Presence Of Hexane Research Articles

An elementary reaction-kinetic model for the gas-phase formation of 1,3,6,8- and 1,3,7,9-tetrachlorinated dibenzo- p-dioxins from 2,4,6–trichlorophenol

A 71-step reaction-kinetic model for the formation of 1,3,6,8- and 1,3,7,9-tetrachlorodibenzo- p-dioxins (TCDDs) from the oxidation of 2,4,6-trichlorophenol in the presence of hexane is developed based on experimental data and a simpler model that was previously published in the literature. The rate of reaction of phenoxyl-radicals with molecular oxygen has recently been experimentally demonstrated to be at least five orders of magnitude slower than the rate used in the previous model. With this correction, inclusion of radical-radical recombination reactions of 2,4,6-trichlorophenoxyl-radicals, and other minor modifications, the revised model yields satisfactory agreement between experimental and predicted concentrations of TCDDs above 900 K. The results of this study indicate that high-temperature, gas-phase reactions of chlorinated phenols that contain an ortho-chlorine will form poly-chlorinated dibenzo- p-dioxins (PCDDs) in yields approximately four to five orders of magnitude greater than believed, based on the previous modeling results.

Assessment of the process of cottonseed oil bleaching in hexane

This work has been initiated to assess the feasibility of bleaching cottonseed oil in miscella as a processing step next to alkali refining in miscella. Alkali refining of cottonseed oil in miscella has several advantages over conventional refining technologies with respect to oil quality, oil losses and process cost. Therefore, the process efficiency of the bleaching of cottonseed oil in presence of hexane (at a volumetric ratio of 1:1), has been studied and compared to that without solvent. The process efficiency has been evaluated according to the decolourization capacity, the oil losses on spent earth, the filtration rate of the oil from the clay and the acidity of the bleached oil as well as its peroxide content. The bleaching in presence of hexane was carried out at 25oC whereas that by conventional bleaching at 110oC. Different clay loads were used in each of the two bleaching techniques and the colour indices of the oils before and after bleaching determined in each case. The results were used to predict Freundlich adsorption equations for the oil pigments in both cases. These equations were then used to predict the colour of the oils obtained by bleaching of refined oils of different grades. The results have shown that oil decolourization is more efficient in presence of solvent when the starting oil is of an acceptable grade and the reverse is true for low grade oils. Also, the possibility of oil oxidation during bleaching is less in presence of solvent. Moreover, the bleaching in miscella has proved two other additional advantages over conventional bleaching. The filtration of oil from clay is much faster in miscella bleaching and the oil losses on spent earth is lower. This will be reflected on the overall process economy.

Enzymatic synthesis of aroma compound xylosides using transfer reaction by Trichoderma longibrachiatum xylanase.

Enzymatic synthesis of aroma compound xylosides was performed by Trichoderma longibrachiatum xylanase. Information concerning the nature of xylosides present in the reaction medium was obtained by GC-EI-MS, by GC-NCI-MS of TFA derivatives, and by positive FAB-MS of the reaction mixtures. Moreover, the structures of isolated benzyl beta-D-xylopyranoside and 4-O-beta-xylopyranosyl-beta-D-xylopyranoside were established by (1)H and (13)C NMR and heteronuclear two-dimensional ((1)H-(13)C) chemical shift correlation. The results obtained for hexyl and benzyl alcohol xylosides indicated that a reaction implying a transfer of one to two or three xylose units from xylan was involved. The enzyme was able to recognize xylobiose, xylotriose, and xylan as xylose donors. Benzyl xyloside, produced independently of xylobioside and xylotrioside, was found as the major kinetic product of the reaction. Benzyl xyloside was produced in higher quantities and at a higher rate than that obtained for the di- and trixyloside derivatives. The maximum production for benzyl xyloside, 1.29 g/L, was obtained in the presence of hexane (50%) used as cosolvent. Xylosides and xylobiosides of several aroma compounds, (Z)-hex-3-en-1-ol, heptan-2-ol, geraniol, nerol, and citronellol, were synthesized in different amounts, from 850 mg/L for (Z)-hex-3-en-1-yl xylosides to 1.5 mg/L for citronellyl xylosides. No synthesis occurred when menthol, linalool, and eugenol were used as acceptors.

Enhancement of the catalytic oxidation of hydrogen-lean chlorinated VOCs in the presence of hydrogen-supplying compounds

The complete catalytic oxidation of trichloroethylene (TCE) over alumina-supported noble metal catalysts (Pt and Pd) and in the presence of hydrogen-rich compounds, i.e. water, hexane and toluene was evaluated. Experiments were performed at conditions of lean TCE concentration (around 1000ppm) in air, between 250 and 550°C in a conventional fixed-bed reactor. Hexane and toluene were added to the feedstream in a concentration of around 1000ppm and water concentration varied from 1000 to 15000ppm. TCE oxidation occurred faster in the presence of hexane and toluene over both catalysts. Over palladium catalysts, water did not alter catalytic activity, whereas over platinum catalysts water enhanced TCE oxidation at low temperatures (<400°C) but inhibited it at higher temperatures (>400°C). Selectivity to HCl was much improved by feeding water as a hydrogen-supplying reactant; 7500ppm of water enhanced HCl outputs from 39.4 to 78.0% with Pd, and from 37.5 to 58.9% with Pt. Selectivities to C2Cl4, formed by chlorination of the feed, and Cl2 were greatly reduced. On the other hand water promoted complete oxidation of TCE to CO2, and thus reduced selectivity to CO. In the presence of hexane and toluene, formation of HCl was also enhanced. Hexane showed higher inhibition ability than toluene over both catalysts for the C2Cl4 and Cl2 formation. Unlike in the presence of water, selectivity to CO increased, as a consequence of partial oxidation of both hydrocarbons.

Aldolase stability in the presence of organic solvents

Rabbit muscle aldolase (RAMA) and trout muscle aldolase (TRMA) retained 100% activity in the presence of hexane, cyclohexane and toluene. Both enzymes retained greater than 80% activity in the presence of 20% (v/v) methanol. In the presence of 20% (v/v) N,N-dimethylformamide RAMA and TRMA were inactive, but at least 50% activity could be restored by returning the enzymes to an aqueous environment.

Immobilized Lipase - Catalyzed Fish Oil Hydrolysis in Organic Solvent

Immobilized lipase from Mucor miehei catalyzed the hydrolysis of cod liver oil in the presence of hexane was studied. The research was conducted to observe the effect of hexane on degree of hydrolysis, glyceride profile and EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) contents. Enzymatic hydrolyses were carried out in a waterbath shaker at 50°C for 48 hours. Reaction mixtures contained of 1 g cod liver oil, hexane, Tris HCl buffer pH 7.5, and 10% (w/w oil) immobilized enzyme. Addition of various amount of hexane decreased the degree of hydrolysis and changed glyceride profile. Hexane to buffer ratio of 1:9 and 9:1 yielded 77% and 64% hydrolyses respectively. The results showed that degree of hydrolysis was affected by the oil concentration in the solvent system, not by the oil concentration in the overall system. It was observed that after hydrolysis, EPA dan DHA contents in the forms of glycreride and free fatty acid were higher in the addition of hexane than that of in the absence of hexane

Organic solvent-tolerant mutants of Pseudomonas aeruginosa display multiple antibiotic resistance.

Organic solvent-tolerant mutants of Pseudomonas aeruginosa selected in the presence of hexane exhibited increased resistance to a variety of structurally unrelated antimicrobial agents, including beta-lactams, fluoroquinolones, chloramphenicol, tetracycline, and novobiocin, a phenotype typical of nalB multidrug-resistant mutants. Western immunoblotting with antibodies specific to components of the three known multidrug efflux systems in P. aeruginosa demonstrated that the solvent-tolerant mutants displayed increased expression of the MexAB-OprM system and decreased expression of the MexEF-OprN system. Sequence analysis of mexR, the repressor gene of mexAB-oprM efflux operon, identified a nonsense mutation and a point mutation in the mexR genes of two solvent-tolerant mutants. These results emphasize the importance of the MexAB-OprM efflux system in organic solvent tolerance and the ability of environmental pollutants to select bacteria with a medically relevant antibiotic-resistant phenotype.

Improvement in the determination of mancozeb residues by the carbon disulfide evolution method using flow injection analysis.

The sample decomposition of the carbon disulfide evolution method for the determination of dithiocarbamate residues was carried out in a closed vial in the presence of hexane. The evolved carbon disulfide was extracted by the organic solvent and injected in a flow system for its quantification as copper complex. The conditions for batch decomposition, flow injection determination, and association of both were investigated with sodium diethyldithiocarbamate as model substance. An one-channel flow system was employed where the carrier stream was the ethanolic ethylenediamine/copper solution. The determination range was of 0. 01-1.26 microg of CS(2), with a relative standard deviation of 0.06% (n = 10), with a sample throughput of 45 samples/h. The association of the batch decomposition with the flow system was carried out with the fungicide mancozeb and was applied to the analysis of its residue in potato, lettuce, cucumber, and green bean crops. The approach allowed the analysis of 11 samples in triplicate in 2 h, with recoveries between 85% and 92% and relative standard deviation about 2%.

Copolymerization of propene and 1-hexene using metallocene amide compounds

Copolymerization of propene and 1-hexene has been carried out at 30°C in toluene under atmospheric pressure by using three isospecific metallocene amide compounds, rac-(EBI)Zr(NMe2)2 (EBI = ethylenebis(1-indenyl), rac-1), rac-(EBI)Zr(NC4H8)2 (rac-2), and rac-Me2Si(1-C5H2-2-Me-4-t-Bu)2Zr(NMe2)2 (rac-3), in the presence of methylaluminoxane (MAO) or [Ph3C][B(C6F5)4]. The rate enhancements in the presence of 1-hexene were recorded as a function of the catalytic systems. The incorporation of 1-hexene decreases in the following order: rac-2/MAO > rac-3/Al(i-Bu)3/[Ph3C][B(C6F5)4] > rac-1/MAO. All copolymers investigated in this study have a nearly random sequence distribution.

Enzymatic decrease in the phenolic content of canola meal using concentrated aqueous or aqueous/hexane slurries

AbstractAn enzymatic process to decrease the phenolic content in canola meal was investigated. The new method was based on the addition of an enzyme preparation from the white‐rot fungus Trametes versicolor to concentrated meal‐buffer slurries. This approach eliminated the extraction of the valuable meal components such as proteins and carbohydrates. Two systems were considered: (i) slurries with canola meal concentrations higher than 33% [w/v]; (ii) slurries with canola meal concentrations equal to or less than 12.5% [w/v] with n‐hexane as the main component of the continuous phase.The concentration of sinapic acid esters decreased by 99% after a 1.5, 2 and 3 hour long treatment of the meal with an initial moisture content of 75% at 90°C, 70°C and 50°C, respectively. The process was carried out at temperaturs as high as 110°C. Both the enzyme and the moisture concentrations influenced the enzymatic process and their action was coupled. The concentration of oxygen strongly affected the process.The enzymatic process was able to be carried out in the presence of hexane as the main component of the continuous phase. The optimum temperature for such a process was 30–40°C, At 30°C, after 1 h of treatment, the meal phenolic content was decreased by 97%. The water uptake by the meal was diminished in the presence of hexane.

F-Bonded (1-Fluorohexane)pentacarbonyltungsten(0)

Fluoroalkanes, potentially ambidentate, can interact with W through coordination of F or agostically through a three-center, two-electron C(H)−M bond. The site of bonding of 1-fluorohexane to [W(CO)5] in (1-C6H13F)W(CO)5 generated by pulsed laser flash photolysis of W(CO)6/1-fluorohexane solutions in the absence and presence of 1-hexene as a trapping nucleophile has been evaluated. The data indicate that W−F bonding is favored and suggest that linkage isomerization takes place through an intramolecular pathway.

Chemically induced phase separation: a new technique for the synthesis of macroporous epoxy networks

We have developed a new technology, based on chemically induced phase separation, that allows for the synthesis of porous epoxies with a closed cell morphology and a narrow pore size distribution in the micrometre range. The potential of this technique for the synthesis of new types of porous thermosets is enlightened by the comparison with the current state of the art on technologies for the preparation of macroporous polymeric materials. The strategy of the chemically induced phase separation technique, as a general approach for the synthesis of macroporous thermosets with controlled morphology is presented. The particular system reported is a diglycidylether of bisphenol-A cured with 2,2′-bis(4-amino-cyclohexyl)-propane in the presence of hexane or cyclohexane. Depending on the hexane concentration, the morphology can be varied ranging from a monomodal to bimodal distribution. By regarding the kinetics and the development of a bimodal distribution, we surmise that the phase separation proceeds via a nucleation and growth mechanism. The influence of internal and external reaction parameters, such as chemical nature of the solvent, solvent concentration and curing temperature on the final morphology are reported. These porous materials are characterized by a significantly lower density without any loss in thermal stability compared to the neat matrix.

Effect of Aliphatic Nonaqueous Phase Liquids on Naphthalene Biodegradation in Multiphase Systems

AbstractBiodegradation of naphthalene by a Coryneform bacterium was examined in multiphase aqueous slurry systems containing a nonaqueous phase liquid (NAPL). The evolution of 14CO2 provided an index of biodegradation under aerobic conditions. The effect of NAPL hydrophobicity was evaluated by considering a homologous series of n‐alkanes (C6–C16). Experiments were conducted in NAPL‐water and soil‐NAPL‐water systems where the inoculum was pre‐incubated with a sandy aquifer material. Relative to aqueous systems, conversion to CO2 increased in the presence of decane, dodecane, and hexadecane. Biodegradation was apparent, but decreased in the presence of octane, and was negligible in the presence of hexane. Thus biodegradation was sustained in multiphase systems where log Kow of the NAPL was &gt;5, and was inhibited in systems where the log Kow of the NAPL was &lt;4. Naphthalene partitioning between water and each of the NAPLs was similar, indicating that the observed differences in biodegradation among the homologous series were not due to differences in naphthalene distribution. Naphthalene sorption to the sandy aquifer material was minimal and the aquifer material did not significantly modify biodegradation. Mineralization rates were reduced in multiphase systems when compared with aqueous systems; CO2 production curves were described with a first‐order kinetic model. Reduced mineralization rates in soil‐NAPL‐water systems can be explained by the lower aqueous phase concentration. This was not the case in the NAPL‐water system, suggesting a direct effect of the NAPL on the bacteria.

Properties of a polyimide gas separation membrane in natural gas streams

Carbon dioxide and methane permeabilities have been measured for dense film and asymmetric membrane prepared from an aromatic polyimide (6FDA/DMB). Selectivities for CO 2 CH 4 of up to 55 were determined for mixture oof these gases. Permeability of gases through the membrane was found to be dependent upon the carbon dioxide and higher hydrocarbon concentrations that can also be present in natural gas streams. In addition to carbon dioxide having an impact on methane permeability, the presence of hexane or toluene cut CO 2 CH 4 selectivities in half. Lowered selectivities from ideal test conditions are a result of plasticization of the polyimide by these components. Results for the polyimide are contrasted with values obtained from cellulose acetate films which are less impacted by hydrocarbon impurities. The polyimide depends more upon diffusivity factors than cellulose acetate to generate high selectivity. Thermal and physical properties of 6FDA/DMB polymer and membrane are also described.

Modification of the nutritional properties of fats using lipase catalysed directed interesterification

A method for producing a monounsaturated cooking oil from beef tallow has been investigated. Immobilised lipases were used to interesterify tallow during fractional crystallisation from melted tallow, both with and without hexane present. Significant increases in the unsaturated fatty acid content of the liquid fractions were achieved by the use of upases. The water content of the enzyme beads appeared to have a large effect on reaction rates and free fatty acid formation. The presence of hexane greatly improved the efficiency of the reaction by improving the efficiency of crystal filtration.

Rapid, Sensitive, and Specific Thiobarbituric Acid Method for Measuring Lipid Peroxidation in Animal Tissue, Food, and Feedstuff Samples

A rapid aqueous acid extraction thiobarbituric acid method for measuring malondialdehyde as a marker of lipid peroxidation in animal tissue, food, and feedstuff samples has been developed. Sample is homogenized with aqueous trichloroacetic acid in the presence of hexane and butylated hydroxytoluene, and the homogenate is centrifuged. Following reaction with thiobarbituric acid reagent, malondialdehyde is directly quantified on the basis of the third-derivative absorption spectrum of the pink complex formed. Further purification is not required because the derivative transformation of the conventional analytical band at around 532 nm virtually eliminates spectral interferences arising from other compounds. The effect of antioxidants and the optimum conditions for the reaction have been established, and the analytical performance of the new method has been evaluated. The applicability of the method on various animal tissue, food, and feedstuff samples has been also tested. Owing to its simplicity and increased sensitivity and specificity, the method may be preferred over other methods for estimating the extent of lipid peroxidation.

The influence of solvent type on solvent-pesticide interactions in bioassays

The effect of solvent type on solvent-pesticide interactions was examined by interacting the fungicide captan with the solvents acetone, ethanol, methanol, hexane, dimethyl sulfoxide (DMSO), andN,N-dimethylformamide (DMF), using growth of the fungiPythium ultimum, Sclerotinia homeocarpa, andPestalotia sp. as a toxicity criterion. DMF, ethanol, and methanol were generally the most toxic solvents tested, yielding EC50 values from 0.51 to 2.29% (v/v). The least toxic solvent was hexane, with EC50 values up to 36.60% (v/v). Acetone and DMSO evidenced median toxicity, yielding EC50 values of 1.99 to 12.07% (v/v). WithP. ultimum andS. homeocarpa, captan interacted synergistically with all solvents tested except hexane, with the actual solvent concentration at which synergism occurred being dependent upon the level of captan. Hexane interacted additively with 2.5 ppm captan towardsS. homecarpa, antagonistically with 5.0 ppm captan towardsP. ultimum and synergistically with captan in all other combinations tested. WithPestalotia sp., captan interacted antagonistically with acetone, ethanol, and methanol, and synergistically with hexane, DMSO, and DMF. Captan was more toxic towardsP. ultimum when dissolved in DMSO, and less toxic in the presence of hexane and DMF. WithS. homeocarpa, captan was more toxic with ethanol and DMSO, and less toxic when dissolved in acetone, methanol, and hexane. DMSO and hexane elicited less toxicity from captan when tested towardsPestalotia sp., while acetone, ethanol, and methanol elicited the greatest toxicity.

Thermodynamic studies on adsorption at interfaces: IV. Dodecylammonium chloride at water/air interface

The thermodynamic treatment of the adsorption at water oil interface developed in the previous papers has been extended so as to be applied to the adsorption at water/air interface. The surface tension of the aqueous solution of dodecylammonium chloride (DAC) has been measured as a function of temperature and concentration. By applying the thermodynamic relations, the entropy of surface formation Δs and the surface density of DAC Γ 1 H have been calculated. Further, we have shown that the energy of surface formation Δ u can be evaluated numerically. It has been observed that the values of Δs and Δ u decrease, while the value of Γ 1 H increases, with increasing concentration of DAC. It has been found that the adsorbed film transforms from a gaseous to an expanded state at a relatively low concentration, which has been proved thermodynamically. Such a behavior seems to be similar to that at water hexane interface except for the phase transition. The mutual interaction between DAC molecules in the adsorbed film appears to be weakened by the presence of hexane.

High Pressure Liquid Chromatographic Determination of Satratoxins G and H in Cereal Grains

A high pressure liquid chromatographic (HPLC) method is described for the detection and quantitative determination of satratoxins G and H in cereal grains. The toxins are extracted from the sample by blending with methanol--water (55 + 45) in the presence of hexane, followed by partitioning into chloroform. The chloroform extract is further purified on a 10 g silica gel column. A high pressure liquid chromatograph, equipped with a microparticle silica gel column and a 254 nm absorbance detector, is used for the determination. Additional confirmation of identity is obtained by mass spectrometry or by a brine shrimp bioassay of the HPLC eluates corresponding to the retention times of satratoxins G and H. The recoveries of added satratoxins G and H from wheat samples averaged 65% for G and 71% for H (200--1000 mg/kg). The coefficients of variation (CV) were 15% for G and 14% for H. The lower limit of detection was 200 microgram/kg for wheat. Analysis of corn, oats, and barley samples (400 microgram/kg of each toxin added) gave comparable recoveries. Only the corn extract exhibited HPLC interferences at the retention time for satratoxin H. The method was also used to analyze samples of corn, oats, wheat, barley, and rice on which Stachybotrys atra had been cultured.