First generation biofuels

Last updated on April 26th, 2024 at 01:05 pm

First generation biofuels like ethanol (bioethanol) and biodiesel are produced from mostly edible biomass^[2][16]. This biomass sources are divided into two main groups; sugar and starch crops. The main sugar crops grown are sugar cane and sugar beet, while for starch crops, they are corn and wheat. Other marginal feedstock utilised include whey, barley, potato wastes and sugar beet^[16].

According to OECD-FAO 2019^[22], China is projected to be the largest producer of wheat as feedstock, followed by India and the European Union. For these countries, the bulk of the production is for local consumption. Whereas, for countries like Russia, Australia, close to half of the local production is exported.

In terms of market share for corn (maize) production, United States is still the leader, followed closely by China. For sugar cane, Brazil is still the largest producer. This is followed by India and Thailand.

How it is produced?

Ethanol

From sugar crops, ethanol is produced mainly via the natural process of fermentation involving C6 sugars like glucose using yeasts like Saccharomyces cerevisiae^[21][28]. Leading countries that currently produce ethanol are the United States and Brazil^[9][27](Fig.1).

Production of ethanol from sugar cane for usage as vehicle fuel is well-established and carried out mainly in Brazil^[1][13][16]. This was done via the Proálcool program started in 1975 to reduce their dependency on gasoline^[1][17]. This was done by blending varying proportions of ethanol with gasoline to create ethanol-fuel mixture. Such mixtures are also used in NASCAR competitions (Fig.2).    

Whereas, production of ethanol from starch crops like corn is popular in the United States^[9][22]. For this mode of production, an additional step is required to break down the starch involving the enzyme: α-amylase to release the sugar molecules for the subsequent fermentation process to obtain ethanol^[16]. 

Biodiesel

Biodiesel production are also divided into four main groups (generation) depending on their feedstock. First generation biodiesel are produced from edible vegetable oils that include but not limited to rapeseed oil, soybean oil and coconut oil^[27]. Currently, in terms of biodiesel production, the projected leader is the European Union, with the United States and Indonesia, a close second and third^[22]. Production is carried out via two main process; pyrolysis and transesterification.

• Pyrolysis can be divided into a few different types that differs in processing time and biomass temperature^[3][24]. For production of biodiesel, fast pyrolysis at a temperature range of 400°C to 600°C is carried out to heat the biomass to obtain bio-oil^{[6][14][24][27]}
• Bio-oil can be utilised as a boiler fuel and turbines for generation of heat and power, or can be upgraded to meet the usage of the fuel^[8].

Upgrading processes carried out include hydrotreating and hydrocracking. Hydrotreating or hydrogenation involves the reacting of bio-oil with hydrogen for the removal of sulphur and oxygen^[8][14]. The resultant hydrotreated bio-oil can be reacted again with hydrogen to create smaller chains of hydrocarbon to meet the specifications of gasoline and diesel fuel^[8][14].

• Transesterification is a reversible process where fatty acid chains are reacted with excess alcohol in the presence of catalyst, which is usually a strong base, to get a final mixture of fatty acids and glycerin (glycerol)^[18].

Depending on the type of alcohol used, the type of fatty acids range from fatty acid methyl ester (FAME) if methanol is used, fatty acid ethyl ester (FAEE) if ethanol is used. However, methanol is usually used as higher biodiesel yield of 91.05% is obtained, compared to 77.4% if ethanol is used^[6][19].

Prospects for first generation biofuels

Production of biofuels using cultivated edible biomass has the below advantages and disadvantages:

Advantages 

Easy production and effective results

First generation biofuels are made from readily available feedstock with a comparatively easy conversion process^[27]. Usage of biofuels give rise to improved air quality especially for urban centres with reduced emissions of carbon monoxide from 50g per km driven to less than 5.8g per km driven^[13][15]. Ethanol produced from sugarcane has reduction rates between 40 and 62% in greenhouse gas (GHG) emissions compared to gasoline^[28].

Biodiesel can also be used in existing diesel engines, with no fear of sulphur (SOx) emission. In addition, biodiesel has a high flashpoint with achievement of complete combustion thus producing reduced emissions of hydrocarbons, carbon monoxide, and black smoke^[14].

Useful by-products

Besides ethanol, co-products like DDGS (distillers dried grains with solubles) arising from fermentation of corn can be used as animal feed and has a high market value due to its nutritional content^[19].

Useful by-products like bagasse and vinasse are also generated from the fermentation process.

• Bagasse is used for paper production^[26] and generation of power for usage within the sugar mills^[28].
• Vinasse is an aqueous effluent from distillation that comprises of water, organic matter, and mineral elements like potassium. It can be used for sugarcane ferti-irrigation, reducing costs on imports of chemical fertilizers^[25].
• Agricultural residues has also been mooted as potential feedstock for the production of bio-oil via pyrolysis^[4].

Disadvantages

Environmental impact

Cultivation of biofuel crops can potentially impact the environment through deforestation and competition for water and land resources between food crops and other services^[12]. One obvious example are oil palm trees, which are commonly grown in Malaysia and Indonesia, often on previously rainforest areas specifically cleared for this purpose, or in areas used previously for rubber or coconut cultivation.

Expansion of sugarcane cultivation in Latin America is carried out on lands previously cleared for cultivation of other crops. Thus, increased sugar cane cultivation for ethanol production is unlikely to cause deforestation but cause indirect land use change through displacement of crops or livestock into forests or grasslands.

Food versus fuel

Diversion of food crops meant for consumption to biofuels production can cause increases in food prices that result in issues like social unrest^[28]. With issues like war, one way to mitigate this issue will be to extend the production of biodiesel to other feedstock^[27]. The feedstock are divided into different generations:

• Second generation feedstocks: Non-food crops that include jatophra and cotton seed. Ongoing tests involving the growth of these bioenergy crops on potential marginal land not suitable for agriculture reduces competition with arable land^[5]. These non-food crops like jatophra, used-oils (third generation feedstock) are also cheaper compared to soybean, canola and palm^[15].

• Third generation feedstocks: Animal fat, micro-algae and waste oil.^[7][10][14] Advances made in studies involving the usage of animal fat/ or waste oil with animal fat to produce biodiesel is particularly useful for countries: with limited landspace for bioenergy crop cultivation^[14], dependent on imports/ limited oil stores.^[21]
• Fourth generation feedstocks: Usage of synthetic biology to engineer "designer organisms" or improve natural biological systems in the current feedstock. This allows the production of produce high-quality biofuels with high PFCE (photon-to-fuel conversion efficiency)^[2].

References

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