The Pauper and The Prince: Glycerol in a View from Biofuels and Biorefineries

BECCARIA, A.; IGLESIAS, AA; COMELLI, R.A

e-Book: Glycerol: Production, Structure and Applications

Nova Science Publishers

Lugar: New York; Año: 2012;

Glycerol (1,2,3-propanetriol, abbrev. Gro), a sweet-tasting alcohol, was discovered in the 18th century (1779) by the Swedish chemist C.W. Scheele, who isolated the poly-alcohol after heating olive oil and litharge. The chemical is also known as glycerin or glycerine. It is abundant in nature after being a component of many lipids and a main compatible solute produced by cells for osmoregulation, to manage water activity variations in the medium. Also, many microorganisms are able to use glycerin as a source for carbon and energy. Main physicochemical properties of Gro can be summarized by being a colorless, odorless, highly hygroscopic and viscous liquid having a boiling point at 290 ºC, a specific gravity of 1.26 and a molecular weight of 92.09 (Pagliaro and Rossi, 2008). It forms crystals at low temperatures that tend to melt at 17.9 ºC. All its characteristics make of Gro a compound of utility for inclusion in different industrial processes and/or for being a key constituent in several chemical preparations. Without trying to make a detailed and complete listing of its applications, chief uses of the polyol include: -        Gro is extensively used in the pharmaceutical and cosmetic industries taken advantage of its emollient, humectant and demulcent properties (Pagliaro and Rossi, 2008). Also, its capability as a solvent (alone or as stabilizer in combination with water and alcohols) for preparation of different formulations and elixirs carrying active ingredients for variable purposes going from tinctures to key agents benign for specific treatments (i.e. theophyllin and xanthine drivatives with clinical applications for respiratory diseases). -        Food industry has Gro as a key compound of many utilities: preservative moistening agent for baked goods, preservative for juices, anti-crystallization mediator in candies, and solvent of chemicals serving as carriers of color and flavors (Pagliaro and Rossi, 2008). -        Gro is used as a plasticizer of different polysaccharides, such as starches (Qiao et al., 2011) or chitosan (Epure et al., 2011), this application being decidedly relevant for the production of biodegradable polymers with improved properties as plastic-like compounds. -        Gro conversion into nitroglycerin serves in contrasting applications (Pagliaro and Rossi, 2008). Thus, the nitro-derivative is a main component in production of dynamites and explosives; although it also has a laudable use as an active component in medication for heart disease, since nitroglycerin has the capacity of generate nitric oxide (Agvald et al., 2002). Although the many faceted uses and applications for Gro, its market value is in down-hill, principally because the rapid expansion of biodiesel production that generated a glut of the polyol (Johnson and Taconi, 2007). Biodiesel is produced from triacylglycerides contained in animal fats or vegetable oils through transesterification with low molecular weight alcohols (mainly methanol or ethanol). The process generates methyl-(or ethyl-) esters of fatty acids as the major biodiesel product and about 10% (v/v) of Gro as a by-product. This is not only converting the polyol in a low value chemical; but it is further creating an environmental problem because of the limited possibility for disposal, which is also quite expensive (da Silva et al., 2009). The situation is obligating to revisit current uses and the design of new processes for adding value to the propanetriol. For the latter, overall possibilities include the finding for new applications of the chemical as well as its conversion to other molecules serving in different industry systems, in a way improving competitiveness in the productive chain of the biodiesel business. Paradoxical to the relatively pauper state of affairs for Gro, it can be visualized as a key compound for developing processes in the emerging field of biorefineries. Limited reserves of petroleum and the associated dramatic increases in its price, together with critical environmental concerns and climate changes provoked by the use of fossil fuels are creating obligatory demands for generate renewable fuels as well as for reconvert industrial processes. The necessity is to make them more ecology-friendly and compatible with a sustainable environment. This leads to the concept of biorefinery, which embraces different technologies allowing convert biomass into materials, chemicals and energy (Ohara, 2003; Kamm and Kamm, 2004, 2007; Schell et al., 2008; Amidon and Liu, 2009). In this framework, the positioning of Gro as a by-product in a process to obtain biofuel that needs to be revalorized is relevant and it represents a fair challenge for the development of biorefinery tools. In the present work we analyze current and potential ways to valorize glycerol. Globally, we review chemical as well as biological approaches and we analyze possibilities for combine strategies to develop biorefinery-like solutions.