Babita Behera

Unraveling the packing pattern leading to gelation using SS NMR and X-ray diffraction: direct observation of the evolution of self-assembled fibers

A detailed understanding of the mode of packing patterns that leads to the gelation of low molecular mass gelators derived from bile acid esters was carried out using solid state NMR along with complementary techniques such as powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and polarizing optical microscopy (POM). Solid state 13C{1H} cross polarization (CP) magic angle spinning (MAS) NMR of the low molecular mass gel in its native state was recorded for the first time. A close resemblance in the packing patterns of the gel, xerogel and bulk solid states was revealed upon comparing their 13C{1H}CPMAS NMR spectral pattern. A doublet resonance pattern of 13C signals in 13C{1H}CPMAS NMR spectra were observed for the gelator molecules, whereas the non-gelators showed simple singlet resonance or resulted in the formation of inclusion complexes/solvates. PXRD patterns revealed a close isomorphous nature of the gelators indicating the similarity in the mode of the packing pattern in their solid state. Direct imaging of the evolution of nanofibers (sol–gel transition) was carried out using POM, which proved the presence of self-assembled fibrillar networks (SAFINs) in the gel. Finally powder X-ray structure determination revealed the presence of two non-equivalent molecules in an asymmetric unit which is responsible for the doublet resonance pattern in the solid state NMR spectra.

Catalytic cracking of jatropha-derived fast pyrolysis oils with VGO and their NMR characterization

Lignocellulosic biomass-derived fast pyrolysis oils are potential second-generation bio-fuels towards the reduction of greenhouse gas (GHG) emissions and carbon foot prints. This study pertains to co-process the Jatropha-derived heavy or tar fraction of fast pyrolysis oil (FPO) with vacuum gas oil (VGO) and hydrodeoxygenated fast pyrolysis oil (HDO) with VGO in a standard refinery fluid catalytic cracking (FCC) unit. The crude fast pyrolysis oil from Jatropha curcas is produced at 530 °C and atmospheric pressure using a bubbling fluidized bed pyrolyzer. The heavy fraction of FPO is hydrodeoxygenated over Pd/Al2O3 catalyst into HDO in an autoclave reactor at 300 °C and pressure of 80 bar. Further, HDO is co-processed with petroleum-derived VGO in an advanced cracking evaluation (ACE-R) unit to convert it into refinery FCC product slate hydrocarbons at a blending ratio of 5 : 95. FPO and HDO are characterized using 31P NMR, whereas FCC distillates, which are obtained on the co-processing of VGO with fast pyrolysis oil and HDO, are characterized using 1H and 13C NMR spectroscopy techniques. The 31P NMR analysis of crude FPO and HDO indicated that hydroxyl, carboxylic and methoxy groups are reduced during the hydrodeoxygenation of FPO. The experimental results at the iso-conversion level on the co-processing of HDO with VGO indicated a higher yield of liquefied petroleum gases (LPG), while lower yields of gasoline and LCO have been observed as compared to FPO co-processing with VGO and co-processing of pure VGO. Furthermore, the results of co-processing of FPO with VGO indicated that the yields of gasoline and LCO increased from 29 to 35 wt% and 14.8 to 20.4 wt%, respectively, whereas the yields of dry gas and LPG decreased from 2.1 to 1.4 wt% and 38.8 to 23.7 wt%, respectively, for an increase in the blending ratio from 5% to 20%. Therefore, it can be concluded that the co-processing of HDO with VGO in a FCC unit would be feasible in order to achieve a higher yield of LPG.

Microwave-assisted surface-initiated redox polymerization of acrylamide with functionalized graphene oxide for aqueous lubricant additive

A fast and efficient approach for the synthesis of nanocomposites of polyacrylamide-grafted-functionalized graphene oxide (FGO-PAM) through microwave-assisted surface initiated-redox polymerization (SI-RP) of acrylamide using functionalized graphene oxide and Ce(IV) ions as a redox couple in aqueous medium is reported. The nanocomposites are characterized by FT-IR, UV-Vis, Raman, XRD, TGA, FE-SEM, and HRTEM. These characterizations indicate a facile synthesis of macromolecular brushes of polyacrylamide on the surface of the graphene oxide. The high dispersion ability and composition ratio of the components facilitate the exploration and evaluation of the lubrication characteristics of this nanocomposite as an additive in an aqueous medium. The results showed a substantial reduction of the friction coefficient (46–55%) and improvement in anti-wear properties (13–37%), due to the formation of lubricating nanolayers of the nanocomposite between the two frictional surfaces, thus qualifying this nanocomposite as an aqueous lubricating additive for tribological application.

A graphene/hemin hybrid material as an efficient green catalyst for stereoselective olefination of aldehydes

A hemin/graphene composite, prepared by mixing an aqueous solution of graphene oxide (GO) with hemin and sonicating the suspension for 5 h at room temperature, was investigated for olefination of aldehydes using ethyl diazoacetate in the presence of triphenylphosphine. Efficient olefination of aromatic aldehydes with high (E)-selectivity was obtained, revealing that rGO/hemin is a promising heterogeneous catalyst for the olefination reaction. The as-synthesized catalyst could easily be recovered from the reaction mixture and was subsequently used for several runs without any significantly loss in activity and selectivity.

Chapter 12 NMR studies of FCC feeds, catalysts and coke

Abstract NMR has become an indispensable tool for characterizing a variety of complex materials, includingheavy petroleum fractions, catalysts and coke. Determination of average molecular parameter by NMR is useful for the analysis of complex hydrocarbons like coal liquids, heavy oils, synthetic oils and high boiling petroleum fractions. This not only gives a brief idea of the molecules present but can also be used for prediction of crackability and coking tendency of the feedstock under a particular condition of operation. Although solid state NMR has not attained the resolution as of liquids, it has been proved as a better technique for molecular level characterization particularly in catalysis. This is because of the use of magic angel spinning, cross polarization (CP) and heteronuclear decoupling techniques in conjunction with routine and sophisticated solid experiments. In this chapter, NMR has been used to study the feeds, catalysts and coke of the FCC process of refining industries. Fluid catalytic cracking (FCC) feeds from two Indian refineries are structurally characterized by inverse gated decoupled 13C and distortionless enhancement by polarization transfer (DEPT) NMR methods. Detailed structural analyses are completely supported by a range of NMR information including chemical shifts of 1H and 13C, CHn type distributions and 1H-13C connectivities from 2D HETCOR NMR. The average structural parameters obtained from NMR analysis give a brief idea about the nature of feeds used in the FCC units. 29Si MAS, 27Al MAS and 27Al 3QMAS NMR methods are employed to study the structure of fresh and spent catalyst obtained after stripping. Other analytical techniques like HPLC, microcalorimetry, XRD, TGA, IR are used to compliment or augment the inferences obtained from NMR. The changes in structure of catalyst are described in terms of framework Si/Al ratio, the relative distribution of various acid sites (different framework Si atoms) and the changes in their relative populations and changes in unit cell sizes. The variations in structure of two catalysts are correlated in terms of their quadrupolar coupling constant values at the site of octahedral and tetrahedral Al nuclei obtained from the MQMAS studies. The soluble and insoluble coke concentrates are extracted from the spent FCC catalysts by chemical methods and are studied by different NMR techniques. Conventional 1H and 13C NMR is used to derive the average structure of soluble coke. Quantitative data about the insoluble coke aromaticity are obtained from solid state13C SHPE/MAS NMR. The information of protonated and non-protonated carbons are obtained from Dipolar Dephasing (DD) experiments in combination with SHPE/MAS. The compositional variation in the feed and changes in catalyst properties are used to explain the nature and structural differences of the coke.