BIOFUEL CONVERSION PROCESSES

Webmaster: Thitipat Puttathamkul No.14 M5/5

References: https://www.energy.gov/eere/bioenergy/biofuel-basics , https://www.conserve-energy-future.com , https://www.britannica.com/technology/biofuel

https://www.iea.org/energy-system/low-emission-fuels/biofuels

DECONSTRUCTION Producing advanced biofuels (e.g., cellulosic ethanol and renewable hydrocarbon fuels) typically involves a multistep process. First, the tough rigid structure of the plant cell wall—which includes the biological molecules cellulose, hemicellulose, and lignin bound tightly together—must be broken down. This can be accomplished in one of two ways: high temperature deconstruction or low temperature deconstruction. High-Temperature Deconstruction High-temperature deconstruction makes use of extreme heat and pressure to break down solid biomass into liquid or gaseous intermediates. There are three primary routes used in this pathway: Pyrolysis Gasification Hydrothermal liquefaction. During pyrolysis, biomass is heated rapidly at high temperatures (500°C–700°C) in an oxygen-free environment. The heat breaks down biomass into pyrolysis vapor, gas, and char. Once the char is removed, the vapors are cooled and condensed into a liquid “bio-crude” oil. Gasification follows a slightly similar process; however, biomass is exposed to a higher temperature range (>700°C) with some oxygen present to produce synthesis gas (or syngas)—a mixture that consists mostly of carbon monoxide and hydrogen. When working with wet feedstocks like algae, hydrothermal liquefaction is the preferred thermal process. This process uses water under moderate temperatures (200°C–350°C) and elevated pressures to convert biomass into liquid bio-crude oil. Low-Temperature Deconstruction Low-temperature deconstruction typically makes use of biological catalysts called enzymes or chemicals to breakdown feedstocks into intermediates. First, biomass undergoes a pretreatment step that opens up the physical structure of plant and algae cell walls, making sugar polymers like cellulose and hemicellulose more accessible. These polymers are then broken down enzymatically or chemically into simple sugar building blocks during a process known as hydrolysis.

Types of Biofuels

Some long-exploited biofuels, such as wood, can be used directly as a raw material that is burned to produce heat. The heat, in turn, can be used to run generators in a power plant to produce electricity. A number of existing power facilities burn grass, wood, or other kinds of biomass.Liquid biofuels are of particular interest because of the vast infrastructure already in place to use them, especially for transportation. The liquid biofuel in greatest production is ethanol (ethyl alcohol), which is made by fermenting starch or sugar. Brazil and the United States are among the leading producers of ethanol. In the United States ethanol biofuel is made primarily from corn (maize) grain, and it is typically blended with gasoline to produce “gasohol,” a fuel that is 10 percent ethanol.The second most common liquid biofuel is biodiesel, which is made primarily from oily plants (such as the soybean or oil palm) and to a lesser extent from other oily sources (such as waste cooking fat from restaurant deep-frying). Biodiesel, which has found greatest acceptance in Europe, is used in diesel engines and usually blended with petroleum diesel fuel in various percentages. The use of algae and cyanobacteria as a source of “third-generation” biodiesel holds promise but has been difficult to develop economically. Some algal species contain up to 40 percent lipids by weight, which can be converted into biodiesel or synthetic petroleum. Some estimates state that algae and cyanobacteria could yield between 10 and 100 times more fuel per unit area than second-generation biofuels.

Various Advantages of Biofuels

Cost Benefit

Efficient Fuel

Durability of vehicles' engine

Easy to Source

Renewable

Reduce green house gases

Disadvantages of Biofuels

High cost of Production

Monoculture

Use of Fertilizers

Shortage of food

Industrial Pollution

INNOVATION

Many biofuel production pathways have achieved commercial status, including ethanol production from corn and sugarcane, fatty acid methyl esters (FAME) biodiesel, hydrotreated vegetable and waste oil (HVO) renewable diesel and hydrotreated esters and fatty acids (HEFA) biojet kerosene from vegetable oils and waste oils. Others are on the cusp of commercialisation: the alcohol-to-jet (ATJ) route from ethanol production is expected to become commercial at the end of 2023, while other companies are exploring novel oilseed crops that avoid competition with arable land.