Accumulation of acid sites on natural clinoptilolite under recurring dehydration

A new ¹H NMR approach was applied to study the influence of recurring dehydration on the acidity of a natural Ca-rich zeolite clinoptilolite. It has been found that thermal cycling progressively increases the rate of the proton exchange between water molecules in the rehydrated state. The observed effect is interpreted as a result of the irreversible accumulation of specific structural defects represented by Brønsted acid sites: each dehydration at 720 K adds to the acid sites in an amount of the order of 10^?3 per unit cell. The number of these defects, detected by NMR in hydrated mineral, is in reasonable agreement with their amount estimated for the dehydrated state with an IR-spectroscopy CO-probe method. A comparison of the results obtained for two distinct zeolite samples shows that the Ca²⁺ ions are of first importance in the dehydration-induced formation of the active acid sites. The barrier for the proton-transfer reaction between the acid sites and H₂O molecules in hydrated clinoptilolite is found to be 46 kJ mol^?1, which is not too different from the value of 54 kJ mol^?1 reported recently for natural chabazite.     

碱性长石Al—Si有序化进程中微结构和^29Si NMR谱的表现

笔者用Ｘ射线粉末衍射技术,对六个天然钾长石中的铝在Ｔ１Ｏ四面体位置的占位率进行了测定,它们的Ｔ１Ｏ值从０．２８变化到０．７９。对它们的透射电子显微镜研究表明,两个Ｔ１Ｏ为０．２８和０．３１的高透长石有对电子束异常过敏的调制结构,无法记录到它们的衍射像,在另外三个样品中,都见到芦席状结构,并夹杂着具一定宽度的片晶组成的格子双晶。片晶宽度随Ｔ１Ｏ的变大而增加。而在产于一个霞石正长岩中的正长石中没有观察     

Correlations between 29Si, 17O and 1H NMR properties and local structures in silicates: an ab initio calculation

In order to gain insight into the correlations between ²⁹Si, ¹⁷O and ¹H NMR properties (chemical shift and quadrupolar coupling parameters) and local structures in silicates, ab initio self-consistent field Hartree-Fock molecular orbital calculations have been carried out on silicate clusters of various polymerizations and intertetrahedral (Si-O-Si) angles. These include Si(OH)₄ monomers (isolated as well as interacting), Si₂O(OH)₆ dimers (C₂ symmetry) with the Si-O-Si angle fixed at 5° intervals from 120° to 180°, Si₃O₂(OH)₈ linear trimers (C₂ symmetry) with varying Si-O-Si angles, Si₃O₃(OH)₆ three-membered rings (D₃ and C₁ symmetries), Si₄O₄(OH)₈ four-membered ring (C₄ symmetry) and Si₈O₁₂(OH)₈ octamer (D₄ symmetry). The calculated ²⁹Si, ¹⁷O and ¹H isotropic chemical shifts (δ_i ^Si, δ_i ^O and δ_i ^H) for these clusters are all close to experimental NMR data for similar local structures in crystalline silicates. The calculated ¹⁷O quadrupolar coupling constants (QCC) of the bridging oxygens (Si-O-Si) are also in good agreement with experimental data. The calculated ¹⁷O QCC of silanols (Si-O-H) are much larger than those of the bridging oxygens, but unfortunately there are no experimental data for similar groups in well-characterized crystalline phases for comparison. There is a good correlation between δ_i ^Si and the mean Si-O-Si angle for both Q ¹ and Q ², where Q ⁿ denotes Si with n other tetrahedral Si next-nearest neighbors. Both the δ _i ^O and the ¹⁷O electric field gradient asymmetry parameter, η of the bridging oxygens have been found to depend strongly on the O site symmetry, in addition to the Si-O-Si angle. On the other hand, the ¹⁷O QCC seems to be influenced little by structural parameters other than the Si-O-Si angle, and is thus expected to be the most reliable ¹⁷O NMR parameter that can be used to decipher Si-O-Si angle distribution information. Both the ¹⁷O QCC and the ²H QCC of silanols decrease with decreasing length of hydrogen bond to a second O atom (Si-O-H···O), and the δ _i ^H increase with the same parameter. Received: 18 July 1997 / Revised, accepted: 23 February 1998     

核磁共振测井技术在桩海地区及其它油田中的应用

阐明核磁共振测井（NMR）在储层评价中的作用。利用NMR测井资料对桩海地区长堤油田的储层特性及产能、复杂岩性储层的孔隙度作出评价，并在电阻率测井资料显示不好的复杂储层条件下进行油气水层识别，以及指导完井和钻井方案的实施等。不阐明了核磁共振测井技术具有常规测井技术所不具备的特点，特别是定量的评价孔隙流体流动特性、准确划分产层、直接识别油气水等优点，从而有利于解复杂的地质问题。     

Fluid Property Discrimination in Dolostone Reservoirs Using Well Logs

The Ordovician Majiagou Formation is one of the main gas-producing strata in the Ordos Basin,China.The identification of hydrocarbon-bearing intervals via conventional well logs is a challenging task.This study describes the litholog of Ma 5(Member 5 of Majiagou Formation)dolostones,and then analyzes the responses of various conventional well logs to the presences of natural gas.The lithology of the gas bearing layers is dominantly of the dolomicrite to fine to medium crystalline dolomite.Natural gas can be produced from the low resistivity layers,and the dry layers are characterized by high resistivities.Neutron-density crossovers are not sensitive to the presences of natural gas.In addition,there are no significant increases in sonic transit times in natural gas bearing layers.NMR(nuclear magnetic resonance)logs,DSI(Dipole Sonic Imager)logs and borehole image logs(XRMI)are introduced to discriminate the fluid property in Majiagou dolostone reservoirs.The gas bearing intervals have broad NMR T_2(transverse relaxation time)spectrum with tail distributions as well as large T_(2gm)(T_2 logarithmic mean values)values,and the T_2 spectrum commonly display polymodal behaviors.In contrast,the dry layers and water layers have low T_(2gm) values and very narrow T_2 spectrum without tails.The gas bearing layers are characterized by low V_p/V_s ratios,low Poisson’s ratios and low P-wave impedances,therefore the fluid property can be discriminated using DSI logs,and the interpretation results show good matches with the gas test data.The apparent formation water resistivity(AFWR)spectrum can be derived from XRMI image logs by using the Archie’s formula in the flushed zone.The gas bearing layers have broad apparent formation water resistivity spectrum and tail distributions compared with the dry and water layers,and also the interpretation results from the image logs exhibit good agreement with the gas test data.The fluid property in Majiagou dolostone reservoirs can be discriminated through NMR logs,DSI logs and borehole image logs.This study helps establish a predictable model for fluid property in dolostones,and have implications in dolostone reservoirs with similar geological backgrounds worldwide.     

C and N NMR analysis of some fungal melanins in comparison with soil organic matter

A variety of fungal melanins with natural ¹⁵N abundance are characterized by solid-state ¹³C and ¹⁵N NMR spectroscopy and are compared to solid-state ¹³C and ¹⁵N NMR spectra of organic matter from representative soils. In all solid-state ¹⁵N NMR spectra the peptide/amide region (−220 to −285 ppm) dominates with more than 70% of the total intensity. The region between −285 and −375 ppm, assigned to amino and ammonium groups, always contains more than half of the remaining intensity. The area in the region from −30 to −220 ppm, where aromatic heterocycles would show signals, makes up less than 10% of the total intensity. These findings call into question common structural models for melanins. The solid-state ¹³C NMR spectra, on the other hand, reveal large differences when the melanins are compared to each other, and to composts and soils. The concentration of the aromatic carbon varies from 5 to 40% in the melanin series. The ratio C_aro/N_tot and C_ali/N_tot were calculated, and confirm that nitrogen in these samples is bound in C_a-groups rather than in aromatic heterocyclic structures.     

Structural modifications of vitrinite and alginite concentrates during pyrolitic maturation at different heating rates. A combined infrared, C NMR and microscopical study

Immature vitrinite samples from a Miocene lignite seam of western Germany (H/C = 1.14, O/C = 0.41) and alginite concentrates from a Tasmanite deposit of Australia (H/C = 1.60, O/C = 0.10) were pyrolyzed in a stream of argon at heating rates of 0.1 and 2.0°C/min up to temperatures varying from 200 to 670°C. The solid maceral residues were subjected to elemental and microscopical analysis and studied by IR and ¹³C CP/MAS NMR spectroscopy with respect to structural modifications.The maximum pyrolytic weight loss amounts to 60% of the initial organic matter in the case of vitrinite and to 85% for alginite, the onset of degradation reactions being shifted to higher temperatures with increasing rate of heating. Both infrared and NMR spectra of the vitrinite samples indicate a rapid decomposition of the cellulose component upon heating whereas lignin related structures such as aromatic ether linkages remain remarkably stable. The main hydrocarbon release from vitrinite occurs at very early evolution stages (T_max = 296°C, R_m = 0.20% at 0.1°C/min; T_max = 337°C, R_m = 0.23 at 2.0°C/min). Hydrocarbon generation from alginite requires higher temperatures (T_max = 388 and 438°C) and is completed within a distinctly narrower temperature range.The pronounced increase of vitrinite reflectance between 350 and 670°C seems to be associated with a rather time-consuming reorganization of the residual organic material. The concomitant growth of polyaromatic units is illustrated by the increasing intensity ratio of the aromatic ring stretching vibration bands at 1600 and 1500 cm⁻¹. These reactions are moreover marked by increasing loss of phenolic oxygen and by increasing conversion of aliphatic carbon into fixed aromatic carbon.     

秋茄叶中卢丁的分离与鉴定

红树林中的秋茄Kandelia candle叶乙醇萃取物，经大孔离子交换树脂DA201吸附柱色谱，聚酰胺柱色谱分离，甲醇反复结晶，得浅黄色针状结晶。^1H NMR,^13C NMR,UV和IR分析，确定了该结晶化合物卢丁，其分子式为C27H30O16，分子量为610.51。     

孔隙介质润湿性的核磁共振刻度特征的测量

核磁共振测量技术已能够快速而无损地获得孔隙介质的物性信息, 但对于颗粒表面润湿性的测量还处于定性到半定量的水平.采用毛细管法和玻璃板法对经不同浓度二甲基二氯硅烷溶液处理的玻璃表面润湿性测量, 然后对核磁共振方法测量的孔隙介质润湿性结果进行标定, 进而得到孔隙介质润湿性系列的刻度特征.实验表明, 对于玻璃颗粒孔隙介质, 核磁共振测量的结果在作为表面处理剂的二甲基二氯硅烷溶液浓度0 %~ 0.7%变化范围内才与孔隙介质润湿性的变化有着明确的对应关系.在此范围之外, 对应的驰豫时间的变化虽然较大, 但其对于润湿性的刻度已没有明确的作用.      

固化盐渍土核磁共振微观特征

采用核磁共振技术,对不同配比的水玻璃、石灰+粉煤灰及石灰+粉煤灰+水玻璃的固化盐渍土的微观特征进行检测,结合无侧限抗压强度试验,分析了各固化方案的盐渍土固化效果,讨论了强度成因的微观特征机制。结果表明,不同固化土的孔隙特征有较大差异。石灰+粉煤灰固化盐渍土大孔隙减少;石灰+粉煤灰+水玻璃固化盐渍土孔隙总体积减少,但同时有大孔隙生成;水玻璃固化盐渍土孔隙总体增多,但随水玻璃浓度增大,孔隙体积有所减小。石灰+粉煤灰+水玻璃固化盐渍土抗压强度远大于其他固化方案,但是其孔隙结构并不是最优,说明颗粒间的胶结情况对固化效果的影响远大于孔隙特征。