pH Swing Research Articles

Exploiting the Phenomenon of Liquid-Liquid Phase Separation for Enhanced and Sustained Membrane Transport of a Poorly Water-Soluble Drug.

Recent studies on aqueous supersaturated lipophilic drug solutions prepared by methods including antisolvent addition, pH swing, or dissolution of amorphous solid dispersions (ASDs) have demonstrated that when crystallization is slow, these systems undergo liquid-liquid phase separation (LLPS) when the concentration of the drug in the medium exceeds its amorphous solubility. Following LLPS, a metastable equilibrium is formed where the concentration of drug in the continuous phase corresponds to the amorphous solubility while the dispersed phase is composed of a nanosized drug-rich phase. It has been reasoned that the drug-rich phase may act as a reservoir, enabling the rate of passive transport of the drug across a membrane to be maintained at the maximum value for an extended period of time. Herein, using clotrimazole as a model drug, and a flow-through diffusion cell, the reservoir effect is demonstrated. Supersaturated clotrimazole solutions at concentrations below the amorphous solubility show a linear relationship between the maximum flux and the initial concentration. Once the concentration exceeds the amorphous solubility, the maximum flux achieved reaches a plateau. However, the duration for which the high flux persists was found to be highly dependent on the number of drug-rich nanodroplets present in the donor compartment. Macroscopic amorphous particles of clotrimazole did not lead to the same reservoir effect observed with the nanodroplets formed through the process of LLPS. A first-principles mathematical model was developed which was able to fit the experimental receiver concentration-time profiles for concentration regimes both below and above amorphous solubility, providing support for the contention that the nanodroplet phase does not directly diffuse across the membrane but, instead, rapidly replenishes the drug in the aqueous phase that has been removed by transport across the membrane. This study provides important insight into the properties of supersaturated solutions and how these might in turn impact oral absorption through effects on passive membrane transport rates.

산 처리와 pH 조절을 이용한 사문석군 광물로부터 규소와 철산화물 회수 및 광물 탄산화 연구

The objectives of this study were to recover silica and iron oxides and sequestration using serpentine via various acid dissolution and pH swing processes. Serpentine collected from Guhang-myeon in S. Korea were mainly composed of antigorite and magnetite consisting of (45.3 wt.%), MgO (41.3 wt.%), (12.2 wt.%). Serpentine pulverized () and then dissolved in 3 different acids, HCl, , . Residues treated with acidic solution were recovered from the solution (step 1). And then the residual solution containing dissolved serpentine was titrated using . And pH of the solution increased up to pH

Continuous crystallization using a sonicated tubular system for controlling particle size in an API manufacturing process

A pH swing crystallization that was very sensitive toward scale-up and required specific equipment due to the non-Newtonian characteristics of the fluid, has been investigated using continuous crystallization (CC) as a means to improve particle size control, scalability and potentially reduce manufacturing cost. A sonicated tubular crystallizer was designed and shown to allow the pH swing crystallization to be operated robustly without blockage, to give a wide range of desired particle size. The results were compared with crystallization in a premixing semi-batch system and a simple addition semi-batch system under similar conditions. Interestingly, it was found that the sonicated tubular system was the only one of the three systems that gave the desired control for small particle size (1–7μm). Even though the productivity of the sonicated tubular crystallizer still needs to be increased to allow CC and numbering-up to become cost competitive with batch crystallization, we have demonstrated the potential of continuous tubular crystallization as a useful alternative method to conventional batch operation.

A low-cost flexible pH sensor array for wound assessment

The pH level in a chronic wound bed is a key indicative parameter for assessment of the healing progress. Due to fragility and inability to measure multiple wound regions simultaneously, commercial glass microelectrodes are not well-suited for spatial mapping of the wound pH. To address this issue, we present an inexpensive flexible array of pH sensors fabricated on a polymer-coated commercial paper (palette paper). Each sensor consists of two screen-printed electrodes, an Ag/AgCl reference electrode and a carbon electrode coated with a conductive proton-selective polymeric (polyaniline, PANI) membrane. Laser-machining is used to create a self-aligned passivation layer with access holes that is bonded over the sensing and reference electrodes by lamination technology. Characterization of the pH sensors reveal a linear (r2=0.9734) relationship between the output voltage and pH in the 4–10pH range with an average sensitivity of −50mV/pH. The sensors feature a rise and fall time of 12 and 36s for a pH swing of 8-6-8. The sensor biocompatibility is confirmed with human kertinocyte cells.

Extraction of l-Tryptophan by Hydroxyl-Functionalized Ionic Liquids

In this work, several hydroxyl-functionalized ionic liquids (ILs) were synthesized and used to extract tryptophan from the aqueous phase. The experimental results indicated that the hydroxyl-functionalized ILs presented better extraction ability than the dialkylimidazolium-based ILs. The extraction efficiency was significantly influenced by the pH of the aqueous phase. Moreover, the cationic form of tryptophan preferred to transfer into the IL phase, thereby suggesting a cation-exchange extraction mechanism. Driving forces of the extraction processes included hydrogen bonding, hydrophobicity, π–π stacking, and the screening effect. Among these factors, hydrogen bonding was the main parameter, as suggested by the results of thermodynamic analysis. After extraction, [C1C6OHim]NTf2 could be reused by using the pH swing effect. These findings demonstrate that [C1C6OHim]NTf2 is a good alternative to conventional solvents for recovering tryptophan from the aqueous phase.

A regenerable precipitant-solvent system for CO2 mitigation and metals recovery

This work describes a new resource engineering process for greenhouse gas control and metals recovery, and reports initial progress in its development. Central to this process is a regenerable solvent-precipitant system that enables pH-swing via a change in operational temperatures. In this particular contribution, various liquid-phase aliphatic tertiary amines and acids were examined to identify the suitable components that afford pH control between 10 and 2, deemed necessary for metal hydroxide precipitation and leaching metals from magnesium-bearing solids, respectively. Within the desired operational constraints (Tmax≤110°C, Pmax≤1bar, tmax≤2h), we found the triethylamine–sulphuric acid aqueous system (Et3N–H2SO4–H2O) has sufficiently covered the pH regimes of interest, affording a pH swing (at 25°C) between 10.5 and 1.9. Triethylamine (Et3N) provided the highest acid neutralising capacity of 7mol H+L−1 Et3N, capable of aqueous alkalisation to pH>10.5 (25°C, 1bar), and recoverable at ≤105°C (1.0bar) via fractional distillation. As for the acid component, H2SO4 allows for the formation of an acidic aqueous solution (pH 1.9, 25°C, 1bar) resulting from the partial liberation of Et3N from the acid-bound Et3N·H+ and HSO4− counter anion dissociation.

ChemInform Abstract: Carbon Dioxide Mineral Carbonation Through PH‐Swing Process: A Review

AbstractReview: 15 refs.

Modification of mesoporous silica magnetite nanoparticles by 3-aminopropyltriethoxysilane for the removal of Cr(VI) from aqueous solution

Silica magnetite nanoparticles (S-MNPs) as core were embedded in mesoporous silica shells by using cetyltrimethylammonium bromide (CTAB) as a surfactant. Then, the resultant mesoporous silica-magnetite nanoparticles (M-S-MNPs) were modified with 3-aminopropyltriethoxysilane (APTES) as a coupling agent in dry hexane solvent. APTES-grafted mesoporous silica magnetite nanoparticles (A-M-S-MNPs) were characterized by XRD, FTIR spectroscopy, EDX, TEM, elemental analysis, TGA/DTA technique. Results demonstrate that the obtained A-M-S-MNPs were nearly spherical in shape with 25 nm thick mesoporous silica shell. The adsorption behavior of the nanocomposite was examined in removing of Cr(VI) ion with concentrations 20, 30 and 50 mg/L at optimum pH level of 2. In this study a pH swing adsorption was observed too. The adsorption kinetic data were modeled using pseudo-second-order kinetics and intraparticle diffusion equations. The obtained results for intraparticle diffusion model show that the adsorption mechanisms are different in low and in high concentrations of Cr(VI) ion. According to the parameters of the Langmuir isotherm, the maximum adsorption capacity (qm) of A-M-S-MNPs for Cr(VI) increases as the temperature rises from 298 to 318 K. For better understanding of adsorption mechanism, quantum mechanical methods were applied. The results indicate that the electrostatic and hydrogen bond interactions between surface functional groups and HCrO4− ions have an important role in adsorption process. The easy separation from aqueous solution by an external magnetic field, rapid adsorption, regeneration, and reusability of A-M-S-MNPs are interesting points as an effective adsorbent for the removal of Cr(VI) ions.

Carbon dioxide capture and storage by pH swing mineralization using recyclable ammonium salts and flue gas mixtures

AbstractCO2 mineral sequestration through the employment of silicate rocks such as serpentine is an important technology for the mitigation of CO2 emissions. Most mineral carbonation works in this study use pure CO2. The indirect carbonation process employed different flue gases (5, 15, 25% CO2) and the presence of SOx and NOx. Also, the direct contact of CO2 with the Mg source was compared to the indirect reaction of Mg with CO2 as NH4CO3. The impact of variables such as temperature, solid‐liquid ration (S/L), and molar ratio of additives on carbonation rate and degree was studied. An average carbonation efficiency of about 90% was achieved at 80°C after 30 min for indirect mineral carbonation process. The carbonation efficiency decreased to 50‒60% when the process was directly employed. The carbonation efficiency obtained in the presence of 15‒25% CO2 was very similar to that with 100% CO2 at 140°C, while at 80°C, the carbonation efficiency in presence of flue gas (40‒55%) was much larger compared to that using pure C02 (10% after 3 h). SOx and NOx co‐removal efficiency was 54.4% and 18% at 140˚C and 20 bar, respectively.

PH-Controlled selection between one of three guests from a mixture using a coordination cage host.

We demonstrate the use of a simple pH swing to control the selection of one of three different guests from aqueous solution by a coordination cage host. Switching between different guests is based on the fact that neutral organic guests bind strongly in the cage due to the hydrophobic effect, but for acidic or basic guests, the charged (protonated or deprotonated) forms are hydrophilic and do not bind. The guests used are adamantane-1,3-dicarboxylic acid (H2A) which binds at low pH when it is neutral but not when it is deprotonated; 1-amino-adamantane (B) which binds at high pH when it is neutral but not when it is protonated; and cyclononanone (C) whose binding is not pH dependent and is therefore the default guest at neutral pH. Thus an increase in pH can reversibly switch the host between the three different bound states cage·H2A (at low pH), cage·C (at medium pH), and cage·B (at high pH) in succession.

Mineral carbonation of red gypsum via pH-swing process: Effect of CO2 pressure on the efficiency and products characteristics

The objective of this study was to investigate the feasibility of indirect carbonation of red gypsum through pH swing process. The effect of CO2 pressure as one of the major controlling parameters in carbonation process was investigated in details. The dissolution of red gypsum was performed using 2M H2SO4 at 70°C for 60min reaction time. The pH was regulated using NH4OH, which also precipitated out the impurities from the solution. Finally, the calcium rich solution was poured in an autoclave reactor and CO2 was injected into the reactor for carbonate precipitation. The experimental results showed that the Fe, the main impurity can be effectively separated prior to carbonation stage (92–95%). At low pH the Fe was separated while at high pH Ca was precipitated as carbonate. The carbonation efficiency was directly affected by the CO2 pressure and the maximum efficiency (100%) was achieved when 8bar CO2 pressure was used. In addition, carbonation experiments resulted in CaCO3 production in the form of calcite, aragonite, and vaterite with 98% purity.

Silicate rock dissolution by ammonium bisulphate for pH swing mineral CO2 sequestration

A wide range of mineral resources and different technical approaches can be employed to permanently sequester the CO2 into stable carbonates through mineral carbonation. The aim of this work was to investigate the dissolution and carbonation of olivine, pyroxene and amphibole-rich rocks using an ammonium salt pH swing mineral carbonation process. The effect of temperature (50, 70 and 100°C) and time (5, 10, 15, 30, 60, 120, 180min) and the dissolution kinetics were studied using a batch reactor at ambient pressure. Temperature had a direct effect on the rates of mineral dissolution reactions. The higher dissolution efficiency using olivine with particles 75–150μm was 77% in 3h at 100°C, with a limitation due to product layer diffusion with apparent activation energy of 31kJmol−1. The final CO2 sequestration efficiency using olivine was 70wt.%. Besides, only about 30% of Mg was extracted from pyroxene and amphibole at 100°C due to polymerisation of non-dissolved silica and deposition of sulphate minerals on their surface. Therefore, amphibole and pyroxene-rich rocks do not represent a resource for this process. Ammonia-based mineral carbonation could integrate geological storage where the last is not feasible and where CO2 emitters and olivine resources are closely co-located.

Carbon Dioxide Mineral Carbonation Through pH-swing Process: A Review

The promotion of carbon dioxide (CO2) reduction methods is due to the fact that the CO2 concentration has been increasing rapidly in 21st century. In order to prevent further damage of the environment caused by greenhouse gases, CO2 concentration should be stabilized by increasing CO2 fixation, which can reduce CO2 emission into the atmosphere. Mineral carbon sequestration or mineral carbonation is the process of utilizing minerals, mostly rich in calcium and magnesium (Ca/Mg) as the feedstock in reaction with CO2 to produce stable solid carbonates. Mineral carbonation through indirect pH swing process is a very effective method for producing calcium and magnesium carbonates. The Ca/Mg ions are extracted out of feedstock using suitable solvents at low pH condition and then in the second step the leached Ca/Mg ions are carbonated at elevated pH condition. In this paper the state-of-the-art of the carbonation involving pH swing method is updated.

CO2 Sequestration Using a Novel Na-salts pH Swing Mineral Carbonation Process

Abstract The main drawback of the indirect pH swing carbonation processes proposed so far is linked to the large amount of energy required to recycle the chemicals used to accelerate the reactions. The dissolution and carbonation steps of an alternative mineral carbonation pH swing process that employs sodium-based salts has been studied in order to minimize energy requirements typically associated to ammonium based mineral carbonation processes. The dissolution carried out at 70 °C using NaHSO 4 gave Mg extraction efficiency comparable to that of NH 4 HSO 4 with about 50% of Mg brought into solution as MgSO4. In addition, the carbonation experiments (90% efficiency) demonstrate that NaHSO 4 and NaOH can be used in a combined process to mineralize CO 2 . The feasibility of the other process steps and optimization of the dissolution and carbonation are discussed.

Performance Evaluation of Carbon Dioxide Sequestration in Oil Shale Fly Ashes

Abstract This work investigated the performance of oil shale fly ashes (OSFA) as feedstock for CO 2 mineral carbonation using an ammonium salts based pH swing process. A CO 2 uptake of 156 kg CO 2 /t ash was obtained for the OSFA from cyclones. This CO 2 uptake was similar to that previously obtained using a direct mineral carbonation process with less favorable process scale up conditions. Among pulverised fuel ashes, OSFA samples collected from the electrostatic precipitation tend to present lower CO 2 uptake compared to the OSFA sample obtained from the cyclones. OSFA from circulating fluidised beds were found to be less attractive for CO 2 sequestration process with ammonium salts.

Mass and Energy Balance of NH4-salts pH Swing Mineral Carbonation Process Using Steel Slag

A basic evaluation of the entire NH4-salts pH swing mineral carbonation process steel slag based system including CO2 capture, ammonia absorption and regeneration of additives, has been investigated to evaluate its feasibility at industrial scale. Heat released from mineral dissolution, pH adjustment and precipitation of impurities, carbonation reaction and CO2 capture was 2.3 MWh/tCO2 and could be recovered using heat exchangers and reused within the mineralization process to heat-up the incoming streams of steel slag, ammonium sulphate and water. Heat required, mainly from water evaporation and regeneration of additives, is reported to be 20 MWh/tCO2.

Mineral carbonation of PGM mine tailings for CO2 storage in South Africa: A case study

The ultra-fine milled tailings generated during the processing of PGM ores in South Africa have a theoretical potential to sequester significant amounts of CO2 (∼14Mt per annum) through mineral carbonation. Mg-bearing orthopyroxene is the major sequestrable mineral in these tailings, which also contains significant quantities of Ca-bearing plagioclase, as well as minor quantities of clinopyroxene, olivine, serpentine and hornblende. In this study, the feasibility of using PGM tailings to sequester CO2 has been investigated empirically using the two-step, pH swing method. The rates and extents of cation (Ca, Mg and Fe) extraction and subsequent carbonation were determined and compared. Both organic (oxalic and EDTA) and HCl solutions were utilised in the cation extraction step, which was conducted at time periods up to 8h and at a temperature of 70°C. The extents of cation dissolution were relatively low under all experimental conditions investigated, particularly for the case of Mg (between 3.3% and 5.0% extraction). A comparison of the extents of leaching with the mineralogical composition of the tailings indicated that the extracted Mg originated primarily from clinopyroxene, with the orthopyroxene remaining relatively inert under the experimental conditions. Subsequent carbonation of the acid leach solution after pH adjustment with NaOH resulted in the rapid formation of a number of carbonate minerals, including gaylussite (Na2Ca(CO3)2·5(H2O)), magnesite (MgCO3), hydromagnesite (Mg5(CO3)4(OH)2·4H2O), dolomite (CaMg(CO3)2), ankerite (Ca(Fe,Mg)(CO3)2), and siderite (FeCO3). On the basis of these findings, further studies will be focused on developing a better understanding of the factors affecting the dissolution of Mg-bearing orthopyroxene minerals, and on exploring alternative leach reagents and conditions, with a view to developing a more effective process for the accelerated carbonation of PGM tailings.

Separation of bisphenol-A by unimolecular micelles formed by pH-responsive polymer grafted onto polypropylene nonwoven fabrics

A novel pH-responsive random copolymer, prepared from equimolar concentrations of sodium 2-(acrylamido)-2-methylpropanesulfonate (NaAMPS) and sodium 12-methacrylamidododecanoate (NaMmD), formed a pH-responsive unimolecular micelle. The copolymer was grafted onto a polypropylene nonwoven fabric (PPNWF) by a plasma-initiated polymerization method. The formation of a unimolecular micelle of poly(NaAMPS-co-NaMmD) was observed to occur at a pH of around 9. Then, using the polymer-grafted PPNWF as a separation medium, the adsorption behaviors of bisphenol-A (BPA), which is a representative hydrophobic endocrine disruptor, were examined. The adsorption amount of BPA on the polymer-grafted PPNWF reached a maximum value at a pH of around 9, and it decreased significantly as the pH increased further. The reversible adsorption and desorption of BPA by the pH swing was achieved. Furthermore, it was found that the adsorption of BPA onto the polymer-grafted PPNWF occurred via encapsulation within the hydrophobic microdomains and adsorption on the pendent hydrophobic groups outside of the micelles by the hydrophobic interaction. The amount of BPA encapsulated within the hydrophobic microdomains in the micelles increased by changing the pH gradually.

Electrochemical CO2 Capture Using Resin-Wafer Electrodeionization

Energy-efficient capture of CO2 from power-plant flue gas is one of the grand challenges to reduce greenhouse gas (GHG) emissions. Current CO2-capture technologies are limited by parasitic energy loss, inefficient capture, and unfavorable process economics. We present a novel electrochemical method for CO2 capture from coal-fired power-plant flue gas. The method utilizes in-situ electrochemical pH control with a resin wafer electrodeionization (RW-EDI) device that continuously shifts the pH of the process fluid between basic and acidic in sequential chambers (pH swing). This pH swing enables capture of CO2 from flue gas in the basic chamber followed by release (recovery) of the captured CO2 (purified) in the acidic chamber of the same device. The approach is based on the sensitivity of the thermodynamic equilibrium of CO2 hydration/dehydration reactions over a narrow pH range. The method enables simultaneous absorption (capture) of CO2 from flue gas and desorption (release) at atmospheric pressure without heating, vacuum, or consumptive chemical usage. In other words, the method concentrates CO2 from ∼15% in flue gas to >98% in the recovery stream. To the best of our knowledge, this is the first experimental study focusing on simultaneous capture and release (recovery) of CO2 using an electrochemical method. We describe the method, the role of operating parameters on CO2 recovery, and advancements in process design and engineering for improved efficiency. We report on a method to enhance gas/liquid mixing inside the RW-EDI, which significantly increased CO2 capture rates. We also discuss the importance of using an enzyme/catalyst in enhancing the reaction kinetics. CO2 capture was observed to be a strong function of gas and liquid flow rates and applied electrical field. Up to 80% of the CO2 was captured from a simulated flue gas stream with >98% purity. The results indicate that a narrow pH swing from 8 to 6 (near-neutral pH) could offer a viable pathway for energy-efficient CO2 capture if the reaction kinetics are enhanced. Carbonic anhydrase enzyme enhances the reaction kinetics at near-neutral pH; however, the enzyme lost activity due to the instability at the operating conditions. This observation highlighted the necessity of robust enzymes/catalysts to enhance kinetics of CO2 recovery near-neutral pH.

Enhancing Mg extraction from lizardite-rich serpentine for CO2 mineral sequestration

Carbon capture and storage by mineralisation (CCSM) is a promising technology that sequesters CO2 from flue gases into stable mineral carbonates. Although the development of indirect pH swing processes (dissolution at acid pH and carbonation at basic pH) able to recycle the chemicals used are promising, there are still limitations in reaction rate of mineral dissolution being slow in view of a large deployment of the technology. The extraction of Mg from lizardite using magnesium bisulphate has been studied as a function of temperature, reagent concentration, solid to liquid ratio, thermal and mechanical pre-activation. Although the overall highest Mg extraction (95%) was obtained after 3h, the reduction of the dissolution time to 1h can consistently reduce the volumes to be treated per unit time leading to low capital costs in a hypothetical mineralisation plant. About 80% of Mg was extracted from lizardite in 1h at 140°C, 2.8M NH4HSO4, particles <250μm and a solid to liquid ratio of 100g/l. At 140°C, serpentine undergoes extensive structural modifications as indicated by XRD and FTIR analyses, producing amorphous silica and accelerating the kinetics of the reaction. Particles with diameter less than 250μm were obtained by grinding the lizardite at 925rpm for 10min consuming 33kWh/trock.