Max Witt Chem 1A Fall 2010 Lab Section 600
Biofuels: Which is the Best? Abstract: In this experiment, I attempted to determine which of several biofuels would be the best to replace petroleum through the measurement of energy density through calorimetry and environmental toxicity through a seed assay. Although biodiesel has a higher energy density than ethanol, and is less toxic to plants, it also is unfeasible to produce in sufficient quantities. I combined this data with research, to recommend Cellulosic Ethanol as the most viable long-term solution, and biodiesel as the best short-term supplement.
Introduction: In the USA, we have a taste for excessive consumption, whether for food or fuel. The difficulty that arises is that we become dependent on Saudi despots to satiate our unquenchable thirst for petroleum products. Luckily, Americans are able to produce far more food than we can consume. The excess food could be converted into biofuels, to supplement our petroleum requirements. The moral questions regarding the use of food to run cars while there are people starving in the world is not the subject of a chemistry paper. What I will examine are the questions of toxicity, efficiency, and feasibility of various alternative fuel schemes. Of the several fuel options, some are more familiar than others are. In Berkeley, biodiesel, produced from oily seeds, such as soybeans, is particularly common. It is compatible with the many old Mercedes and Volvo diesel Sedans and Station wagons, which dot the Berkeley hills, as well as more
modern Volkswagens. Another is ethanol, produced from the fermentation of corn, sugarcane, or other grains. Ethanol is already present in concentrations of up to 10% in gasoline sold in California. The two remaining fuels examined were Methanol, which is commonly used for high performance engines due to its extremely high Octane Rating, and 2-butanol, another bio-alcohol. The most detailed analysis of the fuels was limited to Biodiesel (methyl-linoleate). The tests included calorimetry, production/synthesis yield, and a seed assay for Bio-toxicity testing. The seed assay tested samples of all the types of biofuels used in this experiment. These experiments will show some statistics that appear at first glance to be important, but upon further examination, are almost irrelevant. The eco-toxicity test is the most pertinent of the tests, concerning the determining the effects of the biofuels on the environment. Yet even this test is severely limited in its scope, which reiterates the complexity of the choice of a new fuel source.
Method The procedures for these series of three labs were common analytical techniques. For the lab that this report focuses on, the method focused around a simple “Bomb” calorimeter made from a soda can. A known volume or mass of water at know temperature was placed in a soda can, above a wick type lamp of known mass. The lamp was lit, and allowed to burn, heating the water, and the change in mass reflected the amount of the test substance burned. The calorimeter was calibrated using ethanol, which has a known Heat of combustion. The same procedure was followed, but the calculations were done in the opposite direction to find the factor to correct for lost heat in the calorimeter device. The other experiments were the synthesis of biodiesel from soybean oil, and a Seed Assay. The synthesis was a straightforward process involving the NaOH catalyzed reaction of Methanol and
Soybean oil. The resulting product was purified by heating to vaporize the methanol, and the final quantity was measured. The seed assay involved the preparation of serial dilutions of the various biofuels candidates, in which we attempted to germinate radish or lettuce seeds. Control groups were also kept. The percentage of seeds which germinated, and their root lengths were recorded.
Results: For the Calorimetry experiment, I created a spreadsheet to aid calculations.
Fuel
Grams Moles Burned Burned
Biodiesel Biodiesel Biodiesel
0.5208 0.001769 0.6626 0.00225 0.9786 0.003323
21.6 20.2 20.6
32 31.5 32.5
10.4 11.3 11.9
Ethanol Ethanol Ethanol
0.554 0.012025 0.7674 0.016657 0.7682 0.016675
21 21 21
31.8 30 31.6
10.8 9 10.6
T initial
T final
Change in T
Average
C cal in kj/C
q cal in kj
H Comb in kj/Mol
20.10216 11366.13 21.84177 9706.831 23.00151 6921.372 -1.42298 20.87532 -2.36533 17.3961 -2.01039 20.48874
-1.9329
Average H Comb for Biodiesel in kJ/mol 9331.446 Measured data is in standard text. Bold indicates a calculated value. I followed the following procedure to calculate the data:
-
Calculate Moles Burned o
-
(Grams burned)/(Molar Mass)
Calculate C cal (Heat Capacity of the calorimeter) o
Take known heat of combustion for ethanol, multiply by moles of ethanol burned for each test. Divide by change in temperature for each respective test.
o -
Calculate average of the three. (-1.9329 kj/(degree C))
Next, I calculated the values for q cal (the amount of heat absorbed by the calorimeter and the surroundings.) for each of the tests. o
-
C cal * (Change in T)
Finally, I calculated H comb (the heat of combustion for biodiesel) and averaged the three results. o
Q cal / (Moles Burned)
The average came out to 9330 kj/mol
Discussion My experimental value of the heat of combustion for biodiesel was actually quite good, considering that it was obtained with an old soda can. The percent error was about 13%, which is reasonable, given the difficulty in burning biodiesel fully through a low-pressure combustion. Diesel fuel is not particularly flammable, but burns well when subjected to the high pressure and temperature conditions of a forced induction diesel engine. Marine diesel engines are capable of running on fuels that are almost like tar. To improve this test, the calibration should have been carried out with a test fuel that burns in a similar way to biodiesel, or with an oxidizer to speed the reaction. The important thing to realize with these values is that the heat capacity does not directly determine the overall efficiency. There are many efficiencies that can be discussed at length. For
example, the miles per gallon rating is only directly applicable to fossil fuels, and determining fuel tank size. Many biofuels, such as ethanol, have a much lower energy density than gasoline. Ethanol has a third the energy density, biodiesel, about 2/3, when compared to gasoline. Hydrogen has double the energy density per gram, yet it is extremely hard to contain in sufficient quantities. For comparing different types of fuel, it is important to look at the other efficiencies involved, such as the thermodynamic efficiency, which is largely dependent on engine design, and gives a large advantage to diesels, where some engines approach a 50% thermodynamic efficiency. In addition, there are questions of production efficiency. Currently, most ethanol is produced through a fermentation of sugars from corn. This method is shockingly inefficient, and basically “recycles” nonrenewable fuels such as diesel, gasoline, and natural gas into ethanol. Various studies (including one at UC Berkeley) estimate that the energy production efficiency of ethanol ranges from 526% over what is used in the form of fossil fuels. Worse still, is the fact that greenhouse gas emissions could even increase due to biofuels, and most likely have a negligible benefit. (Alexander E. Farrell, 2006) In the future, this will likely change, as production of cellulosic (derived from cellulose) alcohols is scaled up and streamlined. Rather than requiring the use of food products and grain, it can use cellulose, which is produced as waste from countless sources, including farming and paper disposal, or as a simple crop, such as bamboo or grass, which do not require fertilizer and careful tending.
Graphical representations of various estimates of efficiencies in Greenhouse Gas Emissions and petroleum use, from (Alexander E. Farrell, 2006). Other biofuels experience the same problem. Most Methanol and hydrogen are produced from natural gas. The US, with its golden fields of grain, just barely has enough arable land to produce the soybeans necessary to provide enough biodiesel for the population. In the near term, there is no technology that can replace petroleum, although there are some that can supplement it. I think that in the near term, biodiesel is the best option for a supplement to the US fuel supply. This is because it is relatively non-toxic, per reported values and my own research on a past lab, and a reasonable amount can be produced from waste. This waste includes animal fat and other by-products. In addition, diesel engines are extremely reliable and long lasting, which reduces their energy footprint, as the cars themselves last longer, using less energy to replace them.
In addition, for the near term, it makes more sense to use the petroleum we have carefully, such as using smaller, more efficient vehicles, without the environmental impact of a hybrid battery. Examples include the Ford Fiesta, which gets over 40 mpg without the assistance of a hybrid drive train. In Europe, Volkswagen Automotive Group produces the Polo, a subcompact car that returns well over 70 mpg running on diesel. Trains need to replace trucks, as a freight train can carry 1 ton of freight 436 miles on 1 gallon of diesel fuel (Association of American Railroads). In the long term, it is vital to create a stable, renewable source of energy. Cellulosic alcohol is probably the best option. It is very feasible in the near future to produce in large amounts, with minimal energy use in its production. It burns very cleanly, further reducing greenhouse gas emissions and smog forming pollutants. Like biodiesel, although not to the same degree, it is compatible with existing vehicles, albeit with slight modifications. Whatever we do to stop our consumption of petroleum, we must ensure that it is done in an open manner, free from political influence of large corporations which stand to benefit from taxpayer funded subsidies, and with the best interests of the world in mind.
Bibliography Alexander E. Farrell, 1. R. (2006). Ethanol Can Contribute to Energy and Environmental Goals. Science , 506 - 508. Douskey, M. (2010). Chemistry 1A Lab Manual. Berkeley: Hayden McNeil.
