Influence of Natural Mordenite Activation Mode on Its Efficiency as Support of Nickel Catalysts for Biodiesel Upgrading to Renewable Diesel.

In the present work, natural mordenite originated from volcanic soils in Greek islands, activated using HCl solution and HCl solution followed by NaOH solution, was used as support for preparing two metallic nickel catalysts (30 wt.% Ni). The catalysts were thoroughly characterized (XRF, N2 adsorption-desorption, SEM, XRD, TEM, H2-TPR, NH3-TPD) and evaluated for biodiesel upgrading to green (renewable) diesel. Double activation of natural mordenite optimized its supporting characteristics, finally resulting in a supported nickel catalyst with (i) enhanced specific surface area (124 m2 g-1) and enhanced mean pore diameter (14 nm) facilitating mass transfer; (ii) easier nickel phase reduction; (iii) enhanced Ni0 dispersion and thus high active surface; (iv) balanced population of moderate and strong acid sites; (v) resistance to sintering; and (vi) low coke formation. Over the corresponding catalyst, the production of a liquid consisting of 94 wt.% renewable diesel was achieved, after 9 h of reaction at 350 °C and 40 bar H2 pressure, in a semi-batch reactor under solvent-free conditions.

Nickel-Alumina Catalysts for the Transformation of Vegetable Oils into Green Diesel: The Role of Preparation Method, Activation Temperature, and Reaction Conditions.

Two nickel alumina catalysts containing 60 wt. % Ni were synthesized by wet impregnation and co-precipitation in order to study the effect of preparation methods on the catalytic efficiency concerning the transformation of sunflower oil into green diesel. The effect of activation temperature on the catalytic efficiency of the most active catalyst was also studied. The catalysts were characterized using various techniques and which were evaluated in the aforementioned reaction using a semi-batch reactor. The catalyst prepared by co-precipitation exhibited a higher specific surface area and smaller mean crystal size of the nickel nanoparticle (higher nickel metallic surface). These justify its higher efficiency with respect to the corresponding catalyst synthesized by wet impregnation. The increase in the activation temperature from 400 to 600 °C increased the size of the nickel nanoparticles through sintering, thus destroying the small pores. These led to a decrease in the nickel surface and specific surface area and, thus, to a decrease in the catalytic efficiency. The optimization of the reaction conditions over the most active catalyst (prepared by co-precipitation and activated at 400 °C) leads to the complete transformation not only of the sunflower oil (edible oil) but also of waste cooking oil (non-edible oil) into green diesel. The liquid produced after the hydrotreatment for these two feedstocks for 7 h, at H2 pressure 40 bar and temperature 350 °C using 100 mL of oil and 1 g of catalyst was composed of 97 and 96 wt. % of green diesel, respectively.

Rethinking the molecular structures of WVIOx sites dispersed on titania: distinct mono-oxo configurations at 430 °C and temperature-dependent transformations.

The structural properties of the (WOx)n phase dispersed on TiO2 (P25, anatase) at surface densities of 0.5-4.5 W nm-2 (i.e. up to approximately a monolayer) were explored by using in situ Raman and FTIR spectroscopy, in situ Raman/18O exchange and Raman spectroscopy in static equilibrium at temperatures of 175-430 °C. Deciphering the temperature and coverage dependence of the spectral features under oxidative dehydration conditions showed that (i) the (WOx)n dispersed phase is heterogeneous at 430 °C consisting of two distinct mono-oxo species: Species-I with C3v-like OW(-O-)3 configuration (WO mode at 1009-1014 cm-1) and Species-II with C4v-like OW(-O-)4 configuration (WO mode at 1003-1009 cm-1); (ii) the OW(-O-)3 site is formed with first order of priority and its formation ceases after the complete consumption of the most basic hydroxyls that are titrated first, hence is abundant at low coverage (<1.5 W nm-2); (iii) the OW(-O-)4 site prevails over the OW(-O-)3 site at medium to high coverage (≥2 W nm-2) and partially occurs in associated (polymerized) coverages above 2 W nm-2; (iv) lowering the temperature in the 430 → 250 → 175 °C sequence does not affect the structural and vibrational properties of OW(-O-)3 but leads to the gradual transformation of the OW(-O-)4 site to a di-oxo (O)2W(-O-)3 site (with a symmetric stretching mode at ∼985 cm-1) and the partial association of adjacent OW(-O-)4 units. All temperature-dependent structural/configurational transformations are fully reversible in the 430-175 °C range and are interpreted at the molecular level by a mechanism involving water molecules retained at the surface that act in a reversible temperature-dependent mediative manner resulting in hydroxylation (upon cooling, e.g. to 250 °C) and dehydroxylation (upon heating, e.g. to 430 °C). The Raman spectra obtained for the hydroxyl region confirm the successive hydroxylation/dehydroxylation steps during temperature cycles (e.g. 430 → 250 → 430 °C). One can tune the speciation of the dispersed (WOx)n phase under dehydrated conditions by appropriate control of temperature and coverage.

Mineral Montmorillonite Valorization by Developing Ni and Mo-Ni Catalysts for Third-Generation Green Diesel Production.

Four Ni catalysts and one Mo-Ni catalyst supported on montmorillonite were synthesized, characterized by various techniques and evaluated, under solvent-free conditions, for the production of green diesel from waste cooking oil. The optimum Ni content was found to be 20 wt.%. The addition of 2 wt.% Mo to the catalyst resulted in a considerable increase in the amount of green diesel hydrocarbons. The Mo species, moreover, led to a decrease in the (C15 + C17)/(C16 + C18) ratio, which is beneficial from the viewpoint of carbon atom economy. The promoting action of Mo was mainly attributed to the synergy between the oxygen vacancies on the surface of the well-dispersed Mo(V) and Mo(VI) oxides and the neighboring Ni0 sites. The optimum reaction conditions, for achieving a proportion of liquid product in the green diesel hydrocarbons (C15-18) equal to 96 wt.%, were found to be 350 °C, 3 g of catalyst per 100 mL of waste cooking oil and 13 h reaction time. These conditions correspond to an LHSV of 2.5 h-1, a value that is considered quite reliable from the viewpoint of industrial applications. Thus, the cheap and abundant mineral montmorillonite is proved a promising support for developing efficient Ni-Mo catalysts for green diesel production.

Bacterial Cellulose Production Using the Corinthian Currant Finishing Side-Stream and Cheese Whey: Process Optimization and Textural Characterization.

The aim of this work was to develop bioprocesses to produce a high-value microbial product, bacterial cellulose (BC), utilizing the industrial side-stream of Corinthian currants finishing (CFS), with/without the addition of N-sources and cheese whey, and at various process conditions (temperature, pH level, and sugar concentration). For the optimization of BC production, the response surface methodology based on the central composite design was applied. Among the possible retrieved combinations, the most ideal conditions for BC in CFS extracts supplemented with N-source were 28 °C, pH 6.42, and 46.24 g/L concentration of sugars. In a similar manner, the best conditions for BC production in CFS/whey mixtures were pH 6.36, 50.4% whey percentage in the mixture, and 1.7% yeast extract. The textural characteristics of the produced BC, at different times of production and using different drying methods, were studied by scanning electron microscopy, X-ray diffractometry, porosimetry, Fourier-transform infrared spectroscopy, and thermogravimetric/differential thermal analysis, revealing increased porosity of BC compared with delignified cellulosic materials of plant origin, and a level of crystallinity that depended on the BC production time. The proposed methodology can be used to produce foods with potential prebiotic properties, using the highly nutritious CFS and the abundant cheese whey effluent as raw materials.