Formation of furans upon electron-beam heating of cellulose

Similarity between cotton cellulose and sulfate and sulfite pine celluloses in degradation during electron-beam distillation has been shown. The yield of the distillate liquid slightly depends on the type of cellulose and makes up ∼60 wt %. The product liquid contains organic compounds with molecular masses of 32 to 128, of which furfural and its derivatives prevail. Electron-beam distillation can be used as an effective method for the manufacturing of furfural and other furan derivatives from cellulose (along with the traditional pentosan conversion processes). It has been shown that grinding and preheating of cellulose lead to an increase in the proportion of furfural and other furans in the condensates.     

Study of azeotropic mixtures with the advanced distillation curve approach

Classical methods for the study of complex fluid phase behavior include static and dynamic equilibrium cells that usually require vapor and liquid recirculation. These are sophisticated, costly apparatus that require highly trained operators, usually months of labor-intensive work per mixture, and the data analysis is also rather complex. Simpler approaches to the fundamental study of azeotropes are highly desirable, even if they provide only selected cuts through the phase diagram. Recently, we introduced an advanced distillation curve measurement method featuring: (1) a composition explicit data channel for each distillate fraction (for both qualitative and quantitative analysis), (2) temperature measurements that are true thermodynamic state points that can be modeled with an equation of state, (3) temperature, volume and pressure measurements of low uncertainty suitable for equation of state development, (4) consistency with a century of historical data, (5) an assessment of the energy content of each distillate fraction, (6) trace chemical analysis of each distillate fraction, and (7) corrosivity assessment of each distillate fraction. We have applied this technique to the study of azeotropic mixtures, for which this method provides the bubble point temperature and dew point composition, completely defining the thermodynamic state from the Gibbs phase rule perspective. In this paper, we present the application of the approach to several simple binary azeotropic mixtures: ethanol + benzene, 2-propanol + benzene, and acetone + chloroform.     

Thermodynamics of mixtures formed by polycyclic aromatic hydrocarbons with long chain alkanes

Thermodynamic properties of polycyclic aromatic hydrocarbons (PAH) and long chain alkanes determine the phase behaviour of heavy petroleum fractions. Studying thermodynamic excess functions of these systems is difficult and consequently experimental data available in the literature are scarce. Enthalpies of mixing of 13 PAH-alkane systems at temperature above the melting point of both components are reported in this paper. Morever, 13 solid-liquid equilibria of the same family of systems are presented. Experimental results were correlated using S.S.F. model (Rogalski and Malanowski, 1977). Several regularities observed in the liquid-solid phase diagrams of the systems studied are discussed     

Formation of complexes,colloids and precipitates in aqueous mixtures of lignin sulphonate and some cationic polymers

A quantitative study has been carried out of the formation of polyelectrolyte complexes between calcium lignin sulphonate (LS) and three cationic polyelectrolytes, two polytrimethylaminoethylmethacrylates (I and II) with different molecular weight and one acrylamide copolymer. The parameters studied were the weight ratio of the oppositely charged polymers, the concentration of NaCl and the temperature. Separated molecular weight fractions of LS were studied in combination with I. The interactions were found to result in soluble complexes, colloids or macroscopic precipitates, mainly depending on the polymer weight ratio and the molecular weight of LS. For fractions with M_w was ⪢ 1000 the complexation between I and LS was stoichiometric when LS was present in excess of charge equivalence, resulting in formation of only macroscopic precipitate and quantitative precipitation. Soluble polyelectrolyte complexes were formed with LS if the M_w was < 1000 and I was in excess. Very stable colloids were formed with this LS fraction and I. In unfractionated LS, these soluble complexes are probably adsorbed on precipitating particles containing high molecular weight LS and I.     

S-Shaped composition dependence of excess thermodynamic quantities for cyclohexane mixtures with globular alkanes

Expansion coefficients , isothermal compressibilities, thermal pressure coefficients and heat capacities have been measured at 25°C for the cyclohexane+trans-decalin system. An S-shaped composition dependence, positivelnegative for highllow cyclohexane compositions is found for C _p ^E dV ^E /dT and the thermal expansion contribution to C _p ^E namely VT. The thermal motion contribution to C _p ^E , namely C _v is close to zero. The positive excursion of these mixing quantities at high cyclohexane content is anomalous. Correspondingly, the mixing quantity-VT deviates strongly in this region from the predicted equality with H ^E . The literature and this work show that all these excess quantities behave similarly for cyclohexane mixed with cyclooctane, methylcyclohexane and some highly branched alkanes. The unusual composition dependence of the thermodynamic quantities is consistent with order occurring when any large alkane molecule of globular shape is added to cyclohexane. This is speculatively associated with an interference by the globular alkane with the relatively free rotation of cyclohexane molecules.     

Protolytic properties of lignin in binary mixtures of water with aprotic solvents

Acid dissociation constants for three main types of phenol structural fragments of lignin in binary mixtures of water with N,N-dymethylformamide, dimethyl sulfoxide, and 1,4-dioxane were determined by spectrophotometric potentiometric titration. The effect of solvent on lignin protolytic properties was examined on the basis of the Kamlet-Taft principle of linear relationship of free solvation energies. It was found that nonspecific interactions with solvent make the dominating contribution to the effect of the medium.     

A NMR method for the analysis of mixtures of alkanes with different deuterium substitutions

¹³C NMR at 125.76 MHz with ¹H and ²H decoupling, ²H NMR at 76.77 MHz with ¹H decoupling, and ¹H NMR at 500.14 MHz with ²H decoupling were employed as analytical tools to study the complex mixtures of deuterated ethanes resulting from the catalytic H–D exchange of normal ethane with gas-phase deuterium in the presence of a platinum foil. Reference samples consisting of 1:1 binary mixtures of pure normal ethane and ethane-d_n (n=1–6) were used to identify the peak positions in the ¹³C, ²H, and ¹H NMR spectra due to each individual isotopomer, and the effect of isotopic substitution on the chemical shifts was determined in each case. While the NMR of all three nuclei worked well for the identification of the individual components of the 1:1 standard mixtures, both ¹H and ²H NMR suffered from inadequate resolution when studying complex reaction mixtures because of the broadening of the lines due to ¹H–¹H (¹H NMR) and ²H–²H (²H NMR) couplings. ¹³C NMR was therefore determined to be the method of choice for the quantitative analysis of the reaction mixtures. Using the ¹³C NMR results, a correlation that takes into account the primary and secondary isotope substitution effects on chemical shifts was deduced. This equation was used for the identification of the individual components of the mixtures, and integration of the individual observed resonances was then employed for quantification of their composition. This study shows that ¹³C NMR with ¹H and ²H decoupling is a viable procedure for studying mixtures of deuterated ethanes. Furthermore, the additivity of the isotopic effects on chemical shifts and the transferability of the values obtained with ethane to other molecules makes this approach general for the analysis of other isotopomer mixtures.     

Kinetics of the reaction of O3 with selected benzenediols

The kinetics of the reaction of O₃ with the aromatic vicinal diols 1,2‐benzenediol, 3‐methyl‐1,2‐benzenediol, and 4‐methyl‐1,2‐benzenediol have been investigated using a relative rate technique. The rate coefficients were determined in a 1080‐L smog chamber at 298 K and 1 atm total pressure of synthetic air using propene and 1,3‐butadiene as reference compounds. The following O₃ reaction rate coefficients (in units of cm³ molecule^?1 s^?1) have been obtained: k(1,2‐benzenediol) = (9.60 ± 1.12) × 10^?18, k(3‐methyl‐1,2‐benzenediol) = (2.81 ± 0.23) × 10^?17, k(4‐methyl‐1,2‐benzenediol) = (2.63 ± 0.34) × 10^?17. Absolute measurements of the O₃ rate coefficient have also been carried out by measuring the decay of the dihydroxy compound in an excess of O₃. The results from these experiments are in good agreement with the relative determinations. Atmospheric implications are discussed. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 223–230, 2003     

Thermochemical study of the solvation of alkanes in mixtures of methanol with butyl alcohol isomers

A calorimetric method was applied at 25 °C to measure the enthalpies of dissolution of cyclohexane, heptane, and decane in the methanol-n-butanol mixed solvent and hexadecane in mixtures of methanol withn-, iso-, andtert-butyl alcohols. The standard enthalpies of dissolution of alkanes were determined. It was shown that the equation proposed in the literature for calculation of the enthalpies of dissolution of alkanes in mixtures with nonspecific intermolecular solvent-solvent interactions describes satisfactorily the enthalpies of dissolution of alkanes in mixtures of methanol withn- andiso-butyl alcohols. It was suggested that there is no preferential solvation of alkanes by one of the mixed solvent components in the MeOH−BuⁿOH and MeOH−BuⁱOH mixtures; in the MeOH−Bu^tOH system, the composition of alkane solvation shell differs slightly from the solvent composition in the bulk. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 271–274, February, 1999.     

Rotational dynamics of UVITEX-OB in alkanes, alcohols and binary mixtures

Steady-state and time resolved fluorescence anisotropy measurements were carried out to study the rotational diffusion dynamics of UVITEX-OB (U-OB) in series of alcohols, alkanes and binary mixtures of toluene and butanol at room temperature. The experimentally measured rotational reorientation times were compared with those estimated by the hydrodynamic and molecular models developed for microscopic friction. The experimental results are in good agreement with theoretical slip hydrodynamics and a deviation towards subslip behavior is noted. Also a faster rotation of the probe in binary mixture of toluene and butanol is noted as compared to that in alcohols and alkanes.     

Mechanochemical activation of aluminum: 5. Formation of aluminum carbide upon heating of activated mixtures

The mechanical activation of thermal synthesis of aluminum carbide Al₄C₃ in Al-15 wt % C and Al-30 wt % C mixtures is studied with differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy. It is found that the mechanical treatment of powders results in an essential reduction in the temperature of carbide synthesis. A correlation between the temperature of the onset of synthesis and size L of the coherent scattering region of aluminum is established. When the doses of absorbed mechanical energy exceed 15–20 kJ/g and, as a result, the L value decreases to 20 nm, the synthesis proceeds by a solid-phase mechanism at a temperature significantly lower than the melting point of aluminum and the synthesis temperature reduces by 800°C. The particle size of the formed aluminum carbide and unreacted aluminum after heating to 900°C is 20–40 nm. At doses D = 50–80 kJ/g, the heat of the formation of carbide from activated samples is about two times lower compared to the standard value. The possible sources of this discrepancy are discussed.     

Relative volatilities of ionic liquids by vacuum distillation of mixtures

The relative volatilities of a variety of common ionic liquids have been determined for the first time. Equimolar mixtures of ionic liquids were vacuum-distilled in a glass sublimation apparatus at approximately 473 K. The composition of the initial distillate, determined by NMR spectroscopy, was used to establish the relative volatility of each ionic liquid in the mixture. The effect of alkyl chain length was studied by distilling mixtures of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids, or mixtures of N-alkyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids, with different alkyl chain lengths. For both classes of salts, the volatility is highest when the alkyl side chain is a butyl group. The effect of cation structure on volatility has been determined by distilling mixtures containing different types of cations. Generally speaking, ionic liquids based on imidazolium and pyridinium cations are more volatile than ionic liquids based on ammonium and pyrrolidinium cations, regardless of the types of counterions present. Similarly, ionic liquids based on the anions [(C2F5SO2)2N](-), [(C4F9SO2)(CF3SO2)N](-) , and [(CF3SO2)2N](-) are more volatile than ionic liquids based on [(CF3SO2)3C](-) and [CF3SO3](-), and are much more volatile than ionic liquids based on [PF6](-).     

Isomer effects in the excess enthalpies of mixtures of alkanes and cycloalkanes

Using the Picker flow calorimeter, excess molar enthalpies H ^E have been obtained at 25°C for mixtures of 1,2-, 1,3- and 1,4-cis- and trans-dimethylcyclohexane and cis- and trans-decalin with n-hexadecane and the highly branched C₁₆ isomer, 2,2,4,4,6,8,8-heptamethylnonane. Values of H ^E are also obtained for cis- and trans-decalin mixed with C₆, C₇, and C₉ isomers. Anomalously low values of H ^E occur for normal alkanes mixed with cycloalkanes in the di-equatorial configuration, suggesting the presence of a negative contribution in H ^E possibly due to a restriction of n-alkane molecular motion by the flat, plate-like cycloalkane.     

Effect of absorbed dose on the postradiation dry distillation of cellulose and lignin

The postradiation dry distillation of cellulose and lignin has been studied. During the course of irradiation to 3 MGy, the weights of samples remained almost unchanged. The overpoints of lignin and cellulose irradiated at 2.2 MGy decrease by ～80° and ～100°, respectively. A third of the condensate from cellulose and almost a half that from lignin were distilled off at lower temperatures. Thermally unstable compounds are formed in cellulose; these compounds are predominantly converted into furans upon subsequent heating. The distillation of irradiated lignin affords a smaller amount of tar, but it is richer in methoxyphenols. The aqueous organic fraction distilled off has a higher concentration of soluble organic compounds.     

Dependence on chain length of NMR relaxation times in mixtures of alkanes

Many naturally occurring fluids, such as crude oils, consist of a very large number of components. It is often of interest to determine the composition of the fluids in situ. Diffusion coefficients and nuclear magnetic resonance (NMR) relaxation times can be measured in situ and depend on the size of the molecules. It has been shown [D. E. Freed et al., Phys. Rev. Lett. 94, 067602 (2005)] that the diffusion coefficient of each component in a mixture of alkanes follows a scaling law in the chain length of that molecule and in the mean chain length of the mixture, and these relations were used to determine the chain length distribution of crude oils from NMR diffusion measurements. In this paper, the behavior of NMR relaxation times in mixtures of chain molecules is addressed. The author explains why one would expect scaling laws for the transverse and longitudinal relaxation times of mixtures of short chain molecules and mixtures of alkanes, in particular. It is shown how the power law dependence on the chain length can be calculated from the scaling laws for the translational diffusion coefficients. The author fits the literature data for NMR relaxation in binary mixtures of alkanes and finds that its dependence on chain length agrees with the theory. Lastly, it is shown how the scaling laws in the chain length and the mean chain length can be used to determine the chain length distribution in crude oils that are high in saturates. A good fit is obtained between the NMR-derived chain length distributions and the ones from gas chromatography.