Glycerol Production and Transformation: A Critical Review with Particular Emphasis on Glycerol Reforming Reaction for Producing Hydrogen in Conventional and Membrane Reactors

Abstract

Glycerol represents an emerging renewable bio-derived feedstock, which could be used as a source for producing hydrogen through steam reforming reaction. In this review, the state-of-the-art about glycerol production processes is reviewed, with particular focus on glycerol reforming reactions and on the main catalysts under development. Furthermore, the use of membrane catalytic reactors instead of conventional reactors for steam reforming is discussed. Finally, the review describes the utilization of the Pd-based membrane reactor technology, pointing out the ability of these alternative fuel processors to simultaneously extract high purity hydrogen and enhance the whole performances of the reaction system in terms of glycerol conversion and hydrogen yield.

Upgrading the Glycerol from Biodiesel Production as a Source of Energy Carriers and Chemicals—A Technological Review for Three Chemical Pathways

“…Also, GSR is an endothermic, high operation cost reaction, evolving towards products with an rise of the number of moles and thereby favored by low pressure and high temperatures [13,73], but if the two reactions occur in the same reactor, the hydrogen purity is reduced by the formation of substantial amounts of methane and carbon dioxide. Indeed, along with the reaction above, secondary or side reactions can occur, such as the formation of methane through methanation or glycerol hydrogenolysis or methanol steam reforming:…”

“…The common thermodynamic approach to evaluate the yield of hydrogen and other products and the influence of operative variables is performed by the minimization of the Gibbs free energy of the system [13,79,80,84]. As mentioned above, given the interconnection and complexity of the framework of chemical reactions involved in GSR for hydrogen production, intermediate byproducts end up in the product stream, reducing the purity of hydrogen delivered.…”

“…However, newly developed energy nickel-based catalysts were found with performance comparable to noble metal catalysts. The effort for improving the performance of nickel, aiming to improve it, is nevertheless surmounting the drawbacks of Ni-based catalysts [13,73,79].…”

“…The global production of crude glycerol was of about 4 Mtons in 2012 with a projection of 4200 ML by 2020 [14]. This increased production was of course reflected on a drastic falling of the stuff prices with the prices of refined glycerol declining from about 3200 $/ton in EU and 2000 $/ton in the US in 1995 to under 500 $/ton and 600 $/ton in 2010 [13]. The prices of crude glycerol were lower by about a threefold factor.…”

Glycerol steam reforming over calcium deficient hydroxyapatite supported nickel catalysts

“…for hydrogen fuel cells) [15]. The literature data show few routes in which this process could be realized: aqueous phase reforming [16], autothermal reforming [17], gasification in supercritical water [18] and steam reforming [19][20][21][22][23][24]. Especially big hopes are connected with the steam reforming reaction.…”