Economy & Energy
Year XIII-No 74
July - September
2009
ISSN 1518-2932

 

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Liquid Biofuels in Brazil

Omar Campos Ferreira

Biofuels correspond to about 24 % of the energy supply in Brazil and to 28% of all consumed fuel. The most important are firewood in the residential, agriculture, cattle-raising and industrial areas, charcoal in steelworks and ethanol in road transport. Recently (2002) the Federal Government established the Program for Alternative Sources Incentive – PROINFA – in order to introduce renewable sources for electricity generation and created in 2003 the National Biodiesel Program aiming at complementing the fuel supply for transport.

 Sugarcane Products

Sugarcane is the second most important renewable source of energy in the Brazilian energy matrix and according to some projections it may become the most important one.

Source:Ministry of Mines and Energy

Sugarcane originated in India and was introduced in Brazil, then a Portuguese colony, in the 19th century and had adapted to the Brazilian Northeast climate and became the basis of the longest economical cycle in the country. The main product of the sugarcane industry until the middle of last century was sugar; alcohol was produced only as a solvent, antiseptic and for domestic uses. During the Second World War many experiments were made to substitute gasoline for alcohol but the end of the war determined gasoline consumption restart. The break out of the oil prices crisis in 1973 with the supply embargo by OPEP brought back the project of using alcohol in transport vehicles, then supported by engines technology developed at the Aeronautical Institute of Technology – CTA.

The Alcohol Program – PROÁLCOOL, created by the Federal Government in 1975, with financial and fiscal incentives and the participation of the industry (sugarcane and vehicles producers) has determined the addition of anhydrous alcohol to gasoline that has notably decreased the emission of chemical pollutants (carbon monoxide, hydrocarbons and lead) and has developed engines for hydrated alcohol.

In 1975 about 87% of the sugarcane produced (68 Mt/year) was for sugar production; in 2007 the two products were equally divided (491 MT/year). In this time interval agricultural productivity has grown from 35 to 70 t/ha.year, using varieties of the saccharum officinarum species and industrial productivity increased from 40 to 75 liters per ton of sugarcane; in the best farming, 85 t/ha.y was harvested and 88 l/tsugar.  was extracted. The Copersucar Technology Center, the Luiz de Queiroz Agriculture High School and several Universities and Brazilian Technology Centers have collaborated in this effort.

Between 1980 and 2005, the alcohol production cost decreased from 109 to 30 US$/barrel, following the learning curve shown below[1]

Figure 2

Finally the creation of the Alternative Sources Program for electricity generation in 2002 has opened a vigorous market for bagasse and the perspective of gasification of this byproduct of alcohol and sugarcane for cogeneration of electricity and process heat via gas-vapor combined cycle.

 Sugarcane processing for alcohol production

The sugarcane crop duration is 200 days (April to October) on the average, along the dry season. At harvesting sugarcane stalk contains from 14 to 15% of sugars that can be reduced by fermentation, from 10 to 13% of cellulosic fibers and between 76 and 72% of water. Harvest is still made manually in most farming after the straw is burned in order to facilitate the handling of the sugarcane; the environmental legislation of the São Paulo state has fixed the limit for total harvest mechanization, namely the year 2031. Sugarcane is transported to the mills in trucks, it is weighted at the entrance, washed for removal of earth and other impurities, cut into small pieces and grinded for separation of the sugarcane juice from the bagasse (the fibrous part of the sugarcane); the juice is filtered, decanted and chemically treated in order to adjust the pH and the concentration of sugar and nutrients for fermentation and then stored in tanks where the yeast is added for fermentation by the bacteria of the  Saccharomyces cerevisiae species that will transform the sugars (mainly saccharose) into glycose and alcohol through the following reactions:  

C12H22O11 + H2O             2 C6H12O6                      4 C2 H5OH + 4 CO2 + heat

      (saccharose)       invertase   ( glycose )        zimase         ( ehanol) 

The yeast containing in the ethanol and water mixture (fermentation wine) is recovered for new fermentations; the fermentation wine is sent to distillation towers where most of the water is extracted, producing hydrated alcohol with a content of 93% of ethanol in mass. The distillation byproduct is vinhoto, a mixture of water, organic matter and sugarcane nutrients with high acidity (pH=4) and biochemical demand of oxygen (DBO= 25g/liter) that goes back to the sugarcane fields as fertilizer or is submitted to bio-digestion, emitting methane-rich biogas and concentrated fertilizer. Production of anhydrous alcohol with 99% of ethanol is the result of extractive distillation of hydrated alcohol using as extractors cycle-hexane or ethylene glycol.

The energy balance is highly positive; accounting for the commercial energy (fuel and electricity) used in all phases of the process (farming, transport and conversion) and the energy contained in alcohol and bagasse has a proportion of 7:1 (solar radiation and the equivalent energy from rain irrigation are considered as natural benefits).

Alcohol production flow chart

Uses of sugarcane products

a – Anhydrous alcohol

Anhydrous alcohol is used for composing “C gasoline”, containing presently up to 25% of alcohol in volume (26% in mass); the range of alcohol content in C gasoline, between 20 and 25%, aims at adjusting the sugar and alcohol production taking into account the variation of sugarcane availability and the demands of the market. This mixture presents higher resistance to deterioration than that of pure gasoline (A gasoline) and has a virtual octane rating of 90 what permitted to increase the compression ratio of the new engines from 7:1 to 9.5:1 resulting in a gain of 11% in efficiency and decreasing about 60% the CO and HC emissions relative to the original values (A gasoline) even without a catalyst and eliminated lead emissions. The introduction of electronic control of ignition and catalyst has practically evened emissions from hydrated and C gasoline engines (the present levels in g/km are from 0.5 to 0.7 for CO, from 0.11 to 0.15 for HC, from 0.08 to 0.14 for NOx and from 0.004 to 0.017 for aldehydes). The alcohol price for consumers in 2006 was R$ 215/bep[2] (US$ 38.0/GJ).

b – Hydrated alcohol

Vehicles designed for using hydrated alcohol entered the market in 1980 and reached their peak in 1987, when they were 94% of the licensed vehicles. By initiative of the Federal Government the implementation of hydrated alcohol vehicles had the help of State Governments Technological Support Centers and University laboratories. Through agreements (protocol) between the Government and the car industry; efforts were combined to decrease the specific consumption (liter/kilometer) and the public was informed about the results through the publication of a bulletin (Escolha Certa) for consumer orientation. The compression ratio of hydrated alcohol engines is 12:1 and the thermal efficiency is about 16% higher than that of C gasoline engine and this gain is due on one hand to the higher compression ratio and on the other hand to the high vaporization heat of hydrated alcohol which turns the air-fuel mixture closer to the isothermal step of the Carnot cycle.

As a combined effect of the oil price decrease, the increase of the international sugar price and the financial difficulties of the Government, that decreased incentives for alcohol consumption, alcohol supply presented problems in 1988 when it was necessary to import methanol to complement supply; the anhydrous alcohol production became a priority. Sales of hydrated alcohol fueled vehicle dropped below 1% in 2000 suggesting decadence of the use of this fuel. From then on a new escalade of oil prices and the introduction of flexible fuel engines in 2003 reactivated the consumption of hydrated alcohol.

c - Flex fuel

The technology of flex fuel engines developed in Brazil is different from those of other countries because it uses software that processes information from oxygen sensors (lambda gauge), from rotation and temperature in order to identify the type of mixture that is being used and appropriately regulate the electronic injection instead of using specific sensors to differentiate the fuels; the companies involved are Robert Bosch and Magnetti-Marelli. The sale of vehicles with these engines started in 2003 and grew geometrically at a rate of 80% annually; the result of restarting hydrated alcohol consumption is measured by consumption in 2006 (7.19 Mm3) and that in 2003 (4.61 Mm3).

From 1997 to 2006, anhydrous alcohol consumption grew from 4.77 to 6.14 Mm3 (102 to 132 PJ); that of hydrated alcohol has varied from 8.3 to 7.19 Mm3 (170 to 147 PJ). Comparatively, automotive gasoline consumption varied from 14.16 to 14.44 Mtoe (593 to 605 TJ). The consumption of 13.3 Mm3 in 2006 makes alcohol responsible for 31% of fuel consumption for Otto cycle engines (individual and light commercial transport)[3]; in terms of useful energy the share of alcohol in the Otto fleet is estimated in 36%. The consumer prices are US$ 215/bep (US$ 38.00/GJ) for alcohol and US$ 210/bep (US$ 36.69 $/GJ) A gasoline.

d – Sugarcane bagasse

The use of sugarcane bagasse for electricity generation creates additional support for alcohol production and therefore we will present basic information about the corresponding potential.

Bagasse produced by sugarcane crushing is used as fuel for steam generation that drives the electricity generator and small turbines that drive the grinders and other mechanical equipment and supplies heat process. The older plants consume the bagasse totality to feed the low pressure boiler (21 bar or kgf/cm2), generating only the internally consumed electricity. In the two last decades the efficiency of sugar and alcohol production has been improved so that it will generate surplus electricity to complement the public network supply then mainly supplied (90% of demand) by hydroelectricity that is the characteristic of the Brazilian electric system. Generation from sugarcane bagasse presents some advantages relative to other forms of generation in part because of the coincidence of the high season harvest and the minimum abundance of water in the reservoirs of hydroelectric plants. Furthermore the proposed generation benefits from the infrastructure of the sugarcane industry highly concentrated in the Southeast region and therefore close to the electricity demanding centers. These conditions result in low investment for generation and the low cost of bagasse whose gathering and transport are already paid by the main activity of the plant what makes the electricity cost competitive with that of hydroelectric generation.

The old plants produce steam at 21 bar (kgf/cm2) and 300o C and turbines operate in counter-pressure (discharge free from residual steam); in order to improve the energy efficiency in the sugar and alcohol production so that bagasse consumption will be reduced and surplus electricity will be produced; it is now proposed to use boilers at 80 bar and 480 oC with steam extraction and condensation and in the future the gasification of bagasse and sugarcane straw to generate electricity in a gas-steam combined cycle. It is estimated that these changes will permit to go from 10 to150 kWh/tsugarcane, in the first phase of modernization and to 300 kWh/tsugarcane in the final phase (bagasse and straw gasification and gas-steam combined cycle). Considering a span of 30 years and the internal demand of sugar and alcohol, the sugarcane production would reach 1 billion tons/year and the surplus electricity would be 180 TWh/year, equivalent to about 12% of the projected electricity demand in 2030, according to the National Energy plan for 2030. The importance of this complementation to hydro electricity would need the guaranty of electricity supply and consequently that of sugarcane production

Alcohol exports

The exports of fuel alcohol are recent in Brazil according to Graphic 1 below; the largest alcohol importer is the United States, namely 70% of the commercialized volume. The export surge observed from 2000 on has compensated the slow recover of hydrated alcohol consumption caused by the introduction of flex-fuel vehicles using the installed capacity estimated in 18 Mm3/year.

In spite of the low number of figures, a logistic curve was fitted to exports (Volterra-Lotka equation), and it is foreseen an upper limit of 67 Mm3 (Graphics 2 and 3) that would be reached around 2020 (Graphic 4). The maximum export value taken from the adjusted curve (Graphic 2) would be 5.5 Mm3/year.

Graphic 1 – Balance of alcohol fuel market

Graphic 2 – Logistic of alcohol export

Graphic 3 – Linear logistic of alcohol exports

Graphic 4 – Projection of alcohol fuel exports

New facts like the higher interest of other countries regarding renewable fuels may change the pace and maximum rate of exports; presently there are no concrete data about this issue.

Factors that condition alcohol exports

The possibility of increasing exports depends on the sugarcane cultivated area, on the agricultural and industrial productivity of the sugarcane area, on the production capacity of the distillery equipment, on the transport infrastructure and on the introduction of new technology concerning biomass conversion. The summarized analysis of these factors is presented below.

1 – Sugarcane cultivating area

According to data from the Ministry of Agriculture, Livestock  and Supply - MAPA, Brazil has 90 million hectares that are not used and 177 million that are occupied by extensive cattle-raising (table that follows), besides 440 million of native forests and environmental reserves (restricted to natural resources extraction: palm oil, babassu oil, ruber plant, etc.); the area presently occupied by permanent and temporary cultivation is 62.5 million ha of which 10.3% or 6.3 million ha are for sugarcane cultivation. In 2007 about 490 million tons of sugarcane were harvested and equally divided for sugar and alcohol production, resulting in 18 million liters of alcohol and 26 million tons of sugar. It is agreed that the area occupied for extensive cattle-raising can be reduced by ensiling plants species with higher agricultural productivity for cattle feeding; this effect, that would be more pronounced in flat areas where farming mechanization permits higher gains (profits), is already occurring in soybean cultivation expansion that occupies about 20 Mha.

The upper limit for export would correspond to occupation of part of the area appropriate for agriculture that is not used and part of the area presently occupied by extensive cattle-raising (supposed to be half of it); assuming that these areas would be distributed in the future between food and energy agriculture, in the proportion of areas presently used by these categories (see table), sugarcane farming would have an areas of 18Mha, sufficient for tripling production.

Considering the hypothesis from the presented logistic study, the expansion of sugarcane farming, once the 5.5 m3/ha.year production is maintained, would be 1 Mha (0.6% of the area appropriate for agriculture) in the next 15 years. Therefore, there is no physical limitation to reach this goal. Furthermore, the sugarcane fraction for alcohol production could continue to grow since the sugar market is growing together with the population (2% annually) and it may be considered as vegetative whereas the world energy market is in crisis.

 Therefore, it is reasonable to plan in Brazil and in other countries with similar climate and demographic density the expansion of sugarcane production without impairing the food agriculture and without affecting the environment, as long as the development of appropriate technologies for this purpose is fostered.

2 – Agricultural and industrial productivity

In the present development model concerning sugarcane production, the apparent productivity obtained through genetic improvement of the plant tends to saturation as it is shown in the graphic below.

Graphic 5 –Agro-industrial productivity of sugarcane [4]

When the productivity study was carried out, most of the sugarcane farming was not irrigated and this fact limited the recoverable sugar content (RSC). We believe that irrigation would permit to increase the RSC but we do not have more recent data in order to test this hypothesis; according to information from the Copersucar site, the maximum RSC in sugarcane is 18% while the actual average content measured is 14%.

3 – Equipment production for distilleries

In a Seminar held in Rio de Janeiro in August 2003, the national industrial capacity in equipment production for distilleries,  Dedini S.A – Indústrias de Base, the largest producer of distilleries equipment, has informed that the industry has supplied in 10 years about 200 complete distilleries; presently reference fabrication capacity would be, according to the same source, 60 plants per year (production expansion up to 4 M m3/year).

4 – Transport infrastructure

The transport system regarding alcohol transport to the distribution basis and ports is considered adequate to the present production level; however the expansion of the production capacity is growing inwards and this may bring transport difficulties, mainly during the soybean harvest which is cultivated more intensely in the region of sugarcane expansion. In order to circumvent possible difficulties, alcohol producers and distributors are planning new tansport routes combining highways, railways hydro-ways and pipelines. According to an ANP Technical Note[5], the legislation regarding transport licensing will be revised for this purpose.

5 – New technologies

Besides improvements applicable to the existing plants, such as vacuum or supercritical CO2 alcohol extraction, the substitution of driving turbines for electrical engines, alcohol dehydration using special membranes and others that save steam, new routes for alcohol production from cellulosic materials, such as wood, grass, alcohol bagasse itself, agricultural residues (straw, peels, endocarp) and organic waste, by chemical or enzymatic hydrolysis are being developed.

Presently these routes are not yet competitive with that of fermentation/distillation but they might be competitive with fossil fuel extraction. The flowchart below shows some new practices.

Fonte: DEDINI S. A.

Conclusions

Alcohol fuel production in Brazil is a consolidated practice that has energy and economical efficiency compatible with the national development level. Manpower-intensive and practiced in the whole country, production is an instrument for income distribution and technological education dissemination. Stimulated and guided by the Government at the initial phase, the alcohol activity is now completely private and has strongly demonstrated the possibility of the partial substitution of fossil fuel for renewable ones.

In political terms, alcohol production has contributed to the consolidation of energy autonomy and to the strengthening of the Brazilian industry; in ecological terms it has contributed to maintaining the air quality; in social terms it has aggregated to the market a large number of menial workers (1.5 million direct jobs), opening to future generations access to the educational and health systems.

Since it is economically profitable, the alcohol industry can support the effort to develop new technologies as the Copersucar Technological Center (presently the Sugarcane Industry Technological Center) has done.

Biodiesel

The National Program for Biodiesel Production and Use was established by the Federal Government in 2003 with the purpose, incentives and structure similar to those of the Alcohol Program. The immediate motivation is to decrease the imports of diesel oil due to the circumstantial fact of the inadequate capacity for refining the heavy oils extracted from some Brazilian fields. An Inter-ministerial Working Group was established that has proposed the following guidelines for the Program:

- Biodiesel introduction in the national energy matrix in a sustainable way permitting the diversity of energy sources and energy safety;

- Creation of job and income, specially in the countryside, for family agriculture and in the production of oleaginous raw material;

- Reduction of regional disparities, permitting the development of the more needy regions of the country:  North, Northeast, and Semi-arid;

- Decrease of pollutants emission and of costs related to mitigation of the so called pollution damages, specially in large urban areas;

- Foreign exchange saving due to reduction of diesel imports;

-Concession of fiscal incentives and implementation of public policies directed to disadvantaged producers and regions, granting financing and technical assistance and permitting the economical, social and environmental sustainability of biodiesel production;

 - Flexible regulation, permitting the use of different oleaginous raw materials and technological routes (ethyl or methyl transesterification, cracking, etc.)

Biodiesel can be produced from vegetal oils, from animal fat and from residues of the food industry. The original formulation of the Program favors the use of vegetal oils that is better adjusted to the mentioned guidelines; other raw materials would be used in a complementary way. Vegetal oils are mixtures of esters derived from glycerol that it has in the chain.

Vegetal oils are mixtures of esters derived from glycerol and they have fatty acids with 7 or more carbon molecules. The two ways of production are transesterification and thermal cracking of vegetal oils; both lead to the decomposition of complex esters with long chains to compounds with shorter chains with properties similar to those of diesel oil from petroleum.

In general the chains are linear (figure below) and present simple and/or double links and so the fatty acids are divided in saturated fatty acids (groups of the -CH2- type) and unsaturated ones (-CH=CH- links), with specific physical-chemical properties; both types are found in oils of different species of oil plants and this affects in different ways the characteristics of the produced fuel (viscosity, calorific power, stability, formation of deposits in the engine, etc.)

The composition of vegetal oils in terms of fatty acids is shown in Table 1; it can be noticed the large diversity of saturated and unsaturated acids share.[6].

 Table 1 – Composition of vegetale oils

Some scientific names: 1 – Acronomia sclerocarpa 2 – Elaeis guineensis 3 – Attalea compta 4 – Orbygnia barbosiana 5 – Astrocaryum campestre 6 – Cocos capitata 7 – Caryocar brasiliense 9 – Mauritia flexuosa  10 – Jatropha curcas 11 – Joannesia Princeps

The physical properties of some oils compared to those of diesel oil are shown in Table 2 where it can be seen that the calorific power and the oil cetane index are not much different from that corresponding to diesel oil but the viscosity and the cloud point are quite higher; high viscosity makes it difficult oil nebulization in the air, inside the engine’s cylinder resulting in an incomplete combustion with the consequent loss of power and efficiency of the engine; the high cloud point permits the oil crystallization at temperatures close to room temperature  and this makes it difficult the engine cold-start. With these characteristics, vegetal oils in natura would be a fuel with lower quality that that of diesel oil. Transterification and cracking attenuate the disadvantages of vegetal oils.

Table 2 – Physical-chemical characteristics of vegetal oils and diesel oil from petroleum 

Characteristics

Palm (Pulp)

Babaçu

Peanut

Soyabean

Diesel Oil

Calorific power (Kcal/Kg)

8946

9049

9458

9421

10950

Cetane Índex

38 - 40

38

39 - 41

36 – 39

40

Viscosity at 37,8° (cSt)

36,8

30,3

41,1

36,8

2,0 – 4,3

Cloud Point (°C)

31,0

26,0

19,0

13,0

0

Distillation Temperature in °C  to distillate 90% of volume (°C)

359

349

349

370

338

Conradson Carbon Residue of 10%  of residue (% weight)

0,54

0,28

0,49

0,54

0,35

Source: R. Stem, J . C. Guibet e J. Graile (02)

Transesterification essentially consists of the substitution of glycerol for alcohol with a smaller chain (methanol or ethanol); the reaction carried out by basic catalysis using sodium and potassium hydroxides and potassium carbonate and produces esters (methylic or ethylic) with shorter chains than those of the original ester and with more uniform characteristics.

The reaction is carried out at low temperature (40 to 45°C) and has glycerine as by-product that is used in the pharmaceutical, food and cosmetics industries; increasing the offer of glycerine from the transestratification process opens new possibilities for its use in the production of etileneglycol and methanol, in the oil industry (perforating fluids), in the PVC production and fabrication of membranes for fuel cell, besides the uses in biogas production and direct burn in boilers. The equipments required for transesterification are simple, namely a steel-carbon reactor, agitators and indirect heating system using steam or oil, similar to the equipment used in vegetal oil extraction for the food industry. The operation sequence is the same for the different types of vegetal oils.

The vegetal oil extracted by crushing the fruit of oleaginous plants is filtered and then is introduced in the reactor together with alcohol (in excess) and the catalyst; the mixture is heated by the steam or oil bath and agitated; the excess alcohol accelerates the reaction and it is recovered by distillation. The mixture containing biodiesel is cooled, centrifuged to separate the glycerine and eliminate solid residues and then washed. The chemical efficiency of converting the original ester to esters with a shorter chain is more than 90% in mass and reaches 97% in some cases both for the methyl and ethyl base procedure. The agricultural productivity, of crucial importance for the viability of the Program, is shown in the Table below for some native species.

Table 3 –Agriculture productivity of some oil plants

Products

Palm

Macaúba

Indaiá

Pinhão-Manso

t/ha

kcal/ha

(x106)

t/ha

kcal/ha

(x106)

t/ha

kcal/ha

(x106)

t/ha

kcal/ha

(x106)

Pulp oil

4,73

41,5

2,62

24,9

0,64

0,61

-

-

Raquis

2,40

9,6

2,10

8,4

0,83

4,8

-

-

Fiber

2,48

10,4

3,31

13,9

2,19

9,2

2,23

9,3

Endocarp

1,90

9,1

2,67

12,8

3,34

16,0

-

-

Almond oil

0,29

2,5

0,38

3,2

0,34

2,9

3,04

25,8

Almond filter cake

(10% óleo)

0,29

1,5

0,32

1,6

0,18

0,9

1,73

8,7

(1)             145 palm trees/hs.        (16,0 t of fruits/ha)

(2)             200 palm trees/hs. .         (14,0 t of fruits/ha)

(3)           1200 palm trees/hs. .       (10,0 t of fruts/ha)

(4)           1200 plants/ha. .                 (6,0 t of seeds/ha)

Source: CETEC

The direct economic benefits are the substitution of imported diesel oil and, in the case of decentralized production, the decrease of transport costs. The diesel oil consumption practically determines the oil volume used in Brazil because it is its most consumed product; even though there exists the technology to increase the diesel fraction in refining, import seems circumstantially the best option as compared to the investments required for fitting the refining structure to the characteristics of the oil extracted in Brazil; it is estimated that about 6% of the share of diesel oil is imported (2,4 M m3/year) at a price of 2.5 to 3 US$ billion annually. In order to decrease imports, the Biodiesel Program has determined the mixture of 2% of biodiesel with diesel from 2008 on (0,800 Mm3) and 5% from 2013 on (over 2.000 Mm3).

Program Development

The Program was started based on soybean oil produced in the Southwest/Center West region and on castor plant oil produced in the Northeast region. The native species with higher agricultural productivity are not yet domesticated and the natural occurrences are not considered sufficient to support production in the planned scale. Biodiesel production has reached 900,000 m3 in 2007, exceeding the goal to supply 2% to the mixture until the end of 2008. There are no official data about the shares of the different oleaginous plants in production; information surveyed at the press has assigned predominance to soybean oil (90%).

Conclusions

Biodiesel Production Program is completing the first stages; an intense research and development work is necessary to incorporate to production the oleaginous plants of higher productivity. Considering the Pro-Alcohol experience, this program will reach maturity in the next two decades.


 

[1] “Ethanol Learning Curve”, Goldemberg, J. et al, 2003

[2] Barrel equivalent  petroleum

[3] Diesel oil is used for mass transport (buses), load transport and electricity generation in remote areas.

[4] “Potential of Ethanol Production from Sugarcane”, Ferreira, O. C, Economy and Energy (http://www.ecen.com) no 34/2.003

[5] “Present state of the Brazilian alcohol fuel industry”, ANP, 2007

[6] “Produção de combustíveis líquidos a partir de óleos vegetais”, Martins, H. et al, Fundação Centro Tecnológico de Minas Gerais, 1983

 

Graphic Edition/Edição Gráfica:
MAK
Editoração Eletrônic
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Revised/Revisado:
Friday, 16 September 2011
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