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161.
The effect of O2 and N2O on alkane reactivity and olefin selectivity in the oxidative dehydrogenation of ethane, propane, n-butane, and iso-butane over highly dispersed VOx species (0.79 V/nm2) supported on MCM-41 has been systematically investigated. For all the reactions studied, olefin selectivity was significantly improved upon replacing O2 with N2O. This is due to suppressing COx formation in the presence of N2O. The most significant improving effect of N2O was observed for iso-butane dehydrogenation: S(iso-butene) was ca. 67% at X(iso-butane) of 25%.Possible origins of the superior performance of N2O were derived from transient experiments using 18O2 traces. 18O16O species were detected in 18O2 and 18O2–C3H8 transient experiments indicating reversible oxygen chemisorption. In the presence of alkanes, the isotopic heteroexchange of O2 strongly increased. Based on the distribution of labeled oxygen in COx and in O2 as well as on the increased COx formation in sequential O2–C3H8 experiments, it is suggested that non-lattice oxygen species (possibly of a bi-atomic nature) originating from O2 are non-selective ones and responsible for COx formation. These species are not formed from N2O. 相似文献
162.
液态烷烃C5+是汽油、柴油、航空燃油等当前社会的运输燃料的主要成分。本文综述了利用木质纤维素衍生平台化学品制备液体燃料的研究进展,着重总结了生物质衍生平台化学品通过碳链增长得到长链含氧化合物,然后经过加氢脱氧(HDO)得到C7+液体烷烃的技术研究进展。木质纤维素衍生平台化学品包括山梨醇、糠醛、5-羟甲基糠醛(HMF)、环戊酮、甲基呋喃、酚类、丙酮、丁醇、乙醇、乙酰丙酸、γ-戊内酯等。其中,糠醛、5-羟甲基糠醛和环戊酮在碱性催化剂作用下能与其他羰基化合物发生羟醛缩合反应实现碳链增长;甲基呋喃、苯类及苯酚类衍生物可以在强酸催化作用下通过烷基化/羟烷基化反应实现碳链增长;丙酮能与乙醇、丁醇发生α-烷基化反应实现碳链增长;乙酰丙酸可以转化为戊酸、丁烯或当归内酯,再分别通过酮基化反应、烯烃齐聚反应和加成反应实现碳链增长。诸多利用生物质衍生物化学品制备长链烷烃的路径中,利用5-羟甲基糠醛和甲基呋喃制备长链烷烃的技术路线存在路径过长、原料不易获取的问题;利用环戊酮和苯酚类物质能够得到高密度长链环烷烃,是一条有竞争力的路线;糠醛和乙酰丙酸易于从生物质中大规模制取,且利用糠醛和乙酰丙酸制备长链烷烃的反应路径短,较易实现工业应用。 相似文献
163.
164.
几何平均连接性指数:一种修正的分子连接性指数 总被引:1,自引:0,他引:1
本文试图改进Kier和Hall提出的分子连接性指数,提供一种更加完美的分子表征和分子设计技术。根据分子连接性指数定义,本文对其进行几何平均修正,使其更具解释性和丰富的含义,并命名为几何平均连接性指数(GMCI)。新的分子连接性指数用于一组含3-8个碳原子的烷烃7种性质的QSAR/QSPR研究,统计结果表明,由几何平均连接性指数所建模型普遍比传统的分子连接性指数所建模型要好。 相似文献
165.
Robert E. Doolittle Adron T. Proveaux Hans T. Alborn Robert R. Heath 《Journal of chemical ecology》1995,21(11):1677-1695
Monomethyl and dimethylalkanes with one, two, three, four, five, and seven methylene groups separating the methyl branches were synthesized and analyzed by magnetic sector and quadrupole storage (ion trap) mass spectrometry. The spectra produced by the magnetic sector instrument were in good agreement with previously reported data, whereas the ion trap spectrometer produced ions resulting from cleavages adjacent to the branching points, markedly different than those from the magnetic sector instrument. Fragmentation patterns show that the ion trap mass spectrometer can be used to characterize branched alkanes in nanogram and subnanogram quantities. 相似文献
166.
Dennis R. Nelson David A. Carlson Charlotte L. Fatland 《Journal of chemical ecology》1988,14(3):963-987
The alkanes (methylalkanes) were analyzed from both sexes of four members of thepalpalis group of tsetse flies,Glossina fuscipes fuscipes, G. palpalis gambiensis, G. palpalis palpalis, G. tachinoides plus onefusca group member, G. brevipalpis, to determine structures, abundances, and the presence of unique or specific methylalkanes. These insects are unique in that trimethylalkanes were major components except in femaleG. tachinoides and both sexes ofG. brevipalpis where 2-methylalkanes were the major components. The identification of novel long-chain tetramethylalkanes, including 11,15,19,23-tetramethylpentatriacontane, a minor component of femaleG. f. fuscipes, G. p. gambiensis, andG. p. palpalis, is reported here. Tetramethylalkanes were significant components of both sexes ofG. brevipalpis. The major tetramethylalkane in G.brevipalpis is 3,7,11,15-tetramethylhen-triacontane. The use of the methylalkanes as taxonomic indicators in tsetse is discussed. 相似文献
167.
G. R. Somayajulu 《International Journal of Thermophysics》1988,9(4):567-575
Two new equations are proposed for the enthalpy of vaporization from the triple point to the critical point. One of these equations containing four parameters is exceptionally good for fitting the data. The other equation containing three parameters is quite adequate for fitting the data but it is exceptionally suited for interpolation when the data do not cover the entire range. These equations have been tested using the enthalpy of vaporization of water from the triple point to the critical point and are compared with other equations.Nomenclature
T
c
Critical temperature, K
-
T
t
Triple point, K
-
T
x
Any particular temperature, K
-
T
r
Reduced temperature
-
P
r
Reduced pressure
-
R
Gas constant
-
P
Vapor pressure
-
X
(T
c–T)/T
c
-
Y
(T
c–T)/T
-
X
x
(T
c–T)/(T
c–T
x)
-
X
t
(T
c–T)/(T
c–T
t)
-
H
vt
Enthalpy of vaporization at the triple point, kJ · mol–1
-
H
vx
Enthalpy of vaporization at any temperature x, kJ · mol–1
-
Z
v
Compressibilty factor of the saturated vapor
-
Z
1
Compressibilty factor of the saturated liquid Relative deviation = 100[Hv(obs)–Hv(cal)]/Hv(obsd) Standard deviation = { [H
v(obs)–H
v(cal)]2/(No. points — No. parameters)}0.5 相似文献
168.
169.
J. Szafranek E. Maliński E. Dubis E. Hebanowska J. Nawrot P. Oksman K. Pihlaja 《Journal of chemical ecology》1994,20(9):2197-2212
Branched hydrocarbons were identified in the lipids ofLeptinotarsa decemlineata Say andTribolium destructor by gas chromatography, ordinary electron impact mass spectrometry, and linked, scanned, daughterion monitoring. This methodology allowed us to revise our earlier results based only on GC-MS data confirming the existence of only monomethyl-, dimethyl-, and trimethylalkanes in the hydrocarbons ofL. decemlineata Say. The hydrocarbons fromTribolium destructor consist ofn-alkanes, 3-methylalkanes, internally branched monomethylalkanes and dimethylalkanes. Daughter-ion monitoring can be particularly important for distinguishing between incidentally overlapped GC peaks of hydrocarbons from different series. A trace, for example, of dimethylalkane coeluating withn-alkane was easily identified in GC peak of hydrocarbon mixture ofT. destructor. Link scans confirmed also molecular weights for the compounds without molecular ions in the mass spectra. Structural assignment of the compounds were verified by comparison of the experimental and calculated values of the GC retention Kovats indexes (KI). 相似文献
170.
Aligned carbon nanotubes (CNTs) were synthesized by nebulized spray pyrolysis of solutions of organometallics in carbon precursor solvents. Four types of straight-chained alkanes including n-pentane, n-hexane, n-heptane and n-octane were used as precursor solvents for synthesis of aligned CNTs. The results from scanning electron microscopy, transmission electron microscopy and Raman spectroscopy show that the CNTs obtained from them have different diameters and degrees of graphitization. It is found that the n-heptane is the most suitable for the growth of aligned CNTs with high quality and yield. The thermodynamic properties of precursory carbon sources such as boiling point and formation enthalpy are considered to play a decisive role in the synthesis of CNTs. It will be very helpful for the controllable preparation of aligned CNTs at relatively low cost. 相似文献