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Fuel 86 (2007) 2806–2809

Glycerol based automotive fuels from future biorefineries

Sandun Fernando *, Sushil Adhikari, Kiran Kota, Ranjitha Bandi

Department of Agricultural and Biological Engineering, Mississippi State University, Mississippi State, MS 39762, USA

Received 22 June 2006; received in revised form 12 February 2007; accepted 9 March 2007Available online 16 April 2007

Abstract

After the energy crisis in the 1970s, considerable attention was focused on the development of alternate energy resources. At present,there is a renewed interest in biofuels due to increasing concerns about energy security and environmental pollution. One such biobasedfuel that is being widely commercialized is biodiesel. With the increasing production of biodiesel a glut of glycerol has been created, caus-ing market prices to plummet. This situation warrants finding alternative uses for glycerol. This study attempted to identify the possi-bility of blending glycerol and glycerol based co-products, such as propanediol and propanol with gasoline as oxygenates. The studyrevealed that there is a possibility to use glycerol and its derivatives with gasoline as an automotive fuel. Octane number and the heatingvalue of different mixtures of gasoline, ethanol, and glycerol and its derivatives are presented.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Glycerol; Propanediol; Propanol; Gasoline; Ethanol

1. Introduction

Considerable attention was focused on the developmentof alternate energy sources after the energy crisis in the1970s. Currently, there is a renewed interest in renewablefuels due to skyrocketing energy prices coupled withincreased concerns of dwindling petroleum resources[1,2]. Biomass is one of the few resources that have thepotential to meet the challenges of sustainable and greenenergy systems. In order to produce useful chemicals andfuels from biomass, a system similar to a petroleum refin-ery is proposed, which is known as a ‘‘biorefinery’’, andthe details regarding biorefineries can be found elsewhere[3]. According to the National Renewable Energy Labora-tory (NREL), ‘‘a biorefinery is a facility that integrates bio-mass conversion processes and equipment to produce fuels,power, and chemicals from biomass’’ [4]. To achieve thegoals of sustainable development, biorefineries have to playa dominant role in the future. Ethanol and biodiesel plantscan be taken as example constituents of biorefineries. The

0016-2361/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.fuel.2007.03.030

* Corresponding author. Tel.: +1 662 325 3282; fax: +1 662 325 3853.E-mail address: sf99@abe.msstate.edu (S. Fernando).

main goal of a biorefinery is to produce high-value low-vol-ume chemicals and low-value high-volume fuels with a ser-ies of unit operations. Ethanol and biodiesel are low-valuehigh-volume outputs of biorefineries that are already usedin transportation. The chemicals of concern, i.e. glycerol,propanediol, propanol and ethanol, are also expectedproducts from future biorefineries.

With the increased production of biodiesel, a glut ofglycerol has been created [5,6] which not only has reducedworld glycerol market prices but also has generated envi-ronmental concerns associated with contaminated glyceroldisposal. Although blending glycerol with gasoline is a pos-sibility, immiscibility of glycerol in gasoline hinders thisoption. We have attempted to convert glycerol into a prod-uct that could be blended with gasoline. Glycerol can becatalytically converted into a mixture of lower alcoholswith sulfated ZrO2 and other catalysts or with microorgan-isms such as Klebsiella pneumoniae, Clostridium pasteuria-

num, Citrobacter freundii, and Enterobacter agglomerans

[7–11]. Converting glycerol to a mixture of alcohols withspecific concentrations enables glycerol to be blended withgasoline. In this study, we attempt to establish specificcomponent concentrations that keep a three-component

S. Fernando et al. / Fuel 86 (2007) 2806–2809 2807

(ternary) system consisting of gasoline, glycerol, and anamphiphile in a single microemulsion phase making themmiscible in each other. Propanol and ethanol were usedas amphiphiles to make glycerol and gasoline miscible. Thisconcept could be used by biodiesel producers to develop aco-product that could be blended with gasoline to makefuture biorefinery production economics more favorable.

There are several advantages of blending oxygenatedhydrocarbons into petroleum based fuels. The most evidentis the displacement of petroleum fuel by the renewablecounterparts. Also oxygenated hydrocarbons are reportedto improve the tailpipe emissions profile significantly [7].Blends of 10% dry ethanol with unleaded gasoline (E10)and E85 (blend of 85% ethanol with 15% gasoline) arealready marketed in several countries around the worldincluding the United States for spark ignition engines[12,13]. Ethanol–diesel emulsions can give beneficial resultsin terms of emission reduction in diesel engines [14]. About41% reduction in particulate matter and 5% in NOx emis-sions can be realized with 15% ethanol–diesel blends[14,15]. Also, blends up to 20% of biodiesel in petroleumdiesel, widely popular around the world in compressionignition engines, are reported to improve emissions signifi-cantly [16]. The aforementioned renewable alternatives areexpected to displace petroleum based fuels while helpinglong-term sustainability of the biorefinery industry, whichis still in its infancy.

The overall objective of this research is to find usefulapplications of the low-value high-volume products thatare produced from biorefineries. This paper discusses theternary phase diagrams of selected biorenewable compo-nents. Based on the stability of the systems, selected mix-tures were analyzed for octane number with a view to theidea that certain mixtures could be used as alternate fuelsfor gasoline engines. Heating values of the selected mix-tures are also determined based on the simple mathematicalformula given in:

E ¼P3

i¼1V iqiEiP3

i¼1V iqi

; ð1Þ

where Vi is the volume of the fuel i in the mixture, qi is thedensity of the fuel i, and Ei is the specific energy of fuel i.

Table 1Selected properties of different fuels

Fuel Chemicalformula

Net energyvalue (MJ/kg),ASTM D240

Density @15 �C (g/l),ASTMD4052

Distillation, ASTMD86

IBP(�F)

FBP(�F)

Residue(%)

Ethanol C2H5OH 26.86 794.3 172.1 185.3 0.0Gasoline C8H18 43.19 754.0 94.1 415.1 0.9Glycerol C3H8O3 16.13 1264.0 – – –Propanediol C3H8O2 21.66 1039.7 362.1 365.5 0.1Propanol C3H8O 30.75 833.1 205.5 206.2 0.0

Table 1 presents some of the key properties of the fuelsthat were used in the analysis along with their chemical for-mula. Propanediol and propanol can be derived from glyc-erol [8]. The extraction of one oxygen atom from glycerolproduces propanediol, and similarly, removing one oxygenatom from propanediol produces propanol. ASTM D#refers to the method used to determine the correspondingvalues based on the American Society for Testing andMaterials (ASTM) methods.

2. Materials and methods

We studied different combinations of glycerol, propanol,propanediol, and ethanol and their phase behavior in gas-oline. While developing the ternary phase diagrams, any ofthe two aforementioned compounds were taken of fixedquantities in a conical flask. Then, the third compoundwas taken in a burette and titrated in a drop by drop fash-ion, while the mixture in the conical flask was continuouslymixed by shaking to ensure the contents in the flask werewell mixed. The point of which a clear liquid suddenlyturns turbid was taken as the phase boundary. More detailsof the development procedure of phase diagrams could befound elsewhere [17,18]. The same procedure was repeatedfor all possible combinations of the nine compoundsdescribed earlier.

3. Results and discussion

Fig. 1 shows the ternary phase diagram and the distri-bution of phases of a gasoline, glycerol, and propanolthree-component system (for clarity the intensity of colors1

has been faded to represent respective concentrations ofthe three-components at any selected point inside the tri-angle). As can be seen in Fig. 1, higher concentrationsof gasoline in a mixture of propanol and glycerol resultsin two phases. The highest volume percentage of gasolinethat could be mixed in a mixture of propanol and glycerolwithout separating into two phases was approximately55%. Other phase diagrams are depicted in Fig. 2. Basedon the ternary phase diagrams, the following observationswere noted: (i) ethanol, glycerol, and propanediol are com-pletely miscible in one another irrespective of the propor-tions mixed; (ii) as the glycerol concentration increasedabove 35%, the glycerol, propanol, and ethanol mixturesfailed to stay in a single phase; (iii) in the case of a gaso-line, glycerol, and ethanol blend, only a small portion ofthe diagram was occupied by a single phase, suggestingthat they are immiscible; (iv) only a small quantity of pro-panediol could be used with a mixture of gasoline and eth-anol because most of the mixtures separated into twophases; (v) based on the different proportions of propane-

1 For interpretation of color in Fig. 1, the reader is referred to the webversion of this article.

Fig. 1. Ternary phase diagram of gasoline–glycerol–propanol.

Table 2Sample composition, its energy value and octane number

Sampleno.

Composition (vol%) Energyvalue(MJ/kg)

Octane number

MON RONa

1 Glycerol (6%), propanol(60%), and gasoline (34%)

33.25 >100 N

2 Ethanol (30%), glycerol (30%),and propanediol (40%)

20.83 >100 N

3 Propanol (40%), gasoline(20%), and propanediol (40%)

28.63 >100 N

4 Ethanol (14%), gasoline (76%),and propanediol (10%)

38.05 84.0 93.9

5 Propanol (33%), ethanol (33%),and propanediol (34%)

25.60 >100 N

N: Not measured.a RON for all the samples except 4 was over the measurable range of the

equipment.

2808 S. Fernando et al. / Fuel 86 (2007) 2806–2809

diol, propanol, and gasoline, it was found that a higherpercentage of propanol in the mixture results in a two-phase region; (vi) higher concentrations of an individualcomponent in a gasoline, ethanol, and propanol blendcause a single-phase region; (vii) ethanol, propanediol,and propanol are completely miscible in each other; and(viii) glycerol, propanediol, and gasoline are immiscibleto each other.

Based on the nine ternary phase diagrams, five sampleswere selected for primary fuel property analysis. Octanenumber, which is one of the important parameters forspark ignition engines, was measured for the selectedblends. The mixture of glycerol (6 vol%), propanol(60 vol%), and gasoline has an energy value of 33.25 MJ/kg and a motor octane number (MON) of greater than100. Research octane number (RON) was not measured

Fig. 2. Ternary phase diagrams of the selected components. (

if the MON was greater than 100. This was due to RONsabove 100 was over the measurable range of the equipment.Table 2 depicts the energy value and octane numbers forthe selected mixtures.

4. Conclusions

The phase study revealed that the amount of glycerolthat could be successfully blended with gasoline variedwidely depending on the amount of n-propanol amphiphilepresent. Sample # 4 has the highest energy value among thesamples tested. Analyses for primary fuel properties ofglycerol, propanediol, propanol, ethanol, and gasolineblends suggest that certain blends could be used as sparkignition fuels. The octane numbers of most of the sampleblends were greater than 100.

Note: 1 refers to single phase and 2 refers to two phase.)

S. Fernando et al. / Fuel 86 (2007) 2806–2809 2809

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