Etherification of glycerol into short-chain polyglycerols over MgAl LDH/CaCO3 nanocomposites as heterogeneous catalysts to promote circular bioeconomy.

Glycerol is a byproduct from biodiesel production via conventional transesterification processes, representing approximately 10 wt% of the mass of biodiesel produced. Because of increasing biodiesel consumption, the volume of glycerol being produced has grown significantly, leading to a large surplus and, consequently, a dramatic drop in its market value. Thus, the valorization of glycerol into chemicals is a promising pathway toward sustainability in biodiesel industries. This study focused on upgrading biodiesel plant-derived glycerol into short-chain polyglycerols (PG), which are used as intermediates for producing emulsifiers in several consumer products, via catalytic etherification. To enhance environmental sustainability, solvent-free etherification of glycerol was performed over mixed oxides derived from magnesium-aluminum layered double hydroxides (MgAl LDH). For the first time, natural dolomite, a mixed calcium and magnesium carbonate (CaMg [CO3]2), was used as an Mg source in the preparation of MgAl LDH/CaCO3 nanocomposites via hydrothermal synthesis. The calcined MgAl LDH/CaCO3 nanocomposites were characterized by highly dispersed small crystallites of magnesium oxide. Their textural and acid-base properties were tuned by varying the Mg:Al molar ratio. The MgAl LDH/CaCO3 (an Mg:Al molar ratio of 1:1) calcined at 500 °C exhibited a superior catalytic performance to the MgAl LDH available commercially and the one synthesized by conventional co-precipitation. The nanocomposite catalyst displayed selectivity of >99% toward short-chain PG at 52.1 mol% glycerol conversion.

Single- and two-step hydrothermal liquefaction of microalgae in a semi-continuous reactor: Effect of the operating parameters.

This work investigated an influence of operating conditions on the biocrude yield and properties obtained from hydrothermal liquefaction (HTL) of Coelastrum sp. microalgae in a two-step sequential HTL (THTL) and a single-step HTL (SHTL) using a semi-continuous system. A higher biocrude yield with a lower nitrogen content was obtained with the THTL process than the SHTL one. The operating temperature, pressure and water flow rate were sequentially varied in a univariate analysis for a 2 h reaction time to optimize the obtained biocrude yield. Increasing the temperature improved the biocrude yield, but the second step temperature should not be higher than 320 °C to prevent the thermal cracking to gaseous compounds. The optimal conditions of THTL were preliminarily temperature of 200 and 320 °C and pressure of 7 and 20 MPa for the first and second step, respectively, both with a water flow rate of 0.50 mL/min.

Pt/Al2O3-catalytic deoxygenation for upgrading of Leucaena leucocephala-pyrolysis oil.

The aim of this study was to improve the quality of bio-oil produced from the pyrolysis of Leucaena leucocephala trunks via catalytic deoxygenation using Pt/Al2O3 (Pt content=1.32% (w/w)). The minimum molar ratio of oxygen/carbon (O/C) at 0.14 was achieved when the amount of catalyst was 10% (w/w, bio-oil) and was applied under 4 bar of initial nitrogen pressure at 340°C for 1h. The reaction mechanism of the catalytic deoxygenation, in terms of reforming, water-gas shift and dehydration reactions, was proposed. To consider the effect of different biomass types on the efficiency of catalytic deoxygenation, the bio-oils obtained from the pyrolysis of sawdust, rice straw and green microalgae were likewise evaluated for direct comparison.