Elucidation of the fine structure of poly(vinyl chloride) by hydrogenation and 13C-NMR analysis of low molecular weight fractions

The following experiment was performed based on the assumption that the characteristic structural features of high molecular weight poly(vinyl chloride) (PVC) should be present to the same extent in its low molecular weight fractions. Two PVC fractions of molecular weight, 1500 and 800, respectively, (0.14% of total polymer) were isolated from bulk PVC (M_n 32,000) by extraction with methanol. This extract was transformed into paraffins by a new hydrogenation method using an excess of Raney nickel in order to facilitate identification. ¹³C-NMR spectral data of the paraffins showed that almost 2 out of 1000 carbon atoms were linked to a side chain with more than five carbon atoms, and 5 out of 1000 carbon atoms were methyl branched. Gas chromatography-mass spectrometry (GC–MS) analyses confirmed that the low molecular weight paraffins consisted of a sequence of even-numbered homologs. These findings suggest indirectly that the surprisingly low degradation temperature of PVC is due to the arrangement of the chlorine atoms rather than to the branching of the alkyl chain.     

Sodium and hydrogen tetrachloroaluminate catalysts for molecular weight reduction of hydrocarbons

Sodium and hydrogen tetrachloroaluminates (NaAlCl₄ and HAlCl₄) have been evaluated as catalysts for the molecular weight reduction of hydrocarbons. The NaAlCl₄ is the major molecular weight reduction and synthesis component, and HAlCl₄ adds a hydrogenation function. The optimum catalyst composition, for the petroleum AC-20 resid and shale oil feeds studied, was found to be 2.5–4.5 wt.% HAlCl₄ in NaAlCl₄. To convert these feeds completely into gasoline range materials, a hydrogen partial pressure and a hydrogen consumption of 950 psia and 900 scf/bbl, respectively, are estimated to be required. About 40% of the hydrogen consumption would be for contaminant removal. Above a hydrogen partial pressure of about 450 psia, the liquid products produced contained less than 100 ppm each of sulfur and nitrogen contaminants. The C₆C₁₃ molecular weight portion of the liquid products contained about 55% aromatics, 8% naphthenes, 33% branched paraffins and 4% normal paraffins (weight basis).     

Molecular size evaluation of linear and branched paraffins from the gasoline pool by DFT quantum chemical calculations

A good approach of the critical molecular dimensions of 35 linear and branched C5-C8 paraffins by DFT quantum chemical calculations at B3LYP/6-31G** level of theory in gas phase is described. In this context, we found that either the determined molecular width or width-height average values can be used as critical measures in the analysis for selection of molecular sieves materials, depending on their pore size and shape. The molecular width values for linear and monosubstituted paraffins are 4.2 and 5.5 Å, respectively. In the case of disubstituted paraffins, the values are 5.5 Å for 2,3-, 2,4-, 2,5- and 3,4-disubstituted and for 2,2- and 3,3-disubstituted are 6.7-7.1 Å. The values for ethyl-substituted are 6.1-6.7 Å and for trisubstituted isoparaffins are 6.7. In order to select a porous material for selective separation of isoparaffins and paraffins, the zeolite diffusivity can be correlated with the critical diameter of the paraffins according to the geometry-limited diffusion concept and the effective minimum dimensions of the molecules. The calculated values of CPK molecular volume of the titled paraffins showed a good discrimination between the number of carbons and molecular size.     

Cracking of C9 paraffins over xylene isomerization catalysts

The mechanism for cracking C₉ paraffins was studied in a series of experiments using feeds containing approximately 1.0% of one paraffin in a mixture of the three xylene isomers. Over a catalyst containing the medium pore molecular sieve AMS-1B, linear paraffins cracked more rapidly than branched paraffins. This difference was moderated somewhat by the addition of a hydrogenation metal to the catalyst. A similar effect is noted for catalysts containing the large pore zeolite Y where cracking of branched paraffins was favored in the absence of a hydrogenation metal. These shifts in cracking rates are shown to be consistent with a mechanism which involves an increase in the cracking rate due to the dehydrogenation activity of the metal and a decrease in cracking due to the hydrogenation activity of the metal. The distribution of cracked products indicates that the C₉ paraffins isomerize to an equilibrium distribution prior to cracking. The absence of isomerized C₉ paraffins in the product stream indicates that hydride abstraction is slow compared to either isomerization or cracking.     

饱和烷烃的偏心因子与分子的拓扑

本文用图论的方法研究了饱和烷烃的Pitzer偏心因子.发现Wiener数是一个能够很好地衡量分子结构“偏心”程度的拓扑指数,在Pitzer偏心因子与Wiener数之间存在着很好的比例关系,据此能够预测异构烷的偏心因子.预测结果表明,与实验值间的一致是令人满意的.     

烷烃混合物二元相互作用参数的新型关联式

针对偏离二参数对应状态原理的复杂流体,以Mie势能函数和London色散力理论为基础,引入基于Joffee和Stewart虚拟临界规则的Leland分子形状系数,推导得到状态方程中二元相互作用参数k_ij的新型关联式.取Mie势能函数的参数n为3时,无需经过实验数据返算,关联式可直接计算和预测烷烃混合物k_ij;除了物质的临界性质外,k_ij还是温度、组成、摩尔体积、偏心因子和离子化势能的函数.将关联式初步应用于Peng-Robinson状态方程计算烷烃类混合物的临界压力,计算值与实验值平均偏差小于2.40％,取得满意的结果.     

Normal fatty acids in sediments

Normal fatty acids have been found by several investigators in a number of sediments ranging in age from Precambrian to Recent. This paper summarizes these occurrences. A variety of molec-ular distributions have been observed. In most sediments, even-carbon-numbered normal fatty acids are much more abundant than those with odd carbon numbers ; in some sediments, however, concentrations of even- and odd-carbon-numbered normal fatty acids are about equal. Normal fatty acids have been postulated as pos-sible precursors for normal paraffin hydrocarbons in petroleum because of 1) structural similarities between the two kinds of molecules, 2) ubiquity of fatty acids in biological materials, 3) fatty acid-normal paraffin relationships in sediments, and 4) distribution of normal paraffins in some crude oils. Evidence suggests that normal fatty acids may be precursors for many normal paraffins of intermediate and high molecular weights found in petroleum. Detailed mechanisms of chemical reactions by which normal paraffins can be de-rived from fatty acids in sediments under geo-logically reasonable conditions have yet to be defined.     

Coal flash pyrolysis: 2. Polymethylene compounds in low temperature flash pyrolysis tars

Pyrolysis of coals at low temperatures (< 600 °C) produces tars containing the precursors of the low molecular weight aliphatic hydrocarbons, such as ethylene and propylene, observed on flash pyrolysis of the coals at higher temperatures (700–800 °C). This is shown by further pyrolysis of these low temperature tars at high temperatures. Various methods, including isolation by h.p.l.c. were used to confirm the presence of straight chain paraffin and olefin pairs (C₁₄C₂₆ and above) in the low temperature tars. Pyrolysis of pure paraffins and olefins in this molecular weight range at temperatures > 700 °C produce ethylene, propylene and other cracking products similar to those obtained on flash pyrolysis of coal.     

Determination of the main products and intermediates of the Oxidation of Medium Normal Paraffins in dependence on the conversion indirect evidence for the importance of bifunctional intermediates

The mole numbers of the starting paraffins, of the intermediate alcohols and ketones with the same chain lengths, of the lower alkan-2-ones, of the carboxylic acids, and of the esters were determined at different reaction times for the oxidations of n-tridecane, n-tetradecane, and n-pentadecane with molecular oxygen at 140°C in the presence of 0.1% Mn-stearate. In the stationary region of the oxidation about 1.2 moles of acids and 0.7 moles of esters are formed from 1 mole of paraffin consumed. The relative oxidation rates of alcohols and of ketones with reference to the starting paraffins were estimated from the mole numbers of the starting paraffins, the alcohols and the ketones at the maxima of the alcohols and the ketones. These values are higher than those determined by competitive oxidations, and this discrepancy is an indirect evidence of the formation of bifunctional intermediates from the starting paraffins. The relative rates of the formation of alcohols, ketones, and bifunctional products from normal paraffins were estimated.     

化学反应活性指标与基元反应动力学参数的关系及链烷烃热裂解过程模型

本文采用广义休克尔法(EHMO)与全略微分重叠法(CNDO/2)计算了链烷烃及其自由基的反应活性指标.通过分析已知的基元反应动力学参数与这些指标间的关系,提出一种预测基元反应速率常数的方法.对链烷烃热裂解速度常数的预测,证明该法是可靠的.在此基础上,采用平推流反应器(PFR)模型及拟稳态假设描述C_4~-烃类热裂解过程,模拟了c_4~-单一烃及混合烃的热裂解过程.模拟结果与文献中的总包反应实验数据吻合良好,证明所建模型是正确、可靠的.     

Binary liquid–liquid equilibria of aniline–paraffin and furfural–paraffin systems

Binary liquid-liquid-equilibria data for several aniline-paraffin and furfural-paraffin systems have been taken. These data along with data for other aniline-hydrocarbon and furfural-hydrocarbon systems from literature have been correlated using UNIFAC model. The UNIFAC group interaction parameters have been found to have a linear temperature dependence. The CH₂ groups in cyclo and non cyclo paraffins require different interaction parameters. It was also found that a scaling of the combinatorial term is necessary for higher molecular weight hydrocarbons.     

Correlating the solubility of supercritical gases in high‐molecular weight substances using a density‐dependent equation

Chrastil (1982) established that the solubility of a substance in a supercritical fluid can be correlated with the density of the pure supercritical gas. Recently, the solubility of supercritical fluids in different organic liquids was successfully correlated as a function solely of the supercritical fluid density, since we demonstrated that the supercritical fluid density also defines the solubility of the gas in the liquid phase. In this work, the solubility of supercritical carbon dioxide in high‐molecular weight substances, such as high‐molecular weight paraffins, alcohols, fatty acids, fatty acid methyl and ethyl esters, has been correlated and constants provided. More than 20 binary systems comprising around 1000 solubility data points were correlated, obtaining regression coefficients greater than 0.96 and confirming the goodness of the density‐dependent equation previously reported. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Supercritical Chromatography of Paraffins on a Molecular Sieve: Analytical and Preparative Scale

Abstract

Supercritical carbon dioxide has been used as the mobile phase in chromato-graphic investigations of higher paraffins on molecular sieve 5A at temperatures from 40 to 200°C and pressures up to 20 MPa. The pressure and temperature dependence of retention data of paraffins up to eicosane found experimentally are discussed and compared with results of model calculations. Furthermore, some physicochemical applications of the high pressure retention data seem to be possible. A pressure-programmed group separation process permitting analytical and preparative scale separations of n- and isoparaffin mixtures is outlined.     

斯德哥尔摩公约对我国氯化石蜡产业的影响及对策建议

简述了我国氯化石蜡的产业现状,分析了将属于斯德哥尔摩公约受控范围的持久性有机污染物短链氯化石蜡对我国氯化石蜡产业的影响并提出对策建议。     

Gasadsorptionschromatographie höherer Kohlenwasserstoffe. Normalparaffinbestimmung durch temperaturprogrammierte Segregations-Gaschromatographie an 5A Molekularsieb

Gas Adsorption Chromatography of Higher Hydrocarbons. Determination of Normal Paraffins by Temperature-Programmed Segregation Gas Chromatography on 5A Molecular Sieve A fast temperature program makes it possible to determine the normal paraffins up to C 20 in the concentration range between 0.1 and 99.9 percent (molecule type analysis). From the group peak of the normal paraffins we can obtain on line the distribution of the carbon numbers. As the normal paraffin selectivity of the molecular sieve S ≈ 1 can be assumed. Isoparaffin memory could not be detected. The new method makes it possible to perform analysis with great accuracy within three minutes or less. Connected to a computer it is excellently suitable for large series of samples. Under the standard conditions of this method only a little paraffin cracking has been found. Type and quantity of the cracked products proved to be independent of the chain length of the individual normal paraffin.     

长链正构烷烃（n-C16~C20）脱氢制直链单烯烃反应热力学分析

对长链正构烷烃（n-C₁₆~C₂₀）一次脱氢制直链单烯烃反应进行了详细的热力学分析,考察反应温度、反应压力、氢烃物质的量比和原料碳数对热力学平衡的影响。结果表明,n-C₁₆~C₂₀脱氢反应的平衡常数及平衡转化率随烷烃碳数的增大而增加;提高温度和降低压力均可显著提高平衡转化率,降低氢烃物质的量比在一定程度上提高平衡转化率。适宜的工艺条件为：反应温度>430 ℃,反应压力(0.10~0.20) MPa,氢烃物质的量比为6~8。     

卤化石蜡系列阻燃剂研究进展

综述了卤化石蜡系列阻燃剂的品种、性能和用途。并讨论了溴化石蜡的几种溴化反应方法,即烯烃法、N-溴代丁二酰亚胺法和氧化汞催化法,指出溴素法生产溴化及溴氯化石蜡是卤化石蜡合成工艺的突破。最后对卤化石蜡的生产方法进行了简要介绍。     

Average Molecule Construction of Petroleum Fractions Based on 1H-NMR

The calculation of chemical structures and physical properties is the basis of petroleum refining optimization. In this article, a method to build an average molecule model for hydrocarbons and petroleum fractions is developed. ¹H-NMR, molecular weight, and elemental composition were used as input parameters to construct a single molecular model that represents the average chemical structure. The average molecules were constructed by assembling the average building blocks, which are a set of predefined structural fragments, covering typical hydrocarbon and heteroatom functional groups in petroleum systems. After applying a group contribution method to the derived molecule, the bulk property of a sample could be directly calculated. The method was validated by being applied to various model compounds (including paraffins, cycloalkanes, aromatics, and heteroatom-containing species), where it successfully predicted the average building blocks, unit sheets number, and physical properties. The application of this method to petroleum fractions was demonstrated. © 2018 American Institute of Chemical Engineers AIChE J, 65: 270–280, 2019     

Diffusion of radioactively tagged penetrants through rubbery polymers. II. Dependence on molecular length of penetrant

The diffusion of radioactively tagged n-hexadecane, n-dotriacontane, and a polybutadiene oligomer with molecular weight 1600 has been studied in 12 rubbery polymers. Diffusion coefficients were obtained from the theory for the thin smear method: for n-hexadecane and for n-dotriacontane (with one exception), in the form appropriate for a completely miscible polymer–penetrant pair, and for the oligomer in the form appropriate for slow entry of the penetrant across the penetrant–polymer interface. For the four flexible linear penetrants, n-dodecane, n-hexadecane, n-dotriacontane, and oligomer, the ratios of diffusion coefficients (or translational friction coefficients) are nearly the same in every polymer. It is concluded that these penetrants travel with similar segmentwise motions, although that is not the case with bulkier, more rigid penetrants. For the three normal paraffins, the friction coefficient is approximately proportional to molecular weight, but that for the oligomer is smaller than would be predicted on this basis.