Para-xylene Maximization—Part VI: Shape-Selective Platinum-Promoted Methylation of Toluene

Abstract

The need for increased production of para-xylene, which is the primary material for producing the polyester fibers, activated this research. Although the alkylation reaction is acid catalyzed, we found that a Pt promoter activates this reaction by virtue of the presence of a vacant d-orbital in the Pt atom. In this work, a series of catalysts containing 0.1, 0.2, or 0.3% Pt in H-ZSM-5 zeolite was tested for alkylating toluene with methanol, aiming to produce the xylenes and maximizing para-xylene production in a temperature range of 300°C–500°C in the presence of hydrogen flow in a continuous-flow fixed-bed reactor. The catalysts were characterized by temperature programmed desorption (TPD) of ammonia for acid sites distribution analysis and platinum dispersion in the catalysts by hydrogen chemisorption. Moreover, the diffusion resistance extent in the current catalysts during the alkylation reaction has been evaluated via estimation of the Thiele modulus, Φ _L . The selectivity for para-xylene production was found to increase systematically with increasing the Pt content in the catalysts, whereas the unloaded zeolite did not follow this order. The Φ _L values calculated were accordingly found to increase also with increasing Pt content in the catalysts. Although para-xylene was the highest on the 0.3% Pt/H-ZSM-5 catalyst, the heavy undesired trimethylbenzenes were the lowest to be formed on this catalyst.     

Effect of pendant group of polysiloxanes on the thermal and mechanical properties of polybenzoxazine hybrids

Polybenzoxazine (PBa) was successfully hybridized with polysiloxanes by synchronizing two reactions; ring-opening polymerization of benzoxazine (Ba) and sol–gel process of diethoxysilanes. Diethoxydimethylsilane, diethoxymethylphenylsilane, and diethoxydiphenylsilane were used as precursors for the formation of polydimethylsiloxane (PDMS), polymethylphenylsiloxane (PMPS), and polydiphenylsiloxane (PDPS), respectively. The effect of pendant group of polysiloxane on the optical, mechanical, and thermal properties of PBa–polysiloxane hybrids was studied. The progress of sol–gel process was confirmed by IR, ¹H NMR and size exclusion chromatography. Opaque PBa–PDMS hybrid films were obtained up to 15 wt% of PDMS content, corresponding to the phase separation with 1–2 μm domain size of PDMS as observed from the scanning electron microscope. Meanwhile, transparent PBa–polysiloxane hybrid films were obtained up to 29 wt% for PMPS and 36 wt% for PDPS, which revealed no apparent domain of PMPS and PDPS, indicating high compatibility of the polysiloxanes with PBa. Dynamic viscoelastic analysis (DMA) of the PBa–PDMS hybrid revealed two glass transition temperatures corresponding to PDMS and PBa components, while the DMA of the PBa–PMPS and PBa–PDPS hybrids revealed only one glass transition temperature. The tensile strength and elongation at break of the hybrid films increased with increasing polysiloxane content. Thermogravimetric analysis revealed high weight residue at 850 °C for PBa–polysiloxanes with phenyl group.     

Thermal and textural characteristics of modified silica

A silica gel characterised as predominently microporous, with the remaining pores of limited dimensions which do not permit capillary condensation, is modified with aqueous solutions of acetic acid, glycine and β-alanine. The modified samples are investigated and compared with a water soaked sample by means of differential thermal analysis, thermogravimetry and i.r. spectroscopy. Textural measurements are also carried out on the parent samples and those produced in the temperature range 110–600°C. Acetic acid is both physically and chemically adsorbed; a surface ester is formed. Both amino acids are physically adsorbed but no chemical interaction has been detected. Glycine and β-alanine decompose differently when adsorbed on to the silica surface than when in the pure state. The specific surface area decreases upon modification, reaching half the value of the pure silica for the β-alanine modified sample. Pore structure analysis, shows that the microporous nature of the modified samples decreases in the modifier order acetic acid < glycine < β-alanine. The adsorbed β-alanine molecules block most of the micropores present.     

Analysis of K sets of data, with differential emphasis on agreement between and within sets

A general class of methods for (partial) rotation of a set of (loading) matrices to maximal agreement has been available in the literature since the 1980s. It contains a generalization of canonical correlation analysis as a special case. However, various other generalizations of canonical correlation analysis have been proposed. A new general class of methods for each such alternative generalization of canonical correlation is proposed. Together, these general classes of methods form a superclass of methods that strike a compromise between explaining the variance within sets of variables and explaining the agreement between sets of variables, as illustrated in some examples. Furthermore, one general algorithm for finding the solutions for all methods in all general classes is offered. As a consequence, for all methods in the superclass of methods, algorithms are available at once. For the existing methods, the general algorithm usually reduces to the standard algorithms employed in these methods, and thus the algorithms for all these methods are shown to be related to each other.     

5-Nitro-1,2,4-triazole-3-one: A review of recent advances（英）

The 3-Nitro-1,2,4-triazole-5-one (NTO) is a high energydensity materials of keen interest for both commercial and scientific worlds owing to its reduced sensitivity, better thermal stability and high performances. It plays a significant role to replace the current energetic ingredients. In this review, we summarize various strategies involved in the synthesis of NTO as well as the existing approaches to tailor its particle morphology and sizes. The most prominent properties of NTO, such as insensitivity and performance, which are usually required to produce efficient formulations,have been concisely discussed. In addition, this overview reports on some newer forms of NTO including derivatives and co-crystals available inthe literature, which can enhance the NTO features and extend its applications. The advantages and shortcomings of various NTO forms for specific and potential use are also highlighted together with the attempts made to overcome these issues. Therefore, efforts will certainly continue to improve characteristics and performances of NTO either by chemical modification or by co-crystallization in order to produce promisingformulations for widespread applications in the near future.     

Curing behaviour and mechanical properties of dicarboxylated telechelic poly(ε-caprolactone)s/styrene–(epoxidized butadiene)–styrene triblock copolymer reactive blends

End-carboxylated telechelic poly(ε-caprolactone)s (XPCLs) with different molecular weights were blended into a triblock copolymer of styrene–(epoxidized butadiene)–styrene (ESBS) to investigate the curing behaviour and the mechanical properties of the XPCL/ESBS binary reactive blend. It was found that the time–torque cure curve showed a significant torque increase after a very short induction period, in which the degree of the torque increase depended on the molecular weight of XPCL. This indicates that substantial crosslinking reaction takes place between the XPCLs and the epoxidized polybutadiene of the ESBS. Stress–strain curves of the blends after cure depended on the molecular weight of XPCL and the blend ratio. The XPCL/ESBS blends had sufficient thermal stability to show elastomeric behaviour at elevated temperature above the glass transition of the styrene domains of ESBS because of formation of crosslinking points between unlike polymer components by the reactive blending. © 1999 Society of Chemical Industry     

Tensile properties,degradation behavior,and water absorption of sago starch plastic films

Sago starch plastic films were prepared by a blending and casting method using various amounts of additives. The additives were glycerol (GLY), polyethylene glycol (PEG), and glutaraldehyde (GLU). Results indicated that the films had an optimum tensile strength of about 2.6 MPa and an optimum elongation at break of 74%. Meanwhile, a GLU content of five parts by weight gave the best tensile properties. Elongation at break of the films increased while tensile strength decreased upon increasing the level of plasticizer (GLY and PEG). The addition of plasticizer also increased the water absorption and soil burial degradation rate. However, the addition of GLU gave opposite results. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers     

A simple pathway in preparation of controlled porosity of biphasic calcium phosphate scaffold for dentin regeneration

A simple pathway in preparation of biphasic calcium phosphate scaffold of hydroxyapatite/beta-tricalcium phosphate with controlled pore size, shape and porosity using phosphoric acid and calcium carbonate was successfully developed. Microporosity was controlled by adjusting temperature and soaking time of the sintering process while macroporosity was obtained through addition of polyethylene spherical particles. The advantage of this method is that a highly pure biphasic calcium phosphate scaffold consisting of hydroxyapatite/beta-tricalcium phosphate in a controlled ratio of 20/80 with a mean pore size of 300 μm and 65% porosity can be produced. These properties of scaffold are of high potential for use in dentin regeneration.     

Polypropylene/(waste tire dust)/(short glass fiber composites): Effects of silane coupling agent and dynamic vulcanization

Polypropylene (PP) and waste tire dust (WTD) were internally mixed with various amounts of short glass fiber (SGF) to form a series of PP/WTD/SGF composites, with and without addition of a silane coupling agent, γ‐aminopropyltrimethoxysilane (γ‐APS), and dynamic vulcanization (DV). The effects of γ‐APS, and DV on the properties of the composites were investigated. The PP/WTD/SGF composites were prepared by using WTD of 250–500 μm dimensions at different SGF loadings (5, 10, 15, and 20 parts per hundred parts of polymer). The results revealed that the addition of γ‐APS and DV increased the equilibrium torque, tensile properties except elongation at break, and swelling resistance of the composites. Because of the incorporation of γ‐APS and DV, the thermal stability was enhanced, and scanning electron micrographs showed improved adhesion between the PP/WTD matrix and SGF. Analysis by Fourier transform infrared was performed on the composites with and without addition of γ‐APS and DV in order to study the interactions among the PP, WTD, SGF, and the amino functional group of the silane. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers.     

Response of mosquitoes (Diptera: Culicidae) to carbon dioxide and octenol in Egypt

The radioprotective effect of the leaf extract of Ocimum sanctum (OE) in combination with WR-2721 (WR) was investigated on mouse bone marrow. Adult Swiss mice were injected intraperitoneally (i.p.) with OE (10 mg/kg on 5 consecutive days), or 100-400 mg/kg WR (single dose) or combination of the two or double-distilled water (DDW) and whole-body exposed to 4.5 Gy gamma-irradiation (RT). Metaphase plates were prepared from femur bone marrow on days 1, 2, 7 and 14 post-treatment and chromosomal aberrations were scored. The maximum number of aberrant cells was observed at 24 h after irradiation in all the groups. However, pretreatment with OE or WR individually resulted in a significant decrease in aberrant cells as well as different types of aberrations. The combination of the two further enhanced this effect; resulting in a 2-fold increase in the protection factor (PF = 6.68) compared to 400 mg/kg WR alone. The percent aberrant cells decreased linear-quadratically with WR dose when given individually, while in the OE + WR pretreatment animals the values showed a linear dose response. Combination of OE with WR doses above 200 mg/kg completely eliminated rings, polyploidy and pulverization of chromosomes. Percent aberrant cells decreased with time in all groups, though the values remained higher than normal even on day 14 in the RT alone as well as those treated with single agent + RT. WR doses above 200 mg/kg before RT resulted in significantly higher frequency of aberrant cells compared to RT and OE + RT groups on day 14, suggesting delayed WR toxicity; but combination of OE with WR brought down these values to normal level, indicating that OE combination, in addition to enhancing WR protection, may also act as a detoxifier. The protective effect of OE and WR is also reflected in the enhancement of bone marrow CFU survival. Both OE and WR possessed significant free radical scavenging activity in vitro. The combination of the two further enhanced this effect, suggesting that the enhanced free radical scavenging activity by combining the two protectors results in the higher bone marrow cell protection. The significant elevation in chromosome protection obtained by combining OE with WR, with reduction in the latter's toxicity at higher doses, suggests that the combination may have promise for radioprotection in humans.