三种不同拓扑结构的分子筛在甲醇制烯烃反应中的性能对比

采用XRD、SEM、N₂吸附-脱附、NH₃-TPD研究了3种不同拓扑结构的分子筛SAPO-34、Al-ITQ-13和ZSM-5分子筛的孔结构、酸性分布对其甲醇制低碳烯烃中反应性能的影响.结果表明,SAPO-34对乙烯具有最好选择性,可达52.3%;ZSM-5和Al-ITQ-13则对丙烯具有良好的选择性可达50.3%和50.0%,丙烯选择性相当,但兼顾乙烯时,Al-ITQ-13较ZSM-5高,可达18.4%.3种分子筛反应性能的差异主要是其拓扑结构的不同引起的.孔道结构越小则越有利于小分子产物的生成,具有八元环结构的SAPO-34分子筛对小分子乙烯具有最高的选择性,而同时具有九元环和十元环结构的Al-ITQ-13由于孔道中含有一套九元环结构,使其与ZSM-5分子筛相比,在丙烯选择性相当的情况下,小分子产物乙烯明显增加.     

环己烯水合制备环己醇的研究Ⅰ. 分子筛结构及晶粒大小的影响

考察了三种不同结构的分子筛(ZSM-5,MCM-22及β)以及不同晶粒大小的ZSM-5分子筛对环己烯水合反应的催化活性. 结果表明,具有12元环孔道体系的β分子筛对环己烯的转化率(9.6%)最高,但对环己醇的选择性(35.4%)最差. MCM-22分子筛的活性很低,其环己烯转化率只有0.8%. 而孔口为10元环结构的ZSM-5分子筛则具有较高的活性(环己烯转化率7.5%)和产物选择性(99.2%),因此是较好的水合催化剂. ZSM-5分子筛的晶粒大小对其环己烯水合反应活性有明显的影响,分子筛晶粒越细,则水合反应活性越高,其原因在于晶粒变细增大了分子筛的外比表面积,从而增加了接近孔口处的活性中心的数量.     

碱处理法改善Pt／ZSM-5异构化性能

制备了一系列不同条件下碱处理的ZSM-5样品,以调控其酸性和孔道结构. 考察了酸性和孔道结构对Pt/ZSM-5的异构化性能的影响. 样品的晶相、酸性及结构分别通过X射线衍射、 NH3程序升温脱附及N2吸附-脱附表征. 结果表明,缓和的碱处理导致ZSM-5上强酸中心减少,催化剂异构化活性下降; 而苛刻条件下的碱处理使得ZSM-5上强酸中心增加、大量中孔产生及催化剂异构化活性明显提高. 催化剂的异构化活性取决于分子筛上强酸中心的量,与孔道结构无关; 而异构体的分布不仅与孔道结构有关,而且与正己烷转化率密切相关,与分子筛的酸性无关.     

PtSnNa/SUZ-4:丙烷脱氢反应的高效催化剂

丙烷脱氢制丙烯是优化利用炼厂气和油田伴生气资源的一条重要途径.随着丙烯需求量的逐步增加,丙烷脱氢制丙烯日益受到重视.负载型PtSn/γ-Al2O3催化剂具有优良的丙烷脱氢活性和选择性,但在高温、低氢压的反应条件下,催化剂易积炭而失活.近年来,选用了微孔分子筛如ZSM-5和介孔分子筛如SBA-15和MCM-41作为PtSn催化剂的载体,结果表明,具有规整孔道结构的负载型PtSn/分子筛催化剂的丙烷脱氢反应稳定性明显优于PtSn/γ-Al2O3催化剂.SUZ-4分子筛与ZSM-5分子筛结构相似且孔径相当,所不同的是ZSM-5由十元环交叉孔道组成,而SUZ-4由十元环和八元环孔道垂直相交组成.我们用微型催化反应装置结合XRD、BET比表面积和孔体积测试、NH3吸附-程序升温脱附(NH3-TPD)、氢化学吸附、热重分析(TG)、H2程序升温还原(H2-TPR)和程序升温氧化(TPO)等多种物理化学手段研究了负载型PtSnNa/SUZ-4和PtSnNa/ZSM-5催化剂的结构和丙烷脱氢反应性能,以及这两种催化剂在丙烷脱氢反应中催化性能差异的原因.实验结果显示,在丙烷脱氢反应中,负载型PtSnNa/SUZ-4催化剂上丙烯选择性和反应稳定性明显优于PtSnNa/ZSM-5催化剂,说明载体一定程度上会影响催化剂上丙烷脱氢反应性能.XRD,BET比表面积和孔体积测试等表征手段结果表明,SUZ-4和ZSM-5的孔体积和比表面积比较接近,载体的结构又类似,且两者的积碳量也相近,故载体的基本性质和积碳量的差异不是引起催化剂性能差异的原因.NH3-TPD结果表明,H-SUZ-4的酸强度明显强于H-ZSM-5.由于浸渍法制备负载型PtSn催化剂所用前体为具有强酸性的混合溶液(H2PtCl6+SnCl4),存在于SUZ-4分子筛孔道内表面的强酸中心不利于上述前体与SUZ-4分子筛孔道内表面结合.ZSM-5分子筛孔道内表面比较弱的强酸中心,促进了催化剂前体在ZSM-5分子筛孔道内表面的分散与结合.和ZSM-5为载体的催化剂相比,PtSnNa/SUZ-4上Pt粒子大部分分散在载体的外表面,从而金属上的积碳不易引起催化剂的失活.故多孔材料上Pt的分布是影响催化活性差异的主要原因.为进一步证明多孔材料上Pt的分布是影响催化活性差异的主要原因,我们通过二苯并噻吩预处理催化剂的手段证明Pt粒子在分子筛孔内外的分布情况.由于二苯并噻吩的尺寸比较大(0.8 nm)不能进入到分子筛的孔道内(SUZ-4:0.56 nm,ZSM-5:0.56 nm),所以载体孔道外的部分Pt会被二苯并噻吩预处理而失去活性,而孔道内的Pt不会因为预处理仍具有催化活性.实验结果表明,PtSnNa/SUZ-4经过二苯并噻吩预处理后,催化活性大大降低;而PtSnNa/ZSM-5经过二苯并噻吩预处理后,催化活性几乎没有变化.说明PtSnNa/SUZ-4上Pt粒子大部分分散在载体的外表面,从而金属上的积碳不易引起催化剂的失活.     

ZSM-5分子筛骨架铝落位对甲醇转化制芳烃催化性能影响

采用水热合成法,在合成过程中通过添加矿化剂、尿素和改变硅源,制备了不同骨架铝落位的ZSM-5分子筛。通过SEM、XRD、BET、XRF、MAS NMR、NH_3-TPD和Py-FTIR等表征手段对分子筛的形貌、织构、骨架铝落位和酸性进行了系统研究,同时考察了不同ZSM-5分子筛催化剂甲醇制芳烃的催化性能。研究结果表明,制备的ZSM-5分子筛均具有结晶度高和形貌均一等特点,但在骨架铝落位和酸性方面存在显著差异。椭球状ZSM-5分子筛的骨架铝主要分布于直通孔道或正弦孔道中,并表现出较多的酸性位。块状分子筛中骨架铝主要落位在孔道交叉处,且具有较低的强酸量。在甲醇制芳烃反应中,骨架铝主要位于直通或正弦孔道并表现出较多酸性位的椭球状ZSM-5分子筛催化剂具有较高的活性稳定性和芳烃选择性。     

1-丁烯在MCM-22分子筛中的吸附与扩散：Monte Carlo与动力学模拟研究

采用巨正则Monte Carlo方法和分子动力学方法研究了1-丁烯在MCM-22分子筛中的吸附现象和扩散行为,得到了1-丁烯吸附在该分子筛孔道中的相互作用能和在不同孔道中的扩散轨迹和扩散系数.结果表明1-丁烯在MCM-22分子筛中主要存存两个相互作用能区间,1-丁烯优先吸附在十元环孔道中;1-丁烯的扩散和移动主要发生在十二元环超笼的中部,十元环孔道中的1-丁烯扩散速度明显小于十二元环超笼系统中的扩散速度.     

11-丁烯在MCM-2222分子筛中的吸附与扩散: Monte Carlo与动力学模拟研究

采用巨正则Monte Carlo方法和分子动力学方法研究了11-丁烯在MCM-2222分子筛中的吸附现象和扩散行为, 得到了11-丁烯吸附在该分子筛孔道中的相互作用能和在不同孔道中的扩散轨迹和扩散系数. 结果表明11-丁烯在MCM-2222分子筛中主要存在两个相互作用能区间, 11-丁烯优先吸附在十元环孔道中; 11-丁烯的扩散和移动主要发生在十二元环超笼的中部, 十元环孔道中的11-丁烯扩散速度明显小于十二元环超笼系统中的扩散速度.     

不同晶粒ZSM-5沸石分子筛对合成气羰基化反应性能的影响

对沸石分子筛而言,分子筛的孔道、孔径、孔容和微孔等物理性质和酸性影响它的活性.通过调节和控制以上物理性质能够提高产物选择性和收率,降低副产物,从而促进反应性能提高活性.我们考察了ZSM-5分子筛的晶粒度和硅铝比对合成气羰基化反应性能的影响.结果表明,晶粒度小及具有一定比例的中强酸中心的ZSM-5沸石分子筛对反应有利,但晶粒度比较大即1和3μm的ZSM-5沸石分子筛目标产物选择性比较低.纳米级的ZSM-5沸石分子筛催化剂在反应中表现出较高的活性及较低的副产物选择性,是适宜的合成气羰基化反应催化剂载体.温度考察结果可知,反应温度为300℃时,效果为最佳.其中, 30～50 nm的ZSM-5沸石分子筛催化剂CO转化率为55%,乙酸甲酯和甲酸甲酯选择性之和为52%,而晶粒度3μm时, CO转化率仅为25%,乙酸甲酯和甲酸甲酯选择性之和为20%,是30～50 nm沸石分子筛的一半.当反应继续升温时,副产物的选择性也随之增加,是因为所生成的中间产物和甲醇等继续进行各种反应生成二甲醚、芳烃、烷烃以及裂解生成CO_2等干气.     

水蒸气处理对ZSM-5酸性及其催化丁烯裂解性能的影响

 考察了水蒸气处理温度和时间对ZSM-5分子筛酸性及其催化丁烯裂解性能的影响. 结果表明,通过水蒸气处理可降低ZSM-5分子筛的酸量和酸强度,明显提高产物中丙烯与乙烯的选择性和收率,抑制副产物芳烃和低碳烷烃的生成. 用柠檬酸脱除水蒸气处理过程中产生的非骨架铝,可提高ZSM-5分子筛孔道的容碳能力,从而提高催化剂的稳定性. 考察了反应条件对催化剂性能的影响,结果表明较佳的反应条件为WHSV=3.5～8.8 h-1,p=0.06～0.1 MPa,θ=600～620 ℃.     

低钠条件下MCM-22分子筛的动态合成及其在甲烷无氧芳构化中的催化性能

由于 MCM- 2 2分子筛 [1] 具有独特的结构性质 ,故在许多烃类转化反应中已表现出突出的催化特性 [2～ 4 ] .我们在甲烷无氧芳构化的前期工作中发现 [5] ,酸性适当 ,具有交叉孔道且孔径与苯的动力学直径 (～ 0 .6nm)相当的分子筛载体活性较高 .MCM- 2 2的酸性与 ZSM- 5相当 [6 ,7] ,且拥有两套互不相通的多维孔道体系 [8] ,一套为二维正弦孔道 ,有效孔径为十元环 ( 0 .4nm× 0 .59nm) ;另一套亦为十元环孔道体系 ( 0 .4nm× 0 .54nm) ,但含有内径为十二元环的超笼 ( 0 .71 nm× 0 .71 nm× 1 .82 nm) .因此 ,以 MCM- 2 2为载体的催化剂…     

非那雄胺合成工艺改进

非那雄胺能抑制5α-还原酶的活性,明显降低二氢睾酮水平,是一种治疗良性前列腺增生的有效药品。该合成工艺以甾烯酮酸为原料,将其与氯化亚砜反应,无须分离即与叔丁胺反应得17β-酰胺化合物,再氧化开环,环合,氢化,脱氢合成了非那雄胺。经元素分析、IR、1HNMR、13CNMR、MS分析表征了其结构。该法无须使用昂贵的2,2-二吡啶二硫化物和剧毒药品苯亚硒酸酐,且以乙酸铵代替氨气,降低了对设备的要求和腐蚀,更适用于工业生产。     

Dichroism of absorption and polarization of phosphorescence of molecules of the closed form of nitrobenzospirothiopyran

The spectral-polarization characteristics of absorption and phosphorescence of molecules of the initial form of nitro-substituted indolinospirobenzothiopyran were studied in oriented polyethylene films and in solutions with different polarity. An oscillator model of the electron transitions responsible for the formation of absorption and luminescence spectra was suggested. It was established that the principal differences in the spectral and photophysical properties of the compound studied and its oxygen-containing analog are associated with the fact that the electronegativity of the S atom is lower than that of the O atom. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1143–1146, June, 1997.     

Synthesis of phenolic components of Grains of Paradise

Two vanilloids, (5E)-8-(4-hydroxy-3-methoxyphenyl)oct-5-en-4-one (1) and 4-[3-hydroxydecyl]-2-methoxyphenol (2), isolated from the dried seeds of Grains of Paradise (Aframomum melegueta), were synthesized; the latter compound was made as the S-enantiomer and the material derived from the seeds was found to be a 1:1.7 mixture of the R and S isomers. The synthetic route used should allow the preparation of analogs having extended alkyl chains and consequently different lipophilicity, and 3, a homolog of 2, was also prepared.     

Study of hydration of two cements of different strengths

Main hydration products of two cement pastes, i.e. CSH-gel, portlandite (P) (and specific surface S) were studied by static heating, and by SEM, TEM and XRD, as a function of cement strength (C-33 and C-43) hydration time (th) and subsequent hydration in water vapour.Total change in mass on hydration and air drying, M_o, increased with strength of cement paste and with hydration time. Content of water escaping at 110 to 220°C, defined as water bound with low energy, mainly interlayer and hydrate water, was independent on cement strength but its content increased with (th). Content of chemically bound (zeolitic) water in CSH-gel, escaping at 220-400°C, was slightly dependent on strength and increased with (th). It was possibly derived from the dehydroxylation of CSH-gel and AFm phase. Portlandite water, escaping at 400-500°C, was independent on cement strength and was higher on longer hydration. Large P crystals were formed in the weaker cement paste C-33. Smaller crystals were formed in C-43 but they increased with (th). Carbonate formated on contact with air (calcite, vaterite and aragonite), decomposed in cement at 600-700^oC. It was high in pastes C-33(1 month) and C-43(1 month), i.e. 5.7 and 3.3%, respectively; it was less than 1% after 6 hydration months (low sensitivity to carbonation) in agreement with the XRD study showing carbonates in the air dry paste (1month), and its absence on prolonged hydration (6 months) and on acetone treatment. Water vapour treatment of (6 months) pastes or wetting-drying increased this sensitivity.Nanosized P-crystals, detected by TEM, could contribute to the cement strength; carbonate was observed on the rims of gel clusters.This revised version was published online in November 2005 with corrections to the Cover Date.     

Acid hydrolysis of carboxymethylcellulose of low degree of substitution

Cotton cellulose was swollen in a sodium hydroxide solution and carboxymethylated by a two-bath method for different periods of time for each process. The kinetics of acid hydrolysis and the crystallinity of the swollen and carboxymethylated samples were measured. The proportion of broken bonds, rate constants for hydrolysis, and permeability of cellulose to hydrolyzing agents were calculated. The susceptibility of glycosidic linkages to acid hydrolysis was improved by carboxymethylation more than by swelling in alkali. The increased accessibility of carboxymethylcellulose to acid was regarded as a consequence of increased intra-and intercrystalline swelling and of the glycosidic bonds' weakness caused by the electron-attracting carboxymethyl group on the C-6 position.     

恶臭嗅辨实验室建设探讨

针对恶臭测试的环境影响问题,提出了解决的实例方案,并对方案的要点及优缺点进行讨论,此方案在实际操作中具有较好的效果。     

氯氧化镁生成热的研究

用氧化镁氯化镁水溶液制备了8水合氯氧化镁[nMg(OH)2·MgCl2·8H2O], 并测定了其在盐酸中的溶解热, 实验结果表明, 氯氧化镁溶解热与n值呈线性关系, 根据溶解热求出5Mg(OH)2·MgCl2·8H2O和3Mg(OH)2·MgCl2·8H2O的生成热分别为-7727.1和5888.1kJ·mol^1^-。     

Estimation of Kinetic Parameters of Thermal Oxidation of Ilmenite

The aim of the presented work was the investigation of thermal oxidation of ilmenite in static air atmosphere. The investigations were carried out by use of a derivatograph (MOM, Hungary). The changes of crystallographic structure of investigated samples were identified by X-ray diffractometry on Philips PW-1710 diffractometer. In temperature above 500°C appears structure of hematite Fe₂O₃. On the basis of the thermogravimetric measurements, the contracting area and contracting volume models were found as the best fitting experimental data. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mechanism of action of base-catalyzed oxygenation of phenol derivatives

Cyclopropyl derivative of 2,6-di-tert-butylphenol is synthesized as a probe to investigate the mechanism of base-catalyzed autooxidation of phenol derivatives. Our study indicates that one electron reduction of molecular oxygen from phenolate gives phenoxyl radical 3, a key intermediate of autooxidation. The coupling of phenoxyl radical and superoxide radical gives peroxylate anion 4 and produces the final epoxy alcohol adduct 6.