Untreated B100 (100% biodiesel) emits roughly 10% more NOx emissions than regular diesel. Additionally, the government mandates to use biodiesel, by supporting feedstock prices, encourage deforestation in developing countries. In the near term, this concern is being addressed by governments exploring mandates that specify feedstock sourcing in more detail, and by companies that establish "green credits" vetting the life-cycle impact analyses of different feedstocks.
Biodiesel, on its own, can begin to congeal around 14-68 degrees F, necessitating the use of heated storage vessels and blending tanks. The cloudpoint is related to the mix of esters in the biodiesel, and consequently on the feedstock, with a feedstock like tallow tending to congeal at the higher end of the range and certain seed oils, such as canola, congealing at the low point. This issue is less noticeable when biodiesel is blended with regular diesel: at B5 or less, the cloudpoints are basically the same.
When biodiesel contains unreacted monoglycerides and triglycerides, they can attract water into the biodiesel, which is otherwise immiscible. This contamination can lead to the fuel congealing at a warmer temperature (as the water cools and sets into ice crystals), as well as supporting corrosion, microbial contamination, and engine component deterioration.
A major hurdle facing commercial biodiesel production is the cost of producing the fuel. Vegetable oil seed procurement, transport, storage and oil extraction accounts for at least 75% of the cost of producing biodiesel. The cost varies depending on the feedstock used. For example, based on the market price for industrial rapeseed grown in Washington and Idaho, the estimated cost of producing biodiesel is $2.56 per gallon of rapeseed methyl ester. Recent estimates put the cost of production in the range of $1.30 per gallon (using waste grease feedstock) to $2.00 or more per gallon using soybean oil.
A blended fuel of 20% biodiesel and 80% petroleum diesel could reduce the production cost to about $1.10 per gallon, assuming a petroleum diesel cost of 90 cents per gallon and a soybean biodiesel cost of $1.80. Use of lower-cost organic oil feedstock, such as waste food-processing oil or tallow, would further reduce the production cost of biodiesel and biodiesel-blended fuel.
According to current international convention, carbon released through biomass combustion is excluded from reported energy-related emissions. The release of carbon from biomass combustion is assumed to be balanced by the uptake of carbon when the feedstock is grown, resulting in zero net emissions over some period of time. However, analysts have debated whether increased use of biomass energy may result in a decline in terrestrial carbon stocks, leading to a net positive release of carbon rather than the zero net release assumed by its exclusion from reported energy-related emissions. (ref: “Annual Energy Outlook 2010 With Projections Through 2035,” US Energy Information Administration, April 2010)
Carbon dioxide emissions from biomass energy combustion, 2008-2035 (million metric tons)
(ref: “Annual Energy Outlook 2010 With Projections Through 2035,” US Energy Information Administration, April 2010)
One major challenge to commercialization is uncertainty of using a new biofuel, nobody has used butanol commercially as a fuel so they do not know if carmakers will accept it even if research says they're better than ethanol. Another issue is whether biobutanol costs on a commercial scale can really be proven competitive against ethanol production.
(ref: “Biobutanol for fuel expected in five years,” Chemical News & Intelligence, February 20, 2009)
Some reports have also state that the U.S. fuel distribution infrastructure may not be prepared to distribute 36 billion gallons of biofuels by 2022, as required under the EISA Act.
(ref: “Biobutanol promising but technology not yet developed, says NREL engineer,” Biofuels Digest, November 12, 2008)Research by Eliza Brannigan
