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1.
Pereira Ernandes B. de Castro Heizir F. De Moraes Flávio F. Zanin Gisella M. 《Applied biochemistry and biotechnology》2002,98(1-9):977-986
Microbial lipase from Candida rugosa immobilized into porous chitosan beads was tested for esterification selectivity with butanol and different organic acids
(C2–C12), and butyric acid and different aliphatic alcohols (C2–C10). After 24 h, the acids tested achieved conversions of
about 40–45%. Acetic acid was the only exception, and in this case butanol was not consumed. Different alcohols led to butyric
acid conversions >40%, except for ethanol, in which case butyric acid was converted only 26%. The system’s butanol and butyric
acid were selected for a detailed study by employing an experimental design. The influence of temperature, initial catalyst
concentration, and acid:alcohol molar ratio on the formation of butyl butyrate was simultaneously investigated, employing
a 23 full factorial design. The range studied was 37–50°C for temperature (X1), 1.25–2.5% (w/v) for the catalyst concentration (X2), and 1 and 2 for the acid:alcohol molar ratio (X3). Catalyst concentration (X2) was found to be the most significant factor and its influence was positive. Maximum ester yield (83%) could be obtained
when working at the lowest level for temperature (37°C), highest level for lipase concentration (2.5% [w/v]), and center level
of acid:alcohol molar ratio (1.5). The immobilized lipase was also used repeatedly in batch esterification reactions of butanol
with butyric acid, revealing a half-life of 86 h. 相似文献
2.
Barbara Pilawa Andrzej B. Więckowski Robert Pietrzak Helena Wachowska 《Central European Journal of Chemistry》2007,5(1):330-340
Microwave saturation of multi-component EPR spectra of oxidized lignite Mequinenza (Spain) with a carbon content of 65.1 wt
% and with a high sulphur content of 10.3 wt % was studied. The coal was oxidized with nitric acid (NHO3), peroxyacetic acid (PAA), and in O2/Na2CO3 system. Three different groups of paramagnetic centres exist in the coal samples analyzed. The EPR spectrum of the demineralised
coal was a superposition of broad Gauss (ΔB
pp
= 0.75 mT), broad Lorentz 1 (ΔB
pp
= 0.42 mT) and narrow Lorentz 3 lines (ΔB
pp
= 0.08 mT). The three EPR components with linewidths: 0.58–0.77 mT (Gauss line), 0.30–0.39 mT (Lorentz 1 line) and 0.05–0.06
mT (Lorentz 3 line) were recorded for the oxidized coal. The g-values were obtained for the samples studied in the ranges 2.0043–2.0046 (Gauss lines), 2.0035–2.0038 (Lorentz 1 lines) and
2.0032–2.0034 (Lorentz 3 lines). The broad Gauss and Lorentz 1 lines saturate at low microwave powers. The narrow Lorentz
3 lines of demineralised coal were not saturated at microwave power from the range considered. After the coal oxidation with
HNO3, PAA and in O2/Na2CO3 system, the microwave saturation of the narrow Lorentz 3 lines was also observed, which indicated a degradation of the multi-ring
aromatic structures upon oxidation.
相似文献
3.
Mauricio P. de Paula Talita M. Lacerda Márcia D. Zambon Elisabete Frollini 《Cellulose (London, England)》2012,19(3):975-992
The present work is inserted into the broad context of the upgrading of lignocellulosic fibers. Sisal was chosen in the present
study because more than 50% of the world’s sisal is cultivated in Brazil, it has a short life cycle and its fiber has a high
cellulose content. Specifically, in the present study, the subject addressed was the hydrolysis of the sisal pulp, using sulfuric
acid as the catalyst. To assess the influence of parameters such as the concentration of the sulfuric acid and the temperature
during this process, the pulp was hydrolyzed with various concentrations of sulfuric acid (30–50%) at 70 °C and with 30% acid
(v/v) at various temperatures (60–100 °C). During hydrolysis, aliquots were withdrawn from the reaction media, and the solid
(non-hydrolyzed pulp) was separated from the liquid (liquor) by filtering each aliquot. The sugar composition of the liquor
was analyzed by HPLC, and the non-hydrolyzed pulps were characterized by viscometry (average molar mass), and X-ray diffraction
(crystallinity). The results support the following conclusions: acid hydrolysis using 30% H2SO4 at 100 °C can produce sisal microcrystalline cellulose and the conditions that led to the largest glucose yield and lowest
decomposition rate were 50% H2SO4 at 70 °C. In summary, the study of sisal pulp hydrolysis using concentrated acid showed that certain conditions are suitable
for high recovery of xylose and good yield of glucose. Moreover, the unreacted cellulose can be targeted for different applications
in bio-based materials. A kinetic study based on the glucose yield was performed for all reaction conditions using the kinetic
model proposed by Saeman. The results showed that the model adjusted to all 30–35% H2SO4 reactions but not to greater concentrations of sulfuric acid. The present study is part of an ongoing research program, and
the results reported here will be used as a comparison against the results obtained when using treated sisal pulp as the starting
material. 相似文献
4.
Summary C2−C16 dicarboxylic acids were esterified in aqueous solution in the presence of sulfuric acid. Esterification in water/n-propanol
mixtures with mole ratios between 0.03 and 2.21 can be utilized for the quantitative determination of dicarboxylic acids by
gas chromatography. The presence of water does not interfere at water/n-propanol mole ratios below 0.45. For mole ratios above
0.45 anhydrous sodium sulfate has been used for binding the water. The mole ratio range tested was 0.12–0.99 for anhydrous
sodium sulfate/water, and 0.16–2.55 for sulfuric acid/anhydrous sodium sulfate. 相似文献
5.
Uzma K. H. Bangi A. Parvathy Rao H. Hirashima A. Venkateswara Rao 《Journal of Sol-Gel Science and Technology》2009,50(1):87-97
Experimental results on the physico-chemical properties of ambiently dried sodium silicate based aerogels catalyzed with various
acids are reported. The aerogels were prepared by hydrolysis and polycondensation of sodium silicate followed by subsequent
washings, surface chemical modification and ambient pressure drying using 10 various acid catalysts consisting of strong and
weak acids. The strength and concentration of acids have the major effect on the gelation of sol and hence the physico-chemical
properties of the silica aerogels. Strong acids such as HCl, HNO3 and H2SO4 resulted in shrunk (70–95%) aerogels whereas weak acids such as citric and tartaric acids resulted in less shrunk (34–50%)
aerogels. The physical properties of silica aerogels were studied by measuring bulk density, volume shrinkage (%), porosity
(%), pore volume, thermal conductivity, contact angle with water, Transmission Electron Microscopy (TEM), Atomic Absorption
Spectroscopy (AAS), Fourier Transform Infrared Spectroscopy (FTIR), Thermo Gravimetric-Differential Thermal (TG-DT) analyses
and N2 adsorption–desorption BET surface analyzer. The best quality silica aerogels in terms of low density (0.086 g/cm3), low volume shrinkage (34%), high porosity (95%), low thermal conductivity (0.09 W/m K) and hydrophobic (148°) were obtained
for molar ratio of Na2SiO3:H2O:citric acid:TMCS at 1:146.67:0.72:9.46 with 20 min gelation time. The resulting aerogels exhibited the thermal stability
up to around 420 °C. 相似文献
6.
Surface treatment of linear low density polyethylene and low density polyethylene blends is investigated herein using nitric
acid, sulfuric acid, and chromic acid. These chemical treatments not only make the surface rough but also introduce polar
groups. A new method, “sulfonic groups index” (SI) is employed to quantify the newly generated polar groups in the wavenumber
of 1,250–840 cm−1 in the Fourier transform infrared spectra. The SI values effectively indicate that the most polar groups are incorporated
into the chromic acid-etched samples among the three inorganic acids, which is also confirmed by scanning electron microscopy
and roughness tests. Besides, annealing treatment can enhance the crystallinity X
c of all etched samples which plays a predominant role in the increase of roughness within 2 h. As etching time increases,
chain scission and destruction of amorphous parts happen and roughness increases a lot for chromic acid-treated samples, but
for sulfuric acid- and nitric acid-treated samples, the destruction of amorphous parts may not happen so that the roughness
has not many changes. 相似文献
7.
Summary The simultaneous quantitation of acids and sugars as their trimethyl silyl (TMS) derivatives has been extended in order to
identify and quantitate the simple acid and sugar constituents in the hydrolyzates of various immunostimulant, water-soluble
polysaccharides obtained from various Basidiomycetes, such as Armillariella mellea, Auricularia auricula-judae, Coriolus versicolor,
Flammulina velutipes, Fomes fomentarius, Ganoderma applanatum, Ganoderma lucidum, Pleurotus ostreatus, Schizophyllum commune,
Trametes hirsuta. Optimum hydrolysis conditions, performed with 2 M trifluoroacetic acid (TFAA) for five hrs, proved the presence
of several sugars and acids with maximum recovery. (i) the total sugar/sugar alcohol content of polysaccharides varied between
20- and 65% and consisted of arabitol (0.01–10.2%), arabinose (0.09–1.3%), ribose (0.2–1.8%), fucose (0.3–1.2%), mannitol
(0.01–5.3%), sorbitol (0.01–0.05%), galactiol (0.04%), fructose (0.08–0.8%), galactose (0.9–29%), glucose (10–53%), uronic
acids (0.14–3.7%), sucrose (0.03–2%), trehalose (0.2–1%), cellobiose (0.01–0.6%), maltose (0.2–1.9%), other disaccharides
(0.2–8%). (ii) The total of acids varied from 1.5 to 30% including o-phosphoric (1.3–19%), malic (0.08–4.7%), citric (0.08–4.7%),
isocitric; (3%) and C16−C18 fatty acids (1–6%). 相似文献
8.
Tengborg Charlotte Stenberg Kerstin Galbe Mats Zacchi Guido Larsson Simona Palmqvist Eva Hahn-Hägerdal Bärbel 《Applied biochemistry and biotechnology》1998,(1):3-15
The pretreatment of softwood with sulfuric acid impregnation in the production of ethanol, based on enzymatic hydrolysis,
has been investigated. The parameters investigated were: H2SO4 concentration (0.5 – 4.4% w/w liquid), temperature (180 – 240°C), and residence time (1-20 minutes). The combined severity
(log Ro-pH) was used to combine the parameters into a single reaction ordinate. The highest yields of fermentable sugars,
i.e., glucose and mannose, were obtained at a combined severity of 3. At this severity, however, the fermentability declined
and the ethanol yield decreased. In a comparison with previous results, SO2 impregnation was found to be preferable, since it resulted in approximately the same sugar yields, but better fermentability. 相似文献
9.
Liquid-liquid extraction of uranium (VI) from hydrobromic acid solutions with dibenzo-24-crown-8 in nitrobenzene have been
investigated. Uranium(VI) was quantitatively extracted from 6.0–8.0M hydrobromic acid with 0.001–0.01M dibenzo-24-crown-8
and was quantitatively stripped from the organic phase with 0.1–1.0M hydrochloric acid, 0.5–10M nitric acid, 2–10M perchloric
acid, 3.0–10M sulfuric acid or 3.0–10M acetic acid. It was possible to separate uranium(VI) from a number of elements in binary
mixtures. Most of the elements showed very high tolerance limit Uranium(VI) was also separated from a number of associated
elements in multicomponent mixtures. The method is very simple, selective, rapid and highly reproducible (approximately±2%)
and was applied to the analysis of uranium in geological samples. 相似文献
10.
G. L. Sharipov A. M. Abdrakhmanov R. Kh. Gainetdinov 《Russian Chemical Bulletin》2005,54(8):1793-1797
A comparative study of the sonoluminescence spectra of water and argon-saturated aqueous H2SO4 solutions was carried out. At an H2SO4 concentration of 18 mol L−1, the sulfuric acid sonoluminescence is fifty times more intense than water sonoluminescence. The sulfuric acid luminescence
spectrum differs from the water sonoluminescence spectrum caused by the emission of excited water molecules and OH radicals
from the gas phase of cavitation bubbles. The sulfuric acid sonoluminescence spectrum exhibits maxima at 330, 420, 500, and
630 nm. Emitters of sonoluminescence of sulfuric acid are the singlet (330–340 nm) and triplet (∼420 nm) excited SO2 molecules formed by sonolysis of H2SO4 molecules. Another product of sonolysis of H2SO4, atomic oxygen, is assumed to be responsible for the luminescence at λ = 630 nm.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1742–1745, August, 2005. 相似文献
11.
G. P. Sharnin I. F. Falyakhov F. G. Khairutdinov 《Chemistry of Heterocyclic Compounds》1980,16(3):272-274
The kinetics of nitration of 2-picrylaminopyridine with nitric acid in 85– 96% sulfuric acid were studied by a spectrophotometric
method. It is shown that 2-picrylaminopyridine undergoes the reaction in the protonated form. The kinetic parameters of the
nitration and the relative reactivity as compared with benzene were calculated.
See [1] for communication 3.
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 363–365, March, 1980. 相似文献
12.
N. L. Zaichenko A. S. Shashkov L. S. Kol'tsova A. I. Shienok V. S. Marevtsev 《Russian Chemical Bulletin》2005,54(7):1720-1727
Nitration of photochromic spirophenanthrooxazine with three different reagents (cupric nitrate, NaNO2 in acetic acid, and HNO3-H2SO4) was studied. The major reaction products were specified and characterized by 1H and 13C NMR and mass spectra. The mechanisms of their formation were proposed. Only the nitration with a mixture of nitric and sulfuric
acids yielded a photochromic product containing the nitro group in the phenanthrene fragment.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1670–1677, July, 2005. 相似文献
13.
G. A. Kolyagin I. S. Vasil’eva V. L. Kornienko 《Russian Journal of Electrochemistry》2011,47(3):282-287
This paper reports on the effects of the K2SO4, H2SO4, NaCl, HCl, and tetrabutylammonium bromide concentrations (0.01–0.0002 M) and the presence of formic, acetic, and butyric
acids in the electrolyte on the kinetic characteristics of oxygen reduction to H2O2 in a carbon black gas-diffusion electrode (GDE) and on the H2O2 accumulation kinetics in electrolyte at current densities of 30–100 mA/cm2. The introduction of K2SO4 and tetrabutylammonium bromide in the electrolyte led to an increase in the transfer coefficient α and a decrease in the
coefficients in the Tafel equation. The concentration and the current efficiency of H2O2 decreased with the salt to acid concentration ratio. The organic acids reduced the current efficiency of H2O2 and increased the electrode polarization. Peracids with a current efficiency of up to 0.27% and concentration of up to 7.5
mM were obtained. Solutions of H2O2 with concentrations of 0.6–3.3 M and current efficiencies of 17–75% were obtained at current densities of 30–100 mA/cm2 in electrolytes with salt and inorganic acid concentrations of 0.9–40 g/l and in the presence of organic acids. 相似文献
14.
The extraction of chromium(VI) from aqueous hydrochloric, nitric and sulfuric acid solutions by diphenyl-2-pyridylmethane(DPPM)
dissolved in chloroform has been studied. Chromium(VI) is quantitatively extracted from hydrochloric acid solutions in the
range 0.1–1M. With increasing acid concentration, the extraction of chromium diminishes and in concentrated acid solutions
practically all the chromium remains in the aqueous phase. The quantitative back-extraction of chromium from the organic phase
is possible with HCl or HNO3 at concentrations higher than 5M through the use of reducing agents. The composition of the extracted chromium(VI) species
was studied in solution. The complexes (DPPMH)+HCrO
4
−
and (DPPMH)2Cr2O
7
−
are extracted for tracer and macro amounts of chromium(VI) respectively. The data have been utilized for the separation of
chromium(VI) from base metal ions. 相似文献
15.
Sumera Mahboob Rohama Gill Muhammad Mazhar Gabriele Kociok-Köhn Kieran C. Molloy 《Monatshefte für Chemie / Chemical Monthly》2008,139(9):1019-1024
A series of trichlorogermyl-substituted dicarboxylic acids of general formula HOOC–R′–COOH where R′=–CH2CH(GeCl3)CH2– 1, –CH(CH2GeCl3)CH2– 2, –CH(GeCl3)CH2– 3 and –CH(CH3)CH(GeCl3)– 4 were synthesized by the hydrogermylation reaction of unsaturated acids, such as trans-glutaconic (2-pentenedioic acid), itaconic (methylenebutanedioic acid), fumaric (2-butenedioic acid), and citraconic (2-methyl-2-butenedioic
acid) acids with HGeCl3, which was produced in situ by the reaction of GeO2 with 37% HCl in presence of NaH2PO2 · H2O. All these compounds were characterized by melting point, CHN analysis, FTIR, and multinuclear NMR (1H; 13C; H,H-COSY). X-Ray crystal structures of 1 and 2 were analyzed to show supramolecular structures in which central Ge atom in each of these structures is four-coordinated
with a slightly distorted tetrahedral geometry. Structurally, both compounds adopt supramolecular forms via strong intermolecular O–H–O interactions through 8-membered and 22-membered hydrogen bonded rings.
Supplementary material to this paper is available in electronic form at
Correspondence: Muhammad Mazhar, Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan. 相似文献
16.
The process of sodium ethylenediaminetetraacetate (EDTA) mineralization by cerium(IV) in nitric acid medium was studied in
batch and continuous feeding modes. In the batch mode EDTA solution was fed into the reactor in one stroke and in the continuous
mode it was fed with a constant flow rate during a definite time interval. Cerium(IV) concentration was kept at high and constant
level by selecting correct relation between cerium(IV) production in the electrochemical cell and the EDTA added. During the
organic mineralization process cerium(IV) is reduced to cerium(III). The process was carried out at different temperatures,
concentrations of nitric acid and cerium(IV). To obtain the limiting factors in the batch mode reaction, the dependence of
CO2 evolution with time and carrier gas blowing rate was studied. Application of the model previously developed by us to the
continuous process gave us the possibility to calculate pseudo first order kinetic constant on the basis of CO2 evolution data of both EDTA destruction regimes during feeding mode and after stopping organic addition. The efficiency of
organic destruction estimated on the basis of CO2 evolved was in the range 75–95% and on the basis of liquid phase residual organic carbon analysis 95–99%. 相似文献
17.
The appearance of oscillations depends critically on the pH for a closed system of ClO2–I2–ethyl acetoacetate in the absence of sulfuric acid, and was investigated by determining the absorbance of I3− with reaction time at 280 nm. The pH should be 2.2–3.8. The initial concentration of ethyl acetoacetate, chlorine dioxide,
iodine, and sulfuric acid has great influence on the oscillation at 581 nm for I3−–starch complex (SI3−). The oscillation occurs as long as the reactants are mixed at 280 nm. There is no pre-oscillatory period. However, at 581 nm,
there is an induction period. The curve’s shape at 581 nm is very different from that at 280 nm. The oscillation becomes more
obvious by adding starch at 581 nm for I3−–starch complex (SI3−) than that observed without adding starch at 280 nm. The oscillation curve is more regular and smooth by adding starch at
581 nm than that without adding starch at 280 nm. The amplitude and the number of oscillations are associated with the initial
concentration of reactants. The higher the initial concentration of ethyl acetoacetate, the bigger the amplitude. Also, the
number of oscillations becomes small. An opposite influence exists for chlorine dioxide and iodine. The higher the initial
concentration of sulfuric acid, the bigger the amplitude. Also, the number of oscillations becomes large. The equations for
the triiodide ion reaction rate changing with reaction time and the initial concentrations on the oscillation stage were obtained.
The intermediates were detected by the online FTIR analysis. Based upon the experimental data in this work and in the literature,
a plausible reaction mechanism was proposed for the oscillation reaction. 相似文献
18.
Shamas-Ud-Zuha Mudassar A. Qureshi M. Ejaz 《Journal of Radioanalytical and Nuclear Chemistry》1978,44(1):83-90
The partition behaviour of cobalt into 4-(5-nonyl)pyridine (NPy) in benzene from aqueous hydrochloric, nitric and sulfuric
acid media containing variable amounts of potassium thiocyanate is described. Cobalt is quantitatively extracted by NPy from
0.1–1M KSCN solutions at 0.01 M concentration of the mineral acids. The extraction mechanism and the possible compositions
of the extracted species are discussed. The effects of foreign salts on the extraction of cobalt from three mineral acid solutions
are reported. Several elements including those which are of some interest in connection with the separation of cobalt were
tested for extraction from 0.01 M solutions of mineral acids 0.3 M with respect to KSCN and their factors for separation from
cobalt were estimated. 相似文献
19.
V. M. Bondareva E. V. Ovchinnikova T. V. Andrushkevich 《Reaction Kinetics and Catalysis Letters》2008,94(2):327-335
The oxidation of nicotinic acid (NA) over binary vanadia-titania catalysts with different contents of residual sulfate ions
(0.2 and 2.8 wt. %) was studied at 250–300°C in the feed reaction mixture of the composition NA: O2: H2O = 0.01–0.17: 5–20: 0–20 (vol. %), with nitrogen as a balance. The kinetic parameters of the process were determined. It
was shown that even a ten-fold increase in the content of residual sulfate ions in the samples has no significant effect on
the kinetics of the NA oxidation. 相似文献
20.
《Analytical letters》2012,45(7):407-412
Abstract A commercial acid concentration meter containing an N-type silicon anode and stainless cathode has been used to selectively measure hydrofluoric acid in mixtures containing nitric, phosphoric and sulfuric acids. At very high weight ratios of acid to HF (> 10:1) a suppression in HF response was noted for all acids examined. At lower ratios or higher HF values only nitric acid influences HF response with a sensitizing or catalytic effect not appreciably dependent on HNO, concentration. 相似文献