MCM-22分子筛的合成、性质与催化应用

MCM-22分子筛具有独特的晶体结构、适宜的酸性和较高的稳定性,在烯烃与苯烷基化反应、甲烷无氧芳构化、催化裂化、烯烃芳构化及甲苯歧化等方面显示出广阔的应用前景。在总结大量相关研究的基础上,就目前MCM-22分子筛的合成、性质和催化应用方面的研究成果进行了概括和评述。     

Preparation of sulfated alumina supported on mesoporous MCM-41 silica and its application in esterification

New types of mesoporous SA/MCM-41 solid acid catalysts were prepared by loading sulfated alumina (SA) on MCM-41. The prepared catalysts were characterized by XRD, IR, N₂ physisorption, elemental analysis, FT-IR of adsorbed pyridine and NH₃-TPD. The esterification of acetic acid with n-butanol and citric acid with n-butanol were used as model reactions to test the catalytic activities and reusability of the SA/MCM-41 solid acid catalysts. Compared with SA catalyst, SA/MCM-41 catalysts exhibited higher catalytic performances, which were attributed to their high BET surface area and large pore volume. Moreover, 20SA/MCM-41 solid acid catalyst showed excellent reusability in both esterifications.     

The preparation and purification of monoglycerides. II. Direct esterification of fatty acids with glycerol

Studies have been made on the direct esterification reaction with various saturated and unsaturated fatty acids using more than theoretical concentration of glycerol (for maximum monoglyceride production) at 180C reaction temperature and in presence and absence of alkaline catalyst. The results show that the maximum monoglyceride formed is in the range of 55–60% of the fatty product at equilibrium stage of the reaction. The alkaline catalyst substantially increases the initial rate of reaction without appreciably lowering the time required for reaching the equilibrium concentration of monoglyceride in the resulting reaction mixture. Catalyst helps in depressing diglyceride formation.     

MCM-22、MCM-49和MCM-56三种分子筛的合成

MWW结构分子筛是一类新型的催化材料,具有独特的10元环孔道和12元环孔穴结构,在多种反应中表现出良好的催化活性。以六亚甲基亚胺作为模板剂,合成了MCM-22、MCM-49和MCM-56三种分子筛,并详细考察了不同硅源、凝胶配比、晶化温度和晶化时间对合成过程的影响。结果表明,凝胶配比和晶化温度对分子筛物相的影响较大。以硅胶粉为硅源,无论在何种晶化时间下都不能得到MCM-56,只能合成出MCM-49。而以碱性硅溶胶为硅源,在较短的晶化时间内就可以得到MCM-56。     

MCM-22、MCM-49和MCM-56分子筛的表征

MWW结构分子筛是一类新型的催化材料,具有独特的10元环孔道和12元环孔穴结构、优良的水热稳定性和特殊的酸中心分布,在多种反应中表现出良好的催化活性。以六亚甲基亚胺为模板剂,合成了具有MWW结构的MCM-22、MCM-49和MCM-56三种分子筛,并采用XRD、BET、TG/DTG和SEM手段对合成分子筛进行了表征,表明它们具有相同的单层结构,彼此之间的区别只有层间排列的结合层度和结合方式不同。MCM-56是薄层结构,晶体的层数少,MCM-22和MCM-49是多层结构,层数多。MCM-22的层间结合比较疏松,MCM-49的层间结合比较紧密。     

Sugar ester-modified lipase for the esterification of fatty acids and long-chain alcohols

The esterification reaction of a long-chain fatty acid and a fatty alcohol with a surfactant-modified lipase in a microaqueousn-hexane system was studied. Various lipases from different sources were first modified with a surfactant of the sugar ester type to improve their dispersibility in apolar organic solvents. This enzyme modification technique converted inactive crude lipases to highly active biocatalysts for the esterification of long-chain fatty acids and fatty alcohols in a microaqueous n-hexane system. The hydrophilic-lipophilic balance value and chainlength of the fatty acid residue of the fatty acid sugar ester, used for modifying the lipases, significantly influenced the amount of precipitated lipase that was dissolved in the aqueous solution, the protein content of the lipase-surfactant complex and its esterification activity.     

The immobilization of iron(III) aminopyridine complex on MCM-41: its preparation and characterization

2-Aminopyridinyl iron(III) complex was grafted on chlorosilane modified mesoporous MCM-41 to give MCM-Py-Fe(III). The immobilization was confirmed by FT-IR, ¹³C, ²⁹Si, ¹⁵N CP/MAS NMR, nitrogen adsorption–desorption study and elemental analysis. The powder XRD and TEM microscopy studies of the hybrid material confirmed the retention of the well-ordered honeycomb hexagonal structure in MCM-Py-Fe(III). The specific surface area of MCM-Py-Fe(III) was found to be 455 m² g^?1 and it had a pore volume of 0.27 cm³ g^?1 with an average pore diameter of 26.7 Å. The ¹³C CP/MAS NMR of MCM-Py-Fe(III) showed chemical shifts in the range of 113–155 ppm, which was assigned to the aromatic carbons in the pyridine ring. The ¹⁵N CP/MAS NMR showed the presence of chemical shifts at 550, 426 and 401 ppm for the three nitrogen atoms in the catalyst.     

Sulfonated polystyrene: A catalyst with acid and superabsorbent properties for the esterification of fatty acids

In this work, catalysts with acid and superabsorbent properties were obtained by sulfonation of expanded polystyrene and used to promote the esterification of oleic acid with ethanol. The prepared superabsorbent polymers (SAP) showed high concentration of active sulfonic acid sites (0.7-5.9 mmol acid sites g⁻¹) and high water absorption capacity (445-900 g_water g⁻¹). It was observed that the catalytic activity increased with the number of acid site and water absorption capacity. Turnover frequencies suggested that the catalytic activity depends on the accessibility/diffusion processes determined by the crosslinks in the polymer. Commercial sulfonic acid resins and polyacrylate based superabsorbent polymers showed very low activities compared with the SAP produced. The SAP also showed higher activity compared to the homogeneous catalyst p-toluenesulfonic acid. The higher activity of the prepared SAP is discussed in terms of the acidity of sulfonic groups combined with the water absorption which shifts the esterification equilibrium.     

MCM-41的制备及用于吡拉西坦缓释性能研究

以十六烷基三甲基溴化铵（CTAB）为模板剂,正硅酸乙酯（TEOS）为硅源,合成MCM-41分子筛.以其做载体,吡拉西坦为模型药物,研究了吡拉西坦在MCM-41分子筛的负载与释放性能.并通过扫描电子显微镜（SEM）、粉末X-射线衍射（XRD）和傅立叶变换红外光谱（FT-IR）等方法对MCM-41分子筛以及负载吡拉西坦后的样品进行表征.研究了吡拉西坦的负载量及释放性能,定时检测了制备药物在模拟体液中的释放过程,从而确定以MCM-41作为吡拉西坦缓释载体的可能性.     

Synthesis and characterization of nanocomposite MCM-48-PEHA-DEA and its application as CO2 adsorbent

Three nanocomposites containing MCM-48-35PEHA-15DEA (35 and 15 as weight percent of amine addition), MCM-48-30PEHA-20DEA and MCM-48-25PEHA-25DEA of mesoporous silica MCM-48 modified by the mixture of pentaethylenehexamine (PEHA) and diethanolamine (DEA) have been synthesized and used to study the adsorption of carbon dioxide (CO₂). They are characterized by low angle x-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Brunauer-Emmet-Teller (BET) analysis. MCM-48-35PEHA-15DEA (as optimized adsorbent) shows CO₂ adsorption capacity of 0.51 (m·mol CO₂/g-adsorbent) at 1 bar and 298 K, much higher than CO₂ adsorption capacity on polyethyleneimine, pyrrolidinepropyl and polymerized aminopropyl loaded MCM-48.     

Synthesis of layered MCM-22(P) in the presence of hexamethonium cations and its transformation into EUO- and MWW-type zeolites

Layered MCM-22(P) was synthesized in the presence of hexamethonium (HM) cations. Compared to zeolite EU-1 (EUO-type structure), which crystallizes in similar conditions, its formation is favored at high HM concentrations (HM/SiO₂ ≥ 0.3) and in the absence of Na₂O. HM-containing MCM-22(P) was used as starting material for zeolite formation. Upon hydrothermal treatment, HM-MCM-22(P) transforms into zeolite EU-1 and upon calcination into a MWW-type zeolite. Transformation mechanisms were studied by standard characterization techniques such as XRD, SEM and TEM. Catalytic properties of the MWW-type zeolite obtained from this precursor were evaluated in a m-xylene isomerization reaction. Compared to zeolite MCM-22 prepared with hexamethyleneimine, a higher catalytic activity and an increased isomerization selectivity were observed and discussed.     

Magnetically active nanocomposite aerogels: preparation,characterization and application for water treatment

Journal of Porous Materials - Magnetically active nanocomposite aerogels were prepared, characterized and used for water treatment. These materials were characterized by SEM, TEM, XRD, FT-IR and...     

Metal oxides as heterogeneous catalysts for esterification of fatty acids obtained from soybean oil

The growing demand for renewable energy sources stimulates the development of new technologies for biofuel production. Biodiesel synthesis by esterification of fatty acids is a favorable route, because, differently from transesterification, it does not produce glycerin and uses cheaper raw materials. In this work the study of metal oxides and their performance as Lewis acid catalysts in the esterification of fatty acids obtained from soybean oil presented promising results in heterogeneous catalysis, with reaction yields as high as 89%. The influence of variables such as temperature, reaction time and the amount of catalyst in the reaction yield was also evaluated. The possibility of recycling tin oxide was also studied, showing that it was possible to reuse the catalyst up to ten times without significant losses in its catalytic activity.     

Structural effects of WO3 incorporation on USY zeolite and application to free fatty acids esterification

Zeolites have occupied a distinguished position due to their unique properties as solid acids and catalytic results achieved in several industrial reactions. This work studied the influence of supported WO₃ on USY zeolite structure, acidity and activity towards an esterification reaction. High dispersion of WO₃ species on USY was achieved, but at higher loading (?11.4%), microcrystalites of WO₃ were detected below the theoretical monolayer coverage (∼32%). Tungsten species were deposited preferentially inside the zeolite structure and interacted with the Brønsted sites of USY as well as on silanol surface groups with the formation of small aggregates. In addition, dealumination took place, especially in the samples with high WO₃ loading. USY had the most and the strongest acidic sites (Brønsted type), but the incorporation of WO₃ decreased the amount and the strength of the new sites. However, all WO₃/USY catalysts were more active than USY in the esterification of oleic acid with ethanol (conversion above 74%, 2 h at 200 °C). The calculation of the TOF for a 1 h reaction demonstrated that 11.4% WO₃/USY was the most active catalyst. Furthermore, it had the lowest rate of deactivation of acid sites after the reaction (∼13% after four cycles). The better performance of the 11.4% WO₃/USY sample was also attributed to a better distribution of strength of the acidic sites and a more hydrophobic character of the synthesized material.     

Spinnability of SPPESK and its application in esterification

The electrospinning of sulfonated poly(phthalazinone ether sulfone ketone) (SPPESK) and its blend with polyether sulfone (PES) were investigated and the blend nanofibers were applied as a catalyst in esterification. Attempts to electrospin pure SPPESK resulted in electrospraying rather than electrospinning. However, a blend polymer solution of SPPESK and PES resulted in smooth electrospinning when SPPESK content was lower than 9 wt%. The geometrical properties such as fiber diameter and distribution, surface chemical properties such as inter-molecular interaction and crystalline, mechanical properties were investigated by SEM, FTIR, XRD, etc. The catalytic activities of SPPESK-PES nanofibers were measured by esterification of ethanol with acetic acid. A pseudo-homogeneous model was established to describe the kinetics of esterification with nanofiber as a catalyst. The results showed that the SPPESK-PES blend nanofiber had a high specific surface area (46.7–58.9 m²/g), good mechanical properties, good catalytic properties (ethanol conversion up to 80 % when reacted 8 h), and good forward rate constants (10.0?×?10^?3–14.6?×?10^?3 L/(mol?min)).     

Essential fatty acids: its transformations and functions

Essential fatty acids, in animals, pertain to two different fatty acid families: the linoleic and the linolenic. These, and the non-essential families of oleic and palmitoleic are produced by action of the enzymes proper. The lack of essential fatty acids produces typical symptoms that are accompanied by fatty acid compositions, also typical, utilized with diagnostic value. The biological effects of essential fatty acids can be specific and nonspecific. The latter manifest themselves particularly in the phospholipid composition and, therefore, in the structure and fluency of the membranes. In contrast, specific essential fatty acids act in the formation of prostaglandins, prostacyclins, tromboxans and leucotriens. Each essential fatty acid produces specific effects, depending on the prostanoids formed and the tissue in question.     

The preparation and characterization of the methoxy derivatives of polyunsaturated fatty acids: Stabilized product analogs of lipoxygenase catalysis

The products from the action of soybean lipoxygenase on a series of polyunsaturated fatty acids have been converted in 2 steps into the corresponding methoxy derivatives. The product hydroperoxides were reduced in situ to alcohols with sodium borohydride. The ethers were generated by treatment of the alcohols with sodium hydride and methyl iodide in tetrahydrofuran. 13-Methoxy-9(Z),11(E)-octadecadienoic, 15-methoxy-11(Z),13(E)-eicosadienoic and 15-methoxy-5(Z),8(Z),11(Z), 13(E)-eicosatetraenoic acids were thus prepared. The methyl ethers were analyzed and the structures established by high performance liquid chromatography, nuclear magnetic resonance and infrared spectrometry, polarimetry and mass spectroscopy (as methyl esters). The methylation reaction proceeds without molecular rearrangements or racemiziation.     

A novel castor oil-based polyurethane/layered zirconium phosphonate nanocomposites: preparation,characterization, and properties

A new type of layered zirconium glycine-N,N-dimethylphosphonate (ZGDMP), with the functional groups –COOH, has been prepared and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). Situ polymerization method was employed to prepare castor oil-based polyurethane/layered zirconium phosphonate (PU/ZGDMP-n) nanocomposite films. The structure and morphology of ZGDMP in PU matrix have been characterized by XRD, SEM, TEM, and Fourier transform infrared spectroscopy. The results show that the morphology and properties of PU-based nanocomposites greatly depend on the functional groups –COOH because of the chemical reactions and physical interactions involved. The tensile test shows that the tensile strength and elongation at break for the nanocomposite films increase with the loading of ZGDMP as compared to those of the virgin PU.     

Cellulose esterification with fatty acids and acetic anhydride in lithium chloride/N,N-dimethylacetamide medium

Homogeneous esterification of cellulose with saturated fatty acids (n-octanoic to n-octadecanoic) was accomplished with acetic anhydride co-reactant in lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) medium. Cellulose mixed triesters (CMT) were obtained after 5 h at 130°C with an average of 2.2 acetyl groups and 0.8 fatty substituents per anhydroglucose unit. A mixed acetic-fatty anhydride, formed in situ, accounts for the grafting of the fatty moiety. The purified products were characterized and compared to the analogous cellulose simple fatty triesters (CST) that were synthesized from fatty acid chlorides in pyridine medium. Dynamic contact angle with water, glass transition, and storage moduli were correlated with the length of the fatty substituents. The CMT proved to be highly hydrophobic and more mechanically resistant than the CST.     

高自由酸油脂甲酯化反应动力学与相分离模拟

为了降低生物柴油的生产成本、提高过程效率,研究了高自由脂肪酸油脂一步法制取脂肪酸甲酯的催化剂体系.提出水解-酯化耦合反应机理,建立拟均相催化反应动力学模型,并借助多物理场模拟软件COMSOL Multiphy-sics和流程模拟软件Aspen Plus 11对甘油水混合物与脂肪酸甲酯的分离过程和相平衡进行模拟研究.结果...