The paper describes the results of a co-operative research project aimed at the energetic exploitation of the biodiesel derived glycerol. The research objective is the definition and validation of a synthesis process for conversion of glycerol in an oxygenated fuel additive (glycerol alkyl–ether) suitable for blending with diesel and biodiesel.
The employed facilities, methodologies and first results from engine tests are described, including a preliminary Life Cycle Assessment (LCA).
Etherification of glycerol with tert-butyl alcohol and isobutylene allowed to identify the suitable experimental conditions required to obtain a mixture predominantly composed of higher glycerol ethers (GEM). Novel catalysts, based on perfluorosulphonic ionomers as active species and spherical silica as support, were found to be stable and easy reusable allowing to obtain mixtures containing very low amount of monoethers and oligomers considered as undesired products.
Engine tests with blends of GEM in diesel fuels revealed good combustion and emission performances when compared both to neat diesel fuel and a blend diesel/biodiesel.
LCA analysis indicates that the GEM/diesel blend generates an environmental impact which is lower than the one of neat diesel.
Pending the large-scale production of second generation biofuels [1], in the near future the biodiesel production should increase in order to approach the EU target of biofuel consumption for the year 2020 [2]. As a result, also the production of glycerol, which is the main by-product of the transesterification process, will grow proportionally. So, the question arises from a cost-effective and efficient use of such a glycerol surplus. The combustion of glycerol “as it is” would represent a desirable solution. Unfortunately, because of its detrimental physical and chemical properties, raw glycerol is hardly usable in conventional energy production plants, such as fuel burners or internal combustion engines (ICEs). However, a proper design of the burner and refractory combustion chamber could allow to effectively burn crude glycerol, although a high particulate matter concentration is detected at the exhaust [3]. Alternative routes for glycerol recovery are represented by its energetic upgrading into high value products, such as synthesis of gases [4] and oxygenate additives for gasoline, biodiesel and diesel fuels [5].
In order to increase the energetic exploitation of the biodiesel production chain, a co-operative research project was started in 2010, aimed at recycling the biodiesel-derived glycerol in energy generating systems. The project was partially founded by MiPAAF, the Italian Ministry of Agriculture, Food and Forestry. It consists of three research lines: (i) conversion of the raw glycerol in a fuel suitable for ICEs; (ii) pyrolysis of biomass soaked with glycerol for syngas production; (iii) combustion of glycerol in a flameless oxy-burner.
The first research line, described in the present work, is focused on the development of a synthesis process for converting glycerol in a fuel suitable for ICEs. The final goal should be the definition and validation of an etherification process of raw glycerol for the production of an oxy-fuel that can be blended with diesel and biodiesel. An industrially relevant route for the conversion of glycerol into oxygenated chemicals involves the etherification to tert-butyl ethers [6], [7] and [8]. In particular, since mono-tert-butyl ethers of glycerol (MBG) have a low solubility in diesel fuel, the etherification of glycerol, taking place with a consecutive reaction path, should be mainly addressed towards the formation of a mixture of di- (DBG) and/or tri-ethers (TBG) [6], [7], [8] and [9].
The project aims at a complete evaluation of the production process (in laboratory scale), as well as the validation of the Glycerol–Ethers Mixture (GEM) of DBG and/or TBG as fuel in experimental engine tests, with two main advantages: (i) the increase of the energy and CO2 Well-To-Wheel (WTW) factor of the biodiesel supply chain; (ii) the addition of a high-quality oxy-fuel in the mineral fuels which contributes to the reduction of pollutant emissions from diesel engines.
The GEM production process for glycerol exploitation was also subjected to Life Cycle Analysis (LCA), from which the impact to human health, quality of ecosystems, and resources has been evaluated. The present paper illustrates the employed facilities, methodologies and the results of the research activity.
The preliminary results of a co-operative research project aimed to the energetic exploitation of the biodiesel chain derived glycerol have been discussed. It was outlined that:
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New Hyflon® based catalysts supported on spherical silica are promising systems for carrying out the etherification reaction of glycerol with isobutylene, offering the possibility to operate at low temperature (70 °C) with total glycerol conversion to GEM and very low mono tert-butyl ether glycerol and di-isobutylene formation.
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The obtained GEM is effective for in-cylinder soot suppression without significant impact on the in-cylinder combustion process and on the other regulated pollutant emissions (NOx, HC and CO).
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LCA indicates that the GEM/diesel blends (both with TBA and IB additives) generate in a combustion process a much lower impact than the neat diesel.
The described results represent a first global evaluation of the opportunity in the production and use a glycerol-derived synthetic in a diesel engine for automotive application. It is implied that further investigations are required to assess:
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Issues related to the use of raw glycerol in the production chain.
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GEM compatibility with all required fuel standards.
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GEM impact on engine reliability.
