Kinetic modeling studies of heterogeneously catalyzed biodiesel synthesis reactions

The heterogeneously catalyzed transesterification reaction for the production of biodiesel from triglycerides was investigated for reaction mechanism and kinetic constants. Three elementary reaction mechanisms Eley-Rideal (ER), Langmuir-Hinshelwood-Hougen-Watson (LHHW), and Hattori with assumptions, such as quasi-steady-state conditions for the surface species and methanol adsorption, and surface reactions as the rate-determining steps were applied to predict the catalyst surface coverage and the bulk concentration using a multiscale simulation framework. The rate expression based on methanol adsorption as the rate limiting in LHHW elementary mechanism has been found to be statistically the most reliable representation of the experimental data using hydrotalcite catalyst with different formulations

Facile route to conformal hydrotalcite coatings over complex architectures:a hierarchically ordered nanoporous base catalyst for FAME production

An alkali- and nitrate-free hydrotalcite coating has been grafted onto the surface of a hierarchically ordered macroporous-mesoporous SBA-15 template via stepwise growth of conformal alumina adlayers and their subsequent reaction with magnesium methoxide. The resulting low dimensional hydrotalcite crystallites exhibit excellent per site activity for the base catalysed transesterification of glyceryl triolein with methanol for FAME production

Catalysing sustainable fuel and chemical synthesis

Concerns over the economics of proven fossil fuel reserves, in concert with government and public acceptance of the anthropogenic origin of rising CO2 emissions and associated climate change from such combustible carbon, are driving academic and commercial research into new sustainable routes to fuel and chemicals. The quest for such sustainable resources to meet the demands of a rapidly rising global population represents one of this century’s grand challenges. Here, we discuss catalytic solutions to the clean synthesis of biodiesel, the most readily implemented and low cost, alternative source of transportation fuels, and oxygenated organic molecules for the manufacture of fine and speciality chemicals to meet future societal demands

Catalytic conversion of lignin to low molecular weight compounds

Nowadays lignocellulosic materials represent the higher renewable natural resource in the world. These materials consist of 34–50% cellulose, 19–34% hemicellulose and 11–30% lignin. Unlike cellulose, lignin is a three-dimensional aromatic polymer including three main phenylpropane units, namely p-coumaril, coniferyl and sinapyl alcohol which are linked by C-O-C or C-C bonds. To valorize this material it is necessary to achieve its depolymerization to monomers or dimers that typically results from the cleavage of β-O-4 linkages. Literature already reported several approaches to depolymerize lignin using both homogeneous and heterogeneous catalysts. Yuan et all have considered a homogeneous route in this scope using NaOH as catalyst. This solution is however by far non-green leading to no-recyclable wastes. Heterogeneous catalysts offer an alternative. The use of noble metals like Pt or Rh supported on carbon, at 473 K, under H2 pressure, was shown to yield over 50% in monomers and dimers . Cheaper metals as copper represent a more versatile route but the reported example uses high energetic supercritical conditions. The use of inexpensive metals such as Ni may offer another alternative. In this study we propose an inexpensive route presenting results obtained using as active species, nickel in different environments such as NiOx, (NiAl)Ox, (NiMgAl)Ox thus looking also for the effect of basicity in this reaction. These materials were prepared using specific protocols and characterized by several techniques like: XRD, DRIFT, BET, and TEM. The catalysts were tested in autoclave conditions at different temperature (423-473K) under H2 pressure. The lignin was extracted from Miscanthus plants into formic acid / acetic acid / water mixture. Since it is not soluble in water its solubilization was achieved in an [BMIM]OAc ionic liquid, selected from a screening of a series of ILs. On the other side, the analysis of the reaction products is a complicate issue in this chemistry. This was carried out with a chromatographic system equipped with a Detector Triple Quad LC/MS, and a MS Ion Source type, working simultaneously in both APCI and ESI modes. The analysis of the reaction products indicated both polar and less polar compounds with a m/z signal varying from 80 till 900. The population of the different class molecules was carefully analyzed as a function of the nature of the catalyst and the reaction conditions. The higher extent of lignin depolymerization was around 54% and was obtained using a (NiAl)Ox catalyst. Under these conditions the predominant class was that with m/z of 200-300 a.u. Finally the stability of the catalysts was checked looking for their separation and recyclability in several successive cycles

Hydrogenolysis of lignin over Ru-based catalysts: The role of the ruthenium in a lignin fragmentation process

peer reviewedThe catalytic performances of two different classes of catalysts containing nickel or/and ruthenium as the active sites were studied in the depolymerisation of lignin isolated from Miscanthus × giganteus. The catalysts were prepared either by coprecipitation (ie, (RuNiMgAlO)x, (RuNiAlO)x, (NiAlO)x, (NiMgAlO)x) or by wet impregnation (ie, Ru/Al2O3) and characterized by nitrogen physisorption (BET), XRD, XPS, NH3-TPD, Raman and H2-TPR techniques. The experimental results indicate that the presence of ruthenium led to dimers as dominant products. © 2018 Elsevier B.V

Catalytic hydroprocessing of lignin under thermal and ultrasound conditions

Lignin isolated from Miscanthus x giganteus using acidic (FAL) and alkali (AL) conditions was thereafter subjected to the catalytic depolymerization under thermal or ultrasounds activation. The characterization of lignins was achieved by thermogravimetric analysis and FTIR. Three different classes of catalysts, containing nickel as active species, have been prepared in this scope: (i) nano-Ni by reduction of NiCl2 with NaBH4 under ultrasonication, (ii) Fe3O4-(NiMgAlO)x and (NiAlO)x by calcination of Mg(Ni)–Al hydrotalcite incorporated Fe3O4 followed by reduction with hydrogen, and (iii) NiO(111) nanosheets by reduction of Ni(NO3)2 with urea in benzyl alcohol. The catalysts were characterized by XRD and XPS techniques. Reduced mixed oxides displayed a moderate activity while a significant increase in conversion (up to 90%) was observed in the presence of nano-Ni(0). NiO(111) nanosheets catalysts performed very close to nano-Ni(0). The conversion and the mass distribution of the reaction products were strongly related to the procedure used for the extraction of ligning. In all the case AL led to a better depolymerization. The performances of the tested catalysts under ultrasound conditions were inferior to those tested under conventional heating conditions. The nature of the solvent was also found to be very important in this process. Thus, ionic liquid [BMIM]OAc led to the best results in autoclave conditions, and methanol under ultrasounds.TECHNOSE. Bioraffinerie végétale. Chimie et technologie des structures osidique

Nanocrystalline rhenium-doped TiO2: an efficient catalyst in the one-pot conversion of carbohydrates into levulinic acid. The synergistic effect between Brønsted and Lewis acid sites

Catalytic activity of TiO2, 2%Re–TiO2 and 10%Re–TiO2 in the conversion of carbohydrates into levulinic acid under autoclave conditions was evaluated. These materials were prepared by aerogel method, for the first time to the best of our knowledge, and characterized by XPS, SEM-EDX, DRIFTS, DR UV-vis, Raman, N2 adsorption/desorption isotherms, TGA and XRD. Further, the surface acidity was probed by NH3-TPD and pyridine-FT-IR where it was observed that increasing the amount of rhenium doped into TiO2 led to an increase in the total number of acid sites (Lewis + Brønsted) but with an overall lower strength. The presence of both Brønsted and Lewis acid sites led to the hypothesis that these materials may be well suited for conversion of carbohydrates into levulinic acid. Indeed a levulinic acid yield of 57% was reached over 10%Re–TiO2 for a low mass ratio catalyst to glucose (1 : 5). Moreover, the 10%Re–TiO2 catalyst was reused in the conversion of glucose for four catalytic cycles without a significant loss of the catalytic activity