Valorization of Glycerol: Production of Added Value chemicals

Project leaders

Francesco Frusteri, AndrÁs Tompos

Agreement

UNGHERIA - HAS (MTA) - Accademia Ungherese delle Scienze

Call

CNR/HAS (MTA) 2016-2018

Department

Engineering, ICT and technologies for energy and transportation

Thematic area

Engineering, ICT and technologies for energy and transportation

Status of the project

New

Research proposal

The increase in biodiesel production results in the accumulation of glycerol in large quantities (it represents the 10wt.% of byproduct of transesterification reaction). Then, although the glycerol has many commercial applications in cosmetic and pharmaceutical industries, the development of new efficient ways of converting it to added-value products is necessary to support the eco-sustainability of the global process of biomass transportation. Considering its highly functionalized nature, it can readily be oxidized, reduced, halogenated, etherified and esterified to obtain alternative commodity chemicals. On this account, etherification or acetilization of glycerol represent some important approaches, as they will directly afford compounds that can be used as fuel additives, intermediates in the pharmaceutical industry, agrochemicals or non-ionic surfactants.
Specifically, an appealing strategy is represented by the transformation of glycerol into oxygenated fuel additives to gain benefits both in terms of environmental compliance and efficiency of diesel engines: i.e. glycerol ethers, acetyl glycerol and glycerol acetals, when used as additives, contribute to decrease the emissions of PM, hydrocarbons, CO and unregulated aldehyde; moreover, they can act as cold flow improvers and viscosity reducer for biodiesel, antiknock additives for gasoline and octane boosters for gasoline as an alternative to commercial trialkylethers. Nevertheless, several catalytic and technological aspects must be still considered in order to develop an economically feasible process of glycerol conversion.
The research here proposed will be focused on the study of some catalytic reactions to convert glycerol into added value products: i) etherification in presence of an O-alkylant agent to polysubstituted ethers; ii) ketalization of glycerol to solketal in presence of acetone; iii) etherification of glycerol to poliglycerols compounds. In such reactions, water is formed as by-product with consequent negative effects on catalytic activity and selectivity. In fact, the water formed during the reaction competes with reactants on the active site adsorption, preventing the total glycerol conversion and the formation of desired compounds. For this reason, in such a study an innovative batch reactor coupled with a permselective membrane able to eliminate the water of reaction is proposed. For technological reasons, the pervaporation configuration which exploits the gas phase recirculation through the membrane (instead of liquid phase) will be used: the advantage of this technique lies in the fact that the liquid phase, where the reaction occurs, is not influenced and furthermore a low energy consumption to perform the gas recirculation is required.
To date, the catalytic etherification of glycerol has been studied using isobutylene (IB) or tert-butyl alcohol (TBA) but, in this study, the use of bio-ethanol or bio-butanol (potential products from biomass fermentation) will be exploited. For example, the di- and tri-poly-butyl substituted ethers (DBGs and TBG) could have a large potential for diesel formulation because of their solubility in such fuel. Likewise, the mono-butyl glyceryl ether (MBG) could be used as green solvent for catalysis or as precursor for surfactants synthesis. Anyhow, glycerol etherification reaction in presence of linear alcohols is not widely studied since it is thermodynamically much more difficult than in presence of TBA.
As regards the acetylization reaction, glycerol reacts with an aldehyde or a ketone fo torm an acetal or a ketal respectively: in particular solketal is formed by the acid catalyzed reaction between glycerol and acetone. It can be used as an additive to improve transportation fuel properties as a combustion promoter, as a plasticizer in polymer industry and a solvent in pharmaceutical industry. Both these chemical transformations of glycerol proceed in the presence of an acid catalyst: traditionally the most used solid acids for the production of esters, ethers, acetals and ketals have been ion-exchange organic resins, such as A-15 and acid zeolites. Nevertheless, these catalysts have shown certain limitations due to low surface areas and lack of thermal stability, in the case of ion-exchange resins or mass transfer resistance for diffusion with in a microporous network, for zeolites. In this context, novel Hyflon-based catalysts will be used, since they have already shown a very good performance in the etherification of glycerol in presence of TBA, resulting to be more selective than commercial A-15 towards polyethers products. Such system combines the hydrophobic/hydrophilic and acid properties of the perfluorosulfonic ionomer Hyflon and the structural features of microspherical silica used as carrier.
The glycerol oligomerization to polyglycerols (PGs) is another possible route for glycerol valorisation due to the wide field of application of PGs as polymer additives, lubricants, plasticizers, emulsifiers, stabilizers and dispersants. In this case glycerol etherification is catalysed by both acid and bases, as mesoporous materials and base-modified zeolites. For this reason, different solid acid-base catalysts will be employed in the attempts of optimize the reaction conditions and control the glycerol polymerization.

Research goals

In such proposal, the aim is the valorisation of glycerol by converting it into added-values products by performing environmentally friendly catalytic processes. Specifically the attention will be focused at exploring the feasibility of efficient routes for additives production based on: i) etherification of glycerol to polyethers by using biobutanol or bioethanol; ii) acetylation of glycerol with biomass based acetone to solketal. The use of an innovative batch reactor coupled with a permselective membrane will be exploited in the attempt of overcoming equilibrium limits arising from the water (byproduct) formation during the reactions and improving desired compounds productivity. The elimination of the water could allow to shift the reaction towards polyethers which are more soluble into diesel fuel in respect to monoethers. The research will be focused towards the development of active solid catalysts which result to be selective and easily recovered/recycled and the optimization of reaction parameters (i.e. catalyst amount, temperature, reaction time, stirring speed, pressure, feed composition). Oligomerization of glycerol to polyglicerols will be studied in a batch reactor too, by using different acid-base solid catalysts, in the attempt of selectively produce one desired oligomers which could be used as fuel lubrificant or find wide field of applications in cosmetics, polymers, food-additives, pharmaceuticals industry and so on.

Last update: 19/04/2024