Cationic Flocculants Carrying Hydrophobic Functionalities: Applications for Solid/Liquid Separation

Enhanced oil recovery using hyperbranched polyglycerol polymer-coated silica nanoparticles

Functionalized Fe₃O₄-SiO₂ magnetic nanoparticles (Fe-Si-MNPs) coated with hyperbranched polyglycerol polymer were prepared and tested for oil recovery from oil in water (O/W) emulsions. The structure, chemistry, and surface modifications of the newly developed demulsifier (PSiMNPs) were analyzed, and the percentage demulsification efficiency (%η_dem) was tested at differing concentrations of surfactant (C_sur), oil (C_oil), and demulsifier (D_PSiMNPs). The developed PSiMNPs can be separated from the solution by a magnetic field, regenerated using ethanol, and reused several times. The reported %η_dem was ≥80% for all the studied C_oil. The %η_dem improved as the C_sur and pH decreased, with maximum values of 98.8% and 98.5% achieved at C_sur = 0.05 g/L and a pH = 4, respectively. A D_PSiMNPs = 100 mg/L was sufficient to achieve %η_dem of 99.4% for C_oil = 100 mg/L and slightly decreased to ~93% for C_oil ~4000 mg/L. The PSiMNPs can be reused up to 15 times with a steady %η_dem of 89.1% for C_oil = 100 mg/L and 88.6% for C_oil = 4000 mg/L. The adsorption of oil on the PSiMNPs follows Freundlich isotherm with maximum adsorption capacity (q_max) of 192.8 g/mg and Langmuir constant (b) of 28.06 mg/L for C_oil = 900 mg/L. The q_max of the recycled PSiMNPs slightly decreased to 189.08 g/mg. The kinetic of oil recovery follows the PSO with a K₂ of 0.0169 g/mg. min. Surface modification of Fe-Si-MNPs enhanced the oil adsorption, increased the adsorption capacity, and extended the service life resulting in a better cost and process feasibility.

Interaction Mechanism of Anionic Lignin and Cationic Soft Surface in Saline Systems

Lignin has a complicated three-dimensional structure that is different from other synthetic and bio-based materials. In this work, we first examined the physicochemical behavior, i.e., apparent hydrodynamic radius (R_h) and ζ-potential, of carboxymethylated lignin (CM) in a saline system. Then, the detailed interaction and adsorption behavior of CM on a cationic poly(diallyldimethylammonium chloride) (PDADMAC)-coated surface were investigated in a saline system by a quartz crystal microbalance with dissipation. The theoretical and experimental adsorption data revealed that CM made limited surface coverage at a low salt concentration via charge neutralization following an intrinsic compensation mechanism. At a higher salt concentration, the adsorption of CM was improved significantly following the extrinsic compensation mechanism and nonionic interaction (e.g., hydrophobic interaction). The adsorption affinity of CM in the urea environment revealed the contribution (10-30%) of hydrogen bonding in the adsorption of CM on the PDADMAC surface. Contrary to what was found for the CM, the adsorption of a linear poly(acrylic acid-acrylamide) (PAM) on the PDADMAC surface exhibited a dramatic decrease at higher salinity, possibly due to the absence of nonionic and hydrophobic interactions between PAM and the surface. The findings of this study showed the superior adsorption performance of the lignin-based polyelectrolytes to the synthetic ones in salt-containing systems.

The Demulsification Properties of Cationic Hyperbranched Polyamidoamines for Polymer Flooding Emulsions and Microemulsions

Polymer flooding emulsions and microemulsions caused by tertiary oil recovery technologies are harmful to the environment due to their excellent stability. Two cationic hyperbranched polyamidoamines (H-PAMAM), named as H-PAMAM-HA and H-PAMAM-ETA, were obtained by changing the terminal denotation agents to H-PAMAM, which was characterized by 1H NMR, FT-IR, and amine possession, thereby confirmed the modification. Samples (300 mg/L) were added to the polymer flooding emulsion (1500 mg/L oil concentration) at 30 °C for 30 min and the H-PAMAM-HA and H-PAMAM-ETA were shown to perform at 88% and 91% deoil efficiency. Additionally, the increased settling time and the raised temperature enhanced performance. For example, an oil removal ratio of 97.7% was observed after dealing with the emulsion for 30 min at 60 °C, while 98.5% deoil efficiency was obtained after 90 min at 45 °C for the 300 mg/L H-PAMAM-ETA. To determine the differences when dealing with the emulsion, the interfacial tension, ζ potential, and turbidity measurements were fully estimated. Moreover, diametrically different demulsification mechanisms were found when the samples were utilized to treat the microemulsion. The modified demulsifiers showed excellent demulsification efficiency via their obvious electroneutralization and bridge functions, while the H-PAMAM appeared to enhance the stability of the microemulsion.

Study of Synthesis and Flocculation Properties of New Modified Hydrophobic Organic Polymer P(AM-DM-DMC12)

A new modified hydrophobic organic polymer P(AM-DM-DMC12) is synthesized by free radical polymerization of three monomers in aqueous solution using a REDOX initiator system. Its structure is characterized by FT-IR and 1H-NMR, the effect of reaction conditions on the product is studied, and the flocculation performance and mechanism are discussed with the aim of wastewater turbidity and COD removal rate. The results showed that the synthesized compounds accorded with the target structure, and the optimum synthetic conditions are as follows: the molar ratio of AM, DM, and DMC12 is 4 : 1 : 1, total mass fraction of monomer is 35%, the mass fraction of redox initiator is 0.06%, and the molecular weight of P(AM-DM-DMC12) is 1.02×107. Moreover, the flocculation effect of P(AM-DM-DMC12) is obviously better than that of PAM, and it has the advantages of short flocculation time, low dosage, and wide application range of pH and has a good industrial application value and prospect.

Polyamphoteric flocculants for the enhanced separation of cellular suspensions

The efficient concentration and separation of microorganisms from dilute culture suspensions is crucial to the success and productivity of many biotechnological processes. This article presents the design and characterization of polyamphoteric flocculants with a tunable, zwitterionic character for the enhanced separation of biocolloidal suspensions of yeast, wastewater, microalgae, and potentially other cellular systems. The polyamphoteric flocculants have overall molecular charges dependent upon the system pH, thereby providing a strong electrostatic attraction to the diverse but predominantly negatively-charged cellular surfaces of the biological suspensions. The polyamphoteric flocculants with tailored charge character are shown to have higher flocculation efficiencies than comparable cationic polyelectrolytes, and have an enhanced ability to 1) adsorb to the diverse range of charge character in cellular suspensions, 2) operate over an extended range of suspension pHs, and 3) operate at lower flocculant concentrations. These enhanced flocculation properties are shown to arise, perhaps counterintuitively, due to interactions between the negatively-charged functionality on the flocculant and the predominantly negatively-charged biocolloids.

STATEMENT OF SIGNIFICANCE

This article presents the design and characterization of polyamphoteric flocculants for the separations of biocolloidal suspensions of importance in the production of biopharmaceuticals, microalgal cultures for nutraceuticals and biofuels, and wastewater treatment. The polyamphoteric flocculants consist of tunable, mixed charges dependent upon system pH, thereby providing strong electrostatic attraction to the diversely-charged surfaces of cellular suspensions. Enhanced flocculation efficiencies are achieved, as compared to cationic polyelectrolyte flocculants, and result from the ability of polyampholytes to adsorb to a diverse range of charge character and operate over an extended range of pH conditions.

Destabilization dynamics of clay and acid-free polymers of ferric and magnesium salts in AMD without pH adjustment

The physicochemical treatment was employed to treat acid mine drainage (AMD) in the removal of turbid materials using clay only (exp A) and a combination of clay, FeCl3 and Mg(OH)2 (exp B) to form a polymer. A 5 g sample of clay (bentonite) was added to 1.2 L of AMD and treated in a jar test at 250 rpm for 2 min and reduced to 100 rpm for 10 min. A 200 mL sub-sample from the 1.2 L mother liquor was poured into five 500 mL glass beakers, and 20 mL dosages of a polymer of 0.1 M Fe(3+) in (FeCl3) and 0.1 M Mg(2+) in (Mg(OH)2) was added to the beakers. The samples were allowed to settle for 1 h, after which the supernatant was analyzed for pH, total suspended solids (TSS), dissolved oxygen (DO) and oxidation-reduction potential (ORP) (exp A). A similar set of experiments was conducted where 200 mL of the AMD sample was poured into 500 mL glass beakers and (20-60 mL) dosages of a combination of 5 g clay, 0.1 M Fe(3+) (FeCl3) and Mg(2+) (Mg(OH)2) polymer was added and similar mixing, settling time and measurements were conducted (exp B). The polymers used in exp A exhibited TSS removal efficiency (E%) which was slightly lower compared with the polymer used in exp B, above 90%. Clay has a high TSS removal efficiency in the treatment of the AMD, indicating that adsorption was a predominant process in exps A and B. The scanning electron microscope (SEM) micrographs of the AMD sludge of both exps A and B, with a rigid and compacted structure consisting of dense flocs surrounded by the smaller flocs bound together, corroborate the fact that adsorption is a predominant process.

Interactions between colloidal particles in the presence of an ultrahighly charged amphiphilic polyelectrolyte

A novel amphiphilic polyelectrolyte denoted as PAGC8 and a traditional amphiphilic polyelectrolyte denoted as PASC8 were prepared. PAGC8 consisted of gemini-type surfactant segment based on 1,3-bis (N,N-dimethyl-N-octylammonium)-2-propyl acrylate dibromide, while PASC8 incorporated acryloyloxyethyl-N,N-dimethyl-N-dodecylammonium bromide as single chain surfactant units within its repeat unit structure. Turbidity, stability, and zeta potential measurements were performed in the presence of PAGC8 and PASC8, respectively, to evaluate their effectiveness in inducing solid/liquid separations. It was found that the maximum transmittance was observed before the zeta potential values reached the isoelectric point, implying that not only charge neutralization but also charge-patch mechanism contributed to the separation process. Colloid probe atomic force microscopy technique was introduced to directly determine the interactions between surfaces in the presence of ultrahighly charged amphiphilic polyelectrolyte. On the basis of the AFM results, we have successfully interpreted the influence of the charge density of the polyelectrolytes on the phase stability. Electrostatic interaction played the dominant role in the flocculation processes, although both electrostatic interaction and hydrophobic effect provided contributions to the colloidal dispersions. The attractions upon surfaces approach in the case of PAGC8 were significantly larger than that of PASC8 due to the higher charge density. The strong peeling events upon retraction in the presence of PAGC8 implied that the hydrophobic effect was stronger than that of PASC8, which displayed the loose pulling events. A strong attraction was identified at shorter separation distances for both systems. However, these interactions cannot be successfully described by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloid stability due to the participation of charge-patch and strong hydrophobic effect. To account for the additional interactions, we proposed an extended DLVO empirical model to explain the non-DLVO forces in the systems. A reasonable physical model was also proposed to further describe the interactions between surfaces in the two amphiphilic polyelectrolyte systems.

Polyelectrolyte adsorption, interparticle forces, and colloidal aggregation

This review summarizes the current understanding of adsorption of polyelectrolytes to oppositely charged solid substrates, the resulting interaction forces between such substrates, and consequences for colloidal particle aggregation. The following conclusions can be reached based on experimental findings. Polyelectrolytes adsorb to oppositely charged solid substrates irreversibly up to saturation, whereby loose and thin monolayers are formed. The adsorbed polyelectrolytes normally carry a substantial amount of charge, which leads to a charge reversal. Frequently, the adsorbed films are laterally heterogeneous. With increasing salt levels, the adsorbed mass increases leading to thicker and more homogeneous films. Interaction forces between surfaces coated with saturated polyelectrolyte layers are governed at low salt levels by repulsive electric double layer interactions, and particle suspensions are stable under these conditions. At appropriately high salt levels, the forces become attractive, principally due to van der Waals interactions, but eventually also through other forces, and suspensions become unstable. This situation can be rationalized with the classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO). Due to the irreversible nature of the adsorption process, stable unsaturated layers form in colloidal particle suspensions at lower polyelectrolyte doses. An unsaturated polyelectrolyte layer can neutralize the overall particle surface charge. Away from the charge reversal point, electric double layer forces are dominant and particle suspensions are stable. As the charge reversal point is approached, attractive van der Waals forces become important, and particle suspensions become unstable. This behaviour is again in line with the DLVO theory, which may even apply quantitatively, provided the polyelectrolyte films are sufficiently laterally homogeneous. For heterogeneous films, additional attractive patch-charge interactions may become important. Depletion interactions may also lead to attractive forces and suspension destabilization, but such interactions become important only at high polyelectrolyte concentrations.

Destabilization of colloidal suspensions by multivalent ions and polyelectrolytes: from screening to overcharging

The destabilization of charged colloidal suspensions is studied in the presence of polyelectrolytes and the corresponding oligomers. Two different systems are investigated, namely, negatively charged particles in the presence of polyamines and positively charged ones in the presence of polycarboxylates. Multivalent oligomers of low valence destabilize the particles by screening according to the Schulze-Hardy rule. Polyelectrolytes induce destabilization by overcharging. Both regimes can be observed for oligomers of intermediate valence. The stability data of any valence can be rather well described by the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO), indicating that the interactions are mainly governed by van der Waals and electrostatic double-layer forces.

Influence of the degree of ionization and molecular mass of weak polyelectrolytes on charging and stability behavior of oppositely charged colloidal particles

Positively charged amidine latex particles are studied in the presence of poly(acrylic acid) (PAA) with different molecular masses under neutral and acidic conditions by electrophoresis and time-resolved dynamic light scattering. Under neutral conditions, where PAA is highly charged, the system is governed by the charge reversal induced by the quantitatively adsorbing polyelectrolyte and attractive patch-charge interactions. Under acidic conditions, where PAA is more weakly charged, the following two effects come into play. First, the lateral structure of the adsorbed layers becomes more homogeneous, which weakens the attractive patch-charge interactions. Second, polyelectrolyte adsorption is no longer quantitative and partitioning into the solution phase is observed, especially for PAA of low molecular mass.

Novel biodegradable flocculanting agents based on cationic amphiphilic polysaccharides

Flocculation properties of a series of cationic polysaccharides, with N-alkyl-N,N-dimethyl-N-(2-hydroxypropyl)ammonium chloride pendent groups attached to a dextran backbone, were evaluated in clay dispersions with respect to length of the alkyl substituent, molar mass, the charge density, and polycation dose. According to turbidimetric results, the alkyl chain length greatly influenced the optimum polymer dose as well as the width of the flocculation window since both increased from an ethyl to a butyl group and decreased for when octyl or dodecyl group was present. The residual turbidity values also varied with the charge density but no dramatic effect was observed with the molar masses investigated. These findings together with the negative value of the zeta potential at the optimum polymer dose and floc size measurements, point to contributions from both patch and bridging mechanisms for the flocculation process.

Electrostatic stabilization of charged colloidal particles with adsorbed polyelectrolytes of opposite charge

Repulsive electrostatic double-layer forces are responsible for the stabilization of charged colloidal particles in the presence of adsorbed polyelectrolytes of opposite and high line charge densities. This mechanism is revealed by studies of electrophoretic mobility and colloidal stability performed with dynamic light scattering as a function of the polyelectrolyte dose and the ionic strength for two different types of latex particles and four different types of polyelectrolytes. The dependence of these quantities is very similar for bare charged latex particles and the same particles in the presence of the different oppositely charged polyelectrolytes. Positively charged particles in the presence of anionic polyelectrolytes behave analogously to negatively charged particles in the presence of cationic polyelectrolytes.