Alkaline Hydroxide Research Articles

A new recovery process of carbon dioxide from alkaline carbonate solution via electrodialysis

AbstractBipolar membrane electrodialysis is applied to CO2 recovery from alkaline carbonate solution. CO2 in flue gas is captured by an alkaline hydroxide absorbing solution to form an alkaline carbonate solution. The captured CO2 is recovered from the alkaline carbonate solution via bipolar membrane electrodialysis, and the alkaline solution is regenerated simultaneously. To reduce the power requirement for CO2 recovery, this study considers optimal design and operation. Three membrane arrangements were compared, and the results indicate the membrane arrangement comprising a bipolar membrane and cation exchange membrane is the most energy saving. With further optimization of operation conditions, the minimum power requirement for CO2 recovery was reduced to 2.1 MJ/kg‐CO2 (or 2.1 GJ/t‐CO2). © 2009 American Institute of Chemical Engineers AIChE J, 2009

Activation of polymer blend carbon nanofibres by alkaline hydroxides and their hydrogen storage performances

In the present work we study the hydroxide activation (NaOH and KOH) of phenol-formaldehyde resin derived CNFs prepared by a polymer blend technique to prepare highly porous activated carbon nanofibres (ACNFs). Morphology and textural characteristics of these ACNFs were studied and their hydrogen storage capacities at 77 K (at 0.1 MPa and at high pressures up to 4 MPa) were assessed, and compared, with reported capacities of other porous carbon materials. Phenol-formaldehyde resin derived carbon fibres were successfully activated with these two alkaline hydroxides rendering highly microporous ACNFs with reasonable good activation process yields up to 47 wt.% compared to 7 wt.% yields from steam activation for similar surface areas of 1500 m 2/g or higher. These nano-sized activated carbons present interesting H 2 storage capacities at 77 K which are comparable, or even higher, to other high quality microporous carbon materials. This observation is due, in part, to their nano-sized diameters allowing to enhance their packing densities to 0.71 g/cm 3 and hence their resulting hydrogen storage capacities.

New insights on the direct activation of isotropic petroleum pitch by alkaline hydroxides

The paper provides interesting evidences that a low softening point isotropic petroleum pitch can be used as a good carbon precursor for the preparation of activated carbons. The activation is carried out by KOH and/or NaOH and the resulting activated carbons present well developed porosity. Such hydroxide activations can be done directly on the pristine petroleum pitch (P) or on the pitch that has been submitted to an air stabilisation followed by a N 2 heat treatment (TAN). In general, KOH activation produces better results than NaOH, both in terms of porosity and yield, the results obtained for the activation of TAN being impressive because of the good porosity developments and high yields reached. The different treatments carried out over the petroleum pitch precursor clearly show that they significantly influence the extent of microporosity development. This is due to different changes occurring in the porous structure of the precursor as a function of the treatment carried out. The efficiency of the activation process increases as the mesophase content of the precursor decreases, as well as the mesophase formation during the activation process is avoided.

Temperature and alkaline hydroxide treatment effects on hydrogen sorption characteristics of multi-walled carbon nanotube–graphite mixture

Temperature and alkaline hydroxide treatment effects on the surface area and pore structure of the cathode deposit multi-walled carbon nanotube (MWCNT)–graphite mixture were investigated in a temperature range of 600–800 °C. Hydrogen sorption properties of the MWCNT–graphite mixture samples were studied by varying the alkaline hydroxide-activation temperature. Pore characterization of modified MWCNT–graphite mixture was performed with the observation of adsorption–desorption isotherms of N 2 at 77 K. Hydrogen sorption of the non-treated and treated MWCNT–graphite mixture was carried out using a volumetric apparatus at 77 K. The highest surface area of the sample was obtained as 275 m 2 g −1 by treatments with KOH at 600 °C. The increase in the specific surface area of MWCNT–graphite sample mixture was about 13 times. The maximum amount of hydrogen adsorbed on the MWCNT–graphite sample mixture was found as 0.75 and 0.54 wt.% by chemical treatments with KOH at 600 °C and NaOH at 700 °C, respectively whereas it was 0.01 wt.% for the original sample. The hydrogen sorption capacity was enhanced considerably by KOH treatments at 600 °C.

A Soluble and Highly Conductive Ionomer for High‐Performance Hydroxide Exchange Membrane Fuel Cells

Hydrogen proton exchange membrane fuel cells (PEMFCs) have been demonstrated to have high power density and reasonable energy density. Their commercialization, however, has been hampered by the high cost and low durability of their electrocatalysts. By switching from an acidic medium to a basic one, hydroxide (OH ) exchange membrane fuel cells (HEMFCs) have the potential to solve the problems of catalyst cost and durability while achieving high power and energy density. In a basic environment, the cathode oxygen reduction over-potential can be significantly reduced, leading to high fuel cell efficiency, and catalysts in basic medium are also more durable. In addition, the facile cathode kinetics allows nonprecious metals to be used as catalysts, thus drastically reducing the cost of the fuel cell. Further, HEMFCs can offer fuel flexibility (e.g., methanol, ethanol, ethylene glycol, etc.) because of their low overpotential for hydrocarbon fuel oxidation and reduced fuel crossover. One of the most significant problems for HEMFCs is the lack of a soluble ionomer that can be used in the catalyst layer to build an efficient three-phase boundary and thus drastically improve the utilization of the catalyst particles and reduce the internal resistance. One of the most desirable properties of an ionomer for use in the catalyst layer is high solubility in low-boiling-point water-soluble solvents such as ethanol and (nor 2-)propanol, because these solvents are easy and safe to handle and remove during the electrode preparation. The ionomer should also have high hydroxide conductivity and alkaline stability. For PEMFCs, Nafion has been the ionomer of choice because it meets these requirements. But for HEMFCs, the most commonly used material for the hydroxide exchange membrane (HEM) is a quaternary ammonium hydroxide containing polymer that has poor solubility in the aforementioned simple solvents, low hydroxide conductivity, and poor alkaline stability. For example, Tokuyama Co. very recently reported two types of soluble quaternary ammonium hydroxide containing polymers (product code: A3Ver2, soluble in tetrahydrofuran or n-propanol, and AS-4, soluble in n-propanol); however, as a result of their low hydroxide conductivity, their incorporation into the catalyst layers of HEMFCs only led to a moderate improvement in performance. In another case, Park et al. prepared an ionomer solution of the trimethylamine (TMA) and N,N,N’,N’-tetramethyl-1,6-hexanediamine (TMHDA) based polysulfone– methylene quaternary ammonium hydroxide (T/TPQAOH) in dimethylacetamide (DMAc, b.p. 166 8C). Similar to the Tokuyama results, the low hydroxide conductivity of the ionomer significantly limited the improvement in fuel cell performance, and in addition, removal of the high-boilingpoint solvent is considered difficult and unsafe in the presence of finely dispersed catalysts. Owing to the lack of a soluble highly conductive solid ionomer, aqueous solutions of KOH or NaOH have been previously used in the electrodes, where the introduction of metal cations (M) offsets the key advantages of a HEMFC over traditional liquid-electrolytebased alkaline fuel cells (AFCs). Furthermore, owing to the lack of a good ionomer as the binder, non-ionic conductive PTFE and proton-conductive Nafion ionomers were used as substitutes in the electrodes, even though these materials were known to have no hydroxide conductivity. Recently, Varcoe et al. reported a TMHDA-based polyvinylbenzylcrosslinked quaternary ammonium hydroxide (TPCQAOH) electrochemical interface to enhance HEMFC performance. Because the polymer used was not soluble in ionomer form, one could question its ability to form an efficient three-phase-boundary structure in the catalyst layer, thereby limiting performance. Moreover, the hydroxide conductivity and stability of the electrochemical interface are still of concern because it is based on quaternary ammonium hydroxide groups. Quaternary phosphonium containing polymers showed excellent solubility in methanol. The strong basicity of the tertiary phosphine suggests that quaternary phosphonium hydroxides are very strong bases. Therefore in this work, we synthesized a new quaternary phosphonium based ionomer that is soluble in low-boiling-point water-soluble solvents and is highly hydroxide conductive: tris(2,4,6-trimethoxyphenyl) polysulfone-methylene quaternary phosphonium hydroxide (TPQPOH; Scheme 1). The TPQPOH ionomer exhibits excellent solubility in pure methanol, ethanol, and n-propanol and in their aqueous solutions (50 wt% in water, see Table S1 in the Supporting Information). On the other hand, the TPQPOH is insoluble in pure water, even at 80 8C, suggesting that it can be used in the [*] Dr. S. Gu, Dr. R. Cai, T. Luo, Dr. Z. Chen, M. Sun, Y. Liu, Prof. Dr. Y. S. Yan Department of Chemical and Environmental Engineering University of California—Riverside Riverside, CA 92521 (USA) Fax: (+1)951-827-5696 E-mail: yushan.yan@ucr.edu Homepage: http://www.engr.ucr.edu/faculty/chemenv/ yushanyan.html

Regularities of the change in colloid-chemical properties of silica hydrosols in the presence of alkali metal hydroxides

The effect exerted by type of alkaline hydroxide additive on the change in turbidity and on the formation of silica hydrosol spatial structures was studied. Silica depolymerization in an alkaline solution to form active silicic acids was studied depending on the aging time of the system, size of sol particles, and the type of alkaline hydroxide additive.

Alkaline Hydroxide Induced High Level of Alkali Metal Concentration Effect on the Characteristics of LTO Layer

The control and evaluations of alkali metal such as Na have been important issues in device process. LTO layer was deposited on backside of wafer as backseal of epitaxial substrate. The backseal wafer with LTO was evaluated to study effect of Na contamination which was observed after NaOH mixture dip. We found Na out diffusion from LTO layer inducing surface oxidation rate increase in oxidation process. These phenomena considered to Na property of low boiling temperature point. However, Na from LTO layer did not affect epitaxial process because of hydrogen pre-baking in epitaxy process.

Phenol Hydroxylation over Alkaline Treated TS-1 Catalysts

Alkaline treatment on TS-1 can selective remove silica from the framework while MFI zeolitic framework remains intact, which creates new large micropores or even mesopores and increases Si/Ti ratio in the alkaline treated TS-1. Among various alkaline hydroxide, CsOH treatment leads to partial destruction of MFI structure. All the desilicated TS-1 samples show enhanced phenol conversion and dihydroxylbenzene (DHB) yield in acetone solvent by two folds, which can be attributed to the higher Ti/Si ratio and improved diffusivity. Pore structure modified with alkaline treatment affects significantly reaction pathway and product selectivity. The initial product over the parent TS-1 and NaOH treated TS-1 is mainly 4-hydroxycyclohexa-2,5-dienone and catechol enriched DHB, respectively.

Hydrothermal conversion of chrysotile to amorphous silica or brucite

Chrysotile (Mg3Si2O5(OH)4) was treated hydrothermally in acid or alkaline hydroxide solution. By hydrothermal treatment in 1 M HCl, HNO3 or H2SO4 solution at 180°C for 48 h chrysotile changed to amorphous silica by complete extraction of magnesium component and its fibrous morphology was held in spite of changing chemical composition. The maximum specific surface area (SBET) of the fiberous amorphous silica was 127 m2/g. It was converted to Mg(OH)2 by complete dissolution removal of silica component in 20 M NaOH or KOH solution at 180°C for 48 h and the fiberous morphology of chrysotile disappeared.

Synthesis and characterisation of palladium nanoparticles for catalytic applications

We report a simple wet chemical method to synthesise palladium nanoparticles and test their performance as an activator for the electroless copper deposition reaction. A mixture of ethylene glycol and alkaline hydroxide ions is indispensable to initiate and catalyse the chemical reduction of palladium salt. The presence of a polyvinylpyrrolidone (PVP) in the solution mixture was also found to be essential and acted as a protective agent to isolate the nanoparticles and prevent the agglomeration. The crystallinity, size and morphology and structural features of the produced nanoparticles are investigated by powder X-ray diffraction (XRD), transmission electron microscopy (TEM). The performance of the nanoparticles as a catalyst for electroless deposition of copper on both silicon and epoxy substrates is also presented.

The preparation of an adsorbent from mixtures of sewage sludge and coal-tar pitch using an alkaline hydroxide activation agent

The increasing generation of sewage sludge and its subsequent treatment are very sensitive environmental problems. For the more stable and sanitary treatment of this sewage sludge, there have been many studies, including the recent attempt to prepare an adsorbent from sewage sludge via recycling. In this study, of the adsorbent preparation methods, chemical activation was utilized, and in order to find the optimum conditions, several variables were tested, such as the activation agent concentration, activation temperature and activation time. The activation agents used in this study were alkaline hydroxides: KOH and NaOH. The properties of prepared adsorbent were also measured by analyzing the iodine adsorptivity and surface area. In addition, the prepared adsorbent, the BOD, COD, SS, T-N and T-P removal efficiencies from the effluent water of a sewage treatment plant were examined via column test. From the test, the optimum conditions for KOH-activation were 1 mol/l, 800 °C and 1.5 h for the activation agent concentration, activation temperature and activation time, respectively; whereas those for NaOH-activation were 1.25 mol/l, 850 °C and 1.5 h. From the application of the prepared adsorbent to the effluent water of the sewage treatment plant, the measured BOD, COD, SS, T-N and T-P removal efficiencies, the P1-800 adsorbent had the highest efficiencies for BOD, COD and SS of 56.68, 57.76 and 81.45%, respectively.

Alkaline Hydroxide Induced High Level of Alkali Metal Concentration Effect on the Characteristics of LTO

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Spongy gel-like layered double hydroxide–alkaline phosphatase nanohybrid as a biosensing material

Formation of new bio-nanohybrid material was obtained by immobilization of alkaline phosphatase within a Mg(2)Al LDH by "soft chemistry" coprecipitation synthesis, resulting in an original spongy gel-like morphology allowing the preservation of the enzyme structure and activity even at low pH values thanks to the buffering property of the basic host structure.

An intermediate-temperature direct ammonia fuel cell with a molten alkaline hydroxide electrolyte

This paper describes the development and testing of a direct ammonia fuel cell utilizing a molten alkaline hydroxide electrolyte at temperatures between 200 and 450 °C. The advantages of a molten hydroxide fuel cell include the use of a highly conductive and very low-cost electrolyte, inexpensive base metal electrocatalysts, a wide operating temperature range, fuel flexibility, and fast electrode kinetics. The direct use of ammonia in such a fuel cell, even at temperatures as low as 200 °C, is made possible due to the very chemically aggressive nature of the melt. A test cell was constructed using a KOH–NaOH eutectic mixture and produced approximately 40 mW cm −2 of power at 450 °C while operating on a stream of pure ammonia fed to the anode and compressed ambient air fed to the cathode.

Further insights into the activation process of sewage sludge-based precursors by alkaline hydroxides

The present work extends previous activation results obtained with a sewage sludge to others and deepens into the study and characterisation of sewage sludge-based sorbents prepared by alkaline hydroxide activation. Results obtained show that different sewage sludges, whose compositions and treatments vary from each other, can be successfully activated by KOH. A wide range of porosities are achieved, being remarkable that the activation of a biologic sewage sludge leads to surface areas in the range of 1900 m 2 g −1 using a very low KOH/precursor ratio. Some of the prepared sorbents exhibit an important mineral matter contribution, which has shown to be porous as well. The chemical changes occurring during the activation of these precursors were followed by different techniques. The combination of conventional and in situ XRD allowed us to conclude that KOH acts not only as an activating agent of the carbonaceous matter present in the sludge-based precursors, but also produces a reaction (alkaline fusion) with the inorganic matter present in the precursors. Regarding the activation of the carbonaceous part, the sludge-based precursors show specific features when compared to other conventional carbon precursors. A considerable proportion of the nitrogen from the microorganisms present in the sludges is maintained after the pyrolysis, leading to an interesting nitrogen enriched carbonaceous precursor. These findings could be of relevance considering that these sorbents are promising for odorous compounds removal, such as those derived from wastewater treatment plants, and for other environmental applications requiring porous sorbents.

Computationals-Block Thermochemistry with the Correlation Consistent Composite Approach

The correlation consistent composite approach (ccCA) is a model chemistry that has been shown to accurately compute gas-phase enthalpies of formation for alkali and alkaline earth metal oxides and hydroxides (Ho, D. S.; DeYonker, N. J.; Wilson, A. K.; Cundari, T. R. J. Phys. Chem. A 2006, 110, 9767). The ccCA results contrast to more widely used model chemistries where calculated enthalpies of formation for such species can be in error by up to 90 kcal mol-1. In this study, we have applied ccCA to a more general set of 42 s-block molecules and compared the ccCA DeltaHf values to values obtained using the G3 and G3B model chemistries. Included in this training set are water complexes such as Na(H2O)n+ where n = 1 - 4, dimers and trimers of ionic compounds such as (LiCl)2 and (LiCl)3, and the largest ccCA computation to date: Be(acac)2, BeC10H14O4. Problems with the G3 model chemistries seem to be isolated to metal-oxygen bonded systems and Be-containing systems, as G3 and G3B still perform quite well with a 2.7 and 2.6 kcal mol-1 mean absolute deviation (MAD), respectively, for gas-phase enthalpies of formation. The MAD of the ccCA is only 2.2 kcal mol-1 for enthalpies of formation (DeltaHf) for all compounds studied herein. While this MAD is roughly double that found for a ccCA study of >350 main group (i.e., p-block) compounds, it is commensurate with typical experimental uncertainties for s-block complexes. Some molecules where G3/G3B and ccCA computed DeltaHf values deviate significantly from experiment, such as (LiCl)3, NaCN, and MgF, are inviting candidates for new experimental and high-level theoretical studies.

Adsorption of phenol onto activated carbons having different textural and surface properties

Adsorption of phenol in aqueous phase onto activated carbons (ACs) having different textural and surface properties has been considered. Six types of ACs were used: three were commercial, and three were obtained from Kraft lignin chemically activated with sodium hydroxide, potassium hydroxide or ortho-phosphoric acid. The apparent surface areas of the commercial ACs varied from 620 to 1320 m 2/g, while ACs made from lignin presented surface areas as high as 1300 m 2/g and 2900 m 2/g when prepared with H 3PO 4 and alkaline hydroxides, respectively; moreover, the highest proportion of microporosity was found for ACs derived from lignin. A kinetic study was carried out, showing that the phenol adsorption data may be correctly adjusted, for all the ACs tested, by an equation corresponding to a pseudo second-order chemical reaction. Freundlich, Langmuir and Tempkin equations were tested for modelling the adsorption isotherms at equilibrium, and it was concluded that Langmuir model fitted adequately the experimental data. However, Tempkin model fitted even better the adsorption data obtained with ACs derived from lignin activated with alkaline hydroxides, which are characterized by the highest number of surface groups. Remarkably high phenol adsorption capacities were found for the ACs prepared by activation of Kraft lignin with NaOH and KOH: 238 and 213 mg/g of AC, respectively. Finally, the adsorption of phenol was found to depend not only on the micropore volume, but also on the total amount of carbonyl and basic groups and on the ratio of acid to basic groups.

A New Generation of Sludge-Based Adsorbents for H2S Abatement at Room Temperature

The present paper discusses H2S removal by a new generation of sewage-sludge-derived materials which are characterized by their outstanding textural properties when compared to previous materials obtained by pyrolysis and/or activation of similar precursors. Alkaline hydroxide activation was used to prepare adsorbents/catalysts covering a wide range of porosities (SBET values from 10 to 1300 m2 g(-1)). Our results outline that textural properties are important for H2S abatement. However, not only highly porous sorbents, but also a high metallic content and a basic pH of these materials are required to achieve good performances. Proper combinations of textural properties and alkalinity render superior performances with retention values (x/M) as high as 456 mg of H2S removed per g of material. These retention capacities outperform previously published data for sewage-sludge derived materials and those achieved with commercial materials (including some activated carbons). Sulfur titration shows that most H2S is removed in the form of elemental sulfur, especially in the sewage/NaOH materials.

Activated carbons prepared by pyrolysis of mixtures of carbon precursor/alkaline hydroxide

In the present paper, heat-treatments in N 2 atmosphere of mixtures of different precursors and alkaline hydroxides are studied. The paper analyses the effect that the precursors’ nature (coals, lignocellulosic materials and carbon fibre) has on the final porosity of the resulting activated carbons. The results show that this physical mixing method can be effectively used for all the selected precursors, both with NaOH and KOH. However, differences in adsorption capacity and porosity distribution are observed depending on the precursor and on the hydroxide used. The different behaviour exhibited by both activating agents can be explained by the different structural order in the raw materials. As a general trend, NaOH is more efficient in the activation of low structural-ordered materials, whereas KOH is more effective for the highly ordered materials, what indicates differences in the activation performance of both hydroxides. The results obtained from precursors submitted to a pyrolysis step previous to the heat-treatment of the carbon precursor–hydroxide mixtures corroborate the observed tendencies.

Methodical study of the chemical activation of Kraft lignin with KOH and NaOH

A commercially available Kraft lignin was chemically activated with two alkaline hydroxides, viz NaOH and KOH, using different preparation conditions. The activation was made at various temperatures, hydroxide to lignin mass ratios, activation times, flow rates of inert gas, and heating rates. The resultant activated carbons were characterised in terms of BET surface area, total, micro and meso-pore volumes, average pore width, carbon yield and packing density. The influence of each parameter of the synthesis on the properties of the activated carbons is discussed, and the action of each hydroxide is methodically compared. It is the first time that so many preparation parameters and so many pore texture characteristics are simultaneously considered for two closely related activating agents of the same lignin precursor. Whatever the preparation conditions, it is shown that KOH leads to the most microporous materials, having surface areas and micropore volumes typically 1.5 and 1.2 times higher than those obtained with NaOH, which is in agreement with some early works. However, the surface areas and the micropore volumes obtained in the present study are much higher than in previous studies, up to 3100 m 2/g and 1.5 cm 3/g, respectively, using KOH. The thorough study of the way each preparation parameter influences the properties of the final materials brings insight into the activation mechanisms. Each time it was possible, the results of lignin chemically activated with hydroxides were compared with those obtained with anthracites: explanations of similarities and differences were systematically looked for.