Evaluation of physical and chemical characteristics of biofuel from tropical
fruits
Evaluación de las características físicas y químicas de biocombustible a partir de frutas
tropicales
José Villarroel Bastidas
Master in Food Processing, research professor, Faculty of
Engineering Sciences, Quevedo, Ecuador
jvillarroel@uteq.edu.ec, https://orcid.org/0000-0002-9013-
3776
Gissela Rocio Cobeña Cedeño
Agroindustrial Engineer, Faculty of Engineering Sciences,
Quevedo, Ecuador gisselarced.cobena@uteq.edu.ec
https://orcid.org/0000-0002-0572-8987
Bryan Josué Espinoza-Oviedo
Master, Faculty of Engineering Sciences, Quevedo, Ecuador
bespinoza@uteq.edu.ec, https://orcid.org/0000-0002-9013-
3739
jvillarroel@uteq.edu.ec
Abstract
The different wastes generated by farmers engaged in the
production of pineapple, papaya and banana generate
large amounts of waste without an adequate treatment for
them, with a fermentation process, and then applying a
distillation method, bioethanol can be obtained from all
this type of waste. The present work is focused on
obtaining bioethanol from the wastes of three tropical
fruits by means of fermentation applying different
percentages of yeast. A completely randomized block
experimental design was applied with factorial
arrangement A x B where factor A is equal to the types of
fruits (papaya, guineo and pineapple), while factor B is
equal to the three levels of Saccharomyces cerevisiae
yeast (0%, 0.05% and 0.10%), which gives a total of 18
experimental units: ° Brix, pH, turbidity, alcoholic
degrees, acidity, density and specific heat; for validation
of the research, an analysis of combustion power between
a mixture of 10% ethanol and 90% gasoline was
subjected. The results obtained indicate that the sample
(guineo + 0.05% yeast) showed better chemical and
physical characteristics Brix (16.5), density (0.9834
g/cc), specific heat (2.398 kJ/ kg), alcoholic (17.33 °GL),
acidity (0.820) being the best treatment for bioethanol
production.
Key words: Specific heat, density, alcoholic strength,
combustion power.
http://centrosuragraria.com/index.php/revista, Published by: Edwards Deming
Institute, Quito - Ecuador, July - September vol. 1. Num. 9 2021, This work is
licensed under a Creative Commons License, Attribution-NonCommercial-
ShareAlike 4.0 International. https://creativecommons.org/licenses/by-nc-
sa/4.0/deed.es
Abstract
Los diferentes desperdicios que generan los agricultores que se dedican a la producción de piña, papaya
y guineo generan grandes cantidades de desechos sin que exista un tratamiento adecuado para los
mismos, con un proceso fermentativo, para luego aplicar un método de destilación se podrá obtener
bioetanol de todo este tipo de desechos. El presente trabajo está enfocado en la obtención de bioetanol
a partir de los desechos de tres frutas tropicales mediante la fermentación aplicando diferentes
porcentajes de levadura, Se Aplicó un Diseño experimental de bloques Completamente al Azar con
arreglo factorial A x B donde factor A es igual a los tipos de frutas (papaya, guineo y piña), mientras
que factor B es igual a los tres niveles de levadura Saccharomyces cerevisiae (0%, 0,05% y 0,10%), los
mismos que da un total de 18 unidades experimentales, se realizaron diversos análisis como: ° Brix,
pH, turbidez, grados alcohólicos, acidez, densidad y calor especifico; para la validación de la
investigación se sometió a un análisis de poder de combustión entre una mezcla del 10% de etanol y
90% de gasolina. Los resultados obtenidos indican que la muestra (guineo+ 0,05% de levadura), mostró
mejores características químicas y físicas Brix (16,5), Densidad (0,9834 g/cc), Calor especifico (2,398
kJ/ kg), alcohólicos (17,33 °GL), Acidez (0,820) siendo el mejor tratamiento para la producción de
bioetanol.
Palabras clave: Calor específico, densidad, grados alcohólicos, poder de combustión.
Introduction
Bioethanol has been identified as the most widely used biofuel worldwide as it contributes
significantly to the reduction of crude oil consumption and environmental pollution. It can be
produced from various types of feed materials such as sucrose, starch, lignocellulosic and algae
biomass through fermentation process by microorganisms Borras, (2013) Biofuels currently
represent a potential source of renewable energy, in addition to the fact that they could generate
new and large markets for agricultural producers (Romo-Fernandez et al., 2013, p. 34).
Biofuels are those biofuels such as alcohols, ethers, esters and other chemical products that
come from cellulosic-based organic compounds (biomass) extracted from wild or cultivated
plants, which replace to a greater or lesser extent the use of gasoline in transportation or
intended to produce electricity Déniz & Verona, (2015).
Second generation (2G) biofuels differ from first generation biofuels in two aspects: They are
obtained from vegetables that do not have a food function, and they are produced with
technological innovations that will allow them to be more environmentally friendly and
advanced than the current ones Romo-Fernandez et al., (2013)
Biofuels of biological origin can replace part of the consumption of traditional fossil fuels, such
as oil and coal; this type of fuel is almost always in liquid form and is used to drive combustion
engines in land transportation. The most developed and used biofuels are bioethanol and
biodiesel; biodiesel, also known as biogas oil or diester, is a renewable fuel that substitutes
Received March 02, 2020
Approved: October 03, 2020
Villarroel, Cobeña
July - September vol. 1. Num. 9 2021
51
diesel and comes from the processing of vegetable oils, both natural and recycled (soybean,
sunflower, palm, etc.) and animal fats, de Oliveira & Abadía, (2013).
In this way, the accumulation of waste would be reduced, giving an added value to vegetable
waste, contributing to the production of clean energy that does not pollute our environment.
First generation biofuels refer to those produced from raw materials of edible origin (sugars,
starches and vegetable oils) through conventional and commercially well-established
technologies, including fermentation, transesterification, etc. (Ramírez, 2013, p. 87).
At present, Borras, lignocellulosic biomass and especially agro-industrial by-products are no
longer waste-problem products, but have become potential raw materials for various
agricultural and industrial processes, one of the most important being the production of fuel
alcohol (2013).
The main disadvantage of first-generation ethanol is that the use of food resources as fuel may
threaten the food supply to a large part of the population, while, on the other hand, food prices
could also increase. Only if an adequate sustainability strategy is defined for the production
and use of biomass, it could be claimed, in the future, that biofuels, as renewable energy, are
environmentally and socially convenient Ruiz & Galicia, (2016). These new fuels open up the
possibility of obtaining more environmentally friendly fuels that do not compete with food
crops, that also collaborate doubly against climate change and that are produced using our own
resources and, therefore, reduce our external dependence on fossil fuels (Espinosa-Bueno et
al., 2010, p. 34). The purification and enrichment in alcohol of these ethanol-water mixtures is
currently carried out using distillation as a separation process, whose energy consumption is
high with respect to the energy content of the product achieved Barrasa,(2017).
Materials and methods
We will study 3 types of fruit residues, which are not very industrialized, for which we will
apply in this type of research an analysis of variance with the structured tukey significance test
with 3 study factors referring to the types of fruit, and different percentages of yeast referring
to the times and temperatures.
For the study of the results obtained, a completely randomized block design was used with an
AxB factorial arrangement, where Factor A is the fruit used in fermentation and Factor B is the
percentage of yeast, giving a total of 18 treatments with two replicates. The variables used are:
°Brix, pH, Turbidity, Alcoholic degrees, Acidity, Density and Calorimetry.
Table 1. Study variables
Factors
Symbolog
y
a0
A: Fruit
a1
a2
b0
B: Percentage of yeasts
b1
b2
With the 18 samples, the respective analyses were performed on each sample, the physical
analyses of: turbidity, density, specific heat and chemical analyses such as pH, °Brix, acidity
and alcoholic strength.
In the last analysis, all the samples are distilled, obtaining a single distilled sample as the best
treatment. This analysis was carried out by combining ethanol (10%) and gasoline (90%),
tested in a mechanical engine of the Quevedo State Technical University.
The pH analyses were carried out in the Unit Operations Laboratory with an equipment called
"OAKLON" by inserting the electrode in each sample, and with the pH measuring strips to
obtain the pH values of the raw material.
The Brix degrees were measured in an "ATAGO" Brixometer of the raw material received, and
of the ethanol, one to two drops of the sample were placed and then the percentage indicated
by the equipment was observed.
It was carried out by titration by means of NaOH (Sodium Hydroxide) consumption at 0.1 of
Normality in a 10 ml sample of the extracted bioethanol, C20H14O4 (Phenolphthalein) was
used as indicator, procedure based on NTE INEN 341 Alcoholic beverages. Determination of
acidity. The pH measurement was based on standard NTE INEN 0973 (1984), which consisted
of using a pH meter, introducing the electrode into the liquid sample of the product and the oil
sample was used directly for the measurement.
Acidez(%)= !
V
NaOH
!
mL
"
× N
NaOH #
meq
mL
$
×!
0.064g
meq
"
W
peso de la muestra
!
%&'(')'
"
"
×100
(1)
It was carried out in an equipment called Alcoholimeter, 90 ml was measured for each sample
in a 100 ml test tube, and then the alcoholmeter was introduced into the substance and the
equipment was rotated in such a way that when it stopped, the level of alcoholic degree of each
ethanol sample could be read. The best treatment obtained, the °GL was taken in an
"AQUEOUS LAB" equipment, a Portable Refractometer, in the following way: it is placed (1-
2 drops) in the device and the value obtained is visualized.
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53
In the determination of the density of a liquid (ethanol) with the pycnometer method, the mass
of the liquid in three different situations is needed. The masses must be determined in an
analytical balance, the values obtained are the mass of the empty pycnometer, then the mass of
the pycnometer with water and finally the mass of the pycnometer with the solution (ethanol)
with these 3 data for each sample is placed in the formula, and determine the value obtained
from each treatment.
This analysis is performed in a "HACH TURBIDIMETER" equipment, which allows us to
obtain the values in NTU (Nephelometric Turbidity Unit). To do this, turn on the equipment,
introduce a sample of 30 ml of the substance, press "enter" and wait 60 seconds where the
machine automatically gives us the turbidity level of the treatment.
The sample is measured by a test tube, a value of 160 ml, is placed in the equipment, where
you will find a thermometer which raises its temperature according to the heat of each sample
that is constantly moving with a stirrer, the temperature should start at 25°C and reach
maximum 60°C, the solution, reacts to 6 volts, and 1 ampere; which operates at current. The
values given by the machine are determined by a stopwatch, which starts at 0 seconds and ends
in approximately 1 hour, then the specific heat is determined by means of a physical formula.
The combustion power was determined by distilling all the samples, obtaining only one sample
as the best treatment, which had 70°GL. This analysis was carried out by combining ethanol
with gasoline and testing it in a mechanical engine of the Quevedo State Technical University.
The statistical analysis of the results obtained for the study variables was carried out by means
of an analysis of variance (ADEVA) and to determine significant differences, the Tukey
significance test was applied (p ≤ 0.05); this analysis was performed in the statistical program
STATGRAPHICS Centurión XVI version 16.2.04.
Result
Graph 1: Results of mean difference between fruit types (papaya, banana and pineapple) in the
Tukey significance test (p < 0.05). 1. °Brix; 2. pH; 3. Turbidity; 4. ° Alcoholic.
In graph 1, there was a significant difference in the °Brix, the highest value was present in
banana = 16.5 and a lower value in pineapple = 8.58; regarding pH, papaya presented the
highest value with an average of 5 while pineapple obtained an average pH of 4 with the lowest
value; In the turbidity results, there was a significant difference, the pineapple obtained the
most relevant value 7.45 NTU while the papaya obtained 1.24 NTU being the lowest value;
the guineo had the highest alcohol content with 17.33 °GL and the papaya had the lowest value
with an alcohol content of 7.16 °GL.
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July - September vol. 1. Num. 9 2021
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Graph 2: Results of the difference of means between the types of fruit (papaya, banana and
pineapple) in the Tukey significance test (p < 0.05). Acidity; 2. Density; 3. Calorimetry.
In graph 2, there was a significant difference in acidity, finding the highest value in Guineo =
0.823, while the lowest value was obtained in Papaya = 0.610, as for density a significant
difference was found in the variables where the highest value was found in Papaya = 0.9935
having the lowest value in the factor Pineapple = 0.9828 in calorimetry analysis also found a
significant difference between its values had the lowest values Papaya = 1.038 and the highest
in Guineo = 2.398.
Table 2. Mean values of the interactions for each of the analyses.
Factor
A
Fac
tor
B
Brix
(%)
pH
turbidi
ty
°GL
acidity
density
calorimetry
Papaya
0%
14,5
4,5
4,945
0,89
0,96804
5
2,62153
Papaya
0,5
0%
4,5
5,265
0,8565
0,99112
2,54871
Papaya
1,0
0%
4,5
2,34
0,7225
0,99119
5
2,02584
Guineo
0%
7,5
5
2,5
0,64
0,99458
5
1,03782
Guineo
0,5
0%
8,5
5
0,865
5,5
0,653
0,99297
5
1,03952
Guineo
1,0
0%
11,25
5
0,355
0,5375
0,99297
5
1,0395
Pineappl
e
0%
8,5
6,27
17,5
0,78
0,98374
1,82045
Pineappl
e
0,5
0%
6,245
14,5
0,554
0,98886
5
3,4868
Pineappl
e
1,0
0%
8,25
9,825
0,58
0,97592
1,83502
Table 2 shows the results of the Tukey significance test (p<0.05) applied to the A*B Interaction
(Fruit vs. Percentage of yeast) in the following variables: With respect to the °Brix did not
present significant difference, standing out as the highest value (20 °Brix) in the interaction
Papaya vs 0.05% and in lower value 7.5 °Brix the interaction guineo vs 0%; in relation to pH,
no significant difference was observed between the means of the interactions, presenting pH
values in the interactions ranging from 4 to 5; According to the Turbidity values, there was no
significant difference, with the highest value of 9.825 NTU for the interaction (Pineapple vs.
1%) and the lowest value of 0.355 NTU for the interaction (banana vs. 1%); in the alcohol
content, no significant difference was observed, with the highest value of 24 °GL for the
interaction (Papaya vs. 0%) and the lowest value of 5.5 °GL for the interaction (banana vs.
0.05%); With respect to acidity, no difference was observed, obtaining the highest value (0.89
%) for the interaction (Papaya vs 0%) and the interaction (Guineo vs 1%) presented the lowest
value with an acidity of 0.5375 %; with respect to density, a significant difference was
observed, where the interaction (Guineo vs 0%) presented the highest density (0.994585 g/cc)
and the interaction (Papaya vs 0%) presented the lowest density (0.968045 g/cc); According to
the calorimetry results, there was a significant difference, where the a2b1 interaction
(Pineapple vs. 0.05%) had the highest value (3.4868) and the lowest value (1.03782) was the
interaction (Guineo vs. 0%).
According to the results of °Brix, papaya = 9.0) and pineapple = 8.58 are within the ranges
established (max. 15 °Brix) by Ramírez & Ibarra, (2015). in their study of continuous ethanol
production from rejection banana (peel and pulp) using immobilized cells; while (guineo)
presented a slightly elevated value (16.5 °Brix) to those established by Ramírez & Ibarra,
(2015), this means that the fermentation process was not fully complied with.
In relation to pH, the guineo (a1 = 4.5) and pineapple (a2 = 4) are within the established ranges
(max 4.8 pH) by Carvalho Junior, Armando Mariante; Maciel Raimundo, Julio Cesar; In their
evaluation of Bioethanol from sugarcane energy for sustainable development; Chapter 5
Villarroel, Cobeña
July - September vol. 1. Num. 9 2021
57
Advanced technologies in the sugarcane agroindustry. While in papaya = 5) is out of range due
to the fact that Papaya contains a higher content of hydrogen ions, so it must undergo a
stabilization process, in terms of the pH values given by Ballesteros et al. (2021). In their
Obtención de una bebida alcohólica a partir de mucílago de cacao, mediante fermentación
anaerobia en diferentes tiempos de inoculación their maximum value is 4.33 leaving the
Pineapple = 4 within the ranges, while papaya and guineo contain higher values compared to
the referent research.
Regarding Turbidity, the factor Papaya (1.24 NTU) and Guineo (4.18 NTU) are close to the
ranges established by Mayor & Martel, (2015), in Caracterización ambiental de las vinazas de
residuos de caña de azúcar resultantes de la producción de etanol, mentions that the point of
turbidity obtained in their research is maximum 4.745 NTU, while in pineapple (7.45 NTU) is
above this range.
As for the results of alcoholic degrees in papaya = 7.16 is within the parameters established by
Vazquez, H.J, & Acosta, O. In their evaluation of Alcoholic fermentation: An option for the
production of renewable energy from agricultural waste. The alcoholic values have a range of
(8 - 12 °GL max), while in guineo = 17.33), and pineapple = 15.33 are not within the established
ranges, since the degradation of the sugars of these fruits was in higher percentage.
In the values obtained in the acidity analysis based on the data of Goya Baquerizo, Mariuxi
Jessenia in her Obtención de una bebida alcohólica a partir de mucílago de cacao, mediante
fermentación anaerobia en diferentes tiempos de inoculación Ruiz & Maldonado, (2014).
Where it presents that the maximum acidity values are 1.14 mg, it is considered that the factors
studied in this research obtain acidity values within the established range in Papaya = 0.610
and Guineo = 0.823, pineapple = 0.638.
In the density results papaya = 0.9935 guineo = 0.9834 and pineapple (0.9828) show values
different from those specified in the density standard (maximum 0.792), in its evaluation of
sugarcane bioethanol energy for sustainable development; Chapter 2 (ethanol as vehicle fuel),
this means that based on this research the bioethanol extracted from these three tropical fruits
obtained lower alcohol content, since the higher the °GL the lower the density, while based on
the research (Romo-Fernandez et al., 2013, p. 4), in their study of continuous ethanol
production from reject banana (peel and pulp) using immobilized cells. The results of the
factors were found to be within the range established by the same (1.05 maximum).
In relation to the specific heat the factors Papaya = 1,038 kJ/kg Guineo = 2,398 kJ/kg and
Pineapple = 2,380 kJ/kg, present relatively low values in comparison with the value exposed
in the investigated article, it is exposed that the maximum value of the specific heat is 28,225
kJ/kg the results are within the established range, as for the relation with the article Colombia
in the fuel era, it indicates that the maximum value of specific heat is 2,386 kJ/kg where the
value of the factors papaya = 1.038 and pineapple = 2.380 are within the established range
while guineo = 2.398) reflects a small alteration in its result concluding that it is not within the
established range, this means that the reduction of the specific heat is due to the oxygen content
in the structure of the guineo fruits that compose the bioethanol and, therefore, the percentage
of carbon is lower than in the commercial diesel fuel.
Conclusions
With regard to the fruits evaluated in the bioethanol production process, it is concluded that the
guineo obtained better physical-chemical characteristics in the bioethanol obtained, standing
out in the following variables: °Brix (16.5), Density (0.9834 g/cc), Specific heat (2.398 kJ/ kg),
alcoholic (17.33 °GL), Acidity (0.820).
In the percentages of Saccharomyces cerevisina yeast that were studied (0%, 0.05% and 1%),
it is concluded that all the factors studied contain the necessary characteristics to obtain an
optimum process, in terms of reference with the cited bibliographies, from which a comparison
is made with the studies of other fruits based on the established ranges, finding a significant
difference in the density and specific heat variable, The optimum density was obtained in
relation to the yeast percentage, since the lower the density, the better quality bioethanol will
be obtained, while in relation to the specific heat, the most optimum value is 0.05 % of yeast,
obtaining the highest value of specific heat, thus concluding that based on this study the most
optimum percentage is 0.05 %, which reflects the results with the best characteristics for the
final product. By means of the material balance it was concluded that the interaction with
(guineo vs. yeast at 0.05%) presented the highest amount of bioethanol extracted (1000g) while
the lowest yield was obtained in the interaction (papaya vs. yeast at 0%), concluding that guineo
+ 0.05% yeast is the most optimal interaction.
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