共查询到20条相似文献,搜索用时 31 毫秒
1.
Jackie Y. Ying Jay B. Benziger Alexandra Navrotsky 《Journal of the American Ceramic Society》1993,76(10):2571-2582
Structural and energetic changes of alkoxide silica during densification were followed in situ using photoacoustic Fourier-transform infrared spectroscopy (PAS-FTIR), transposed temperature drop calorimetry, and drop solution calorimetry. Acid-catalyzed silica gels contained higher concentrations of adsorbed water, silanol groups, and unreacted alkoxy groups than did the base-catalyzed gels/precipitates. The surface species in acid-catalyzed gels were removed easily, allowing this material to be densified at 800°C. The densified material was both structurally and energetically equivalent to fused silica glass. Base-catalyzed gels had fewer silanol groups in the green state, but free silanol groups emerged during drying at 500°C. The base-catalyzed gels did not densify below 1000°C, maintaining a high surface area of 100 m2 /g. Base-catalyzed alkoxide gels comprised strained ring structures; their IR spectra were similar to those of fumed silica, but they were energetically much less stable. 相似文献
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A Novel Method for the Production of Biodiesel from the Whole Stillage-Extracted Corn Oil 总被引:1,自引:0,他引:1
Hossein Noureddini Santosh R. P. Bandlamudi Emily A. Guthrie 《Journal of the American Oil Chemists' Society》2009,86(1):83-91
The extraction of corn oil from whole stillage and condensed distillers’ solubles (CDS) with hexane and its conversion to
biodiesel were investigated. The analysis of the extracted oil showed 6–8 wt.% free fatty acid (FFA) in this oil. Acid, base,
acid–base, and acid–base catalyzed transesterifications with intermediate neutralization with anion exchange resin were investigated.
Experiments were performed with model corn oil substrates which contained 1.0–6.0 wt.% FFA. The effect of catalyst at 0.50–1.25 wt.%
was studied at a 1:8 oil/methanol molar ratio. At 6.0 wt.% FFA concentration, the acid-catalyzed scheme was slow and resulted
in less than 20% yield after 4 h, while the base-catalyzed was mostly consumed by the FFA and very little conversion was achieved.
The acid–base catalyzed scheme succeeded in reducing the FFA content of the oil through the acid-catalyzed stage, and yields
in excess of 85% were achieved after the second stage of the reaction with a base catalyst. However, formation of water and
soap prevented the separation of product phases. An alternative acid–base catalyzed scheme was examined which made use of
a strong anion exchange resin to neutralize the substrate after the initial acid-catalyzed stage. This scheme resulted in
the effective removal of the acid catalyst as well as the residual FFA prior to the base-catalyzed stage. The subsequent base-catalyzed
stage resulted in yields in excess of 98% for a 7.0 wt.% FFA corn oil and for the corn oil extracted from CDS. 相似文献
5.
介绍了1990年以来全世界化学工业中投入生产的新酸碱催化过程。这些过程采用的催化剂主要为沸石,杂多酸,离子交换树脂,改性氧化锆和超强碱等,涉及的反应类型包括均相和多相催化的液相和气固相反应。同时对酸碱催化未来的研究方向进行了评述。 相似文献
6.
B. Serdarevich 《Journal of the American Oil Chemists' Society》1967,44(7):381-393
Isomerization of isopropylidene glycerol ketals and benzylidene glycerol acetals was studied, and isoraerization equilibria
were established. Reaction of benzaldehyde with glycerol gave four benzylidene glycerol isomers, which were separated by column
chromatography and characterized by NMR spectroscopy and other methods.
Isomerization of 1- and 2-monoglycerides and of 1,2- and 1,3-diglycerides, and their separation by column chromatography,
are described. Mechanisms of isomerization in mono- and diglycerides and factors which affect them are discussed.
Isomerization of 1- and 2-glycerophosphates and of cyclic glycerophosphates by acid and base was also studied. Hydrolysis
products of L-3-glycerylphosphorylcholine and 2-glycerylphosphorylcholine were separated by column chromatography and characterized
by periodic acid oxidation, optical rotation, and NMR spectroscopy. No isomerization of unhydrolyzed L-3-glycerylphosphorylcholine
and 2-glycerylphosphorylcholine was observed. Evidence indicated that acid-catalyzed hydrolyses of phosphoglycerides are under
thermodynamic control whereas most base-catalyzed hydrolyses are under kinetic control. 相似文献
7.
废餐饮油制备生物柴油研究现状与应用前景 总被引:5,自引:0,他引:5
介绍了利用废餐饮油制备生物柴油的研究现状与应用前景;叙述了酸催化、碱催化和酶催化的酯交换制备生物柴油工艺,以及每种工艺的优缺点.阐述了我国利用餐饮废油制取生物柴油的意义和利用餐饮废油制取生物柴油的商业化生产的可行性. 相似文献
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Michael J. Readey Ran-Rong Lee † John W. Halloran ‡ Arthur H. Heuer 《Journal of the American Ceramic Society》1990,73(6):1499-1503
Chemical coprecipitation was used to produce ultrafine and easily sinterable MgO-stabilized and (MgO, Y2 O3 ) stabilized ZrO2 powders. The sintering behavior is very sensitive to post-precipitation washing because "hard" agglomerates form when the precipitated gels are washed with water, whereas "soft" agglomerates form when they are washed with ethanol. The soft agglomerates pack uniformly, resulting in homogeneous shrinkage of powder compacts to near-theoretical density. The hard agglomerates result in compacts which have regions of localized densification and a signifiint fraction of residual porosity. 相似文献
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FAME was produced by a two-step in-situ transesterification of acid oil (AO) with methanol in a novel continuous flow ultrasonic reactor system composed of four ultrasonic reactors with different frequency. The hydrodynamic behavior of the reactor was investigated by a step response technique, and the effect of ultrasonic frequency on mono-alkyl esters of long chain fatty acids (FAMEs) formation was also investigated. The production process includes an in-situ sulfuric acid-catalyzed esterification of AO with methanol in the first two ultrasonic reactors successively followed by an in-situ base-catalyzed transesterification in the other two ultrasonic reactors. The AO initial free fatty acids (FFA) content about 17.5 w% was cut down to less than 1 w% by sulfuric acid-catalyzed esterification. FAME yields in excess of 97.0% identified by gas chromatography/mass spectrometry (GC/MS) were obtained by the two-step in-situ reaction. The maximum and minimum volumetric productivity could reach 13.76 L·h?1 and 10.24 L·h?1 respectively. 相似文献
11.
Synthesis of resorcinol-formaldehyde/silica composite aerogels and their low-temperature conversion to mesoporous silicon carbide 总被引:1,自引:0,他引:1
Ke ChenZhihao Bao Ai DuXiurong Zhu Guangming WuJun Shen Bin Zhou 《Microporous and mesoporous materials》2012,149(1):16-24
Resorcinol-formaldehyde/silica composite (RF/SiO2) gels were acid-catalyzed formed in one pot at 27 °C within 60 min, and then dried to aerogels with supercritical fluid CO2. After carbonization in nitrogen atmosphere and a magnesiothermic reaction at 700 °C, RF/SiO2 aerogels were successfully converted to monolithic mesoporous silicon carbide (SiC aerogels). The starting RF/SiO2 aerogels had an interpenetrating organic/inorganic network and the resulting SiC products preserved monolithic mesoporous morphology similar to the original templates. The as-synthesized SiC aerogels consisted of nanocrystalline β-SiC, possessed a BET surface area of 232 m2/g and showed sufficient mesoporosity. They had a direct band gap of about 3.2 eV (less than that of bulk β-SiC) and showed photoluminescence at room temperature. The mechanisms about the formation of RF/SiO2 gels and the conversion to SiC aerogels were discussed. Potentially, the reported method can be used to convert many metal or semimetal oxide/carbon composite aerogels to carbide aerogels at relatively low temperature for many catalytic, electronic, photonic and thermal applications. 相似文献
12.
Biodiesel production from tobacco (Nicotiana tabacum L.) seed oil with a high content of free fatty acids 总被引:2,自引:0,他引:2
The production of fatty acid methyl esters (FAME) from crude tobacco seed oil (TSO) having high free fatty acids (FFA) was investigated. Due to its high FFA, the TSO was processed in two steps: the acid-catalyzed esterification (ACE) followed by the base-catalyzed methanolysis (BCM). The first step reduced the FFA level to less than 2% in 25 min for the molar ratio of 18:1. The second step converted the product of the first step into FAME and glycerol. The maximum yield of FAME was about 91% in about 30 min. The tobacco biodiesel obtained had the fuel properties within the limits prescribed by the latest American (ASTM D 6751-02) and European (DIN EN 14214) standards, except a somewhat higher acid value than that prescribed by the latter standard (<0.5). Thus, tobacco seeds (TS), as agricultural wastes, might be a valuable renewable raw material for the biodiesel production. 相似文献
13.
Conversion of allylic hydroxy oleate to conjugated linoleic acid and methoxy oleate by acid-catalyzed methylation procedures 总被引:12,自引:0,他引:12
Martin P. Yurawecz Jennifer K. Hood John A. G. Roach Magdi M. Mossoba Daniel H. Daniels Yuoh Ku Michael W. Pariza Sou F. Chin 《Journal of the American Oil Chemists' Society》1994,71(10):1149-1155
Conjugated linoleic acid (CLA), a term describing a group of conjugated octadecadienoic acids that are both naturally occurring
and formed during food processing, is the subject of considerable current research because of the recently reported antioxidant
and anticarcinogenic properties of these compounds. Allylic hydroxy oleates (AHOs), secondary products of lipid autoxidation,
have also been found in foods. By means of high-performance liquid chromatography with ultraviolet detection, gas chromatography/mass
spectrometry and gas chromatography/matrix isolation/Fourier transform infrared spectroscopy, we determined that currently
used acid-catalyzed methylation procedures convert AHOs to CLA and other products that potentially yield high values in determination
of CLA in foods. A mixture of AHOs, containing mainly (8- and 11-)hydroxy-9-octadecadecenoates, was synthesized and tested
by methylation procedures with the following catalysts: BF3, HCl, NaOMe and tetramethylguanidine. Both the BF3 and the HCl procedures converted AHOs to CLA. The base-catalyzed procedures did not convert AHOs to CLA. 相似文献
14.
Claudia M. Berlanga-Reyes Elizabeth Carvajal-Millan Kevin B. Hicks Madhav P. Yadav Agustín Rascón-Chu Jaime Lizardi-Mendoza Alma R. Toledo-Guillén Alma R. Islas-Rubio 《International journal of molecular sciences》2014,15(10):19106-19118
Wheat bran arabinoxylan (WBAX) gels entrapping standard model proteins at different mass ratios were formed. The entrapment of protein affected the gel elasticity and viscosity values, which decreased from 177 to 138 Pa. The presence of protein did not modify the covalent cross-links content of the gel. The distribution of protein through the network was investigated by confocal laser scanning microscopy. In mixed gels, protein aggregates forming clusters were detected at protein/polysaccharide ratios higher than 0.25. These clusters were not homogeneously distributed, suggesting that WBAX and protein are located in two different phases. The apparent diffusion coefficient (Dm) of proteins during release from mixed gels was investigated for mass ratios of 0.06 and 0.12. For insulin, Dm increased significantly from 2.64 × 10−7 to 3.20 × 10−7 cm2/s as the mass ratio augmented from 0.06 to 0.12. No significant difference was found for Dm values of ovalbumin and bovine serum albumin released from the mixed gels. The results indicate that homogeneous protein/WBAX gels can be formed at low mass ratios, allowing the estimation of Dm by using an analytical solution of the second Fick’s law. 相似文献
15.
Dehydration of gels prepared by the sol-gel process from metal alkoxides in the systems B2 O3 -SiO2 and ZrO2 -SiO2 was determined by measuring the shrinkage of the gel on heating. Dehydration was enhanced with increased ZrO2 content, whereas it decreased with B2 O3 content. Diffusion of water was also measured in the nonporous glasses obtained by heating the gels. The diffusion rate was independent of the composition of the glass. 相似文献
16.
MARTIN J. MURTAGH EARL K. GRAHAM CARLO G. PANTANO 《Journal of the American Ceramic Society》1986,69(11):775-779
The elastic moduli of several organometallic silica gels were measured using pulse-superposition interferometry (PSP). A series of gels were prepared under acid-catalyzed conditions where the molar ratio of water to tetraethoxysilane (TEOS) in the sol was varied (4:1, 12:1, 16:1, and 24:1). It was found that the elastic moduli varied systematically with the hydrolysis conditions used to prepare the gels, as well as with the relative humidity used to equilibrate the gels before and during the PSP measurement. The experimental PSP data for the gels were evaluated using a composite model (matrix plus pores) and then the elastic moduli of the gel matrix were determined by applying a correction for porosity based on a self-consistent-scheme (SCS) approximation. The results show that the elastic moduli of the gel matrix also exhibit a systematic dependence upon the preparation conditions, but they always fall below the corresponding values for fused silica. Even when excess water Was used to hydrolyze the TEOS, this did not lead to a fully polymerized silica matrix structure. It is suggested that the lowered matrix moduli values are due to the presence of residual hydroxy and ethoxy groups which are internal to a polymeric structure. 相似文献
17.
R. O. Butterfield 《Journal of the American Oil Chemists' Society》1969,46(6):320-322
2-Methyoxyethyl esters of linseed and safflower oils were made by a base-catalyzed transesterification and 2-chloroethyl esters
by acid-catalyzed esterification of the free acids. Both esters were distilled in vacuum. Countercurrent distribution (CCD)
of the two linseed esters with a hexane-acetonitrile solvent system indicated that partition coefficients for the individual
esters are one half those of the corresponding methyl esters. These lower partition coefficients permit solvent ratios nearer
to one to be used in both CCD and counter double current distribution (CDCD) and they also reduce loading and transferring
errors. Selectivity of the system toward number of double bonds and carbon chain length is the same as when methyl esters
are used. Conditions were determined for the CDCD preparations of 2-methoxyethyl and 2-chloroethyl linolenate and linoleate
from linseed and safflower oils, respectively.
Presented at the AOCS Meeting, New York, October 1968.
No. Utiliz. Res. Dev. Div., ARS, USDA. 相似文献
18.
《Polymer》2002,43(11):3217-3222
The thermoreversible gelation of blends of polystyrene-block-poly(ethylene/butylene)-block-polystyrene (SEBS) and polystyrene-block-poly(ethylene/propylene) (SEP) copolymers in n-octane was studied. The solvent is selective for the polyolefine blocks of the copolymers. The influence of the composition of the hybrid gels on the sol-gel transition and on the mechanical properties of the gels was analyzed. The sol-gel transition temperature increased with the concentration of both type of copolymers and did not depend on the hybrid gel composition for SEBS2 proportions higher than 50% at a total copolymer concentration higher than 6 wt%. The mechanical properties of the different gels were examined through oscillatory shear and compressive stress relaxation measurements. The elastic storage modulus increased with the triblock copolymer concentration but kept almost constant with the diblock copolymer concentration for SEBS concentrations higher than 5.0%. The stress relaxation rate was not dependent on the concentration of triblock and diblock copolymers, but the hybrid gels show lower stress relaxation rates than the pure SEBS2 gels. In the hybrid SEBS/SEP gels the SEP chains impart stability to the micelles or nodes of the network whereas the SEBS chains are responsible for the bridges that keep the gel as one-phase system. 相似文献
19.
Crosslinked poly(N-isopropylacrylamide) (PNIPA) gels with different crosslink densities in the form of rods and beads were prepared by free-radical crosslinking copolymerization. Solution and inverse suspension polymerization techniques were used for the gel synthesis. The gels were utilized to concentrate dilute aqueous solutions of penicillin G acylase (PGA), bovine serum albumin (BSA), and 6-aminopenicillanic acid (6-APA). The discontinuous volume transition at 34°C observed in the gel swelling was used as the basis of concentrating dilute aqueous protein solutions. PNIPA gels formed below 18°C were homogeneous, whereas those formed at higher temperatures exhibited heterogeneous structures. The water absorption capacity of PNIPA gels in the form of beads was much higher, and their rate of swelling was much faster than the rod-shaped PNIPA gels. It was also found that the polymerization techniques used significantly affect the properties of PNIPA gels. The separation efficiency decreased when the protein molecules PGA or BSA in the external solution were replaced with small-molecular-weight compounds, such as 6-APA. The protein separation efficiency by the gel beads increased to 100% after coating the bead surfaces with BSA. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 805–814, 1998 相似文献
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Poly[N‐isopropylacrylamide‐co‐[2‐(methylthio)ethyl methacrylate]], poly(NIPA‐co‐MTEMA) gels were prepared by free radical polymerization in aqueous solution. The homogeneous and heterogeneous gels were prepared by using 10 mM MTEMA in 5.0%(v/v) ethanol at 10°C and 30 mM MTEMA in 20%(v/v) ethanol at 50°C, in 1.0 and 1.5M NIPA solution, respectively. Homogeneous and heterogeneous gels had swelling ratios at 540 ± 28% and 551 ± 37%, respectively. The extraction of Au(III) ion was studied in batch method. The optimum pHs for the extraction of Au(III) by homogeneous and heterogeneous gels were 1–3 and 1–5, respectively. The suitable extraction time was 3 h at 50°C when using a rod‐shaped copolymer (0.7 cm diameter and 1 cm length). The adsorption behavior obeyed the Langmuir and Freundlich isotherms. The maximum sorption capacities of Au(III) onto homogeneous and heterogeneous gels were 62.8 and 322 μmol/g, respectively. The desorption equilibrium was reached within 2–3 h at 10°C by 0.1M thiourea in 5%(v/v) HCl. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献