共查询到16条相似文献,搜索用时 15 毫秒
1.
Weidong An Jin Ki Hong Peter N. Pintauro Kathleen Warner William Neff 《Journal of the American Oil Chemists' Society》1998,75(8):917-925
A new electrochemical method has been devised and tested for the moderate temperature/atmospheric pressure hydrogenation of edible oils, fatty acids, and fatty acid methyl esters. The method employed a solid polymer electrolyte (SPE) reactor, similar to that used in H2/O2 fuel cells, with water as the source of hydrogen. The key component of the reactor was a membrane-electrode-assembly, composed of a RuO2 powder anode and either a Pt-black or Pd-black powder cathode that were hot-pressed as thin films onto the opposing surfaces of a Nafion cation-exchange membrane. During reactor operation at a constant applied current, water was back-fed to the RuO2 anode, where it was oxidized electrochemically to O2 and H+. Protons migrated through the Nafion membrane under the influence of the applied electric field and contacted the Pt or Pd cathode, where they were reduced to atomic and molecular hydrogen. Oil was circulated past the back side of the cathode and unsaturated triglycerides reacted with the electrogenerated hydrogen species. The SPE reactor was operated successfully at a constant applied current density of 0.10 A/cm2 and a temperature between 50 and 80°C with soybean, canola, and cottonseed oils and with mixtures of fatty acids and fatty acid methyl esters. Reaction products with iodine values in the range of 60–105 were characterized by a higher stearic acid content and a lower percentage of trans isomers than those produced in a traditional hydrogenation process. 相似文献
2.
K. Warner W. E. Neff G. R. List Peter Pintauro 《Journal of the American Oil Chemists' Society》2000,77(10):1113-1118
Soybean oils were hydrogenated either electrochemically with Pd at 50 or 60°C to iodine values (IV) of 104 and 90 or commercially
with Ni to iodine values of 94 and 68. To determine the composition and sensory characteristics, oils were evaluated for triacylglycerol
(TAG) structure, stereospecific analysis, fatty acids, solid fat index, and odor attributes in room odor tests. Trans fatty acid contents were 17 and 43.5% for the commercially hydrogenated oils and 9.8% for both electrochemically hydrogenated
products. Compositional analysis of the oils showed higher levels of stearic and linoleic acids in the electrochemically hydrogenated
oils and higher oleic acid levels in the chemically hydrogenated products. TAG analysis confirmed these findings. Monoenes
were the predominant species in the commercial oils, whereas dienes and saturates were predominant components of the electrochemically
processed samples. Free fatty acid values and peroxide values were low in electrochemically hydrogenated oils, indicating
no problems from hydrolysis or oxidation during hydrogenation. The solid fat index profile of a 15∶85 blend of electrochemically
hydrogenated soybean oil (IV=90) with a liquid soybean oil was equivalent to that of a commercial stick margarine. In room
odor evaluations of oils heated at frying temperature (190°C), chemically hydrogenated soybean oils showed strong intensities
of an undesirable characteristic hydrogenation aroma (waxy, sweet, flowery, fruity, and/or crayon-like odors). However, the
electrochemically hydrogenated samples showed only weak intensities of this odor, indicating that the hydrogenation aroma/flavor
would be much less detectable in foods fried in the electrochemically hydrogenated soybean oils than in chemically hydrogenated
soybean oils. Electrochemical hydrogenation produced deodorized oils with lower levels of trans fatty acids, compositions suitable for margarines, and lower intensity levels of off-odors, including hydrogenation aroma,
when heated to 190°C than did commercially hydrogenated oil. 相似文献
3.
Current efficiency for soybean oil hydrogenation in a solid polymer electrolyte reactor 总被引:4,自引:0,他引:4
Soybean oil has been hydrogenated electrocatalytically in a solid polymer electrolyte (SPE) reactor, similar to that in H2/O2 fuel cells, with water as the anode feed and source of hydrogen. The key component of the reactor was a membrane electrode assembly (MEA), composed of a precious metal-black cathode, a RuO2 powder anode, and a Nafion® 117 cation-exchange membrane. The SPE reactor was operated in a batch recycle mode at 60°C and one atmosphere pressure using a commercial-grade soybean oil as the cathode feed. Various factors that might affect the oil hydrogenation current efficiency were investigated, including the type of cathode catalyst, catalyst loading, the cathode catalyst binder loading, current density, and reactant flow rate. The current efficiency ordering of different cathode catalysts was found to be Pd>Pt>Rh>Ru>Ir. Oil hydrogenation current efficiencies with a Pd-black cathode decreased with increasing current density and ranged from about 70% at 0.050Acm–2 to 25% at 0.490Acm–2. Current pulsing for frequencies in the range of 0.25–60Hz had no effect on current efficiencies. The optimum cathode catalyst loading for both Pd and Pt was 2.0mgcm–2. Soybean oil hydrogenation current efficiencies were unaffected by Nafion® and PTFE cathode catalyst binders, as long as the total binder content was 30wt% (based on the dry catalyst weight). When the oil feed flow rate was increased from 80to 300mlmin–1, the oil hydrogenation current efficiency at 0.100Acm–2 increased from 60% to 70%. A high (70%) current efficiency was achieved at 80mlmin–1 by inserting a nickel screen turbulence promoter into the oil stream. 相似文献
4.
Robert L. Wolff 《Journal of the American Oil Chemists' Society》1993,70(3):219-224
Fifteen samples of commercial edible soybean and rapeseed oils (and mixtures of these) from Belgium, Great Britain and Germany
have been analyzed for theirtrans-polyunsaturated fatty acid content. Only one sample out of the 13 refined samples, and the two cold-pressed samples, contained
trace amounts oftrans isomers. Others contained between 1 and 3.3% of their total fatty acids as geometrical isomers of linoleic and linolenic
acids. The degree of isomerization (DI) of linolenic acid varied between 10.5 and 26.9%. Combining results obtained in this
study together with corresponding data for French oils (totalling 21 samples) indicates that the relative percentages of individual
linolenic acid geometrical isomers depend on linolenic acid DI. Relationships linking these parameters could be approximated
by straight lines, at least for DIs lying between 9 and 30%. Extrapolation to DI=0 suggests that the relative probabilities
of isomerization of double bonds in positions 9, 12, and 15 are 41.7, 6.1 and 52.1%, respectively, at the very beginning of
the isomerization reaction. At that time, the probability of a simultaneous isomerization of double bonds in positions 9 and
15 is close to zero. Thet,c,t isomer is apparently formedvia thec,c,t and thet,c,c isomers, the former being somewhat more prone to a second geometrical isomerization than the latter. The relative proportion
of thec,t,c isomer is practically independent from the DI, at least between 9 and 30%, which would suggest that this isomer is an “end-product”
of thecis-trans isomerization reaction. 相似文献
5.
Peter J. Wan Mukana wa Muanda Jesse E. Covey 《Journal of the American Oil Chemists' Society》1992,69(9):876-879
Refined and bleached soybean oil was hydrogenated with and without ultrasonic energy in a batch system. Reactions were carried
out at 170°C with 0.02% nickel catalyst (Nysel, Harshaw/Filtron Partnership, Cleveland, OH) or 50 ppm nickel in the oil. Hydrogen
pressure was varied from 15 to 90 psig. After 20 min, the average reaction rate was about five times faster in the presence
of ultrasonic energy. Hydrogenation rate generally increased with increasing hydrogen pressure when ultrasonic energy was
applied. However, the increasing rate is more sinusoidal in nature than linear. 相似文献
6.
The electrocatalytic properties of an AB5-type hydrogen storage alloy towards the electrochemical hydrogenation of unsaturated organic compounds have been studied by a solid electrolyte method using electrochemical hydrogenation of nitrobenzene as a model reaction. Voltammetric studies reveal that the kinetics of the nitrobenzene electro-reduction on the hydrogen storage alloy electrode is similar to that on a Ni electrode. Aniline and p-aminophenol are produced as the reaction products. Compared to the Ni electrode, the production of aniline is considerably promoted on the hydrogen storage alloy electrode. Modifying the alloy surface with a thin layer of Cu enhances the reaction selectivity and current efficiency for aniline formation. Compared to a Cu electrode, the electrochemical hydrogenation of nitrobenzene to aniline is promoted on the Cu-modified alloy electrode. The hydrogenation promotion effect is attributed to the chemical reaction between nitrobenzene and metal hydrides that are electrochemically generated in situ. Hydrogen storage alloys therefore make it possible to intensify the electrochemical hydrogenation process of unsaturated organic compounds. 相似文献
7.
Robert L. Wolff 《Journal of the American Oil Chemists' Society》1992,69(2):106-110
The fatty acid compositions of rapeseed and soybean oils marketed in France have been determined by gas liquid chromatography
on a fused-silica capillary column coated with a 100% cyanopropyl polysiloxane stationary phase. Under the operating conditions
employed, methyl esters of linolenic acid geometrical isomers could be separated and quantitated easily without any other
complementary technique. With only one exception, all samples under study (eight salad oils and five food samples) contain
geometrical isomers of linolenic acid in measurable, although variable, amounts. Totaltrans-18:3 acids may account for up to 3% of total fatty acids. This value corresponds to a degree of isomerization (percentage
oftrans isomers relative to total octadecatrienoic acids) of 30%. Examination of our data indicates that the distribution pattern
of linolenic acid geometrical isomers does not depend on the degree of isomerization. The two main isomers always have thec,c,t and thet,c,c configurations. These isomers occur in the almost invariable relative proportions of 47.8±1.7% and 41.1±1.0%, respectively.
The third mono-trans isomer is present in lower amounts−6.5±0.7%. The only di-trans isomer that can be quantitated with sufficient accuracy is thet,c,t isomer (4.9±1.5%). Mono-trans isomers of linoleic acid are also present in these oils. However, their maximum percentages are lower than those determined
for linolenic acid geometrical isomers. In the oils showing the highest degrees of isomerization,trans isomers of linoleic acid account for 0.5% (rapeseed oils) and 1% (soybean oils) of total fatty acids. Taking into account
all data, it would appear that the probability of isomerization of linolenic acid is about 13–14 times that of linoleic acid. 相似文献
8.
Electrolytic synthesis of succinic acid in a flow reactor with solid polymer electrolyte membrane 总被引:2,自引:0,他引:2
S.S. Vaghela G. Ramachandraiah P.K. Ghosh D. Vasudevan 《Journal of Applied Electrochemistry》2002,32(11):1189-1192
This paper describes the galvanostatic synthesis of succinic acid from maleic acid in an ion exchange membrane flow cell. The electrolysis was carried out at stainless steel, lead and copper cathodes under variable conditions of current density and substrate concentration. Depending upon the experimental conditions, the yield of succinic acid varied from 95 and 99% with a coulombic efficiency of 80–99%. The product was characterized by various physicochemical techniques, viz. 1H-NMR, IR and UV–Visible spectroscopy and elemental analysis. The operational conditions giving maximum yield of product were identified. The mechanism of electrochemical reduction of maleic acid and advantages of using a catholyte without supporting electrolyte are discussed. 相似文献
9.
A novel low-temperature process for the electrochemical hydrogenation of canola oil is described. An emulsion of oil and water
containing formic acid and a nickel hydrogenation catalyst, placed in the cathode compartment of an electrolysis cell and
subjected to an electrical current, underwent hydrogenation at temperatures as low as 45°C. At these low temperatures of hydrogenation,
the trans FA content of the hydrogenated canola oil was very low as compared with that of the edible oils hydrogenated by commercial
processes using high temperature and high partial pressure of hydrogen gas. Because of its adverse health effects, a high
trans FA content in edbile oils is viewed as undesirable. In addition to the commercially available nickel supported on silica,
amorphous nickelphosphorus alloys supported on a variety of substrates were also used. Amorphous alloys are generally very
corrosion resistant because of the absence of grain boundaries. A mechanism for hydrogenation using the hydrogen transfer
agent of formic acid and its continuous regeneration at the cathode was evoked to explain the experimental data. 相似文献
10.
Yoshie Kitayama Masahiro Muraoka Megumi Takahashi Tatsuya Kodama Eriko Takahashi Mutsuo Okamura 《Journal of the American Oil Chemists' Society》1997,74(5):525-529
Catalytic activity and selectivity for hydrogenation of linoleic acid (cis-9,cis-12 18:2) were studied on Pt, Pd, Ru, and Ir supported on Al2O3. Stearic acid (18:0) and 10 different octadecenoic isomers (18:1) in the products could be separated completely by using a new capillary column coated by isocyanopropyl trisilphenylene siloxane for gas-liquid chromatography. The monoenoic acid isomers and dienoic acid isomers in the products on the various catalysts showed different distributions. The catalysts exhibited nearly equal selectivity for stearic acid formation. The 12-position double bond in linoleic acid has higher reactivity than the 9-position double bond in catalytic hydrogenation on platinum-group metal catalysts. In addition to hydrogenation products of linoleic acid, geometrical and positional dienoic acid isomers (trans-9,trans-12; trans-8,cis-12; cis-9,trans-13; trans-9,cis-13; cis-9,trans-12 18:2), due to isomerization of linoleic acid during hydrogenation, were contained in the reaction products. Ru/Al2O3 exhibited the highest activity for isomerization of linoleic acid with the noble metal catalysts. Conjugated octadecadienoic acid isomers have been observed in products of the reaction on Pt/Al2O3, Ru/Al2O3, and Ir/Al2O3. Catalytic activities of noble metals for positional and geometric isomerization of linoleic acid during hydrogenation decreased in the sequence of Ru ≥ Pt > Ir » Pd. 相似文献
11.
Long‐term testing of a high temperature polymer electrolyte membrane fuel cell: The effect of reactant gases 下载免费PDF全文
F. Javier Pinar Nadine Pilinski Peter Wagner 《American Institute of Chemical Engineers》2016,62(1):217-227
The investigations have been conducted with different oxidants and fuels with the aim of determining the state‐of‐the‐art of commercially available high temperature polymer electrolyte fuel cells based on polybenzimidazole for its application in combined heat and power generation systems. The fuel cell test performed with synthetic reformate (?63 μV/h) showed an increase of anode charge and mass transfer resistances. This behavior has suggested that CO may be generated from the CO2 included in the synthetic reformate via reverse water gas shift reaction. The fuel cell test performed with pure O2 developed the highest degradation rates (?70 μV/h) due to fast oxidative degradation of membrane electrode assembly materials such as cathode catalyst and membrane. Fuel cell operation with H2/air exhibited the lowest degradation rates (?57 μV/h) and it requires longer investigating times to identify the different degradation mechanisms. Moreover, fuel cell tests performed with air suggested longer break‐in procedures to complete catalyst activation and redistribution of electrolyte. © 2015 American Institute of Chemical Engineers AIChE J, 62: 217–227, 2016 相似文献
12.
Jianfeng Liu 《Electrochimica acta》2008,53(13):4435-4446
The cathode catalyst layer (CCL) is the major competitive ground for reactant transport, electrochemical reaction, and water management in a polymer electrolyte fuel cell (PEFC). Our model, presented here, accounts for the full coupling of random porous morphology, transport properties, and electrochemical conversion in CCLs. It relates spatial distributions of water, oxygen, electrostatic potential, and reaction rates to the effectiveness of catalyst utilization, water handling capabilities, and voltage efficiency. A feedback mechanism, involving the non-linear coupling between liquid water accumulation and oxygen depletion is responsible for the transition from a state of low partial saturation with high voltage efficiency to a state with excessive water accumulation that corresponds to highly non-uniform reaction rate distributions and large voltage losses. The transition between these states could be monotonous or it could involve bistability in the transition region. We introduce stability diagrams as a convenient tool for assessing CCL performance in dependence of composition, porous structure, wetting properties, and operating conditions. 相似文献
13.
N. Wagner 《Journal of Applied Electrochemistry》2002,32(8):859-863
The most common methods used to characterize the electrochemical performance of fuel cells are to record current–voltage U(i) curves. However, separation of electrochemical and ohmic contributions to the U(i) characteristics requires additional experimental techniques. The application of electrochemical impedance spectra (EIS) is an approach to determine parameters which have proved to be indispensable for the development of fuel cell electrodes and membrane electrode assemblies (MEAs). This paper proves that it is possible to split the cell impedance into electrode impedances and electrolyte resistance by varying the operating conditions of the fuel cell (current load) and by simulation of the measured EIS with an equivalent circuit. Furthermore, integration in the current density domain of the individual impedance elements enables the calculation of the individual overpotentials in the fuel cell and the determination of the voltage loss fractions. 相似文献
14.
Devinder Singh M. E. Rezac P. H. Pfromm 《Journal of the American Oil Chemists' Society》2009,86(1):93-101
Partial hydrogenation of vegetable oils is carried out to improve the chemical stability and raise the melting point to produce
semi-solid products such as margarine. Trans fatty acids formed during traditional hydrogenation have come under intense scrutiny with regard to human health. Here we
report partial hydrogenation of soybean oil using a high performance integral-asymmetric polyetherimide membrane sputtered
with platinum to deliver hydrogen directly to or near the catalytic sites. Oil flows past the platinum-coated “skin” side
of the membrane while dissolved molecular and some atomic hydrogen is supplied from the highly porous substructure of the
membrane. The membrane has a high hydrogen flux but is essentially impermeable to soybean oil. Hydrogenation using our metal/polymer
catalytic composite membrane produced oil with only 4 wt.% total trans fatty acids and 14.5 wt.% C18:0 saturates at IV of 95 while the conventional Pt/C slurry reactor produced more than 10 wt.%
TFA and the same amount of C18:0 saturates under similar conditions of temperature and pressure. Our concept requires hydrogen
pressures of only about 65 psi and temperatures near 70 °C. The polymeric base membranes used here have been mass produced
and can be packaged in spiral wound modules. The relatively mild reaction conditions and the direct pathway to produce useful
membrane modules combine to make our concept promising for near-term application. 相似文献
15.
Robert L. Wolff 《Journal of the American Oil Chemists' Society》1994,71(10):1129-1134
To understand the heat-inducedcis-trans isomerization of ethylenic bonds in octadecatrienoic acids, pine seed oil, which contains the unusual nonmethylene-interrupted
pinolenic (cis-5,cis-9,cis-12 18∶3) acid as a major component, was heated under vacuum at 240°C for 6 h together with linseed and borage oils. As a
results, a small percentage of pinolenic acid undergoescis-trans isomerization. The main isomer that accumulates is thetrans-5,cis-9,trans-12 18∶3 acid. Minor amounts of the three mono-trans isomers are also present. Identification of isomers was realized by combining gas-liquid chromatography on a CP Sil 88 capillary
column, argentation thin-layer chromatography and comparing the equivalent chainlengths of artifacts to those of isomers present
in NO2-isomerized pine seed oil. Hydrazine reduction was used to demonstrate that there was no positional shift of double bonds.
Heat-induced geometrical isomerization of pinolenic acid differs from that of α- and γ-linolenic acids in at least two aspects.
The reaction rate is slower (about one-fourth), and mono-trans isomers are formed in low amounts. 相似文献
16.
Bijay P. TripathiVinod K. Shahi 《Progress in Polymer Science》2011,36(7):945-979
Organic-inorganic nanocomposite polymer electrolyte membrane (PEM) contains nano-sized inorganic building blocks in organic polymer by molecular level of hybridization. This architecture has opened the possibility to combine in a single solid both the attractive properties of a mechanically and thermally stable inorganic backbone and the specific chemical reactivity, dielectric, ductility, flexibility, and processability of the organic polymer. The state-of-the-art of polymer electrolyte membrane fuel cell technology is based on perfluoro sulfonic acid membranes, which have some key issues and shortcomings such as: water management, CO poisoning, hydrogen reformate and fuel crossover. Organic-inorganic nanocomposite PEM show excellent potential for solving these problems and have attracted a lot of attention during the last ten years. Disparate characteristics (e.g., solubility and thermal stability) of the two components, provide potential barriers towards convenient membrane preparation strategies, but recent research demonstrates relatively simple processes for developing highly efficient nanocomposite PEMs. Objectives for the development of organic-inorganic nanocomposite PEM reported in the literature include several modifications: (1) improving the self-humidification of the membrane; (2) reducing the electro-osmotic drag and fuel crossover; (3) improving the mechanical and thermal strengths without deteriorating proton conductivity; (4) enhancing the proton conductivity by introducing solid inorganic proton conductors; and (5) achieving slow drying PEMs with high water retention capability. Research carried out during the last decade on this topic can be divided into four categories: (i) doping inorganic proton conductors in PEMs; (ii) nanocomposites by sol-gel method; (iii) covalently bonded inorganic segments with organic polymer chains; and (iv) acid-base PEM nanocomposites. The purpose here is to summarize the state-of-the-art in the development of organic-inorganic nanocomposite PEMs for fuel cell applications. 相似文献