Concentrated Mineral Acids Research Articles

Graft copolymerization of methyl acrylate onto sago starch using ceric ammonium nitrate as an initiator

The graft copolymerization of methyl acrylate onto sago starch was carried out by a free radical initiating process. The free radicals were produced by the chemical initiation method in which ceric ammonium nitrate was used as an initiator. It was found that the percentages of grafting, grafting efficiency, and rate of grafting were all dependent on the concentration of ceric ammonium nitrate (CAN), methyl acrylate (MA), sago starch (AGU), mineral acid (H2SO4), and reaction temperature and period. The variables affecting the graft copolymerization were thoroughly examined. The optimum yield of grafting was obtained when the concentration of CAN, MA, AGU, and H2SO4 were used at 8.77 × 10−3, 0.803, 0.135, and 0.175 mol L−1, respectively. The optimum reaction temperature and period were 50°C and 60 min, respectively. The rate of graft polymerization was explored on the basis of experimental results and reaction mechanism. The evidence of grafted copolymers was investigated by using FTIR spectroscopy, TG, and DSC analysis.

Formation of mesoporous silicates using Triton XN surfactants in the presence of concentrated mineral acids

Mesoporous silicates have been prepared from synthesis mixtures with different acid contents using Triton XN surfactants with short poly(ethylene oxide) (PEO) chains. At very high acid contents, even Triton X45 (nEO = 5.0) with a very low cloud point, gives mesoporous solids. Triton X114 (nEO = 8.0) and Triton X100 (nEO = 10.0) give high quality (HQ) products within a well-defined range of acid contents. HQ products give sharper XRD peaks and narrower pore size distributions than low quality (LQ) products. We attribute the formation of the HQ products to the altered organisation of the surfactant and the formation of hydrogen-bonded adducts with the PEO chains. The N2 adsorption–desorption parameters of the solids obtained by calcining silica–Triton XN mesophases are governed by the hydrophilicity of the surfactant, which in turn depends on the length of the PEO chains and on the acid content. Increased hydrophilicity leads to a decrease in the surface area, adsorption volume and pore diameter of the products.

Determination of total chromium in tannery waste water by inductively coupled plasma-atomic emission spectrometry, flame atomic absorption spectrometry and UV–visible spectrophotometric methods

The determination of total chromium in different streams of tannery effluents were carried out by the digestion of samples in a HNO 3/H 2SO 4 mixture followed by KMnO 4 oxidation, which resulted in the complete conversion of Cr(III) to Cr(VI). The Cr(VI) (Cr 2O 7 2−) species present in these samples were estimated by inductively coupled plasma-atomic emission spectrometry (ICP-AES), flame atomic absorption spectrometry (FAAS) and UV–visible spectrophotometry (1,5-diphenyl carbazide method). The results obtained from these methods were critically evaluated. UV–visible spectrophotometry was found to be better suited for this analysis when compared with the other two methods. Since these solutions contain relatively high concentrations of chromium (200–2400 mg/l), the need for preconcentration did not arise. The higher values obtained in the case of ICP-AES and FAAS methods can be attributed to the matrix effect arising out of high concentration of mineral acids and electrolytes. In addition, the values obtained in the latter methods (ICP-AES and FAAS) are comparable with each other, indicating that the interferences influence the results almost equally in both techniques. The statistical treatment of data indicates that the differences between the methods are within the acceptable range.

Retention of Some Metal Ions and Their Separation on Silica Gel Modified with Acid Red 88

Acid Red 88 is strongly extracted by chloroform solutions of Aliquat 336 by an ion exchange mechanism and for its reextraction from the ion pair formed, relatively high concentrations of mineral acids are required. By impregnation of silica with the ion pairs between the cation of Aliquat 336 and the anion of the dye a chelating sorbent for metal ions can be obtained. The sorbent prepared may be successfully used for separation of mixtures of various metal ions by the column extraction chromatography technique, additional purification of sodium and potassium salts from ions of heavy metals and for concentration of trace amounts of ions of various metals from aqueous solutions followed by their quantitative determination. The sorbent can be used repeatedly in the process of sorption and desorption of metal ions (especially those forming less stable complexes with the reagent) after regeneration with solutions of perchloric acid.

Organosolv pretreatment for enzymatic hydrolysis of poplars: isolation and quantitative structural studies of lignins

Lignins could become important sources of chemical feedstocks and fuels if fractionation of the polymeric constituents of lignocellulosic materials could be improved. To utilize these polymeric components, it is important to understand their composition, chemical characteristics, and properties as a function of how the separation of the polymers is conducted. This paper presents characterization of several lignins as a function of fractionation method and isolation. Organosolv lignins were isolated from pulping liquors obtained by pulping Populus tremuloides (aspen) at 165 °C for 1–2.5 h with methanol: water (70 : 30 by volume). Pulping catalysts were various concentrations of mineral acids (H2SO4 or H3PO4) or salts (NaHSO4). Lignins were isolated by: (1) precipitation through the addition of water of the major lignin fraction (water–insoluble lignin) and (2) solubilization in acetone to yield a small fraction of acetone-soluble lignin. The characterization of these materials was performed through extensive quantitative 13C-NMR and by use of the Distortionless Enhancement by Polarization Transfer (DEPT) NMR sequence to assess the major types of structures formed under these conditions. In addition infra-red spectral data obtained using the DRIFT technique were employed to investigate a few of the structural characteristics. Simple functional groups were also analyzed by chemical methods for comparison. Correlation of differences in the structures of the organosolv lignins was made with the severities of the organosolv pretreatments which were expressed in terms of combined severity factors that incorporated time, temperature, and catalyst effects (pH of the pulping liquor). At low severity, the alkyl aryl ether bonds, the predominant bonds in native lignin, were hydrolyzed leading to materials with low ether bond content, high phenolic hydroxyl content, some methanol incorporation at the side chain, and a small amount of carbon-carbon condensed structures. Quantitation of minor structures such as syringaresinol and p-hydroxybenzoate is given, and the key types of structures present. As the severity increases, a higher extent of carbon-carbon condensation and side-chain degradation was observed while the ether bonding content was decreased. These lignins have low apparent weight-average molecular weights and low polydispersities. The lignins isolated from high severity organosolv pretreatments were completely different from native lignins. The degree of side chain degradation was high, and the number of carbons conventionally employed to describe a lignin repeating unit was substantially decreased from nine to eight or less.

The Kinetics and Mechanism of Interaction of Fe40Ni40B20 Amorphous Metallic Alloys with Mineral Acid Media

Abstract The paper emphasizes the importance of amorphous metallic alloys thin films for magnetic coatings as well as their characterisation with respect to the mineral acid medium in a more qualitative way. The kinetics and mechanism of the interaction of Fe–Ni–B amorphous alloys films with various concentrations of mineral acids (o-phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid,) were studied. On the basis of the weighing method used we deduced that the overall physically and chemically complicated process consists of simultaneous formation of oxides on the surface of the thin films, their dissolution and moreover dissolution of the metal (Fe, Ni) and metalloid (B) elements through a tendency of all of them to react with hydrogen ions. It should be stressed that dissolution of the two-dimensional amorphous metallic alloys-ribbons significantly differs from such dissolution of the metal bulk systems.

Coupled electron and proton transfers: compared behaviour of oxometalates in aqueous solution or after entrapment in polymer matrices

Abstract The anion PW 12 O 3− 40 is very sparingly soluble in concentrated mineral acid solutions. This shortcoming has impeded the kind of study that demonstrated the merging of the first two waves of SiW 12 O 4− 40 and P 2 W 18 O 6− 62 by an EEC mechanism in aqueous solutions. Entrapment of PW 12 O 3− 40 in protonated slightly quaternized poly(4-vinylpyridine) films (QPVP) or in polyaniline films (PANI) has now permitted such a study. As also observed previously, a negative potential shift of the first redox wave of the heteropolyanion is obtained when the acid concentration in the bathing solution increases. All the results are compared with those obtained for QPVP–SiW 12 O 4− 40 , QPVP–P 2 W 18 O 6− 62 , PANI–SiW 12 O 4− 40 and PANI–P 2 W 18 O 6− 62 composites. In each case, the same EEC mechanism is operative. EQCM experiments were also very useful in this issue. Except for the case of PW 12 O3− 40 which could not be studied in concentrated acid solutions, all other systems show that the merging of waves necessitates higher acid concentrations in solution than when the heteropolyanions are entrapped in polymer matrices. This observation was termed the ‘microenvironment effect’. In the present work, confocal microscopy measurements of fluorescence intensity variation between bathing solutions and appropriate composites show directly the existence of differences of pH between the two phases. The results concord with predictions from Donnan effects, and reinforce such an explanation for the ‘microenvironment effect’.

Silica Gel Treated with a Mixture of Aliquat 336 and Acid Alizarin Violet N and Its Application

Acid Alizarin Violet N is strongly extracted by chloroform solutions of Aliquat 336 by an ion-exchange mechanism. Relatively high concentrations of mineral acids are required for its reextraction from the ion pair formed. By impregnation of silica with ion pairs composed of the cation of Aliquat 336 and the anion of the dye, a chelating sorbent for metal ions can be obtained. The sorbent prepared may be successfully used for the separation of mixtures of various metal ions by the column extraction chromatography technique, for additional purification of sodium and potassium salts from the ions of heavy metals, and for the concentration of trace amounts of ions of various metals from aqueous solutions followed by their quantitative determination. The sorbent can be used repeatedly for the sorption and desorption of metal ions (especially those forming less stable complexes with the reagent) after regeneration with solutions of chloric(VII) acid. The effect of hydrophobicity of the chelating reagent on the stability of its ion pair with the tetraalkylammonium cation has been confirmed. Acid Alizarin Violet N forms less stable ion pairs with Aliquat 336 than the more hydrophobic Calmagit.

Pd-Cu Supported on Anionic Polymers - Promising Catalysts for Removal of Nitrates from Drinking Water

Removal of nitrates from drinking water by catalytic hydrogenation over polymer supported Pd-Cu catalysts was studied. Precursors of the catalysts were prepared by ion exchange using microporous polymer cation-exchange resin Dowex 50 W X 4 in acid form and acetone-water solution of Pd and Cu acetates. The metals (approximately 2 and 0.5 wt.% of Pd and Cu, respectively) were reduced with NaBH4 in ethanol at room temperature or with H2 in MeOH at 50 °C and 1 MPa. Catalysts made it possible to reduce nitrate content in water from 100 mg/l to less than 50 mg/l after 4 h of batch treatment with hydrogen-nitrogen mixture (43 vol.% H2) at ambient temperature and atmospheric pressure under vigorous stirring of the reaction mixture. The importance of acid sites of the catalyst for the selective hydrogenation of nitrates to nitrogen was demonstrated by a higher overall selectivity (about 60 mole %) obtained on catalysts containing acid sites than on catalysts without acid sites (about 20 mole %). Catalysts bearing acid sites are promising candidates for removal of nitrates, formed ammonia, as well as other cations because of parallel acting as catalysts and cation exchangers. The used catalysts were regenerated with a low concentrated mineral acid.

Properties of modified zirconia used as friedel-crafts-acylation catalysts

Both precipitated and aerogel synthesized zirconia were modified employing gaseous and solid compounds, respectively, as well as concentrated mineral acids. The sulfur and phosphorous-containing samples were characterized by nitrogen adsorption, X-ray diffraction, FTIR pyridine adsorption, ammonia TPD, and 1-butene isomerization. Modification of zirconia samples results in enhanced Brønsted acidity and catalytic activity. Especially ammonium sulfate and sulfite generate strong acidic centers at the surface in high concentrations. As was shown on the basis of XPS measurements the final calcination step in air converts the sulfite into surface sulfate, resulting finally in the same, or at least very similar, surface states of both differently treated samples. Some few degrees enhanced catalytic activities were obtained using sulfated zirconia aerogels. Applied to the benzoylation of anisole, a slurry of these catalytically active zirconia samples yields similar high conversion degrees as nonafluorobutanesulfonic acid known as an excellent catalyst for this reaction in homogeneous solution. There is evidence to assume that the benzoylation reaction under the conditions used occurs exclusively at Brønsted acid sites but not at Lewis sites. A hypothetical path for the action of a sulfated zirconia surface in the catalytic step is proposed.

Classical dry ashing of biological and agricultural materials. Part II. Losses of analytes due to their retention in an insoluble residue

Retention of selected analytes (Cd , Cr, Cu, Mn, Pb, Zn) in solid residue which remains undissolved in 1.5% HNO 3 used as a leaching medium after classical dry ashing of ten materials (alfalfa lea ves, NIST SRM 1569 Brewer' s Yeast, blood meal, meat-bone meal, feather-bone meal, silage residue , litter, pond sediment, coal waste , IRM NSC-21 Industrial Compost Vitahum) was studied . The elements remaining in the residue were determined mainly b y AAS after dissolution of this residue in the mix - ture of HF + HNO 3. In several instances, pressurized wet digestion, alkaline fusion, stripping voltammetry and instrumental neu- tron acti vation were also applied. Increasing concentr ation of mineral acid in leaching medium which does not contain HF, plus increasing final volume of the solution, suppresses significantly this type of analyte losses in the majority of matrices tested . However, for industrial compost and standard reference material NIST 1569 Br ewer' s Yeast, application of an HF step is neces - sary for quantitative release of the analytes (in particular chromium) into solution.

A 1H and 195Pt NMR study of the protonation mediated interconversion of mono- ( S) versus bidentate S, O) co-ordination of Pt(II) by N−acyl- N′, N′-dialkylthioureas

Treatment of cis-[Pt(L− S, O) 2] in CDCl 3 solution, directly in an NMR tube with concentrated mineral acid HX and/or HY (X = Cl −, Y = Br −), leads to the reversible protonation of the co-ordinated ligand of these complexes across the aqueous-organic phase boundary; these processes have been followed by means of 195Pt and 1H NMR. Treatment with HCl yields of cis- and trans-[Pt(HL)−S 2 Cl 2] species, in addition to the partially-ring-opened [Pt(L n − S, O)(HL n − S)Cl] complex in solution, the cis-[Pt(HL− S) 2Cl 2] complex predominating in solution at steady-state. These species are rapidly and reversibly converted back to only the cis-[Pt(L− S, O) 2] complex on washing of the CDCl 3 solution with aqueous ammonia. Similar observations pertain to protonation by HBr, yielding the corresponding bromo complexes; treatment of cis-[Pt(L− S, O) 2] in CDCl 3 with a mixture of HCl and HBr, leads to the formaiton of mixed-halide species of cis- and trans-[Pt(HL− S) 2XY] in addition to the [Pt(HL− S) 2) 2X 2] and [Pt( HL t- S) 2Y 2] as well as the partially-ring-opened [Pt(L n − S, O)(HL n − S)X/Y] complexes in solution, which revert to cis-[Pt( L− S, O) 2] on treatment with aqueous base. These observations clearly have important consequences in the use of N-acyl- N′ N′-dialkylthioureas for the solvent extraction of the platinum metals.

Modifying Nylon 6 by Treating with Dichlorobenzenesulfonyl Chloride

Sulfonation of nylon 6 fibers by 2,5 dichlorobenzenesulfonyl chloride (dbsc) has a great effect on the heat and chemical stability of the fibers. Sulfur content, carbon residue, degree of crimp, and solubility in formic acid are all determined, the effects of dbsc concentration, reaction temperature, and reaction time are studied. Increasing dbsc concentration and temperature are more effective at increasing the sulfur content in modified fibers than increasing reaction time. The best results are obtained with a dbsc concentration of 25% and a reaction temperature of 115°C for 4 hours. At these conditions, the modified fibers have 4.9% sulfur content, 26.4% carbon residue, 97.5% degree of crimp, and lose solubility in formic acid, concentrated mineral acids, and aqua regia. They do not burn when put in direct flames, but glow and char without losing fiber form. No melting occurs at up to 1000°C, and the activation energy of decomposition is 194 kJ/mole compared to 46 kJ/mole for the unmodified fibers. Strength properties decrease.

The application of solid sorbents for the purification of aluminum contaminated chemicals used as modifiers in electrothermal atomic absorption spectrometry.

Various microcolumns with solid sorbents (ion exchange resins, functionalised cellulose sorbents, chelating resins) have been tested with respect to their ability for the purification of aluminum contaminated chemicals used as modifiers in electrothermal atomic absorption spectrometry. The purification of NaNO(3), Mg(NO(3))(2), K(2)SO(4) and (NH(4))(2)HPO(4) has been the most effective with an almost 100% efficiency, when Spheron-Oxine was used as chelating resin. The sorption of aluminum from KOH solution has been found to be very high (around 90%) for all investigated sorbents. However, the best results have been obtained with anion-exchange resins. It has been difficult to purify concentrated mineral acids (HCl, H(2)SO(4)). A retention of aluminum above 80% has been achieved only when Cellex P, Chelex 100 or Amberlite XAD-2 have been used.

Sugar Beet Grown Using Nutrient Film Technique: Yield and Nutritional Quality

Sugar beet (Beta vulgaris L cv Great Western Sugar) was grown using the nutrient film technique with a half-strength modified Hoagland nutrient solution to determine its biomass yield and nutritional quality. After 6 months, storage root and foliage weights per plant were 493.1 g and 551.0 g, respectively. Sucrose content in the fresh storage root was 118.4 g kg -1 but was less than 10 g kg -1 in the fresh leaves and petioles. Some nutrients in the leaves and petioles were analysed to evaluate their potential as a leafy vegetable. Fresh leaf protein, total dietary fibre, mineral (Ca, Mg, Zn, Fe and K), vitamin (carotene, ascorbic acid and thiamine) and oxalic acid concentrations were similar to those of consumer-accepted green vegetables.

Kinetics and equilibria in the nitric acid–nitrous acid–sodium thiocyanate system

The nature of the red species formed in acidic solutions containing nitrous acid and thiocyanate ion has been confirmed to be ONSCN. The alternative literature interpretation in terms of ONSCNH+ arises from neglect of activity coefficients and partial protonation of SCN– to HNCS in moderately concentrated mineral acid. The kinetics of the nitrous acid-catalysed oxidation of thiocyanate in moderately concentrated nitric acid is controlled by rate-determining formation of N2O4 at even modest concentrations of thiocyanate. Literature work on this system is discussed.

Alloy nicrofer 2509 Si 7, a new corrosion-resistant material for operation with hot concentrated mineral acids

Thanks to adequate choice of alloying components (chromium and nickel)was it possible to devise a ductile austenitic chrome-nickel steel containing 7% Si. It is very corrosion-resistant in 96% H2SO 4 at 150~ and in 98.5% H2SO 4 at 200~ and also in boiling highly concentrated nitric acid. This steel is very ductile in the deformed state, and in the quenched state it lends itself well to cold forming. However, to attain sufficient ductility of welded joints, welding must be carried out with low heat input and with subsequent heat treatment to solid solution. The new steel can be used as corrosion-resistant coating of large structures made of carbon steel, and that also reduces production costs. For welding of objects, with small cross section, e.g., in making straight-seam electrically welded pipes with small wall thickness, the most efficient way is laser welding. For large structures clad sheets have to be used. The new steel can also serve as material for shaped casting including components and housings of pumps, etc. Jointly with the Institute of High-Quality Steels of the I. P. Bardin Central Research Institute of Ferrous Metals we investigated the influence of the content of alloying elements (silicon in the range 5-7.5 %, chromium 9-19 %, nickel 19-26 %), and as a result we studied the ductility of Nicrofer 2509 Si 7 in the hot state, its microstructure, and also its corrosion resistance in hot concentrated sulfuric acid and nitric acids. It was established that when the silicon content is increased, a fully austenitic structure can be ensured when there is 9 % chromium and 25 % nickel content. Corrosion resistance in 96, 98.5, and 99.5% H2SO 4 was investigated at 150, 175, and 200~ by immersion of hotrolled, cold-formed, and quenched specimens for a period of up to 21 days. The dependence of the true corrosion rate and of the theoretical one, obtained as a result of the mathematical processing of the test results in 96% H2SO 4 at 150~ on the content of elements (El = 8.166 0.982 Si 0.057 Cr 0.021 Ni) shows (Fig. 1) that the decisive influence is exerted by the silicon content whereas chromium and nickel play a secondary role. When we assume that the chromium content is 9% and nickel content is 25% (this ensures the austenitic structure of the steel), then, with 7% Si content the theoretical corrosion rate is 0.25 mm/year. This is perfectly satisfactory for 96% H2SO 4 at 150~ While working out the composition of the steel we obtained the dependence of the corrosion rate in 98% HNO 3 at 100~ on the chromium and silicon content which shows that a silicon content Of more than 7% does not reduce the corrosion rate any more (Fig. 2). Table 1 presents the chemical composition of Nicrofer 2509 Si 7, the alloy 700 Si (No. 1.4390 according to the catatog of Krupp VDM) and one of the first industrial melts (sheet 16 mm thick) whose microstructure after quenching at 1100~ is completely austenitic and is marked by high ductility (65 > 70%) at room and elevated temperatures (see Table 2). An important characteristic used in stress analysis, viz., yield strength a0. 2 at room temperature (HB < 200), is more than 240 N/ram 2. The physical properties of alloy 700 Si at room and elevated temperatures are presented in Table 3, its density is 7.6 g/cm 3, melting point is 1330~ magnetic permeability is < 1.005. Microanalysis of the structure of steel Nicrofer 2509 Si 7 in dependence on the tempering temperature and tempering time showed that after brief holding at 700-900~ the phase FesNi3Si 2 segregates on grain boundaries and in the body of the

A solid composite pH sensor based on quinhydrone

AbstractA solid composite pH sensor can be made from quinhydrone, solid paraffin and surface‐modified graphite powder. It exhibits an almost theoretical slope of the potential–pH dependence (−57.7 mV at 25°C), a formal potential E0′ = 0.6922V (vs. NHE), low standard deviations for repeated measurements (0.04 pH units), fast potential response (15s) and a working range up to pH 9.5. The sensor can be used in moderately concentrated mineral acids and, unlike the conventional quinhydrone electrode, it is also applicable for measurements in milk. The sensor shows the same salt effect and sensitivity towards strong oxidants and reductants as the conventional quinhydrone electrode. The surface modified graphite was prepared by boiling graphite powder with concentrated nitric acid. By voltammetry it was shown that the surface of the modified graphite contains surface‐confined redox centers similar to those in quinhydrone, which can catalyze the electron transfer of the quinhydrone on the surface of the sensor.

Study on the concentration of acids by membrane distillation

The membrane distillation (MD) process was applied for the concentration of different mineral acids, such as, sulfuric phosphoric, hydrochloric and nitric acids. The MD of a citric acid solution as an example of an organic acid was also investigated. The experiments were carried out keeping the warm feed and cold solution temperatures at 333 and 293 K, respectively. The data obtained indicate that the volume flux of a permeate decreased with an increase of acid concentration in the feed. The reduction of acid content in the permeate, close to 100%, for non-volatile acids was independent of the acid concentration in the feed. The amounts of hydrochloric or nitric acids in the permeate increased with a rise of the acid concentration in the feed, reaching the azeotropic composition. The effect of the polarisation phenomena on the concentration process of sulfuric acid is discussed.

Reactivity of Chromium Oxide in Aqueous Solutions. 2. Acid Dissolution

The influence of the type and the concentration of several mineral acids (HNO 3 , H 2 SO 4 , and HCI) on the dissolution of two different chromium (hydrous) oxides was investigated at 25 and 65 °C. The results were interpreted using a combined approach that takes into account the electrochemical nature of the process, the surface complexation, and multiple-site models for the dissolution of very passive covalent oxides. The attack by protons on oxo bonds is the critical step that strongly enhances the rate of the process at higher acidities. The reactivity of chromium (hydrous) oxides is shown to be related to the degree of cross-linking and not to the water contents.