Increasing Hydrocarbon Content Research Articles

Catalytic pyrolysis of microalgal lipids to liquid biofuels: Metal oxide doped catalysts with hierarchically porous structure and their performance

Catalytic pyrolysis of lipids is an alternative pathway for alternative aviation fuel production with advantages of H2-free and mild reaction conditions. However, it is still hindered by coking of catalysts and low selectivity of kerosene. In this research, composite catalysts were synthesized via postsynthesis method (alkali treatment) followed by doping of metal oxides (ZnO, La2O3, and CeO2). Catalytic performance of as-synthesized catalysts was evaluated during catalytic pyrolysis of microalgal lipids. The characterization of BET, XRD, SEM, NH3-TPD for catalysts indicated that alkaline treatment increased the mesoporous structure (5.28–5.91 nm) of microporous zeolite HZSM-5 to form a hierarchically porous structure without apparent disruption of crystal structure of zeolite, while doping of metal oxides (about 10 wt%) enhanced the performance of hetero-atoms (oxygen and nitrogen) removal. The acidity of as-synthesized catalysts significantly decreased from 1175.61 μmol/g (HZSM-5) to 406.77 μmol/g (Ce-MHZ). After catalytic pyrolysis carbon number distribution and compound type of produced liquid fuels tended to high kerosene components (above 40%) and increased hydrocarbon content with reduced content of oxygen-containing compounds. The hierarchically porous zeolite also presented aromatization for aromatic hydrocarbons in alternative aviation fuels. Catalytic mechanism was also elucidated including complex reactions of decarboxylation, decarbonylation, carbon chain cracking, and aromatization.

Synergistic effect of active metal–acid sites on hydrodeoxygenation of lignin-derived phenolic compounds under mild conditions using Ru/C-HPW catalyst

Hydrodeoxygenation (HDO) is an indispensable reaction in the field of fuel and chemical production, and the synergistic effect of metal–acid sites in the catalyst makes great influence to it. Herein, a bifunctional catalyst of Ru/C combined with phosphotungstic acid (HPW) was employed for the hydrodeoxygenation (HDO) of lignin-derived compounds to make full use of the synergistic effect of active metal–acid sites. HPW possessed a temperature-controlled phase-transfer behavior, which made it dispersed well on the surface of Ru/C catalyst and resulted in a close integration of acid site with metal site. Ru/C-HPW catalyst also owned the advantage of high reaction rate and good recyclability, which exhibited no obvious catalytic activity loss after 5 runs. Lignin-derived phenolic compounds including monomers and dimers enabled to obtain an efficient transformation to cycloalkanes at the temperature of 200 °C. Moreover, a high HDO reaction efficiency of raw lignin-oil was also observed in this study, with the increasing hydrocarbon content from 5.5% to 78.9%. This novel catalytic system can achieve a high HDO efficiency under mild conditions.

Effect of Calcium-Based Catalysts on Pyrolysis Liquid Products from Municipal Sludge

Aimed to obtain high-quality pyrolysis liquid products, the effects of different calcium-based catalysts and temperatures on liquid products from catalytic pyrolysis of municipal sludge (moisture of 50%) were studied. Results showed that the liquid product yield reached maximum at 600 °C and then decreased. The catalyst capability of catalysts decreased the yield of liquid products in the order of poorly soluble in water (Ca(OH)2, CaCO3, CaO) > soluble in water (CaCl2, Ca(H2PO4)2·H2O). High temperature strengthened the aromatization, and the breaking of the oxygen-containing functional group in liquid products resulted in the decrease of O/C and H/C molar ratios and the increase of four components yield in gaseous products. At 600 °C, the catalysts significantly reduced the O content of liquid products and increased hydrocarbon content. Meantime, CaO additive increased the content of C to 85.34%, and the relative content of aromatics reached 83.99% at 800 °C, which is suitable as chemical raw materials. However, the Ca(OH)2 group had the highest aliphatics content, and the H/C molar ratio was 1.42 at 400 °C, which is suitable as fuel.

Influence of CeO2 Addition to Ni–Cu/HZSM-5 Catalysts on Hydrodeoxygenation of Bio-Oil

Hydrodeoxygenation (HDO) of bio-oil is a method of bio-oil upgrading. In this paper, x%CeO2–Ni–Cu/HZSM-5 (x = 5, 15, and 20) was synthesized as an HDO catalyst by the co-impregnation method. The HDO performances of x%CeO2–Ni–Cu/HZSM-5 (x = 5, 15, and 20) in the reaction process was evaluated and compared with Ni–Cu/HZSM-5 by the property and the yield of upgrading oil. The difference of the chemical composition between bio-oil and upgrading oil was evaluated by GC-MS. The results showed that the addition of CeO2 decreased the water and oxygen contents of upgrading oil, increased the high heating value, reduced acid content, and increased hydrocarbon content. When the CeO2 addition was 15%, the yield of upgrading reached the maximum, from 33.9 wt% (Ni–Cu/HZSM-5) to 47.6 wt% (15%CeO2–Ni–Cu/HZSM-5). The catalytic activities of x%CeO2–Ni–Cu/HZSM-5 (x = 5, 15, and 20) and Ni–Cu/HZSM-5 were characterized by XRD, N2 adsorption–desorption, NH3-Temperature-Programmed Desorption, H2-Temperature-Programmed Reaction, TEM, and XPS. The results showed that the addition of CeO2 increased the dispersion of active metal Ni, reduced the bond between the active metal and the catalyst support, increased the ratio of Bronsted acid to total acids, and decreased the reduction temperature of NiO. When the CeO2 addition was 15%, the activity of catalyst reached the best. Finally, the carbon deposition resistance of deactivated catalysts was investigated by a Thermogravimetric (TG) analysis, and the results showed that the addition of CeO2 could improve the carbon deposition resistance of catalysts. When the CeO2 addition was 15%, the coke deposition decreased from 41 wt% (Ni–Cu/HZSM-5) to 14 wt% (15%CeO2–Ni–Cu/HZSM-5).

Phenothiazinium photosensitisers XI. Improved toluidine blue photoantimicrobials

The phenothiazinium derivative toluidine blue O (TBO) is widely employed as a photoantimicrobial agent in clinical trialling, particularly in dentistry. However, its activity against a range of pathogenic microbial species is not significantly different to that of the standard photoantimicrobial methylene blue. In the current study, derivatives of TBO with varying hydrocarbon substitution in chromophore position 2 were synthesised via the established anilinethiosulphonic route, using the mild oxidant silver(II) carbonate to allow substituent preservation.The resulting series of analogues demonstrated the expected increases in visible absorption wavelength and lipophilicity with increasing hydrocarbon content, as well as decreased aggregation for derivatives with bulkier substituents, and all produced singlet oxygen on illumination in vitro. Screening against a range of bacterial and fungal pathogens relevant to infection control showed remarkable increases in activity relative to the parent compound, particularly against the clinically important Gram-negative bacterium Pseudomonas aeruginosa. In addition, in order to demonstrate clinical relevance, the photoactivities of the new derivatives against microbial targets were compared to conventional antibacterial and antifungal drugs, as well as biocides commonly used for local disinfection. Activity here was also generally greater than that of the conventional agents used for comparison, considerably so relative to the local disinfectant agents.

Effect of cobalt enrichment on growth and hydrocarbon accumulation of Botryococcus braunii with immobilized biofilm attached cultivation

The effects of cobalt enrichment on the growth and hydrocarbon accumulation were studied with biofilm attached cultivation. Under biofilm attached cultivation conditions, the microalga Botryococcus braunii survived high concentration of cobalt (50× normal level). The crude hydrocarbon content as well as the long C chain component (C31) increased under Co enrichment treatment indicating the activity of key enzyme that catalyze hydrocarbon synthesis might be enhanced by Co enrichment. The reduced carbohydrate and protein contents accompanied by increased hydrocarbon content for Co enrichment treatment indicating the Co was also an effective factor that controls the carbon flow of B. braunii. Under Co enrichment treatment, totally 1473.9μmol of Co element was consumed to produce one gram of algal biomass, indicating this attached cultivation method is high efficient in heavy metal elements removal.

Structural and chemical characterization of SnO2-based nanoparticles as electrode material in Li-ion batteries

Improvement of long-term stability of electrode materials in Li-ion batteries requires a detailed understanding of influence of synthesis parameters on surface chemistry and on properties. Therefore, bare SnO2 and core/shell nanoparticles with SnO2 core and a hydrocarbon shell are synthesized in an Ar/20% O2 microwave plasma, deposited as porous nanoparticle films in situ on heated Ni-substrates, and finally assembled as anodes in Swagelok cells. In a comprehensive study, we investigate structure, particle size, chemistry, morphology, and water content of the nanoparticles using X-ray diffraction, transmission electron microscopy, specific surface area analysis, and coulometric water titration. The thicknesses of the nanoparticle films and their surface chemistry are investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. SnO2 nanoparticles are crystalline, with a tetragonal cassiterite structure. Primary particle sizes around 3 nm are reached for the bare SnO2 particles, 5–8 nm for the cores of the core/shell nanoparticles. A minimum microwave power of 900 W is necessary to synthesize SnO2 nanoparticles without precursor residuals as pristine SnO2 particles for the subsequent coating step. In the coating step increasing hydrocarbon content can be correlated with increasing carbon-precursor feeding rate. Water uptake, stemming either from the process, or due to atmospheric contamination, can successfully be reduced by a thermal treatment. The still remaining water is a function of specific surface area. Finally, bare SnO2 versus core/shell nanoparticles are compared regarding the influence of the shell on the electrochemical properties. The principal improved functionality of the developed anodes in Swagelok cells is demonstrated.

Traction of Lubricated Rolling Contacts between Thin-Film Coatings and Steel

Tribological thin-film coatings can enhance the performance of mechanical components such as bearings and gears. Although a lubricant is present in most applications, the interactions of the lubricant with the coated surfaces are not always well understood. In the present study, Stribeck curves (i.e., traction coefficient vs. dimensionless film thickness λ) were generated for lubricated rolling contact between coated and uncoated surfaces. Chromium nitride, tungsten carbide–reinforced amorphous hydrocarbon, and silicon-incorporated diamond-like carbon coatings were evaluated. Compositions, hydrogen concentrations, Raman spectra, and surface energies are reported for the films. A ball-on-flat test configuration was used in 5%, 50%, and 100% slide-to-roll conditions. The test lubricant was a polyalphaolefin containing rust and oxidation inhibitor additives only. Differences in traction performance were observed for different coating types. Traction coefficients decreased at high λ with increased hydrocarbon content in the coating. Coating micro-texture and composition were believed to influence traction as λ became small.

Electrical resistivity of frozen and petroleum-contaminated fine-grained soil

Both positive and negative resistivity anomalies associated with contaminated soil have been reported in the recent literature. By positive we mean expected increases of resistivity with decreasing water content, increasing hydrocarbon content, and freezing. In this investigation, we tested these findings by measuring the electrical resistivity of samples of fine-grained soils contaminated with petroleum and by performing a field survey of an abandoned petroleum storage site where drilling and sampling confirmed soil contamination. In the laboratory, the cylindrical silt samples demonstrated a three-order-of-magnitude decrease in resistivity as water content increased. A corresponding resistivity increase was observed when water content was held at a constant level and petroleum percent was increased incrementally to saturation. Resistivity and temperature were also measured along a vertical profile as both the frost and petroleum front advanced beneath the surface of a large, unsorted silty-sand sample. Resistivity of the uncontaminated silty sand increased from 400 to 4000 Ω m as the soil froze; resistivity further increased to 10,000 Ω m when the soil was both frozen (−3.0°C) and contaminated. In the field we contoured resistivity, determined by Wenner array profiling within the containment berm of a storage tank where spills occurred sporadically during the 25-year operation period. Increasing values of apparent resistivity compare favorably with documented residual petroleum contamination and corroborates our laboratory measurements. We conclude that residual petroleum on soil particle surfaces results in a permanent increase in soil resistivity and that positive anomalies should be expected in most common situations.

Equilibrium and dynamic behavior for systems containing nonionic surfactants, n-hexadecane, triolein and oleyl alcohol

Phase behavior and electrical conductivity experiments were carried out for systems containing water, nonionic surfactants, triolein, n-hexadecane and oleyl alcohol. In systems where the amount of triolein was equal to or greater than the amount of n-hexadecane, the surfactant appeared successively in the lamellar liquid crystalline phase L α, the sponge phase D′, a bicontinuous microemulsion D and an oil-rich microemulsion O m as the system was made more lipophilic. The temperatures of the various phase transitions decreased with increasing hydrocarbon content. In one system five phases were found to coexist simultaneously: L α, D′, D, and excess water and oil. Conductivity measurements indicated no major change in microstructure of either D′ or D phases when the n-hexadecane-to-triolein ratio was changed from zero to one. In systems where the amount of hydrocarbon was much greater than the amount of triolein, the usual microemulsion phase behavior was seen with continuous variation of oil and water solubilization over a wide range. Videomicroscopy contacting experiments were consistent with the phase behavior results in that the D′ phase was observed as one intermediate phase when drops rich in triolein were injected into aqueous surfactant solutions but not when the drops were mainly hydrocarbon. In the latter case, microemulsions were seen which inverted continuously until the surfactant concentration in the drops became high enough that the lamellar phase formed.

Ellipsometry Studies of the Self-Assembly of Nonionic Surfactants at the Silica-Water Interface: Kinetic Aspects

The nature of layers of a series of poly(ethy1ene glycol) monoalkyl ethers (C,,Em) adsorbed on silica surfaces has been systematically investigated by means of null ellipsometry. The results show that adsorption remains low until a well-defined concentration ((=0.6-0.9)cmc) is exceeded. Then, as surfactants in the interfacial region start to self-absemble, it increases abruptly and plateau adsorption is generally observed prior to the cmc. The normal extension of the interfacial aggregates is relatively constant from intermediate to high surface coverage. Increasing the ethylene oxide to hydrocarbon ratio results in a decreased adsorption. The mean optical thickness, on the other hand, is relatively independent of the number of ethylene oxide groups in the surfactant but almost linearly dependent on the length of the hydrocarbon tail. The values obtained for these parameters suggest that the adsorbed layer is built up of discrete surface aggregates, or micelles, with dimensions resembling those observed in bulk solution. A more refined optical model of the adsorbed layer confirms the notion of surface micelles growing with increasing hydrocarbon content. It also points out that the extension of the surface micelles is slightly larger than the measured mean optical thickness. In addition to studies of neat CS, surfactants, we also examine the adsorption of mixed surfactant systems. Changes observed in adsorption on altering the bulk ratio of two surfactants are well correlated to the bulk micellar surfactant ratio calculated by ideal solution theory.

Morrow Channel Case Histories Using a New Exploration Approach

Seven Morrow channel-sand, oil, and gas traps in eastern Colorado and western Kansas have been investigated using the deep induction exploration (DINEX) method. This deep sounding technique is capable of measuring the resistivity of the complete sedimentary section as a function of depth well into the basement with a high degree of accuracy. All of the oil and gas traps surveyed showed well-defined, robust, and deep-seated resistivity anomalies very closely associated with the traps. Two areas where the Morrow sands were in the log had very little to no resistivity anomalies. The methodology for doing deep induction soundings and processing is inexpensive and rapid. A high-power transmitter and grounded-wire antenna are used to induce the received magnetic fields. The receiver system is backpackable, making data acquisition discrete and ideal in sensitive and rugged areas. According to Archie's law, the resistivity of a porous rock varies with the volume and arrangement of the pores and even more with the conductivity and amount of contained water. During the development of an oil and gas trap, large volumes of water migrate through the trap, resulting in a number of diagenetic changes in the section associated with the trap. As a result of cementation,more » mineralization, and increased hydrocarbon content, the resistivity of the rocks in close proximity to the oil and gas deposits is altered.« less

Effects of the aliphatic carboxylate series of salts on the conformation of proteins.

The effects of the aliphatic acid series of salts, formate, acetate, propionate, butyrate, valarate, and caproate, on the conformation of sperm whale myoglobin, human hemoglobin A, and horse heart cytochrome c were investigated by spectral measurements in the Soret region, optical rotation, and intrinsic viscosity measurements. The effectiveness of the aliphatic acid salts as unfolding reagents for proteins is found to increase with increasing hydrocarbon content of the alkyl chains of the salts, which is analogous in behavior to effects of the urea, amide, and alcohol series of protein denaturants. The denaturation midpoints, Sm, as a function of the unfolding reagent were analyzed using the equations of Peller (Peller, L. (1959), J. Phys, Chem- 63, 1199) and Flory (Flory, P.J. (1957), J. Cell. Comp. Physiol. 49, 175) with binding constants based in part on the Scherage-Nemethy theory of hydrophobic bonding or evaluated from free-energy transfer data of nonpolar amino acid side chains from aqueous to nonaqueous solvents. The summation of the polar KP and hydrophobic KHphi contributions of solvent to protein amino acid side chain interactions were found to give best account of the protein denaturation data. Intrinsic viscosity and optical rotation data obtained on hemoglobin and myoglobin at high salt concentrations, above the unfolding transition regions, indicate that the product of denaturation by the aliphatic acid salts is less unfolded than in 6 M guanidine hydrochloride solutions. Residual elements of the helical regions of the proteins seem to either escape unfolding or are reformed at high concentrations of the denaturing salts.

Thermodynamics of bolaform electrolytes. IV. Enthalpies and partial molal heat capacities in H2O, D2O, and dimethylsulfoxide

The partial molal heats of solution ΔH s o and the partial molal heat capacities of solution ΔC p o of the bolaform salts [Et3N(CH2)nNEt3]Br2 and [allyl3N(CH2)nNallyl3]Br2 have been obtained at infinite dilution in dimethylsulfoxide (DMSO). A comparison of these data with the results of previous thermodynamic studies of the same solutes in aqueous solvents has been carried out. The observed differences have been interpreted in terms of solute-induced solvent structural effects occurring in aqueous solvent media. Partial molal heat capacities of the bolaform salts at infinite dilution in DMSO, H2O, and D2O have been calculated from ΔC p o data and previously reported values of the heat capacities of the crystalline state. The data clearly show that the structure-promoting capabilities of these salts in aqueous solvents increase with increasing hydrocarbon content. A comparison of contributions to partial molal heat capacities of methylene groups in the bolaform and R4N+ series of salts reveals that similarities exist between the solvation effects of CH2 groups in the normal alkyl chain of the R4N+ cations and in the bridging alkyl chain of the bolaform cation.

Premixed Combustion in a Baffle Combustor and the Effect of Steam Injection

Details are given of the operation of a 90 deg annular sector of a ceramic-lined baffle-type combustor utilising premixed propane/air or propane/air/steam composition at ambient inlet conditions. Gas analyses are used to determine the combustion efficiencies, temperatures and compositions at a plane 8.9 in. downstream of the primary baffle. The results indicate the potential of the system for a low pollution chamber. They also show that most of the additional loss in efficiency, when steam is injected into the system, is due to increased hydrocarbon content.

Thermodynamics of bolaform electrolytes. I. Heat capacities and enthalpies in H2O and D2O

The partial molal heats of solution at infinite dilution, ΔH s o , of bolaform salts [Et3N(CH2)nNEt3]Br2 and [allyl3N(CH2)nNallyl3]Br2, have been measured in H2O and D2O at 25°C using a solution calorimeter. The values of ΔH s o were endothermic for almost all of the compounds studied. Values of ΔH s o were obtained as a function of temperature for several homologs in H2O and D2O. Positive ΔC p o values obtained from least-squares analyses of the ΔH s o vs T data show an almost linear dependence on the number of methylene groups between the nitrogen centers. Whereas the enthalpy of transfer from H2O to D2O is small and endothermic, relatively large positive heat capacity of transfer data, increasing with increased hydrocarbon content of the salts, were observed. The ability of the bolaform cation to act as a model for cation-cation pairing in R4NX systems is discussed.

On the Structural Stability and Solvent Denaturation of Proteins: III. DENATURATION BY THE AMIDES

Abstract The denaturation of sperm whale myoglobin, horse heart cytochrome c, and bovine α-chymotrypsinogen by various water-miscible amides has been investigated by spectral, difference spectral, and optical rotatory dispersion methods. As in the case of denaturants of the type of alcohols, glycols, and ureas, the effectiveness of the amides was found to increase with increasing hydrocarbon content and alkyl substitution of their functional amino groups. Branching of the hydrocarbon portion of the substituent groups of the latter compounds decreased their effectiveness as protein denaturants. Analysis of the denaturation data based on the theories of Peller and Flory, with appropriate binding constants and Setschenow parameters calculated from the solubilities of N-acetyl-l-tryptophan ethyl ester, has shown that hydrophobic interactions play an increasingly important role with increasing hydrocarbon content in the mode of action of the amides as denaturants.

On the Structural Stability and Solvent Denaturation of Proteins: I. DENATURATION BY THE ALCOHOLS AND GLYCOLS

Abstract The effects of the water-miscible straight chain and branched alcohols and glycols on the native conformation of sperm whale myoglobin, cytochrome c, and α-chymotrypsinogen have been investigated by spectral, difference spectral, and optical rotatory dispersion methods. Based on the midpoints of the denaturation transitions, that is, the amount of alcohol or glycol required to produce 50% denaturation at 25°, it is concluded that the effectiveness of the alcohols as protein denaturants increases with increasing chain length or hydrocarbon content, in conformance of what is expected of the disorganization of the hydrophobic interior of these proteins revealed by their detailed three-dimensional x-ray structure. As a rule, branching of the hydrocarbon portion of the alcohols tends to reduce their effectiveness as protein denaturants. The glycols are found to be less effective than the corresponding alcohols, suggesting that increased polarity or hydrogen-bonding capacity is of secondary importance when compared with the effects of increasing hydrocarbon content. The theories of Peller and Flory, used to account for the effects of denaturants and salts on the temperature transition of proteins and polypeptides, were extended to the analysis of isothermal denaturation data, with appropriate binding and Setschenow parameters based on free energy of transfer data taken from the literature or calculated from N-acetyl-l-tryptophan ethyl ester solubilities. The denaturation midpoints, Sm, based on the assumption of a hydrophobic mechanism of alcohol-protein side chain interactions, are found to be in satisfactory agreement with the experimentally obtained Sm values. Both the increased hydrophobicity with increasing chain length and the somewhat reduced effectiveness of the alcohols on branching are in most cases correctly predicted. For the straight chain alcohols, fairly satisfactory agreement with the experimental data is also obtained with binding constants based on estimates of free energies of hydrophobic bond formation, obtained by Scheraga and associates using the Nemethy and Scheraga theory of hydrophobic bonding.

EFFECT OF ELECTROLYTE ENVIRONMENT ON DIVALENT TARTRATE ION MOBILITY

The variation of the electrophoretic mobility, uT, of divalent tartrate ion with changing electrolyte environment has been studied. Mobilities were determined from boundary velocity measurements at 1.00 °C in the Tiselius electrophoresis apparatus. The solutions used, which were adjusted to pH 8.3–8.5, were principally either 0.04667 M C2T or 0.01 M C2T–0.11 M CA, where C+, T=, and A− are, respectively, a univalent cation, divalent tartrate ion, and a univalent anion. Relative viscosities, ηrcl, of a number of these solutions were also obtained. For a given anion environment, the variation of uT with changing cation is characterized by a minimum at sodium and a maximum at tetramethylammonium for a series of six alkali metal and tetraalkylammonium ions. For the alkali metal cations and for tetrapropylammonium ion, uT undergoes a distinct decrease when the solution is changed from 0.04667 M C2T to 0.01 M C2T–0.11 M CCl. For all solutions containing an anion A−, uT decreases with increasing hydrocarbon content of A− for a given cation. Possible ion association, obstruction, and ion–solvent interaction effects are considered.

Nonaqueous solutions of DNA: Factors determining the stability of the helical configuration in solution

The disorganization of the aqueous helical configuration of deoxyribonucleic acid (DNA) by a number of structurally related organic solvents has been investigated. In all the solvents investigated, denaturation is accompanied by 35–50% increase in absorbance (at 259 mμ) and a decrease in optical rotation (at 436 mμ) of 200–350 °. The following observations have been made: ( a) The effectiveness of the denaturant increases with both chain length and increasing hydrocarbon content. Thus ethyl and propyl alcohols were found to be more effective than methanol. ( b) The alkyl-substituted solvents N,N′-dimethylformamide, dimethyl sulfoxide, and tetramethylurea are the most effective denaturants among the various solvents employed. The midpoints of the denaturation transition due to these solvents in the presence of 1–5 × 10 −2 M salt, range from 19 to 27 mole % (57–62 vol.%), and the changes produced in optical rotation (at 436 mμ) upon denaturation are of the order of −300 to −350 °. ( c) N,N′-dimethylformamide is a more effective DNA denaturant than formamide. ( d) Increasing the hydroxyl content of the solvent, on the other hand, had no significant effect; the denaturation midpoints in methanol-water and ethylene glycol-water mixtures (in the presence of 0.5–5 × 10 −2 M salt) occur at 80 ± 1 mole % (90 ± 2 vol.%) of the nonaqueous component. These observations demonstrate the importance of hydrophobic forces and argue against the assignment of the stability of the aqueous configuration of DNA solely to hydrogen bonds. Except in dimethyl sulfoxide, DNA denaturation by the organic solvents employed could be largely reversed by water in the presence of electrolyte.