The ever increasing industrial production of commodity and specialty chemicals inexorably depletes the finite primary fossil resources available on Earth. The forecast of population growth over the next 3 decades is a very strong incentive for the identification of alternative primary resources other than petro-based ones. In contrast with fossil resources, renewable biomass is a virtually inexhaustible reservoir of chemical building blocks. Shifting the current industrial paradigm from almost exclusively petro-based resources to alternative bio-based raw materials requires more than vibrant political messages; it requires a profound revision of the concepts and technologies on which industrial chemical processes rely. Only a small fraction of molecules extracted from biomass bears significant chemical and commercial potentials to be considered as ubiquitous chemical platforms upon which a new, bio-based industry can thrive. Owing to its inherent assets in terms of unique process experience, scalability, and reduced environmental footprint, flow chemistry arguably has a major role to play in this context. This review covers a selection of C2 to C6 bio-based chemical platforms with existing commercial markets including polyols (ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, 1,4-butanediol, xylitol, and sorbitol), furanoids (furfural and 5-hydroxymethylfurfural) and carboxylic acids (lactic acid, succinic acid, fumaric acid, malic acid, itaconic acid, and levulinic acid). The aim of this review is to illustrate the various aspects of upgrading bio-based platform molecules toward commodity or specialty chemicals using new process concepts that fall under the umbrella of continuous flow technology and that could change the future perspectives of biorefineries.

Continuous Flow Upgrading of Selected C2-C6 Platform Chemicals Derived from Biomass.

Once a biorefinery is ready to operate, the main processed materials need to be completely evaluated in terms of many different factors, including disposal regulations, technological limitations of installation, the market, and other societal considerations. In biorefinery, glycerol is the main by-product, representing around 10% of biodiesel production. In the last few decades, the large-scale production of biodiesel and glycerol has promoted research on a wide range of strategies in an attempt to valorize this by-product, with its transformation into added value chemicals being the strategy that exhibits the most promising route. Among them, C3 compounds obtained from routes such as hydrogenation, oxidation, esterification, etc. represent an alternative to petroleum-based routes for chemicals such as acrolein, propanediols, or carboxylic acids of interest for the polymer industry. Another widely studied and developed strategy includes processes such as reforming or pyrolysis for energy, clean fuels, and materials such as activated carbon. This review covers recent advances in catalysts used in the most promising strategies considering both chemicals and energy or fuel obtention. Due to the large variety in biorefinery industries, several potential emergent valorization routes are briefly summarized.

Recent Advances in Glycerol Catalytic Valorization: A Review

Carbon dioxide methanation over Ni-Cu/SiO2 catalysts

Conversion of biodiesel synthesis waste to hydrogen in membrane reactor: Theoretical study of glycerol steam reforming

Ni supported and co-precipitated catalysts promoted by Mg were evaluated for hydrogen production by the glycerol steam reforming. The samples were prepared by incipient wetness impregnation of alumina and by the continuous co-precipitation method. The catalysts were characterized by XRD, SBET, TPR, NH3-TPD, TPO and SEM/TEM. The catalytic tests were performed in the range from 500 to 650 °C in a fixed bed tubular reactor. The gaseous products were analyzed online by gas chromatography. It was found that the partial substitution of Ni by Mg improves the dispersion of Ni, decreases the acidity of the catalysts and increases the resistance to sintering of Ni. The unreduced catalysts presented higher selectivity for H2 than the previously reduced catalysts. The catalyst unreduced impregnated with 20% Ni showed the highest selectivity in the production of hydrogen (55%), at the temperature of 650 °C. Unreduced samples prepared by co-precipitation presented smaller Ni0 crystallite size after the reaction. The catalyst reduction step is unnecessary for this reaction.

Hydrogen production by glycerol steam reforming over Ni based catalysts prepared by different methods.

Catalytic conversion of glycerol to olefins over Fe, Mo, and Nb catalysts supported on zeolite ZSM-5

Ni–Al and Co–Al mixed oxides derived from hydrotalcites were prepared by coprecipitation and evaluated in CO2 methanation. The catalysts were characterized by N2 physisorption, XRD, H2-TPR, NH3-TPD, CO2-TPD, TPO and SEM/EDS. The catalytic tests were performed at atmospheric pressure in a fixed-bed reactor, with a gas mixture of CO2/H2/N2 in a ratio of 1/4/15 and GHSV of 60 000 mL gcat−1 h−1, in the temperature range of 200−400 °C. The high density of basic sites and enhanced reducibility presented in the Ni–Al catalyst favored CO2 adsorption, which allows the achievement of around 90% CO2 conversion and 100% CH4 selectivity at 300 °C. The low number of basic sites found in Co–Al was responsible for the lower methanation activity. Both catalysts showed high stability at 400 °C for 5 h without noticeable deactivation, due to the high resistance to sintering associated with the small size of the metal crystallites.

Dirléia S. Lima

Papers

Hydrogen production by glycerol steam reforming over Ni based catalysts prepared by different methods.

Catalytic conversion of glycerol to olefins over Fe, Mo, and Nb catalysts supported on zeolite ZSM-5

CO2 methanation over Ni–Al and Co–Al LDH-derived catalysts: the role of basicity

Hydrothermal synthesis of analcime without template

New insights on the electronic factor of the SMSI effect in Pd/TiO2 nanoparticles