Biofuels Part II: The Secret Life of Vegetable Oil
- Essentially all plants and animals store energy by making a class of molecules called triglycerides, more commonly known as fats and oils.
- Vegetable oils can be burned as fuel in diesel engines but they get too thick to use in cold weather.
- Biodiesel is made by reacting vegetable oils with methanol to break the oils into smaller pieces resulting in fuels with viscosities low enough to be used on cold winter days.
- Using biodiesel does not increase the amount of carbon dioxide in the atmosphere.
- Piedmont Biofuels operates a biodiesel plant right down the road in Pittsboro, NC.
At first this all sounds great, but biodiesel has several downsides which are primarily related to selection of the vegetable oil. The biodiesel industry began with and remains dependent upon oil from soy beans. If you run soy beans through a press you get approximately 20% oil which can be converted to biodiesel and 80% high-protein meal which is highly sought after as cattle feed. The ability to sell the both the oil and the meal makes soy beans an attractive crop from an economic standpoint.
During the 1990’s millions and millions of dollars were invested all over the globe in building biodiesel factories. This trend was driven by three factors: the desire for a transportation fuel which did not exacerbate global warming, a growing acceptance that petroleum oil supplies were beginning to show their limits, and generous government subsidies for renewable fuels. In order to supply these new biodiesel factories global cultivation of soy beans skyrocketed.
Much of the increase in production has occurred in Brazil where monumental swaths of the rain forest have been cleared to grow soy beans. The extent of deforestation is so vast that it is difficult to comprehend by just reviewing the numbers. So instead people tend to use geographic analogies. Here are my two favorites: “the current rate of deforestation in Brazil just for soy beans is equal to the size of the state of Connecticut every year”, and “between 2005 and 2009 the amount of forest cleared in Brazil to grow soy beans was equal to the size of Greece”. This degree of environmental devastation has somewhat tarnished the luster of biodiesel. In addition to deforestation, the conversion of arable land from food to fuel production has resulted in some of the dramatic food price increases which have occurred around the world in recent years. I should note that the food-versus-fuel problem is much more critical for ethanol compared to biodiesel. I’m planning to address ethanol next week.
Since almost all of “life” stores energy as fats and/or oils there are many possible feed stocks for biodiesel in addition to soy beans. For example, biodiesel can be made from poultry fat, though this is uncommon because poultry fat comes with difficult to manage impurities such as beaks and feet. Furthermore, poultry fat fetches a high price as an ingredient in animal feed making it too expensive to use for biodiesel. This is also true of other animal fats and oils. Therefore essentially all of biodiesel is made from plant (vegetable) oils.
The allure of a plant as a source for biodiesel is primarily dependent upon the amount of oil you can garner per acre during a growing season. For soy beans this is approximately 80 gallons. Let’s pause for a moment and consider what a remarkably small amount this is. Picture an acre of soy beans and then consider that the amount of oil you end up with is only slightly more than can fill a typical rain barrel. If that example is hard for you to visualize consider that an acre of soy beans can only provide enough fuel to fill your automobile gas tank four times. A typical American drives his or her car approximately 15,000 miles per year. Therefore even a diesel car which gets 30 miles per gallon would require 25 acres of soy beans to fuel that car for a year.
The examples above should help you to understand why millions and millions and millions of acres of soy beans need to be cultivated in order to generate a meaningful amount of fuel. The table below lists the oil yields for some several of the plants which can be used to make biodiesel.
60 to ???
The number listed for oil palm is not a typo. Oil palm’s natural range is limited to Southeast Asia which means that far fewer potential acres of land available for oil palm compared to soy beans. Nevertheless, much of the remaining rain forest in Malaysia and Indonesia is being converted to oil palm plantations. Since palm oil has traditionally been used for cooking oil in low income parts of the world biodiesel production is reducing the availability of a key dietary resource for populations ranging from Vietnam to Ethiopia.
I listed peanuts and sun flower primarily for reference. If you’ve been to the grocery store over at any point in the last few decades you’ll know that peanuts and sun flower seeds fetch far too high of a price for human consumption to be economically viable as a fuel source.
The search for the perfect biodiesel feed stock continues. The two options which get the most press as potential saviors are jatropa and algae. Let me state up front that I am a skeptic on both.
Jatropa is a class of shrubs which grow in warm climates. The spin on jatropa is almost always that “it can be grown in marginal land and, therefore, does not compete with food production.” Published estimates of the amount of oil which can be extracted from an acre of jatropa range from as low as 60 to over 600 gallons per acre. The reason for this wide range you ask? Jatropa can, in fact, be grown on marginal lands but this results in more modest production levels. To get higher yields of oil from jatropa it must be grown on fertile soil with plenty of sunlight and water, places more commonly known as farmland. To make matters worse, unlike soy beans where the meal left over after extracting the oil is a valuable and nutritious food source, jatropa meal is toxic.
Algae get the most press as the “next generation” source for biofuels. The appeal is clear. Algae grow remarkably fast and grow in water instead of on land. You can find published estimates of oil production from algae of up to 5,000 gallons per acre, enough to get rather excited about. To keep the section on the challenges of algae at a reasonable length I think I’ll use bullet points:
· There are a staggeringly large number of species of algae, but only a few generate a reasonable amount of oil.
· Those that do produce oil tend not to be vigorous growers, so if grown in the open they are overwhelmed native species.
· This means that algae for biodiesel will need to be produced inside of glass tubes inside of factories rendering the entire concept of calculating production per acre moot.
· Lastly, algae only tend to make oils when they are under stress from lack of nutrients. It’s a defense mechanism to store energy for use later, just like animals storing fat to survive the winter. Unfortunately an algae population under stress, while making more oil per individual, has a reduced rate of reproduction, thereby mitigating the advantage.
For algae to become a viable source for biodiesel, a genetically modified strain must be invented which can complete with native species in open environments and generate oil at normal rather than stressed conditions. The risk here would be in creating the aquatic version of kudzu which would destroy natural aquatic ecosystems by crowding out native species.
Piedmont Biofuels has adopted a unique approach to biodiesel production. They collect cooking oil (mostly vegetable oil, but also mixed with greases from animal fats as well) from local restaurants after it has been used to make French fries or fried chicken. Being used for cooking causes some thermal degradation and introduces impurities requiring Piedmont to pre-treat the oil before converting it to biodiesel. The expense and effort required for pretreatment are more than offset by the fact that the used oil is free. The downside of this approach is the limited amount of used cooking oil that is available. Piedmont’s production is now less than half what it was when they opened the plant in 2005 when they used soy oil.
I hope this review is helpful as background the next time you read or listen to a news story on biodiesel. I’m planning on two more installments in my biofuels fuels series. Next week on I’ll review ethanol (as a fuel not as a libation!). In the fourth installment, I’ll discuss my perspective on the role and impact of biofuels in the 21st century