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destined to ethanol production, together with farming waste and sugar cane bagasse. The
drawback of these raw materials consists in the complexity of the phenomena involved in
converting the biomass into ethanol. Various studies have been conducted on the process of
bioethanol production starting from various raw materials, including lignocellulose
materials, cereals (McAloon et al., 2000; Cardona et al., 2005), and sugar cane (Quintero et
al., 2008).
3.5 Converting syngas into ethanol
Bioethanol can also be obtained by means of chemical processes (Sánchez & Cardona, 2008;
Demirbas, 2005), which may or may not demand the presence of microorganisms in the
fermentation stage. Gasification of a biomass to obtain syngas (CO + H
2
), followed by the
catalytic conversion of the syngas, has the potential for producing ethanol in large
quantities. The catalysts most often used and studies are those based on rhodium (Rh) (Holy
& Carey, 1985; Yu-Hua et al., 1987; Gronchi et al.; 1994).
The geometrical structure of the active site seems to be:



0 n
xy
Rh Rh O M


 (9)
where part of the Rh occurs as Rh
+

and the promoter ion (M
n+
) is in close contact with these
Rh species. The carbon monoxide is then hydrogenated to form an absorbed species -CH
x
-
that is then inserted in the absorbed CO. Hydrogenation of these absorbed species leads to
the formation of ethanol (Subramani & Gangwal, 2008).
Another mechanism considered valid for ethanol formation involves the use of acetate
(acetaldehyde formation followed by reduction) and is known, in the cases of Rh-based
catalysts, to be promoted by manganese (Luo et al., 2001).
In this case, ethanol is formed by direct hydrogenation of tilt-absorbed CO molecules,
followed by CH
2
insertion on the surface of the CH
2
-O species to form an absorbed
intermediate species. Ethanol is produced by hydrogenation of the intermediate species of
CH
2
-O. Acetaldehyde is formed by the insertion of CO on the surface of the CH
3
-Rh species,
followed by hydrogenation. The catalyst’s performance can be improved by modifying its
composition and preparing the ideal conditions for the reaction (Subramani & Gangwal,
2008). Manganese (Lin et al., 1995), Samarium and Vanadium (Luo et al., 2001) can also be
used as promoter ions in processes involving Rh.
4. Environmental issues
The greenhouse gases (GHGs) are gases occurring in the Earth's atmosphere that absorb in
the infrared field (carbon dioxide, ozone, methane, nitrogen oxides, carbon monoxide and so

on). This feature enables them to trap the heat of the sun reflected back from the Earth's
surface.
The GHG that occurs in the largest quantities is carbon dioxide, and that is why it attracts so
much attention. In fact, the carbon cycle is a delicate balance between carbon accumulation,
release and recycling that enables vegetable and animal species to survive. Problems linked
to CO
2
began to emerge at the start of the industrial era: the ever-increasing use of fossil
fuels as a source of energy meant that the carbon dioxide trapped for centuries in the fossils
was being put back into the atmosphere, with no correspondingly reinforced recycling
mechanism, which relies on chlorophyllic photosynthesis).

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In addition to reducing carbon dioxide emissions, bioethanol can be seen as a no-impact fuel
because the amount of CO
2
released into the atmosphere is compensated by the amount of
CO
2
converted into oxygen by the plants grown to produce the bioethanol (Ferrel &
Glassner, 1997).
4.1 Carbon sequestering
In the analysis of the environmental impact of bioethanol (and other biofuels too), some of
the key factors concern the impact of the increasing quantities of dedicated crops on soil
carbon levels and subsequent photosynthesis: these changes will also influence the
atmospheric concentrations of GHG such as CO
2
and CH

4
.
The main problem concerns the fact that, when a system in equilibrium experiences
persistent changes, it can take decades before a new equilibrium with a constant carbon
level is reached. Taking the current situation in Europe as concerns wheat and sugar beet
crops, there is an estimated depletion of approximately 0.84 t of C or 3.1 t CO
2
equivalent
ha
-1
years
-1
from the ground. If no crops were grown on the soil, this depletion would be
even greater, i.e. 6.5 t of C each year for sugar beet and 4.9 t of C for wheat. Apart from the
effects on ground carbon levels, there are also signs of other adverse effects indirectly linked
to crops grown for energy purposes, such as the increase in the amount of C in the
atmospheric levels of GHG. Irrigation with good-quality water also exacerbates carbon
sequestering: the water used for irrigation contains dissolved calcium and carbon dioxide
(in the form of HCO
3
-
); Ca and HCO
3
-
react

together, giving rise to the precipitation of
CaCO
3
and the consequent release of CO

2
into the atmosphere. In the typical dry conditions
of the USA, further reactions take place and irrigation is responsible for the transfer of CO
2

from the ground into the atmosphere (Rees et al., 2005). An important type of crop that can
be used to reduce soil carbon sequestering is defined as "zero tillage”, which means that it
can be grown year after year without disturbing the soil. Seed crops (such as wheat) may be
zero tillage, but not root crops (such as Panicum virgatum). Zero tillage has variable effects,
and in some cases carbon sequestering in the soil may even increase, but this phenomenon
can be completely overturned by a one-off application of conventional tillage. If only the
carbon in the soil is considered, zero tillage leads in the long term to less global warming
than growing conventional crops in damp climates, but in areas with dry climates, there is
no certainty of any such beneficial effect (Six et al., 2004). Using straw from cereals can
increase the carbon levels in the soil. Such residue is useful in maintaining soil carbon levels
(Blair et al., 1998; Blair and Crocker, 2000) because it has a low rate of breakdown, so it is
important for the residue to go back into the ground in order to keep the farming system
sustainable. Since removing the residue from the ground has other negative effects too, such
as an increased soil erosion and a lesser availability of macro- and micronutrients, some
have suggested in the United States (Lal, 2005) that it would be advisable to remove only 20-
40% of the residue for the purposes of bioethanol production, whereas it was claimed
(Sheehan et al., 2004) that if up to 70% of the residue were removed to produce bioethanol,
the carbon levels would initially decline and then remain stable for about 90 years.
Increasing the land used to grow energy crops would have a substantial impact on the
concentrations of carbon-containing gases in the atmosphere. If areas covered with forest
were converted into arable land, the carbon sequestering would go from values of around
50-145 tha
-1
to approximately 50-200 tha
-1

, assuming a 60-year rotation (Reijinders &
Huijbregts, 2007).

Advances in the Development of Bioethanol: A Review

633
4.2 Emissions
Mixing bioethanol with petrol, even in modest proportions, increases the octane number of
the fuel and reduces the percentage of aromatic and carcinogenic compounds, and
emissions of NO
x
, smoke, CO, SO
x
and volatile organic compounds (VOC). But there is also
an increase in the emissions of formaldehyde and acetaldehyde. On the other hand, modern
bioethanol production systems have an energy ratio (or net usable energy) of around 2 to 7,
depending on the crops and processes used. The composition of petrols can influence the
emissions of organic compounds: those containing aromatic hydrocarbons such as benzene,
toluene, xylene and olefins produce relatively high concentrations of reactive hydrocarbons,
while petrols formulated using oxygenated compounds (such as those mixed with
bioethanol) may contain lower quantities of aromatic compounds.
The problem of petrols with high concentrations of aromatic compounds lies in their
marked tendency to emit uncombusted hydrocarbons, which are difficult for catalytic
converters to oxidize as well as being precursors of photochemical contamination. All
oxygenated fuels have the potential for reducing the emissions of carbon monoxide (CO)
and uncombusted hydrocarbons, which are also "photochemically" less reactive than the
hydrocarbons of normal petrols. Because ethanol acts as an oxygenating agent on the
exhaust gases of an internal combustion engine fitted with a three-way catalytic converter,
adding ethanol to petrol (Poulopoulos et al., 2001) leads to an effective 10% reduction in the
emission of CO, as well as a general reduction in aromatic hydrocarbon emissions. Using

four-stroke engines, with four cylinders and electronic injection, fueled with various ethanol
and petrol mixtures (Al-Hasan, 2003) reduced the CO emissions by about 46.5%. The anti-
detonating features of petrols are very important and depending essentially on their
chemical composition.
Life cycle analysis taking the "well to wheel” approach showed that the GHG emissions
from bioethanol obtained from sugar beet are around 40-60% lower than the emissions from
petrols obtained from fossil fuels (Reijinders & Huijbregts, 2007). Mixing bioethanol with
diesel oil improves the fuel’s combustion (Lapuerta et al., 2008) and reduces the size of the
particles in the exhaust without increasing their quantity. Using an E10 mixture reduces the
total hydrocarbon emissions because of ethanol’s greater heat of vaporization.
CO emissions increase if moderate amounts of ethanol are added to diesel oil, while they
diminish as the proportion of ethanol increases (Li et al., 2005). Conversely, NO
x
emissions
decrease with a low or moderate quantity of ethanol, but increase if more ethanol is added.
The total hydrocarbons (THC) also increase with different proportions of ethanol and
different speeds.
5. Conclusions
Although bioethanol is a valid alternative to fossil fuels and has a low environmental
impact, its use is nonetheless posing problems relating to the use of raw materials such as
cereals, which are fundamental to the food industry.
Increasing the farmland used to grow energy crops for the production of biofuels means
competing with food crops. Many studies have attempted to assess the need for farmland
for crops for producing ethanol. The yield in bioethanol per hectare naturally depends on
the crops used, but reference can be made to the mean productivity in Europe (weighted
according to the type of crop), which is currently estimated at around 2790 liters/hectare
(based on a mean yield in seeds of 7 tons/hectare and 400 liters/ton).

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Although bioethanol can be produced successfully in temperate climates too, the tropical
climates are better able to ensure a high productivity. In Brazil, sugar cane is used to
produce approximately 6200 liters/hectare (an estimate based on a crop yield of 69
tons/hectare and 90 liters/ton). The productivity of bioethanol from sugar cane is high in
India too, with a yield of approximately 5300 liters/hectare. If bioethanol from sugar cane
becomes a commodity used worldwide, then South America, India, Southeast Asia and
Africa could become major exporters.
Research is focusing on alternatives, concentrating on innovative raw materials such as
Miscanthus Giganteus, an inedible plant with a very high calorific value (approximately
4200 Kcal/kg of dry matter), or filamentous fungi such as Trichoderma reesei, which can
break down the bonds of complex lignocellulose molecules.
This article summarizes the main raw materials that can be used to produce bioethanol,
from the traditional to the more innovative, and the principal production processes
involved. It also analyses the issues relating to emissions and carbon sequestering.
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27

Effect of Fried Dishes Assortment on Chosen
Properties of Used Plant Oils as Raw Materials
for Production of Diesel Fuel Substitute
Marek Szmigielski, Barbara Maniak,
Wiesław Piekarski and Grzegorz Zając
University of Life Sciences in Lublin
Poland
1. Introduction
Utilization of post-frying plant oils which are waste product of operation of, serving fried
products, gastronomical points, for many years has been growing and complex problem of
technological, ecological and economical nature. It must be noted that methods of solving
this problem were subject of numerous research [Alcantara 2000; Buczek and Chwiałkowski
2005; Dzieniszewski 2007; Leung and Guo 2006]. Conception of utilization of post-frying
plant oils as components for production of substitute of diesel fuel seems to be promising.
However, it is necessary to investigate in detail properties of such oils, so that elaborated
technologies of their utilization are optimal. Answer to question concerning influence of
assortment of fried products on quality of post-frying oil, and its usefulness, when aspect of
differences in utilization of particular batches of such oil, obtained after frying various food
products, seems to be the most significant issue.
Most commonly used method of frying food in gastronomical points is deep frying. During
this type of frying, processed food is submerged in frying medium and contacts oil or fat
with most of its external surface. The main role of frying medium is keeping processed food
in proper position to source of heat and transferring proper amount of heat energy into a
fried product [Drozdowski, 2007; Ledóchowska and Hazuka, 2006]. Frying fat, which is a
frying medium, and products subjected to culinary processing form a specific system in
which partial penetration of these two compounds and two-way transfer of energy and
weight take place. As a result of frying, product loses significant amount of water and,
depending on its composition, some of its compounds e.g. food dyes, taste and flavour
compounds and partially, transferred to frying fat, lipids. They are replaced with some
amount of frying fat, which content in fried food, according to approximate data, may vary

significantly and reach even 40% [Ledóchowska and Hazuka, 2006].
Water present in processed products and released during submersion frying has got diverse
and multi directional influence on changes occurring in oil, among which is, causing partial
increase of acid number (AN) of oil, fat hydrolysis. Moreover, transport of heat emitted with
released water vapours favours decrease of temperature of fried food and partly inhibits
oxidation transformations of fat by displacing oxygen in it [Ledóchowska and Hazuka,
2006].

Biofuel's Engineering Process Technology

640
Oxygen dissolved in frying fat together with water vapour are also significant factors of so
called thermooxidative transformations, which have not been fully explained yet. As a result
of these transformations numerous substances, having complex and not fully determined
structure, are formed. They are precursors of secondary transformations, products of which
can be usually classified in one of two categories: volatile compounds (hydrocarbons, fatty
acids and carboxylic compounds) and non-volatile (monomers, dimers, polymers and also
some aldehydes and ketones, as well as fatty acids characterizing with changed melting
point) [Drozdowski 2007, Paul and Mittal 1996, Blumenthal 1991, Choe and Min 2006, Clark
and Serbia 1991, Hoffman 2004, Ledóchowska and Hazuka 2006].
Gastronomical fryers are usually containers having fairly high capacity, in which, next to the
surface layer, which is environment determining properties of processed product, some
volume of oil deposited near a bottom of a fryer can be distinguished. Bottom zone of a
fryer, adjacent usually to the source of heat emission and having relatively low content of
oxygen and water vapour, favours free radical or polymerization transformations of
unsaturated fatty acids occurring in frying fat. The most common result of these
transformations are numerous, having complex structure, non-polar thermal polymers.
Macroscopic result of this type of reactions are increase of viscosity and darkening as well as
increase of melting point of frying medium, what results in change of its state of
aggregation. Products of these transformations are main components of dark brown

deposits found on walls of a fryer, which can be a reason for many problems related to
utilization of such oil [Hoffman 2004].
It should be noted that direction and intensity of frying fat transformations depends on
numerous factors accompanying this process during frying of food products. In literature
[Ledóchowska and Hazuka 2006] at least few groups of such factors are named. As the basic
ones, conditions of carrying out the process (its duration, temperature and periodicity) and
degree of unsaturation of fatty acids in triglycerides of fat, are mentioned. Among all factors
affecting properties of frying medium many other, accompanying frying process, like
oxygen availability and amount and composition of compounds released from food (e.g. pro
and antioxidants and presence of water), play a significant role [Ledóchowska and Hazuk’a
2006].
2. Assessment of usability of post-frying edible oils as a raw material for
production of diesel fuel substitute
2.1 Materials and methods
2.1.1 Preparation of samples for Investigation
In this research, comparison of influence of fried dishes assortment (potato chips and
breadcrumbs coated fish fingers) on physicochemical properties and quality of post-frying
plant oils to be utilized as raw materials for production of, used as a substitute of diesel fuel,
fatty acids methyl esters, was conducted. Main focus of the research was on evaluation of
effect of fried dishes assortment on quality of obtained post-frying oils (rapeseed, sunflower
and soybean) with regard to their utilization as a substrate for production of engine biofuel.
In model conditions of laboratory investigation, usability of post-frying waste oils as raw
materials for production of fatty acids methyl esters was evaluated. Three most commonly
used edible oils (rapeseed, sunflower and soybean) were used as material for this research.
From total amount of each of raw oils, sample for laboratory analyses was taken. It was
marked as "0" and was used as a reference sample. Remaining amount of each of oils was
Effect of Fried Dishes Assortment on Chosen Properties of Used
Plant Oils as Raw Materials for Production of Diesel Fuel Substitute

641

divided into three batches and poured into separate containers. Batch no. 1 was prepared
by means of cyclic, five-time heating without fried product. Particular cycle within this
batch comprised of heating whole amount of oil to temperature of approximately 180
o
C, and
than maintaining it in such temperature for 10 min. Next, oil was left to cool down in room
temperature and than a sample, to be used for laboratory analyses, was taken. The sample
was marked as "heating I - without fried product". After 24 hours all described above
actions were repeated yielding sample marked as "heating II - without fried product".
Whole process of heating, cooling and sampling was repeated, yielding samples marked as
"heating without fried product" bearing following, respective to number of cycle, labels: III,
IV and V.
Preparation of oil from batch no. 2 was differed from previously presented in only one way.
After heating it to 180
o
C, in each of three investigated oils, potato chips, prepared of
purchased raw potatoes and cut to the size and shape of frozen potato chips found in trade,
were fried.
After frying and separating chips, oil was cooled down to room temperature and than
samples for research were taken. They were marked as "heating I - process of chips frying".
Repeating whole process enabled obtaining samples marked following, respective to
number of cycle, labels: III, IV and V.
Third part of oil (batch no. 3) was heated same way as batch no. 2 but in this case purchased
breadcrumbs coated fish fingers were the fried product. After frying and separating
breadcrumbs coated fish fingers, oil was cooled down to room temperature and than
samples for research were taken. They were marked as "heating I - process of breadcrumbs
coated fish fingers frying". Repeating whole process enabled obtaining samples marked
following, respective to number of cycle, labels: III, IV and V.
2.2 Laboratory test
Oil samples obtained in conformity with chosen methodology were subjected to laboratory

tests, which comprised of following analyses: determination of peroxide number (PN), acid
number (AN) and composition of fatty acids. Determination of peroxide number (PN) in
conformity with [ISO 3960] was based on titration of iodine released from potassium iodide
by peroxides present in the sample, calculated per their weight unit. Results of analyses
were expressed in millimoles of oxygen per weight unit of the sample.
Determination of acid number (AN) in conformity with [PN-ISO 660] was conducted by
means of titration and evaluation of acidity of a sample, and expressed in numeric form in
millilitres of 0,1M solution of sodium hydroxide, calculated per weight unit of analysed oil.
Determination of fatty acids composition was conducted by means of method based on
utilization of gas chromatography [Krełowska – Kułas, 1993]. Sample of fat was subjected to
alkaline hydrolysis in anhydrous environment with utilization of methanol solution of
sodium hydroxide. As a result of this reaction, fatty acids of investigated oil were
transformed into a mixture of sodium soaps, which than were subjected of reaction of
esterification with anhydrous solution of hydrogen chloride in methanol, yielding mixture
of fatty acids methyl esters.
Obtained methyl esters were separated in a chromatographic column and than their
participation in a sum of fatty acids was determined [Krełowska – Kułas, 1993].
Chromatographic separation was conducted by means of gas chromatograph with nitrogen
as carrier gas, packed column (2,5 m with stationary phase PEGA - polyethylene glycol
adipate on carrier GAZ-ChROM-Q) and flame ionization detector.

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642
2.3 Engine tests
Samples of soybean oil which remained after laboratory samples had been taken from each
of three batches, differentiated by type of initial preparation (frying potato chips, frying
breadcrumbs coated fish fingers and heating without fried product), were separately
subjected to esterification with methanol. Fatty acids methyl esters were obtained by
method analogous to the one used in investigation of fatty acids composition by means of

gas chromatography. Fuel obtained this way was used in engine tests including main
engine work parameters. Four mixtures were prepared, each containing 90% diesel fuel
and 10% addition of fatty acids methyl esters obtained in research and marked as:
a. M1 - esters obtained from purchased fresh soybean oil,
b. M2 - esters obtained from soybean oil subjected to five-time cyclic heating, without
addition of fried product,
c. M3 - esters obtained from soybean oil, previously used for five-time cyclic frying of
potato chips,
d. M4 - esters obtained from soybean oil, previously used for five-time cyclic frying of
breadcrumbs coated fish fingers.
Results of internal combustion engine running on diesel fuel (DF) were used as reference for
determination of work parameters of engine powered with fuel blends. Above mentioned
fuel mixtures, were used for powering 2CA90 diesel engine installed on dynamometric
stand for purpose of conducting measurements of its energetic work parameters. Test bed
comprised of following devices:
- internal combustion diesel engine 2CA90;
- dynamometric stand composed of eddy-current brake AMX210 and control-
measurement system AMX201, AMX 211;
- fuel consumption measuring system;
- system measuring engine parameters: exhaust gasses temperature - tsp, engine oil
temperature - tol, oil pressure -pol;
- system measuring state of environment: temperature of environment - tot, atmospheric
pressure - pa, and air humidity - φ.
Measurements for each of investigated fuels were conducted and obtained results of
energetic parameters were elaborated. Data yielded by measurements was used to draw
external characteristics of the engine for rotational speed ranging from minimal to nominal.
Carried out research included kinematic and dynamic parameters of the engine: torque -
Mo, rotational speed - n, time in which set amount of investigated fuel was used - τ. Amount
of fuel used for purpose of this characteristic was 50 g. Methodology of measurements and
methods of measurements and results reduction of power and torque, were in conformity

with norms: PN-88/S-02005, BN-79/1374-03.
3. Result of investigation
Raw, purchased plant oils characterised with typical properties, fulfilling requirements of
recommended in Poland norm [PN – A - 86908] with regard to peroxide number (PN) and
acid number (AN) (fig. 2 and 3).
Heating edible oils in conditions corresponding to frying potato chips, breadcrumbs coated
fish fingers and heating without a product lead to significant changes of investigated oils
properties. It caused mainly distinct changes of acid number (AN) and peroxide number
(PN).
Effect of Fried Dishes Assortment on Chosen Properties of Used
Plant Oils as Raw Materials for Production of Diesel Fuel Substitute

643
Differences in properties of oils subjected to cyclic heating without fried product and in
which potato chips or breadcrumbs coated fish fingers were fried may result from course of
temperature changes for various investigated batches (Fig. 1).


Fig. 1. Course of rapeseed oil temperature changes in relation to time of potato chips and
breadcrumbs coated fish fingers frying (presented data based on authors own research
[Szmigielski et al. 2009] )
The highest temperature for each of investigated oils and in each of five heating cycles was
observed in case of samples heated without fried products, in which temperature remained
at 180
o
C. Changes of temperature of oil heated in the process of frying potato chips or
breadcrumbs coated fish fingers had dynamic course, reaching the lowest value in
approximately beginning of fifth minute. However, value of this minimum was depended
on weight of fried product but main factor was fried product to frying medium weight ratio
(fig. 1).

Conducted research show that heating plant oils caused noticeable increase of peroxide
number (PN) value, when compared to samples not subjected to thermal processing. It

Biofuel's Engineering Process Technology

644
must be noted that diverse course and intensity of these changes were observed in case of
samples heated without product, samples heated in process of potato chips and
breadcrumbs coated fish fingers frying (Fig. 2).

0
10
20
30
40
50
60
f
r
e
s
h


o
i
l
1
2
3

4
5
heating in process of potato chips frying
heating without fried product
heating in process of breadcrumbs coated fish fingers frying
number of cycles heating
PN
[meq O
2
*
kg
-1
]

Fig. 2. Peroxide number of rapeseed oil subjected to cyclic heating [mMO kg-1]/ data for oil
heated in process of potato chips frying and heated without addition of product according
to Szmigielski et al. 2008/
Typical course of peroxide number changes in relation to number of frying cycle was
presented in Fig. 2. In case of each of five heating cycles, highest value of peroxide number in
rapeseed and soybean oils was observed in samples heated without a product [Szmigielski et
al. 2008]. It was characteristic, that in these samples peroxide number value increased fast until
third or fourth cycle, after which decrease of its value was noted (Fig. 2). Most probable cause
of such course of peroxide number changes, in relation to heating cycles, is formation of
oxidation products, which partially evaporate from the environment of reaction in form of
volatile products. An exception to the rule were analyses conducted for samples of soybean oil
(firs and second cycle of heating), in which temporarily highest value was observed in samples
heated in process of breadcrumbs coated fish fingers frying [Szmigielski et al. 2011]. Most
probably it results from influence of fat present in fried product on a final result of
determination.
Effect of Fried Dishes Assortment on Chosen Properties of Used

Plant Oils as Raw Materials for Production of Diesel Fuel Substitute

645
Samples of oil heated in the process of potato chips frying, characterised with lower values
of peroxide number, for each of five heating cycles, when compared to samples heated
without the fried product. Stabilizing effect of potato chips, caused by sorption of oxidation
products on their surface or partial absorption of frying fat, is most commonly mentioned
probable cause of such course of PN changes in these samples [Maniak et al. 2009,
Szmigielski et al. 2008, 2009, 2011]. It should be noted (Fig. 1) that PN level in samples of
rapeseed and soybean oil heated in process of potato chips frying [Szmigielski et al. 2008],
had similar course, stabilizing respectively at approx. 2 mMo/100g and approx. 1,5
mMo/100g [Szmigielski et al. 2011] (with exemption of null samples and first cycle of
soybean oil heating). Results of investigation of soybean and rapeseed oil samples heated
without fried product differed significantly - reaching almost two times higher value of
peroxide number (PN) than respective samples heated in process of potato chips frying. As
opposed to this research, heating sunflower oil in process of potato chips frying caused only
slight decrease of its peroxide number (PN) when compared to samples heated without
fried product [Maniak et al. 2009].
Typical course of acid number (AN) changes of heated oil samples in relation to number of
frying cycles was presented in Fig. 3. Acid number of heated oil samples was higher than in
raw oil, however, heating in process of potato chips frying caused stabilization of acid
number value (AN) at similar level (0,02 mgKOH/g) regardless of number of oil heating
cycles, while heating without the product caused systematic increase of AN. Very similar
course of acid number changes of investigated post-frying oils was also observed in
analogous research on rapeseed oil [Szmigielski et al. 2008] and sunflower oil samples
[Maniak et al. 2009]. It is believed, that the most probable cause of observed changes of acid
number of these samples is sorption of oxidation products on surface of, subjected to
culinary processing, potato chips or partial absorption of oil surrounding the product into
its deeper, more distant from surface of investigated raw product layers.
Acid number (AN) of plant oils (rapeseed and soybean) heated in the process of frying

breadcrumbs coated fish fingers was increasing systematically. It should be noted that AN
for first two cycles of heating remained at level similar or lower than AN determined in
respective samples heated in the process of potato chips frying. However, starting from the
third heating cycle AN exceeded this value and was systematically increasing with each of
heating cycles, reaching values lower than in respective samples of soybean oil heated
without fried product (fig. 3). It is believed that two opposing processes were the most
probable cause of above described course of changes of acid number (AN) in samples of oils
heated in process of breadcrumbs coated fish fingers frying. Increase of AN value should
probably be explained with oxidation of fatty acids and hydrolytic effect of water vapour,
released from product as a result of frying, while reduction of its level occurred as an effect
of sorption of oxidation products on surface of fried product [Szmigielski et al. 2009; 2011].
Five-time cyclic heating of plant oils caused significant changes in composition of fatty
acids, which can be simply characterised as significant decrease of fatty acids content. It
concerns mainly unsaturated fatty acids, and significant increase of oxidation products
content, what can be easily observed on example of soybean oil (fig. 4-6). Similar course of
fatty acids composition changes of investigated post-frying oils was also observed in
research of, subjected to cyclic heating, samples of rapeseed oil [Szmigielski et al. 2008;2009]
and sunflower oil [Maniak et al. 2009]. Five-time cyclic frying of breadcrumbs coated fish
fingers or potato chips caused partial stabilization of fatty acids composition, what can be
noted in case of two, dominating in soybean, fatty acids i.e. oleic and linolic. Their content in
typical raw soybean oil often exceeds 75% (fig. 3-5), [Staat and Vallet 1994, Tys et al. 2003].

Biofuel's Engineering Process Technology

646
Heating this oil only slightly changed proportion of oleic to linolic acid, for in raw oil, on
one particle of oleic acid approx. two particles of linolic acid are found. After process of
heating, this rate is approx. 1,5 - from 1,4 for sample heated without fried product to 1,50 for
sample heated in the process of frying potato chips, and up to 1,63 when sample of oil
heated in the process of frying breadcrumbs coated fish fingers is investigated.

Similar effect, when ratio of unsaturated fatty acids (oleic and linolic) is taken into
consideration, was also observed in research of sunflower oil used as frying fat in cyclic
frying of potato chips.
Fresh sunflower oil usually contains over 80% of these fatty acids, while, statistically on one
particle of oleic acid 2,47 particles of linolic acids are found. After five-time cyclic heating in
process of potato chips frying this proportion remains unchanged, while it changes only in
case of oil heated without fried product [Maniak et al. 2009].
In fresh rapeseed oil, proportion of linolic acid to oleic acid is 1 : 2,72. Five-time cyclic
heating in process of potato chips frying caused significant change of this proportion to 1 :
2,37, while, for example, effect of disturbance of this fatty acids ratio occurring during
similar cycle of heating without fried product reached 1:3,77 [Szmigielski et al. 2008]. The
same processes of heating caused also slight changes of saturated fatty acids ratio. In fresh
soybean oil, on one particle of stearic acid 2,66 particles of palmitic acid are found, while
after five cycles of heating this ratio was from 1 : 2,1 in oil heated without product (Fig. 4), 1
: 2,31 in oil subjected to heating in process of potato chips frying (Fig. 6) to 1 : 2,38 in oil
subjected to heating in process of breadcrumbs coated fish fingers frying (Fig. 5).

0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
fr
e
s

h
o
i
l
1
2
3
4
5
AN
[mg
KOH*
g
-1
]
number of cycles heating

Fig. 3. Acid number of rapeseed oil subjected to cyclic heating [mgKOH g
-1
]/ data for oil
heated in process of potato chips frying and heated without addition of product according
to Szmigielski et al. 2008/
Effect of Fried Dishes Assortment on Chosen Properties of Used
Plant Oils as Raw Materials for Production of Diesel Fuel Substitute

647

0
10
20

30
40
50
60
70
80
90
100
p
a
l
m
i
t
i
c

a
c
i
d
s
t
e
a
r
i
c

a

c
i
d
o
l
e
i
c

a
c
i
d
l
i
n
o
l
e
i
c

a
c
i
d
l
i
n
o

l
e
n
i
c

a
c
i
d
p
r
o
d
u
c
t
s

o
f

o
x
i
d
a
t
i
o

n
Commercial soybean oil Oil after I cycle of heating
Oil after II cycle of heating Oil after III cycle of heating
Oil after IV cycle of heating Oil after V cycle of heating
[% content]

Fig. 4. The composition of fatty acids of soybean oil treated five-time cyclic heating, heating
without fried product /presented data based on authors own research [Szmigielski et al.
2011]/

Biofuel's Engineering Process Technology

648

0
10
20
30
40
50
60
70
80
p
a
l
m
i
t
i

c

a
c
i
d
s
t
e
a
r
i
c

a
c
i
d
o
l
e
i
c

a
c
i
d
l
i

n
o
l
e
i
c

a
c
i
d
l
i
n
o
l
e
n
i
c

a
c
i
d
p
r
o
d
u

c
t
s

o
f

o
x
i
d
a
t
i
o
n
Commercial soybean oil Oil after I cycle of heating Oil after II cycle of heating
Oil after III cycle of heating Oil after IV cycle of heating Oil after V cycle of heatin
g
[
% content]



Fig. 5. The composition of fatty acids of soybean oil treated five-time cyclic heating, heating
in process of breadcrumbs coated fish fingers frying /presented data based on authors own
research [Szmigielski et al. 2011]/
Effect of Fried Dishes Assortment on Chosen Properties of Used
Plant Oils as Raw Materials for Production of Diesel Fuel Substitute

649

0
10
20
30
40
50
60
70
80
90
p
a
l
m
i
t
i
c

a
c
i
d
s
t
e
a
r

i
c

a
c
i
d
o
l
e
i
c

a
c
i
d
l
i
n
o
l
e
i
c

a
c
i
d

l
i
n
o
l
e
n
i
c

a
c
i
d
p
r
o
d
u
c
t
s

o
f

o
x
i
d

a
t
i
o
n
Commercial soybean oil Oil after I cycle of heating
Oil after II cycle of heating Oil after III cycle of heating
Oil after IV cycle of heating Oil after V cycle of heating
[% content]

Fig. 6. The composition of fatty acids of soybean oil treated five-time cyclic heating heating
in process of potato chips frying /presented data based on authors own research
[Szmigielski et al. 2011]/

Biofuel's Engineering Process Technology

650
Similar, slight fluctuations of stearic and palmitic acids ratio were noted after five-time
cyclic heating of rapeseed oil, and ranged from 1 : 2,97 in fresh oil, to 1 : 3,03 after heating in
process of cyclic potato chips frying and 1 : 2,94 after cyclic heating without fried product
[Szmigielski et al. 2008].
It should be noted that similar cyclic heating of sunflower oil did not cause change of ratio
of two main saturated fatty acids present in investigated oil e.g. stearic acid and palmitic
acid. The ratio was 1 : 1,69. Both in fresh sunflower oil and in oil after five-time cyclic
heating without fried product or heated in process of potato chips frying, this ratio did not
change [Maniak et al. 2009].
Presented in graphs 7-10 research data, obtained during engine tests, in which mixtures of
diesel fuel containing 10% of fatty acids methyl esters were utilised, indicate on similar
character of changes of investigated parameters of 2CA90 engine powered with methyl
esters obtained from purchased raw soybean oil and post-frying oils obtained after five-time

cyclic heating without fried product as well as five-time cyclic frying of potato chips or
breadcrumbs coated fish fingers. Mixtures containing 10% addition of esters have similar
influence on changes of power and torque of investigated engine in relation to its rotational
speed (Fig. 7 and 8).
Curves of specific and hourly fuel consumption for investigated fuel mixtures, containing
10% addition of fatty acids methyl esters, characterised with higher values of energetic
parameters, when compared to diesel fuel, for each of five investigated rotational speeds. It
should be noted that they characterize with identical nature and high similarity of their
course, what suggests insignificance of differences between them. Analogous results of
research were obtained by Szmigielski et al. [2009], who, in similar conditions, investigated
rapeseed oil samples.
4. Conclusion
1. Model, cyclic heating of plant oils, and especially three first cycles, contribute to
significant changes in composition of their fatty acids. Significant changes of peroxide
number (PN) and acid number (AN) of investigated oils were noted. Content of
unsaturated fatty acids decreases, while increase of oxidation products is observed.
2. Heating plant oils in process of frying products like breadcrumbs coated fish fingers or
potato chips affects stabilization of amount of peroxide products present in post-frying
oil, what leads to decrease of peroxide number (PN) of such oil in comparison to
process of heating without fried products.
3. Acid number (AN) of post-frying oils obtained after frying potato chips stabilized,
while frying breadcrumbs coated fish fingers and heating oil without fried product
contributed to gradual increase of AN.
4. Frying breadcrumbs coated fish fingers and potato chips favours stabilisation of
proportion of fatty acids in investigated post-frying oils, and the proportion is similar to
one noted in case of purchased raw oils.
5. Change of properties of post-frying plant oils occurring during stage of chemical
conversion to fatty acids methyl esters, contributes to unification of properties of
biofuels prepared on base of various batches of post-frying oils and favours utilization
of post-frying oils which proved as suitable for production of biofuel as fresh vegetable

oils.
6. Unidentified oxidation products undergo similar transformations in the process of fatty
acids methyl esters formation, and are not a significant obstacle in correct operation of
diesel engines powered with such biofuel.
Effect of Fried Dishes Assortment on Chosen Properties of Used
Plant Oils as Raw Materials for Production of Diesel Fuel Substitute

651
7. Results of research confirmed usability of post-frying plant oils as a raw material for
production of diesel fuel biocomponent.
8. It is currently necessary to elaborate efficient ways of recovery of post-frying fats from
points of small gastronomy, and technology of their purification and utilization as
components of fuel for diesel engines.


5
6
7
8
9
10
11
12
13
1500 1700 1900 2100 2300 2500 2700 2900 3100 n [rpm]
Ne [kW]
DF
M1
M2
M3

M4

Fig. 7. Changes of the course of engine power 2CA90 powered by diesel fuel (ON) and
mixtures containing 90% diesel fuel and 10% methyl esters of fatty acids and diesel fuel: M1
- esters obtained from purchased fresh soybean oil, M2 - esters obtained from soybean oil
without addition of fried product, M3 - esters obtained from soybean oil frying of potato
chips, M4 - esters obtained from soybean oil frying of breadcrumbs coated fish fingers.
/presented data based on authors own research /[Szmigielski et al. 2011]/

Biofuel's Engineering Process Technology

652


30
32
34
36
38
40
42
44
46
48
50
1500 1700 1900 2100 2300 2500 2700 2900 3100
M
o [Nm]
DF
M1

M2
M3
M4
n [rpm]


Fig. 8. Changes of the course of engine torque 2CA90 powered by diesel fuel (ON) and
mixtures containing 90% diesel fuel and 10% methyl esters of fatty acids and diesel fuel: M1
- esters obtained from purchased fresh soybean oil, M2 - esters obtained from soybean oil
without addition of fried product, M3 - esters obtained from soybean oil frying of potato
chips, M4 - esters obtained from soybean oil frying of breadcrumbs coated fish fingers.
/presented data based on authors own research /[Szmigielski et al. 2011]/
Effect of Fried Dishes Assortment on Chosen Properties of Used
Plant Oils as Raw Materials for Production of Diesel Fuel Substitute

653


250
270
290
310
330
350
370
390
410
430
1500 1700 1900 2100 2300 2500 2700 2900 3100
g

e [g · ( kWh
-1
)]
DF M1
M2
M3 M4
n [rpm]


Fig. 9. Changes of the course of unitary fuel consumption engine 2CA90 powered by diesel
fuel (ON) and mixtures containing 90% diesel fuel and 10% methyl esters of fatty acids and
diesel fuel: M1 - esters obtained from purchased fresh soybean oil, M2 - esters obtained from
soybean oil without addition of fried product, M3 - esters obtained from soybean oil frying
of potato chips, M4 - esters obtained from soybean oil frying of breadcrumbs coated fish
fingers. /presented data based on authors own research /[Szmigielski et al. 22011]/

Biofuel's Engineering Process Technology

654

1,5
2,0
2,5
3,0
3,5
4,0
4,5
5,0
1500 1700 1900 2100 2300 2500 2700 2900 3100
DF M1

M2
M3 M4
n [rpm]
Gp [k
g
· h
-1
]

Fig. 10. Changes of the course of hourly fuel consumption engine 2CA90 powered by diesel
fuel (ON) and mixtures containing 90% diesel fuel and 10% methyl esters of fatty acids and
diesel fuel: M1 - esters obtained from purchased fresh soybean oil, M2 - esters obtained from
soybean oil without addition of fried product, M3 - esters obtained from soybean oil frying
of potato chips, M4 - esters obtained from soybean oil frying of breadcrumbs coated fish
fingers. /presented data based on authors own research /[Szmigielski et al. 2011]/
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