快速扫描量热法研究聚对苯二甲酸-1,4-环己烷二甲醇酯的结晶和熔融行为

采用快速扫描量热法(FSC)结合传统的差示扫描量热仪(DSC)考察了聚对苯二甲酸-1,4-环己烷二甲醇酯(PCT)聚酯在接近玻璃化转变(T_g)和熔融温度(T_m)范围(100~270 ℃)的结晶和熔融行为。 较大过冷度时PCT聚酯结晶较快,FSC有效地抑制降温过程结晶的发生,而较低过冷度下传统DSC可以避免样品降解对实验结果的影响,二者的结合能很好地对PCT聚酯结晶动力学进行测量,实验结果表明在175 ℃时结晶速率最快。 并且利用Flash DSC对等温结晶温度下形成的片晶熔点进行加热速率的相关测量,在熔融动力学建模的基础上进行校准,以确定零加热速率下片晶的熔点。 Hoffman-Weeks方程中T_m与结晶温度(T_c)的线性关系与T_c=T_m的交点给出了PCT晶体的平衡熔融温度$T_m^o$为315 ℃。     

甲醇在超临界环已烷中形成簇团的Monte Carlo初探

用Ｍｏｎｔｅ Ｃａｒｌｏ方法研究了甲醇－环己烷体系的微观结构随压力（密度）的变化情况，结果表明，在临界区域甲醇分子的聚集最为明显，形成的甲醇团簇尺寸最大，溶剂分子在甲醇周围的局部密度则在低于临界区或亚临界区较大。     

聚合物-溶剂-超临界CO2三元体系的相行为

研究了聚合物-超临界二氧化碳二元体系溶解性,并考查了添加共溶剂对溶解性的影响,结果表明,添加共溶剂会大大提高CO2的溶解度.此外,还研究了聚合物-溶剂-超临界二氧化碳三元体系在高压时的相行为, 探讨了组分性质、含量等对温度-压力相图的影响.随着CO2含量的增加,压力-温度相图L-LV（单一液相向液气两相共存）边界线的斜率会出现突变点,发生由L-LV边界线向L-LL（单一液相向液液两相共存）边界线的过渡, 而L-LV边界线对不同聚合物并不敏感.     

聚酯在超临界甲醇中的降解特性

研究在间歇高压反应器中聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)及聚碳酸酯(PC)在超临界甲醇中的降解反应;通过建立聚酯在超临界甲醇中的降解反应模型,探讨了聚酯在甲醇中降解的机理。结果表明:PET、PBT和PC在甲醇溶液中的降解具有共性,均可分为超临界区、非临界区和中间过渡区三个区域。在超临界区聚酯完全溶于甲醇并降解为原料单体,且对苯二甲酸二甲酯(DMT)和碳酸二甲酯(DMC)的收率均大于90%;聚酯的降解是在聚合物分子链的无规断裂和聚酯进行酯交换反应的双重作用下发生的。     

Zr-Mn-K催化剂超临界相合成甲醇与异丁醇的研究

用共沉淀法和超临界流体干燥法,分别制备了Ｚｒ－Ｍｎ－Ｋ沉淀型催化剂和超细催化剂．以正十一～十三烷的混合物为超临界介质,在反应温度３６０～４１０℃、合成气压力７．５ＭＰａ、ＧＨＳＶ１７００ｈ－１及介质压力２．０８ＭＰａ的实验条件下,分别考察了超细催化剂和沉淀催化剂的气相和超临界相催化合成气制甲醇、异丁醇的性能．气相和超临界相反应的研究均表明,超细催化剂催化合成异丁醇的活性高于沉淀催化剂;在超临界条件下反应,超细催化剂上产物的异丁醇含量较高（为２３％～３２％）,甲醇含量为２２％～３３％,其它醇均在１０％左右．气相与超临界相反应结果的对比显示,超临界流体促进产物的脱附与传递,提高了ＣＯ的转化率．但超临界流体对甲烷的萃取作用强于对醇的萃取,醇选择性低于气相反应．在超临界条件下合成甲醇、异丁醇仍遵循异丁醇形成的链增长机理,超临界流体改变了链增长各步骤的相对速度,致使超临界相反应的产物分布不同于气相反应的产物分布．     

助剂Cr对Cu/SiO2催化碳酸酯加氢制甲醇性能的影响

碳酸酯催化加氢制甲醇作为二氧化碳定向转化的间接路径具有重要意义.采用蒸氨法合成了一系列助剂铬修饰的Cr_x-Cu/SiO₂催化剂，系统考察了其对碳酸二乙酯催化加氢性能的影响.研究表明，3 wt%铬修饰量的催化剂活性最优.在反应温度503 K、氢气压力2.5 MPa及液时空速1.0 h^-1条件下，碳酸二乙酯的转化率可达99%，目标产物甲醇的收率和时空得率分别为86.2%和5.6 mmol_MeOH·g_cat^-1·h^-1.采用X射线粉末衍射（XRD）、N₂吸脱附、透射电镜（TEM）、氢气程序升温还原（H₂-TPR）、X射线光电子能谱（XPS）和原位漫反射傅里叶变换红外光谱（In-situ DRIFTS）等手段表征了铬的修饰对催化剂物化性质的影响.结果表明，相较于未修饰的Cu/SiO₂催化剂，少量铬修饰所得Cr_x-Cu/SiO₂催化剂表面活性铜物种的分散度显著提高，且由部分铜和铬相互作用形成的亚铬酸铜物相优化了不同价态铜物种的表面分布状况及催化剂对底物的吸附构型，有效提升了其对碳酸二乙酯催化加氢制甲醇的反应性能和稳定性.     

溶液制备过程引入的甲醇对阿特拉津UV光氧化速率和降解机理的影响

在低压汞灯（253.7 nm）光照条件下，研究了样品制备过程中引入的有机溶剂甲醇对目标有机物阿特拉津光氧化降解速率的影响规律，并系统地分析了其影响机理.研究结果表明：反应体系中含有低浓度（<0.1%）有机溶剂甲醇时，不会对阿特拉津在单独UV工艺中的降解动力学产生影响；对UV/H₂O₂工艺中阿特拉津降解动力学的影响较小，但此含量的甲醇却能显著地降低阿特拉津在UV/TiO₂工艺中的降解速率.甲醇对阿特拉津在不同光氧化工艺中降解动力学的影响是甲醇与阿特拉津竞争光量子、改变溶液极性和淬灭活性氧化物种等作用的综合结果，但反应体系中甲醇的存在及含量未改变阿特拉津降解产物的种类及降解途径.本研究的结果可为探索溶液制备时引入到反应体系中的有机溶剂对有机目标物光氧化速率的影响提供新的研究视角，同时也能为文献中目标物配制在不同溶剂中的降解速率差异提供合理解释.     

超临界相CO加氢合成甲醇,异丁醇的研究

以正十一～十三烷的混合物为超临界介质,在反应温度３６０～４１０℃、合成气压力７５ＭＰａ、进气空速１７００ｈ－１、介质压力１７８ＭＰａ、总压９３ＭＰａ的实验条件下,研究了固定床反应器中Ｚｎ－Ｃｒ、Ｃｕ－Ｚｎ－Ｃｒ催化剂在超临界相和气相条件下合成甲醇、异丁醇的性能。结果表明,超临界相反应的ＣＯ转化率高于气相反应。在超临界条件下反应,醇类选择性随着温度升高下降较慢,而气相反应醇类选择性随着温度升高下降较快。气相反应产物以甲醇、异丁醇为主,含少量乙醇和正丙醇,超临界相反应的产物分布与气相反应的明显不同,甲醇含量减少,乙醇、正丙醇和异丁醇都有不同程度增加。超临界流体的存在对合成醇链增长有影响,在不同催化剂上的产物分布有较大差异     

超临界二氧化碳偶合超声预处理强化玉米秸秆酶水解(英)

提出了一个木质纤维素生物质预处理的全绿色加工过程.以玉米秸秆和玉米芯为原料,以超临界CO₂和超声偶合法对木质纤维素进行预处理.超临界CO₂预处理条件为:压力15-25 MPa,温度120₁70℃,含水量50%,反应时间0.5₄ h.超声场功率600W,温度80℃,作用时间2-8 h.用纤维素酶水解反应获得的还原糖总量来评价预处理效果.结果表明,单纯超临界CO₂和超临界CO₂偶合超声预处理都能够提高生物质水解反应还原糖产量.对于玉米芯,超临界CO₂预处理（170℃,20 MPa,3 0min）后,还原糖产率为62%（未预处理的为12%）.对于玉米秸秆（170℃,20 MPa,2.5 h）,还原糖产率为46.4%.对于玉米芯,超临界CO₂偶合超声预处理（600 W,80℃下超声处理6 h,然后用170℃,20 MPa超临界CO₂预处理30 min）后,还原糖产率为87%.对于玉米秸秆,超临界CO₂偶合超声预处理（600 W,80℃下超声处理8 h,然后用170℃,20 MPa超临界CO₂预处理1 h）后,还原糖产率为25.5%.与未处理生物质相比,X射线衍射结果表明玉米秸秆和玉米芯在超临界CO₂和超声预处理后其结晶度没有明显变化.扫描电镜分析则发现木质纤维素的表面积显著增加.     

聚合物-溶剂-超临界CO_2三元体系的相行为

研究了聚合物－超临界二氧化碳二元体系溶解性,并考查了添加共溶剂对溶解性的影响,结果表明,添加共溶剂会大大提高ＣＯ２的溶解度．此外,还研究了聚合物－溶剂－超临界二氧化碳三元体系在高压时的相行为,探讨了组分性质、含量等对温度 压力相图的影响．随着ＣＯ２含量的增加,压力－温度相图Ｌ－ＬＶ（单一液相向液气两相共存）边界线的斜率会出现突变点,发生由Ｌ－ＬＶ边界线向Ｌ－ＬＬ（单一液相向液液两相共存）边界线的过渡,而Ｌ－ＬＶ边界线对不同聚合物并不敏感．     

H and H NMR studies of cyclohexane nanocrystals in controlled pore glasses

The formation and behaviour of cyclohexane and cyclohexane-d₁₂ nanocrystals in mesoporous solids of well-defined dimensional constraints are studied by ¹H and ²H NMR. The NMR line widths, spin–spin relaxation times (T₂), spin–lattice relaxation times (T₁) and diffusivities (D) were measured as a function of temperature, and the results are discussed with reference to the values obtained for the bulk materials. The confined solids exhibit substantial changes in the phase behaviour and molecular dynamics. Thus, the line-shape measurements reveal a two-phase system consisting of a highly mobile component at the surface of the pore and a plastically crystalline phase in the centre of the pore. The liquid-like surface layer in the mesopores is observable well below the reduced transition temperature of the confined cyclohexane. However, the T₂ and diffusion measurements show that the mobile phase also embraces a minor component attributed to non-frozen liquid in pockets or offshoots.     

Nuclear quadrupole resonance in 2,4-dinitrochlorobenzene

A study of the spin lattice relaxation (T₁) and the nuclear quadrupole resonance frequency (ν_Q) gives an important information about the dynamics of molecular groups in molecular solids. In the present paper, we analyze the contributions of the reorientational motion of nitro groups of 2,4-dinitrochlorobenzene to the NQR parameters of the chlorine nucleus in the molecule.

We found two contributions to T₁ and ν_Q due to the onset of the reorientation of nitro groups in the molecule; one of these contributions is mostly due to intermolecular effects in the crystal. For the chlorine nuclei, the efficiency of the modulation mechanism is usually provided by the change of the electric field gradient due to the moving molecular group; this gives us a way of how to assign each contribution to T₁ from the ortho and para positions of the NO₂ groups in the molecule. It is observed that there are two different potential barriers depending on the position of the nitro groups in the molecule. The behavior in the temperature dependence of the line width shows a thermal history dependence of the molecular crystal.     

Investigation of the proton mobility in CsH(SO4)0.76(SeO4)0.24 crystal by H NMR spectroscopy

Crystals of CsH(SO₄)_0.76(SeO₄)_0.24 formulation were studied by ¹H NMR spectroscopy. The ¹H line-shape, the T₁ and T₂ relaxation times were determined as a function of temperature. The activation energies deduced from the temperature dependence of relaxation times were compared with the activation energy issued from conductivity measurements. The results obtained are discussed and supported by the Ngai model.     

Surface modification of γ-alumina membranes by silane coupling for CO2 separation

Top layers of γ-Al₂O₃ composite membranes have been modified by the silane coupling technique using phenyltriethoxysilane for improving the separation factor of CO₂ to N₂. The separation efficiency of the modified membranes was strongly dependent upon the hydroxylation tendency of the support materials and the amount of the special functional group (i.e. phenyl radical) which was coupled onto a top layer. The separation factor through the TiO₂ supported γ-Al₂O₃ membrane was found to be fairly enhanced by silane coupling, but in case of the -Al₂O₃ supported membrane was not. The CO₂/N₂ separation factor through the modified γ-Al₂O₃/TiO₂ composite membrane is 1.7 at 90°C and ΔP = 2 × 10⁵ Pa for the binary mixture containing 50 vol% CO₂. The separation factor is proportional to the CO₂ concentration in the gas mixture, and the modified membrane is stable up to 100°C. The main mechanism of the CO₂ transport through the modified γ-Al₂O₃ layer is known to be a surface diffusion.     

二氧化碳加氢制甲醇多相催化剂研究进展

化石燃料的利用为人类社会带来了前所未有的繁荣和发展. 然而, 化石燃料燃烧引起的过量的二氧化碳(CO₂)排放导致全球气候变化和海洋酸化; 而且作为一种有限的资源, 化石燃料的消耗将迫使人们寻找其它碳源以维持可持续的发展. 利用可再生能源获取电能分解水制得的绿色氢气(H₂)与捕集后的CO₂反应制成甲醇, 不仅能有效利用工业废气中多余的CO₂, 还能获取清洁、 可再生的甲醇化学品, 该过程的技术核心是开发高效稳定的CO₂加氢制甲醇催化剂. 本文综合评述了现有研究关注较多的多相催化CO₂加氢制甲醇催化剂的反应机理和构效关系, 总结了目前多相催化CO₂加氢制甲醇催化剂(Cu基催化剂、 贵金属与双金属催化剂、 氧化物催化剂以及其它新型催化剂)的设计与合成方面的研究进展, 最后对该领域所面临的机遇和挑战进行了展望.     

Space-resolved low frequency dynamics in entangled polymers

A T_1ρ filter for the NMR imaging of solid polymers is presented. T_1ρ is the relaxation time in the rotating frame, which is sensitive to the molecular motion and whose spectral density falls in the range of slow dynamics, namely motion characterized by correlation times ranging between 10⁻² and 10⁻⁵ s. The method allows one to obtain a good spatial resolution without the need of strong field gradients and without the effects related to the spatial encoding manipulation of the spin system.     

Field-cycling NMR detection of magnetoacoustically manipulated nematic ordered states: Memory effects

The proton spin–lattice relaxation time (T₁) dispersion was studied under simultaneous sonication in the nematic phase of 5CB. It appears that metastable ordered states subject to a memory effect can be induced by the combined action of an amplitude-modulated ultrasonication and a pulsed magnetic field. We argue that the acoustic amplitude modulation adds instability to the nematic phase through director order fluctuation enhancement. Different manipulated states of the director were unambiguously identified by the Larmor frequency dispersion of T₁. The field-cycling NMR technique was used for T₁ measurements.     

Molecular dynamics study of the ferroelectric liquid crystal CI IPNOC by proton spin-lattice relaxation

Proton spin-lattice relaxation studies were carried out in the S_A and S*_C phases of the liquid crystal CI IPNOC using both conventional and fast field cycling NMR techniques. T₁ dispersion curves were obtained at two different temperatures for each mesophase covering frequencies from 10² to 3 × 10⁸ Hz. In both mesophases the T₁ data can be described assuming the presence of three different relaxation mechanisms, namely local molecular rotations, molecular self-diffusion and collective motions. The self-diffusion constant D₁ was evaluated for several temperatures and the activation energy associated with the diffusion process was obtained. The expected contribution of the soft-mode for the spin-lattice relaxation could not be separated from the contribution of other collective motions. The correlation times associated with the rotations around the molecular long axis and with the fluctuations of this axis were evaluated for both the S_A and the S*_C phases.     

Triplet-EPR spectroscopy on the Diels-Alder adduct of C60 and 4,5-dimethoxy-o-quinodimethane in frozen solution

Pulsed-EPR spectroscopy was used to study a modified C₆₀ molecule (1) in its photoexcited triplet state. The analysis of the triplet EPR lineshape shows a break of the high symmetry of the lowest populated triplet state of C₆₀ due to the modification of the C₆₀ unity. The reported temperature dependence of the spectra is influenced by relaxation effects. Lineshape simulations based on a triplet Hamiltonian including anisotropic T₁/T₂ relaxation were performed. The results are discussed in relation to the behaviour of pure ³C₆₀.     

A new strategy for supercritical fluid extraction of copper ions

Complexation combined with supercritical fluid extraction was used to extract Cu²⁺. The effects of pressure, temperature, and total volume of CO₂ on the efficiency of extraction were systematically investigated. The extraction recovery was low (57.32%) only by pure supercritical CO₂. Addition of a suitable amount of methanol (v/v=5%) to supercritical CO₂ could enhance the extraction of Cu²⁺ (72.69%, relative standard deviation (R.S.D.)=2.12%, n=3), and the recovery increased largely (90.52%, R.S.D.=2.20%, n=3) in the presence of nonionic surfactant Triton X-100. Reverse micelle formation is presented as a new strategy of improving the extraction of metal ions with supercritical CO₂ in this paper.