Alkali Hydroxide Solutions Research Articles

Identifying an Optimal Post-Capture pH for Hydroxide-Based Reactive Capture in Industrial Applications

Reactive capture - the integration of carbon dioxide (CO2) capture and upgrade - bypasses the energy-intensive CO2 regeneration step and thereby offers potential to reduce both capital and energy costs. Alkali hydroxide solutions are a common type of capture solution for reactive capture, wherein CO2 is chemically absorbed in the form of carbonate and/or bicarbonate. The composition and pH of the post-capture solution depend on the CO2 concentration of the CO2 source used and the capture duration. Lower pH levels yield higher bicarbonate concentrations, facilitating greater CO2 release during the reactive capture step and resulting in enhanced electrolysis performance. For example, direct electrochemical reduction of a pure carbonate solution (pH~12.2) has a theoretical carbon monoxide (CO) Faradaic efficiency (FE) cap at 50%, but no cap exists for a pure bicarbonate solution (pH~8.2), leading to better electrolysis performance and lower operating expenditures (OPEX) for the capture and conversion cycle. However, achieving a low pH post-capture solution with higher bicarbonate content slows the capture rate, necessitating either a bigger contactor or longer capture time, thereby increasing capital expenditures (CAPEX) for the capture step. Using a silver catalyst, we report here the electrolysis energy efficiency (EE) of CO2 to CO using a 2M potassium hydroxide solution with a post-capture pH ranging from 13.5 (hydroxide and carbonate mix) to 8.2 (pure bicarbonate). We conducted a technical-economic analysis (TEA) to assess the CAPEX and OPEX of an industrial-scale reactive capture plant that captures both point source (10%) and atmospheric (420 ppm) CO2 using 2M potassium hydroxide with different post-capture pH values. The TEA includes a sensitivity analysis to account for improvements in electrolysis performance and reduced costs due to technological advancement and economies of scale in the future. Our results demonstrate that there is an optimal post-capture pH for potassium hydroxide-based reactive capture that balances the capture cost and electrolysis performance. This study serves as a guideline for choosing an industrial relevant pH to work with for future hydroxide-based reactive capture research.

Alkali hydroxide (LiOH, NaOH, KOH) in water: Structural and vibrational properties, including neutron scattering results.

Structural and vibrational properties of aqueous solutions of alkali hydroxides (LiOH, NaOH, and KOH) are computed using quantum molecular dynamics simulations for solute concentrations ranging between 1 and 10M. Element-resolved partial radial distribution functions, neutron and x-ray structure factors, and angular distribution functions are computed for the three hydroxide solutions as a function of concentration. The vibrational spectra and frequency-dependent conductivity are computed from the Fourier transforms of velocity autocorrelation and current autocorrelation functions. Our results for the structure are validated with the available neutron data for 17M concentration of NaOH in water [Semrouni et al., Phys. Chem. Chem. Phys. 21, 6828 (2019)]. We found that the larger ionic radius [rLi+<rNa+<rK+] and higher concentration disturb the hydrogen-bond network of water, resulting in more disordered cationic hydration shell. Our abinitio simulation data for solute concentrations ranging between 1 and 10M can be used to guide future elastic and inelastic neutron-scattering experiments.

Chemical Absorption of CO2 Enhanced by Solutions of Alkali Hydroxides and Alkoxides at Room Temperature

AbstractThis article presents the study of CO2 capture through aqueous solutions with high basicity conditions. Systematic experiments were conducted to assess the performance of alcohols mixed with aqueous alkaline hydroxides for carbon dioxide capture. Alcohols can work as a catalyst in the capture of CO2 providing greater basicity, a lower surface tension, and an amphiphilic character in the polar aqueous solvent/ (nonpolar CO2 and N2) gas mixture interface, and a lower temperature of solvent regeneration. The results showed that short‐chain alcohols, such as methanol and ethanol, and alkaline metals of greater molar mass (i. e., K compared to Na) can produce greater basicity and a higher CO2 absorption rate in the mixtures than conventional aqueous solutions such as ammonia or monoethanolamine in the same concentration. DFT calculations of electronic and thermodynamic properties for CO2 absorption reactions were carried out to analyze the nucleophilic trend of the short‐chain alkoxides studied. The volumetric proportion between water and alcohol, as well as the concentration of alkaline hydroxide, influences the rate of CO2 absorption, the temperature of regeneration and volatility of the solvent, and the formation of precipitates. CO2 absorption rates greater than 90 % v/v and solvent regeneration temperatures of approximately 78 °C were achieved using ethanol, water, and KOH.

Waste-derived glass as a precursor for inorganic polymers: From foams to photocatalytic destructors for dye removal

Synthetic alumino-silicate glasses may yield inorganic polymers, through activation with alkali hydroxide solutions. In this framework, we formulated a glass prepared by the melting of red mud from bauxite refinement, combined with coal combustion fly ash, discarded pharmaceutical glass and a minor addition of sodium carbonate. The activation with 6 M NaOH aqueous solution allowed for the manufacturing of highly porous foams, by gas generation at the early stages of gelation. These foams featured an extensive formation of zeolite at cell walls which, combined with the presence of magnetite formed upon cooling of the melt, favoured the application of the foams as sorbents for dye removal from contaminated water. The powders prepared by crushing the highly porous foams showed an excellent water purification ability documented by efficient removal of methylene blue used as a model contaminant. The specific iron oxide polymorph facilitated both magnetic recovery of dispersed powders and photocatalytic destruction of the dye under UV irradiation.

Development and Characterization of Geopolymers Based on a Kaolinitic Clay

Geopolymers today constitute an alternative to be considered with the aim, not of completely replacing cement, but of widening the possibilities available at the time of decision-making because this type of clay-based binder has a low impact environmental and thermal compared to Portland cement. The methods used to obtain eco-friendly building units from waste materials can be separated into three general categories: firing, cementing and geo-polymerization. The reaction of solid aluminosilicate materials with a highly concentrated aqueous alkali hydroxide or silicate solution produces a synthetic alkali aluminosilicate material called a ‘geopolymer. Geopolymers based on clay materials from Burkina Faso were developed and then characterized for use in construction. The results of the characterization of the clay mineral material referenced TAN as well as its calcined forms TAN-700 and TAN-800 have shown by several analysis techniques (DRX, IR, ICP-AES) that TAN contains kaolinite (71%), quartz (20%), illite (4%) and goethite (2%). TAN-700 and TAN-800 are essentially made of quartz. These clays are each mixed with the alkaline solution (sodium hydroxide solution 8 mol.L^-1) in a mass ratio (alkaline solution/clay) ranging from 0.33 to 0.36. The results of the mechanical and mineralogical tests of the geopolymers produced showed that the grade GP-MK₀ produced had the best performance favorable for its use in construction. Indeed, its linear shrinkage (3.44%) is low and the compressive strength (22.50 MPa) is greater than 4 MPa. This performance of GP-MK₀ is due to the formation of a phase rich in silica and in alumina (Na₂(AlSiO₄)₆(OH)₂·2H₂O).

Alkali-cation-incorporated and functionalized iron oxide nanoparticles for methyl blue removal/decomposition

Enhancing the rate of decomposition or removal of organic dye by designing novel nanostructures is a subject of intensive research aimed at improving waste-water treatment in the textile and pharmaceutical industries. Despite radical progress in this challenging area using iron-based nanostructures, enhancing stability and dye adsorption performance is highly desirable. In the present manuscript alkali cations are incorporated into iron oxide nanoparticles (IONPs) to tailor their structural and magnetic properties and to magnify methyl blue (MB) removal/decomposition capability. The process automatically functionalizes the IONPs without any additional steps. The plausible mechanisms proposed for IONPs incubated in alkali chloride and hydroxide solutions are based on structural investigation and correlated with the removal/adsorption capabilities. The MB adsorption kinetics of the incubated IONPs is elucidated by the pseudo second-order reaction model. Not only are the functional groups of –OH and –Cl attached to the surface of the NPs, the present investigation also reveals that the presence of alkali cations significantly influences the MB adsorption kinetics and correlates with the cation content and atomic polarizability.

Methodology for pH measurement in high alkali cementitious systems

A methodology for calibrating pH meters in highly alkaline solutions such as those relevant to cementitious systems is presented. This methodology uses an extended form of the Debye-Hückel equation to generate a calibration curve of pH vs. the measured electrochemical potential (mV) based on a series of aqueous alkali hydroxide solutions of known concentrations. This methodology is compared with the ‘built-in’ process of calibration based upon pH 4, 7, and 10 standard solutions. The built-in calibration process underestimates the real pH values by up to 0.3 log units, which is attributed to the alkali error. A spreadsheet for determining the calibration curve and its application to pH meter readings is provided as Supporting Information. The implications of improperly calibrated pH meters on interpreting solution chemistry in cementitious systems are discussed.

Seepage water quality of a soil treated with alkali-activated cement at room temperature

Modern societies are great producers of waste because of their energy and natural resource needs. Many of these wastes are disposed of in landfills, which require a significantly sized area of soil and special geotechnical conditions. The reaction between alumina-silicate and an aqueous alkali hydroxide and silicate solution produces an alkali-activated cement (AAC). The use of AAC, an inorganic material with a chemical structure of polymeric Si–O–Al bonds, can promote the stabilisation and immobilisation of a wide variety of waste sources containing hazardous materials. The purpose of this study is to evaluate the effect of curing conditions on the resistance and permeability and in the quality of the seepage water generated over time in transport infrastructure platforms built with soil stabilised with AAC. The strength results show that the material meets the requirements for use in building low-cost roads. Permeability tests of AAC samples show a relatively low permeability (between 10−8 and 10−7 m/s), a positive factor for environmental and geotechnical considerations. However, this permeability still results in significant leachate water with quality and contaminant issues, particularly in chromium (Cr), cadmium (Cd), aluminium (Al), sodium and silicon (Si), and high pH.

Rheological characterization of low-calcium fly ash suspensions in alkaline silicate colloidal solutions for geopolymer concrete production

The rheological behavior of low-calcium fly ash suspensions in activating solutions of colloidal silica and alkali hydroxide is investigated. The study is aimed at relating the rheological behavior of alkali-silicate activated low-calcium fly ash (AAF) suspensions with Portland cement paste suspensions. The yield stress and the viscosity of the AAF suspensions increase with the alkalinity of the colloidal solution, which is due to changes in the surface charges on fly ash particles with the change in the ionic medium. Increasing the alkalinity results in a less negative zeta potential of fly ash in the alkaline solution of colloidal silica and an increase in the yield srtess of the AAF suspension. The thixotropic behavior in AAF suspensions is associated with structure breakdown to a finely dispersed suspension of particles produced by shearing. Energy measurements indicate a very slow change in the internal particle structure with age at room temperature. A comparison of AAF suspensions is presented with suspensions of Portland cement in water, which are proportioned for similar physical flow characteristics and yield stress. AAF suspensions have a larger solid fraction than the cement suspensions in water of comparable yield stress. The zeta potential of cement particles in water is less negative when compared to fly ash in alkaline-silicate solutions. The AAF suspensions of comparable yield stress exhibit a significantly higher viscosity than the cement suspensions in water. Cement paste and AAF suspensions exhibit a rate dependent yield response. Cement paste suspensions exhibit a threshold strain rate for minimum yield stress. In AAF suspensions there is a continuous decrease in the yield stress at lower strain rates. The thixotropic behavior in cement paste is influenced by chemical ageing which produces a rapid recovery of yield stress. In comparison, there is very little ageing at room temperature in the AAF suspensions and a very slow recovery of yield stress after shearing.

Synthesis, characterization, and crystal structure of aqua-bis-(4,4'-dimeth-oxy-2,2'-bi-pyridine)[μ-(2R,3R)-tartrato(4-)]dicopper(II) octa-hydrate.

Typical electroless copper baths (ECBs), which are used to chemically deposit copper on printed circuit boards, consist of an aqueous alkali hydroxide solution, a copper(II) salt, formaldehyde as reducing agent, an l-(+)-tartrate as complexing agent, and a 2,2'-bi-pyridine derivative as stabilizer. Actual speciation and reactivity are, however, largely unknown. Herein, we report on the synthesis and crystal structure of aqua-1κO-bis-(4,4'-dimeth-oxy-2,2'-bi-pyri-dine)-1κ2 N,N';2κ2 N,N'-[μ-(2R,3R)-2,3-dioxidosuccinato-1κ2 O 1,O 2:2κ2 O 3,O 4]dicopper(II) octa-hydrate, [Cu2(C12H12N2O2)2(C4H2O6)(H2O)]·8H2O, from an ECB mock-up. The title compound crystallizes in the Sohncke group P21 with one chiral dinuclear complex and eight mol-ecules of hydrate water in the asymmetric unit. The expected retention of the tartrato ligand's absolute configuration was confirmed via determination of the absolute structure. The complex mol-ecules exhibit an ansa-like structure with two planar, nearly parallel bi-pyridine ligands, each bound to a copper atom that is connected to the other by a bridging tartrato 'handle'. The complex and water mol-ecules give rise to a layered supra-molecular structure dominated by alternating π stacks and hydrogen bonds. The understanding of structures ex situ is a first step on the way to prolonged stability and improved coating behavior of ECBs.

Electrochemical CO Reduction: A Property of the Electrochemical Interface.

Electrochemical CO reduction holds the promise to be a cornerstone for sustainable production of fuels and chemicals. However, the underlying understanding of the carbon-carbon coupling toward multiple-carbon products is not complete. Here we present thermodynamically realistic structures of the electrochemical interfaces, determined by explicit ab initio simulations. We investigate how key CO reduction reaction intermediates are stabilized in different electrolytes and at different pH values. We find that the catalytic trends previously observed experimentally can be explained by the interplay between the metal surface and the electrolyte. For the Cu(100) facet with a phosphate buffer electrolyte, the energy efficiency is found to be limited by blocking of a phosphate anion, while in alkali hydroxide solutions (MOH, M = Na, K, Cs), OH* intermediates may be present, and at high overpotential the H* coverage limits the reaction. The results provide insight into the electrochemical interface structure, revealing the limitations for multiple-carbon products, and offer a direct comparison to experiments.

A Laboratory Investigation of Soil Stabilization Using Enzyme and Alkali-Activated Ground Granulated Blast-Furnace Slag

Development and use of non-traditional stabilizers such as enzyme and alkali-activated ground granulated blast-furnace slag (GGBS) for soil stabilization helps to reduce the cost and the detrimental effects on the environment. The objective of this study is to investigate the effectiveness of alkali-activated GGBS and enzyme as compared to ordinary Portland cement (OPC) on the soil collected from Tilda region of Chhattisgarh, India. Geopolymers are alkali alumino-silicates produced when combining a solid alumina-silicate with an aqueous alkali hydroxide or silicate solution. Various dosages of the selected stabilizers have been used and evaluated for the effects on optimum moisture content (OMC), maximum dry density, plasticity index, unconfined compressive strength (UCS) and shear strength parameters. Effect of curing period has also been studied. Microstructural changes of the stabilized soils show aggregation of particles. Significant improvement in properties of soil is observed with the addition of stabilizers leading to an increase in OMC, UCS and shear strength parameters. It is observed that the cohesion of soil sample increases significantly with the addition of stabilizers whereas there is a marginal change in angle of internal friction. Thus, the findings recommend the use of non-conventional stabilizer such as alkali-activated GGBS and enzyme as suitable and environmental friendly as compared to OPC for soil stabilization.

Corrosion Behavior Mechanism of Borosilicate Glasses Towards Different Leaching Solutions Evaluated by the Grain Method and FTIR Spectral Analysis Before and After Gamma Irradiation

Three selected borosilicate glasses of commercial applications were prepared and studied for their corrosion behavior by the accepted grain test method towards acidic and alkaline solutions and distilled water before and after gamma irradiation. The work was supplemented by investigating the FT infrared absorption spectra of the glasses after immersion through the KBr disc technique. The same IR measurements have been repeated after gamma irradiation. Experimental weight loss data reveal limited changes which vary with the type of leaching solution and its strength. Alkali hydroxide solutions cause more weight loss than acidic solutions due to their reactions with all glass constituents including silicate and borate species beside modifier ions while distilled water and acidic solutions react or attack the modifier ions through ion exchange corrosion behavior. FTIR spectral results show characteristic vibrational peaks due to combined silicate and borate groups which reveal an interconnected compact network structure within the mid region of wavenumber range 800–1400 cm−1. This is due to the presence of four structural building units consisting mainly of SiO4 beside BO3, BO4 and AlO4 groups. The vibrational spectra slightly change with the immersion media because of the strong and compact network structure usually identified in borosilicate glasses. The commercial glass of the Schott type is the most durable studied glass because of high silica content (75%) together with combined 10% B2O3 and 5% Al2O3. Gamma irradiation results indicate minor changes in the weight loss data due to the compact network structure of the three commercial borosilicate glasses studied.

Alkali activated slag binder: effect of cations from silicate activators

Two blast furnace slags were activated by alkali hydroxide and alkali silicate solutions possessing different modulus (0.5, 1 and 2), as well as cations (sodium and potassium). Their properties, including the setting time, heat of hydration, compressive strength as well as porosity and morphology have been investigated on both fresh and hardened pastes. The results showed that the cations of these silicate activators exerted a significant effect on the performance of the alkali activated slag binder, whereby the mechanical strength of the binder was promoted greater by the potassium silicate solution as compared to by the sodium silicate solution.

A pH-responsive phase transformation of a sulfonated metal–organic framework from amorphous to crystalline for efficient CO2capture

We report a pH-responsive phase transformation of a sulfonated MOF from amorphous UiO-66-SO3H to crystalline UiO-66-SO3M (M = Li, Na, K). Such transformation is obtained via neutralizing UiO-66-SO3H with the according alkali hydroxide solutions. EXAFS and FTIR results suggest that the recovered crystallinity can be attributed to the breakage of strong hydrogen bonds among the sulfonic acids in UiO-66-SO3H as well as the subsequent charge repulsion in UiO-66-SO3M to expand the collapsed framework.

New methods for utilization of waste polyethylene terephthalate

New promising methods for utilizing waste polyethylene terephthalate (PET) are presented. At the first stage, partial thermal destruction of PET in an enclosure resulting in the formation of a fragile material takes place. The obtained material may be ground to a fine powder for further use as a filler. In addition, the powder of partially destructed PET reacts with alkali and ammonium hydroxide solutions resulting in the formation of corresponding terephthalate solutions, from which it is possible to obtain solid terephthalates. These terephthalates may be valuable functional materials, as well as precursors for nanodispersed oxides.

Ambient and Elevated Temperature Geopolymerization Behaviour of Class F Fly Ash

Geopolymerization is the process, where synthetic alkali activated alumino-silicate material is produced by reaction of a solid alumino-silicate with a highly concentrated aqueous alkali hydroxide or silicate solution. Depending on the raw material selection and processing conditions, geopolymers can exhibit a wide variety of properties and characteristics, including high compressive strength, fast or slow setting, acid resistance, and fire resistance. Fly ash, a by-product of coal fired power plant, is produced during combustion of coal. Fly ash is a powdery, aluminosilicate material along with minor impurities which is suitable for geopolymer reaction. The geopolymerization behaviour of class F fly ash has been studied in a temperature range of 27°-55°C using isothermal conduction calorimeter with different alkali concentrations. It was observed that the rate of reaction got intensified and increased with temperature. Compressive strength of the resulting geopolymer was also found to increase with temperature more significantly during early days. Attempt has been made to correlate the reaction with structure and properties.

Spent FCC Catalyst for Preparing Alkali-Activated Binders: An Opportunity for a High-Degree Valorization

Spent FCC catalyst is a waste from the petrochemical industry which has excellent pozzolanic properties, containing more than 90% silica and alumina. Its similarity to metakaolin creates interesting prospects for its use in the production of alkali-activated binders. In this study, the alkali activation of this residue, spent FCC catalyst, through mixtures with alkali hydroxide and silicate solutions (both sodium and potassium) has been carried out. The alkali cation had an important role in the nature of AA-FCC pastes: some differences in the mass loss in the thermogravimetric tests and in the X-ray mineral characterization were found. No significant differences in compressive strength were observed for mortars cured for 3 days in several conditions: room temperature and 65oC. Prepared AA-FCC mortars had a compressive strength of about 65-70 MPa. Microstructural studies showed that an amorphous, dense and compact microstructure was obtained, independent of the activating solution and curing condition.

Chemical Sequence and Kinetics of Alkali–Silica Reaction Part II. A Thermodynamic Model

This manuscript describes development of a thermodynamic model for the chemical sequence of the alkali–silica reaction (ASR) process in the model, closed reactive system consisting of mixture of reactive silica mineral, calcium hydroxide, and alkali hydroxide solution. The focus of the first part of the study is on formulating the kinetic rate law for silica dissolution as a function of several factors, including pH, temperature, concentration of alkalis in solution, and type of the reactive silica mineral. This kinetic rate law was then incorporated into the commercial modeling software (Geochemist's Workbench®) in an attempt to simulate the chemical sequence of the ASR process. Once the proper input data and parameters were selected, the model generated reasonably accurate predictions of the distribution of species in the reacting system and captured distinct features of experimental data. In addition, this model suggested that the thermodynamic equilibrium condition among reactant (reactive silica mineral), products, and ionic species in the solution resulted in the threshold value of alkali concentration needed for the ASR to take place. Though the application of the proposed model is currently limited to the closed ASR system, the model may offer the possibility of the establishment of the unified theory which can bridge the gap between fundamental (chemical) mechanisms of ASR and the mechanical responses of concrete by providing the kinetic basis for the evolution of ASR process.

单分散锐钛矿型TiO&lt;sub&gt;2&lt;/sub&gt;亚微米球的制备与光催化性能研究

以钛酸四正丁酯为钛源，柠檬酸为辅助剂，无水乙醇为溶剂，采用溶剂热法制备了单分散锐钛矿型TiO2亚微米级球，并研究了其对罗丹明的光催化降解性能。此外，以制备的TiO2亚微米级球为前驱体，利用其与浓碱的水热反应，制备了具有等级结构的钛酸盐纳米线球和纳米管球。 Uniform anatase TiO2 sub-microspheres composed of nanoparticles were prepared via a citric acid as assisted hydrolysis of tetra-n-butyl titanate in ethanol under solvothermal conditions. The photocatalytic activity of the as-prepared TiO2 spheres was evaluated by the photodegradation of RhB. The as-prepared TiO2 spheres were treated with concentrated alkali hydroxide solution to transform nanoparticles into nanotubes, leading to the formation of hierarchically structured TiO2 spheres consisting of nanotubes.