Dilute Acid Conditions Research Articles

De Novo Approaches to the Solid-Phase Separation of Titanium(IV) and Scandium(III): Translating Speciation Data to Selective On-Bead Chelation toward Applications in Nuclear Medicine.

The solution chemistry of the hydrolytic, early-transition-metal ions Ti4+ and Sc3+ represents a coordination chemistry challenge with important real-world implications, specifically in the context of 44Ti/44Sc and 45Ti/NatSc radiochemical separations. Unclear speciation of the solid and solution phases and tertiary mixtures of mineral acid, organic chelators, and solid supports are common confounds, necessitating tedious screening of multiple variables. Herein we describe how thermodynamic speciation data in solution informs the design of new solid-phase chelation approaches enabling separations of Ti4+ and Sc3+. The ligands catechol (benzene-1,2-diol) and deferiprone [3-hydroxy-1,2-dimethyl-4(1H)-pyridone] bind Ti4+ at significantly more acidic conditions (2-4 pH units) than Sc3+. Four chelating resins were synthesized using either catechol or deferiprone with two different solid supports. Of these, deferiprone appended to carboxylic acid polymer-functionalized silica (CA-Def) resin exhibited excellent binding affinity for Ti4+ across a wide range of HCl concentrations (1.0-0.001 M), whereas Sc3+ was only retained in dilute acidic conditions (0.01-0.001 M HCl). CA-Def resin produced separation factors of >100 (Ti/Sc) in 0.1-0.4 M HCl, and the corresponding Kd values (>1000) show strong retention of Ti4+. A model 44Ti/44Sc generator was produced, showing 65 ± 3% yield of 44Sc in 200 μL of 0.2 M HCl with a significant 44Ti breakthrough of 0.1%, precluding use in its current form. Attempts, however, removed natSc in loading fractions and a dilute (0.4 M HCl) wash and recovered 80% of the loaded 45Ti activity in 400 μL of 6 M HCl. The previously validated 45Ti chelator TREN-CAM was used for comparative proof-of-concept reactions with the CA-Def eluent (in HCl) and literature-reported hydroxamate-based resin eluents (in citric acid). CA-Def shows improved radiolabeling efficiency with an apparent molar activity (AMA) of 0.177 mCi nmol-1, exceeding the established methods (0.026 mCi nmol-1) and improving the separation and recovery of 45Ti for positron emission tomography imaging applications.

In vivo cadmium-assisted dilute acid pretreatment of the phytoremediation sweet sorghum for enzymatic hydrolysis and cadmium enrichment

Phytoremediation with energy crops is considered an integrated technology that provides both environment and energy benefits. Herein, the sweet sorghum cultivated on Cd-contaminated farmland (1.21 mg/kg of Cd in the soil) showed promising phytoremediation potential, and the approach for utilizing sorghum stalks was explored. Sweet sorghum bagasse with Cd contamination was pretreated with dilute acid in order to improve enzymatic saccharification and achieve Cd recovery, resulting in harmless and value-added utilization. After pretreatment, hemicelluloses were dramatically degraded, and the lignocellulosic structures were partially deconstructed with xylan removal up to 98.1%. Under the optimal condition (0.75% H2SO4), the highest total sugar yield was 0.48 g/g of raw bagasse; and nearly 98% of Cd was enriched in the liquid phase. Compared with normal biomass, Cd reduced the biomass recalcitrance and further facilitated the deconstruction of biomass under super dilute acid conditions. This work provided an example for the subsequent valorization of Cd-containing biomass and Cd recovery, which will greatly facilitate the development of phytoremediation of heavy metal contaminated soil.

Optimizing room temperature binder free TiO2 paste for high efficiency flexible polymer dye sensitized solar cells

Binder free TiO2 paste is prepared using tert-butyl alcohol in dilute acidic conditions at room temperature for flexible polymer dye sensitized solar cells (DSSCs). The present paper reports the detailed studies carried out to elucidate the importance of stirring times during the paste preparation on the final device performance. The maximum conversion efficiency of 4.2% was obtained for flexible DSSCs fabricated on tin doped indium oxide/polyethylene naphthalate substrates using TiO2 paste prepared with an optimum stirring time of 8 h. The effect of optimum stirring times on the device characteristics has been understood in terms of the detailed morphology and surface area measurements.

Evaluation of tropical seaweeds as feedstock for bioethanol production

Limited resources of freshwater and decreasing fossil fuel resources are two main reasons to consider the ocean as a huge resource for producing food, feed, fertilizer and feedstock for fuel. In this study, twenty-nine tropical seaweeds (11 green, 10 red and 8 brown seaweeds) collected in Malaysia were assessed as potential feedstock for bioethanol production. Total carbohydrate content ranged from 12.16 to 71.22% dry weight (DW) with total reducing sugar content ranging from 5.17 to 34.12% DW. During hydrolysis using dilute sulphuric acid, the dominant fermentation inhibitors were 5-hydroxymethylfurfural and phenolic compounds. Overliming was found to reduce the content of fermentation inhibitors by up to 79%. The red seaweeds, Kappaphycus alvarezii (Doty) Doty ex P.C.Silva and Gracilaria manilaensis Yamamoto and Trono, were selected for optimization of saccharification and fermentation of the hydrolysate, because they had the highest carbohydrate contents and are commercially cultivated. The most suitable dilute acid conditions obtained in present study was sulphuric acid (2.5%, w v−1) treatment at 121 °C for 40 min that produced 0.29 and 0.34 g g−1 DW reducing sugar for K. alvarezii and G. manilaensis, respectively. Fermentation of the hydrolysates with Saccharomyces cerevisiae produced bioethanol yields of 20.90 g L−1 (71.0% of theoretical yield) for K. alvarezii and 18.16 g L−1 (67.9% theoretical yield) for G. manilaensis.

Pretreatment of trace element-enriched biomasses grown on phytomanaged soils for bioethanol production

Phytotechnologies are a set of sustainable, ecological options notably for alleviating pollutant linkages induced by contaminated soils. However, concerns exist regarding the processing of trace elements (TE)-enriched biomass and the fate of TEs in the end-products. The fractionation of phytoremediation TE-enriched non-woody lignocellulosic (tobacco) and woody (birch, willow) phytoremediation-borne biomasses was studied using ethanol organosolv, soda and dilute acid pretreatments. TE distribution in the process fractions (pulp, liquid effluents and lignin) was further examined. In dilute acid conditions, a wood pretreatment performed at 170°C in the presence of 2% w/w of sulfuric acid allowed an efficient extraction of the metals in the water effluent (≈90% for Mn and Zn) producing a clean pulp. A soda pretreatment resulted in a low metal extractability, especially at high temperature. At 170°C or above with 15% w/w of NaOH, metals were mostly recovered in the cellulosic pulp (70%- 98%). Using organosolv pulping, the TE contents were in the decreasing order: pulp≫water stream>lignin. The TE organosolv extraction in the liquid phase varied depending on the TE metal and on the species but was generally low. Metal extractability increased with the water content in the solvent of the organosolv pulping but decreased with temperature. Enzymatic hydrolyses of TE-enriched and metal-free pulps were investigated and it was concluded that the TE concentrations had little or no effect on polysaccharide enzymatic hydrolysability by cellulases. The final destination of the various fractions for valorization in a biorefinery setting is discussed, regarding their TE content.

2D NMR characterization of wheat straw residual lignin after dilute acid pretreatment with different severities

Abstract The chemical characteristics of wheat straw lignin pretreated under dilute acid conditions were compared. After pretreatment, the lignin content of the solid residue increased as temperature increased (from 160°C to 190°C) and with the amount of acid added (0%, 0.25%, or 1% H2SO4). Pretreatment at 190°C with increasing concentrations of acid catalyst led to a decrease in glucan content, whereas the glucan content remained almost constant at 160°C pretreatment regardless of the acid concentration. The xylan content decreased in proportion with increased acid concentration and pretreatment temperature. The residual lignins were characterized by solution-state, two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy and size-exclusion chromatography (SEC). Results showed that more ether bonds were cleaved with increased pretreatment temperature and lower pH, whereas the levels of carbon-carbon bonded structures (e.g. phenylcoumaran and resinol units) were hardly affected. With a pretreatment of 160°C and 1% H2SO4, the majority of the β-O-4 bonds were cleaved. In addition, lignin depolymerization was more evident than repolymerization at higher pretreatment temperatures and lower pH. Documenting lignin structural changes as a function of pretreatment parameters provides a tool for biorefineries to gain flexibility in processing parameters with full control over the final properties of the products.

Hydrolysis of cellulose to glucose over carbon catalysts sulfonated via a plasma process in dilute acids

A sulfonation route for carbon materials under dilute acid conditionsviaa plasma process.

Effect of dilute acid pretreatment conditions and washing on the production of inhibitors and on recovery of sugars during wheat straw enzymatic hydrolysis

Pretreatment is an essential process to break down recalcitrant biomass and dilute acid hydrolysis is one of the most efficient and cost effective pretreatment technologies available today. However there are potential disadvantages in using dilute acid as a pretreatment, such as the production of degradation products, which inhibits the ensuing processing chain and limits its adoption. In this work, wheat straw was pretreated under varying dilute acid conditions; the resulting degradation products were determined and the quality of sugar stream generated via enzymatic saccharification was monitored. The dilute acid pretreatment conditions were: temperatures of 140 and 160 °C, sulfuric acid concentrations of 5, 10 and 20 dm3 m−3 and reaction times of 10, 20, 30, 45 and 60 min. Pretreated wheat straw was washed with six dilutions of water and hydrolyzed with commercial cellulase enzymes for 24–48 h. Optimal conditions for pretreating wheat straw were determined as: 140 °C, 10 dm3 m−3 sulfuric acid concentration and a 30 min reaction time. At these conditions, the glucose yield from wheat straw was maximized at 89% of the theoretical maximum, while the concentrations of formic acid, furfural, acetic acid and 5-hydroxymethylfurfural were 32.37 ± 4.91, 12.08 ± 1.69, 7.98 ± 1.02 and 1.14 ± 0.22 g kg−1, respectively. Increases in pretreatment severity led to increases in inhibitor generation, as well as a 27% reduction in monosaccharide yield. Rinsing with deionized water was effective in removing inhibitors, such as 86% of furfural. The formation of inhibitors was thus observed to depend on dilute acid pretreatment conditions.

Degradable and salt-responsive random copolymers

We report a class of degradable stimuli-responsive random copolymers that exhibit high sensitivity to ionic strength (salt concentration). Cationic random copolymers, poly(ε-caprolactone)-co-poly(ε-caprolactone-graft-quaternary ammonium) (PCL-co-P(CL-g-QA)), were synthesized by a combination of ring-opening polymerization and copper-catalyzed click chemistry. Random copolymers with various compositions of QA were prepared by adjusting the ratio of CL and substituted CL. Due to the presence of cationic QA groups at the polymer side chain, these random copolymers showed salt concentration (or ionic strength)-dependent solubility. In salt-free water or water with low ionic strength of salt (NaCl, CaCl2), random copolymers were soluble due to the overwhelming domination of electrostatic repulsive Coulomb interactions between cationic QA species over attractive hydrophobic interactions between CL segments. The solubility of copolymers decreased with the increase of ionic strength of salt solution due to the screening effect of free ions to reduce the repulsive Coulomb interactions between QA species and thus a significant change of macromolecular conformations. It was found that the salt responsiveness of synthesized random copolymers was maximized when the CL-g-QA fraction was ∼15 mol% in the copolymers. These random copolymers were readily degradable under dilute acidic conditions.

Acid Hydrolysis and Utilization of Distillers' Grains

Distillers' grains (DG) has high cellulose contents and is suitable for conversion to reducing sugar under dilute acid conditions. The effects of the hydrolysis conditions, including acid concentration, solid to liquid ratio, reaction temperature and time, were discussed, as well as the changes of microstructure and groups after hydrolysis. The conversion rate of reducing sugar could reach 25.07% (g/100g DG) when the hydrolysis conditions are as follows: the concentration of sulphuric acid is 5% (wt), the temperature is 120 °C, the ratio of sulphuric acid solution volume (mL) to weight of DG (g) is 30:1 and the reaction time is 10 h.

Optimum conditions for dilute acid hydrolysis of hemicellulose in dried distillers grains with solubles

Corn dried distillers grains (DDGS) had high hemicellulose contents and were suitable for conversion to pentose under dilute acid conditions. The effects of the hydrolysis conditions, including reaction temperature (110–130 °C), time (30–90 min), and acid concentration (2–4%, w/v), on profile and yield of mono-sugars were determined using response surface methodology. Three major sugars, namely xylose, arabinose, and glucose were generated during dilute acid hydrolysis. Reaction temperature, time, and acid concentration had significant effects on xylose and arabinose yields, while glucose yield was affected only by temperature and acid concentration. Lower reaction temperature and longer reaction time favorably affected xylose and arabinose yields. The optimum levels of the independent variables were 112 °C reaction temperature for 84.5 min and 3.1% (w/v) acid concentration. The corresponding predicted responses were xylose yield of 267.3 mg/g dry matter, arabinose yield of 121.2 mg/g dry matter, and glucose yield of 46.3 mg/g dry matter. The selected second-order models were deemed the best since the experimental values were close to the predicted values at the optimum conditions, and high correlation coefficients ( R 2) were obtained for all models.

Controlled production of oligosaccharides from amylose by acid-hydrolysis under microwave treatment: Comparison with conventional heating

Controlled production of malto-oligosaccharides from pure amylose has been realised in a fast, cheap and easy way with good potentials for later scale up. Pure amylose (20 g L −1) was hydrolysed under dilute acidic conditions (0.45 M HCl, 90 °C) with two sorts of heating: microwave irradiation and conventional heating. The kinetics of oligosaccharide production were followed by high-performance anion exchange chromatography. Microwave treatment was shown to be more efficient. A similar range of oligosaccharides as with the conventional heating procedure was observed, but without any appearance of degradation compounds (brown products) and a 10 times faster production rate leading to very short production times (maximum 15 min).

Pectins in the fruits of Japanese quince ( Chaenomeles japonica)

The pectin content, composition and physico-chemical properties were studied in the fruits of two genotypes of Japanese quince. On average, the fruits contained 11 g pectins/100 g dry fruit and 1.4 g pectins/100 g fresh fruit. A sequential extraction was used to isolate the pectins from the fruits. The cells from the flesh were examined using a confocal laser scan microscope, fresh and after each extraction step of the sequence. The dilute acid conditions were the most efficient for pectin extraction. Pectins extracted by water or potassium oxalate had higher (>600 ml/g) intrinsic viscosities than the pectins extracted by dilute acid (<400 ml/g). Anionic exchange chromatography was performed on the acid-extracted pectins. They were constituted of four populations, the first one being mainly composed of arabinans, the second one of homogalacturonans, the third one of rhamnogalacturonans. The composition of the last one varied with the genotype studied.

Surface dissolution of calcium phosphate glass ceramics in dilute acid conditions

Abstract Calcium phosphate glass–ceramic materials in the P2O5–CaO–SiO2–K2O system were prepared from mineral and industrial waste raw materials. They were characterized by chemical analysis, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Tricalcium phosphate (α and β-Ca3(PO4)2), tetracalcium phosphate (Ca4P2O9) and glassy phases were identified in various proportions. The materials were treated in water, ammonium citrate, ammonium acetate and citric acid solutions. The mechanism of attack of the different phosphate phases in dilute acid conditions was established mainly following the P, Si, Ca, K concentrations versus time by inductively coupled plasma optical emission spectroscopy (ICP–OES). The results show that these glass–ceramic materials can be used as controlled released fertilisers.

An Ultrasonically Facilitated Boron-Doped Diamond Voltammetric Sensor for Analysis of the Priority Pollutant 4-Chlorophenol

Electroanalysis of the ‘priority pollutant’, 4-chlorophenol, is largely unreported in the scientific literature, due mainly to the electrode passivation observed from oxidative by-products. Work is presented which details the combination of high-intensity ultrasound with a mechanically and chemically robust boron-doped diamond electrode allowing successful development of an aqueous 4-chlorophenol voltammetric sensor. The surface regeneration abilities of power ultrasound, through cavitational erosion of electrodeposited 4-chlorophenol by-products, facilitates a reproducible, insonated limiting-current oxidative signal in dilute acid conditions, with increased mass-transport offering enhanced sensitivity. A lower limit of detection of 1 μM and a linear range of 1–300 μM are reported; the technique being analytically useful over a concentration range where aquatic 4-chlorophenol pollution is known to occur. The use of power ultrasound during the electrooxidation of 4-chlorophenol at boron-doped diamond has also been shown to be advantageous in the electrochemical degradation of the substance, potentially offering further waste-water clean-up applications of this dual technology.

Vanadium-Catalysed Oxidative Bromination Using Dilute Mineral Acids and Hydrogen Peroxide: An Option for Recycling Waste Acid Streams

Vanadium pentoxide, V2O5, catalyses the two-electron oxidation of Br- to Br+, using aqueous hydrogen peroxide under dilute acidic conditions. In this system, kinetic studies show that HBr can be replaced with a combination of an alkali bromide salt (NaBr, KBr) and a dilute mineral acid (e.g., HCl, H2SO4, HNO3, H3PO4). The salt/acid/peroxide system may be used for in situ or ex situ oxidative bromination, e.g. of various aromatic compounds. The application of the above concept towards the recycling of industrial acid waste is discussed. The cost effectiveness, E factors, and hazard factors for several bromination and oxidative bromination reagent systems are compared.

Reactions of 5-trifluoroacetyl-3,4dihydro-2H-pyran with zinc reagents

One pot reaction of 5-trifluoroacetyl-3,4-dihydro-2H-pyran with alkyl bromides Rbr in the presence of zinc powder gave the corresponding alcohol ( CH 2) 3OCH=C C(R)(CF 3)OH (R: CH 2CO 2Me, 3a; CH 2CHCH 2- 3b); 3a readily hydrolysed to the corresponding carboxylic acid under dilute acidic conditions, intramolecular cyclo addition of this acid afforded a bicyclo lactone.

Thickness control and defects in oriented mesoporous silica films

By using a surfactant-based synthesis strategy, we have earlier demonstrated that the polymerization and growth of silicate micellar assemblies at the air–water interface, under quiescent and dilute acidic aqueous conditions, yields free-standing sub-micron thickness hexagonal mesoporous silica films in which the channels are oriented parallel to the film surface. TEM imaging studies of these thin films showed that microscopic defects pervade the channel structure with topologies resembling those found in lyotropic liquid crystals. This suggested that the mesoporous silica film evolved from silicification of a surface lyotropic silicate mesophase. Herein it is demonstrated that film growth, defect structure, extent of polymerization, and mesoporosity sensitively depend on the choice of synthesis acidity, temperature and mixing, and in the case of supported films, on the choice of substrate. In particular, a ten-fold increase in the thickness of the film can be obtained by simply lowering the acidity and moving to ambient temperature conditions whilst an alteration in mixing conditions can change the film from a discrete to a continuous morphology. Combined PXRD, TEM and nitrogen adsorption studies show that the silica films are hexagonal, oriented and mesoporous. Furthermore, the observation of a focal conic fan-type texture in the free-standing films shows that defect controlled director fields, that exist in a precursor hexagonal lyotropic silicate mesophase, are preserved in the channel structure of the mesoporous silica phase. Proof-of-existence of liquid crystalline texture in such free-standing mesoporous silica films, provides direct evidence that film growth evolves from the cooperative assembly and organization of silicate micellar species at the air–water interface.

Beckmann Rearrangement of Cyclohexanone Oxime under Dilute Acidic Conditions in Micellar Media

The paper reports the Beckmann rearrangement of cyclohexanone oxime to caprolactam in micellar media under dilute acidic conditions. The anomalous hydrogen ion concentration experienced in the vicinity of the interface can be gainfully exploited to carry out the reaction and change the product pattern. The phase behavior and reaction product distribution at various temperatures and surfactant and acid concentrations are analyzed with a view to optimizing the system performance.

Mechanistic studies of the Fischer indole reaction

Kinetic and solvent isotope effects were measured for the Fischer indole reactions of four hydrazones. Under neat acid conditions (5% P 2 O 5 /MeSO 3 H) the KIE's ranged from 3.2 to 5.8, while the solvent isotope effects (k H /K D ) ranged from 0.4 to 0.7. Under dilute acid conditions in sulfolane solvent, both isotope effects were near unity