Equilibrium and crystallographic measurements of the binary tetrahydrofuran and helium clathrate hydrates

Clathrate compounds are crystalline materials formed by a physical interaction between host and relatively light guest molecules. Various types of nano-sized cages surrounded by host frameworks exist in the highly unique crystalline structures and free guest molecules are entrapped in an open host-guest network. Recently, we reported two peculiar phenomena, swapping and tuning, naturally occurring in the hydrate cages. Helium, one of the smallest light guest molecules, must be the challengeable material in the sense of physics and moreover possesses versatile applications in the field of superconductivity technology and thermonuclear industry. In this regard, we attempted for the first time to synthesize helium hydrates at moderate temperature and pressure conditions. According to inclusion phenomena, helium itself normally cannot form clathrate hydrates due to being too small molecularly without the help of hydrate former molecules (sI, sII, and sH formers). In this study, the hydrate equilibria of the binary clathrate hydrate containing tetrahydrofuran, helium, and water were determined at 2, 3, 5.56 THF mol%. Direct volumetric measurements were also carried out to confirm the exact amount of helium captured in the hydrate cages. Finally, the crystalline structure of the formed mixed hydrates was identified by powder X-ray diffraction, resulting in structure II.     

Isobaric vapor–liquid equilibria for mixtures of tetrahydrofuran, 2-propanol, and 2,2,4-trimethylpentane at 101.3 kPa

Vapor–liquid equilibrium (VLE) at 101.3 kPa have been determined for a ternary system (tetrahydofuran + 2-propanol + 2,2,4-trimethylpentane) and its constituent binary systems (tetrahydrofuran + 2-propanol, tetrahydrofuran + 2,2,4-trimethylpentane, and 2-propanol + 2,2,4-trimethylpentane). The activity coefficients of liquid mixtures were calculated from the modified Raoult's law. Thermodynamic consistency tests were performed for all VLE data. The VLE data of the binary mixtures and ternary mixtures were correlated using the Margules, Wilson, NRTL, and UNIQUAC activity-coefficient models. The models with their best-fitted interaction parameters of the binary systems were used to predict the ternary vapor–liquid equilibrium. All VLE data are also used to calculate the reduced excess molar Gibbs free energy g^E/RT and the deviations in the boiling point ΔT. The calculated quantities of g^E/RT and ΔT were fitted to variable-degree polynomials in terms of liquid composition.     

从四氢呋喃、甲醇、水三元混合物系中分离四氢呋喃的研究

叙述了以液—液萃取、间歇精馏为手段，从四氢呋喃、甲醇、水三元混合物系中分离四氢呋喃的方法。四氢呋喃纯度超过９８％，收率６４．８％。     

Biodiesel Feedstock from Emulsions Produced by Aqueous Processing of Yellow Mustard

The multi-stage treatment of stable oil-in-water emulsions produced during non-enzymatic aqueous processing of dehulled yellow mustard flour with cyclic ethers [tetrahydrofuran (THF) and 1,4-dioxane] was investigated to produce a single-phase oil-solvent-water miscella suitable for biodiesel production. While the single-stage treatment of yellow mustard emulsion recovered 97 % and 95 % of the oil by using 4:1 THF:oil and 9:1 dioxane:oil weight ratios, respectively, miscella phases containing more than 7 % water formed, which made them unsuitable as biodiesel feedstock. Multi-stage treatments of the emulsion using lower THF:oil and dioxane:oil weight ratios were further developed to produce oil-solvent-water miscella phases with low water content. While three-stage extraction of emulsions using 0.5:1, 1:1, 1.5:1, and 2:1 dioxane:oil weight ratios did not destabilize the emulsion, three-stage extraction using 0.5:1 and 0.75:1 THF:oil weight ratios effectively recovered over 97 % of the oil, resulting in the production of oil-rich miscella phases containing only 1 % and 1.5 % water, respectively. These miscella phases were analyzed for free fatty acid and phosphorus contents and proved to be excellent feedstocks for the preparation of high-purity methyl esters through single-phase base-catalyzed transmethylation.     

Treatment of Groundwater Contaminated with 1,4-Dioxane,Tetrahydrofuran, and Chlorinated Volatile Organic Compounds Using Advanced Oxidation Processes

Ozonation and four types of advanced oxidation processes, including O₃/H₂O₂, O₃/UV, O₃/H₂O₂/UV, and UV/H₂O₂, were evaluated for the treatment of contaminated groundwater at a Superfund site in Simpsonville, South Carolina using bench-scale, batch ozone and UV apparatuses. Although the contaminants of concern were 1,4-dioxane, 1,1-dichloroethene, and trichloroethene, several other chlorinated organics as well as tetrahydrofuran were found in the groundwater samples. The O₃/H₂O₂ treatment with O₃ and H₂O₂ doses of 6 and 1.5 mg/L, respectively, and the UV/H₂O₂ treatment with UV and H₂O₂ doses of 1,000 mJ/cm and 20 mg/L, respectively, were sufficient to degrade 200 µg/L of 1,4-dioxane, 110 µg/L of 1,1-dichloroethene, and 10 µg/L of trichloroethene below their performance standards of 10, 7, and 4 µg/L, respectively. Due to a high bromide concentration (0.35 mg/L) in the groundwater sample, bromate formation was found to be significant in ozone-based treatment, including O₃/H₂O₂.     

Hydrierung von Diethylsuccinat zu γ‐Butyrolacton, 1,4‐Butandiol und Tetrahydrofuran

The shortage of fossil resources necessitates the search for alternative sources for the production of important bulk chemicals. Diethyl succinate derived from biobased succinic acid can be used as a renewable alternative to fossil resources for the production of γ‐butyrolactone, 1,4‐butanediol and tetrahydrofuran. Commercially available ZnO‐free copper catalysts in a fixed‐bed reactor show promising selectivity to C4 products, but 1,4‐butanediol dehydration to tetrahydrofuran occurs over acidic sites, like alumina and zirconia.     

Synthesis of tetrahydrofuran from maleic anhydride on Cu–ZnO–ZrO2/H-Y bifunctional catalysts

A series of bifunctional Cu–ZnO–ZrO₂/H-Y catalysts of different compositions were prepared by coprecipitating sedimentation method and were characterized by surface area and XRD analyses. The catalytic performance in synthesis of tetrahydrofuran was evaluated and optimized in a three-phase slurry batch reactor. The experimental results showed that the appropriate ratio of Cu/ZnO in the hydrogenation catalyst was 50/45, for which the conversion of maleic anhydride (MA) and selectivity of tetrahydrofuran (THF) reached 100% and 46%, respectively, at 50 bar and 493 K after 6 h of operation. Also, according to these results, it was demonstrated that the incorporation of zirconium oxide in the catalyst formulation enhanced the catalytic activity, and tetrahydrofuran selectivity was increased to 55%. Ultimately, it was concluded that the bifunctional catalyst of Cu–ZnO–ZrO₂/H-Y was an appropriate catalyst to produce THF from MA with high activity, selectivity and stability.     

不同分子量聚乙烯吡咯烷酮对四氢呋喃水合物形成及生长的影响

聚乙烯吡咯烷酮(以下简称PVP)作为一种抑制能力较强、应用较成熟的水合物动力学抑制剂(以下简称KHIs),一直是国内外学者关注和研究的焦点,但对于不同分子量PVP对水合物形成的影响情况还存在着争议。为此,在常压、变温条件下进行了四氢呋喃(以下简称THF)水合物形成模拟实验,研究了相同加量条件下、不同分子量的PVP对THF水合物形成及生长的影响,并从宏观现象、介观结构和微观机制3个层面对影响机理进行了分析和探讨。结果表明:(1)对于THF水合物的形成,PVP的抑制能力随分子量的增大逐渐增强;(2)对于THF水合物的生长,PVP分子量介于8 000~58 000时,抑制效果较接近且相对较弱,但抑制作用稳定,PVP分子量介于270 000~1 500 000时,在THF水合物生长初始阶段PVP的抑制效果较好,但整个实验过程THF水合物形成的平均速率相对较快,且PVP分子量越大这一现象越明显;(3)PVP的存在增强了THF水合物聚集体的聚集强度。结论认为,该研究成果对于KHIs的研发和实际应用均具有较重要的参考价值。     

大孔强酸性树脂对1,4-丁二醇脱水催化作用的研究

考察了大孔强酸性树脂对1,4 丁二醇脱水制四氢呋喃的催化作用。结果表明,大孔强酸性树脂对1,4 丁二醇脱水制四氢呋喃催化作用明显优于一般强酸性树脂。     

Electrochemical reaction of lithium alanate dissolved in diethyl ether and tetrahydrofuran

We present electrochemical properties of lithium alanate (LiAlH₄) dissolved in aprotic ethers – diethyl ether (Et₂O) and tetrahydrofuran (THF) – under an Ar atmosphere of 1 atm at 298 K. Specific conductivities of both LiAlH₄–THF and LiAlH₄–Et₂O solutions are measured by AC four-terminal method. Cyclic voltammetry is performed with using a beaker-type electrochemical cell consisted of a Ni wire, Ni mesh and Li wire as a working, counter and reference electrode, respectively. In order to clarify the electrochemical behavior, anodic polarization of LiAlH₄–THF solution is measured. The current density of 1.0 M LiAlH₄–THF solution reaches to 1 A cm⁻², which is higher than the LiAlH₄–Et₂O solution. Quantitative analysis of H₂ gas generated on the working electrode during the potentiostatic electrolysis tells that the number of electrons involved in the anodic reaction at the limiting current is one in case of the LiAlH₄–THF solution. We propose conceivable electrochemical reactions of LiAlH₄ in the non-aqueous ethereal solutions.