and mass transfer resistance

The optimization of simulated moving bed systems is a complex task, and one of the difficulties is the lack of simulation methods that are sufficiently accurate and fast to be incorporated in the optimization algorithms. This paper presents a simulation of an adsorption column with finite differences based on a Lagrangian approach. The results obtained with this integration method were compared to values reported in the literature; the comparison shows that the accuracy of the integration method is not lower than that obtained with published methods and that this integration method requires a much lower cost in computation time. Various simulations were compared with experimental data for injections of caffeine and sodium 2-naphthalenesulfonate and with published results for the separation of isomers of omeprazole. The effects of axial diffusion and resistance to mass transfer on the elution curves were studied, and the simulation results were compared with the known theoretical analytical solution for a linear isotherm.     

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.     

Foam breaking — key process in detoxification of kraft mill effluents by foam separation

A study was undertaken to demonstrate on pilot plant scale the performance of a turbine foam breaking system and to develop the design parameters for large scale application. Among various configurations a 3-blade vaned-disc turbine was found to be optimal for foam breaking. Major process variables controlling foam breaking were system design, tip velocity, rotation speed, and foam load. A foam breaking system with only restricted liquid draw-off performed 3 - 16 times better than a conventional flow through system. A 38 cm diameter turbine operating at 1800 τ/min (3600 cm/s tip velocity) collapsed up to 1.2 m³/min (42 ft³/min) of foam. Design equations developed for sizing of foam breakers suggest that a 61 cm (2-ft) diameter 21 kW turbine will collapse 4.7 m³/min of foam. For a 95 × 10³m³/d foam separation plant, approximately 12 foam breakers are required. Capital costs are estimated at $108,000.     

连续式泡沫分离法去除废水中Cr~(3+)的研究

采用连续式泡沫分离法分离废水中的Cr3+离子。考察了废水的pH、表面活性剂的加入量、空气流量和反应时间对Cr3+的脱除率的影响,确定最佳的操作工艺条件为混合废水pH=6.0、空气流量350 mL/min、表面活性剂质量浓度为170 mg/L、反应时间为30 min,此时Cr3+的脱除率可达95.31%,浮选塔排出的残液中Cr3+的质量浓度0.5 mg/L,完全符合排放标准。     

Simultaneous treatment of dye wastewater and surfactant wastewater by foam separation: Experimental and mesoscopic simulation study

Foam separation for simultaneous removal of rhodamine B (RhB) and cetyl trimethyl ammonium bromide (CTAB)/sodium dodecyl benzene sulfonate (SDBS) from model wastewater was studied. The effect of the surfactant type, aeration rate, temperature, and initial pH on the removal efficiency and enrichment ratio of dye/surfactant were investigated. The results indicated that electrostatic attraction between the dye and surfactant have a great effect on the recovery of the dye and surfactant. The aeration rate has significant influence on the CTAB and RhB removal and enrichment, while the initial pH has a great effect on the RhB removal, but little effect on CTAB removal. Moreover, dissipative particle dynamics (DPD) was employed to simulate the interaction between the surfactant and the dye.     

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.