Renewable fuels, also known as clean fuels, have several advantages over fossil fuels. They are considered good for the environment, and one can produce them wherever there is plant life, making them immune to Organisation of the Petroleum Exporting Countries (OPEC) fuel embargoes. Various governments have established mandated usage of renewable fuels at significant levels. In 2003, the EU set a directive to obtain 5.75% of transportation fuel needs from renewable fuels by 2010. The EU now has a target of 10% by 2020. The US Congress enacted various renewable fuels standards (RFS) mandates, culminating in the 2007 Energy Independence and Security Act (EISA), that guarantees a US market of renewable biofuels amounting to 36 billion gal./y by 2022.
But the economic, fuel production and consumption circumstances that fueled the boom in renewables legislation in the 2000s have largely been reversed. Are clean fuels ultimately doomed?
Biodiesel use is mandated under EISA. The Environmental Protection Agency (EPA) set a target of 1.28 billion gal. for US markets in 2013. The most common production method, known as base catalysed transesterification, is to react vegetable oil with methanol in the presence of lye. This process removes glycerine, and the resulting mono alkyl esters of long chain fatty acids perform similarly to petroleum diesel. Although most biodiesel is made from soybean byproducts, anything from recycled oils from chip vats to coffee grounds can be used. The fuel is environmentally benign, biodegradable when spilled, and reduces the amount of exhaust particulates.
But biodiesel has been known to clog fuel filters, form gels in cold weather and absorb water (which reduces the heat of combustion and promotes corrosion and microbe growth). Its energy content is approximately 11% less than petroleum diesel, making it less fuel efficient by volume. Its high oxygen content also increases nitrogen oxide emissions.
Finally, biodiesel is more costly than fossil fuel diesel. When the EPA announced its 2013 target, industry response was negative. ‘Given the exorbitant cost of biodiesel, its poor performance qualities, significant fraud in the biodiesel industry, and the drought facing our nation’s farmers and ranchers, this is a bad decision at the wrong time,’ said American Fuel & Petrochemical Manufacturers (AFPM) president, Charles Drevna.
Ethanol is the main biofuel being produced under the aegis of the EISA. An ethanol facility extracts sugars from plants (corn in the US, sugarcane in Brazil), then ferments the sugar into alcohol using yeast. The alcohol, at 8% volume, is then repeatedly distilled until it reaches over 99% purity.
Like gasoline and diesel, ethanol emits greenhouse gases (GHGs), in the form of CO2. But because ethanol is made from living organisms that trap carbon during photosynthesis, net lifecycle analyses generally conclude that its impact on GHG is neutral, or beneficial. Ethanol is also an efficient replacement of methyl tertiary butyl ether (MTBE), a gasoline additive that was phased out due to a propensity to contaminate surface and groundwater.
Ethanol’s energy content is significantly lower, however; it takes approximately 1.5 ltrs of ethanol to drive as far as 1 ltr of gasoline. Ethanol is very corrosive, and high concentrations can dissolve seals and gaskets in pipelines, containers and engines. Production is also costly; capital costs range up to US$ 33 000/bpd of capacity. Price surges in staple commodities such as corn have been linked to its usage for fuel.
Compressed natural gas
In North America, compressed natural gas (CNG) is currently used to replace gasoline in some taxi and delivery vehicle fleets, but it accounts for only a tiny fraction of the fuel use. CNG has various advantages that make it a candidate to control a sizable portion of the fuel market in the near future. Life cycle emission studies conducted by the Argonne National Laboratory show that CNG emits up to 11% lower GHGs than gasoline, as well as dramatically lowering the amount of carbon monoxide and nitrogen oxides coming out of the tailpipe. In addition, CNG is non-toxic, and will not harm soil or water.
Hydrogen is one of the most common elements on earth. As a fuel, it reduces urban pollution, cuts down dramatically on GHGs, and enhances energy security for oil importing nations. Hydrogen can be obtained from water through the electrolysis process; a strong electrical current is passed through water to generate bubbles of hydrogen at the cathode.
Algae and other microbes hold great promise. They thrive in non-commercial environments with little more than basic nutrients and sunshine. They grow far more rapidly than conventional crops, and generate a much higher fraction of their biomass as oil (up to 60%, versus 2 - 3% for soybeans).
In conclusion, it is relevant to note that renewables have been around in significant amounts for less than a decade, and that growing pains are inevitable. Yet much has been accomplished in terms of meaningful production, distribution and acceptance by the public. A great deal of regulatory refinement and legislation needs to be done to work out the wrinkles, and R&D promises a host of new clean fuel sources. Clearly, there is a market for clean fuel, but equally as clearly, the market has to evolve for it to prosper.
The full article can be found in the September issue of Hydrocarbon Engineering.
Read the article online at: https://www.hydrocarbonengineering.com/gas-processing/03092013/cleaned_right_out/