MODEL FOR THE CORRECTION OF THE SPECIFIC GRAVITY OF BIODIESEL FROM
RESIDUAL OIL
Tatiana Aparecida
Rosa da Silva
Instituto
Federal de Educação, Ciência e Tecnologia de São Paulo, Campus Avaré, Brazil
E-mail: tatyqui2@yahoo.com.br
Douglas Queiroz Santos
Federal University of Uberlândia, Institute of Chemistry, Brazil
E-mail: quimicodouglas@yahoo.com.br
Ana Paula de Lima
Federal University of Uberlândia, Institute of Chemistry, Brazil
E-mail: analimaquimica@gmail.com
Waldomiro Borges Neto
Federal University of Uberlândia, Institute of Chemistry, Brazil
E-mail: wbn@iqufu.ufu.br
Submission: 27/03/2013
Accept: 03/04/2013
ABSTRACT
Biodiesel is an
important fuel with economic benefits, social and environmental. The production
cost of the biodiesel can be significantly lowered if the raw material is
replaced by a alternative material as residual oil. In this study, the variation of specific gravity with temperature
increase for diesel and biodiesel from residual oil obtained by homogeneous
basic catalysis. All properties analyzed for biodiesel are within specification
Brazil. The determination of the correction algorithm for the specific gravity
function of temperature is also presented, and the slope of the line to diesel
fuel, methylic biodiesel (BMR) and ethylic biodiesel (BER) from residual oil
were respectively the values -0.7089, -0.7290 and -0.7277. This demonstrates
the existence of difference of the model when compared chemically different
fuels, like diesel and biodiesel from different sources, indicating the
importance of determining the specific algorithm for the operations of
conversion of volume to the reference temperature.
Keywords: biodiesel,
residual oil, correction algorithm, specific gravity.
1. INTRODUCTION
In
recent years the demand for renewable fuels has greatly increased, is
increasing the price of oil or by concern for the environment due to climate
change induced by the use of fossil fuels, making renewable energy sources
extremely important (BALAT and BALAT, 2010, DABDOUB et al., 2009, NAMASIVAYAM et
al., 2010). In this context, biodiesel plays an important role, especially in
Brazil, with economic benefits, social and environmental. Although the
increased emission of nitrogen compounds, biodiesel provides the reduction of
pollutants such as particulate matter, carbon monoxide, polycyclic aromatic
hydrocarbons (carcinogenic compounds) and sulfur oxides in relation to
petroleum diesel, based on the entire production cycle and consumption. The
role of biodiesel is beneficial, contributing to the longevity and efficiency
of diesel engines, serving markets that request a fuel cleaner and safer (ABU-JRAI
et al., 2009, ALTUN et al., 2008, DEMIRBAS, 2009).
The
cost reduction in the production of biodiesel becomes essential, assuming the
raw material has a share in the cost of the final product above 80%, therefore
cheap raw materials such as residual oils and fats have attracted the attention
of producers of biodiesel due to its low cost (HAAS et al., 2006). The
recycling of frying oil as biofuel not only deprive an unwanted compound of the
environment, but also allow the generation of an alternative energy source,
renewable and less polluting waste which would be transformed into a source of
energy (LAM et al., 2010).
For
the production of biodiesel the technologic (BALAT and BALAT, 2010) most
commonly used in the world is the trans esterification (ENCINAR et al., 2011, KNOTHE,
2005, SHARMA et al., 2008, WANG et al., 2007). The biodiesels’ of various
sources may be physico-chemical properties significantly different; by varying
the fatty acid profile and the qualities of biodiesel produced by trans
esterification reaction is influenced by productive route (VALENTE et al.,
2011).
Specific
gravity is one of the most important properties of fuels, because injection
systems, pumps and injectors must deliver the amount of fuel precisely adjusted
to provide proper combustion. It is an intensive property that is independent
of the quantity, can be indicative of pure and can also be used to perform
conversions by volume (ALPTEKIN and CANAKCI, 2008, CASTRO et al., 2005, TAT and
VAN GERPEN, 2000, RODRÍGUEZ-ANTÓN et al., 2008).
In
Brazil, measure the volume of fuel to generate billing commercial transactions
is performed at 20.0 °C (reference temperature), such as loading and unloading
operations occur at ambient temperature it is necessary to convert the
environment volume for the volume at the reference temperature(SANTOS and VIEIRA,
2010). The ABNT NBR 15512 recommends that to convert the specific gravity and
volume to the reference temperature, the table is used for derivatives of
petroleum.
Data
conversion of specific gravity were obtained in the 70's, where resources were
smaller, the equipment were not as sensitive and not had so many varieties of
fuels and biofuels. Furthermore, it is important to note that since this is a
table prepared for derivatives of petroleum is a big difference in chemical
structure, on the one hand hydrocarbons (petroleum) and other alkyl esters
(biodiesel).
With
the inclusion of biodiesel in Brazil's energy matrix is necessary to know a
mathematical algorithm for the correction of specific gravity, to avoid the use
of current models lagged as recommended by the ABNT NBR 15512.
This
study aims to determine the mathematical algorithm to correct the specific
gravity of methylic and ethylic biodiesel from residual oil and compare it with
diesel.
2. EXPERIMENTAL
Biodiesel
used was obtained by ethylic trans esterification (BER) and methylic alkaline
(BMR), using as raw material the residual oil. The reaction conditions were
rotating at 80 rpm, the molar ratio alcohol: oil 7:1, catalyst, potassium
hydroxide at a concentration of 1.7 wt% being to ethylic temperature of 35 °C
and reaction time of 30 minutes and the methyl temperature of 48 °C and
reaction time 60 minutes. After the alkaline transesterification reaction, the
system resulted in two phases with impure biodiesel being formed at the top and
glycerine at the bottom. The biodiesel was removed from the mixture, adjusted
the pH to near 7 and then washed 3 times with water at 80 °C. Residual water
was removed by rotary evaporation and the biodiesel obtained.
The
methods used to analyze the biodiesel were: acidity ASTM D-664, humidity ASTM D-6304,
viscosity ASTM D-445 e D-446, oxidative stability EN
14112, flash point ASTM D-93, specific gravity ASTM
D-4052, peroxide index NBR 9678, free glycerol
NBR 15771 and carbon residue ASTM 4730. The specific
gravity was determined on a Kyoto
density/specific mass meter (model DA-500), according
to ASTM D-4052, within
the temperature range of 10 to 50 °C at
intervals of 5 °C. The
calibration was performed with water,
the default uncertainty of expanded of
which is ± 0.01 kg m-3, in order to ensure the
reliability of the metrological experiments.
Using simple
linear regression of μ versus T
it was possible to determine the mathematical
algorithms for the correction of
the specific gravity of ethylic (BER) and
methylic (BMR) biodiesels
obtained from residual oil. The collected data were
analyzed using the Statistica 7.0 StatSoft.
3. RESULTS AND DISCUSSION
The physical-chemical properties of biodiesel are
directly related to fuel quality (DABDOUB et al., 2009). In the
characterization of methylic and ethylic biodiesel from residual oil, were
performed some analyzes shown in Table 1.
Table 1. Physical and chemical properties of
methylic (BMR) and ethylic (BER) biodiesel fom residual oil
PROPERTIES |
UNITS |
BMR |
BER |
ANP |
METHOD |
Water |
mg kg-1 |
127.8 |
129.5 |
<500 |
ASTM D-6304 |
Acidity |
mg KOH g-1 |
0.27 |
0.37 |
<0.50 |
ASTM D-664 |
Free glycerol |
% mass |
8.55×10-5 |
1.07×10-4 |
< 0.02 |
NBR 15771 |
Specific gravity |
kg m-3 |
880.7 |
877.1 |
850 – 900 |
ASTM D-4052 |
Flash Point |
oC |
176 |
175 |
>100 |
ASTM D-93 |
Viscosity |
mm2 s-1 |
4.2 |
4.5 |
3.0 – 6.0 |
ASTM D-445 |
Carbon residue |
wt % |
0.003 |
0.011 |
< 0.050 |
ASTM 4730 |
Peroxide value |
meq kg-1 |
4.11 |
3.70 |
--- |
NBR 9678 |
Oxidative Stability |
hours |
6.36 |
7.19 |
>6.00 |
EN 14112 |
All
results meet the specification of ANP (2012) and the methylic and ethylic
biodiesel have slightly different values due to the slight difference in the
structure of methylic and ethylic esters.
Moisture
is a very important parameter for the quality of biodiesel, since water can
cause an unwanted reaction (hydrolysis) decompose biodiesel and producing free
fatty acids, which can cause the development of engine problems. As the
moisture content, the acidity of a fuel is an essential factor control since
the presence of free fatty acids may trigger a whole oxidation of the fuel, and
is also responsible for oxidation of the internal engine parts, causing
corrosion and formation deposits. The acidity is also within the specification
(KNOTHE, 2007).
According to the results, the
washing procedure was effective to remove free glycerin. Fuels with excess free
glycerin cause clogging of fuel filters, deposition of glycerol in the storage
tanks and therefore problems in the combustion engine. Moreover, the burning of
glycerin leads, among other toxic compounds, acrolein is a carcinogen aldehyde
can cause respiratory problems for long periods inspired case as in traffic
jams inside tunnels, something frequently in large cities (ATADASHI et al.,
2010).
The fluid dynamic properties of a fuel, which are
important as regards the operation of injection compression engines (diesel engines),
are the viscosity and specific gravity. These properties have great influence
on the movement and fuel injection (MORÓN-VILLARREYES et al., 2007, JORGE et
al., 2005).
The parameter specific gravity is
within the limits accepted by ANP for both, the ethylic and methylic biodiesel
of residual oil. There an essential property affecting the development of the
engine, since fuel air ratio in the combustion chamber are affected by it (HOEKMAN
et al., 2011). The flash point, which is the temperature at which a flammable
liquid becomes in the presence of a flame or sparks. This property is of
importance only as regards the safety of transport, handling and storage, and
may indicate contamination by alcohol. Methylic biodiesel was lower than that
of ethylic biodiesel probably due to the length of the carbon be smaller, the
value found is close to the reported by Dantas and colleagues (ATADASHI et al.,
2010, DANTAS et al., 2011).
A major objective of biodiesel
production is to reduce the viscosity of triglycerides to values close to the
diesel, because this property is an important parameter for the injection
system of vehicles and the fuel pumping system. Both biodiesels meet the
specification stating different viscosity of diesel oil (DANTAS et al., 2011).
The burning of the esters produced
was almost complete with only minimal residual negligible smaller than the
maximum required by ANP, providing a fuel quality. These residues can cause the
formation of sludge in the region of the nozzle, which can cause problems in
operation and, in severe cases, irreparable damage to internal parts.
Although not a requirement of the fuel analysis of the peroxide have proven to be an interesting study object, since the oxidation reaction is often suggested by the increase in peroxide value over the storage period.
The biodiesel showed good oxidative stability. Fuel can
lead to unstable increased viscosity and the formation of gums, sediment, or
other deposits. More ideas on these degradation processes are provided in
reviews recent literature on the subject (HOEKMAN et al., 2011).
Table 2, there are measured values of specific gravity as a function of temperature (10 to 50 °C) methylic and ethylic biodiesel of residual oil, BMR and BER, respectively and diesel. The specific gravity to 20 °C for methylic and ethylic esters from residual oil of respectively 880.7 kg m-3, and 877.1 kg m-3, and 855.2 kg m-3 to diesel oil to 293.15K. These values found for the biodiesels are close to values found in literature for different materials, ranging from 873 to 883 kg m-3. The slight difference is due to the change of the raw material used, shows that different variations in volume, according to each molecule of biodiesel.
Table 2. Measured values of specific gravity as
a function of temperature of the biodiesels’ from residual oil and diesel oil
T/°C |
BER (kg m-3) |
BMR (kg m-3) |
DIESEL (kg m-3) |
10 |
884.4 |
888.1 |
862.2 |
15 |
880.8 |
884.4 |
858.7 |
20 |
877.1 |
880.7 |
855.2 |
25 |
873.4 |
877.0 |
851.7 |
30 |
869.8 |
873.5 |
848.1 |
35 |
866.2 |
869.8 |
844.6 |
40 |
862.6 |
866.2 |
841.0 |
45 |
858.9 |
862.5 |
837.5 |
50 |
855.3 |
858.9 |
833.9 |
Order
to facilitate trade in these products, value all business operations and
establish the prices to the volumes referred to a reference temperature of 20.0
°C it is necessary to fix the volume of ambient temperature to the reference
temperature in Brazil, being needed for this mathematical algorithm to
determine this correction.
Currently the Brazilian standard ABNT NBR 15512 of 1970 provides that for correction of volume and specific gravity to the temperature of reference is used a single table. This standard is applied to petroleum products coming from non-renewable sources and how old does not include chemically different compounds such as biodiesel, a fuel cleaner and come from a renewable source. The calculation of the correct volume is important for dealers and biodiesel industries; because they pay the price per liter of biofuel and this calculation must be in accordance to the raw material used.
From the data in Table 2 was prepared Figure 1 to determine mathematical algorithm. Note that the specific gravity is a decreasing linear function of temperature and shows that the slope sensitivity to temperature being the diesel fuel, BMR and BER these values were respectively, 0.7089 kg m-3 T-1, 0.7290 kg m-3 T-1 and 0.7277 kg m-3 T-1.
Figure
1. Linear regression of specific gravity versus temperature of diesel fuel, BMR
and BER.
Statistical methods allow to characterize the experimentally data obtained and evaluate the quality of these data on the assumption that the random errors contained in the analytical results follow in most cases a Gaussian distribution, or normal. Through statistical analysis of linear regression of the data specific gravity is possible to accept the mathematical algorithm and provide through a simple statistical test, called F-test if the regression is significant within a confidence level (SKOOG et al., 2007).
Residual
analysis is essential to evaluate the fit of any model. A model that leaves much
waste is a bad model. In an ideal model would be no waste, ie, the results
observed were equal to those (MONTGOMERY, 2001). It can be found in Figure 2 for
both biodiesels alternating vertical deviations of points about straight line
are called residues, which can be concluded that the variance of errors is
constant and that there is the presence of systematic errors.
Figure
2. Residue versus the predicted
value from data specific gravity for BMR and BER.
Data from methylic and ethylic
biodiesel behave near normal distribution, according to Figure 3, showing
adaptation of the mathematical model the system studied.
Figure
3. Distribution of the residuals for data specific gravity about the line
indicating normal to BMR and BER.
Table 3 shows the statistical linear regression. The model fit was also expressed by a coefficient of determination (R2), equal to 0.999 for both cases, as the R2 value is near the theoretical, it can be said that modeling was adequate and the sensitivity of the model (slope) whose values are ± 0.0033 for BMR and ± 0.0025 for BER. From analysis of variance (ANOVA) determined the value of the F statistic, the Fcalculated values are larger than the Ftabulated, to BMR Fcalculated = 2.69 × 105 and to BER Fcalculated = 4.70 × 105, showing that the model is predictive and significant at a confidence level of 95%, and no reported lack of fit within the range evaluated.
Table
3. Data linear regression to diesel fuel, BER and BMR for determination
algorithm to correct specific gravity
SAMPLE |
DATA REGRESSION |
R2 |
Fcalculated |
Ftabulated |
p-value |
|
Linear Coefficient |
Slope |
|||||
Diesel |
869.27 |
-0.7089 |
99.99% |
9.3×105 |
5.59 |
4.52×10-18 |
BER |
891.70 |
-0.7277 |
99.99% |
4.7×105 |
5.59 |
3.71×10-18 |
BMR |
895.30 |
-0.7290 |
99.99% |
2.7×105 |
5.59 |
2.61×10-17 |
The linear coefficient represents physically the initial specific gravity, therefore, the algorithms for correction of volume adopt the following Equations 2-4 for methylic and ethylic biodiesel and diesel, respectively, in the temperature range studied:
Equation 2
Equation 3
Equation 4
Comparing
the slope of the BMR, the BER and diesel perceive a considerable difference
between them and the values determined by Yoon and colleagues(Yoon, 2008). The
difference found when comparing different sources of fuels such as diesel and
biodiesel, suggests that the algorithm has to be determined for each fuel,
which differs from that recommended by the ABNT NBR 15512 that evaluates the
correction of the specific gravity of biodiesel using table of petroleum
products.
CONCLUSIONS
This
work it was possible the modeling algorithm to correct specific gravity of
biodiesel from residual oil. According to statistical data, the mathematical
algorithm to correct specific mass is a linear model and predictive and
significant at a confidence level of 95%, described by the equations presented
with slope of 0.7089 for diesel oil, 0.7290 for methylic (BMR) and 0.7277 for
the ethylic biodiesel (BER) from residual oil.
The
results show that biodiesel from residual oil presents thermal behavior
different from that of diesel and biodiesel, and between biodieseis there is a
subtle difference. Importantly, the ABNT NBR 15512 recommends that the bases
and distribution terminals to correct specific gravity at temperature 20 °C
should be based on the conversion table used for petroleum products and in this
work demonstrate that this approach is not the most appropriate for the matrix
of biodiesel from residual oil.
ACKNOWLEDGMENT
The
authors thank FAPEMIG and CNPq for financial support and scholarships.
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