Foam fractionation for the separation of SDBS from its aqueous solution: Process optimization and property test

https://doi.org/10.1016/j.seppur.2021.118305Get rights and content

Highlights

  • RSM was used to optimize the operation conditions of foam fractionation.

  • The molecular stability of SDBS in foam fractionation had been evaluated.

  • Surface activity and foam property of recovered SDBS solution were tested.

  • The repetitive separation of SDBS by foam fractionation was performed.

  • SDBS molecules were aggregated after repetitious adsorption and desorption.

Abstract

Foam fractionation is an adsorption bubble separation technique allowing recovery and immediate reuse of surfactants. This work was aimed at investigating the variations in recovery efficiency and physicochemical property of sodium dodecyl benzene sulfonate (SDBS) through multiple foam fractionation operation. First, a suitable SDBS concentration of 0.05 g/L was determined for preparing feeding solution. Subsequently, effects of volumetric air flow rate, height ratio of liquid phase and foam phase, and pore diameter of gas distributor on recovery efficiency of SDBS were investigated, respectively. Response surface methodology (RSM) was used to optimize the operating conditions of foam fractionation for separating SDBS. Under the conditions of volumetric air flow rate 80 mL/min, height ratio of liquid phase and foam phase 1:2, and pore diameter of gas distributor 0.180 mm, enrichment ratio and recovery percentage of SDBS were 134.83 ± 6.74 and 63.43 ± 3.17%, respectively. In repetitive separation experiments, the maximum separation number of recovered SDBS by foam fractionation was 3. Experimental results of surface activity and foam properties of recovered SDBS solution suggested that the interfacial adsorption and desorption processes had induced the structural transition and irreversible aggregation of SDBS molecules after multiple foam fractionation operation.

Introduction

Surfactants are a group of compounds with special amphiphilic molecular structure and they have been extensively used in the fields of washing, mining, petroleum exploiting, leather making and paper manufacturing, etc. The global market for surfactants is predicted to stand at USD 39.86 billion by 2021 [1]. According to diverse sources, surfactants can be divided into synthetic, natural-based and biological types. Due to the low cost (approximately $2 per kg) and good stability, synthetic surfactants hold over 75% of industrial consumption of all surfactants [2]. Wastewater analysis indicates that synthetic surfactants are the predominant organic contaminants in both concentration and frequency [3]. However, synthetic surfactants are difficult to be efficiently removed in sewage treatment plants because most of their constituents are non-biodegradable [4]. Once these surfactants are dispersed into environmental compartments, they can display detrimental effects on the survival of aquatic microorganisms (e.g., heterotrophic nanoflagellates and ciliates), degradation of other hazardous compounds (e.g., phenanthrene and pyrene) and breeding of amphibian organisms at a very low concentration [5], [6], [7], [8]. Moreover, the presence of synthetic surfactants in water may cause much damage to humans in the form of dermatitis, irritation and respiratory problems [9]. Many techniques had been proposed to eliminate synthetic surfactants from wastewater, involving flocculation, photocatalytic degradation, ion exchange and nano-filtration [10], [11]. Although these techniques have surfactant elimination capability, their popularity in application is limited by disadvantages, such as high operation cost, complex regeneration of substrate materials and easy secondary pollution.

Currently, foam fractionation has drawn considerable attention in the area of sewage treatment owing to its merits of simplistic device, mild operating conditions (inert gases and room temperature), free reagent consumption and large handing capacity [12]. This technique is a physical separation method employing bubbles as adsorbing media [13]. In a foam fractionation process, gas is injected in the solution for generating bubbles. Then, surfactant molecules with surface activity rapidly adsorb onto the gas-liquid interface of bubbles due to favorable thermodynamics [14]. This tends to lower the surface tension of the interface, thus producing a rising froth bed above the solution pool. As foam rises up in the column, entrained solution drains back along the Plateau borders and vertices due to gravity. Foam is collapsed to form a surfactant rich solution, called the foamate, when it is discharged out from the column. Obviously, foam fractionation process consists of three critical stages, including interfacial adsorption, foam drainage and foam collapse. Unlike other physical separation methods, foam fractionation allows for immediate reuse of both purified water and recovered surfactants [15]. At present, most researchers are mainly committed to improving surfactant elimination performance of foam fractionation through optimizing operating conditions and developing novel separation columns [16], [17]. However, on an industrial scale, entrepreneurs are more concerned about recovery and reuse of surfactant in terms of economic effectiveness and emission reduction. During foam fractionation, surfactant molecules would successively undergo interfacial adsorption and desorption processes, which easily induce structure transition. Bubble aging and coalescence could significantly affect adsorption capacity and arrangement state of surfactant molecules [18]. Moreover, the discharge of entrained solution from foam contributed to increasing the surfactant concentration in the foamate, even exceeding its critical micelle concentration (cmc). The self-association of surfactant molecules would prevent the decrease in surface tension of a solution [19]. These obstacles made the cyclic utilization and repetitive separation of surfactant even more challenging.

It had been well confirmed that protein molecules would suffer denaturation in foam fractionation because interfacial adsorption would induce the occurrence of molecular aggregation [20]. On the gas-liquid interface, the spatial structures of adsorbed protein molecules were partially unfolded in order to expose more hydrophobic groups. Once the interface disappeared, desorbed protein molecules were difficult to timely restore their original structures and they would be aggregated together via hydrophobic interaction. Aggregation phenomenon normally resulted in a large loss of protein functionality, especially catalytic activity of enzymes [21]. Compared to proteins, synthetic surfactants had lower hydrophile lipophilic balance and cmc values. Corti et al. (2000) had found that nonpolar hydrocarbon chains in synthetic surfactants had the trends to be stretched and gathered on the gas-liquid interface [22]. So far, there were not any references on reuse and separation properties of recovered synthetic surfactants by foam fractionation.

The objective of present work was to study the variations in recovery efficiency and physicochemical property of synthetic surfactant through multiple foam fractionation operation. As a model surfactant, sodium dodecyl benzene sulfonate (SDBS) was used due to its extensive industrial applications [23]. The cmc value of SDBS was 0.516 g/L [24]. Foam fractionation device was a normal vertical column. First, a suitable SDBS concentration in the feeding solution was determined to insure the smooth flow of entrained solution in foam. Subsequently, effects of volumetric air flow rate, height ratio of liquid phase and foam phase, and pore diameter of gas distributor on recovery efficiency of SDBS were investigated, respectively. Response surface methodology (RSM) was used to optimize the operating conditions of foam fractionation for separating SDBS. The repetitive separation of SDBS by foam fractionation was performed and property of recovered SDBS was tested.

Section snippets

Materials and reagents

SDBS (98% purity) was purchased from Shanghai Aladdin Biochemical Technology Co. Ltd., China. Pyrene (99%) was supplied from Tianjin Fengchuan chemical reagent Co. Ltd., China.

Determination of SDBS concentration

SDBS concentration of sample solution was determined by a spectrophotometer (752 N, Shanghai Precision Instruments, China) at a absorption wavelength of 223 nm. The linear-fitting equation was Y = 0.02883X + 0.0165, where Y and X are absorbance and SDBS concentration (0.005–0.025 g/L), respectively. Linear correlation

SDBS concentration

As seen from Fig. 2, the maximum liquid content of foam increased from 15.43% to 24.26%, and the liquid content half-life increased from 53 s to 224 s as SDBS concentration increased from 0.02 g/L to 0.10 g/L. A high SDBS concentration of feeding solution contributed to improving adsorption mass transfer of gas-liquid interface [26]. Before reaching saturation adsorption, the larger the surface excess of SDBS molecules was, the higher the liquid holding capacity of bubbles should get. The thick

Conclusion

In this work, the variations in recovery efficiency and physicochemical property of sodium dodecyl benzene sulfonate (SDBS) through multiple foam fractionation operation had been investigated. First, a suitable SDBS concentration of 0.05 g/L was determined for preparing feeding solution. The operating conditions of foam fractionation for separating SDBS were optimized by using RSM. Under optimal operating conditions of volumetric air flow rate 80 mL/min, height ratio of liquid phase and foam

Declaration of Competing Interest

None.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (No.21908041), Science and Technology Project of Hebei Education Department, China (No. QN2018079), Natural Science Foundation of Hebei Province, China (B2020202070) and Graduate Student Innovation Foundation of Hebei Province, China (CXZZBS2020039).

References (61)

  • R. Ghosh et al.

    Removal of trace hexavalent chromium from aqueous solutions by ion foam fractionation

    J. Hazard. Mater.

    (2019)
  • X. Li et al.

    Process intensification of foam fractionation by successive contraction and expansion

    Chem. Eng. Res. Des.

    (2011)
  • N. Li et al.

    Recovery of silk sericin from the filature wastewater by using a novel foam fractionation column

    Chem. Eng. Process.

    (2018)
  • K. Matsuoka et al.

    Removal of alkali metal ions from aqueous solution by foam separation method

    J. Mol. Liq.

    (2018)
  • N. Saravani et al.

    Influence of various process parameters on the biosorptive foam separation performance of o-cresol onto Bacillus cereus and Cetyl Trimethyl Ammonium Bromide

    J. Taiwan. Inst. Chem. E.

    (2016)
  • P. Basarova et al.

    Bubble adhesion onto the hydrophobic surface in solutions of non-ionic surface-active agents

    Colloid. Surface. A.

    (2016)
  • I. Barackov et al.

    Investigation of structural changes of β-casein and lysozyme at the gas–liquid interface during foam fractionation

    J. Biotechnol.

    (2012)
  • J.S. Lioumbas et al.

    Foam free drainage and bubbles size for surfactant concentrations below the CMC

    Colloid. Surf. A.

    (2015)
  • S. Sharaf et al.

    Global and local hydrodynamics of bubble columns–effect of gas distributor

    Chem. Eng. J.

    (2016)
  • R. Mohammadi et al.

    Extraction optimization of pepsin-soluble collagen from eggshell membrane by response surface methodology (RSM)

    Food. Chem.

    (2016)
  • M. Dastkhoon et al.

    Simultaneous removal of dyes onto nanowires adsorbent use of ultrasound assisted adsorption to clean waste water: chemometrics for modeling and optimization, multicomponent adsorption and kinetic study

    Chem. Eng. Res. Des.

    (2017)
  • S.J. Mousavi et al.

    Experimental design data for the zinc ions adsorption based on mesoporous modified chitosan using central composite design method

    Carbohyd. Polym.

    (2018)
  • G. Para et al.

    Surface activity of cationic surfactants, influence of molecular structure

    Colloid. Surf. A.

    (2010)
  • L. Martinez-Balbuena et al.

    Applicability of the Gibbs Adsorption Isotherm to the analysis of experimental surface-tension data for ionic and nonionic surfactants

    Adv. Colloid. Interface.

    (2017)
  • M. Terashima et al.

    Influence of pH on the surface activity of humic acid: micelle-like aggregate formation and interfacial adsorption

    Colloid. Surf. A.

    (2004)
  • L. Pineiro et al.

    Fluorescence emission of pyrene in surfactant solutions

    Adv. Colloid. Interface.

    (2015)
  • A. Chaudhuri et al.

    Organization and dynamics in micellar structural transition monitored by pyrene fluorescence

    Biochem. Bioph. Res. Co.

    (2009)
  • Q. Sun et al.

    Aqueous foam stabilized by partially hydrophobic nanoparticles in the presence of surfactant

    Colloid. Surf. A

    (2015)
  • J.K. Novev et al.

    Evaporating foam films of pure liquid stabilized via the thermal Marangoni effect

    Chem. Eng. Sci.

    (2017)
  • J. Wang et al.

    Effects of surface rheology and surface potential on foam stability

    Colloid. Surface. A.

    (2016)
  • Cited by (0)

    View full text