Dilute NaOH Solution Research Articles

Bio-Inspired phosphate adsorption by Copper-Decorated weak base anion exchanger

Hybrid-based phosphate adsorbents have high adsorption ability but are challenged with regeneration because of strong bonding. Inspired by phosphate-binding proteins (PBPs) which reached a trade-off between high adsorption and regeneration ability by binding phosphate species with multiple hydrogen bonds, a weak-base anion (WBA) exchange resin was decorated with Cu2+ ions to develop an alternative advanced phosphate adsorbent. Different from the role of metal species in the promoted adsorption of existing hybrid-based adsorbents, the Cu2+ ions mainly drove phosphate diffusion from the liquid to the resin and then induced the phosphate species to bond with multiple –NH2+/–NH groups. Such adsorption exhibited a high entropy (ΔS0 = 132.47 J/mol-K) and was highly exergonic (ΔG0 = -16.83 ∼ -20.14 kJ/mol). Moreover, it enhanced the phosphate selectivity because the driving force for the sorption process originated from the complexation. During the regeneration, the Cu2+-to-Cu-O- transformation could occur under weak alkaline conditions and repelled the adsorbed phosphate species to facilitate desorption. Therefore, the Cu-WBA resin not only exhibited high phosphate adsorptions (31.94 to 61.03 mg-P/g) and high competing-anion tolerance but also was successfully recovered with a diluted NaOH solution (0.05 N). Detailed adsorption behaviors under different pHs, temperatures, and interference of competing anions were examined, and the mechanisms were elucidated.

Assessment of pervaporative concentration of dairy solutions vs ultrafiltration, nanofiltration and reverse osmosis

Concentrating raw milk or semi-finished dairy products is an important step in dairy industry to produce milk powder or products enriched in certain components, or to reduce product volume and energy consumption during transportation. This study deals with pervaporative concentration of dairy solutions vs ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO). While the highest flux was observed with the UF, pervaporation (PV) exhibited almost complete retention of dairy solids. A decline in flux due to concentration polarization and membrane fouling was observed in all the membrane processes at different extents. The UF, NF and RO experienced severe flux declines at a dairy solid content above 16 wt%, while the flux decline in pervaporation was much less significant, even at a feed solid content as high as 40 wt%. Unlike UF, NF and RO where the external mass transfer resistance due to membrane fouling and concentration polarization dominated the overall mass transfer, pervaporative mass transport in dehydrating the dairy solutions was mainly determined by the membrane itself. The UF membrane suffered from irreversible fouling and the fouled membrane could not be fully cleaned even with a 0.1 M NaOH solution, whereas the fluxes in NF and RO could be restored significantly by rinsing the membrane surfaces with a dilute NaOH solution (0.1 mM). In pervaporation, the permeation flux was fully restored by a simple water rinse due to nonporous structure of the membrane and its hydrophilic surface.

Hydrogen bonding-orientated selectivity of phosphate adsorption by imine-functionalized adsorbent

• N C@CMPS was successfully grafted with imine group. • imine group can distinguish protonated phosphate from deprotonated competing anions. • imine group has stronger interaction force toward P(V) than that of amine group. • P(V) adsorption on N C@CMPS is slightly exothermic. • N C@CMPS can be repeatedly used for P(V) adsorption. The development of phosphate-selective adsorbents is essential for addressing eutrophication-associated problems and issues about lack of phosphorus resources. In this study an imine-functionalized adsorbent (N C@CMPS) was synthesized for this purpose; briefly, the commercially available precursor, chloromethylated polystyrene adsorbent (CMPS), was grafted with ethylenediamine (EDA) to yield the intermediate (EDA@CMPS), which was subsequently subjected to synchronous elimination to yield the product with imine functional group (N C@CMPS). Spectroscopic analyses and macroscopic experiments were then employed to evaluate the as-prepared adsorbent. As compared with CMPS, EDA@CMPS, and two commercial amine-based adsorbents, N C@CMPS exhibited much higher adsorption capacity and selectivity toward phosphate [P(V)]; such improvement can be primarily attributed to the imine group of N C@CMPS and their difference in the acid-base property. The imine group, acting as the recognition unit to distinguish P(V) from background anions, can solely serve as H-bond acceptors and exclusively interact with the protonated P(V) species (H 2 PO 4 - and HPO 4 2- , H-bond donors) under neutral pH but not with the deprotonated anions such as Cl - , NO 3 – , and SO 4 2- . the thermodynamic parameters confirm the spontaneous and slightly exothermic nature of P(V) adsorption on N C@CMPS, according with the domination of hydrogen bonding interactions. N C@CMPS also exhibited very broad applicability for P(V) adsorption over a wide range of pH (3 ∼ 10). Furthermore, the exhausted N C@CMPS can be efficiently regenerated with the combination of dilute NaOH solution and dilute HNO 3 solution for repeated use.

Removal of sulfanilamide by tailor-made magnetic metal-ceramic nanocomposite adsorbents

Three tailor-made magnetic metal-ceramic nanocomposites, obtained from zeolite A (ZA1 and ZA2) and a natural clinoptilolite (LB1), have been used as adsorbents to remove sulfanilamide (SA), a sulfonamide antibiotic of common use, from water.A patented process for the synthesis of nanocomposites has been suitably modified to maximize the efficiency of the SA removal, as well as to extend the applicability of the materials.The role played by the main process parameters (kinetic, pH, initial concentration of SA) has been characterized. The significant effect of the pH on the SA removal has been explained identifying two possibly coexisting mechanisms of SA adsorption, based on polar and hydrophobic interactions, respectively.The adsorption kinetics have been in all cases described by the pseudo second-order model. The adsorption isotherms obtained with ZA1 have been satisfactorily described by the Langmuir model, suggesting a monolayer adsorption of SA on the magnetic nanocomposites resulting from a uniform surface energy. The isotherms obtained with LB1 could be described by a more complex approach, deriving by the additive superposition of Langmuir and Sips models.In order to ensure an effective removal of the antibiotic and a proper recycle of the magnetic adsorbents, a sustainable regeneration procedure of the exhausted adsorbent has been developed, based on the treatment with a dilute solution of NaOH.

Enhanced phosphate removal with fine activated alumina synthesized from a sodium aluminate solution: performance and mechanism.

Fine activated alumina (FAA) acting as an adsorbent for phosphate was synthesized from an industrial sodium aluminate solution based on phase evolution from Al(OH)3 and NH4Al(OH)2CO3. This material was obtained in the form of γ-Al2O3 with an open mesoporous structure and a specific surface area of 648.02 m2 g−1. The phosphate adsorption capacity of the FAA gradually increased with increases in phosphate concentration or contact time. The maximum adsorption capacity was 261.66 mg g−1 when phosphate was present as H2PO4− at a pH of 5.0. A removal efficiency of over 96% was achieved in a 50 mg L−1 phosphate solution. The adsorption of phosphate anions could be explained using non-linear Langmuir or Freundlich isotherm models and a pseudo-second-order kinetic model. Tetra-coordinate AlO4 sites acting as Lewis acids resulted in some chemisorption, while (O)nAl(OH)2+ (n = 4, 5, 6) Brønsted acid groups generated by the protonation of AlO4 or AlO6 sites in the FAA led to physisorption. Analyses of aluminum-oxygen coordination units using Fourier transform infrared and X-ray photoelectron spectroscopy demonstrated that physisorption was predominant. Minimal chemisorption was also verified by the significant desorption rate observed in dilute NaOH solutions and the high performance of the regenerated FAA. The high specific surface area, many open mesopores and numerous highly active tetra-coordinate AlO4 sites on the FAA all synergistically contributed to its exceptional adsorption capacity.

Facile preparation of reduced graphene oxide for removing tetracycline from water: Kinetics and thermodynamics studies

ABSTRACT In this study, reduced graphene oxide (rGO) was successfully produced from graphite precursor by chemical oxidation and exfoliation processes that were followed by a reduction process under mild conditions. SEM/EDX, XRD, FT-IR, BET, pHpzc were conducted to characterize the as-synthesized materials. Impacts of different factors such as contact time, temperature, pH of the solution, adsorbent load, and tetracycline (TC) concentration on TC removal efficiency were examined. Furthermore, the adsorption kinetics, thermodynamics, and isotherms were also investigated. As the result, the adsorption process of TC onto rGO was spontaneous, endothermic, and governed by both physisorption and chemisorption. The maximum uptake calculated from the Langmuir isotherm model was 58.03 mg/g. rGO material could be regenerated by using methanol and diluted NaOH solutions. The findings in this work provided complete data on the TC adsorption process onto rGO and the process of the recovery and reuse of rGO.

Micro-networked metal coating using self-cracked WO3 inorganic thin film as sacrificial layer: Application to transparent flexible electrodes

A method of fabricating a micro-networked metal electrode using a self-cracking WO3 oxide thin film as a sacrificial layer is presented. The width of the formed crack can be adjusted to a size of 10 to 40 µm by adjusting the wet-etching time in dilute NaOH solution, and accordingly, the electrical conductivity and transmittance of the electrode can be adjusted. An electrical conductivity of approximately 100 Ω/sq was measured at an average transmittance of 95.6% in the visible light region, and when applied to a flexible substrate, the electrical resistance was maintained stable even with repeated bending tests. The method proposed in this study can be applied to various transparent flexible electrode devices.

Toward rational design of ceramic coatings generated on valve metals by plasma electrolytic oxidation: The role of cathodic polarisation

Plasma electrolytic oxidation (PEO) has attracted significant attention as a promising eco-friendly technology for the deposition of ceramic-like oxide coatings with superior wear- and corrosion resistance as well as biomedical, catalytic, magnetic, dielectric and optical properties. However, the industrial implementation of PEO has been hindered by a poor understanding of the mechanisms underlying plasma-assisted electrochemical coating formation. This study compares the characteristics of PEO processes on different valve metals in a dilute aqueous solution of NaOH and Na2SiO3 under pulsed unipolar and bipolar polarisation conditions. The focus is given to the influence of the nature of the valve metal on the transition to the soft sparking regime characterised by reduced energy consumption whilst yielding sintered coating materials enriched with crystalline phases. In-situ dynamic voltammetry analysis was employed to study the effects of the net current ratio and local negative charge injection using diagnostic pulses embedded in the polarisation signal. It has been demonstrated that soft sparking is a characteristic feature of valve metals such as Mg, Al, Zr and Ta that form insulating surface oxides with negligible electronic conductivity, whereas Ti and Nb form semiconducting oxides, which do not exhibit a characteristic voltage drop, although some features of spark softening were detected. This generalisation paves a way for implementation of a model known as ‘digital twin’ to the rational design of the PEO processes for deposition of the functional ceramics.

Removal of Trace Aluminum Impurity for High-Purity GdCl3 Preparation using an Amine-Group-Functionalized Ionic Liquid

Aluminum, as an associated metal with rare-earth resources, is a common impurity in rare-earth separation products. In the traditional P507-kerosene-HCl system, tremendous aluminum impurity (8875 mg/L herein) is often enriched in GdCl3 solutions because of the similar extraction sequence during rare-earth separation. In this work, a new amine-group-functionalized ionic liquid (IL) was developed to remove trace aluminum impurity from high-purity GdCl3 solutions, overcoming the drawbacks of strong hydrophilicity and complicated compositions of the organic phase, as well as other impurities introduced and tremendous saline wastewater produced inevitably. Methyltrioctylammonium hydroxide (N1888OH), instead of the water soluble ammonium hydroxide (NH4OH), was used to dissociate the dimer of sec-octylphenoxy acetic acid (CA12) and synthesize cation- and anion-bifunctionalized IL [N1888][CA12]. The separation factor of Al/Gd was as high as 36. The influences of pH, salting-out agent, extraction time, temperature, and stripping efficiency on the extraction efficiency were evaluated. The result showed that high-purity GdCl3 solution was obtained with low aluminum impurity of 10 ppm after five-stage countercurrent extraction. Due to the weak interaction between the metal and IL, very dilute HCl solution (0.07 mol/L) and NaOH solution (0.07 mol/L) were in favor of metal stripping and IL regeneration.

The adsorption of lemon yellow dye using cationic cellulose fibers from rice straw as a sustainable biosorbent in aqueous media

A biosorbent was prepared from the cellulose fibers found in rice straw through cationic modification. The effects of the dosage, pH, contact time, and initial concentration of lemon yellow dye were explored. The static adsorption results showed that cationic modification drastically improved the adsorption capacity of straw cellulose fiber. The maximum equilibrium adsorption capacity value was 137.6 mg/g and the highest removal reached 99%. The pseudo-second-order kinetic model was a good fit for the adsorption process, together with the Langmuir isotherm model. The adsorption reaction was spontaneous, and the adsorption process was an exothermic reaction, which was shown by the thermodynamic model. As the adsorption time became longer, the effluent concentration became larger until reaching equilibrium. The time was 420 min. After desorption using a dilute NaOH solution, the maximum adsorption capacity was still 36.1 mg/g and the maximum removal still reached 36.2%. The parameters calculated from the Yoon-Nelson model have a good fit with the experimental data. In short, cationic straw cellulose fiber is an effective and easy to prepare biosorbent. This work offers a new method for dye wastewater purification and solves the effective utilization of rice straw resources.

Preparation and characterization of curdlan with unique single-helical conformation and its assembly with Congo Red

Elucidating the structure-activity relationship of curdlan is hampered by a lack of characterization with unique specific conformations (i.e., single- or triple-helix). In this study, single-helical curdlan is generated in dilute NaOH solutions at 35−50 °C, and characterized with NMR, SAXS, and GPC. The conformational transition from coil to single-helix and the intramolecular hydrogen bond interaction are explored using NMR. It is found that the two aforementioned types of curdlan interact with Congo Red in very different ways. Single-helical curdlan can encapsulate Congo Red to form a stable, supramolecular dye assembly, which is demonstrated by the shortest distance between the H3 of curdlan and the phenyl groups of Congo Red, and also the same self-diffusion coefficients of Congo Red and curdlan. In contrast, random-coil curdlan interacts weakly with Congo Red and cannot enwrap it. This study offers insight into the specific structure-activity relationship of beta-(1,3)-glucans.

Desulfurization scrubbing in a squared spray column for a 720 kW marine diesel engine: Design, construction, simulation, and experiment

Square-shaped absorption towers are compact and provide high volumetric efficiency, enabling the installation of closed-loop flue gas desulfurization (FGD) in limited spaces of a ship. For FGD processes, diluted sodium hydroxide (NaOH) has been considered as a viable absorbent. Thus, a square-shaped scrubber with square spray nozzle distributor using a diluted NaOH solution was proposed for marine sulfur oxides removal, aiming to reduce volume/space, weight, pressure drop, investment, and operating and maintenance costs while increasing efficiency. A systematic methodology for the square-shaped FGD design was proposed, experiments to treat the flue gas released from a marine diesel engine (720 kW) were performed, and simulation and sensitivity analyses were conducted using Aspen Plus V10. Good agreement was observed between experimental and simulated results. A liquid-to-gas mass ratio of approximately 4.32 kg.kg−1 provided SO2 removal efficiency higher than 95 %. Most part of mass and heat transfers occurred in the bottom section of the scrubber and a low pressure drop was achieved.

Construction and performance of a simple and efficient g-C3N4 photocatalytic hydrogen production system.

Surface and bulk structure modification is an effective strategy to improve the photocatalytic performance of g-C3N4 (CN). In this work, dilute NaOH solution was used in situ to regulate the CN structure for enhanced photocatalytic hydrogen evolution reaction (HER). Characterization results indicate that after treatment with dilute NaOH solution, the surface of CN was hydroxylated, resulting in the change of CN structure and the increase of BET specific surface area. Furthermore, some Na+ ions can be intercalated into the framework of CN, and form the Na–N bond. These modifications boost the HER activity of CN. The test carried out in 7.5 mM NaOH solution shows the highest activity and it is almost 3.7 times higher than that performed in water. Control tests indicate that hydroxides of other alkali and alkali earth metals such as LiOH, KOH, Ca(OH)2, and Ba(OH)2 have similar promotion effects. This work demonstrates a valid and simple way to enhance the HER activity of CN through performing the reaction in a weakly alkaline solution.

Exploitation of flow-based procedures for reagentless hydrochlorothiazide determination and accelerated degradation studies of pharmaceutical preparations

Drug quality assessment and stress testing are important to ensure both treatment efficacy and patient safety. High performance liquid chromatography may be considered a standard technique for pharmaceutical analysis, showing good precision and accuracy, but it also involves relatively high cost and low analytical frequency. Flow injection analysis presents high sample throughput, lower cost and might be used for selective drug analysis with an appropriate assay and/or detector. In this paper, for the first time, photoreactions promoted by UV radiation were employed for reagentless spectrophotometric determination of hydrochlorothiazide. Optimized parameters led to a linear range of 50 to 500 mg L-1, estimated limit of detection of 3.0 mg L-1 and 24 determinations per hour. The use of diluted NaOH solution as a carrier allowed solubilization of hydrochlorothiazide and analysis without organic solvents. The presence of the most common excipients was evaluated and no significant interferences were observed. The results from the analysis of samples by the proposed and by the reference procedures demonstrated accuracy and matching results. The proposed in-line photolysis of the pharmaceutical, performed in 5 min, is a promising alternative to the conventional hydrolytic forced degradation, which requires elevated temperature and prolonged time period. To evaluate the degree of photoconversion, a capillary zone electrophoresis method was developed, which performed well for separations manifesting good analytical frequency and reduced amount of waste. The combination of in-line photodegradation followed by separation by capillary electrophoresis is a promising approach for the stress test of hydrochlorothiazide in pharmaceutical formulations.

Comparison of Various Electrode Fabrication Methods for Use in an Electrolyzer to Produce of HCl and NaOH from NaCl

Many researches on CO2 capture and utilization (CCU) are being actively pursued to suppress its global warming effects and to utilize CO2 as a feedstock for producing useful organic and inorganic substances such as methanol, formic acid, and carbonates through biological, thermal, photochemical and electrochemical methods.This study focuses on the fabrication methods of anodes for use in an electrolyzer to produce alkali (NaOH) and hydrochloric acid (HCl) by splitting a brine (aqueous NaCl) that would be used to convert carbon dioxide into carbonate minerals at a subsequent stage. The electrolyzer consists of an anode, a membrane 1, a middle plate, a membrane 2 and a cathode. A hydrogen gas is supplied to the anode compartment, a dilute NaOH aqueous solution is to the cathode, and a feed solution of NaCl is to the middle plate. The membranes can be both cationic ones. Upon applying a voltage of around 1.5V, HCl is produced at the anode, and NaOH is produced at the cathode.This study is focused on the fabrication methods to make active and durable anodes. The anode is usually made of Pt particles dispersed on porous and electrically conductive substrates. The fabrication methods can be appropriately chosen depending on the types of substrates. In this study, two types of substrates were used, carbon cloth and carbon paper. In case of using a carbon cloth as substrate, two types of fabrication methods were used, a spraying method and a screen printing method while in case of using a carbon paper an electroplating method was used. When using a spraying method, an appropriate amount Pt/C catalyst powder was dispersed in an aqueous isopropyl alcohol(IPA) solution containing a given amount of Nafion ionomer to make a catalyst ink. The catalyst ink was sprayed on a carbon cloth using a nitrogen spray gun to make an anode consisting a Pt-catalyst coated a carbon cloth having a thickness of 0.45 mm. After drying in an oven, it was used as anode for the electrolyzer. In the case of screen printing method, a viscous catalyst slurry was made by mixing an appropriate amount of catalyst powder, IPA, Nafion ionomer and glycerin, which was then spread on the surface of a carbon cloth (CC) using a silk screen having a proper mesh size. The resulting slurry-coated CC was put in a vacuum oven at 150oC to remove the glycerin, followed by a pretreatment step to swell the dried ionomer in the catalyst layer. The Pt loading was 0.30 mg/cm2. The electroplating method was used to plate Pt on the surface of a carbon paper (CP) having a thickness of 0.20mm. The CP was first pre-treated in a H2SO4 solution and then immersed in a plating solution consisting of H2PtCl6 in a 0.5M solution. Electroplating of Pt was carried out by applying a current of 20 mA/cm2 to deposit 0.30mg-Pt/cm2.Those fabricated anodes were installed in an electrolyzer cell using Nafion 115 as membrane 1 and 2 and a Ni mesh electrode as cathode. The cell performance was measured by supplying H2 into the anode side and a dilute NaOH solution into the cathode side while applying a voltage of 1.5V to the cell. As shown in the figure, the cell performances vary depending on the anode fabrication methods, indicating the structure of anode affects the cell performance. Therefore, in order to improve the performance of the anodes, various fabrication factors need to be optimized to make the structure of the catalyst layer suitable for the reaction. Figure 1

Sea urchin-like FeOOH functionalized electrochemical CNT filter for one-step arsenite decontamination

Advanced nanotechnologies for efficient arsenic decontamination remain largely underdeveloped. The most abundant inorganic arsenic species are neutrally-charged arsenate, As(III), and negatively-charged arsenite, As(V). Compared with As(V), As(III) is 60 times more toxic and more difficult to remove due to high mobility. Herein, an electrochemical filtration system was rationally designed for one-step As(III) decontamination. The key to this technology is a functional electroactive carbon nanotube (CNT) filter functionalized with sea urchin-like FeOOH. With the assistance of electric field, CNT-FeOOH anodic filter can in situ transform As(III) to less toxic As(V) while passing through. Then, as-produced As(V) could be effectively sequestrated by FeOOH. The sufficient exposed sorption sites, flow-through design, and filter’s electrochemical reactivity synergistically guaranteed a rapid arsenic removal kinetic. The underlying working mechanism was unveiled based on systematic experimental investigations and theoretical calculations. The system efficacy can be adapted across a wide pH range and environmental matrixes. Exhausted CNT-FeOOH filters could be effectively regenerated by chemical washing with diluted NaOH solution. Outcomes of the present study are dedicated to provide a straightforward and effective strategy by integrating electrochemistry, nanotechnology, and membrane separation for the removal of arsenic and other similar heavy metals from water bodies.

Mild O2-aided alkaline pretreatment effectively improves fractionated efficiency and enzymatic digestibility of Napier grass stem towards a sustainable biorefinery

Napier grass is a promising energy source on account of its strong adaptability and high productivity. Herein, an O2-aided alkaline pretreatment with mild operating conditions was developed to modify Napier grass stem structure for improving its fractionated efficiency and enzymatic digestibility. Compared with the conventional alkaline pretreatment, it could be proceeded at lower temperature (80 °C) and dilute NaOH solution (1%) to remove over 80% lignin and retain 92% cellulose. The recovered lignin possessed typical structures of native lignin and well-preserved molecular weight, anticipating feasible potential in preparation of biomaterials or aromatic chemicals. Coupled with the enzymatic hydrolysis managements of solid remain and hydrolysate after the pretreatment, the recovery yields of glucose and xylose based on the raw material feeds reached 89.7% and 90.2%, respectively. This contribution demonstrates a highly-reliable strategy to fractionate Napier grass stem for maximizing fermentation sugar production and valorizing lignin toward sustainable biorefinery processes.

From cyclohexanone to photosensitive polyesters: Synthetic pathway, basic characterization, and photo-/halochromic properties

A bifunctional photosensitive monomer, 2,6-bis-(4-hydroxybenzylidene)cyclohexanone (DHCH) was successfully synthesized by the condensation reaction of cyclohexanone with p-hydroxybenzaldehyde in the presence of hydrochloric acid, as a catalyst. Based on DHCH, a series of new photosensitive polyesters were prepared by a polycondensation reaction, in solution, using two phosphonic dichlorides, namely, phenylphosphonic dichloride and phenyl dichlorophosphate, or two aromatic dichlorides, namely, terephthaloyl chloride and terephthaloyl-bis-(4-oxybenzoylchloride). The synthesis of monomer and polymers was structurally confirmed by FT-IR and NMR spectroscopies. The thermal behavior of polyesters was investigated by DSC measurements and polarized optical microscopy observations, which evidenced thermotropic liquid crystalline properties for some of the studied polymers. The photoresponsive properties of the prepared polyesters were extensively investigated in CHCl3 and DMSO solutions, under irradiation with UV light (254 and 365 nm) at different time intervals and after successive titrations with acid/base solutions. Under UV light irradiation, these compounds undergo photocrosslinking reactions and their photoluminescence properties were strongly enhanced. Deprotonation (under the basic conditions) of the polymers led to the emergence of a new absorption band (with maximum at 508 nm), accompanied by a photochromic behavior. This color change, from colorless to orange, observed upon titration with dilute NaOH solution, was completely recovered to its original colorless after the addition of an equivalent amount of dilute HCl solution. The reversible color changes (halochromic properties) observed upon protonation/deprotonation prove that these polymers have potential applications in chemical sensors.

CO2 Measurement of Synthetic Biogas by Passing It through Dilute NaOH Solution

The feasibility of measuring CO2 content in biogas was evaluated in this research. Firstly, Curtipot pH simulator was used to visualize the titration behaviors of various percentages of dissolved CO2 in a wide range of concentrations of NaOH solution. As a general output of those simulations, it was shown that when the titration curves of different CO2 content samples are separated enough, titration can provide precise information about the value of dissolved CO2. Also, when the ratio of the molar concentration of NaOH to the molar concentration of CO2 is in the range of 1 to 2(equivalent to the stoichiometric ratio of bicarbonate and carbonate), the separability of the curves is enough satisfactory to be used for precise determination of CO2; Outside this range, the accuracy of data segregation by titration diminishes. Moreover, when the ratio of the molar concentration of NaOH to CO2 is between 1 and 2, by only a one-time probing, it is possible to determine the concentration of CO2 in the standard NaOH solution. In this case, titration over a wide range of pH does not provide more reliable and accurate information. The effects of temperature CO2 measurement shows that a difference of even 10 °C can only cause less than 1% decrease in CO2 estimation. Finally, a comparison between gas chromatography and pH measurement was performed and the experimental results showed closeness the results of our proposed method with that of GC(less than 0.05% relative error). This method can be used in designing a non-expensive measuring method that would pave down the road for developing countries.

Alkalinity of Electro-Activated Aqueous Solutions

Electro-activated alkaline (basic) solution known as catholyte has been reported to have a number of unique properties. The changes in the pH and alkalinity of the catholyte were monitored in the current study. A full-factorial design was applied in order to examine the effects of current, time of treatment, and salt concentration on the electro-activated solutions treated in 4 types of configurations. Two configurations were constructed as three-compartment cells with chambers separated by anion exchange membrane (AEM) and cation exchange membrane (CEM) with different dispositions in the cell. The other two configurations were two-compartment cells with chambers separated by either an AEM or a CEM. For pH increase, time was the most significant factor, whereas for the alkalinity the cell configuration had a significant impact. Thus, when CEM was used to separate central and cathodic compartments in a three-cell reactor, or anodic and cathodic compartments in a two-cell reactor only current and time were found to be highly significant. On the other hand, when the AEM was used the salt concentration appeared to be an important factor too. Maximum values for pH (pH 12) and alkalinity (25.46 ± 0.31 mmol/L) were obtained after 60 min of treatment and 0.2 A current, and regardless of NaCl concentrations when CEM was used, whereas maximum values for the AEM membrane were achieved only with maximum NaCl concentration of 1 M. Despite highly alkaline medium (pH ~ 12) the strength of the solution was comparable to dilute NaOH solution (~0.03 M).