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Biofuel
2017 Mattia Piron. All rights reserved.

  1. Environmental pollution
  2. Types of biofuels
  3. Bibliography

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Immagine di copertina

JUNE 4th, 2018

 

Biofuels are defined as all fuels of natural origin, coming from renewable sources, i.e. energy sources that can regenerate themselves autonomously and at zero cost (or almost) by exploiting almost exclusively the energy provided by the sun.

 

Environmental pollution       top

Compared to fossil fuels, biofuels are cleaner because:

  • They do not put new CO2 into the atmosphere;
  • They do not release sulfur (the cause of acid rain), polycyclic aromatic hydrocarbons, or heavy metals;
  • he risk of environmental disasters in the event of an accident (e.g., spilled oil tankers) is prevented.

They do, however, present sources of pollution:

  • Substances such as carbon monoxide and unburned hydrocarbons are still released into the atmosphere;
  • They require specially cultivated fields to produce fuel, taking away food resources.

 

Types of biofuels       top

 

Oleaginosis

  • Oil: In Diesel cycle engines, vegetable oil can be used as fuel. It should be considered that the viscosity of the oil is much higher than that of diesel fuel, and does not match with the high pressures and micrometric holes of the injection system of modern diesel engines. It can be used with special devices, such as heat exchangers that heat the oil before it enters the injection system. In this case, the engine must be started and stopped with diesel fuel and only when the engine is hot can the oil be used.
  • Biodiesel: This is a derivative of natural oil. It undergoes certain chemical treatments (transesterification) in order to guarantee particular properties (flammability, viscosity, water content...). Biodiesel can also be produced from used oil, representing an excellent opportunity for recycling.

 

Sugary fermentation

  • Bioethanol: It is an ethyl alcohol obtained from biomass, very volatile and flammable. It is widely used as a fuel in Brazil, where it covers more than 20% of the demand for fuels. it is produced from sugary sources (such as beet, sugar cane or other) that are transformed into molasses, which is then fermented. In the case of plants rich in sucrose it is a simple operation, it is sufficient to extract the sugars with warm water, while in those based on starches or cellulose enzymes are needed to extract the sugar contained. During the fermentation of molasses, the sugar contained is transformed into ethanol. This must then be distilled, to extract the ethanol from the rest of the constituents. This ethanol could be used pure in Otto cycle engines. In reality, the combustion of ethanol requires a different stoichiometric ratio than that of gasoline, so vehicles would require modifications to the fuel system.
  • Methanol: It is obtained through the synthesis of carbon monoxide. The carbon source used is methane or coal. Methanol can be used:
    • As a fuel, blended with gasoline, at various percentages, on specially modified engines.
    • As a reagent, to produce biodiesel
    • As fuel to produce electricity, in special fuel cells
    • As a gasoline additive, replacing tetraethyl lead.

    Compared to ethanol has a high toxicity by ingestion (lethal to humans, even in small doses) and inhalation. Exhaust pollutant emissions are quite similar to those of ethanol. The prevalent use of methanol is in the production of MTBE, to be used as a gasoline additive. In the sporting field it is used pure as fuel in the engines of speedway motorcycles. Thanks to the high anti-knock power of methanol, compression ratios of 18:1 can be reached (against the 10-12:1 normally used for gasoline), improving thermal efficiency and therefore power.

  • The case of Brazil: In Brazil, the production of ethanol for transport began in the 1970s, with the aim of reducing the country's dependence on petroleum. Subsequently, as petroleum prices fell and sugar prices rose, there was a reduction in alcohol cars in favor of gasoline. As the price of petroleum rose again beginning in the 2000s, alcohol car production increased again, although not to the levels of the 1970s. Today, about 20% of cars on the road are Flex-Fuel, meaning they can run on 100% alcohol, 100% gasoline, or any percentage in between.

 

Anaerobic digestion

Biogas: This is a gas obtained from biomasses mainly composed of methane. In smaller percentages it contains carbon dioxide, hydrogen and nitrogen. It can be obtained from any organic substance through anaerobic digestion: the biomass is accumulated in special tanks, called digesters, where anaerobic bacteria "digest" it producing gas. This gas is aspirated and can be used directly in turbines or gas engines to produce electricity, or it can be compressed and accumulated to be sold. It finds use in the disposal of household waste, which can be recycled to create gas, and sludge (the solid portion not turned into gas), which is used as fertilizer.

 

Biofuels from algae

There is a particular species of microalgae that contains up to 50% oil, which is 20-30% more efficient than rapeseed or sunflower crops. It would take only 4% of the U.S. land area to produce enough biodiesel from algae to meet America's current oil needs. In addition, algae grows very well in desert areas with high solar irradiation, so it is possible to exploit land that would otherwise be unsuitable for other types of crops. This is currently an immature technology.

 

Bibliography       top

  1. BIOcarburanti fai-da-te, Roy Virgilio, Editrice Aam Terra Nuova, 2008

 

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