167

Chemistry and Technology of Fuels and Oils, Vol. 47, No. 3, July, 2011 (Russian Original No.3, May-June, 2011)

CURRENT PROBLEMS. Alternative Fuels

COMPARISON OF LIQUID BIOFUELS AND PETROLEUM

FUELS: ENVIRONMENTAL PROPERTIES

K. E. Pankin, Yu. V. Ivanova, R. I. Kuz’mina,

and S. N. Shtykov

____________________________________________________________________________________________________

N. G. Chernyshevskii Saratov State University. Translated from Khimiya i Tekhnologiya Topliv i Masel,

No.3, pp. 3 – 6, May – June, 2011.

0009-3092/11/4703–0167 © 2011 Springer Science+Business Media, Inc.

The environmental properties of different types of liquid biofuels are examined: bioalcohols, biodiesel,

and others. They are compared with the same properties of petroleum fuels. It is shown that the properties

of biofuels differ considerably from those of petroleum fuels.

Key words: biofuel, environmental properties.

Automobile transport occupies a leading place in atmospheric pollution with emissions of greenhouse

gases and toxic substances, especially in big cities, where the majority of vehicles is concentrated, and the

appearance of noxious and hazardous substances in the air immediately affects the health and wellness of people

as well as the urban environment. In order to reduce the adverse effect on the environment, increasingly stringent

standards of fuel toxicity and of internal combustion engines (ICE) are being introduced vigorously, new types

of ICEs are being developed in compliance with these standards, fuel injection and forced ignition systems are

being perfected, and so on.

In order to ascertain the merits and demerits of biofuels in comparidon with fuels of petroleum origin, let

us examine some of their environmental properties: toxicity of the fuel itself and its combustion products as well

as emission of carbon dioxide.

Toxicity of fuel. A notable merit of biofuels is that they have no toxic effect on the environment and are

biodegradable. Close scrutiny of these properties of the biofuel, however, revealed an intricate picture, which

makes it difficult to draw an unequivocal conclusion about the nature of its effect on the environment. For

instance, the basic elements of the sanitary laws in the Russian Federation are maximum permissible

concentration (MPC), approximate safe levels of effect (ASLE), and approximate permissible levels (APL) of

substances in environmental objects, of which the most vital for human beings are air and water because they

enter into the organism. Unfortunately, scientif ic and technical l i terature contains no information

about MPC, ASLE, and APL for substitutes of conventional diesel fuel, but in corresponding normative

168

Table 1

Substance

Maximum permissible concentration

in water in air

for fishery, mg/dm3

for household (drinking) purposes, mg/dm3

in working zone, mg/m3

in atmosphere of inhabited

locality, mg/m3

Methanol 0.15 3 15/5 1/0.5

Ethanol 0.01 – 2000/1000 5/–

Commercial-grade fish oil (GOST 1304-76) 0.5 – – –

Hydrogenated vegetable and marine animal fats 0.01 – – –

Special animal fat – – – 0.2 (ASLE)

Light tall oil 0.1 – – 0.01(APL) 0.5 (ASLE)

Cottonseed oil – – – 0.1 (ASLE)

Castor oil – 0.2 (APL) – –

Esters of synthetic C11-C15 fatty acids – – 5/– –

Ester of ethylene glycol and fatty acids – 0.7 – –

Synthetic C10-C

16 fatty acids – – – 0.1 (ASLE)

Synthetic primary fatty alcohols 0.5 – – –

C2-C10 saturated aliphatic hydrocarbons – – 900/300 –

Petroleum gasoline (fuel solvent) – – 300/100 5/1.5

Petroleum products 0.05 0.1 – 5

Crude oil – 0.3 – –

Solar oil (mixture of hydrocarbons) 0.01 – – –

Mineral (petroleum) oils – – 5/– –

Mineral (petroleum) oils: spindle, machine (engine), cylinder, etc. – – – 0.05 (ASLE)

Notes. 1. In the numerator – maximum one-time (incidental) MPC, in the denominator – per-shift average

(in atmospheric air of inhabited locality, this parameter is substituted by daily average).

2. Slash indicates that the MPC is not standardized.

3. Special animal fat is a mixture of palmitic (40 %), oleic (15 %), and stearic (45 %) acids, the ASLE is based on

stearic acid.

4. Composition of light tall oil. %: higher fatty acids – 58, butyric acid – less than 4, unsaponifiable substances – 35-37,

oxidized substances – 0.2.

documents [1-7] their values are found for various fats (lipids) of both vegetable and animal origin, synthetic

esters of fatty acids, fatty alcohols, etc. These values are adduced in Table 1.

Analysis of the data in Table forces one to have doubts about the safety of action of some substances of

biological origin on the environment. For example, the MPC of methanol and ethanol in fishery waters

is 0.15 and 0.01 mg/dm3, respectively, whereas the MPC of petroleum products is 0.05 mg/dm3, i.e., ethanol is

five times as toxic as petroleum products. A similar picture is noticed as well for atmospheric and working-area

air, for which the MPC, ASLE, and APL of petroleum products and alcohols are close to or even lower than those

of alcohols.

169

Even more surprising are the data for vegetable and animal fats as well as for esters thereof. For instance,

the maximum incidental (one-time) MPC for esters based on synthetic C11

-C15

fatty acids is 5 mg/m3, and for

benzine it is 900 mg/m3, i.e., for the environment, fatty acid esters are 180 times more harmful than benzine.

According to normative documents, the MPC of petroleum products in fishery waters is 0.05 mg/dm3 (for solar

oil, it is 0.01 mg/dm3), whereas the MPC of hydrogenated vegetable and animal fats, it is only 0.01 mg/dm3.

While considering biodegradability of biofuels as an advantage, it must be mentioned, however, that

hydrolysis of methyl esters of fatty acids causes formation inside the bacterium cell of methanol, which, after it

reaches a certain concentration, annihilates it.

Emission of carbon dioxide. In the process of complete combustion of an organic motor fuel (biofuel),

only two components are formed: carbon dioxide and water. Both these substances are held responsible for

Earth’s climate change because it is believed that their presence in the atmosphere causes greenhouse effect. But

these substances differ distinctly in thermodynamic properties: water vapor is capable of condensing and, therefore,

disappearing from the atmosphere, whereas carbon dioxide, being a gaseous substance in a wider temperature and

pressure range, remains in the atmosphere until it is fixed by photo-synthesizing organisms.

Substances, which are highly promising substitutes of conventional fuels, carbon and hydrogen

contents (wt. %) in them, and ratio of the number of carbon dioxide molecules to the number of water molecules

formed upon complete oxidation of each of these substances are listed in Table 2. The last parameter, in our view,

portrays the qualitative picture of carbon dioxide emission. In order to track its variation with variation of

composition and structure of molecules, several homologs and isomers are also included in Table 2.

As can be seen , wi th increase o f molecu la r weigh t o f the o rgan ic subs tance i t s ca rbon

content (wt. %) increases, whereas hydrogen content (wt. %) decreases. For instance, carbon constitutes 75 % of

the molecular weight in the case of methane and 85 % in the case of eicosane. The same picture is noticed as we

pass from saturated hydrocarbons to aromatic: in the case of benzene, carbon constitutes as much as 90 % of the

molecular weight. Increased carbon content causes higher carbon dioxide formation upon complete combustion

of the molecule.

Thus, to reduce carbon dioxide emission, it is necessary to use low-molecular saturated organic compounds.

From this standpoint, methane (CO2 : H

2O = 0.5) is environmentally the most attractive alternative to conventional

types of fuel . The picture is the same for methanol and ethanol, for which the ratio CO2 : H

2O is

0.50 and 0.66, respectively.

In the case of diesel fuel, the picture is opposite. For instance, biodiesel fuel has a higher molecular

weight than conventional diesel fuel but contains less carbon, which means it should emit less carbon dioxide

upon combustion. Nonetheless, this picture is misleading because the reason for reduced share of carbon in the

molecule is presence of oxygen in the molecules of fats and methyl esters of fatty acids. Calculation of

the CO2 : H

2O rat io in this case showed a s l ight increase, rather than decrease, in carbon dioxide

emission (1.08 against 1 for conventional diesel fuel). So, if from the point of carbon dioxide emission switch to

a lower-molecular fuel (alcohols substituting benzene) is justified, substitution of higher-molecular biodiesel for

petroleum diesel does not withstand criticisms. Based on this fact, use of a fuel derived from vegetable will not

eliminate the problem of carbon dioxide emission to the atmosphere.

Toxicity of biofuel combustion products. ICEs have a large number of different operation conditions, for

which various fuel blend compositions and various forced ignition conditions, etc. are required. The simplest

way to simultaneously save fuel and reduce toxicity of exhaust gases is to use in all ICE operation conditions

maximally impoverished (lean) fuel blends [9-11]. The engine operation on lean blends remains by and large

satisfactory because this happens due to a decrease in engine power (because the lean blend burns very slowly

170

Table 2

Substance Formula Mol. wt., g/mole

Content, wt. % CO2:H2O

carbon hydrogen

Methane СН4 16 75 25 0.5

Ethane С2Н6 30 80 20 0.67

Propane С3Н8 44 81.82 18.18 0.75

Butane С4Н10 58 82.75 17.25 0.83

Pentane С5Н12 72 83.33 16.67 0.85

Hexane С6Н14 86 83.72 16.28 0.86

Cyclohexane С6Н12 84 87.80 12.20 1

1-Hexene С6Н12 84 87.71 12.29 1

1-Hexine С6Н10 82 87.80 12.20 1.2

1,5-Hexadiene С6Н10 82 87.80 12.20 1.2

Cyclohexadiene С6Н8 80 90 10 1.5

1,3,5-Hexatriene С6Н8 80 90 10 1.5

Benzene С6Н6 78 92.31 7.69 2

Eicosane С20Н42 282 85.10 14.90 0.95

Methanol СН3ОН 32 37.50 12.50 0.5

Ethanol С2Н5ОН 46 52.17 13.04 0.67

Gasoline ~С8Н16 ~110–120 85.5 14.5 ~1

Rapeseed oil С57Н102О6 ? 882* 77.55 11.56 ~1.12

Rapeseed oil triglyceride С61Н44О6 ~936* 78.41 11.54 ~1.13

MEHA** С23Н44О6 ~352* 78.41 12.50 ~1.04

MERO*** С19Н35О6 ~295* 77.29 11.86 ~1.08

Diesel fue ~С14Н28 ~180–200 87.0 12.6 ~1

Notes. *Mol. wt. values are taken from [8].

** Methyl ester of heneicosanic acid.

*** Methyl ester of rapeseed oil.

and, in limiting cases, generally ceases to be ignited by electric spark), deterioration in starting of the cold engine,

and increase in emission of nitrogen oxides (because the lean blend contains excess oxygen which is capable of

oxidizing, at the point of ignition, the nitrogen occurring in the air). Also, in superlean blend, the catalytic

neutralizer ceases to perform because the principle of its performance is based on a group of chemical reactions

depicted by the general scheme:

222xnn NOHCONOCOHC ++→++

in accordance with which most complete combustion of the fuel is not conducive to regeneration of the nitrogen

from its oxides.

The toxicity of exhaust gases generally depends on the condition of burning of the fuel in the ICE and

depends little on the fuel itself, of course if the ICE uses a fuel it was not designed for. All fuel burning conditions

can be divided into normal and abnormal. In the case of normal burning condition, the fuel blend burns without

171

significant emission of CnH

m and NO

x and without knocking. Abnormal conditions are those where

the ICE operates on a fuel-air mixture of non-optimal composition, forced ignition occurs at the non-optimal

moment, the engine knocks, and many others.

The toxicity of ICE exhaust gases does not depend on the origin of the fuel because any organic fuel can

be oxidized fully, but depends a great deal on the condition of its combustion. To date, the only indisputable fact

that favors use of biofuel is absence of sulfur in it because vegetable organisms hardly assimilate it.

Thus, comparison of environmental properties has clearly shown that in absolute majority of cases fuels

of biological origin do not have significant advantages over fuels of petroleum origin.

REFERENCES

1. A Catalog of Fishery Standards: Maximum Permissible Concentrations and Approximate Safe Levels of

Action of Noxious Substances for Fishery Waters [in Russian], VNIRO, Moscow (1999), p. 120.

2. GN (State Standard) 2.1.5.1315-03: Maximum Permissible Concentrations of Chemical Substances in

Water from Drinking and Service Water Mains [in Russian], approved 27 April 2003 by the Chief State

Physician of Sanitation of the Russian Federation, registered 19 May 2003 at the Ministry of Justice of

the Russian Federation, Registration No. 4550.

3. GN 2.1.6.1338-03: Maximum Permissible Concentrations of Pollutants in Atmospheric Air of Population

Centers [in Russian], approved 31 May 2003 by the Chief State Physician of Sanitation of the Russian

Federation, registered 11 June 2003 at the Ministry of Justice of the Russian Federation, Registration

No. 4679.

4. GN 2.1.5.1339-03: Approximate Safe Levels of Action of Pollutants in Atmospheric Air of Population

Centers [in Russian], approved 21 May 2003 by the Chief State Physician of Sanitation of the Russian

Federation, registered 9 June 2003 at the Ministry of Justice of the Russian Federation, Registration No.

4663.

5. GN 2.2.5.1313-03: Maximum Permissible Concentrations of Noxious Substances in Working Area Air

[in Russian], approved 27 April 2003 by the Chief State Physician of Sanitation of the Russian Federation,

registered 19 May 2003 at the Ministry of Justice of the Russian Federation, Registration No. 4568.

6. GN 2.2.5.1314-03: Approximate Safe Levels of Action of Noxious Substances in Working Area Air [in

Russian], approved 27 April 2003 by the Chief State Physician of Sanitation of the Russian Federation,

registered 19 May 2003 at the Ministry of Justice of the Russian Federation, Registration No. 4552.

7. GN 2.1.5.1316-03: Approximate Permissible Levels of Chemical Substances in Water from Drinking

and Service Water Mains [in Russian], approved 27 April 2003 by the Chief State Physician of Sanitation

of the Russian Federation, registered 19 May 2003 at the Ministry of Justice of the Russian Federation,

Registration No. 4557.

8. V. G. Semenov and A. A. Zinchenko, Khim. Tekhnol. Topl. Masel, No. 1, 29-35 (2005).

9. A. R. Kul’chitskii, Toxicity of Automobile and Tractor Diesel Engines: A Textbook [in Russian],

OOO Akademicheskii Proekt, Moscow (2004), p. 400.

10. V. A. Markov, R. M. Bashirov, and I. I. Gabitov, Toxicity of Exhaust Gases of Diesel Engines [in Russian],

N. É. Bauman MGTU, Moscow (2002), p. 376.

11. L. V. Grekhov, Fuel Equipment of Electrically Controlled Diesel Engines: Teaching and Training Aid [in

Russian], Legion-Avtodata, Moscow (2003), p. 176.